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1

Evaluation of Superpave Mixtures Containing Hydrated Lime.  

National Technical Information Service (NTIS)

The use of hydrated lime in Hot-Mix Asphalt (HMA) mixtures can reduce permanent deformation, long-term aging, and moisture susceptibility of mixtures. In addition, hydrated lime increases the stiffness and fatigue resistance of mixtures. This study evalua...

A. Raghavendra L. N. Mohammad S. Cooper S. Kabir

2013-01-01

2

WHY IS TYPE S HYDRATED LIME SPECIAL?  

Microsoft Academic Search

Type S hydrated lime is defined by high early plasticity, high water-retention values, limited oxide content, and minimal coarse fraction. These qualities are highly valued for plaster and mortar. At the turn of the 19th Century in the United States, lime calcined from dolomitic limestone in Ohio was recognized as the best lime for interior plaster use. Starting about 1910,

Margaret L. Thomson

3

Molecular models of a hydrated calcite mineral surface  

NASA Astrophysics Data System (ADS)

Hydrated mineral surfaces play an important role in many processes in biological, geological, and industrial applications. An energy force field was developed for molecular mechanics and molecular dynamics simulations of hydrated carbonate minerals and was applied to investigate the behavior of water on the (101¯4) calcite surface. The force field is a significant development for large-scale molecular simulations of these systems, and provides good agreement with experimental and previous modeling results. Simulations indicate that water molecules are significantly ordered near the calcite surface. The predominant surface configuration (75-80%) results from coordination of a water molecule with a single calcium cation-carbonate anion pair, while the less common situation involves water coordination with two ion pairs. Surface restructuring and variation in coordination in the water layers results in distinct distances for water oxygens above the calcite surface—a two-component first monolayer (2.3 and 3.0 Å) and a secondary monolayer (5.0 Å). The different coordinations also alter lateral displacement, hydrogen bonding, and surface-normal orientation of the water molecules. The ordering of water molecules and the formation of a unique hydrogen bonding network at the calcite surface influence the physical properties of the interfacial water. Surface exchange of water molecules is observed by molecular dynamics simulation to occur at a rate of one exchange per 10 ps. Diffusion coefficients derived from mean square displacement analysis of atomic trajectories indicate a dependence of water transport based on the distance of the water molecules from the calcite surface.

Perry, Thomas D.; Cygan, Randall T.; Mitchell, Ralph

2007-12-01

4

Preparation and characterization of fly ash\\/hydrated lime sorbents for SO 2 removal  

Microsoft Academic Search

Coal combustion fly ash and its mixtures with lime and hydrated lime are being widely studied for use as sorbents in desulfurization processes. In this work, coal fly ash has been slurried with hydrated lime in a Parr pressure reactor. In order to study the preparation process of the solids, the influence of the operation variables (temperature, time, fly ash\\/Ca(OH)2

J. Fernández; J. Renedo; A. Garea; J. Viguri; J. A. Irabien

1997-01-01

5

Lime Stabilization: Reactions, Properties, Design, and Construction.  

National Technical Information Service (NTIS)

For many years, various forms of lime, including products with varying degrees of purity, have been utilized successfully as soil stabilizing agents. However, hydrated high calcium lime Ca(OH)2, monohydrated dolomitic lime Ca(OH)2 MgO, calcitic quicklime ...

1987-01-01

6

Disposal, recycle, and utilization of modified fly ash from hydrated lime injection into coal-fired utility boilers  

SciTech Connect

This paper presents an assessment of the disposal, utilization, and recycle of a modified fly ash from the injection of hydrated lime into a coal-fired utility boiler. The hydrated lime injection process is being developed by the US Environmental Protection Agency (EPA) as a low-cost alternative for achieving moderate degrees of SO/sub 2/ control at coal-fired power plants. In this process, hydrated lime is injected into the upper furnace where the flue gas temperature is about 2200{sup 0}F (1200{sup 0}C). The hydrated lime decomposes, and the resulting quicklime, CaO, captures SO/sub 2/ according to a formula given.

Dahlin, R.S.; Lishawa, C.L.; Clark, C.C. (Southern Research Inst., Birmingham, AL (USA)); Nolan, P.S. (U.S. Environmental Protection Agency, Research Triangle Park, NC (US))

1987-01-01

7

The elimination of Salmonella typhimurium in sewage sludge by aerobic mesophilic stabilization and lime hydrated stabilization.  

PubMed

This study observed the effects of two methods, aerobic mesophilic stabilization and lime hydrated stabilization of sewage sludge upon the survival of Salmonella typhimurium. Raw (primary) sludges from the mechanical biological municipal sewage treatment plant were used. Aerobic stabilization and lime hydrated stabilization were carried out in a laboratory fermentor. Aerobic stabilization was carried out in the mesophilic temperature range (from 25.70+/-0.40 to 37.82+/-1.38 degrees C). Lime hydrated was used at an amount of 10 kg/m(3) for the stabilization. Sludge samples were inoculated with a broth culture of S. typhimurium. Quantitative and qualitative examinations of the presence of S. typhimurium were carried out. Aerobic mesophilic stabilization caused elimination S. typhimurium within 48 h. The T(90) value of S. typhimurium was 6.66+/-0.20 h. During the lime hydrated stabilization pH values significantly increased from 5.66+/-0.07 to 12.12+/-0.02 (P<0.01). S. typhimurium was inactivated within 1h and the T(90) value was 0.19+/-0.01 h. Our study confirmed that the treatment of sewage sludge with lime hydrated was significantly more effective than the aerobic mesophilic stabilization, (P<0.01). PMID:17931859

Plachá, Iveta; Venglovský, Ján; Maková, Zuzana; Martinéz, José

2008-07-01

8

Mechanism of hydration of the metakaolin–lime–water system  

Microsoft Academic Search

The reaction kinetics of a mixture of metakaolin and lime (calcium hydroxide) in water at 60°C has been investigated using thermal analysis. The numerical results have been used to determine the nature of the reaction. It is shown that, on the whole, this pozzolanic reaction is diffusion controlled and can be represented by the Jander diffusion equation. The paper discusses

Joseph Cabrera; Moisés Fr??as Rojas

2001-01-01

9

A Study on Solidification of Abandoned Mine Tailings with Hydrated Lime  

NASA Astrophysics Data System (ADS)

Solidification is one of the stabilization processes for wastes and their components to reduce their toxicity and migration rates to surroundings. Hydrated limes were applied as cementing materials to solidify heavy metal contaminated tailings from the Geumjang mine and the solidified tailing specimens were tested for their appropriateness in accordance with the suggested test methods. In the preliminary tests for the solidified tailing specimens, all the specimens have higher uniaxial compressive strengths than 3.5kgf/cm2, the standard recommended for land reclamation solids by EPA(Environmental Protection Agency). Even in leaching tests for the solidified tailing specimens, concentrations of heavy metals such as As, Cd, Cu, Pb, and Zn were decreased significantly below the environmental warning standards in comparison with those of raw tailing samples. The optimum mixing ratio of tailings, hydrated lime, and water was determined through the preliminary tests. The solidified mixtures of mine tailings and hydrated lime through pozzolanic reaction were tested for their durability against repeated freezing and thawing processes. After repeated freezing and thawing, the uniaxial compressive strengths of all the solidified mixture specimens decreased in comparison with those before test but still higher than 3.5kgf/cm2, and concentrations of heavy metals such as As, Cd, Cu, Pb, and Zn were below the standards. Effluents in the repetitive artificial tests show pH's of 7.4 to 9.1 and concentrations of heavy metals such as As, Cd, Cu, Pb, and Zn of below 0.05ppm. Conclusively this study shows potential applicability of hydrated limes to in-situ stabilization of abandoned mine tailings.

Min, K.; Lee, H.

2008-12-01

10

Methanogenic calcite, 13C-depleted bivalve shells, and gas hydrate from a mud volcano offshore southern California  

USGS Publications Warehouse

Methane and hydrogen sulfide vent from a cold seep above a shallowly buried methane hydrate in a mud volcano located 24 km offshore southern California in?? 800 m of water. Bivalves, authigenic calcite, and methane hydrate were recovered in a 2.1 m piston core. Aragonite shells of two bivalve species are unusually depleted in 13C (to -91??? ??13C), the most 13C-depleted shells of marine macrofauna yet discovered. Carbon isotopes for both living and dead specimens indicate that they used, in part, carbon derived from anaerobically oxidized methane to construct their shells. The ??13C values are highly variable, but most are within the range -12??? to -91???. This variability may be diagnostic for identifying cold-seep-hydrate systems in the geologic record. Authigenic calcite is abundant in the cores down to ???1.5 m subbottom, the top of the methane hydrate. The calcite is depleted in 13C (??13C = -46??? to -58???), indicating that carbon produced by anaerobically oxidized methane is the main source of the calcite. Methane sources include a geologic hydrocarbon reservoir from Miocene source rocks, and biogenic and thermogenic degradation of organic matter in basin sediments. Oxygen isotopes indicate that most calcite formed out of isotopic equilibrium with ambient bottom water, under the influence of gas hydrate dissociation and strong methane flux. High metal content in the mud volcano sediment indicates leaching of basement rocks by fluid circulating along an underlying fault, which also allows for a high flux of fossil methane. ?? 2006 Geological Society of America.

Hein, J. R.; Normark, W. R.; McIntyre, B. R.; Lorenson, T. D.; Powell, II, C. L.

2006-01-01

11

Hydration layer structures on calcite facets and their roles in selective adsorptions of biomolecules: A molecular dynamics study  

NASA Astrophysics Data System (ADS)

The selective adsorptions of biomolecules onto crystal faces are the key issues in the studies of biomineralization. Frequently, the adsorption processes are understood by using the direct binding model between organic compounds and inorganic crystals during the molecular dynamic studies. However, water molecules near crystals always exhibit intense ordering and preferential orientation to form structured hydration layer. By using the adsorption of poly acrylic acid oligomer, acrylic acid (AA) dimer, onto calcite as an example, we demonstrate that the induced hydration layers contribute significant effects on the organic-inorganic interactions. In particular, on calcite (104) plane, two carboxyl groups of AA dimer both interact with the crystal but the molecule has to compete with water due to the well-structured hydration layer. On (110) plane, although only one carboxyl group of AA dimer interacts with this surface, the water layer is relatively loose so that the molecule can easily replace water. With a consideration of the hydration layer, our free energy analysis indicates that AA dimer has a stronger interaction with (110) face than with (104) face, which is consistent with the experimental observations. The study follows that the attachment of organic additive onto inorganic crystal facet is greatly mediated by near-surface hydration layers, and therefore, the critical role of structured water layers must be taken into account in the understanding of biomineralization interfaces.

Zhu, Beibei; Xu, Xurong; Tang, Ruikang

2013-12-01

12

Simultaneous removal of colour, phosphorus and disinfection from treated wastewater using an agent synthesized from amorphous silica and hydrated lime.  

PubMed

An agent synthesized from amorphous silica and hydrated lime (CSH-lime) was investigated for its ability to simultaneously remove the colour, phosphorus and disinfection from the effluents from wastewater treatment plants on swine farms. CSH-lime removed the colour and phosphate from the effluents, with the colour-removal effects especially high at pH 12, and phosphorous removal was more effective in strongly alkaline conditions (pH > 10). Colour decreased from 432 +/-111 (mean +/- SD) to 107 +/- 41 colour units and PO4(3-)P was reduced from 45 +/- 39 mg/L to undetectable levels at the CSH-lime dose of 2.0% w/v. Moreover, CSH-lime reduced the total organic carbon from 99.0 to 37.9 mg/L at the dose of 2.0% w/v and was effective at inactivating total heterotrophic and coliform bacteria. However, CSH-lime did not remove nitrogen compounds such as nitrite, nitrate and ammonium. Colour was also removed from dye solutions by CSH-lime, at the same dose. PMID:23837353

Yamashita, Takahiro; Aketo, Tsuyoshi; Minowa, Nobutaka; Sugimoto, Kiyomi; Yokoyama, Hiroshi; Ogino, Akifumi; Tanaka, Yasuo

2013-01-01

13

In-place stabilization of pond ash deposits by hydrated lime columns  

SciTech Connect

Abandoned coal ash ponds cover up vast stretches of precious land and cause environmental problems. Application of suitable in situ stabilization methods may bring about improvement in the geotechnical properties of the ash deposit as a whole, converting it to a usable site. In this study, a technique of in-place stabilization by hydrated lime columns was applied to large-scale laboratory models of ash ponds. Samples collected from different radial distances and different depths of the ash deposit were tested to study the improvements in the water content, dry density, particle size distribution, unconfined compressive strength, pH, hydraulic conductivity, and leachate characteristics over a period of one year. The in-place stabilization by lime column technique has been found effective in increasing the unconfined compressive strength and reducing hydraulic conductivity of pond ash deposits in addition to modifying other geotechnical parameters. The method has also proved to be useful in reducing the contamination potential of the ash leachates, thus mitigating the adverse environmental effects of ash deposits.

Chand, S.K.; Subbarao, C. [Indira Gandhi Institute of Technology, Orissa (India). Dept. of Civil Engineering

2007-12-15

14

Investigation of fatigue properties of granite asphalt mixtures containing hydrated lime  

NASA Astrophysics Data System (ADS)

This paper presents the results of a laboratory study of evaluating the fatigue characteristics of granite asphalt mixtures (GAM) using different testing methods. In the study, the fatigue performances of GAM were evaluated with Superpave indirect tensile test (IDT) and four-point beam fatigue test. Specimens were conditioned by four different methods: (1) one cycle of freeze-thaw (F-T), (2) two cycles of F-T, (3) immersion in 60°C water bath for 30min (4) immersion in 60°C water bath for 48h, and contrastive analysis was made with unconditioned specimens. Investigation of moisture damage influence on the fatigue properties of GAM with and without Hydrated Lime (HL) was done. The results from this study indicated that both Superpave IDT and four-point beam fatigue test agreed with each other in ranking the fatigue property of GAM. Increasing F-T cycles or immersion time would decrease fatigue life in GAM, and the addition of HL was effective to prolong the fatigue life in GAM.

Wu, Shaopeng; Huang, Xu

2009-12-01

15

The effect of temperature on the hydration rate and stability of the hydration phases of metakaolin–lime–water systems  

Microsoft Academic Search

The paper presents the results of a study carried out to determine the effect of curing temperature on the kinetics of reaction of a metakaolin (MK)\\/lime mixture. MK and analytical grade Ca(OH)2 were mixed in a ratio of 1:1 by weight and with a water\\/binder ratio of 2.37. Specimens were cured at 20 and 60 °C. In the first case,

Moisés Fr??as Rojas; Joseph Cabrera

2002-01-01

16

Effect of Lime on Hydration of Pastes Containing Gypsum and Calcium Aluminates or Calcium Sulfoaluminate.  

National Technical Information Service (NTIS)

Chemical reactions responsible for ettringite formation in the commercial expansive cements are reviewed. X-ray diffraction analyses of the hydrated expansive compounds showed that in the presence of Ca(OH)2 and CaSO4 the tricalcium aluminate hydrated ver...

P. K. Mehta

1973-01-01

17

Preparation of a new sorbent with hydrated lime and blast furnace slag for phosphorus removal from aqueous solution.  

PubMed

The removal of dissolvable inorganic phosphate (H(2)PO(4)(-)) by sorbents prepared from hydrated lime (HL) and blast furnace slag (BFS) was fundamentally studied by an orthogonal experiment design. Based on statistic analysis, it is revealed that the weight ratio of BFS/HL is the most significant variable, and an optimized preparation condition is figured out. With the increase of HL content, the adsorption capacity increases, suggesting that the HL plays the important role in the removal process in the gross. However, in the lower HL content, it is interesting that the adsorption capacity of as-prepared sorbents exceed the sum of the capacities of the same ratio of BFS and HL. The further analysis indicate the excess capacities linearly depend on the specific surface area of sorbents, suggesting that the removal of H(2)PO(4)(-) is closely related with the microstructure of sorbents in the lower HL content, according to the characterization with SEM, XRD and pore analysis. Additionally, an adsorption model and kinetic are discussed in this paper. PMID:19124194

Gong, Guozhuo; Ye, Shufeng; Tian, Yajun; Wang, Qi; Ni, Jiandi; Chen, Yunfa

2009-07-30

18

Mechanical effects of the hydration of periclase to brucite in calcite-periclase aggregates; an experimental study  

NASA Astrophysics Data System (ADS)

It has long been recognized that deformation and fluid flow are intimately coupled. For example hydration phenomena are often localized in zones of intense deformation. We investigated the opposite phenomenon looking at the deformation that is generated by hydration. This scenario may be relevant in the context of serpentinization, where large positive volume changes are associated with the hydration of olivine. This positive volume change may be accommodated by fracturing, which in turn provides fluid pathways leading to a positive feedback. We select the model reaction: MgO (Periclase) + H2O -> Mg(OH)2 (Brucite), which involves a positive volume change of the solids of about 100%, i.e. swelling by a factor of two with respect to the initial volume of periclase. Using the hot isostatic pressing technique we prepared dense (

Kuleci, Hakan; Schmidt, Christian; Rybacki, Eric; Dresen, Georg; Abart, Rainer

2013-04-01

19

Hydrate adhesive and tensile strengths  

NASA Astrophysics Data System (ADS)

The physical properties of hydrate-bearing sediments depend on the interaction between hydrates and minerals. In particular, hydrates prefer to nucleate on mineral surfaces, therefore, the hydrate-mineral adhesive strength and the tensile strength of the hydrate mass itself affect the mechanical response of hydrate-bearing sediments. In this study, ice and hydrates made with various guest molecules (CO2, CH4, and THF) are formed between mica and calcite substrates. Adhesive and tensile strengths are measured by applying an external pull-out force. Results show that tensile failure occurs in CO2 and CH4 hydrates when calcite is the substrate, while ice and all hydrates exhibit adhesive failure on mica. The debonding strength is higher when calcite substrates are involved rather than mica substrates. A nominal pull-out strength of 0.15 ± 0.03 MPa can be adopted for mechanical analyses of hydrate-bearing sediments.

Jung, J. W.; Santamarina, J. Carlos

2011-08-01

20

Immobilisation of Fe floc: Part 1, pre-treatment of floc with slaked lime  

NASA Astrophysics Data System (ADS)

A series of radioactive iron (Fe 3+) hydroxide flocs are produced during reprocessing of nuclear fuel at Sellafield, UK. Before the flocs can be successfully encapsulated in a pulverised fuel ash/ordinary Portland cement composite cement to form a durable cemented wasteform, they need to be pre-treated with slaked lime. This paper reports results after investigating the reaction between a simulant floc and the slaked lime and shows that the floc reacts readily to form an X-ray amorphous hydrated calcium ferrite. Calcite (CaCO 3), formed from carbonation of Ca(OH) 2, appears to contribute to the formation of a crystalline iron hydroxy carbonate phase (Fe 6(OH) 12(CO 3)). This work concludes that pre-treatment allows a pozzolanic reaction to occur between the pulverised fuel ash and the Ca(OH) 2 produced during cement hydration. This increases the quantity of C sbnd S sbnd H formed and increases the compressive strength of the hardened wasteform enough to withstand forces generated during curing and prevent cracking.

Collier, N. C.; Milestone, N. B.; Hill, J.; Godfrey, I. H.

2009-08-01

21

Lime Pretreatment  

NASA Astrophysics Data System (ADS)

Lime pretreatment has proven to be a useful method for selectively reducing the lignin content of lignocellulosic biomass without significant loss in carbohydrates, thus realizing an important increase in biodigestibility. In lime pretreatment, the biomass is pretreated with calcium hydroxide and water under different conditions of temperature and pressure. It can be accomplished in one of three fashions: (1) short-term pretreatment that lasts up to 6 h, requires temperatures of 100-160°C, and can be applied with or without oxygen (pressure ~200 psig); (2) long-term pretreatment taking up to 8 weeks, requiring only 55-65°C, and capable of running with or without air (atmospheric pressure); and (3) simple pretreatment requiring 1 h in boiling water, without air or oxygen. Nonoxidative conditions are effective at low lignin contents (below ~18% lignin), whereas oxidative conditions are required for high lignin contents (above ~18% lignin).

Sierra, Rocio; Granda, Cesar Benigno; Holtzapple, Mark T.

22

Use of Lime as Antistrip Additive for Mitigating Moisture Susceptibility of Asphalt Mixes Containing Baghouse Fines.  

National Technical Information Service (NTIS)

This study investigated the effectiveness of hydrated lime as an antistrip additive for mixes containing excess baghouse fines. Wet process of lime addition was used without marination. One percent lime was added to asphalt mixes containing 5.5% Boone and...

A. A. Tayebali A. V. Shidhore

2005-01-01

23

EFFECT OF AIR ENTRAINMENT ON FREEZE-THAW DURABILITY OF TYPE S PORTLAND CEMENT-LIME MASONRY MORTARS  

Microsoft Academic Search

Portland cement-Type S hydrated lime mo rtars are used extensively throughout the United States and Canada. Air entrained Type S hydrated lime may be used interchangeably with non-air entrained Type S hydrated lime in ASTM C 270 (Standard Specification for Mortar for Unit Masonry), but there is no preference toward either product where freeze-thaw conditions are prevalent. There appears, therefore,

Michael J. Tate; Margaret L. Thomson

24

Immobilization and leaching characteristics of arsenic from cement and/or lime solidified/stabilized spent adsorbent containing arsenic.  

PubMed

Solidification/stabilization (S/S) of hazardous iron oxide coated cement (IOCC) spent adsorbent containing arsenic (As(III)) was investigated in the present study. Cement and lime-based S/S effectiveness was evaluated by performing semi-dynamic leach tests. The S/S effectiveness was evaluated by measuring effective diffusion coefficients (D(e)) and leachability indices (LX). It was found that though cement or lime alone were efficient in preventing arsenic leaching (D(e) being in range of 10(-10) to 10(-12) for all the matrices) from the solidified matrices, the best combination for arsenic containment in the matrix was obtained when a mixture of cement and lime was used. The LX values for all the matrices were higher than 10, suggesting that the S/S treated arsenic sludge are acceptable for "controlled utilization". Calcite formation along with precipitation and conversion into non-soluble forms (calcium arsenite, calcium hydrogen arsenate hydrates, calcium hydrogen arsenates, etc.) were found to be the responsible mechanism for low leaching of arsenic from the solidified/stabilized samples. A linear relationship between cumulative fraction (CFR) of arsenic leached and square root of leach time (R(2) ranging from 0.90 to 0.94) suggested that the diffusion is the responsible mechanism for arsenic leaching. Thus, cement and lime show effective containment of the As(III) within the matrix thus indicating S/S by cement and lime, which is also a low-cost option, as a suitable management option for the toxic As(III) sludge. PMID:17913352

Kundu, Sanghamitra; Gupta, A K

2008-05-01

25

High surface area calcite  

NASA Astrophysics Data System (ADS)

Calcite (CaCO3) is important in many fields—in nature, because it is a component of aquifers, oil reservoirs and prospective CO2 storage sites, and in industry, where it is used in products as diverse as paper, toothpaste, paint, plastic and aspirin. It is difficult to obtain high purity calcite with a high surface area but such material is necessary for industrial applications and for fundamental calcite research. Commercial powder is nearly always contaminated with growth inhibitors such as sugars, citrate or pectin and most laboratory synthesis methods deliver large precipitates, often containing vaterite or aragonite. To address this problem, we (i) adapted the method of carbonating a Ca(OH)2 slurry with CO2 gas to develop the first simple, cheap, safe and reproducible procedure using common laboratory equipment, to obtain calcite that reproducibly had a surface area of 14-17 m2/g and (ii) conducted a thorough characterization of the product. Scanning electron microscopy (SEM) revealed nanometer scale, rhombohedral crystals. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) confirmed highly crystalline, pure calcite that more closely resembles the dimensions of the biogenic calcite produced by algae in coccoliths than other methods for synthesizing calcite. We suggest that this calcite is useful when purity and high surface area are important.

Schultz, L. N.; Andersson, M. P.; Dalby, K. N.; Müter, D.; Okhrimenko, D. V.; Fordsmand, H.; Stipp, S. L. S.

2013-05-01

26

Development, Construction, and Use of Lime and Alum Application Systems in Alberta, Canada  

Microsoft Academic Search

Between 1986 and 1993, a variety of systems, ranging from simple to complex, were designed for lime (slaked lime (Ca(OH)2) or calcite (CaCO3)) and alum (Al2(SO4)3) application to water bodies in Alberta, Canada. Application systems were used both experimentally, to determine the effectiveness of lime and alum in reducing phosphorus and algae, and commercially, for the treatment of water bodies

Mark S. Serediak; Ellie E. Prepas; Tom P. Murphy; Jay Babin

2002-01-01

27

Efficiency of natural calcite precipitation compared to lake marl application used for water quality improvement in an eutrophic lake  

Microsoft Academic Search

Since the 1980s, several in-lake restoration methods for eutrophied lakes have been developed based on artificially induced calcite precipitation and lime additions. The aim of these measures is to improve water quality and reduce the incidence of cyanobacterial blooms by increasing P adsorption and removal through natural calcite precipitation. The authors compared the relative efficiencies of lake marl application and

Eva Walpersdorf; Thomas Neumann; Doris Stüben

2004-01-01

28

Dislocation Creep in Magnesium Calcite  

Microsoft Academic Search

To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850° C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg

L. Xu; X. Xiao; B. J. Evans

2003-01-01

29

Lattice Dynamics of Calcite  

Microsoft Academic Search

The phonon dispersion relations for the lowest-ten external branches, and for wave vectors along the optic axis, ahve been measured in calcite, CaCO3, at room temperature, by means of inelastic-neutron-scattering techniques. The results are shown to be consistent with a simple shell model containing ten adjustable parameters.

E. R. Cowley; A. K. Pant

1973-01-01

30

Elastic constants of calcite  

USGS Publications Warehouse

The recent measurements of the elastic constants of calcite by Reddy and Subrahmanyam (1960) disagree with the values obtained independently by Voigt (1910) and Bhimasenachar (1945). The present authors, using an ultrasonic pulse technique at 3 Mc and 25??C, determined the elastic constants of calcite using the exact equations governing the wave velocities in the single crystal. The results are C11=13.7, C33=8.11, C44=3.50, C12=4.82, C13=5.68, and C14=-2.00, in units of 1011 dyncm2. Independent checks of several of the elastic constants were made employing other directions and polarizations of the wave velocities. With the exception of C13, these values substantially agree with the data of Voigt and Bhimasenachar. ?? 1962 The American Institute of Physics.

Peselnick, L.; Robie, R. A.

1962-01-01

31

The Effect of Liming and Fertilization on Yields of Maize and Winter Wheat  

Microsoft Academic Search

SUMMARY Effect of different rates of hydrated lime and zeolite tuffs, as lime materials, mineral and organic fertilizers upon the yield of maize and winter wheat grain was studied in an exact field trial set up on Eutric Gleysol, near Karlovac, Central Croatia. The following crops were cultivated during the study period: 1999 and 2001 - maize, 1999\\/00 and 2001\\/02

Ivica KISIÆ

2004-01-01

32

Problem of the hydration resistance of calcium oxide  

SciTech Connect

A study was made of the hydration tendencies of lime of varying degrees of sinterability. Some ways are indicated of increasing the hydration resistance of CaO. The investigation used pure grade calcium oxide. The lime was calcined at 1300, 1750, and 1950/sup 0/C with a soak of 2 h. To change the hydration resistance of the lime the additives Y/sub 2/O/sub 3/, MnO/sub 2/, and Cr/sub 2/O/sub 3/ were incorporated in the composition. Specimens prepared from lime with additions of yttrium oxide formed solid solutions on the basis of CaO during firing at 1950/sup 0/C. This contributed to an increase in the hydration resistance. Specimens prepared from CaO with additions of manganese and chromium oxides, fired at 1750/sup 0/C, also had a high hydration resistance.

Pitak, N.V.; Turchinova, L.N.; Gavrish, A.M.; Gul'ko, N.V.; Romanenko, S.N.

1988-09-01

33

Genesis and geometry of the Meiklejohn Peak lime mud-mound, Bare Mountain Quadrangle, Nevada, USA: Ordovician limestone with submarine frost heave structures—a possible response to gas clathrate hydrate evolution  

Microsoft Academic Search

During the Early Middle Ordovician (Early Whiterockian) the Meiklejohn Peak lime mud-mound, a large whaleback or dolphin back dome, grew on a carbonate ramp tens to hundreds of kilometres offshore. This ramp extended from the northwest margin of Laurentia into the open waters of the ancestral Pacific Ocean to the north. The mound developed in an outer ramp environment, in

Federico F Krause

2001-01-01

34

Lime Application Methods.  

National Technical Information Service (NTIS)

High calcium lime is widely used for the modification and stabilization of subgrades composed of fine-grained soils. Lime is available in a variety of forms and may be applied using several methods. This report contains the results of a study on the mixin...

M. O'Connor R. L. Parsons

2006-01-01

35

Calcite/barium fluoride ultraviolet polarizing prism  

NASA Astrophysics Data System (ADS)

A calcite/barium fluoride polarizing prism gives improved ultraviolet transmittance compared with a calcite/calcite ultraviolet polarizing prism. Beam spatial distortion is transmitted because of variations in absorption (and path length) in the calcite half of the calcite/barium fluoride prism.

Wu, Fuquan; Li, Guohua; Huang, Jiayin; Yu, Dehong

1995-07-01

36

Direct visualization of single ions in the Stern layer of calcite.  

PubMed

Calcite is among the most abundant minerals on earth and plays a central role in many environmental and geochemical processes. Here we used amplitude modulation atomic force microscopy (AFM) operated in a particular regime to visualize single ions close to the (1014) surface of calcite in solution. The results were acquired at equilibrium, in aqueous solution containing different concentrations of NaCl, RbCl, and CaCl(2). The AFM images provide a direct and atomic-level picture of the different cations adsorbed preferentially at certain locations of the calcite-water interface. Highly ordered water layers at the calcite surface prevent the hydrated ions from directly interacting with calcite due to the energy penalty incurred by the necessary restructuring of the ions' solvation shells. Controlled removal of the adsorbed ions from the interface by the AFM tip provides indications about the stability of the adsorption site. The AFM results show the familiar "row pairing" of the carbonate oxygen atoms, with the adsorbed monovalent cations located adjacent to the most prominent oxygen atoms. The location of adsorbed cations near the surface appears better defined for monovalent ions than for Ca(2+), consistent with the idea that Ca(2+) ions remain further away from the surface of calcite due to their larger hydration shell. The precise distance between the different hydrated ions and the surface of calcite is quantified using MD simulation. The preferential adsorption sites found by MD as well as the ion residence times close to the surface support the AFM findings, with Na(+) ions dwelling substantially longer and closer to the calcite surface than Ca(2+). The results also bring new insights into the problem of the Stern and electrostatic double layer at the surface of calcite, showing that parameters such as the thickness of the Stern layer can be highly ion dependent. PMID:23339738

Ricci, Maria; Spijker, Peter; Stellacci, Francesco; Molinari, Jean-Francois; Voïtchovsky, Kislon

2013-02-19

37

Imaging surface contacts: power law contact distributions and contact stresses in quartz, calcite, glass and acrylic plastic  

Microsoft Academic Search

A procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials, while the surfaces are subjected to static loads or undergoing frictional slip. Static loading experiments with quartz, calcite, soda-lime glass and acrylic plastic at normal stresses to 30 MPa yield power law distributions of contact areas from the smallest contacts that

James H. Dieterich; Brian D. Kilgore

1996-01-01

38

Hydration of bagasse ash-blended portland cement  

Microsoft Academic Search

Hydration of bagasse ash (BA)-blended portland cement has been studied by employing a number of experimental techniques. It is found that in presence of BA setting times are increased and free lime is decreased. The compressive strength values increased with hydration time in the presence of BA and the values were found to be higher than that of control. The

N. B Singh; V. D Singh; Sarita Rai

2000-01-01

39

Water transfer properties and shrinkage in lime-based rendering mortars  

NASA Astrophysics Data System (ADS)

Rendering is the practice of covering a wall or a building façade with one or more layers of mortar, with the main aim to protect the masonry structure against weathering. The render applied must show high flexibility, good adhesion and compatibility with the support (i.e. stone, brick) and, overall, it should be characterised by low water absorption and high water vapour permeability. Water (in the solid, liquid and vapour state) is one of the main factors that drive construction materials to deterioration. Therefore, to evaluate the quality and durability of a rendering mortar, thus ensuring its protective function in the masonry structure, it is fundamental to assess the behaviour of this mortar towards water. Mortars were elaborated with a calcitic dry hydrated lime, a calcareous aggregate, a pozzolan, a lightweight aggregate, a water-retaining agent and a plasticiser. Four types of lime mortars were prepared, in which the binder-to-aggregate ratios were 1:3, 1:4, 1:6 and 1:9 by weight, whilst the pozzolan was kept at 10% of the lime (by mass) and the total admixtures proportion was less than 2% of the total mass. The influence of the characteristics of mortars pore system on the amount of water absorbed and the kinetics of absorption was investigated by means of: free water absorption and drying; capillary uptake; water permeability; water vapour permeability. Interesting deductions can be made from the values of water and water vapour permeability found for mortars: the former increases exponentially with the sand volume of the mortar, whilst the latter increases almost exponentially with the initial water content added to the mortar mixes during their elaboration. However, the relationship obtained between porosity of mortars and permeability values is not really clear. This finding suggests that the permeability of a material cannot be estimated on the basis of its porosity as it can be made for the capillary uptake and free water absorption. Another aspect to be considered in the evaluation of the decay caused by water is the high shrinkage suffered by renders when they are applied on an extended surface (i.e. a wall), especially when they are aerial lime-based mortars. The shrinkage causes the formation of fissures that become an easy way for water to entry and diffuse through the mortar pore system. This factor is rarely taken into consideration during the hydric assays performed in the laboratory, since mortar samples of 4x4x16 or 4x4x4 cm in size do not undergo to such degree of shrinkage. For this reason, we have also studied the shrinkage of these mortars and considered it in the final assessment of mortars hydric properties. The shrinkage was evaluated according to a non-standardized method, by means of a shrinkage-measuring device that measures the mortar dimensional variations over time. This measurement has shown that the highest the lime content the biggest the mortar shrinkage and, consequently, the strongest the decay due to water.

Arizzi, A.; Cultrone, G.

2012-04-01

40

Lime pretreatment of switchgrass  

SciTech Connect

Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of switchgrass. After studying many conditions, the recommended pretreatment conditions are: time = 2 h, temperature = 100{degrees}C and 120{degrees}C, lime loading = 0.1 g Ca(OH){sub 2}/9 dry biomass, water loading = 9 mL/g dry biomass. Studies on the effect of particle size indicate that there was little benefit of grinding below 20 mesh; even coarse particles (4-10 mesh) digested well. Using the recommended pretreatment conditions, the 3-d reducing sugar yield was five times that of untreated switchgrass, the 3-d total sugar (glucose + xylose) yield was seven times, the 3-d glucose yield was five times, and the 3-d xylose yield was 21 times. A material balance study showed that little glucan (approx 10%) was solubilized as a result of the lime pretreatment, whereas about 26% of xylan and 29% of lignin became solubilized. 35 refs., 4 figs., 6 tabs.

Chang, V.S.; Burr, B.; Holtzapple, M.T. [Texas A& M Univ., College Station, TX (United States)

1997-12-31

41

Mineral phases of green liquor dregs, slaker grits, lime mud and wood ash of a Kraft pulp and paper mill.  

PubMed

Four residues generated in a Kraft, pulp and paper plant, were characterized by X-ray fluorescence spectroscopy (XFA), powder X-ray diffraction (XRD), thermogravimmetric analysis (TG) and Fourier transform infrared spectroscopy (FTIR). A quantitative phase composition model, that accounts for the observed data and for the physico-chemical conditions of formation, was postulated for each material. Emphasis was given on the identification of the mineral components of each material. The green liquor dregs and the lime mud contain Calcite and Gipsite. The slaker grits contains Calcite, Portlandite, Pirssonite, Larnite and Brucite. The Calcite phase, present in the dregs and in the lime mud, has small amounts of magnesium replacing calcium. The wood ash contains Quartz as the major crystalline mineral phase. PMID:17316983

Martins, Fernanda Machado; Martins, Joaniel Munhoz; Ferracin, Luiz Carlos; da Cunha, Carlos Jorge

2007-08-17

42

Surface hydration of aqueous calcium minerals as studied by Fourier transform Raman and infrared spectroscopy  

NASA Astrophysics Data System (ADS)

Rapid hydration reactions of several calcium minerals are studied using Fourier transform (FT) Raman and infrared (IR) spectroscopy. Oleate adsorption over aqueous synthetic fluorite, calcite and gypsum (pH 9) is investigated and adsorption mechanisms are discussed.

Holmgren, Allan; Wu, Liuming; Forsling, Willis

1994-10-01

43

Isotopic analysis for degradation diagnosis of calcite matrix in mortar.  

PubMed

Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (delta(13)C and delta(18)O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO(2) and water during calcite formation and degradation processes. Isotopic change of the initial delta(13)C and delta(18)O in carbonate matrix was caused by alteration of the primary source of CO(2) and H(2)O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO(2) from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter delta(18)O and delta(13)C in lime mortar. PMID:19784637

Dotsika, E; Psomiadis, D; Poutoukis, D; Raco, B; Gamaletsos, P

2009-12-01

44

HOW PLASTIC IS YOUR LIME?  

Microsoft Academic Search

A case history is described in which a weathered, non-durable, basalt proposed for base course for the Trans - Caprivi Highway in the wettest area of Namibia could not be reduced to non-plastic with SANS 824-quality lime during construction as required, even after extended curing. Adding more lime simply increased the plasticity index. It was established that the excess plasticity

F. Netterberg

45

Why calcite can be stronger than quartz  

NASA Astrophysics Data System (ADS)

In the Neves area (Eastern Alps), calcite forms asymmetric centimeter-scale single-crystal porphyroclasts in quartz mylonites developed during hydrous amphibolite facies metamorphism at ˜550°C. Under these conditions, coarse calcite was clearly stronger than the surrounding polycrystalline, dynamically recrystallized, quartz matrix. Experimental results indicate that coarse calcite is less strain rate sensitive than wet quartzite, consistent with an inversion in strength on extrapolation to natural strain rates. For this to occur, wet quartzite must be weak, flowing at differential stress of <10 MPa. The lack of high-temperature twins (showing bulging or recrystallization) in calcite clasts is consistent with such low stresses during shear zone development under near peak metamorphic conditions. The maximum effective viscosity ratio of coarse calcite to quartzite for these conditions is probably not large (<10). However, numerical modeling shows that ratios of around 2 are sufficient to maintain near rigid calcite clast behavior for power law rheology with stress exponents appropriate to quartz (n ˜ 3-4) and coarse calcite (n ? 6). The inversion in relative strength reflects the difference in influence of water on the crystal plastic flow of calcite and quartz: water has a dramatic effect for quartz but little or no effect for calcite. Quartz-rich rocks under hydrous amphibolite facies conditions in the middle to lower crust are therefore relatively weak (in fact, weaker than coarse calcite) and flow at much lower stresses than dry quartz-rich rocks at similar crustal levels.

Mancktelow, Neil S.; Pennacchioni, Giorgio

2010-01-01

46

Clathrate hydrates  

SciTech Connect

Clathrate hydrates or gas hydrates are solid solutions. Water molecules are linked through hydrogen bonding and create cavities (host lattice) that can enclose a large variety of molecules (guests). There is no chemical bonding between the host water molecules and the enclosed guest molecule. The clathrate hydrate crystal may exist at temperatures below as well as above the normal freezing point of water. Clathrate hydrates have been a source of problems in the energy industry because the conditions at which oil and gas are produced, transported, and processed are frequently suitable for clathrate hydrate formation. Naturally occurring clathrate hydrates in the earth, containing mostly methane, are regarded as a future energy resource. These methane hydrates, however, are potentially threatening to the global environment if they decompose due to the greenhouse effect. Several innovative separations based on clathrate hydrate formation with applications in a variety of industrial sectors have been examined in the laboratory and pilot-plant stage. This paper reviews the status of current knowledge on clathrate hydrates. The emphasis is on the aspects related to technological problems and opportunities that arise from the artificial or natural formation and decomposition of clathrate hydrates. However, a description of the fundamentals of formation, properties, and structure is also presented, and aspects related to the molecular simulation are discussed. Studies on calorimetric properties, orientational disorder, guest-guest interactions, and nuclear magnetic resonance are not reviewed, but literature references are made. Clathrate hydrates arouse great interest within chemical and petroleum engineering, chemistry, earth, and environmental sciences.

Englezos, P. (Univ. of British Columbia, Vancouver, British Columbia (Canada). Dept. of Chemical Engineering)

1993-07-01

47

Structure and phase investigations on crystallization of 11 A tobermorite in lime sand pellets  

SciTech Connect

The present work examines the crystallization behaviour of 11 A tobermorite and its dependence on the reactivity of different silica sources (quartz sand, grain-size {<=} 0.30 mm; quartz powder, grain-size {<=} 0.08 mm; inflated clay sand, grain-size {<=} 0.50 mm and raw perlite, grain-size {<=} 1 mm). The influence of different C/S ratios (calcium/silica ratio: 0.53, 0.83) was also investigated. For simulation of the industrial production process of lime sand products, a synthesis of lime sand pellets was carried out with a hydrothermal treatment (T = 200 deg. C, t = 40.5 h). The C-S-H phases were characterized by ESEM, EDX and X-ray powder diffraction. The investigations revealed that the grain-size, C/S ratio and porosity of the silica sources influence the formation of 11 A tobermorite. A formation of 11 A tobermorite using inflated clay sand with a grain-size {<=} 0.50 mm and a high porosity was only found with a C/S ratio of 0.53. This indicates a negative influence of an increase of lime content inside the synthesis mixture for tobermorite crystallization. Besides, a formation of xonotlite inside big pores of the lime sand pellet with inflated clay sand could be observed. The formation of portlandite and calcite was detected in all samples. The amount of calcite increased with the grain-size and with a higher C/S ratio.

Hartmann, A. [Materials Science Section, Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628 CN, Delft (Netherlands)]. E-mail: a.hartmann@tudelft.nl; Buhl, J.-Ch. [Institute of Mineralogy, University Hannover, D-30167 Hannover (Germany); Breugel, K. van [Materials Science Section, Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628 CN, Delft (Netherlands)

2007-01-15

48

Structure of the (1014) Surfaces of Calcite, Dolomite, and Magnesite under Wet and Dry Conditions  

SciTech Connect

Atomistic computer simulation methods have been employed to model the structure of the (10{bar 1}4) surfaces of calcite, dolomite and magnesite. The authors calculations show that under vacuum conditions, calcite undergoes the greatest degree of surface relaxation with rotation and distortion of the carbonate group accompanied by movement of the calcium ion. The magnesite surface is the least distorted of the three carbonates, with dolomite being intermediate to the two end members. When water molecules are placed on the surface to produce complete monolayer coverage, the calcite surface is stabilized and the amount of relaxation is substantially reduced. In contrast, the dolomite and magnesite surfaces are destabilized by hydration as indicated by a significant increase in the surface energies relative to the dry surface.

WRIGHT,KATE; CYGAN,RANDALL T.; SLATER,BEN

2000-06-12

49

Why calcite can be stronger than quartz  

Microsoft Academic Search

In the Neves area (Eastern Alps), calcite forms asymmetric centimeter-scale single-crystal porphyroclasts in quartz mylonites developed during hydrous amphibolite facies metamorphism at ?550°C. Under these conditions, coarse calcite was clearly stronger than the surrounding polycrystalline, dynamically recrystallized, quartz matrix. Experimental results indicate that coarse calcite is less strain rate sensitive than wet quartzite, consistent with an inversion in strength on

Neil S. Mancktelow; Giorgio Pennacchioni

2010-01-01

50

A thermodynamic approach to the hydration of sulphate-resisting Portland cement.  

PubMed

A thermodynamic approach is used to model changes in the hydrate assemblage and the composition of the pore solution during the hydration of calcite-free and calcite-containing sulphate-resisting Portland cement CEM I 52.5 N HTS. Modelling is based on thermodynamic data for the hydration products and calculated hydration rates for the individual clinker phases, which are used as time-dependent input parameters. Model predictions compare well with the composition of the hydrate assemblage as observed by TGA and semi-quantitative XRD and with the experimentally determined compositions of the pore solutions. The calculations show that in the presence of small amounts of calcite typically associated with Portland cement, C-S-H, portlandite, ettringite and calcium monocarbonate are the main hydration products. In the absence of calcite in the cement, however, siliceous hydrogarnet instead of calcium monocarbonate is observed to precipitate. The use of a higher water-to-cement ratio for the preparation of a calcite-containing cement paste has a minor effect on the composition of the hydrate assemblage, while it significantly changes the composition of the pore solution. In particular, lower pH value and higher Ca concentrations appear that could potentially influence the solubility and uptake of heavy metals and anions by cementitious materials. PMID:16529919

Lothenbach, Barbara; Wieland, Erich

2006-01-01

51

A thermodynamic approach to the hydration of sulphate-resisting Portland cement  

SciTech Connect

A thermodynamic approach is used to model changes in the hydrate assemblage and the composition of the pore solution during the hydration of calcite-free and calcite-containing sulphate-resisting Portland cement CEM I 52.5 N HTS. Modelling is based on thermodynamic data for the hydration products and calculated hydration rates for the individual clinker phases, which are used as time-dependent input parameters. Model predictions compare well with the composition of the hydrate assemblage as observed by TGA and semi-quantitative XRD and with the experimentally determined compositions of the pore solutions. The calculations show that in the presence of small amounts of calcite typically associated with Portland cement, C-S-H, portlandite, ettringite and calcium monocarbonate are the main hydration products. In the absence of calcite in the cement, however, siliceous hydrogarnet instead of calcium monocarbonate is observed to precipitate. The use of a higher water-to-cement ratio for the preparation of a calcite-containing cement paste has a minor effect on the composition of the hydrate assemblage, while it significantly changes the composition of the pore solution. In particular, lower pH value and higher Ca concentrations appear that could potentially influence the solubility and uptake of heavy metals and anions by cementitious materials.

Lothenbach, Barbara [Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Concrete and Construction Chemistry, Uberlandstrasse 129, 8600 Duebendorf (Switzerland)]. E-mail: barbara.lothenbach@empa.ch; Wieland, Erich [Paul Scherrer Institute, Nuclear Energy and Safety Department, Laboratory for Waste Management, 5232 Villigen PSI (Switzerland)

2006-07-01

52

Steam floods using lime and soda treatment  

Microsoft Academic Search

When the mineral content of the water used for thermal recovery processing has considerable hardness, it is usually desirable to consider lime-soda softening. Lime and soda, acting in combination, will precipitate out the calcium and magnesium salts, or the hardness of the water (lime = calcium hydroxide; soda = sodium carbonate). The amount of lime and soda used to soften

1965-01-01

53

Modelling the chemistry in lime kilns.  

National Technical Information Service (NTIS)

Many chemical reactions, besides the main reaction, calcining of lime mud to calcium oxide, can effect on the operation of a lime kiln. Formation of lime pellets at the hot end is strongly effected by the presence of sodium and sulfur in the lime mud and ...

R. Backman

1992-01-01

54

Simulating Succinate-Promoted Dissolution at Calcite {104} Steps  

NASA Astrophysics Data System (ADS)

Organic molecules of a wide range of molecular weights from small organic acids, amino-acids, acidic peptides and acidic proteins to humic and fulvic acids play a key role in modulating nucleation, crystal growth and dissolution of calcium carbonate polymorphs. In general, these acidic molecules inhibit calcite growth and, promote dissolution preferentially along specific crystallographic directions, in the process, regulating crystal shape and size, and even whether a metastable polymorph (e.g., vaterite or aragonite) is nucleated first. For example, chiral faces of calcite are selected by chiral amino-acids and the unusual {hk0} faces are expressed in the presence of amino-acids [Orme et al., 2001], and unusual heptagonal dissolution etch-pit are seen in the presence of succinate compared to the normal rhombohedral pits in water alone [Teng et al., 2006]. Thus, the presence of unusual crystal morphologies may indicate organic-mediated growth, thus serving as a biosignature. We have conducted the Molecular Dynamics (MD) simulations using the Consistent Valence Force Field (CVFF) as implemented in the FORCITE© module of the Materials Studio © software package (Accelrys, Inc. TM) to model the adsorption of succinate, a dicarboxylic acid, and charge- balancing Na+ ions on dry and hydrated steps in different directions on the {104} cleavage face of calcite [Mkhonto and Sahai, in prep.]. At the site of succinate adsorption, we find elongation of the interatomic distances (Ca-OCO3,i) between surface Ca2+ cation and the oxygen of the underlying inorganic CO32- anion the first surface layer of calcite, compared to the corresponding distances in the presence of water alone, suggesting greater ease of surface Ca2+ detachment. This result is consistent with the empirically observed increase in overall dissolution rate with succinate [Teng et al., 2006]. Furthermore, succinate adsorption lowers the step energies, which explains the appearance of steps in the unsusual [42-1] and [010] directions in the presence of succinate as observed by Atomic Force Microscopy [Teng et al., 2006]. Finally, the calculated succinate adsorption energies at hydrated steps decreases in the sequence [-441] > [42-1] > [010], which also corresponds to the sequence of steps opening at dissolution etch-pits in the presence of succinate [Teng et al., 2006]. Our study provides a strong example of the utility of MD simulations in exploring organic-mediated mineral crystal dissolution (and growth) mechanisms, resulting in unusual morphologies, that may serve as biosignatures on Earth, and potentially on Mars and other worlds.

Mkhonto, D.; Sahai, N.

2008-12-01

55

A model for trace metal sorption processes at the calcite surface: Adsorption of Cd2+ and subsequent solid solution formation  

USGS Publications Warehouse

The rate of Cd2+ sorption by calcite was determined as a function of pH and Mg2+ in aqueous solutions saturated with respect to calcite but undersaturated with respect to CdCO3. The sorption is characterized by two reaction steps, with the first reaching completion within 24 hours. The second step proceeded at a slow and nearly constant rate for at least 7 days. The rate of calcite recrystallization was also studied, using a Ca2+ isotopic exchange technique. Both the recrystallization rate of calcite and the rate of slow Cd2+ sorption decrease with increasing pH or with increasing Mg2+. The recrystallization rate could be predicted from the number of moles of Ca present in the hydrated surface layer. A model is presented which is consistent with the rates of Cd2+ sorption and Ca2+ isotopic exchange. In the model, the first step in Cd2+ sorption involves a fast adsorption reaction that is followed by diffusion of Cd2+ into a surface layer of hydrated CaCO3 that overlies crystalline calcite. Desorption of Cd2+ from the hydrated layer is slow. The second step is solid solution formation in new crystalline material, which grows from the disordered mixture of Cd and Ca carbonate in the hydrated surface layer. Calculated distribution coefficients for solid solutions formed at the surface are slightly greater than the ratio of equilibrium constants for dissolution of calcite and CdCO3, which is the value that would be expected for an ideal solid solution in equilibrium with the aqueous solution. ?? 1987.

Davis, J. A.; Fuller, C. C.; Cook, A. D.

1987-01-01

56

Crystal lattice tilting in prismatic calcite.  

PubMed

We analyzed the calcitic prismatic layers in Atrina rigida (Ar), Haliotis iris (Hi), Haliotis laevigata (HL), Haliotis rufescens (Hrf), Mytilus californianus (Mc), Pinctada fucata (Pf), Pinctada margaritifera (Pm) shells, and the aragonitic prismatic layer in the Nautilus pompilius (Np) shell. Dramatic structural differences were observed across species, with 100-?m wide single-crystalline prisms in Hi, HL and Hrf, 1-?m wide needle-shaped calcite prisms in Mc, 1-?m wide spherulitic aragonite prisms in Np, 20-?m wide single-crystalline calcite prisms in Ar, and 20-?m wide polycrystalline calcite prisms in Pf and Pm. The calcite prisms in Pf and Pm are subdivided into sub-prismatic domains of orientations, and within each of these domains the calcite crystal lattice tilts gradually over long distances, on the order of 100 ?m, with an angle spread of crystal orientation of 10-20°. Furthermore, prisms in Pf and Pm are harder than in any other calcite prisms analyzed, their nanoparticles are smaller, and the angle spread is strongly correlated with hardness in all shells that form calcitic prismatic layers. One can hypothesize a causal relationship of these correlated parameters: greater angle spread may confer greater hardness and resistance to wear, thus providing Pf and Pm with a structural advantage in their environment. This is the first structure-property relationship thus far hypothesized in mollusk shell prisms. PMID:23806677

Olson, Ian C; Metzler, Rebecca A; Tamura, Nobumichi; Kunz, Martin; Killian, Christopher E; Gilbert, Pupa U P A

2013-08-01

57

Etch Pits on Calcite Cleavage Faces  

Microsoft Academic Search

THIS communication describes some of the effects observed on calcite cleavage faces after etching with dilute acid. Puchegger1 has reported etch pits which formed a rib-like pattern on either side of scratch marks made on calcite. More striking features are described here.

H. Watts

1959-01-01

58

Trace concentration - Huge impact: Nitrate in the calcite/Eu(III) system  

NASA Astrophysics Data System (ADS)

The interactions of trivalent lanthanides and actinides with secondary mineral phases such as calcite is of high importance for the safety assessment of deep geological repositories for high level nuclear waste (HLW). Due to similar ionic radii, calcium-bearing mineral phases are suitable host minerals for Ln(III) and An(III) ions. Especially calcite has been proven to retain these metal ions effectively by both surface complexation and bulk incorporation. Since anionic ligands (e.g., nitrate) are omnipresent in the geological environment and due to their coordinating properties, their influence on retentive processes should not be underestimated. Nitrate is a common contaminant in most HLW forms as a result of using nitric acid in fuel reprocessing. It is also formed by microbial activity under aerobic conditions. In this study, atomic force microscopy investigations revealed a major influence of nitrate upon the surface of calcite crystals. NaNO3 causes serious modifications even in trace amounts (<10-7 M) and forms a soft surface layer of low crystallinity on top of the calcite crystal. Time-resolved laser fluorescence spectroscopy of Eu(III) showed that, within this layer, Eu(III) ions are incorporated, while losing most of their hydration shell. The results show that solid solution modelling for actinides in calcite must take into account the presence of nitrate in pore and ground waters.

Hofmann, Sascha; Voïtchovsky, Kislon; Schmidt, Moritz; Stumpf, Thorsten

2014-01-01

59

Authigenic carbonates from the Cascadia subduction zone and their relation to gas hydrate stability  

Microsoft Academic Search

Authigenic carbonates are intercalated with massive gas hydrates in sediments of the Cascadia margin. The deposits were recovered from the uppermost 50 cm of sediments on the southern summit of the Hydrate Ridge during the RV Sonne cruise SO110. Two carbonate lithologies that differ in chemistry, mineralogy, and fabric make up these deposits. Microcrystalline high-magnesium calcite (14 to 19 mol%

Gerhard Bohrmann; Jens Greinert; Erwin Suess; Marta Torres

1998-01-01

60

Comparison of surface properties between kaolin and metakaolin in concentrated lime solutions.  

PubMed

The surface adsorption of calcium hydroxide onto kaolin and metakaolin was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clays to calcium hydroxide solutions of various concentrations. Both clays adsorb calcium and hydroxyl ions but differently. Kaolin adsorbs calcium hydroxide not only at the edges of the clay particles but also onto the basal faces. The adsorbed hydrated calcium ions form a layer on the clay particle surfaces, preventing further dissolution of the clay mineral platelet. Metakaolin shows high pozzolanic activity, which provides the quick formation of hydrated phases at the interfaces between metakaolin and lime solutions. The nature of the hydration products has been investigated using X-ray diffraction (XRD) and differential thermal analysis (DTA). The most important hydrated phases like CSH (hydrated calcium silicate) and C(2)ASH(8) (gehlenite) have been identified. PMID:19682702

Konan, K L; Peyratout, C; Smith, A; Bonnet, J-P; Rossignol, S; Oyetola, S

2009-11-01

61

Effect of pH on calcite growth at constant a/a ratio and supersaturation  

NASA Astrophysics Data System (ADS)

In situ Atomic Force Microscopy (AFM) was used to study the growth of calcite at a constant supersaturation ( ? = 6.5) and solution stoichiometry (a/a=1) in the pH range 7.5-12. The calcite growth rate decreased with increasing pH in the studied range. The results can be successfully explained by the surface complexation model for calcite growth and by considering the effect of OH - ions on solute hydration. At pH below 8.5, growth occurs mainly by CaCO 30 incorporation at >CaHCO 30 surface sites. CaCO 30 should be more easily incorporated than free Ca 2+ ions, as water exchange is usually faster if water molecules in the ion hydration shells are substituted by other ligands, as in CaCO 30. However, at pH above 9, Ca 2+ incorporation at >CaHCO 30 sites also contributes to calcite growth as a result of the increased frequency of water exchange in calcium hydration shells due to the presence of strongly hydrated OH -. This also leads to an increase in the solid-liquid interfacial tension at high pH, which seems to reduce the nucleation rate and increase the average size of crystals precipitated in macroscopic, non-seeded experiments. The reduction of calcite growth rate is a consequence of decreasing surface concentration of active growth sites (i.e., >CaHCO 30) with increasing pH under our experimental conditions. Changes in two-dimensional island morphology were observed at high pH (12), possibly due to the stabilization of polar scalenohedral faces by the presence of OH - ions. This work may help to improve our understanding of the effects of carbonate-solution reactions resulting from potential changes in the pH of the oceans and surface waters in response to variations in atmospheric CO 2, as well as in understanding calcite precipitation in highly alkaline environments both natural (e.g., alkali lakes) and artificial (e.g., cement carbonation).

Ruiz-Agudo, E.; Putnis, C. V.; Rodriguez-Navarro, C.; Putnis, A.

2011-01-01

62

Immobilization of metal-containing waste in alkali-activated lime–RHA cementitious matrices  

Microsoft Academic Search

This research investigated the immobilization potential of alkali-activated lime–rice husk ash (RHA) for synthetic Cr(OH)3, Fe(OH)3, Zn(OH)2 and zinc cyanide plating sludge. The binder consists of hydrated lime and RHA at a weight ratio of 45:55. Waterglass (Na2SiO3) with SiO2\\/Na2O?3 and anhydrous sodium carbonate (Na2CO3) were used as alkali activator between 0 and 8 wt.% of the binder. Results showed that

Suwimol Asavapisit; Donald E. Macphee

2007-01-01

63

Lime pretreatment of lignocellulosic biomass  

NASA Astrophysics Data System (ADS)

Lignocellulose is a valuable alternative energy source. The susceptibility of lignocellulosic biomass to enzymatic hydrolysis is constrained due to its structural features, so pretreatment is essential to enhance enzymatic digestibility. Of the chemicals used as pretreatment agents, it has been reported that alkalis improve biomass digestibility significantly. In comparison with other alkalis such as NaOH and ammonia, lime (calcium hydroxide) has many advantages; it is very inexpensive, is safe, and can be recovered by carbonating wash water. The effects of lime pretreatment were explored on switchgrass and poplar wood, representing herbaceous and woody biomass, respectively. The effects of pretreatment conditions (time, temperature, lime loading, water loading, particle size, and oxygen pressure) have been systematically studies. Lime alone enhances the digestibility of switchgrass significantly; under the recommended conditions, the 3-d total sugar (glucose + xylose) yields of lime-treated switchgrass were 7 times that of untreated sample. When treating poplar wood, lime must be combined with oxygen to achieve high digestibility; oxidative lime pretreatment increased the 3-d total sugar yield of poplar wood to 12 times that of untreated sample. In a fundamental study, to determine why lime pretreatment is effective, the effects of three structural features on enzymatic digestibility were studied: lignin content, acetyl content, and crystallinity index (CrI). Poplar wood was treated with peracetic acid, potassium hydroxide, and ball milling to produce model lignocelluloses with a broad spectrum of lignin contents, acetyl contents, and CrI, respectively. Enzymatic hydrolysis was performed on the model lignocelluloses to determine the digestibility. Correlations between lignin/carbohydrate ratio, acetyl/carbohydrate ratio, CrI and digestibility were developed. The 95% prediction intervals show that the correlations predict the 1-h and 3-d total sugar conversions of a biomass sample within a precision of 5% and 20%, respectively. The digestibility of a variety of lime-treated biomass and ball-milled alpha-cellulose was compared to the correlations determined from the model compounds. The agreement between the measured and predicted values shows that the correlations are satisfactory and the three structural features---lignin content, acetyl content, and CrI---are the major factors that determine enzymatic digestibility.

Chang, Shushien

64

Why calcite can be stronger than quartz  

NASA Astrophysics Data System (ADS)

Calcite and quartz are two of the most common minerals in the continental crust and it is therefore not surprising that these minerals have been extensively studied since the very beginning of laboratory rock mechanics experiments. Extending such laboratory data to geological deformation rates around 10-14 s-1 requires an extrapolation of more than 7 orders of magnitude, with correspondingly large uncertainties. Extrapolation is based on the assumption that flow parameters are constant with changing conditions and that parameters not included in the flow law have a negligible influence on the creep properties. The validity of this extrapolation can only be tested, at least semi-quantitatively, by comparison with naturally deformed rocks. Observations generally indicate that quartz is significantly stronger than calcite in natural rocks, with quartz forming porphyroclasts in calcite marble mylonites, or with quartzite layers being folded or boudinaged within a weaker calcite marble matrix. However, in the Neves area (Tauern Window, Eastern Alps), shearing of Alpine coarse grained quartz-calcite veins under hydrous amphibolite facies conditions (ca. 550Ë? C) produced quartz mylonites containing asymmetric cm-scale single crystal calcite porphyroclasts. Under these conditions, coarse calcite is clearly stronger than the surrounding polycrystalline, dynamically recrystallized, quartz matrix. The important parameter controlling this difference in observed natural behaviour is the grain size of the calcite. Although there is considerable variation, uncertainty and even contradiction in the published experimental results, we show that extrapolation of laboratory creep data on calcite single crystals and coarse marbles, together with the corresponding data for wet quartzites, is indeed consistent with these natural observations. Extrapolation indicates an inversion in the relative strength of coarse calcite and quartz at a strain rate around 10-11 s-1, corresponding to a differential flow stress of ca. 50 MPa. At lower strain rates and stresses, wet quartz should be weaker than coarse calcite crystals. Field evidence (flow of quartz-rich layers even for orientations with very low resolved shear stress) and the preserved microstructure (lack of recrystallized or bulged twins in the calcite porphyroclasts) in the Neves area are also consistent with flow stresses of less than ca. 50 MPa. These low values during deformation under water-rich amphibolite facies conditions are in marked contrast to the much higher differential stresses reported for the flow (and fracture) of quartz-rich rocks under dry conditions in the middle to lower crust.

Mancktelow, N. S.; Pennacchioni, G.

2009-04-01

65

The effects of varying gypsum content on thaumasite formation in a cement:Lime:Sand mortar at 5 °C  

Microsoft Academic Search

An air entrained cement:lime:sand mortar containing high purity powdered calcite was crushed and portions stored in water together with varying quantities of gypsum. All mixes are stored at 5 °C. The reaction products were monitored at intervals over a period of several months by means of X-ray diffraction analysis. Ettringite, later followed by thaumasite was produced by mixes of high

M. E. Gaze

1997-01-01

66

The Alumina- Lime Soda Water Treatment Process.  

National Technical Information Service (NTIS)

A new pretreatment process for brackish water desalting has been developed and evaluated in the laboratory. The alumina-lime-soda process involves treating raw saline water with sodium aluminate and lime, separating precipitated solids, and neutralizing t...

J. W. Nebgen E. P. Shea S. Y. Chiu

1973-01-01

67

Sodium polyacrylate mediated dispersion of calcite  

Microsoft Academic Search

The stabilising action of sodium polyacrylate (NaPA) on colloidal dispersions of calcite has been investigated through measurement\\u000a of viscosity, electrophoretic mobility and solution ion concentration. The dose of NaPA was in the range 0 to 28 mg per g\\u000a of calcite and the dispersions were prepared at a solids content of 70% (by weight). The ionic strength of the dispersions

K. R. Rogan; A. C. Bentham; G. W. A. Beard; I. A. George; D. R. Skuse

68

Spectroscopic characterization of natural calcite minerals  

Microsoft Academic Search

The FT-IR, FT-Raman, NMR spectral data of ten different limestone samples have been compared. FT-IR and FT-Raman spectral data show that calcium carbonate in limestone, principally in the form of calcite, as identified by its main absorption bands at 1426, 1092, 876 and 712cm?1. The sharp diffractions at the d-spacings, 3.0348, 1.9166 and 1.8796 confirm the presence of calcite structure

S. Gunasekaran; G. Anbalagan

2007-01-01

69

Do organic ligands affect calcite dissolution rates?  

NASA Astrophysics Data System (ADS)

Steady state Iceland-spar calcite dissolution rates were measured at 25 °C in aqueous solutions containing 0.1 M NaCl and up to 0.05 M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those most likely to be present in either (1) aquifers at the conditions pertinent to CO 2 sequestration or (2) soil/early diagenetic environments: acetate, phthalate, citrate, EDTA 4-, succinate, D-glucosaminate, L-glutamate, D-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate, fumarate, malonate, and gallate. Results show that the presence of <0.05 mol/kg of these organic anions changes calcite dissolution rates by less than a factor of 2.5 with the exception of citrate and EDTA 4-. The presence of 0.05 mol/kg citrate and EDTA 4- increases calcite dissolution rates by as much as a factor of 35 and 500, respectively, compared to rates in organic anion-free solutions. Further calcite dissolution experiments were performed in the presence of organic polymers similar to bacterial exudates, cell exopolysaccharides, and analogs of microbial cell envelopes: alginate, lichen extract, humic acid, pectin, and gum xanthan. In no case did the presence of <100 ppm of these organics change calcite dissolution rates by more than a factor of 2.5. Results obtained in this study suggest that the presence of aqueous organic anions negligibly affects calcite forward dissolution rates in most natural environments. Some effect on calcite reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to calcite.

Oelkers, Eric H.; Golubev, Sergey V.; Pokrovsky, Oleg S.; Bénézeth, Pascale

2011-04-01

70

Effects of forest liming on soil processes  

Microsoft Academic Search

On the basis of a field experiment in Norway spruce with acid irrigation and compensatory liming of the soil surface (Höglwald, S-Bavaria), liming effects are described as lime dissolution rate, transformation of carbonate buffer to exchange buffer, time required for deacidification of soil and drainage water, mobilization of Cu and Pb, changes in soil organisms, humus decomposition, and nitrogen turnover.

Karl Kreutzer

1995-01-01

71

LIME FGD SYSTEMS DATA BOOK  

EPA Science Inventory

The Data Book is intended to aid engineers in understanding the process design features that are unique to lime flue gas desulfurization (FGD) systems. It is intended to supplement, not replace, basic information on engineering design. It is addressed to engineers who must design...

72

Lime pretreatment of lignocellulosic biomass  

Microsoft Academic Search

Lignocellulose is a valuable alternative energy source. The susceptibility of lignocellulosic biomass to enzymatic hydrolysis is constrained due to its structural features, so pretreatment is essential to enhance enzymatic digestibility. Of the chemicals used as pretreatment agents, it has been reported that alkalis improve biomass digestibility significantly. In comparison with other alkalis such as NaOH and ammonia, lime (calcium hydroxide)

Shushien Chang

1999-01-01

73

Comparison of solidification/stabilization effects of calcite between Australian and South Korean cements  

SciTech Connect

The differences in the effect of calcite on the strength and stability of Pb-rich wastes solidified and stabilized using Australian and South Korean ordinary Portland cements are examined in this study. Pb-rich waste stabilized using Australian OPC has been shown to possess both substantially higher unconfined compressive strength and lead immobilization ability than South Korean OPC as a result of its higher C{sub 3}S content and the associated enhanced degree of precipitation of lead on the surfaces of silicate phases present. Calcite addition is observed to have an accelerating effect on the OPC-induced solidification/stabilization of Pb-rich wastes as gauged by the unconfined compressive strength and leachability of the solids formed. This effect is observed to be far more dramatic for South Korean OPC than for Australian OPC. Using scanning electron microscopy, waste stabilized with cement and calcite was observed to develop significantly greater proportions of hydrated crystals than wastes stabilized with cement alone. The results of X-ray diffraction studies have shown that the presence of calcite in South Korean OPC results in greater acceleration in the formation of portlandite than is the case for Australian OPC.

Lee, Dongjin [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Waite, T. David [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia)]. E-mail: d.waite@unsw.edu.au; Swarbrick, Gareth [School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Lee, Sookoo [School of Environmental Engineering, Seoul National University of Technology, Nowon-Gu, Seoul, 139-743 (Korea, Republic of)

2005-11-15

74

DTA–TGA of unstirred autoclaved metakaolin–lime–quartz slurries. The formation of hydrogarnet  

Microsoft Academic Search

DTA–TGA was used to monitor the evolution of hydration products in unstirred autoclaved metakaolin–lime–quartz slurries with reaction time. Hydrogarnet was always one of the first phases formed at all metakaolin additions and invariably appeared before 11Å tobermorite. These findings explain apparent inconsistencies in the literature because the continued existence of hydrogarnet depends on such factors as reaction time and bulk

Danielle S Klimesch; Abhi Ray

1998-01-01

75

Thermodynamic modelling of the hydration of Portland cement  

SciTech Connect

A thermodynamic model is developed and applied to calculate the composition of the pore solution and the hydrate assemblage during the hydration of an OPC. The calculated hydration rates of the individual clinker phases are used as time dependent input. The modelled data compare well with the measured composition of pore solutions gained from OPC as well as with TGA and semi-quantitative XRD data. The thermodynamic calculations indicate that in the presence of small amounts of calcite typically included in OPC cements, C-S-H, portlandite, ettringite and calcium monocarbonates are the main hydration products. The thermodynamic model presented in this paper helps to understand the interactions between the different components and the environment and to predict the influence of changes in cement composition on the hydrate assemblage.

Lothenbach, Barbara [Empa, Laboratory for Concrete and Construction Chemistry, Uberlandstrasse 129, 8600 Duebendorf (Switzerland)]. E-mail: barbara.lothenbach@empa.ch; Winnefeld, Frank [Empa, Laboratory for Concrete and Construction Chemistry, Uberlandstrasse 129, 8600 Duebendorf (Switzerland)

2006-02-15

76

Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule  

PubMed Central

Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40–200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism.

Politi, Yael; Metzler, Rebecca A.; Abrecht, Mike; Gilbert, Benjamin; Wilt, Fred H.; Sagi, Irit; Addadi, Lia; Weiner, Steve; Gilbert, P. U. P. A.

2008-01-01

77

The coordination of Mg in foraminiferal calcite  

NASA Astrophysics Data System (ADS)

The Mg/Ca ratio of foraminiferal calcite is a widely accepted and applied empirical proxy for ocean temperature. The analysis of foraminifera preserved in ocean sediments has been instrumental in developing our understanding of global climate, but the mechanisms behind the proxy are largely unknown. Analogies have been drawn to the inorganic precipitation of calcite, where the endothermic substitution of Mg for Ca is favoured at higher temperatures. However, evidence suggests that foraminiferal Mg incorporation may be more complex: foraminiferal magnesium is highly heterogeneous at the sub-micron scale, and high Mg areas coincide with elevated concentrations of organic molecules, Na, S and other trace elements. Fundamentally, the incorporation mode of Mg in foraminifera is unknown. Here we show that Mg is uniformly substituted for Ca within the calcite mineral lattice. The consistency of Mg-specific X-ray spectra gathered from nano-scale regions across the shell ('test') reveals that the coordination of Mg is uniform. The similarity of these spectra to that produced by dolomite shows that Mg is present in an octahedral coordination, ideally substituted for Ca in a calcite crystal structure. This demonstrates that Mg is heterogeneous in concentration, but not in structure. The degree of this uniformity implies the action of a continuous Mg incorporation mechanism, and therefore calcification mechanism, across these compositional bands in foraminifera. This constitutes a fundamental step towards a mechanistic understanding of foraminiferal calcification processes and the incorporation of calcite-bound palaeoenvironment proxies, such as Mg.

Branson, Oscar; Redfern, Simon A. T.; Tyliszczak, Tolek; Sadekov, Aleksey; Langer, Gerald; Kimoto, Katsunori; Elderfield, Henry

2013-12-01

78

Rehabilitating acid soils for increasing crop productivity through low-cost liming material.  

PubMed

Productivity of red and lateritic soils is low because of their acidity and deficiencies in few essential nutrients viz., nitrogen, phosphorus, calcium, zinc, boron, molybdenum etc. We compared the effectiveness of basic slag, a low-cost liming material, with that of calcite as an ameliorant for these soils using mustard followed by rice as test crops. Experiments were conducted with three levels of each of basic slag and calcite along with a control on farmers' fields at 14 different locations. Influence of farmyard manure (FYM) and poultry manure (PM) on the effectiveness of the slag was also tested. On an average, basic slag performed better than calcite in increasing yields of both mustard and rice and left over higher amounts of available Ca, Si and Zn in residual soils. The slag also improved N, P, K and Ca nutrition of mustard and Si and Zn nutrition of rice with a favorable benefit:cost (B:C) ratio over the calcite (4.82 vs. 1.44). Effectiveness of the basic slag improved when it was applied in combination with FYM or PM (B:C, 5.83 and 6.27). Basic slag can, therefore, be advocated for use in the acidic red and lateritic soils for economically improving their productivity. PMID:20659758

Bhat, Javid Ahmad; Kundu, Manik Chandra; Hazra, Gora Chand; Santra, Gour Hari; Mandal, Biswapati

2010-09-15

79

Solubility and surface spectroscopy of zinc precipitates on calcite  

NASA Astrophysics Data System (ADS)

The Sorption and precipitation of Zn was investigated in equilibrium calcite (CaCO 3(s)) suspensions at Zn concentrations that approached and exceeded the solubility of known zinc carbonate solids. Surface-enhanced precipitation was not observed and CaCO 3(s) did not nucleate Zn solids when the aqueous ion activity product (IAP) was below the equilibrium IAP of the least soluble, kinetically viable Zn phase. The CaCO 3(s) surface was not requisite for Zn precipitation. When CaCO 3(s) was present the precipitate formed a surface coating or discrete Zn particles bound to the surface. X-ray photoelectron spectroscopy, X-ray diffraction, and energy dispersive X-ray spectrometry of both Zn-treated CaCO 3(s) and isolated Zn particles implied, but did not confirm, that the precipitate was hydrozincite [ Zn5( OH) 6( CO3) 2( S) ] or its hydrated form. Zinc-treated calcite maintained Zn concentrations that agreed with the solubility of a synthetic hydrozincite measured by Schindler et al. (1969). Direct measurements showed that the equilibrium solubility of the precipitate exceeded that of a natural hydrozincite ( log IAP = a 5Zn2+a 2CO 2-3 /a 6H+ = 6.41 ± 0.51 ) and was less than a natural smithsonite ( logIAP = aZn2+aCO2-3 = -10.53 ± 0.10). It is suggested that a poorly ordered form of hydrozincite that regulates Zn activities at higher levels than well-crystallized natural varieties readily precipitates in CaCO 3(aq)/CaCO 3(s) systems. The environmental significance of this phase is unknown.

Zachara, J. M.; Kittrick, J. A.; Dake, L. S.; Harsh, J. B.

1989-01-01

80

Calcite mesocrystals: "morphing" crystals by a polyelectrolyte.  

PubMed

Crystallization of calcite from different concentrated calcium chloride solutions by the CO(2) vapor diffusion technique in the presence of polystyrenesulfonate (PSS) yields defined assemblies of nanoparticles with unusual morphology. From the typical calcite rhombohedra, the morphology can be systematically varied via rounded edges and truncated triangles to concavely bent lens-like shapes. Although these "crystals" are apparently well facetted as observed in light microscopy, electron microscopy analysis and BET isotherms reveal that the structures are highly porous and are composed of almost perfectly three-dimensionally aligned calcite nanocrystals, scaffolded to the final, partly curved structures. The formation of all mesostructures is discussed within the framework of a polymer-mediated structure-formation process, in which the polymer is acting in four different ways. The present model case also provides evidence for the importance of nonclassical mesoscopic processes in polymer-controlled crystallization in general. PMID:16800016

Wang, Tongxin; Antonietti, Markus; Cölfen, Helmut

2006-07-24

81

Adsorption of sevoflurane by soda-limes.  

PubMed

Dry soda-lime adsorbs significant quantities of halothane, thus influencing on the speed of the induction of anaesthesia with the agent and also on the recovery from anesthesia. Sevoflurane is a new inhaled anesthetic. Although the chemical degradation of sevoflurane with soda-lime has been studied, no information is available about its adsorption by soda-lime. This issue can not be neglected clinically. Two different soda-limes were placed in saturated vapour of sevoflurane for 17 hours to weight adsorbed sevoflurane. Then soda-limes adsorbing sevoflurane was sealed in a test tube after air-drying for 1) 0 min, 2) 10 min, 3) 30 min and 4) 17 hours. The vapour phase of sevoflurane in the test tube at various temperatures were determined using gas chromatography. Sevoflurane vapour concentrations in the test tubes increased in a temperature-dependent manner. Those in the conventional soda-lime were higher than those in the new soda-lime under any experimental conditions. Sevoflurane was released from soda-limes even after air-drying for 17 hours. These results show that much amount of sevoflurane is adsorbed by soda-limes and is released easily in the air. Thus there is a possibility for our patients to inhale unexpected inhaled anesthetics, if we use our anesthetic machine repeatedly. PMID:15278543

Kudo, M; Kudo, T; Matsuki, A

1992-07-01

82

Fly ash chemical classification based on lime  

SciTech Connect

Typically, total lime content (CaO) of fly ash is shown in fly ash reports, but its significance is not addressed in US specifications. For certain applications a low lime ash is preferred. When a class C fly ash must be cementitious, lime content above 20% is required. A ternary S-A-C phase diagram pilot is given showing the location of fly ash compositions by coal rank and source in North America. Fly ashes from subbituminous coal from the Powder River Basin usually contain sufficient lime to be cementitious but blending with other coals may result in calcium being present in phases other than tricalcium aluminate. 9 refs., 1 fig.

Fox, J. [BASF Construction Chemicals, LLC (United States)

2007-07-01

83

Alternate deposition of oriented calcite and amino acid layer on calcite substrates.  

PubMed

Material synthesis inspired by novel nacre architecture and mechanism is popular and has attracted more and more attention. In this paper, iso-oriented calcite tablets/layers and amino acid layers were formed alternately on calcite wafers. It is interesting that the neonatal calcite tablets/layers have the same crystal orientation with their inorganic substrates through amino acid layers. It is quite possible that the amino acid layers in this study could transfer crystal orientation from formed inorganic layers to neighboring neonatal layers due to their fixed and appropriate structures, which may imply the process of nacre formation, and the role of aligned organic matrix sheets in nacre. Moreover, it could provide a new way to produce oriented calcite tablets/layers. PMID:18841888

Qiao, Li; Feng, Qingling; Li, Zhuo; Lu, Shanshan

2008-10-30

84

Olefin hydration  

SciTech Connect

An improved process for the hydration of olefins to alcohols is described wherein the improvement comprises contacting said olefins with the catalytic composition comprising a perfluorinated ion-exchange polymer containing sulfonic acid groups supported on an inert carrier wherein said carrier comprises calcined shot coke with a mean pore diameter of about 1,000 Angstroms in the presence of water at a temperature of from about 180 C to about 250 C.

Butt, M.H.D.; Waller, F.J.

1993-08-03

85

Lime Use in Wastewater Treatment: Design and Cost Data.  

National Technical Information Service (NTIS)

The report presents design and cost information on lime use in wastewater treatment applications. It includes design and cost information on lime handling, liquid processing, solids generation and dewatering, lime recovery and ultimate ash disposal. The r...

D. S. Parker E. de la Fuente L. O. Britt M. L. Spealman R. J. Stenquist

1975-01-01

86

The ionic conductivity in high-pressure polymorphs of calcite  

Microsoft Academic Search

Ionic conductivity of polycrystalline calcite containing varying amounts of PO43-ions was measured in the pressure range of 1–6 GPa and at room temperature. Electrical conductivity increased with pressure corresponding to the phase transition of calcite I to calcite II. The conductivity in calcite III decreased exponentially with pressure. Calculated activation volumes of the conductivity varied with PO43-content in the range

M. Ishikawa; A. Sawaoka; M. Ichikuni

1982-01-01

87

Marine Diagenesis of Shallow Marine Lime-Mud Sediments: Insights from dgrO18 and dgrC13 Data.  

PubMed

Shallow marine lime-mud sediments of the Ste. Genevieve Formation (Mississippian), in part of the Illinois Basin, underwent at least three diagenetic changes: (i) local dolomitization in seawater or a brine, producing dolostone having average deltaC(13) of +2.5 per mille and deltaO(18) of +1.9 per mille (versus PDB-1); (ii) more usually cementation of unreplaced CaCO(3), in intrasediment seawater, yielding isotopically marine lime mudstone mainly composed of calcite, 4-micron or finer, with deltaO(18) of from -1 to +1 per mille; (iii) later partial alteration of CaCO(3), in permeable dolomitic rocks, by isotopically "lighter" waters, to calcite with an estimated deltaO(18) of -10 per mille or less. Isotope data appraised by petrographic analysis thus suggest "submarine" cementation of these carbonates in shallow marine conditions. PMID:17812283

Choquette, P W

1968-09-13

88

Calcite microneedle arrays produced by inorganic ion-assisted anisotropic dissolution of bulk calcite crystal.  

PubMed

Besides studies on the mineralization process, research on the demineralization of minerals provides another way to understand the crystallization mechanism of biominerals and fabricate crystals with complicated morphologies. The formation of ordered arrays of c-axis-oriented calcite microneedles with a tri-symmetric structure and lengths of more than 20??m was realized on a large scale for the first time through anisotropic dissolution of calcite substrates in undersaturated aqueous solution in the presence of ammonium salts. The lengths and the aspect ratios of the calcite microneedles can be tuned by simply changing the concentrations of the ammonium salts and the dissolution time. The shape of the transverse cross sections of the calcite microneedles obtained in the presence of NH4 Cl and NH4 Ac is almost regularly triangular. The tri-symmetric transverse cross-section geometry of the calcite microneedles could be attributed to the tri-symmetric feature of rhombohedral calcite atomic structures, the synergetic interactions between electrostatic interaction of ammonium ions and dangling surface carbonate groups, and the ion incorporation of halide ions. PMID:24644237

Long, Xia; Meng, Ruijie; Wu, Weike; Ma, Yurong; Yang, Dong; Qi, Limin

2014-04-01

89

Calcite precipitation induced by polyurethane-immobilized Bacillus pasteurii  

Microsoft Academic Search

Polyurethane (PU) foam was used to immobilize the whole cell of Bacillus pasteurii. The immobilized cells exhibited the rates of calcite precipitation and ammonia production as high as those of the free cells. Scanning electron micrographs identified the cells embedded in calcite crystals throughout PU matrices. Calcite in PU showed little effect on the elastic modulus and tensile strength of

Sookie S. Bang; Johnna K. Galinat; V. Ramakrishnan

2001-01-01

90

Biologically induced calcite and its isotopic composition in Lake Ontario  

Microsoft Academic Search

We studied water, sediment trap, and core samples from eastern Lake Ontario to reconstruct the factors controlling the biologically induced production and sedimentation of calcite during so-called whiting events. Calcite accumulation and its isotopic composition are controlled by a complex set of interrelated factors, including temperature, primary productivity, and the abundance of pica-cyanobacteria during the stratified period. Calcite precipitation is

David A. Hodell; Claire L. Schelske; Gary L. Fahnenstiel; Lisa L. Robbins

1998-01-01

91

in situ Calcite Precipitation for Contaminant Immobilization  

SciTech Connect

in situ Calcite Precipitation for Contaminant Immobilization Yoshiko Fujita (Yoshiko.fujita@inl.gov) (Idaho National Laboratory, Idaho Falls, Idaho, USA) Robert W. Smith (University of Idaho-Idaho Falls, Idaho Falls, Idaho, USA) Subsurface radionuclide and trace metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of DOE’s greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide strontium-90, is co-precipitation in calcite. Calcite, a common mineral in the arid western U.S., can form solid solutions with trace metals. The rate of trace metal incorporation is susceptible to manipulation using either abiotic or biotic means. We have previously demonstrated that increasing the calcite precipitation rate by stimulating the activity of urea hydrolyzing microorganisms can result in significantly enhanced Sr uptake. Urea hydrolysis causes the acceleration of calcium carbonate precipitation (and trace metal co-precipitation) by increasing pH and alkalinity, and also by liberating the reactive cations from the aquifer matrix via exchange reactions involving the ammonium ion derived from urea: H2NCONH2 + 3H2O ? 2NH4+ + HCO3- + OH- urea hydrolysis >X:2Ca + 2NH4+ ? 2>X:NH4 + Ca2+ ion exchange Ca2+ + HCO3- + OH- ? CaCO3(s) + H2O calcite precipitation where >X: is a cation exchange site on the aquifer matrix. This contaminant immobilization approach has several attractive features. Urea hydrolysis is catalyzed by the urease enzyme, which is produced by many indigenous subsurface microorganisms. Addition of foreign microbes is unnecessary. In turn the involvement of the native microbes and the consequent in situ generation of reactive components in the aqueous phase (e.g., carbonate and Ca or Sr) can allow dissemination of the reaction over a larger volume and/or farther away from an amendment injection point, as compared to direct addition of the reactants at a well (which can lead to clogging). A final particularly attractive characteristic of this approach is its long-term sustainability; the remediation scheme is geared toward environments that are already saturated with respect to calcite, and in such systems the bulk of any newly precipitated calcite will remain stable once engineered manipulations cease. This means that the co-precipitated contaminants will be effectively sequestered over the long term. We are currently conducting integrated field, laboratory, and computational research to evaluate a) the relationships between urea hydrolysis rate, calcite precipitation rate, and trace metal partitioning under environmentally relevant conditions; and b) the coupling between flow/flux manipulations and calcite precipitate distribution and metal uptake. We are also assessing the application of geophysical and molecular biological tools to monitor the relevant chemical and physical processes. The primary emphasis is on field-scale processes, with the laboratory and modeling activities designed specifically to support the field studies. Field experiments are being conducted in perched water (vadose zone) at the Vadose Zone Research Park (VZRP) at the Idaho National Laboratory; the VZRP provides an uncontaminated setting that is an analog of the 90Sr-contaminated vadose zone at the Idaho Nuclear Technology and Engineering Center. A summary of results to date will be presented.

Yoshiko Fujita; Robert W. Smith

2009-08-01

92

The role of silicate surfaces on calcite precipitation kinetics  

NASA Astrophysics Data System (ADS)

The aim of this study is to illuminate how calcite precipitation depends on the identity and structure of the growth substrate. Calcite was precipitated at 25 °C from supersaturated aqueous solutions in the presence of seeds of either calcite or one of six silicate materials: augite, enstatite, labradorite, olivine, basaltic glass and peridotite rock. Calcite saturation was achieved by mixing a CaCl2-rich aqueous solution with a NaHCO3-Na2CO3 aqueous buffer in mixed-flow reactors containing 0.5-2 g of mineral, rock, or glass seeds. This led to an inlet fluid calcite saturation index of 0.6 and a pH equal to 9.1. Although the inlet fluid composition, flow rate, and temperature were identical for all experiments, the onset of calcite precipitation depended on the identity of the seeds present in the reactor. Calcite precipitated instantaneously and at a constant rate in the presence of calcite grains. Calcite precipitated relatively rapidly on labradorite, olivine, enstatite, and peridotite (mainly composed of Mg-olivine) surfaces, but more slowly on augite and basaltic glass. Calcite precipitation rates, however, became independent of substrate identity and mass over time, and all rates approach 10-9.68 ± 0.08 mol/s for ?10 day long experiments and 10-9.21 ± 0.2 mol/s for ?70 day long experiments. Scanning Electron Microscope images showed olivine, enstatite and peridotite surfaces to be covered extensively with calcite coatings at the end of the experiments. Less calcite was found on labradorite and augite, and the least on basaltic glass. In all cases, calcite precipitation occurs on the mineral, rock or glass surfaces. Calcite precipitation on these surfaces, however, negligibly affects the dissolution rates of the silicate grains. These results support ultramafic and basalt carbonation as a long-term carbon storage strategy, as calcite readily precipitates on the surfaces of minerals contained in these rocks without inhibiting their dissolution.

Stockmann, Gabrielle J.; Wolff-Boenisch, Domenik; Bovet, Nicolas; Gislason, Sigurdur R.; Oelkers, Eric H.

2014-06-01

93

Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation  

USGS Publications Warehouse

Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (?c). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and ?c=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10?4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10?4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

Michael M Reddy

2012-01-01

94

Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation  

NASA Astrophysics Data System (ADS)

Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (?c). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and ?c=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10-4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10-4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

Reddy, Michael M.

2012-08-01

95

Estimativa da porosidade de argamassas de cimento e cal pelo método de cálculo de volumes Porosity estimation of cement-lime mortar through the volume calculation method  

Microsoft Academic Search

The presence of lime in mixed mortars is responsible for the increase in the demand for mixing water for a given consistency. The additional water, which is not consumed in the cement hydration, remains free in the system and when evaporating it leads to high porosity in the hardened mortar. This paper presents the method of volume calculation as a

Valdecir Angelo Quarcioni; Fabiano Ferreira Chotoli; Sergio Cirelli Ângulo; Mario Sergio Guilge; Gilberto de Ranieri Cavani; Alessandra Lorenzetti de Castro; Maria Alba Cincotto

96

Sorption of divalent metals on calcite  

Microsoft Academic Search

The sorption of seven divalent metals (Ba, Sr, Cd, Mn, Zn, Co, and Ni) was measured on calcite over a large initial metal (Me) concentration range in constant ionic strength (I = 0.1), equilibrium CaCOâ(s)-CaCOâ(aq) suspensions that varied in pH. At higher initial Me concentrations (10⁻⁵ to 10⁻⁴ mol\\/L) geochemical calculations indicated that the equilibrium solutions were saturated with discrete

J. M. Zachara; C. E. Cowan; C. T. Resch

1991-01-01

97

Biogenic calcite granules--are brachiopods different?  

PubMed

Brachiopods are still one of the least studied groups of organisms in terms of biomineralization despite recent studies indicating the presence of highly complex biomineral structures, particularly in taxa with calcitic shells. Here, we analyze the nanostructure of calcite biominerals, fibers and semi-nacre tablets, in brachiopod shells by high-resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM). We demonstrate that basic mechanisms of carbonate biomineralization are not uniform within the phylum, with semi-nacre tablets composed of spherical aggregates with sub-rounded granules and fibers composed of large, triangular or rod-like particles composed of small sub-rounded granules (40-60 nm). Additionally, proteinaceous envelopes surrounding calcite fibers have been shown for the first time to have a dual function: providing a micro-environment in which granules are produced and acting as the organic template for particle orientation as fiber components. In summary, these new findings in brachiopod shells reveal a complex and distinctive style of biomineralization among carbonate-producing organisms. PMID:23026148

Pérez-Huerta, Alberto; Dauphin, Yannicke; Cusack, Maggie

2013-01-01

98

Lime-pozzolana mortars in Roman catacombs: composition, structures and restoration  

SciTech Connect

Analyses of microsamples collected from Roman catacombs and samples of lime-pozzolana mortars hardened in the laboratory display higher contents in carbonated binder than other subaerial Roman monuments. The measured environmental data inside the Saint Callistus and Domitilla catacombs show a constant temperature of 15-17 deg C, a high CO{sub 2} content (1700 to 3500 ppm) and a relative humidity close to 100%. These conditions and particularly the high CO{sub 2} concentration speed-up the lime calcitization roughly by 500% and reduce the cationic diffusion to form hydrous calcium aluminosilicates. The structure of Roman catacomb mortars shows (i) coarser aggregates and thicker beds on the inside, (ii) thin, smoothed, light and fine-grained external surfaces with low content of aggregates and (iii) paintings and frescoes on the outside. The observed high porosity of the mortars can be attributed to cracking after drying linked with the high binder content. Hardened lime lumps inside the binder denote low water/mortar ratios for slaking. The aggregate tephra pyroclasts rich in aluminosilicate phases with accessorial amounts of Ba, Sr, Rb, Cu and Pb were analysed through X-ray diffraction (XRD), electron microprobe analysis (EMPA) and also by environmental scanning electron microscopy (ESEM) to identify the size and distribution of porosity. Results support procedures using local materials, special mortars and classic techniques for restoration purposes in hypogeal backgrounds.

Sanchez-Moral, Sergio [Museo Nacional de Ciencias Naturales (CSIC), C/ Jose Gutierrez Abascal 2, E-28006 Madrid (Spain)]. E-mail: ssmilk@mncn.csic.es; Luque, Luis [Museo Nacional de Ciencias Naturales (CSIC), C/ Jose Gutierrez Abascal 2, E-28006 Madrid (Spain); Canaveras, Juan-Carlos [Universidad de Alicante, Departamento de Ciencias Tierra and Medio Ambiente, E-03080 Alicante (Spain); Soler, Vicente [Instituto de Productos Naturales y Agrobiologia de Canarias, Avda, Astrofisico Francisco Sanchez 3, E-38206 La Laguna, Tenerife (Spain); Garcia-Guinea, Javier [Museo Nacional de Ciencias Naturales (CSIC), C/ Jose Gutierrez Abascal 2, E-28006 Madrid (Spain); Aparicio, Alfredo [Museo Nacional de Ciencias Naturales (CSIC), C/ Jose Gutierrez Abascal 2, E-28006 Madrid (Spain)

2005-08-01

99

Hydrates of hydrocarbons  

SciTech Connect

Gas hydrates are solid crystalline compounds of water and methane that are similar to snow. They form in and block gas wells and lines and cause fouling of heat exchangers when the gas is cooled. Here, finally, is long-awaited information detailing the successful methods for not only removing gas hydrates but also for preventing their reforming. This book addresses methods of hydrate removal and, most importantly, prevention of hydrate build-up. New topics of using hydrate properties for new technologies and production of gas from natural gas hydrate deposits are also discussed. Information specific to hydrate formation in gas includes: conditions and area of hydrate-carrying rock; estimating gas amounts in gas hydrate deposits; the role of natural gas hydrates in global changes; the physical principles and models of gas hydrate deposit development; results of the Messoyakhi gas hydrate field development; and hydrates in space. Contents includes: Physical-chemical aspects; Properties of hydrates; Mechanism of hydrate formation; Technological appellations of hydrates; Natural hydrates of gases; Conclusion; and Bibliography.

Makogon, Y.F. [Moscow Petroleum Inst. (Russian Federation)

1997-12-31

100

Reactions of lime with aluminate-containing solutions  

Microsoft Academic Search

In the Bayer process for refining alumina, lime (either quicklime or slaked lime) is added to the process liquor to precipitate calcium carbonate and restore alkalinity to the solution. Lime also precipitates calcium aluminate in an unwanted side reaction which consumes both lime and aluminate. The work described in this paper was undertaken to elucidate the mechanism of this precipitation

B. A. Xu; D. E. Giles; I. M. Ritchie

1997-01-01

101

Sr, Cd, Mn and Co distribution coefficients in calcite as a function of calcite precipitation rate  

NASA Astrophysics Data System (ADS)

Distribution coefficients, as a function of precipitation rate, were determined for the metals Sr 2+, Co 2+, Mn 2+ and Cd 2+in calcite. A pH-stat was used to maintain a constant degree of-saturation, and hence precipitation rate, during each coprecipitation run. The precipitation rate was proportional to the degree of supersaturation and the mass of seed crystal introduced. Distribution coefficients (?) as a function of rate were determined using radioactive isotopes for solutions with saturations ? = 1 to ? = 5.5. Strontium distribution coefficients increased with increasing precipitation rate, while Co, Mn and Cd distribution coefficients decreased with increasing precipitation rate. The following rate expressions (at 25°C) were derived: log?Sr = 0.249 log R -1.57 log?Mn = -0.266 log R + 1.35 log?Co = -0.173 log R + 0.68 log?Cd = -0.194 log R + 1.46 where R is the observed precipitation rate in nmoles CaCO 3 per mg seed crystal per min. In separate experiments the uptake of radioactive isotopes was monitored during the recrystallization of calcite seed crystals. Rates of recrystallization were from 100 to 10, 000 times slower than the pH-stat experiments, but yielded distribution coefficients consistent with the above rate expressions. Using gross estimates of biogenic crystal growth rates, aragonite to calcite transformation rates, and the above Sr rate expression, biogenic calcite and diagenetic calcite Sr contents are estimated. These experiments indicate that in addition to solution composition, precipitation rate is a significant factor influencing the trace metal content of naturally occurring calcite.

Lorens, Robert B.

1981-04-01

102

Effects of calcite and magnesite application to a declining Masson pine forest on strongly acidified soil in Southwestern China.  

PubMed

Liming of strongly acidified soil under a Masson pine (Pinus massoniana Lamb.) forest was studied through a seven-year field manipulation experiment at Tieshanping, Chongqing in Southwestern China. To distinguish between the individual effects of Ca(2+) and Mg(2+) addition, we separately applied calcite (CaCO3) and magnesite (MgCO3), rather than using dolomite [CaMg(CO3)2]. Both calcite and magnesite additions caused a significant increase in pH and a decrease in dissolved inorganic monomeric aluminium (Ali) concentration of soil water. Ecological recovery included increases of herb biomass (both treatments) and Mg content in Masson pine needles (magnesite treatment only). However, the growth rate of Masson pine did not increase under either treatment, possibly because of nutrient imbalance due to phosphorus (P) deficiency or limited observation period. In China, acid deposition in forest ecosystems commonly coincides with large inputs of atmogenic Ca(2+), both enhancing Mg(2+) leaching. Calcite addition may further decrease the Mg(2+) availability in soil water, thereby exacerbating Mg(2+) deficiency in the acidified forest soils of southern and southwestern China. The effect of anthropogenic acidification of naturally acid forest soils on P availability needs further study. PMID:24631610

Huang, Yongmei; Kang, Ronghua; Ma, Xiaoxiao; Qi, Yu; Mulder, Jan; Duan, Lei

2014-05-15

103

Effects of Pretreatment and Drying on Composition and Bitterness of High-Dietary-Fiber Powder from Lime Residues  

Microsoft Academic Search

Lime residues after juice extraction were used as a starting raw material to produce high-dietary-fiber powder. The effects of pretreatment—i.e., blanching and ethanol soaking (55–95% v\\/v)—and hot air drying at 60–100°C on the proximate composition and limonin, a substance responsible for bitterness in citrus fruits, were evaluated. Hydration properties—i.e., water retention capacity and swelling capacity—and visual color were also determined.

P. Wuttipalakorn; W. Srichumpuang; N. Chiewchan

2009-01-01

104

Thorough investigation of the oxygen heterocyclic fraction of lime (Citrus aurantifolia (Christm.) Swingle) juice.  

PubMed

Reversed-phase-HPLC analysis by means of superficially porous silica particle columns (fused-core) was applied to the investigation of flavonoids, coumarins, and psoralens in lime juice samples. Hesperidin (367.0 ± 16.0 ppm) and eriocitrin (148.0 ± 7.9 ppm) were the most abundant flavonoids. Fifteen coumarins and furocoumarins were determined, including bergamottin (29.6 ± 1.1 ppm), 5-geranyloxy-7-methoxycoumarin (16.5 ± 0.6 ppm), and oxypeucedanin hydrate (9.9 ± 0.5 ppm) as predominant compounds. These molecules are today well known for their beneficial effects on human health. As a consequence, the present study, beyond investigating for the first time the chemical composition of lime juice, highlights also its health-promoting qualities, due to its content of flavonoids and coumarins. PMID:24478239

Costa, Rosaria; Russo, Marina; De Grazia, Selenia; Grasso, Elisa; Dugo, Paola; Mondello, Luigi

2014-04-01

105

Clathrate hydrates in nature.  

PubMed

Scientific knowledge of natural clathrate hydrates has grown enormously over the past decade, with spectacular new findings of large exposures of complex hydrates on the sea floor, the development of new tools for examining the solid phase in situ, significant progress in modeling natural hydrate systems, and the discovery of exotic hydrates associated with sea floor venting of liquid CO2. Major unresolved questions remain about the role of hydrates in response to climate change today, and correlations between the hydrate reservoir of Earth and the stable isotopic evidence of massive hydrate dissociation in the geologic past. The examination of hydrates as a possible energy resource is proceeding apace for the subpermafrost accumulations in the Arctic, but serious questions remain about the viability of marine hydrates as an economic resource. New and energetic explorations by nations such as India and China are quickly uncovering large hydrate findings on their continental shelves. PMID:21141039

Hester, Keith C; Brewer, Peter G

2009-01-01

106

Zinc isotope fractionation during adsorption on calcite  

NASA Astrophysics Data System (ADS)

Zinc is an important element as a nutrient in the marine biosphere. However, our understanding of its biogeochemical cycling in the oceans is relatively limited. The Zn stable isotope system holds the promise of providing novel insights, since published Zn isotopic values for various natural samples reveal significant fractionations in the marine environment. Surface seawater, basalts, shales, deep-sea clay sediments, sediment trap material, bulk plankton and zooplankton samples, and eolian dust fall within a tight range (?66/64Zn from -0.1 to 0.5‰), but modern ferromanganese crusts (?66/64Zn from 0.5 to 1.2‰), as well as carbonates (?66/64Zn from 0.3 to 1.4‰), are notably enriched in heavy Zn isotopes [1-4]. In this study we seek to constrain the mechanism by which carbonates are enriched in heavier isotopes. In particular, we have conducted experiments to quantify isotope fractionation during adsorption of Zn onto the surfaces of calcite crystals that are in equilibrium with solution. The adsorption experiments were carried out in a series of small-volume batch reactions in a clean laboratory environment, using high-purity reagents and calcite seed crystals. The calcite was equilibrated with the solution prior to addition of Zn at atmospheric CO2 pressure (i.e., in air) for 5 days until a stable pH of 8.3 was reached. Later, a small aliquot of dissolved ZnCl2 was added such that the solution remained undersaturated with respect to hydrozincite. Experimental duration varied among the replicates from 6 to 144 hours, and then all solids and solutions were separated by filtration, purified by ion exchange chromatography, and analyzed by MC-ICP-MS. Zn adsorbed on calcite is isotopically heavier than in the co-existing solutions, with ?68/66Zncalcite-solution of approximately 0.3‰. The variation of ?68/66Zncalcite-solution beyond 24 hours is insignificant, so we infer that isotopic equilibrium is reached by this time. Previous work strongly suggests that a difference in coordination number between dissolved Zn and adsorbed Zn is drives the observed fractionation. Elzinga and Reeder[5] determined using EXAFS (Extended X-ray Absorption Fine Structure) that Zn adsorbed to calcite surfaces is tetrahedrally coordinated, sharing three oxygens with the calcite surface. Meanwhile density functional theory calculations[6] predicted that tetrahedral Zn-O species should be heavier than octahedral Zn-O species. Thus we infer that equilibrium between octahedrally coordinated, dissolved Zn and tetrahedrally coordinated, adsorbed Zn is the mechanism of fractionation in our experiments. Our further studies will determine whether the isotopically heavy pool of adsorbed Zn becomes the Zn incorporated within carbonates; if so, then we are closer to understanding the mechanism by which carbonate rocks in nature are enriched in heavier isotopes of zinc. [1] Bermin et al., 2006, Chem. Geol. 226, 280. [2] Maréchal et al., 2000, Geochem. Geophys. Geosyst. 1, 1999GC-000029. [3] Dong et al., 2013, Talanta 114, 103-109. [4] Pichat et al., 2003, Earth Planet. Sci. Lett. 210, 167-178. [5] Elzinga and Reeder, 2002, Geochim. Cosmochim. Acta 66, 3943-3954. [6] Schauble, 2003, EOS, Trans. AGU, Fall Meet. Suppl. 84(46), B12B-0781.

Dong, S.; Wasylenki, L. E.

2013-12-01

107

Removal of organic magnesium in coccolithophore calcite  

NASA Astrophysics Data System (ADS)

Coccolithophore calcite refers to the plates of calcium carbonate (CaCO3) produced by the calcifying phytoplankton, coccolithophores. The empirical study of the elemental composition has a great potential in the development of paleoproxies. However, the difficulties to separate coccolithophore carbonates from organic phases hamper the investigation of coccoliths magnesium to calcium ratios (Mg/Ca) in biogeochemical studies. Magnesium (Mg) is found in organic molecules in the cells at concentrations up to 400 times higher than in inorganically precipitated calcite in present-day seawater. The aim of this study was to optimize a reliable procedure for organic Mg removal from coccolithophore samples to ensure reproducibility in measurements of inorganic Mg in calcite. Two baseline methods comprising organic matter oxidations with (1) bleach and (2) hydrogen peroxide (H2O2) were tested on synthetic pellets, prepared by mixing reagent grade CaCO3 with organic matter from the non-calcifying marine algae Chlorella autotrophica and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH2OH·HCl + NH4OH)] followed by three consecutive oxidations (using H2O2) yielded the best cleaning efficiencies, removing >99% of organic Mg in 24 h. P/Ca and Fe/Ca were used as indicators for organic contamination in the treated material. The optimized protocol was tested in dried coccolithophore pellets from batch cultures of Emiliania huxleyi, Calcidiscus leptoporus and Gephyrocapsa oceanica. Mg/Ca of treated coccolithophores were 0.151 ± 0.018, 0.220 ± 0.040, and 0.064 ± 0.023 mmol/mol, respectively. Comparison with Mg/Ca literature coccolith values, suggests a tight dependence on modern seawater Mg/Ca, which changes as a consequence of different seawater origins (<10%). The reliable determination of Mg/Ca and Sr/Ca, and the low levels of organic contamination (Fe/Ca and P/Ca) make this protocol applicable to field and laboratory studies of trace elemental composition in coccolithophore calcite.

Blanco-Ameijeiras, S.; Lebrato, M.; Stoll, H. M.; Iglesias-Rodriguez, M. D.; Méndez-Vicente, A.; Sett, S.; Müller, M. N.; Oschlies, A.; Schulz, K. G.

2012-07-01

108

Full Scale Demonstration of Lime Stabilization.  

National Technical Information Service (NTIS)

The project objective was to demonstrate and evaluate the feasibility, economics, and benefits of stabilizing primary, waste activated, septic, and anaerobically digested sludges by lime addition. The project confirmed the findings of previous laboratory ...

R. F. Noland J. D. Edwards M. Kipp

1978-01-01

109

FULL SCALE DEMONSTRATION OF LIME STABILIZATION  

EPA Science Inventory

The project objective was to demonstrate and evaluate the feasibility, economics, and benefits of stabilizing primary, waste activated, septic, and anaerobically digested sludges by lime addition. The project confirmed the findings of previous laboratory and pilot scale tests and...

110

Calcite Crystal Growth Rate Inhibition by Polycarboxylic Acids  

Microsoft Academic Search

Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg\\/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg\\/L. Calcite crystal

Michael M. Reddy; Anthony R. Hoch

2001-01-01

111

Uranyl Incorporation in Organic-Bearing Soil Calcite  

Microsoft Academic Search

Phosphor imaging and fission track maps reveal a close correlation between uranium and organic-rich calcite that lines roots in an ancient caliche soil. Concordant U-Pb ages show that this uranium has not been mobilized since the soil calcite formed 298 ñ 1 Ma ago. Luminescence spectroscopic analysis of the organic-rich calcite demonstrates that uranium is present in the oxidized state.

E. Rasbury; C. Tait; R. J. Donohoe

2003-01-01

112

Cloud Condensation Nucleus Activity of calcite and calcite coated with model humic and fulvic acids  

NASA Astrophysics Data System (ADS)

Many recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of common inactive cloud nuclei, such as mineral aerosol. As many studies have shown that a large fraction of unidentified organic material in aerosol particles is composed of polycarboxylic acids resembling humic substances, the presence of these large molecular weight Humic-Like Substances (HULIS) may also alter the water adsorption and CCN activity of mineral aerosol. Thus, we have measured the water adsorption and CCN activity of model humic and fulvic acids. Additionally, the water adsorption and CCN activity of mineral aerosol particles coated with humic and fulvic acids have been studied. We find that humic and fulvic acids show continual multilayer water adsorption as the relative humidity is raised. Additionally, we find that calcite particles mixed with humic and fulvic acids take up more water by mass, by a factor of two, compared to the uncoated calcite particles at approximately 70% RH. CCN measurements also indicate that internally mixed calcite-humic or fulvic acid aerosols are more CCN active than the otherwise inactive, uncoated calcite particles. Our results suggest that mineral aerosol particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the Earth's atmosphere than single-component mineral aerosol.

Hatch, C. D.; Gierlus, K. M.; Schuttlefield, J. D.; Grassian, V. H.

2007-12-01

113

Protein-induced, previously unidentified twin form of calcite  

PubMed Central

Using single-crystal x-ray diffraction, we found a formerly unknown twin form in calcite crystals grown from solution to which a mollusc shell-derived 17-kDa protein, Caspartin, was added. This intracrystalline protein was extracted from the calcitic prisms of the Pinna nobilis shells. The observed twin form is characterized by the twinning plane of the (108)-type, which is in addition to the known four twin laws of calcite identified during 150 years of investigations. The established twin forms in calcite have twinning planes of the (001)-, (012)-, (104)-, and (018)-types. Our discovery provides additional evidence on the crucial role of biological macromolecules in biomineralization.

Pokroy, B.; Kapon, M.; Marin, F.; Adir, N.; Zolotoyabko, E.

2007-01-01

114

Biogenic and synthetic high magnesium calcite - a review.  

PubMed

Systematic studies on the Mg distributions, the crystal orientations, the formation mechanisms and the mechanical properties of biogenic high-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites in the hard tissues of marine organisms mentioned generally own a few common features as follows. Firstly, the Mg distribution is not uniform in most of the minerals. Secondly, high-Mg calcite biominerals are usually composed of nanoparticles that own almost the same crystallographic orientations and thus they behave like single crystals or mesocrystals. Thirdly, the formation of thermodynamically unstable high-Mg calcites in marine organisms under mild conditions is affected by three key factors, that is, the formation of amorphous calcium (magnesium) carbonate precursor, the control of polymorph via biomolecules and the high Mg/Ca ratios in modern sea. Lastly, the existence of Mg ions in the Mg-containing calcite may improve the mechanical properties of biogenic minerals. Furthermore, the key progress in the synthesis of high-Mg calcites in the laboratory based on the formation mechanisms of the biogenic high-Mg calcites was reviewed. Many researchers have realized the synthesis of high-Mg calcites in the laboratory under ambient conditions with the help of intermediate amorphous phase, mixed solvents, organic/inorganic surfaces and soluble additives. Studies on the structural analysis and formation mechanisms of thermodynamically unstable biogenic high-Mg calcite minerals may shed light on the preparation of functional materials with enhanced mechanical properties. PMID:24291472

Long, Xia; Ma, Yurong; Qi, Limin

2014-01-01

115

Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED)  

SciTech Connect

The pure calcite surface was examined using techniques sensitive to the near-surface (XPS and LEED) immediately after fracture in ultra-high vacuum (10{sup {minus}10} mbar) and then following exposure to various atmospheres and aqueous solutions that were free of trace metals. These spectroscopic techniques allow molecular-level observations that offer the possibility of gaining more insight into geochemical processes elucidated from macroscopic solution studies. Several absolute electron binding energies for the atoms in calcite were redetermined with XPS using the gold dot method. Surface hydration is also supported, independently, by the XPS peak intensity ratios and is consistent with adsorption theory derived from macroscopic solution studies. The modified oxygen Auger parameter, {alpha}{prime}, (using O{sub 1s} and O(KVV)), was found to be 1043.9 eV for all samples of calcite tested, whether powder or cleaved from iceland Spar, clean or contaminated by adventitious carbon, freshly fractured, or exposed briefly to water, or in the process of dissolution or precipitation. LEED patterns of the {l brace}101{r brace} cleavage surface of samples that were freshly fractured in air and that were exposed to dissolving or precipitating solutions showed that the top few atomic layers exhibit long range order. Lattice spacings at the surface are statistically identical to those of bulk calcite, though some surface CO{sub 3} groups may be rotated relative to the bulk structure. This work provides direct, molecular-level evidence for the processes of reconfiguration and hydration at the calcite surface. These results provide a basis for future spectroscopic studies of trace metal adsorption on calcite and subsequent solid-solution formation.

Stipp, S.L.; Hochella, M.F. Jr. (Stanford Univ., CA (United States))

1991-06-01

116

Effect of micromorphological development on the elastic moduli of fly ash-lime stabilized bentonite  

SciTech Connect

The mineralogical and micromorphological changes occurring in fly ash-lime stabilized bentonite were observed and related to changes in elastic moduli of the stabilized mixture. Compacted fly ash, fly ash-lime, bentonite-lime, bentonite-fly ash, and bentonite-fly ash-lime mixtures were prepared and cured at 23C and 50C, for 1, 28, 90 and 180 days. The development of microstructure and cementitous crystals were observed by a scanning electron microscope, and energy dispersive spectrum analyzer and a X-ray diffractometer. The elastic moduli and strengths were obtained from unconsolidated undrained triaxial and unconfined compressive strength tests. The physical test results were compared with changes observed by scanning electron microscopy and X-ray diffraction. CSH gel Type I, II and III, ettringite, afwillite and tetracalcium aluminate thirteen hydrate crystals were identified in the cured specimens. The elastic modulus of the fly ash-lime stabilized bentonite was higher than the untreated bentonite and the increase in elastic modulus corresponded to the curing times when new cementitious crystals were observed. Acicular crystals (CSH Type I and II) and ettringite crystals spanned the pores and increased the contact points where blocky aggregates of equant crystals (CSH III) engulfed the fly ash grains providing support. The compressive strength increased, and the strain at a failure decreased resulting in an increase in the elastic modulus. Some fly ash grains providing support for montmorillonite aggregates dissolved and created weak spots in the matrix, causing a decrease in elastic modulus at longer curing periods. At 50C curing temperature the same cementitious crystals were observed as at 23C. However, the rate of the reactions increased considerably.

Baykal, G.I.

1987-01-01

117

Spectroscopic characterization of natural calcite minerals  

NASA Astrophysics Data System (ADS)

The FT-IR, FT-Raman, NMR spectral data of ten different limestone samples have been compared. FT-IR and FT-Raman spectral data show that calcium carbonate in limestone, principally in the form of calcite, as identified by its main absorption bands at 1426, 1092, 876 and 712 cm -1. The sharp diffractions at the d-spacings, 3.0348, 1.9166 and 1.8796 confirm the presence of calcite structure and the calculated lattice parameters are: a = 4.9781 Å, c = 17.1188 Å. The range of 13C chemical shifts for different limestone samples is very small, varying from 198.38 to 198.42 ppm. The observed chemical shifts are consistent with the identical C-O bonding in different limestone samples. 27Al MAS NMR spectra of the samples exhibit a central line at 1 ppm and another line at 60 ppm corresponding to octahedral and tetrahedral Al ions, respectively. The five component resonances were observed in 29Si MAS NMR spectrum of limestone and these resonances were assigned to Si (4 Al), Si (3 Al), Si (2 Al), Si (1 Al) and Si (0 Al) from low field to high field.

Gunasekaran, S.; Anbalagan, G.

2007-11-01

118

The Coordination of Mg in Foraminiferal Calcite  

NASA Astrophysics Data System (ADS)

The Mg/Ca ratio in calcite shells ('tests') of foraminifera is an empirical ocean temperature proxy widely used to interpret palaeoclimates. We explore the distribution and local environment of Mg in foram tests using STXM and NEXAFS spectroscopy to test the fundamental assumptions behind the proxy, and shed light on the mechanisms underpinning this vital oceanographic tool. Throughout the development of the Mg/Ca proxy, it has been assumed that Mg in foraminifera tests substitutes directly into the calcite lattice (1). This assumption is based on XRD analyses of various high-Mg biogenic carbonates, where Mg concentrations are manifest in the shifted position of diffraction peaks (2, 3). The extrapolation of this trend to foraminiferal calcite links the proxy to inorganic precipitation experiments, and provides a theoretical mechanistic framework to understand the link between Mg/Ca and temperature: the substitution of Mg is endothermic, and favoured at higher temperatures. However, the concentration of Mg in most foraminifera (0-10 mmol/mol Mg/Ca) is below the detection limit of XRD methods, and the analogy to inorganic systems has not been explicitly tested. Electron microprobe (4-6), LA-ICP-MS (7) and high-resolution nanoSIMS mapping (Sadekov, unpub.) of foraminifera tests have revealed the presence of high 'trace element' bands running in plane with the test surface, enriched in Mg, Sr, S, organic molecules and other trace elements. This emphasises a key question highlighted by Dodd (1) when the proxy was still in its infancy: how is Mg incorporated into mineral skeletons? By direct substitution into the calcite lattice, interstitially in a separate distinct mineral phase, or associated with organic compounds? We address this fundamental question using scanning transmission X-ray microscopy (STXM) and X-ray absorption spectroscopy at ALS beamline 11.0.2 to examine the distribution and local atomic environment of Mg in two contrasting species of foraminifera. Our data conclusively demonstrate that the Mg in the high- and low-trace element bands in the two different species is incorporated in the same mode. Foraminiferal Mg K-edge spectra are most similar to that of dolomite, where Ca and Mg are interchangeable and both present in octahedral sites. This indicates that Mg directly substitutes for Ca in the calcite test, validating the assumptions underlying the use of the Mg/Ca proxy. The uniformity of Mg environment also sheds light on the drivers of Mg heterogeneity, suggesting that Mg banding is driven by fluctuations in medium chemistry, rather than any change in Mg incorporation mechanism. The ultimate cause of Mg heterogeneity remains an open question, however. 1. J. R. Dodd, J Paleontology, 1313-1329 (1967). 2. K. E. Chave, J Geol 62, 266-283 (1954). 3. J. Titschack, F. Goetz-Neunhoeffer, J. Neubauer, Am Min 96, 1028 (2011). 4. J. Lipps, P. Ribbe, J Paleontology 41, 492-496 (1967). 5. A. Y. Sadekov, S. M. Eggins, P. de Deckker, G3 6, Q12P06 (2005). 6. J. Erez, Rev Min Geochem 54, 115 (2003). 7. A. Y. Sadekov, S. M. Eggins, G. P. Klinkhammer, Y. Rosenthal, Earth Planet Sc Lett 292, 312-324 (2010).

Branson, O.; Redfern, S. A.; Tyliszczak, T.; Sadekov, A.; Langer, G.; Elderfield, H.

2012-12-01

119

Authigenic carbonates from the Cascadia subduction zone and their relations to gas hydrate stability  

SciTech Connect

Authigenic carbonates are intercalated with massive gas hydrates in sediments of the Cascadia margin. The deposits were recovered from the uppermost 50 cm of sediments on the southern summit of the Hydrate Ridge during the RV Sonne cruise SO110. Two carbonate lithologies that differ in chemistry, mineralogy, and fabric make up these deposits. Microcrystalline high-magnesium calcite (14 to 19 mol% MgCO{sub 3}) and aragonite are present in both semiconsolidated sediments and carbonate-cemented clasts. Aragonite occurs also as a pure phase without sediment impurities. It is formed by precipitation in cavities as botryoidal and isopachous aggregates within pure white, massive gas hydrate. Variations in oxygen isotope values of the carbonates reflect the mineralogical composition and define two end members: a Mg-calcite with {delta}{sup 18}O = 4.86% PDB and an aragonite with {delta}{sup 18}O = 3.68% PDB. On the basis of the ambient bottom-water temperature and accepted equations for oxygen isotope fractionation, the authors show that the aragonite phase formed in equilibrium with its pore-water environment, and that the Mg-calcite appears to have precipitated from pore fluids enriched in {sup 18}O. Oxygen isotope enrichment probably originates from hydrate water released during gas-hydrate destabilization.

Bohrmann, G.; Greinert, J.; Suess, E. [GEOMAR, Kiel (Germany). Forschungszentrum fuer Marine Geowissenschaften] [GEOMAR, Kiel (Germany). Forschungszentrum fuer Marine Geowissenschaften; Torres, M. [Oregon State Univ., Corvallis, OR (United States). Coll. of Oceanic and Atmospheric Sciences] [Oregon State Univ., Corvallis, OR (United States). Coll. of Oceanic and Atmospheric Sciences

1998-07-01

120

Investigation of Accelerated Curing of Soil-Lime and Lime-Fly Ash-Aggregate Mixtures.  

National Technical Information Service (NTIS)

The objectives of this investigation were to examine current mix design procedures for soil-lime and lime-fly ash-aggregate mixtures and to develop accelerated curing test procedures for estimating long-term field strengths. Unconfined compression tests w...

F. C. Townsend R. T. Donaghe

1976-01-01

121

Colloidal stability of calcite dispersion treated with sodium polyacrylate  

Microsoft Academic Search

The stabilising action of sodium polyacrylate on colloidal dispersions of calcite has been investigated through measurement of viscosity, ion concentration and electrophoretic mobility. The dose of sodium polyacrylate was in the range 0 to 28 mg per g of calcite and the dispersions were prepared at a sodids content of 70% (by weight). The ionic strength of the dispersions, ca.

K. R. Rogan; A. C. Bentham; I. A. George; D. R. Skuse

1994-01-01

122

Nanofiber calcite in Asian dust and its atmospheric roles  

Microsoft Academic Search

Calcite is the most important mineral in Asian dust, and it reacts with atmospheric gases during its long-range transport. Mineralogical and chemical analyses of Asian dust and source soils showed two types of calcite that differ greatly in morphology and origin: (i) micron-sized irregular particles derived from the erosion of bedrock, and (ii) nanosized fibers that were chemically precipitated in

Gi Young Jeong; Youngsin Chun

2006-01-01

123

The kinetics of microstructural evolution during deformation of calcite  

Microsoft Academic Search

There is a strong coupling between the microstructure and the strength of rocks that is thought to play a key role in the evolution of shear zones and in our ability to interpret the mechanics of natural deformation processes. To investigate the microstructural evolution of calcite-rich rocks, we have performed a series of hydrostatic and deformation experiments on synthetic calcite

Nicholas Austin; Brian Evans

2009-01-01

124

The effect of high curing temperature on the reaction kinetics in MK/lime and MK-blended cement matrices at 60 deg. C  

SciTech Connect

It is well known that the pozzolanic reaction between metakaolin (MK) and calcium hydroxide produces CSH, C{sub 2}ASH{sub 8} (stratlingite), C{sub 4}AH{sub 13} and C{sub 3}ASH{sub 6} (hydrogarnet). However, the presence or absence of these hydrated phases depends on different parameters, such as curing temperature, matrix used, etc. This paper shows the results of a study in order to know the effect of high curing temperature (60 deg. C) on the kinetics of the pozzolanic reaction in different matrices. MK/lime (calcium hydroxide) and MK-blended cement matrices were studied in samples stored and cured at 60 deg. C and up to 123 days of hydration. The nature, sequence and crystallinity of the hydrated phases were analysed using differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Results showed that the sequence and formation of the hydrated phases was different in both matrices cured at 60 deg. C. In an MK/lime matrix, C{sub 2}ASH{sub 8}, C{sub 4}AH{sub 13} and C{sub 3}ASH{sub 6} were the main hydrated phases; while in an MK-blended cement, stratlingite was the sole hydrated phase issued from pozzolanic reaction. The DTA and XRD data also reveal an important fact: there is no evidence of the presence of hydrogarnet in blended cements.

Rojas, Moises Frias; Sanchez de Rojas, M.I

2003-05-01

125

Fractal Statistics of Modeled Zoning Patterns in Calcite  

NASA Astrophysics Data System (ADS)

In recent years, the phenomenon of oscillatory zoning has been established in more than 70 rock-forming and accessory minerals having been formed in different geological media [Shore & Fowler, 1996]. Observations of oscillatory zoning in solution-grown calcite crystals are reported by Reeder et al. [1990]. In these calcites periodic zonal variations in Mn2+ content were not correlated with changes in any bulk solution parameters, and it was interpreted that the oscillatory behavior developed autonomously. Wang and Merino [1992] describe a dynamic model for calcite grown from an aqueous solution containing growth-inhibiting cations such as Mn2+. This model, based on a feedback involving H+ accumulation, surface adsorption, and calcite growth inhibition is able to autonomously produce oscillatory changes of Ca2+ and H2CO3 concentrations adjacent to a calcite growth surface without large-scale changes in bulk water chemistry.

Bryksina, Natalia; Halden, Norman; Mejia, Sergio

126

The ionic conductivity in high-pressure polymorphs of calcite  

NASA Astrophysics Data System (ADS)

Ionic conductivity of polycrystalline calcite containing varying amounts of PO{4/3-}ions was measured in the pressure range of 1 6 GPa and at room temperature. Electrical conductivity increased with pressure corresponding to the phase transition of calcite I to calcite II. The conductivity in calcite III decreased exponentially with pressure. Calculated activation volumes of the conductivity varied with PO{4/3-}content in the range of 0.94 5.34 cm3/mol. This variation corresponded to the lattice parameter change of calcite I due to PO{4/3-}incorporation and indicated the contribution of CO{3/2-}-vacancies associated with PO{4/3-}ions to the conductivity.

Ishikawa, M.; Sawaoka, A.; Ichikuni, M.

1982-11-01

127

Transformation of echinoid Mg calcite skeletons by heating  

NASA Astrophysics Data System (ADS)

Interambularcral plates of echinoid Heterocentrotus trigonarius, composed of Mg calcite 1 (?14 mol% MgCO 3), were heated in three timed series of experiments at 300°C. Dried plate fragments and fragments with added water were heated separately in pressurized bombs. X-ray powder diffractometry, unit cell dimensions, and phase compositions are used to monitor reaction progress. After 10 h heating in the bombs dolomite (43.5 mol% MgCO 3) and Mg calcite appear (4-7 mol% MgCO 3); by 20 h all Mg calcite 1 is consumed, and at 120 h dolomite composition has evolved to ?47 mol% MgCO 3 and calcite to ?2 mol% MgCO 3. Whole plates heated at 300°C in an open muffle furnace develop dolomite (?42 mol% MgCO 3) and Mg calcite 2 (?6 mol% MgCO 3) after 10 h and remain compositionally invariant throughout subsequent heating to 620 h. Limited skeletal water catalyzes the early reaction but escapes from the open furnace and consequently reaction ceases after ?10 h. The experimentally produced dolomite has relative Mg-Ca ordering of 75% to 79%. The stabilization of echinoid Mg calcite by heating at 300°C to a mixture of dolomite and calcite occurs through a dissolution/precipitation reaction. The alteration fabric produced within the stereom consists of irregularly shaped, branched dolomite crystals > 5 ?m homoaxially set in a calcite 2 (bomb) or Mg calcite 2 (furnace) matrix. Round and tubular pores 1 to 5 ?m are randomly distributed throughout this fabric. The stereom pore system remains intact during furnace heating but is destroyed during heating in bombs. The texture of experimentally stabilized echinoid skeletons is different from that of fossil echinoderms that are composed of microrhomic dolomite homoaxially set in a single calcite crystal.

Dickson, J. A. D.

2001-02-01

128

Natural Gas Hydrates  

Microsoft Academic Search

This paper reports on gas clathrates (commonly called hydrates), which are crystalline compounds that occur when water form a cage-like structure around smaller guest molecules. Gas hydrates of interest to the natural gas hydrocarbon industry are composed of water and eight molecules: methane, ethane, propane, isobutane, normal butane, nitrogen, carbon dioxide, and hydrogen sulfide. Hydrate formation is possible in any

E. Sloan Jr.; E. D. Jr

1991-01-01

129

LIME KILN BUILDING, KILN BOTTOM SHOWING ROTATOR GEAR. (GEAR IS ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

LIME KILN BUILDING, KILN BOTTOM SHOWING ROTATOR GEAR. (GEAR IS POINTED DOWN FOR PROPER ORIENTATION). - Solvay Process Company, Lime Kiln Building, Between Willis & Milton Avenues, Solvay, Onondaga County, NY

130

Structure and bonding environments at the calcite surface as observed with X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED)  

NASA Astrophysics Data System (ADS)

The pure calcite surface was examined using techniques sensitive to the near-surface (XPS and LEED) immediately after fracture in ultra-high vacuum (10 -10 mbar) and then following exposure to various atmospheres and aqueous solutions that were free of trace metals. These spectroscopic techniques allow molecular-level observations that offer the possibility of gaining more insight into geochemical processes elucidated from macroscopic solution studies. Several absolute electron binding energies for the atoms in calcite were redetermined with XPS using the gold dot method. The results are 290.1 ± 0.1 eV for C 1 s, 347.7 and 351.2 ± 0.15 eV for Ca 2 psol3/2 and Ca 2 psol1/2, respectively, and 531.9 ± 0.15 eV for O 1 s. Photoelectron energy shifts from main peak positions suggest that immediately after fracture in ultra-high vacuum, bond reconfiguration leads to the formation of carbide-like bonds between Ca and C at the surface. Calcite that has been exposed to water, even as vapour from the atmosphere, shows binding energy shifts that indicate the presence of S · CO 3H and S · CaOH where S · represents the calcite surface. Surface hydration is also supported, independently, by the XPS peak intensity ratios and is consistent with adsorption theory derived from macroscopic solution studies. The modified oxygen Auger parameter, ?', (using O 1 s and O(KVV)), was found to be 1043.9 eV for all samples of calcite tested, whether powder or cleaved from Iceland Spar, clean or contaminated by adventitious carbon, freshly fractured, or exposed briefly to water, or in the process of dissolution or precipitation. LEED patterns of the {101} cleavage surface of samples that were freshly fractured in air and that were exposed to dissolving or precipitating solutions showed that the top few atomic layers exhibit long range order. Lattice spacings at the surface are statistically identical to those of bulk calcite, though some surface CO 3 groups may be rotated relative to the bulk structure. This work provides direct, molecular-level evidence for the processes of reconfiguration and hydration at the calcite surface. These results provide a basis for future spectroscopic studies of trace metal adsorption on calcite and subsequent solid-solution formation.

Stipp, Susan L.; Hochella, Michael F., Jr.

1991-06-01

131

Controlling local packing and growth in calcium-silicate-hydrate gels.  

PubMed

We investigate the development of gels under out-of-equilibrium conditions, such as calcium-silicate-hydrate (C-S-H) gels that form during cement hydration and are the major factor responsible for cement mechanical strength. We propose a new model and numerical approach to follow the gel formation upon precipitation and aggregation of nano-scale colloidal hydrates, whose effective interactions are consistent with forces measured in experiments at fixed lime concentrations. We use Grand Canonical Monte Carlo to mimic precipitation events during Molecular Dynamics simulations, with their rate corresponding to the hydrate production rate set by the chemical environment. Our results display hydrate precipitation curves that indeed reproduce the acceleration and deceleration regime typically observed in experiments and we are able to correctly capture the effect of lime concentration on the hydration kinetics and the gel morphology. Our analysis of the evolution of the gel morphology indicates that the acceleration is related to the formation of an optimal local crystalline packing that allows for large, elongated aggregates to grow and that is controlled by the underlying thermodynamics. The defects produced during precipitation favor branching and gelation that end up controlling the deceleration. The effects on the mechanical properties of C-S-H gels are also discussed. PMID:24652466

Ioannidou, Katerina; Pellenq, Roland J-M; Del Gado, Emanuela

2014-02-28

132

Gas hydrate and humans  

USGS Publications Warehouse

The potential effects of naturally occurring gas hydrate on humans are not understood with certainty, but enough information has been acquired over the past 30 years to make preliminary assessments possible. Three major issues are gas hydrate as (1) a potential energy resource, (2) a factor in global climate change, and (3) a submarine geohazard. The methane content is estimated to be between 1015 to 1017 m3 at STP and the worldwide distribution in outer continental margins of oceans and in polar regions are significant features of gas hydrate. However, its immediate development as an energy resource is not likely because there are various geological constraints and difficult technological problems that must be solved before economic recovery of methane from hydrate can be achieved. The role of gas hydrate in global climate change is uncertain. For hydrate methane to be an effective greenhouse gas, it must reach the atmosphere. Yet there are many obstacles to the transfer of methane from hydrate to the atmosphere. Rates of gas hydrate dissociation and the integrated rates of release and destruction of the methane in the geo/hydro/atmosphere are not adequately understood. Gas hydrate as a submarine geohazard, however, is of immediate and increasing importance to humans as our industrial society moves to exploit seabed resources at ever-greater depths in the waters of our coastal oceans. Human activities and installations in regions of gas-hydrate occurrence must take into account the presence of gas hydrate and deal with the consequences of its presence.

Kvenvolden, K. A.

2000-01-01

133

Calcite growth kinetics: Modeling the effect of solution stoichiometry  

NASA Astrophysics Data System (ADS)

Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth rate on the cation to anion ratio in solution, we extend the growth model for binary symmetrical electrolyte crystals of Zhang and Nancollas (1998) by combining it with the surface complexation model for the chemical structure of the calcite-aqueous solution interface of Wolthers et al. (2008). To maintain crystal stoichiometry, the rate of attachment of calcium ions to step edges is assumed to equal the rate of attachment of carbonate plus bicarbonate ions. The model parameters are optimized by fitting the model to the step velocities obtained previously by atomic force microscopy (AFM, Teng et al., 2000; Stack and Grantham, 2010). A variable surface roughness factor is introduced in order to reconcile the new process-based growth model with bulk precipitation rates measured in seeded calcite growth experiments. For practical applications, we further present empirical parabolic rate equations fitted to bulk growth rates of calcite in common background electrolytes and in artificial seawater-type solutions. Both the process-based and empirical growth rate equations agree with measured calcite growth rates over broad ranges of ionic strength, pH, solution stoichiometry and degree of supersaturation.

Wolthers, Mariëtte; Nehrke, Gernot; Gustafsson, Jon Petter; Van Cappellen, Philippe

2012-01-01

134

Laboratory study using paper mill lime mud for agronomic benefit  

Microsoft Academic Search

Annual ryegrass (Lolium perenne L.) is an important cool-season forage grass in the southeastern US. Since large portions of soils in this region are too acidic for optimum ryegrass production, there exists an opportunity to use lime mud waste from numerous regional pulp and paper mills as an agricultural liming material. In this study, four lime mud application rates, 2.25

Jiajie He; Clifford R. Lange; Mark Dougherty

2009-01-01

135

46 CFR 148.230 - Calcium oxide (lime, unslaked).  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Calcium oxide (lime, unslaked). 148.230...for Certain Materials § 148.230 Calcium oxide (lime, unslaked). (a) When transported by barge, unslaked lime (calcium oxide) must be carried in an...

2013-10-01

136

Mechanochemical treatment of high silica bauxite with lime  

Microsoft Academic Search

The mechanochemical processing of bauxite with lime has been investigated. The milling of bauxite and lime mixtures in an attritor mill resulted in the formation of an iron rich hydrogarnet phase in bauxite\\/lime slurries containing greater than 9% CaO. Up to 90% of the quartz contained in the bauxite was found to have been removed by the hydrogarnet reaction. The

P. G. McCormick; T. Picaro; P. A. I. Smith

2002-01-01

137

46 CFR 148.04-23 - Unslaked lime in bulk.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 2010-10-01 false Unslaked lime in bulk. 148.04-23 Section 148.04-23...for Certain Material § 148.04-23 Unslaked lime in bulk. (a) Unslaked lime in bulk must be transported in unmanned,...

2010-10-01

138

46 CFR 148.04-23 - Unslaked lime in bulk.  

Code of Federal Regulations, 2010 CFR

...2009-10-01 2009-10-01 false Unslaked lime in bulk. 148.04-23 Section 148.04-23...for Certain Material § 148.04-23 Unslaked lime in bulk. (a) Unslaked lime in bulk must be transported in unmanned,...

2009-10-01

139

27 CFR 9.27 - Lime Kiln Valley.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Lime Kiln Valley. 9.27 Section 9.27...American Viticultural Areas § 9.27 Lime Kiln Valley. (a) Name. The name...viticultural area described in this section is âLime Kiln Valley.â (b) Approved...

2010-04-01

140

27 CFR 9.27 - Lime Kiln Valley.  

Code of Federal Regulations, 2010 CFR

...2009-04-01 2009-04-01 false Lime Kiln Valley. 9.27 Section 9.27...American Viticultural Areas § 9.27 Lime Kiln Valley. (a) Name. The name...viticultural area described in this section is âLime Kiln Valley.â (b) Approved...

2009-04-01

141

Flavour quality of dehydrated lime [ Citrus aurantifolia (Christm.) Swingle  

Microsoft Academic Search

The hydro-distilled volatile oils of fresh and dehydrated lime [Citrus aurantifolia (Christm.) Swingle] fruit were subjected to GC and GC–MS. A total of 32 compounds, constituting > 98% of the volatiles of fresh lime fruit, were identified. Five sesquiterpene hydrocarbons and two sesquiterpene alcohols were found and identified for the first time in lime fruit. The volatiles from the dehydrated

A. Ramesh Yadav; A. S. Chauhan; M. N. Rekha; L. J. M. Rao; R. S. Ramteke

2004-01-01

142

LIME STABILIZATION AND ULTIMATE DISPOSAL OF MUNICIPAL WASTEWATER SLUDGES  

EPA Science Inventory

Twenty-eight lime stabilization facilities were visited. None of these plants were originally designed for sludge lime stabilization. Lime stabilization was instituted either as a permanent sludge handling mechanism to replace a more costly process, as an interim sludge handling ...

143

Strontium incorporation into calcite generated by bacterial ureolysis  

NASA Astrophysics Data System (ADS)

Strontium incorporation into calcite generated by bacterial ureolysis was investigated as part of an assessment of a proposed remediation approach for 90Sr contamination in groundwater. Urea hydrolysis produces ammonium and carbonate and elevates pH, resulting in the promotion of calcium carbonate precipitation. Urea hydrolysis by the bacterium Bacillus pasteurii in a medium designed to mimic the chemistry of the Snake River Plain Aquifer in Idaho resulted in a pH rise from 7.5 to 9.1. Measured average distribution coefficients (D EX) for Sr in the calcite produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic calcites (0.02-0.4). They were also higher than values for calcite produced abiotically by ammonium carbonate addition (0.3). The precipitation of calcite in these experiments was verified by X-ray diffraction. Time-of-flight secondary ion mass spectrometry (ToF SIMS) depth profiling (up to 350 nm) suggested that the Sr was not merely sorbed on the surface, but was present at depth within the particles. X-ray absorption near edge spectra showed that Sr was present in the calcite samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of calcite precipitation, where faster precipitation was associated with greater Sr uptake into the solid. The presence of bacterial surfaces as potential nucleation sites in the ammonium carbonate precipitation treatment did not enhance overall precipitation or the Sr distribution coefficient. Because bacterial ureolysis can generate high rates of calcite precipitation, the application of this approach is promising for remediation of 90Sr contamination in environments where calcite is stable over the long term.

Fujita, Yoshiko; Redden, George D.; Ingram, Jani C.; Cortez, Marnie M.; Ferris, F. Grant; Smith, Robert W.

2004-08-01

144

Use of wastes of the sugar industry as pozzolana in lime-pozzolana binders: Study of the reaction  

SciTech Connect

Mineralogical studies of different wastes of the sugar industry, mainly sugar cane bagasse ash and sugar cane straw ash, have shown that such by-products are likely to be pozzolanic. Their use in lime-pozzolana binders could become an interesting alternative for developing countries. This paper presents a study that was aimed at monitoring the reaction between lime and wastes of the sugar industry having pozzolanic properties by evaluating (1) content of calcium hydroxide, dependent on time; (2) development of the pore structure, dependent on time; (3) study on the reaction products at different stages; and (4) mechanical properties of hardened pastes. The presence of calcium hydroxide was confirmed by x-ray diffraction analysis and thermogravimetric analysis of powder from samples of hydrated lime-pozzolana pastes. The reaction products in hydrated pastes were observed in a scanning electron microscope, and the pore structure was assessed using a mercury intrusion porosimeter. The results of the study show that sugar cane bagasse ash does not act like a reactive pozzolana, mainly due to the presence of unburned material and carbon, whereas sugar cane straw ash shows good pozzolanic activity comparable to that of rice husk ash.

Hernandez, J.F.M. [Univ. Central de las Villas, Santa Clara (Cuba); Middendorf, B.; Gehrke, M.; Budelmann, H. [Univ. of Kassel (Germany). Dept. of Structural Materials

1998-11-01

145

Determination of the pozzolanic activity of fluid catalytic cracking residue. Thermogravimetric analysis studies on FC3R-lime pastes  

SciTech Connect

Spent fluid catalytic cracking catalyst (FC3R) from a petrol refinery played a pozzolanic role in portland cement system as revealed by previous experimental data. In the present study, the pozzolanic activity of FC3R was investigated by means thermogravimetry (TG) of cured lime-FC3R pastes. The influence of pozzolan/lime ratio on the pozzolanic activity was investigated. Due to the chemical composition of FC3R is similar to metakaolin (MK), and knowing that MK has a high pozzolanic activity, the latter was used as a material of comparison in this study. The scope of the study is the determination of the pozzolanic activity of FC3R and the evaluation of amount and nature of pozzolanic products. The products obtained from the reaction between FC3R components (SiO{sub 2}/Al{sub 2}O{sub 3}) and calcium hydroxide (CH) have been characterized, finding that the main pozzolanic reaction product was similar to hydrated gehlenite (calcium aluminosilicate hydrate) CSH and CAH were also formed in the reaction. FC3R showed higher pozzolanic reactivity than metakaolin, for low-lime content pastes and early curing age. Thermogravimetry, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) became very useful techniques for evaluation of reactivity.

Paya, J.; Monzo, J.; Borrachero, M.V.; Velazquez, S.; Bonilla, M

2003-07-01

146

Preparation of macroporous lime from natural lime by swelling method with acetic acid for high-temperature desulfurization  

Microsoft Academic Search

To develop a highly active calcium oxide high-temperature desulfurization sorbent, a method of preparation of macroporous calcium oxides from lime was studied. This method is composed of two steps: swelling of the lime and calcination of the swelled sample. Swelling occurred when lime was exposed to the vapor of acetic acid. The swelling resulted from calcium acetate formation in the

Eiji Sasaoka; Norimasa Sada

1998-01-01

147

Combustion of Methane Hydrate  

NASA Astrophysics Data System (ADS)

A significant methane storehouse is in the form of methane hydrates on the sea floor and in the arctic permafrost. Methane hydrates are ice-like structures composed of water cages housing a guest methane molecule. This caged methane represents a resource of energy and a potential source of strong greenhouse gas. Most research related to methane hydrates has been focused on their formation and dissociation because they can form solid plugs that complicate transport of oil and gas in pipelines. This dissertation explores the direct burning of these methane hydrates where heat from the combustion process dissociates the hydrate into water and methane, and the released methane fuels the methane/air diffusion flame heat source. In contrast to the pipeline applications, very little research has been done on the combustion and burning characteristics of methane hydrates. This is the first dissertation on this subject. In this study, energy release and combustion characteristics of methane hydrates were investigated both theoretically and experimentally. The experimental study involved collaboration with another research group, particularly in the creation of methane hydrate samples. The experiments were difficult because hydrates form at high pressure within a narrow temperature range. The process can be slow and the resulting hydrate can have somewhat variable properties (e.g., extent of clathration, shape, compactness). The experimental study examined broad characteristics of hydrate combustion, including flame appearance, burning time, conditions leading to flame extinguishment, the amount of hydrate water melted versus evaporated, and flame temperature. These properties were observed for samples of different physical size. Hydrate formation is a very slow process with pure water and methane. The addition of small amounts of surfactant increased substantially the hydrate formation rate. The effects of surfactant on burning characteristics were also studied. One finding from the experimental component of the research was that hydrates can burn completely, and that they burn most rapidly just after ignition and then burn steadily when some of the water in the dissociated zone is allowed to drain away. Excessive surfactant in the water creates a foam layer around the hydrate that acts as an insulator. The layer prevents sufficient heat flux from reaching the hydrate surface below the foam to release additional methane and the hydrate flame extinguishes. No self-healing or ice-freezing processes were observed in any of the combustion experiments. There is some variability, but a typical hydrate flame is receiving between one and two moles of water vapor from the liquid dissociated zone of the hydrate for each mole of methane it receives from the dissociating solid region. This limits the flame temperature to approximately 1800 K. In the theoretical portion of the study, a physical model using an energy balance from methane combustion was developed to understand the energy transfer between the three phases of gas, liquid and solid during the hydrate burn. Also this study provides an understanding of the different factors impacting the hydrate's continuous burn, such as the amount of water vapor in the flame. The theoretical study revealed how the water layer thickness on the hydrate surface, and its effect on the temperature gradient through the dissociated zone, plays a significant role in the hydrate dissociation rate and methane release rate. Motivated by the above mentioned observation from the theoretical analysis, a 1-D two-phase numerical simulation based on a moving front model for hydrate dissociation from a thermal source was developed. This model was focused on the dynamic growth of the dissociated zone and its effect on the dissociation rate. The model indicated that the rate of hydrate dissociation with a thermal source is a function of the dissociated zone thickness. It shows that in order for a continuous dissociation and methane release, some of the water from the dissociated zone needs to be drained. The results

Roshandell, Melika

148

Subaerial meteoric calcitization and lithification of high-magnesian calcite muds, Belize  

SciTech Connect

Holocene ({lt}1000-1500 yrs old) high-magnesian calcite-dominated muddy sediments (1 m thick) on subaerially exposed cays in northern Belize are in the process of being converted to low-magnesian calcite micrite. Mineralogic stabilization and attendant lithification result from interaction of the sediments with meteoric fluids believed to be derived from seasonal upward discharge through subjacent Pleistocene limestones. The initial marine-derived sediments, composed of {gt}85% HMC (and minor skeletal aragonite), consist of mud and associated soritid and miliolid foraminifera both with MgCO{sub 3} content of 11-15 mol%, and isotopic compositions of -1.0 to -2.5{per thousand} PDB (O), 0 to +1.5{per thousand} PDB (C). With depth, lithified LMC crusts appear in the section, and the Mg concentration of the sediments and associated crusts decreases rapidly to 3 mol% or less, with a corresponding isotopic depletion to values approaching -7.0{per thousand} (O) and -5.8{per thousand} (C). Concomitantly there is progressive dissolution of skeletal aragonite in the sediments, reduction of porosity due to cementation by LMC, and in the muds, a decrease in Sr and increase in Mn contents. The resultant petrofabric of these lithified LMC deposits, derived from the alteration of HMC-dominated muds, is characterized by micrite with patches of pore-filling micritic and microsparitic LMC cements. Such a fabric is similar to and can be confused easily with calcitized aragonite-dominated precursor muds, except for the relative rarity in the samples examined of aragonite relicts in component microspar and/or pseudospar.

Mazzullo, S.J.; Bischoff, W.D. (Wichita State Univ., KS (United States))

1991-03-01

149

An Aerobic Digestion of Lime Sludge.  

National Technical Information Service (NTIS)

The purpose of this project was to determine the feasibility of using anaerobic digestion to treat sludges from the low-level lime addition process for phosphorus removal. Because digester supernatant is normally recycled to the influent of the sewage tre...

B. A. Bell E. A. Kobylinski

1982-01-01

150

Calcite crystal growth rate inhibition by polycarboxylic acids  

USGS Publications Warehouse

Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg/L. Calcite crystal growth rate inhibition by cyclic polycarboxyclic acids appears to involve blockage of crystal growth sites on the mineral surface by several carboxylate groups. Growth morphology varied for growth in the absence and in the presence of both THFTCA and CPTCA. More effective growth rate reduction by CPTCA relative to THFTCA suggests that inhibitor carboxylate stereochemical orientation controls calcite surface interaction with carboxylate inhibitors. ?? 20O1 Academic Press.

Reddy, M. M.; Hoch, A. R.

2001-01-01

151

The steam reforming of phenol over natural calcite materials  

Microsoft Academic Search

Five natural calcite materials of different geographical origin were studied towards the steam reforming of phenol reaction and the activity results obtained were correlated with some of their physico-chemical properties. It was found that the specific catalytic activity (?mol\\/(m2s)) of the calcite material following calcination at 850°C was not correlated with the BET area and the primary crystal size of

Domna A. Constantinou; Angelos M. Efstathiou

2009-01-01

152

Mechanical twinning in calcite considered with the concept of ferroelasticity  

Microsoft Academic Search

The mechanical twinning of calcite is compared with ferroelastic behavior. For calcite a paraelastic prototype phase does\\u000a not exist, therefore a virtual prototype is defined with cubic m3m symmetry. Using this condition the strain tensors of all\\u000a domain states of mechanical twinning are calculated. With the use of the strain tensors, application of Sapriel's strain compatibility\\u000a law gives the crystallographic

S. Bueble; W. W. Schmahl

1999-01-01

153

The effect of dissolved magnesium on diffusion creep in calcite  

Microsoft Academic Search

We experimentally tested a series of synthetic calcite marbles with varying amounts of dissolved magnesium in a standard triaxial deformation machine at 300 MPa confining pressure, temperatures between 700 and 850°C, stresses between 2 and 100 MPa, and strain rates between 10?7 and 10?3 s?1. The samples were fabricated by hot isostatic pressing of a mixture of calcite and dolomite

Marco Herwegh; Xiaohui Xiao; Brian Evans

2003-01-01

154

Estimation of vorticity from fibrous calcite veins, central Maine, USA  

Microsoft Academic Search

An estimate for the vorticity of a mid-Paleozoic deformation was made using deformed and\\/or rotated calcite veins as natural vorticity and shear-strain gauges in a northern part of the U.S. Appalachians. The spatial distribution of extended, shortened, and shortened-then-extended elongate fibrous calcite veins in limestone layers were used to construct a Mohr circle for the position gradient tensor H, from

H. A. Short; S. E. Johnson

2006-01-01

155

Methane Hydrate Field Program  

SciTech Connect

This final report document summarizes the activities undertaken and the output from three primary deliverables generated during this project. This fifteen month effort comprised numerous key steps including the creation of an international methane hydrate science team, determining and reporting the current state of marine methane hydrate research, convening an international workshop to collect the ideas needed to write a comprehensive Marine Methane Hydrate Field Research Plan and the development and publication of that plan. The following documents represent the primary deliverables of this project and are discussed in summary level detail in this final report. • Historical Methane Hydrate Project Review Report • Methane Hydrate Workshop Report • Topical Report: Marine Methane Hydrate Field Research Plan • Final Scientific/Technical Report

None

2013-12-31

156

The differnces between bond lengths in biogenic and geologocal calcite.  

SciTech Connect

We used high-resolution neutron powder diffraction to accurately measure the atomic positions and bond lengths in biogenic and geological calcite. A special procedure for data analysis was developed in order to take into account the considerable amounts of magnesium present in all the investigated samples. As a result, in biogenic calcite we found some atomic bonds to have significantly different lengths as compared to those in geological calcite, after the contribution of magnesium is accounted for. The maximum effect (elongation up to 0.7%) was found for the C-O bonds. We also analyzed changes in frequencies and spectral widths of normal vibrations of carbonate groups in biogenic calcite (as compared to geological calcite) measured by Raman and Fourier transform IR techniques. Surprisingly, the frequency shifts after subtracting the magnesium contribution are close to zero. At the same time, substantial spectral broadening (up to 1.2%) in biogenic calcite as compared to geological samples was detected. Possible explanations for the experimental findings are discussed.

Zlotoyabko, E.; Caspi, E. N.; Fieramosca, J. S.; Von Dreele, R. B.; Marin, F.; Mor, G.; Politi, Y.; Addadi, L.; Weiner, S. (X-Ray Science Division); ( PNS); (Technion-Israel Inst. of Tech.); (Nuclear Research Centre); (Univ. de Bourgogne); (Weizmann Inst. of Science)

2010-01-01

157

Stable isotope `vital effects' in coccolith calcite  

NASA Astrophysics Data System (ADS)

Uncertainties about the origin of the many disequilibrium or 'vital effects' in a variety of calcifying organisms, and whether these effects are constant or variable, have hampered paleoceanographic application of carbon and oxygen isotopic ratios. Unraveling the source of these effects will improve paleoceanographic applications and may provide new information on changes in cell physiology and ecology. Culture of eight species of coccolithophorids, a dominant marine phytoplankton group, reveals a 5‰ array of disequilibrium or 'vital effects' in both the carbon and oxygen isotopic composition of coccolith calcite. In moderate light and nutrient-replete cultures, oxygen isotopic fractionation and carbon isotopic fractionation correlates directly with cell division rates and correlates inversely with cell size across a range of species. However, when growth rates of a single species are increased or decreased by higher or lower light levels, ? 18O is relatively invariant. Likewise, growth rate variations as a function of temperature do not influence coccolith ? 18O; the slope of the ? 18O vs. temperature relation in cultures of both Gephyrocapsa oceanica and Helicosphaera carteri is the same as for abiogenic carbonates. This suggests a constant, species-specific isotopic fractionation which does not vary with cell physiology. The constancy of vital effects suggests that coccolith stable isotopes will provide reliable phase for paleoceanographic reconstruction of temperature and seawater chemistry, as long as monospecific fractions are analyzed or changes in nannofossil assemblages are accounted for with species-specific correction factors. We suspect that the cell size, and its constraints on the rate of CO 2 diffusion relative to C fixation, may be the first order influence on coccolith stable isotope vital effects. A quantitative model of this process may provide important constraints on mechanisms of carbon acquisition of coccolithophorids in both modern and extinct species.

Ziveri, P.; Stoll, H.; Probert, I.; Klaas, C.; Geisen, M.; Ganssen, G.; Young, J.

2003-05-01

158

Effect of repeated steam hydration reactivation on CaO-based sorbents for CO2 capture.  

PubMed

Samples of natural limestone and commercial calcium carbonate were subjected to successive calcination and carbonation reactions in a TGA and to repeated activity restoration by steam hydration. Steam hydration of spent lime, followed by heating in CO(2), was shown to be an effective method for repeatedly restoring high CO(2) capture activity to spent lime during a large number of CO(2) capture cycles. Steam hydration was also shown to reduce the decay rate of the CO(2) capture activity by increasing the rate of carbonation in the diffusion controlled regime. Repeated hydration-carbonation-calcination cycles led to a considerable expansion of the particles through the formation of large vesicles, likely to lead to high attrition levels when applied in fluidized beds. Based on SEM observation of the particles during hydration-carbonation-calcination cycling, a model was proposed for their progressive weakening. It was concluded that strategies to reduce this weakening must limit the growth of the cracks in the crystal as they are cycled repeatedly. PMID:21114320

Materi?, By Vlatko; Sheppard, Carolyn; Smedley, Stuart I

2010-12-15

159

Preparation, characterization and cytocompatibility of bioactive coatings on porous calcium-silicate-hydrate scaffolds  

Microsoft Academic Search

The major goal of this research was to investigate and characterize the deposition of a biomimetic apatite-like coating onto the surface of 3D porous calcium-silicate-hydrate scaffolds with suitable bioactivity for potential application in bone tissue engineering. Basically, Portland cement, water, sand and lime were mixed for preparing the slurry which was poured into molds, and fine aluminum powder was added

Alexandra A. P. Mansur; Herman S. Mansur

2010-01-01

160

Primary magmatic calcite reveals origin from crustal carbonate  

NASA Astrophysics Data System (ADS)

We have investigated lava flows representative of the whole eruptive history of the Colli Albani ultrapotassic volcanic district (Central Italy). One of the most intriguing features concerning some of these lava flows is the occurrence of primary, magmatic calcite in the groundmass. The primary, magmatic nature of calcite has been inferred by microtextural investigations showing that it typically occurs i) interstitially, associated with clinopyroxene, nepheline and phlogopite, ii) in spherical ocelli, associated with nepheline, fluorite and tangentially arranged clinopyroxene, and iii) in corona-like reaction zones around K-feldspar xenocrysts. These microtextural features distinctly indicate that calcite crystallized from a carbonate melt in a partially molten groundmass, implying that the temperature of the system was above the solidus of the hosted lava flow (> 850 °C). Geochemical features of calcite crystals (i.e., stable isotope values and trace element patterns) corroborate their primary nature and give insights into the origin of the parental carbonate melt. The trace element patterns testify to a high-temperature crystallization process (not hydrothermal) involving a carbonate melt coexisting with a silicate melt. The high ?18O (around 27‰ SMOW) and wide ?13C (? 18 to + 5‰ PDB) values measured in the calcites preclude a mantle origin, but are consistent with an origin in the crust. In this framework, the crystallization of calcite can be linked to the interaction between magmas and carbonate-bearing wall rocks and, in particular, to the entrapment of solid and/or molten carbonate in the silicate magma. The stability of carbonate melt at low pressure and the consequent crystallization of calcite in the lava flow groundmass are ensured by the documented, high activity of fluorine in the studied system and by the limited ability of silicate and carbonate melts to mix at syn-eruptive time scales.

Gozzi, Fernando; Gaeta, Mario; Freda, Carmela; Mollo, Silvio; Di Rocco, Tommaso; Marra, Fabrizio; Dallai, Luigi; Pack, Andreas

2014-03-01

161

Uranyl Incorporation in Organic-Bearing Soil Calcite  

NASA Astrophysics Data System (ADS)

Phosphor imaging and fission track maps reveal a close correlation between uranium and organic-rich calcite that lines roots in an ancient caliche soil. Concordant U-Pb ages show that this uranium has not been mobilized since the soil calcite formed 298 ñ 1 Ma ago. Luminescence spectroscopic analysis of the organic-rich calcite demonstrates that uranium is present in the oxidized state. More or less comparable luminescence spectra were collected using a CW lamp at room temperature and at liquid nitrogen (LN2) temperature. Spectra for inorganic U species are generally greatly enhanced at liquid nitrogen temperatures over room temperature and thus the similarity may suggest that the U is bound to organic matter. UV-excitation Raman spectroscopy of the calcite samples reveals a vibrational signature that is, in addition to the calcite peaks, essentially identical to that of sodium humate, acquired under similar conditions and consistent with those reported previously for humate substances. Since these spectra are dominated by the carbon backbone structure, the persistence of a carbon backbone structure is noted, but persistence of the ligating functional groups cannot be proven directly. We suggest that this sample records a snapshot of the process of uranium complexation with organic acids in natural systems. In our model organic acids with active functional groups that complex uranyl are sorbed onto the calcite surface and then incorporated as humate into the mineral with further calcite precipitation. Further, the uranyl complex is preserved through near-surface reducing conditions and temperatures to the conditions associated with 2700 meters burial depths. These combined observations suggest that the encapsulating calcite not only prevents reduction of uranium in the surface environment, but also inhibits the breakdown of the humate with burial. Due to the long time scale of immobilization of uranium, evidenced by the age of the calcite, this study has profound implications for understanding sampling for U-series and U-Pb dating of carbonates as well as for developing strategies for nuclear waste management. This study also has implications for any other deposits where uranium is associated with organic matter.

Rasbury, E.; Tait, C.; Donohoe, R. J.

2003-12-01

162

Nuclear anomalies in the buccal cells of calcite factory workers  

PubMed Central

The micronucleus (MN) assay on exfoliated buccal cells is a useful and minimally invasive method for monitoring genetic damage in humans. To determine the genotoxic effects of calcite dust that forms during processing, MN assay was carried out in exfoliated buccal cells of 50 (25 smokers and 25 non-smokers) calcite factory workers and 50 (25 smokers and 25 non-smokers) age- and sex-matched control subjects. Frequencies of nuclear abnormalities (NA) other than micronuclei, such as binucleates, karyorrhexis, karyolysis and ‘broken eggs', were also evaluated. Micronuclei and the other aforementioned anomalies were analysed by two way analysis of covariance. The linear correlations between the types of micronucleus and nuclear abnormalities were determined by Spearman's Rho. There was a positive correlation between micronuclei and other types of nuclear abnormalities in accordance with the Spearman's Rho test. Results showed statistically significant difference between calcite fabric workers and control groups. MN and NA frequencies in calcite fabric workers were significantly higher than those in control groups (p < 0.05). The results of this study indicate that calcite fabric workers are under risk of significant cytogenetic damage.

2010-01-01

163

A Raman spectroscopic comparison of calcite and dolomite.  

PubMed

Raman spectroscopy was used to characterize and differentiate the two minerals calcite and dolomite and the bands related to the mineral structure. The (CO3)(2-) group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the calcite and dolomite were observed at 1440, 1088, 715 and 278 cm(-1). The significant differences between the minerals calcite and dolomite are observed by Raman spectroscopy. Calcite shows the typical bands observed at 1361, 1047, 715 and 157 cm(-1), and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm(-1) for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. Calcite has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral. PMID:23988531

Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L

2014-01-01

164

Calcite epitaxy on Au and Ag (1 1 1)  

NASA Astrophysics Data System (ADS)

Crystallization control is an intensely studied field. This study concerns synthesis of epitaxial calcite on Au and Ag substrate without the use of any template. The crystals were analyzed in situ by micro-Raman spectroscopy and ex situ by Scanning Electron Microscopy (SEM) and Electron Backscattering Diffraction (EBSD). Undersaturated solution containing only calcium and hydrogen carbonate is used. Electrochemically induced dissolved oxygen reduction on the metal electrode was used to increase the pH of the solution in the vicinity of the metallic surface, leading to calcium carbonate formation. The calcite crystals so obtained were uniform in size and orientation and presented a (0 0 1) face parallel to the Au or Ag (1 1 1) surface. In order to verify the selectivity of those surfaces, calcium carbonate was also crystallized on copper (1 1 1) adlayers electrodeposited on gold (1 1 1) film. The epitaxial calcite appeared only on Au or Ag substrate when various rhombohedra could be evidenced on the copper modified surface. From these results, an epitaxial relationship has been suggested where hexagonal symmetry of the (0 0 1) calcite plane was in a R30° ?3×?3 arrangement on the Au (1 1 1) surface. This led to a mismatch for lattice parameters below 0.5%. Moreover the cathodic shift of potential needed to form epitaxial calcite on silver was an indirect proof that the first plane in contact with gold was a calcium one.

Teghidet, Hassiba; Bernard, Marie Claude; Borensztajn, Stephan; Chaal, Lila; Joiret, Suzanne; Saidani, Boualem

2011-09-01

165

Electrical conduction and polarization of calcite single crystals  

NASA Astrophysics Data System (ADS)

The electrical conductivity and polarization properties of calcite single crystals with three orientations, namely, a (00.1) plane perpendicular to the crystallographic c axis (10.0) plane parallel to the crystallographic c axis, and a (10.4) cleavage plane, were studied by both complex impedance and thermally stimulated depolarization current (TSDC) measurements. Conductivities for (00.1)-, (10.0)-, and (10.4)-oriented single calcite crystals at 400-600 °C were 1.16 × 10-7 - 1.05 × 10-5, 7.40 × 10-8 - 4.27 × 10-6, and 4.27 × 10-7 - 2.86 × 10-5 ?-1 m-1, respectively, and the activation energies for conduction were 112, 103, and 101 kJ mol-1, respectively. The TSDC spectra verified the electrical polarizability of calcite crystals. The activation energy for depolarization, estimated from TSDC spectra, of the (00.1)-, (10.0)-, and (10.4)-oriented calcite substrates were 112, 119, and 114 kJ mol-1, respectively. Considering the correlation between the processes of conduction and electric polarization, we proposed the mechanisms of conduction and polarization in calcite on the assumption of oxide ion transport.

Wada, Norio; Horiuchi, Naohiro; Wang, Wei; Hiyama, Tetsuo; Nakamura, Miho; Nagai, Akiko; Yamashita, Kimihiro

2012-10-01

166

Rate limitations of lime dissolution into coal ash slag  

SciTech Connect

The rate-limiting mechanisms of lime dissolution from a solid pellet into coal ash slag and synthetic slag was investigated using an experiment involving a rotating cylinder of lime in a liquid slag bath at temperatures of 1450-1650{degree}C. Scanning electron microscopy (SEM) analysis of the slag composition around the lime cylinder was used to determine the nature of the boundary layer surrounding the pellet and the calcium concentration profile. Predictions using shrinking core models of a cylindrical pellet were compared to experimental results, suggesting that diffusion through the slag boundary layer and the change of the phase of lime from solid to liquid in the boundary layer combine to limit the process. These results indicate that a combination of controlling steps: diffusion through the boundary layer and the phase change of lime from solid to liquid, must be considered when predicting lime dissolution rates. 24 refs., 5 figs., 3 tabs.

L.K. Elliott; John A. Lucas; Jim Happ; John Patterson; Harry Hurst; Terry F. Wall [University of Newcastle, Callaghan, NSW (Australia). School of Chemical Engineering

2008-11-15

167

Gas hydrate measurements at Hydrate Ridge using Raman spectroscopy  

Microsoft Academic Search

Oceanic gas hydrates have been measured near the seafloor for the first time using a seagoing Raman spectrometer at Hydrate Ridge, Oregon, where extensive layers of hydrates have been found to occur near the seafloor. All of the hydrates analyzed were liberated from the upper meter of the sediment column near active gas venting sites in water depths of 770–780m.

K. C. Hester; R. M. Dunk; S. N. White; P. G. Brewer; E. T. Peltzer; E. D. Sloan

2007-01-01

168

Lime Pretreatment of Sugarcane Bagasse for Bioethanol Production  

Microsoft Academic Search

The pretreatment of sugarcane bagasse with lime (calcium hydroxide) is evaluated. The effect of lime pretreatment on digestibility\\u000a was studied through analyses using central composite design (response surface), considering pretreatment time, temperature,\\u000a and lime loading as factors. The responses evaluated were the yield of glucose from pretreated bagasse after enzymatic hydrolysis.\\u000a Experiments were performed using the bagasse as it comes

Sarita C. Rabelo; Rubens Maciel Filho; Aline Carvalho Costa

2009-01-01

169

Rate limitations of lime dissolution into coal ash slag  

Microsoft Academic Search

The rate-limiting mechanisms of lime dissolution from a solid pellet into coal ash slag and synthetic slag was investigated using an experiment involving a rotating cylinder of lime in a liquid slag bath at temperatures of 1450-1650°C. Scanning electron microscopy (SEM) analysis of the slag composition around the lime cylinder was used to determine the nature of the boundary layer

Liza K. Elliott; John A. Lucas; Jim Happ; John Patterson; Harry Hurst; Terry F. Wall

2008-01-01

170

Spectroscopic study of phase transitions in natural calcite mineral  

NASA Astrophysics Data System (ADS)

The process and the formation of new minerals upon heating the carbonate rocks containing clay minerals, together with calcite are determined with thermal analysis, X-ray diffraction, infrared and Raman spectroscopy. The calcite-calcium oxide phase transition sequence was followed up to 947 °C in naturally occurring limestone samples. The spectral variations of the internal modes of the carbonate trigonal ( ?1, ?2, ?3 and ?4) were used to probe the structural phase transitions. The calcium oxide phase (which on reaction with atmospheric water forms portlandite) with an onset temperature of around 950 °C was also characterized by the appearance of the infrared mode around 450 cm -1. The minerals, which were formed upon heating the calcite, were calcium oxide and wollastonite.

Gunasekaran, S.; Anbalagan, G.

2008-04-01

171

COLOR REMOVAL FROM KRAFT PULPING EFFLUENT BY LIME ADDITION. CAPSULE REPORT  

EPA Science Inventory

A full scale process for lime decolorization of kraft pulping total mill effluent was operated. Slaked lime addition was followed by primary sedimentation for removal of mixed fibrous and lime decolorization sludges. The clarified effluent subsequently underwent biochemical stabi...

172

Interaction of uranyl with calcite in the presence of EDTA.  

PubMed

Adsorption of uranyl at the surface of calcite was investigated by using batch sorption experiments and synchrotron X-ray standing wave (XSW) measurements. Aqueous solutions containing 236U(VI) (4.5 x 10(-7) to 1.0 x 10(-4) M) and EDTA (5.0 x 10(-7) to 1.1 x 10(-4) M) were reacted for 90 s to 60 min with freshly cleaved calcite (104) surfaces and calcite powders. Surface exchange coefficients, sorption kinetics, and influence of powder surface area/solution volume (SA/V) ratio were investigated by alpha-counting of 236U. Powder sorption results at SA/V = 870 cm2/mL fit a Freundlich isotherm [log [U]surface (in monolayers) = log K + n log [U]aq (in moles/L)], where K = 1.9+/-0.5 and n = 0.9+/-0.1, consistent with uptake of U(VI) by a specific surface reaction where the availability of sorption sites is nonlimiting in the U concentration range measured. Measured U(VI) coverages along this isotherm, based on the calcite (104) surface Ca site density, ranged from 0.04% to 5.4% of a monolayer. Steady state surface coverages were obtained within 90 s. Sorption of U(VI) on calcite (104) single-crystal cleavage surfaces using identical solutions yielded higher coverages, because of increased step density induced by dissolution at the relatively low SA/V ratio (approximately 1) of these measurements. The crystallographic location of the sorbed U(VI) was examined with the synchrotron XSW technique. Measurements were performed at the Advanced Photon Source on fresh calcite (104) cleavage surfaces reacted for 90 s with U(VI) solutions. Coherent fractions for sorbed U ranged from 0.14 to 0.62, and the mean value of the U coherent position was 0.84+/-0.02. This position was independent of dissolved U(VI) concentration and corresponds to a distance between the U atom and the calcite (104) plane of 2.55+/-0.06 A. These results are consistent with U(VI) adsorption atthe calcite surface as an inner-sphere uranyl-carbonate surface complex bonded with the outer oxygen atom(s) of a single surface carbonate group. Steric considerations allow this observed U(VI) surface complex to occur both at step sites ((441)_ and (481)_) and on terrace areas adjacent to Ca vacancies. PMID:15506202

Rihs, Sophie; Sturchio, Neil C; Orlandini, Kent; Cheng, Likwan; Teng, Henry; Fenter, Paul; Bedzyk, Michael J

2004-10-01

173

Modelling excess surface energy in dry and wetted calcite systems  

Microsoft Academic Search

We have combined the calcite force field of Hwang et al. (J. Phys. Chem. B 105:4,122–4,127, 2001) with the F3C water model\\u000a and a hybrid Lennard-Jones\\/van der Waals 3-site potential for CO2 to investigate the $${\\\\left({10\\\\overline14}\\\\right)}$$ and $${\\\\left( {10\\\\overline10}\\\\right)}$$ cleaving surfaces of calcite under dry and wetted conditions. The wetting fluid included both pure water and water–carbon\\u000a dioxide mixture. Excess surface

Bjørn Kvamme; Tatyana Kuznetsova; Daniel Uppstad

2009-01-01

174

Cyanobacterial Calcite Precipitation - Laboratory Study on Different Spatial Scales  

NASA Astrophysics Data System (ADS)

Lacustrine calcite precipitation with sedimentation rates up to 1 mm per year can result in large carbonate deposits. Varved lake sediments high in calcite content are now intensively studied as high-resolution continental archives for environmental change. Especially in oligotrophic hardwater lakes, eukaryotic and prokaryotic picoplankton was found to be important in the overall process of calcite precipitation. Rates and mechanisms of bacteria-surface mediated precipitation reactions, however, remain poorly understood. For interpreting geochemical and isotopic information stored in sediments, it is essential to know the carbonate precipitation mechanisms and the governing environmental factors. Thus, laboratory experiments with picoplankton under controlled conditions were combined with electron and atomic force microscopy in order to obtain insights into the details of the calcite precipitation mechanisms of cyanobacteria. This study aimed at evaluating the potential of such laboratory studies and investigating the influence of environmental parameters as a first step. Under carefully controlled chemical and physical conditions, precipitation of calcite was induced by adding cultures of picocyanobacteria to supersaturated solutions of CaCO3 at different CaCl2/NaHCO3 ratios. The cell suspensions were purged with an artificial atmosphere at constant CO2 concentration. Abiotic solutions were used as reference systems. Chemical conditions such as pH, calcium and carbonate concentrations were continuously monitored by ion selective electrodes. The influence of supersaturation in the range of ? = 2 - 20 on biogenic precipitation was quantified at different ratios of calcium (0.7 - 48 mM) /carbonate (6 ? M - 35 ? M). In a series of bulk experiments it was possible to detect critical values of supersaturation for the onset of precipitation both with and without cells, both in the range of ? = 5 - 10. The morphology of the precipitates was analyzed by scanning electron microscopy. Both, initial crystals (<500 nm) and larger grown crystals (>10 ? m) showed rhombohedral and hexagonal-prism shapes characteristic for calcite. Ultrathin-sections ( ˜100nm) of the cyanobacteria cells and the attached calcite crystals were prepared by Focused Ion Beam. This technique allowed us to preserve the cell wall - crystal interface as intact as possible in order to perform Transmission Electron Microscopy (TEM) analysis of the sections. Using TEM-Electron Energy Loss Spectroscopy, carbon bonds in both calcite crystals and cyanobacteria cells were detected and identified. The carbon absorption spectra are significantly different to discriminate the organic and inorganic carbon. Thus, the absorption peaks are the fingerprints of the analyzed material and can be used to analyze the transition zone between the cell and the particle.

Obst, M.; Mavrocordatos, D.; Gasser, P.; Dittrich, M.

2003-12-01

175

Capture of gas-phase arsenic oxide by lime: kinetic and mechanistic studies.  

PubMed

Trace metal emission from coal combustion is a major concern for coal-burning utilities. Toxic compounds such as arsenic species are difficult to control because of their high volatility. Mineral sorbents such as lime and hydrated lime have been shown to be effective in capturing arsenic from the gas phase over a wide temperature range. In this study, the mechanism of interaction between arsenic oxide (As2O3) and lime (CaO) is studied over the range of 300-1000 degrees C. The interaction between these two components is found to depend on the temperature; tricalcium orthoarsenate (Ca3As2O8) is found to be the product of the reaction below 600 degrees C, whereas dicalcium pyroarsenate (Ca2As2O7) is found to be the reaction product in the range of 700-900 degrees C. Maximum capture of arsenic oxide is found to occur in the range of 500-600 degrees C. At 500 degrees C, a high reactivity calcium carbonate is found to capture arsenic oxide by a combination of physical and chemical adsorption. Intrinsic kinetics of the reaction between calcium oxide and arsenic oxide in the medium-temperature range of 300-500 degrees C is studied in a differential bed flow-through reactor. Using the shrinking core model, the order of reaction with respect to arsenic oxide concentration is found to be about 1, and the activation energy is calculated to be 5.1 kcal/mol. The effect of initial surface area of CaO sorbent is studied over a range of 2.7-45 m2/g using the grain model. The effect of other major acidic flue gas species (SO2 and HCl) on arsenic capture is found to be minimal under the conditions of the experiment. PMID:11349294

Jadhav, R A; Fan, L S

2001-02-15

176

Hydrate morphology: Physical properties of sands with patchy hydrate saturation  

USGS Publications Warehouse

The physical properties of gas hydrate-bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase. The host sediment grain size and the state of effective stress determine the hydrate morphology in sediments; this information can be used to significantly constrain estimates of the physical properties of hydrate-bearing sediments, including the coarse-grained sands subjected to high effective stress that are of interest as potential energy resources. Reported data and physical analyses suggest hydrate-bearing sands contain a heterogeneous, patchy hydrate distribution, whereby zones with 100% pore-space hydrate saturation are embedded in hydrate-free sand. Accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate-bearing sands and captures observed physical-property dependencies on hydrate saturation. For example, numerical modeling results of sands with patchy saturation agree with experimental observation, showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations. The hydrate-patch size itself impacts the physical properties of hydrate-bearing sediments; for example, at constant hydrate saturation, we find that conductivity (electrical, hydraulic and thermal) increases as the number of hydrate-saturated patches increases. This increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate-saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross-section of the specimen.

Dai, S.; Santamarina, J. C.; Waite, William F.; Kneafsey, T. J.

2012-01-01

177

Hydrate morphology: Physical properties of sands with patchy hydrate saturation  

NASA Astrophysics Data System (ADS)

The physical properties of gas hydrate-bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase. The host sediment grain size and the state of effective stress determine the hydrate morphology in sediments; this information can be used to significantly constrain estimates of the physical properties of hydrate-bearing sediments, including the coarse-grained sands subjected to high effective stress that are of interest as potential energy resources. Reported data and physical analyses suggest hydrate-bearing sands contain a heterogeneous, patchy hydrate distribution, whereby zones with 100% pore-space hydrate saturation are embedded in hydrate-free sand. Accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate-bearing sands and captures observed physical-property dependencies on hydrate saturation. For example, numerical modeling results of sands with patchy saturation agree with experimental observation, showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations. The hydrate-patch size itself impacts the physical properties of hydrate-bearing sediments; for example, at constant hydrate saturation, we find that conductivity (electrical, hydraulic and thermal) increases as the number of hydrate-saturated patches increases. This increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate-saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross-section of the specimen.

Dai, S.; Santamarina, J. C.; Waite, W. F.; Kneafsey, T. J.

2012-11-01

178

High strain deformation of calcite-anhydrite aggregates  

NASA Astrophysics Data System (ADS)

Localization of deformation in nature occurs dominantly in polyphase rocks. However, high strain experimental deformation studies have up to now mainly been performed on monophase materials. In order to study the process of localization as well as the interaction between different phases during deformation, a calcite-anhydrite aggregate was deformed in torsion to large amounts of shear strain. Calcite and anhydrite do not chemically react and have similar strengths at the deformation conditions performed in this study. However, the deformation behaviour of the two phases is strikingly different with increasing strain. The synthetic calcite-anhydrite aggregates were produced from reagent powders by HIP-ping (Bruhn et al., 1999). Torsion experiments were performed on fine-grained (5-8 micrometers) calcite-anhydrite samples with volume proportions of 30/70, 50/50 and 70/30 and on the pure end-member samples (100% calcite and 100% anhydrite). The experiments were performed at 600 °C, 300 MPa confining pressure and a constant shear strain rate of 1.10-3 s-1. A maximum shear strain of 12.5 was reached. With progressive deformation the samples deformed more and more inhomogeneously. On a bulk sample scale progressive localization of the deformation was observed. This is in contrast to previous experiments in torsion performed on monophase materials (including calcite and anhydrite) where deformation always remained very homogeneous. The rheological data showed that the pure anhydrite was the strongest material and calcite the weakest. However after a shear strain of 1, the anhydrite end-member weakened dramatically until similar stresses were reached at high shear strains of 3 as for the pure calcite end-member. The calcite-anhydrite mixtures had strengths in between those of the end-members and showed a weakening behaviour between the end-members. Microstructural analysis of SEM backscatter electron images of the two phase samples show that in the localized zones preferred alignments of both phases are present. Very thin layers (about 5 micrometer thick, roughly one grain) of calcite and anhydrite alternate with each other. By contrast, in the non-localized parts of the sample the two phases are still homogeneously mixed as in the starting material. The alignment of single phases causes localization of deformation in this two-phase aggregate, because the laminar microstructure corresponds to the minimum strength (lower bound) configuration in simple shear. These results suggest that the presence of two or more phases may play an important role in localization in nature. Reference: Bruhn, D.F., Olgaard, D.L., Dell'Angelo, L.N., 1999. Evidence for enhanced deformation in two-phase rocks: Experiments on the rheology of calcite-anhydrite aggregates. Journal of Geophysical Research B104, 707-724.

Barnhoorn, A.; Bystricky, M.; Kunze, K.; Burlini, L.

2003-04-01

179

Rheological behaviour of hydraulic lime-based grouts. Shear-time and temperature dependence  

NASA Astrophysics Data System (ADS)

This paper deals with the coupled effect of temperature and fly ash (FA) addition on rheological behaviour of natural hydraulic lime (NHL5) based grouts, currently used in masonry consolidation. The use of a grout injection technique for masonry consolidation may lead to an increase of hydrostatic pressure and lead to structural damage. This means that the thixotropic effects become self-evident in grout design. It was shown that there is a relation between the structuration rate of each grout and the pressure that occurs inside masonry during its consolidation. According to the results, it seems also that there is a grout threshold temperature ( T limit) that separates a domain where the grout build-up structure area is almost constant, from another where flocculation area starts to increase significantly. We believe that in the first region the thixotropic effects are almost isolated from the irreversible effects (due to hydration). For the NHL5 based grout T limit=20 °C and for the grout with NHL5+15 % of FA T limit=15 °C. Grouts' characterization based on maximum resisting time, structuration rate and on the analysis of the hydraulic lime grout behaviour tested at different shear rates was performed using a shear thinning model and assuming that the structure is shear- and time-dependent. The goal is to use this methodology during mix proportioning and design for masonry injection purpose. The tested grout compositions were optimized compositions obtained in previous research using the design of experiments method.

Bras, Ana; Henriques, Fernando M. A.; Cidade, M. T.

2013-05-01

180

EVALUATION OF HAZARDOUS WASTE INCINERATION IN A LIME KILN: ROCKWELL LIME COMPANY  

EPA Science Inventory

During a one-week test burn, hazardous waste was used as supplemental fuel and co-fired with petroleum coke in a lime kiln in eastern Wisconsin. Detailed sampling and analysis was conducted on the stack gas for principal organic hazardous constituents (POHCs), particulates, parti...

181

HYDRATE CORE DRILLING TESTS  

Microsoft Academic Search

The ''Methane Hydrate Production from Alaskan Permafrost'' project is a three-year endeavor being conducted by Maurer Technology Inc. (MTI), Noble, and Anadarko Petroleum, in partnership with the U.S. DOE National Energy Technology Laboratory (NETL). The project's goal is to build on previous and ongoing R&D in the area of onshore hydrate deposition. The project team plans to design and implement

John H. Cohen; Thomas E. Williams; Ali G. Kadaster; Bill V. Liddell

2002-01-01

182

Immobilization of lead and cadmium in solid residues from the combustion of refuse using lime and phosphate  

SciTech Connect

This patent describes a method of immobilizing lead and cadmium in a free flowing particulate dry solid residue which maintains its free flowing particulate nature after the immobilizing treatment. The dry solid residue comprises fly ash and mixtures of fly ash with bottom ash resulting from the incineration of municipal waste, comprising contacting the dry solid residue with at least one water soluble phosphate in an amount equivalent to about 1 to about 8% by weight of phosphoric acid based on the total residue in the presence of a free lime source selected from the group consisting of lime, hydrated lime, flue gas scrubber product, and combinations thereof, in an amount sufficient to furnish from about 1 to about 25 parts by weight calcium hydroxide per 5 parts by weight of fly ash whereby the leaching of cadmium and lead is reduced to a level no more than 1 ppm cadium and 5 ppm lead as determined in an EPA test performed on the resulting dry treated residue.

O'Hara, M.J.; Surgi, M.R.

1988-04-12

183

Calcite epitaxy on Au and Ag (1 1 1)  

Microsoft Academic Search

Crystallization control is an intensely studied field. This study concerns synthesis of epitaxial calcite on Au and Ag substrate without the use of any template. The crystals were analyzed in situ by micro-Raman spectroscopy and ex situ by Scanning Electron Microscopy (SEM) and Electron Backscattering Diffraction (EBSD). Undersaturated solution containing only calcium and hydrogen carbonate is used. Electrochemically induced dissolved

Hassiba Teghidet; Marie Claude Bernard; Stephan Borensztajn; Lila Chaal; Suzanne Joiret; Boualem Saidani

2011-01-01

184

Bioremediation of Cd by microbially induced calcite precipitation.  

PubMed

Contamination by Cd is a significant environmental problem. Therefore, we examined Cd removal from an environmental perspective. Ureolysis-driven calcium carbonate precipitation has been proposed for use in geotechnical engineering for soil remediation applications. In this study, 55 calcite-forming bacterial strains were newly isolated from various environments. Biomineralization of Cd by calcite-forming bacteria was investigated in laboratory-scale experiments. A simple method was developed to determine the effectiveness of microbially induced calcite precipitation (MICP). Using this method, we determined the effectiveness of biomineralization for retarding the flow of crystal violet through a 25-mL column. When the selected bacteria were analyzed using an inductively coupled plasma optical emission spectrometer, high removal rates (99.95%) of Cd were observed following incubation for 48 h. Samples of solids that formed in the reaction vessels were examined using a scanning electron microscope. The CdCO3 compounds primarily showed a spherical shape. The results of this study demonstrate that MICP-based sequestration of soluble heavy metals via coprecipitation with calcite may be useful for toxic heavy metal bioremediation. PMID:24458656

Kang, Chang-Ho; Han, Sang-Hyun; Shin, Yujin; Oh, Soo Ji; So, Jae-Seong

2014-03-01

185

Experimentelle Bildung von Forsterit und Calcit aus Tremolit und Dolomit  

Microsoft Academic Search

The equilibrium temperature for the reaction: 1 tremolite + 11 dolomite 8 forsterite + 13 Calcit + 9 CO 2 + 1 H 2 O was experimentally determined as a function of the CO 2 -content of the CO 2 -H 2 O fluid phase for the total pressures of 500 and 1000 bars. The results are plotted as two

Paul Metz

1967-01-01

186

Utricular otoconia of some amphibians have calcitic morphology  

NASA Technical Reports Server (NTRS)

This report concerns the morphological features of otoconia removed from the inner ear of four amphibian species. Results from scanning electron microscopic examination are compared based on the site of origin. These results show that utricular otoconia have a mineral structure that mimics calcite, rather than the widely accepted idea that they are mineralized by calcium carbonate of the aragonite polymorph.

Pote, K. G.; Ross, M. D.

1993-01-01

187

Orientational order-disorder phase transition in calcite  

Microsoft Academic Search

We have performed inelastic neutron scattering experiments on calcite in the ordered phase, focusing on a zone boundary F-point that shows X-ray diffuse scattering. At this position we have observed an incipient soft mode along with a column of inelastic scattering ranging in energy between the soft mode energy and zero energy. The intensity of this scattering varies dramatically with

M. Hagen; M. T. Dove; M. J. Harris; U. Steigenberger; B. M. Powell

1992-01-01

188

Using neutron diffraction to investigate mechanical twinning in calcite  

Microsoft Academic Search

Mechanical twinning in calcite provides one of the most widely used methods for inferring the orientation and magnitude of the stresses and strains that are responsible for natural rock deformation, and yet the strong sensitivity of twinning activity to microstructural variables such as grain size and lattice preferred orientation remains poorly characterized. This reflects the fact that whole sample behaviour,

P. F. Schofield; S. J. Covey-Crump

2010-01-01

189

Preheating and incubation of cane juice prior to liming: a comparison of intermediate and cold lime clarification.  

PubMed

In the U.S., cold lime clarification remains the clarification process of choice in raw sugar manufacturing. A comparative study of cold vs intermediate lime clarification was undertaken at a factory that operated intermediate liming (approximately 30% mixed juice (MJ) of pH 5.2 +/- 0.3 was preheated to 87-93 degrees C to help maintain clean limed juice heaters, incubated at approximately 54 degrees C, and then limed) but still had the pipes to revert to cold liming (MJ incubated and limed at approximately 40 degrees C) for this study. Hourly samples were collected over a 6 h sampling period across cold and intermediate clarification processes on two consecutive days, respectively, and this was repeated three times across the 1999 grinding season. A total of 1.57% less sucrose was lost to inversion reactions across intermediate rather than cold liming. In intermediate liming, which required approximately 4.6% less lime, preheating of only 30% of the MJ markedly removed color (-29%), dextran (-10%), and starch (-24%) and caused large flocs to form that settled faster in the clarifiers. Faster settling led to an impressive 4.6% (season average) more turbidity removal across the clarifiers in intermediate rather than cold liming. Intermediate clarified juice (CJ) turbidity (season average 2028 ICU +/- 675) was approximately half of cold CJ turbidity (average 3952 ICU +/- 1450) with over 2-fold more CJ turbidity control. Subsequent turbidity values and control were significantly improved in the final evaporator syrup samples too. For both processes, juice incubation caused approximately 10% color removal, but this was offset by color formation on liming, because of the alkaline degradation of invert; however, overall, more color was removed than formed in intermediate liming. Starch was reduced in the incubator tank, for both processes, because added filtrate reduced the acidity enabling natural diastase from the cane to degrade starch. Some dextran occasionally formed in the incubator tank, in both processes. Summed across measured parameters, intermediate liming appears to offer several advantages over cold liming. PMID:11804517

Eggleston, Gillian; Monge, Adrian; Pepperman, Armand

2002-01-30

190

Investigation of Copper Sorption by Sugar Beet Processing Lime Waste  

EPA Science Inventory

In the western United States, sugar beet processing for sugar recovery generates a lime-based waste product (~250,000 Mg yr-1) that has little liming value in the region?s calcareous soils. This area has recently experienced an increase in dairy production, with dairi...

191

Mitigation of acid deposition: Liming of surface waters. Final report  

SciTech Connect

In recent years acid deposition has become a serious concern internationally. Scientific literature has documented the acidification of numerous lakes and streams in North America and Scandinavia resulting in the depletion or total loss of fisheries and other aquatic biota. Liming represents the only common corrective practice aimed specifically at remediating an affected acid receptor. This report reviews a range of liming technologies and liming materials, as well as the effect of surface-water liming on water quality and aquatic biota. As background to the liming discussion, the hydrologic cycle and the factors that make surface waters sensitive to acid deposition are also discussed. Finally, a brief review of some of the liming projects that have been conducted, or are currently in operation is presented, giving special emphasis to mitigation efforts in Maryland. Liming has been effectively used to counteract surface-water acidification in parts of Scandinavia, Canada, and the U.S. To date, liming has generally been shown to improve physical and chemical conditions and enhance the biological recovery of aquatic ecosystems affected by acidification.

Bartoshesky, J.; Price, R.; DeMuro, J.

1989-05-01

192

76 FR 82295 - Central Power & Lime LLC; Notice of Filing  

Federal Register 2010, 2011, 2012, 2013

...Docket Nos. EL12-18-000; QF82-207-007] Central Power & Lime LLC; Notice of Filing December 23, 2011. Take notice that on December 22, 2011, Central Power & Lime LLC, pursuant to sections 18 CFR 292.205(c) and 385.207...

2011-12-30

193

Influences of liming on soil fertility in the Eastern Croatia  

Microsoft Academic Search

Acid soils are widespread in the Eastern Croatia. In general, liming of these soils is a usual recommnedation for their improvement. The first report with regard to liming in Croatia appeared more than 200 years ago. cited the report of an unknown author (Anonimous, 1789). Five experiments were conducted under field conditions in the last 25 years period with purpose

V. Kovacevic; Z. Loncaric; D. Simi; B. Simi

194

AFM-Study on Calcite Nucleation by Cyanobacteria  

NASA Astrophysics Data System (ADS)

Prokaryotic picoplankton plays an important role in lacustrine calcite precipitation, especially in oligotrophic lakes. The mechanisms of cyanobacteria-surface mediated precipitation reactions, however, remain poorly understood. For interpreting geochemical and isotopic information stored in sediments, it is essential to know the carbonate precipitation mechanisms and microscopical details of nucleation on the cell surface. A microscopy study was designed, based on previous results of cyanobacterial calcite precipitation. In order to investigate the nucleation of calcite on the cell surface under controlled conditions, experiments with Synechococcus (PCC 7942) were performed in a flow-through design of an atomic force microscope (AFM). The AFM was operated in `Tapping Mode' providing information on the topography and additionally on physicochemical properties by mapping the phase shift of the oscillating cantilever. For these experiments cells were immobilized on glass slides. As the basic requirement, growth experiments were performed in order to ensure that the fixed cells were alive. To our knowledge one of the first times the successive steps of a cyanobacterial cell division were observed by AFM. The growth of cell agglomerates was monitored over a period of 6 days. AFM images finally reveal the formation of a cyanobacterial biofilm on the glass surface. These observations were supported by the results obtained by epifluorescence microscopy. In a second step, calcite nucleation experiments were performed. Under carefully controlled physical and chemical conditions, nucleation of calcite was enhanced by flushing the fluid cell of the AFM with supersaturated solutions of CaCO3 (CaCl2 and NaHCO3). These solutions were 7 and 10 times supersaturated. As the result of the addition of the CaCO3-solution, changes of the microtopography and physicochemical properties of the cell surface were observed. In our study in-situ-AFM was shown to be powerful tool investigating mechanisms of biomineralization and nucleation under controlled natural conditions.

Obst, M.; Kuehn, H.; Dittrich, M.

2004-12-01

195

Calcite solubility in supercritical CO 2?H 2O fluids  

NASA Astrophysics Data System (ADS)

An extraction-quench apparatus was used to measure calcite solubilities in supercritical CO 2?H 2O mixtures. Experiments were conducted at 1 kbar and 2 kbar, between 240°C and 620°C and from XCO 2 = .02 toXCO 2 = .15 in order to determine the solubility behavior as a function of pressure, temperature and CO 2 content. The results indicate that calcite solubilities under these conditions behave similarly to previously investigated calcite solubilities at lower pressures and temperatures (SHARP and Kennedy, 1965). At constant XCO 2, the solubility increases with increasing pressure, but it decreases with increasing temperature. When the temperature and pressure are constant, the calcite solubility rises with increasing XCO 2 to a maximum value at XCO 2 between 0.02 and 0.05. For higher CO 2 contents, up to XCO 2 = .15, the calcite solubility decreases, probably due to the decrease of H 2O activities to values significantly below unity. The solubility behavior can be successfully modeled by making the assumption that Ca ++ is the dominant calcium species and that the carbon-bearing species are CO 2(aq) and HCO -3. Since for these dilute H 2O?CO 2 fluids, all activity coefficients can be assumed to not differ significantly from unity, ionization constants for the reaction H 2O + CO 2(aq) H + + HCO -3 can be calculated at 1 and 2 kbar between 250°C and 550°C. These calculated values are in good agreement with the low temperature determinations of the ionization constants for this reaction determined by Read (1975). Values of the molal Gibbs free energy of CO 2(aq) obtained in our study exhibit a much greater positive departure from ideality than those calculated with the modified Redlich-Kwong equations of either Flowers (1979) or Kerrick and Jacobs (1981) for dilute CO 2 aqueous solutions.

Fein, Jeremy B.; Walther, John V.

1987-06-01

196

Molecular ordering of ethanol at the calcite surface.  

PubMed

To produce biominerals, such as shells, bones, and teeth, living beings create organic compounds that control the growth of the solid phase. Investigating the atomic scale behavior of individual functional groups at the mineral-fluid interface provides fundamental information that is useful for constructing accurate predictive models for natural systems. Previous investigations of the activity of coccolith-associated polysaccharides (CAP) on calcite, using atomic force microscopy (AFM) [Henriksen, K., Young, J. R., Bown, P. R., and Stipp, S. L. S. Palentology 2004, 43 (Part 3), 725-743] and molecular dynamics (MD) modeling [Yang, M., Stipp, S. L. S., and Harding, J. H. Cryst. Growth Des. 2008, 8 (11), 4066-4074], have suggested that OH functional groups control polysaccharide attachment. The purpose of this work was to characterize, using X-ray reflectivity (XR) combined with molecular dynamics (MD) simulations, the structuring on calcite of a layer of the simplest carbon chain molecule that contains an OH group, ethanol (CH(3)-CH(2)-OH). We found evidence that EtOH forms a highly ordered structure at the calcite surface, where the first layer molecules bond with calcite. The ethanol molecules stand up perpendicularly at the interface or nearly so. As a consequence, the fatty, CH(3) ends form a new surface, about 6 Å from the termination of the bulk calcite, and beyond that, there is a thin gap where ethanol density is low. Following is a more disordered layer that is two to three ethanol molecules thick, about 14 Å, where density more resembles that of bulk liquid ethanol. The good agreement between theory and experiment gives confidence that a theoretical approach can offer information about behavior in more complex systems. PMID:22060260

Pasarín, I S; Yang, M; Bovet, N; Glyvradal, M; Nielsen, M M; Bohr, J; Feidenhans'l, R; Stipp, S L S

2012-02-01

197

A mechanistic model for calcite crystal growth using surface speciation  

NASA Astrophysics Data System (ADS)

A new mechanistic model for the crystal growth kinetics of calcite is presented, accounting for the presence of various surface complexes. Calcite crystal growth rates were determined with the constant composition method at ? c (calcite supersaturation) values of 1.5-9.8. In general the rate increases with ? c, but variations in CO 2 partial pressures and the (CO 32-)/(Ca 2+) ratio also have a major effect on the crystal growth rate. These effects are eliminated by assuming that calcite crystal growth proceeds through three reversible reactions, in which CaCO 30(aq) and Ca 2+(aq) are incorporated at specific surface complexes. The model derived rates closely follow the experimental rates over the entire experimental range ( r = 0.996, n = 23). The obtained rate constants indicate that CaCO 30(aq) is ?20 times more reactive than Ca 2+(aq) at the calcite-water interface. This agrees with the fact that dehydration of metal ions precedes crystal growth and, in analogy with other metal-ligand complexes, the CO 32- ligand will increase the rate of water exchange of Ca. This model is a modified version of a rhodochrosite crystal growth model (Sternbeck, 1997) which allows for the comparison of reaction mechanisms and rate constants. The rate constants for incorporation of CaCO 30(aq) at the mineral surface are 55 to 270 times higher than for MnCO 30(aq). This difference can not likely be explained by the water exchange rates, but may be due to the fact that ligand exchange mechanisms for Ca and Mn differ.

Nilsson, Ö.; Sternbeck, J.

1999-01-01

198

Calcite genesis in the Upper Freeport coal bed as indicated by stable isotope geochemistry  

Microsoft Academic Search

The grinding and sizing in float-sink testing of the Upper Freeport coal bed physically separates calcite of different origins. The different origins are distinguished by different isotopic compositions. The isotopic compositions of calcite indicates at least two, possibly three, stages of calcite formation in the Upper Freeport coal bed. Calcite samples obtained from cleat, and isolated from 8x100 mesh-1.8 specific

F. T. Dulong; E. C. Spiker; C. B. Cecil; R. W. Stanton

1985-01-01

199

Thermal behavior of biodegraded lime wood.  

PubMed

The effects of the soft-rot fungus Trichoderma viride Pers., on the thermal behavior of lime wood (Tillia cordata Mill.) were investigated. The lime wood pieces were inoculated with the fungus over a 12-week period. At pre-established time intervals two samples were withdrawn from the medium and analyzed by thermogravimetry and differential calorimetry, and the results were correlated with mass loss. Fungal activity was indicated by continuous decrease of sample mass. Modification of the wood because of the presence of the fungus was evidenced by structural changes that affected its thermal properties, both in respect to the hydrophilicity of the wood (evidenced mainly in desorption process) and in its decomposition behavior. The shape of DTG curves depends on the exposure time of wood to the action of microorganisms. The peak temperature assigned to the decomposition of wood components increases, while the global kinetic parameters for the main peak decrease with increasing exposure time of the wood to the attack by microorganisms. The increased characteristic temperatures of water desorption and cellulose decomposition processes and lower thermal stability could be explained by newly formed structures, mainly the oxidized ones. PMID:20451899

Popescu, Carmen-Mihaela; Manoliu, Alexandru; Lisa, Gabriela; Gradinariu, Petronela; Vasile, Cornelia

2010-06-16

200

Water adsorption and cloud condensation nuclei activity of calcite and calcite coated with model humic and fulvic acids  

NASA Astrophysics Data System (ADS)

Recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of insoluble nuclei, such as mineral dust aerosol. A large fraction of unidentified organic material in aerosol particles is composed of poly-acidic compounds resembling humic substances. The presence of these humic-like substances (HULIS) can alter the water adsorption and CCN activity of mineral dust aerosol. We have measured the CCN activity of model humic and fulvic acids and of mineral dust particles coated with these substances in the laboratory. We find that coatings of humic and fulvic acids on calcite particles significantly increases water adsorption compared to uncoated particles. CCN measurements indicate that humic- or fulvic acid-coated calcite particles are more CCN active than uncoated calcite particles. Additionally, thicker coatings of humic or fulvic acids appear to result in more efficient CCN activity. Thus, mineral dust particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the atmosphere than uncoated mineral dust particles, potentially altering the effect of mineral dust on the Earth's climate. In addition to the experimental results, we have explored a newly modified Köhler theory for predicting the CCN activity of insoluble, wettable particles based on multi layer water adsorption measurements of calcite.

Hatch, Courtney D.; Gierlus, Kelly M.; Schuttlefield, Jennifer D.; Grassian, Vicki H.

201

Mechanical and leaching behaviour of slag-cement and lime-activated slag stabilised/solidified contaminated soil.  

PubMed

Stabilisation/solidification (S/S) is an effective technique for reducing the leachability of contaminants in soils. Very few studies have investigated the use of ground granulated blast furnace slag (GGBS) for S/S treatment of contaminated soils, although it has been shown to be effective in ground improvement. This study sought to investigate the potential of GGBS activated by cement and lime for S/S treatment of a mixed contaminated soil. A sandy soil spiked with 3000mg/kg each of a cocktail of heavy metals (Cd, Ni, Zn, Cu and Pb) and 10,000mg/kg of diesel was treated with binder blends of one part hydrated lime to four parts GGBS (lime-slag), and one part cement to nine parts GGBS (slag-cement). Three binder dosages, 5, 10 and 20% (m/m) were used and contaminated soil-cement samples were compacted to their optimum water contents. The effectiveness of the treatment was assessed using unconfined compressive strength (UCS), permeability and acid neutralisation capacity (ANC) tests with determination of contaminant leachability at the different acid additions. UCS values of up to 800kPa were recorded at 28days. The lowest coefficient of permeability recorded was 5×10(-9)m/s. With up to 20% binder dosage, the leachability of the contaminants was reduced to meet relevant environmental quality standards and landfill waste acceptance criteria. The pH-dependent leachability of the metals decreased over time. The results show that GGBS activated by cement and lime would be effective in reducing the leachability of contaminants in contaminated soils. PMID:21420148

Kogbara, Reginald B; Al-Tabbaa, Abir

2011-05-01

202

Performance of lime-BHA solidified plating sludge in the presence of Na2SiO3 and Na2CO3.  

PubMed

This research investigated the performance of lime-BHA (black rice husk ash) solidified plating sludge with 2 wt% NaO from Na(2)SiO(3) and Na(2)CO(3) at the level of 0, 30 and 50 wt%. The sludge was evaluated for strength development, leachability, solution chemistry and microstructure. The lime-BHA solidified plating sludge with Na(2)SiO(3) and Na(2)CO(3) had higher early strength when compared to the control. The addition of Na(2)SiO(3) and Na(2)CO(3) increased the OH(-) concentration and decreased the Ca(2+) and heavy metal ions in solution after the first minute. The XRD patterns showed that the addition of Na(2)SiO(3) resulted in the formation of calcium silicate hydrates, while the addition of Na(2)CO(3) resulted in CaCO(3). The heavy metals from the plating sludge, especially Zn, were immobilized in calcium zincate and calcium zinc silicate forms for the lime-BHA with and without Na(2)SiO(3) solidified wastes, while samples with Na(2)CO(3) contained Zn that was fixed in the form of CaZnCO(3). The cumulative leaching of Fe, Cr and Zn from the lime-BHA solidified plating sludge decreased significantly when activators were added, especially Na(2)CO(3). PMID:21549500

Piyapanuwat, Rungroj; Asavapisit, Suwimol

2011-09-01

203

Crystal growth of calcite from calcium bicarbonate solutions at constant PCO2 and 25??C: a test of a calcite dissolution model  

USGS Publications Warehouse

A highly reproducible seeded growth technique was used to study calcite crystallization from calcium bicarbonate solutions at 25??C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described calcite growth at low PCO2 (< 10-3 atm). Good agreement was found between observed crystallization rates and those calculated from the calcite dissolution rate law and mechanism proposed by Plummer et al. (1978). ?? 1981.

Reddy, M. M.; Plummer, L. N.; Busenberg, E.

1981-01-01

204

Fracture-aperture alteration induced by calcite precipitation  

NASA Astrophysics Data System (ADS)

Mineral precipitation significantly alters the transport properties of fractured rock. Chemical solubility gradients that favor precipitation induce mineral growth, which decreases the local aperture and alters preferential flow paths. Understanding the resulting development of spatial heterogeneities is necessary to predict the evolution of transport properties in the subsurface. We present experimental results that quantify the relationship between mineral precipitation and aperture alteration in a transparent analog fracture, 7.62cm x 7.62cm, with a uniform aperture of ~200 ?m. Prior to flow experiments, a pump circulated a super-saturated calcite solution over the bottom glass, coating the glass surface with calcite. This method of seeding resulted in clusters of calcite crystals with large reactive surface area and provided micro-scale variability in the aperture field. A continuous flow syringe pump injected a reactive fluid into the fracture at 0.5 ml/min. The fluid was a mixture of sodium bicarbonate (NaHCO3, 0.02M) and calcium chloride (CaCl2 0.0004M) with a saturation index, ?, of 8.51 with respect to calcite. A strobed LED panel backlit the fracture and a high-resolution CCD camera monitored changes in transmitted light intensity. Light transmission techniques provided a quantitative measurement of fracture aperture over the flow field. Results from these preliminary experiments showed growth near the inlet of the fracture, with decreasing precipitation rates in the flow direction. Over a period of two weeks, the fracture aperture decreased by 17% within the first 4mm of the inlet. Newly precipitated calcite bridged individual crystal clusters and smoothed the reacting surface. This observation is an interesting contradiction to the expectation of surface roughening induced by mineral growth. Additionally, the aperture decreased uniformly across the width of the fracture due to the initial aperture distribution. Future experiments of precipitation within variable-aperture fields will investigate the dependency of growth patterns on heterogeneous aperture distributions. (a) Aperture strain (?b/bi) after 14 days. Precipitation is concentrated near the inlet and decreases in the flow direction. (b) Width-averaged profiles of the initial and final aperture field show changes in aperture and smoothing that results from calcite precipitation between the initial discrete crystals.

Jones, T.; Detwiler, R. L.

2013-12-01

205

Arsenic-bearing calcite in natural travertines: evidence from sequential extraction, ?XAS, and ?XRF.  

PubMed

Recent studies demonstrated that synthetic calcite may host considerable amounts of arsenic (As). In this paper, the concentration of As in natural calcite was determined using two novel, specifically designed, sequential extraction procedures. In addition, the oxidation state of As and its distribution between calcite and coexisting Fe-oxyhydroxides was unravelled by ?XRF elemental mapping and As K-edge ?XAS spectroscopy. Our results conclusively demonstrate that arsenic can be found in natural calcite up to 2 orders of magnitude over the normal crustal As abundances. Because of the large diffusion of calcite in the environment, this phase may exert an important control on As geochemistry, mobility, and bioavailability. PMID:23738848

Costagliola, Pilario; Bardelli, Fabrizio; Benvenuti, Marco; Di Benedetto, Francesco; Lattanzi, Pierfranco; Romanelli, Maurizio; Paolieri, Mario; Rimondi, Valentina; Vaggelli, Gloria

2013-06-18

206

Microbial activity affected by lime in a long-term no-till soil  

Microsoft Academic Search

Under conventional farming practices, lime is usually applied on the soil surface and then incorporated into the soil to correct soil acidity. In no-till (NT) systems, where lime is surface applied or only incorporated into the soil to very shallow depth, lime will likely not move to where it is required within reasonable time. Consequently, lime may have to be

Juan P. Fuentes; David F. Bezdicek; Markus Flury; Stephan Albrecht; Jeffrey L. Smith

2006-01-01

207

Gas Hydrates: It's A Gas!  

NSDL National Science Digital Library

In this activity, students will investigate the occurrence of gas hydrates on the ocean floor. They will discover the importance of carbon, where carbon is stored on Earth, and that the largest reservoir of carbon is gas hydrates. Students will discover that Earth's climate changes, and how the greenhouse effect works. They will also learn about the potential of hydrates as a major new energy resource and explore the conditions under which hydrates form.

208

Leaching behavior of lime-fly ash mixtures  

SciTech Connect

As part of a larger investigation that included numerical and field-based components, the use of lime to reduce the leachability of a coal combustion fly ash was evaluated in the laboratory. The focus of this paper is on the experimental assessment of lime-fly ash leachability through sequential leach (SL), freeze-thaw (FT), and wet-dry (WD) leaching as well as multileachant sequential extraction (SE) tests. The results suggest that lime addition reduces the leachability for Cd, Se, and to some extent As. They also suggest that Cr is rendered more leachable with increasing lime content, for the conditions and low levels tested. It appears that there is a threshold lime content ({gt} 1.0%) that must be exceeded prior to reducing the leachability of As and Se. In particular, this threshold likely corresponds to the level at which appreciable cementitious reactions have developed. For example, in the case of As after the first cycle of leaching, the concentration was below the reporting limit (10 {mu} g/L) for 0% lime. However, at 0.5% lime amendment, the leached concentration increased to nearly 50 {mu} g/L. Subsequent lime additions reduced this concentration. No such threshold was observed for Cd leachability as was expected as a direct consequence of hydroxide precipitation, which is well established under the measured pH conditions. As such, Cd mobility is insensitive to the extent to which cementitious reactions are initiated. Overall, the results suggest that while lime stabilization may be effective for reducing leachability, sufficient amounts must be added; otherwise, the leachability of some constituents can actually be exacerbated.

Daniels, J.L.; Das, G.P. [University of North Carolina, Charlotte, NC (United States). Dept. of Civil Engineering

2006-01-15

209

Geobacillus thermoglucosidasius Endospores Function as Nuclei for the Formation of Single Calcite Crystals  

PubMed Central

Geobacillus thermoglucosidasius colonies were placed on an agar hydrogel containing acetate, calcium ions, and magnesium ions, resulting in the formation of single calcite crystals (calcites) within and peripheral to the plating area or parent colony. Microscopic observation of purified calcites placed on the surface of soybean casein digest (SCD) nutrient medium revealed interior crevices from which bacterial colonies originated. Calcites formed on the gel contained [1-13C]- and [2-13C]acetate, demonstrating that G. thermoglucosidasius utilizes carbon derived from acetate for calcite formation. During calcite formation, vegetative cells swam away from the parent colony in the hydrogel. Hard-agar hydrogel inhibited the formation of calcites peripheral to the parent colony. The calcite dissolved completely in 1 M HCl, with production of bubbles, and the remaining endospore-like particles were easily stained with Brilliant green dye. The presence of DNA and protein in calcites was demonstrated by electrophoresis. We propose that endospores initiate the nucleation of calcites. Endospores of G. thermoglucosidasius remain alive and encapsulated in calcites.

Murai, Rie

2013-01-01

210

Chemistry and petrography of calcite in the KTB pilot borehole, Bavarian Oberpfalz, Germany  

USGS Publications Warehouse

The KTB pilot borehole in northeast Bavaria, Germany, penetrates 4000 m of gneiss, amphibolite, and subordinate calc-silicate, lamprophyre and metagabbro. There are three types of calcite in the drilled section: 1) metamorphic calcite in calc-silicate and marble; 2) crack-filling calcite in all lithologies; and 3) replacement calcite in altered minerals. Crack-filling and replacement calcite postdate metamorphic calcite. Multiple calcite generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks. Crack-filling mineral assemblages that include calcite originally formed at temperatures of 150-350??C. Presently, crack-filling calcite is in chemical and isotopic equilibrium with saline to brackish water in the borehole at temperatures of ???120??C. The saline to brackish water contains a significant proportion of meteoric water. Re-equilibration of crack-filling calcite to lower temperatures means that calcite chemistry tells us little about water-rock interactions in the crystal section of temperatures higher than ~120??C. -from Author

Komor, S. C.

1995-01-01

211

Obsidian Hydration: A New Paleothermometer  

Microsoft Academic Search

The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960), who noted that the thickness of the hydrated layer on obsidian artifacts increases with time. This approach is, however, sensitive to temperature and humidity under earth-surface conditions. This has made obsidian hydration dating more difficult, but potentially

Lawrence M. Anovitz; Lee R. Riciputi; David R. Cole; Mostafa Fayek; J. Michael Elam

2006-01-01

212

Obsidian hydration: A new paleothermometer  

Microsoft Academic Search

The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960), who noted that the thickness of the hydrated layer on obsidian artifacts increases with time. This approach is, however, sensitive to temperature and humidity under earth-surface conditions. This has made obsidian hydration dating more difficult, but potentially

Lawrence M. Anovitz; Lee R. Riciputi; David R. Cole; Mostafa Fayek; J. Michael Elam

2006-01-01

213

Gas hydrate cool storage system  

Microsoft Academic Search

The invention presented relates to the development of a process utilizing a gas hydrate as a cool storage medium for alleviating electric load demands during peak usage periods. Several objectives of the invention are mentioned concerning the formation of the gas hydrate as storage material in a thermal energy storage system within a heat pump cycle system. The gas hydrate

M. P. Ternes; R. J. Kedl

1984-01-01

214

Microbially-Mediated Subsurface Calcite Precipitation for Removal of Hazardous Divalent Cations  

SciTech Connect

We are investigating microbially-mediated acceleration of calcite precipitation and co-precipitation of hazardous divalent cations (e.g., 90Sr) in calcite saturated subsurface systems. In theory, the addition of urea to an aquifer or vadose zone and its subsequent hydrolysis by indigenous microbes will cause an increase in alkalinity, pH and calcite precipitation. Lab studies indicated the ability of various bacteria to precipitate calcite through urea hydrolysis and that incorporation of strontium in biogenically-formed calcite is greater than in abiotically formed calcite. Results from a field experiment in a pristine location in the Snake River Plain aquifer involving the phased addition of molasses and then urea showed increases in total cell numbers, rate of urea hydrolysis and calcite formation during the study. The combined diagnostic approaches of microbiology, molecular ecology and analytical chemistry demonstrate the feasibility of this biogeochemical manipulation for subsurface remediation at arid Western DOE sites such as Hanford and INEEL.

Colwell, Frederick S.; Smith, R.W.; Ferris, F. Gratn; Ingram, Jani C.; Reysenbach, A.-L.; Fujita, Yoshiko; Tyler, T.L.; Taylor, J.L.; Banta, A.; Delwiche, M.E.; McLing, T.; Cortez, Marnie, M.; Watwood, M.E.

2003-03-27

215

Molecular Expressions: Optical Microscopy Primer - Birefringence in Calcite Crystals  

NSDL National Science Digital Library

This item is an interactive Java simulation for students of introductory physics or optics relating to birefringence. It features a virtual calcite crystal superimposed over the word "Birefringence". Due to the refractive properties of this type of crystal, the letters appear as a ghosted double image. The user can rotate the crystal and the polarizer to alter the transmission axis. This item is part of a larger collection of materials on introductory optics developed by the National High Magnetic Field Laboratory.

Davidson, Michael; Parry-Hill, Matthew J.; Murphy, Douglas B.; Spring, Kenneth R.; Long, John

2008-08-23

216

Kinetics of dry grinding of industrial minerals: calcite and barite  

Microsoft Academic Search

This paper presents the kinetics study of dry ball milling of calcite and barite minerals. The experimental mill used was a laboratory size of 209 mm diameter, 175 mm length, providing a total mill volume of 6001 cm3, with a total mass of 5.6 kg of steel balls of 46, 26 and 12.8 mm diameter, so as to occupy 20%

E Teke; M Yekeler; U Ulusoy; M Canbazoglu

2002-01-01

217

Oxygen Isotope Fractionation between Coexisting Calcite and Dolomite.  

PubMed

The oxygen isotopic composition of calcite from carbonate rocks of the lower unit of the Flagstaff formation (Paleocene) exposed along the western margin of the Wasatch Plateau, Utah, is about 7 per mil lower than that of coexisting dolomite, suggesting that isotopic equilibration of these two minerals can occur at relatively low temperatures. Unlike recent isotopic evidence presented by Degens and Epstein, the data do not preclude a primary chemical origin for the dolomite. PMID:17802014

Weber, J N

1964-09-18

218

Cosmogenic Chlorine36 Production in Calcite by Muons  

Microsoft Academic Search

At depths below a few metres, 36Cl production in calcite is initiated almost entirely by cosmic ray muons. The principal reactions are (1) direct negative muon capture by Ca; 40Ca(??,?)36Cl, and (2) capture by 35Cl of secondary neutrons produced in muon capture and muon-induced photodisintegration reactions. We have determined rates for 36Cl and neutron production due to muon capture in

J. O. H. Stone; J. M. Evans; L. K. Fifield; G. L. Allan; R. G. Cresswell

1998-01-01

219

Spin-lattice coupling of Mn2+ ions in calcite  

Microsoft Academic Search

It is found theoretically that the spin-lattice coupling constant GA1 is proportional to the axial zero-field splitting parameter D for a 6S-state ion in D3d symmetry. A study of the ratio GA\\/sup \\/\\/1D provides an effective way of deciding the relative importance of the various mechanisms which contribute to the zero-field splitting. For Mn2+ in calcite (CaCO3) the spin-orbit coupling

Yu Wan-Lun; Zhao Min-Guang

1987-01-01

220

Arsenite sorption and co-precipitation with calcite  

Microsoft Academic Search

Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log [As(OH)3 degrees \\/ Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model. At low concentrations, As(OH)3 degrees is adsorbed by complexation to surface Ca surface sites, as

Gabriela Roman-Ross; Gabriel Cuello; Xavier Turrillas; Alejandro Fernandez-Martinez; Laurent Charlet

2008-01-01

221

Arsenite sorption and co-precipitation with calcite  

Microsoft Academic Search

Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log ?As(III) vs. log [As(OH)3°\\/Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model [Farley, K.J., Dzombak, D.A., Morel, F.F.M., 1985. A surface precipitation model for the sorption of cations on metal

G. Román-Ross; Gabriel Cuello; Xavier Turrillas; A. Fernández-Martínez; Laurent Charlet

2006-01-01

222

Fast diffusion along mobile grain boundaries in calcite  

Microsoft Academic Search

Experimental measurements of grain boundary diffusion are usually conducted on static boundaries, despite the fact that grain\\u000a boundaries deep in the Earth are frequently mobile. In order to explore the possible effect of boundary mobility on grain\\u000a boundary diffusion rates we have measured the uptake of 44Ca from a layer of 44Ca-enriched calcite powder during the static recrystallization of a

Andrew McCaig; Stephen J. Covey-Crump; Walid Ben Ismaïl; Geoffrey E. Lloyd

2007-01-01

223

Thermodynamic Aspects of the Vaterite-Calcite Phase Transition  

Microsoft Academic Search

Although vaterite is the least stable anhydrous calcium carbonate polymorph, it is formed as a metastable phase in some normal\\u000a and pathological biomineralisation processes. In this work, thermodynamic aspects of the vaterite-calcite phase transition\\u000a were comprehensively studied. Vaterite samples were prepared by different methods and characterised for the composition, crystal\\u000a structure, specific surface and grain size. All products were identified

G. Wolf; E. Königsberger; H. G. Schmidt; L.-C. Königsberger; H. Gamsjäger

2000-01-01

224

Texture effects on megahertz dielectric properties of calcite rock samples  

Microsoft Academic Search

Dielectric measurements have been made from 0.5 to 1300 MHz on Whitestone, a quarried calcite rock, saturated with salty water. Whitestone shows a large increase in dielectric permittivity (dispersion) at the low end of this frequency range. When the conductivity of the water is varied, the dielectric permittivity of Whitestone is found to scale as water conductivity\\/frequency, i.e., as the

W. E. Kenyon

1984-01-01

225

Evaluation and Performance of Hydrated Lime and Limestone Powder in Porous Asphalt  

Microsoft Academic Search

Porous asphalt mixture or Open Graded Friction Course (OGFC) has many benefits that resulted in its extensive use and development. OGFC improves the friction of a wet pavement, surface reflection, traffic noise, wet weather driving conditions by allowing the water to drain through its porous structure and reduces the hydroplaning, the splashing and spraying of water in the air (acts

Mahmoud Ameri; Mohsen Aboutalebi Esfahani

2008-01-01

226

Growth modification of seeded calcite using carboxylic acids: atomistic simulations.  

PubMed

Molecular dynamics simulations were used to investigate possible explanations for experimentally observed differences in the growth modification of calcite particles by two organic additives, polyacrylic acid (PAA) and polyaspartic acid (p-ASP). The more rigid backbone of p-ASP was found to inhibit the formation of stable complexes with counter-ions in solution, resulting in a higher availability of p-ASP compared to PAA for surface adsorption. Furthermore the presence of nitrogen on the p-ASP backbone yields favorable electrostatic interactions with the surface, resulting in negative adsorption energies, in an upright (brush conformation). This leads to a more rapid binding and longer residence times at calcite surfaces compared to PAA, which adsorbed in a flat (pancake) configuration with positive adsorption energies. The PAA adsorption occurring despite this positive energy difference can be attributed to the disruption of the ordered water layer seen in the simulations and hence a significant entropic contribution to the adsorption free energy. These findings help explain the stronger inhibiting effect on calcite growth observed by p-ASP compared to PAA and can be used as guidelines in the design of additives leading to even more marked growth modifying effects. PMID:20304410

Aschauer, Ulrich; Spagnoli, Dino; Bowen, Paul; Parker, Stephen C

2010-06-01

227

Arsenic uptake by natural calcite: An XAS study  

NASA Astrophysics Data System (ADS)

As-bearing travertine rocks from Tuscany (Italy), where previous studies suggested the existence of a CO 32- ? AsO 33- substitution in the calcite lattice, were investigated with X-ray Absorption Spectroscopy (XAS) at the As K-edge (11,867 eV). In two of the studied samples, XANES indicates that As is in the 5+ oxidation state only, and EXAFS analysis reveals a local environment typical of arsenate species. For these samples, the lack of detectable second shell signals suggests a poorly ordered environment, possibly corresponding to an adsorption onto oxide and/or silicate phases. On the other hand, in the third sample XANES reveals a mixed As oxidation state (III and V). This sample also presents evident next nearest neighbor coordination shells, attributed to As-Ca and As-As contributions. The occurrence of next neighbor shells is evidence that part of As is incorporated in an ordered lattice. Furthermore, the local structure revealed by EXAFS is compatible with As incorporation in the calcite phase, as further supported by DFT simulations. The observation of next neighbors shells only in the As(III)-rich sample suggests the substitution of the arsenite group in place of the carbonate one (CO 32- ? AsO 33-). The conclusion of this work is that uptake of As by calcite is in general less favored than adsorption onto iron oxhydroxides, but could become environmentally important wherever the latter phenomenon is hindered.

Bardelli, F.; Benvenuti, M.; Costagliola, P.; Di Benedetto, F.; Lattanzi, P.; Meneghini, C.; Romanelli, M.; Valenzano, L.

2011-06-01

228

Calcite deposition at Miravalles geothermal field, Costa Rica  

SciTech Connect

The calcite deposition problem at Miravalles has been studied since it was observed in the first three wells drilled on the slopes of the Miravalles Volcano. Long-term tests have been carried out to study reservoir characteristics. The change in the production behavior of the wells with the restriction imposed by the deposited calcite has been studied trying to evaluate and quantify the scaling problem. Work is being done on predictions of the deposition rate, location and distribution of the deposited mineral inside the wells. This work was compared with real data obtained from caliper logs of the wells before and after production. The feasibility of the first 55 MW power plant has been demonstrated. It was considered that the solution for the calcite problem is the reaming during discharge of the wells trying at the same time to minimize the cleaning interventions with a new well design. It is believed, due to the thermodynamics and chemical characteristics of the extracted fluids, that it is possible to find a non-deposition zone which will permit the drilling of wells without a scaling problem.

Vaca, L.; Alvarado, A.; Corrales, R. (Instituto Costarricense de Electricidad, San Jose (Costa Rica))

1989-01-01

229

Visualization of acoustic cavitation effects on suspended calcite crystals.  

PubMed

The acoustic cavitation (42,080 Hz, 7.1 W cm(-2) or 17 W) effects on suspended calcite crystals, sized between 5 and 50 ?m, have been visualized for the first time using high speed photography. High speed recordings with a duration of 1 s containing up to 300,000 frames per second, revealed the effect of cluster and streamer cavitation on several calcite crystals. Cavitation clusters, evolved from cavitation inception and collapse, caused attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation was observed to cause deagglomeration only. Cavitation on the surface gave the crystals momentum. However, it is shown that breakage of accelerated crystals by interparticle collisions is unrealistic because of their small sizes and low velocities. Crystals that were accelerated by bubble expansion, subsequently experienced a deceleration much stronger than expected from drag forces, upon bubble collapse. Experiments with pre-dried crystals seemed to support the current theory on bubble nucleation through the presence of pre-existing gas pockets. However, experiments with fully wetted crystals also showed the nucleation of bubbles on the crystal surface. Although microjet impingement on the crystal surface could not be directly visualized with high speed photography, scanning electron microscopy (SEM) analysis of irradiated calcite seeds showed deep circular indentations. It was suggested that these indentations might be caused by shockwave induced jet impingement. Furthermore, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures. PMID:20579928

Wagterveld, R M; Boels, L; Mayer, M J; Witkamp, G J

2011-01-01

230

Alternative origins for nannobacteria-like objects in calcite  

NASA Astrophysics Data System (ADS)

More than 40 calcite-precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical-, rod-, and ovoid-shaped objects that have been widely interpreted as evidence of nanometer-scale life (i.e., nannobacteria). Individual experiments included the addition of soluble organic compounds, common species of eubacteria, or phage-induced eubacterial lysates. These experiments indicate that many of the nanometer-scale objects have inorganic or nonnannobacterial origins. In the precipitation experiments, calcite formed euhedral crystals 50 800 nm in diameter and smaller (<50 nm) anhedral or rounded particles or protocrystals. The small anhedral or rounded solids resembled nannobacteria. The relative amount of anhedral or rounded calcite was greatest in experiments with a dissolved organic component. These controlled experiments are in accord with observations that rounded nanometer-scale objects are more common in minerals formed in organic-rich environments. Bacterial fragments occur as rounded to irregularly shaped particles that included cell-wall fragments, expulsed cytoplasm, and relict capsules that also closely resembled nannobacteria. Acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer-scale features that resembled nannobacteria in natural carbonates. The shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching. Much caution is advisable in interpreting the origin of rounded features <50 nm.

Kirkland, Brenda L.; Lynch, F. Leo; Rahnis, Michael A.; Folk, Robert L.; Molineux, Ian J.; McLean, Robert J. C.

1999-04-01

231

Earthworm-produced calcite granules: A new terrestrial palaeothermometer?  

NASA Astrophysics Data System (ADS)

In this paper we show for the first time that calcite granules, produced by the earthworm Lumbricus terrestris, and commonly recorded at sites of archaeological interest, accurately reflect temperature and soil water ?18O values. Earthworms were cultivated in an orthogonal combination of two different (granule-free) soils moistened by three types of mineral water and kept at three temperatures (10, 16 and 20 °C) for an acclimatisation period of three weeks followed by transfer to identical treatments and cultivation for a further four weeks. Earthworm-secreted calcite granules were collected from the second set of soils. ?18O values were determined on individual calcite granules (?18Oc) and the soil solution (?18Ow). The ?18Oc values reflect soil solution ?18Ow values and temperature, but are consistently enriched by 1.51 (± 0.12)‰ in comparison to equilibrium in synthetic carbonates. The data fit the equation 1000 ln ? = [20.21 ± 0.92] (103 T-1) - [38.58 ± 3.18] (R2 = 0.95; n = 96; p < 0.0005). As the granules are abundant in modern soils, buried soils and archaeological contexts, and can be dated using U-Th disequilibria, the developed palaeotemperature relationship has enormous potential for application to Holocene and Pleistocene time intervals.

Versteegh, Emma A. A.; Black, Stuart; Canti, Matthew G.; Hodson, Mark E.

2013-12-01

232

Aluminum Sulfate 18 Hydrate  

ERIC Educational Resources Information Center

A chemical laboratory information profile (CLIP) of the chemical, aluminum sulfate 18 hydrate, is presented. The profile lists physical and harmful properties, exposure limits, reactivity risks, and symptoms of major exposure for the benefit of teachers and students using the chemical in the laboratory.

Young, Jay A.

2004-01-01

233

Desalination Through Methane Hydrate.  

National Technical Information Service (NTIS)

In one embodiment, this invention pertains to desalination of seawater by feeding methane into seawater at a depth exceeding 100 meters to form methane hydrate which rises to where it is decomposed into methane and water, and recovering water. Methane is ...

M. D. Max R. E. Pellenbarg

1997-01-01

234

Imaging surface contacts: Power law contact distributions and contact stresses in quartz, calcite, glass and acrylic plastic  

USGS Publications Warehouse

A procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials, while the surfaces are subjected to static loads or undergoing frictional slip. Static loading experiments with quartz, calcite, soda-lime glass and acrylic plastic at normal stresses to 30 MPa yield power law distributions of contact areas from the smallest contacts that can be resolved (3.5 ??m2) up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces. In each material, increasing normal stress results in a roughly linear increase of the real area of contact. Mechanisms of contact area increase are by growth of existing contacts, coalescence of contacts and appearance of new contacts. Mean contacts stresses are consistent with the indentation strength of each material. Contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self-similar. The contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies. The contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap. Synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography.

Dieterich, J. H.; Kilgore, B. D.

1996-01-01

235

Hydrothermal replacement of calcite by Mg-carbonates  

NASA Astrophysics Data System (ADS)

The transport of heat and mass through the Earth's crust is coupled to mineral reactions and the exchange of isotopes and elements between different phases. Carbonate minerals are a major constituent of the Earth's crust and play an important role in different physical, chemical and even biological processes. In this experimental study, the element exchange reaction between calcite (CaCO3) and a Mg-rich fluid phase is investigated under hydrothermal conditions. Single crystals of calcite (2x2x2 mm) react with 1 ml of a 1 M MgCl2 solution at 200° C in a Teflon-lined steel autoclave for different times between one day and four weeks. The reaction leads to the formation of a porous reaction front and the pseudomorphic replacement of calcite by dolomite [CaMg(CO3)2] and magnesite (MgCO3). Scanning electron microscopy revealed that the reaction rim consists of small Mg-carbonate rhombs closely attached to each other, suggesting that the replacement reaction takes place by a dissolution-precipitation mechanism. Typically, the observed reaction front can be divided into two different domains. The outer part of the reaction rim, i.e. from the mineral surface in contact to the fluid inwards, consists of magnesite, whereas the inner part of the rim surrounding the unreacted calcite core consists of Ca-rich dolomite. The formation of a porous microstructure that varies in different parts of the reaction rim is a direct result of the large molar volume change induced by the replacement of calcite by magnesite and dolomite. The developing porosity therefore creates fluid pathways that promote the progress of the reaction front towards the unreacted core of the single crystal. Compositional profiles measured perpendicular to the mineral surface across the reactions rims using electron microprobe (EMPA) further revealed a compositional gradient within the reaction rim with regard to the structure-forming elements Mg and Ca. Here, the amount of Mg incorporated in both product phases increases with increasing distance from the unreacted calcite core, countered by a decrease of Ca incorporated. Both the coexistence of two different product phases and the distinct compositional gradient within the forming reaction rim are unequivocal signs of a chemical zonation of Ca and Mg in the fluid phase which mediates the element exchange between the reaction interface and the bulk solution. Atomic adsorption spectroscopy revealed that the Ca/Mg ratio in the reacted fluid increases as a function of time, reflecting the progressive exchange of Mg and Ca between the fluid and the solid phase. The time-dependence of the evolving Ca/Mg ratio can be fitted with a square root of time relation that indicates a transport controlled reaction. We interpret the hydrothermal replacement of calcite to operate via a dissolution/re-precipitation mechanism, whereas the reaction progress is controlled by the transport of the structure forming elements through the developing reaction rim.

Jonas, Laura; Mueller, Thomas; Dohmen, Ralf

2014-05-01

236

Lime-Fly Ash-Stabilized Bases and Subbases.  

National Technical Information Service (NTIS)

This report presents the results of a comprehensive review and assessment of current technology for lime-fly ash stabilization of soil materials in bases and subbases. Information is presented on the factors to be considered in mixture design, constructio...

1976-01-01

237

EVALUATION OF LIME PRECIPITATION FOR TREATING BOILER TUBE CLEANING WASTES  

EPA Science Inventory

The report gives results of an evaluation of lime precipitation for treating boiler tube cleaning wastes. In this project, wastewater samples were collected from six boiler tubeside chemical cleanings, using complexing and chelating agents. The samples represented: (1) ammoniacal...

238

Evaluation of Lime Precipitation for Treating Boiler Tube Cleaning Wastes.  

National Technical Information Service (NTIS)

The report gives results of an evaluation of lime precipitation for treating boiler tube cleaning wastes. In this project, wastewater samples were collected from six boiler tubeside chemical cleanings, using complexing and chelating agents. The samples re...

P. J. Rogoshewski D. D. Carstea

1980-01-01

239

Effect of lime bonds on the sintering of aluminous bodies  

Microsoft Academic Search

Conclusions Various lime bonds have different effects on the densification of aluminous bodies during drying and firing. Of the bonds investigated the greatest action on the sintering of the alumina is exerted by gypsum.

A. A. Pirogov; M. M. Mirak'yan; V. V. Primachenko

1970-01-01

240

Changes in soil bacterial communities following liming of acidified forests  

Microsoft Academic Search

To counteract forest decline due to anthropogenic acidification, two catchments located on granite and on sandstone bedrock were limed (2.5t\\/ha). The catchments are located in strongly affected areas in the Vosges Mountains of northeastern France. Four years after liming, structure of soil bacterial communities and community-level physiological profiling (CLPP) were investigated at two seasons. Bacterial communities were compared with those

Hugues Clivot; Christophe Pagnout; Delphine Aran; Simon Devin; Pascale Bauda; Pascal Poupin; François Guérold

241

Retrofit costs for lime\\/limestone FGD and lime spray drying at coal-fired utility boilers  

Microsoft Academic Search

The paper gives results of a research program the objective of which was to significantly improve engineering cost estimates currently being used to evaluate the economic effects of applying SO2 controls to existing coal-fired utility boilers. The costs of retrofitting conventional lime\\/limestone wet flue gas desulfurization (L\\/LS FGD) and lime spray drying (LSD) FGD at 100-200 coal-fired power plants are

T. E. Emmel; J. W. Jones

1990-01-01

242

Simulating the Dissolution and Precipitation of Calcite in Soils using a Soil Hydrological Model  

NASA Astrophysics Data System (ADS)

The spatial distributions of calcite rich horizons within dryland soils are commonly used as proxies for ancient precipitation regimes. As water percolates through a soil, it dissolves minerals, such as calcite, transporting the soluble minerals downward. As soil water is removed by evaporation or root water uptake the water solution may become supersaturated resulting in precipitation of calcite at a new depth. Greater amounts of annual precipitation are thought to result in deeper leaching, yielding deeper calcite horizons. However, other variables such as temperature, root water uptake, soil CO2 concentrations, and soil hydraulic parameters may also influence the solubility and precipitation depth of calcite, confounding otherwise simple relationships between calcite distribution and precipitation. There have been multiple empirical calibrations of depth to Bk (a subsoil horizon rich in calcite) as a proxy for mean annual precipitation (MAP), some of which are soil-order specific. However, it is difficult to constrain all variables using natural soils because the appropriate soil sequences do not always exist. To help quantify the factors controlling the distribution of calcite in soils, we simulated calcite movement using the soil hydrologic model HYDRUS. This approach builds on previous modeling efforts and incorporates several advancements, including a more accurate representation of soil water flow and CO2 transport. We used an irrigation pattern consisting of 2 days of precipitation followed by 8 days of evaporation applied to the surface of a sandy loam soil column 1 meter in depth. This irrigation pattern was repeated during 8, 50, 200, and 500 year simulations with MAP of 73 cm/year. Simulated Bk horizon depth increased with run time and began to stabilize at 500 years. Simulated calcite concentration profiles qualitatively match the commonly observed calcite distribution pattern in dryland soils; after the 500 year simulation, calcite was progressively leached from the upper third of the column and accumulated at a horizon 35 cm below the soil surface. This simulation considered soil evaporative flux as the sole sink for soil moisture. The spatial distribution of simulated calcite accumulation is also related to evaporation rate; larger evaporation rates result in thinner, more concentrated calcite horizons because less moisture is available to leach calcite deeper into the column. Increased simulation run time and the addition of root water uptake, root attributed CO2 production, calcite dust influx at the surface, and the use of measured meteorological variables as boundary conditions will increase the accuracy of the model. Once validated against natural soils, we will use the model to determine the relative importance of multiple variables on calcite accumulation and dissolution.

Meyer, N. A.; Breecker, D. O.

2011-12-01

243

Calcite production by coccolithophores in the south east Pacific Ocean  

NASA Astrophysics Data System (ADS)

BIOSOPE cruise covered an oceanographic transect through the centre of the South Pacific Gyre (SPG) from the Marquesas archipelago to the Peru-Chile upwelling (PCU). Water samples from 6 depths in the euphotic zone were collected at 20 stations. The concentrations of suspended calcite particles, coccolithophores cells and detached coccoliths were estimated together with size and weight using an automatic polarizing microscope, a digital camera, and a collection of softwares performing morphometry and pattern recognition. Some of these softwares are new and described here for the first time. The coccolithophores standing stocks were usually low and reached maxima west of the PCU. The coccoliths of Emiliania huxleyi, Gephyrocapsa spp. and Crenalithus spp. (Order Isochrysidales) represented more than 30% of all the suspended calcite particles detected in the size range 0.1 46 ?m (22% of PIC in term of calcite weight). These species grew preferentially in the Chlorophyll maximum zone. In the SPG their maximum cell concentrations were recorded between depth of 150 and 200 m, which is unusually deep for these taxa. The weight of coccoliths and coccospheres were correlated to their size. Large and heavy coccoliths and coccospheres were found in regions with relatively high fertility in the Marquises Island and in the PCU. Small and light coccoliths and coccospheres were found west of the PCU. This distribution is strongly related to ocean chemistry in particular to alkalinity and to carbonate ions concentration. The biotic (coccolithophores production) influence on calcification is mainly driven at the local scale (depth) whereas the abiotic (carbonate chemistry) plays its most important role at the regional (horizontal) level. Here 94% of the variability of coccolith and coccosphere weight can be explained by a change in 7 environmental variables.

Beaufort, L.; Couapel, M.; Buchet, N.; Claustre, H.; Goyet, C.

2008-08-01

244

Principles of Calcite Dissolution in Human and Artificial Otoconia  

PubMed Central

Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV). The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic) otoconia (calcite gelatin nanocomposits) and natural calcite were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM). Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution) whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution) of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of calcite dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV.

Walther, Leif Erik; Blodow, Alexander; Buder, Jana; Kniep, Rudiger

2014-01-01

245

Passivation of the calcite surface with phenylmalonate and benzylmalonate ions.  

PubMed

We explored the affinity of calcite to adsorbed organic molecules as an approach to the conservation of cultural heritage built of marble and limestone. The utilization of phenylmalonic and benzylmalonic acids provided a hydrophobic adsorptive interface, adequate to prevent processes of aqueous weathering. Samples of marble powder (polycrystalline calcite) were impregnated with solutions of phenylmalonic and benzylmalonic acid at three concentrations (5 x 10(-2), 5 x 10(-3), and 5 x 10(-4) M) and different pH values (6.00, 7.00, and 8.00). The surface charge of the calcite suspensions was determined by potentiometric measurements under equilibrium conditions at room temperature in aqueous solution of the dicarboxylic acids, in order to understand the influence of the electrokinetic potential in the surface association. The adsorbed amounts were determined by calculation of the thermodynamic equilibria of solutions. The presence of the organic interface on the mineral surface was corroborated by Raman spectroscopy and small-angle X-ray scattering (SAXS). The results indicate effective adsorption of both dicarboxylic acids as a function of the concentration and pH, and several other conditions that favors coulombic interaction, an absence of electrophoretic mobility or surface electroneutrality related to the solid surface potentials. The coverage of pores by dicarboxylic adsorbate modified the geometrical pore shape and the pore size distribution, filling all the pores of larger than 80 A diameter, giving as a result a mesoporous structure. This change in the surface morphology by organic adsorbates constitutes a modification in the diffusional processes of the environment on the mineral surface. PMID:15848404

Salinas-Nolasco, Manlio F; Méndez-Vivar, Juan; Lara, Víctor H; Bosch, Pedro

2005-06-01

246

Unusual calcite stromatolites and pisoids from a landfill leachate collection system  

NASA Astrophysics Data System (ADS)

Low-magnesium calcite stromatolites and pisoids were found to have precipitated within the leachate collection system piping of a Palm Beach County, Florida, landfill. The stromatolites and pisoids formed in an aphotic and anoxic environment that was at times greatly supersaturated with calcite. The stromatolites are composed of branching cylindrical bundles of concentrically laminated radial fibrous crystals. The pisoids consist of concentric layers of radial fibrous and microcrystalline calcite. Bacteria, likely sulfate reducing, appear to have acted as catalysts for calcite crystal nucleation, and thus the formation of the stromatolites and pisoids. The leachate system stromatolites provide a recent example of stromatolites that formed largely by cement precipitation. By acting as catalysts for calcite nucleation, bacteria may cause more rapid cementation than would have occurred under purely abiotic conditions. Rapid calcite precipitation catalyzed by bacteria has interfered with the operation of the Palm Beach County landfill leachate collection by obstructing pipes and may be an unrecognized problem at other landfill sites.

Maliva, Robert G.; Missimer, Thomas M.; Leo, Kevin C.; Statom, Richard A.; Dupraz, Christophe; Lynn, Matthew; Dickson, J. A. D.

2000-10-01

247

Strain rate dependent calcite microfabric evolution at natural conditions  

NASA Astrophysics Data System (ADS)

Crystal plastic deformational behaviour of calcite has been the focus of many experimental studies. Different strain rates, pressure and temperature conditions have been addressed to investigate a wide range of deformation regimes. However, a direct comparison with natural fault rocks remains difficult because of extreme differences between experimental and natural strain rates. A flanking structure developed in almost pure calcite marble on Syros (Cyclades, Greece). Due to rotation of a planar feature (crack) a heterogeneous strain field in the surrounding area occurred resulting in different strain domains and the formation of the flanking structure. Assuming that deformation was active continuously during the development of the flanking structure, the different strain domains correspond to different strain-rate domains. The outcrop thus represents the final state of a natural experiment and gives us a great opportunity to get natural constraints on strain rate dependent deformation behaviour of calcite. Comparing the microfabrics in the 1 to 2.5 cm thick shear zone and the surrounding host rocks, which formed under the same metamorphic conditions but with different strain rates, is the central focus of this study. Due to the extreme variation in strain and strain rate, different microstructures and textures can be observed corresponding to different deformation mechanisms. With increasing strain rate we observe a change in dominant deformation mechanism from dislocation glide to dislocation creep and finally diffusion creep. Additionally, a change from subgrain rotation to bulging recrystallization can be observed in the dislocation creep regime. Crystallographic preferred orientations (CPO) and the grade of intracrystalline deformation were measured on a FEI Quanta 3D FEG instrument equipped with an EDAX Digiview IV EBSD camera. At all strain rates clear CPOs developed leading to the assumption that calcite preferentially deforms within the dislocation creep field. However, we can also find clear evidence for grain size sensitive deformation mechanisms at smaller grain sizes (3.6 ?m) consistent with experimental observations and determined flaw laws. The results of this study are compared with experimental data, closing the gap between experimental and natural geological strain rates.

Rogowitz, Anna; Grasemann, Bernhard; Huet, Benjamin; Habler, Gerlinde

2014-05-01

248

Evidence for an organic origin of pedogenic calcitic nanofibres  

NASA Astrophysics Data System (ADS)

Calcium carbonate nanofibres are found in numerous terrestrial environments, often associated with needle fibre calcite. This study attempts to mimic the natural system and generate comparable crystalline structures. A comparison of natural and synthesized nanofibre structures, using HRTEM as well as electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), has demonstrated that this type of nanocrystal can result from precipitation on organic templates, most likely cellulose nanofibres. This study emphasizes the fundamental role of organic templates in the precipitation of calcium carbonate in vadose environments, even at the nanoscale.

Cailleau, Guillaume; Dadras, Massoud; Abolhassani-Dadras, Sousan; Braissant, Olivier; Verrecchia, Eric P.

2009-04-01

249

Simulations of calcite crystallization on self-assembled monolayers.  

PubMed

This paper presents simulations of calcium carbonate ordering in contact with self-assembled monolayers. The calculations use potential-based molecular dynamics to model the crystallization of calcium carbonate to calcite expressing both the (00.1) and (01.2) surfaces. The effect of monolayer properties: ionization; epitaxial matching; charge density; and headgroup orientation on the crystallization process are examined in detail. The results demonstrate that highly charged surfaces are vital to stimulate ordering and crystallization. Template directed crystallization requires charge epitaxy between both the crystal surface and the monolayer. The orientation of the headgroup appears to make no contribution to the selection of the crystal surface. PMID:18672912

Freeman, Colin L; Harding, John H; Duffy, Dorothy M

2008-09-01

250

Calcite dissolution: an in situ study in the Panama Basin  

SciTech Connect

The results of an in situ study of calcite dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.

Thunell, R.C. (Univ. of South Carolina, Columbia); Keir, R.S.; Honjo, S.

1981-05-08

251

Methane Clathrate Hydrate Prospecting  

NASA Technical Reports Server (NTRS)

A method of prospecting for methane has been devised. The impetus for this method lies in the abundance of CH4 and the growing shortages of other fuels. The method is intended especially to enable identification of subpermafrost locations where significant amounts of methane are trapped in the form of methane gas hydrate (CH4(raised dot)6H2O). It has been estimated by the U.S. Geological Survey that the total CH4 resource in CH4(raised dot) 6H2O exceeds the energy content of all other fossil fuels (oil, coal, and natural gas from non-hydrate sources). Also, CH4(raised dot)6H2O is among the cleanest-burning fuels, and CH4 is the most efficient fuel because the carbon in CH4 is in its most reduced state. The method involves looking for a proxy for methane gas hydrate, by means of the combination of a thermal-analysis submethod and a field submethod that does not involve drilling. The absence of drilling makes this method easier and less expensive, in comparison with prior methods of prospecting for oil and natural gas. The proposed method would include thermoprospecting in combination with one more of the other non-drilling measurement techniques, which could include magneto-telluric sounding and/or a subsurface-electrical-resistivity technique. The method would exploit the fact that the electrical conductivity in the underlying thawed region is greater than that in the overlying permafrost.

Duxbury, N.; Romanovsky, V.

2003-01-01

252

Surfactant effects on gas hydrate formation  

Microsoft Academic Search

Micellar solutions were found to increase gas hydrate formation rate and alter formation mechanism for ethane and natural gas hydrates. A critical micellar concentration (CMC) of sodium dodecyl sulfate water solution was found to be 242 ppm at hydrate-forming conditions, where CMC was best determined by hydrate induction time. At surfactant concentrations above the CMC, hydrate formation rates in a

Y. Zhong; R. E. Rogers

2000-01-01

253

Hydration of a low-alkali CEM III/B-SiO{sub 2} cement (LAC)  

SciTech Connect

The hydration of a low-alkali cement based on CEM III/B blended with 10 wt.% of nanosilica has been studied. The nanosilica reacted within the first days and 90% of the slag reacted within 3.5 years. C-S-H (Ca/Si {approx} 1.2, Al/Si {approx} 0.12), calcite, hydrotalcite, ettringite and possibly straetlingite were the main hydrates. The pore water composition revealed ten times lower alkali concentrations than in Portland cements. Reducing conditions (HS{sup -}) and a pH value of 12.2 were observed. Between 1 month and 3.5 years of hydration more hydrates were formed due to the ongoing slag reaction but no significant differences in the composition of the pore solution or solid phase assemblage were observed. On the basis of thermodynamic calculations it is predicted that siliceous hydrogarnet could form in the long-term and, in the presence of siliceous hydrogarnet, also thaumasite. Nevertheless, even after 3.5 year hydration, neither siliceous hydrogarnet nor thaumasite have been observed.

Lothenbach, Barbara, E-mail: barbara.lothenbach@empa.ch [Empa, Laboratory for Concrete and Construction Chemistry, CH-8600 Duebendorf (Switzerland); Le Saout, Gwenn; Ben Haha, Mohsen; Figi, Renato [Empa, Laboratory for Concrete and Construction Chemistry, CH-8600 Duebendorf (Switzerland); Wieland, Erich [PSI, Laboratory for Waste Management, CH-5232 Villigen PSI (Switzerland)

2012-02-15

254

The ubiquitous nature of accessory calcite in granitoid rocks: Implications for weathering, solute evolution, and petrogenesis  

USGS Publications Warehouse

Calcite is frequently cited as a source of excess Ca, Sr and alkalinity in solutes discharging from silicate terrains yet, no previous effort has been made to assess systematically the overall abundance, composition and petrogenesis of accessory calcite in granitoid rocks. This study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks. Calcite is found to be universally present in a concentration range between 0.028 to 18.8 g kg-1 (mean = 2.52 g kg-1). Calcite occurrences include small to large isolated anhedral grains, fracture and cavity infillings, and sericitized cores of plagioclase. No correlation exists between the amount of calcite present and major rock oxide compositions, including CaO. Ion microprobe analyses of in situ calcite grains indicate relatively low Sr (120 to 660 ppm), negligible Rb and 87Sr/86Sr ratios equal to or higher than those of coexisting plagioclase. Solutes, including Ca and alkalinity produced by batch leaching of the granitoid rocks (5% CO2 in DI water for 75 d at 25??C), are dominated by the dissolution of calcite relative to silicate minerals. The correlation of these parameters with higher calcite concentrations decreases as leachates approach thermodynamic saturation. In longer term column experiments (1.5 yr), reactive calcite becomes exhausted, solute Ca and Sr become controlled by feldspar dissolution and 87Sr/ 86Sr by biotite oxidation. Some accessory calcite in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration. However, the ubiquitous occurrence of calcite also suggests formation during late stage (subsolidus) magmatic processes. This conclusion is supported by petrographic observations and 87Sr/86Sr analyses. A review of thermodynamic data indicates that at moderate pressures and reasonable CO2 fugacities, calcite is a stable phase at temperatures of 400 to 700??C. Copyright ?? 2005 Elsevier Ltd.

White, A. F.; Schulz, M. S.; Lowenstern, J. B.; Vivit, D. V.; Bullen, T. D.

2005-01-01

255

Anisotropic lattice distortions in biogenic calcite induced by intra-crystalline organic molecules  

Microsoft Academic Search

We have performed precise structural measurements on five different calcitic seashells by high-resolution X-ray powder diffraction on a synchrotron beam line and by laboratory single crystal X-ray diffraction. The unit cell parameters a and c of biogenic calcite were found to be systematically larger than those measured in the non-biogenic calcite. The maximum lattice distortion (about 2·10?3) was detected along

Boaz Pokroy; Andrew N. Fitch; Frederic Marin; Moshe Kapon; Noam Adir; Emil Zolotoyabko

2006-01-01

256

Effects of magnesium ions on near-equilibrium calcite dissolution: Step kinetics and morphology  

Microsoft Academic Search

Dissolution kinetics at the aqueous solution-calcite (101¯4) interface at 50 °C were investigated using in situ atomic force microscopy (AFM) to reveal the influence of magnesium concentration and solution saturation state on calcite dissolution kinetics and surface morphology. Under near-equilibrium conditions, dissolved Mg2+ displayed negligible inhibitory effects on calcite dissolution even at concentrations of 10-4molal(m). Upon the introduction of 10-3mMg2+,

Man Xu; Steven R. Higgins

2011-01-01

257

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C  

Microsoft Academic Search

Uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone, analytical grade calcite, and superpure calcite. The tests were performed at 28°C-150°C, effective stresses of 20-47 MPa, and a pore pressure of 20 MPa, using presaturated CaCO3 solution as the pore fluid. Sample grain sizes ranged from 12 to 86 mum. The aim was to

Xiangmin Zhang; Christopher J. Spiers; Colin J. Peach

2010-01-01

258

Compaction creep of wet granular calcite by pressure solution at 28°C to 150°C  

Microsoft Academic Search

Uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone, analytical grade calcite, and superpure calcite. The tests were performed at 28°C–150°C, effective stresses of 20–47 MPa, and a pore pressure of 20 MPa, using presaturated CaCO3 solution as the pore fluid. Sample grain sizes ranged from 12 to 86 ?m. The aim was to

Xiangmin Zhang; Christopher J. Spiers; Colin J. Peach

2010-01-01

259

Water release patterns of heated speleothem calcite and hydrogen isotope composition of fluid inclusions  

Microsoft Academic Search

Speleothem fluid inclusions are a potential paleo-precipitation proxy to reconstruct past rainwater isotopic composition (?18O, ?D). To get a better insight in the extraction of inclusion water from heated speleothem calcite, we monitored the water released from crushed and uncrushed speleothem calcite, heated to 900 °C at a rate of 300 °C\\/h, with a quadrupole mass spectrometer. Crushed calcite released water in

Sophie Verheyden; Dominique Genty; Olivier Cattani; Martin R. van Breukelen

2008-01-01

260

Rapid gas hydrate formation process  

DOEpatents

The disclosure provides a method and apparatus for forming gas hydrates from a two-phase mixture of water and a hydrate forming gas. The two-phase mixture is created in a mixing zone which may be wholly included within the body of a spray nozzle. The two-phase mixture is subsequently sprayed into a reaction zone, where the reaction zone is under pressure and temperature conditions suitable for formation of the gas hydrate. The reaction zone pressure is less than the mixing zone pressure so that expansion of the hydrate-forming gas in the mixture provides a degree of cooling by the Joule-Thompson effect and provides more intimate mixing between the water and the hydrate-forming gas. The result of the process is the formation of gas hydrates continuously and with a greatly reduced induction time. An apparatus for conduct of the method is further provided.

Brown, Thomas D.; Taylor, Charles E.; Unione, Alfred J.

2013-01-15

261

Global occurrences of gas hydrate  

USGS Publications Warehouse

Natural gas hydrate is found worldwide in sediments of outer continental margins of all oceans and in polar areas with continuous permafrost. There are currently 77 localities identified globally where geophysical, geochemical and/or geological evidence indicates the presence of gas hydrate. Details concerning individual gas-hydrate occurrences are compiled at a new world-wide-web (www) site (http://walrus.wr.usgs.gov/globalhydrate). This site has been created to facilitate global gas-hydrate research by providing information on each of the localities where there is evidence for gas hydrate. Also considered are the implications of gas hydrate as a potential (1) energy resource, (2) factor in global climate change, and (3) geohazard.

Kvenvolden, K. A.; Lorenson, T. D.

2001-01-01

262

Diagenesis of calcite cement in Frio Formation sandstones and its relationship to formation water chemistry  

SciTech Connect

Calcite cement is one of the most volumetrically important diagenetic minerals formed during burial of Frio Formation sandstones from the Corpus Christi area of Texas. Syndepositional calcite is restricted to shore-zone sandstones, whereas later, post-quartz-over-growth, burial-diagenetic calcite is present in both shore-zone and shelf sandstones. The {delta}{sup 18}O of burial-diagenetic calcite becomes depleted with depth. Chemical and textural evidence favors partial dissolution and reprecipitation (recrystallization) with consequent isotopic resetting as being responsible for the change in calcite {delta}{sup 18}O with progressive burial. The change in calcite {sup 87}Sr/{sup 86}Sr with depth also supports progressive recrystallization of calcite. There is a strong relationship between the {sup 87}Sr/{sup 86}Sr and trace element composition of calcite and formation water from individual growth-fault blocks. Significant differences in strontium isotopic and trace element composition exist between adjacent fault blocks, implying that each fault block has behaved as a chemically separate system since the time of calcite precipitation.

Lynch, F.L.; Land, L.S. [Univ. of Texas, Austin, TX (United States). Dept. of Geological Sciences

1996-05-01

263

Gas hydrate cool storage system  

DOEpatents

The invention presented relates to the development of a process utilizing a gas hydrate as a cool storage medium for alleviating electric load demands during peak usage periods. Several objectives of the invention are mentioned concerning the formation of the gas hydrate as storage material in a thermal energy storage system within a heat pump cycle system. The gas hydrate was formed using a refrigerant in water and an example with R-12 refrigerant is included. (BCS)

Ternes, M.P.; Kedl, R.J.

1984-09-12

264

High-pressure gas hydrates.  

PubMed

It has long been known that crystalline hydrates are formed by many simple gases that do not interact strongly with water, and in most cases the gas molecules or atoms occupy 'cages' formed by a framework of water molecules. The majority of these gas hydrates adopt one of two cubic cage structures and are called clathrate hydrates. Notable exceptions are hydrogen and helium which form 'exotic' hydrates with structures based on ice structures, rather than clathrate hydrates, even at low pressures. Clathrate hydrates have been extensively studied because they occur widely in nature, have important industrial applications, and provide insight into water-guest hydrophobic interactions. Until recently, the expectation-based on calculations-had been that all clathrate hydrates were dissociated into ice and gas by the application of pressures of 1 GPa or so. However, over the past five years, studies have shown that this view is incorrect. Instead, all the systems so far studied undergo structural rearrangement to other, new types of hydrate structure that remain stable to much higher pressures than had been thought possible. In this paper we review work on gas hydrates at pressures above 0.5 GPa, identify common trends in transformations and structures, and note areas of uncertainty where further work is needed. PMID:18259632

Loveday, J S; Nelmes, R J

2008-02-21

265

Environmental controls on the Emiliania huxleyi calcite mass  

NASA Astrophysics Data System (ADS)

Although ocean acidification is expected to impact (bio)calcification by decreasing the seawater carbonate ion concentration, [CO32-], there exists evidence of non-uniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions on the role of environmental factors other than acidification and on the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including temperature, nutrient (nitrate and phosphate) availability, and seawater carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying well above the modern lysocline. The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of phosphorus and temperature in determining coccolith mass by affecting primary calcification and possibly driving the E. huxleyi morphotype distribution. This evidence does not necessarily argue against the potentially important role of the rapidly changing seawater carbonate chemistry in the future, when unabated fossil fuel burning will likely perturb ocean chemistry beyond a critical point. Rather our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high CO2 world and improve interpretation of paleorecords.

Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.

2013-06-01

266

Upscaling Calcite Growth Rates From the Mesoscale to the Macroscale  

SciTech Connect

Quantitative prediction of mineral reaction rates in the subsurface remains a daunting task partly because a key parameter for macroscopic models, the reactive site density, is poorly constrained. Here we report atomic force microscopy (AFM) measurements on the calcite surface of monomolecular step densities, treated as equivalent to the reactive site density, as a function of aqueous calcium-to-carbonate ratio and saturation index. Data for the obtuse step orientation are combined with existing step velocity measurements to generate a model that predicts overall macroscopic calcite growth rates. The model is quantitatively consistent with several published macroscopic rates under a range of alkaline solution conditions, particularly for two of the most comprehensive data sets without the need for additional fit parameters. The model reproduces peak growth rates and its functional form is simple enough to be incorporated into reactive transport or other macroscopic models designed for predictions in porous media. However, it currently cannot model equilibrium, pH effects, and may overestimate rates at high aqueous calcium-to-carbonate ratios. The discrepancies in rates at high calcium-to-carbonate ratios may be due to differences in pre-treatment, such as exposing the seed material to SI 1.0 to generate/develop growth hillocks, or other factors.

Bracco, Jacquelyn N [ORNL; Stack, Andrew G [ORNL; Steefel, Carl I [Lawrence Berkeley National Laboratory (LBNL)

2013-01-01

267

Crystallographic orientation inhomogeneity and crystal splitting in biogenic calcite.  

PubMed

The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopy-electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the calcite lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research. PMID:23804442

Checa, Antonio G; Bonarski, Jan T; Willinger, Marc G; Faryna, Marek; Berent, Katarzyna; Kania, Bogusz; González-Segura, Alicia; Pina, Carlos M; Pospiech, Jan; Morawiec, Adam

2013-09-01

268

Nyerereite from calcite carbonatite at the Kerimasi Volcano, Northern Tanzania  

NASA Astrophysics Data System (ADS)

The extinct Quaternary Kerimasi volcano located in the southern part of the Gregory Rift, northern Tanzania, contains both intrusive and extrusive calciocarbonatites. One carbonate mineral with a high content of Na and Ca has been found in a sample of volcanic carbonatite, which is probably a cumulate rock. On the basis of Raman spectroscopy and SEM/EDS, this mineral was identified as nyerereite, ideally Na2Ca(CO3)2. It occurs as solid inclusions up to 300 × 200 ?m in size in magnetite and contains (wt. %) 25.4-27.4 Na2O, 26.0-26.8 CaO, 1.6-1.9 K2O, 0.6-1.8 FeO, 0.3-0.6 SrO, <0.4 BaO, 1.4-2.3 SO3, and 0.6-0.9 P2O5. The average mineral formula is (Na1.84K0.08)?1.92(Ca1.00Fe0.03Sr0.01)?1.04[(CO3)1.91(SO4)0.05(PO4)0.02]?1.98. A few inclusions in magnetite also contain calcite, which is considered here to be a late-stage, subsolidus mineral. The occurrence of nyerereite in carbonatite supports Hay's (1983) idea that some of the extrusive carbonatites at the Kerimasi volcano were originally alkaline rich and contained both calcite and nyerereite as primary minerals.

Zaitsev, A. N.

2010-12-01

269

Environmental controls on the Emiliania huxleyi calcite mass  

NASA Astrophysics Data System (ADS)

Although ocean acidification is expected to impact (bio) calcification by decreasing the seawater carbonate ion concentration, [CO32-], there is evidence of nonuniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions about the role of environmental factors other than acidification and about the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including seawater temperature, nutrient (nitrate and phosphate) availability, and carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying above the modern lysocline (with the exception of eight samples that are located at or below the lysocline). The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of seawater nutrient availability (phosphate and nitrate) and carbonate chemistry (pH and pCO2) in determining coccolith mass by affecting primary calcification and/or the geographic distribution of E. huxleyi morphotypes. Our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high-CO2 world and improve interpretation of paleorecords.

Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.

2014-04-01

270

Porosity and hydric behavior of typical calcite microfabrics in stalagmites  

NASA Astrophysics Data System (ADS)

Petrophysical techniques commonly used for material characterization are applied for the first time to speleothem samples to investigate the porosity and hydric behavior of calcite stalagmites used in paleoclimatology. These techniques allow the determination of the stalagmites' potential to undergo diagenetic transformations when substantial changes in drip waters occur in the cave environment. The petrophysical techniques include water absorption under vacuum and by capillarity, nuclear magnetic resonance, environmental scanning electron microscopy, and mercury intrusion porosimetry. The studied samples comprise five common calcite microfabrics, which have markedly different porosities and hydric behaviors and, as a consequence, different sensibilities to diagenetic processes related to the influx of water. The experiments show that stalagmites can behave as complex, small-scale hydrological systems and that the circulation of water through them by complex nets of interconnected pores might be common. As the circulation of water favors diagenetic transformations that involve geochemical and isotopic changes, the characterization of flow patterns is key for outlining areas that are susceptible to such modifications, which is critical to paleoclimatic studies that are based on speleothems because geochemical and stable isotopic data are used as paleoenvironmental proxies and absolute ages are obtained by using radioactive isotope ratios. These potential modifications also have obvious implications for studies based on fluid inclusions in speleothems. The integrated methodology, which uses primarily non-destructive techniques, shows a high potential for characterization of any type of speleothem and other continental carbonates such as tufas or sinters.

Muñoz-García, M. B.; López-Arce, P.; Fernández-Valle, M. E.; Martín-Chivelet, J.; Fort, R.

2012-07-01

271

Calcite (1 0 4)-water interface structure, revisited  

NASA Astrophysics Data System (ADS)

The structure of the calcite (1 0 4)-water interface is reassessed using a new set of high-precision specular X-ray reflectivity measurements. In situ measurements of the specular reflectivity signal to a vertical structural resolution of 0.45 Å are used to define the interfacial structure, including vertical displacement patterns of the Ca and CO3 groups as well as the nature of interfacial water. These new data show two organized interfacial water layers, consistent with previous results, and distortion of the interfacial calcite structure to a depth of four to six unit cells, at least two deeper than previously reported. These results are in reasonable agreement with recent computational studies, at least in terms of the locations of the first and second water layers. The difference between the interfacial structure derived from previous X-ray reflectivity results and that presented here emphasizes the need for high-precision measurements to provide a robust understanding of the interfacial structures of reactive minerals in aqueous environments.

Fenter, P.; Sturchio, N. C.

2012-11-01

272

Seismic reflections associated with submarine gas hydrates.  

National Technical Information Service (NTIS)

Gas hydrates are often suggested as a future energy resource. This doctoral thesis improves the understanding of the concentration and distribution of natural submarine gas hydrates. The presence of these hydrates are commonly inferred from strong bottom ...

K. Andreassen

1995-01-01

273

78 FR 26337 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY...meeting of the Methane Hydrate Advisory Committee...Energy, Office of Oil and Natural Gas, 1000 Independence Avenue...purpose of the Methane Hydrate Advisory Committee...

2013-05-06

274

75 FR 9886 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY...meeting of the Methane Hydrate Advisory Committee...Energy, Office of Oil and Natural Gas, Washington, DC 20585...purpose of the Methane Hydrate Advisory Committee...

2010-03-04

275

76 FR 59667 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY...meeting of the Methane Hydrate Advisory Committee...Energy, Office of Oil and Natural Gas, Washington, DC 20585...purpose of the Methane Hydrate Advisory Committee...

2011-09-27

276

77 FR 40032 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY...meeting of the Methane Hydrate Advisory Committee...Energy, Office of Oil and Natural Gas, 1000 Independence Avenue...purpose of the Methane Hydrate Advisory Committee...

2012-07-06

277

78 FR 37536 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY...meeting of the Methane Hydrate Advisory Committee...Energy, Office of Oil and Natural Gas, 1000 Independence Avenue...purpose of the Methane Hydrate Advisory Committee...

2013-06-21

278

Report on national workshop on gas hydrates.  

National Technical Information Service (NTIS)

In a few carefully selected locations, hydrates should be studied intensively: (1) to identify precisely the amounts and distribution of gas hydrates, (2) to identify the large-scale chemical and geological factors that control hydrate emplacement and to ...

1991-01-01

279

Seismic studies of gas hydrate bearing sediments at Hydrate Ridge  

NASA Astrophysics Data System (ADS)

In recent years, gas hydrates have become the focus of many research projects, since their economic potential, their role as a natural hazard and their impact on climate is yet not well known. To shed more light on these complex gas hydrate environments and to give rise to possible answers, a broad range of seismic experiments were carried out across Hydrate ridge. Simultaneous recordings of near-angle (single-channel surface streamer) and wide-angle reflection seismics (ocean bottom seismometers) were conducted within a broad frequency range, covering a dense grid of seismic profiles across and around Hydrate ridge. A well pronounced bottom simulating reflector (BSR), marking the base of the gas hydrate stability zone (GHSZ), has been imaged and its amplitude and frequency behavior investigated in more detail. AVA (amplitude variations with offset) analysis of both P- and S- waves were the key elements of quantifying the amount of gas hydrates within the sediments and/or the amount of free gas beneath the GHSZ. A pinnacle-like structure on the southwestern flank of the southern summit of Hydrate ridge was covered with high-resolution seismic sparker lines. The observed variations in the BSR´s amplitude and its discontinuity suggest possible pathways for fluids and/or methane below the pinnacle. Drill site information of ODP (Ocean Drilling Program) Leg 146 and recent Leg 204, covering the northern and southern summit of Hydrate ridge, provide additional and necessary information that was implemented in our investigations.

Papenberg, C.; Petersen, J.; Klaeschen, D.

2003-04-01

280

A complex clathrate hydrate structure showing bimodal guest hydration.  

PubMed

Interactions between hydrophobic groups in water, as well as biomolecular hydration more generally, are intimately connected to the structure of liquid water around hydrophobic solutes. Such considerations have focused interest on clathrate hydrates: crystals in which a hydrogen-bonded network of water molecules encages hydrophobic guest molecules with which the water interacts only by non-directional van der Waals forces. Three structural families of clathrate hydrates have hitherto been recognized: cubic structure I (2M(S)-6M(L) x 46H2O), cubic structure II (16M(S) x 8M(L)-136H2O) and hexagonal structure H (M(L) x 3M(S) x 2M(S) x 34H2O) hydrates (here M(L) and M(S) are the hydrophobic guest sites associated with large and small cavities, respectively). Here we report a new hydrate structure: 1.67 choline hydroxide-tetra-n-propylammonium fluoride x 30.33H2O. This structure has a number of unusual features; in particular the choline guest exhibits both hydrophobic and hydrophilic modes of hydration. Formally the structure consists of alternating stacks of structure H and structure II hydrates, and might conceivably be found in those settings (such as seafloor deposits over natural-gas fields) in which clathrate hydrates form naturally. PMID:9989406

Udachin, K A; Ripmeester, J A

1999-02-01

281

Influence of chemical and physical characteristics of cement kiln dusts (CKDs) on their hydration behavior and potential suitability for soil stabilization  

SciTech Connect

The interaction of CKDs with a given soil depends on the chemical and physical characteristics of the CKDs. Hence, the characterization of CKDs and their hydration products may lead to better understanding of their suitability as soil stabilizers. In the present article, four different CKD powders are characterized and their hydration products are evaluated. A detailed chemical (X-ray diffraction), thermogravimetric and morphological (scanning electron microscope) analyses of both the CKD powders and the hydrated CKD pastes are presented. In general, high free-lime content ({approx} 14-29%) CKDs, when reacted with water produced significant amounts of calcium hydroxide, ettringite and syngenite. These CKDs also developed higher unconfined compressive strength and higher temperature of hydration compared to CKDs with lower amounts of free-lime. An attempt was made to qualitatively correlate the performance of CKD pastes with the chemical and physical characteristics of the original CKD powders and to determine their potential suitability as soil stabilizers. To that effect a limited unconfined compressive strength testing of CKD-treated kaolinite clays was performed. The results of this study suggest that both the compressive strength and the temperature of hydration of the CKD paste can give early indications of the suitability of particular CKD for soil stabilization.

Peethamparan, Sulapha [Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544 (United States); School of Civil Engineering, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN. 47907-2051 (United States)], E-mail: speetham@princeton.edu; Olek, Jan [School of Civil Engineering, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN. 47907-2051 (United States)], E-mail: olek@purdue.edu; Lovell, Janet [Charles Pankow Concrete Materials Laboratory, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN. 47907-2051 (United States)], E-mail: lovell@purdue.edu

2008-06-15

282

Effect of ionic strength on the Mg content of calcite: Toward a physical basis for minor element uptake during step growth  

NASA Astrophysics Data System (ADS)

This experimental study determined the effect of ionic strength (IS) on the uptake of Mg into calcites that grew by the classical step propagation process. Using flow-through AFM and defined solution chemistry, calcite was grown in NaCl and KCl solutions of known supersaturation state while measuring the corresponding growth kinetics. Analysis of the resulting calcite compositions by SIMS shows that Mg content is inversely correlated with IS for both electrolytes. A sixfold increase in IS decreases the Mg-content by up to 40%. Overgrowths that developed in NaCl solutions contain more Mg than samples that grew in KCl solutions. The corresponding kinetic measurements reveal that step propagation rates are independent of IS within experimental error but are electrolyte-specific. In NaCl solutions, steps with the obtuse geometry move significantly faster than acute steps, but in KCl solutions, the acute and obtuse steps move at similar rates. Analysis of the data suggests that the decrease in Mg content with increasing IS arises from the interplay of ion-kink interactions between the background cations (Na + or K +), the primary solute cation (Ca 2+), and the impurity (Mg 2+). A simple physical model proposes that increasing levels of electrolytes block the attachment of the strongly hydrated Mg 2+ ion relative to Ca 2+ but the effects are step-specific for each type of electrolyte. Whereas K + interacts weakly with kink sites along both step directions, Na + interacts preferentially with acute steps and, consequently, slows their rate of step propagation relative to obtuse steps. Because Na + increases the fraction of the surface that develops from acute steps and because Mg is preferentially incorporated into the kink sites of acute steps, calcite overgrowths developed in NaCl solutions contain more Mg than those in grown in KCl. Thus, the salt-specific Mg contents measured in this study can be explained by shifts in the distribution of step types and the ability of each step type to incorporate Mg. The findings reconcile apparent discrepancies regarding the effect of IS on calcite kinetics and Mg incorporation observed in laboratory-based studies.

Stephenson, A. E.; Hunter, J. L.; Han, N.; DeYoreo, J. J.; Dove, P. M.

2011-08-01

283

REMOVAL OF BERYLLIUM FROM DRINKING WATER BY CHEMICAL COAGULATION AND LIME SOFTENING  

EPA Science Inventory

The effectiveness of conventional drinking water treatment and lime softening was evaluated for beryllium removal from two drinking water sources. ar test studies were conducted to determine how common coagulants (aluminum sulfate and ferric chloride and lime softening performed ...

284

Draft Final Risk Assessment Lime Settling Basins. Version 2.1.  

National Technical Information Service (NTIS)

The preferred alternative Lime Settling Basins (LSB) Interim Response Action (IRA) selected to inhibit further migration of contaminants from the LSB included moving the stockpiled lime sludge adjacent to the LSB back into the LSB, the construction of a s...

1990-01-01

285

EVALUATION OF BIOAEROSOL COMPONENTS, GENERATION FACTORS, AND AIRBORNE TRANSPORT ASSOCIATED WITH LIME TREATMENT OF CONTAMINATED SEDIMENT  

EPA Science Inventory

Lime treatment has been used in contaminated sediment management activities for many purposes such as dewatering, improvement of physical properties, and reducing contaminant mobility. Exothermic volatilization of volatile organic compounds from lime-treated sediment is well kno...

286

Liming, reacidification, and the mobilization of cadmium from sediments  

SciTech Connect

Over several decades severe acidification of streams and lakes has taken place in Scandinavia and North America, with catastrophic consequences for aquatic life. In certain water systems in southern Norway fish populations have been completely eliminated by severe acidification. This fish mortality has been attributed largely to increased concentrations of toxic aluminum and, since liming counteracts acidification and reduces the aluminum levels in the water, it has become the most widespread remedy to restore fish habitats. Cadmium concentrations in the water are also pH-dependent and, therefore, affected by liming. This laboratory experiment was conducted to clarify the significance of liming as a factor in reducing cadmium concentrations from lake water and the behavior of cdamium following reacidification. In addition the behavior of organic materials under varying pH conditions was studied. 16 refs., 4 figs., 2 tabs.

Fimreite, N.; Nenseter, B.; Steen, B. [Telemark College, Bo (Norway)] [Telemark College, Bo (Norway)

1996-12-01

287

Shock response of soda lime glass at 6 GPA  

NASA Astrophysics Data System (ADS)

This paper describes the results of a variety of shock wave experiments performed on soda lime glass to understand the modifying influence of so called "Failure wave" on its compression, under single shock, release, and tension. These experiments were done to a peak shock induced stress of around 6-7 GPa. Shock induced response was recorded by means of VISAR. The results of these experiments performed on soda lime glass at 6-7 GPa indicate that: (i) The effect of failure wave propagation is to lower the impedances of failed glass under both shocked compressed and released states and the effect is not initiated instantaneously at the impact surface. (ii) Failure wave velocity is determined to be 1.42 km/s. (iii) The spall strength of soda lime glass in the region transversed by failure wave is not negligible i.e., the pull-back velocity is around 50 m/s.

Dandekar, Dattatraya

2012-03-01

288

Lime pretreatment of sugarcane bagasse for bioethanol production.  

PubMed

The pretreatment of sugarcane bagasse with lime (calcium hydroxide) is evaluated. The effect of lime pretreatment on digestibility was studied through analyses using central composite design (response surface), considering pretreatment time, temperature, and lime loading as factors. The responses evaluated were the yield of glucose from pretreated bagasse after enzymatic hydrolysis. Experiments were performed using the bagasse as it comes from an alcohol/sugar factory (non-screened bagasse) and bagasse in the size range from 0.248 to 1.397 mm (screened bagasse) (12-60 mesh). It was observed that the particle size presented influence in the release of fermentable sugars after enzymatic hydrolysis using low loading of cellulase and beta-glucosidase (3.5 FPU/g dry pretreated biomass and 1.0 IU/g dry pretreated biomass, respectively). PMID:19050835

Rabelo, Sarita C; Maciel Filho, Rubens; Costa, Aline Carvalho

2009-05-01

289

Remediation of Pb-contaminated soils by washing with hydrochloric acid and subsequent immobilization with calcite and allophanic soil.  

PubMed

Removal of heavy metals from contaminated soil is not popular because of its high cost. Reducing the bioaccessible heavy metals content to an allowable level by washing with inorganic acids and subsequent immobilization of remained metals may be a low cost option for soil remediation. The applicability of this combined treatment was investigated using three different types of soil, a kaolinitic, a smectitic and an allophanic soil, which were artificially contaminated with Pb. The effectiveness of the treatment was evaluated using two main criteria: (i) reduction of the HCl extractable Pb (bioaccessible Pb) below 150 mg kg(-1), reduction of water extractable Pb below the concentration of 0.01 mg L(-1). These values correspond to allowable levels suggested by the Japanese Ministry of Environment. The soils were washed batch-wise at a solution to soil ratio of 5 L kg(-1) successively with 1 mol L(-1) HCl and 0.1 mol L(-1) CaCl(2) solutions. The two solutions were separated by filtration from one batch and reused for washing the next batch of soil without processing. The Pb concentration in the solutions increased after repeated use and removal efficiency gradually declined. The efficiency of the treatment was highly dependent on the type of soil. In the kaolinitic soil, HCl extractable Pb content of the soil from the first batch was about 50 mg kg(-1) and it exceeded 150 mg kg(-1) in that from sixth batch. But the combined soils from 1st to 10th batches gave bioaccessible Pb content barely below 150 mg kg(-1). For the smectitic soil having higher cation exchange capacity, the acceptable number of times of reuse was estimated to be 4. For the allophanic soil, treatment with the HCl solution was efficient only for the first batch of the soil, and the reuse of the acid solution was found to be ineffective. The application of 50 g kg(-1) of calcite or slacked lime was effective for reducing the water extractable Pb content. To keep soil pH near neutral and secure long term stability, the application of 50 g kg(-1) of calcite and 100 g kg(-1) of allophanic soil was chosen as the best method. This combination of amendments could reduce the water extractable Pb to almost undetectable levels after 3 days of aging. PMID:17267106

Isoyama, Masahiro; Wada, Shin-Ichiro

2007-05-17

290

Ductile flow of methane hydrate  

USGS Publications Warehouse

Compressional creep tests (i.e., constant applied stress) conducted on pure, polycrystalline methane hydrate over the temperature range 260-287 K and confining pressures of 50-100 MPa show this material to be extraordinarily strong compared to other icy compounds. The contrast with hexagonal water ice, sometimes used as a proxy for gas hydrate properties, is impressive: over the thermal range where both are solid, methane hydrate is as much as 40 times stronger than ice at a given strain rate. The specific mechanical response of naturally occurring methane hydrate in sediments to environmental changes is expected to be dependent on the distribution of the hydrate phase within the formation - whether arranged structurally between and (or) cementing sediments grains versus passively in pore space within a sediment framework. If hydrate is in the former mode, the very high strength of methane hydrate implies a significantly greater strain-energy release upon decomposition and subsequent failure of hydrate-cemented formations than previously expected.

Durham, W. B.; Stern, L. A.; Kirby, S. H.

2003-01-01

291

Liming Poultry Manures to Kill Pathogens and Decrease Soluble Phosphorus  

SciTech Connect

Received for publication September 9, 2005. Stabilizing phosphorus (P) in poultry waste to reduce P losses from manured soils is important to protect surface waters, while pathogens in manures are an emerging issue. This study was conducted to evaluate CaO and Ca(OH){sub 2} for killing manure bacterial populations (pathogens) and stabilizing P in poultry wastes and to investigate the influence on soils following amendment with the treated wastes. Layer manure and broiler litter varying in moisture content were treated with CaO and Ca(OH){sub 2} at rates of 2.5, 5, 10, and 15% by weight. All treated wastes were analyzed for microbial plate counts, pH, and water-soluble phosphorus (WSP), while a few selected layer manures were analyzed by phosphorus X-ray absorption near edge structure (XANES). A loamy sand and a silt loam were amended with broiler litter and layer manure treated with CaO at rates of 0, 2.5, 5, 10, and 15% and soil WSP and pH were measured at times 1, 8, and 29 d. Liming reduced bacterial populations, with greater rates of lime leading to greater reductions; for example 10% CaO applied to 20% solids broiler litter reduced the plate counts from 793 000 to 6500 mL{sup -1}. Liming also reduced the WSP in the manures by over 90% in all cases where at least 10% CaO was added. Liming the manures also reduced WSP in soils immediately following application and raised soil pH. The liming process used successfully reduced plate counts and concerns about P losses in runoff following land application of these limed products due to decreased WSP.

Maguire,R.; Hesterberg, D.; Gernat, A.; Anderson, K.; Wineland, M.; Grimes, J.

2006-01-01

292

A calcite permeable reactive barrier for the remediation of Fluoride from spent potliner (SPL) contaminated groundwater  

Microsoft Academic Search

The use of calcite (CaCO3) as a substrate for a permeable reactive barrier (PRB) for removing fluoride from contaminated groundwater is proposed and is illustrated by application to groundwater contaminated by spent potliner leachate (SPL), a waste derived from the aluminium smelting process. The paper focuses on two issues in the implementation of calcite permeable reactive barriers for remediating fluoride

Brett D. Turner; Philip J. Binning; Scott W. Sloan

2008-01-01

293

Nanoripples formation in calcite and indium phosphide (InP) single crystals  

Microsoft Academic Search

In this project we studied the formation of nanoripples in calcite and InP single crystals by continuous scanning using the nanoindenter in the ambient environment and by Argon ion irradiation under ultra high vacuum conditions, respectively. Formation of tip induced nanowear ripples is studied on a freshly cleaved calcite single crystal as a function of scanning frequency and contact load

Ramakrishna Gunda

2007-01-01

294

Magnetic susceptibility as a tool to study deformed calcite with variable impurity content  

Microsoft Academic Search

A set of calcite mylonites were systematically sampled along the basal shear zone of the Morcles Nappe, located in the southwestern Swiss Alps, to investigate the relationship among crystallographic preferred orientation (CPO), chemistry, and anisotropy of magnetic susceptibility (AMS). Second-phase minerals are ?10 vol % of the rock. The substitution of trace impurities for Ca in the calcite crystal lattice,

Bjarne S. G. Almqvist; Marco Herwegh; Volkmar Schmidt; Thomas Pettke; Ann M. Hirt

2010-01-01

295

Effect of Mg on the Grain Growth and Dislocation Creep of Calcite  

Microsoft Academic Search

We tested the effect of variations in the amount of the solute impurity (Mg) on grain growth and strength of calcite aggregate. Synthetic marbles were produced by hot isostatic pressing mixtures of powders of calcite and dolomite at 850° C and 300 MPa confining pressure for different intervals (2 to 30 hrs). The HIP treatment resulted in homogeneous aggregates of

L. Xu

2004-01-01

296

Effect of Solute Impurity of Mg on the Microstructure of Calcite  

Microsoft Academic Search

We produced synthetic marbles by hot isostatic pressing (HIPing) mixtures of calcite and dolomite powders for different intervals (2 to 30 hrs) at 850°C and 300 MPa confining pressure. The HIP treatment resulted in macroscopically homogeneous calcite aggregates with Mg content ranging from 0.5 to 17 mol%. We performed creep tests on samples after HIP at differential stresses from ~

L. Xu; B. J. Evans; J. Renner

2006-01-01

297

The role of disseminated calcite in the chemical weathering of granitoid rocks  

Microsoft Academic Search

Accessory calcite, present at concentrations between 300 and 3000 mg kg?1, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. Calcite occurs as fillings in microfractures, as disseminated grains within the silicate matrix,

Art F White; T HOMAS D. BULLEN; DAVISON V. VIVIT; MARJORIE S. SCHULZ; DAVID W. CLOW

1999-01-01

298

[Research on Raman spectra of calcite phase transition at high pressure].  

PubMed

The present research studied the process of phase transition from calcite-I to calcite-III under the condition of high hydrostatic pressure using hydrothermal diamond anvil cell and Raman spectrum technique. The hydrothermal diamond anvil cell is the most useful instrument to observe sample in-situation under high temperature and high pressure. The authors can get effective results from this instrument and pursue further research. The method of Raman spectra is the most useful measure tool and it can detect the material according to the spectrum. The result shows that three characteristic Raman peaks of calcite-I move to high-position with adding pressure. Water media in system becomes frozen at the pressure of 1103 MPa, and there is no change in the structure of calcite-I. The abrupt change of characteristic Raman peaks of calcite-I happens when the system pressure reaches 1752 MPa, and changed characteristic Raman peaks explain that calcite-I changes to calcite-III. There are two types of calcite-III, and type A happens in the system because of the effect of hydrostatic pressure. The characteristic Raman peak in different areas of minerals shows that the degree of phase transition becomes larger from inner part to edge part. The research also shows the advantage of hydrothermal diamond anvil cell and Raman spectrum for qualitative analysis of mineral structure using in-situ technique. PMID:22007398

Wang, Shi-Xia; Zheng, Hai-Fei

2011-08-01

299

Struvite and calcite crystallization induced by cellular membranes of Myxococcus xanthus  

NASA Astrophysics Data System (ADS)

In this work we have proved that struvite and calcite crystals can be obtained in the presence of the cellular membrane fraction of Myxococcus xanthus, when appropriate supersaturated solutions are used. Probably, the negative charged points of the external side of the cellular structures could reduce the metastability field of struvite and calcite, acting as heterogeneous nuclei of crystallization.

González-Muñoz, Ma Teresa; Omar, Nabil Ben; Martínez-Cañamero, Magdalena; Rodríguez-Gallego, Manuel; Galindo, Alberto López; Arias, JoséMa

1996-06-01

300

Interactions between calcite precipitation (natural and artificial) and phosphorus cycle in the hardwater lake  

Microsoft Academic Search

The influence of calcite precipitation on the phosphorus cycle in stratified hardwater lake was studied before and during experiments with a new restoration technique. Surveys of the chemical composition of water column and monitoring of settling particles of Lake Luzin (North–East) showed that calcite precipitation occurs each year over 2–3 periods during spring and summer. The change of the phosphorus

Maria Dittrich; Rainer Koschel

2002-01-01

301

Speciation of aluminium, arsenic and molybdenum in excessively limed lakes  

Microsoft Academic Search

The possible existence of the potentially toxic oxyanions of Al (Al(OH)4?), As (HAsO42?), and Mo (MoO42?) was examined in excessively limed lakes. In-situ dialysis (MWCO 1 kDa) was performed in the surface and bottom waters of two excessively limed lakes (pH 7.1–7.7) and one acidic lake (pH?5.4). The dialysable metal concentrations were compared to the equilibrium distribution of species as calculated

Carin Sjöstedt; Teresia Wällstedt; Jon Petter Gustafsson; Hans Borg

2009-01-01

302

Gas Hydrate Petroleum System Analysis  

NASA Astrophysics Data System (ADS)

In a gas hydrate petroleum system, the individual factors that contribute to the formation of gas hydrate accumulations, such as (1) gas hydrate pressure-temperature stability conditions, (2) gas source, (3) gas migration, and (4) the growth of the gas hydrate in suitable host sediment can identified and quantified. The study of know and inferred gas hydrate accumulations reveal the occurrence of concentrated gas hydrate is mostly controlled by the presence of fractures and/or coarser grained sediments. Field studies have concluded that hydrate grows preferentially in coarse-grained sediments because lower capillary pressures in these sediments permit the migration of gas and nucleation of hydrate. Due to the relatively distal nature of the deep marine geologic settings, the overall abundance of sand within the shallow geologic section is usually low. However, drilling projects in the offshore of Japan, Korea, and in the Gulf of Mexico has revealed the occurrence of significant hydrate-bearing sand reservoirs. The 1999/2000 Japan Nankai Trough drilling confirmed occurrence of hydrate-bearing sand-rich intervals (interpreted as turbidite fan deposits). Gas hydrate was determined to fill the pore spaces in these deposits, reaching saturations up to 80% in some layers. A multi-well drilling program titled "METI Toaki-oki to Kumano-nada" also identified sand-rich reservoirs with pore-filling hydrate. The recovered hydrate-bearing sand layers were described as very-fine- to fine-grained turbidite sand layers measuring from several centimeters up to a meter thick. However, the gross thickness of the hydrate-bearing sand layers were up to 50 m. In 2010, the Republic of Korea conducted the Second Ulleung Basin Gas Hydrate (UBGH2) Drilling Expedition. Seismic data clearly showed the development of a thick, potential basin wide, sedimentary sections characterized by mostly debris flows. The downhole LWD logs and core data from Site UBGH2-5 reveal that each debris flows is characterized by basal silt- to sand-rich clay dominated stratigraphic units. The upper most debris flow at Site UBGH2-5 extends into the overlying gas hydrate stability zone and IR core scans indicate that this section contains some amount of gas hydrate. The UBGH2 LWD and coring program also confirmed the occurrence of numerous volcaniclastic and siliciclastic sand reservoirs that were deposited as part of local to basin-wide turbidite events. Gas hydrate saturations within the turbidite sands ranged between 60-80 percent. In 2009, the Gulf of Mexico (GOM) Joint Industry Project (JIP) drilled seven wells at three sites, finding gas hydrate at high concentration in sands in four wells, with suspected gas hydrate at low to moderate saturations in two other wells. In the northern GOM, high sedimentation rates in conjunction with salt tectonism, has promoted the formation of complex seafloor topography. As a result, coarse-grained deposition can occur as gravity-driven sedimentation traversing the slope within intra-slope "ponded" accommodation spaces.

Collett, T. S.

2012-12-01

303

Kinetic inhibitor of hydrate crystallization.  

PubMed

We present the results of a combined theoretical/experimental study into a new class of kinetic inhibitor of gas hydrate formation. The inhibitors are based on quaternary ammonium zwitterions, and were identified from a computational screen. Molecular dynamics simulations were used to characterize the effect of the inhibitor on the interface between a type II hydrate and natural gas. These simulations show that the inhibitor is bifunctional, with the hydrophobic end being compatible with the water structure present at the hydrate interface, while the negatively charged functional group promotes a long ranged water structure that is inconsistent with the hydrate phase; the sulfonate-induced structure was found to propagate strongly over several solvation shells. The compound was subsequently synthesized and used in an experimental study of both THF and ethane hydrate formation, and was shown to have an activity that was comparable with an existing commercial kinetic inhibitor: PVP. PMID:14759217

Storr, Mark T; Taylor, Paul C; Monfort, Jean-Pierre; Rodger, P Mark

2004-02-11

304

Age constraints on fluid inclusions in calcite at Yucca Mountain  

SciTech Connect

The {sup 207}Pb/{sup 235}U ages for 14 subsamples of opal or chalcedony layers younger than calcite formed at elevated temperature range between 1.88 {+-} 0.05 and 9.7 {+-} 1.5 Ma with most values older than 6-8 Ma. These data indicate that fluids with elevated temperatures have not been present in the unsaturated zone at Yucca Mountain since about 1.9 Ma and most likely since 6-8 Ma. Discordant U-Pb isotope data for chalcedony subsamples representing the massive silica stage in the formation of the coatings are interpreted using a model of the diffusive loss of U decay products. The model gives an age estimate for the time of chalcedony formation around 10-11 Ma, which overlaps ages of clay minerals formed in tuffs below the water table at Yucca Mountain during the Timber Mountain thermal event.

Neymark, Leonid A.; Amelin, Yuri V.; Paces, James B.; Peterman, Zell E.; Whelan, Joseph F.

2001-04-29

305

Shock-induced effects in calcite from Cactus Crater  

NASA Technical Reports Server (NTRS)

The paper discusses shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.

Vizgirda, J.; Ahrens, T. J.; Tsay, F.-D.

1980-01-01

306

Paired gill slits in a fossil with a calcite skeleton.  

PubMed

The chordates, hemichordates (such as acorn worms) and echinoderms (such as starfish) comprise the group Deuterostomia, well established as monophyletic. Among extant deuterostomes, a skeleton in which each plate has the crystallographic structure of a single crystal of calcite is characteristic of echinoderms and is always associated with radial symmetry and never with gill slits. Among fossils, however, such a skeleton sometimes occurs without radial symmetry. This is true of Jaekelocarpus oklahomensis, from the Upper Carboniferous of Oklahoma, USA, which, being externally almost bilaterally symmetrical, is traditionally placed in the group Mitrata (Ordovician to Carboniferous periods, 530-280 million years ago), by contrast with the bizarrely asymmetrical Cornuta (Cambrian to Ordovician periods, 540 to 440 million years ago). Using computer X-ray microtomography, we describe the anatomy of Jaekelocarpus in greater detail than formerly possible, reveal evidence of paired gill slits internally and interpret its functional anatomy. On this basis we suggest its phylogenetic position within the deuterostomes. PMID:12075349

Dominguez, Patrício; Jacobson, Antone G; Jefferies, Richard P S

2002-06-20

307

Critical occlusion via biofilm induced calcite precipitation in porous media  

NASA Astrophysics Data System (ADS)

A model for biofilm induced calcite precipitation with pressure driven flow is presented at the scale of a single pore within a porous medium. The system, an extension of previous work (Zhang and Klapper 2010 Water Sci. Technol. 61 2957–64, Zhang and Klapper 2011 Int. J. Non-Linear Mech. 46 657–66), is based on a mixture model including biomaterial, mineral, and water with dissolved components. Computational results suggest the possibility of critical occlusion in the sense that there is a distinguished trans-pore pressure head such that for pressure drops below this level, pore clogging occurs relatively quickly while for pressure drops above, clogging occurs after much longer times if at all. Beyond its relevance to engineered biofilm applications, this phenomenon is suggestive of the subtleties of embedding simple biofilm models in larger media.

Zhang, Tianyu; Klapper, Isaac

2014-05-01

308

Understanding control of calcitic biomineralization-proteomics to the rescue.  

PubMed

The avian eggshell is one of the fastest calcifying processes known and represents a unique model for studying biomineralization. Eggshell strength is a crucial economic trait for table egg production, and ensures that a safe egg reaches the consumer kitchen. However, a common toolkit for eggshell mineralization has not yet been defined. In this issue, label-free MS-based protein quantification technology has been used by Sun et al. (Proteomics 2013, 13, 3523-3536) to detect differences in protein abundance between eggshell matrix from strong and weak eggs and between the corresponding uterine fluids bathing strong and weak eggs. Proteins associated with the formation of strong eggshells are identified, which are now candidates for further investigations to define the regulatory relationship between specific eggshell matrix proteins and calcite crystal texture. PMID:24307661

Hincke, Maxwell T

2013-12-01

309

A primer on gas hydrates  

SciTech Connect

Natural-gas hydrates are ice-like mixtures of gas and water in which the gas molecules, mainly methane, are trapped within a framework of cages, that is within a clathrate, of water molecules. Gas hydrates are stable under pressure and temperature conditions that occur worldwide in two distinct locations: (1) in polar regions, where temperatures are cold enough for onshore and offshore permafrost to be present, and (2) in offshore sediment of outer continental and insular margins, where there are cold bottom-water temperatures and deep waters, exceeding 300 to 500 m. Samples of gas hydrates have been recovered in 14 areas of the world, and geophysical and geochemical evidence for them has been found in about 30 other areas. Many oceanic occurrences of gas hydrates are inferred, mainly on the basis of the appearance on marine seismic-reflection profiles of a pronounced bottom-simulating reflection, commonly called a BSR. BSR's indicating gas hydrates are useful in estimating geothermal gradients and heat flow in oceanic sediments and, in conjunction with other seismic information, in assessing the amount of methane within and below the gas-hydrate interval. During gas-hydrate formation, salt ions are excluded from the crystal structure; therefore pore-water freshening is observed with gas-hydrate occurrence. The total amount of methane in gas hydrates around the world likely exceeds 10[sup 19] g of methane carbon ([approximately] 20x10[sup 15] m[sup 3] of methane gas = [approximately] 7x10[sup 5] trillion cubic feet (Tcf)). Because gas hydrates represent a large amount of methane within 2,000 m of the Earth's surface, they are considered to be an unconventional, potential source of fossil fuel. 51 refs., 11 figs., 1 tab.

Kvenvolden, K.A. (Geological Survey, Menlo Park, CA (United States))

1993-01-01

310

An Integrated Approach to Model Predictive Control of an Industrial Lime Kiln  

Microsoft Academic Search

The lime kiln is one of the key pieces of process equipment within the chemical recovery cycle of a pulp and paper mill. Its operational objective is to convert lime mud into calcium oxide (lime) that can be further used in the causticizing process in order to produce white liquor. Relatively large amounts of energy are required in the calcination

Terrance T. Chmelyk

311

Essential oil composition of Kaffir lime: Comparative analysis between controlled steam distillation and hydrodistillation extraction process  

Microsoft Academic Search

A controlled steam distillation process was performed to extract essential oil of Kaffir lime. Water temperature in the process was controlled by ON\\/OFF controller. System performance was quantified based on oil production rate and assessment on the compositions in Kaffir lime leaves and peels respectively. The Kaffir lime essential oil compounds were identified by retention time and percentage area by

N. Kasuan; M. Yunus; M. H. F. Rahiman; S. R. S. Aris; M. N. Taib

2009-01-01

312

Inactivation of Ascaris suum eggs during storage in lime treated sewage sludge  

Microsoft Academic Search

Survival and development of Ascaris suum eggs in sewage sludge mixed with 10% w\\/w of quick lime (85% CaO) has been examined. Fresh collected A. suum eggs were mixed in sewage sludge during lime treatment. The development of the eggs was followed every second week during a 10 weeks period and again after 5 months, parallel with control eggs. Lime

Lis Eriksen; Peter Andreasen; Bente Ilsøe

1996-01-01

313

Retention of SO2 Emission of Coal Combustion by Using Lime in Briquetting  

Microsoft Academic Search

In this study, the effect of lime on control of SO2 emissions was investigated by briquetting of coal particles with various lime contents. The influence of the added lime was determined not only from the view of its contribution to environmental aspects but also in terms of effects on the thermal features and reaction kinetics of coal. The extent of

N. Emre Altun; Cahit Hicyilmaz; A. Suat Bagci

2006-01-01

314

Beneficial Utilization of Lime Sludge for Subgrade Stabilization: A Pilot Investigation.  

National Technical Information Service (NTIS)

Water plants annually produce thousands of tons of lime sludge from the water treatment procedures. The lime sludge is then discharged into a retention pond. When the storage limit is reached, lime sludge is usually disposed into landfills, where they are...

2010-01-01

315

40 CFR 180.1231 - Lime; exemption from the requirement of a tolerance.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Lime; exemption from the requirement of a tolerance...Exemptions From Tolerances § 180.1231 Lime; exemption from the requirement of a tolerance...tolerance is established for residues of lime. [70 FR 33363, June 8,...

2010-07-01

316

40 CFR 180.1232 - Lime-sulfur; exemption from the requirement of a tolerance.  

Code of Federal Regulations, 2010 CFR

...2010-07-01 2010-07-01 false Lime-sulfur; exemption from the requirement...Exemptions From Tolerances § 180.1232 Lime-sulfur; exemption from the requirement...tolerance is established for residues of lime-sulfur. [70 FR 33363, June...

2010-07-01

317

The quantitative determination of calcite associated with the carbonate-bearing apatites  

USGS Publications Warehouse

The CO2 combined as calcite in carbonate-bearing apatites as been distinguished from that combined as carbonate-apatite, or present in some form other than calcite, by use of X-ray powder patterns, differential thermal analyses, and differential solubility tests. These methods were applied to several pure apatite minerals, to one fossil bone, and to a group of phosphorites from the Phosphoria formation of Permian age from Trail Canyon and the Conda mine, Idaho, and the Laketown district, Utah. With the exceptions of pure fluorapatite, pure carbonate-flueorapatite, and one phosphorite from Trail Canyon, these substances contain varying amounts of calcite, but in all the samples an appreciable part of the carbonite content is not present as calcite. The results of solubility tests, in which the particle size of sample and the length of solution time were varied, imply that the carbonate content is not due to shielded calcite entrapped along an internal network of surfaces.

Silverman, Sol R.; Fuyat, Ruth K.; Weiser, Jeanne D.

1951-01-01

318

Precipitation of calcite induced by Synechocystis sp. PCC6803.  

PubMed

Calcite with laminate structure was successfully prepared by culturing Synechocystis sp. PCC6803 with different concentrations of calcium chloride (CaCl?) in BG11 media. S. PCC6803 was examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser confocal scanning microscope (LCSM) and energy dispersive spectroscopy (EDS). The effects of Ca²? concentrations and pH values on calcification were investigated and the micro morphs of the CaCO? crystals were observed by means of SEM. These results showed that CaCO? crystals could be more easily formed with increasing the concentration of CaCl? in S. PCC6803 culture solution. S. PCC6803 could largely bind calcium ions, most of which were present in extracellular polymeric substances and on the cell wall. Inside the cells there were a lot of circular areas rich in calcium ions without the crystallization of calcium. Some cells produced a thicker gelatinous sheath outside of the translucent organic thin layer. And the cells inside also produced major changes that the original chloroplasts were almost transformed into starch grains whose sizes were from 0.5 to 1 ?m with relatively uniform in sizes. At the same time the cell sizes significantly reduced to only about 8-9 ?m almost changing to half of its original diameters. The calcite crystals with a highly preferred orientation induced by S. PCC6803 were observed with X-ray diffraction (XRD). A critical implication was that S. PCC6803 could induce bio-calcification and then mediate the further growth of CaCO? crystals in the biological system. PMID:23543209

Han, Zuozhen; Yan, Huaxiao; Zhou, Shixue; Zhao, Hui; Zhang, Yan; Zhang, Ningning; Yao, Chuankai; Zhao, Lin; Han, Chunyan

2013-10-01

319

Thermodynamics of magnesian calcite solid-solutions at 25??C and 1 atm total pressure  

USGS Publications Warehouse

The stability of magnesian calcites was reexamined, and new results are presented for 28 natural inorganic, 12 biogenic, and 32 synthetic magnesian calcites. The magnesian calcite solid-solutions were separated into two groups on the basis of differences in stoichiometric solubility and other physical and chemical properties. Group I consists of solids of mainly metamorphic and hydrothermal origin, synthetic calcites prepared at high temperatures and pressures, and synthetic solids prepared at low temperature and very low calcite supersaturations (??calcite ??? 1.5) from artificial sea water or NaClMgCl2CaCl2 solutions. Group I solids are essentially binary s of CaCO2 and MgCO2, and are thought to be relatively free of structural defects. Group II solid-solutions are of either biogenic origin or are synthetic magnesian calcites and protodolomites (0-20 and ??? 45 mole percent MgCO3) prepared at high calcite supersaturations (??calcite??? 3) from NaClNa2SO4MgCl2CaCl2 or NaClMgCl2CaCl2 solutions. Group II solid-solutions are treated as massively defective solids. The defects include substitution foreign ions (Na+ and SO42-) in the magnesian calcite lattice (point defects) and dislocations (~2 ?? 109 cm-2). Within each group, the excess free energy of mixing, GE, is described by the mixing model ge = X(1- x)[A0 + A1(2x - 1)], where x is the mole fraction of the end-member Ca0.5Mg0.5CO3 in the solid-solution. The values of A0 and A1 for Group I and II solids were evaluated at 25??C. The equilibrium constants of all the solids are closely described by the equation ln Kx = x(1-x) RT[A0 + A1(2x- 1)]+ (1 - x) ln [KC(1- x)]+ x ln (KDx), where KC and KD are the equilibrium constants of calcite and Ca0.5Mg0.5CO3. Group I magnesian calcites were modeled as sub-regular solid-solutions between calcite and dolomite, and between calcite and "disordered dolomite". Both models yield almost identical equilibrium constants for these magnesian calcites. The Group II magnesian calcites were modeled as sub-regular solid-solutions between defective calcite and protodolomite. Group I and II solid-solutions differ significantly in stability. The rate of crystal growth and the chemical composition of the aqueous solutions from which the solids were formed are the main factors controlling stoichiometric solubility of the magnesian calcites and the density of crystal defects. The literature on the occurrence and behavior of magnesian calcites in sea water and other aqueous solutions is also examined. ?? 1989.

Busenberg, E.; Niel, Plummer, L.

1989-01-01

320

Adhesive carrier particles for rapidly hydrated sorbent for moderate-temperature dry flue gas desulfurization.  

PubMed

A rapidly hydrated sorbent for moderate-temperature dry flue gas desulfurization was prepared by rapidly hydrating adhesive carrier particles and lime. The circulation ash from a circulating fluidized bed boiler and chain boiler ash, both of which have rough surfaces with large specific surface areas and specific pore volumes, can improve the adhesion, abrasion resistance, and desulfurization characteristics of rapidly hydrated sorbent when used as the adhesive carrier particles. The adhesion ability of sorbent made from circulation ash is 67.4% higher than that of the existing rapidly hydrated sorbent made from fly ash, the abrasion ratio is 76.2% lower, and desulfurization ability is 14.1% higher. For sorbent made from chain boiler ash, the adhesion ability is increased by 74.7%, the desulfurization ability is increased by 30.3%, and abrasion ratio is decreased by 52.4%. The abrasion ratios of the sorbent made from circulation ash having various average diameters were all about 9%, and their desulfurization abilities were similar (approximately 150 mg/g). PMID:20481549

Li, Yuan; You, Changfu; Song, Chenxing

2010-06-15

321

Microstructure and hydration characteristics of artificial pozzolana-cement pastes containing burnt kaolinite clay  

SciTech Connect

The reaction of pozzolana with the lime liberated during the hydration process of Portland cement modifies some properties of cement and resulting concrete. This study aimed to investigate experimentally the change occurring in the phase composition and microstructure of pozzolanic cement pastes containing activated kaolinite clay. The artificial pozzolana (burnt kaolinite clay) were thermally activated by firing at 850 C for two hours. The ordinary Portland cement (OPC) was partially replaced by different amounts of activated kaolinite clay by weight. The changes in the electrical conductivity were reported during setting and hardening processes after gauging with water. The change occurring in the phase composition and microstructure of cement pastes were investigated by differential thermal analysis and scanning electron microscopy. The results of this investigation show that, the thermal activated kaolinite clay prolonged the initial and final setting times and reduced the porosity, it also improved the microstructure of the formed hydrates by recrystallization of hydrated calcium silicates (mainly as CSH-(I)) together with the formation of hexagonal calcium aluminate hydrate (mainly as C{sub 4}AH{sub 13}).

Morsy, M.S.; Hanna, G.B. [Building Research Center, Cairo (Egypt)] [Building Research Center, Cairo (Egypt); El-Enein, S.A.A. [Ain Shams Univ., Cairo (Egypt). Faculty of Science] [Ain Shams Univ., Cairo (Egypt). Faculty of Science

1997-09-01

322

Treatment of Liming Effluent from Tannery using Membrane Separation Processes  

Microsoft Academic Search

A treatment method of liming effluent of a tannery is tested using hybrid membrane separation processes. The effluent after gravity settling and alum coagulation is subjected to ultrafiltration followed by nanofiltration. The optimum alum dose is obtained by analyzing the effluent using various concentrations of alum. The membrane separation processes are conducted in a continuous cross flow mode. The effects

Chandan Das; Sirshendu De; Sunando DasGupta

2007-01-01

323

Further Investigations of Alumina-Lime-Soda Water Recovery Applications.  

National Technical Information Service (NTIS)

Findings of a laboratory study undertaken to define the range of applications of the alumina-lime-soda process have been reported. This process was effective for the removal of calcium sulfate at pH 12, and for the removal of dissolved silica in the pH ra...

J. W. Nebgen G. D. Hinshaw

1980-01-01

324

Distribution of polycyclic aromatic hydrocarbons in lime spray dryer ash  

Microsoft Academic Search

Four lime spray dryer (LSD) ash samples were collected from a spreader stoker boiler and measured for their concentrations of 16 U.S. EPA specified polycyclic aromatic hydrocarbons (PAHs). Results showed that the total measured PAH concentration correlated with the organic carbon content of the LSD ash. Each LSD ash sample was then separated using a 140 mesh sieve into two

Ping Sun; Panuwat Taerakul; Linda K. Weavers; Harold W. Walker

2005-01-01

325

Forest Liming on Mineral Soils. Results of Finnish Experiments.  

National Technical Information Service (NTIS)

The chemical properties of the soil, nutrient status of the trees and stand production are examined in approximately 20-year-old liming experiment in the study. The material consist of 96 experiments in the pine and spruce stands.The following treatments ...

J. Derome Kukkola M. E. Maelkoenen

1986-01-01

326

K'qizaghetnu Ht'ana (Stories from Lime Village).  

ERIC Educational Resources Information Center

A cross section of Athabascan life as related by eight inhabitants of Lime Village, Alaska, is given in this document. The short narratives are printed in English and in Dena'ina. Illustrations accompany the text. The stories tell of making eagle feather robes, birchbark or mooseskin boats, a raincoat from black bear intestines, and boots from…

Bobby, Pete; And Others

327

Liming Effects on Soil Chemistry in Forest Stands.  

National Technical Information Service (NTIS)

The aim of the present study has been to investigate the effects of liming on soil chemistry (pH, base saturation, cation exchange capacity, total carbon and total nitrogen) and humus morphology, and also to extablish the duration of these effects. During...

L. Hallbaecken B. Popovic

1985-01-01

328

Lime pretreatment and fermentation of enzymatically hydrolyzed sugarcane bagasse.  

PubMed

Sugarcane bagasse was subjected to lime (calcium hydroxide) pretreatment and enzymatic hydrolysis for second-generation ethanol production. A central composite factorial design was performed to determine the best combination of pretreatment time, temperature, and lime loading, as well as to evaluate the influence of enzymatic loadings on hydrolysis conversion. The influence of increasing solids loading in the pretreatment and enzymatic hydrolysis stages was also determined. The hydrolysate was fermented using Saccharomyces cerevisiae in batch and continuous mode. In the continuous fermentation, the hydrolysates were concentrated with molasses. Lime pretreatment significantly increased the enzymatic digestibility of sugarcane bagasse without the need for prior particle size reduction. In the optimal pretreatment conditions (90 h, 90 °C, 0.47 glime/g bagasse) and industrially realistic conditions of hydrolysis (12.7 FPU/g of cellulase and 7.3 CBU/g of ?-glucosidase), 139.6 kglignin/ton raw bagasse and 126.0 kg hemicellulose in the pretreatment liquor per ton raw bagasse were obtained. The hydrolysate from lime pretreated sugarcane bagasse presented low amounts of inhibitors, leading to ethanol yield of 164.1 kgethanol/ton raw bagasse. PMID:23334836

Rabelo, Sarita C; Maciel Filho, Rubens; Costa, Aline C

2013-03-01

329

Potential of Plant Extracts for Controlling Citrus Canker of Lime  

Microsoft Academic Search

Five plant extracts of Hibiscus subdariffa Linn., Psidium guajava Linn., Punica granatum Linn., Spondias pinnata (Linn.f.)Kurz, and Tamarindus indica Linn. were evaluated for control of canker disease on Citrus aurantifolia (lime) caused by Xanthomonas axonopodis pv. citri (XC) (synonym X. campestris pv. citri ) under greenhouse condition. Aqueous extracts of H. subdariffa, P. granatum, S. pinnata, and T. indica exhibited

Chalida Leksomboon; Niphone Thaveechai; Wichai Kositratana

330

LIME SPRAY DRYER FLUE GAS DESULFURIZATION COMPUTER MODEL USERS MANUAL  

EPA Science Inventory

The report describes a lime spray dryer/baghouse (FORTRAN) computer model that simulates SO2 removal and permits study of related impacts on design and economics as functions of design parameters and operating conditions for coal-fired electric generating units. The model allows ...

331

HAZARDOUS WASTE COMBUSTION IN INDUSTRIAL PROCESSES: CEMENT AND LIME KILNS  

EPA Science Inventory

The report summarizes the results of several studies relating to hazardous waste combustion in cement and lime kilns. The tests included in the study are four kilns tested by the U.S. Environmental Protection Agency, four kilns tested by State agencies or the kiln operator, two C...

332

Characterization of Carbide Lime to Identify Sulfite Oxidation Inhibitors.  

National Technical Information Service (NTIS)

The report gives results of a study of carbide lime--a by-product of acetylene manufacture, primarily calcium hydroxide--used in a flue gas desulfurization (FGD) system at Louisville Gas and Electric (LGE). The study was undertaken to: identify sulfite io...

L. J. Holcombe K. W. Luke

1978-01-01

333

Distribution of polycyclic aromatic hydrocarbons in lime spray dryer ash  

SciTech Connect

Four lime spray dryer (LSD) ash samples were collected from a spreader stoker boiler and measured for their concentrations of 16 U.S. EPA specified polycyclic aromatic hydrocarbons (PAHs). Results showed that the total measured PAH concentration correlated with the organic carbon content of the LSD ash. Each LSD ash sample was then separated using a 140 mesh sieve into two fractions: a carbon-enriched fraction ({gt}140 mesh) and a lime-enriched fraction ({lt}140 mesh). Unburned carbon was further separated from the carbon-enriched fraction with a lithiumheteropolytungstate (LST) solution. PAH measurements on these different fractions showed that unburned carbon had the highest PAH concentrations followed by the carbon-enriched fraction, indicating that PAHs were primarily associated with the carbonaceous material in LSD ash. However, detectable levels of PAHs were also found in the lime-enriched fraction, suggesting that the fine spray of slaked lime may sorb PAH compounds from the flue gas in the LSD process. 37 refs., 5 figs., 4 tabs.

Ping Sun; Panuwat Taerakul; Linda K. Weavers; Harold W. Walker [Ohio State University, Columbus, OH (United States). Department of Civil and Environmental Engineering and Geodetic Science

2005-10-01

334

CHARACTERIZATION OF CARBIDE LIME TO IDENTIFY SULFITE OXIDATION INHIBITORS  

EPA Science Inventory

The report gives results of a study of carbide lime--a by-product of acetylene manufacture, primarily calcium hydroxide--used in a flue gas desulfurization (FGD) system at Louisville Gas and Electric (LGE). The study was undertaken to: identify sulfite ion oxidation inhibitors in...

335

Ettringite formation in historic bath brick–lime plasters  

Microsoft Academic Search

Two types of historic hydraulic brick–lime plasters from a selected Ottoman bath are examined to characterize their technology and the appropriateness of their use in bath. The first type of plaster is original and structurally sound, while the historic repair plaster is the second type and is found to have deteriorated despite being exposed to the same environment. This difference

Hasan Böke; Sedat Akkurt

2003-01-01

336

EFFECTS OF LIME (CAO) ON THE ENDOTOXIN LEVELS OF BIOSOLIDS  

EPA Science Inventory

Lime addition is a common practice for treating biosolids in order to meet EPA 503 requirements for land application. Since this treatment kills the majority of microorganisms, will it increase the level of endotoxins present in biosolids? And, if endotoxin levels are increased, ...

337

In Situ Raman Analyses of Natural Gas and Gas Hydrates at Hydrate Ridge, Oregon  

Microsoft Academic Search

During a July 2004 cruise to Hydrate Ridge, Oregon, MBARI's sea-going laser Raman spectrometer was used to obtain in situ Raman spectra of natural gas hydrates and natural gas venting from the seafloor. This was the first in situ analysis of gas hydrates on the seafloor. The hydrate spectra were compared to laboratory analyses performed at the Center for Hydrate

E. T. Peltzer; S. N. White; R. M. Dunk; P. G. Brewer; A. D. Sherman; K. Schmidt; K. C. Hester; E. D. Sloan

2004-01-01

338

Observations related to tetrahydrofuran and methane hydrates for laboratory studies of hydrate-bearing sediments  

Microsoft Academic Search

The interaction among water molecules, guest gas molecules, salts, and mineral particles determines the nucleation and growth behavior of gas hydrates in natural sediments. Hydrate of tetrahydrofuran (THF) has long been used for laboratory studies of gas hydrate-bearing sediments to provide close control on hydrate concentrations and to overcome the long formation history of methane hydrate from aqueous phase methane

J. Y. Lee; T. S. Yun; J. C. Santamarina; C. Ruppel

2007-01-01

339

Gas hydrate concentration and characteristics within Hydrate Ridge inferred from multicomponent seismic reflection data  

Microsoft Academic Search

A seismic experiment composed of streamer and ocean bottom seismometer (OBS) surveys was conducted in the summer of 2002 at southern Hydrate Ridge, offshore Oregon, to map the gas hydrate distribution within the hydrate stability zone. Gas hydrate concentrations within the reservoir can be estimated with P wave velocity (Vp); however, we can further constrain gas hydrate concentrations using S

Dhananjay Kumar; Mrinal K. Sen; Nathan L. Bangs

2007-01-01

340

Effective kinetic inhibitors for natural gas hydrates  

Microsoft Academic Search

Kinetic inhibition is a new means of preventing flow channel blockage by natural gas hydrates. In kinetic inhibition the system is allowed to exist within the hydrate thermodynamic stability zone, so that small crystals are stabilized without agglomerating to larger hydrate masses which plug pipelines. A hydrate formation mechanism is reviewed to suggest the new inhibition method. Macroscopic experiments on

J. P. Lederhos; J. P. Long; A. Sum; R. L. Christiansen; E. D. Sloan

1996-01-01

341

Storing natural gas as frozen hydrate  

Microsoft Academic Search

The formation of natural gas hydrates is a well-known problem in the petroleum and natural gas industries. Hydrates are solid materials that form when liquid water and natural gas are brought in contact under pressure. Hydrate formation need not be a problem. On the contrary, it can be an advantage. The volume of hydrates is much less than that of

J. S. Gudmundsson; A. A. Khokhar; M. Parlaktuna

1994-01-01

342

Physical properties of sediments containing gas hydrates  

Microsoft Academic Search

In order to better understand the occurrence and distribution of gas hydrates and their effects on acoustic and thermal measurements in ocean sediments, the authors have conducted a program of experimental research to study thermal conductivity and acoustic wave velocity in hydrates and sediments containing hydrate. The most significant result of these studies is that the formation of hydrate tends

Robert D. Stoll; George M. Bryan

1979-01-01

343

Alcohol cosurfactants in hydrate antiagglomeration.  

PubMed

Because of availability, as well as economical and environmental considerations, natural gas is projected to be the premium fuel of the 21st century. Natural gas production involves risk of the shut down of onshore and offshore operations because of blockage from hydrates formed from coproduced water and hydrate-forming species in natural gas. Industry practice has been usage of thermodynamic inhibitors such as alcohols often in significant amounts, which have undesirable environmental and safety impacts. Thermodynamic inhibitors affect bulk-phase properties and inhibit hydrate formation. An alternative is changing surface properties through usage of polymers and surfactants, effective at 0.5 to 3 weight % of coproduced water. One group of low dosage hydrate inhibitors (LDHI) are kinetic inhibitors, which affect nucleation rate and growth. A second group of LDHI are antiagglomerants, which prevent agglomeration of small hydrate crystallites. Despite great potential, work on hydrate antiagglomeration is very limited. This work centers on the effect of small amounts of alcohol cosurfactant in mixtures of two vastly different antiagglomerants. We use a model oil, water, and tetrahydrofuran as a hydrate-forming species. Results show that alcohol cosurfactants may help with antiagglomeration when traditional antiagglomerants alone are ineffective. Specifically, as low as 0.5 wt. % methanol cosurfactant used in this study is shown to be effective in antiagglomeration. Without the cosurfactant there will be agglomeration independent of the AA concentration. To our knowledge, this is the first report of alcohol cosurfactants in hydrate antiagglomerants. It is also shown that a rhamnolipid biosurfactant is effective down to only 0.5 wt. % in such mixtures, yet a quaternary ammonium chloride salt, i. e., quat, results in hydrate slurries down to 0.01 wt. %. However, biochemical surfactants are less toxic and biodegradable, and thus their use may prove beneficial even if at concentrations higher than chemical surfactants. PMID:18671355

York, J Dalton; Firoozabadi, Abbas

2008-08-28

344

Gas Hydrates: It's a Gas  

NSDL National Science Digital Library

In this activity, students will discover the importance of carbon, where carbon is stored on Earth, and that the largest reservoir of carbon is in the form of gas hydrates where methane and other hydrocarbon gases are trapped in a lattice of water molecules in deep sea sediments. Students will learn how climate change is related to the greenhouse effect. They will also learn about the potential of hydrates as a major new energy resource, and explore the conditions under which hydrates form. In addition, students will understand the use of acoustics for mapping the sea floor and sub-sea floor.

345

Hydrates represent gas source, drilling hazard  

SciTech Connect

Gas hydrates look like ordinary ice. However, if a piece of such ice is put into warm water its behavior will be different from the ordinary melting of normal ice. In contrast, gas hydrates cause bubbles in the warm water, which indicates the high content of gas in the hydrate crystals. The presence of four components is required: gas itself, water, high pressure, and low temperature. The paper discusses how hydrates form, hydrates stability, South Caspian hydrates, and hydrates hazards for people, ships, pipelines, and drilling platforms.

Bagirov, E. [Azerbaijan Academy of Sciences, Baku (Azerbaijan); Lerche, I. [Univ. of South Carolina, Columbia, SC (United States)

1997-12-01

346

Hydration water and microstructure in calcium silicate and aluminate hydrates  

Microsoft Academic Search

Understanding the state of the hydration water and the microstructure development in a cement paste is likely to be the key for the improvement of its ultimate strength and durability. In order to distinguish and characterize the reacted and unreacted water, the single-particle dynamics of water molecules in hydrated calcium silicates (C3S, C2S) and aluminates (C3A, C4AF) were studied by

Emiliano Fratini; Francesca Ridi; Sow-Hsin Chen; Piero Baglioni

2006-01-01

347

New waste based clinkers: Belite and lime formulations  

SciTech Connect

This work describes the formulation of new belite-based (CR2) and lime-based (CR3) cementitious materials derived from industrial wastes, such as sludges (generated in the Al-anodising and surface coating industrial processes, potable water filtration/cleaning operations and in marble sawing processes) and foundry sand. Powder mixtures were prepared and fired at different temperatures. For comparison, similar formulations were prepared with pre-treated and commercially available natural raw materials and processed in similar conditions. The thermal process was followed by differential scanning calorimetry (DSC) and high-temperature powder X-ray diffraction (HT-XRD) studies. The CR2 clinker was found to contain belite as the main cementitious phase, the main polymorph being identified by NMR. The CR3 clinker contained common cementitious phases, such as C{sub 3}A and C{sub 3}S, but free lime and calcium aluminium oxide sulphates were also identified by high temperature XRD and NMR. Then the corresponding cement was prepared and the evolution of the mechanical strength with time was evaluated. The lime-based cement obtained from wastes shows a stronger hardening character than the standard material, which tends to show dusting phenomena due to the presence of a reasonable amount of free lime (as the result of its expansive reaction with ambient moisture). Some fluxing impurities (e.g. alkalis) present in the waste materials improve the overall reactivity of the mixture and induces the combination of the lime in CR3. Raman, XPS and FIB techniques were used to fully characterise the aged cements.

Raupp-Pereira, Fabiano [Ceramics and Glass Engineering Department, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Ball, Richard James [University of Bristol, Interface Analysis Centre, Oldbury House, 121 St Michael's Hill, Bristol, BS2 8BS (United Kingdom)], E-mail: richard.ball@bristol.ac.uk; Rocha, Joao [Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Labrincha, Joao A. [Ceramics and Glass Engineering Department, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Allen, Geoffrey C. [University of Bristol, Interface Analysis Centre, Oldbury House, 121 St Michael's Hill, Bristol, BS2 8BS (United Kingdom)

2008-04-15

348

The relationships among lemons, limes and citron: a chromosomal comparison.  

PubMed

Lemons, limes and citron constitute a group of closely related Citrus species, whose species delimitations and taxonomic relationships are unclear. In order to identify karyotypic similarities and species relationships within this group, the CMA+/DAPI- banding pattern and the distribution of the 5S and 45S rDNA sites of 10 accessions of lime, lemon, and citron were investigated. The four cultivars of C. limon analyzed showed the same pattern of CMA+ bands and rDNA sites, suggesting that they originated from a single germplasm, later differentiated by distinct somatic mutations. The lemons C. jambhiri, C. limonia and C. volkameriana displayed karyotypes very similar to each other, but they differed from C. limon by the absence of a single chromosome with one band in each telomere. The limes, C. aurantifolia and C. limettioides, seemed less related to each other and exhibited different heteromorphic chromosome pairs. In C. aurantifolia, the presence of a chromosome type unknown in all other Citrus species cytologically known so far supports the assumption that this accession may be derived from a hybrid with a species from the subgenus Papeda or from another genus. Citrus medica was the only homozygous accession of this group and all of its chromosome types were clearly represented in limes and lemons, some of them forming heteromorphic pairs. The analysis of the distribution of rDNA sites allowed a further refinement of the comparison among accessions. The lemons and limes were heterozygous for all rDNA sites, whereas C. medica was entirely homozygous. These data support the hypothesis that C. medica is a true species while the other nine accessions are hybrids. PMID:15753587

Carvalho, R; Soares Filho, W S; Brasileiro-Vidal, A C; Guerra, M

2005-01-01

349

OBSERVED GAS HYDRATE MORPHOLOGIES IN MARINE SEDIMENTS  

Microsoft Academic Search

Small-scale morphology of gas hydrate is important for understanding the formation of gas hydrate deposits, for estimating the concentrations of gas hydrate from geophysical data, and for predicting their response to climate change or commercial production. The recent use of borehole pressure coring tools has allowed marine gas-hydrate-bearing sediments to be recovered with centimeter to sub-millimeter gas hydrate structures preserved

Melanie Holland; Peter Schultheiss; John Roberts; Matthew Druce

350

TRIASSIC LIME MICRITES FROM THE WESTERN BALKANIDES: EVIDENCE FOR PREVAILING ABIOTIC PRECIPITATION OF THE ORIGINAL LIME MUDS  

Microsoft Academic Search

Micritic matrix in limestones is considered as less reli- able indicator for primary abiotic carbonate mineralogy compared to ooids and penecontemporaneous cements. The main reason is related to the possibility that precur- sor lime muds may be partly or entirely not a result of physicochemical precipitation. The latter is still chal- lenged for modern occurrences of marine muds despite certain

Athanas G. Chatalov

351

Heavy metals in wastewater: Modelling the hydroxide precipitation of copper(II) from wastewater using lime as the precipitant  

SciTech Connect

The effect of effluent composition (Cl{sup {minus}}, SO{sub 4}{sup 2{minus}} or CO{sub 3}{sup 2{minus}}) on the efficiency of the hydroxide precipitation of Cu(II) modelling lime (CaO) as the precipitant has been predicted using the solubility domain approach and has been experimentally validated. Solubility domains were based on the phases that were found to be solubility-limiting for systems representing potential effluent chemical composition limits. The generated solubility domains generally encompassed the experimentally observed solubilities, thereby providing effluent treatment quality assurance ranges for the hydroxide precipitation process. The presence of gypsum (CaSO{sub 4{center_dot}}2H{sub 2}O) and calcite (CaCO{sub 3}) as secondary precipitates had little effect on the observed residual Cu(II) solubilities, with Cu(II) mobility being governed by the least-soluble kinetically precipitated (rather than thermodynamically favored) phase in the system under study.

Baltpurvins, K.A.; Burns, R.C.; Lawrance, G.A. [Univ. of Newcastle, New South Wales (Australia). Dept. of Chemistry] [Univ. of Newcastle, New South Wales (Australia). Dept. of Chemistry

1996-12-31

352

Effect of Second-phase Particles on Static Adjustment of Calcite Grain Boundaries in Carbonate Mylonites  

NASA Astrophysics Data System (ADS)

Static adjustment of grain boundaries during the waning stage of deformation with sustained heat (e.g. at the end of an orogeny) has not been studied much, although it is important for the interpretation of microstructural status during the main stage of deformation. We report here that static adjustment of calcite grain boundaries is dependent on second-phase particles in carbonate mylonites from the Geounri Shear Zone in the Taebaeksan Basin of South Korea. The carbonate mylonites consist of relic (porphyroclastic) calcites (120-400 ?m) and dynamically recrystallized calcites (30-35 ?m) with second-phase particles (15-20 ?m) of quartz and phyllosilicates. Both calcite grains contain mechanical twins and the twins are wider (10-20 ?m thick) in the relic calcites than in the dynamically recrystallized ones (1-3 ?m thick). In the layers of carbonate mylonite with less than 3% of second phases, grain boundaries of calcites are straight with triple junctions. In contrast, calcite grain boundaries are lobate to wavy in the layers with more than 3% of second phases, suggesting dynamic grain boundary migration. Calcite grains in both layers show a strong lattice preferred orientation indicating dominant slip system of basal with minor one of rhomb . We interpret that the foam texture of calcite in the mylonite layers with less than 3% of second phases was produced during the waning stage of the main deformation with a sustained heat since both syntectonic and posttectonic chloritoid porphyroblasts occur in adjacent phyllonite layers in the shear zone. 3% volume fraction of second-phase particles might be a critical value above which deformation microstructures of the main phase were ‘frozen’ without static adjustment in our carbonate mylonites.

Ree, J.; Lee, S.; Jung, H.

2010-12-01

353

Obsidian hydration: A new paleothermometer  

NASA Astrophysics Data System (ADS)

The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960), who noted that the thickness of the hydrated layer on obsidian artifacts increases with time. This approach is, however, sensitive to temperature and humidity under earth-surface conditions. This has made obsidian hydration dating more difficult, but potentially provides a unique tool for paleoclimatic reconstructions. In this paper we present the first successful application of this approach, based on combining laboratory-based experimental calibrations with archaeological samples from the Chalco site in the Basin of Mexico, dated using stratigraphically correlated 14C results and measuring hydration depths by secondary ion mass spectrometry. The resultant data suggest, first, that this approach is viable, even given the existing uncertainties, and that a cooling trend occurred in the Basin of Mexico over the past 1450 yr, a result corroborated by other paleoclimatic data.

Anovitz, Lawrence M.; Riciputi, Lee R.; Cole, David R.; Fayek, Mostafa; Elam, J. Michael

2006-07-01

354

Obsidian Hydration: A New Paleothermometer  

SciTech Connect

The natural hydration of obsidian was first proposed as a dating technique for young geological and archaeological specimens by Friedman and Smith (1960), who noted that the thickness of the hydrated layer on obsidian artifacts increases with time. This approach is, however, sensitive to temperature and humidity under earth-surface conditions. This has made obsidian hydration dating more difficult, but potentially provides a unique tool for paleoclimatic reconstructions. In this paper we present the first successful application of this approach, based on combining laboratory-based experimental calibrations with archaeological samples from the Chalco site in the Basin of Mexico, dated using stratigraphically correlated 14C results and measuring hydration depths by secondary ion mass spectrometry. The resultant data suggest, first, that this approach is viable, even given the existing uncertainties, and that a cooling trend occurred in the Basin of Mexico over the past 1450 yr, a result corroborated by other paleoclimatic data.

Anovitz, Lawrence {Larry} M [ORNL; Riciputi, Lee R [ORNL; Cole, David R [ORNL; Fayek, Mostafa [ORNL; Elam, J. Michael [University of Tennessee, Knoxville (UTK)

2006-01-01

355

Module 11 – Withdrawing Nutrition, Hydration  

Cancer.gov

Module eleven of the EPEC-O Self-Study Original Version discusses the general aspects of withholding or withdrawing of life-sustaining therapies, and presents a specific application to artificial nutrition and hydration.

356

Gas Hydrate Cool Storage System.  

National Technical Information Service (NTIS)

The invention presented relates to the development of a process utilizing a gas hydrate as a cool storage medium for alleviating electric load demands during peak usage periods. Several objectives of the invention are mentioned concerning the formation of...

M. P. Ternes R. J. Kedl

1984-01-01

357

Hydrate formation and growth in pores  

NASA Astrophysics Data System (ADS)

Gas hydrates consist of guest gas molecules encaged in water cages. Methane hydrate forms in marine and permafrost sediments. In this study, we use optical, mechanical and electrical measurements to monitor hydrate formation and growth in small pores to better understand the hydrate pore habit in hydrate-bearing sediments. Hydrate formation in capillary tubes exposes the complex and dynamic interactions between nucleation, gas diffusion and gas solubility. The observation of hydrate growth in a droplet between transparent plates shows that the hydrate shell does not grow homogeneously but advances in the form of lobes that invade the water phase; in fact, the hydrate shell must be discontinuous and possibly cracked to justify the relatively fast growth rates observed in these experiments. Volume expansion during hydrate formation causes water to flow out of menisci; expelled water either spreads on the surface of water-wet substrates and forms a thin hydrate sheet, or remains next to menisci when substrates are oil-wet. Hydrate formation is accompanied by ion exclusion, yet, there is an overall increase in electrical resistance during hydrate formation. Hydrate growth may become salt-limited in trapped water conditions; in this case, aqueous brine and gas CH4 may be separated by hydrate and the three-phase system remains stable within the pore space of sediments.

Jung, Jong-Won; Santamarina, J. Carlos

2012-04-01

358

Methane Hydrate Synthesis in the DOE/METC Gas Hydrates Laboratory: Technical Note.  

National Technical Information Service (NTIS)

In the Department of Energy (DOE), Morgantown Energy Technology Center's (METC's) Gas Hydrates Laboratory, a proven method of synthesizing methane hydrate has been developed. The synthesis technique involves conversion of frost to gas hydrate in a high-pr...

K. Dominic

1986-01-01

359

Activators of photoluminescence in calcite: evidence from high-resolution, laser-excited luminescence spectroscopy  

USGS Publications Warehouse

Laser-excited luminescence spectroscopy of a red-algal, biogenic calcite and a synthetic Mn-calcite can make the distinction between organic and trace-element activators of photoluminescence. Organic-activated photoluminescence in biogenic calcite is characterized by significant peak shifts and increasing intensity with shorter-wavelength excitation and by significant decreases in intensity after heating to ??? 400??C. In contrast, Mn-activated photoluminescence shows no peak shift, greatest intensity under green excitation and limited changes after heating. Examination of samples with a high-sensitivity spectrometer using several wavelengths of exciting light is necessary for identification of photoluminescence activators. ?? 1990.

Pedone, V. A.; Cercone, K. R.; Burruss, R. C.

1990-01-01

360

Structure of the hydrated electron  

Microsoft Academic Search

An intuitive 4-water structure of the hydrated electron based on recent threshold photoionization studies is analyzed in light of past kinetic, thermodymamic, and spectroscopic measurements. It is concluded that the equilibrium state of the hydrated electron may actually be the complex (OH ...H3O)(aq). The central feature is an H2O anion with a large distortion of one OH bond caused by

H. F. Hameka; G. W. Robinson; C. J. Marsden

1987-01-01

361

Heavily Hydrated Salts on Europa  

NASA Astrophysics Data System (ADS)

Telescopic and spacecraft observations indicate the ubiquitous presence of water ice on the surface of Europa. Additional components include hydrogen peroxide and possibly both sulfur dioxide and carbon dioxide. Irradiation by charged particles and possible communication with a convecting interior may also have led to the creation and exposure of additional surface compounds. Disrupted terrains on Europa, including linea, chaos regions, impact basins and significant portions of the trailing hemisphere reveal spectral evidence for an additional component. Near-infrared reflectance spectroscopy from Galileo NIMS (Near-Infrared Mapping Spectrometer) indicates that this material is highly hydrated, as evidenced by strongly asymmetric absorption features attributed to waters of hydration at 1.5 and 2.0 microns. New laboratory studies of heavily hydrated salts demonstrate that as the number of waters of hydration increases, the similarity to spectral observations of Europa becomes more pronounced. We have conducted cryogenic reflectance spectroscopy of the highly hydrated sulfate compounds epsomite, mirabilite, hexahydrite, bloedite and magnesium sulfate dodecahydrate, measured at temperatures relevant to the surface of Europa ( 100K). We present results of these studies, along with modeling results which constrain relative abundances of hydrated materials on Europa. Thus far, no material studied can by itself account for the observed spectral character of the reddish, disrupted Europan terrains. However, there are possible mixtures of materials which give reasonable approximations to the Europa observations, subject to considerations of uniqueness and both physical and chemical viability.

Dalton, J. B.

2005-08-01

362

Natural gas hydrates with locally different cage occupancies and hydration numbers in Lake Baikal  

Microsoft Academic Search

Knowledge of cage occupancies and hydration numbers (n) of naturally occurring gas hydrate in a local environment is important for the improvement in global estimates of hydrate-bound natural gas. We report on local differences in cage occupancies and hydration number of gas hydrates from Lake Baikal. Natural gas hydrates of both structures I and II (sI and sII) and ranging

Masato Kida; Akihiro Hachikubo; Hirotoshi Sakagami; Hirotsugu Minami; Alexey Krylov; Satoshi Yamashita; Nobuo Takahashi; Hitoshi Shoji; Oleg Khlystov; Jeffrey Poort; Hideo Narita

2009-01-01

363

The influence of impurities on the growth rate of calcite  

NASA Astrophysics Data System (ADS)

The effects of 34 different additives on the growth rate of calcite were investigated. An initial growth rate of about one crystal monolayer (3 × 10 -8 cm) per minute was adjusted at a constant supersaturation which was maintained by a control circuit. Then the impurity was added step by step and the reduction of the growth rate was measured. The impurity concentration necessary to reduce the initial growth rate by a certain percentage increased in the order Fe 2+, ATP, P 3O 5-10, P 2O 4-7, (PO 3) 6-6, Zn 2+, ADP, Ce 3+, Pb 2+, carbamyl phosphate, Fe 3+, PO 3-4, Co 2+, Mn 2+, Be 2+, ?-glycerophosphate, Ni 2+, Cd 2+, "Tris", phenylphosphate, chondroitine sulphate, Ba 2+, citrate, AMP, Sr 2+, tricarballylate, taurine, SO 2-4, Mg 2+ by 4 orders of magnitude. The most effective additives halved the initial growth rate in concentrations of 2 × 10 -8 mol/1. For Fe 2+ the halving concentration was nearly proportional to the initial rate. The mechanism of inhibition by adsorption of the impurities at growth sites (kinks) is discussed.

Meyer, H. J.

1984-05-01

364

Influence of geometry upon crack healing rate in calcite  

NASA Astrophysics Data System (ADS)

Crack healing experiments were conducted at 780°, 815°, and 850° C in dry carbon dioxide over periods of 0.5 to 1320 h on small penny-shaped cracks of known geometry in Stahl calcite. As observed by previous investigators, healing initiates with the formation of tubes around the leading edge of the crack, followed by the pinching off of spherical bubbles from these tubes. Pillars and peninsular structures formed and grew at cleavage steps and other surface irregularities, greatly accelerating the healing process in some cracks. The crack tip regression distance at constant temperature follows a simple power law in time; although, with the exception of one crack at 850° C, the time exponent systematically decreases from 0.59 at 780° C to 0.15 and 0.07 at 815° and 850° C, respectively. Only the largest exponent is consistent with existing theory: the two smaller time exponents are, as yet, unexplained. Healing rates are strongly inversely dependent upon crack aperture, in qualitative agreement with theory. For example, cracks with maximum apertures of less than 60 nm (6×10-8 m) healed completely in 0.5 to 25 h at 850° C; while fatter cracks, with maximum apertures of about 700 nm, showed very little healing after up to 1320 h at the same temperature. At 780° C, the functional dependence of healing rate upon crack aperture was consistent with several aspects of the present model.

Hickman, Stephen H.; Evans, Brian

1987-10-01

365

Energy resource potential of natural gas hydrates  

USGS Publications Warehouse

The discovery of large gas hydrate accumulations in terrestrial permafrost regions of the Arctic and beneath the sea along the outer continental margins of the world's oceans has heightened interest in gas hydrates as a possible energy resource. However, significant to potentially insurmountable technical issues must be resolved before gas hydrates can be considered a viable option for affordable supplies of natural gas. The combined information from Arctic gas hydrate studies shows that, in permafrost regions, gas hydrates may exist at subsurface depths ranging from about 130 to 2000 m. The presence of gas hydrates in offshore continental margins has been inferred mainly from anomalous seismic reflectors, known as bottom-simulating reflectors, that have been mapped at depths below the sea floor ranging from about 100 to 1100 m. Current estimates of the amount of gas in the world's marine and permafrost gas hydrate accumulations are in rough accord at about 20,000 trillion m3. Disagreements over fundamental issues such as the volume of gas stored within delineated gas hydrate accumulations and the concentration of gas hydrates within hydrate-bearing strata have demonstrated that we know little about gas hydrates. Recently, however, several countries, including Japan, India, and the United States, have launched ambitious national projects to further examine the resource potential of gas hydrates. These projects may help answer key questions dealing with the properties of gas hydrate reservoirs, the design of production systems, and, most important, the costs and economics of gas hydrate production.

Collett, T. S.

2002-01-01

366

Contribution to the Interpretation of Flotability Characteristics of the Calcite/Apatite System.  

National Technical Information Service (NTIS)

Studies of morphology and determinations of chemical composition of apatite and calcite samples from Jacupiranga, (SP), Brazil, and Itataia (CE), Brazil, were compared with results of microflotation tests. The microflotation tests were carried out with pu...

S. M. Assis G. Silva Maia J. M. Silva E. M. Coelho

1985-01-01

367

Hydroxyapatite synthesis from biogenic calcite single crystals into phosphate solutions at ambient conditions  

NASA Astrophysics Data System (ADS)

Hydroxyapatite is one of the most important bone substitute biomaterials. Here, it has been successfully overgrown on biogenic seed crystals at ambient conditions. Single crystals of calcite from Atrina rigida, Paracentrotus lividus and Heterocentrotus mammillatus have been soaked in phosphate solution with different concentrations and pHs for 2 months. X-ray powder diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy have been used to characterize soaking precipitates. The results show that the conversion of calcite to hydroxyapatite occurs to an extent which depends on composition and morphology of seed crystals, and starting concentration and pH of phosphate solutions. In the same experimental conditions, synthetic calcite single crystals did not convert to hydroxyapatite. The morphological observations suggest for hydroxyapatite formation, a mechanism that involves a superficial dissolution of calcite and a subsequently overgrowth of hydroxyapatite. Moreover, the final architectural assembly of the hydroxyapatite crystals resembles the shape of the starting biogenic seed crystals.

Marchegiani, Francesca; Cibej, Eleonora; Vergni, Patrizia; Tosi, Giovanna; Fermani, Simona; Falini, Giuseppe

2009-08-01

368

High School Forum: "Invitations to Enquiry": The Calcite/Acid Reaction.  

ERIC Educational Resources Information Center

Describes a high school chemistry experiment which involves the reaction between calcite and hydrochloric and sulfuric acids. This reaction can be carried out as a projected demonstration and on an individual basis. (HM)

Herron, J. Dudley, Ed.; Driscoll, D. R.

1979-01-01

369

Simulation of calcite dissolution and porosity changes in saltwater mixing zones in coastal aquifers  

USGS Publications Warehouse

Thermodynamic models of aqueous solutions have indicated that the mixing of seawater and calcite-saturated fresh groundwater can produce a water that is undersaturated with respect to calcite. Mixing of such waters in coastal carbonate aquifers could lead to significant amounts of limestone dissolution. The potential for such dissolution in coastal saltwater mixing zones is analyzed by coupling the results from a reaction simulation model (PHREEQE) with a variable density groundwater flow and solute transport model. Idealized cross sections of coastal carbonate aquifers are simulated to estimate the potential for calcite dissolution under a variety of hydrologic and geochemical conditions. Results show that limestone dissolution in mixing zones is strongly dependent on groundwater flux and nearly independent of the dissolution kinetics of calcite. -from Authors

Sanford, W. E.; Konikow, L. F.

1989-01-01

370

Deletion of the LIME adaptor protein minimally affects T and B cell development and function.  

PubMed

LIME (Lck-interacting membrane protein) is a transmembrane adaptor that associates with the Lck and Fyn protein tyrosine kinases and with the C-terminal Src kinase (Csk). To delineate the role of LIME in vivo, LIME-deficient mice were generated. Although Lime transcripts were expressed in immature and mature B and T cells, the absence of LIME impeded neither the development nor the function of B and T cells. TCR transgenic mice deprived of LIME showed, however, a 1.8-fold enhancement in positive selection. Since B cells and activated T cells express LIME and the related adaptor NTAL, mice lacking both adaptors were generated. Double-deficient mice showed no defect in the development and function of B and T cells, and the lack of LIME had no effect on the autoimmune syndrome that develops in aged NTAL-deficient mice. In contrast to a previous report, we further showed that this autoimmune syndrome develops in the absence of T cells. Therefore, our in vivo results refute all the previous roles postulated for LIME on the basis of studies of transformed B and T cells and demonstrate that LIME has no seminal role in the signaling cassette operated by antigen receptors and coreceptors. PMID:17918199

Grégoire, Claude; Simova, Sarka; Wang, Ying; Sansoni, Amandine; Richelme, Sylvie; Schmidt-Giese, Anja; Simeoni, Luca; Angelisova, Pavla; Reinhold, Dirk; Schraven, Burkhart; Horejsi, Vaclav; Malissen, Bernard; Malissen, Marie

2007-11-01

371

The potential for phosphorus pollution remediation by calcite precipitation in UK freshwaters  

NASA Astrophysics Data System (ADS)

This paper examines the potential for calcium carbonate to reduce phosphate pollution in freshwaters by co-precipitation, a process known as a "self cleansing mechanism". Calcium carbonate saturation levels and phosphate concentrations (SRP - soluble reactive phosphate) across the major eastern UK river basins are examined to test for solubility controls. The study shows that calcite saturation varies for each catchment as a function of flow and biological activity rather than by direct regulation by SRP. Indeed, there is no evidence, for any of the rivers studied, that calcite solubility controls hold. However, for groundwater and groundwater-fed springs in the Chalk of the Thames basin, calcite saturation is observed with associated low SRP levels. A self-cleansing mechanism may well be operative within the Chalk due to two factors. Firstly, there is a high potential for nucleation on the calcite micro-crystals in the aquifer. Secondly, there are within aquifer reactions that remove the calcite nucleating inhibitors (SRP and dissolved organic carbon, DOC) to levels lower than those occurring within the rivers do. These inhibitors enter the catchment at very high concentrations in association with agricultural pollution (fertilizer application and animal slurry) and household contamination (e.g. sewage sources from septic tanks). Under low flow conditions, when the saturation index for calcite is at its highest, so too is the concentration of the nucleation inhibitor SRP. Companion work shows that calcite precipitation can occur at the water-sediment interface of the river and this may involve SRP removal. The data, as a whole, define an apparent bound for calcite solubility control where in the presence of nucleating centres, SRP must be less than 4 mM-P l-1 and DOC must be less than 150 mM-C l-1: a condition that does not seem to pertain within most UK rivers.

Neal, Colin

372

Sorption of phosphate onto calcite; results from batch experiments and surface complexation modeling  

NASA Astrophysics Data System (ADS)

The adsorption of phosphate onto calcite was studied in a series of batch experiments. To avoid the precipitation of phosphate-containing minerals the experiments were conducted using a short reaction time (3 h) and low concentrations of phosphate (?50 ?M). Sorption of phosphate on calcite was studied in 11 different calcite-equilibrated solutions that varied in pH, P, ionic strength and activity of Ca 2+, CO32- and HCO3-. Our results show strong sorption of phosphate onto calcite. The kinetics of phosphate sorption onto calcite are fast; adsorption is complete within 2-3 h while desorption is complete in less than 0.5 h. The reversibility of the sorption process indicates that phosphate is not incorporated into the calcite crystal lattice under our experimental conditions. Precipitation of phosphate-containing phases does not seem to take place in systems with ?50 ?M total phosphate, in spite of a high degree of super-saturation with respect to hydroxyapatite (SI HAP ? 7.83). The amount of phosphate adsorbed varied with the solution composition, in particular, adsorption increases as the CO32- activity decreases (at constant pH) and as pH increases (at constant CO32- activity). The primary effect of ionic strength on phosphate sorption onto calcite is its influence on the activity of the different aqueous phosphate species. The experimental results were modeled satisfactorily using the constant capacitance model with >CaPO 4Ca 0 and either >CaHPO 4Ca + or > CaHPO4- as the adsorbed surface species. Generally the model captures the variation in phosphate adsorption onto calcite as a function of solution composition, though it was necessary to include two types of sorption sites (strong and weak) in the model to reproduce the convex shape of the sorption isotherms.

Ugilt Sø, Helle; Postma, Dieke; Jakobsen, Rasmus; Larsen, Flemming

2011-05-01

373

The influence of morphology of ultra-fine calcite particles on decomposition kinetics  

Microsoft Academic Search

The decomposition kinetics of reference calcite and three ultra-fine samples with different morphologies are investigated.\\u000a The kinetic parameters and rate equation are obtained according to the methods reported in our previous studies. Compared\\u000a with the reference calcite, a considerable diminution of the activation energy E\\u000a a up to 70–80 kJ mol?1 is observed in the case of three ultra-fine samples.

Y.-L. Ren; X. Wang; M. Shui; R.-S. Li

2008-01-01

374

Dependence of calcite growth rate and Sr partitioning on solution stoichiometry: Non-Kossel crystal growth  

Microsoft Academic Search

Seeded calcite growth experiments were conducted at fixed pH (10.2) and two degrees of supersaturation (?=5, 16), while varying the Ca2+ to CO32- solution ratio over several orders of magnitude. The calcite growth rate and the incorporation of Sr in the growing crystals strongly depended on the solution stoichiometry. At a constant degree of supersaturation, the growth rate was highest

G. Nehrke; G.-J. Reichart; P. Van Cappellen; C. Meile; J. Bijma

2007-01-01

375

Characterization of tensile behaviour of hybrid short glass fibre\\/calcite particle\\/ABS composites  

Microsoft Academic Search

The tensile properties of hybrid, injection molded, short glass fibre (SGF)\\/calcite particle\\/acrylonitrile-butadiene-styrene (ABS) composites have been investigated. To gain an insight into some possible combined effect of the SGF\\/ABS interfacial adhesion strength and the calcite particle\\/ABS adhesion strength on the tensile properties of the hybrid composites, the glass fibres employed in the investigation were as-received and sized with an aminosilane\\/polyurethane

Shao-Yun Fu; Bernd Lauke

1998-01-01

376

Calcite genesis in the Upper Freeport coal bed as indicated by stable isotope geochemistry  

SciTech Connect

The grinding and sizing in float-sink testing of the Upper Freeport coal bed physically separates calcite of different origins. The different origins are distinguished by different isotopic compositions. The isotopic compositions of calcite indicates at least two, possibly three, stages of calcite formation in the Upper Freeport coal bed. Calcite samples obtained from cleat, and isolated from 8x100 mesh-1.8 specific gravity sink fraction and -100 mesh size fraction, are enriched in /sup 13/C. The dispersion in /sup 18/O values for all three sample types, as measured by the standard deviation, is 2.7 per mil relative to SMOW, which may indicate similar temperature of formation. In contrast, calcite from the 1.275 specific gravity float fraction is depleted in /sup 13/C (mean = -4.6 per mil), indicative of CO/sub 2/ generated from the oxidation of organic matter. The standard deviation of /sup 18/O values for these samples is 9.2 per mil, probably indicating variation in the temperature of formation. Limestone samples associated with the Upper Freeport coal bed are slightly depleted in /sup 13/C (mean = -3.1 per mil). Genesis of calcite in the coal apparently resulted from biotic, as well as, thermogenic processes. A second stage of calcite formation, resulting from fermentation and methanogenesis is in cleat, and in the 8x100 mesh-1.8 specific gravity sink and -100 mesh size fractions. Part of the calcite in the 1.275 specific gravity float fraction may have formed from thermally generated CO/sub 2/ released during coalification.

Dulong, F.T.; Spiker, E.C.; Cecil, C.B.; Stanton, R.W.

1985-01-01

377

Fractionation of carbon and oxygen isotopes and magnesium between coexisting metamorphic calcite and dolomite  

Microsoft Academic Search

Fractionations of carbon and oxygen isotopes and magnesium between coexisting dolomite and calcite have been determined for\\u000a marbles and calcareous schists of a wide variety of metamorphic environments from Vermont and the Grenville Province of Ontario.\\u000a Concordant equilibrium fractionations are given by 83% of the samples. Calibration of the isotopic thermometers using the\\u000a Mg-calcite solvus thermometer gave in the temperature

Simon M. F. Sheppard; Henry P. Schwarcz

1970-01-01

378

Distribution of vesicular-arbuscular mycorrhizal fungi in coal, lignite, and calcite mine spoils of India  

Microsoft Academic Search

We assessed vesicular-arbuscular mycorrhizal (VAM) fungi in coal, lignite, and calcite mine spoils. The level of VAM fungal infection and the population of VAM species in plants on the coal-waste sites were similar to those in plants on the calcite mine spoil. The plants on the coal-waste sites and their associated VAM fungi included Tephrosia purpurea (L.) Pers. with Glomus

V. Ganesan; S. Ragupathy; B. Parthipan; D. B. Rajini Rani; A. Mahadevan

1991-01-01

379

Origin of sulfate in barite and calcite cements in the Jebel Madar salt dome (Oman)  

NASA Astrophysics Data System (ADS)

Jebel Madar is a 500-m high mountain rising in the desert at the Oman Foothills. The Jebel consists of Triassic to Cretaceous carbonate host rocks forming the carapace of a salt dome. Halokinesis caused major fracturing and faulting at Jebel Madar, and the resulting structures acted as the main pathways for fluids that generated diagenetic cements composed of both barite and calcite. The spatial distribution of calcite and barite occurrences shows that calcite is formed in large abundance along the three main faults, whereas barite is more concentrated along faults further away from the three main ones. The stable carbon and oxygen isotope composition of calcite and fluid inclusion data from both calcite and barite show a distinct evolution of the fluid with a highly saline component towards more mixing with meteoric water. This is in agreement with clumped isotopes data on calcite cements indicating an evolution towards lower temperatures, consistent with doming of the Jebel and greater input of lower-temperature descending meteoric fluids. Here, we present sulphur and oxygen isotopic data on barite that suggest a link between the barite formation and the Precambrian salt underlying Jebel Madar. The average ?34S measured in barite is 33‰ CDT (1? = 5‰; n = 33), which falls at the lower end of the ?34S range reported for the Ara Group anhydrite. The average ?18O in the same barite samples is 23‰ VSMOW (1? = 2‰; n = 33). Data from the barite will be compared with sulphur isotopes from the carbonate-associate sulfate in the calcite cements. The overall goal of our research is to gain a better insight in the formation process of barite and calcite in Jebel Madar and its link with salt tectonics. We would like to acknowledge the financial support of QCCSRC (funded jointly by Qatar Petroleum, Shell and the Qatar Science & Technology Park) and the GSA Laubach fund for this study.

Vandeginste, V.; John, C. M.; Gilhooly, W. P.

2012-12-01

380

Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?  

NASA Astrophysics Data System (ADS)

Calcitic nanofibres are ubiquitous habits of secondary calcium carbonate (CaCO3) accumulations observed in calcareous vadose environments. Despite their widespread occurrence, the origin of these nanofeatures remains enigmatic. Three possible mechanisms fuel the debate: (i) purely physicochemical processes, (ii) mineralization of rod-shaped bacteria, and (iii) crystal precipitation on organic templates. Nanofibres can be either mineral (calcitic) or organic in nature. They are very often observed in association with needle fibre calcite (NFC), another typical secondary CaCO3 habit in terrestrial environments. This association has contributed to some confusion between both habits, however they are truly two distinct calcitic features and their recurrent association is likely to be an important fact to help understanding the origin of nanofibres. In this paper the different hypotheses that currently exist to explain the origin of calcitic nanofibres are critically reviewed. In addition to this, a new hypothesis for the origin of nanofibres is proposed based on the fact that current knowledge attributes a fungal origin to NFC. As this feature and nanofibres are recurrently observed together, a possible fungal origin for nanofibres which are associated with NFC is investigated. Sequential enzymatic digestion of the fungal cell wall of selected fungal species demonstrates that the fungal cell wall can be a source of organic nanofibres. The obtained organic nanofibres show a striking morphological resemblance when compared to their natural counterparts, emphasizing a fungal origin for part of the organic nanofibres observed in association with NFC. It is further hypothesized that these organic nanofibres may act as templates for calcite nucleation in a biologically influenced mineralization process, generating calcitic nanofibres. This highlights the possible involvement of fungi in CaCO3 biomineralization processes, a role still poorly documented. Moreover, on a global scale, the organomineralization of organic nanofibres into calcitic nanofibres might be an overlooked process deserving more attention to specify its impact on the biogeochemical cycles of both Ca and C.

Bindschedler, S.; Cailleau, G.; Braissant, O.; Millière, L.; Job, D.; Verrecchia, E. P.

2014-05-01

381

Catalytic sulphation of limestone\\/lime with platinum  

Microsoft Academic Search

The effects of the presence of a Pt catalyst on the limestone\\/lime sulphation process were investigated by thermal analysis methods to provide a better understanding of the factors limiting gas desulphurization when Ca-based sorbents are used. It was found that for the Pt-catalysed sulphation of precalcined limestone the weight increase is above 100% higher under isothermal and dynamic conditions (up

K. Wieczorek-Ciurowa

1992-01-01

382

Lime pretreatment of crop residues bagasse and wheat straw  

Microsoft Academic Search

Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of two common crop residues:\\u000a bagasse and wheat straw. A systematic study of pretreatment conditions suggested that for short pretreatment times (1–3 h),\\u000a high temperatures (85-135°C) were required to achieve high sugar yields, whereas for long pretreatment times (e.g., 24 h),\\u000a low temperatures (50–65°C) were effective.

Vincent S. Chang; Murlidhar Nagwani; Mark T. Holtzapple

1998-01-01

383

Mechanical properties of natural hydraulic lime-based mortars  

Microsoft Academic Search

One hundred eighty different mortars made with a natural hydraulic lime (NHL) and different kinds of aggregates were prepared to be used in restoration works. The factors affecting the mechanical behavior have been studied at long-term test. Compressive and flexural strengths of the specimens were discussed according to curing time, binder\\/aggregate ratios, attributes of the aggregates and porosity.Three phases of

J. Lanas; J. L. Pérez Bernal; M. A. Bello; J. I. Alvarez Galindo

2004-01-01

384

Landfill methane oxidation response to vegetation, fertilization, and liming  

Microsoft Academic Search

Landfills are the fourth largest global source and the largest US source (USDOE, 1997) of anthropogenic CHâ emissions. Since gram-for-gram, CHâ has 21 times the 100-yr global-warming potential of COâ (USEPA, 1990). CHâ release into the atmosphere has important implications for global climate change. This study was conducted to evaluate the effects of vegetation, N fertilizers, and lime addition on

Helene A. Hilger; Arthur G. Wollum; Morton A. Barlaz

2000-01-01

385

Sea urchin tooth mineralization: Calcite present early in the aboral plumula  

PubMed Central

In both vertebrate bone, containing carbonated hydroxyapatite as the mineral phase, and in invertebrate hard tissue comprised of calcium carbonate, a popular view is that the mineral phase develops from a long-lived amorphous precursor which later transforms into crystal form. Important questions linked to this popular view are: When and where is the crystallized material formed, and is amorphous solid added subsequently to the crystalline substrate? Sea urchin teeth, in which the earliest mineral forms within isolated compartments, in a time and position dependent manner, allow direct investigation of the timing of crystallization of the calcite primary plates. Living teeth of the sea urchin Lytechinus variegatus, in their native coelomic fluid, were examined by high-energy synchrotron x-ray diffraction. The diffraction data show that calcite is present in the most aboral portions of the plumula, representing the very earliest stages of mineralization, and that this calcite has the same crystal orientation as in the more mature adoral portions of the same tooth. Raman spectroscopy of the aboral plumula confirms the initial primary plate mineral material is calcite and does not detect amorphous calcium carbonate; in the more mature adoral incisal flange, it does detect a broader calcite peak, consistent with two or more magnesium compositions. We hypothesize that some portion of each syncytial membrane in the plumula provides the information for nucleation of identically oriented calcite crystals that subsequently develop to form the complex geometry of the single crystal sea urchin tooth.

Stock, Stuart R.; Veis, Arthur; Xiao, Xianghui; Almer, Jonathan D.; Dorvee, Jason R.

2012-01-01

386

Microstructural control of calcite via incorporation of intracrystalline organic molecules in shells  

NASA Astrophysics Data System (ADS)

It is widely accepted that organic substances regulate or influence the structure of biominerals, but its direct evidences are not plenty. Here we show that the crystallographic microstructures in biotic calcites arise from incorporated intracrystalline organic molecules (IOMs), through a comparison between biotic calcites in shells and synthetic ones with the IOMs extracted from the shells. Although the prismatic layers of a pearl oyster (Pinctada fucata) and a pen shell (Atrina pectinata) morphologically resemble each other, the crystallographic features of constituent calcites are considerably different; in Pinctada, the IOMs are distributed inhomogeneously to form small-angle grain boundaries and associated crystal defects, whereas in Atrina, the IOMs are distributed almost homogeneously and defects are rare in the calcite crystals. We conducted in vitro calcite syntheses in the presence of the IOMs in EDTA-soluble extracts from the prisms. The IOMs in the extracts from Pinctada and Atrina were incorporated into synthetic calcites in a different manner, exhibiting defect-rich/free features as observed in the natural shells. With regard to amino acid compositions of the IOMs, the extract from Atrina has a higher proportion of acidic amino acids than that from Pinctada, implying that acidic proteins do not correlate directly to their affinity for calcium carbonate crystals.

Okumura, Taiga; Suzuki, Michio; Nagasawa, Hiromichi; Kogure, Toshihiro

2013-10-01

387

The promotion effect of coexisting hygroscopic composition on the reaction between oxalic acid and calcite during humidifying process  

NASA Astrophysics Data System (ADS)

Internally mixed oxalic acid with mineral dust has been frequently detected in field measurements (Sullivan and Prather, 2007; Wang et al., 2012; Yang et al., 2009). Meanwhile, Furukawa and Takahashi (Furukawa and Takahashi, 2011) found that most of the oxalic acid in mineral mixture is present as metal oxalate complexes in the aerosols, however, the formation mechanism of these complexes is not well known. It was reported that cloud process of H2C2O4/CaCO3 mixture could lead to the formation of calcium oxalate (Gierlus et al., 2012). Recently, we used Raman spectroscopy to investigate the hygroscopic behavior of H2C2O4/CaCO3 mixture below saturation condition as well as the effect of coexisting hygroscopic compositions, e.g. Ca(NO3)2, NaCl, NH4NO3, and (NH4)2SO4. It was found that there was no interaction between H2C2O4 and calcite without third component during humidifying process under ambient condition. In contrast, the presence of coexisting Ca(NO)3, NaCl, or NH4NO3 could promote the reaction between H2C2O4 and calcite by providing an aqueous circumstance after deliquescence, resulting in the formation of calcium oxalate hydrates. Moreover, substitution of strong acid (HNO3) by medium acid (H2C2O4) occurred when water vapor was absorbed in Ca(NO3)2/H2C2O4 mixture (Ma and He, 2012). As for (NH4)2SO4, there existed a competition effect between (NH4)2SO4 and H2C2O4 for the reaction with CaCO3. CaCO3 was preferentially reacted with (NH4)2SO4 to form gypsum in the solution, while the residual NH4+ and C2O42- ions were bonded to (NH4)2C2O4 after efflorescence. These results implies a potential formation pathway of metal oxalate complexes in the atmosphere and also suggests that synergistic effect between different constituents in humidifying process of mixed particles should be considered in future hygroscopic behavior studies.

Ma, Q.; He, H.

2012-12-01

388

Speciation of aluminium, arsenic and molybdenum in excessively limed lakes.  

PubMed

The possible existence of the potentially toxic oxyanions of Al (Al(OH)(4)(-)), As (HAsO(4)(2-)), and Mo (MoO(4)(2-)) was examined in excessively limed lakes. In-situ dialysis (MWCO 1 kDa) was performed in the surface and bottom waters of two excessively limed lakes (pH 7.1-7.7) and one acidic lake (pH approximately 5.4). The dialysable metal concentrations were compared to the equilibrium distribution of species as calculated with the geochemical code Visual MINTEQ incorporating the CD-MUSIC and Stockholm Humic models for complexation onto colloidal ferrihydrite and dissolved organic matter. Arsenic and molybdenum in the excessively limed lakes were to a large extent present in the dialysable fraction (>79% and >92% respectively). They were calculated to exist as free or adsorbed oxyanions. Most of the Al was observed to reside in the colloidal fraction (51-82%). In agreement with this, model predictions indicated aluminium to be present mostly as colloids or bound to dissolved organic matter. Only a small fraction was modelled as Al(OH)(4)(-) ions. In most cases, modelled values were in agreement with the dialysis results. The free concentrations of the three oxyanions were mostly low compared to toxic levels. PMID:19540566

Sjöstedt, Carin; Wällstedt, Teresia; Gustafsson, Jon Petter; Borg, Hans

2009-09-01

389

Energy reduction in beet sugar processing by cossette liming  

SciTech Connect

Under appropriate conditions of temperature and fresh Ca(OH)/sub 2/ application, demethylation occurs in the pectin in the cell walls of sugar beet cossettes, allowing Ca/sup 2 +/ to precipitate the pectin as calcium pectate. The calcium pectate will not degrade and pass into solution during subsequent hot extraction of sugar from the cossettes. This retention of pectin in the pulp was shown by 10 to 20% increases in solids weight in the pulp for a number of processing conditions. The toughened pulp produced by retention of calcium pectate allowed easier mechanical dewatering of the pulp which could save considerably on the heat normally required to dry the pulp for cattle feed. Beyond data reported in this paper, there are qualitative indications that the sugar juice extracted from limed cossettes is purer than standard juice, for pectin and colloidal materials remain in the pulp. Thus, much less purification of the juice with lime would be necessary than is required in standard beet-sugar processing, and the current 2% CaO used for purification may be cut almost in half. This represents another energy saving, for production of CaO at the factory is a major consumer of energy. These, along with other possible energy savings resulting from cossette liming (such as less water used for extraction, cold extraction, ion exchange of the purer juice), could produce an overall saving up to 20% of the energy currently used in beet-sugar processing. Some of these possibilities will be further investigated.

Randall, J.M.; Camirand, W.M.; Neumann, H.J.

1981-01-01

390

The Variation in ?47 Within Calcite-Dolomite Mixed Systems  

NASA Astrophysics Data System (ADS)

This work focuses on understanding the formation of Tertiary aged dolomites found off of the Great Bahama Bank (GBB) using the ?47 method. The samples used were collected from Clino, a ?670m core drilled on the surface of GBB. The core penetrated mixtures of shallow to deep water sediments composed of varying amounts of low-magnesium calcite (LMC), aragonite, and dolomite. The concentration of dolomites varies between 0 to >50% over short intervals. A previous study identified three different environments for the formation of these dolomites: 1) associated with non-depositional surfaces and the oxidation of organic material, 2) background dolomite with Mg2+ supplied by diffusion and dissolution of HMC, and 3) massive dolomites formed in reef sediments with actively circulating seawater. Although the mechanisms of dolomitization were constrained using ?13C, ?18O, trace elements and Sr isotopes, ?47 paleothermometry would provide additional valuable information in order to further constrain the nature of dolomitization. Samples were collected from previously studied intervals in which the composition (dolomite 8-48%) had been determined using X-ray diffraction (XRD). The ?47 was measured on the bulk sediments. The samples were then treated with a series of buffered acetic acid leaches in order to remove the less stable aragonite and LMC. The sample remaining after each treatment was collected and measured using XRD to determine the percent dolomite. The process continued until all aragonite and LMC was removed. The ?47 of each separate was measured. The results can be plotted relative to temperature using a variety of different equations to account for the variation of mineralogy. The same approach can be applied to the ?18O of the water. Based on these results and assumptions of the temperature of dolomitization, the relationship between ?47 and temperature in dolomite can be derived.

Murray, S.; Swart, P. K.

2013-12-01

391

Comparison of stromal hydration techniques for clear corneal cataract incisions: conventional hydration versus anterior stromal pocket hydration.  

PubMed

Anterior stromal pocket hydration was compared with conventional hydration for preventing wound leak after 2.8 mm uniplanar clear corneal incisions (CCIs) in patients having routine cataract surgery. Conventional hydration involves hydration of the lateral walls of the main incision with visible whitening of the stroma. The anterior stromal pocket hydration technique involves creation of an additional supraincisional stromal pocket overlying the main incision, which is then hydrated instead of the main incision. Sixty-six eyes of 48 patients were included in the data analysis with 33 assigned to each study group. The anterior stromal pocket hydration technique was significantly better than conventional hydration in preventing wound leak due to direct pressure on the posterior lip of the incision. PMID:22624890

Mifflin, Mark D; Kinard, Krista; Neuffer, Marcus C

2012-06-01

392

Solution composition-dependence of the Ca isotope composition of inorganic calcite  

NASA Astrophysics Data System (ADS)

Laboratory experiments have shown that the Ca isotope composition of calcite precipitated from aqueous solution may be sensitive to solution chemistry, temperature, and solution pH. Generally, inorganic calcite precipitation experiments yield calcite crystals that are enriched in the light isotope of Ca relative to the parent solution. Previous studies by Lemarchand et al. (2004) and Tang et al. (2008) showed that the Ca isotope composition (?44Ca) of calcite varies systematically with precipitation rate (R). The studies, however, obtained the opposite relationship between ?44Ca and R despite precipitating calcite at comparable pH, temperature, and Ca2+ as well as CO32- ion concentrations. There is evidence that Ca isotope variability in calcite reflects a mass dependence on reaction rate coefficients, but it is unknown if the mass dependence varies with solution chemistry. A potentially important difference between the studies is that Lemarchand et al. (2004) used parent solutions with higher ionic strength (0.85 versus 0.035). The purpose of this study is to determine the solution composition dependence, if any, on Ca isotope incorporation during calcite growth from aqueous solutions. For our experiments, a beaker containing 300 mL of CaCl2+NH4Cl solution was placed in a container filled with 1 atm of an N2+CO2 gas mixture. The degree of supersaturation with respect to calcite was controlled by the pCO2 of the gas, which was constantly replenished. As CO2 dissolved into solution, calcite crystals grew on the beaker walls. The pH of the solution was maintained by an autotitrator with NaOH as the titrant. Calcite precipitation rates are typically expressed in mmol/m2/hr, but this is difficult to quantify as the reactive surface area of the crystals is not controlled. Relative growth rates are determined by weighing the amount of calcite precipitated over the course of an entire experiment on a fixed surface area. This provides a first estimate of R and we are investigating methods for improving this aspect of the results. Experiments have yielded calcite crystals enriched in the light isotope of Ca relative to the parent solution by 0.4‰ to 1.6‰. Growth rates are estimated to range from 0.01 to 131 mmol/m2/hr, overlapping with the rates from Lemarchand et al. (2004) and Tang et al. (2008). In experiments where we use a solution with high ionic strength (0.7), we find that ?44Ca in calcite increases with increasing precipitation rate. This is in agreement with the findings of Lemarchand et al. (2004), although Ca isotopes are more fractionated in our experiments. We are exploring if a solution with lower ionic strength reproduces the results of Tang et al. (2008), in which ?44Ca in calcite decreased with increasing precipitation rate. Our hypothesis is that solution chemistry may play an important role in calcium isotope incorporation in calcite and we will present results using different parent solution compositions that explore this relationship. The ultimate goal is to understand the molecular scale controls on isotope separation at the mineral surface during crystal growth.

Gonzales, M. S.; Watkins, J. M.; Depaolo, D. J.

2010-12-01

393

(U-Th)/He dating and He diffusion in calcite from veins and breccia  

NASA Astrophysics Data System (ADS)

Knowledge of He retention in crystalline calcite is mandatory to estimate the possibility of (U-Th)/He dating of calcite. To this aim, fault-filling calcite crystals from the Eocene/Oligocene Gondrecourt graben, Paris Basin, Eastern France, have been sampled, based on their relatively old, Eocene-Oligocene, precipitation age and cold thermal history (<40°C since precipitation). The samples were sorted into three main tectonic and morphological groups, including successively (1) micro-fracture calcites, (2) breccia and associated geodic calcites, and (3) vein and associated geodic calcites. (U-Th)/He dating of 63 calcite fragments yields ages dispersed from 0.2×0.02 to 35.8×2.7 Ma, as well as two older dates of 117×10 and 205×28 Ma (1s). These He ages correlate to grain chemistry, such as to Sr and ?REE concentrations or (La/Yb)N ratios, and these correlations probably reflect the evolution of parent fluid. Only the oldest He ages are in agreement with the He-retentive character of calcite as determined by Copeland et al. (2007), and these ages were obtained for the most recently precipitated crystals. To better understand the large He-age scatter and why calcites precipitated earlier show younger ages, He diffusion experiments have been conducted on 10 Gondrecourt calcite fragments from 3 samples with He ages of 0.2 to 6 Ma. In addition, a crystallographic investigation by X-Ray Diffraction (XRD) performed on similar samples reveals that the crystal structure evolves with increasing temperature, showing with micro-cracks and cleavage opening. These XRD results indicate that, in fault-filling calcite, He retention is controlled by multiple diffusion domains (MDD, Lovera et al., 1991) with various sizes, and therefore, evolves through time with strong consequences on (U-Th)/He age. We thus interpret the Gondrecourt calcite (U-Th)/He age scatter of older samples as a consequence of cleavage opening due to a succession of calcite crystallization phases related to the deformation history. Finally, we propose that the crystallization age of a calcite crystal with a known thermal history can nevertheless be retrieved by the (U-Th)/He method provided the He diffusion pattern can be measured by careful step-heating degassing analysis. Copeland, P., Watson, E.B., Urizar, S.C., Patterson, D., Lapen, T.J., 2007. Alpha thermochronology of carbonates. Geochim. Cosmochim. Acta, 71: 4488-4511. Cros, A. Gautheron, C., Pagel, M., Berthet, P., Tassan-Got, L., Douville, E., Pinna-Jamme, R., Sarda, P., submitted GCA, He behavior in calcite filling viewed by (U-Th)/He dating, He diffusion and crystallographic studies. Lovera, O.M., Richter, F.M., Harrison, T.M., 1991. Diffusion domains determined by 39Ar released during step heating. Journal of Geophysical Research, 96: 2057-2069.

Gautheron, C.; Cros, A.; Pagel, M.; Berthet, P.; Tassan-Got, L.; Douville, E.; Pinna-Jamme, R.; Sarda, P.

2013-12-01

394

Complex gas hydrate from the Cascadia margin.  

PubMed

Natural gas hydrates are a potential source of energy and may play a role in climate change and geological hazards. Most natural gas hydrate appears to be in the form of 'structure I', with methane as the trapped guest molecule, although 'structure II' hydrate has also been identified, with guest molecules such as isobutane and propane, as well as lighter hydrocarbons. A third hydrate structure, 'structure H', which is capable of trapping larger guest molecules, has been produced in the laboratory, but it has not been confirmed that it occurs in the natural environment. Here we characterize the structure, gas content and composition, and distribution of guest molecules in a complex natural hydrate sample recovered from Barkley canyon, on the northern Cascadia margin. We show that the sample contains structure H hydrate, and thus provides direct evidence for the natural occurrence of this hydrate structure. The structure H hydrate is intimately associated with structure II hydrate, and the two structures contain more than 13 different hydrocarbon guest molecules. We also demonstrate that the stability field of the complex gas hydrate lies between those of structure II and structure H hydrates, indicating that this form of hydrate is more stable than structure I and may thus potentially be found in a wider pressure-temperature regime than can methane hydrate deposits. PMID:17230188

Lu, Hailong; Seo, Yu-taek; Lee, Jong-won; Moudrakovski, Igor; Ripmeester, John A; Chapman, N Ross; Coffin, Richard B; Gardner, Graeme; Pohlman, John

2007-01-18

395

Retrofit costs for lime/limestone FGD and lime spray drying at coal-fired utility boilers  

SciTech Connect

The paper gives results of a research program the objective of which was to significantly improve engineering cost estimates currently being used to evaluate the economic effects of applying SO2 controls to existing coal-fired utility boilers. The costs of retrofitting conventional lime/limestone wet flue gas desulfurization (L/LS FGD) and lime spray drying (LSD) FGD at 100-200 coal-fired power plants are being estimated under this program. The retrofit capital cost estimating procedures used for L/LS FGD and LSD FGD make two cost adjustments to current procedures used to estimate FGD costs: cost adders (for items not normally included in FGD system costs; e.g., demolition and relocation of existing facilities) and cost multipliers (to adjust capital costs for site access, congestion, and underground obstructions).

Emmel, T.E.; Jones, J.W.

1990-01-01

396

High-temperature enthalpy at the orientational order-disorder transition in calcite: implications for the calcite\\/aragonite phase equilibrium  

Microsoft Academic Search

The enthalpy of calcite has been measured directly between 973 K and 1325 K by transposed-temperature- drop calorimetry. The excess enthalpy has been analysed in terms of Landau theory for this tricritical phase transition. The zero-point enthalpy and entropy allow estimates of the parameters a and C in the Landau expansion for free energy which expresses excess free energy ?G

S. A. T. Redfern; E. Salje; A. Navrotsky

1989-01-01

397

The use of AMS for the dating of lime mortars  

NASA Astrophysics Data System (ADS)

In the production of lime mortars CaCO 3 is converted to CaO. Upon setting the CaO reacts with atmospheric CO 2 to form CaCO 3. Attempts to date mortars based on the carbon content of the CaCO 3 have been hampered by two major factors. The original CaCO 3 may not have been completely converted to CaO during heating and the sample will then contain dead carbon leading to an incorrect date. Secondly, marble chips from a construction site may have been added as part of the aggregate material. This will also add dead carbon and produce an erroneous date. The lime mortars contain a second possible source of carbon for dating. Small fragments of charcoal and plant material are often found upon crushing of the sample. This material can be used as the source of carbon for dating. Potential sources of dead carbon in this part of the sample would be if coal was used in the heating process. The use of AMS to determine 14C in lime mortars significantly reduces the amount of sample required and allows measurements to be made on standing structures. The comparison of 14C in lime mortars should allow original and reconstructed or repaired areas of architecturally and historically significant buildings to be discerned. An attempt to apply this method is being made at Pontigny Abbey, a Cistercian church in northern Burgundy which has been dated approximately to the mid-12th century. The building has flying buttresses which appear to belong to the original building campaign, although this structural support is not presently believed to have been developed until several decades later. Conventional art historical methods have been unable to determine whether the flying buttresses are original or added. Recent examinations point to the possibility that they are part of the original structure. Measurements of the 14C content of the plant material found in the lime mortars of the flying buttresses, the earliest parts of the building, and known reconstructed areas of the abbey were attempted.

Tubbs, Laura Ellen; Kinder, Terryl N.

1990-12-01

398

The role of disseminated calcite in the chemical weathering of granitoid rocks  

USGS Publications Warehouse

Accessory calcite, present at concentrations between 300 and 3000 mg kg-1, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. Calcite occurs as fillings in microfractures, as disseminated grains within the silicate matrix, and as replacement of calcic cores in plagioclase. Flow-through column experiments, using de-ionized water saturated with 0.05 atm. CO2, produced effluents from the fresh granitoid rocks that were dominated by Ca and bicarbonate and thermodynamically saturated with calcite. During reactions up to 1.7 yr, calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates, principally biotite. Mass balance calculations indicate that most calcite had been removed during this time and accounted for 57-98% of the total Ca released from these rocks. Experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution. The lack of excess Ca and alkalinity indicated that calcite had been previously removed by natural weathering. The extent of Ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks. High Ca/Na ratios relative to plagioclase stoichiometries indicate excess Ca in the Yosemite, Loch Vale, and other alpine watersheds in the Sierra Nevada and Rocky Mountains of the western United States. This Ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains. In contrast, Ca/Na flux ratios are comparable to or less than the Ca/Na ratios for plagioclase in the subtropical Panola and tropical Rio Icacos watersheds, in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport-limited weathering. These results indicate that the weathering of accessory calcite may strongly influence Ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces.

White, A. F.; Bullen, T. D.; Vivit, D. V.; Schulz, M. S.; Clow, D. W.

1999-01-01

399

Polymorphs and Hydrates of Acyclovir  

PubMed Central

Acyclovir (ACV) has been commonly used as an antiviral for decades. Although the crystal structure of the commercial form, a 3:2 ACV/water solvate, has been known since 1980s, investigation into the structure of anhydrous ACV has been limited. Here, we report the characterization of four anhydrous forms of ACV and a new hydrate in addition to the known hydrate. Two of the anhydrous forms appear as small needles and are stable to air exposure, whereas the third form is morphologically similar but quickly absorbs water from the atmosphere and converts back to the commercial form. The high-temperature modification is achieved by heating anhydrous form I above 180°C. The crystal structures of anhydrous form I and a novel hydrate are reported for the first time.

LUTKER, KATIE M.; QUINONES, ROSALYNN; XU, JIADI; RAMAMOORTHY, AYYALUSAMY; MATZGER, ADAM J.

2011-01-01

400

Polymorphs and hydrates of acyclovir.  

PubMed

Acyclovir (ACV) has been commonly used as an antiviral for decades. Although the crystal structure of the commercial form, a 3:2 ACV/water solvate, has been known since 1980s, investigation into the structure of anhydrous ACV has been limited. Here, we report the characterization of four anhydrous forms of ACV and a new hydrate in addition to the known hydrate. Two of the anhydrous forms appear as small needles and are stable to air exposure, whereas the third form is morphologically similar but quickly absorbs water from the atmosphere and converts back to the commercial form. The high-temperature modification is achieved by heating anhydrous form I above 180 °C. The crystal structures of anhydrous form I and a novel hydrate are reported for the first time. PMID:21280051

Lutker, Katie M; Quiñones, Rosalynn; Xu, Jiadi; Ramamoorthy, Ayyalusamy; Matzger, Adam J

2011-03-01

401

Hydration of Purines, Pyrimidines, Nucleosides, and Nucleotides.  

National Technical Information Service (NTIS)

Hydration is a major factor determining the structure of deoxyribonucleic acid (DNA). It was therefore of interest to examine the hydration of the molecular constituents of DNA (purines, pyrimidines, nucleosides, nucleotides, and related compounds) and to...

M. Falk

1964-01-01

402

Physical properties of hydrate-bearing sediments  

NASA Astrophysics Data System (ADS)

Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate-bearing sediments. Formation phenomena include pore-scale habit, solubility, spatial variability, and host sediment aggregate properties. Physical properties include thermal properties, permeability, electrical conductivity and permittivity, small-strain elastic P and S wave velocities, shear strength, and volume changes resulting from hydrate dissociation. The magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate-bearing sediments to changes in mechanical, thermal, or chemical boundary conditions. These predictions are vital for mitigating borehole, local, and regional slope stability hazards; optimizing recovery techniques for extracting methane from hydrate-bearing sediments or sequestering carbon dioxide in gas hydrate; and evaluating the role of gas hydrate in the global carbon cycle.

Waite, W. F.; Santamarina, J. C.; Cortes, D. D.; Dugan, B.; Espinoza, D. N.; Germaine, J.; Jang, J.; Jung, J. W.; Kneafsey, T. J.; Shin, H.; Soga, K.; Winters, W. J.; Yun, T.-S.

2009-12-01

403

Compact apparatus for photogeneration of hydrated electrons  

NASA Technical Reports Server (NTRS)

Flash-photolysis instrument generates hydrated electrons and studies their reactions. It has a three-dimensional, multiple-reaction cell and the capacity to produce up to .1 micromole hydrated electron in a single 40 microsec light pulse.

Hart, E.; Schmidt, K.

1970-01-01

404

Physical Properties of Natural Gas Hydrate Deposits.  

National Technical Information Service (NTIS)

Natural gas hydrates form in polar regions and in ocean bottom sediments and they may represent a considerable energy resource. Unfortunately, so little is known about the physical properties of hydrate deposits that it is difficult to develop geophysical...

C. Pearson

1982-01-01

405

Natural Gas Hydrates Update 1998-2000  

EIA Publications

Significant events have transpired on the natural gas hydrate research and development front since "Future Supply Potential of Natural Gas Hydrates" appeared in Natural Gas 1998 Issues and Trends and in the Potential Gas Committee's 1998 biennial report.

David F. Morehouse

2001-04-25

406

Preparation of macroporous lime from natural lime by swelling method with acetic acid for high-temperature desulfurization  

SciTech Connect

To develop a highly active calcium oxide high-temperature desulfurization sorbent, a method of preparation of macroporous calcium oxides from lime was studied. This method is composed of two steps: swelling of the lime and calcination of the swelled sample. Swelling occurred when lime was exposed to the vapor of acetic acid. The swelling resulted from calcium acetate formation in the sample. The swelling rate was at a maximum in the presence of acetic acid and depressed by the presence of water vapor. The swelled sample was converted to macroporous calcium oxide by heating to 850 C. The reactivity of the macroporous calcium oxide for the removal of SO{sub 2} or H{sub 2}S in the presence of H{sub 2}O vapor was higher than that of the calcined raw limestone. In particular, its SO{sub 2} removal capacity and the oxidative character of CaS to CaSO{sub 4} and Cao were greatly improved by this swelling method. These characteristics were also compared with those of a sample prepared from limestone by this swelling method.

Sasaoka, Eiji; Sada, Norimasa; Uddin, M.A. [Okayama Univ. (Japan)] [Okayama Univ. (Japan)

1998-10-01

407

Natural gas hydrates; vast resource, uncertain future  

USGS Publications Warehouse

Gas hydrates are naturally occurring icelike solids in which water molecules trap gas molecules in a cagelike structure known as a clathrate. Although many gases form hydrates in nature, methane hydrate is by far the most common; methane is the most abundant natural gas. The volume of carbon contained in methane hydrates worldwide is estimated to be twice the amount contained in all fossil fuels on Earth, including coal.

Collett, T. S.

2001-01-01

408

Greenhouse gas hydrates in the ocean  

Microsoft Academic Search

CH4 and CO2 hydrates occur in the deep ocean and sea floor sediment. CH4 hydrates are found in enormous quantities along all the continental margins; CO2 hydrates appear to be a transient anomaly. The magnitude of the carbon pool locked in the CH4 hydrate reservoir is not known precisely, but estimates range from 103 to 106 Gt C. Opening of

S. M. Masutani

2004-01-01

409

Methane hydrates and their HF doped analogues  

NASA Astrophysics Data System (ADS)

A computational study is carried out to simulate methane hydrates as well as to know the effect of HF doping on their stability and structure. By using ab initio molecular dynamics simulation interaction of methane with HF doped clathrate hydrates is studied. The total energy profiles present insights into the stability and structure of methane hydrates. The HF doping increases the stability of the methane hydrates without any distortion of the cage when methane is encapsulated in 512 cages.

Mondal, Sukanta; Giri, Santanab; Chattaraj, Pratim Kumar

2013-07-01

410

Long-term field-scale experiment on using lime filters in an agricultural catchment.  

PubMed

The River Yläneenjoki catchment in southwest Finland is an area with a high agricultural nutrient load. We report here on the nutrient removal performance of three on-site lime-sand filters (F1, F2, and F3), established within or on the edge of the buffer zones. The filters contain burnt lime (CaO) or spent lime [CaO, Ca(OH), and CaCO]. Easily soluble lime results in a high pH level (>11) and leads to an efficient precipitation of soluble phosphorus (P) from the runoff. Water samples were taken from the inflow and outflow of each site in different hydrological situations. The length of the monitoring period was 4 yr for F1, 6 yr for F2, and 1.5 yr for F3. F1 and F2 significantly reduced the suspended solids (SS), total P (PTOT), and dissolved reactive P (DRP) in the treated water. The proportional reduction (%) varied but was usually clearly positive. Filter F3 was divided into two equal parts, one containing burnt lime and the other spent lime. Both filter parts removed PTOT and SS efficiently from the water; the burnt-lime part also removed DRP. The mixed-lime part removed DRP for a year, but then the efficiency decreased. The effect of filters on nitrogen compounds varied. We conclude that sand filters incorporating lime can be used together with buffer zones to reduce both P and SS load to watercourses. PMID:22370403

Kirkkala, Teija; Ventelä, Anne-Mari; Tarvainen, Marjo

2012-01-01

411

Introduction to magnesium-enhanced lime flue gas desulfurization: Videotape workbook  

SciTech Connect

This workbook presents an introduction to the chemistry involved in a magnesium-enhanced lime FGD system. It covers the factors affecting the efficiency of magnesium-enhanced lime FGD system operation, emphasizing how an undestanding of the chemistry will help avoid some common problems. The ways in which ion activity and dissolved alkalinity affect sulfur dioxide removal, how relative saturations influence solids formation, and the importance of lime preparation all are explained. This tape is an introduction only; future tapes will cover lime/limestone FGD performance indicators and troubleshooting in more detail.

Not Available

1988-01-01

412

Hydration of highly charged ions.  

PubMed

Based on a series of ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulations, the broad spectrum of structural and dynamical properties of hydrates of trivalent and tetravalent ions is presented, ranging from extreme inertness to immediate hydrolysis. Main group and transition metal ions representative for different parts of the periodic system are treated, as are 2 threefold negatively charged anions. The results show that simple predictions of the properties of the hydrates appear impossible and that an accurate quantum mechanical simulation in cooperation with sophisticated experimental investigations seems the only way to obtain conclusive results. PMID:22298911

Hofer, Thomas S; Weiss, Alexander K H; Randolf, Bernhard R; Rode, Bernd M

2011-08-01

413

Hydration of highly charged ions  

PubMed Central

Based on a series of ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulations, the broad spectrum of structural and dynamical properties of hydrates of trivalent and tetravalent ions is presented, ranging from extreme inertness to immediate hydrolysis. Main group and transition metal ions representative for different parts of the periodic system are treated, as are 2 threefold negatively charged anions. The results show that simple predictions of the properties of the hydrates appear impossible and that an accurate quantum mechanical simulation in cooperation with sophisticated experimental investigations seems the only way to obtain conclusive results.

Hofer, Thomas S.; Weiss, Alexander K.H.; Randolf, Bernhard R.; Rode, Bernd M.

2011-01-01

414

[Hypodermoclysis hydration in the elderly].  

PubMed

Hydration with hypodermoclysis in elderly patients. Hypodermoclysis is a technique which consists in the administration of fluids into the subcutaneous tissue for the treatment of mild to moderate dehydration. The article starts from the case of a 74 year old man that, after a stroke, was unable to eat or drink, and was then hydrated with continuous hypodermoclysis for 45 days, obtaining a recovery of the clinical and psychological conditions. An update of the available knowledge on hypodermoclisis, together with some comments on the clinical case are presented. PMID:23164967

Brugnolli, Anna; Bevilacqua, Anita; Clodig, Majda; Danielis, Matteo

2012-01-01

415

Gas Hydrate and Pore Pressure  

NASA Astrophysics Data System (ADS)

Many efforts have been devoted to quantify excess pore pressures related to gas hydrate dissociation in marine sediments below the BSR using several approaches. Dissociation of gas hydrates in proximity of the BSR, in response to a change in the physical environment (i.e., temperature and/or pressure regime), can liberate excess gas incrising the local pore fluid pressure in the sediment, so decreasing the effective normal stress. So, gas hydrate dissociation may lead to excess pore pressure resulting in sediment deformation or failure, such as submarine landslides, sediment slumping, pockmarks and mud volcanoes, soft-sediment deformation and giant hummocks. Moreover, excess pore pressure may be the result of gas hydrate dissociation due to continuous sedimentation, tectonic uplift, sea level fall, heating or inhibitor injection. In order to detect the presence of the overpressure below the BSR, we propose two approachs. The fist approach models the BSR depth versus pore pressure; in fact, if the free gas below the BSR is in overpressure condition, the base of the gas hydrate stability is deeper with respect to the hydrostatic case. This effect causes a discrepancy between seismic and theoretical BSR depths. The second approach models the velocities versus gas hydrate and free gas concentrations and pore pressure, considering the approximation of the Biot theory in case of low frequency, i.e. seismic frequency. Knowing the P and S seismic velocity from seismic data analysis, it is possibile to jointly estimate the gas hydrate and free gas concentrations and the pore pressure regime. Alternatively, if the S-wave velocity is not availbale (due to lack of OBS/OBC data), an AVO analysis can be performed in order to extract information about Poisson ratio. Our modeling suggests that the areas characterized by shallow waters (i.e., areas in which human infrastructures, such as pipelines, are present) are significantly affected by the presence of overpressure condition. Moreover, the knoweledge of seismic velocities can be considered an powerful tool to detect the overpressure in case that the pore pressure is equal to the hydrostatic pressure plus the 50% of the difference between the lithostatic and the hydrostatic pressure. In conclusions, an accurate analysis of the BSR nature and the pore pressure are required to improve the reliability of the gas-phase estimation for different target, such as gas hydrate and free gas exploitations and environmental studies.

Tinivella, Umberta; Giustiniani, Michela

2014-05-01

416

Thermal and Evolved Gas Behavior of Calcite Under Mars Phoenix TEGA Operating Conditions  

NASA Technical Reports Server (NTRS)

The Mars Phoenix Scout Mission with its diverse instrument suite successfully examined several soils on the Northern plains of Mars. The Thermal and Evolved Gas Analyzer (TEGA) was employed to detect organic and inorganic materials by coupling a differential scanning calorimeter (DSC) with a magnetic-sector mass spectrometer (MS). Martian soil was heated up to 1000 C in the DSC ovens and evolved gases from mineral decomposition products were examined with the MS. TEGA s DSC has the capability to detect endothermic and exothermic reactions during heating that are characteristic of minerals present in the Martian soil. Initial TEGA results indicated the presence of endothermic peaks with onset temperatures that ranged from 675 C to 750 C with corresponding CO2 release. This result suggests the presence of calcite (CaCO3. CaO + CO2). Organic combustion to CO2 is not likely since this mostly occurs at temperatures below 550 C. Fe-carbonate and Mg-carbonate are not likely because their decomposition temperatures are less than 600 C. TEGA enthalpy determinations suggest that calcite, may occur in the Martian soil in concentrations of approx.1 to 5 wt. %. The detection of calcite could be questioned based on previous results that suggest Mars soils are mostly acidic. However, the Phoenix landing site soil pH was measured at pH 8.3 0.5, which is typical of terrestrial soils where pH is controlled by calcite solubility. The range of onset temperatures and calcite concentration as calculated by TEGA is poorly con-strained in part because of limited thermal data of cal-cite at reduced pressures. TEGA operates at <30 mbar while most calcite literature thermal data was obtained at 1000 mbar or higher pressures.

Ming, D.W.; Niles, P.B.; Morris, R.V.; Boynton, W.V.; Golden, D.C.; Lauer, H.V.; Sutter, B.

2009-01-01

417

The role of citrate and phthalate during Co(II) coprecipitation with calcite  

NASA Astrophysics Data System (ADS)

The influence of citrate and phthalate on Co coprecipitation with calcite was investigated using a combination of batch experiments, Fourier-transform infra-red (FT-IR) spectroscopy, and thermogravimetric analysis (TGA) over a wide range of precipitation rates. Steady-state growth conditions (at constant [Ca], [Co], DIC, and pH) were generally achieved within 3-5 h, after which Co(II) partitioning into calcite was evaluated. Only minor differences are observed in the partition coefficient ( Kd) trends with and without citrate and phthalate as a function of calcite precipitation rate except at very low rates. Slight inhibition of calcite growth is observed in the presence of citrate or phthalate, which can be attributed to adsorption at surface sites. TGA curves for samples coprecipitated with citrate show a significant mass loss between 375 and 550 °C, whereas the weight-loss curves for the Co-phthalate coprecipitates are indistinguishable from those of the organic-free Co coprecipitates. This indicates that citrate is incorporated into calcite during calcite crystallization, whereas phthalate is excluded. FT-IR spectra for the sample with citrate show a broad absorption in the range 3700-3100 cm -1, which is attributable to water molecules coordinated to citrate coprecipitated with calcite. The preferential incorporation of citrate over phthalate likely reflects differences in both aqueous speciation and conformation of the carboxylate groups. This new finding may provide new insight to the factors that control the behavior of macromolecules and their incorporation into the structure of calcium carbonate during biomineralization.

Lee, Young J.; Reeder, Richard J.

2006-05-01

418

Coprecipitation of Chromate with Calcite: Batch Experiments and X-ray Absorption Spectroscopy  

SciTech Connect

Batch experiments, combined with in situ spectroscopic methods, are used to examine the coprecipitation of Cr(VI) with calcite, including partitioning behavior, site-specific distribution of Cr on the surface of calcite single crystals, and local coordination of Cr(VI) in the calcite structure. It is found that the concentration of Cr incorporated in calcite increases with increasing Cr concentration in solution. The calculated apparent partition coefficient, K{sub d}*, is highest at low Cr solution concentration, and decreases to a constant value with increasing Cr solution concentration. DIC images of the (1 0 {bar 1} 4) surface of calcite single crystals grown in the presence of CrO{sub 4}{sup 2-}exhibit well-defined growth hillocks composed of two pairs of symmetrically nonequivalent vicinal faces, denoted as + and -, which reflect the orientation of structurally nonequivalent growth steps. Micro-XRF mapping of the Cr distribution over a growth hillock shows preferential incorporation of Cr into the -- steps, which is considered to result from differences in surface structure geometry. XANES spectra confirm that incorporated Cr is hexavalent, and no reduction of Cr(VI) in the X-ray beam was observed up to 2 days at room temperature. EXAFS fit results show the incorporated Cr(VI) has the expected first shell of 4 O at {approx}1.64 {+-} 0.01 {angstrom}, consistent with CrO{sub 4}{sup 2-}. Best fit results show that the second shell is split with {approx}2.5 Ca at {approx}3.33 {+-} 0.05 and {approx}2.2 Ca at 3.55 {+-} 0.05 {angstrom}, which confirms the incorporation of chromate into calcite. Consideration of possible local coordination indicates that significant distortion or disruption is required to accommodate CrO{sub 4}{sup 2-}in the calcite structure.

Tang,Y.; Elzinga, E.; Lee, Y.; Reeder, R.

2007-01-01

419

An Investigation Into the use of Calcite Fossils as Alpha Thermochronometers  

NASA Astrophysics Data System (ADS)

Diffusion studies of He in calcite suggest a potential to use carbonates as an alpha thermochronometer (Tc ~ 65°C). These results are all from coarse-grained calcite and dolomite but carbonate mud is a common constituent in many limestones. However, coarse calcite can usually be found in even the most micritic limestones in the form of biotic allochems. We have investigated the suitability of using crinoid columnals and shells of the bivalve Inoceramus for alpha thermochronolgy in limestones. After the death of a crinoid, the high-Mg calcite converts to low-Mg calcite with no loss of optical continuity, and the porosity is filled with syntaxial cement thus becoming permineralized. Bivalves undergo typical diagenesis where the high- Mg calcite converts to low-Mg calcite. Two of four crinoid samples yield reasonable alpha ages: A crinoid from the Thrifty Fm. (Pennsylvanian) in Texas gives an age of 120 Ma (0.7-4.0 ppm U) and one from the Edwardsville Fm. of the Borden Group (Lower Mississippian) in Indiana gives an age of 64 Ma (0.9 ppm U). Each of these results are consistent with the tectonic history of the regions. Crinoid pieces from the New Providence Shale Mbr. of the Borden Fm. (Lower Mississippian) in Kentucky have very low [U] (less than 90 ppb) and give Archean ages. Crinoids from the Hughes Creek Shale (Permian) in Kansas have seemingly robust amounts of U (0.7-2.1 ppm) but this sample also seems to be dominated by common He, yielding Proterozoic ages. Inoceramus from the Burditt Fm. of the Austin Gr. (Upper Cretaceous) in Texas gives an age of 0.5 Ma, suggesting that the closure temperature may be much lower than 65°C. Our preliminary conclusion is that crinoid columnals with more than 500 ppb U may be generally suitable for alpha thermochronology but that the closure temperature of He in Inoceramus shells may be too low for geologic application.

Cox, K. L.; Copeland, P.; Lapen, T. J.; Ausich, W. I.

2006-12-01

420

Hydration mechanisms of mineral trioxide aggregate  

Microsoft Academic Search

Camilleri J. Hydration mechanisms of mineral trioxide aggre- gate. International Endodontic Journal, 40, 462-470, 2007. Aim To report the hydration mechanism of white mineral trioxide aggregate (White MTA, Dentsply, Tulsa Dental Products, Tulsa, OK, USA). Methodology The chemical constitution of white MTA was studied by viewing the powder in polished sections under the scanning electron microscope (SEM). The hydration of

J. Camilleri

2007-01-01

421

Tuning ionic liquids for hydrate inhibition.  

PubMed

Pyrrolidinium cation-based ionic liquids were synthesized, and their inhibition effects on methane hydrate formation were investigated. It was found that the ionic liquids shifted the hydrate equilibrium line to a lower temperature at a specific pressure, while simultaneously delaying gas hydrate formation. PMID:21547283

Kim, Ki-Sub; Kang, Jeong Won; Kang, Seong-Pil

2011-06-14

422

Using neutron diffraction to investigate mechanical twinning in calcite  

NASA Astrophysics Data System (ADS)

Mechanical twinning in calcite provides one of the most widely used methods for inferring the orientation and magnitude of the stresses and strains that are responsible for natural rock deformation, and yet the strong sensitivity of twinning activity to microstructural variables such as grain size and lattice preferred orientation remains poorly characterized. This reflects the fact that whole sample behaviour, which is what is monitored in conventional rock deformation experiments, does not provide an adequate indicator of the onset and progress of twinning during any given deformation test. Consequently, our understanding of the way that microstructural variables produce their effect is reliant upon inferences made from examination of the deformation microstructures after the experiment. The penetrating nature of neutrons offers a means of circumventing this difficulty. By performing the deformaton test in a neutron beamline then the elastic strains in different lattice directions may be obtained as a function of load. This permits not only the formation of permanent twins themselves to be detected but also allows any precursory phenomena to the formation of those twins to be monitored as the test proceeds. We have performed neutron diffraction experiments of this kind on Carrara marble (grain size 150µm), Solnhofen limestone (grain size 5µm), and a naturally deformed Carrara marble that has a significant lattice preferred orientation. All the experiments were on cylindrical samples 10mm in diameter and about 24mm long, loaded in uniaxial compression to strains of less than 1%, at temperatures in the range 20° to 600°C. The Solnhofen limestone, which does not twin at these conditions, behaves in a linear elastic manner with homogeneous lattice strains parallel to the direction of loading. In the Carrara marble the lattice strains are strongly nonlinear with two sharp changes in the slope of the stress/lattice strain curve occurring at stresses of about 5-10MPa and at about 40-70MPa. The values of these stresses decrease monotonically with increasing temperature and, in the textured marble, depend upon the direction of loading with respect to the lattice preferred orientation. Below the upper of these stresses the deformation is fully recoverable. Examination of the relative magnitude of the lattice strains and changes in diffraction peak intensity indicates that the lower stress corresponds to the onset of elastic twinning and the upper stress to the onset of permanent twinning. In order to recover the stiffness tensor for the elastic twinning we are correlating the neutron diffraction data with Schmid factor (for twinning) maps generated by electron backscattered diffraction.

Schofield, P. F.; Covey-Crump, S. J.

2010-12-01

423

The calcite\\/water interface II. Effect of added lattice ions on the charge properties and adsorption of sodium polyacrylate  

Microsoft Academic Search

The origin of the surface potential of calcium carbonate in aqueous dispersions and the dissolution of calcite in systems containing excess Ca2+ and CO2?3 have been the subjects of this study. In addition, stabilization of calcite particles with an anionic polyelectrolyte (sodium polyacrylate (NaPA)) and the effect on surface potential and dissolution of calcite have been studied. Preferential dissolution of

Rasmus Eriksson; Juha Merta; Jarl B. Rosenholm

2008-01-01

424

Effect of fatty acids, water composition and pH on the wettability alteration of calcite surface  

Microsoft Academic Search

Fatty acids in presence of water film alter calcite surface to oil-wet. The wettability alteration is dependent on the structure of the fatty acids, water composition and pH. Long chain fatty acid (stearic acid), strongly adsorbs onto the calcite surface from “oil phase” (n-C10) in oil\\/water\\/calcite system as indicated by contact angle measurements. On the other hand, short chain fatty

K. A. Rezaei Gomari; A. A. Hamouda

2006-01-01

425

Variable export fluxes and efficiencies for calcite, opal, and organic carbon in the Atlantic Ocean: A ballast effect in action?  

Microsoft Academic Search

Latitudinal variability in export fluxes and efficiencies (ThE) of calcite, opal, and particulate organic carbon (POC) were examined during a basin-scale Atlantic Ocean cruise. A clear relationship between integrated euphotic zone POC and calcite export combined with similarities in average ThE for calcite (0.26), opal (0.31), and POC (0.29) implies a potential association between biomineral and POC export. However, such

Sandy J. Thomalla; Alex J. Poulton; Richard Sanders; Robert Turnewitsch; Patrick M. Holligan; Mike I. Lucas

2008-01-01

426

The thermodynamics and kinetics of calcite crystallization: Baseline for understanding biomineral formation  

NASA Astrophysics Data System (ADS)

Calcite is the most abundant bio-mineral that forms in the nearly ubiquitous presence of aspartic acid-rich organic matrices. This study investigated the interactions of aspartic acid (Asp) with calcite surfaces and the kinetic and thermodynamic effect of Asp on calcite crystallization. The interactions of Asp with calcite {101¯4} faces were examined through dissolution experiments using in situ Fluid Cell AFM and ex situ optical methods. A change in etch pit morphologies on {101¯4} faces after the introduction of Asp suggests that the Asp-calcite crystal face interactions are direction-specific. The effect of Asp on calcite crystallization was examined by characterizing growth spirals in Asp-free and Asp-bearing solutions. In the absence of Asp, measured critical step length scaled linearly with 1/sigma where sigma is the supersaturation. This linear relationship confirmed the Gibbs-Thomson prediction and yielded the step edge free energy for calcite crystallization. After the introduction of Asp, a change in the morphology of growing spirals and a reduction of step edge free energies were observed. These findings demonstrate the possible energetic controls of Asp during calcite biomineralization. Complex kinetic behavior was observed for step advancement in each direction in the absence and presence of Asp. The non-linear dependence of step velocity upon supersaturation was attributed to impurity effect and the kinetic coefficients of step advancement were obtained in Asp-free solutions based upon the models of impurity impact. A comparison of the kinetic data in Asp-free and Asp-bearing solutions suggests that Asp is not a growth inhibitor for calcite crystallization. Rate expressions for spiral growth based upon surface processes and the theories of crystal growth were derived and compared with those based upon chemical affinities of precipitation reactions. An analysis of the relationship between the two types of rate laws demonstrated that affinity-based rate equations only approximate spiral growth under special conditions: growth proceeds by single soured, single spirals at near equilibrium supersaturations. This suggests that, in general, it is not appropriate to deduce growth mechanisms from macroscopic kinetic measurements.

Teng, Hui Henry

427

Gas hydrate cool storage system  

Microsoft Academic Search

This invention is a process for formation of a gas hydrate to be used as a cool storage medium using a refrigerant in water. Mixing of the immiscible refrigerant and water is effected by addition of a surfactant and agitation. The difficult problem of subcooling during the process is overcome by using the surfactant and agitation and performance of the

Mark P. Ternes; Robert J. Kedl

1985-01-01

428

Hydration modeling of calcium sulphates  

Microsoft Academic Search

The CEMHYD3D model has been extended at the University of Twente in the last ten years [1,2]. At present the cement hydration model is extended for the use of gypsum. Although gypsum was present in the model already, the model was not suitable for high contents of gypsum and did not include the transitions between the different calcium sulphate phases

Korte de A. C. J; H. J. H. Brouwers; Hashem Al-Mattarneh; Kamal N. Mustapha; Muhd Fadhil Nuruddin

2008-01-01

429

Hydration of bilayered graphene oxide.  

PubMed

The hydration of graphene oxide (GO) membranes is the key to understand their remarkable selectivity in permeation of water molecules and humidity-dependent gas separation. We investigated the hydration of single GO layers as a function of humidity using scanning force microscopy, and we determined the single interlayer distance from the step height of a single GO layer on top of one or two GO layers. This interlayer distance grows gradually by approximately 1 Å upon a relative humidity (RH) increase in the range of 2 to ?80%, and the immersion into liquid water increases the interlayer distance further by another 3 Å. The gradual expansion of the single interlayer distance is in good agreement with the averaged distance measured by X-ray diffraction on multilayered graphite oxides, which is commonly explained with an interstratification model. However, our experimental design excludes effects connected to interstratification. Instead we determine directly if insertion of water into GO occurs strictly by monolayers or the thickness of GO layers changes gradually. We find that hydration with up to 80% RH is a continuous process of incorporation of water molecules into single GO layers, while liquid water inserts as monolayers. The similarity of hydration for our bilayer and previously reported multilayered materials implies GO few and even bilayers to be suitable for selective water transport. PMID:24922580

Rezania, B; Severin, Nikolai; Talyzin, Alexandr V; Rabe, Jürgen P

2014-07-01

430

Santaclaraite, a new calcium-manganese silicate hydrate from California.  

USGS Publications Warehouse

Santaclaraite, ideally CaMn4(Si5O14(OH))(OH).H2O, occurs as pink and tan veins and masses in Franciscan chert in the Diablo Range, Santa Clara and Stanislaus counties, California. It is associated with four unidentified Mn silicates, Mn-howieite, quartz, braunite, calcite, rhodochrosite, kutnahorite, baryte, harmotome, chalcopyrite and native copper. Santaclaraite is triclinic, space group B1, a 15.633(1), b 7.603(1) , c 12.003(1) A, alpha 109.71(1)o, beta 88.61(1)o, gamma 99.95(1) o, V 1322.0(3) A3; Z = 4. The strongest lines of the X-ray pattern are 7.04(100), 3.003(84), 3.152(80), 7.69(63), 3.847(57) A. Crystals are lamellar to prismatic (flattened on (100)), with good cleavage on (100) and (010); H. 61/2 Dcalc. 3.398 g/cm3, Dmeas. 3.31 (+ or -0.01); optically biaxial negati