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1

Transmethylation of trimethylbenzenes and toluene on H- and Ni\\/H-mordenites  

Microsoft Academic Search

Under pressure in the presence of hydrogen the calculated transmethylation equilibrium composition was approached on synthetic H-mordenite at 350°C, on natural H-mordenites at 450–500°C. The high activity of H-mordenite is maintained without deactivation by using the reduced Ni, H-form of synthetic mordenite with a nickel content of 2.4 mass %.

S. Szakács; J. Papp; D. Lejtovicz; D. Kalló

1982-01-01

2

Organic iodine removal from simulated dissolver off-gas streams using partially exchanged silver mordenite  

Microsoft Academic Search

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide adsorption of partially exchanged silver mordenite was examined for the effects of NO\\/sub x\\/, humidity, filter temperature, and degree of silver exchange. Partially exchanged silver mordenite, in general, achieved significantly

Jubin

1982-01-01

3

NO ADSORPTION CAPACITY ON COBALT ION EXCHANGED H-MORDENITE  

Microsoft Academic Search

Co,H-Zeolites have been extensively studied for the SCR of NOx with CH4 in excess oxygen. However, there are some aspects that have not yet been elucidated. In order to study the effect of the Co species on the NO adsorption capacity of Co,H-mordenites, experiments were performed on different cobalt- containing catalysts with different treatments (heated in He, O2 and H2).

Laura B. Gutierrez; Andrea Feser; Eduardo E. Miró; María A. Ulla

4

Organic iodine removal from simulated dissolver off-gas streams using silver-exchanged mordenite  

Microsoft Academic Search

The removal of methyl iodide by absorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide absorption of silver mordenite was examined for the effects of NO\\/sub x\\/, humidity, iodine concentration, filter temperature, and filter pretreatment. The highest iodine loading achieved in these tests has been

Jubin

1980-01-01

5

Organic iodine removal from simulated dissolver off-gas systems utilizing silver-exchanged mordenite  

Microsoft Academic Search

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The adsorption of methyl iodide on silver mordenite was examined for the effect of NO\\/sub x\\/, humidity, iodine concentration, filter temperature, silver loadings and filter pretreatment. The highest iodine loading achieved in these

Jubin

1981-01-01

6

Organic iodine removal from simulated dissolver off-gas streams using partially exchanged silver mordenite  

SciTech Connect

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide adsorption of partially exchanged silver mordenite was examined for the effects of NO/sub x/, humidity, filter temperature, and degree of silver exchange. Partially exchanged silver mordenite, in general, achieved significantly higher silver utilizations than the fully exchanged material. Silver utilizations of > 95% were achieved, assuming the formation of AgI. The experimental results indicate that CH/sub 3/I loadings increase proportionally with silver loading up to 5 wt % silver and then appear to level off. Tests conducted to determine the effect of temperature on the loading showed higher loadings at 200/sup 0/C than at either 150 or 250/sup 0/C. The presence of NO, NO/sub 2/, and H/sub 2/O vapor showed negligible effects on the loading of CH/sub 3/I. In contrast to iodine loaded onto fully exchanged silver mordenite, the iodine loaded onto the partially exchanged silver mordenite could not be stripped by either 4.5% hydrogen or 100% hydrogen at temperatures up to 500/sup 0/C. A study of the regeneration characteristics of fully exchanged silver mordenite indicates a decreased adsorbent capacity after complete removal of the iodine with 4.5% hydrogen in the regeneration gas stream at 500/sup 0/C. The loss of adsorbent capacity was much higher for silver mordenite regenerated in a stainless steel filter housing than in a glass filter housing. A cost evaluation for the use of the partially exchanged silver mordenite shows that the cost of the silver mordenite on a once-through basis is < $10/h of operation for a 0.5-t/d reprocessing plant.

Jubin, R.T.

1982-01-01

7

Recycle of iodine-loaded silver mordenite by hydrogen reduction  

SciTech Connect

In 1977 and 1978, workers at Idaho National Engineering Laboratory (INEL) developed and tested a process for the regeneration and reuse of silver mordenite, AgZ, used to trap iodine from the dissolver off-gas stream of a nuclear fuel reprocessing plant. We were requested by the Airborne Waste Management Program Office of the Department of Energy to perform a confirmatory recycle study using repeated loadings at about 150/sup 0/C with elemental iodine, each followed by a drying step at 300/sup 0/C, then by iodine removal using elemental hydrogen at 500/sup 0/C. The results of our study show that AgZ can be recycled. There was considerable difficulty in stripping the iodine at 500/sup 0/C.; however, this step went reasonably well at 550/sup 0/C or slightly higher, with no apparent loss in the iodine-loading capacity of the AgZ. Large releases of elemental iodine occurred during the drying stage and the early part of the stripping stage. Lead zeolite, which was employed in the original design to trap the HI produced, is ineffective in removal of I/sub 2/. The process needs modification to handle the iodine. Severe corrosion of the stainless steel components of the system resulted from the HI-I/sub 2/-H/sub 2/O mixture. Monel or other halogen-resistant materials need to be examined for this application. Because of difficulty with the stripping stage and with corrosion, the experiments were terminated after 12 cycles. Thus, the maximum lifetime (cycles) of recycle AgZ has not been determined. Mechanistic studies of iodine retention by silver zeolites and of the behavior of silver atoms on the reduction stage would be of assistance in optimizing silver mordenite recycle.

Burger, L.L.; Scheele, R.D.

1982-11-01

8

Local structure of aluminum in zeolite mordenite as affected by temperature.  

PubMed

The local aluminum structure in zeolite mordenite was studied at temperatures up to 1000 K in a vacuum by Al K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The interatomic aluminum-oxygen distances and the number of coordinating oxygen atoms were determined by Fourier transform analyses of experimental Al K-edge XANES spectra and the fits of the nearest oxygen atoms contributions, using a limited number of variables. The values of fixed parameters for Fourier transform and fit are established from the spectrum of Na-mordenite, considered the reference compound for the studied zeolites H-mordenites, which was also used to test the accuracy and the stability of the determined structural parameters. To reveal the aluminum coordination in H-mordenite at various temperatures, the Fourier transform peak of the coordinating oxygen polyhedron was fitted first with a single-shell model, and the obtained structural information was refined by the fits, on the basis of the most plausible models for the aluminum coordination environment. The choice of such models for each temperature was performed according to the qualitative predictions on the aluminum local atomic structure provided by the preedge data analysis and 27Al magic angle spinning (MAS) NMR experiments. By this method, the presence of sixfold aluminum atoms, aside from the fourfold ones, in H-mordenite at room temperature was revealed quantitatively, and the concentrations of these mixed coordinations were determined; the structural distortion of the oxygen tetrahedron around aluminum in dehydrated H-mordenite at T = 575 K was found to be strong, and the corresponding Al-O distances for this distortion were obtained; for H-mordenite at 985 K, the presence of threefold coordinated aluminum atoms, aside from the fourfold ones, was revealed, and an estimate of the amount of threefold aluminum was given. PMID:16852309

Bugaev, Lusegen A; van Bokhoven, Jeroen A; Sokolenko, Andrei P; Latokha, Yana V; Avakyan, Leon A

2005-06-01

9

Organic iodine removal from simulated dissolver off-gas systems utilizing silver-exchanged mordenite  

SciTech Connect

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The adsorption of methyl iodide on silver mordenite was examined for the effect of NO/sub x/, humidity, iodine concentration, filter temperature, silver loadings and filter pretreatment. The highest iodine loading achieved in these tests was 142 mg CH/sub 3/I per g of substrate on fully exchanged zeolite, approximately the same as elemental iodine loadings. A filter using fully exchanged silver mordenite operating at 200/sup 0/C obtained higher iodine loadings than a similar filter operating at 150/sup 0/C. Pretreatment of the sorbent bed with hydrogen rather than dry air, at a temperature of 200/sup 0/C, also improved the loading. Variations in the methyl iodide concentration had minimal effects on the overall loading. Filters exposed to moist air streams attained higher loadings than those in contact with dry air. Partially exchanged silver mordenite achieved higher silver utilizations than the fully exchanged material. The partially exchanged mordenite also achieved higher loadings at 200/sup 0/C than at 250/sup 0/C. The iodine loaded onto these beds was not stripped at 500/sup 0/C by either 4.5% hydrogen or 100% hydrogen; however, the iodine could be removed by air at 500/sup 0/C, and the bed could be reloaded. A study of the regeneration characteristics of fully exchanged silver mordenite indicates limited adsorbent capacity after complete removal of the iodine with 4.5% hydrogen in the regeneration gas stream at 500/sup 0/C. The loss of adsorbent capacity is much higher for silver mordenite regenerated in a stainless steel filter housing than in a glass filter housing.

Jubin, R.T.

1981-01-01

10

Heulandite and mordenite-rich tuffs from Greece: a potential source for pozzolanic materials  

Microsoft Academic Search

The microcystalline mass of the Pliocene tuffs of Santorini and Polyegos islands, in the South Aegean Volcanic Arc, Greece, is very rich in zeolite minerals, more specifically heulandite type 3, i.e. clinoptilolite, and mordenite. In Santorini, clinoptilolite is the dominant authigenic phase and it was formed in a semi-closed system, by the activity of interstitial water within the volcaniclastic sequence.

K. P. Kitsopoulos; A. C. Dunham

1996-01-01

11

Optimization of lead adsorption of mordenite by response surface methodology: characterization and modification  

PubMed Central

Background In order to remove heavy metals, water treatment by adsorption of zeolite is gaining momentum due to low cost and good performance. In this research, the natural mordenite was used as an adsorbent to remove lead ions in an aqueous solution. Methods The effects of adsorption temperature, time and initial concentration of lead on the adsorption yield were investigated. Response surface methodology based on Box-Behnken design was applied for optimization. Adsorption data were analyzed by isotherm models. The process was investigated by batch experiments; kinetic and thermodynamic studies were carried out. Adsorption yields of natural and hexadecyltrimethylammonium-bromide-modified mordenite were compared. Results The optimum conditions of maximum adsorption (nearly 84 percent) were found as follows: adsorption time of 85-90 min, adsorption temperature of 50°C, and initial lead concentration of 10 mg/L. At the same optimum conditions, modification of mordenite produced 97 percent adsorption yield. The most appropriate isotherm for the process was the Freundlich. Adsorption rate was found as 4.4. Thermodynamic calculations showed that the adsorption was a spontaneous and an exothermic process. Conclusions Quadratic model and reduced cubic model were developed to correlate the variables with the adsorption yield of mordenite. From the analysis of variance, the most influential factor was identified as initial lead concentration. At the optimum conditions modification increased the adsorption yield up to nearly 100 percent. Mordenite was found an applicable adsorbent for lead ions especially in dilute solutions and may also be applicable in more concentrated ones with lower yields. PMID:24393442

2014-01-01

12

Kinetic study and modelization of n-butenes oligomerization over H-mordenite  

SciTech Connect

n-Butenes have been oligomerized at temperatures lower than 450 K in the liquid phase over H-mordenite in a continuously stirred tank reactor. The composition and molecular weight of the products are very dependent on reaction temperature. Products are essentially dimers, trimers, and tetramers. The complex reactions were modeled by taking into account only the type of carbonium ion; the initial rates showed that the oligomerization reactions followed a Rideal mechanism. The dimerization rate constants of butenes and oligomers decrease with increasing number of carbon atoms of the olefins, while the adsorption constants increase with the hydrocarbon chain length. A model for the conversion of butenes to liquid products over H-Mordenite is proposed. This model fits the experimental data rather well, although some simplifying approximations were made to describe these complex reactions.

Ngandjui, L.M.T.; Thyrion, F.C. [Louvain Univ., Louvain-la-Neuve (Belgium). Chemical Engineering Inst.

1996-04-01

13

Crystallization and morphology of mordenite zeolite influenced by various parameters in organic-free synthesis  

SciTech Connect

Research highlights: {yields} Seed, gel composition and silicon source affect the crystallization process of MOR. {yields} Seed, gel composition and silicon source influence the morphology of MOR. {yields} Low silica concentration results in MOR with high c/b aspect ratio. {yields} Novel nano fiber-like MOR with c/b aspect ratio of 89 was organic-free synthesized. {yields} The morphology of MOR influences its mesopore property and thermal stability. -- Abstract: A series of mordenite zeolites with different morphologies were synthesized via a facile organic-free hydrothermal route, and characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectrometer and N{sub 2} adsorption-desorption techniques. Influences of synthetic parameters, including seed crystal, silicon precursor, SiO{sub 2}/Al{sub 2}O{sub 3}, Na{sub 2}O/SiO{sub 2} and H{sub 2}O/SiO{sub 2}, on mordenite crystallization were investigated systematically. It was found that mordenite zeolites with various morphologies, such as fiber-like, rod-like, prism-like and needle-like ones could be synthesized in control. Especially, novel nano fiber-like MOR crystals with high c/b aspect ratio were prepared from low silica concentration system, which was manipulated by using small initial SiO{sub 2}/Al{sub 2}O{sub 3} ratio, large H{sub 2}O/SiO{sub 2} and silicon source with slow dissolution rate. Moreover, mordenite samples with various morphologies exhibited different mesopore property and thermal stability.

Zhang, Ling [State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian P.O. Box 110, 116023 (China) [State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian P.O. Box 110, 116023 (China); Graduate University of Chinese Academy of Sciences, Beijing 100049 (China); Xie, Sujuan; Xin, Wenjie; Li, Xiujie; Liu, Shenglin [State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian P.O. Box 110, 116023 (China)] [State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian P.O. Box 110, 116023 (China); Xu, Longya, E-mail: lyxu@dicp.ac.cn [State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian P.O. Box 110, 116023 (China)] [State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian P.O. Box 110, 116023 (China)

2011-06-15

14

Determination of Ni(II) uptake mechanisms on mordenite surfaces: A combined macroscopic and microscopic approach  

NASA Astrophysics Data System (ADS)

The uptake mechanisms of Ni(II) on mordenite were investigated by macroscopic experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy. The results demonstrated that Ni(II) could be retained via different mechanisms, depending on pH, ionic strength, temperature, etc. At low pH, the uptake of Ni(II) is primarily dominated by cation exchange and/or outer-sphere surface complexation. The interatomic distances of Ni-O (˜2.05 Å) and the coordination number (˜6.0) are similar to those of Ni(II)(aq) reference sample, suggesting that Ni(II) is present in an [Ni(H 2O) 6] 2+ octahedral environment at low pH. With increasing pH, the uptake of Ni(II) on mordenite tends to form inner-sphere surface complexes and precipitation/co-precipitation at high pH. The uptake of Ni(II) on mordenite becomes more favorable with increasing temperature, and the EXAFS spectra analysis show a trend from outer-sphere surface complexation at low temperature to inner-sphere surface complexation at high temperature. The addition of HA/FA increases Ni(II) uptake at low pH and decreases Ni(II) uptake at high pH. Enhanced Ni(II) uptake is attributed to the formation of "ligand-bridging" ternary surface complexes that are adsorbed on mordenite surface, while reduction is attributed to the formation of soluble Ni(II)-HA/FA complexes in solution that compete with uptake processes. The findings presented in this study are important toward a molecular-level description of Ni(II) uptake processes at the water-mineral interface.

Yang, Shitong; Sheng, Guodong; Tan, Xiaoli; Hu, Jun; Du, Jinzhou; Montavon, Gilles; Wang, Xiangke

2011-11-01

15

Organic iodine removal from simulated dissolver off-gas streams using silver-exchanged mordenite  

SciTech Connect

The removal of methyl iodide by absorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The methyl iodide absorption of silver mordenite was examined for the effects of NO/sub x/, humidity, iodine concentration, filter temperature, and filter pretreatment. The highest iodine loading achieved in these tests has been 34 mg CH/sub 3/I per g of substrate, approximately five times less than the elemental iodine loadings. Results indicate that a filter operating at a temperature of 150/sup 0/C obtained higher iodine loadings than a similar filter operating at 100/sup 0/C. Pretreatment of the sorbent bed with hydrogen, rather than dry air, at a temperature of 200/sup 0/C also improved the loading. Variations in the methyl iodide concentration had minimal effects on the overall loading. Filters exposed to moist air streams attained higher loadings than those in contact with dry air. A study of the regeneration characteristics of silver mordenite indicates limited adsorbent capacity after complete removal of the iodine with 4% hydrogen in the regeneration gas stream at 500/sup 0/C. 9 figures.

Jubin, R.T.

1980-01-01

16

Location of MTBE and toluene in the channel system of the zeolite mordenite: Adsorption and host-guest interactions  

SciTech Connect

This paper reports a study of the location of Methyl Tertiary Butyl Ether (MTBE) and toluene molecules adsorbed in the pores of the organophylic zeolite mordenite from an aqueous solution. The presence of these organic molecules in the zeolite channels was revealed by structure refinement performed by the Rietveld method. About 3 molecules of MTBE and 3.6 molecules of toluene per unit cell were incorporated into the cavities of mordenite, representing 75% and 80% of the total absorption capacity of this zeolite. In both cases a water molecule was localized inside the side pocket of mordenite. The saturation capacity determined by the adsorption isotherms, obtained by batch experiments, and the weight loss given by thermogravimetric (TG) analyses were in very good agreement with these values. The interatomic distances obtained after the structural refinements suggest MTBE could be connected to the framework through a water molecule, while toluene could be bonded to framework oxygen atoms. The rapid and high adsorption of these hydrocarbons into the organophylic mordenite zeolite makes this cheap and environmental friendly material a suitable candidate for the removal of these pollutants from water. - graphical abstract: Location of MTBE (a) and toluene (b) in mordenite channels (projection along the [001] direction). Highlights: Black-Right-Pointing-Pointer We investigated the MTBE and toluene adsorption process into an organophilic zeolite mordenite. Black-Right-Pointing-Pointer The presence of MTBE and toluene in mordenite was determined by X-ray diffraction studies. Black-Right-Pointing-Pointer About 3 molecules of MTBE and 3.6 molecules of toluene per unit cell were incorporated into the zeolite cavities. Black-Right-Pointing-Pointer MTBE is connected to the framework through a water molecule. Black-Right-Pointing-Pointer Toluene is directly bonded to framework oxygen atoms.

Arletti, Rossella, E-mail: rossella.arletti@unito.it [Department of Earth Sciences, University of Torino Via Valperga Caluso 35, I-10125, Torino (Italy)] [Department of Earth Sciences, University of Torino Via Valperga Caluso 35, I-10125, Torino (Italy); Martucci, Annalisa; Alberti, Alberto [Department of Earth Sciences, University of Ferrara, Via G. Saragat 1, I-44100, Ferrara (Italy)] [Department of Earth Sciences, University of Ferrara, Via G. Saragat 1, I-44100, Ferrara (Italy); Pasti, Luisa; Nassi, Marianna [Department of Chemistry, University of Ferrara, Via L. Borsari 26, I-44100 Ferrara (Italy)] [Department of Chemistry, University of Ferrara, Via L. Borsari 26, I-44100 Ferrara (Italy); Bagatin, Roberto [Research Centre for Non-Conventional Energy-Istituto ENI Donegani, Environmental Technologies, Via Fauser 4, I-28100 Novara (Italy)] [Research Centre for Non-Conventional Energy-Istituto ENI Donegani, Environmental Technologies, Via Fauser 4, I-28100 Novara (Italy)

2012-10-15

17

Reaction of butanes on Na, H-Y zeolites and H-mordenites  

SciTech Connect

The reaction chemistry for the conversion of isobutane and n-butane on H-mordenites was compared with that on Na,H-Y zeolites in continuous flow experiments. The close resemblance of the product distribution as a function of conversion suggests that identical mechanism for conversion is effective on both types of zeolites. Hydrogen and methane from isobutane and in addition ethane and ethylene from n-butane were expected to be formed in chain initiation processes, while propene and butenes were expected to be formed in chain termination processes. The major products, alkanes, are produced in chain carrying hydride and methyl transfer. A rate of initiation approximately 10-fold higher than with mordenites having stronger Bronsted acid sites is required to reach identical conversion with Y-zeolites. The yield of individual products on zeolites with identical structure and at identical temperature was almost independent of the Si/Al ratio or the Na{sup +} content of zeolites but depended on the conversion; at identical conversion the chain length on zeolites with different activity was similar. 28 refs., 9 figs., 6 tabs.

Engelhardt, J. [Central Research Inst. for Chemistry of the Hungarian Academy of Sciences, Budapest (Hungary)] [Central Research Inst. for Chemistry of the Hungarian Academy of Sciences, Budapest (Hungary)

1996-12-01

18

Effect of cation exchange on hydrogen adsorption property of mordenite for isotope separation  

NASA Astrophysics Data System (ADS)

Zeolite easily exchanges its cation to another. As a result, pore size changes easily. Cation-exchanged mordenite type zeolite (MOR) has been reported to have comparatively good isotope separation capability at temperatures higher than 77 K. However, correlations between adsorption capacities, adsorption rate, cation variety, and cation exchange ratio have not been clearly indicated. In this work, the cation (Na+) of synthetic mordenite type zeolite (Na-MOR) was exchanged by alkaline metal ion or alkaline earth ion (e.g., Li+, K+, Mg2+ and Ca2+). Then, adsorption capacities of H2 and D2 were investigated at 77 K, 159 K, 175 K and 195 K. Adsorption capacities on Li-MOR and Ca-MOR became larger than that of Na-MOR at a low-pressure range, while that of K-MOR became smaller. Micro-pore size indicated that only K-MOR was clearly shifting to smaller size. In the case of alkaline metal, cations with lower atomic numbers may lead to increased adsorption capacities.

Kawamura, Yoshinori; Iwai, Yasunori; Munakata, Kenzo; Yamanishi, Toshihiko

2013-11-01

19

Alkylations of benzene, alkylbenzenes, and halobenzenes catalyzed by protonated mordenite pretreated with chlorofluorocarbons  

SciTech Connect

The chlorofluorocarbon (CFC) treatment of protonated mordenite (HM) was carried out in a flow reactor under ordinary pressure, usually at 600C for 10 min using CCIF{sub 3} as a treatment agent. The mordenite structure was almost completely retained during the CFC treatment. Evidence for dealumination and surface fluorination was observed by XPS examination. Decrease of surface acidity, as seen by NH{sub 3-}TPD, accompanied the treatment. The function of HM as a catalyst for alkylations of benzene and alkylated or halobenzenes with methanol was greatly enhanced by the CFC treatment. In particular, the activity maintenance was remarkably improved. Thus, in the alkylations at 300C under the molar ratios of CH{sub 3}OH/Aromatic compound = 1 and W/F = 81.2 (for toluene) or 97.5 (for 1,2,4-trimethylbenzene (TBM)) g h/mol, the conversions at the initial stage of the run were increased from 27 to 65% (for toluene) and from 12 to 47% (for TMB) by CFC treatment of the Hm catalyst. In addition, the conversions of benzene and TMB were well maintained at about 60 and 40%, respectively, throughout the running time of 3 h in the reactions catalyzed by the treated HM, while the conversions of benzene and TMB rapidly decreased and became almost zero within 90 min in the reaction catalyzed by untreated HM.

Kodama, Hiroto; Okazaki, Susumu (Ibaraki Univ. (Japan))

1991-12-01

20

Kinetic and equilibrium studies of the removal of ammonium ions from aqueous solution by rice husk ash-synthesized zeolite Y and powdered and granulated forms of mordenite.  

PubMed

The removal of ammonium from aqueous solutions using zeolite NaY prepared from a local agricultural waste, rice husk ash waste was investigated and a naturally occurring zeolite mordenite in powdered and granulated forms was used as comparison. Zeolite NaY and mordenite were well characterized by powder X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis and the total cation exchange capacity (CEC). CEC of the zeolites were measured as 3.15, 1.46 and 1.34 meq g(-1) for zeolite Y, powdered mordenite and granular mordenite, respectively. Adsorption kinetics and equilibrium data for the removal of NH(4)(+) ions were examined by fitting the experimental data to various models. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The equilibrium pattern fits well with the Langmuir isotherm compared to the other isotherms. The monolayer adsorption capacity for zeolite Y (42.37 mg/g) was found to be higher than that powdered mordenite (15.13 mg/g) and granular mordenite (14.56 mg/g). Thus, it can be concluded that the low cost and economical rice husk ash-synthesized zeolite NaY could be a better sorbent for ammonium removal due to its rapid adsorption rate and higher adsorption capacity compared to natural mordenite. PMID:19879040

Yusof, Alias Mohd; Keat, Lee Kian; Ibrahim, Zaharah; Majid, Zaiton Abdul; Nizam, Nik Ahmad

2010-02-15

21

Alkylation of o-cresol by methanol on Ni-H-mordenite  

SciTech Connect

Experiments on alkylation were carried out in a laboratory reactor with a stationary layer of catalyst at a temperature of 320-400/sup 0/. The analysis of the liquid and gaseous products was carried out by the GLC method on a LKhM-72 chromatograph; dimethyl phthalate was the liquid phase. Results of the alkylation of o-cresol by methanol was shown at different temperatures and per volume feed rates of the liquid raw material. Reaction parameters were influenced by the molar ratio of the raw material components. Results indicated a parallel-consecutive mechanism of the alkylation of o-cresol by methanol on this contact. It was shown that high activity of Ni-H-mordenite is present in the heterogeneous alkylation of o-cresol by methanol, by which 2,6- and 2,4-xylenols can be obtained in high yields.

Akhmedov, V.M.; Agaev, A.A.; Mamedov, S.E.; Mamedov, F.A.

1987-12-01

22

Heulandite and mordenite-rich tuffs from Greece: a potential source for pozzolanic materials  

NASA Astrophysics Data System (ADS)

The microcystalline mass of the Pliocene tuffs of Santorini and Polyegos islands, in the South Aegean Volcanic Arc, Greece, is very rich in zeolite minerals, more specifically heulandite type 3, i.e. clinoptilolite, and mordenite. In Santorini, clinoptilolite is the dominant authigenic phase and it was formed in a semi-closed system, by the activity of interstitial water within the volcaniclastic sequence. In Polyegos, mordenite dominates and it was formed by hydrothermal alteration of pyroclastics. Experiments described in this work show that the presence of the zeolite minerals has created materials with excellent pozzolanic properties. Tuffs from the two areas were calcined at 760 °C and for 12 h and then mixed with lime in a constant ratio of 1 part lime to 3 parts calcined tuff. As a result, the free lime content of the lime-calcined tuff mixtures was reduced from 25% to 2.05% (Santorini) and 1.31% (Polyegos). Compressive strength tests were carried out on concrete cubes made with 100% Portland cement as the cementitious agent, to be used as reference cubes, and concrete cubes in which the Portland cement has been replaced in 4% and 7% proportions by the calcined tuff as pozzolans. The free lime estimation and the compressive strength tests were all carried out in accordance with the British Standards Institution (BS 4550 and BS 1881) guidelines. Early stage measurements of the compressive strength showed that pozzolan-bearing concrete cubes reached values as high as 140% of the reference cubes. The pozzolan-bearing concrete cubes maintained this superior strength throughout the entire one year period of the experiments. After 360 days, they finally maintained 107% of the compressive strength of the reference cubes.

Kitsopoulos, K. P.; Dunham, A. C.

1996-09-01

23

Isomerization of C{sub 8} aromatics over a Pt/mordenite catalyst: A statistical model  

SciTech Connect

A statistical approach was used to analyze the behavior of the isomerization of the C{sub 8} aromatics fraction on a commercial Pt/mordenite catalyst. In particular, the effects that the operating variables, temperature, pressure, space velocity, and hydrogen to hydrocarbon ratio had on the yield of p-xylene and loss of xylenes were studied. To this end, a sequential experimental design with a linear model in the first stage and a quadratic model in the second stage was used. The results of the linear model indicated that the temperature, pressure, and space velocity were the most influential factors for the yield of p-xylene, while for the loss of xylenes, pressure and space velocity were 2 times more important than temperature. The results from the quadratic model indicate the existence of an important curvature effect, especially with respect to the space velocity, and therefore the linear model by itself cannot describe adequately the behavior of the reaction system in the whole range of operating conditions.

Gonzalex, H.; Rodriguez, A.; Cedeno, L.; Ramirez, J. [UNAM, Mexico City (Mexico). Dept. de Ingenieria Quimica; Aracil, J. [Univ. Complutense, Madrid (Spain). Dept. de Ingenieria Quimica

1996-11-01

24

FTIR spectroscopy study of CO adsorption on Pt-Na-mordenite.  

PubMed

Different carbonyls are formed after CO adsorption at ambient temperature on a Pt-Na-mordenite (Pt-Na-MOR) sample. Pt(3+)(CO)(2) dicarbonyls (nu(s) at 2205 cm(-1) and nu(as) at 2167 cm(-1)) are decomposed without formation of monocarbonyls. The respective mixed-ligand species, Pt(3+)((12)CO)((13)CO), formed after (12)CO-(13)CO coadsorption, display bands at 2192 and 2131 cm(-1), in excellent agreement with the theoretically calculated values. Pt(2+)-CO species absorb at 2145 cm(-1) and are not able to accept a second CO molecule. Pt(+)-CO carbonyls are characterized by a band at 2111 cm(-1). Under CO equilibrium pressure, these species are converted into dicarbonyls (nu(s) at 2135 cm(-1) and nu(as) at 2101 cm(-1)). The respective mixed-ligand species, Pt(+)((12)CO)((13)CO), manifest bands at 2123 and 2069 cm(-1), in good agreement again with the theory. Different carbonyls of metallic platinum are observed below 2100 cm(-)(1). In addition, weakly adsorbed CO was registered as Na(+)-CO complexes (2177 and 2165 cm(-1)) and Na(+)-OC-Na(+) species (2138 cm(-1)). It was found that during desorption of CO platinum was reduced, ultimately to metal. However, heating in a NO + O(2) mixture leads to reoxidation of the metal particles and restoration of the initial state of the sample. PMID:16316120

Mihaylov, Mihail; Chakarova, Kristina; Hadjiivanov, Konstantin; Marie, Olivier; Daturi, Marco

2005-12-01

25

Spectroscopic characterization of dealuminated H-mordenites: The role of different aluminum species on the SCR of NO with methane  

SciTech Connect

In order to understand the role of different aluminum species in the selective catalytic reduction of nitrogen oxides with methane over H-mordenites, solids with varying Si/Al ratios (5.9-16.9) were prepared by acid leaching. They were thoroughly characterized before and after reaction. The distribution of Al was determined through {sup 27}Al MAS NMR. All the samples presented three signals, one at 54 ppm corresponding to lattice Al{sup IV}, another at 0 ppm associated with octahedrally coordinated Al, and a broad band, BB (ca 100 ppm wide), assigned to aluminum containing species. As the spinning rate increased up to 11.3 kHz, a decrease of the BB intensity and an increase of the Al{sup IV} signal took place, while the Al{sup VI} slightly increased. The best estimate of lattice aluminum was obtained from the Al{sup IV} peak intensity. Despite the high spinning rate employed, it was possible to observe only between 70-80% of the total Al present in the samples. The catalysts were also analyzed by XRD, FTIR, and {sup 129}Xe NMR of physisorbed Xenon. 48 refs., 13 figs., 6 tabs.

Lezcano, M.; Ribotta, A.; Miro, E. [Instituto de Investigaciones en Catalisis y Petroquimica, Sante Fe (Argentina)] [and others] [Instituto de Investigaciones en Catalisis y Petroquimica, Sante Fe (Argentina); and others

1997-06-01

26

Review of the thermal stability and cation exchange properties of the zeolite minerals clinoptilolite, mordenite, and analcime; applications to radioactive waste isolation in silicic tuff  

SciTech Connect

Silicic tuffs of the southern Great Basin and basalts of the Columbia River Plateau are under investigation as potential host rocks for high- and intermediate-level radioactive wastes. Nonwelded and partially welded tuffs may contain major amounts (> 50%) of the zeolite minerals clinoptilolite, mordenite, and analcime. Densely welded tuffs and some basalt flows may contain clinoptilolite as fracture filling that limits the permeability of these rocks. The cation exchange properties of these zeolite minerals allow them to pose a formidable natural barrier to the migration of cationic species of various radionuclides in aqueous solutions. However, these minerals are unstable at elevated temperatures and at low water-vapor pressures and may break down either by reversible dehydration or by irreversible mineralogical reactions. All the breakdown reactions occurring at increased temperature involve a net volume reduction and evolution of fluids. Thus, they may provide a pathway (shrinkage fractures) and a driving force (fluid pressure) for release of radionuclides to the biosphere. These reactions may be avoided by keeping zeolite-bearing horizons saturated with water and below about 85{sup 0}C. This may restrict allowable gross thermal loadings in waste repositories in volcanic rocks.

Smyth, J.R.; Caporuscio, F.A.

1981-06-01

27

Molecular adsorption and metal-support interaction for transition-metal clusters in zeolites: NO adsorption on Pdn (n=1-6) clusters in mordenite  

NASA Astrophysics Data System (ADS)

The adsorption of NO molecules on Pdn clusters of varying size (n=1-6) located in the main channel of mordenite and the interaction of the metallic clusters with the zeolitic framework were investigated using ab initio density-functional calculations under periodic boundary conditions. The supported clusters are created by binding Pdn2+ cations to the inner cavity of a deprotonated Al-exchanged zeolite with an Al/Si ratio of 1/11, such that a charge-neutral system is created. Compared to the highly symmetric structures of the gas-phase clusters, the clusters bound to the zeolitic framework undergo appreciable geometric distortions lowering their symmetry. The distortions are induced by strong interactions with ``activated'' framework oxygens located close to the charge-compensating Al/Si substitution sites, but the cluster forms also weaker bonds to ``nonactivated'' oxygen atoms. The interaction with the framework also affects the electronic and magnetic properties of the clusters. While in the gas phase all clusters (except the isolated Pd atom with a closed d10 ground state) have a paramagnetic moment of 2?B, in the zeolite clusters with two to four atoms have zero magnetic moment, while the Pd5 cluster has a magnetic moment of 2?B and for the Pd6 cluster, it is even enhanced to 4?B (but the magnetic energy differences relative to low-spin configurations are modest). Analysis of the magnetization densities shows that in all clusters with zero total moment (singlet ground state), there are sites with excess spin densities of opposite sign. The influence of the cluster-support interaction on the chemical properties of the clusters has been tested by the adsorption of NO molecules. The results demonstrate the interplay between the molecule-cluster and cluster-framework interactions, which can lead to an increase or decrease in the adsorption energy compared to NO on a gas-phase cluster. While on the gas-phase cluster adsorption in low-coordination sites (vertex or bridge) is preferred, for the cluster in the zeolite adsorption in threefold coordinated hollow or twofold bridge sites is preferred. The magnetic properties of the clusters and of the paramagnetic NO molecule play an important role. For the supported clusters with zero magnetic moment, upon adsorption the spin of the molecule is transferred to the cluster (and induces also a modest polarization of the framework). For magnetic clusters, spin pairing induces a reduced magnetic moment of the NO-Pdn complex. The redshift of the NO stretching frequencies is reduced compared to the free clusters by the cluster-support interaction for the smaller clusters, while it remains essentially unchanged for the larger clusters. A detailed electronic analysis of the cluster-support interactions and of the adsorption properties is presented.

Grybos, Robert; Benco, Lubomir; Bu?ko, Tomas; Hafner, Jürgen

2009-03-01

28

The growth of zeolites A, X and mordenite in space  

NASA Technical Reports Server (NTRS)

Zeolites are a class of crystalline aluminosilicate materials that form the backbone of the chemical process industry worldwide. They are used primarily as adsorbents and catalysts and support to a significant extent the positive balance of trade realized by the chemical industry in the United States (around $19 billion in 1991). The magnitude of their efforts can be appreciated when one realizes that since their introduction as 'cracking catalysts' in the early 1960's, they have saved the equivalent of 60 percent of the total oil production from Alaska's North Slope. Thus the performance of zeolite catalysts can have a profound effect on the U.S. economy. It is estimated that a 1 percent increase in yield of the gasoline fraction per barrel of oil would represent a savings of 22 million barrels of crude oil per year, representing a reduction of $400 million in the United States' balance of payments. Thus any activity that results in improvement in zeolite catalyst performance is of significant scientific and industrial interest. In addition, due to their 'stability,' uniformity, and, within limits, their 'engineerable' structures, zeolites are being tested as potential adsorbents to purify gases and liquids at the parts-per-billion levels needed in today's electronic, biomedical, and biotechnology industries and for the environment. Other exotic applications, such as host materials for quantum-confined semiconductor atomic arrays, are also being investigated. Because of the importance of this class of material, extensive efforts have been made to characterize their structures and to understand their nucleation and growth mechanisms, so as to be able to custom-make zeolites for a desired application. To date, both the nucleation mechanics and chemistry (such as what are the 'key' nutrients) are, as yet, still unknown for many, if not all, systems. The problem is compounded because there is usually a 'gel' phase present that is assumed to control the degree of supersaturation, and this gel undergoes a continuous 'polymerization' type reaction during nucleation and growth. Generally, for structure characterization and diffusion studies, which are useful in evaluating zeolites for improving yield in petroleum refining as well as for many of the proposed new applications (e.g., catalytic membranes, molecular electronics, chemical sensors) large zeolites (greater than 100 to 1000 times normal size) with minimum lattice defects are desired. Presently, the lack of understanding of zeolite nucleation and growth precludes the custom design of zeolites for these or other uses. It was hypothesized that the microgravity levels achieved in an orbiting spacecraft could help to isolate the possible effects of natural convection (which affects defect formation) and minimize sedimentation, which occurs since zeolites are twice as dense as the solution from which they are formed. This was expected to promote larger crystals by allowing growing crystals a longer residence time in a high-concentration nutrient field. Thus it was hypothesized that the microgravity environment of Earth orbit would allow the growth of large, more defect-free zeolite crystals in high yield.

Sacco, Albert, Jr.; Bac, N.; Coker, E. N.; Dixon, A. G.; Warzywoda, J.; Thompson, R. W.

1994-01-01

29

The effect of iron on the biological activities of erionite and mordenite  

Microsoft Academic Search

Epidemiological data has demonstrated that environmental and\\/or occupational exposure to mineral particulates may result in the development of pulmonary fibrosis, bronchogenic carcinoma and malignant mesothelioma many years following exposure. It has been suggested that the genotoxic effects of fibrous particulates, such as asbestos, is due in part to the generation of reactive oxygen species (ROS) from iron associated with the

Estelle Fach; Robert Kristovich; John F. Long; W. James Waldman; Prabir K. Dutta; Marshall V. Williams

2003-01-01

30

The effect of iron on the biological activities of erionite and mordenite Estelle Facha  

E-print Network

exposure to mineral particulates may result in the development of pulmonary fibrosis, bronchogenic exposure to mineral particulates may result in the development of pulmonary fibrosis, bronchogenic December 2002 Abstract Epidemiological data has demonstrated that environmental and/or occupational

Dutta, Prabir K.

31

Iodine-fixation studies at the Pacific Northwest Laboratory. [Silver mordenite  

Microsoft Academic Search

The aim of the iodine program at PNL is to develop technologies that will provide safe and effective removal and packaging of ¹²⁹I for interim storage and shipping and for permanent isolation. Iodine recovery and fixation processes, and the evaluation of fixation compounds and materials are included in the program. Iodine-containing compounds have been evaluated on the basis of chemical

L. L. Burger; R. D. Scheele

1981-01-01

32

Crystal Structure of MCM-71 - a New Zeolite in the Mordenite Group  

SciTech Connect

The crystal structure of the aluminosilicate, MCM-71, was determined by a match of the powder X-ray diffraction pattern to one calculated from a theoretically predicted framework model. The unit cell contains 48 T-sites and 96 framework oxygens, where T = 41.1 Si, 6.9 Al. It crystallizes in space group Cmca, a = 7.4422(2), b = 18.5324(5), c = 19.1877(5) {angstrom}. The framework contains an elliptical 10-membered ring channel (4.3 x 6.5 {angstrom}) and an orthogonal undulating 8-membered ring channel (3.6 x 4.7 {angstrom}) to constitute a two-dimensional network of channels. Considering the aluminosilicate framework as a silicate, the crystal density is 1.77 g/cm{sup 3} and the T-site framework density is 17.8 T/1000 A{sup 3}. The structure was refined against Debye-Scherrer and Bragg-Brentano powder synchrotron data by the Rietveld procedure. While non-framework oxygen atoms, consistent with water content, could be justified by TGA measurements, it was not possible to derive an accurate extra-framework model using synchrotron data from hydrated specimens. Refinement against powder data from an anhydrous specimen subsequently detected the presence of extra-framework aluminum, identified also by solid state NMR measurements.

Dorset, D.; Roth, W; Kennedy, G; Dhingra, S

2008-01-01

33

Determination of Ni(II) Uptake Mechanisms on Mordenite Surfaces:1 A Combined Macroscopic and Microscopic Approach2  

E-print Network

at the water-mineral31 interface.32 33 1. Introduction34 The frequency and severity of heavy metal pollutants23 spectra analysis show a trend from outer-sphere surface complexation at low24 temperature to inner in surface and ground water are35 of great concern to scientists due to the potential hazardous effects

Paris-Sud XI, Université de

34

Thermodynamics of Binary and Ternary Ion Exchange in Zeolites: The Exchange of Sodium, Ammonium and Potassium Ions in Mordenite  

Microsoft Academic Search

In many ion exchanges that involve zeolites, more than two types of exchanging ions are involved. Most work to date has been concerned with equilibria involving two different types of ion only. In this paper, a recently devised thermodynamic treatment for exchange equilibria involving three ions is tested experimentally. In section 1 the most important aspects of this thermodynamic model

P. Fletcher; K. R. Franklin; R. P. Townsend

1984-01-01

35

Copper-exchanged mordenites as active catalysts for NO selective catalytic reduction by propene under oxidising conditions: Effect of Si\\/Al ratio, copper content and Brönsted acidity  

Microsoft Academic Search

CuMOR catalysts with different Si\\/Al ratios and copper contents, prepared from the acid and sodium forms, were studied in NO reduction with propene in the presence of excess oxygen. It was observed that the influence of zeolite Si\\/Al ratio on CuMOR catalytic activity for NO SCR by propene depends on the catalyst copper content, the reverse being also true. For

C. Torre-Abreu; M. F. Ribeiro; C. Henriques; F. R. Ribeiro

1997-01-01

36

Effect of natural zeolite on methane production for anaerobic digestion of ammonium rich organic sludge.  

PubMed

The effect of an inorganic additive on the methane production from NH(4+)-rich organic sludge during anaerobic digestion was investigated using different kinds of inorganic adsorbent zeolites (mordenite, clinoptilolite, zeolite 3A, zeolite 4A), clay mineral (vermiculite), and manganese oxides (hollandite, birnessite). The additions of inorganic materials resulted in significant NH4+ removals from the natural organic sludge ([NH4+]=1, 150 mg N/l), except for the H-type zeolite 3A and birnessite. However, an enhanced methane production was only achieved using natural mordenite. Natural mordenite also enhanced the methane production from the sludge with a markedly high NH4+ concentration (4500 mg N/l) during anaerobic digestion. Chemical analyses of the sludge after the digestion showed considerable increases in the Ca2+ and Mg2+ concentrations in the presence of natural mordenite, but not with synthetic zeolite 3A. The effect of Ca2+ or Mg2+ addition on the methane production was studied using Na(+)-exchanges mordenite and Ca2+ or Mg(2+)-enriched sludge. The simultaneous addition of Ca2+ ions and Na(+)-exchanged mordenite enhanced the methane production; the amount of produced methane was about three times greater than that using only the Na(+)-exchanged mordenite. In addition, comparing the methane production by the addition of natural mordenite or Ca2+ ions, the methane production with natural mordenite was about 1.7 times higher than that with only Ca2+ ions. The addition of 5% and 10% natural mordenite were suitable condition for obtaining a high methane production. These results indicated that the Ca2+ ions, which are released from natural mordenite by a Ca2+/NH4+ exchange, enhanced the methane production of the organic waste at a high NH4+ concentration. Natural mordenite has a synergistic effect on the Ca2+ supply as well on the NH4+ removal during anaerobic digestion, which is effective for the mitigation of NH4+ inhibition against methane production. PMID:15491827

Tada, Chika; Yang, Yingnan; Hanaoka, Toshiaki; Sonoda, Akinari; Ooi, Kenta; Sawayama, Shigeki

2005-03-01

37

Interaction between zeolites and cluster compounds. Part 1.?Adsorption of iron pentacarbonyl on zeolites  

Microsoft Academic Search

Received 1 1 th November, 1982 The adsorption isotherms of Fe(CO), on Nay, HY and Linde L zeolites obtained in McBain balances show micropore adsorption, whereas additional capillary condensation is found with zeolite omega and Na-mordenite. The pores and\\/or cages of the zeolites studied are completely filled with the complex upon saturation, with the exception of Na-mordenite. Their behaviour is

Thomas Bein; Peter A. Jacobs

1983-01-01

38

Transalkylation of toluene with trimethylbenzenes over large-pore zeolites  

Microsoft Academic Search

Zeolites Beta, mordenite and Y were evaluated for their activity in transalkylation reaction of toluene with trimethylbenzenes. Zeolite Beta was found to possess the highest conversion in toluene–trimethylbenzene transalkylation as well as a higher stability in time-on-stream compared with mordenite and zeolite Y. The effect of Si\\/Al ratio in zeolite Beta was evaluated and it was found that transalkylation activity

Andrea Krej?í; Sulaiman Al-Khattaf; Muhammad Ashraf Ali; Martina Bejblová; Ji?í ?ejka

2010-01-01

39

Constructing a polyfunctional zeolite-encaged metal catalyst for the multistage oxidation of ethanol into ethyl acetate  

SciTech Connect

To construct an efficient polyfunctional catalyst for the given multistage reaction, the authors previously studied the catalysts HNaY, clinosorb, H-clinoptilolite, and H-mordenite in the reaction of esterification of ethanol with acetic acid; CuH-clinoptilolite, Cu-clinosorb, CuH-mordenite, and CuHNaY in the reaction of oxidative dehydration of ethanol; PdH-clinoptilolite, Pd-clinosorb, PdH-mordenite, and PdHNaY in the oxidation of ethanol; and CuPdH-clinoptilolite in the oxidative transformation of ethanol into ethyl acetate. The catalytic activity of these zeolites and other Pd- and Cu-containing zeolite catalysts, which the authors synthesized by the ion-exchange technique, was studied in a flow-circulating set-up.

Shakhtakhtinskii, T.N.; Aliev, A.M.; Kuliev, A.R. [Institute of Theoretical Problems of Chemical Technology, Baku (Azerbaijan)

1995-08-01

40

Catalytic pyrolysis of woody biomass in a fluidized bed reactor: Influence of the zeolite structure  

Microsoft Academic Search

Catalytic pyrolysis of biomass from pine wood was carried out in a fluidized bed reactor at 450°C. Different structures of acidic zeolite catalysts were used as bed material in the reactor. Proton forms of Beta, Y, ZSM-5, and Mordenite were tested as catalysts in the pyrolysis of pine, while quartz sand was used as a reference material in the non-catalytic

A. Aho; N. Kumar; K. Eränen; T. Salmi; M. Hupa; D. Yu. Murzin

2008-01-01

41

Catalytic Transformation of Toluene over High Acidity Y-Zeolite Based S. Al-Khattaf*  

E-print Network

was impregnated with 8.5 wt% of phosphorus to enhance p-xylene selectivity. Peng et al [9] studied toluene to that of mordenite and much higher than that of ZSM-5. The fraction of p-xylene in xylene isomers (para zeolites which were modified with phosphorus, boron, or magnesium compounds. The increment of p-xylene

Al-Khattaf, Sulaiman

42

A multitechnique characterization of the acidity of dealuminated mazzite  

SciTech Connect

The authors endeavored to characterize the acidity of stream-dealuminated mazzite through various techniques. Isomerization of n-paraffin over the platinum/mazzite catalyst indicated higher activity and selectivity than that of commercial platinum/mordenite. 44 refs., 9 figs., 7 tabs.

McQueen, D. [Laboratoire de Materiaux Catalytiques et Catalyse en Chimie Organique, Montpellier (France)] [Laboratoire de Materiaux Catalytiques et Catalyse en Chimie Organique, Montpellier (France); [Centre de Recherche Elf-Antar France, Solaize (France); Fitoussi, F.; Schulz, P. [Center de Recherche Elf-Antar France, Solaize (France)] [and others] [Center de Recherche Elf-Antar France, Solaize (France); and others

1996-07-01

43

Alteration history studies in the Exploratory Studies Facility, Yucca Mountain, Nevada, USA  

Microsoft Academic Search

By mid-1995, the Exploratory Studies Facility (ESF) extended about 1. 1 km from Exile Hill westward toward Yucca Mountain, mostly within densely welded, devitrfied Tiva Canyon Tuff. Secondary mineral occurrences in this unit include breccia cements of mordenite, a fibrous zeolite, and vapor-phase deposits of silica, alkali feldspar, apatite, hollandite, amphibole, and zircon. Calcite is also a common secondary mineral

S. S Levy; S. J. Chipera; D. I. Norman

1996-01-01

44

Natural zeolites in environmentally friendly processes and applications  

Microsoft Academic Search

An outline of the occurrences, features and environmental uses of the main sedimentary zeolites, namely chabazite, clinoptilolite, mordenite and phillipsite, is presented. After pointing out that zeolite-bearing rocks should not be considered as substitutes for synthetic zeolites, as they are lacking of purity and constancy of composition, three major areas of environmental application are identified: soil amendment, cement manufacture and

Carmine Colella

1999-01-01

45

Journal of Catalysis 245 (2007) 110123 www.elsevier.com/locate/jcat  

E-print Network

of DME reactions with acetyl groups formed by stoichiometric reactions of acetic anhydride. These studies: Carbonylation; Acid; Zeolite; Mordenite; Dimethyl ether; Methanol; Carbon monoxide; Methyl acetate; Acetic acid; Carboxylic acid 1. Introduction Methanol carbonylation accounts for 60% of acetic acid production worldwide

Iglesia, Enrique

46

Penentuan kapasiti dan jenis pencerapan Zeolit asli terhadap bahan pencelup sintetik  

Microsoft Academic Search

Abstrak. Zeolit yang dikenali sebagai penapis molekul mempunyai sifat keliangan dan luas permukaan tinggi telah digunakan sebagai bahan penjerap untuk menjerap bahan pencelup daripada air sisa berwarna. Zeolit mordenit asli yang berasal dari Indonesia telah diubahsuai kepada bentuk yang bersifat bes dan dikaji sifat penjerapannya terhadap bahan pencelup sintetik bes kuning 11. Seterusnya, jenis penjerapan sampel zeolit terhadap bahan pencelup

Chai Mee Kin; Asiah Hussain; Pengajian Sains; Jalan Kajang-Puchong

47

A comparative study on the transalkylation of diisopropylbenzene with benzene over several zeolitic materials in supercritical CO 2 and liquid phase  

Microsoft Academic Search

This work describes the catalysts screening and the analysis of the effect of supercritical carbon dioxide on the transalkylation of diisopropylbenzene with benzene. The catalysts included three acidic commercial zeolites: beta, Y and mordenite with different aluminum contents (e.g. Si\\/Al molar ratio). Their performance was compared in terms of cumene yield and selectivity, taking into account the competitive isomerization, and

J. L. Sotelo; L. Calvo; A. Pérez-Velázquez; D. Capilla; F. Cavani; M. Bolognini

2006-01-01

48

Fenton Chemistry of FeIII Zeolitic Minerals Treated with  

E-print Network

understand asbestos toxicity. Erionite is carcinogenic, while mordenite is relatively benign. No iron), which can reduce FeIII to FeII. In this study, we have compared the Fenton reactivity of Fe of hydroxyl radicals with dimethyl sulfoxide. Fenton reactivity was most marked with AA followed by GSH

Dutta, Prabir K.

49

Efficient removal of cesium from low-level radioactive liquid waste using natural and impregnated zeolite minerals.  

PubMed

The objective of the proposed work was focused to provide promising solid-phase materials that combine relatively inexpensive and high removal capacity of some radionuclides from low-level radioactive liquid waste (LLRLW). Four various zeolite minerals including natural clinoptilolite (NaNCl), natural chabazite (NaNCh), natural mordenite (NaNM) and synthetic mordenite (NaSM) were investigated. The effective key parameters on the sorption behavior of cesium (Cs-134) were investigated using batch equilibrium technique with respect to the waste solution pH, contacting time, potassium ion concentration, waste solution volume/sorbent weight ratio and Cs ion concentration. The obtained results revealed that natural chabazite (NaNCh) has the higher distribution coefficients and capacity towards Cs ion rather than the other investigated zeolite materials. Furthermore, novel impregnated zeolite material (ISM) was prepared by loading Calix [4] arene bis(-2,3 naphtho-crown-6) onto synthetic mordenite to combine the high removal uptake of the mordenite with the high selectivity of Calix [4] arene towards Cs radionuclide. Comparing the obtained results for both NaSM and the impregnated synthetic mordenite (ISM-25), it could be observed that the impregnation process leads to high improvement in the distribution coefficients of Cs+ ion (from 0.52 to 27.63 L/g). The final objective in all cases was aimed at determining feasible and economically reliable solution to the management of LLRLW specifically for the problems related to the low decontamination factor and the effective recovery of monovalent cesium ion. PMID:19656622

Borai, E H; Harjula, R; Malinen, Leena; Paajanen, Airi

2009-12-15

50

Isomerization of ethylbenzene and m-xylene on zeolites  

SciTech Connect

Simultaneous isomerizstion of ethylbenzene and m-xylene on zeolite catalysts, including Pt/mordenite, Pt/USY, Pt/ZSM-5, and Pd/ZSM-5, was studied. Experimental results indicated that Pt/ZSM-5 was the superior catalyst for these reactions. Pd/ZSM-5 is better than Pt/USY, although, both are good enough for the reactions, in comparison with Pt/mordenite. A kinetic model with plausible reaction paths was proposed for the isomerization. The estimated reaction rate constants and activation energies indicated that the transformation of m-xylene to o- or p-xylene might be limited by the mass-transfer rate of the diphenylmethane-type intermediate, and the formation of o-xylene from ethylbenzene could be restricted by the smaller protonated cyclopropane intermediate.

Hsu, Y.S.; Lee, T.Y.; Hu, H.C.

1988-06-01

51

Removal of MTBE and other organic contaminants from water by sorption to high silica zeolites  

SciTech Connect

Select zeolites with high SiO{sub 2}/Al{sub 2}O{sub 3} ratios were shown to effectively remove methyl tert-butyl ether (MTBE), chloroform, and trichloroethylene (TCE) from water. In laboratory studies using batch sorption equilibria, high Si large-port mordenite and ZSM-5 (silicalite) were found to have sorption properties for MTBE and TCE superior to activated carbon. for example, at an equilibrium solution concentration of 100 {micro}g/L, high Si mordenite retained 8--12x more MTBE than either of two powdered activated carbons used as reference sorbents. Sorption results also highlight the importance of pore size and SiO{sub 2}/Al{sub 2}O{sub 3} ration on contaminant removal efficiencies by zeolites.

Anderson, M.A.

2000-02-15

52

Deactivation behaviors of zeolite and silica-alumina catalysts in the degradation of polyethylene  

Microsoft Academic Search

For chemical recycling of waste plastics, HZSM-5, HY, and H-mordenite zeolites and silica-alumina were examined as catalysts for the degradation of polyethylene in a fixed-bed flow reactor system, and their activities and deactivation behaviors caused by coke deposition were studied. HZSM-5 catalyst was fond to be very effective for the production of gasoline-range fuel oils mainly consisting of isoparaffins and

Yoshio Uemichi; Masahiko Hattori; Toshihiro Itoh; Junko Nakamura; Masatoshi Sugioka

1998-01-01

53

Development of Ag°Z for bulk ¹²⁹I removal from nuclear fuel reprocessing plants and PbX for ¹²⁹I storage  

Microsoft Academic Search

Tests were conducted to develop Ag-exchanged mordenite (AgZ) for removal of gaseous ¹²⁹I from nuclear fuel reprocessing plants. The effects of bed depth and hydrogen pretreatment on the elemental (Iâ) iodine loading of AgZ were examined. The tests indicated that reduced AgZ (Ag°Z) had about twice the capacity for iodine as AgZ, and at least 15-cm bed depths should be

T. R. Thomas; B. A. Staples; L. P. Murphy

1978-01-01

54

Occlusion potential of zeolites for mixed and non-nitrate salts  

Microsoft Academic Search

Occluded salts in the form of salt complexes exhibit the interesting properties unattainable in bulk state. In this study, occlusion of non-nitrate salts and co-occlusion of mixed nitrate salts were attempted to further expand occlusion potential of zeolites. The non-nitrate salts such as KClO3 and KH2PO4 were occluded by mordenite, although they do not establish stable molten state. Their occlusions

Man Park; Choong Lyeal Choi; Jong Soo Kim; Dong Hoon Lee; Kwang Seop Kim; Nam Ho Heo; Jyung Choi

2003-01-01

55

Removal of MTBE and other organic contaminants from water by sorption to high silica zeolites  

Microsoft Academic Search

Select zeolites with high SiOâ\\/AlâOâ ratios were shown to effectively remove methyl tert-butyl ether (MTBE), chloroform, and trichloroethylene (TCE) from water. In laboratory studies using batch sorption equilibria, high Si large-port mordenite and ZSM-5 (silicalite) were found to have sorption properties for MTBE and TCE superior to activated carbon. for example, at an equilibrium solution concentration of 100 μg\\/L, high

Michael A. Anderson

2000-01-01

56

1H\\/ 27Al TRAPDOR NMR studies on aluminum species in dealuminated zeolites  

Microsoft Academic Search

Aluminum species in several dealuminated zeolites (ultrastable HY, HZSM-5 and mordenite) were investigated in detail by means of the newly introduced 1H\\/27Al TRAPDOR method in combination with 27Al MAS NMR, and the quadrupole coupling constants (QCCs) for aluminum atoms associated with these species were obtained. A signal at ca. 6.8 ppm, due to water molecules adsorbed on Lewis acid sites,

Feng Deng; Yong Yue; Chaohui Ye

1998-01-01

57

Oxygen and hydrogen isotope geochemistry of zeolites  

NASA Technical Reports Server (NTRS)

Oxygen and hydrogen isotope ratios for natural samples of the zeolites analcime, chabazite, clinoptilolite, laumontite, mordenite, and natrolite have been obtained. The zeolite samples were classified into sedimentary, hydrothermal, and igneous groups. The ratios for each species of zeolite are reported. The results are used to discuss the origin of channel water, the role of zeolites in water-rock interaction, and the possibility that a calibrated zeolite could be used as a low-temperature geothermometer.

Karlsson, Haraldur R.; Clayton, Robert N.

1990-01-01

58

Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution  

Microsoft Academic Search

An Australian natural zeolite was collected, characterised and employed for basic dye adsorption in aqueous solution. The natural zeolite is mainly composed of clinoptiloite, quartz and mordenite and has cation-exchange capacity of 120meq\\/100g. The natural zeolite presents higher adsorption capacity for methylene blue than rhodamine B with the maximal adsorption capacity of 2.8×10?5 and 7.9×10?5mol\\/g at 50°C for rhodamine B

Shaobin Wang; Z. H. Zhu

2006-01-01

59

Transalkylation of toluene and 1,2,4-trimethylbenzene over large pore zeolites  

Microsoft Academic Search

Large pore zeolites, H-beta, H-mordenite (H-MOR) and H-omega, were dealuminated by steam treatment followed by acid leaching and were applied for transalkylation of toluene and 1,2,4-trimethylbenzene. The acidic properties of catalysts were examined by using TPD of ammonia and in situ FT-IR spectroscopy in the OH stretching region as well as pyridine adsorbed catalysts. XRD, mid-infrared spectroscopy and 29Si and

Yong-Kul Lee; Se-Ho Park; Hyun-Ku Rhee

1998-01-01

60

Summary of FY 2010 Iodine Capture Studies at the INL  

SciTech Connect

Three breakthrough runs using silver mordenite sorbents were conducted and a dynamic sorption capacity estimated based on MeI analysis from a 2" bed. However, it is now believed the data for the first 2 runs is incomplete because the contributions from elemental iodine were not included. Although the only source of iodine was MeI, elemental iodine was generated within the sorbent bed, presumably from a recombination reaction likely catalyzed by silver mordenite. On-line effluent analysis with a GC was only capable of analyzing MeI, not I2. Scrub samples drawn during Run #3, which are specific for I2, show significant levels of I2 being emitted from a partially spent Ag-mordenite bed. By combining MeI and I2 analyses, a well defined total iodine breakthrough curve can be generated for Run #3. At the conclusion of Run #3 (IONEX Ag-900 was the sorbent) the effluent level from Bed 2 was approaching 70% of the feed concentration. The leading bed (Bed 1) had an estimated average loading of 66 mg I/g sorbent, Bed 2's was 52 mg I/g. The corresponding silver utilizations (assuming formation of AgI) were about 59% and 46%, respectively. The spent sorbents are being sent to Sandia National Laboratories for confirmatory analysis of iodine and silver utilization as well as source material for waste form development.

Daryl R. Haefner; Tony L. Watson; Michael G. Jones

2010-08-01

61

Test Plan to Demonstrate Removal of Iodine and Tritium from Simulated Nuclear Fuel Recycle Plant Off-gas Streams using Adsorption Processes  

SciTech Connect

This letter documents the completion of the FCR&D Level 4 milestone for the Sigma Team – Off-Gas - ORNL work package (FT-14OR031202), “Co-absorption studies - Design system complete/test plan complete” (M4FT-14OR0312022), due November 15, 2013. The objective of this test plan is to describe research that will determine the effectiveness of silver mordenite and molecular sieve beds to remove iodine and water (tritium) from off-gas streams arising from used nuclear fuel recycling processes, and to demonstrate that the iodine and water can be recovered separately from one another.

Bruffey, Stephanie H. [ORNL] [ORNL; Spencer, Barry B. [ORNL] [ORNL; Jubin, Robert Thomas [ORNL] [ORNL

2013-12-11

62

Catalytic transformations of olefins on HZSM5 observed by radiolysis/EPR  

SciTech Connect

A new method for elucidating elementary reaction steps in zeolite catalysis was demonstrated for reactions of isobutene and other monoolefins on HZSM5. Radiolysis was used to `spin label` reaction products, and EPR was used for product analysis. The evolution of products was revealed by quenching the reactions cryogenically in a series of equilibrium experiments. Isobutene dimerization and isomerization occur on HZSM5 even at 77 K, and cracking occurs below room temperature. The radiolysis/EPR results allow a consistent interpretation of the literature on EPR signals that arise spontaneously upon interaction of acyclic olefins with air-activated H-Mordenite and HZSM5. 55 refs., 10 figs., 2 tabs.

Piocos, E.A.; Han, P.; Werst, D.W. [Argonne National Lab., IL (United States)] [Argonne National Lab., IL (United States)

1996-04-25

63

Zeolite crystal growth in space - What has been learned  

NASA Technical Reports Server (NTRS)

Three zeolite crystal growth experiments developed at WPI have been performed in space in last twelve months. One experiment, GAS-1, illustrated that to grow large, crystallographically uniform crystals in space, the precursor solutions should be mixed in microgravity. Another experiment evaluated the optimum mixing protocol for solutions that chemically interact ('gel') on contact. These results were utilized in setting the protocol for mixing nineteen zeolite solutions that were then processed and yielded zeolites A, X and mordenite. All solutions in which the nucleation event was influenced produced larger, more 'uniform' crystals than did identical solutions processed on earth.

Sacco, A., Jr.; Thompson, R. W.; Dixon, A. G.

1993-01-01

64

Fourier self-deconvolution of the IR spectra as a tool for investigation of distinct functional groups in porous materials: Brønsted acid sites in zeolites.  

PubMed

For many decades, IR and FT-IR spectroscopy has generated valuable information about different functional groups in zeolites, metal-organic frameworks (MOFs), and other porous materials. However, this technique cannot distinguish between functional groups in different local environments. Our study demonstrates that this limitation could be overcome by using Fourier self-deconvolution of infrared spectra (FSD-IR). We apply this method to study three acidic mordenite zeolites and show (i) that these zeolites contain six distinct Brønsted acid sites (BAS) as opposed to 2-4 different BAS previously considered in literature and (ii) that the relative amounts of these BAS are different in the three zeolites examined. We then analyze possible locations of six BAS in the mordenite structure and explain a number of conflicting results in literature. On this basis, we conclude that the FSD-IR method allows direct visualization and examination of distributions of distinct BAS in zeolites, thus providing a unique research opportunity, which no other method can provide. Given the similarities in the IR analysis of different functional groups in solids, we expect that the FSD-IR method will be also instrumental in the research into other porous materials, such as solid oxides and MOFs. The latter point is illustrated by FSD of the IR spectrum of hydroxyl groups in a sample of ?-alumina. PMID:24219854

Vazhnova, Tanya; Lukyanov, Dmitry B

2013-12-01

65

Comparative study of the removal of coke from protonic zeolites  

SciTech Connect

The transformation of methanol was carried out at 400{degrees}C on four protonic zeolites: USHY (framework Si/Al ratio equal to 5), HZSM5 (Si/Al = 45), two mordenites HMOR (Si/Al = 7.5) and HMORDA (Si/Al = 80) prepared by dealumination of HMOR through hydrothermal and acid treatments. The composition of coke determined through the method developed in the authors` laboratory depended slightly on the zeolite. The amount of coke removed for the zeolites through oxidative treatment was determined as function of the temperature and for various coke contents. The rate of coke removal depended slightly on the coke content and on the coke composition by very much on the zeolite. In particular the coke of HMORDA and of HZSM5 was eliminated at high temperature only.

Gnep, N.S.; Roger, P.; Magnoux, P.; Guisnet, M. [Laboratoire de Catalyse en Chimie Organique, Poitiers (France)

1993-12-31

66

Multiple zeolite structures from one ionic liquid template.  

PubMed

This study reports the use of 1-butyl-3-methyl imidazolium methanesulfonate ionic liquid as a template in the synthesis of zeolites. It is found that the silicon source determines the formation of beta (BEA), mordenite framework inverted (MFI), or analcime (ANA) zeolites. Depending on this source, different preorganized complexes are obtained that drive the formation of the different zeolite structures. In the presence of ethanol, the ionic liquid form preorganized complexes that drive the formation of MFI. In its absence, BEA is obtained. Whereas, the large amount of sodium present when using sodium metasilicate leads to ANA formation. A molecular simulation study of the relative stability of the template-framework system and location of the template provides further insight into the mechanism of synthesis. PMID:23255393

Martínez Blanes, José María; Szyja, Bart?omiej M; Romero-Sarria, Francisca; Centeno, Miguel Ángel; Hensen, Emiel J M; Odriozola, José Antonio; Ivanova, Svetlana

2013-02-01

67

Solvent effects in Acid-catalyzed biomass conversion reactions.  

PubMed

Reaction kinetics were studied to quantify the effects of polar aprotic organic solvents on the acid-catalyzed conversion of xylose into furfural. A solvent of particular importance is ?-valerolactone (GVL), which leads to significant increases in reaction rates compared to water in addition to increased product selectivity. GVL has similar effects on the kinetics for the dehydration of 1,2-propanediol to propanal and for the hydrolysis of cellobiose to glucose. Based on results obtained for homogeneous Brønsted acid catalysts that span a range of pKa values, we suggest that an aprotic organic solvent affects the reaction kinetics by changing the stabilization of the acidic proton relative to the protonated transition state. This same behavior is displayed by strong solid Brønsted acid catalysts, such as H-mordenite and H-beta. PMID:25214063

Mellmer, Max A; Sener, Canan; Gallo, Jean Marcel R; Luterbacher, Jeremy S; Alonso, David Martin; Dumesic, James A

2014-10-27

68

Gas phase synthesis of MTBE from methanol and isobutene over dealuminated zeolites  

SciTech Connect

Gas phase synthesis of MTBE from methanol and isobutene has been investigated over different zeolites. It is shown that bulk Si/Al ratio has a marked influence on the formation of MTBE. H-beta zeolite was found to be as active as acid Amberlyst-15 (reference catalyst), and noticeably superior to non- and dealuminated forms of H-Y, H-ZSM-5, zeolite omega, and H-mordenites. Screening test results obtained over other catalysts (SAPOs and pillared clays) are briefly commented. The contribution of the external surface of the zeolites to the reaction is discussed. In the case of H-Y zeolites, it is shown that extra framework Al species ({sup 27}Al NMR signal at 30 ppm) have a detrimental effect on the reaction. 64 refs., 12 figs., 3 tabs.

Collignon, F.; Mariani, M.; Moreno, S.; Remy, M.; Poncelet, G. [Universite Catholique de Louvain (Belgium)] [Universite Catholique de Louvain (Belgium)

1997-02-01

69

Xenon NMR studies of dynamics and exchange in zeolites  

SciTech Connect

We have found, despite earlier reports to the contrary, that for many microporous solids with one-dimensional channels (ZSM-12, ALPO-5, VPI-5, SSZ-24) the chemical shift has an anisotropic component. For ALPO-11, a detailed model has been developed which accounts for the loading-dependent chemical shift in terms of intraparticle exchange of statistical distributions of xenon atoms with 0, 1 or 2 nearest neighbors. A similar model can be applied to ZSM-12 up to moderate loadings. At higher loading levels 2D exchange methods show that interparticle exchange occurs as well. The same approach was used to study interparticle exchange in X and Y zeolite mixtures, exchange amongst zeolite clusters of up to 8 xenon atoms in the supercages of AgA zeolite, and main channel - side pocket exchange in mordenite. The parameters derived are directly relevant to the understanding of sorption and diffusion processes in zeolites.

Moudrakovski, I.L.; Ratcliffe, C.I.; Ripmeester, J.A. [Steacie Institute for Molecular Sciences, Ottawa, Ontario (Canada)

1996-10-01

70

BTX abatement using Chilean natural zeolite: the role of Brønsted acid sites.  

PubMed

In wastewater treatment facilities, air quality is not only affected by conventional unpleasant odour compounds; toxic volatile organic compounds (VOCs) are also found. In this study, the adsorptive capacity of Chilean natural zeolite toward VOC removal was evaluated. Moreover, the influence of zeolite chemical surface properties on VOC elimination was also investigated. Three modified zeolite samples were prepared from a natural Chilean zeolite (53% clinoptilolite, 40% mordenite and 7% quartz). Natural and modified zeolite samples were characterised by nitrogen adsorption at 77 K, elemental analyses and X-ray fluorescence (XRF). Chemical modifications of natural zeolite showed the important role of Brønsted acid sites on the abatement of VOCs. The presence of humidity has a negative effect on zeolite adsorption capacity. Natural zeolites could be an interesting option for benzene, toluene and xylene vapour emission abatement. PMID:22907462

Alejandro, S; Valdés, H; Manero, M-H; Zaror, C A

2012-01-01

71

Surfactants from biomass: a two-step cascade reaction for the synthesis of sorbitol fatty acid esters using solid acid catalysts.  

PubMed

Sorbitol fatty esters have been prepared through a two-step catalytic process which involves the protection of the polyalcohol by ketalization followed by esterification with the fatty acid. Inorganic molecular sieves with different pore topologies as well as heteropolyacids (HPA) were used as acid catalysts to perform both the ketalization and the esterification step. These catalysts are found to hydrolyze the ketal function and promote the esterification between the free hydroxy groups and oleic acid in a cascade process. The results show a positive shape-selectivity effect when the process is carried out using tridirectional, and especially monodirectional (mordenite), zeolites, such that the ratio of mono- to higher esters and the hydroxy number of the final product are increased as compared to those obtained for the homogeneous-catalyzed process. PMID:18605669

Corma, Avelino; Hamid, Sharifah B A; Iborra, Sara; Velty, Alexandra

2008-01-01

72

Adsorption properties of Cs{sup +} for composite adsorbents and their irradiation stabilities  

SciTech Connect

Novel composite adsorbents using impregnation-precipitation methods have been developed; these fine crystals are loaded in the macro-pores of porous silica gels and zeolites. The 2 following composite adsorbents: KCoFC-NM (NM: natural mordenite, 0.4-1.0 mm), KCoFC-SG (SG: porous silica gel, NH and Q-10)) were prepared by impregnation-precipitation methods. This article presents the results of tests about their characterization, their selective adsorption ability of Cs{sup 137} and their irradiation stability. It is shown that the KCoFC-SG and KCoFC-NM composites are thus efficient for the selective separation of Cs{sup 137} in low-level radioactive waste (LLW) containing highly concentrated sodium nitrate.

Susa, Shunsuke; Mimura, Hitoshi [Tohoku University, Aramaki-Aza-Aoba 6-6, Aoba-ku, Sendai, Miyagi 980-8579 (Japan); Ito, Yoshiyuki; Saito, Yasuo [Japan Atomic Energy Agency, Muramatsu 4-33, Tokai-mura, Naka-gun, Ibaraki 319-1194 (Japan)

2013-07-01

73

Evidence for the presence of a bimolecular pathway in the isomerization of xylene on some large-pore zeolites  

SciTech Connect

Using deuterated para-xylene as a reactant, the authors have found that more than 20% of the meta- and ortho-xylenes, obtained when using a HY zeolite as catalyst, are formed via a bimolecular mechanism. This involves, as an intermediate complex, a molecule of trimethylbenzene and another of xylene. The bimolecular process is less important in the case of mordenite, and does not occur in Zeolite Beta at low levels of conversion. The relative proportion of uni- to bimolecular mechanism depends on: reaction conditions, zeolite composition, and zeolite structure. Some of the mechanistic conclusions, reached when using xylene isomerization and transalkylation as a test reaction on faujasite zeolites, should be revised in light of these results. Finally, transalkylation between trimethylbenzenes and xylenes is proposed as a test reaction for 12 membered-ring (MR) zeolites since structural differences can be better established than when the conventional xylene isomerization-transalkylation reaction is used.

Corma, A. (Universidad Politecnica de Valencia (Spain)); Sastre, E. (Instituto de Catalisis y Petroleoquimica, Madrid (Spain))

1991-05-01

74

Preparation for kinetic measurements on the silicates of the Yucca Mountain potential repository. [Final report], June 15, 1993--September 30, 1993  

SciTech Connect

Part 1, ``The Preparation of Clinoptilolite, Mordenite and Analcime,`` summarized progress made during the contract period on preparing Na-end member clinoptilolite, mordenite, and analcime. The objective is to use the prepared zeolites to determine rates of dissolution and precipitation in laboratory flow-through systems in both this lab to 350 C and by the geochemists at Yale University to about 80 C. Because clinoptilolite represents the most complicated phase of these three zeolites and it is most abundant at Yucca Mountain, the authors have concentrated most of their efforts on its preparation. They have collected, high-concentration natural clinoptilolite samples. A hindered settling technique that takes advantage of the relatively low specific gravity of clinoptilolite coupled with ultrasonic cleaning in deionized water has been employed. This material is now a mixed Na-K zeolite which must then be converted to the pure Na-end member composition. In Part 2, ``Draft Manuscript on the Heterogeneous Kinetics of Cristobalite,`` experiments on the rates of reactions of dissolution and precipitation of cristobalite were carried at 150--300 C. Results show that cristobalite may precipitate from hydrothermal solution if the concentration of Si(OH){sub 4} exceeds that at quartz saturation and is less than that of amorphous silica saturation and if there are cristobalite nuclei present. Such nuclei may occur where there has been devitrification of volcanic glasses, for example. Cristobalite has refused to crystallize in the absence of such nuclei. Steady state concentrations were reached experimentally after starting at 150 {degree} with initially supersaturated solutions and at 200 C starting with either supersaturated or undersaturated solutions. From the steady state conditions, equilibrium constants can be derived.

NONE

1993-12-31

75

Revised mineralogic summary of Yucca Mountain, Nevada  

SciTech Connect

We have evaluated three-dimensional mineral distribution at Yucca Mountain, Nevada, using quantitative x-ray powder diffraction analysis. All data were obtained on core cuttings, or sidewall samples obtained from drill holes at and around Yucca Mountain. Previously published data are included with corrections, together with new data for several drill holes. The new data presented in this report used the internal standard method of quantitative analysis, which yields results of high precision for the phases commonly found in Yucca Mountain tuffs including opal-CT and glass. Mineralogical trends with depth previously noted are clearly shown by these new data. Glass occurrence is restricted almost without exception to above the present-day static water level (SWL), although glass has been identified below the SWL in partially zeolitized tuffs. Silica phases undergo well-defined transitions with depth, with tridymite and cristobalite occurring only above the SWL, opal-CT occurring with clinoptilolite-mordenite tuffs, and quartz most abundant below the SWL. Smectite occurs in small amounts in most samples but is enriched in two distinct zones. These zones are at the top of the vitric nonwelded base of the Tiva Canyon Member and at the top of the basal vitrophyre of the Topopah Spring Member. Our data support the presence of several zones of mordenite and clinoptilolite-heulandite as shown previously. New data on several deep clinoptililite-heulandite samples coexisting with analcime show that they are heulandite. Phillipsite has not been found in any Yucca Mountain samples, but erionite and chabazite have been found once in fractures. 21 refs., 17 figs.

Bish, D.L.; Chipera, S.J.

1989-03-01

76

Tabulation and evaluation of ion exchange data on smectites, certain zeolites and basalt  

SciTech Connect

An extensive search of the literature has been made for ion exchange data on smectites, certain zeolites and basalt. The data are in the form of thermodynamic equilibrium constants, corrected selectivity coefficients, and distribution coefficients. Room temperature alkali and alkaline earth metal cation ion exchange data for smectites are extensive. Correlation between the exchange free energies of alkali metal cations on Camp Berteau montmorillonite values with their Debeye-Hueckel parameter was found. Significant differences in values of exchange constants for the same reaction on different smectites were noted. While this in part may be attributable to differences in experimental procedures, much of the variance is probably due to differences in charge densities and the effective field strengths of the smectites. Differences in field strength are related to the type and amount of substitution on intercrystalline octahedral and tetrahedral sites. Data on smectites suggest that cation exchange selectivities are very strong functions of temperature. Experiments on the exchange properties of clinoptilolite and mordenite have been generally confined to alkali and alkaline earth cations although data for certain transition metal ions are also available for synthetic mordenite. The temperature dependences of zeolite exchange selectivities remain largely unknown. Distribution coefficients for groundwater-basalt systems have been measured for a variety of elements at temperatures up to 150/sup 0/C. Steady state concentrations are often never achieved either from the sorption or the desorption side. Classical models of ion exchange have been applied successfully to zeolite and smectite exchange reactions. The sorption behavior of a basalt is better treated with models of the interface which take surface ionization and complexation into account.

Benson, L.V.

1980-05-01

77

Studies of anions sorption on natural zeolites.  

PubMed

This work presents results of FT-IR spectroscopic studies of anions-chromate, phosphate and arsenate - sorbed from aqueous solutions (different concentrations of anions) on zeolites. The sorption has been conducted on natural zeolites from different structural groups, i.e. chabazite, mordenite, ferrierite and clinoptilolite. The Na-forms of sorbents were exchanged with hexadecyltrimethylammonium cations (HDTMA(+)) and organo-zeolites were obtained. External cation exchange capacities (ECEC) of organo-zeolites were measured. Their values are 17mmol/100g for chabazite, 4mmol/100g for mordenite and ferrierite and 10mmol/100g for clinoptilolite. The used initial inputs of HDTMA correspond to 100% and 200% ECEC of the minerals. Organo-modificated sorbents were subsequently used for immobilization of mentioned anions. It was proven that aforementioned anions' sorption causes changes in IR spectra of the HDTMA-zeolites. These alterations are dependent on the kind of anions that were sorbed. In all cases, variations are due to bands corresponding to the characteristic Si-O(Si,Al) vibrations (occurring in alumino- and silicooxygen tetrahedra building spatial framework of zeolites). Alkylammonium surfactant vibrations have also been observed. Systematic changes in the spectra connected with the anion concentration in the initial solution have been revealed. The amounts of sorbed CrO4(2-), AsO4(3-) and PO4(3-) ions were calculated from the difference between their concentrations in solutions before (initial concentration) and after (equilibrium concentration) sorption experiments. Concentrations of anions were determined by spectrophotometric method. PMID:25002191

Barczyk, K; Mozgawa, W; Król, M

2014-12-10

78

Adsorption of As(V) on surfactant-modified natural zeolites.  

PubMed

Natural mordenite (NM), natural clinoptilolite (NC), HDTMA-modified natural mordenite (SMNM) and HDTMA-modified natural clinoptilolite (SMNC) have been proposed for the removal of As(V) from aqueous solution (HDTMA=hexadecyltrimethylammonium bromide). Influence of time on arsenic sorption efficiency of different sorbents reveals that NM, NC, SMNM and SMNC require about 20, 10, 110 and 20h, respectively to reach at state of equilibrium. Pseudo-first-order model was applied to evaluate the As(V) sorption kinetics on SMNM and SMNC within the reaction time of 0.5h. The pseudo-first-order rate constants, k are 1.06 and 0.52h(-1) for 1 and 0.5g of SMNM, respectively. The observed k values 1.28 and 0.70h(-1) for 1 and 0.5g of SMNC, respectively are slightly high compared to SMNM. Surfactant surface coverage plays an important role and a significant increase in arsenate sorption capacity could be achieved as the HDTMA loading level on zeolite exceeds monolayer coverage. At a surfactant partial bilayer coverage, As(V) sorption capacity of 97.33 and 45.33mmolkg(-1) derived from Langmuir isotherm for SMNM and SMNC, respectively are significantly high compared to 17.33 and 9.33mmolkg(-1) corresponding to NM and NC. The As(V) uptake was also quantitatively evaluated using the Freundlich and Dubinin-Kaganer-Radushkevich (DKR) isotherm models. Both SMNM and SMNC removed arsenic effectively over the initial pH range 6-10. Desorption performance of SMNM and SMNC were 66.41% and 70.04%, respectively on 0.1M NaOH regeneration solution. PMID:18565654

Chutia, Pratap; Kato, Shigeru; Kojima, Toshinori; Satokawa, Shigeo

2009-02-15

79

Direct electron crystallographic determination of zeolite zonal structures.  

PubMed

The prospect for improving the success of ab initio zeolite structure investigations with electron diffraction data is evaluated. First of all, the quality of intensities obtained by precession electron diffraction at small hollow cone illumination angles is evaluated for seven representative materials: ITQ-1, ITQ-7, ITQ-29, ZSM-5, ZSM-10, mordenite, and MCM-68. It is clear that, for most examples, an appreciable fraction of a secondary scattering perturbation is removed by precession at small angles. In one case, ZSM-10, it can also be argued that precession diffraction produces a dramatically improved 'kinematical' data set. There seems to no real support for application of a Lorentz correction to these data and there is no reason to expect for any of these samples that a two-beam dynamical scattering relationship between structure factor amplitude and observed intensity should be valid. Removal of secondary scattering by the precession mode appears to facilitate ab initio structure analysis. Most zeolite structures investigated could be solved by maximum entropy and likelihood phasing via error-correcting codes when precession data were used. Examples include the projected structure of mordenite that could not be determined from selected area data alone. One anomaly is the case of ZSM-5, where the best structure determination in projection is made from selected area diffraction data. In a control study, the zonal structure of SSZ-48 could be determined from selected area diffraction data by either maximum entropy and likelihood or traditional direct methods. While the maximum entropy and likelihood approach enjoys some advantages over traditional direct methods (non-dependence on predicted phase invariant sums), some effort must be made to improve the figures of merit used to identify potential structure solutions. PMID:17240069

Dorset, Douglas L; Gilmore, Christopher J; Jorda, Jose Luis; Nicolopoulos, Stavros

2007-01-01

80

Hydrothermal alteration in research drill hole Y-3, Lower Geyser Basin, Yellowstone National Park, Wyoming  

USGS Publications Warehouse

Y-3, a U.S. Geological Survey research diamond-drill hole in Lower Geyser Basin, Yellowstone National Park, Wyoming, reached a depth of 156.7 m. The recovered drill core consists of 42.2 m of surficial (mostly glacial) sediments and two rhyolite flows (Nez Perce Creek flow and an older, unnamed rhyolite flow) of the Central Plateau Member of the Pleistocene Plateau Rhyolite. Hydrothermal alteration is fairly extensive in most of the drill core. The surficial deposits are largely cemented by silica and zeolite minerals; and the two rhyolite flows are, in part, bleached by thermal water that deposited numerous hydrothermal minerals in cavities and fractures. Hydrothermal minerals containing sodium as a dominant cation (analcime, clinoptilolite, mordenite, Na-smectite, and aegirine) are more abundant than calcium-bearing minerals (calcite, fluorite, Ca-smectite, and pectolite) in the sedimentary section of the drill core. In the volcanic section of drill core Y-3, calcium-rich minerals (dachiardite, laumontite, yugawaralite, calcite, fluorite, Ca-smectite, pectolite, and truscottite) are predominant over sodium-bearing minerals (aegirine, mordenite, and Na-smectite). Hydrothermal minerals that contain significant amounts of potassium (alunite and lepidolite in the sediments and illitesmectite in the rhyolite flows) are found in the two drill-core intervals. Drill core y:.3 also contains hydrothermal silica minerals (opal, [3-cristobalite, chalcedony, and quartz), other clay minerals (allophane, halloysite, kaolinite, and chlorite), gypsum, pyrite, and hematite. The dominance of calcium-bearing hydrothermal minerals in the lower rhyolitic section of the y:.3 drill core appears to be due to loss of calcium, along with potassium, during adiabatic cooling of an ascending boiling water.

Bargar, Keith E.; Beeson, Melvin H.

1985-01-01

81

Fracture-coating minerals in the Topopah Spring Member and upper tuff of Calico Hills from drill hole J-13  

SciTech Connect

Fracture-lining minerals from drill core in the Topopah Spring Member of the Paintbrush Tuff and the tuff of Calico Hills from water well J-13 were studied to identify the differences between these minerals and those seen in drill core USW G-4. In USW G-4 the static water level (SWL) occurs below the tuff of Calico Hills, but in J-13 the water table is fairly high in the Topopah Spring Member. There are some significant differences in fracture minerals between these two holes. In USW G-4 mordenite is a common fracture-lining mineral in the Topopah Spring Member, increasing in abundance with depth. Euhedral heulandite >0.1 mm in length occurs in fractures for about 20 m above the lower vitrophyre. In J-13, where the same stratigraphic intervals are below the water table, mordenite is uncommon and euhedral heulandite is not seen. The most abundant fracture coating in the Topopah Spring Member in J-13 is drusy quartz, which is totally absent in this interval in USW G-4. Though similar in appearance, the coatings in the vitrophyre have different mineralogy in the two holes. In USW G-4 the coatings are extremely fine grained heulandite and smectite. In J-13 the coatings are fine-grained heulandite, chabazite, and alkali feldspar. Chabazite has not been identified from any other hole in the Yucca Mountain area. Fractures in the tuff of Calico Hills have similar coatings in core from both holes. In J-13, as in USW G-4, the tuff matrix of the Topopah Spring Member is welded and devitrified and that of the tuff of Calico Hills is zeolitic. 11 refs., 10 figs., 5 tabs.

Carlos, B.

1989-02-01

82

Zeolite-clay mineral zonation of volcaniclastic sediments within the McDermitt caldera complex of Nevada and Oregon  

USGS Publications Warehouse

Volcaniclastic sediments deposited in the moat of the collapsed McDermitt caldera complex have been altered chiefly to zeolites and potassium feldspar. The original rhyolitic and peralkaline ash-flow tuffs are included in conglomerates at the caldera rims and grade into a lacustrine series near the center of the collapse. The tuffs show a lateral zeolitic alteration from almost fresh glass to clinoptilolite, clinoptilolite-mordenite, and erionite; to analcime-potassium feldspar; and finally to potassium feldspar. Vertical zonation is in approximately the same order. Clay minerals in associated mudstones, on the other hand, show little lateral variation but a distinct vertical zonation, having a basal dioctahedral smectite, a medial trioctahedral smectite, and an upper dioctahedral smectite. The medial trioctahedral smectite is enriched in lithium (as much as 6,800 ppm Li). Hydrothermal alteration of the volcaniclastic sediments, forming both mercury and uranium deposits, caused a distinct zeolite and clay-mineral zonation within the general lateral zonation. The center of alteration is generally potassium feldspar, commonly associated with alunite. Potassium feldspar grades laterally and vertically to either clinoptilolite or clinoptilolite-mordenite, generally associated with gypsum. This zone then grades vertically and laterally into fresh glass. The clay minerals are a dioctahedral smectite, a mixed-layer clay mineral, and a 7-A clay mineral. The mixed-layer and 7-A clay minerals are associated with the potassium feldspar-alunite zone of alteration, and the dioctahedral smectite is associated with clinoptilolite. This mineralogical zonation may be an exploration guide for mercury and uranium mineralization in the caldera complex environment.

Glanzman, Richard K.; Rytuba, James J.

1979-01-01

83

Hydrothermal alteration of a rhyolitic hyaloclastite from Ponza Island, Italy  

NASA Astrophysics Data System (ADS)

A rhyolitic hyaloclastite from Ponza island, Italy, has been hydrothermally altered producing four distinct alteration zones based on XRD and field textures: (1) non-pervasive argillic zone; (2) propylitic zone; (3) silicic zone; and (4) sericitic zone. The unaltered hyaloclastite is a volcanic breccia with clasts of vesiculated obsidian in a matrix of predominantly pumice lapilli. Incomplete alteration of the hyaloclastite resulted in the non pervasive argillic zone, characterized by smectite and disordered opal-CT. Obsidian clasts, some pumice lapilli, and pyrogenic plagioclase and biotite are unaltered. Smectite has an irregular flakey morphology, although euhedral particles are occasionally observed. The propylitic zone is characterized by mixed-layer illite/smectite (I/S) with 10 to 85% illite (I), mordenite, opal-C and authigenic K-feldspar (akspar). The matrix of the hyaloclastite is completely altered and obsidian clasts are silicified; however, plagioclase and biotite phenocrysts remain unaltered. Flakey I/S replaces pumice, and mordenite, akspar and silica line and fill pores. I/S particles are composed predominantly of subequant plates and euhedral laths. The silicic zone is characterized by highly illitic I/S with ? 90% I, quartz, akspar and occasional albite. In this zone the matrix and clasts are completely altered, and pyrogenic plagioclase shows significant alteration. Illitic I/S has a euhedral lath-like morphology. In the sericitic zone the hyaloclastite altered primarily to illitic I/S with ? 66% I, quartz, and minor akspar and pyrite. Clay minerals completely replace pyrogenic feldspars and little evidence remains of the original hyaloclastite texture. Unlike other zones, illitic I/S is fibrous and pure illite samples are composed of euhedral laths and hexagonal plates. The temperatures of hydrothermal alteration likely ranged from 30 to 90 °C for the argillic zone, from 110 to 160 °C for the propylitic zone, from 160 to 270 °C for the silicic zone, and were possibly as high as 300 °C for the sericitic zone. The four zones occur as linear bands that increase in intensity north of the bentonite mine at Cala dell'Acqua. The alteration zones have two orientations and may be structurally controlled by E-W- and NE-SW-trending faulting which is consistent with the dominant structural trends of the Pontine archipelago. Finally, hydrothermal alteration most likely involved seawater based on the geologic evolution of Ponza.

Ylagan, Robert F.; Altaner, Stephen P.; Pozzuoli, Antonio

1996-12-01

84

Incredible antibacterial activity of noble metal functionalized magnetic core-zeolitic shell nanostructures.  

PubMed

Functionalized magnetic core-zeolitic shell nanostructures were prepared by hydrothermal and coprecipitation methods. The products were characterized by Vibrating Sample Magnetometer (VSM), X-ray powder diffraction (XRD), Fourier Transform Infrared (FTIR) spectra, nitrogen adsorption-desorption isotherms, and Transmission Electron Microscopy (TEM). The growth of mordenite nanoparticles on the surface of silica coated nickel ferrite nanoparticles in the presence of organic templates was also confirmed. Antibacterial activity of the prepared nanostructures was investigated by the inactivation of Escherichia coli as a gram negative bacterium. A new mechanism was proposed for inactivation of E. coli over the prepared samples. In addition, the Minimum Inhibitory Concentration (MIC) and reuse ability were studied. TEM images of the destroyed cell wall after the treatment time were performed to illustrate the inactivation mechanism. According to the experimental results, the core-shell nanostructures which were modified by organic agents and then functionalized with noble metal nanoparticles were the most active. The interaction of the noble metals with the organic components on the surface of nanostructures was studied theoretically and the obtained results were used to interpret the experimental results. PMID:24411359

Padervand, M; Janatrostami, S; Karanji, A Kiani; Gholami, M R

2014-02-01

85

Lithology, mineralogy, and paleontology of Quaternary lake deposits in Long Valley Caldera, California  

USGS Publications Warehouse

Drill cores and cuttings from two drill holes, about 3 km apart, in Long Valley caldera, Mono County, California, were studied using x-ray diffraction and optical methods. A thick sequence of tuffs and lake sediments was encountered in LVCH-1 (1,000 ft deep) and Republic well 66-29 (6,920 ft deep), drilled in the southeast part of the Long Valley caldera. Ostracods, diatoms, and isotopic data indicate that the sediments and tuffs were deposited in a shallow caldera lake which changed in salinity over time. Conditions ranged from very saline in the older lake to fresh in the youngest. The sequence of secondary minerals from top to bottom is: clinoptilolite, mordenite, analcime, K-feldspar (and albite). In some geothermal systems, this sequence of secondary minerals is a function of temperature; however, the paleontological and isotopic data indicate that the change in secondary minerals with increasing depth is due to the older strata being deposited in a more saline environment. No mineralogical evidence of hydrothermal alteration is present, although the high lithium content of some clays and feldspars and the isotopic composition of some sulfate (gypsum) seems to require a hydrothermal source. (Lantz-PTT)

Fournier, R.B.

1989-01-01

86

Characterization of Binary Ag-Cu Ion Mixtures in Zeolites: Their Reduction Products and Stability to Air Oxidation  

SciTech Connect

A series of Ag+-Cu2+ binary mixtures with different Ag/Cu ratios were supported on mordenite with different Si/Al ratios and were subsequently reduced under hydrogen in the temperature range 323K - 473K. Ag and Cu K-edge X-ray Absorption Spectroscopy (XAS) was conducted on these systems in-situ to monitor the reduction species formed and the kinetics of their reduction. In-situ XANES clearly demonstrates that the formation of silver particles is severely impeded by the addition of copper and that the copper is converted from Cu(II) to Cu(I) during reduction and completely reverts back to Cu(II) during cooling. There are no indications at any stage of the formation of bimetallic Ag-Cu clusters. Interestingly, the Ag/Cu ratio appears to have no influence of the reduction kinetics and reduction products formed with only the highest Si/Al ratio (MR = 128) investigated during this study having an influence on the reduction and stability to air oxidation.

Fiddy, Steven [CCLRC Daresbury Laboratory, Daresbury, Warrington, UK, WA4 4AD (United Kingdom); Petranovskii, Vitalii [CCMC-UNAM, Apdo Postal 2681, 22800 Ensenada. B.C., (Mexico); Ogden, Steve [Department of Chemistry, University of Southampton, Southampton (United Kingdom); Iznaga, Inocente Rodriguez [Laboratorio Ingenieria de Zeolitas, Instituto de Materiales y Reactivos (IMRE) - Universidad de la Habana. Zapata y G. s/n. Havana0400 (Cuba)

2007-02-02

87

Status of radioiodine control for nuclear fuel reprocessing plants  

SciTech Connect

This report summarizes the status of radioiodine control in a nuclear fuel reprocessing plant with respect to capture, fixation, and disposal. Where possible, we refer the reader to a number of survey documents which have been published in the last four years. We provide updates where necessary. Also discussed are factors which must be considered in developing criteria for iodine control. For capture from gas streams, silver mordenite and a silver nitrate impregnated silica (AC-6120) are considered state-of-the-art and are recommended. Three aqueous scrubbing processes have been demonstrated: Caustic scrubbing is simple but probably will not give an adequate iodine retention by itself. Mercurex (mercuric nitrate-nitric acid scrubbing) has a number of disadvantages including the use of toxic mercury. Iodox (hyperazeotropic nitric acid scrubbing) is effective but employs a very corrosive and hazardous material. Other technologies have been tested but require extensive development. The waste forms recommended for long-term storage or disposal are silver iodide, the iodates of barium, strontium, or calcium, and silver loaded sorbents, all fixed in cement. Copper iodide in bitumen (asphalt) is a possibility but requires testing. The selection of a specific form will be influenced by the capture process used.

Burger, L.L.; Scheele, R.D.

1983-07-01

88

Ion exchange in a zeolite-molten chloride system  

SciTech Connect

Electrometallurgical treatment of spent nuclear fuel results in a secondary waste stream of radioactive fission products dissolved in chloride salt. Disposal plans include a waste form that can incorporate chloride forms featuring one or more zeolites consolidated with sintered glass. A candidate method for incorporating fission products in the zeolites is passing the contaminated salt over a zeolite column for ion exchange. To date, the molten chloride ion-exchange properties of four zeolites have been investigated for this process: zeolite A, IE95{reg_sign}, clinoptilolite, and mordenite. Of these, zeolite A has been the most promising. Treating zeolite 4A, the sodium form of zeolite A , with the solvent salt for the waste stream-lithium-potassium chloride of eutectic melting composition, is expected to provide a material with favorable ion-exchange properties for the treatment of the waste salt. The authors constructed a pilot-plant system for the ion-exchange column. Initial results indicate that there is a direct relationship between the two operating variable of interest, temperature, and initial sodium concentration. Also, the mass ratio has been about 3--5 to bring the sodium concentration of the effluent below 1 mol%.

Woodman, R.H.; Pereira, C. [Argonne National Lab., IL (United States). Chemical Technology Div.

1997-07-01

89

Radionuclide Leaching from Organic Ion Exchange Resin  

SciTech Connect

Laboratory tests were performed to examine the efficacy of leach treatments for decontaminating organic ion exchange resins (OIER), which have been found in a number of samples retrieved from K East Basin sludge. Based on process records, the OIER found in the K Basins is a mixed-bet strong acid/strong base material marketed as Purolite{trademark} NRW-037. Radionuclides sorbed or associated with the OIER can restrict its disposal to the Environmental Restoration Disposal Facility (ERDF). The need for testing to support development of a treatment process for K Basin sludge has been described in Section 4.2 of ''Testing Strategy to Support the Development of K Basins Sludge Treatment Process'' (Flament 1998). To help understand the effects of anticipated OIER elutriation and washing, tests were performed with well-rinsed OIER material from K East Basin floor sludge (sample H-08 BEAD G) and with well-rinsed OIER having approximately 5% added K East canister composite sludge (sample KECOMP). The rinsed resin-bearing material also contained the inorganic ion exchanger Zeolon-900{trademark}, a zeolite primarily composed of the mineral mordenite. The zeolite was estimated to comprise 27 weight percent of the dry H-08 BEAD G material.

Delegard, C.H.; Rinehart, D.E.

1999-04-02

90

Coupling of alcohols to ethers: The dominance of the surface S{sub N}2 reaction pathway  

SciTech Connect

Coupling of alcohols to ethers, important high value oxygenates, proceeds on acid catalysts via general pathways that uniquely control product composition, oxygen retention, chirality inversion, and kinetics. The dominant pathway is the S{sub N}2 reaction with competition of the alcohols for the surface acid sites. This is exemplified by formation of methyl(ethyl) isobutylether (M(E)IBE) from methanol(ethanol)/isobutanol mixtures, retention of oxygen ({sup 18}O) of the heavier alcohol, and optimum rate as a function of concentration of either reactant alcohol. The S{sub N}2 pathway in the confinement of zeolite pores exhibits additional features of a near-100% selectivity to dimethylether (DME) in H-mordenite and a near-100% selectivity to chiral inversion in 2-pentanol/ethanol coupling to 2-ethoxypentane in HZSM-5. A minor reaction pathway entails olefin or carbenium intermediates, as exemplified by the formation of methyl tertiarybutyl ether (MTBE) from methanol/isobutanol mixtures with oxygen retention of the lighter alcohol. Calculations of transition state and molecular modeling of the oxonium-involving pathways dramatically demonstrate how the reaction path selects the products.

Klier, K.; Feeley, O.C.; Johansson, M.; Herman, R.G. [Lehigh Univ., Bethlehem, PA (United States)

1996-12-31

91

Gold nanoparticles as efficient antimicrobial agents for Escherichia coli and Salmonella typhi  

PubMed Central

Background It is imperative to eliminate bacteria present in water in order to avoid problems in healthy. Escherichia coli and Salmonella typhi bacteria are two common pollutants and they are developing resistance to some of the most used bactericide. Therefore new biocide materials are being tested. Thus, gold nanoparticles are proposed to inhibit the growth of these two microorganisms. Results Gold nanoparticles were supported onto clinoptilolite, mordenite and faujasite zeolites. Content of gold in materials varied between 2.3 and 2.8 wt%. The size, dispersion and roughness of gold nanoparticles were highly dependent of the zeolite support. The faujasite support was the support where the 5 nm nanoparticles were highly dispersed. The efficiency of gold-zeolites as bactericides of Escherichia coli and Salmonella typhi was determined by the zeolite support. Conclusions Gold nanoparticles dispersed on zeolites eliminate Escherichia coli and Salmonella typhi at short times. The biocidal properties of gold nanoparticles are influenced by the type of support which, indeed, drives key parameters as the size and roughness of nanoparticles. The more actives materials were pointed out Au-faujasite. These materials contained particles sized 5 nm at surface and eliminate 90–95% of Escherichia coli and Salmonella typhi colonies. PMID:23331621

2013-01-01

92

Biaxial Q-shearing of 27Al 3QMAS NMR spectra: insight into the structural disorder of framework aluminosilicates.  

PubMed

In this contribution, we present the application potentiality of biaxial Q-shearing of (27)Al 3QMAS NMR spectra in the analysis of structural defects of aluminium units in aluminosilicates. This study demonstrates that the combination of various shearing transformations of the recorded (27)Al 3QMAS NMR spectra enables an understanding of the broadening processes of the correlation signals of disordered framework aluminosilicates, for which a wide distribution of (27)Al MAS NMR chemical shifts and quadrupolar parameters (i.e., second-order quadrupolar splitting and quadrupole-induced chemical shifts) can be expected. By combining the suitably selected shearing transformation procedures, the mechanisms of the formation of local defects in aluminosilicate frameworks, including Al/Si substitution effects in the next-nearest neighbouring T-sites, variations in bond angles, and/or variations in the physicochemical nature of charge-balancing counter-ions, can be identified. The proposed procedure has been extensively tested on a range of model aluminosilicate materials (kyanite, ?-alumina, metakaolin, analcime, chabazite, natrolite, phillipsite, mordenite, zeolite A, and zeolite Y). PMID:24333044

Kobera, Libor; Brus, Jiri; Klein, Petr; Dedecek, Jiri; Urbanova, Martina

2014-01-01

93

Deuterium NMR characterization of Bronsted acid sites and silanol species in zeolites  

SciTech Connect

Solid-state deuterium NMR has been used to characterize Bronsted acid sites and nonacidic silanol species in D-Y, D-mordenite, and D-ZSM-5 zeolites. Bronsted acid deuterons may be static, with quadrupole coupling constants (QCC) near 240 kHz and asymmetries ({eta}) of 0. These acidic deuterons may also be motionally averaged to give QCC = 120 kHz and {eta} = 1, consistent with jumping between two oxygen sp{sup 3} orbitals. These results indicate that the acid deuteron does not remain fixed in the Al-O-Si plane. Isolated silanol species display a narrow, axially symmetric powder pattern, consistent with an Si-O-D bond angle of 116{degree}. Most of the silanol species are more densely packed, and the variety of hydrogen-bonded positions possible results in a Gaussian peak about 56 kHz wide. Deuterium NMR shows promise as a technique for characterizing both acidic and nonacidic hydroxyl groups in zeolites. 55 refs., 7 figs., 2 tabs.

Kobe, J.M.; Gluszak, T.J.; Dumesic, J.A.; Root, T.W. [Univ. of Wisconsin, Madison, WI (United States)

1995-04-13

94

Comparison between leached metakaolin and leached diatomaceous earth as raw materials for the synthesis of ZSM-5.  

PubMed

Inexpensive raw materials have been used to prepare ZSM-5 zeolites with SiO2/Al2O3 molar ratios in the range 20 - 40. Kaolin or Bolivian diatomaceous earth was used as aluminosilicate raw materials and sodium hydroxide and n-butylamine were used as mineralizing agents and template. Dealumination of the raw materials by acid leaching made it possible to reach appropriate SiO2/Al2O3 ratios and to reduce the amount of iron and other impurities. After mixing the components and aging, hydrothermal treatment was carried out and the products were recovered The results clearly show for the first time that well-crystallized ZSM-5 can be directly prepared from leached metakaolin or leached diatomaceous earth using sodium hydroxide and n-butylamine as mineralizing agents and template under appropriate synthesis conditions. A longer induction time prior to crystallization was observed for reaction mixtures prepared from leached diatomaceous earth, probably due to slower digestion of the fossilized diatom skeletons as compared with that for microporous leached metakaolin. The use of leached diatomaceous earth allowed higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of Mordenite formed, which was related to the high calcium content of diatomaceous earth. Another considerable advantage of diatomaceous earth over kaolin is that diatomaceous earth does not require heat treatment at high temperature for metakaolinization. PMID:25019042

Aguilar-Mamani, Wilson; García, Gustavo; Hedlund, Jonas; Mouzon, Johanne

2014-01-01

95

Radical formation in the adsorption of trimethylbenzenes on crystalline and amorphous aluminosilicates  

SciTech Connect

The formation and conversion of cation radicals (CR) in the absorption of the isomers of trimethylbenzene (TMB), pseudocumene and mesitylene on Y zeolites, a high-silica wide-pore mordenite, the UHS zeolite TsVM, which belong to the class of pentasils, and on an amorphous aluminosilicate (AS) have been studied by EPR. It is shown that the formation of CR takes place in the adsorption of TMB on dehydrated specimens of the H-forms of the zeolites and amorphous AS in the presence of O/sub 2/. The possible structure of the CR formed, the paths for their conversion, as well as the structure of the radical-forming center are discussed. A mechanism is suggested for the formation and conversion of CR at an oxidizing-reducing center activated by oxygen. The radical processes which take place on the zeolites and amorphous AS are associated with the selectivity of the catalytic reactions involving the participation of TMB and also with the deactivation of the catalysts.

Surin, S.A.; Fedorova, L.A.; Gullyev, C.; Chukin, G.D.; Nefedov, B.K.; Radchenko, E.D.

1987-04-01

96

Petrology, sedimentology, and diagenesis of hemipelagic limestone and tuffaceous turbidities in the Aksitero Formation, central Luzon, Philippines  

USGS Publications Warehouse

The Aksitero Formation of central Luzon is an upper Eocene and lower Oligocene sequence of evenly bedded hemipelagic limestone with a few thin interlayers of tuffaceous turbidites. The limestone consists chiefly of planktonic foraminifers and calcareous nannofossils, with up to 30 percent of noncarbonate components, chiefly volcaniclastic debris. The tuff layers are graded beds. Composed mainly of glass shards, pumice fragments, crystals, and fine-grained volcanic rock fragments. Hydrocarbons migrated into the pores of the tuffaceous layers early during diagenesis but they were subsequently flushed out and only bitumen remains, chiefly as thin coatings on grains and wthin pumice vesicles. Later during diagenesis, zeolites (mordenite and c1inoptilolite) and secondary calcite preferentially replaced glass shards and pumice fragments. Deposition of the Aksitero Formation probably occurred at depths of at least 1,000 meters within a subsiding basin adjacent to an active island arc system. Submarine ash eruptions of silicic composition caused volcaniclastic turbidity currents that occasionally reached the basin floor. The more proximal facies of these volcaniclastic deposits may be prospective for hydrocarbons.

Garrison, Robert E.; Espiritu, E.; Horan, L.J.; Mack, L.E.

1979-01-01

97

Binding and catalytic reduction of NO by transition metal aluminosilicates  

SciTech Connect

The objective of this research is to provide the scientific understanding of processes that actively and selectively reduce NO in dilute exhaust streams, as well as in concentrated streams, to N{sub 2}. Experimental studies of NO chemistry in transition metal-containing aluminosilicate catalysts are being carried out with the aim of determining the chemical rules for NO reduction on non-precious metals. The catalyst supports chosen for this investigation are A and Y zeolites, mordenite, and monoliths based on cordierite. The supported transition metal cations that were examined are principally the first row redox metals, e.g. Cr(2), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Cu(I). The reactions of interest are the reductions of NO by H{sub 2}, CO, and CH{sub 4}, as well as the disproportionation of NO. Rare earth cations that possess redox properties were placed in the more shielded sites, e.g. Site I in Y zeolite, prior to or simultaneously with the exchange procedure with the transition metal cations. Theoretical calculations of the electronic structure of the transition metal cations in zeolitic sites were carried out by ab initio methods. The aim of this part of the research is to find the best match between the metal-based antibonding orbitals and the antibonding orbitals of the NO molecule such that the N-O bond is weakened and is readily broken. 9 refs., 4 figs., 3 tabs.

Klier, K.; Herman, R.G.; Hou, Shaolie.

1991-09-01

98

Growth of Megaspherulites In a Rhyolitic Vitrophyre  

NASA Technical Reports Server (NTRS)

Megaspherulites occur in the middle zone of a thick sequence of rhyolitic vitrophyre that occupies a small, late Eocene to early Oligocene volcanic-tectonic basin near Silver Cliff, Custer County, Colorado. Diameters of the megaspherulites range from 0.3 m to over 3.66 m, including a clay envelope. The megaspherulites are compound spherulites. consisting of an extremely large number (3.8 x 10(exp 9) to 9.9 x 10(exp 9)) of individual growth cones averaging 3 mm long by 1.25 mm wide at their termination. They are holocrystalline, very fine- to fine-grained, composed of disordered to ordered sanidine (orthoclase) and quartz, and surrounded by a thin K-feldspar, quartz rich rind, an inner clay layer with mordenite, and an outer clay layer composed wholly of 15 A montmorillonite. Whole rock analyses of the megaspherulites show a restricted composition from their core to their outer edge, with an average analyses of 76.3% SiO2, 0.34% CaO, 2.17% Na2O, 6.92% K2O, 0.83% H2O+ compared to the rhyolitic vitrophyre from which they crystallize with 71.07% SiO2, 0.57% CaO, 4.06% Na2O,4.l0% K2O, and 6.40% H2O+. The remaining oxides of Fe2O3 (total Fe), A12O3, MnO,MgO, TiO2, P2O5, Cr2O3, and trace elements show uniform distribution between the megaspherulites and the rhyolitic vitrophyre. Megaspherulite crystallization began soon after the rhyolitic lava ceased to flow as the result of sparse heterogeneous nucleation, under nonequilibrium conditions, due to a high degree of undercooling, delta T. The crystals grow with a fibrous habit which is favored by a large delta T ranging between 245 C and 295 C, despite lowered viscosity, and enhanced diffusion due to the high H2O content, ranging between 5% and 7%. Therefore, megaspherulite growth proceeded in a diffusion controlled manner, where the diffusion, rate lags behind the crystal growth rate at the crystal-liquid interface, restricting fibril lengths and diameters to the 10 micron to 15 micron and 3 micron and 8 micron ranges respectively. Once diffusion reestablishes itself at the crystallization front, a new nucleation event occurs at the terminated tips of the fibril cones and a new cone begins to develop with a similar orientation (small angle branching) to the earlier cones. During crystallization, these fibril cones impinge upon each other, resulting in fibril cone-free areas. These cone-free areas consist of coarser, fine-grained phases, dominated by quartz, which crystallized from the melt as it accumulated between the crystallizing K-feldspar fibrils of the cones. The anhydrous nature of the disordered to ordered sanidine (orthoclase) and quartz, suggests that water in the vitrophyre moved ahead of the crystallization front, resulting in a water rich fluid being enriched in Si, K, Na, Mg, Ca, Sr, Ba, and Y. The clay layers associated with the megaspherulites are therefore, the result of the deuteric alteration between the fractionated water and the vitrophyre, as indicated by the presence of the minerals mordenite and montmorillonite. This silica rich fluid also resulted in the total silicification of the megaspherulites within the upper 3 m of the vitrophyre.

Smith, Robert K.; Tremallo, Robin L.; Lofgren, Gary E.

2000-01-01

99

Zeolitization of intracaldera sediments and rhyolitic rocks in the 1.25 Ma lake of Valles caldera, New Mexico, USA  

NASA Astrophysics Data System (ADS)

Quantitative X-ray diffraction analysis of about 80 rhyolite and associated lacustrine rocks has characterized previously unrecognized zeolitic alteration throughout the Valles caldera resurgent dome. The alteration assemblage consists primarily of smectite-clinoptilolite-mordenite-silica, which replaces groundmass and fills voids, especially in the tuffs and lacustrine rocks. Original rock textures are routinely preserved. Mineralization typically extends to depths of only a few tens of meters and resembles shallow "caldera-type zeolitization" as defined by Utada et al. [Utada, M., Shimizu, M., Ito, T., Inoue, A., 1999. Alteration of caldera-forming rocks related to the Sanzugawa volcanotectonic depression, northeast Honshu, Japan — with special reference to "caldera-type zeolitization." Resource Geol. Spec. Issue No. 20, 129-140]. Geology and 40Ar/ 39Ar dates limit the period of extensive zeolite growth to roughly the first 30 kyr after the current caldera formed (ca. 1.25 to 1.22 Ma). Zeolitic alteration was promoted by saturation of shallow rocks with alkaline lake water (a mixture of meteoric waters and degassed hydrothermal fluids) and by high thermal gradients caused by cooling of the underlying magma body and earliest post-caldera rhyolite eruptions. Zeolitic alteration of this type is not found in the later volcanic and lacustrine rocks of the caldera moat (? 0.8 Ma) suggesting that later lake waters were cooler and less alkaline. The shallow zeolitic alteration does not have characteristics resembling classic, alkaline lake zeolite deposits (no analcime, erionite, or chabazite) nor does it contain zeolites common in high-temperature hydrothermal systems (laumontite or wairakite). Although aerially extensive, the early zeolitic alteration does not form laterally continuous beds and are consequently, not of economic significance.

Chipera, Steve J.; Goff, Fraser; Goff, Cathy J.; Fittipaldo, Melissa

2008-12-01

100

Distribution and chemistry of fracture-lining minerals at Yucca Mountain, Nevada  

SciTech Connect

Yucca Mountain, a >1.5-km-thick sequence of tuffs and subordinate lavas in southwest Nevada, is being investigated as a potential high-level nuclear waste repository site. Fracture-lining minerals have been studied because they may provide information on past fluid transport and because they may act as natural barriers to radionuclide migration within the fractures. Cores from seven drill holes have been studied to determine the distribution and chemistry of minerals lining fractures at Yucca Mountain. Fracture-lining minerals in tuffs of the Paintbrush Group, which is above the static water level at Yucca Mountain, are highly variable in distribution, both vertically and laterally across the mountain, with the zeolites mordenite, heulandite, and stellerite widespread in fractures even though the tuff matrix is generally devitrified and nonzeolitic. Where heulandite occurs as both tabular and prismatic crystals in the same fracture, the two morphologies have different compositions, suggesting multiple episodes of zeolite formation within the fractures. Manganese-oxide minerals within the Paintbrush Group are rancieite and lithiophorite. The silica polymorphs (quartz, tridymite, and cristobalite) generally exist in fractures where they exist in the matrix, suggesting that they formed in the fractures at the same time they formed in the matrix. Fluorite, calcite, and opal occur over tridymite in some lithophysal cavities. Calcite also occurs over zeolites in fractures unrelated to lithophysal cavities and is often the youngest mineral in a given fracture. The clays smectite, palygorskite, and sepiolite are common in fractures in the Paintbrush Group in drill core USW GU-3; smectite is an abundant fracture-coating mineral in all drill cores at Yucca Mountain.

Carlos, B.A.; Chipera, S.J.; Bish, D.L.

1995-12-01

101

Zeolite-supported Metal Complexes of Rhodium and of Ruthenium: a General Synthesis Method Influenced by Molecular Sieving Effects  

SciTech Connect

A general method for synthesis of supported metal complexes having a high degree of uniformity is presented, whereby organometallic precursors incorporating acetylacetonate (C{sub 5}H{sub 7}O{sub 2}{sup -}, acac) ligands react with zeolites incorporating OHgroups near Al sites. The method is illustrated by the reactions of Rh(acac)(CO){sub 2} and of cis-Ru(acac){sub 2}({eta}{sup 2}-C{sub 2}H{sub 4}){sub 2} with zeolites slurried in n-pentane at room temperature. The zeolites were H-Beta, H-SSZ-42, H-Mordenite, and HZSM-5. Infrared (IR) and extended X-ray absorption fine structure spectra of the zeolites incorporating rhodium complexes indicate the formation of Rh(CO){sub 2}{sup +} bonded near Al sites; similar results have been reported for the formation of zeolite-supported Rh({eta}{sup 2}-C{sub 2}H{sub 4}){sup 2+} from Rh(acac)({eta}{sup 2}-C{sub 2}H{sub 4}){sub 2}. IR spectra of the supported rhodiumgem-dicarbonyls include sharp, well-resolved {nu}{sub CO} bands, demonstrating that the sites surrounding each metal complex are nearly equivalent. The frequencies of the {nu}{sub CO} bands show how the composition of the zeolite influences the bonding of the supported species, demonstrating subtle differences in the roles of the zeolite as ligands. When the zeolite has pore openings larger than the critical diameter of the precursor organometallic compound, the latter undergoes facile transport into the interior of the zeolite, so that a uniform distribution of the supported species results, but when the precursors barely fit through the zeolite apertures, the mass transport resistance is significant and the supported metal complexes are concentrated near the pore mouths.

Ogino, I.; Chen, C; Gates , B

2010-01-01

102

Thorium removal by different adsorbents.  

PubMed

The removal of radiotoxic Th(4+) from aqueous solutions has been explored using two different groups of adsorptive materials (e.g. two activated carbons and four zeolites-two natural and two synthetic). The activated carbons were prepared from solvent extracted olive pulp (SEOP) and olive stone (OS) by a two-step physical activation method with steam. They were characterized by N(2) at 77K adsorption, Hg porosimetry and by determination of their iodine number. All carbons prepared are of the H-type (e.g. contain mainly basic surface oxides) confirmed by the results of the Boehm's method. The natural zeolites, clinoptilolite (NaCLI) and mordenite (NaMOR), were pretreated with Na(+) before the adsorption experiments, while the synthetic ones, NaX and NaA, were provided in their commercial sodium form. The natural zeolites, NaCLI and NaMOR, utilized 11.5 and 38.6% of the theoretical ion-exchange capacity, based on Al content, respectively, while NaX and NaA utilized 41.5 and 45.9%, respectively. The activated carbons showed better removal capability than NaCLI. NaMOR, showed comparable results to the carbon originated from OS, but lower removal capability than the carbon originated from SEOP. The synthetic zeolites showed the highest removal ability for thorium ions due to their increased ion-exchange capacity because of their cleaner and larger framework channels and their higher number of ion-exchange sites. The carbons adsorption capacity mainly depends on the content and nature of functional surface groups. The adsorption data were fitted to Langmuir and Freundlich models. The former achieved best fits and was further applied to obtain the respective Langmuir constant and maximum adsorption capacity for each system. PMID:12573830

Metaxas, Michail; Kasselouri-Rigopoulou, Vasilia; Galiatsatou, Polymnia; Konstantopoulou, Cathrine; Oikonomou, Dimitrios

2003-02-28

103

Ion exchange and dehydration experimental studies of clinoptilolite: Implications to zeolite dating  

SciTech Connect

Variable effects were noted on the argon (Ar) and potassium (K) contents of clinoptilolite fractions used in ion-exchange and dehydration experiments. The K contents of clinoptilolite fractions were differently affected during cation exchange with Ca-, Cs-, K-, and Na-chloride solutions. Ar was generally less affected during these experiments, except for a Na-clinoptitolite fraction exchanged for five days. Loss of Ar during organic heavy-liquid treatment and cleaning using acetone and deionized water does occur, as indicated by comparing the amounts of radiogenic Ar of treated and untreated fractions. Moreover, a regular decrease in radiogenic Ar contents was noted in clinoptilolite fractions during dehydration experiments at different temperatures for 16 hours. Comparable losses do not occur from saturated samples that were heated in 100 C for more than five months. Water appears to play a vital role in stabilizing the clinoptilolite framework structure and in the retention of Ar. The radiogenic Ar depletion pattern noted in clinoptilolite fractions dehydrated in unsaturated environment at different temperatures is similar to variations in the amount of radiogenic Ar observed in clinoptilolite samples from the unsaturated zone of an altered tuff. These results can be used to evaluate the extent of zeolitic water (and hence Ar) retention in unsaturated geologic settings. The utility of alkali zeolites (e.g., phillipsite, clinoptilolite, and mordenite) from low-temperature, open-hydrologic alteration as potential dateable minerals was evaluated using the K/Ar method as part of the Yucca Mountain Site Characterization Project, which is evaluating Yucca Mountain, Nevada, as a potential high-level radioactive waste repository site.

WoldeGabriel, G.

1995-02-01

104

Sorption of cesium and strontium from concentrated brines by backfill barrier materials  

SciTech Connect

The sorption of radionuclides from potentially intruding groundwater at a nuclear waste repository is a major chemical function of backfill barriers. In this study, various materials (including clays, zeolites and an inorganic ion exchanger) were screened for the sorption of the fission products cesium and strontium in concentrated brines. Representative brines A and B for the Waste Isolation Pilot Plant (WIPP), a proposed radioactive waste repository and test facility in bedded salt were used. Sorption properties were quantified using empirical distribution coefficients, k/sub d/. Of the materials examined, sodium titanate had the highest k/sub d/ for the sorption of Sr(II) in both brine A (k/sub d/ = 125 ml/g) and brine B(k/sub d/ = 500 to 600 ml/g). A mordenite-type zeolite was the most effective getter for Cs(I) in brine A (k/sub d = 27 ml/g), while illite yielded the highest k/sub d/ for Cs(I) in brine B (k/sub d/ = 115 ml/g). The relative merit of these k/sub d/ values is evaluated in terms of calculated estimates of breakthrough times for a backfill barrier containing the getter. Results show that a backfill mixture containing these getters is potentially an effective barrier to the migration of Sr(II) and Cs(I), although further study (especially for the sorption of cesium from brine A) is recommended. Initial mechanistic studies revealed competing ion effects which would support an ion exchange mechanism. K/sub d/'s were constant over a Sr(II) concentration range of 10/sup -11/ to 10/sup -5/ M and a Cs(I) concentration range of 10/sup -8/ to 10/sup -5/ M, supporting the choice of a linear sorption isotherm as a model for the results. Constant batch composition was shown to be attained within one week.

Winslow, C D

1981-03-01

105

Assessment of Methods to Consolidate Iodine-Loaded Silver-Functionalized Silica Aerogel  

SciTech Connect

The U.S. Department of Energy is currently investigating alternative sorbents for the removal and immobilization of radioiodine from the gas streams in a nuclear fuel reprocessing plant. One of these new sorbents, Ag0-functionalized silica aerogels, shows great promise as a potential replacement for Ag-bearing mordenites because of its high selectivity and sorption capacity for iodine. Moreover, a feasible consolidation of iodine-loaded Ag0-functionalized silica aerogels to a durable SiO2-based waste form makes this aerogel an attractive choice for sequestering radioiodine. This report provides a preliminary assessment of the methods that can be used to consolidate iodine-loaded Ag0-functionalized silica aerogels into a final waste form. In particular, it focuses on experimental investigation of densification of as prepared Ag0-functionalized silica aerogels powders, with or without organic moiety and with or without sintering additive (colloidal silica), with three commercially available techniques: 1) hot uniaxial pressing (HUP), 2) hot isostatic pressing (HIP), and 3) spark plasma sintering (SPS). The densified products were evaluated with helium gas pycnometer for apparent density, with the Archimedes method for apparent density and open porosity, and with high-resolution scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) for the extent of densification and distribution of individual elements. The preliminary investigation of HUP, HIP, and SPS showed that these sintering methods can effectively consolidate powders of Ag0-functionalized silica aerogel into products of near-theoretical density. Also, removal of organic moiety and adding 5.6 mass% of colloidal silica to Ag0-functionalized silica aerogel powders before processing provided denser products. Furthermore, the ram travel data for SPS indicated that rapid consolidation of powders can be performed at temperatures below 950°C.

Matyas, Josef; Engler, Robert K.

2013-09-01

106

Test results from the GA technologies engineering-scale off-gas treatment system  

SciTech Connect

One method for reducing the volume of HTGR fuel prior to reprocessing or spent fuel storage is to crush and burn the graphite fuel elements. The burner off-gas (BOG) contains radioactive components, principally H-3, C-14, Kr-85, I-129, and Rn-220, as well as chemical forms such as CO/sub 2/, CO, O/sub 2/, and SO/sub 2/. The BOG system employs components designed to remove these constitutents. Test results are reported for the iodine and SO/sub 2/ adsorbers and the CO/HT oxidizer. Silver-based iodine adsorbents were found to catalyze the premature conversion of CO to CO/sub 2/. Subsequent tests showed that iodine removal could not be performed downstream of the CO/HT oxidizer since iodine in the BOG system rapidly deactivated the Pt-coated alumina CO catalyst. Lead-exchanged zeolite (PbX) was found to be an acceptable alternative for removing iodine from BOG without CO conversion. Intermittent and steady-state tests of the pilot-plant SO/sub 2/ removal unit containing sodium-exchanged zeolite (NaX) demonstrated that decontamination factors greater than or equal to 100 could be maintained for up to 50 h. In a reprocessing flowsheet, the solid product from the burners is dissolved in nitric or Thorex acid. The dissolver off-gas (DOG) contains radioactive components H-3, Kr-85, I-129, Rn-220 plus chemical forms such as nitrogen oxides (NO/sub x/). In the pilot-scale system at GA, iodine is removed from the DOG by adsorption. Tests of iodine removal have been conducted using either silver-exchanged mordenite (AgZ) or AgNO/sub 3/-impregnated silica gel (AC-6120). Although each sorbent performed well in the presence of NO/sub x/, the silica gel adsorbent proved more efficient in silver utilization and, thus, more cost effective.

Jensen, D.D.; Olguin, L.J.; Wilbourn, R.G.

1984-06-01

107

Hot springs: poor sites to seek relict organic matter  

NASA Astrophysics Data System (ADS)

It has been suggested repeatedly in the search for extraterrestrial life that hot spring systems are choice locations. On the Earth these sites commonly exhibit a rich community of microbial organisms, however, analyses of siliceous hot spring deposits at Yellowstone National Park, Wyoming, USA, indicate that at least parts of these sites are not favorable for the preservation of the organic matter (biomarkers) comprising the microbes. In an 11m long core into a relict siliceous hot spring, the upper 1 to 2m are dominantly composed of porous opal-A with some calcite (although no calc ite was present at the surface) and patches of amorphous Mn -oxides. In the zone 5m below the surface, the silica is dominantly opal-CT (i.e., diagenetically altered opal-A) and authigenic Mn-oxides are common. Abundant zeolites (mordenite and heulandite), bladed cristobalite lepisheres, chalcedony cements, and calcite veins are common 7 to 11m below the surface. Paragenesis is complicated, it involves numerous episodes of mineral precipitation and dissolution indicative of fluctuating hydrochemical regimes. Analyses of the organic remains (by ToF-SIMs) further attest to the highly reactive hydrochemical regime. Microbial organic matter, which is abundant at the surface, is essentially totally removed from the lower part of the core, estimated to be considerably less than 1,000 years old, even within deposits that display abundant silicified microbial body fossils. This degradation of organic matter is readily understandable given the hot, mildly acidic, oxygen-rich waters coursing through these porous siliceous sinters. Thus, in these deposits, silicified body fossils of microbes remain but organic matter (biomarkers) does not. That is, although the reliability of body fossils of microbes have been questioned, they are the best preserved remains of microbes in these hot spring deposits. The results of these analyses indicate that: (1) sites immediately adjacent to hot spring orifices, where the waters are the hottest, are not the best loci to find preserved organic matter, (2) depending upon sample site, mineralized body fossils may be the best preserved evidence of extraterrestrial microbes, and (3) absence of organic matter (biomarkers) may not, by itself, be a significant indicator of the absence of former life.

Chafetz, H.; Guidry, S.

108

Geological, mineralogical and geochemical characteristics of zeolite deposits associated with borates in the Bigadiç, Emet and Kirka Neogene lacustrine basins, western Turkey  

NASA Astrophysics Data System (ADS)

The Bigadiç, Emet and Kirka lacustrine basins of western Turkey may be considered as Tibet-type graben structures that were developed during the Miocene within the Izmir-Ankara suture zone complex. The volcanic-sedimentary successions of these basins are made up of mudstone, carbonate (limestone and dolomite) and detrital rocks, and also of crystal or vitric tuffs about 135 to 200 m thick. The Degirmenli (Bigadiç), Emirler (Bigadiç) Köpenez (Emet) and Karaören (Kirka) tuffs constituting the zeolite deposits are situated beneath four borate deposits (colemanite, ulexite, borax). The most abundant diagenetic silicate minerals are K- and Ca-clinoptilolites in the zeolite deposits, and Li-rich trioctahedral smectites (stevensite, saponite and hectorite) and K-feldspar in the borate deposits. In the Degirmenli, Emirler, Köpenez and Karaören deposits, the following diagenetic facies were developed from rhyolitic glasses rich in K and poor in Na: (glass+smectite), (K-clinoptilolite+opal-CT), (Ca-clinoptilolite+K-feldspar±analcime± quartz) and (K-feldspar+analcime+quartz). K-feldspar which is also rarely associated with phillipsite (Karaören) and heulandite (Degirmenli and Karaören), succeeds clinoptilolite and precedes analcime in these diagenetic facies where dioctahedral smectites, opal-CT and quartz are the latest minerals. No diagenetic transformations exist between clinoptilolite, K-feldspar and analcime that were formed directly from glass. The lateral facies distributions resulted from the differences in salinity and pH of pore water trapped during deposition of the tuffs, but vertical distributions in vitric tuffs seem to have been controlled by the glass/liquid ratio of the reacting system and the permeability or diffusion rate of alkali elements. The Bigadiç, Emet and Kirka zeolite deposits which were formed in saline basins rich in Ca and Mg ions, show similar chemical changes, i.e. loss of alkalis and gain in alkaline-earth elements that have taken place during the diagenetic transformation of rhyolitic glasses to dioctahedral smectites or clinoptilolite. The absence of sodic zeolites such as mordenite, erionite, chabazite and silica-rich phillipsite is mainly due to the very high K/Na ratio of the starting materials rather than initial alkaline conditions or high Na content in lake waters.

Gündogdu, M. N.; Yalçin, H.; Temel, A.; Clauer, N.

1996-09-01

109

Minerals produced during cooling and hydrothermal alteration of ash flow tuff from Yellowstone drill hole Y-5  

USGS Publications Warehouse

A rhyolitic ash-flow tuff in a hydrothermally active area within the Yellowstone caldera was drilled in 1967, and cores were studied to determine the nature and distribution of primary and secondary mineral phases. The rocks have undergone a complex history of crystallization and hydrothermal alteration since their emplacement 600,000 years ago. During cooling from magmatic temperatures, the glassy groundmass underwent either devitrification to alkali feldspar + ??-cristobalite ?? tridymite or granophyric crystallization to alkali feldspar + quartz. Associated with the zones of granophyric crystallization are prismatic quartz crystals in cavities similar to those termed miarolitic in plutonic rocks. Vapor-phase alkali feldspar, tridymite, magnetite, and sporadic ??-cristobalite were deposited in cavities and in void spaces of pumice fragments. Subsequently, some of the vapor-phase alkali feldspar crystals were replaced by microcrystalline quartz, and the vapor-phase minerals were frosted by a coating of saccharoidal quartz. Hydrothermal minerals occur primarily as linings and fillings of cavities and fractures and as altered mafic phenocrysts. Chalcedony is the dominant mineral related to the present hydrothermal regime and occurs as microcrystalline material mixed with various amounts of hematite and goethite. The chalcedony displays intricate layering and was apparently deposited as opal from silica-rich water. Hematite and goethite also replace both mafic phenocrysts and vapor-phase magnetite. Other conspicuous hydrothermal minerals include montmorillonite, pyrite, mordenite, calcite, and fluorite. Clinoptilolite, erionite, illite, kaolinite, and manganese oxides are sporadic. The hydrothermal minerals show little correlation with temperature, but bladed calcite is restricted to a zone of boiling in the tuff and clearly was deposited when CO2 was lost during boiling. Fractures and breccias filled with chalcedony are common throughout Y-5 and may have been produced by rapid disruption of rock caused by sudden decrease of fluid pressure in fractures, most likely a result of fracturing during resurgent doming in this part of the Yellowstone caldera. The chalcedony probably was deposited as opal or ??-cristobalite from a pre-existing silica floc that moved rapidly into the fractures and breccias immediately after the sudden pressure drop. ?? 1978.

Keith, T.E.C.; Muffler, L.J.P.

1978-01-01

110

Adsorption of Amino Acids (Ala, Cys, His, Met) on Zeolites: Fourier Transform Infrared and Raman Spectroscopy Investigations  

NASA Astrophysics Data System (ADS)

Minerals adsorb more amino acids with charged R-groups than amino acids with uncharged R-groups. Thus, the peptides that form from the condensation of amino acids on the surface of minerals should be composed of amino acid residues that are more charged than uncharged. However, most of the amino acids (74%) in today's proteins have an uncharged R-group. One mechanism with which to solve this paradox is the use of organophilic minerals such as zeolites. Over the range of pH (pH 2.66-4.50) used in these experiments, the R-group of histidine (His) is positively charged and neutral for alanine (Ala), cysteine (Cys), and methionine (Met). In acidic hydrothermal environments, the pH could be even lower than those used in this study. For the pH range studied, the zeolites were negatively charged, and the overall charge of all amino acids was positive. The conditions used here approximate those of prebiotic Earth. The most important finding of this work is that the relative concentrations of each amino acid (X=His, Met, Cys) to alanine (X/Ala) are close to 1.00. This is an important result with regard to prebiotic chemistry because it could be a solution for the paradox stated above. Pore size did not affect the adsorption of Cys and Met on zeolites, and the Si/Al ratio did not affect the adsorption of Cys, His, and Met. ZSM-5 could be used for the purification of Cys from other amino acids (Student-Newman-Keuls test, p<0.05), and mordenite could be used for separation of amino acids from each other (Student-Newman-Keuls test, p<0.05). As shown by Fourier transform infrared (FT-IR) spectra, Ala interacts with zeolites through the group, and methionine-zeolite interactions involve the COO, , and CH3 groups. FT-IR spectra show that the interaction between the zeolites and His is weak. Cys showed higher adsorption on all zeolites; however, the hydrophobic Van der Waals interaction between zeolites and Cys is too weak to produce any structural changes in the Cys groups (amine, carboxylic, sulfhydryl, etc.); thus, the FT-IR and Raman spectra are the same as those of solid Cys.

Carneiro, Cristine E. A.; de Santana, Henrique; Casado, Clara; Coronas, Joaquin; Zaia, Dimas A. M.

2011-06-01

111

Structure-property relationship of metal-organic frameworks (MOFs) and physisorbed off-gas radionuclides.  

SciTech Connect

We report on the host-guest interactions between metal-organic frameworks (MOFs) with various profiles and highly polarizable molecules (iodine), with emphasis on identifying preferential sorption sites in these systems. Radioactive iodine 129I, along with other volatile radionuclides (3H, 14C, Xe and Kr), represents a relevant component in the off-gas resulted during nuclear fuel reprocessing. Due to its very long half-life, 15.7 x 106 years, and potential health risks in humans, its efficient capture and long-term storage is of great importance. The leading iodine capture technology to date is based on trapping iodine in silver-exchanged mordenite. Our interests are directed towards improving existent capturing technologies, along with developing novel materials and alternative waste forms. Herein we report the first study that systematically monitors iodine loading onto MOFs, an emerging new class of porous solid-state materials. In this context, MOFs are of particular interest as: (i) they serve as ideal high capacity storage media, (ii) they hold potential for the selective adsorption from complex streams, due to their high versatility and tunability. This work highlights studies on both newly developed in our lab, and known highly porous MOFs that all possess distinct characteristics (specific surface area, pore volume, pore size, and dimension of the window access to the pore). The materials were loaded to saturation, where elemental iodine was introduced from solution, as well as from vapor phase. Uptakes in the range of {approx}125-150 wt% I2 sorbed were achieved, indicating that these materials outperform all other solid adsorbents to date in terms of overall capacity. Additionally, the loaded materials can be efficiently encapsulated in stable waste forms, including as low temperature sintering glasses. Ongoing studies are focused on gathering qualitative information with respect to localizing the physisorbed iodine molecules within the frameworks: X-ray single-crystal analyses, in conjunction with high pressure differential pair distribution function (d-PDF) studies aimed to identify preferential sites in the pores, and improve MOFs robustness. Furthermore, durability studies on the iodine loaded MOFs and subsequent waste forms include thermal analyses, SEM/EDS elemental mapping, and leach-durability testing. We anticipate for this in-depth analysis to further aid the design of advanced materials, capable to address major hallmarks: safe capture, stability and durability over extended timeframes.

Nenoff, Tina Maria; Chupas, Peter J. (Argonne National Laboratory); Garino, Terry J.; Rodriguez, Mark Andrew; Chapman, Karena W. (Argonne National Laboratory); Sava, Dorina Florentina

2010-11-01

112

FINAL REPORT REGULATORY OFF GAS EMISSIONS TESTING ON THE DM1200 MELTER SYSTEM USING HLW AND LAW SIMULANTS VSL-05R5830-1 REV 0 10/31/05  

SciTech Connect

The operational requirements for the River Protection Project - Waste Treatment Plant (RPP-WTP) Low Activity Waste (LAW) and High Level Waste (HLW) melter systems, together with the feed constituents, impose a number of challenges to the off-gas treatment system. The system must be robust from the standpoints of operational reliability and minimization of maintenance. The system must effectively control and remove a wide range of solid particulate matter, acid mists and gases, and organic constituents (including those arising from products of incomplete combustion of sugar and organics in the feed) to concentration levels below those imposed by regulatory requirements. The baseline design for the RPP-WTP LAW primary off-gas system includes a submerged bed scrubber (SBS), a wet electrostatic precipitator (WESP), and a high efficiency particulate air (HEPA) filter. The secondary off-gas system includes a sulfur-impregnated activated carbon bed (AC-S), a thermal catalytic oxidizer (TCO), a single-stage selective catalytic reduction NOx treatment system (SCR), and a packed-bed caustic scrubber (PBS). The baseline design for the RPP-WTP HLW primary off-gas system includes an SBS, a WESP, a high efficiency mist eliminator (HEME), and a HEPA filter. The HLW secondary off-gas system includes a sulfur-impregnated activated carbon bed, a silver mordenite bed, a TCO, and a single-stage SCR. The one-third scale HLW DM1200 Pilot Melter installed at the Vitreous State Laboratory (VSL) was equipped with a prototypical off-gas train to meet the needs for testing and confirmation of the performance of the baseline off-gas system design. Various modifications have been made to the DM1200 system as the details of the WTP design have evolved, including the installation of a silver mordenite column and an AC-S column for testing on a slipstream of the off-gas flow; the installation of a full-flow AC-S bed for the present tests was completed prior to initiation of testing. The DM1200 system was reconfigured to enable testing of the baseline HLW or LAW off-gas trains to perform off-gas emissions testing with both LAW and HLW simulants in the present work. During 2002 and 2003, many of these off-gas components were tested individually and in an integrated manner with the DM1200 Pilot Melter. Data from these tests are being used to support engineering design confirmation and to provide data to support air permitting activities. In fiscal year 2004, the WTP Project was directed by the Office of River Protection (ORP) to comply with Environmental Protection Agency (EPA) Maximum Achievable Control Technology (MACT) requirements for organics. This requires that the combined melter and off-gas system have destruction and removal efficiency (DRE) of >99.99% for principal organic dangerous constituents (PODCs). In order to provide confidence that the melter and off-gas system are able to achieve the required DRE, testing has been directed with both LAW and HLW feeds. The tests included both 'normal' and 'challenge' WTP melter conditions in order to obtain data for the potential range of operating conditions for the WTP melters and off-gas components. The WTP Project, Washington State Department of Ecology, and ORP have agreed that naphthalene will be used for testing to represent semi-volatile organics and allyl alcohol will be used to represent volatile organics. Testing was also performed to determine emissions of halides, metals, products of incomplete combustion (PICs), dioxins, furans, coplanar PCBs, total hydrocarbons, and COX and NOX, as well as the particle size distribution (PSD) of particulate matter discharged at the end of the off-gas train. A description of the melter test requirements and analytical methods used is provided in the Test Plan for this work. Test Exceptions were subsequently issued which changed the TCO catalyst, added total organic emissions (TOE) to exhaust sampling schedule, and allowing modification of the test conditions in response to attainable plenum temperatures as well as temperature increases in the sulfur impr

KRUGER AA; MATLACK KS; GONG W; BARDAKCI T; D'ANGELO NA; BRANDYS M; KOT WK; PEGG IL

2011-12-29

113

Geothermometry, geochronology, and mass transfer associated with hydrothermal alteration of a rhyolitic hyaloclastite from Ponza Island, Italy  

USGS Publications Warehouse

A rhyolitic hyaloclastite from Ponza Island, Italy, was hydrothermally altered, producing four distinct alteration zones based on X-ray diffraction mineralogy and field textures: (1) nonpervasive argillic zone; (2) propylitic zone; (3) silicic zone; and (4) sericitic zone. The unaltered hyaloclastite is volcanic breccia with clasts of vesiculated obsidian in a matrix of predominantly pumice lapilli. Incomplete alteration of the hyaloclastite resulted in the nonpervasive argillic zone, characterized by smectite and disordered opal-CT. The other three zones exhibit more complete alteration of the hyaloclastite. The propylitic zone is characterized by mixed-layer illite-smectite (I-S) with 10 to 85% I, mordenite, opal-C, and authigenic K-feldspar (akspar). The silicic zone is characterized by I-S with ???90% I, pure illite, quartz, akspar, and occasional albite. The sericitic zone consists primarily of I-S with ???66% I, pure illite, quartz, and minor akspar and pyrite. K/Ar dates of I-S indicate hydrothermal alteration occurred at 3.38 ?? 0.08 Ma. Oxygen isotope compositions of I-S systematically decrease from zones 1 to 4. In the argillic zone, smectite has ??18 O values of 21.7 to 22.0??? and I-S from the propylitic, silicic, and sericitic zones ranges from 14.5 to 16.3???, 12.5 to 14.0???, and 8.6 to 11.9???, respectively. ??18 O values for quartz from the silicic and sericitic zones range from 12.6 to 15.9???. By use of isotope fractionation equations and data from authigenic quartz-hosted primary fluid inclusions, alteration temperatures ranged from 50 to 65 ??C for the argillic zone, 85 to 125 ??C for the propylitic zone, 110 to 210 ??C for the silicic zone, and 145 to 225 ??C for the sericitic zone. Fluid inclusion data and calculated ??18 O water values indicate that hydrothermal fluids were seawater dominated. Mass-transfer calculations indicate that hydrothermal alteration proceeded in a relatively open chemical system and alteration in the sericitic zone involved the most extensive loss of chemical species, especially Si. Systematic gains in Mg occur in all alteration zones as a result of I-S clay mineral formation, and systematic losses of Na, Ca, and K occur in most zones. With the exception of Ca, calculations of mass transfer associated with hydrothermal alteration on Ponza agree with chemical fluxes observed in laboratory experiments involving hydrothermal reactions of rhyolite and seawater. The anomalous Ca loss at Ponza may be due to hydrothermal formation of anhydrite and later low-temperature dissolution. On the basis of Mg enrichments derived from circulating seawater, we estimate the following minimum water/rock ratios: 9, 3, 6, and 9 for the argillic, propylitic, silicic, and sericitic zones, respectively. Hydrothermal fluid pH for the propylitic and silicic zones was neutral to slightly basic and relatively acidic for the sericitic zone as a result of condensation of carbonic and perhaps other acids. Copyright ?? 2003 Elsevier Science Ltd.

Altaner, S.P.; Ylagan, R.F.; Savin, S.M.; Aronson, J.L.; Belkin, H.E.; Pozzuoli, A.

2003-01-01