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1

Effects of Dolomitic and Calcitic Limes on Strength Development in Mixtures with Two Clay Minerals.  

National Technical Information Service (NTIS)

Conflicting reports about the relative effectiveness of two principal lime types, dolomitic monohydrated and calcitic hydrated, in soil stabilization have resulted in a need to re-evaluate the response to lime stabilization of the reactive components in s...

W. C. Ormsby E. B. Kinter

1972-01-01

2

Bitumen Aging and Hydrated Lime.  

National Technical Information Service (NTIS)

Since the beginning of the 1970s, hopes have been that hydrated lime, beside being a useful antistripping agent, also might work as an inhibitor of bitumen hardening. These expectations appeared to be supported by the results of several laboratory investi...

L. S. Johansson

1998-01-01

3

Stockpiling Hydrated Lime-Soil Mixtures.  

National Technical Information Service (NTIS)

The concept and feasibility of stockpiling and reusing hydrated lime-soil mixtures to stabilize particular areas on stabilization projects after the mixing contractor has departed were examined. In chemical stabilization of subgrades, situations often ari...

C. Sun T. C. Hopkins T. L. Bakcham

2007-01-01

4

Sulfation of calcitic and dolomitic lime mortars in the presence of diesel particulate matter  

NASA Astrophysics Data System (ADS)

The sulfation of four types of calcitic and dolomitic lime mortars exposed to SO2 in the presence of particulate matter from diesel vehicle exhaust emissions has been investigated. The binders mineralogy and mortars texture are the main factors influencing the formation of deleterious sulfate salts. The type of binder also influences the pore size distribution and the total porosity of the mortars: for equal aggregate (quartz or dolomite), dolomitic lime mortars have smaller pores and higher porosity than calcitic ones. During the first 24 h exposure to SO2, calcitic lime mortars undergo a higher weight increase than dolomitic ones due to rapid formation of gypsum on their surface. However, at the end of the sulfation test (10 days), dolomitic mortars show a higher weight increase due to massive formation of epsomite and gypsum, which is facilitated by their higher porosity and the high reactivity of Mg phases in the porous and partially carbonated binder. Control samples (not covered with diesel particulate matter) also develop calcium and magnesium sulfates upon long term exposure to SO2. This is due to the presence of uncarbonated Ca and Mg hydroxides that promote SO2 fixation as sulfates. However, the amount and size of sulfate crystals are significantly smaller than those observed on samples covered with diesel particulate matter. These results show that diesel particulate matter enhances the sulfation of lime mortars and demonstrate that sulfation of dolomitic lime is an important mechanism for the in situ formation of highly soluble and deleterious hydrated magnesium sulfates (epsomite and hexahydrite). The use of dolomitic limes in the conservation of monuments exposed to air pollution in urban environments may therefore pose a significant risk.

Cultrone, G.; Arizzi, A.; Sebastián, E.; Rodriguez-Navarro, C.

2008-12-01

5

Laboratory Investigation of Hydrated Lime as an Antistripping Additive.  

National Technical Information Service (NTIS)

The purpose of this laboratory study was to determine the effectiveness of hydrated lime as an antistripping additive when used in bituminous mixes incorporating aggregates frequently used in such mixes in Virginia. The application of 1% hydrated lime to ...

G. W. Maupin

1983-01-01

6

Effect of calcitic and dolomitic lime on physicochemical properties of a Chilean Andisol  

Microsoft Academic Search

Changes in surface reactivity produced by different types of liming in a Chilean Andisol were determined. Barros Aranas soil with 53% aluminum (Al) saturation and 4.8 pH was incubated with different amounts of calcitic and dolomitic lime. Each cmol of calcitic or dolomitic lime applied per kg of soil increased the pH with 0.13 and 0.16 units, respectively. Consequently, the

M. L. Mora; G. Baeza; C. Pizarro; R. Demanet

1999-01-01

7

Response of eleven forage species to treatment of acid soil with calcitic and dolomitic lime  

Microsoft Academic Search

The cost and difficulty of applying lime on hilly pastures or small forage fields makes it appropriate to devote attention to efficiency of lime utilization. This study evaluated effects of calcitic and dolomitic lime on yield and mineral composition of 11 forage species grown on soil with a low base status of 0.46 cmolc as Ca and 0.18 cmolc as

A. L. Pires; J. L. Ahirichs; C. L. Rhykerd

1992-01-01

8

Hybrid ryegrass response to acid soil treatment with calcitic and dolomitic lime  

Microsoft Academic Search

Since ryegrass (Lolium sp.) is a widely grown cool?season forage grass, its magnesium concentration is of special interest to ruminant livestock producers. This study was conducted to investigate the effect of calcitic or dolomitic lime addition on dry matter yield and mineral composition of hybrid ryegrass, Lolium (multiflorum x perenne x perenne) grown in eight acidic soils. Each soil received

A. L. Pires; J. L. Ahlrichs; C. L. Rhykerd

1991-01-01

9

Furnace injection of pressure hydrated lime  

Microsoft Academic Search

Pressure-hydrators are used to produce a highly reactive sorbent with a surface area and pore size distribution which enables maximum utilization of available calcium. The hydrator vessel is operated at pressures of 90 to 150 psig with temperatures up to 300°F. Upon expulsion of the reacted quicklime\\/saturated steam mix from the hydrator, water trapped inside the pore network of the

G. F. Weber; M. H. Bobman; T. P. Dorchak

1985-01-01

10

Sulfation of calcitic and dolomitic lime mortars in the presence of diesel particulate matter  

Microsoft Academic Search

The sulfation of four types of calcitic and dolomitic lime mortars exposed to SO2 in the presence of particulate matter from diesel vehicle exhaust emissions has been investigated. The binders mineralogy\\u000a and mortars texture are the main factors influencing the formation of deleterious sulfate salts. The type of binder also influences\\u000a the pore size distribution and the total porosity of

G. Cultrone; A. Arizzi; E. Sebastián; C. Rodriguez-Navarro

2008-01-01

11

Furnace Injection of Pressure Hydrated Lime.  

National Technical Information Service (NTIS)

Pressure-hydrators are used to produce a highly reactive sorbent with a surface area and pore size distribution which enables maximum utilization of available calcium. The hydrator vessel is operated at pressures of 90 to 150 psig with temperatures up to ...

G. F. Weber M. H. Bobman T. P. Dorchak

1985-01-01

12

Effects of direct land application of calcitic lime and lime- and cement kiln dust-sanitized biosolids on the chemical and spectroscopic characteristics of soil lipids  

SciTech Connect

To determine the extent to which applications of calcitic lime and sanitized biosolids affect the quality of soil organic matter (SOM), lipids extracted from an unamended soil (CON) and from soils amended with calcitic lime (CAL), and lime (LSB)- and cement kiln dust (CDB)-sanitized biosolids were characterized by chemical analysis and Pyrolysis-Gas chromatography (Py-GC). From diethyl ether (DEE) and CHCl[sub 3] soluble lipids, and from weight ratios of the extracts, the organic matter in the soil amended with CDB-treated biosolids seemed to be more biodegraded and biochemically inert than the organic matter in soils that received LSB-treated biosolids and calcitic lime and that in the control soil.

Dinel, H.; Schnitzer, M.; Pare, T.; Topp, E. (Agriculture and AgriFood Canada, Ottawa, Ontario (Canada)); Lemee, L.; Ambles, A. (Univ. de Poitiers (France). Lab. de Chimie); Pelzer, N. (Univ. du Quebec, Montreal (Canada))

1999-05-01

13

Kinetic study of hydrated lime reaction with HCl.  

PubMed

Hydrochloride (HCl) is an acidic pollutant present in the flue gas of most municipal or hazardous waste incinerators. Hydrated lime (Ca(OH)2) is often used as a dry sorbent for injection in a spray reactor to remove HCI. However, due to the short residence time encountered, this control method has generally been found to have low conversion efficiencies which results in the high lime usage and generates large amount of fly ash as solid wastes. A fundamental study was carried outto investigate the kinetics of HCl-lime reaction under simulated flue gas conditions in order to better understand the process thereby providing a basis for an optimized lime usage and reduced fly ash production. The initial reaction rate and conversion of three limes were studied using a thermogravimetric analyzer by varying the gas flow rate, temperature (170-400 degrees C), and HCI concentrations (600-1200 mg/m3) as well as the associated particle size and surface area of the limes. The initial lime conversions were found to rely mostly on the residence time, while the ultimate lime conversions were strongly influenced by temperature and the reaction products. CaOHCI was found to be the primary product in most cases, while for one specific lime, CaCl2 was the ultimate conversion product after an extended time period. The true utilization of lime in flue gas cleanup is thus higher when CaOHCl is considered as the final product than those based on CaCl2 as the final product, which has been commonly used in previous studies. The initial reaction was controlled by diffusion of HCl in gas phase and the subsequent reaction by gaseous diffusion through the developing product layer. Increasing the HCI concentration raised the initial rate as well as conversion. However, overloading the lime with excessive HCI caused clogging at its surface and a drop in the ultimate conversion. Limes with smaller particle diameters and higher surface areas were found to be more reactive. The effect of gas-phase mass transfer was minimized when an optimum flow rate was chosen, and in the absence of internal diffusion the reaction was found to be first order with respect to HCI concentration. PMID:12831043

Yan, Rong; Chin, Terence; Liang, David Tee; Laursen, Karin; Ong, Wan Yean; Yao, Kaiwen; Tay, Joo Hwa

2003-06-01

14

Hydrated lime for metals immobilization and explosives transformation: Treatability study.  

PubMed

Fragmentation grenades contain Composition B (RDX and TNT) within a steel shell casing. There is the potential for off-site migration of high explosives and metals from hand grenade training ranges by transport in surface water and subsurface transport in leachate. This treatability study used bench-scale columns and mesocosm-scale laboratory lysimeters to investigate the potential of hydrated lime as a soil amendment for in situ remediation of explosives and metals stabilization in hand grenade range soils. Compared to the unamended soil there was a 26-92% reduction of RDX in the leachate and runoff water from the lime treated soils and a 66-83% reduction of zinc in the leachate and runoff water samples; where the hand grenade range metals of concern were zinc, iron, and manganese. The amended soil was maintained at the target pH of greater than 10.5 for optimum explosives decomposition. The treatability study indicated a high potential of success for scale-up to an in situ field study. PMID:22445717

Martin, W Andy; Larson, S L; Nestler, C C; Fabian, G; O'Connor, G; Felt, D R

2012-03-03

15

Use of Hydrated Lime in Bituminous Mixtures to Decrease Hardening of the Asphalt Cement.  

National Technical Information Service (NTIS)

When asphaltic cement hardens, cracking and raveling occur which cause deterioration of the pavement. It was found that the addition of hydrated lime in bituminous mixtures decreases the rate of hardening of the asphalt, thereby, prolonging the life of th...

C. V. Chachas

1971-01-01

16

Sludge ash/hydrated lime on the geotechnical properties of soft soil.  

PubMed

In this study, an effort to improve the properties and strength of soil, sewage sludge ash (SSA) and hydrated lime are applied to stabilize soft cohesive subgrade soil. Five different ratios (in weight percentage), 0%, 2%, 4%, 8%, and 16%, of sludge ash/hydrated lime are proposed for mixture with cohesive soil. Then, the effects of the different proportions of SSA/hydrated lime on soft cohesive soil are studied. Test results indicate that the unconfined compressive strength of specimens with additives was raised from three to seven times better than that of the untreated soil, and swelling behaviors were also effectively reduced for those specimens. Results of triaxial compression test indicate that the shear strength parameter, c, rose with an increased amount of additives and improved from 30 to 50-70kPa. On the whole, SSA/hydrated lime could particularly improve the geotechnical properties of cohesive subgrade soil. PMID:17141407

Lin, Deng-Fong; Lin, Kae-Long; Hung, Min-Jui; Luo, Huan-Lin

2006-11-06

17

Properties of waste soil—hydrated lime composite  

NASA Astrophysics Data System (ADS)

There are vast zones of clay soils which are generally extracted up to 3m deep (active layer). Owing to humidity variations throughout the year, this type of soil causes much damage to structures due to continuous changes in volume. Very often the clay is discarded and substituted by inert materials at the construction stage. The use of hydrated lime with this type of soil is a treatment that aims to inhibit the already volumetric instability by using the resulting mixture as inert material (Nelson, J.D., Miller, D.J.: Expansive Soils, Problems and Practice in Foundation and Pavement Engineering. John Wiley & Sons, Inc., USA, (1992)). Additionally, it is known that such a mixture also improves the strength properties, and it is possible to use it as a resistant inert composite, at low cost, for construction material. Nevertheless, due to the lack of tracking of this composite over time, safety issues related to the durability of such properties are uncertain. Because of the above, in this work, the composite was subjected to a constant exposure to temperature to simulate the evolution process of the composition on a laboratory scale, assuming that the acquired properties originate from the mineralogical composition created at the time of the sample. The permanence of such composition is associated to the properties acquired since the beginning.

López-Lara, T.; Horta-Rangel, J.; Hernández-Zaragoza, J. B.; Castaño, V. M.

2006-06-01

18

Survival of Cryptosporidium parvum oocysts in the presence of hydrated lime.  

PubMed

To investigate the effects of hydrated lime on the survival of Cryptosporidium oocysts, the percentage viability of oocysts was assessed using fluorescent in situ hybridisation. In the absence of lime and with lime at a concentration of 1 per cent, there was a gradual decline in oocyst viability during the 10-day trial. Although the addition of 5 or 10 per cent lime caused the total number of oocysts to decrease, there appeared to be an increase in the proportion of potentially viable oocysts. PMID:20208077

Zintl, A; Keogh, B; Ezzaty-Mirhashemi, M; De Waal, T; Scholz, D; Mulcahy, G

2010-03-01

19

Effects of hydrated lime and quicklime on the decay of buried human remains using pig cadavers as human body analogues  

Microsoft Academic Search

Recent casework in Belgium involving the search for human remains buried with lime, demonstrated the need for more detailed understanding of the effect of different types of lime on cadaver decomposition and its micro-environment. Six pigs (Sus scrofa) were used as body analogues in field experiments. They were buried without lime, with hydrated lime (Ca(OH)2) and with quicklime (CaO) in

Eline M. J. Schotsmans; John Denton; Jessica Dekeirsschieter; Tatiana Ivaneanu; Sarah Leentjes; Rob C. Janaway; Andrew S. Wilson

20

Lake liming in different types of acid lakes using various types of calcite powders and methods  

Microsoft Academic Search

Results from experiments show that instant dissolution efficiency of calcite powder increases with finer particles, and that initial dissolution efficiency decreases with and increased dose. The Sverdrup model predicts and the results show that the dissolution efficiency is dependent on pH, dose, depth and grinding. Dry application can reduce the dissolution efficiency by 40% in relation to a well slurried

H. Sverdrup; P. Warfvinge

1988-01-01

21

[Bactericidal effect of hydrated lime in aqueous solution].  

PubMed

This study determined the bactericidal effect of the supernatants of saturated solutions of common lime and of micronized calcium hydroxide (Ca(OH)2) (1500 mg/L), which was used as a control, compared with disinfectants made of solutions of 0.33% colloidal silver (0.0016 mg/L), toluene sulfachloramine (41 mg/L) with sodium bicarbonate (9 mg/L), and sodium hypochlorite (5 mg/L). The test involved four strains of Vibrio cholerae 01, V. parahaemolyticus, Escherichia coli, Salmonella typhimurium, Shigella flexneri, Sh. sonnei, and Sa. enterititidis. These bacteria were inoculated into the bactericidal substances listed above and, after different incubation times, the number of surviving bacteria was determined in vitro by using a counting plate. The results were expressed in colony-forming units (CFU). An in situ estimate was made of the amount of V. cholerae on 35 strawberries and 35 radishes (having a weight of about 10 g per unit) after they were washed under a flow of potable water, submerged in the supernatant of the saturated lime solution (1.5 g/L), or both. The greatest bactericidal effect was obtained against V. cholerae 01 and was observed in 3 minutes. Other enterobacteria were resistant to the effect for up to 30 minutes. PMID:7779285

Muñoz Ruiz, C; Collazo Ponce, A; Alvarado, F J

1995-04-01

22

Effects of three forms of nitrogen fertilizer, phosphorus, and hydrated lime on abandoned mine land reclamation  

Microsoft Academic Search

Three field experiments were established to study the effects of ammonium nitrate (NHâNOâ), sodium nitrate (NaNOâ), and nitroform (UF), in combinations with hydrated lime and triple superphosphate (TSP), on selected properties and revegetation of mine soils associated with the Little Clarksburg and Upper Freeport coals. The three experimental areas were extremely acid, pH 4.1 or less, and devoid of vegetation.

J. C. Vandevender; J. C. Sencindiver

1982-01-01

23

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

24

Iron blast furnace slag/hydrated lime sorbents for flue gas desulfurization.  

PubMed

Sorbents prepared from iron blast furnace slag (BFS) and hydrated lime (HL) through the hydration process have been studied with the aim to evaluate their reactivities toward SO2 under the conditions prevailing in dry or semidry flue gas desulfurization processes. The BFS/HL sorbents, having large surface areas and pore volumes due to the formation of products of hydration, were highly reactive toward SO2, as compared with hydrated lime alone (0.24 in Ca utilization). The sorbent reactivity increased as the slurrying temperature and time increased and as the particle size of BFS decreased; the effects of the liquid/solid ratio and the sorbent drying conditions were negligible. The structural properties and the reactivity of sorbent were markedly affected by the BFS/HL ratio; the sorbent with 30/70 ratio had the highest 1 h utilization of Ca, 0.70, and SO2 capture, 0.45 g SO2/g sorbent. The reactivity of a sorbent was related to its initial specific surface area (Sg0) and molar content of Ca (M(-1)); the 1 h utilization of Ca increased almost linearly with increasing Sg0/M. The results of this study are useful to the preparation of BFS/HL sorbents with high reactivity for use in the dry and semidry processes to remove SO2 from the flue gas. PMID:15382877

Liu, Chiung-Fang; Shih, Shin-Min

2004-08-15

25

Natural organic matter and the formation of calcium-silicate-hydrates in lime-stabilized smectites: A thermal analysis study  

Microsoft Academic Search

Processes accounting for the negative effects of soil organic matter on strength development in lime-stabilized soils are not clearly understood. We used heat-flow differential scanning calorimetry and thermogravimetry to elucidate how natural organic matter (NOM) content and source influences the formation of calcium-silicate-hydrates (CSHs) in lime-stabilized smectites. The formation of CSH, was strongly correlated with strength (r?0.95) and decreased with

Omar R. Harvey; John P. Harris; Bruce E. Herbert; Eric A. Stiffler; Stephen P. Haney

2010-01-01

26

[Use of hydrated lime for disinfection of sewage sludge containing Salmonella typhimurium and Ascaris suum as model pathogens].  

PubMed

Hydrated lime was lethal to the strain of Salmonella typhimurium (Sk 14/39) after 60 min of exposure. In the control without addition of hydrated lime this strain was still viable after 168 hours, counting 6.1 x 10(5) pathogens/l ml sludge. 168-hr disinfection of primary sludges with 10 g/l hydrated lime showed no significant reduction in the viability of Ascaris suum eggs. In three experiments, the number of viable eggs was reduced only by 3.6%. Indicator microorganisms, except psychrophilic ones that survive for only 24 hr, were destroyed after 60 min of exposure. The temperature of stabilized sludges did not vary considerably during experiments, ranging between 21 and 25 degrees C. With the addition of Ca(OH)2, sludge pH increased to the values for COD, organic matters and total nitrogen were reduced throughout the experiments. The values for sludge dry residues remained unchanged. PMID:8966964

Plachý, P; Juris, P; Plachá, I; Venglovský, J

1996-08-01

27

Engineering properties of water/wastewater-treatment sludge modified by hydrated lime, fly ash and loess.  

PubMed

The purpose of this research was to present engineering properties of modified sludge from water/wastewater treatment by modifiers such as hydrated lime, loess, and fly ash. The proper mixing ratio was determined to hold the pH of the modified sludge above 12.0 for 2 h. Laboratory tests carried out in this research included particle analysis, compaction and CBR, SEM and X-ray diffraction, unconfined compression test, permeability test, and TCLP test. The main role of lime was to sterilize microorganisms in the sludge. The unconfined strength of the modified sludge by fly ash and loess satisfied the criteria for construction materials, which was above 100 kPa. The permeability of all the mixtures was around 1.0 x 10(-7) cm/s. Extraction tests for hazardous components in modified sludge revealed below the regulated criteria, especially for cadmium, copper, and lead. The present study suggested that the use of lime, fly ash, and loess be an another alternative to modify or stabilize water/wastewater treatment sludge as construction materials in civil engineering. PMID:12420922

Lim, Sungjin; Jeon, Wangi; Lee, Jaebok; Lee, Kwanho; Kim, Namho

2002-10-01

28

Effects of hydrated lime and quicklime on the decay of buried human remains using pig cadavers as human body analogues.  

PubMed

Recent casework in Belgium involving the search for human remains buried with lime, demonstrated the need for more detailed understanding of the effect of different types of lime on cadaver decomposition and its micro-environment. Six pigs (Sus scrofa) were used as body analogues in field experiments. They were buried without lime, with hydrated lime (Ca(OH)(2)) and with quicklime (CaO) in shallow graves in sandy loam soil in Belgium and recovered after 6 months of burial. Observations from these field recoveries informed additional laboratory experiments that were undertaken at the University of Bradford, UK. The combined results of these studies demonstrate that despite conflicting evidence in the literature, hydrated lime and quicklime both delay the decay of the carcass during the first 6 months. This study has implications for the investigation of clandestine burials and for a better understanding of archaeological plaster burials. Knowledge of the effects of lime on decomposition processes also has bearing on practices involving burial of animal carcasses and potentially the management of mass graves and mass disasters by humanitarian organisations and DVI teams. PMID:22030481

Schotsmans, Eline M J; Denton, John; Dekeirsschieter, Jessica; Ivaneanu, Tatiana; Leentjes, Sarah; Janaway, Rob C; Wilson, Andrew S

2011-10-24

29

DISPOSAL, RECYCLE, AND UTILIZATION OF MODIFIED FLY ASH FROM HYDRATED LIME INJECTION INTO COAL-FIRED UTILITY BOILERS  

EPA Science Inventory

The paper gives results of an assessment of the disposal, utilization, and recycle os a modified fly ash from the injection of hydrated lime into a coal-fired utility boiler. The process, developed as a low-cost alternative for achieving moderate degrees of SO2 control at coal-fi...

30

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

31

Utilization of calcite and waste glass for preparing construction materials with a low environmental load.  

PubMed

In this study, porous calcite materials are hydrothermally treated at 200 °C using powder compacts consisting of calcite and glasses composed of silica-rich soda-lime. After treatment, the glasses are converted into calcium aluminosilicate hydrates, such as zeolite phases, which increase their strength. The porosity and morphology of new deposits of hydrothermally solidified materials depend up on the chemical composition of glass. The use of calcite and glass in the hydrothermal treatment plays an important role in the solidification of calcite without thermal decomposition. PMID:21794973

Maeda, Hirotaka; Imaizumi, Haruki; Ishida, Emile Hideki

2011-07-26

32

Modeling dry-scrubbing of gaseous HCl with hydrated lime in cyclones with and without recirculation.  

PubMed

A mathematical model describing the dry-scrubbing of gaseous hydrogen chloride (HCl) with solid hydrated lime particles (Ca(OH)(2)) was developed and experimentally verified. The model applies to cyclone systems with and without recirculation, where reaction and particle collection occurs in the same processing unit. The Modified Grain Model was selected to describe the behavior of the reaction process and it was assumed that the gas and the solid particles flow in the reactor with a plug flow. In this work, this behavior is approximated by a cascade of N CSTRs in series. Some of the model parameters were estimated by optimization taking into account the experimental results obtained. A good agreement was observed between the experimental results and those predicted by the model, where the main control resistance is the diffusion of the gaseous reactant in the layer of solid product formed. PMID:20185231

Chibante, Vania G; Fonseca, Ana M; Salcedo, Romualdo R

2010-01-28

33

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

34

Trichloroethylene decomposition and in-situ dry sorption of Cl-products by calcium oxides prepared from hydrated limes  

Microsoft Academic Search

A comparison of CaOs produced by calcining two types of hydrated lime and calcium carbonate was made for decomposition of trichloroethylene and in-situ dry sorption of the decomposed Cl-products using a lab-scale gas flow type tubular packed bed reactor. About 20mg of CaO sample was mixed with about 2g of Al2O3 particles and packed in the reactor and allowed to

Yoshimi Gotoh; Goichi Iwata; Kyaw Choh; Mitsuhiro Kubota; Hitoki Matsuda

2011-01-01

35

Removal of sulfur dioxide from a continuously operated binary fluidized bed reactor using inert solids and hydrated lime  

Microsoft Academic Search

Sulfur dioxide pollutant was treated in the laboratory with hydrated lime particles having a mean diameter of 9.1?m in a continuously operating binary fluidized bed reactor also containing inert sand particles with sizes varying from 500 to 590?m. The influence of temperature (500, 600, 700 and 800°C) on the reaction medium, of the superficial velocity of the gas (0.8, 1.0

R. Pisani; D. de Moraes

2004-01-01

36

Toward a conceptual model of the calcite surface: hydration, hydrolysis, and surface potential  

NASA Astrophysics Data System (ADS)

Because of a recent increase in interest in the properties of the calcite surface, there has also been an increase in activity toward development of mathematical models to describe calcite's surface behaviour, particularly with respect to adsorption and precipitation. For a mathematical model to be realistic, it must be based on a sound conceptual model of atomic structure at the interface. New observations from high resolution techniques have been combined with previously published data to resolve the apparent conflict with results from electrokinetic studies and to present a picture of what the calcite surface probably looks like at the atomic scale. In ultra-high vacuum (10 -10 mbar), a cleaved surface remains unreacted for at least an hour, but the unreacted surface does not remain as a termination of the bulk structure. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and atomic force microscopy (AFM) show that the outer-most atomic layer relaxes and the surface slightly restructures. In air, dangling bonds are satisfied by hydrolysed water. XPS and time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveal the presence of adsorbed OH and H. In AFM images, the features so typical of calcite, namely, alternate-row offset, pairing and height difference, as well as the consistent dependence of these features on the force and direction of tip scanning, are best explained by OH filling of the vacant O sites created during cleavage on the Ca octahedra. Thus there is solid evidence to indicate the presence of OH and H chemi-sorbed at the termination of the bulk calcite structure. Wet chemical studies, however, show that calcite's pH pzc (zero point of charge) varies with sample history and solution composition. Electrophoretic mobility measurements indicate that the potential-determining ions are not H + and OH -, but rather Ca 2+ and CO 32- (or HCO 3- or H 2CO 30). This apparent conflict is resolved by a slight modification of the electrical double layer (EDL) model. At the bulk termination, hydrolysis species are chemi-bonded. At the Stern layer, adsorption attaches Ca 2+ and CO 32- (or other carbonate species), but the hydrolysis layer keeps them in outer-sphere coordination to the surface. With dehydration, loss of the hydrolysis species results in direct contact between adsorbed ions and the bulk termination, therefore, inner-sphere sorption is equivalent to extension of the three dimensional bulk network, which is precipitation. Attachment of ions with size and charge compatible with Ca and CO 3 likewise results in coprecipitation and solid-solution formation.

Stipp, S. L. S.

1999-10-01

37

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

38

The 7.6-Angstrom Reaction Product in Smectite Clay-Lime Mixtures.  

National Technical Information Service (NTIS)

Several mixtures of hydrated lime with one of three smectite (swelling) clays and water were made. Some mixtures contained fly ash and a little calcite. The strength and mineralogical composition were followed by X-ray diffraction as a function of age. Th...

A. D. Buck K. Mather

1979-01-01

39

Investigation of the Rheology and Microstructure of Hydrated Lime and Sand for Mortars Reference: Abell, A.B., and Nichols, J.M., \\  

Microsoft Academic Search

This paper presents the investigation and characterization of Type S hydrated lime in aged solutions with sand and with subsequent addition of Portland cement. The plastic mortar workability and flow as prescribed by ASTM Standards C207 and C270, the rheological properties, the microstructure of the lime-sand slurries, and the hardened microstructure and properties as prescribed by ASTM Standard C109\\/C 109Mhave

40

Managing Salmonella Typhimurium and Escherichia coli O157:H7 in soil with hydrated lime - An outdoor study in lysimeters and field plots.  

PubMed

An outbreak of Salmonella Typhimurium or E. coli O157:H7 among domestic animals can have great financial consequences for an animal enterprise but also be a threat for public health as there is a risk for transmission of the infection through the environment. In order to minimize disease transmission, it is important to treat not only the affected animals but also the areas on which they have been kept. In the present study, the effect of hydrated lime as a treatment for Salmonella Typhimurium or E. coli O157:H7 contaminated soil was investigated. The study was performed outdoors, in a lysimeter system and in field plots. The soils were spiked with Salmonella Typhimurium and/or E. coli O157:H7 and hydrated lime was added at three different concentrations (0.5, 1 and 2%). Sampling was performed over one month, and the levels of bacteria were analyzed by standard culture methods. In addition, the soil pH was monitored throughout the study. The results showed that application of 0.5-1 kg hydrated lime per m(2) reduced both Salmonella Typhimurium and E. coli O157:H7 numbers to below the detection limit (2 log10 CFU g-1 soil) in 3-7 days. Lower application rates of hydrated lime did not reduce pathogen numbers in the lysimeter study, but in the field plots no E. coli O157:H7 was detected at the end of the four-week study period regardless of hydrated lime application. A recommended strategy for treating a Salmonella Typhimurium or E. coli O157:H7 contaminated soil could therefore be to monitor the pH over the time of treatment and to repeat hydrated lime application if a decrease in pH is observed. PMID:24138468

Nyberg, Karin A; Vinnerås, Björn; Albihn, Ann

2014-01-01

41

Removal of sulfur dioxide from a continuously operated binary fluidized bed reactor using inert solids and hydrated lime.  

PubMed

Sulfur dioxide pollutant was treated in the laboratory with hydrated lime particles having a mean diameter of 9.1 microm in a continuously operating binary fluidized bed reactor also containing inert sand particles with sizes varying from 500 to 590 microm. The influence of temperature (500, 600, 700 and 800 degrees C) on the reaction medium, of the superficial velocity of the gas (0.8, 1.0 and 1.2 m/s), and of the Ca/S molar ratio (1, 2 and 3) on the SO2 removal efficiency were investigated for an inflow gas concentration of 1000 ppm and an initially static bed height of 10.0 cm. The pollutant removal efficiency proved to depend on the temperature and the velocity of the gaseous flow and was strongly influenced by the Ca/S molar ratio. The maximum efficiency of 97.7% was achieved at a temperature of 700 degrees C, a Ca/S ratio of 3 and a velocity of 0.8 m/s. The lime particles' mean residence time was determined by an indirect method, which consisted of integrating the gas concentration curves normalized with respect to time. Based on a calculation of the critical transition velocities, it was concluded that the reactor operated in a bubbling regime under each condition investigated here. PMID:15177758

Pisani, R; de Moraes, D

2004-06-18

42

Paving Asphalt; Reduction of Oxidative Hardening of Asphalts by Treatment with Hydrated Lime-A Mechanistic Study.  

National Technical Information Service (NTIS)

This study showed that lime treatment removes polar, viscosity-building components and reduces the susceptibility of the asphalt to laboratory oxidative hardening. The beneficial effects of lime treatment in reducing asphalt oxidative hardening were attri...

H. Plancher E. L. Green J. C. Petersen

1977-01-01

43

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

2008-11-30

44

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

45

Effect of Planting Site Preparation, Hydrated Lime, and DBCP (1, 2-dibromo-3-chloropropane) on Populations of Macroposthonia xenoplax and Peach Tree Short Life in Georgia.  

PubMed

Annual postplanting applications of 40.7 kg/ha DBCP (1,2-dibromo-3-chloropropane) controlled Macroposthonia xenoplax (Raski, 1952) deGrisse and Loof, 1965 in peach tree short life sites, reduced bacterial canker incidence from 74% to 6%, and inreased the average life of the trees from 3.9 to 6.8 yr for a 7-yr test period. Hydrated lime at 5.5 kg per planting site reduced bacterial canker incidence from 81% 57 % and increased the tree longevity from 2.6 to 6.0 yr. Populations M. xenoplax were inversely correlated with tree longevity. PMID:19295753

Wehunt, E J; Weaver, D J

1982-10-01

46

Effect of Planting Site Preparation, Hydrated Lime, and DBCP (1, 2-dibromo-3-chloropropane) on Populations of Macroposthonia xenoplax and Peach Tree Short Life in Georgia  

PubMed Central

Annual postplanting applications of 40.7 kg/ha DBCP (1,2-dibromo-3-chloropropane) controlled Macroposthonia xenoplax (Raski, 1952) deGrisse and Loof, 1965 in peach tree short life sites, reduced bacterial canker incidence from 74% to 6%, and inreased the average life of the trees from 3.9 to 6.8 yr for a 7-yr test period. Hydrated lime at 5.5 kg per planting site reduced bacterial canker incidence from 81% 57 % and increased the tree longevity from 2.6 to 6.0 yr. Populations M. xenoplax were inversely correlated with tree longevity.

Wehunt, E. J.; Weaver, D. J.

1982-01-01

47

Kinetics of the reaction of hydrated lime with SO{sub 2} at low temperatures: effects of the presence of CO{sub 2}, O{sub 2}, and NOx  

SciTech Connect

The effects of the presence Of CO{sub 2}, O{sub 2}, and NOx in the flue gas on the kinetics of the sulfation of hydrated lime at low temperatures were studied using a differential fixed-bed reactor. When O{sub 2} and NOx were not present together the reaction kinetics was about the same as that under gas mixtures containing SO{sub 2}, H{sub 2}O, and N2 only. When both O{sub 2} and NOx were present, sulfation of hydrated lime was greatly enhanced, forming a large amount of calcium sulfate in addition to calcium sulfite. Sulfation of hydrated lime was well described by the surface coverage model, despite the gas-phase conditions being different. Relative humidity is the major factor affecting the reaction, and its effect was more marked when both O{sub 2} and NOx were present. The kinetic model equations obtained in this work can be used to describe the sulfation of hydrated lime in the low-temperature dry and semidry flue gas desulfurization processes with or without an upstream NOx removal unit.

Liu, C.F.; Shih, S.M. [National Taiwan University, Taipei (Taiwan). Dept. of Chemical Engineering

2008-12-15

48

Summary report on geochemical barrier special study. [Geochemically modify tailings to immobilize contaminants with modifiers such as peat, limestone, and hydrated lime  

SciTech Connect

Long-term management of uranium mill tailings must provide assurance that soluble contaminants will not migrate beyond the Point of Compliance. Conventional management alternatives provide containment through the use of physical barriers which are designed to prevent migration of water through the tailings pile. An alternative is to geochemically modify the tailings to immobilize the contaminants. This investigation examined three potential geochemical modifiers to determine their ability to immobilize inorganic groundwater contaminants found in uranium mill tailings. These modifiers were hydrated lime (Ca(OH)[sub 2]), limestone (CaCO[sub 3]), and a sphaegnum peat moss. This investigation focused on both the geochemical interactions between the tailings and the modifiers, and the effects the modifiers had on the physical strength of the tailings. The geochemical investigations began with characterization of the tailings by X-ray diffraction and scanning electron microscopy. This was followed by batch leaching experiments in which various concentrations of each modifier were added to tailings in shaker flasks and allowed to come to equilibrium. Finally, column experiments were conducted to simulate flow through a tailings pile. The results show that all of the modifiers were at least moderately effective at immobilizing most of the groundwater contaminants of concern at uranium mill tailings sites. Hydrated lime was able to achieve 90 percent concentration reduction of arsenic, cadmium, selenium, uranium, and sulfate when added at a two percent concentration. Limestone was somewhat less effective and peat removed greater than 90 percent of arsenic, lead, uranium, and sulfate at a one percent concentration. The column tests showed that kinetic and/or mass transfer limitations are important and that sufficient time must be allowed for the immobilization reactions to occur.

Not Available

1988-12-01

49

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

50

Watershed Liming  

Microsoft Academic Search

Watershed liming is one method used to increase the alkalinity and reduce the aluminum content of surface waters. To increase the understanding of the processes involved in soil liming and develop a tool for planning and evaluating terrestrial liming operations, a mathematical model was developed. The model includes key soil processes such as limestone dissolution, cation exchange, and the leaching

Per Warfvinge; Harald Sverdrup

1988-01-01

51

ONTARIO'S EXPERIMENTAL LAKE NEUTRALIZATION PROJECT: CALCITE ADDITIONS AND SHORT-TERM CHANGES IN LAKE CHEMISTRY  

Microsoft Academic Search

This paper presents a preliminary analysis of chemical changes associated with the addition of 84 tonnes of fine calcite (mean diameter 9 ?m) in dry form during Aug. 11–16, 1983, to Bowland Lake, a remote and highly acidic lake near Sudbury, Ontario. A Canso water bomber was used to apply the calcite to the lake surface. Immediately following liming, the

L. A. Molot; J. G. Hamilton; G. M. Booth

1984-01-01

52

Hydration, hydration, hydration.  

PubMed

Throughout the world, large numbers of manual workers perform physically demanding labour in conditions of high environmental heat stress. Although the importance of adequate hydration in combating heat stress is universally recognized, studies in a range of worker groups have demonstrated a disturbingly poor hydration level in a high proportion of at-risk workers. Management of work in hot environments traditionally focuses on environmental monitoring, while strategies to promote and ensure good hydration behaviour are often haphazard at best. An example is given of simple guidelines for adequate and appropriate fluid intake and practical recommendations to foster compliance. PMID:20008893

Miller, Veronica S; Bates, Graham P

2009-12-15

53

An integrated study of limestone behavior during calcination and hydration processes  

NASA Astrophysics Data System (ADS)

One of the most important processes in industrial scale, represents the dissociation of carbonates to lime and CO2. This process, called calcination, occur at relative high temperatures (>9000C). Lime rapidly reacts with the water, liberating high amounts of heat producing Ca(OH)2. For the purpose of the present study five samples of different limestones from different quarries from Greece were collected. The aim of the study was to analyze the behavior of the limestones during calcination and test the hydraulic properties of the quick lime. Limestone particles (1.6-2 cm) were reacted in a pre-heated oven at three different temperatures (900, 1050 and 1200oC) for 30 min in order to produce quick lime. Petrographic features of studied limestones were done using secondary electron microscopy (SEM). X-ray diffractometry and Raman micro-spectroscopy were applied in order to identify the carbonate phases (calcite and dolomite) in the studied limestones. Chemical composition of limestones and limes were determined by Atomic absorption spectroscopy (AAS) method. 25 gr of the produced lime were hydrated by adding 100 ml distilled water having a room temperature (~250C) to produce Ca(OH)2 through the exothermic reaction CaO(s) + H2O(l)-Ca(OH)2(aq). We measured the temperature difference in the water until a maximum value is reached; this value represents the reactivity of the produced slaked lime. Chemical composition and reactivity estimation were done following European Standards EN-459-2. The reactivity of quick lime depends on various factors with the most important being the internal structure of the limestone, calcination temperature/duration applied to the limestone, the admixtures such as the MgO content, hard-burned phenomena etc. The treatment of the experimental results suggests the following: i) The (CaO+MgO)Lime value have similar variation for both samples calcined at temperatures of 1050oC (58-90 wt%) and 1200oC (57-94 wt%); whereas the samples calcined at 900oC share a small (CaO+MgO)Lime value (5-17wt%). ii) The limestones calcined at 9000C have the lowest reactivity values in oppose to the samples calcined at 10500C which show the highest reactivity. The temperature rise of the limestone samples calcined at 12000C was lower than that of the 10500C. iii) At constant reactivity rate the water required to complete hydration is lower; for example, the quick lime calcined at temperature of 10500C needs much less water for hydration relative to the equivalent samples at 12000C. A thorough interpretation of our results suggest that the low reactivity values for the samples calcined at 9000C could be due to the low calcination temperature or the calcination time of 30 min was too short to produce enough lime. The differences in hydraulic behavior of the samples calcined at higher temperatures of 12000C probably indicates that the structure of quick lime becomes more dense and compact and the grains recrystallized tending to become larger, leading to reduction of the existing pore space. Consequently, the hydration process cannot entirely proceed into the interior mass of the quick lime requiring more time to be accomplished.

Leontakianakos, George; Baziotis, Ioannis; Kiousis, George; Giavis, Dimitrios; Tsimas, Stamatios

2010-05-01

54

Effect of Portland cement and lime additives on properties of cold in-place recycled mixtures with asphalt emulsion  

Microsoft Academic Search

Due to lack of previous research on applying additives in Cold In-Place Recycling (CIR) mixes in this study, Portland cement and lime were used as additives. The Portland cement was introduced in powder form and lime was utilized as hydrated lime in powder form and lime slurry, and the effects of each additive on properties of CIR mixes has been

Y. Niazi; M. Jalili

2009-01-01

55

Microstructure and rheology of lime putty.  

PubMed

The rheology of lime binders, which is critical in the final performance of lime mortars and plasters, is poorly understood, particularly in its relationship with the microstructure and colloidal characteristics of slaked lime (Ca(OH)(2)) suspensions (i.e., lime putties). Here, the contrasting flow behavior of lime putties obtained upon slaking (hydration) of soft and hard burnt quicklimes (CaO) is compared and discussed in terms of the differences found in particle size, morphology, degree of aggregation, and fractal nature of aggregates as well as their evolution with aging time. We show that lime putties behave as non-Newtonian fluids, with thixotropic and rheopectic behavior observed for hard and soft burnt limes, respectively. Aggregation of portlandite nanoparticles in the aqueous suspension controls the time evolution of the rheological properties of lime putty, which is also influenced by the dominant slaking mechanism, that is, liquid versus vapor slaking in hard and soft burnt quicklimes, respectively. These results may be of relevance in the selection of optimal procedures and conditions for the preparation of lime mortars used in the conservation of historical buildings. PMID:19916534

Ruiz-Agudo, E; Rodriguez-Navarro, C

2010-03-16

56

Phosphorus removal from piggery effluents of varying quality using lime and physico-chemical treatment methods.  

PubMed

The choice of management practices for the treatment of piggery effluent prior to its disposal to waterways or land is governed by the desire to simultaneously minimise the cost of treatment whilst minimising pollution of the environment. Laboratory experiments were conducted to compare the removal of total and total filterable phosphorus (P) (<0.45 microm) from ortho-phosphate solutions or piggery effluent by hydrated lime or lime kiln dust alone, or from recycled piggery effluent by lime and physico-chemical treatment methods. In addition, the ability of lime to remove P from recycled piggery effluent at an intensive piggery was assessed. Most P in lime treated effluent was present in the >0.45 microm fraction because of the presence of unsettled flocs of P impregnated lime. The efficiency of total P removal by hydrated lime and lime kiln dust decreased as effluent quality declined. The efficiency of removal of total filterable P by hydrated lime or lime kiln dust was not affected by effluent quality. Hydrated lime was more efficient in removing P from effluent or ortho-phosphate solutions, but lime kiln dust was more cost effective. More than 95% of total P was removed from recycled piggery effluent when physico-chemical treatment followed settling with or without lime. The physico-chemical treatment decreased total P mainly by decreasing the number of suspended particles in the effluent and by precipitating some total filterable P as iron, aluminium or calcium compounds. PMID:15091694

Weaver, D M; Ritchie, G S

1994-01-01

57

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

58

Mineralogcial Biosignature of High-Magnesian Calcite  

NASA Astrophysics Data System (ADS)

Some dolomite formations are associated with sediments where sulfate reduction is active. In general, sulfate has been considered to inhibit dolomite formation. However, it was also suggested that the reaction products of sulfate reduction, such as increased alkalinity, may play a more important role in increasing the formation rate of dolomite than sulfate does in inhibiting it. We have investigated the effect of sulfide on Mg-Ca carbonate precipitation. Our results show that high-magnesian calcite which contains as much as 34 mol% magnesite can precipitate from solutions with the presence of certain amount of dissolved sulfide and pyrite crystals. These high-magnesian calcites form unusual micro-scale spheres with cracks on them. High- resolution SEM and TEM results show that these spheres are actually composed of a great number of nano- crystals (~50 nm) stacking together with low-angle grain boundaries. Both synthesized and natural high-magnesian calcites indicate that dissolved and solid sulfides can catalyze the Mg incorporation into calcite lattice. We hypothesize that S2- (or HS-) ions and >S2 on pyrite surface will decrease the hydration / slovation energy of magnesium ions and thus promote nucleation and crystallization of the high-magnesian calcite. In nature environment, the sulfide could be related to microbe-induced sulfate reduction at low temperature using organic carbon and methane as electron donors. Such kind of high-magnesium calcite that is rich in light carbon also indicates involvement of sulfate reducing bacteria. This work is supported by NASA Astrobiology Institute (N07-5489).

Zhang, F.; Konishi, H.; Xu, H.; Roden, E. E.

2008-12-01

59

A lime requirement test for maritime Canada, and response time and effect of liming source on soil ph  

Microsoft Academic Search

An experiment was conducted to determine which of the two lime requirement tests (LRT) used in Maritime Canada (Adams?Evans, SMP) are most appropriate, and to evaluate the effect of two sources of limestone (calcitic and dolomitic) on soil pH during a four month incubation period. Four soils, varying in texture from loamy sand to silty loam, and three rates of

P. R. Warman; B. Harnish; T. Muizelaar

1996-01-01

60

Hydration studies of Bentonite clay  

NASA Astrophysics Data System (ADS)

Bentonite clay when hydrated increases its volume several fold to form a pliable mass. X-ray diffraction showed that as hydration increases, the crystalline peaks due to kaolinite, calcite and quartz are gradually replaced by an amorphous background while the crystalline reflections of montmorillonite remain. Hydration is known to occur through the inclusion of the hydroxyl radical within the layered structure of the clay. Small Angle Neutron Scattering (SANS) data on the dry and hydrated clay confirm the water uptake as found from the level of incoherent scattering at higher values of Q.

Desai, Reshma R.; Erwin Desa, J. A.; Aswal, V. K.

2012-06-01

61

Calcite Dissolution in Saline Waters  

NASA Astrophysics Data System (ADS)

The specific effect of ionic strength on the reaction kinetics of calcite dissolution in intermediate to high ionic strength (0.5 < I < 6.0) solutions applicable to natural waters has been investigated using classical free-drift methods where all other parameters (mCa2+, PCO2, and T) have been held constant. Both phosphate-free solutions of potassium chloride (KCl) and sodium chloride (NaCl) as the dominant ionic strength determining salt were investigated where calcium concentrations were held constant in all solutions at approximately 0.010 molal. Reaction rates were found to vary significantly as a function of ionic strength of the reacting solution, which we suggest is due to the lowered activity of water with an increase in ionic strength which decreases the rate of cation hydration. When modeled with the general rate equation, R = k(1-Ømega)n, first-order kinetics (n=1) are sufficient to fit the experimental data. Furthermore, the rate constant (k) appears to be a function of the square root of the ionic strength of the reacting solution. These results may have potential applications to the response of the ocean to acidification by fossil fuel CO2 as well as CO2 sequestration in subsurface saline waters in calcium carbonate-hosted reservoirs.

Finneran, D. W.; Morse, J. W.

2007-12-01

62

Influence of the aggregate quality on the physical properties of natural feebly-hydraulic lime mortars  

Microsoft Academic Search

This paper examines the influence of the shape, average size and calcite content of the aggregate on strength, porosity, water\\u000a absorption, density and capillary suction of natural feebly-hydraulic lime (NHL 2) mortars. Four types of aggregate were analysed\\u000a in order to determine calcite content, particle shape and average particle size. Four different mortar mixes were then designed\\u000a and produced using

S. Pavía; B. Toomey

2008-01-01

63

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

2013-02-05

64

LIMESTONE AND LIME NEUTRALIZATION OF FERROUS IRON ACID MINE DRAINAGE  

EPA Science Inventory

The U.S. Environmental Protection Agency conducted a 2-yr study on hydrated lime and rock-dust limestone neutralization of acid mine drainage containing ferrous iron at the EPA Crown Mine Drainage Control Field Site near Rivesville, West Virginia. The study investigated optimizat...

65

Influence of slag substitution on some properties of sand-lime aerated concrete  

Microsoft Academic Search

The effect of substitution of sand with granulated slag on some properties of sand-lime aerated concrete was investigated. The compressive strength, the hydration kinetics and the nature of the hydration products were studied for samples autoclaved under 8 atm for different periods from 0.5 to 24 h. The results indicate that the substitution of slag leads to a marked increase

S. A. S. El-Hemaly; A. S. Taha; H. El-Didamony

1986-01-01

66

Sewage sludge treatment with lime.  

PubMed

The article describes the application of lime as a method for treatment and hygienisation of sewage sludges with lime products such as quicklime, slake lime and dolomitic lime. As a result of the increase in temperature and pH-value during sludge and lime mixing most pathogenic vectors of disease (i.e. bacteria, worms, viruses and parasites) are reduced in concentration and viability to manufacture a safe product for further application on agricultural land. PMID:10842835

Herbst, B

2000-01-01

67

Material-Related Forensic Analysis and Special Testing: Assessment of Original Free Lime Content of Weathered Iron and Steel Slag.  

National Technical Information Service (NTIS)

The purpose of Work Order No. 96-09-21 is to conduct Thermogravimetric Analysis and either ASTMC 114 total lime content and/or the anhydrous ethylene glycol total lime content determinations. The hydration and dissolution of calcium oxide to form calcium ...

M. Boyle E. Shkolnik

2000-01-01

68

Hydrate detection  

SciTech Connect

Project objectives were: (1) to create methods of analyzing gas hydrates in natural sea-floor sediments, using available data, (2) to make estimates of the amount of gas hydrates in marine sediments, (3) to map the distribution of hydrates, (4) to relate concentrations of gas hydrates to natural processes and infer the factors that control hydrate concentration or that result in loss of hydrate from the sea floor. (VC)

Dillon, W.P.; Ahlbrandt, T.S.

1992-06-01

69

Hydrate detection  

SciTech Connect

Project objectives were: (1) to create methods of analyzing gas hydrates in natural sea-floor sediments, using available data, (2) to make estimates of the amount of gas hydrates in marine sediments, (3) to map the distribution of hydrates, (4) to relate concentrations of gas hydrates to natural processes and infer the factors that control hydrate concentration or that result in loss of hydrate from the sea floor. (VC)

Dillon, W.P.; Ahlbrandt, T.S.

1992-01-01

70

Crystallization of calcite on chitin  

NASA Astrophysics Data System (ADS)

Chitin, a nitrogen-containing polysaccharide which is a major component of the exoskeletons of arthropods, was found to be a substrate favouring the deposition of calcite crystals from stable supersaturated solutions at pH 8.50 and at 25°C. The crystallization was studied at constant solution supersaturation thus making it possible for relatively large amounts of the overgrowth to be formed and be identified exclusively as calcite. The induction periods varied markedly with supersaturation. The apparent order found from kinetics data was n = 2, thus suggesting a surface diffusion-controlled mechanism.

Manoli, F.; Koutsopoulos, S.; Dalas, E.

1997-12-01

71

Pressure effect on magnesian calcite coating calcite and synthetic magnesian calcite seeds added to seawater in a closed system  

Microsoft Academic Search

When pure crystalline calcite seeds are added to supersaturated seawater, precipitation results in a coating which with time equilibrates at atmospheric pressure with seawater and corresponds to a calcite containing probably only 2 or 3% of MgCO 3 (mole fraction). If synthetic crystalline magnesian calcite is added, the surface layer equilibrates not only with respect to seawater but also in

B. Koch; A. Disteche

1984-01-01

72

Zweiachsig erscheinende Calcite und Dolomite  

Microsoft Academic Search

The biaxiality of calcites and dolomites is explained by twin lamellae. The amount of the axial angle depends from the part of volume built up by the lamellae of equal orientation, and from the twin angle. The birefringence is of minor influence.

R. Rath; D. Pohl

1971-01-01

73

Analysis of CaCO3 products from lime solution  

NASA Astrophysics Data System (ADS)

CaCO3 particles derived from limestone are obtained from quarry in Tuwiri Wetan, Tuban, East Java and have been produced by calcination at temperature of 850°C for 6 hours and by dissolving into water for 24 hours to result in a precipitate at the bottom and a layer floating on the top of the lime solution. Characterization of the as received limestone with XRF and ICP showed a very high purity. Further characterization of secondary precipitatin using XRD showed the presence of CaCO3 (calcite) as much as 35% and Ca(OH)2 (calcium hydroxide) 65%, while the secondary layer contained pure CaCO3 (calcite). Analysis using SEM has revealed the presence cubic shape CaCO3 particles.

Arifin, Zaenal; Pratapa, Suminar; Triwikantoro; Darminto

2013-09-01

74

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

75

Dislocation Creep in Magnesium Calcite  

NASA Astrophysics Data System (ADS)

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 content varied from 0.07 to 0.17 mol%. Creep tests were performed at differential stresses from 20 to 160 MPa at 700 to 800° C. Grain sizes before and after deformation were determined from the images obtained from scanning electron microscope (SEM) and optical microscope. Grain sizes are in the range of 5 to 20 microns depending on the HIP time, and decrease with increasing magnesium content. Both BSE images and chemical analysis suggest that all dolomite are dissolved and the Mg distribution is homogeneous through the sample, after 2 hrs HIP. At stresses below 40 MPa, the samples deformed in diffusion region (Coble creep), as described previously by Herwegh. The strength decreases with increasing magnesium content, owing to the difference of grain size. At stresses above 80 MPa, the stress exponent is greater than 3, indicating an increased contribution of dislocation creep. The transition between diffusion to dislocation creep occurs at higher stresses for the samples with higher magnesium content and smaller grain size. Preliminary data suggests a slight increase in strength with increasing magnesium content, but more tests are needed to verify this effect. In a few samples, some strain weakening may have been evident. The activation energy in the transition region (at 80 MPa) is ˜200 KJ/mol with no dependence on magnesium content, agreeing with previous measurements of diffusion creep in natural and synthetic marbles.

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

2003-12-01

76

Crystallization of calcite on chitin  

Microsoft Academic Search

Chitin, a nitrogen-containing polysaccharide which is a major component of the exoskeletons of arthropods, was found to be a substrate favouring the deposition of calcite crystals from stable supersaturated solutions at pH 8.50 and at 25°C. The crystallization was studied at constant solution supersaturation thus making it possible for relatively large amounts of the overgrowth to be formed and be

F. Manoli; S. Koutsopoulos; E. Dalas

1997-01-01

77

Pseudo dissolution of marine calcite  

NASA Astrophysics Data System (ADS)

An enigma exists regarding observations aimed at determining the extent of calcite dissolution on the Ceara Rise in the western equatorial Atlantic. Based on pore-water gradients for Ca, alkalinity, pH, 13C and 14C, a strong case can be constructed that at a depth of 3.3 km about 30% of the calcite rain dissolves [Martin and Sayles, Geochim. Cosmochim. Acta 60 (1996) 243-263; Hales and Emerson, Geochim. Cosmochim. Acta 61 (1997) 501-514; Martin et al., Geochim. Cosmochim. Acta 61 (2000) 1391-1404]. However, benthic chambers deployed at this site record no Ca or alkalinity flux [Jahnke and Jahnke, Geochim. Cosmochim. Acta (2002) in press]. Further, there is no evidence for shell weight loss or shell breakup between 2.8 and 4.1 km water depth on the Ceara Rise [Broecker and Clark, Global Geochem. Cycles (2002) in press]. A possible scenario which accounts for all but the 14C observations [Martin et al., Geochim. Cosmochim. Acta 61 (2000) 1391-1404] is that coatings formed on the calcite are stirred downward into the respiration-CO 2-rich core-top mixed layer and there redissolve. We term this phenomenon pseudo dissolution.

Broecker, W. S.; Clark, Elizabeth

2003-03-01

78

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

2009-09-26

79

Fly ash with high sulphate and chloride content: solidification and stabilisation using hydraulic lime.  

PubMed

This paper examines the solidification/stabilisation treatment of two fly ash samples from a Municipal Solid Waste (MSW) incineration plant using a lime-pozzolan binder. The two examined fly ash samples were characterised by a high chloride and sulphate content and by a significant concentration of heavy metals. The effective development of hydrate phases during hydration of hydraulic lime-fly ash mixtures allows us to stabilise numerous pollutants in hardened pastes. The release of pollutants into the leachants is limited and decreases with the curing period of the pastes. PMID:12407913

Ubbrìaco, Pietro; Bruno, Paolo; Traini, Angela

2002-09-01

80

Precipitation of different calcite crystal morphologies in the presence of sodium stearate.  

PubMed

The influence of sodium stearate (NaSt) on the precipitation of calcium carbonate during the semicontinuous process of slaked lime carbonation was studied in the systems in which process parameters, like concentration of total dissolved calcium, temperature, CO(2) flow rate and initial addition rate of slaked lime, were controlled. It was found that calcite was the only calcium carbonate polymorph that appeared under the investigated experimental conditions, while FT-IR spectroscopy and thermogravimetric analysis of samples confirmed the presence of stearate on the surface of precipitated calcium carbonate (PCC). Specific surface area of PCC increased with increasing stearate content: the highest value, s = 52.8 m(2) g(-1), was obtained at t = 20 degrees C, c(tot) = 17.0 mmol dm(-3) and the stearate content of m(NaSt)/m(CaO) = 0.03. It was also found that hydrophobic calcite crystals in the form of rhombohedral and scalenohedral morphology can be produced at m(NaSt)/m(CaO) > 0.01. The exception is the case of nanosized PCC production, when much higher concentration of NaSt is needed, m(NaSt)/m(CaO) = 0.22. Minimal amount of stearate necessary to build up the monolayer and corresponding cross sectional area of one stearate molecule were estimated for the obtained calcite morphologies. PMID:18848702

Ukrainczyk, Marko; Kontrec, Jasminka; Kralj, Damir

2008-09-23

81

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

82

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

83

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

84

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

85

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

86

COMBINATION LIMESTONE-LIME NEUTRALIZATION OF FERROUS IRON ACID MINE DRAINAGE  

EPA Science Inventory

Studies were conducted on ferrous-iron acid mine drainage (AMD) treatment by a two-step neutralization process in which rock-dust limestone was mixed with the influent AMD and then hydrated lime was added in a polishing reactor. This combination treatment process resulted in reag...

87

Combination Limestone-Lime Neutralization of Ferrous Iron Acid Mine Drainage.  

National Technical Information Service (NTIS)

Studies were conducted on ferrous-iron acid mine drainage (AMD) treatment by a two-step neutralization process in which rock-dust limestone was mixed with the influent AMD and then hydrated lime was added in a polishing reactor. This combination treatment...

R. C. Wilmoth

1978-01-01

88

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

89

Hydrothermal calcite in the Elephant Moraine  

SciTech Connect

In the course of geologic mapping of the Elephant Moraine on the east antarctic ice sheet, Faure and Taylor (1985) collected several specimens of black botryoidal calcite, composed of radiating acicular crystals that resemble stromatolites. Calcite from this and other specimens is significantly enriched in strontium-87 (the strontium-87/strontium-86 ratio equals 0.71417 +/- 0.00002), carbon-12 (delta carbon-13 equals -22.9 parts per thousand, PDB standard) and oxygen-16 (delta oxygen-18 equals -21.1 parts per thousand, standard mean ocean water) compared with calcite of marine origin. The enrichment in carbon-12 is similar to that of calcite associated with coal in the Allan Hills. The enrichment in oxygen-16 indicates that the calcite from the Elephant Moraine could only have precipitated in isotopic equilibrium with glacial melt water. Therefore, the temperature at which the black calcite precipitated from water of that isotope composition was about 85/sup 0/C. A temperature of this magnitude implies that the black calcite formed as a result of volcanic activity under the east antarctic ice sheet. The enrichment of the black calcite in carbon-12 suggests that it formed in part from carbon dioxide derived from the coal seams of the Weller Formation in the Beacon Supergroup. The isotopic composition of strontium in the black calcite is similar to that of carbonate beds and concretions in the Beacon rocks of southern Victoria Land. A volcanic-hydrothermal origin is also consistent with the very low total organic carbon content of 0.15% in the calcite.

Faure, G.; Taylor, K.S.; Jones, L.M.

1986-01-01

90

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

91

Specific effects of background electrolytes on the kinetics of step propagation during calcite growth  

NASA Astrophysics Data System (ADS)

The mechanisms by which background electrolytes modify the kinetics of non-equivalent step propagation during calcite growth were investigated using Atomic Force Microscopy (AFM), at constant driving force and solution stoichiometry. Our results suggest that the acute step spreading rate is controlled by kink-site nucleation and, ultimately, by the dehydration of surface sites, while the velocity of obtuse step advancement is mainly determined by hydration of calcium ions in solution. According to our results, kink nucleation at acute steps could be promoted by carbonate-assisted calcium attachment. The different sensitivity of obtuse and acute step propagation kinetics to cation and surface hydration could be the origin of the reversed geometries of calcite growth hillocks (i.e., rate of obtuse step spreading < rate of acute step spreading) observed in concentrated (ionic strength, IS = 0.1) KCl and CsCl solutions. At low IS (0.02), ion-specific effects seem to be mainly associated with changes in the solvation environment of calcium ions in solution. With increasing electrolyte concentration, the stabilization of surface water by weakly paired salts appears to become increasingly important in determining step spreading rate. At high ionic strength (IS = 0.1), overall calcite growth rates increased with increasing hydration of calcium in solution (i.e., decreasing ion pairing of background electrolytes for sodium-bearing salts) and with decreasing hydration of the carbonate surface site (i.e., increasing ion pairing for chloride-bearing salts). Changes in growth hillock morphology were observed in the presence of Li +, F - and SO42-, and can be interpreted as the result of the stabilization of polar surfaces due to increased ion hydration. These results increase our ability to predict crystal reactivity in natural fluids which contain significant amounts of solutes.

Ruiz-Agudo, Encarnación; Putnis, Christine V.; Wang, Lijun; Putnis, Andrew

2011-07-01

92

A study on engineering characteristics of asphalt concrete using filler with recycled waste lime.  

PubMed

This study focuses on determining the engineering characteristics of asphalt concrete using mineral fillers with recycled waste lime, which is a by-product of the production of soda ash (Na(2)CO(3)). The materials tested in this study were made using a 25%, 50%, 75%, and 100% mixing ratio based on the conventional mineral filler ratio to analyze the possibility of using recycled waste lime. The asphalt concretes, made of recycled waste lime, hydrated lime, and conventional asphalt concrete, were evaluated through their fundamental engineering properties such as Marshall stability, indirect tensile strength, resilient modulus, permanent deformation characteristics, moisture susceptibility, and fatigue resistance. The results indicate that the application of recycled waste lime as mineral filler improves the permanent deformation characteristics, stiffness and fatigue endurance of asphalt concrete at the wide range of temperatures. It was also determined that the mixtures with recycled waste lime showed higher resistance against stripping than conventional asphalt concrete. It was concluded from various test results that a waste lime can be used as mineral filler and, especially, can greatly improve the resistance of asphalt concrete to permanent deformation at high temperatures. PMID:17408942

Sung Do, Hwang; Hee Mun, Park; Suk keun, Rhee

2007-04-03

93

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

94

Thermodynamic and kinetic description of dolomitization of calcite and calcitization of dolomite (dedolomitization)  

Microsoft Academic Search

Replacement dolomitization of calcite is a chemical process where dolomite comes to occupy the spatial position and volume\\u000a of calcite through simultaneous dissolution of calcite and precipitation of dolomite without effecting a volume change in\\u000a the crystalline portion of the rock. Dissolution and precipitation occur adjacent to one another in conjunction with a narrow\\u000a aqueous boundary film width which separates

James A. Dockal

1988-01-01

95

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

2009-07-14

96

Agricultural Lime in Central Mississippi.  

National Technical Information Service (NTIS)

The 1974 Mississippi Legislature authorized the establishment of a State-operated agricultural lime plant to be located in South Mississippi. The Mississippi Geological Survey was designated as the agency to select the location of the plant site. Limeston...

A. R. Bicker J. H. May

1976-01-01

97

Lime Silico-Phosphate Cement.  

National Technical Information Service (NTIS)

A quick setting lime silico-phosphate cement prepared by reacting Wollastonite (CaSiO3) and buffered phosphoric acid is described. The cement has particular utility in highway patching operations. (Author)

C. E. Semler

1972-01-01

98

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

99

Magnesian calcite sorbent for carbon dioxide capture  

Microsoft Academic Search

Magnesian calcite with controlled properties was synthesized for the removal of carbon dioxide. The results from characterization, reactivity and CO2 capture capacity for different synthesis conditions are reported. The magnesian calcite samples (CaCO3:MgCO3) were synthesized by the coprecipitation of specific amounts of commercially available CaO and MgO by carbon dioxide. Characterization was done with BET, SEM\\/EDS, particle size analysis and

James C. Mabry; Kanchan Mondal

2011-01-01

100

The Elimination of Sodium and Potassium Hydroxides from Desiccated Soda Lime Diminishes Degradation of Desflurane to Carbon Monoxide and Sevoflurane to Compound A but Does Not Compromise Carbon Dioxide Absorption  

Microsoft Academic Search

Normal (hydrated) soda lime absorbent (approxi- mately 95% calcium hydroxide (Ca(OH)2), the remain- ing 5% consisting of a mixture of sodium hydroxide (NaOH) and potassium hydroxide (KOH)) degrades sevoflurane to the nephrotoxin Compound A, and des- iccated soda lime degrades desflurane, enflurane, and isoflurane to carbon monoxide (CO). We examined whether the bases in soda lime differed in their capaci-

M. A. Neumann; M. J. Laster; R. B. Weiskopf; D. H. Gong; R. Dudziak; E. I Eger II

1999-01-01

101

CALCITE PRECIPITATION IN LOW TEMPERATURE GEOTHERMAL SYSTEMS: AN EXPERIMENTAL APPROACH  

Microsoft Academic Search

One of the most common production problems in geothermal fields is calcite (calcium carbonate) scale deposition. Calcite formed in the wellbore and in near wellbore region significantly decreases the output of a production well. Calcite scaling is experienced in almost all the geothermal fields around the world. Calcite may form from hydrolysis, boiling and heating of cooler peripheral fluids. Although

Omer Izgec; Birol Demiral; Henri Bertin; Serhat Akin

102

Are Picoplankton Responsible for Calcite Precipitation in Lakes?  

Microsoft Academic Search

Deposits of lacustrine calcite are important records of en- vironmental changes. In order to interpret these archives, knowledge about the origin of the calcite is essential. It has been accepted that calcite precipitation can be induced by bacteria and algae. However, the detailed mechanisms are still unclear. This review summarizes what is known about the interactions between calcite precipitation and

Maria Dittrich; Martin Obst

2004-01-01

103

Inhibition of calcite growth by alginate  

NASA Astrophysics Data System (ADS)

The kinetics of calcite precipitation in the presence of alginate was investigated using the constant composition technique. In the concentration range investigated (0.0002-0.005 g L -1), alginate inhibits calcite precipitation. The extent of inhibition increased with increased alginate concentration and decreased solution supersaturation. Alginate adsorption, derived from normalized calcite precipitation rates, is described satisfactorily by the Langmuir adsorption model. At lowest supersaturation, alginate adsorption onto calcite probably reaches its maximal uptake of 7.5E-4 g m -2, corresponding to surface coverage of one molecule for each 200-300 nm 2, depending on the molecular mass of alginate. This means that one alginate molecule can be bound over 100-150 Ca surface sites. Initially, on the surface of the inhibited calcite, XPS identified alginate but after further time in solution, when the system had recovered, XPS demonstrated that it disappeared from the surface, presumably buried under the newly formed calcite. The alginate affinity constant decreases with increasing supersaturation, evidence for incomplete adsorption. A simple model based on competition between growth and desorption effectively describes the observed change in the adsorption constant.

Lakshtanov, L. Z.; Bovet, N.; Stipp, S. L. S.

2011-07-01

104

Chloral Hydrate  

MedlinePLUS

... after surgery for pain and to treat alcohol withdrawal.This medication is sometimes prescribed for other uses; ... TesTape or Clinistix to test your urine for sugar. Do not use Clinitest because chloral hydrate can ...

105

Investigation of Hydrated Lime-Asphalt and Aggregate interactions.  

National Technical Information Service (NTIS)

Serviceability of bituminous materials is a desirable asset in the design and construction of highway pavements. Some characteristics of asphalts - aggregates or their mixtures that have an effect on the useful service life of a highway pavement include: ...

B. H. Welch M. L. Wiley

1977-01-01

106

Adsorption of lanthanoid ions on calcite.  

PubMed

The adsorption of 14 trivalent lanthanoid ions and yttrium ion (denoted by Ln3+) on calcite surfaces was investigated under various solution conditions of pH (pH = 6.8-7.8) and calcium ion concentration (pCa = -log[Ca2+]= 2.0 and 3.0), and different surface conditions of calcite crystals (well-developed and rough surfaces). The lanthanoid ions were equilibrated in a solution of ionic strength 0.1 mol dm-3(NaCl) saturated with calcite at 25.0 degrees C using excess (solid) calcite crystals suspended in solution. The concentrations of the lanthanoid ions on the calcite crystals (C(cry)/mol kg-1) and in solution (C(soln)/mol dm-3) were determined by means of inductively coupled plasma-mass spectrometry (ICP-MS). It is found that the distribution ratio (D=C(cry)/C(soln) decreases as the atomic number of the lanthanoid increases showing the so called Tetrad Effect. D values increase with increasing pH, whereas they are independent of the calcium ion concentration (i.e., carbonate ion concentration). These results indicate that lanthanoid ions are adsorbed on the calcite surface together with hydroxide ions, i.e., the adsorption of hydroxo-complexes. The heavy lanthanoid ions (Er3+ to Lu3+) are adsorbed as monohydroxo-complexes, (Ln(OH)2+), whereas those of the light lanthanoids are predominantly adsorbed as dihydroxo-complexes (Ln(OH)2+). Other lanthanoids show competitive adsorption reactions of mono- and dihydroxo complexes. Both successive adsorption constants of hydroxo complexes increase with decreasing atomic number of the lanthanoid. The rough surface of calcite is quite active and the distribution ratio of the lanthanoid ions on the rough surface is much higher than that on the well-developed crystalline surface. Rates of adsorption of lanthanide ions were measured and mechanisms are being discussed PMID:16279010

Sawada, K; Abdel-Aal, K; Tan, K; Satoh, K

2005-10-21

107

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

108

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

109

Wood ash as a liming amendment  

Microsoft Academic Search

Greenhouse and laboratory experiments were carried out to determine the effectiveness of a wood?derived ash as a lime replacement. Treatments included wood ash, wood ash and lime admixtures, and lime amendments (ash amendment ranged from 0 to 20.17 and lime amendment from 0 to 4.06 g\\/kg soil on a dry weight basis). Treatments were compared for influence on soil pH,

W. M. Clapham; L. M. Zibilske

1992-01-01

110

Mathematical model of biofilm induced calcite precipitation.  

PubMed

Microbially modulated carbonate precipitation is a fundamentally important phenomenon of both engineered and natural environments. In this paper, we propose a mixture model for biofilm induced calcite precipitation. The model consists of three phases - calcite, biofilm and solvent - which satisfy conservation of mass and momentum laws with addition of a free energy of mixing. The model also accounts for chemistry, mechanics, thermodynamics, fluid and electrodiffusion transport effects. Numerical simulations qualitatively capturing the dynamics of this process and revealing effects of kinetic parameters and external flow conditions are presented. PMID:20489270

Zhang, T; Klapper, I

2010-01-01

111

Evidence for carbon sequestration by agricultural liming  

Microsoft Academic Search

Agricultural lime can be a source or a sink for CO2, depending on whether reaction occurs with strong acids or carbonic acid. Here we examine the impact of liming on global warming potential by comparing the sum of Ca2+ and Mg2+ to carbonate alkalinity in soil solutions beneath unmanaged vegetation versus limed row crops, and of streams and rivers in

Stephen K. Hamilton; Amanda L. Kurzman; Clay Arango; Lixin Jin; G. Philip Robertson

2007-01-01

112

Lime Residues and Metal Sequestration in Sediments of Excessively Limed Lakes  

Microsoft Academic Search

Sediment profiles from ten excessively limed lakes were used to study the occurrence of lime residues as a result of incomplete\\u000a lime dissolution and the influence of treatment with very high lime doses on the sequestration of metals in lake sediments.\\u000a The sediment profiles were subjected to multi-element analysis and compared to sediment profiles from previous studies of\\u000a lakes limed

Teresia Wällstedt

2011-01-01

113

Deep-Sea Authigenic Calcite and Dolomite.  

National Technical Information Service (NTIS)

Crystals of calcite and, in one case, of dolomite up to 90 millimicron in size are dispersed in pelagic red clay at several sites on the floor of the South Pacific Ocean. They were analyzed by microscopic, x-ray diffraction, electron x-ray microprobe, and...

E. Bonatti

1966-01-01

114

Deep-Sea Authigenic Calcite and Dolomite  

Microsoft Academic Search

Crystals of calcite and, in one case, of dolomite up to 90 mu m in size are dispersed in pelagic red clay at several sites on the floor of the South Pacific Ocean. They were analyzed by microscopic, x-ray diffraction, electron x-ray microprobe, and oxygen isotopic techniques. These carbonates are authigenic and were probably precipitated from hydrothermal solutions connected with

Enrico Bonatti

1966-01-01

115

Cyclic Cratonic Carbonates and Phanerozoic Calcite Seas.  

ERIC Educational Resources Information Center

|Discusses causes of cyclicity in cratonic carbonate sequences and evidence for and potential significance of postulated primary calcite sediment components in past Paleozoic seas, outlining problems, focusing on models explaining existing data, and identifying background. Future sedimentary geologists will need to address these and related areas…

Wilkinson, Bruce H.

1982-01-01

116

Constraining the Pressure Threshold of Impact Induced Calcite Twinning  

NASA Astrophysics Data System (ADS)

To better constrain the pressure threshold of impact-induced calcite twinning, calcite targets have been experimentally impacted. This study has implications for the deformation history of carbonaceous chondrite parent bodies.

Lindgren, P.; Price, M. C.; Lee, M. R.; Burchell, M.

2012-03-01

117

Properties of lime–metakolin mortars for the restoration of historic masonries  

Microsoft Academic Search

Mortars were prepared by mixing metakaolin\\/hydrated lime (with a ratio of ?1 by mass) with sand and were evaluated in order to be used as restoration mortars on historic masonries. During 12-months curing time the chemical reactions were evaluated by thermal analysis (DTA\\/TG), the microstructural properties by mercury intrusion porosimetry (MIP) and the mechanical characteristics (flexural and compressive strength, static

Eleni Aggelakopoulou; Asterios Bakolas; Antonia Moropoulou

2011-01-01

118

Cyanobacterial Calcite Precipitation - Laboratory Study on Different Spatial Scales  

Microsoft Academic Search

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

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

2003-01-01

119

Rare earth elements in natural calcite  

NASA Astrophysics Data System (ADS)

Rare earth elements (REE) have been used for years as a tool for interpreting rock genesis but recently they have come to be used as good analogues for the tri--valent actinides. Although there are abundant data in the literature describing their relative proportions in rocks, data for individual minerals and factors controlling their uptake are lacking. Better understanding of the extent of REE incorporation in all minerals would provide valuable information about the extent of immobilisation one could expect in the event of escape of radioactive elements. When concrete waste repositories break down, calcite forms in the high pH, Ca-rich solutions. Calcium's electronic structure permits significant distortion in its octahedral coordination, so divalent ions substitute extensively when size is compatible. The trivalent REE's, whose radii are similar to calcium, substitute to some extent but the range of possible uptake is unknown. This study was designed to fill that gap. With help from museums and mineral collectors internationally, we have collected a suite of calcite samples from well--characterised genetic environments. These include limestone, dolomite, marble, pegmatite, hydrothermal vein fillings, regionally metamorphosed settings and skarn, as well as several types of calcitic fossils. We used inductively coupled plasma-mass spectroscopy (ICP--MS) with isotope dilution to analyse the REE content. Data show expected trends. The most interesting result so far is that the highest natural REE concentrations are significantly lower than expected from the distribution coefficients we determined experimentally, suggesting calcite takes up essentially all REE's available from solution. This is good news for natural attenuation in the vicinity of decomposing concrete repositories because one could expect immobilisation of the actinides whose behaviour is similar to that of the lanthanides. The negative side is that recrystallisation or dissolution could release them again.

Jensen, J. T.; Harstad, A. O.; Waight, T. E.; Stipp, S. L. S.

2003-04-01

120

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

121

The petrography and microstructure of medieval lime mortars from the west of Scotland: Implications for the formulation of repair and replacement mortars  

Microsoft Academic Search

Twelfth and thirteenth Century lime mortars from the west of Scotland were examined using optical polarising microscopy and\\u000a SEM on impregnated, polished thin sections, and of fracture surfaces by secondary electron SEM. The non-hydraulic calcite\\u000a binder in these mortars is loclly inhomogenouse, exhibiting variations in texture and density. Spongiform binder with porosity\\u000a of size 10–20?m has sharp transitions with neighbouring

John J. Hughes; Simon J. Cuthbert

2000-01-01

122

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

123

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

124

Examination of the system fly ash lime calcined gypsum water  

NASA Astrophysics Data System (ADS)

The feasibility of the utilization of the system fly ash lime calcined gypsum (?-hemihydrate) water (the mass ratio 2:1:2:2.5) for the production of building ceramics was investigated. The system was cured under different conditions, i.e., tap water and ambient air. It was confirmed by X-ray diffraction analysis that three hydration products (gypsum, portlandite and ettringite) were formed in the water-cured system and two (gypsum and portlandite) in the air-cured system. Due to the formation of these products, a compressive strength of 4.01 MPa in the water-cured and 7.83 MPa in air-cured system developed. When the air-cured system was exposed to three alternate heating cooling or three alternate cooling heating cycles, the compressive strength increased (from 7.83 to 9.47 and 10.55 MPa, respectively). The fly ash lime calcined gypsum water systems prepared in this work can be applied for the manufacture of products for internal walls (bricks and blocks).

Marinkovic, S.; Kostic-Pulek, A.

2007-05-01

125

Clathrate Hydrates in Nature  

Microsoft Academic Search

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.

Keith C. Hester; Peter G. Brewer

2009-01-01

126

Calcite crystallization in the presence of europium: Preliminary results  

Microsoft Academic Search

Ubiquitous calcite is found in natural abiogenic and biogenic environments. Europium radionuclide is enlisted as a rare Earth element and frequently occurs in natural samples of calcite. In this study two complementary crystallization methods are tested to investigate possible conditions of europium uptake by calcite. Counter-diffusion-reaction of (Ca2+, Eu3+) and (Na+, CO32-) ions through a porous silica gel (Prieto et

Aikaterini Vavouraki; Ángeles Fernández-González; Manuel Prieto

2010-01-01

127

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

128

Hydrate characterization research overview  

Microsoft Academic Search

Gas hydrate research has been focused primarily on the development of a basic understanding of hydrate formation and dissociation in the laboratory, as well as in the field. Laboratory research on gas hydrates characterized the physical system, which focused on creating methane hydrates samples, tetrahydrofuran (THF) hydrate samples, consolidated rock samples, frost base mixtures, water\\/ice-base mixtures, and water-base mixtures. Laboratory

Malone

1993-01-01

129

CO2 emission accompanying the fracture of calcite  

NASA Astrophysics Data System (ADS)

Time resolved mass spectroscopy of the emissions accompanying the fracture of calcite (rhombohedral CaCO3) show that the principle volatile product, CO2, is released in bursts milliseconds after the fracture event. Similar measurements during the abrasion of calcite and during low temperature thermal decomposition of pulverized calcite show similar CO2 bursts. We argue that the observed bursts reflect localized decomposition of the calcite during the relaxation of reversible plastic deformation created by fracture and abrasion. This implies that mechanical, non-thermal processes play an important role in producing the observed decomposition products.

Dickinson, J. T.; Jensen, L. C.; Langford, S. C.; Rosenberg, P. E.; Blanchard, D. L.

1991-12-01

130

Calcite dissolution: Effects of trace cations naturally present in Iceland spar calcites  

NASA Astrophysics Data System (ADS)

In situ dissolution experiments on a set of pure, optical quality Iceland spar calcite samples from four different localities showed etch pit step retreat rates to be inversely proportional to total inherent trace cation composition. Atomic absorption spectroscopy (AAS) revealed Fe 2+, Mg 2+, Mn 2+ and Sr 2+ in amounts varying from a few to hundreds of ppm. We used a very simple experimental set-up, with an Atomic Force Microscope (AFM) fluid cell and a droplet of MilliQ water. As the calcite dissolved and approached equilibrium with the solution, trace cations were released, which were then present for interaction with the dissolving surface. We monitored continuous free-drift dissolution, in situ, on fresh {101¯4} cleavage surfaces for up to 40 min. Dissolution produced one-layer-deep, rhombic etch pits that continually expanded as we collected images. The rhombohedral symmetry of calcite defines two obtuse and two acute edges on the cleavage surface of etch pits and these, as expected from previous work, had different dissolution rates. Despite identical experimental conditions for all samples, we observed lower step retreat rates for both obtuse and acute edges on calcite characterised by relatively high trace cation composition. Increased cation concentration, particularly Mn, was also correlated with rounding of obtuse-obtuse corners, resulting in obtuse step retreat rates similar to those for acute sides. Physcial limitations of the AFM technique were taken into account when measuring step rate retreat and results were collected only from single-layer etch pits, which represent crystalline calcite with minimal defects. Dissolution rates presented here are thus lower than previous reports for studies of deep etch pits and where the physical limitations of imaging may not have been considered. In addition to molecular-level proof that divalent cations inherent at ppm levels in the calcite affect the dissolution process, these results show that pure, optical quality Iceland spar calcite should not be considered pure in the chemical sense. The results imply that dissolution rates determined for ideal systems with pure, synthetic or natural, materials may be considered as the boundary condition for dissolution in real systems in nature, where cations are always present both in the solution and in the initial solid.

Harstad, A. O.; Stipp, S. L. S.

2007-01-01

131

Method for enhancing the sulfur capture potential of lime using a filter means in the flue gas  

SciTech Connect

A method is provided for improving the sulfur capture potential of lime in the fluidized bed combustion of coal and for improving the flow characteristics of the feed coal therefor comprising collecting partially sulfated limestone particles from the fly ash of the flue gas from the fluidized bed combustor, and (a) retaining said particles in the flue gas stream, thereby hydrating said particles, and returning said particles to the combustor; or (b) mixing said partially sulfated limestone particles with wet coal thereby drying said coal and simultaneously hydrating unreacted calcium oxide to form calcium hydroxide, and recycling said mixture of dry crushed coal and calcium hydroxide into said fluidized bed combustor; or (c) inroducing wet coal in the flue gas upstream from said collected particles, thereby providing moisture to hydrate said particles, and returning said hydrated particles to the combustor.

Ehrlich, S.; Aulisio, C.

1983-10-25

132

The effectiveness of lime-based amendments and bauxite residues at removing phosphorus from piggery effluent.  

PubMed

Piggery effluent may contribute to the eutrophication of waterways, if it is not treated before disposal, because of high levels of phosphorus. Limes and red muds (a residue from bauxite refining) were used to remove phosphorus from piggery effluent (41 mg litre(-1) total P). Lime-based amendments were more effective than the red muds at removing phosphorus when compared at the same liquid: solid ratios. Based on laboratory data, the cost of treating effluent increased rapidly as the final required phosphorus concentration decreased to less than 4 mg litre(-1). Kiln dust was the cheapest amendment tested down to 2 mg litre(-1). Hydrated lime was able to clarify and flocculate the effluent to 1 mg litre(-1) within 60 min. The re-useability of all limes may be determined by a simple pH test. Red mud could be used to remove phosphorus when its pH was lowered to 6.0-6.5 and it is used at liquid:solid ratios <20:1. PMID:15092727

Weaver, D M; Ritchie, G S

1987-01-01

133

LIMEDS  

PubMed Central

Most Decision Support Systems (DSSs) in medicine have been developed in hospital environments, for use in hospitals. Only a few are designed for use by General Practitioners (GPs) in primary care. The work reported in this paper has a twofold aim: [List: see text

Timpka, Toomas

1986-01-01

134

Friction characteristics of Cd-rich carbonate films on calcite surfaces: implications for compositional differentiation at the nanometer scale  

PubMed Central

Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR) model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0–40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.

2009-01-01

135

Interaction of Copper with the Surface of Calcite.  

National Technical Information Service (NTIS)

The interaction of Cu ions in solution with the surface of calcite has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto calcite indicates that the process is rapid and strong in both dis...

M. L. Franklin J. W. Morse

1981-01-01

136

Dissolution of coccolithophorid calcite by microzooplankton and copepod grazing  

NASA Astrophysics Data System (ADS)

Independent of the ongoing acidification of surface seawater, the majority of the calcium carbonate produced in the pelagial is dissolved by natural processes above the lysocline. We investigate to what extent grazing and passage of coccolithophorids through the guts of copepods and the food vacuoles of microzooplankton contribute to calcite dissolution. In laboratory experiments where the coccolithophorid Emiliania huxleyi was fed to the rotifer Brachionus plicatilis, the heterotrophic flagellate Oxyrrhis marina and the copepod Acartia tonsa, calcite dissolution rates of 45-55%, 37-53% and 5-22% of ingested calcite were found. We ascribe higher loss rates in microzooplankton food vacuoles as compared to copepod guts to the strongly acidic digestion and the individual packaging of algal cells. In further experiments, specific rates of calcification and calcite dissolution were also measured in natural populations during the PeECE III mesocosm study under differing ambient pCO2 concentrations. Microzooplankton grazing accounted for between 27 and 70% of the dynamic calcite stock being lost per day, with no measurable effect of CO2 treatment. These measured calcite dissolution rates indicate that dissolution of calcite in the guts of microzooplankton and copepods can account for the calcite losses calculated for the global ocean using budget and model estimates.

Antia, A. N.; Suffrian, K.; Holste, L.; Müller, M. N.; Nejstgaard, J. C.; Simonelli, P.; Carotenuto, Y.; Putzeys, S.

2008-01-01

137

Atomistic simulation of the differences between calcite and dolomite surfaces  

Microsoft Academic Search

Atomistic simulation methods have been used to calculate and compare the surface structures and energies of the {1014}, {0001}, {1010}, {1120} and {1011} surfaces of calcite and dolomite and to evaluate their equilibrium morphologies. The calcite {1014} and the dolomite {1010} and {1120} surfaces are the most stable crystal planes. Investigation of the segregation of Mg and Ca ions in

J. O. Titiloye; N. H. de Leeuw; S. C. Parker

1998-01-01

138

Growth of Vaterite and Calcite Crystals in Gels.  

National Technical Information Service (NTIS)

Crystals of vaterite and calcite have been simultaneously grown in sodium metasilicate-acetic acid gels. The crystals were characterized by x-ray diffraction and infrared spectroscopy. The growth ratios of vaterite and calcite are functions of gel pH valu...

A. Schwartz D. Eckart J. O'Connell K. Francis

1971-01-01

139

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

140

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

141

Strength, Durability And Hydraulic Properties Of Clayey Soil Stabilized With Lime And Industrial Waste Lime  

Microsoft Academic Search

This research aims to study the effect of utilization of industrial waste\\/lime (by-product of sugar factory) on some engineering properties of clayey soil selected from Mosul city. These characteristics are unconfined compressive strength, permeability, soil-water characteristic curve and Durability. The tests were performed at different percentages of lime (2, 4 and 6) % and industrial waste\\/lime (2, 4, 6 and

Suhail A. A. Khattab; Khawla A. K. Al-Juari; Ibrahaim M. A. Al-Kiki

2007-01-01

142

Differences in the immobilization of arsenite and arsenate by calcite  

NASA Astrophysics Data System (ADS)

The sorption and coprecipitation experiments of arsenic (As) with calcite coupled with determinations of the chemical state of As both in the reaction fluid and in calcite were conducted to investigate the influence of the As oxidation state on its immobilization into calcite. The oxidation states of As in calcite and water were determined via As K-edge XANES and HPLC-ICP-MS analysis, respectively. The results of the sorption experiments at pH 8.2 show that only As(V) is distributed to calcite regardless of the As oxidation state in the solution. In coprecipitation experiments, As(V) is preferentially incorporated into calcite over a wide range of pH (7-12). On the other hand, the incorporation of As(III) into calcite is not observed at circumneutral pH. This difference between As(III) and As(V) is attributed to the fact that their dissolved species are neutral vs. negatively charged, respectively, at circumneutral pH (arsenite as H3AsO3; arsenate as H2AsO4- or HAsO42-). As the pH increases (>9), up to 33% of As(III)/Astotal ratio is partitioned into calcite or a precursor of calcite (metastable vaterite formed during the early stage of precipitation). The higher interaction of As with calcite at an alkaline pH compared with circumneutral pH is due to the negative charge of As(III) at alkaline pH. However, the As(III)/Astotal ratio decreases as time progresses and only As(V) can be found finally in calcite. The ratio of distribution coefficients of As(III) and As(V) into calcite (KAs(V)/KAs(III)) at pH ˜7 is larger than 2.1 × 103, suggesting that the oxidation state of As is a significant issue in considering the interaction between As and calcite in groundwater. Moreover, low KAs(III) shows that the sequestration of As via coprecipitation with calcite is not an important chemical process under reducing conditions, such as in the groundwaters in Bangladesh and other As-contaminated areas where As(III) is the dominant dissolved species of As. In the system spiked only with As(III), the XANES analysis detected As(V) in calcite, where the partitioning of As into calcite is very limited as stated above. Therefore, HPLC-ICP-MS and cyclic voltammetric measurements were performed to clarify the As(V)-incorporation mechanism in the As(III) system. As a result, the oxidation of As(III) to As(V) and the stabilization of As(V) in a solution in the presence of the Ca2+ ion are observed. These phenomena result from the formation of calcium arsenate complexes in the aqueous phase. This complexation is an important process for the coprecipitation of As with calcite. Hence, As is incorporated into calcite as As(V) even from the As(III) solution at circumneutral pH, wherein As(III) exists as neutral arsenite with little interaction with calcite.

Yokoyama, Yuka; Tanaka, Kazuya; Takahashi, Yoshio

2012-08-01

143

CFBC ash hydration studies  

Microsoft Academic Search

Hydration studies on CFBC ashes have shown that the acetone technique to prevent hydration in stored samples is relatively effective, only allowing some slight degree of hydration over days in the presence of excess water. In the presence of large excesses of water sufficient to control temperature increases, the degree of bulk mixing has no effect on the degree of

Edward J. Anthony; Lufei Jia; Yinghai Wu

2005-01-01

144

Hydrate characterization research overview  

SciTech Connect

Gas hydrate research has been focused primarily on the development of a basic understanding of hydrate formation and dissociation in the laboratory, as well as in the field. Laboratory research on gas hydrates characterized the physical system, which focused on creating methane hydrates samples, tetrahydrofuran (THF) hydrate samples, consolidated rock samples, frost base mixtures, water/ice-base mixtures, and water-base mixtures. Laboratory work produced measurements of sonic velocity and electrical resistivity of hydrates. As work progressed, areas, such as the Gulf of Mexico and the Guatemala Trench, where gas hydrates are likely to occur were identified, and specific high potential areas were targeted for detailed investigation. The testing of samples and recovered cores from such areas provided information for detection of hydrate formations in the natural environment. Natural gas hydrate samples have been tested for thermal properties, dissociation properties, fracture mechanics, and optical properties. Acoustical properties were investigated both in the laboratory and, as possible, in the field. Sonic velocity and electrical resistivity measurements will continue to be obtained. These activities have been undertaken in hydrate deposits on Alaska`s North Slope, the Gulf of Mexico and the US East coast offshore, as well as other gas hydrate target areas.

Malone, R.D.

1993-06-01

145

Calcite surface structure and reactivity: molecular dynamics simulations and macroscopic surface modelling of the calcite-water interface.  

PubMed

Calcite-water interactions are important not only in carbon sequestration and the global carbon cycle, but also in contaminant behaviour in calcite-bearing host rock and in many industrial applications. Here we quantify the effect of variations in surface structure on calcite surface reactivity. Firstly, we employ classical Molecular Dynamics simulations of calcite surfaces containing an etch pit and a growth terrace, to show that the local environment in water around structurally different surface sites is distinct. In addition to observing the expected formation of more calcium-water interactions and hydrogen-bonds at lower-coordinated sites, we also observed subtle differences in hydrogen bonding around acute versus obtuse edges and corners. We subsequently used this information to refine the protonation constants for the calcite surface sites, according to the Charge Distribution MUltiSite Ion Complexation (CD-MUSIC) approach. The subtle differences in hydrogen bonding translate into markedly different charging behaviour versus pH, in particular for acute versus obtuse corner sites. The results show quantitatively that calcite surface reactivity is directly related to surface topography. The information obtained in this study is not only crucial for the improvement of existing macroscopic surface models of the reactivity of calcite towards contaminants, but also improves our atomic-level understanding of mineral-water interactions. PMID:23042085

Wolthers, M; Di Tommaso, D; Du, Z; de Leeuw, N H

2012-10-08

146

COMPARISON OF SLUDGE CHARACTERISTICS BETWEEN LIME AND LIMESTONE\\/LIME TREATMENT OF ACID MINE DRAINAGE1  

Microsoft Academic Search

The U.S. Geological Survey, in cooperation with the Colorado School of Mines and the U.S. Environmental Protection Agency, has demonstrated the application of pulsed limestone bed (PLB) treatment of acid mine drainage (AMD) at the Argo tunnel discharge near Idaho Springs, Colorado. Current technology for AMD treatment at the Argo facility is neutralization with lime. However, lime neutralization often results

A. W. Miller; P. L. Sibrell; T. R. Wildeman

147

LIME AND CEMENT INDUSTRY PARTICULATE EMISSIONS: SOURCE CATEGORY REPORT. VOLUME 1. LIME INDUSTRY  

EPA Science Inventory

The report gives results of a study to develop particulate emission factors based on cutoff size for inhalable particles for the lime industry. After reviewing available information characterizing particulate emissions from lime plants, the data were summarized and rated in terms...

148

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

149

Influence of water vapour and carbon dioxide on free lime during storage at 80 °C, studied by Raman spectroscopy.  

PubMed

Micro-Raman spectroscopy has been used to follow the reaction of free lime (CaO) exposed for 24h to moist air at 80 °C under conditions of different relative humidities (10-80% RH). X-ray diffraction and SEM imaging were applied as complementary techniques. The conversion of lime to calcium hydroxide and its subsequent carbonation to various calcium carbonate polymorphs was found to strongly depend on the relative humidity. At low RH (10-20%), only Raman spectroscopy revealed the formation of early amorphous CaCO3 which in the XRD patterns was detected only at ?40% RH. However, XRD analysis could identify the crystalline polymorphs formed at higher relative humidities. Thus, between 20 and 60% RH, all three CaCO3 polymorphs (calcite, aragonite and vaterite) were observed via XRD whereas at high relative humidity (80%), calcite was the predominant reaction product. The results demonstrate the usefulness of Raman spectroscopy in the study of minor cement constituents and their reaction products on air, especially of amorphous character. PMID:23639205

Dubina, E; Korat, L; Black, L; Strupi-Šuput, J; Plank, J

2013-04-11

150

Influence of water vapour and carbon dioxide on free lime during storage at 80 °C, studied by Raman spectroscopy  

NASA Astrophysics Data System (ADS)

Micro-Raman spectroscopy has been used to follow the reaction of free lime (CaO) exposed for 24 h to moist air at 80 °C under conditions of different relative humidities (10-80% RH). X-ray diffraction and SEM imaging were applied as complementary techniques. The conversion of lime to calcium hydroxide and its subsequent carbonation to various calcium carbonate polymorphs was found to strongly depend on the relative humidity. At low RH (10-20%), only Raman spectroscopy revealed the formation of early amorphous CaCO3 which in the XRD patterns was detected only at ?40% RH. However, XRD analysis could identify the crystalline polymorphs formed at higher relative humidities. Thus, between 20 and 60% RH, all three CaCO3 polymorphs (calcite, aragonite and vaterite) were observed via XRD whereas at high relative humidity (80%), calcite was the predominant reaction product. The results demonstrate the usefulness of Raman spectroscopy in the study of minor cement constituents and their reaction products on air, especially of amorphous character.

Dubina, E.; Korat, L.; Black, L.; Strupi-Šuput, J.; Plank, J.

2013-07-01

151

Hydration characteristics of tricalcium aluminate phase in mixes containing {beta}-hemihydate and phosphogypsum  

SciTech Connect

The tricalcium aluminte phase was prepared from pure chemicals on a laboratory scale. Five mixes were formulated from the prepared C{sub 3}A phase, {beta}-hemihydate, phosphogypsum, calcium hydroxide and quartz. Different mixes were hydrated at various time intervals, namely, 6, 24, 72 and 168 h. The kinetics of hydration was measured from chemically combined water and combined lime contents. The phase compositions and microstructures of the hydrated products were studied by X-ray diffraction (XRD), differential thermal analysis (DTA)/TG, scanning electron microscopy (SEM) techniques and FT-IR spectroscopy. This work aimed to study the effect of partial to full substitution of phosphogypsum by {beta}-hemihydate on the hydration characteristics and microstructures of tricalcium aluminte phase. The results showed that the combined lime slightly increases with the increase of amounts of phosphogypsum. The XRD patterns showed the increase in the intensities of monosulphate and different forms of calcium aluminate (C{sub 4}AH{sub 13} and C{sub 4}AH{sub 19}) with phosphogypsum content. Ettringite is less stable than monosulphoaluminate, so it transformed into monosulpho-aluminate after 24 h, which persisted up to 168 h. The mechanism of the hydration process of C{sub 3}A phase in the presence of phosphogypsum proceeds in a similar path as with {beta}-hemihydate. Phosphogypsum reacts with C{sub 3}A in the presence of Ca(OH){sub 2} forming sulphoaluminate hydrates, which are responsible for setting regulation in cementitious system.

Radwan, M.M. [National Research Center, Dokki, Cairo (Egypt); Heikal, M. [Chemistry Department, Faculty of Science, Zagazig University, Benha Branch, Benha (Egypt)]. E-mail: ayaheikal@hotmail.com

2005-08-01

152

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

153

Thermoluminescence of the green emission band of calcite  

NASA Astrophysics Data System (ADS)

The thermoluminescence (TL) characteristics of the green emission band of natural calcite are studied. The kinetic parameters of the natural and laboratory-induced defects were estimated. The ?-dose response was studied in the range of 0.01-104 Gy. The fading rate at room temperature is monitored over a period of 30 days. The results showed that calcite has a potential use as a material for ?-ray TL dosimeters for food sterilization, testing of materials and other industrial or reactor procedures.

Soliman, C.; Metwally, Saleh M.

154

Calcite-dolomite geothermometry for iron-bearing carbonates  

Microsoft Academic Search

The effect of the addition of iron on the calcite-dolomite solvus in the system CaCO3-MgCO3 is predicted from an approximate thermodynamic description of the systems CaCO3-MgCO3 and CaCO3-FeCO3. Coexisting calcites and dolomites in 15 samples from the Glockner area of the Tauern Window have been analysed to estimate metamorphic temperatures. These range from about 410 °C at the top of

M. J. Bickle; R. Powell

1977-01-01

155

H20 and OH in echinoid calcite: A spectroscopic study  

Microsoft Academic Search

Proton nuclear magnetic resonance (NMR) and visible and near-infrared (VNIR) re- flectance spectral data and heating experiments indicate that the Mg-rich calcite (com- monly referred to as high-Mg calcite and hereafter as HMC) that is produced by six different species of echinoids contains H20 with mobilities and H bond strengths ranging from those characteristic ofliquid H20 to those observed in

SUSAN J. GAFFEY

156

Gas Hydrate Nucleation Processes  

NASA Astrophysics Data System (ADS)

The onset of gas hydrate nucleation is greatly affected by the thermal history of the water that forms its lattice structure. Hydrate formation experiments were performed in a 72 liter pressure vessel by bubbling carbon dioxide through a 1 liter column at hydrate formation pressures (1.4 to 3.7 MPa) and temperatures (275.0 to 278.0 K) to quantify this effect. They show that when even a fraction ( e. g. 20 %) of the water in which hydrate has formed was recently frozen and thawed, the overpressurization for nucleation was reduced by an average of 50 % versus experiments performed in distilled water. In those experiments where a lower overpressure is present when hydrate nucleated, they tended to form on the surface of bubbles, whereas when a higher amount of overpressure was necessary for hydrate to nucleate, they appeared to form abruptly on bubble surfaces as well as from the bulk liquid phase. In approximation of classical nucleation, hydrate formation could be described as occurring by the spontaneous joining together of arising components of the hydrate lattice. In water that was frozen, and kept at a low temperature (< 275 K), molecular simulation models predict the predominance of water molecules organized as penatmeters, a possible subunit of the hydrate lattice. Our results suggest that in nature, initiation of hydrate formation may be strongly influenced by temperature dependant pre-structuring of water molecules prior to their contact with gas.

David, R. E.; Zatsepina, O.; Phelps, T. J.

2003-12-01

157

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

158

Calcite Farming at Hollow Ridge Cave: Calibrating Net Rainfall and Cave Microclimate to Dripwater and Calcite Chemical Variability  

NASA Astrophysics Data System (ADS)

Stable isotope (?18O and ?13C) and trace element records in cave speleothems are often interpreted as climate changes in rainfall amount or source, cave air temperature, overlying vegetation and atmospheric pCO2. However, these records are difficult to verify without in situ calibration of changes in cave microclimate (e.g., net rainfall, interior ventilation changes) to contemporaneous variations in dripwater and speleothem chemistry. In this study at Hollow Ridge Cave (HRC) in Marianna, Florida (USA), cave dripwater, bedrock, and modern calcite (farmed in situ) were collected in conjunction with continuous cave air pCO2, temperature, barometric pressure, relative humidity, radon-222 activity, airflow velocity and direction, rainfall amount, and drip rate data [1]. We analyzed rain and dripwater ?D and ?18O, dripwater Ca2+, pH, ?13C and TCO2, cave air pCO2 and ?13C, and farmed calcite ?18O and ?13C to examine the relationships among rainwater isotopic composition, cave air ventilation, cave air temperature, calcite growth rate and seasonal timing, and calcite isotopic composition. Farmed calcite ?13C decreases linearly with distance from the front entrance to the interior of the cave during all seasons, with a maximum entrance-to-interior gradient of ??13C = -7‰ . A whole-cave "Hendy test" at distributed contemporaneous farming sites reveals that ventilation induces a +1.9 ± 0.96‰ ?13C offset between calcite precipitated in a ventilation flow path and out of flow paths. Farmed calcite ?18O exhibits a +0.82 ± 0.24‰ offset from values predicted by both theoretical calcite-water calculations and by laboratory-grown calcite [2]. Unlike calcite ?13C, oxygen isotopes show no ventilation effects and are a function only of temperature. Combining our data with other speleothem studies, we find a new empirical relationship for cave-specific water-calcite oxygen isotope fractionation across a range of temperatures and cave environments: 1000 ln ? = 16.1(1000/T) - 24.6 We analyzed anions, cations, and trace elements in dripwater, bedrock, and farmed calcite to examine the relationships between net rainfall, drip rates, drip water chemistry, and calcite chemistry. Dripwater Mg/Ca and Sr/Ca ratios fall on coherent mixing lines between three geochemical endmembers: rainwater, dissolved dolomite, and dissolved limestone. Dripwater Sr/Ca vs. Mg/Ca ratios are also influenced by evaporative enrichment within the epikarst as a function of net rainfall amount [3]. Farmed calcite trace Cation/Ca ratios faithfully track short-term seasonal variations in dripwater chemistry for Na, Mg, Sr, Ba and U. However, speleothem calibrations are unique to each drip site regardless of proximity to one another, suggesting that individual speleothems are unlikely to be useful as a whole-cave hydrologic proxy. [1] Kowalczk, A. J., Froelich, P. N., 2010. Cave air ventilation and CO2 outgassing by radon-222 modeling: How fast do caves breathe? Earth & Planet. Sci. Lett. 289, 209-219. [2] Tremaine, D. M., Froelich, P. N., Wang, Y., 2011. Speleothem calcite farmed in situ: Modern calibration of ?18O and ?13C paleoclimate proxies in a continuously-monitored natural cave system. Geochim. Cosmochim. Acta 75, 4929-4950. [3] Tremaine, D. M., Froelich, P. N., 2012. Speleothem trace element signatures: A modern hydrologic geochemical study of cave drip waters and farmed calcite. Geochim. Cosmochim. Acta (submitted)

Tremaine, D. M.; Kilgore, B. P.; Froelich, P. N.

2012-04-01

159

Comparison of garnet-biotite, calcite-graphite, and calcite-dolomite thermometry in the Grenville Orogen; Ontario, Canada  

Microsoft Academic Search

The Elzevir Terrane of the Grenville Orogen in southern Ontario contains metapelites and abundant graphitic marbles that\\u000a were regionally metamorphosed from the upper greenschist to upper amphibolite facies. Comparative thermometry was undertaken\\u000a with widely used calibrations for the systems garnet-biotite, calcite-dolomite, and calcite-graphite. Temperatures that are\\u000a obtained from matrix biotites paired with prograde garnet near-rim analyses are usually consistent with

Mark A. Rathmell; Margaret M. Streepey; Eric J. Essene; Ben A. van der Pluijm

1999-01-01

160

Lime Research Study South Dakota Interstate Routes (Sixteen Projects).  

National Technical Information Service (NTIS)

The lime research study was initiated to determine if lime stabilization of subgrade soils, subbase gravels and/or base gravels is effective in accomplishing the following objectives: Permanent reduction of plasticity index of subgrade soil and base; redu...

E. B. McDonald

1969-01-01

161

Dynamic Response of Soda-Lime Glass  

NASA Astrophysics Data System (ADS)

Soda-lime glass (SLG) is a highly available low cost glass formulation commonly used in window applications and it may have potential use in transparent ceramic armor. While there has been a great deal of work done to characterize the shock response of fused silica, the primary component of SLG, comparatively little is known about SLG itself. This paper will report the results of characterization experiments conducted at Sandia National Laboratories on a low iron content soda-lime glass commercially available from PPG Industries. Data have been collected over a wide range of stress levels from 4 to 65 GPa. Topics will include the Hugoniot response including non-linear elastic behavior, support for a high stress phase transition, material strength, and evidence for failure of the material under certain conditions. Further, the results will be compared and contrasted with related findings in fused silica as well as work on similar soda-lime glass formulations reported by other researchers.

Alexander, C. Scott

2007-06-01

162

NEW MAGNESIUM - ENHANCED LIME FLUE GAS DESULFURIZATION PROCESS  

Microsoft Academic Search

Carmeuse North America has developed a new magnesium-enhanced-lime-based wet flue gas desulfurization (FGD) process for control of sulfur dioxide emissions. This process is an improvement upon an older magnesium-enhanced lime process, which has been in use in the USA since 1977. The magnesium-enhanced lime process utilizes 2.25 million metric tons of lime annually. Since the year 2000, 27% of this

Lewis Benson

163

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

164

Calcite crystallization in the presence of europium: Preliminary results  

NASA Astrophysics Data System (ADS)

Ubiquitous calcite is found in natural abiogenic and biogenic environments. Europium radionuclide is enlisted as a rare Earth element and frequently occurs in natural samples of calcite. In this study two complementary crystallization methods are tested to investigate possible conditions of europium uptake by calcite. Counter-diffusion-reaction of (Ca2+, Eu3+) and (Na+, CO32-) ions through a porous silica gel (Prieto et al., 1997) was used to examine possible Ca-Eu-Na carbonate solid solution formation. A variety of calcium, carbonate and europium aqueous solution compositions were prepared at high supersaturation with respect to calcite. Crystallization in gel media enables to improve crystal size and facilitates with its characterization. Here, polymorphs of calcium carbonate were obtained in the presence of europium in one month duration gel experiments. An alternative quick method of crystallizing calcium carbonate is the method of vapour diffusion on a crystallization mushroom (Hernández-Hernández et al., 2008). Ammonium bicarbonate solution releases NH3(g) and CO2(g) and in a sitting drop of calcium chloride, nucleation of calcium carbonate is observed. In both diffusion processes calcite crystals and its polymorphs of aragonite and vaterite were obtained and analyzed by scanning electron microscopy (SEM-EDS) and microprobe (EMP). Crystals exhibited a wide variety of forms as a function of the europium mole fraction (XEu,aq.) in the aqueous solution. At XEu,aq. = 0.02 trace of europium was detected into solid calcite crystal structure. This study examines calcite as a potential host mineral for radionuclide deposits such as europium. References Prieto, M. et al., 1997. Geochim. Cosmochim. Acta 61, 3383-3397. Hernández-Hernández, A. et al., 2008. J. Crystal Growth 310, 1754-1759.

Vavouraki, Aikaterini; Fernández-González, Ángeles; Prieto, Manuel

2010-05-01

165

Dolomite-calcite textures in early carbonatites of the Kovdor ore deposit, Kola peninsula, Russia: their genesis and application for calcite-dolomite geothermometry  

Microsoft Academic Search

In early calcite carbonatites of the Kovdor ore deposit four morphological types of dolomite are represented. In the first type, dolomite microcrystals occur as lamellae enclosed by optically continuous calcite. In the second, dolomite microcrystals occur as segmented rods, plates and xenomorphic grains, enclosed by optically discontinuous calcite, and in the third, dolomite is represented by grains of various morphologies,

Anatoly Zaitsev; Ludmila Polezhaeva

1994-01-01

166

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 ...

167

Extractable phosphorus availability indexes as affected by liming  

Microsoft Academic Search

In acidic soils, with high contents of Fe and Al oxides, the effect of liming in increasing P availability to plants has been observed for years. However, commonly used soil tests often fail to show increases in soil P due to liming. This subject was investigated using soil samples and results of leaf analysis of four liming experiments with soybeans,

B. van Raij; J. A. Quaggio

1990-01-01

168

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

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 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...

2011-10-01

169

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

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 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...

2012-10-01

170

Liming placed in a long-term perspective: a paleolimnological study of 12 lakes in the Swedish liming program  

Microsoft Academic Search

Since the 1970s liming has been practised on a large scale in Sweden to mitigate acidification and several thousand lakes\\u000a and streams are limed repeatedly. The Swedish monitoring program ISELAW (Integrated Studies of the Effects of Liming Acidified\\u000a Waters) studies the long-term effects of liming. This paper summarizes the paleolimnological part of the program. Sediment\\u000a cores from 12 lakes were

Matilda Guhrén; Christian Bigler; Ingemar Renberg

2007-01-01

171

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

172

Phosphorus leaching in soils amended with piggery effluent or lime residues from effluent treatment.  

PubMed

Phosphorus (P) in wastes from piggeries may contribute to the eutrophication of waterways if not disposed of appropriately. Phosphorus leaching, from three soils with different P sorption characteristics (two with low P retention and one with moderate P retention) when treated with piggery effluent (with or without struvite), was investigated using batch and leaching experiments. The leaching of P retained in soil from the application of struvite effluent was determined. In addition, P leaching from lime residues (resulting from the treatment of piggery effluent with lime to remove P) was determined in comparison to superphosphate when applied to the same three soils. Most P was leached from sandy soils with low P retention when effluent with or without struvite was applied. More than 100% of the filterable P applied in struvite effluent was leached in sandy soils with low P retention. Solid, inorganic forms of P (struvite) became soluble and potentially leachable at pH<7 or were sorbed after dissolution if there were sufficient sorption sites. In sandy soils with low P retention, more than 39% of the total filterable P applied in recycled effluent (without struvite) was leached. Soil P increased mainly in surface layers after treatment with effluent. Sandy soils pre-treated with struvite effluent leached 40% of the P retained in the previous application. Phosphorus decreased in surface layers and increased at depth in the soil with moderate P retention after leaching the struvite effluent pre-treated soil with water. The soils capacity to adsorb P and the soil pH were the major soil properties that affected the rate and amount of P leaching, whereas the important characteristics of the effluent were pH, P concentration and the forms of P in the effluent. Phosphorus losses from soils amended with hydrated lime and lime kiln dust residues were much lower than losses from soils amended with superphosphate. Up to 92% of the P applied as superphosphate was leached from sandy soils with low P retention, whereas only up to 60% of the P applied in lime residues was leached. The P source contributing least to P leaching was the lime kiln dust residue. The amount of P leached depended on the water-soluble P content, neutralising value and application rate of the P source, and the pH and P sorption capacity of the soil. PMID:15091693

Weaver, D M; Ritchie, G S

1994-01-01

173

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

174

Lime Manufacturing Industry Fourier Transform Infrared Spectroscopy, Austin White Lime Company, Austin, Texas. Final Report.  

National Technical Information Service (NTIS)

The purpose of this testing program is to: (1) quantify hydrogen chloride (HCl) emission levels; and (2) gather screening data on other hazardous air pollutants (HAP) emissions from lime production plants to support a national emission standard for hazard...

2000-01-01

175

Lime Manufacturing Industry Fourier Transform Infrared Spectroscopy, Huron Lime Company, Huron, Ohio. Final Report.  

National Technical Information Service (NTIS)

The purpose of this testing program is to: (1) quantify hydrogen chloride (HCl) emission levels; and (2) gather screening data on other hazardous air pollutants (HAP) emissions from lime production plants to support a national emission standard for hazard...

2000-01-01

176

Lime Kiln Source Characterization. Lime Manufacturing Industry Fourier Transform Infrared Spectroscopy.  

National Technical Information Service (NTIS)

The purpose of this testing program is to obtain uncontrolled and controlled hydrogen chloride (HCI) and speciated hydrocarbon Hazardous Air Pollutants (HAPs) emissions data from lime production plants to support a national emission standard for hazardous...

M. L. Toney

1999-01-01

177

Lime Manufacturing Industry Fourier Transform Infrared Spectroscopy, National Lime and Stone Company, Carey, Ohio. Final Report.  

National Technical Information Service (NTIS)

The purpose of this testing program is to: (1) quantify hydrogen chloride (HCl) emission levels; and (2) gather screening data on other hazardous air pollutants (HAP) emissions from lime production plants to support a national emission standard for hazard...

2000-01-01

178

Hydrates of hydrocarbons  

Microsoft Academic Search

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

Makogon

1997-01-01

179

Desulfurization, in Connection with Coal-Firing, Using Quick-Lime and Powdered Dry Slaked Lime Injection.  

National Technical Information Service (NTIS)

On a 5 MW Danstoker Tagus grate fired boiler, 10 tests have been carried out with injection of quick-lime and powdered dry slaked lime to reduce the emission of sulphur dioxide. The lime was injected together with the secondary air, and through an opening...

T. Wismann

1988-01-01

180

Lime Requirement Experiments in Acid Sulphate Soils  

Microsoft Academic Search

Acid sulphate (AS) soils cover significant areas of the coastal plains in Western Finland. Postglacial land uplift and drainage works expose subsurface iron sulphides to atmospheric oxygen. Subsequent oxidation processes release high amounts of acidity to the soil and to adjacent watercourses. This study surveyed the effects of different lime applications on AS soil pH and runoff acidity in order

Jukka Palko; Kjell Weppling

1994-01-01

181

Dynamic Response of Soda-Lime Glass  

Microsoft Academic Search

Soda-lime glass (SLG) is a highly available low cost glass formulation commonly used in window applications and it may have potential use in transparent ceramic armor. While there has been a great deal of work done to characterize the shock response of fused silica, the primary component of SLG, comparatively little is known about SLG itself. This paper will report

C. Scott Alexander

2007-01-01

182

Fertilizer and Lime: Why They Are Used.  

ERIC Educational Resources Information Center

This unit teaching guide is designed to help teachers explain the principles of fertilizer and lime use. The first of four major sections is a teaching outline keyed to transparency masters and student handouts. Thirteen major areas are covered in the teaching outline: (1) plant needs; (2) uses of fertilizer; (3) nutrients for plant growth; (4)…

McCaslin, Judith Strand

183

Fertilizer and Lime: Why They Are Used.  

ERIC Educational Resources Information Center

|This unit teaching guide is designed to help teachers explain the principles of fertilizer and lime use. The first of four major sections is a teaching outline keyed to transparency masters and student handouts. Thirteen major areas are covered in the teaching outline: (1) plant needs; (2) uses of fertilizer; (3) nutrients for plant growth; (4)…

McCaslin, Judith Strand

184

Investigation of lime stabilised contaminated material  

Microsoft Academic Search

Stabilisation of contaminated materials using inorganic cementitious agents is becoming more widely used in the UK. The method has particular advantages for bulk fill operations such as highway earthworks. Research has been carried out at the Transport Research Laboratory into the long-term durability of lime stabilised material. The trial material was a soft organic silty clay with metal contamination. Testing

J. M Reid; A. H Brookes

1999-01-01

185

Sulfated Macromolecules as Templates for Calcite Nucleation and Growth  

NASA Astrophysics Data System (ADS)

Mineralization of egg and seashells is controlled by an intimate association of inorganic materials with organic macromolecules. Among them, particular polyanionic sulfated macromolecules referred to as proteoglycans have been described to be involved in the calcification of these biominerals. The sulfated moieties of the proteoglycans are part of polymer chains constituted of building-blocks of disaccharide units, referred to as sulfated glycosaminoglycans (GAGs), which are covalently attached to a protein core. By using a sitting drop crystallization assay under controlled conditions of time, pH and reactants concentration, we have tested several sulfated and non-sulfated GAGs (i.e.: dermatan and keratan sulfate, hyaluronic acid and heparin), differing in their sulfonate and carboxylate degree and pattern, in their ability to modify calcium carbonate crystal morphology as observed under scanning electron microscopy. Without the addition of GAGs, regular \\{104\\} rhombohedral calcite crystals were obtained. When hyaluronic acid (HA), a non-sulfated but carboxylated GAG, was added, 20 mm long piles of unmodified calcite crystals were observed. When desulfated dermatan, which is an epimeric form of HA but shorter polymer, having their carboxylate groups in an inverted configuration, was added, isolated rhombohedral \\{104\\} calcite crystals showing rounded corners with planes oriented parallel to the c axis were observed. When dermatan sulfated was added, isolated calcite crystals exhibit a columnar morphology as a \\{hk0\\} cylinder with three \\{104\\} faces forming a cap at both ends. Heparin activity depends on the fraction added. Fast-moving heparin fraction (FM), is an undersulfated, low-molecular-weight heterogeneous polymer, while slow-moving heparin fraction (SM) is an high-molecular-weight homogeneous polymer rich in trisulfated-disaccharide units. When FM was added, isolated calcite crystals displayed rhombohedrical \\{104\\} faces but flat corners of \\{111\\} faces. The addition of the hypersulfated heparin SM induce the formation of large rosette-like aggregated calcite crystals, where the majority of the \\{104\\} faces appeared not to be lost, although aggregation is done by different kind of faces. It is concluded that, the variation of the sulfate and carboxylate content and configuration drastically changed the morphology of the calcite crystals. The production of calcite particles with defined morphologies could be interesting for the design of novel materials with desirable shape- and texture-depending properties. Granted by FONDAP 11980002.

David, M.; Passalacqua, K.; Neira, A. C.; Fernandez, M. S.

2003-12-01

186

Uptake of chloride and carbonate ions by calcium monosulfoaluminate hydrate  

SciTech Connect

Decommissioning of old nuclear reactors may produce waste streams containing chlorides and carbonates, including radioactive {sup 36}Cl{sup -} and {sup 14}CO{sub 3}{sup 2-}. Their insolubilization by calcium monosulfoaluminate hydrate was investigated. Carbonates were readily depleted from the solution, giving at thermodynamic equilibrium monocarboaluminate, monocarboaluminate + calcite, or calcite only, depending on the initial ratio between the anion and calcium monosulfoaluminate hydrate. Chloride ions reacted more slowly and were precipitated as Kuzel's salt, Kuzel's and Friedel's salts, or Friedel's salt only. Rietveld refinement of X-Ray powder diffraction patterns was successfully used to quantify the phase distributions, which were compared to thermodynamic calculations. Moreover, analysing the lattice parameters of Kuzel's salt as a function of its chloride content showed the occurrence of a restricted solid solution towards the sulfate side with general formula 3CaO{center_dot}Al{sub 2}O{sub 3}{center_dot}xCaCl{sub 2}{center_dot}(1 - x)CaSO{sub 4}{center_dot}(12 - 2x){center_dot}H{sub 2}O (0.36 {<=} x {<=} 0.50).

Mesbah, Adel [Commissariat a l'Energie Atomique et aux Energies Alternatives, CEA DEN/DTCD/SPDE, F-30207 Bagnols sur Ceze (France); Clermont Universite, ENSCCF, Laboratoire des Materiaux Inorganiques, BP 10448, F-63000 Clermont-Ferrand (France); Cau-dit-Coumes, Celine, E-mail: celine.cau-dit-coumes@cea.fr [Commissariat a l'Energie Atomique et aux Energies Alternatives, CEA DEN/DTCD/SPDE, F-30207 Bagnols sur Ceze (France); Renaudin, Guillaume [Clermont Universite, ENSCCF, Laboratoire des Materiaux Inorganiques, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR 6002, F-63177 Aubiere (France); Frizon, Fabien [Commissariat a l'Energie Atomique et aux Energies Alternatives, CEA DEN/DTCD/SPDE, F-30207 Bagnols sur Ceze (France); Leroux, Fabrice [Clermont Universite, Universite Blaise Pascal, Laboratoire des Materiaux Inorganiques, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR 6002, F-63177 Aubiere (France)

2012-08-15

187

Fly ash as a liming material for corn production  

SciTech Connect

Fly ash produced as a by-product of subbituminous coal combustion can potentially serve as an alternative liming material without negatively affecting corn (Zea mays L.) production in areas where use of conventional liming materials can be uneconomical due to transportation costs. A study was conducted to determine if fly ash produced from the Nebraska Public Power District Gerald Gentleman Power Station located in Sutherland, NE could be used as an alternative liming material. Combinations of dry fly ash (DFA), wet fly ash (WFA), beet lime (by-product of sugar beet (Beta vulgaris L.) processing) (BL), and agricultural lime (AGL) were applied at rates ranging from 0.43 to 1.62 times the recommended lime rate to plots on four acidic soils (Anselmo fine sandy loam, Hord fine sandy loam, Holdrege sandy loam, and Valentine fine sand). Soil samples were collected to a depth of 0.2 m from plots and analyzed for pH before lime applications and twice periodically after lime application. The Hord and Valentine soils were analyzed for exchangeable Ca, Mg, K, Na,and Al for determination of percent Al saturation on selected treatments and sampling dates. Corn grain yields were determined annually. It is concluded that the fly ash utilized in this study and applied at rates in this study, increases soil pH comparable to agricultural lime and is an appropriate alternative liming material.

Tarkalson, D.D.; Hergert, G.W.; Stevens, W.B.; McCallister, D.L.; Kackman, S.D. [University of Nebraska, North Platte, NE (US)

2005-05-01

188

EXAFS study of rare-earth element coordination in calcite  

NASA Astrophysics Data System (ADS)

Extended X-ray absorption fine-structure (EXAFS) spectroscopy is used to characterize the local coordination of selected rare-earth elements (Nd 3+ , Sm 3+ , Dy 3+ , Yb 3+ ) coprecipitated with calcite in minor concentrations from room-temperature aqueous solutions. Fitting results confirm substitution in the Ca site, but first-shell Nd-O and Sm-O distances are longer than the Ca-O distance in calcite and longer than what is consistent with ionic radii sums for sixfold coordination in the octahedral Ca site. In contrast, first-shell Dy-O and Yb-O distances are shorter than the Ca-O distance and are consistent with ionic radii sums for sixfold coordination. Comparison of Nd-O and Sm-O bond lengths with those in lanthanide sesquioxides and with ionic radii trends across the lanthanide series suggests that Nd 3+ and Sm 3+ have sevenfold coordination in a modified Ca site in calcite. This would require some disruption of the local structure, with an expected decrease in stability, and possibly a different charge compensation mechanism between Nd and Sm vs. Yb and Dy. A possible explanation for the increased coordination for the larger rare-earth elements involves bidentate ligation from a CO 3 group. Because trivalent actinides such as Am 3+ and Cm 3+ have ionic radii similar to Nd 3+ , their incorporation in calcite may result in a similar defect structure.

Elzinga, E. J.; Reeder, R. J.; Withers, S. H.; Peale, R. E.; Mason, R. A.; Beck, K. M.; Hess, W. P.

2002-09-01

189

The behavior of Ni 2+ on calcite surfaces  

Microsoft Academic Search

Transport of Ni2+ in the geosphere plays a role in the formation of ore deposits as well as in the dispersion of contaminants in the environment. Some elements (Cd2+, Zn2+, Na+, K+, and Cl?) are known to diffuse in calcite at the rate of nanometers in months, so questions arose about the ability of Ni2+ to move away from adsorption

U. Hoffmann; S. L. S. Stipp

2001-01-01

190

Age Constraints on Fluid Inclusions in Calcite at Yucca Mountain.  

National Technical Information Service (NTIS)

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 el...

L. A. Neymark Y. V. Amelin J. B. Paces Z. E. Peterman J. F. Whelan

2002-01-01

191

Quantitative estimation of calcite in limestones by differential thermal analysis  

Microsoft Academic Search

A quantitative method is presented for the estimation of calcite in limestones by differential thermal analysis, using calcium hydroxide as an internal standard. The effects of variations due to particle size and impurities such as quartz, iron oxide, organic material, dolomite, magnesite, gypsum and phosphates are discussed.

K. Jehan; M. A. Qaiser; A. H. Khan

1972-01-01

192

Calcite and Picocyanobacteria in Lakes: Factors Affecting Their Interaction  

Microsoft Academic Search

Calcites build large deposits which have been observed in the rock record throughout geological time at various localities around the globe. Carbonate deposits have affected atmospheric carbon dioxide concentration. As it has been generally accepted, inorganic precipitation represents a source of carbon dioxide on short geological time scales and a sink of inorganic carbon at long time scales from millions

M. Dittrich; M. Obst; D. Mavrocordatos

2003-01-01

193

Calcite as a source of excess calcium in rainwater  

Microsoft Academic Search

Snow and rain samples collected in Sendai, Japan, were analyzed for sodium, potassium, magnesium, calcium, and strontium. The chemical composition of the samples can be fairly explained by adding some calcium to diluted seawater. A low Sr\\/Ca ratio in most of the samples showed that the excess calcium over seawater contribution may be derived from calcite contained in soil dust

Masami Ichikuni

1978-01-01

194

Influence of geometry upon crack healing rate in calcite  

Microsoft Academic Search

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

Stephen H. Hickman; Brian Evans

1987-01-01

195

Nucleation and growth kinetics in synthesizing nanometer calcite  

Microsoft Academic Search

The size of nanometer particles uniquely depends not only on the nucleus growth rate but also on the nucleation rate. This paper presents the effect of sodium tripolyphosphate on the microimages, synthesis reaction, nucleation and growth during the synthesizing of nanometer calcite using chemical analysis, SEM technique and Rosin–Ramuler probability statistics theory. The result showed that the calcium hydroxide carbonation

Rong-yi Lin; Jia-Yun Zhang; Pei-xin Zhang

2002-01-01

196

Hydration testing of athletes.  

PubMed

Dehydration not only reduces athletic performance, but also places athletes at risk of health problems and even death. For athletes, monitoring hydration has significant value in maximising performance during training and competition. It also offers medical personnel the opportunity to reduce health risks in situations where athletes engage in intentional weight loss. Simple non-invasive techniques, including weight monitoring and urine tests, can provide useful information. Bioimpedance methods tend to be easy to use and fairly inexpensive, but generally lack the precision and accuracy necessary for hydration monitoring. Blood tests appear to be the most accurate monitoring method, but are impractical because of cost and invasiveness. Although future research is needed to determine which hydration tests are the most accurate, we encourage sports teams to develop and implement hydration monitoring protocols based on the currently available methods. Medical personnel can use this information to maximise their team's athletic performance and minimise heat- and dehydration-related health risks to athletes. PMID:12457417

Oppliger, Robert A; Bartok, Cynthia

2002-01-01

197

Transformations in methane hydrates  

USGS Publications Warehouse

Detailed study of pure methane hydrate in a diamond cell with in situ optical, Raman, and x-ray microprobe techniques reveals two previously unknown structures, structure II and structure H, at high pressures. The structure II methane hydrate at 250 MPa has a cubic unit cell of a = 17.158(2) A?? and volume V = 5051.3(13) A??3; structure H at 600 MPa has a hexagonal unit cell of a = 11.980(2) A??, c = 9.992(3) A??, and V = 1241.9(5) A??3. The compositions of these two investigated phases are still not known. With the effects of pressure and the presence of other gases in the structure, the structure II phase is likely to dominate over the known structure I methane hydrate within deep hydrate-bearing sediments underlying continental margins.

Chou, I. -M.; Sharma, A.; Burruss, R. C.; Shu, J.; Mao, H. -K.; Hemley, R. J.; Goncharov, A. F.; Stern, L. A.; Kirby, S. H.

2000-01-01

198

The behavior of Ni 2+ on calcite surfaces  

NASA Astrophysics Data System (ADS)

Transport of Ni 2+ in the geosphere plays a role in the formation of ore deposits as well as in the dispersion of contaminants in the environment. Some elements (Cd 2+, Zn 2+, Na +, K +, and Cl -) are known to diffuse in calcite at the rate of nanometers in months, so questions arose about the ability of Ni 2+ to move away from adsorption sites at the surface into the bulk. Nickel incorporation into calcite is limited by its high dehydration enthalpy and by its ligand field hindrance to entering the distorted octahedra of calcite, but evidence exists that calcite can tolerate several percent Ni 2+ in the structure. Cleaved samples of Iceland spar were exposed for 1 minute to solutions of 10 -3 M and 10 -2 M Ni(ClO 4) 2, the solution was physically removed and the samples were examined using the surface sensitive techniques: X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) and Atomic Force Microscopy (AFM). XPS and TOF-SIMS showed that Ni 2+ was adsorbed while AFM confirmed that dissolution was taking place. The sample was stored in air and relative surface concentration and physical morphology were monitored for 2 years. Trends in the chemical data suggested statistically significant loss of surface Ni 2+ with time, but the decrease was very close to the limits for significance. AFM images demonstrated that surface topography of the Ni-exposed samples is modified by spontaneous recrystalization in the water layer adsorbed from air in exactly the same way that clean calcite surfaces typically rearrange. This process could bury a small amount of Ni 2+ in the bulk, explaining the very weak loss. Limited burial of Ni 2+ within the near-surface could renew calcite adsorption sites, thus increasing uptake capacity. Evidence indicates that surface recrystalization occurs even in very dry environments (<5% humidity). This means that burial could play a role in Ni 2+ mobility in unsaturated groundwater regimes or in fractures (such as in concrete) where water flow is intermittent. An important point is, however, in comparison to incorporation rates for divalent Cd and Zn, the extent of movement of Ni 2+ is extremely low. Thus, incorporation might have an effect on Ni 2+ retardation in flow paths extending over very long time scales (>10,000 years) such as would be relevant for geological processes and for long-term radioactive waste disposal. However, incorporation by burial would have negligible effect on the amount of Ni 2+ removed from groundwater by adsorption, in systems where the transport times are short (<100 years) such as for drinking water supplies from calcite-bearing porous media.

Hoffmann, U.; Stipp, S. L. S.

2001-11-01

199

ACCURATE LIME RECOMMENDATIONS UNDER SOUTH AFRICAN CONDITIONS  

Microsoft Academic Search

In a trial to test the bioavailability of certain heavy metals from slags, twelve liming materials (including different slags) were applied at three different rates to an Acrisol (sandy loam, pH(Water) of 5.2 and CEC of 4 cmolc kg) from the South African Eastern Highveld. Two Ca(OH)2 incubations were done on the specific soil—one in a soil to solution ratio of 1:1

J. H. van der Waals; A. S. Claassens

2002-01-01

200

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

2012-01-19

201

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

202

Possibility of Lime as a Stabilizer in Compressed Earth Brick (CEB)  

Microsoft Academic Search

This paper highlights the production of lime, chemical reaction during the production process, lime reaction with the soil and the prospective use of lime in the future. The research works that has been carried out showed lime has superior properties than cement in enhancing soil structure and also exhibits less embodied energy than cement. The lime through its chemical composition,

Fetra Venny Riza; Ismail Abdul Rahman; Ahmad Mujahid Ahmad Zaidi

2011-01-01

203

Calcite-dolomite thermometry: Negative evidence from the Marmorilik Formation, West Greenland  

Microsoft Academic Search

Calcite grains from 19 composite dolomite-calcite marble samples from the Marmorilik Formation, West Greenland, have been analysed for Ca, Mg, and Fe with the microprobe in order to estimate metamorphic temperatures using the calcite-dolomite solvus geothermometer. The results show that there are large variations within single samples, and, insofar as any thermal gradient can be detected, it is the opposite

Adam A. Garde

1977-01-01

204

Paleotransport of lanthanides and strontium recorded in calcite compositions from tuffs at Yucca Mountain, Nevada, USA  

Microsoft Academic Search

Secondary calcite occurs in both saturated and unsaturated hydrologic zones (SZ and UZ, respectively) in the tuffs at Yucca Mountain, Nevada, USA. In the upper UZ, the major constituents of the calcite crystal structure (C, O) have surface origins. At greater depth there is a “barren zone,” straddling the water table, where calcite is rare and mixing of surface and

David T. Vaniman; Steve J. Chipera

1996-01-01

205

Hypothetical assessment of regional liming costs for the Adirondacks  

SciTech Connect

Previous studies of lake liming costs in the Adirondacks have developed methods for predicting liming costs for individual lakes and reported these costs both for representative and specific lakes in the region. This study develops a method for estimating lake liming costs for a large number of lakes. The specific objectives of this study consisted of developing a methodology for predicting regional lake liming costs that can be extended to other regions in the United States; developing total and marginal cost (i.e., supply) curves for liming and restocking lakes in the Adirondacks Lake region; and assessing the sensitivity of the total cost and supply curves in the Adirondack Lakes region to alternative selection criteria. Lake liming and restocking costs were estimated using a version of the DeAcid model, modified specifically for this study. 2 figs.

Tawil, J.J.; Bold, F.C. (Research Enterprises, Inc., Richland, WA (USA)); Britt, D.L.; Steiner, A.J. (International Science and Technology, Inc., Reston, VA (USA)); Callaway, J.M. (Pacific Northwest Lab., Richland, WA (USA))

1990-02-01

206

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

207

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

208

A data-driven model of the global calcite lysocline  

NASA Astrophysics Data System (ADS)

Gridded maps of sediment calcium carbonate (calcite) concentration and overlying water saturation state [Archer, 1996] are combined with maps of benthic oxygen fluxes and sediment accumulation rates from Jahnke [1996] and Cweink [1986] to drive a diagenetic model of calcium carbonate preservation in deep-sea sediments. The only model input for which we cannot draw a detailed map is the rain rate of calcite to the seafloor, so I use the model to calculate the calcite rain rate required to simulate the observed distribution of calcite concentration on the seafloor. The predictive power of the model can be checked by searching for input parameters to which the model is sensitive and comparing the model requirements with independent data. The model is sensitive to the ratio of organic carbon to calcite rain rates (the rain ratio) and, within the constraint of pelagic sediment trap rain ratio data, is unable to reproduce the calcite field without respiratory dissolution, the promotion of calcium carbonate dissolution by the oxic degradation of organic carbon. However, relative to variability in sediment trap data, the required model rain ratio is insensitive to the extent of anoxic respiration, the stoichiometric ratio of O:C during respiration, the bioturbation rate, the dissolution rate constant, the effect of borate chemistry, and small offsets in the saturation state for CaCO3. The model is sensitive to the accumulation rate of non-CaCO3 material and predicts an Atlantic/Pacific difference in non-CaCO3 rain rate which is consistent with observations. The model predicts that the dissolution flux of CaCO3 from sediments is 25-40 × 1012 mol yr-1, roughly half of the total deep sea CaCO3 dissolution rate estimated from the water column alkalinity distribution [Broecker and Peng, 1987; Archer and Maier-Reimer, 1994; Wollast, 1994]. The model also predicts that only 20-30% of the flux of CaCO3 to the seafloor globally escapes dissolution.

Archer, David

1996-09-01

209

Formulation and characterization of an appropriate lime-based mortar for use with a porous limestone  

NASA Astrophysics Data System (ADS)

Several studies have shown that the degradation of architectural monuments constructed using Tuffeau stones from Val de Loire region of France over a period of time are often related to use of mortars that are not compatible with the Tuffeau stones. For this reason, it is important to ensure physico-chemical compatibility between Tuffeau and the mortar. To alleviate differences in compatibility characteristics, a mortar is prepared from hydrated lime and aggregates obtained from the crushing of Tuffeau stone and used in this study. The key parameters that influence the strength and durability characteristics such as mechanical resistance, water transfer properties, and physico-chemical properties were identified and studied. Based on these studies, recommendations are offered for the preparation of a more compatible mortar that can be used in the construction and restoration of monuments using Tuffeau stone.

Beck, Kevin; Al-Mukhtar, Muzahim

2008-12-01

210

Compressibility of gas hydrates.  

PubMed

Experimental data on the pressure dependence of unit cell parameters for the gas hydrates of ethane (cubic structure I, pressure range 0-2 GPa), xenon (cubic structure I, pressure range 0-1.5 GPa) and the double hydrate of tetrahydrofuran+xenon (cubic structure II, pressure range 0-3 GPa) are presented. Approximation of the data using the cubic Birch-Murnaghan equation, P=1.5B(0)[(V(0)/V)(7/3)-(V(0)/V)(5/3)], gave the following results: for ethane hydrate V(0)=1781 Å(3) , B(0)=11.2 GPa; for xenon hydrate V(0)=1726 Å(3) , B(0)=9.3 GPa; for the double hydrate of tetrahydrofuran+xenon V(0)=5323 Å(3) , B(0)=8.8 GPa. In the last case, the approximation was performed within the pressure range 0-1.5 GPa; it is impossible to describe the results within a broader pressure range using the cubic Birch-Murnaghan equation. At the maximum pressure of the existence of the double hydrate of tetrahydrofuran+xenon (3.1 GPa), the unit cell volume was 86% of the unit cell volume at zero pressure. Analysis of the experimental data obtained by us and data available from the literature showed that 1) the bulk modulus of gas hydrates with classical polyhedral structures, in most cases, are close to each other and 2) the bulk modulus is mainly determined by the elasticity of the hydrogen-bonded water framework. Variable filling of the cavities with guest molecules also has a substantial effect on the bulk modulus. On the basis of the obtained results, we concluded that the bulk modulus of gas hydrates with classical polyhedral structures and existing at pressures up to 1.5 GPa was equal to (9±2) GPa. In cases when data on the equations of state for the hydrates were unavailable, the indicated values may be recommended as the most probable ones. PMID:21717564

Manakov, Andrey Yu; Likhacheva, Anna Yu; Potemkin, Vladimir A; Ogienko, Andrey G; Kurnosov, Alexander V; Ancharov, Aleksei I

2011-06-29

211

SEM observations on the replacement of Bahaman aragonitic mud by calcite  

NASA Astrophysics Data System (ADS)

Conversion of Holocene aragonitic mud to calcite microspar occurs in fresh pore waters beneath hammocks on the tidal flats of west Andros Island, Bahamas, to a subsurface depth of 2.7 m. The conversion process involves both dissolution of aragonite and precipitation of calcite as a cement in pre-existing pores and displacive calcite crystallization. Neomorphism of aragonite to calcite with preservation of grain shape has not been observed. Resulting diagenetic products are lithified nodules, composed of well-sorted interlocking rhombs of microspar and of stiff, unlithified calcitic aragonite mud.

Steinen, Randolph P.

1982-09-01

212

Factors Influencing the Plasticity and Strength of Lime-Soil Mixtures.  

National Technical Information Service (NTIS)

The influence of lime type, lime percentage, and curing period on the properties of lime-soil mixtures was investigated. Thirty-nine representative Illinois soils were included in the extensive laboratory testing program. (Author)

M. R. Thompson

1967-01-01

213

Hydration of black carbon  

NASA Astrophysics Data System (ADS)

Hydration studies of n-hexane soot particles in the relative H2O pressure range 0.33-0.52 have revealed the nature of the processes between water molecules in the vapor phase and primary reaction sites at the particle surface. Initially, about 40% of the carbon-oxygen functionalities (most likely the carboxylics) on freshly prepared soot reacts irreversibly with water vapor, while at P/Po ? 0.48, the adsorption follows the Dubinin-Radushkevich equation. Determination of these parameters enables calculation of surface coverage at limiting adsorption and at the chemisorption limit for all materials studied. Limiting surface coverage of fresh soot is consistent with a 50% oxygen coverage determined earlier; it increases to about 100% for nitrated soot, which is the most extensively hydrated. Hydration has been shown to increase with soot aging, a phenomenon which has revealed an important role of physisorbed O2 in hydration. Trace-metal incorporation at the 30-110 ppm level significantly increases particle hydration and demonstrates a role of metal centers in the process.

Chughtai, A. R.; Brooks, M. E.; Smith, D. M.

1996-08-01

214

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

215

Raman spectroscopic determination of hydration number of methane hydrates  

Microsoft Academic Search

Hydration numbers of methane hydrates with various water\\/gas ratios of sample were measured by Raman spectroscopy. Artificial methane hydrates were formed at temperatures ranging from 273.2 to 278.4 K, and pressures from 3.0 to 7.0 MPa, with a stirring rate of approximately 500 rpm. Under such nonequilibrium conditions, the obtained hydrate samples had a water\\/gas ratio ranging from 6.4 to

Tsutomu Uchida; Takashi Hirano; Takao Ebinuma; Hideo Narita; Kazutoshi Gohara; Shinji Mae; Ryo Matsumoto

1999-01-01

216

Geobacillus thermoglucosidasius endospores function as nuclei for the formation of single calcite crystals.  

PubMed

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-(13)C]- and [2-(13)C]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. PMID:23455343

Murai, Rie; Yoshida, Naoto

2013-03-01

217

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

218

Evaluation of strengthening mechanisms in calcite single crystals from mollusk shells.  

PubMed

Biogenic single-crystal calcite is often reported to be harder and tougher than geologic calcite in the form of Iceland spar. However, the mechanistic origins of the superior mechanical properties of the biogenic materials are still debated. We investigate the hardness and modulus of biogenic calcite from the prismatic layer of the mollusk Atrina rigida compared with a pure geologic calcite, Iceland spar. On the {001} face, biogenic calcite is found to be 50-70% harder than geologic calcite. This range is due to the fact that changes in azimuthal angle of the indenter tip lead to a hardness variation of ?20% in A. rigida but only ?7% in Iceland spar. The higher hardness and increased anisotropy of biogenic calcite could be accounted for by hardening mechanisms based on hindered dislocation motion rather than crack deflection. PMID:23036948

Kunitake, Miki E; Mangano, Lauren M; Peloquin, John M; Baker, Shefford P; Estroff, Lara A

2012-10-02

219

Drilling Gas Hydrates on hydrate Ridge, Oregon continental margin  

Microsoft Academic Search

During Leg 204, we cored and logged 9 sites on the Oregon continental margin to determine the distribution and concentration of gas hydrates in an accretionary ridge and adjacent slope basin, investigate the mechanisms that transport methane and other gases into the gas hydrate stability zone (GHSZ), and obtain constraints on physical properties of hydrates in situ. A 3D seismic

A. M. Trehu; G. Bohrmann

2002-01-01

220

Sea floor methane hydrates at Hydrate Ridge, Cascadia margin  

NASA Astrophysics Data System (ADS)

The crest of Hydrate Ridge harbors a variety of gas hydrates in near-surface sediments. Hydrate formation and destruction continuously shape the ridge topography. Interstitial Cl-anomaly patterns in conjunction with video-guided sampling have established that the uppermost sediment column contains several distinct layers of gas hydrate which are exposed at the sea floor. A methane-oxidizing bacterial consortium populates the exposures of hydrate; colonies of vent macro-fauna are abundant as well. Discharge of methane from destabilized hydrate at the seafloor stimulates high rates of benthic oxygen consumption. These rates, however, vary by many orders of magnitude spatially and temporally, highlighting the need for implementing seafloor observatories at gas hydrate sites. Two types of hydrate fabrics were observed: A highly porous fabric with an estimated pore space of approx. 60 vol.-% and a massive type, with no visible pore space. Both types contain varying amounts of chloride, which need to be taken into account when estimating hydrate volumes from Cl-depletion of pore waters. The porous hydrate has low bulk density, which may cause periodic release of large chunks of hydrate from the sea floor. They float to the surface and leave behind a chaotic topography of mounds and depressions. These pieces of floating hydrates constitute an important transport mechanism for methane from the seafloor directly to the atmosphere.

Suess, E.; Torres, M. E.; Bohrmann, G.; Collier, R. W.; Rickert, D.; Goldfinger, C.; Linke, P.; Heuser, A.; Sahling, H.; Heeschen, K.; Jung, C.; Nakamura, K.; Greinert, J.; Pfannkuche, O.; Trehu, A.; Klinkhammer, G.; Whiticar, M. J.; Eisenhauer, A.; Teichert, B.; Elver, M.

221

The solubility of Fish Produced High Magnesium Calcite in Seawater  

NASA Astrophysics Data System (ADS)

Fish have been shown to produce high 10 to 30% magnesium calcite as part of the physiological mechanisms responsible for maintaining salt and water balance. The importance of this source to the marine carbon cycle is only now being considered. In this paper we report the first measurements of the solubility of this CaCO3 in seawater. The resulting solubility (pKsp = 5.85 ± 0.07) is more than two times higher than aragonite and similar to the high magnesium calcite generated on the Bahamas Banks (pKsp = 5.90). This high solubility of fish produced CaCO3 renders it soluble in near surface (<2000 m) waters contributing to the input of carbonate to surface ocean waters, and at least partially explaining the increase in total alkalinity above the aragonite saturation horizon.

Woosley, R. J.; Millero, F. J.; Grosell, M.

2011-12-01

222

Incorporation of Mg and Sr in calcite of cultured benthic foraminifera: impact of calcium concentration and associated calcite saturation state  

NASA Astrophysics Data System (ADS)

We investigated the effect of the calcium concentration in seawater and thereby the calcite saturation state (?) on the magnesium and strontium incorporation into benthic foraminiferal calcite under laboratory conditions. For this purpose individuals of the shallow-water species Heterostegina depressa (precipitating high-Mg calcite, symbiont-bearing) and Ammonia tepida (low-Mg calcite, symbiont-barren) were cultured in media under a range of [Ca2+], but similar Mg/Ca ratios. Trace element/Ca ratios of newly formed calcite were analysed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and normalized to the seawater elemental composition using the equation DTE=(TE/Cacalcite)/(TE/Caseawater). The culturing study shows that DMg of A. tepida significantly decreases with increasing ? at a gradient of -4.3×10-5 per ? unit. The DSr value of A. tepida does not change with ?, suggesting that fossil Sr/Ca in this species may be a potential tool to reconstruct past variations in seawater Sr/Ca. Conversely, DMg of H. depressa shows only a minor decrease with increasing ?, while DSr increases considerably with ? at a gradient of 0.009 per ? unit. The different responses to seawater chemistry of the two species may be explained by a difference in the calcification pathway that is, at the same time, responsible for the variation in the total Mg incorporation between the two species. Since the Mg/Ca ratio in H. depressa is 50-100 times higher than that of A. tepida, it is suggested that the latter exhibits a mechanism that decreases the Mg/Ca ratio of the calcification fluid, while the high-Mg calcite forming species may not have this physiological tool. If the dependency of Mg incorporation on seawater [Ca2+] is also valid for deep-sea benthic foraminifera typically used for paleostudies, the higher Ca concentrations in the past may potentially bias temperature reconstructions to a considerable degree. For instance, 25 Myr ago Mg/Ca ratios in A. tepida would have been 0.2 mmol/mol lower than today, due to the 1.5 times higher [Ca2+] of seawater, which in turn would lead to a temperature underestimation of more than 2 °C.

Raitzsch, M.; Dueñas-Bohórquez, A.; Reichart, G.-J.; de Nooijer, L. J.; Bickert, T.

2010-03-01

223

HYDRATE CORE DRILLING TESTS  

SciTech Connect

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 a program to safely and economically drill, core and produce gas from arctic hydrates. The current work scope includes drilling and coring one well on Anadarko leases in FY 2003 during the winter drilling season. A specially built on-site core analysis laboratory will be used to determine some of the physical characteristics of the hydrates and surrounding rock. Prior to going to the field, the project team designed and conducted a controlled series of coring tests for simulating coring of hydrate formations. A variety of equipment and procedures were tested and modified to develop a practical solution for this special application. This Topical Report summarizes these coring tests. A special facility was designed and installed at MTI's Drilling Research Center (DRC) in Houston and used to conduct coring tests. Equipment and procedures were tested by cutting cores from frozen mixtures of sand and water supported by casing and designed to simulate hydrate formations. Tests were conducted with chilled drilling fluids. Tests showed that frozen core can be washed out and reduced in size by the action of the drilling fluid. Washing of the core by the drilling fluid caused a reduction in core diameter, making core recovery very difficult (if not impossible). One successful solution was to drill the last 6 inches of core dry (without fluid circulation). These tests demonstrated that it will be difficult to capture core when drilling in permafrost or hydrates without implementing certain safeguards. Among the coring tests was a simulated hydrate formation comprised of coarse, large-grain sand in ice. Results with this core showed that the viscosity of the drilling fluid must also be carefully controlled. When coarse sand was being cored, the core barrel became stuck because the drilling fluid was not viscous enough to completely remove the large grains of sand. These tests were very valuable to the project by showing the difficulties in coring permafrost or hydrates in a laboratory environment (as opposed to a field environment where drilling costs are much higher and the potential loss of equipment greater). Among the conclusions reached from these simulated hydrate coring tests are the following: Frozen hydrate core samples can be recovered successfully; A spring-finger core catcher works best for catching hydrate cores; Drilling fluid can erode the core and reduces its diameter, making it more difficult to capture the core; Mud must be designed with proper viscosity to lift larger cuttings; and The bottom 6 inches of core may need to be drilled dry to capture the core successfully.

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

2002-11-01

224

Interaction of copper with the surface of calcite  

SciTech Connect

The interaction of Cu ions in solution with the surface of calcite has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto calcite indicates that the process is rapid and strong in both distilled water and seawater. In distilled water, Cu uptake is directly proportional to the concentration of Cu in solution; Cu/sub s/ = K/sub s/Cu/sub 1/. This Cu/sub s/ dependence on Cu/sub 1/ is linear over the entire Cu concentration range studied (0.1 to 200 ..mu..M). Results do not indicate the formation of a precipitate of either malachite or copper carbonate. In seawater, the uptake of Cu is also directly proportional to the concentration of Cu/sub 1/ up to a limiting value of approximately 13 ..mu..M. The average value for K/sub s/ in seawater, 0.24 +- 0.06 (Cu/sub 1/ less than or equal to 13 ..mu..M), is approximately an order of magnitude less than in distilled water. This is probably the result of smaller Cu/sub 1/ activity coefficients and increased site competition by other ions in seawater. Attempts to increase the Cu/sub 1/ concentration above 13 ..mu..M resulted in the additional Cu being deposited on the surface of the calcite. A possible explanation for this behavior is the formation of a precipitate of malachite on the calcite surface. The value of K/sub s/ decreased slightly with increasing solid to solution ratios in seawater.

Franklin, M.L.; Morse, J.W.

1981-05-01

225

Planktic foraminiferal sedimentation and the marine calcite budget  

NASA Astrophysics Data System (ADS)

The vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal CaCO3 budget is presented. Test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples. Modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget, highlighting the importance of ecological, autecological (e.g., reproduction), and biogeochemical conditions that determine the presence or absence of species. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccolithophores, pteropods, and calcareous dinophytes is discussed. Based on the studied regions, the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1.3-3.2 Gt yr-1, equivalent to 23-56% of the total open marine CaCO3 flux. The preservation of tests varies on a regional and temporal scale, and is affected by local hydrography and dissolution. During most of the year (off-peak periods), many tests dissolve above 700-m water depth while settling through the water column, with on average only 1-3% of the initially exported CaCO3 reaching the deep-seafloor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of tests to the formation of deep-sea sediments. On average, ˜25% of the initially produced planktic foraminiferal test CaCO3 settles on the seafloor. The total planktic foraminiferal contribution of CaCO3 to global surface sediments amounts to 0.36-0.88 Gt yr-1, ˜32-80% of the total deep-marine calcite budget.

Schiebel, Ralf

2002-12-01

226

Deformation twinning in calcite, dolomite, and other rhombohedral carbonates  

Microsoft Academic Search

Transmission electron microscope (tem) observations of single and multiple twins in calcite and dolomite are presented, and the results are analysed by means of selected area diffraction and trace analysis. Simple twinning in rhodochrosite and kutnahorite is also analysed. It is shown that the ordered carbonates, such as dolomite, have a common twinning plane {01\\u000a$$\\\\bar 1$$\\u000a2} and this

D. J. Barber; H.-R. Wenk

1979-01-01

227

Crystallographic reorganization of the calcitic prismatic layer of oysters  

Microsoft Academic Search

The calcitic columnar prisms of pteriomorphian bivalves have the crystallographic c-axis oriented perpendicular to the shell surface and the a-axes rotated without any preferential orientation. In oysters, SEM, XRD and EBSD analyses show that individual prisms initially have their a-axes randomly oriented but are able to progressively orient them parallel to those of their neighbors. This ability is apparently confined

Antonio G. Checa; Francisco J. Esteban-Delgado; Joaquín Ramírez-Rico; Alejandro B. Rodríguez-Navarro

2009-01-01

228

Use of coupled passivants and consolidants on calcite mineral surfaces  

SciTech Connect

Deterioration of monuments, buildings, and works of art constructed of carbonate-based stone potentially can be arrested by applying a combination of chemical passivants and consolidants that prevent hydrolytic attack and mechanical weakening. The authors used molecular modeling and laboratory synthesis to develop an improved passivating agent for the calcite mineral surface based on binding strength and molecular packing density. The effectiveness of the passivating agent with and without a linked outer layer of consolidant against chemical weathering was determined through leaching tests conducted with a pH-stat apparatus at pH 5 and 25 C. For the range of molecules considered, modeling results indicate that the strongest-binding passivant is the trimethoxy dianionic form of silylalkylaminocarboxylate (SAAC). The same form of silylalkylphosphonate (SAP) is the second strongest binder and the trisilanol neutral form of aminoethylaminopropylsilane (AEAPS) is ranked third. Short-term leaching tests on calcite powders coated with the trisilanol derivative of SAAC, the triethoxy neutral form of SAP, and the trimethoxy neutral form of AEAPS show that the passivant alone does not significantly slow the dissolution rate. However, all passivants when linked to the sol consolidant result in decreased rates. Combined AEAPS plus consolidant results in a coating that performs better than the commercial product Conservare{reg_sign} OH and at least as well as Conservare{reg_sign} H. The modeling results indicate that there may be a threshold binding energy for the passivant above which the dissolution rate of calcite is actually enhanced. More strongly-binding passivants may aid in the dissolution mechanism or dissociate in aqueous solution exposing the calcite surface to water.

Nagy, K.L.; Cygan, R.T.; Brinker, C.J.; Ashley, C.S. [Sandia National Labs., Albuquerque, NM (United States); Scotto, C.S. [Naval Research Lab., Washington, DC (United States). Optical Sciences Div.

1997-02-01

229

Calcite and dolomite discrimination using airborne SWIR imaging spectrometer data  

Microsoft Academic Search

The SWIR full spectrum imager (SFSI) is a hyperspectral push-broom imager, acquiring imagery in 120 0.010 micrometers wide bands simultaneously covering the 1.20 micrometers to 2.47 micrometers spectral region. During the first flights of the instrument hyperspectral imagery was acquired over a calcite quarry and a dolomite quarry. Both these minerals show distinctive carbonate absorption features in the 1.7 to

Neil Rowlands; Robert A. Neville

1996-01-01

230

A re-evaluation of aragonite versus calcite seas  

Microsoft Academic Search

Some workers have argued that the mineralogy of ancient carbonates may have been different from that of modern sediments,\\u000a with calcite being considered the dominant mineral during the Ordovician, Devonian-mid Carboniferous, and Jurassic-Cretaceous\\u000a to Early\\/Middle Cenozoic (e.g. Sandberg 1983; Wilkinson and Algeo 1989). Variation in carbonate mineralogy has been related\\u000a to the position of global sea level (emergent or submergent

Mohammad H. Adabi

2004-01-01

231

Adhesion of Hydrated Silicate Films.  

National Technical Information Service (NTIS)

We used fracture mechanics test techniques to measure the adhesive bond energy formed between hydrated silica glass surfaces and silicate species deposited from solution. In the case of silicate surfaces hydrated in room temperature water vapor, intermole...

T. A. Michalske K. D. Keefer

1988-01-01

232

Hydration of highly charged ions  

NASA Astrophysics Data System (ADS)

Concise treatment of highly charged ions with very different properties. Performed by ab initio simulations with the recent QMCF-MD methodology. Treating hydrates with extreme stability, labile hydrates and instable systems with (sub-)picosecond proton transfer reactions.

Hofer, Thomas S.; Weiss, Alexander K. H.; Randolf, Bernhard R.; Rode, Bernd M.

2011-08-01

233

Micromorphology of calcite-silica deposits, Yucca Mountain, Nevada  

SciTech Connect

High-level nuclear waste placed at the proposed Yucca Mountain repository must remain isolated for many thousands of years. Concern remains that calcite-silica vein deposits along fault fractures near the proposed repository are not solely pedogenic, but rather record upwelling of groundwater and thus possible routes for transporting radionuclides to the land surface. The purpose of this study was to provide an additional test for whether the calcite-silica deposits have a groundwater (phreatic) origin or a pedogenic origin. This test involved comparing the micromorphic features of the controversial vein deposits with the micromorphic features of known pedogenic and phreatic deposits. Using a combination of thin sections, scanning electron microscopy, x-ray diffraction, and cathodoluminescence, the following micromorphic features were compared : argillans, calcified microorganisms, detrital grains, aquatic microfossils, calcite crystal size and sorting, and opal content. Based on these comparisons, the controversial vein deposits are more similar to pedogenic deposits than phreatic deposits, and thus appear to be of pedogenic origin. 71 refs., 4 figs., 3 tabs.

Monger, H.C.; Adams, H.P. [New Mexico State Univ., Las Cruces, NM (United States)

1996-03-01

234

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

235

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

236

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

237

Interactions of salicylic acid derivatives with calcite crystals.  

PubMed

Investigation of basic interactions between the active pharmaceutical compounds and calcium carbonates is of great importance because of the possibility to use the carbonates as a mineral carrier in drug delivery systems. In this study the mode and extent of interactions of salicylic acid and its amino acid derivates, chosen as pharmaceutically relevant model compounds, with calcite crystals are described. Therefore, the crystal growth kinetics of well defined rhombohedral calcite seed crystals in the systems containing salicylic acid (SA), 5-amino salicylic acid (5-ASA), N-salicyloil-l-aspartic acid (N-Sal-Asp) or N-salicyloil-l-glutamic acid (N-Sal-Glu), were investigated. The precipitation systems were of relatively low initial supersaturation and of apparently neutral pH. The data on the crystal growth rate reductions in the presence of the applied salicylate molecules were analyzed by means of Cabrera & Vermileya's, and Kubota & Mullin's models of interactions of the dissolved additives and crystal surfaces. The crystal growth kinetic experiments were additionally supported with the appropriate electrokinetic, spectroscopic and adsorption measurements. The Langmuir adsorption constants were determined and they were found to be in a good correlation with values obtained from crystal growth kinetic analyses. The results indicated that salicylate molecules preferentially adsorb along the steps on the growing calcite surfaces. The values of average spacing between the adjacent salicylate adsorption active sites and the average distance between the neighboring adsorbed salicylate molecules were also estimated. PMID:21963207

Ukrainczyk, Marko; Gredi?ak, Matija; Jeri?, Ivanka; Kralj, Damir

2011-09-12

238

Modeling steps and kinks on the surface of calcite.  

PubMed

This work presents modeling results on the cleavage face of calcite as well as on steps and isolated kinks on this face. We used static lattice energy minimization and interatomic potentials fitted to bulk properties. The energy needed to cleave a bulk calcite crystal along the [1 0 (-)1 4] plane was calculated to be 0.59 J m(-2) in agreement with previous studies using the same potentials. The perfect surface reconstructs in the top few atomic layers, but its symmetry corresponds to the bulk termination. By contrast, the (1 0 (-)1 4) surface with cleavage steps present reconstructs to form a (2 x 1) super cell. This may help explain experimental observations of (2 x 1) symmetry on calcite surfaces. The energy required to form a monatomic obtuse step is calculated to be 1.3 x 10(-10) J m(-1) and for the acute step, 2.4 x 10(-10) J m(-1), suggesting that obtuse steps dominate on cleaved surfaces. Along the two types of steps, a total of 16 kink geometries exist. We calculated kink defect energy with two different approaches: one where kink pairs were added onto infinitely long steps and one where kinks were placed inside pits on a cleavage surface. Calculations on infinitely long steps show that for vacuum conditions, kink pairs possess roughly identical formation energy, about 1.2-2.2 eV, so based on energetics one cannot expect significant differences in kink site frequency PMID:15511175

Kristensen, Rune; Stipp, S L S; Refson, Keith

2004-11-01

239

Modeling steps and kinks on the surface of calcite  

NASA Astrophysics Data System (ADS)

This work presents modeling results on the cleavage face of calcite as well as on steps and isolated kinks on this face. We used static lattice energy minimization and interatomic potentials fitted to bulk properties. The energy needed to cleave a bulk calcite crystal along the {1 0 1 4} plane was calculated to be 0.59 J m-2 in agreement with previous studies using the same potentials. The perfect surface reconstructs in the top few atomic layers, but its symmetry corresponds to the bulk termination. By contrast, the (1 0 1 4) surface with cleavage steps present reconstructs to form a (2×1) super cell. This may help explain experimental observations of (2×1) symmetry on calcite surfaces. The energy required to form a monatomic obtuse step is calculated to be 1.3×10-10 J m-1 and for the acute step, 2.4×10-10 J m-1, suggesting that obtuse steps dominate on cleaved surfaces. Along the two types of steps, a total of 16 kink geometries exist. We calculated kink defect energy with two different approaches: one where kink pairs were added onto infinitely long steps and one where kinks were placed inside pits on a cleavage surface. Calculations on infintely long steps show that for vacuum conditions, kink pairs possess roughly identical formation energy, about 1.2-2.2 eV, so based on energetics one cannot expect significant differences in kink site frequency.

Kristensen, Rune; Stipp, S. L. S.; Refson, Keith

2004-11-01

240

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.

241

Study of Lime Dissolution Under Forced Convection  

NASA Astrophysics Data System (ADS)

Dissolution of different CaO cubes under force convection in liquid CaO-"FeO"-SiO2 slag was studied at 1873 K (1600 °C). A linear relationship between normalized lengths and time was obtained after the experiment. It was evidently observed that the removal of the interface layer(s) including 2CaO·SiO2 by shear stress was the main mechanism for the dissolution. A stirring rate of approximately 100 rpm was found to be efficient to remove the interface layer(s). The limes with different structures had different dissolution rates.

Deng, Tengfei; Sichen, Du

2012-06-01

242

Cryogenic cave calcite from several Central European caves: age, carbon and oxygen isotopes and a genetic model  

Microsoft Academic Search

Cryogenic cave calcite (CCC), formed by segregation of solutes during water freezing, was found in three Central European caves. This calcite type forms accumulations of loose calcite grains on cave floor. The calcite grains are of highly variable crystal morphology, and of sizes ranging from less than 1 mm to over 1 cm. The most typical feature is their accumulation

Karel Žák; Jan Urban; Václav C??lek; Helena Hercman

2004-01-01

243

Sr isotopic and elemental characteristics of calcites in the Chinese deserts: Implications for eolian Sr transport and seawater Sr evolution  

Microsoft Academic Search

Calcite content, Sr concentrations, and isotopes of calcites in the Chinese deserts are systematically studied in this paper. Calcite contents, which are calculated according to acid-soluble Ca contents in the deserts, are generally higher in the sandy deserts than in the sandy lands and decrease roughly from northwest to northeast of China. Acid-soluble Sr is well correlated with calcite in

Wenbo Rao; Jun Chen; Jiedong Yang; Junfeng Ji; Gengxin Zhang

2009-01-01

244

Reactions of lime with carbonate-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. The work described in this paper was undertaken to elucidate the mechanism of this precipitation reaction about which surprisingly little is known. In the first part of the study, the composition

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

1998-01-01

245

Soil liming as a measure to mitigate acid runoff  

Microsoft Academic Search

Watershed liming is one method to decrease the acidity of surface waters. To gain an understanding of the mechanisms involved in terrestrial liming and to develop a tool for planning and evaluation, a mathematical model has been developed. The model includes key chemical processes such as limestone dissolution, cation-exchange reactions, and leaching and accumulation of dissolved species. The ability of

Per Warfvinge; Harald Sverdrup

1988-01-01

246

The effect of additives on lime dissolution rates. Final report  

Microsoft Academic Search

Based on the previous years` studies concerning the efficiency of SOâ removal by spray dryers with high sulfur coal flue gas, the work for year five included investigations of lime dissolution rates at different slaking conditions and with the effect of additives. The prominent additives that have significant effects on lime dissolution rates were tested with the mini pilot spray

Khang

1996-01-01

247

Lime slurry use at the Industrial Wastewater Pretreatment Facility  

SciTech Connect

The use of lime slurry at the IWPF demonstrated many benefits. Hazardous chemical use was reduced, solids handling was improved, water quality was enhanced and there has been a cost savings. The lime slurry also enabled the plant to begin treating the soluble oil waste, which we were not able to do in the past.

Rice, L.E. [Allied-Signal Aerospace Co., Kansas City, MO (United States). Kansas City Div.; Hughes, R.W. [Professional Services Group, Inc., Kansas City, MO (United States); Baggett, G. [Genex/Praxair, Inc., Kansas City, MO (United States)

1996-04-01

248

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

249

Lime Stabilized Sludge: Its Stability and Effect on Agricultural Land.  

National Technical Information Service (NTIS)

An optimum system for the lime stabilization of municipal sewage sludge was first developed and then evaluated. The primary objectives of this work were: (1) To determine the degree of stability induced in a sludge by lime addition and (2) to determine th...

C. A. Counts A. J. Shuckrow

1975-01-01

250

Similarities Between Lime and Limestone in Wet-Dry Scrubbing.  

National Technical Information Service (NTIS)

The dry reaction between SO sub 2 and lime or calcium carbonate has been investigated at low temperature for application in wet-dry scrubbing. The intention of the study was to compare the reactivity of lime and calcium carbonate when reacting with SO sub...

A. M. Stroemberg H. T. Karlsson J. Bjerle J. Klingspor

1984-01-01

251

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 regionâ??s calcareous soils. This area has recently experienced an increase in dairy production, with dairi...

252

Interaction of copper with the surface of calcite  

SciTech Connect

The interaction of Cu ions in solution with the surface of calcite has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto calcite indicates that the process is rapid and strong in both distilled water and seawater. In distilled water, Cu uptake is directly proportional to the concentration of Cu in solution; Cu/sub s/ = K/sub s/Cu/sub 1/. The average value for K/sub s/ is 3.5 +- 1.7. The Cu/sub s/ dependence on Cu/sub 1/ is linear over the entire Cu concentration range studied (0.1 to 200 ..mu..M). Results do not indicate the formation of a precipitate of either malachite or copper carbonate. A precipitate of the form Cu/sub x/Ca/sub 1-x/CO/sub 3/ may be deposited onto the calcite surface in distilled water. The value of K/sub s/ in distilled water decreased sharply over the solid to solution ratio range of 0.1 to 2 g CaCO/sub 3/ 1/sup -1/. This was followed by a small change in K/sub s/ for solid to solution ratios in the range of 2 to 10 g CaCO/sub 3/ 1/sup -1/. In seawater, the uptake of Cu is also directly proportional to the concentration of Cu/sub 1/ up to a limiting value of approximately 13 ..mu..M. The average value for K/sub s/ in seawater, 0.24 +- 0.06 (Cu/sub 1/ less than or equal to 13 ..mu..M), is approximately an order of magnitude less than in distilled water. This is probably the result of smaller Cu/sub 1/ activity coefficients and increased site competition by other ions in seawater. Attempts to increase the Cu/sub 1/ concentration above 13 ..mu..M resulted in the additional Cu being deposited on the surface of the calcite. A possible explanation for this behavior is the formation of a precipitate of malachite on the calcite surface. The value of K/sub s/ decreased slightly with increasing solid to solution ratios in seawater.

Franklin, M.L.; Morse, J.W.

1981-12-01

253

CO2 Adhesion on Hydrated Mineral Surfaces.  

PubMed

Hydrated mineral surfaces in the environment are generally hydrophilic but in certain cases can strongly adhere CO2, which is largely nonpolar. This adhesion can significantly alter the wettability characteristics of the mineral surface and consequently influence capillary/residual trapping and other multiphase flow processes in porous media. Here, the conditions influencing adhesion between CO2 and homogeneous mineral surfaces were studied using static pendant contact angle measurements and captive advancing/receding tests. The prevalence of adhesion was sensitive to both surface roughness and aqueous chemistry. Adhesion was most widely observed on phlogopite mica, silica, and calcite surfaces with roughness on the order of ?10 nm. The incidence of adhesion increased with ionic strength and CO2 partial pressure. Adhesion was very rarely observed on surfaces equilibrated with brines containing strong acid or base. In advancing/receding contact angle measurements, adhesion could increase the contact angle by a factor of 3. These results support an emerging understanding of adhesion of, nonpolar nonaqueous phase fluids on mineral surfaces influenced by the properties of the electrical double layer in the aqueous phase film and surface functional groups between the mineral and CO2. PMID:24040744

Wang, Shibo; Tao, Zhiyuan; Persily, Sara M; Clarens, Andres F

2013-10-04

254

Calcite twin analysis in syntectonic calcite, Cape Fold Belt, South Africa: Implications for fold and cleavage formation within a shallow thrust front  

Microsoft Academic Search

Lithologies of two formations in the frontal ranges of the Cape Fold Belt, South Africa, host synorogenic calcite precipitated at low metamorphic grade during the end-Permian deformation of this Gondwana-wide orogen. The calcite crystals are mechanically twinned and this deformation is linked to both folding and the formation of an axial planar cleavage with associated extensional veins. Twinning strain analysis

John P. Craddock; Alex W. McKiernan; Maarten J. de Wit

2007-01-01

255

Addition of Calcite Reduces Iron’S Bioavailability in the Pennsylvania Coals—Potential Use Of Calcite for the Prevention Of Coal Workers’ Lung Diseases  

Microsoft Academic Search

In the present study, a hypothesis was tested that the addition of calcite into the Pennsylvania coals may reduce levels of bioavailable iron (BAI), an important component in the mixed coal dust that may contribute to coal workers’ lung diseases. Predetermined proportions of calcite (0, 1, 2, 5, 10% w\\/w) were added into three PA coals. After suspending the mixtures

Qi Zhang; Xi Huang

2005-01-01

256

Speciation of As in calcite by micro-XAFS: Implications for remediation of As contamination in groundwater  

NASA Astrophysics Data System (ADS)

To evaluate the role of calcite as a host phase of arsenic (As) in As-contaminated groundwater, distribution behavior of Asbetween natural calcite and groundwater in deep underground was investigated based on As oxidation state. Speciation analyses of As in natural calcite by ?-XRF-XAFS analyses showed (i) preferentialarsenate uptake by calcite, and (ii) promptness of arsenate uptake by minor iron (Fe) carbonate minerals coprecipitated with calcite. These findings suggest that the effect of calcite on As remediation of the As-contamination systems stronglydepends on arsenite to arsenate ratio (i.e., redox condition) in groundwater, and maybe governed bythe amount of Fe coprecipitated with calcite.

Yokoyama, Y.; Iwatsuki, T.; Terada, Y.; Takahashi, Y.

2013-04-01

257

Reactive uptake of acetic acid on calcite and nitric acid reacted calcite aerosol in an environmental reaction chamber.  

PubMed

The heterogeneous chemistry of gas-phase acetic acid with CaCO(3)(calcite) aerosol was studied under varying conditions of relative humidity (RH) in an environmental reaction chamber. Infrared spectroscopy showed the loss of gas-phase reactant and the appearance of a gaseous product species, CO(2). The acetic acid is observed to adsorb onto the calcite aerosol through both a fast and a slow uptake channel. While the fast channel is relatively independent of RH, the slow channel exhibits enhanced uptake and reaction as the RH is increased. In additional experiments, the calcite aerosol was exposed to both nitric and acetic acids in the presence of water vapor. The rapid conversion of the particulate carbonate to nitrate and subsequent deliquescence significantly enhances the uptake and reaction of acetic acid. These results suggest a possible mechanism for observed correlations between particulate nitrate and organic acids in the atmosphere. Calcium rich mineral dust may be an important sink for simple organic acids. PMID:18075693

Prince, Amy Preszler; Kleiber, Paul D; Grassian, Vicki H; Young, Mark A

2007-11-21

258

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

259

[Hydration in clinical practice].  

PubMed

Water is an essential foundation for life, having both a regulatory and structural function. The former results from active and passive participation in all metabolic reactions, and its role in conserving and maintaining body temperature. Structurally speaking it is the major contributer to tissue mass, accounting for 60% of the basis of blood plasma, intracellular and intersticial fluid. Water is also part of the primary structures of life such as genetic material or proteins. Therefore, it is necessary that the nurse makes an early assessment of patients water needs to detect if there are signs of electrolyte imbalance. Dehydration can be a very serious problem, especially in children and the elderly. Dehydrations treatment with oral rehydration solution decreases the risk of developing hydration disorders, but even so, it is recommended to follow preventive measures to reduce the incidence and severity of dehydration. The key to having a proper hydration is prevention. Artificial nutrition encompasses the need for precise calculation of water needs in enteral nutrition as parenteral, so the nurse should be part of this process and use the tools for calculating the patient's requirements. All this helps to ensure an optimal nutritional status in patients at risk. Ethical dilemmas are becoming increasingly common in clinical practice. On the subject of artificial nutrition and hydration, there isn't yet any unanimous agreement regarding hydration as a basic care. It is necessary to take decisions in consensus with the health team, always thinking of the best interests of the patient. PMID:21428011

Maristany, Cleofé Pérez-Portabella; Segurola Gurruchaga, Hegoi

2011-01-01

260

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

261

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

262

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

2010-03-21

263

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

2011-03-21

264

Investigation of fatigue properties of granite asphalt mixtures containing hydrated lime  

Microsoft Academic Search

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

Shaopeng Wu; Xu Huang

2009-01-01

265

Oxygen isotopes in calcite grown under cave-analogue conditions  

NASA Astrophysics Data System (ADS)

Speleothem oxygen isotopes and growth rates are valuable proxies for reconstructing climate history. There is debate, however, about the conditions that allow speleothems to grow in oxygen isotope equilibrium, and about the correct equilibrium fractionation factors. We report results from a series of carbonate growth experiments in karst-analogue conditions in the laboratory. The setup closely mimics natural processes (e.g. precipitation driven by CO 2-degassing, low ionic strength solution, thin solution film) but with a tight control on growth conditions (temperature, pCO 2, drip rate, calcite saturation index and the composition of the initial solution). Calcite is dissolved in water in a 20,000 ppmV pCO 2 environment. This solution is dripped onto glass plates (coated with seed-carbonate) in a lower pCO 2 environment (<2500 ppmV), where degassing leads to calcite growth. Experiments were performed at 7, 15, 25 and 35 °C. At each temperature, calcite was grown at three drip rates (2, 6 and 10 drips per minute) on separate plates. The mass of calcite grown in these experiments varies with temperature ( T in K) and drip rate ( d_ r in drips min -1) according to the relationship daily growth mass = 1.254 + 1.478 ? 10 -9 ? e0.0679 T + ( e0.00248 T - 2) ? (-0.779 d_ r2 + 10.05 d_ r + 11.69). This relationship indicates a substantial increase of growth mass with temperature, a smaller influence of drip rate on growth mass at low temperature and a non-linear relationship between drip rate and growth mass at higher temperatures. Low temperature, fast dripping conditions are found to be the most favourable for reducing effects associated with evaporation and rapid depletion of the dissolved inorganic carbon reservoir (rapid DIC-depletion). The impact of evaporation can be large so caves with high relative humidity are also preferable for palaeoclimate reconstruction. Even allowing for the maximum offsets that may have been induced by evaporation and rapid DIC-depletion, ? 18O measured in some of our experiments remain higher than those predicted by Kim and O'Neil (1997). Our new results are well explained by equilibrium at a significantly higher ?calcite-water, with a kinetic-isotope effect that favours 16O incorporation as growth rate increases. This scenario agrees with recent studies by Coplen (2007) and Dietzel et al. (2009). Overall, our results suggest that three separate processes cause ? 18O to deviate from true isotope equilibrium in the cave environment. Two of these drive ? 18O to higher values (evaporation and rapid DIC-depletion) while one drives ? 18O to lower values (preferential incorporation of 16O in the solid carbonate at faster growth rates). While evaporation and DIC-depletion can be avoided in some settings, the third may be inescapable in the cave environment and means that any temperature to ? 18O relationship is an approximation. The controlled conditions of the present experiments also display limitations in the use of the Hendy test to identifying equilibrium growth.

Day, C. C.; Henderson, G. M.

2011-07-01

266

Freshwater-phreatic calcite cementation, Schooner Cays, Bahamas  

SciTech Connect

Freshwater-phreatic calcite cementation is an active process on 700 and 2700 yr-old ooid-sand islands in the Schooner Cays, Bahamas. Cement fabrics and textures indicate a general, four-stage model of pore infilling. (1) The precipitation of isolated, decimicron-sized, rhombohedrons of calcite on grain surfaces forms an incipient circumgranular cement. (2) Continued precipitation enlarges crystal sizes and forms new rhombohedral crystals, resulting in a continuous circumgranular rim of cement. (3) Additional cementation quickly masks the circumgranular fabric, producing a partial pore-filling mosaic. (4) The remaining pore space is occluded with a mosaic of calcite cement. Petrographic evidence for the earlier circumgranular rim of cement is not necessarily apparent after the last stage of cementation. Empty pores and all four stages of phreatic-zone cementation were observed in the diagenetically immature 700 yr-old rocks, but only stages 2 through 4 were observed in the diagenetically more mature 2700 yr-old phreatic zone samples. Cements are distributed homogeneously within each pore at every stage, yet because each pore may proceed through the four stages at different rates, each pore can be at a different stage of infilling. This results in an inhomogeneous distribution of cement between pores during the initial stages of cementation. Recognition of a cement stratigraphy similar to that described here should aid in the identification of freshwater-phreatic diagenesis in ancient carbonate rock sequences. Variability in the amount of freshwater-phreatic cement between pores should be expected and not interpreted as the product of different paragenetic sequences.

Budd, D.A.

1985-02-01

267

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

268

Calcite saturation in the River Dee, NE Scotland.  

PubMed

The spatial and temporal variations in calcite (calcium carbonate) solubility within the Dee basin of NE Scotland were assessed using water chemistry data gathered from a network of 59 sites monitored for water quality from June 1996 to May 1997. Calcite solubility, expressed in terms of a saturation index (SIcalcite), was determined from measured streamwater pH, Gran alkalinity and calcium concentrations and water temperature. In general, the waters of the Dee system are undersaturated with respect to calcite, though the saturation index is higher during the summer months indicating a dependency on flow conditions and biological activity. Under low-flow conditions, the streamwaters are dominated by water derived from the lower soil horizons and deeper groundwater stores and therefore, ions such as Gran alkalinity and calcium are at their highest concentrations as they are derived mainly from bedrock weathering. The influence of biological activity on the carbonate system is also evident as the observed pH and estimated EpCO2 values indicate strong seasonal patterns, with the highest pH and lowest EpCO2 values occurring during the summer low-flow periods. Only at three sites in the lowland region of the catchment, during the summer low-flow period, are the waters oversaturated. As such, the Dee system represents an extreme 'end-member' case when compared to many UK rivers that span both under- and oversaturated conditions during the year. Regression analysis highlights a systematic change in the SIcalcite-pH relationship in a broad east-west direction across the Dee system. At sites draining the relatively impermeable upland areas, the regression of SIcalcite against pH gives a straight line with a gradient in the range 1.6-2.4. Correspondingly, under the most extreme alkaline conditions found at sites draining lowland agricultural areas, a straight-line relationship exists but with a gradient of unity. It is concluded that these changes in the SIcalcite-pH relationship are due to variations in the bicarbonate system induced by the flow conditions and biological activity. Given the waters are undersaturated, then calcite precipitation and hence phosphorus co-precipitation cannot occur within the water column. PMID:11846077

Wade, A J; Neal, C; Smart, R P; Edwards, A C

2002-01-23

269

Anisotropic surface coupling while sliding on dolomite and calcite crystals  

NASA Astrophysics Data System (ADS)

High-resolution friction force microscopy has been performed on the (104) surfaces of dolomite and calcite in deionized water. The two rows of oxygen atoms alternating in a zigzag way on top of both surfaces are resolved with similar contrast while scanning along the [421¯] direction. Along the [010] direction, only one row is resolved, provided that the normal loading is large enough. The direction-dependent interaction between the probing tip and surface atoms is explained by numeric calculations based on the Prandtl-Tomlinson model.

Pina, Carlos M.; Miranda, Rodolfo; Gnecco, Enrico

2012-02-01

270

The role of dislocations and surface morphology in calcite dissolution  

Microsoft Academic Search

The authors have measured the dissolution rate for undeformed (ρ â¼ 10³ dislocations{center dot}cm⁻²) calcite to be 3.1 à 10⁻¹° mol{center dot}cm⁻²{center dot}s⁻¹ in free-drift rotating disk experiments at 1,160 rpm, 25C and pH 8.6 in 0.7 M KCl solution far from equilibrium. The rate increased by a factor of â¼ 2.3 for a strained sample (ρ = 6 Ã

IAN N. MACINNIS; SUSAN L. BRANTLEY

1992-01-01

271

Proposed modifications to the method for the determination of available lime  

Microsoft Academic Search

Lime is an important industrial chemical used widely in the steel manufacturing and water treatment industries. One of the major procedures employed to control the quality of lime during its production process is the so-called available lime (Av CaO) method. This method measures the theoretical amount of lime available for neutralisation purposes, and also gives an indication of the degree

J. H. Potgieter; S. S. Potgieter; B. Legodi

2001-01-01

272

Effect of two types of lime on some soil physical attributes of an oxisol from Brazil  

Microsoft Academic Search

Liming is a very important practice, especially in acid soils such as some Oxisols from Brazil, in which the chemical effects of liming are reasonably known. However, the effects of liming on soil physical properties are either not well known or, at least, controversial. In order to verify, under field conditions, the effect of liming on some soil physical attributes

O. M. de Castro; O. A. de Camargo; S. R. Vieira; J. Vasques Filho

1999-01-01

273

DEFINITIVE SOX CONTROL PROCESS EVALUATIONS: LIMESTONE, LIME, AND MAGNESIA FGD PROCESSES  

EPA Science Inventory

The report gives economic and ground-to-ground energy evaluations of limestone slurry, lime slurry, and magnesia (producing sulfuric acid) flue gas desulfurization (FGD) processes. The lime slurry process, using purchased lime and lime calcined onsite, remains lower in capital in...

274

Strong kinetic effects on Sr\\/Ca ratios in the calcitic bivalve Pecten maximus  

Microsoft Academic Search

Although Sr\\/Ca ratios in abiogenic calcite are strongly controlled by precipitation rates, such a kinetic effect has never been demonstrated in calcitic bivalve shells. Therefore, we report Sr\\/Ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve Pecten maximus (age class I). Ratios of Sr\\/Ca were found to be variable among individuals that

Anne Lorrain; David P. Gillikin; Yves-Marie Paulet; Laurent Chauvaud; Alain Le Mercier; Jacques Navez; Luc André

2005-01-01

275

High-magnesian calcite: leaching of magnesium in the deep sea.  

PubMed

The high-magnesian calcite fraction of a shallow-water carbonate sand was converted to low-magnesian calcite after transport to the deep sea; strontium was also leached from the carbonate. Oxygen isotopic ratios indicate that loss of magnesium and strontium took place during recrystallization of the carbonate in the deep sea; this process did not alter textures of skeletal fragments. Previously, high-magnesian, calcite was thought only to dissolve in the deep sea. PMID:17731593

Gomberg, D N; Bonatti, E

1970-06-19

276

A balance analysis of phosphorus elimination by artificial calcite precipitation in a stratified hardwater lake  

Microsoft Academic Search

Elimination of phosphorus was achieved by artificial calcite precipitation in the Dagowsee, a stratified eutrophic hardwater lake. The artificial calcite precipitation was induced by hypolimnetic injection of CaO in enclosures during the summer stagnation. The hypolimnetic injection of CaO was combined with aeration for 1 day. The coprecipitation of phosphorus with calcite was shown by energy dispersive X-ray analysis. The

M. Dittrich; T. Dittrich; I. Sieber; R. Koschel

1997-01-01

277

The effect of additives on lime dissolution rates. Final report  

SciTech Connect

Based on the previous years` studies concerning the efficiency of SO{sub 2} removal by spray dryers with high sulfur coal flue gas, the work for year five included investigations of lime dissolution rates at different slaking conditions and with the effect of additives. The prominent additives that have significant effects on lime dissolution rates were tested with the mini pilot spray drying absorber to see their effects on spray drying desulfurization applications. The mechanisms of these additive effects along with the properties of hygroscopic additives have been discussed and incorporated into the spray drying desulfurization model ``SPRAYMOD-M.`` Slaking conditions are very important factors in producing high quality lime slurry in spray drying desulfurization processes. At optimal slaking conditions, the slaked lime particles are very fine (3-5{mu}m) and the slaked lime has high BET surface areas which are beneficial to the desulfurization. The slaked lime dissolution rate experiments in our study are designed to determine how much lime can dissolve in a unit time if the initial lime surface area is kept constant. The purpose of the dissolution rate study for different additives is to find those effective additives that can enhance lime dissolution rates and to investigate the mechanisms of the dissolution rate enhancement properties for these additives. The applications of these additives on spray drying desulfurization are to further verify the theory that dissolution rate is a rate limiting step in the whole spray drying desulfurization process as well as to test the feasibility of these additives on enhancing SO{sub 2} removal in spray dryers.

Khang, S.J.

1996-07-31

278

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

279

AFM Observations of Weathering and Microbiological Alterations on the Surface of Calcite Buried in Arctic Soil (Spitsbergen)  

NASA Astrophysics Data System (ADS)

This study focused on the direct observation of chemical weathering and biological activity on mineral surfaces in the newly forming arctic soil of West Spitsbergen . Chemical weathering and soil forming processes associated with glaciers may affect several geochemical cycles including global carbon cycle and as a result have negative feedbacks on the global climate. Study areas are the foreland of the Werenskiold glacier, continuously retreating by several meters a year. Several samples of freshly cleaved calcite had been buried in the soils for one year. Samples were analyzed with the use of Atomic Force Microscopy (AFM). Results of AFM investigation show changes observed on a calcite samples located respectively about 2500 meters (sample calcite 1) and 100 m (sample calcite 2) from the glacier front as compared to a control sample calcite 0, that has never been exposed to glacier environment. Samples calcite 1 and calcite 2 were recovered from Spitsbergen after 1 year. Compared to the control sample calcite 0, which displays sharp edges and smooth surfaces, both field-treated samples calcite 1 and calcite 2 display rounded edges, irregular surfaces, numerous dissolution features and rounded pitches associated with bacterial activities. The observations suggest that both samples calcite 1 and 2 undergo intensive and rapid chemical and biological weathering when exposed to relatively unsaturated with respect to calcite glacial meltwaters. Several types of analyses have been applied to various regions and lines on the calcite surface. Selected regions on the calcite surface included (a) the entire area of the observed surface (b) top step region roughness, and (c) bottom step region roughness. Selected line parameters have been calculated along: (a) three randomly selected parallel lines, (b) top step line roughness, and (c) bottom step line roughness. Both surface area roughness and line roughness are calculated as the mean deviation of the height. Significant differences have been observed between the samples in calculated roughness parameters, with increase of these parameters ranging from 28% to 241% in calcite 1 located 2500 m from the glacier front and from 100% to 486% in calcite 2 located 100m from the glacier front, as compared to calcite 0. Roughness of the entire surface area for the control calcite 0 was 5.73nm, which increased by 28% in calcite 1 and by 100% in calcite 2. Top step edge roughness increases from calcite 0 (1.82 nm) by 241% to 6.2 nm in calcite 1 and by 486% to 8.84 nm in calcite 2. Bottom step edge roughness increases from 2.08 in calcite 0 by 98% to 4.52nm in calcite 1 and by 149% to 5.67 nm in calcite 2. Line roughness for calcite 0 is 3.26, which increased by 102% in calcite 1 and by 217% in calcite 2. Top step line roughness increases from 2.04 nm in calcite 0 by 191 % to 5.93 nm in calcite 1 and by 276% to 7.67nm in calcite 2. Bottom step line roughness increases from 2.28 nm in calcite 0 by 198% to 4.52 nm in calcite 1and by 249% to 5.67 nm in calcite 2. In calcite 0

Summers, S.; Matyjasik, M.; Inglefield, C.; Manecki, M.; Plonka, A.; Paget, C.; Park, C.

2008-12-01

280

Upscaling calcite growth rates from the mesoscale to the macroscale.  

PubMed

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 {1014} 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 or pH effects and it 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 pretreatment, such as exposing the seed material to SI ? 1.0 to generate/develop growth hillocks, or other factors. PMID:23713769

Bracco, Jacquelyn N; Stack, Andrew G; Steefel, Carl I

2013-06-20

281

Hydrothermal replacement of calcite by sphalerite in a temperature gradient  

SciTech Connect

The replacement of calcite by sphalerite under near-neutral pH's was investigated experimentally and by numerical modeling. The results showed maximum solubility of Zn at 375/sup 0/C, because at higher temperatures Na-Cl and Ca-Cl ion-pairing becomes nearly as strong as the Zn-Cl complexing, effectively scavenging the available chloride. Solubility decreases below 375/sup 0/C because Zn-Cl complexes become less stable. These calculations were confirmed experimentally: ZnS-saturated chloride solutions were pumped through various pure marble sands and gravels down a temperature gradient. CO/sub 2/-CaCO/sub 4/ reactions were used to buffer the input solution at temperatures 15/sup 0/ above those used for the temperature gradients during replacement. In runs cooler than 375/sup 0/C, sphalerite was deposited when the solution cooled to cause ZnS super-saturation. In runs above 375/sup 0/C, no sphalerite precipitated until the temperature fell well below 375/sup 0/C. Such delayed replacement characteristically has sphalerite disseminated as isolated grains, and the marble showed evidence of dissolution. This process opened void space in solid marbles, permitting increased flow of sulfide-depositing solutions. Thus temperature changes may cause replacement of calcite by sphalerite even where there is no change in the reactivity of the host rock, or its accessibility to ore-forming solutions.

Gould, W.W.; Barnes, H.L.

1985-01-01

282

Calcitic microlenses as part of the photoreceptor system in brittlestars  

NASA Astrophysics Data System (ADS)

Photosensitivity in most echinoderms has been attributed to `diffuse' dermal receptors. Here we report that certain single calcite crystals used by brittlestars for skeletal construction are also a component of specialized photosensory organs, conceivably with the function of a compound eye. The analysis of arm ossicles in Ophiocoma showed that in light-sensitive species, the periphery of the labyrinthic calcitic skeleton extends into a regular array of spherical microstructures that have a characteristic double-lens design. These structures are absent in light-indifferent species. Photolithographic experiments in which a photoresist film was illuminated through the lens array showed selective exposure of the photoresist under the lens centres. These results provide experimental evidence that the microlenses are optical elements that guide and focus the light inside the tissue. The estimated focal distance (4-7µm below the lenses) coincides with the location of nerve bundles-the presumed primary photoreceptors. The lens array is designed to minimize spherical aberration and birefringence and to detect light from a particular direction. The optical performance is further optimized by phototropic chromatophores that regulate the dose of illumination reaching the receptors. These structures represent an example of a multifunctional biomaterial that fulfills both mechanical and optical functions.

Aizenberg, Joanna; Tkachenko, Alexei; Weiner, Steve; Addadi, Lia; Hendler, Gordon

2001-08-01

283

Direct Observation of Microbial Inhibition of Calcite Dissolution  

PubMed Central

Vertical scanning interferometry (VSI) provides a method for quantification of surface topography at the angstrom to nanometer level. Time-dependent VSI measurements can be used to study the surface-normal retreat across crystal and other solid surfaces during dissolution or corrosion processes. Therefore, VSI can be used to directly and nondestructively measure mineral dissolution rates with high precision. We have used this method to compare the abiotic dissolution behavior of a representative calcite (CaCO3) cleavage face with that observed upon addition of an environmental microbe, Shewanella oneidensis MR-1, to the crystal surface. From our direct observations, we have concluded that the presence of the microbes results in a significant inhibition of the rate of calcite dissolution. This inhibition appears to be a 2nd-order effect that is related to the formation of etch pits. The opening of etch pits was greatly inhibited in the presence of added bacteria, suggesting that the bacterial cells exert their effect by inhibiting the formation of etch pits at high-energy sites at the crystal surface caused by lattice defects, e.g., screw or point dislocations. The experimental methodology thus provides a nondestructive, directly quantifiable, and easily visualized view of the interactions of microbes and minerals during weathering (or corrosion) processes or during mineral precipitation.

Luttge, Andreas; Conrad, Pamela G.

2004-01-01

284

Calcite and dolomite discrimination using airborne SWIR imaging spectrometer data  

NASA Astrophysics Data System (ADS)

The SWIR full spectrum imager (SFSI) is a hyperspectral push-broom imager, acquiring imagery in 120 0.010 micrometers wide bands simultaneously covering the 1.20 micrometers to 2.47 micrometers spectral region. During the first flights of the instrument hyperspectral imagery was acquired over a calcite quarry and a dolomite quarry. Both these minerals show distinctive carbonate absorption features in the 1.7 to 2.5 micrometers region. These absorption features are centered at wavelengths approximately 0.1 micrometers shorter in dolomite than in calcite. The two minerals are clearly distinguished using a single Gaussian fit to the prominent carbonate absorption feature near approximately 2.3 micrometers in the quarry reflectance data from the SFSI test flights. The spectral resolution of the airborne spectra also allowed the 2.3 micrometers absorption feature to be resolved into tow closely spaced features. Both these absorption features show the mineralogical shift in band center. This has also been seen in laboratory spectra and a detailed comparison with this data is made.

Rowlands, Neil; Neville, Robert A.

1996-11-01

285

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

286

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

287

Clathrate hydrates for ozone preservation.  

PubMed

We report the experimental evidence for the preservation of ozone (O(3)) encaged in a clathrate hydrate. Although ozone is an unstable substance and is apt to decay to oxygen (O(2)), it may be preserved for a prolonged time if it is encaged in hydrate cavities in the form of isolated molecules. This possibility was assessed using a hydrate formed from an ozone + oxygen gas mixture coexisting with carbon tetrachloride or xenon. Each hydrate sample was stored in an air-filled container at atmospheric pressure and a constant temperature in the range between -20 and 2 degrees C and was continually subjected to iodometric measurements of its fractional ozone content. Such chronological measurements and structure analysis using powder X-ray diffraction have revealed that ozone can be preserved in a hydrate-lattice structure for more than 20 days at a concentration on the order of 0.1% (hydrate-mass basis). PMID:20707330

Muromachi, Sanehiro; Ohmura, Ryo; Takeya, Satoshi; Mori, Yasuhiko H

2010-09-01

288

Hydration of RNA Base Pairs  

Microsoft Academic Search

The hydration patterns around the RNA Watson-Crick and non-Watson-Crick base pairs in crystals are analyzed and described. The results indicate that (i) the base pair hydration is mostly “in-plane”; (ii) eight hydration sites surround the Watson-Crick G-C and A-U base pairs, with five in the deep and three in the shallow groove, an observation which extends the characteristic isostericity of

Pascal Auffinger; Eric Westhof

1998-01-01

289

Hydration of ions under confinement  

Microsoft Academic Search

Molecular dynamics simulations are used to examine the changes in water density and hydration characteristics of NaCl solutions confined in slit-shaped graphitic pores. Using a structural signature, we define the hydration limit as the salt concentration at which a sharp drop in the hydration number is observed. At small pores (H = 8.0–10 Å), confined water does not possess bulk-like features and remains

Ateeque Malani; Sohail Murad; K. G. Ayappa

2010-01-01

290

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

291

Catalyst pretreatment for olefin hydration  

SciTech Connect

This patent describes an improvement in the process for the production of diisopropyl ether or isopropanol by hydration of feedstock containing propene, which comprises contacting the propene feedstock and water in a hydration zone with porous solid metal oxide acidic olefin hydration catalyst under olefins hydration conditions. The improvement comprises: pretreating the porous solid catalyst prior to contacting with the propene feedstock with a wetting agent containing at least one polar aliphatic oxygenated hydrocarbon to substantially wet the solid catalyst and sorb the wetting agent into pores of the solid catalyst.

Child, J.E.; Choi, B.C.; Ragonese, F.P.

1991-04-30

292

SIMS analyses of minor and trace element distributions in fracture calcite from Yucca Mountain, Nevada, USA  

SciTech Connect

Fracture-lining calcite samples from Yucca Mountain. Nevada. obtained as part of the extensive vertical sampling in studies of this site as a potential high-level waste repository, have been characterized according to microbeam-scale (25-30 {mu}m) trace and minor element chemistry and cathodoluminescent zonation patterns, As bulk chemical analyses are limited in spatial resolution and are subject to contamination by intergrown phases, a technique for analysis by secondary ion mass spectrometry (SIMS) of minor (Mn, Fe, Sr) and trace (REE) elements in calcite was developed and applied to eighteen calcite samples from four boreholes and one trench. SIMS analyses of REE in calcite and dolomite have been shown to be quantitative to abundances < 1 x chondrite. Although the low secondary ion yields associated with carbonates forced higher counting times than is necessary in most silicates. Mn, Fe, Sr, and REE analyses were obtained with sub-ppm detection limits and 2-15% analytical precision. Bulk chemical signatures noted by Vaniman (1994) allowed correlation of minor and trace element signatures in Yucca Mountain calcite with location of calcite precipitation (saturated vs. unsaturated zone). For example, upper unsaturated zone calcite exhibits pronounced negative Ce and Eu anomalies not observed in calcite collected below in the deep unsaturated zone. These chemical distinctions served as fingerprints which were applied to growth zones in order to examine temporal chances in calcite crystallization histories: analyses of such fine-scale zonal variations are unattainable using bulk analytical techniques. In addition, LREE (particularly Ce) scavenging of calcite-precipitating solutions by manganese oxide phases is discussed as the mechanism for Ce-depletion in unsaturated zone calcite. 54 refs., 10 figs., 3 tabs.

Denniston, R.F.; Shearer, C.K.; Layne, G.D. [Univ. of New Mexico, Albuquerque, NM (United States); Vaniman, D.T. [Los Alamos National Lab., NM (United States)

1997-05-01

293

Shear Strength and Elastic Properties of Lime-Soil Mixtures.  

National Technical Information Service (NTIS)

The shear strength and elastic properties of soil-lime mixtures and the effects of curing time and soil type on these properties were studied using four typical Illinois soils. Regression equations relating cohesion and modulus of elasticity to unconfined...

M. R. Thompson

1967-01-01

294

Treatment of cotton textile wastewater using lime and ferrous sulfate.  

PubMed

This technical note summarizes the results of a textile wastewater treatment process aiming at the destruction of the wastewater's color by means of coagulation/flocculation techniques using ferrous sulfate and/or lime. All the experiments were run in a pilot plant that simulated an actual industrial wastewater treatment plant. Treatment with lime alone proved to be very effective in removing the color (70-90%) and part of the COD (50-60%) from the textile wastewater. Moreover, the treatment with ferrous sulfate regulating the pH in the range 9.0+/-0.5 using lime was equally effective. Finally, the treatment with lime in the presence of increasing doses of ferrous sulfate was tested successfully, however; it proved to be very costly mainly due to the massive production of solids that precipitated. PMID:12691912

Georgiou, D; Aivazidis, A; Hatiras, J; Gimouhopoulos, K

2003-05-01

295

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...

296

Cation?anion balance in lime?induced chlorosis  

Microsoft Academic Search

Lime?induced chlorosis in plants is characterized by some phenomena which fit into a simple hypothesis that internal pH balance is upset due to shifts in cation?anion balances. These pH changes result in precipitation of Fe in plants and fit our previous hypothesis of competitive dictation as an explanation of the multiple causes of lime?induced chlorosis. The oft?times higher concentrations of

A. Wallace; R. A. Wood; S. M. Soufi

1976-01-01

297

Cation--anion balance in lime-induced chlorosis. [Soybeans  

Microsoft Academic Search

Lime-induced chlorosis in plants is characterized by some phenomena which fit into a simple hypothesis that internal pH balance is upset due to shifts in cation-anion balances. These pH changes result in precipitation of Fe in plants and fit our previous hypothesis of competitive chelation as an explanation of the multiple causes of lime-induced chlorosis. The oft-times higher concentrations of

A. Wallace; R. A. Wood; S. M. Soufi

1976-01-01

298

Shock, release, and tension response of soda lime glass  

SciTech Connect

This work describes the result of shock wave experiments on soda lime glass in which the shock wave profiles were recorded simultaneously at or near the impact surface and the free surface of the glass specimen by means of multi-beam VISAR. Since earlier work indicated that the glass under shock compression does not follow the Gladstone-Dale model, these profiles provide accurate and self consistent values of transit times for shock, release, and tensile waves propagating in soda lime glass.

Dandekar, Dattatraya P. [Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, Maryland 21005 (United States)

1998-07-10

299

76 FR 59667 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY: Office...notice announces a meeting of the Methane Hydrate Advisory Committee. Federal...Committee: The purpose of the Methane Hydrate Advisory Committee is to...

2011-09-27

300

77 FR 40032 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY: Office...notice announces a meeting of the Methane Hydrate Advisory Committee. The Federal...Committee: The purpose of the Methane Hydrate Advisory Committee is to...

2012-07-06

301

75 FR 9886 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY: Department...notice announces a meeting of the Methane Hydrate Advisory Committee. Federal...Committee: The purpose of the Methane Hydrate Advisory Committee is to...

2010-03-04

302

78 FR 26337 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY: Office...notice announces a meeting of the Methane Hydrate Advisory Committee. The Federal...Committee: The purpose of the Methane Hydrate Advisory Committee is to...

2013-05-06

303

78 FR 37536 - Methane Hydrate Advisory Committee  

Federal Register 2010, 2011, 2012, 2013

...DEPARTMENT OF ENERGY Methane Hydrate Advisory Committee AGENCY: Office...notice announces a meeting of the Methane Hydrate Advisory Committee. The Federal...Committee: The purpose of the Methane Hydrate Advisory Committee is to...

2013-06-21

304

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

305

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

306

Planktic Foraminiferal Contribution To The Marine Calcite Budget  

NASA Astrophysics Data System (ADS)

The vertical flux and sedimentation of planktic foraminiferal tests is quantified and a global planktic foraminiferal CaCO3 budget is presented. The eastern North Atlantic, the Arabian Sea, and the Caribbean were identified as key areas for this investiga- tion, covering a wide spectrum of ecological conditions and faunal compositions. Test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples. Population dynamics of modern plank- tic foraminifers are discussed as a prerequesite for the quantification of the calcite budget, highlighting the importance of ecological, autecological (e.g., reproduction), and biogeochemical conditions that determine the presence or absence of species. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccol- ithophores, pteropods, and calcareous dinophytes is discussed. It is assumed that the global planktic foraminiferal calcite flux at 100 m depth amounts to 1.3-3.2 Gigatons per year, equivalent to 23-56% of the total open marine CaCO3 flux. The preservation of tests varies on a regional and temporal scale, and is affected by local hydrogra- phy and dissolution susceptibility of planktic foraminiferal tests. Throughout most of the year (off-peak periods) a major portion of tests is dissolved above 700 m water depth while individually settling through the water column, with on average only 1- 3% of the initially exported CaCO3 reaching the deep sea floor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of the tests to the formation of deep-sea sediments. On an annual average, about one fourth of the ini- tially produced planktic foraminiferal test CaCO3 may settle on the sea floor. The total planktic foraminiferal contribution of CaCO3 to global deep-marine surface sediments amounts to 0.36-0.88 Gt per year, which is 32-80% of the total CaCO3 budget that is estimated at 1.1 Gt per year (e.g., Milliman et al., 1999).

Schiebel, R.

307

Fast diffusion along mobile grain boundaries in calcite  

NASA Astrophysics Data System (ADS)

Experimental measurements of grain boundary diffusion are usually conducted on static boundaries, despite the fact that grain boundaries deep in the Earth are frequently mobile. In order to explore the possible effect of boundary mobility on grain boundary diffusion rates we have measured the uptake of 44Ca from a layer of 44Ca-enriched calcite powder during the static recrystallization of a single crystal of calcite at 900°C. A region about 500 ?m wide adjacent to the powder layer is heterogeneously enriched in 44Ca, and complex zoning patterns, including sharp steps in composition and continuous increases and decreases in 44Ca content, are developed. In metamorphic rocks, these would normally be interpreted in terms of changes in pressure or temperature, Rayleigh fractionation, or episodic fluid infiltration. These explanations cannot apply to our experiments, and instead the zoning patterns are interpreted as being due to variations in grain boundary migration rate. We have applied an analytical model which allows the product of grain boundary diffusion coefficient and grain boundary width ( D GB ?) to be calculated from the grain boundary migration rate and the compositional gradient away from the powder layer. The value of D GB ? in the mobile grain boundaries is at least five orders of magnitude greater than the published value for static boundaries under the same conditions. In order to allow the scale of chemical equilibrium (and hence textural evolution) to be predicted under both experimental and geological conditions, we present quantitative diffusion-regime maps for static and mobile boundaries in calcite, using both published values and our new values for grain boundary diffusion in mobile boundaries. Enhanced diffusion in mobile boundaries has wide implications for the high temperature rheology of Earth materials, for geochronology, and for interpretations of the length- and time-scales of chemical mass-transport. Moreover, zones of anomalously high electrical conductivity in the crust and mantle could be regions undergoing recrystallization such as active shear zones, rather than regions of anomalous mineralogy, water- or melt-content as is generally suggested.

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

2007-02-01

308

AN OPTIMIZATION OF CALCITE GRINDING USING THE TAGUCHI METHOD WITH MULTIPLE PERFORMANCE CHARACTERISTICS  

Microsoft Academic Search

The purpose of this study is to demostrate how the application of Taguchi method can be used to develop an effective optimization process for calcite grinding. In order to observe the influencing degree of contol factors in dry calcite grinding, three control factors namely mill speed, ball size and grinding time on lowest product 80% passing size (d80) were studied

N. Aslan

309

The calcite ??? aragonite transformation in low-Mg marble: Equilibrium relations, transformations mechanisms, and rates  

USGS Publications Warehouse

Experimental transformation of a rather pure natural calcite marble to aragonite marble did not proceed via the expected straightforward polymorphic replacement. Instead, the small amount of Mg in the starting material (0.36 wt %) was excluded from the growing aragonite and diffused preferentially into the remaining calcite grains, producing Mg-rich calcite rods that persisted as relicts. Nucleation of aragonite occurred exclusively on grain boundaries, with aragonite [001] oriented subparallel to calcite [0001]. The aragonite crystals preferentially consumed the calcite crystal on which they nucleated, and the reaction fronts developed preferentially along the {010} and {110} planes of aragonite. Each aragonite neoblast that grew was nearly free of Mg (typically <0.1 wt %). The excess Mg was taken up by the calcite grains in between, stabilizing them and causing a few volume percent rodlike relicts of Mg-enriched calcite (up to 10 wt % MgO) to be left behind by the advancing reaction front. The aragonite growth rates are approximately linear and range from ???3 ?? 10-11 m s-1 at 600??C to ???9 ?? 10-9 m s-1 at 850??C, with an apparent activation enthalpy of 166 ?? 91 kJ mol-1. This reaction mechanism and the resultant texture are akin to cellular precipitation reactions in metals. Similar transformation textures have been reported from high-Mg marbles in Japan and China that disproportionated to low-Mg calcite and dolomite. Copyright 2005 by the American Geophysical Union.

Hacker, B. R.; Rubie, D. C.; Kirby, S. H.; Bohlen, S. R.

2005-01-01

310

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

311

Sr Isotope Tracing of Differences in the Effects of Microorganisms on Weathering of Calcite and Apatite  

Microsoft Academic Search

To study differences in the effects of microorganisms on weathering of calcite and apatite, one strain of Aspergillus niger (A. niger) and one strain of Penicillium glaucum (P. glaucum), which respectively contain the mixture of calcite and apatite were cultivated for 24 days in the sucrose-potato culture medium, supernatant was taken every three days from the culture medium, followed by

S. Chen; B. Lian; H. Y. Zheng; F. Q. Dong

2012-01-01

312

Solubility of calcite and aragonite in seawater at atmospheric pressure and 34. 5% salinity  

Microsoft Academic Search

Direct measurement of the solubility of calcite in seawater is difficult and irreproducible because of kinetic factors that inhibit the attainment of true, reversible equilibrium. To avoid this problem, the solubility product constant for calcite in seawater was determined in the present study by calculation from new measurements of the aragonite solubility product constant in seawater and the differential solubility

Berner

1976-01-01

313

Catalytic Biomineralization of Fluorescent Calcite by the Thermophilic Bacterium Geobacillus thermoglucosidasius?  

PubMed Central

The thermophilic Geobacillus bacterium catalyzed the formation of 100-?m hexagonal crystals at 60°C in a hydrogel containing sodium acetate, calcium chloride, and magnesium sulfate. Under fluorescence microscopy, crystals fluoresced upon excitation at 365 ± 5, 480 ± 20, or 545 ± 15 nm. X-ray diffraction indicated that the crystals were magnesium-calcite in calcite-type calcium carbonate.

Yoshida, Naoto; Higashimura, Eiji; Saeki, Yuichi

2010-01-01

314

Zonation and geochemical patterns of burial calcite cements: Upper Smackover Formation, Clarke County, Mississippi  

Microsoft Academic Search

Cathodoluminescence (CL), trace element concentrations, and isotope compositions of luminescently zoned poikilitic and mosaic calcite cements of the upper Smackover Formation are studied in the Harmony, Pachuta Creek, East Nancy, Goodwater, and Garland Creek fields in Clarke County, Mississippi. These calcites precipitated during burial in a depth range of 100 m to 3 km, a temperature range of 30-100 C,

E. Heydari; C. H. Moore

1993-01-01

315

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

316

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

317

Infrared spectra of hydrated silicates, carbonaceous chondrites, and amorphous carbonates compared with interstellar dust absorptions  

NASA Astrophysics Data System (ADS)

The infrared spectra of C1 and C2 carbonaceous chondrites are similar but not identical to the serpentines, montmorillonites, and chamosites. Hydroxyl or bound water features at 2.7, 2.9 and 6 microns do not change at temperatures from 15 to 300 K; absorption bands at 2.7 and near 2.8 microns can be applied for the determination of a hydrated silicate component in the interstellar dust. The interstellar 3.07-micron band is a broad feature between the 3.1 and 4 micron lines in hydrated silicates; a band at 7 microns in carbonaceous chondrites is probably a carbonate absorption. Finally, an amorphous calcite was produced to investigate order-disorder effects on the infrared carbonate spectra and its spectrum compared with crystalline carbonates.

Knacke, R. F.; Kraetschmer, W.

1980-12-01

318

Hydration of small peptides  

NASA Astrophysics Data System (ADS)

The results for the sequential hydration of small peptides (<15 residues) obtained in our group are reviewed and put in perspective with other work published in the literature where appropriate. Our findings are based on hydration equilibrium measurements in a high-pressure drift cell inserted into an electrospray mass spectrometer and on calculations employing molecular mechanics and density functional theory methods. It is found that the ionic functional groups typically present in peptides, the ammonium, guanidinium, and carboxylate groups, are the primary target of water molecules binding to peptides. Whereas the water-guanidinium binding energy is fairly constant at 9 +/- 1 kcal/mol, the water binding energy of an ammonium group ranges from 7 to 15 kcal/mol depending on how exposed the ammonium group is. A five-residue peptide containing an ammonium group is in favorable cases large enough to fully self-solvate the charge, but a pentapeptide containing a guanidinium group is too small to efficiently shield the charge of this much larger ionic group. The water-carboxylate interaction amounts to 13 kcal/mol with smaller values for a shielded carboxylate group. Both water bound to water in a second solvation shell and charge remote water molecules on the surface of the peptide are bound by 7-8 kcal/mol. The presence of several ionic groups in multiply charged peptides increases the number of favorable hydration sites, but does not enhance the water-peptide binding energy significantly. Water binding energies measured for the first four water molecules bound to protonated bradykinin do not show the declining trend typically observed for other peptides but are constant at 10 kcal/mol, a result consistent with a molecule containing a salt bridge with several good hydration sites. Questions regarding peptide structural changes as a function of number of solvating water molecules are discussed. Not much is known at present about the effect of individual water molecules on the conformation of peptides and on the stability of peptide zwitterions.

Wyttenbach, Thomas; Liu, Dengfeng; Bowers, Michael T.

2005-02-01

319

Calcite twin analysis in syntectonic calcite, Cape Fold Belt, South Africa: Implications for fold and cleavage formation within a shallow thrust front  

NASA Astrophysics Data System (ADS)

Lithologies of two formations in the frontal ranges of the Cape Fold Belt, South Africa, host synorogenic calcite precipitated at low metamorphic grade during the end-Permian deformation of this Gondwana-wide orogen. The calcite crystals are mechanically twinned and this deformation is linked to both folding and the formation of an axial planar cleavage with associated extensional veins. Twinning strain analysis reveals a complex, rotational synfolding history in the upper, thin-layered Prince Albert Formation. Twinned calcite within the fold preserves two unique strain events. The primary shortening strain fabric is layer-parallel and transport-parallel (˜north south). The shortening strain overprint (-5.82%) is layer-normal and plunges steeply to the northeast. These results are inconsistent with a flexural-slip folding mechanism. By contrast, a homogeneous syn-cleavage stress strain field is recorded in the underlying, massive thick-bedded Dwyka Tillite. Analyses of calcite twins in clast-hosted, syn-cleavage fibrous calcite and rare limestone clasts define a sub-horizontal N S shortening, and sub-horizontal, E W extension. The intermediate axis (?2) is vertical and preserves shortening (-5.3%). The extension axis (?3) is horizontal and parallel to the clast ‘tension gash’ (fracture) plane. These deformed syn-cleavage calcite materials provide an independent constraint to the debate about contemporaneous stress strain fields associated with folding and formation of an axial planar cleavage.

Craddock, John P.; McKiernan, Alex W.; de Wit, Maarten J.

2007-07-01

320

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

321

Structural evolution of calcite at high temperatures: Phase V unveiled.  

PubMed

The calcite form of calcium carbonate CaCO3 undergoes a reversible phase transition between Rc and Rm at ~1240?K under a CO2 atmosphere of ~0.4?MPa. The joint probability density function obtained from the single-crystal X-ray diffraction data revealed that the oxygen triangles of the CO3 group in the high temperature form (Phase V) do not sit still at specified positions in the space group Rm, but migrate along the undulated circular orbital about carbon. The present study also shows how the room temperature form (Phase I) develops into Phase V through an intermediate form (Phase IV) in the temperature range between ~985?K and ~1240?K. PMID:24084871

Ishizawa, Nobuo; Setoguchi, Hayato; Yanagisawa, Kazumichi

2013-10-02

322

Structural evolution of calcite at high temperatures: Phase V unveiled  

PubMed Central

The calcite form of calcium carbonate CaCO3 undergoes a reversible phase transition between Rc and Rm at ~1240?K under a CO2 atmosphere of ~0.4?MPa. The joint probability density function obtained from the single-crystal X-ray diffraction data revealed that the oxygen triangles of the CO3 group in the high temperature form (Phase V) do not sit still at specified positions in the space group Rm, but migrate along the undulated circular orbital about carbon. The present study also shows how the room temperature form (Phase I) develops into Phase V through an intermediate form (Phase IV) in the temperature range between ~985?K and ~1240?K.

Ishizawa, Nobuo; Setoguchi, Hayato; Yanagisawa, Kazumichi

2013-01-01

323

Ductile flow of methane hydrate  

NASA Astrophysics Data System (ADS)

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 sediment 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

324

Gas Hydrates Thermomechanics: Final Report.  

National Technical Information Service (NTIS)

Solid CH4 hydrate samples can be built up by pulses of water spray onto a solid surface in a CH4 atmosphere at temperature and pressure within the hydrate stability domain. By pulse spraying into a cylindrical well, clean cylindrical samples approximately...

R. C. Corlett

1988-01-01

325

[Skin hydration and hyaluronic acid].  

PubMed

Skin hydration mechanism is complex. Hyaluronic acid is a widely distributed glycosaminoglycan and one of the chief component of the extracellular matrix. It has a high water retaining ability and has recently been shown to be present in the epidermis. HA plays a central role in hydration and elasticity of skin. PMID:20435251

Masson, F

2010-04-01

326

Hydration in soccer: a review  

Microsoft Academic Search

Hydration should be considered before, during and after the exercise. This review intends to approach the main points of hydration process in soccer. The replacement of fluids during exercise is propor tional to some factors, such as: exercise intensity; climatic conditions; the athlete's ac- climatization; the athlete's physical conditioning; physio- logic individual characteristics and the player's biomechan- ics. Performance is

Cristiano Ralo Monteiro; Isabela Guerra; Turíbio Leite de Barros

2003-01-01

327

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

328

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 (CaCl2) 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 Ca(2+) concentrations and pH values on calcification were investigated and the micro morphs of the CaCO3 crystals were observed by means of SEM. These results showed that CaCO3 crystals could be more easily formed with increasing the concentration of CaCl2 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 CaCO3 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

2013-03-31

329

Solute-controlled dissolution thresholding at near-equilibrium calcite-water interfaces  

NASA Astrophysics Data System (ADS)

Direct measurements at the aqueous solution-calcite (104) interface were performed using in situ atomic force microscopy (AFM) at 50—70 °C to reveal the influence of solution saturation state and magnesium concentration on calcite dissolution kinetics and surface morphology. Under near-equilibrium conditions, time-sequential AFM images demonstrated a linear relationship between step speed and solution saturation state, ?calcite. Dissolved Mg2+ brought negligible inhibitory effects on calcite dissolution at [Mg2+] ? 10-4 molal. Upon the introduction of 10-3 molal Mg2+, however, ?calcite acted as a “switch” for magnesium inhibition. That is, no significant changes in step kinetics were observed at ?calcite ? 0.1, whereas a sudden inhibition from Mg2+ was activated at ?calcite ? 0.2. The presence of the ?-switch in dissolution kinetics indicates the presence of critical undersaturation in accordance with thermodynamic principles. Etch pits formed in Mg-free near-equilibrium solutions exhibited a nearly-triangle shape, while in the presence 10-3 molal Mg2+ the etch pits displayed a unique distorted rhombic profile, different from those formed under far-from-equilibrium conditions. Such inconsistency in calcite step morphologies may be associated with the increased influence of the backward reaction and the anisotropy in net kink detachment rates. The calcite dissolution results presented in this work demonstrate a need to consider fundamental surface interactions that may lead to highly nonlinear near-equilibrium behavior and serve as a foundation for the development of robust geochemical models for the prediction of long-term calcite dissolution kinetics in natural water systems.

Xu, M.; Knauss, K. G.; Higgins, S. R.

2010-12-01

330

Diel cycles in calcite production and dissolution in a eutrophic basin  

SciTech Connect

Calcite production is understood largely as a longer-term phenomenon (e.g., seasonal whitings) that can occur in hardwater lakes, and is significant ecologically because it can slow the rate of eutrophication by reducing, through adsorption, the availability of nutrients to primary producers. In this study the authors show that rapid changes in concentration of dissolved CO{sub 2} by photosynthesis and respiration within a eutrophic basin generated strong day-to-night cycles in calcite production and dissolution. Diel cycles in calcite production and dissolution were large enough that they could drive secondary diel cycles in the availability of metals that strongly sorb to the surfaces of calcite particles. They explored the possibility of the secondary diel cycling of metals by intensive 7-d in situ monitoring of water-quality conditions in a shallow, eutrophic spill-control basin near an industrial facility in eastern Tennessee; inspecting data from a 7-year record of water-quality parameters for this basin; analyzing physicochemical characteristics and mineralogic composition of sediments in the basin; and conducting laboratory experiments to characterize the interaction of calcite with Cd, under solid-liquid nonequilibrium conditions. The authors found that the basin accumulated and stored calcite. In situ monitoring showed that calcite was produced during daylight, and tended to dissolve again at night; the calcite production and dissolution processes seemed to be modulated by dissolved-phase CO{sub 2} dynamics, in concert with large diel fluctuations in pCa, pH, and Po{sub 2}. Laboratory experiments showed a rapid interaction ({lt}6 h) of Cd with calcite, in response to dissolved CO{sub 2} changes. Thus, concentrations of dissolved Cd can vary over daily cycles, mediated by diel changes in calcite production and dissolution. Thermodynamic considerations suggest that other metals, such as Zn, Sr, Ni, and Ba, may demonstrate this behavior as well.

Cicerone, D.S.; Stewart, A.J.; Roh, Y.

1999-10-01

331

Hydration and physical performance.  

PubMed

There is a rich scientific literature regarding hydration status and physical function that began in the late 1800s, although the relationship was likely apparent centuries before that. A decrease in body water from normal levels (often referred to as dehydration or hypohydration) provokes changes in cardiovascular, thermoregulatory, metabolic, and central nervous function that become increasingly greater as dehydration worsens. Similarly, performance impairment often reported with modest dehydration (e.g., -2% body mass) is also exacerbated by greater fluid loss. Dehydration during physical activity in the heat provokes greater performance decrements than similar activity in cooler conditions, a difference thought to be due, at least in part, to greater cardiovascular and thermoregulatory strain associated with heat exposure. There is little doubt that performance during prolonged, continuous exercise in the heat is impaired by levels of dehydration >or= -2% body mass, and there is some evidence that lower levels of dehydration can also impair performance even during relatively short-duration, intermittent exercise. Although additional research is needed to more fully understand low-level dehydration's effects on physical performance, one can generalize that when performance is at stake, it is better to be well-hydrated than dehydrated. This generalization holds true in the occupational, military, and sports settings. PMID:17921463

Murray, Bob

2007-10-01

332

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

333

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

334

Recovery of aluminum oxide by the Ames lime-soda sinter process: scale-up using a rotary kiln  

SciTech Connect

The Ames Lime-Soda Sinter Process provides a means for recovering aluminum oxide from power plant fly ash while producing a residue that can be used in the manufacture of sulfate resistant (Type V) portland cement. The process has been fully researched and its feasibility is now being demonstrated through pilot plant scale investigation. This paper reports results of the pelletized feed preparation by agglomeration in a rotary pan granulator, continuous feed sintering in an electrically heated rotary kiln, and product recovery from the clinker by aqueous extraction, desilication of the filtrate, and precipitation of a hydrated aluminum oxide. Results from earlier bench-scale research have been found to apply consistently to the pilot plant scale work.

Murtha, M.J.; Burnet, G.; Harnby, N.

1985-01-01

335

Controls of carbonate mineralogy and solid-solution of Mg in calcite: evidence from spelean systems  

SciTech Connect

Precipitation of carbonate minerals in spelean systems occurs under a wide range of fluid chemistry, Mg-Ca ratios, alkalinities, pH and temperatures; thus, spelean systems provide ideal settings to determine factors controlling the mineralogy of precipitated carbonates and solid-solution of Mg in calcite. Cave waters and actively-precipitating carbonate speleothems were collected from Carlsbad Caverns National Park, New Mexico and the Mammoth-Flint Cave System, Kentucky. Carbonate mineralogy of precipitated phases was determined by x-ray diffraction, and major and minor element composition of waters and accompanying minerals were determined by Atomic Absorption Spectrophotometry. Results demonstrate that at a constant CO3 concentration the precipitation threshold for calcite to aragonite is controlled dominantly by the Mg/Ca ratio of the ambient fluid. Aragonite precipitation is favored by high Mg/Ca ratios. Conversely, with increasing CO3 concentration at constant fluid Mg/Ca ratios, calcite is preferentially precipitated. Solid-solution of Mg in calcite is positively correlated with both increased Mg/Ca ratios and CO3 concentrations. These data suggest that Mg contents of calcite can not be defined solely in terms of a homogeneous distribution coefficient. Rather, Mg concentrations can be also be affected by the CO3 concentration and degree of calcite saturation, suggesting that the rate of crystal growth also plays and important role in Mg solid-solution in calcites.

Gonzalez, L.A.; Lohmann, K.C.

1985-01-01

336

Kinetics of Cd sorption, desorption and fixation by calcite: A long-term radiotracer study  

NASA Astrophysics Data System (ADS)

Time-dependent sorption and desorption of Cd on calcite was studied over 210 days utilizing 109Cd as a tracer to distinguish between 'labile' and 'non-labile' forms of sorbed Cd. Stabilizing the calcite suspensions for 12 months under atmospheric P CO2 and controlled temperature was necessary to reliably follow Cd dynamics following initial sorption. Results revealed time-dependant Cd sorption and marked desorption hysteresis by calcite under environmentally relevant conditions. Data obtained were fitted to a first-order kinetic model and a concentric shell diffusion model. Both models described the progressive transfer of Cd 2+ to a less reactive form within calcite and subsequent desorption of Cd subject to different initial contact times. The kinetic model provided a better fit to the combined sorption and desorption data ( R2 = 0.992). It differentiates between two 'pools' of sorbed Cd 2+ on calcite, 'labile' and 'non-labile', in which labile sorbed Cd is in immediate equilibrium with the free Cd 2+ ion activity in solution whereas non-labile Cd is kinetically restricted. For the diffusion model ( R2 = 0.959), the rate constants describing Cd dynamics in calcite produced a half-life for Cd desorption of ˜175 d, for release to a 'zero-sink' solution. Results from this study allow comment on the likely mechanisms occurring at the calcite surface following long-term Cd sorption.

Ahmed, Imad A. M.; Crout, Neil M. J.; Young, Scott D.

2008-03-01

337

Hydrated hydride anion clusters.  

PubMed

On the basis of density functional theory (DFT) and high level ab initio theory, we report the structures, binding energies, thermodynamic quantities, IR spectra, and electronic properties of the hydride anion hydrated by up to six water molecules. Ground state DFT molecular dynamics simulations (based on the Born-Oppenheimer potential surface) show that as the temperature increases, the surface-bound hydride anion changes to the internally bound structure. Car-Parrinello molecular dynamics simulations are also carried out for the spectral analysis of the monohydrated hydride. Excited-state ab initio molecular dynamics simulations show that the photoinduced charge-transfer-to-solvent phenomena are accompanied by the formation of the excess electron-water clusters and the detachment of the H radical from the clusters. The dynamics of the detachment process of a hydrogen radical upon the excitation is discussed. PMID:17979342

Lee, Han Myoung; Kim, Dongwook; Singh, N Jiten; Ko?aski, Maciej; Kim, Kwang S

2007-10-28

338

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

2008-07-31

339

Thermal conductivity of hydrate-bearing sediments  

Microsoft Academic Search

A thorough understanding of the thermal conductivity of hydrate-bearing sediments is necessary for evaluating phase transformation processes that would accompany energy production from gas hydrate deposits and for estimating regional heat flow based on the observed depth to the base of the gas hydrate stability zone. The coexistence of multiple phases (gas hydrate, liquid and gas pore fill, and solid

Douglas D. Cortes; Ana I. Martin; Tae Sup Yun; Franco M. Francisca; J. Carlos Santamarina; Carolyn Ruppel

2009-01-01

340

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

341

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

342

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

343

Low-magnesium uranium-calcite with high degree of crystallinity and gigantic luminescence emission.  

PubMed

Cabrera (Madrid) low-Mg calcites exhibit: (i) an unusual twofold elevation in X-ray diffraction pattern intensity; (ii) a 60-fold elevation of luminescence emission, compared to six common natural calcites selected for comparison purposes; (iii) a natural relatively high radiation level of circa 200 nSvh(-1) not detected in 1300 other calcites from the Natural History Museum of Madrid. Calcites were analysed by the X-ray diffraction powder method (XRD), cathodo-luminescence spectroscopy in scanning electron microscopy (CL-SEM), thermoluminescence (TL), differential thermal analysis (DTA), X-ray fluorescence spectrometry (XRF) and particle size distribution (PSD). The Cabrera calcite study shows: (i) helicoidally distributed steps along the (0001) orientation; (ii) protuberance defects onto the (0001) surface, observed by SEM; (iii) XRF chemical contents of 0.03% MgO, 0.013% of Y(2)O(3), and 0.022% of U(3)O(8), with accessory amounts of rare earth elements (REE); (iv) DTA dissociation temperature of 879 degrees C; (v) TL maxima peaks at 233 and 297 degrees C whose areas are 60 times compared to other calcites; (vi) spectra CL-SEM bands at 2.0 and 3.4 eV in the classic structure of Mn(2+) activators; (vii) a twofold XRD pattern explained given that sample is a low-Mg calcite. The huge TL and CL emissions of the Cabrera calcite sample must be linked with the uranyl group presence. This intense XRD pattern in low-Mg calcites could bring into being analytical errors. PMID:17011199

Valle-Fuentes, Francisco-Jose; Garcia-Guinea, Javier; Cremades, Ana; Correcher, Virgilio; Sanchez-Moral, Sergio; Gonzalez-Martin, Rafael; Sanchez-Muñoz, Luis; Lopez-Arce, Paula

2006-09-29

344

Calcite formation in soft coral sclerites is determined by a single reactive extracellular protein.  

PubMed

Calcium carbonate exists in two main forms, calcite and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called "calcite and aragonite seas." Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce calcite despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form calcitic skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces calcite formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single crystals generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of calcite instead of aragonite in the biocalcification process and that -OH, secondary structures (e.g. ?-helices and amides), and other necessary chemical groups are distributed over the center of the calcite crystals. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of crystal formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different calcite-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the crystal structure of calcite in nature. PMID:21768106

Rahman, M Azizur; Oomori, Tamotsu; Wörheide, Gert

2011-07-15

345

Methane hydrate stability in seawater  

SciTech Connect

Experiment data are presented for methane hydrate stability conditions in seawater (S {approximately} 33.5 {per_thousand}). For the pressure range of 2.75-10.0 MPa, at any given pressure, the dissociation temperature of methane hydrate is depressed by approximately {minus}1.1 {degrees}C relative to the pure methane-pure water system. These experimental results are consistent with previously reported thermodynamic predictions and experimental results obtained with artificial seawater. Collectively these results provide a minimum constraint concerning depth ranges over which methane hydrate is stable in the oceanic environment. 25 refs., 1 fig., 1 tab.

Dickens, G.R. [Univ. of Michigan, Ann Arbor, MI (United States); Quinby-Hunt, M.S. [Lawrence Berkeley Lab., CA (United States)

1994-09-15

346

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.

347

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

348

EXPERIMENTAL STUDY OF THE CALCITE PRECIPITATION BASED ON THE UREASE PRODUCTION BACTERIUM ISOLATED FROM PEAT  

NASA Astrophysics Data System (ADS)

In this paper, authors proposed the newly calcite precipitation method for peat. This method can be isolated the urease production bacterium. The main outcomes of this research were: (1) Proposed method can be isolated the urease production bacterium from peat. (2) Urease production bacterium from peat can be accelerate the calcite precipitation at the high pH and high chlorine conditions. (3) Calcite precipitation speed was slower than the B. pasteurii . (4) Proposed method can accelerate the soil strength (Over 400kN/m2 -1D compression test) after 2 week cultivation.

Hata, Toshiro; Sato, Atsuko; Kawasaki, Satoru; Abe, Hirofumi

349

Sr / Mg ratios of modern marine calcite: Empirical indicators of ocean chemistry and precipitation rate  

NASA Astrophysics Data System (ADS)

Holocene biotic and abiotic marine calcite have a similar range of Mg contents (0 to 22 and 4 to 21 mol% MgCO 3 , respectively), yet biotic calcite has Sr 2+ concentrations that are consistently 1250 ppm higher than those of abiotic calcite. As in laboratory experiments, a positive linear relation is observed between D Sr and calcite Mg content. This produces two distinct linear trends on a plot of Sr 2+ vs. Mg 2+ concentrations. Principal axes of variation for both trends have similar slopes, yet distinctly different Sr 2+ concentration intercepts. (Biotic: y = 0.024 x + 1298, r 2 = 0.70; Abiotic: y = 0.027 x + 47, r 2 = 0.77). The similar slopes of these trends reflect the constancy of Mg / Ca and Sr / Ca ratios of modern seawater. Equations describing the dependence of D Sr on calcite Mg content are derived from both trends (Biotic: D Sr = 3.16 x 10 t -6 (ppm Mg) + 0.169; Abiotic: D Sr = 3.52 x 10 -6 (ppm Mg) + 0.0062). Characterization of Sr-Mg trends for Holocene materials allows comparison with analogous trends from ancient samples to estimate relative changes in seawater Mg / Ca and Sr / Ca ratios. The relatively high Sr contents of biotic calcite result from rapid precipitation rates associated with shell accretion in marine organisms. Calcites precipitated from seawater in laboratory experiments have D sr values that are similar to those of biotic marine calcite, suggesting that both precipitate at approximately the same rate. Our estimates of surface area-normalized precipitation rates in planktonic and benthonic foraminifera are comparable to those of seeded, pH-stat experiments. We conclude that the D Sr values for biotic and experimental marine calcite are kinetically controlled, whereas the lower precipitation rates of abiotic marine calcite yield D Sr values that approximate equilibrium conditions. Experimentally derived equations describing the relation between D Sr and calcite precipitation rate indicate that the offset in Sr content between biotic and abiotic calcite is the result of abiotic precipitation rates that are two to five orders of magnitude lower than those of biotic precipitates. However, observations of naturally occurring marine cements suggest that the five-order-of-magnitude offset best represents natural system processes.

Carpenter, Scott J.; Lohmann, Kyger C.

1992-05-01

350

Permeability and Storativity of Calcite-Quartz Aggregates During Deformation  

NASA Astrophysics Data System (ADS)

Permeability, storage capacity and volumetric strain were measured in situ during triaxial deformation on hot-pressed calcite-quartz aggregates containing 10, 20 and 30 wt% quartz. The tests were performed at confining pressure of 300 MPa, pore pressure 50 to 290 MPa, temperature from 298K to 873K and at strain rates of 3.0\\times10-5, 8.3\\times10-5 or 3.0\\times10-4. Either argon gas or water were used as pore fluid. The initial porosities of the starting samples vary from 5% to 9%, with higher porosity correlated to higher amount of quartz. Under pure hydrostatic loading the compaction rate covaries with porosity and increases with increasing of effective pressure. The compaction-induced permeability reduction is partly irreversible and probably owes to plastic processes. Substantial amounts of porosity(4-6%) remain under hydrostatic loading at temperature up to 873K. From the microstructural observation, two kinds of pores can be found: cracks along interface and spherical voids within calcite matrix. Variation in pore structure may influence the permeability. The sensitivity of permeability and storage capacity to effective pressure are higher in the samples with 20% and 30% quartz. During dilatant deformation, permeability is linearly related to storage capacity enhancement. During compactive deformation, all samples show reductions in storage capacity and permeability, but the 20% and 30% samples show smaller reductions in storage capacity. The pore aspect ratio a/c can be estimated at (Fisher and Paterson, 1992): $(a)/(c)=1+(? c)/(?_m ) (? c)/(?_c ?_f )-1&) where a and c are the maximicrons and minimicrons dimensions of the pore respectively, ?_m and ?_f are compressibilities of the mineral and the pore fluid respectively, and ?_c and ?_c are the storativity and porosity of the sample respectively. The experiments suggest that the ratio a/c tend to increase as porosity decreases for 20% and 30% samples, which perhaps indicating that the pores become less equant. Observations of microstructure do show that many spherical pores are eliminated by plastic deformation.

Xiao, X.; Evans, B.

2001-12-01

351

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

352

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...

353

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 ...

354

Selenium Removal from Acidic Waste Water Using Zinc Reduction and Lime Neutralization.  

National Technical Information Service (NTIS)

Improved removal of toxic selenium from zinc smelter acidic gas scrubber effluent was achieved by using zinc dust to precipitate soluble selenium prior to lime neutralization. Lime neutralization alone decreased selenium in the waste water from, typically...

W. N. Marchant R. O. Dannenberg P. T. Brooks

1978-01-01

355

Operational Experience in the Lime Treatment of Effluent from Oxidation Ponds.  

National Technical Information Service (NTIS)

A pilot plant, solids-contact, reactor-clarifier was used to evaluate operational parameters for the lime treatment of oxidation ponds effluent. The effect of magnesium concentration on the clarification and the lime sludge produced was studied. An earlie...

M. Ronen Y. Halbertal

1977-01-01

356

The LIME Interface Specification Language and Runtime Monitoring Tool  

NASA Astrophysics Data System (ADS)

This paper describes an interface specification language designed in the LIME project (LIME ISL) and the supporting runtime monitoring tool. The interface specification language is tailored for the Java programming language and supports two kinds of specifications: (i) call specifications that specify requirements for the allowed call sequences to a Java object instance and (ii) return specifications that specify the allowed behaviors of the Java object instance. Both the call and return specifications can be expressed with Java annotations in several different ways: as past time LTL formulas, as (safety) future LTL formulas, as regular expressions, and as nondeterministic finite automata. We also describe the supporting LIME interface monitoring tool which is an open source implementation of runtime monitoring for the interface specifications implemented using AspectJ.

Kähkönen, Kari; Lampinen, Jani; Heljanko, Keijo; Niemelä, Ilkka

357

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

2008-12-03

358

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

359

The hydration of dental cements.  

PubMed

A study was made of the hydration of dental cements, water being classified as "non-evaporable" and "evaporable". The ratio of these two types of water was found to vary greatly among different cement types, being lesser in zinc oxide and ionic polymer cements and greater in ion-leachable glass and phosphoric acid cements. The cement with the least "non-evaporable" water, i.e., showing least hydration (the zinc polycarboxylate cement), had the lowest strength and modulus and the greatest deformation at failure. A linear relationship was found to exist between strength and the degree of hydration of dental cements. All the cements were found to become more highly hydrated and stronger as they aged. PMID:284040

Wilson, A D; Paddon, J M; Crisp, S

1979-03-01

360

Estimating Net CO2 Emissions From Agricultural Lime Applied to Soils in the U.S  

Microsoft Academic Search

Agricultural lime in the form of crushed limestone and dolomite is applied to U.S. agricultural soils at a rate of 20-30 Tg yr-1. Understanding the ultimate fate of applied lime and associated carbonate species is important for estimating net CO2 emissions from agricultural lime. We provide a history of lime use in the U.S., estimate the fraction of dissolution by

A. C. McBride; T. O. West

2005-01-01

361

Soil pH Variation Within a Soil. III. pH Variation in Limed Soil  

Microsoft Academic Search

There are many methods for determining lime requirement, but no single method is suitable for all soils. A fast and efficient method to evaluate lime effect is needed. Soil buffering capacity tests and column-leaching tests were applied to the limed Van Rockel soil at the depth of 0–30 cm to evaluate pH distribution after liming. Two groups of the Van Rockel

Shih-Lin Hsu; Joe Hung; Arthur Wallace

2004-01-01

362

Crystallization of a polymorphic hydrate system.  

PubMed

Nitrofurantoin can form two monohydrates, which have the same chemical composition and molar ratio of water, but differ in the crystal arrangements. The two monohydrates (hydrates I and II) could be produced independently via evaporative crystallization, where supersaturation and solvent composition were both found to have an effect. Hydrate I showed much slower crystallization than hydrate II. During cooling crystallization, the nucleation and growth of hydrate II was again dominant, consuming all supersaturation and leading to no hydrate I formation. Seeding of hydrate I during cooling crystallization was also applied, but the hydrate I seeds were not able to initiate its nucleation rather than dissolving into crystallizing solution. Although solubility tests revealed that hydrate II is more stable than hydrate I due to its lower solubility (110 +/- 4 and 131 +/- 12 microg/mL for hydrates II and I, respectively), this difference is rather small. Therefore, the small free energy difference between the two hydrates, together with the slow crystallization of hydrate I, both lead to a hindrance of hydrate I formation. Furthermore, the crystal structure of hydrate II demonstrated a higher H-bonding extent than hydrate I, suggesting its more favorable crystallization. This is in good agreement with experimental results. PMID:19569226

Tian, F; Qu, H; Louhi-Kultanen, M; Rantanen, J

2010-02-01

363

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

364

Ultrasonic reactivation of phosphonate poisoned calcite during crystal growth.  

PubMed

The effect of ultrasonic irradiation (42,150 Hz, 17 W dm(-3)/7.1 W cm(-2)) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface. PMID:21463963

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

2011-04-03

365

Stress remagnetization in pyrrhotite-calcite synthetic aggregates  

NASA Astrophysics Data System (ADS)

Stress-induced remagnetization has been applied to multidomain pyrrhotite-calcite synthetic aggregates in a triaxial rig. Experimental deformation used 150MPa confining pressure, a constant strain rate of 10-5 s-1 and applied differential stresses of up to 70MPa. New components of magnetization, parallel to the direction of the pressure vessel field, were added to the pre-deformational magnetization. The intensity of remagnetization (M'-M0) increases with the intensity of the applied differential stress and affects the coercivity fraction below 15mT. Bulk shortening is less than 8 per cent, thus grain rotation cannot explain selective remagnetization of the low-coercivity fraction. Remagnetization is thus attributed to deformational viscous remanent magnetization (DVRM). It is observed that high-coercivity (>15mT) grains do not remagnetize. There is, however, slight progressive rotation of pre-deformational magnetization with increasing strain up to 8 per cent of bulk shortening. The lack of piezoremanent magnetization in the high-coercivity range may be due to defects introduced in pyrrhotite during sample preparation. Experiments using synthetic pyrrhotite, expected to show low dislocation densities, would be necessary to test this effect.

Robion, Philippe; Borradaile, Graham J.

2001-01-01

366

Ductile flow of methane hydrate  

Microsoft Academic Search

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

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

2003-01-01

367

Methane hydrate stability in seawater  

Microsoft Academic Search

Experiment data are presented for methane hydrate stability conditions in seawater (S ⼠33.5 {per_thousand}). For the pressure range of 2.75-10.0 MPa, at any given pressure, the dissociation temperature of methane hydrate is depressed by approximately -1.1 °C relative to the pure methane-pure water system. These experimental results are consistent with previously reported thermodynamic predictions and experimental results obtained with

Gerald R. Dickens; M. S. Quinby-Hunt

1994-01-01

368

Lime and charcoal amendments reduce fluoride absorption by plants cultured in a perlite-peat medium  

Microsoft Academic Search

Lime or activated charcoal effectively reduced fluoride absorption and increased plant dry weight in lettuce (Lactuca sativa L.), perennial ryegrass (Lolium perenne L.), and spinach (Spinacia oleracca L.) grown in a fertilized perlite-peat moss medium. Lime in combination with charcoal surpassed that of charcoal alone in reducing fluoride absorption and increasing yields. While the addition of lime or charcoal raised

R. Sheldrake; G. E. Doss; L. E. Jr. St. John; D. J. Lisk

1978-01-01

369

Lime handling and preparation for two double-alkali FGD systems  

Microsoft Academic Search

The lime handling and preparation system at Northern Indiana Public Service Company's Rollin M. Schahfer Generating Station was designed to efficiently receive, transfer and slake pebble lime reactant for the Units 17 and 18 doublealkali FGD systems. The equipment is capable of receiving lime by rail or by dump truck using common pressure pneumatic systems. The system is designed to

J. R. Henry; D. W. Ellefson; S. M. Katzberger; P. R. Predick; B. A. Wrobel

1983-01-01

370

Application of lime and wood ash to decrease acidification of forest soils  

Microsoft Academic Search

Liming and wood ash application are measures to decrease acidification of forests soils. The assessment of lime requirement can be based on that base saturation, which indicates a low risk of acid toxicity. Because of a wide spread Mg deficiency in Central European forests, Mg containing lime is normally applied. Ash from untreated wood is applied to decrease soil acidity

K. J. Meiwes

1995-01-01

371

Kinetic and thermodynamic factors controlling the distribution of SO32- and Na+ in calcites and selected aragonites  

USGS Publications Warehouse

Significant amounts of SO42-, Na+, and OH- are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO42-. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na+, but very low concentrations of SO42-. The SO42- content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na+ and SO42- increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO42- beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO42- is the same as that of aragonite. Na+ appears to have very little effect on the solubility product of calcites. The amounts of Na+ and SO42- incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient (D) of SO42- in calcite at 25.0??C and 0.50 molal NaCl is described by the equation D = k0 + k1R where k0 and k1 are constants equal to 6.16 ?? 10-6 and 3.941 ?? 10-6, respectively, and R is the rate of crystal growth of calcite in mg??min-1??g-1 of seed. The data on Na+ are consistent with the hypothesis that a significant amount of Na+ occupies interstitial positions in the calcite structure. The distribution of Na+ follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na+ distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na+ contents of calcites are not very accurate indicators of environmental salinities. ?? 1985.

Busenberg, E.; Niel, Plummer, L.

1985-01-01

372

Flexible minerals: self-assembled calcite spicules with extreme bending strength.  

PubMed

Silicatein-? is responsible for the biomineralization of silicates in sponges. We used silicatein-? to guide the self-assembly of calcite "spicules" similar to the spicules of the calcareous sponge Sycon sp. The self-assembled spicules, 10 to 300 micrometers (?m) in length and 5 to 10 ?m in diameter, are composed of aligned calcite nanocrystals. The spicules are initially amorphous but transform into calcite within months, exhibiting unusual growth along [100]. They scatter x-rays like twinned calcite crystals. Whereas natural spicules evidence brittle failure, the synthetic spicules show an elastic response, which greatly enhances bending strength. This remarkable feature is linked to a high protein content. With nano-thermogravimetric analysis, we measured the organic content of a single spicule to be 10 to 16%. In addition, the spicules exhibit waveguiding properties even when they are bent. PMID:23493708

Natalio, Filipe; Corrales, Tomas P; Panthöfer, Martin; Schollmeyer, Dieter; Lieberwirth, Ingo; Müller, Werner E G; Kappl, Michael; Butt, Hans-Jürgen; Tremel, Wolfgang

2013-03-15

373

Experimental investigation of surface energy and subcritical crack growth in calcite  

NASA Astrophysics Data System (ADS)

Subcritical cracking behavior and surface energies are important factors in geological processes, as they control time-dependent brittle processes and the long-term stability of rocks. In this paper, we present experimental data on subcritical cracking in single calcite crystals exposed to glycol-water mixtures with varying water content. We find upper bounds for the surface energy of calcite that decrease with increasing water concentration and that are systematically lower than values obtained from molecular dynamics simulations. The relation of surface energy to water concentration can explain water weakening in chalks. The rate of subcritical crack growth in calcite is well described by a reaction rate model. The effect of increasing water on crack velocity is to lower the threshold energy release rate required for crack propagation. The slope of the crack velocity curve remains unaffected, something which strongly suggests that the mechanism for subcritical cracking in calcite does not depend on the water concentration.

RøYne, Anja; Bisschop, Jan; Dysthe, Dag Kristian

2011-04-01

374

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

375

Surface speciation models of calcite and dolomite\\/aqueous solution interfaces and their spectroscopic evaluation  

Microsoft Academic Search

The composition and density of surface hydroxyl and carbonate groups on calcite and dolomite after contact at 25 C with solutions of different pH (3 to 12) and carbonate concentration (10⁻⁴ â¤Î£COâ⤠0.1 M) were monitored by means of diffuse reflectance infrared (DRIFT) spectroscopy. Both for calcite and dolomite, broad high-intensity absorbance bands at about 3,400 and 1,600 cm⁻¹ were

O. S. Pokrovsky; J. A. Mielczarski; O. Barres; J. Schott

2000-01-01

376

Geochemical preservation potential of high-grade calcite marble versus dolomite marble: implication for isotope chemostratigraphy  

Microsoft Academic Search

The Neoproterozoic Hekkelstrand Marble from the North-Central Norwegian Caledonides contains a calcite marble unit hosting a commercially exploited white dolomite marble deposit, which underwent polyphase amphibolite-facies, Scandian metamorphism. Major and trace element geochemistry, ?18O, ?13C and 87Sr\\/86Sr ratios have been used to define isotopic differences between interbedded calcite and dolomite marbles and to assess their post-depositional isotopic resetting. A high

V. A. Melezhik; D. Roberts; A. E. Fallick; I. M. Gorokhov; A. B. Kusnetzov

2005-01-01

377

Neutralization of sulfuric acid solutions by calcite dissolution and the application to anoxic limestone drain design  

Microsoft Academic Search

Batch reactor (BR) experiments were conducted to measure the effect of hydrodynamics and gypsum coatings on calcite neutralization rates. A factorial array of BR experiments measured the H+ concentration change by calcite dissolution over a pH range of 1.5–3.5 and Na2SO4 concentrations of 0–1M. The rate of H+ concentration change with time was determined by numerical differentiation of H+ concentration

Danielle M. C. Huminicki; J. Donald Rimstidt

2008-01-01

378

Arsenate uptake by calcite: Macroscopic and spectroscopic characterization of adsorption and incorporation mechanisms  

NASA Astrophysics Data System (ADS)

Batch uptake experiments and X-ray element mapping and spectroscopic techniques were used to investigate As(V) (arsenate) uptake mechanisms by calcite, including adsorption and coprecipitation. Batch sorption experiments in calcite-equilibrated suspensions (pH 8.3; PCO 2 = 10 -3.5 atm) reveal rapid initial sorption to calcite, with sorption rate gradually decreasing with time as available sorption sites decrease. An As(V)-calcite sorption isotherm determined after 24 h equilibration exhibits Langmuir-like behavior up to As concentrations of 300 ?M. Maximum distribution coefficient values ( Kd), derived from a best fit to a Langmuir model, are ˜190 L kg -1. Calcite single crystals grown in the presence of As(V) show well-developed rhombohedral morphology with characteristic growth hillocks on (101¯4) surfaces at low As(V) concentrations (?5 ?M), but habit modification is evident at As(V) concentrations ?30 ?M in the form of macrostep development preferentially on the - vicinal surfaces of growth hillocks. Micro-X-ray fluorescence element mapping of (101¯4) surfaces shows preferential incorporation of As in the - vicinal faces relative to + vicinals. EXAFS fit results for both adsorption and coprecipitation samples confirm that As occurs in the 5+ oxidation state in tetrahedral coordination with oxygen, i.e., as arsenate. For adsorption samples, As(V) forms inner-sphere surface complexes via corner-sharing with Ca octahedra. As(V) coprecipitated with calcite substitutes in carbonate sites but with As off-centered, as indicated by two Ca shells, and with likely disruption of local structure. The results indicate that As(V) interacts strongly with the calcite surface, similar to often-cited analog phosphate, and uptake can occur via both adsorption and coprecipitation reactions. Therefore, calcite may be effective for partial removal of dissolved arsenate from aquatic and soil systems.

Alexandratos, Vasso G.; Elzinga, Evert J.; Reeder, Richard J.

2007-09-01

379

Coprecipitation of Uranium(VI) with Calcite: XAFS, micro-XAS, and luminescence characterization  

Microsoft Academic Search

X-ray absorption and luminescence spectroscopies have been used to characterize the local structure and coordination of uranium(VI) species coprecipitated with calcite (CaCO3) from room-temperature aqueous solutions. Different solution chemistries and pHs are found to result in differences in the equatorial coordination of the uranyl species (UO22+) incorporated in the calcite, with multiple coordination environments of uranyl evident in one sample.

Richard J. Reeder; Melissa Nugent; C. Drew Tait; David E. Morris; Steve M. Heald; Kenneth M. Beck; Wayne P. Hess; Anthony Lanzirotti

2001-01-01

380

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

381

Coprecipitation of Uranium (VI) with Calcite: XAFS, Micro-XAS,and Luminescence Characterization  

SciTech Connect

X-ray absorption and luminescence spectroscopies have been used to characterize the local structure and coordination of uranium (VI) species coprecipitated with calcite (CaCO3) in room-temperature aqueous solutions. Different solution chemistries and pHs are found to result in defferences in the equatorial coordination of the uranyl species (UO2/2+) in the calcite, with multiple coordination environments of uranyl evident in one sample.

Reeder, Richard J.; Nugent , Melissa; Tait, C DREW.; Morris, David E.; Heald, Steve M.; Beck, Kenneth M.; Hess, Wayne P.; Lanzirotti, Anthony

2001-04-06

382

Synthetic polycrystalline aragonite to calcite transformation kinetics: experiments at pressures close to the equilibrium boundary  

Microsoft Academic Search

Summary ¶This study experimentally investigated the transformation kinetics of synthetic polycrystalline aragonite to calcite at four temperature\\/pressure conditions (330?°C\\/200?MPa, 380?°C\\/325?MPa, 430?°C\\/580?MPa, and 480?°C\\/875?MPa), close to the calcite-aragonite equilibrium phase boundary. The extents of transformation measured as a function of time in a synthetic system, using in-situ annealed, high purity samples, are consistent with the kinetic model for grain-boundary nucleation and

W.-L. Huang

2003-01-01

383

Initial formation of calcite crystals in the thin prismatic layer with the periostracum of Pinctada fucata.  

PubMed

Although the formation mechanism of calcite crystals in the prismatic layer has been studied well in many previous works, the initial state of calcite formation has not been observed in detail using electron microscopes. In this study, we report that the soft prismatic layer with transparent color (the thin prismatic layer) in the tip of the fresh shell of Pinctada fucata was picked up to observe the early calcification phase. A scanning electron microscope (SEM) image showed that the growth tip of the thin prismatic layer was covered by the periostracum, which was also where the initial formation of calcite crystals began. A cross-section containing the thin calcite crystals in the thin prismatic layer with the periostracum was made using a focused ion beam (FIB) system. In a transmission electron microscope (TEM) observation, the thin calcite crystal (thickness is about 1?m) on the periostracum was found to be a single crystal with the c-axis oriented perpendicular to the shell surface. On the other hand, many aggregated small particles consisting of bassanite crystals were observed in the periostracum suggesting the possibility that not only organic sulfate but also inorganic sulfates exist in the prismatic layer. These discoveries in the early calcification phase of the thin prismatic layer may help to clarify the mechanism of regulating the nucleation and orientation of the calcite crystal in the shell. PMID:23176816

Suzuki, Michio; Nakayama, Seiji; Nagasawa, Hiromichi; Kogure, Toshihiro

2012-10-29

384

Sea urchin tooth mineralization: calcite present early in the aboral plumula.  

PubMed

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. PMID:22940703

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

2012-08-24

385

Unusual calcite cementing of quartz grains on Chandeleur Island Beach, offshore Louisiana  

SciTech Connect

A very unusual calcite cement was found in some beachchips from an unconsolidated beach surface of Chandeleur Island offshore approximately 35 nmi (65 km) south of Mississippi in the Gulf of Mexico. The beachchips are irregularly shaped and are well cemented by this unusual calcite. This calcite crystal structure has not been reported previously as existing in a marine environment. A similar cement has been found in freshwater lake beachrock and in some travertine samples. The calcite crystals are elongate parallel to the c-optic axis, and are composed of bunches of crystallite blades. The crystallite blades of each crystal bunch are pointed and are more bladed than freshwater cement crystals. The intercrystallite pore space contains no fine calcite silt as was observed in the lake samples. Fresh water provided by rainfall may be held in the pore spaces and bounded to the quartz-grain surfaces by ionic attraction. Marine spray above and saline water concentrated underneath from a sandwich effect at the micropore level, allowing rapid growth and precipitation of these very unusual calcite crystals in a single-phase low-salinity fluid.

Mitchell-Tapping, H.J.

1983-09-01

386

Influence of temperature on the composition of magnesian calcite overgrowths precipitated from sea water  

SciTech Connect

A constant disequilibrium technique was used to determine the composition of magnesian calcite overgrowths precipitated on pure calcite seeds from artificial sea water at 5, 25 and 40/sup 0/C. The amount of magnesium incorporated in the overgrowths at a given temperature is independent of the precipitation rate over a wide range of saturation states and is believed to correspond to a composition in true equilibrium with sea water. The distribution coefficient of magnesium, D/sub Mg/sup 2 +///sup c/, in the magnesian calcite overgrowths increases almost linearly with temperature, being 0.0121 +- 0.0013 at 5/sup 0/C, 0.0172 +- 0.0022 at 25/sup 0/C, and 0.0271 +- 0.0013 at 40/sup 0/C. These values apply only to magnesian calcites precipitated from standard composition sea water, since a previous study has shown D/sub Mg/sup 2 +///sup c/ to be a function of the (Mg/sup 2 +/)(Ca/sup 2 +/) ratio in the parent solution. Results of this study are compared with values reported previously by other workers, and with the compositional distribution of naturally occurring magnesian calcite cements and ooids found in sea water. It appears that variations in temperature are not sufficient to account for the compositional variability of naturally occurring inorganic marine magnesian calcite cements.

Mucci, A.

1987-07-01

387

Influence of temperature on the composition of magnesian calcite overgrowths precipitated from seawater  

NASA Astrophysics Data System (ADS)

A constant disequilibrium technique was used to determine the composition of magnesian calcite overgrowths precipitated on pure calcite seeds from artificial seawater at 5, 25 and 40°C. The amount of magnesium incorporated in the overgrowths at a given temperature is independent of the precipitation rate over a wide range of saturation states and is believed to correspond to a composition in true equilibrium with seawater. The distribution coefficient of magnesium, D Mg 2+ c , in the magnesian calcite overgrowths increases almost linearly with temperature, being 0.0121 ± 0.0013 at 5°C, 0.0172 ± 0.0022 at 25°C, and 0.0271 ± 0.0013 at 40°C. These values apply only to magnesian calcites precipitated from standard composition seawater, since a previous study has shown D Mg 2+ c to be a function of the [ Mg 2+ ]/[ Ca 2+ ] ratio in the parent solution. Results of this study are compared with values reported previously by other workers, and with the compositional distribution of naturally occurring magnesian calcite cements and ooids found in seawater. It appears that variations in temperature are not sufficient to account for the compositional variability of naturally occurring "inorganic" marine magnesian calcite cements.

Mucci, Alfonso

1987-07-01

388

Mixing-induced calcite precipitation and dissolution kinetics in micromodel experiments.  

SciTech Connect

Dissolved CO2 from geological CO2 sequestration may react with dissolved minerals in fractured rocks or confined aquifers and cause mineral precipitation. The overall rate of reaction can be limited by diffusive or dispersive mixing, and mineral precipitation can block pores and further hinder these processes. Mixing-induced calcite precipitation experiments were performed by injecting solutions containing CaCl2 and Na2CO3 through two separate inlets of a micromodel (1-cm x 2-cm x 40-microns); transverse dispersion caused the two solutions to mix along the center of the micromodel, resulting in calcite precipitation. The amount of calcite precipitation initially increased to a maximum and then decreased to a steady state value. Fluorescent microscopy and imaging techniques were used to visualize calcite precipitation, and the corresponding effects on the flow field. Experimental micromodel results were evaluated with pore-scale simulations using a 2-D Lattice-Boltzmann code for water flow and a finite volume code for reactive transport. The reactive transport model included the impact of pH upon carbonate speciation and calcite dissolution. We found that proper estimation of the effective diffusion coefficient and the reaction surface area is necessary to adequately simulate precipitation and dissolution rates. The effective diffusion coefficient was decreased in grid cells where calcite precipitated, and keeping track of reactive surface over time played a significant role in predicting reaction patterns. Our results may improve understanding of the fundamental physicochemical processes during CO2 sequestration in geologic formations.

Valocchi, Albert J.; Dewers, Thomas A.; Dehoff, Karl; Yoon, Hongkyu; Werth, Charles J.

2010-12-01

389

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

390

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

391

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, ...

392

Liming Induced Changes in Arsenic Dissolution from Mine Wastes  

Microsoft Academic Search

Incorporation of lime amendments into mine wastes is an effective treatment to neutralize active and potential acidity, reduce soluble metals, and facilitate plant growth. Many mine wastes contain arsenic. In general, the solubility of As (a metalloid) increases with increasing pH. However, a number of laboratory and field studies with mine waste have shown decreased solubility of arsenic with increasing

L. M. Dudley

2009-01-01

393

The dissolution efficiency for different stream liming methods  

Microsoft Academic Search

The dissolution efficiency for different stream liming methods is shown to depend upon the following parameters: Particle size distribution; Initial pH-value; Dose intensity; and Degree of wet slurrying. The particle size distribution and the degree of wet slurrying are the only free variables and when they are determined, the others are determined by the conditions at the dosing site. The

H. U. Sverdrup

1986-01-01

394

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

395

Comparative fluorine uptake by plants in limed and unlimed soil  

Microsoft Academic Search

Investigations were undertaken to determine the extent to which fluorine can be absorbed from soils by plant roots, and the extent to which the absorption can be controlled by liming. Sassafras loamy sand, having a pH value near 5.0 and containg 12 ppm of naturally occurring fluorine, was tranported from near Springtown Corners, NJ, to a greenhouse of the Division

ANNIE M. HURD-KARRER

1950-01-01

396

Effect of Lime on Some Geotechnical Properties of Igumale Shale  

Microsoft Academic Search

This paper reports the outcome of an investigation into the effect of lime on some geotechnical properties of Igumale shale, to ascertain its suitability for use as a modifier or stabilizer in the treatment of the shale. Classification tests, compaction test, California bearing ratio (CBR) and unconfined compressive strength (UCS) tests, were conducted on specimen of Igumale shale. Results of

Joel Manasseh; Agbede I. Olufemi

397

Wet waste flue gas desulfurizing process using lime as absorbent  

Microsoft Academic Search

A wet waste flue gas desulfurizing process using lime as absorbent is disclosed wherein a sulfur oxide-containing waste flue gas is washed with a liquid absorbent containing calcium hydroxide or calcium carbonate for the purpose of removing the sulfur oxide from said waste flue gas, characterized in that an absorbing device is divided into two stages, i.e., a former stage

M. Atsukawa; K. Kamei; N. Shinoda; H. Ushio

1977-01-01

398

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 ...

399

Coal conversion of a multiple burner lime kiln  

SciTech Connect

During 1982 Ash Grove Cement Company contracted with Wagester, Walker, Thornton and Company to convert a Calcimatic rotating hearth kiln at its Portland, Oregon lime plant from gas/oil to coal firing. Increasing costs of natural gas and No. 6 fuel oil made this conversion mandatory if the plant was to remain competitive. Unique features of this project are the distributors of pulverized coal to eighteen small burners around the inner and outer perimeters of the doughnut-shaped kiln, and the attrition-dryer-pulverizer mill. Ash Grove, a century-old lime and cement producer headquartered in Overland Park, Kansas (Kansas City area), looked at various schemes for multiple burner firing before employing Wagester, Walker, Thornton and Company. W.W.T. of Pittsburgh, Pennsylvania was formed in 1980 by acquiring the Solid Fuels Division of the Pullman Swindell Corporation. This division had been active in developing solid fuel firing for brick tunnel kilns, principally in the Southeast. They continue to supply such systems firing wood waste as well as coal to the brick industry and have also converted two Calcimatic lime kilns for Dixie Lime, Sumterville, Florida, a fluid bed calciner for Texas Gulf in Aurora, North Carolina, and a chrome concentrate kiln for Diamond Chemicals at Castle Hayne, North Carolina. Testing and a proposal have been made for INMETCO, Elwood City, Pennsylvania, on an annular hearth furnace for direct reduction of iron ore to metallic iron.

Jones, G.; Thornton, L.W.

1984-02-01

400

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...

401

Lime Treatment of a Hardwater Lake to Reduce Eutrophication  

Microsoft Academic Search

Lime addition was evaluated as a lake rehabilitation technique in Frisken Lake, a naturally eutrophic hardwater lake in British Columbia. Adding 39 tonnes of calcium hydroxide in 1983 and 1984 precipitated more than 85 to 95 percent of the chlorophyll a and 89 to 96 percent of the soluble reactive phosphorus from the epilimnion. The lake was not treated in

T. P. Murphy; K. G. Hall; T. G. Northcote

1988-01-01

402

Soda ash improves lead removal in lime precipitation process  

SciTech Connect

Both laboratory-scale and plant-scale studies were conducted to evaluate the feasibility of using soda ash as a supplemental chemical in the existing lime neutralization-sedimentation process. The purpose was to improve the efficiency of lead removal from a metal finishing wastewater by taking advantage of the lower solubility of lead carbonate. Plant-scale studies indicated that addition of soda ash at about 2 mg Na/sub 2/CO/sub 3/ per mg Pb and at a pH between 8 and 11.5 reduced lead content in the settled effluent consistently to less than 0.3 mg/l. This is considerably lower than the 0.5 mg/1 specified in the sewer use ordinance. After about one year's operation, this modified lime neutralization-sedimentation process has been found to be more stable and reliable, and requires less attendance than the simple lime process. The process can also now be operated at a lower pH (minimum: 7.0) with the addition of soda ash, which has resulted in a lower amount of sludge production, lower lime usage and significantly lower manpower requirements.

Hsu, D.Y. (Greeley and Hansen, Chicago, IL); Riddell, M.D.R.; Bonamico, B.

1982-01-01

403

Shock-wave properties of soda-lime glass  

SciTech Connect

Planar impact experiments and wave profile measurements provided single and double shock equation of state data to 30 GPa. Both compression wave wave profile structure and release wave data were used to infer time-dependent strength and equation of state properties for soda-lime glass.

Grady, D.E. [Applied Research Associates, Inc., Albuquerque, NM (United States); Chhabildas, L.C. [Sandia National Labs., Albuquerque, NM (United States)

1996-11-01

404

Shear deformation under pyramidal indentations in soda-lime glass  

Microsoft Academic Search

The nature of the flow lines that occur in the deformed zone in soda-lime glass under pyramidal indentations has been investigated. A close examination of the deformed zone shows that the spiral flow lines meet at 110°, instead of the 90° required by the ideal rigid-plastic behaviour. The flow lines are indeed shear faults (of negligible thickness) produced by genuine

J. T. Hagan

1980-01-01

405

Coloration processes in soda–lime silicate glasses  

Microsoft Academic Search

The effect of mechanical stretching upon room temperature ? coloration of soda–lime silicate (SLS) glasses has been investigated. Optical absorption measurements were performed to follow the formation and thermal bleaching of the induced color centers. It has been shown that the mechanical deformation reduces the coloration effectivity and thermal stability of the created centers. It has been proposed that increase

B. Macalik; T. Morawska-Kowal

2002-01-01

406

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

407

Variable Rate Lime Application in Louisiana Sugarcane Production Systems  

Technology Transfer Automated Retrieval System (TEKTRAN)

Precision agriculture may offer sugarcane growers a management system that decreases costs and maximizes profits, while minimizing any potential negative environmental impact. The utility of variable-rate (VR) lime application in the initial production year (plant cane) of a 3-yr sugarcane crop cyc...

408

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

409

Oxygen Isotopic Disequilibrium in Bacteriogenic Soil Calcite Precipitated Near Leaking Oil and Gas Wells in Western Canada  

NASA Astrophysics Data System (ADS)

About one third of all oil and gas wells drilled in Western Canada leak natural gas to surface. Leaking gas is oxidized, sometimes completely, by metanotrophic bacteria in soil near the wells. Depending on soil permeability and rate of gas leakage, zones of bacterial oxidation extend from 20 to >500 cm away from the well bores of leaking wells. Thin coatings and aggregates <300 micrometers across of authigenic calcite of both abiotic and bacteriogenic origin are found in the oxidation zones. Abiotic calcite forms crusts comprised of submicron to micron size sparry, euhedral crystals typical of inorganic soil calcite precipitates. Bacteriogenic calcite is closely associated with bacteria and microbial film and forms massive to porous aggregates of subhedral rounded crystals coating or cementing mineral grains. Growth of nanometer size calcite crystals on top of microbial surfaces indicates active involvement of bacteria with calcite precipitation. To constrain the conditions of calcite precipitation \\delta13C and \\delta18O of soil CO2 and soil temperature at two leaking well sites in Saskatchewan were monitored for ca. two years. The \\delta18O of local soil moisture and groundwater were also measured. Results show that \\delta18O (PDB) of bacteriogenic calcite is from 3 to 6 permil lower than this that would precipitate in isotopic equilibrium with local soil moisture at any time during the year. Although \\delta13C of bacteriogenic calcite may be in isotopic equilibrium with local soil CO2 at temperatures close to freezing, decrease of bacterial metabolic rates at such low temperatures would not favor bacteriogenic calcite precipitation. Therefore, \\delta13C may also reflect disequilibrium. In contrast, both \\delta18O and \\delta13C of abiotic calcite are in isotopic equilibrium with soil moisture and soil CO2 at temperatures close to or higher than the average soil temperatures in the area. The small sizes of bacteriogenic calcite aggregates indicate that these precipitated in confined pools of water where local chemistry and pH are easily modified by the microorganisms. Therefore, oxygen and/or carbon isotopic disequilibrium of bacteriogenic calcite is likely the result of bacterial metabolism. The \\delta18O of soil calcite in paleosols has been widely used as a paleothermometer. Bacteriogenic calcite precipitation however is common in soils and not confined to zones of leaking gas oxidation. Likewise oxygen isotopic disequilibrium of bacteriogenic soil calcite may also be a common phenomenon. Therefore, paleosols should be examined for evidence of bacterial involvement in calcite precipitation prior to the use of \\delta18O of soil calcite as a paleothermometer.

Arkadakskiy, S. V.; Muehlenbachs, K.; Mendoza, C.; Szatkowski, B.

2004-12-01

410

Calcite Fluid Inclusion, Paragenetic, and Oxygen Isotopic Records of Thermal Event(s) at Yucca Mountain, Nevada  

SciTech Connect

Yucca Mountain, Nevada, is under consideration as a potential high-level radioactive waste repository situated above the water table in 12.7 Ma tuffs. A wealth of textural and geochemical evidence from low-temperature deposits of calcite and silica, indicates that their genesis is related to unsaturated zone (UZ) percolation and that the level of the potential repository has never been saturated. Nonetheless, some scientists contend that thermal waters have periodically risen to the surface depositing calcite and opal in the tuffs and at the surface. This hypothesis received some support in 1996 when two-phase fluid inclusions (FIs) with homogenization temperatures (Th) between 35 and 75 C were reported from UZ calcite. Calcite deposition likely followed closely on the cooling of the tuffs and continues into the present. The paragenetic sequence of calcite and silica in the UZ is early stage calcite followed by chalcedony and quartz, then calcite with local opal during middle and late stages. Four types of FIs are found in calcite assemblages: (1) all-liquid (L); (2) all-vapor (V); (3) 2-phase with large and variable V:L ratios; and (4) a few 2-phase with small and consistent V:L ratios. Late calcite contains no FI assemblages indicating elevated depositional temperatures. In early calcite, the Th of type 4 FIs ranges from {approx} 40 to {approx} 85 C. Such temperatures (sub-boiling) and the assemblage of FIs are consistent with deposition in the UZ. Some delta 18O values < 10 permil in early calcite support such temperatures. Type 4 FIs, however, seem to be restricted to the early calcite stage, during which either cooling of the tuffs or regional volcanism were possible heat sources. Nonetheless, at present there is no compelling evidence of upwelling water as a source for the calcite/opal deposits.

B. Peterman; R. Moscati

2000-08-10

411

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

412

In situ AFM crystal growth and dissolution study of calcite in the presence of aqueous fluoride  

NASA Astrophysics Data System (ADS)

Fluoride is naturally abundant, encountered in rocks, soil and fresh and ocean water. Calcite crystals, during crystal growth may incorporate fluoride ions into their lattice (Okumura et al., 1983). In situ atomic force microscopy (AFM) has been used to study the growth and dissolution of calcite {104} surfaces in aqueous solutions in the presence of fluoride, using a fluid cell in which the supersaturated and the understaturated solutions respectively, flow over a freshly cleaved calcite crystal. For growth experiments, supersaturation index (S.I.) with respect to calcite was equal to 0.89 and the initial solution pH 10.2. The crystal growth rates were measured from the closure of the rhombohedral etch pits along the [010] direction induced by an initial dissolution step using pure water. The spreading rate of 2-dimensional nuclei was also measured along the same direction. In the presence of low fluoride concentrations (?0.33 mM), the crystal growth rate of calcite was unaffected. At higher concentrations (up to 5 mM) growth rate decreased substantially to 50% of the rate in the absence of fluoride. Potential fluoride sorption over the calcite surface may ascribe the decrease of growth rates. Dissolution experiments were conducted at pH= 7.2 and dissolution rates of calcite were measured from the spreading of rhombohedral etch pits along both [010] and [42] directions. The presence of low concentrations of fluoride (?1.1 mM) in the undersaturated solutions enhanced the dissolution rate along the [42] direction by 50% in comparison with pure water. The morphology of rhombohedral etch pits changed to hexagonal in the presence of fluoride in the undersaturated solutions. The AFM dissolution experiments suggested that the fluoride ions adsorbed onto the calcite surface. Further increase of fluoride concentrations (up to 1.6 mM) resulted in the decrease of the calcite dissolution rate by 60% in both [010] and [42] directions. Reference: Okumura, M, Kitano, Y., Idogaki, M., 1983. Inorporation of fluoride ions into calcite - Effect of organic materials and magnesium ions in a parent solution. Geochemical Journal 17, 257-263.

Vavouraki, A.; Putnis, C. V.; Putnis, A.; Koutsoukos, P. G.

2009-04-01

413

Three-way ANOVA interaction analysis and ultrasonic testing to evaluate air lime mortars used in cultural heritage conservation projects  

Microsoft Academic Search

Lime mortar has been used throughout history despite current substitution by hydraulic mortars (cements). The chemical composition of the lime used in its manufacture, however, is determined by local geology. In addition, the type of slaking, which depends on the amount of water used, gives rise to different types of lime. The result is that the behavior of lime mortar

O. Cazalla; E. Sebastián; G. Cultrone; M. Nechar; M. G. Bagur

1999-01-01

414

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

415

Adhesion of hydrated silicate films  

SciTech Connect

We used fracture mechanics test techniques to measure the adhesive bond energy formed between hydrated silica glass surfaces and silicate species deposited from solution. In the case of silicate surfaces hydrated in room temperature water vapor, intermolecular bonding between hydrated surfaces can be attributed to either hydrogen bonding interactions between adsorbed water molecules (0.15 Jm/sup 2/) or electrostatic bonds formed between adsorbed cations and anionic-nonbridging surface oxygen groups (2.0 Jm/sup 2/). The bonding interaction observed at room temperature depends upon the glass surface composition and the degree of surface hydration. When hydrated silicate solution species are added to the interface and heat treated, adhesion energies as large as the cohesive energy of silica glass can be obtained with heat treatments as low as 200/degree/C. The adhesion of the silicate interfacial film produced by the addition of solution species is greatest for silicate precursors showing a low degree of molecular crosslinking. In addition, the presence of alkali in the silicate solution greatly enhances interface adhesion for heat treatments below 200/degree/C. 9 refs., 10 figs.

Michalske, T.A.; Keefer, K.D.

1988-01-01

416

Well log evaluation of natural gas hydrates  

SciTech Connect

Gas hydrates are crystalline substances composed of water and gas, in which a solid-water-lattice accommodates gas molecules in a cage-like structure. Gas hydrates are globally widespread in permafrost regions and beneath the sea in sediment of outer continental margins. While methane, propane, and other gases can be included in the clathrate structure, methane hydrates appear to be the most common in nature. The amount of methane sequestered in gas hydrates is probably enormous, but estimates are speculative and range over three orders of magnitude from about 100,000 to 270,000,000 trillion cubic feet. The amount of gas in the hydrate reservoirs of the world greedy exceeds the volume of known conventional gas reserves. Gas hydrates also represent a significant drilling and production hazard. A fundamental question linking gas hydrate resource and hazard issues is: What is the volume of gas hydrates and included gas within a given gas hydrate occurrence? Most published gas hydrate resource estimates have, of necessity, been made by broad extrapolation of only general knowledge of local geologic conditions. Gas volumes that may be attributed to gas hydrates are dependent on a number of reservoir parameters, including the areal extent ofthe gas-hydrate occurrence, reservoir thickness, hydrate number, reservoir porosity, and the degree of gas-hydrate saturation. Two of the most difficult reservoir parameters to determine are porosity and degreeof gas hydrate saturation. Well logs often serve as a source of porosity and hydrocarbon saturation data; however, well-log calculations within gas-hydrate-bearing intervals are subject to error. The primary reason for this difficulty is the lack of quantitative laboratory and field studies. The primary purpose of this paper is to review the response of well logs to the presence of gas hydrates.

Collett, T.S.

1992-10-01

417

Well log evaluation of natural gas hydrates  

SciTech Connect

Gas hydrates are crystalline substances composed of water and gas, in which a solid-water-lattice accommodates gas molecules in a cage-like structure. Gas hydrates are globally widespread in permafrost regions and beneath the sea in sediment of outer continental margins. While methane, propane, and other gases can be included in the clathrate structure, methane hydrates appear to be the most common in nature. The amount of methane sequestered in gas hydrates is probably enormous, but estimates are speculative and range over three orders of magnitude from about 100,000 to 270,000,000 trillion cubic feet. The amount of gas in the hydrate reservoirs of the world greedy exceeds the volume of known conventional gas reserves. Gas hydrates also represent a significant drilling and production hazard. A fundamental question linking gas hydrate resource and hazard issues is: What is the volume of gas hydrates and included gas within a given gas hydrate occurrence Most published gas hydrate resource estimates have, of necessity, been made by broad extrapolation of only general knowledge of local geologic conditions. Gas volumes that may be attributed to gas hydrates are dependent on a number of reservoir parameters, including the areal extent ofthe gas-hydrate occurrence, reservoir thickness, hydrate number, reservoir porosity, and the degree of gas-hydrate saturation. Two of the most difficult reservoir parameters to determine are porosity and degreeof gas hydrate saturation. Well logs often serve as a source of porosity and hydrocarbon saturation data; however, well-log calculations within gas-hydrate-bearing intervals are subject to error. The primary reason for this difficulty is the lack of quantitative laboratory and field studies. The primary purpose of this paper is to review the response of well logs to the presence of gas hydrates.

Collett, T.S.

1992-10-01

418

Dissociation heat transfer characteristics of methane hydrates  

SciTech Connect

Knowledge of the interfacial heat transfer phenomenon during the dissociation of gas hydrates is essential in modeling the hydrate dissociation process. Such knowledge has applications in natural gas processing, storage, or transportation; in the drilling and recovery of oil and gas in the presence of gas hydrates; in the desalination of sea water; and in the production of natural gas from hydrate reservoirs. The process of hydrate dissociation is a unique phenomenon in which gas and water are simultaneously produced at the dissociated hydrate surface and play an important role in the mechanism of heat transfer to hydrates. An earlier study of propane hydrate dissociation showed that hydrate dissociation is a heat-transfer-limited process and somewhat similar to the nucleate boiling of liquids. In the present study, heat transfer limitations for methane hydrate dissociation were studied for two reasons. First, a comparison of the results of this study with propane hydrate was desired. Second, the effect of hydrate structure and gas molecule type on the rate of heat transfer during hydrate dissociation was sought.

Kamath, V.A.; Holder, G.D.

1987-02-01

419

Ages and Origins of Calcite and Opal in the Exploratory Studies Facility Tunnel, Yucca Mountain, Nevada  

USGS Publications Warehouse

Deposits of calcite and opal are present as coatings on open fractures and lithophysal cavities in unsaturated-zone tuffs at Yucca Mountain, Nevada, site of a potential high-level radioactive waste repository. Outermost layers of calcite and opal have radiocarbon ages of 16,000 to 44,000 years before present and thorium-230/uranium ages of 28,000 to more than 500,000 years before present. These ages are young relative to the 13-million-year age of the host rocks. Multiple subsamples from the same outer layer typically show a range of ages with youngest ages from the thinnest subsamples. Initial uranium-234/uranium-238 activity ratios between 1 and 9.5 show a distinct negative correlation with thorium-230/uranium age and are greater than 4 for all but one sample younger than 100,000 years before present. These data, along with micrometer-scale layering and distinctive crystal morphologies, are interpreted to indicate that deposits formed very slowly from water films migrating through open cavities. Exchanges of carbon dioxide and water vapor probably took place between downward-migrating liquids and upward-migrating gases at low rates, resulting in oversaturation of mineral constituents at crystal extremities and more or less continuous deposition of very thin layers. Therefore, subsamples represent mixtures of older and younger layers on a scale finer than sampling techniques can resolve. Slow, long-term rates of deposition (less than about 5 millimeters of mineral per million years) are inferred from subsamples of outermost calcite and opal. These growth rates are similar to those calculated assuming that total coating thicknesses of 10 to 40 millimeters accumulated over 12 million years. Calcite has a wide range of delta carbon-13 values from about -8.2 to 8.5 per mil and delta oxygen-18 values from about 10 to 21 per mil. Systematic microsampling across individual mineral coatings indicates basal (older) calcite tends to have the largest delta carbon-13 values and smallest delta oxygen-18 values compared to calcite from intermediate and outer positions. Basal calcite has relatively small strontium-87/strontium-86 ratios, between 0.7105 and 0.7120, that are similar to the initial isotopic compositions of the strontium-rich tuff units, whereas outer calcite has more radiogenic strontium-87/strontium-86 ratios between 0.7115 and 0.7127. Isotopic compositions of strontium, oxygen, and carbon in the outer (youngest) unsaturated-zone calcite are coincident with those measured in Yucca Mountain calcrete, which formed by pedogenic processes. The physical and isotopic data from calcite and opal indicate that they formed from solutions of meteoric origin percolating through a limited network of connected fracture pathways in the unsaturated zone rather than by inundation from ascending ground water originating in the saturated zone. Mineral assemblages, textures, and distributions within the unsaturated zone are distinctly different from those deposited below the water table at Yucca Mountain. The calcite and opal typically are present only on footwall surfaces of a small fraction of fractures and only on floors of a small fraction of lithophysal cavities. The similarities in the carbon, oxygen, and strontium isotopic compositions between fracture calcite and soil-zone calcite, as well as the gradation of textures from detritus-rich micrite in the soil to detritus-free spar 10 to 30 meters below the surface, also support a genetic link between the two depositional environments. Older deposits contain oxygen isotope compositions that indicate elevated temperatures of mineral formation during the early stages of deposition; however, in the youngest deposits these values are consistent with deposition under geothermal gradients similar to modern conditions. Correlations between mineral ages and varying Pleistocene climate conditions are not apparent from the current data. Cumulative evidence from calcite and opal deposits indicate

Paces, James B.; Neymark, Leonid A.; Marshall, Brian D.; Whelan, Joseph F.; Peterman, Zell E.

2001-01-01

420

Paleotemperature Estimation by Tandem ?18O Measurement of Biogenic Carbonate and Gypsum Hydration Water  

NASA Astrophysics Data System (ADS)

One of the fundamental problems in oxygen isotope paleothermometry is the carbonate mineral-water temperature equation is often under constrained. The ?18O of calcite or aragonite can be measured on fossil shell material but a unique temperature solution is not possible without knowing the ?18Owater from which the carbonate precipitated. Gypsum (CaSO4*2H2O) is a hydrated mineral that contains 20.9% water by weight. The isotopic composition of the water from which the gypsum was precipitated can be calculated from the ?18O and ?D of gypsum hydration water provided: (i) the fractionation factors between mother water and crystal water are known; and (ii) no further exchange has occurred between environmental and crystal water after deposition. Here we propose that tandem ?18O measurements of both carbonate and gypsum hydration water in the same samples offers a power tool for determining past temperature. We demonstrate the method using co-occurring gypsum and biogenic carbonate from sediment cores from Lake Peten Itza, Guatemala (17oN, 90oW). Oxygen and hydrogen isotopic results of interstitial and gypsum hydration water from glacial-aged deposits in Lake Peten Itza suggest the gypsum hydration water has not exchanged with sediment pore water. The ?18O and ?D of lake water, calculated from gypsum hydration water and known fractionation factors, fall on a projection of the evaporative line (slope of ~5) defined using modern lakes in the region. Fifteen paired measurements of ostracods and gypsum hydration water in the same samples gave a mean temperature of ~16oC (range 13 to 19 oC) for the Late Glacial (18 to 10 ka), which is 9oC cooler than mean annual temperature in the region today (~25oC). The low glacial temperatures likely reflect winter climate that sets hypolimnetic temperature in warm, monomictic lakes. Our preliminary results support previous findings of much greater glacial tropical cooling during winter on land in Central America than indicated by marine proxies in the nearby Caribbean Sea. Accuracy of the method could be improved by verifying the oxygen and hydrogen isotope fractionation factors between mother water and gypsum hydration water determined in the 1960s and by culturing experiments of the ostracod species (Limnocythere opesta) used in this study to determine the offset from oxygen isotope equilibrium.

Hodell, D. A.; Turchyn, A. V.; Escobar, J.; Curtis, J. H.; Brenner, M.; Gilli, A.; Anselmetti, F.; Ariztegui, D.; Bush, M.; Perez, L.; Schwalb, A.

2010-12-01

421

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

NASA Astrophysics Data System (ADS)

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 calcite with Mg content from 0.5 to 17 mol%. Stress stepping tests and constant strain rate tests were used to examine the effect of Mg content on the dislocation creep of calcite. The grain growth rate under static conditions was decreased with Mg content from 7 to 17 mol%, indicating perhaps that grain boundary mobility is suppressed by the solute drag effect. In the diffusion creep at stresses below 40 Mpa, the strength of calcite decreases with increasing Mg content owing to the difference in grain size at 800° C and 300 MPa confining pressure. The contribution of dislocation creep increases with increasing stress, and the transition between diffusion and dislocation creep occurs at higher stresses for the samples with higher magnesium content and smaller grain size. The creep data were fit assuming a composite flow law consisting of a linear combination of diffusion and dislocation creep and a single-valued grain size. The best agreement was obtained by using a dislocation creep law with exponential dependence of strain rate on stress (e.g. Peierls law). More evidence from microstructure is needed to identify the dominant deformation mechanism conclusively. Most of the samples were compressed up to strains of 0.25; small recrystallized grains are formed resulting in a bimodal grain size distribution in some of the deformed samples. Preliminary data shows that the recrystallized grain sizes are smaller for Mg-calcite compared with that of pure calcite. This study will help to understand the effect of impurities on grain-growth kinetics and strain weakening in localized shear zones.

Xu, L.

2004-12-01

422

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

423

Coprecipitation of chromate with calcite: Batch experiments and X-ray absorption spectroscopy  

NASA Astrophysics Data System (ADS)

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, Kd?, is highest at low Cr solution concentration, and decreases to a constant value with increasing Cr solution concentration. DIC images of the (101¯4) surface of calcite single crystals grown in the presence of CrO42- 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 ˜1.64 ± 0.01 Å, consistent with CrO42-. Best fit results show that the second shell is split with ˜2.5 Ca at ˜3.33 ± 0.05 and ˜2.2 Ca at ˜3.55 ± 0.05 Å, which confirms the incorporation of chromate into calcite. Consideration of possible local coordination indicates that significant distortion or disruption is required to accommodate CrO42- in the calcite structure.

Tang, Yuanzhi; Elzinga, Evert J.; Jae Lee, Young; Reeder, Richard J.

2007-03-01

424

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

425

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

426

Acoustic Determination of Methane Hydrate Disssociation Pressures.  

National Technical Information Service (NTIS)

The unique nature of the molecular structures of gas hydrates results in curious acoustic properties which have yet to be adequately characterized. Understanding the acoustic behavior of hydrates in liquids, in bubbly liquids, and in sediments containing ...

C. A. Greene P. S. Wilson R. B. Coffin

2011-01-01

427

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

428

Sedimentological Control on Hydrate Saturation Distribution in Arctic Gas-Hydrate-Bearing Deposits  

Microsoft Academic Search

Grain size variations along with the relative rates of fluid phases migrating into the zone of hydrate stability, plays an important role in gas-hydrate distribution and its morphologic characteristics. In the Arctic, strata several meters thick containing large saturations of gas hydrate are often separated by layers containing small but nonzero hydrate saturations. Examples are Mt. Elbert, Alaska and Mallik,

J. Behseresht; Y. Peng; S. L. Bryant

2010-01-01

429

Characteristics and reactivity of rapidly hydrated sorbent for semidry flue gas desulfurization  

SciTech Connect

The semidry flue gas desulfurization (FGD) process has many advantages over the wet FGD process for moving sulfur dioxide emissions from pulverized coal-fired power plants. Semidry FGD with a rapidly hydrated sorbent was studied in a pilot-scale circulating fluidized bed (CFB) experimental facility. The sorbent was made from lumps of lime and coal fly ash. The desulfurization efficiency was measured for various operating parameters, including the sorbent recirculation rate and the water spray method. The experimental results show that the desulfurization efficiencies of the rapidly hydrated sorbent were 1.5-3.0 times higher than a commonly used industrial sorbent for calcium to sulfur molar ratios from 1.2 to 3.0, mainly due to the higher specific surface area and pore volume. The Ca(OH){sub 2} content in the cyclone separator ash was about 2.9% for the rapidly hydrated sorbent and was about 0.1% for the commonly used industrial sorbent, due to the different adhesion between the fine Ca(OH){sub 2} particles and the fly ash particles, and the low cyclone separation efficiency for the fine Ca(OH){sub 2} particles that fell off the sorbent particles. Therefore the actual recirculation rates of the active sorbent with Ca(OH){sub 2} particles were higher for the rapidly hydrated sorbent, which also contributed to the higher desulfurization efficiency. The high fly ash content in the rapidly hydrated sorbent resulted in good operating stability. The desulfurization efficiency with upstream water spray was 10-15% higher than that with downstream water spray. 20 refs., 7 figs., 1 tab.

Jie Zhang; Changfu You; Suwei Zhao; Changhe Chen; Haiying Qi [Tsinghua University, Beijing (China). Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering

2008-03-01

430

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

431

[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

432

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

433

Dehydration of plutonium trichloride hydrate  

DOEpatents

A process of preparing anhydrous actinide metal trichlorides of plutonium or neptunium by reacting an aqueous solution of an actinide metal trichloride selected from the group consisting of plutonium trichloride or neptunium trichloride with a reducing agent capable of converting the actinide metal from an oxidation state of +4 to +3 in a resultant solution, evaporating essentially all the solvent from the resultant solution to yield an actinide trichloride hydrate material, dehydrating the actinide trichloride hydrate material by heating the material in admixture with excess thionyl chloride, and recovering anhydrous actinide trichloride is provided.

Foropoulos, J. Jr.; Avens, L.R.; Trujillo, E.A.

1991-12-31

434

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

435

EXAFS Characterization of Uranyl Interaction at the Calcite-Water Interface  

NASA Astrophysics Data System (ADS)

Recent studies using X-ray absorption and luminescence spectroscopies have demonstrated uptake and incorporation of uranyl by calcite. X-ray microprobe studies on uranyl-reacted calcite single crystals reveal that uranyl exhibits preferences for specific surface sites. These preferences are likely expressed upon adsorption of uranyl species at the calcite-water interface. We have used X-ray absorption fine structure (EXAFS), combined with luminescence spectroscopy, to characterize the interactions of uranyl carbonate species with the calcite surface in the pH range 7.4-8.3. To minimize the potential for dissolution or precipitation, solutions were pre-equilibrated with reagent calcite powder for 3 weeks, with pH stabilizing at 8.3. For other experiments, the pH was adjusted initially to achieve a final pH of 7.4 after aging for 3 weeks. Uranyl carbonate solution was added to the pre-equilibrated suspensions to achieve initial U(VI) concentrations ranging from 5 uM to 5 mM. Suspensions were filtered to recover the calcite, but were kept moist to retain the sorbed complexes at the calcite-water interface. Multiple EXAFS spectra were collected using a multi-element Ge detector at beamline 12-BM at the APS and analyzed using standard methods. Fourier transforms (FT) of the spectra contain features corresponding to two axial oxygens and a shell of equatorial oxygens, as well as weaker features at higher R. For suspensions having initial U(VI) concentrations from 5-100 uM, a shoulder is observed in the FT on the high-R side of the equatorial oxygen, and fitting suggests minor splitting of this shell. For higher initial U(VI) concentrations, including the highest U(VI) concentration, 5 mM, the splitting becomes more pronounced. Weak features in the FT at higher-R can be fitted with backscattering from carbon, oxygen, and calcium shells, although fits without calcium provide nearly the same agreement. Luminescence spectroscopy reveals the presence of multiple uranyl species sorbed on the calcite from suspensions with 100 uM U(VI) and lower concentrations. The presence of multiple species may account for the splitting of the equatorial coordination indicated by EXAFS. For higher U(VI) concentrations, the luminescence results are consistent with formation of a schoepite-like precipitate. Understanding the complex interactions of uranyl at the calcite-water interface requires complementary data from multiple techniques.

Reeder, R. J.; Elzinga, E. J.; Tait, C. D.

2002-12-01

436

Physical properties of hydrate-bearing sediments  

Microsoft Academic Search

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,

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

2009-01-01

437

Magnetic Diagenesis in the Gas Hydrate System  

Microsoft Academic Search

Natural gas hydrate is a methane-bearing form of ice which occurs in permafrost and continental slope settings. Geochemical processes associated with gas hydrate formation lead to the growth of iron sulphides which have a geophysically measurable magnetic signature. Detailed magnetic investigation and complementary petrological observations were undertaken on unconsolidated sediments from three gas hydrate (GH) settings: permafrost in fluvial-deltaic silts

R. J. Enkin; T. S. Hamilton; L. Esteban

2009-01-01

438

Dissociation heat transfer characteristics of methane hydrates  

Microsoft Academic Search

Knowledge of the interfacial heat transfer phenomenon during the dissociation of gas hydrates is essential in modeling the hydrate dissociation process. Such knowledge has applications in natural gas processing, storage, or transportation; in the drilling and recovery of oil and gas in the presence of gas hydrates; in the desalination of sea water; and in the production of natural gas

V. A. Kamath; G. D. Holder

1987-01-01

439

Mechanisms of gas hydrate formation and inhibition  

Microsoft Academic Search

The formation of gas hydrates in gas and oil subsea pipelines often results in blockage and shutdown of these pipelines. Modern control methods depend on understanding the mechanisms through which gas hydrates form. This paper reviews our recent studies of clathrate hydrate formation and inhibition mechanisms using neutron diffraction, differential scanning calorimetry (DSC) and a multiple cell photo-sensing instrument. The

C. A. Koh; R. E. Westacott; W. Zhang; K. Hirachand; J. L. Creek; A. K. Soper

2002-01-01

440

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

2011-05-06