Using bentonites to adsorb aflatoxin is an effective method of minimizing the toxicity of aflatoxin to animals and humans. Early studies indicated a more than 10-fold difference in aflatoxin adsorption capacity among different bentonites. The determining mineralogical and chemical properties of the clays in aflatoxin adsorption are still poorly understood. The objective of this study was to test the hypothesis that a bentonite’s selectivity and adsorption capacity for aflatoxin is mainly determined by the ‘size matching’ requirement, on a nm scale, between the non-polar interlayer surface domains and the aflatoxin molecules. The non-polar surface domain size of smectites was varied by (1) selecting smectites with different charge densities; and (2) changing the valence and the size of exchange cations to control the amount of water in the hydration shells of the cations. Infrared spectroscopy and X-ray diffraction were also used to characterize the aflatoxin-smectite complexes to investigate if layer-charge density would affect the bonding strength between aflatoxin and the minerals. A large aflatoxin adsorption capacity and high selectivity for aflatoxin were achieved by selecting smectites that had low charge density as represented by their <110 meq/100 g cation exchange capacity. An individual smectite’s selectivity and adsorption capacity for aflatoxin could be enhanced or weakened by replacing the exchange cation. When the smectite was saturated with divalent cations that have smaller hydrated radius (e.g. Ba2+), the smectite’s adsorption capacity and affinity for aflatoxin were enhanced. Aflatoxin entered the interlayer of all six smectites tested. The strength of its bonding to the smectites was not affected by the layer-charge density of the smectites. The results confirmed the importance of nm-scale polarity and size match between aflatoxin molecules and the adsorbing sites on smectite. The high selectivity for aflatoxin can be achieved by selecting a smectite with adequate charge density or by replacing the exchange cations with divalent cations that have low hydration energy.

The adsorption mechanisms of divalent cations in zeolite nanopore channels can vary as a function of their pore dimensions. The nanopore inner-sphere enhancement (NISE) theory predicts that ions may dehydrate inside small nanopore channels in order to adsorb more closely to the mineral surface if the nanopore channel is sufficiently small. The results of an electron paramagnetic resonance (EPR) spectroscopy study of Mn and Cu adsorption on the zeolite minerals zeolite Y (large nanopores), ZSM-5 (intermediate nanopores), and mordenite (small nanopores) are presented. The Cu and Mn cations both adsorbed via an outer-sphere mechanism on zeolite Y based on the similarity between the adsorbed spectra and the aqueous spectra. Conversely, Mn and Cu adsorbed via an inner-sphere mechanism on mordenite based on spectrum asymmetry and peak broadening of the adsorbed spectra. However, Mn adsorbed via an outer-sphere mechanism on ZSM-5, whereas Cu adsorbed on ZSM-5 shows a high degree of surface interaction that indicates that it is adsorbed closer to the mineral surface. Evidence of dehydration and immobility was more readily evident in the spectrum of mordenite than in that of ZSM-5, indicating that Cu was not as close to the surface on ZSM-5 as it was when adsorbed on mordenite. Divalent Mn cations are strongly hydrated and are held strongly only in zeolites with small nanopore channels. Divalent Cu cations are also strongly hydrated, but can dehydrate more easily, presumably due to the Jahn-Teller effect, and are held strongly in zeolites with medium-sized nanopore channels or smaller.

Bentonite deposits are rare in Brazil and most of their production comes from a single region. A new bentonite occurrence, the Formosa bentonite from northern Brazil, is described here. The occurrence is associated with altered Mesozoic volcanic rocks of the Parnaíba Sedimentary Basin, one of the largest continental flood basalt (CFB) provinces on Earth. The purpose of the present study was to evaluate the physical and chemical properties of a new smectite-bearing deposit in Brazil. Analysis has shown that the major mineral present in the Formosa bentonite is a dioctahedral smectite along with minor amounts of hematite, K-feldspar, and kaolinite. Quartz is absent. A Li+-saturation test (Hofmann-Klemen treatment) revealed a montmorillonite smectite; large interlayer-Mg2+ contents revealed by N2 adsorption/desorption and cation exchange capacity results suggested a Mg-bentonite. This characterization helped to explore the structure-functionality (reactivity) relationship and to develop index tests for industrial applications and the research of new materials.

Use of this material as a desiccant-grade bentonite is envisaged (desiccant-grade bentonites contain Mg2+ and/or Ca2+ as the dominant exchangeable cations), or it could be activated with Na+ for use in many industrial applications (e.g. as a drilling fluid or for pelletizing iron ore). The large areal occurrence of the flood basalts suggests the possibility of very large deposits of these bentonites, a promising new exploration target for this class of industrial minerals in northern Brazil.

Bentonite cake is usually formed on the excavated trench surface that is supported by the bentonite slurry during construction of slurry cutoff walls. The lower hydraulic conductivity of bentonite cakes formed during construction of slurry cutoff walls in comparison to backfill materials provides an additional benefit. In the present study, the hydraulic conductivities of bentonite cakes made using three different bentonites were estimated using the modified fluid-loss test under various pressures. Both the hydraulic conductivities of bentonite cakes and cutoff-wall backfill are important in evaluating the in situ hydraulic performance of slurry cutoff-wall construction. Three bentonite slurry concentrations of 4, 6, and 8% were used to fabricate bentonite cakes that represent common field conditions. X-ray diffraction, cation exchange capacity, and swell-index data were collected to characterize the bentonites. Two modified methods for analyzing fluid-loss test results were used to estimate bentonite cake hydraulic conductivities. In addition, the viscosity as a function of time was measured to explain the sealing capacities of the bentonite slurries. The bentonite-cake hydraulic conductivities ranged from 2.15×10−11 m/s to 2.88×10−10 m/s, which were 10 to 500 times lower than the cutoff wall backfill design. Experimental results for 4 and 6% bentonite slurries were relatively similar, but the 8% slurries were noticeably different. Calculated bentonite-cake thickness and stress distribution indicated that the local void ratio and hydraulic conductivity may vary across the cake thickness. The considerably lower bentonite-cake hydraulic conductivities compared to the cutoff wall backfill design show its significance in slurry cutoff-wall construction practices.

The collector for separating diasporic bauxite serves as a type of flotation reagent by adsorbing selectively on diaspore to make it hydrophobic enough to separate it from the aluminosilicates. Although the flotation process is considered economical in the desilication of Chinese diasporic bauxite, the existing collectors fail to separate these ores because of their poor adsorption selectivity over other minerals. The present study was an attempt to seek a collector for selective flotation of diaspore over aluminosilicates. A novel carboxyl hydroxamic acid compound, 2,2-bis(hydroxycarbamoyl) decanoic acid (BHDA), was designed and synthesized, and the flotation behavior of diaspore, kaolinite, and illite was investigated by flotation tests with BHDA. The interactions between the BHDA and the minerals were also explored by Fourier-transform infrared spectroscopy (FTIR), zeta-potential measurement, and density functional theory (DFT) calculation. Using BHDA as the collector, the pulp pH value affected the floatability of diaspore significantly while the floatability of kaolinite or illite was unaffected or only slightly affected. The dosage of BHDA had little effect on the floatability of the three minerals. The greatest difference in floatability between diaspore and aluminosilicates occurred at mid-range pulp pH (7). Large shifts in characteristic absorption peaks and new absorption peaks were observed for BHDA-treated diaspore but were absent from BHDA-treated aluminosilicates. The change in the negative zeta potential of diaspore was also greater than those of aluminosilicates in the presence of BHDA. The O atoms in the carboxyl and hydroxycarbamoyl of BHDA have highly negative charges, and favorable stereo conditions existed to form five- or six-membered rings, resulting in their coordination with the Al atoms of diaspore, leading to chemisorption in chelate rings; the adsorption of BHDA on kaolinite or illite, on the other hand, was mainly physical in nature. The BHDA was, therefore, highly selective in the flotation between diaspore and aluminosilicates and possibly suitable for the separation of diasporic bauxite.

Mineralization of microbial biomass is a common phenomenon in geothermal habitats, but knowledge of the structure of the minerals formed in these environments is limited. A combination of spectroscopic, microscopic, and stable isotopic methods, as well as the chemical analysis of spring water, were employed in the present study to characterize calcium carbonate minerals deposited in filamentous cyanobacterial mats in different locations of La Duke hot spring, a circumneutral thermal feature near the north entrance of Yellowstone National Park, Montana, USA. Calcite was the primary crystalline mineral phase associated with biofilm-containing deposits closest to the source of the spring and the suspended microbial biomass in a pool further from the source. The carbonate minerals at all sites occurred as aggregated granules, ~2 μm in diameter, in close association with the microbial biomass. Only in the deposits closest to the source were the granules organized as laminated structures interspersed with microbial biomass. The calcium carbonate grains contained two distinct regions: a dense monolithic calcite core and a porous dendritic periphery containing organic matter (OM). Electron energy loss spectroscopy (EELS) indicated that the voids were infilled with OM and carbonates. The EELS technique was employed to distinguish the source of carbon in the organic matter and carbonate mixture. The studies of carbon isotope compositions of the calcium carbonates and the saturation indices for calcite in the spring waters suggest that processes (abiotic vs. biotic) controlling the carbonate formation may vary among the sampling sites.

The Brunauer-Emmett-Teller (BET) theory models the effective specific surface area and water content of solids as a function of the relative vapor pressure of water. A modified form of the BET equation has been used successfully to model water activity in concentrated electrolyte solutions as a function of electrolyte concentration. This modified form, referred to here as the Stokes-Robinson BET model, is based on the electrolyte molality rather than on the mass of solute sorbed. The present study evaluates the Stokes-Robinson form of the BET equation to model water-sorption data on two smectites with different layer charges. One smectite was saturated with Na+ and another with Na+, Ca2+, or Mg2+. These results are compared to the Stokes-Robinson BET results of aqueous electrolyte solutions. Given published data on cation exchange capacities and water-vapor sorption isotherms for various clays, the molality of the aqueous phase in contact with the clay surface is calculated and related to water activity. The Stokes-Robinson BET model was found to describe accurately the water activity as a function of cation molality below water activities of 0.5 for the smectites. Good relative agreement was obtained between the number of water binding sites predicted by the model and the experimental data reported in the literature for other smectites. Water molecules were found to have a significantly greater affinity for montmorillonite than electrolyte solutions with the same cation molality as the montmorillonite interlayer. This modified BET approach simplifies water-activity modeling in highly saline environments because the same equation can be used for both the liquid- and mineral-surface phases.

The mechanism of formation of detrital, beidellite-rich clay occurring in the Agadir basin (Morocco) is well documented, but its detailed characterization is incomplete which limits its application. The aim of the present study was to provide further details of the mineralogical and physico-chemical characteristics of this clay. Bulk raw clay and its Na+-saturated, <2 μm fraction were characterized using chemical, structural, and thermal techniques. Measurements of induced streaming potential (e.g. particle charge) and of specific surface area and porous volume are reported. The raw clay contained carbonate and quartz as associated minerals along with phyllosilicates (<2 μm particle size). X-ray diffraction and scanning electron microscopy analyses showed that the <2 μm fraction was dominated by a dioctahedral smectite. Because dehydroxylation of this mineral occurred at 510°C, and because it re-expanded in ethylene glycol after Li+-saturation followed by heating at 240°C for 24 h, the mineral was shown to be a beidellite rather than montmorillonite. This assertion was further supported by 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra showing predominantly negative charges in the tetrahedral sheets due to notable Al-for-Si substitutions. The chemical composition of the <2 μm fraction showed an Fe2O3 content which was ~7.52 wt.% greater than those of other beidellite occurrences but not so much that it would be identified as a nontronite. The absence of stretching and bending absorption bands corresponding to characteristic (Fe2OH) units in mid-infrared spectra and their corresponding fundamental overtones or combination bands in near-infrared spectra supported this notion. The structural formula of the beidellite in the present study was determined to be (Si7.51Al0.49)(Al2.99Fe0.68Mg0.33) (Ca0.03Na0.54Mg0.11)O20(OH)4, having dioctahedral ferruginous characteristics with almost 60% of the negative charge found in tetrahedral sheets. The cation exchange capacity determined from the structural formula was ~108 meq/100 g. The specific surface area and total pore volume were ~82.2 m2/g and 0.136 cm3/g, respectively. Interestingly, a detrital rather than a hydrothermal-alteration origin, as reported for other beidellite occurrences, explains its natural abundance and emphasizes the great interest in it.

The flavonoid naringin is the main source of the undesirable bitter taste in some citrus juices. In commercial debittering processes, the naringin is adsorbed on non-ionic polymeric resins. Organo-clays (OCs), which have been used as sorbents for organic pollutants, could also have affinity for the naringin molecule, and thus potentially could serve as a debittering agent. The objective of the present study was to characterize the sorption capacity of a prepared OC to evaluate its ability to remove naringin from aqueous solutions, investigating the effect of adsorbent dose, initial concentration of naringin, temperature, contact time, and pH. The OC was prepared by the intercalation of cationic surfactant hexadecyltrimethylammonium bromide in a Mexican bentonite. The host clay and the OC were characterized by X-ray diffraction, Fourier-transform infrared, and nitrogen gas adsorption. The OC showed a surface area of 9.3 m2 g-1, 11.35 nm average pore diameter, and a basal spacing, d001, of 2.01 nm. The adsorbent removed naringin at the rate of 60-72% at 25°C and pH 3. The sorption capacity increased with pH and temperature. Experimental data were well fitted by both Langmuir and Freundlich adsorption models. Most of the sorption took place during the first 10 min and the equilibrium time was reached within 720 min. The rate of sorption was adjusted to pseudo second-order kinetics.

The purpose of the present investigation was to apply a discriminant function analysis (DFA) to quantitative mineralogical data from 124 Paleogene and Neogene bentonitic clays from the northern Western Desert of Egypt in order to establish an objective procedure for grouping the samples at three distinctly recognizable, but partially overlapping, levels of classification. These levels were province or geographic region, geologic age, and quarry. Quantitative mineralogical data were obtained by means of X-ray diffraction procedures employing least-squares fitting of simulated and standard mineral patterns with those from the laboratory. All data were transformed by a log-ratio procedure prior to the DFA. Fe-rich smectite (Feoct-1.4 a.p.f.u.), coarsely crystalline kaolinite, Fe-poor I-S (random with 60% S layers), quartz, and illite were the most important discriminator minerals. S-moderate I-S (random with 70% S), S-rich I-S (random with 80% S), two varieties of finely crystalline kaolinite, feldspar, and amorphous matter were also present. Calcite and gypsum were present in some samples. The median wt.% values for Fe-rich smectite, coarsely crystalline kaolinite, Fe-poor I-S, quartz, and illite in all samples were 16.6, 16.0, 15.2, 4.2, and 3.7, respectively. Abundances of quartz and feldspar have a good positive correlation, and finely crystalline kaolinite and Fe-rich smectite are negatively correlated. Other specific mineral associations are difficult to interpret visually because of the numbers of classes and variables employed in the investigation; however, DFA was successful in identifying statistically significant differences amongst the groups.

At the province level, the back-classification of the samples was successful 92% of the time at the highest probability level, or 100% if the first plus second probability results were utilized. For samples of the same age, 80% of the first-choice assignments were correct and >90% were correct when the second choice was included. At the quarry level, the predictability rate ranged from 76 to >90%. Using both probability results, only seven of the samples were misclassified. In a blind test of quarry samples, the DFA assignment was 80% correct. These tests confirm the objective reliability of class assignments based on DFA. Results based on this data set can be used to classify new samples in future geologic interpretations and economic exploitation of the deposits in the region.

Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proved to be one of the most sensitive parameters for detecting changes of mineral properties such as swelling capacity and illitization in alteration experiments. Whether measured differences in CEC values of bentonite buffer samples before and after an experiment are (1) actual differences caused by clay structural changes such as illitization or (2) simply data scatter due to the different methods used by international research teams is an open question. The aim of this study was to measure the CEC of clay samples in five different laboratories using the same method and to evaluate the precision of the values measured. The Cu-trien method and four reference materials of the Alternative Buffer Material (ABM) test project in Äspö, Sweden, were chosen for this interlaboratory study. The precision of the Cu-trien method, which uses visible spectroscopy, was very good with a standard deviation of ±0.7–2.1 meq/100 g for CECs that ranged from 11 to 87 meq/100 g. For the same CEC range, analysis of Cu-trien index cations using inductively coupled plasma (mass spectrometry) and atomic absorption spectroscopy were less precise with a standard deviation of ±2.8–3.9 meq/100 g. Based on the measured precision, greater measured differences in Cu-trien CEC and exchangeable cation values of bentonite buffer samples, before and after an experiment, might be actual differences. Great care must be taken when interpreting measured CEC differences, and analytical characterization of any structural changes may be needed. Compared with results from the ‘International Soil-Analytical Exchange’ (iSE) program for soils, most absolute concentrations were much larger for the clays studied; however, for the two parameters exchangeable Ca2+ and CEC the range was similar to the iSE ring test and, most importantly, the precision was comparable. Future studies should discuss the accuracy of CEC and exchangeable cation values and compare them to alternative CEC methods in which care is taken to prevent dissolution of soluble minerals, such as calcite and gypsum.

K-Ar measurements were used in this study of upland Savannah River Site soils to distinguish between sorbed K and the K remaining in remnants of primary minerals. Study of sorbed K contributes to understanding further the interaction of alkali metals (Cs in particular) with the soils. Primary mineral K and the associated radiogenic Ar were studied to characterize soil mica with respect to its provenance and its relationship to hydroxy-interlayered vermiculite. K-Ar age values of Na-saturated clay fractions from five samples of these soils range in age from 270 to 370 Ma. After a moderate acid treatment (6% HNO3 v/v, ~1 mol dm-3, 3 h, 80°C) of the clay fractions, K-Ar age values (270-325 Ma) were little changed on the whole, but they were more closely grouped near 300 Ma. Earlier work had shown that most of the K in these soils is found in material resistant to moderate acid extraction. The K-Ar age values show that this acid-resistant material is much older than any pedogenic minerals could be, even much older than the sedimentary parent rocks from which the soils were derived. These observations support earlier inferences by others that the K in these well leached soils is largely in remnants of primary muscovite from the parent sediments. Age values near 300 Ma suggest that the muscovite is largely from proximal Piedmont terranes of the Appalachian orogen, where the K-Ar relationship in most micas was set by Alleghanian tectonic processes late in the Paleozoic Era. The structural location of the K within mica, shown by the retention of the associated radiogenic Ar, is in contrast to the sorption-dominated behavior of the Cs and most of the Rb in these soils during pedogenesis. Stronger acid treatment (~6 mol dm-3 HNO3, 3 h, 100°C) extracted substantial fractions of both the K and the radiogenic Ar from bulk-soil portions, indicating destruction of some of the primary mica. K-Ar age values for the sand-rich bulk soils were not useful for this study because the sand contains excess radiogenic Ar, probably in sand-sized vein quartz.

Freshwater has become increasingly scarce in many countries. To reduce the consumption of freshwater, the use of saline water resources in industry could provide an opportunity to meet the challenge of water-supply sustainability. However, the presence of electrolytes in saline water causes the coagulation of kaolinite, the colloid stability of which plays a key role in the processing of a number of minerals. Therefore, the dispersion of kaolinite in saline water was studied here. Electrophoretic mobility and colloid stability studies were conducted on a sodium hexametaphosphate-kaolinite system in the presence of NaCl, KCl, CaCl2, and MgCl2, the major electrolytes in saline water resources. The effect of each electrolyte on kaolinite dispersion was studied. Based on the studies of individual electrolytes, a method was developed to disperse kaolinite in 1:1 diluted synthetic seawater with distilled water, which may potentially reduce the consumption of freshwater by 50% when applied in industry.

This study uses the data from Miocene rocks of the Carpathian Foredeep to test the performance of the computer programs QUANTA and BESTMIN in aiding the interpretation of geophysical log data. These programs were designed to help trace trends in the mineral composition of rocks, the chemical composition of minerals, and the effects of these data on petrophysical and geophysical logging parameters. Chemical and X-ray diffraction data for 65 samples of shales, sandstones, and carbonates taken from cored wells in the molasse basin of the Carpathian Foredeep were processed. Compositional differences were detected between rocks sourced from the platform and rocks sourced from the Carpathians. Quartz, K-feldspar, and zircon were more abundant in the coarse-grained rocks (sandstones), while calcite, ankerite, siderite, pyrite, barite, halite, celestite, apatite, anatase, chlorite, 2:1 minerals, and organic matter were more abundant in the fine-grained rocks (shales). Plagioclase reached its maximum in coarse shales. Ankerite, chlorite, and dioctahedral 2:1 minerals had more Fe in the coarse-grained rocks. The dioctahedral 2:1 minerals in fine-grained rocks had a greater concentration of smectitic layers. This information permitted the precise calculation of grain density, porosity, adsorbed water, and some geophysical logging parameters. It also permitted the calibration of well-log response, in particular, the macroscopic neutron absorption cross-section (Σa) combined with the photoelectric absorption factor (P{e}) or with Pe + Ca (calcium content, measurable in wells by spectroscopic techniques) with porosity and cation exchange capacity (CEC). The NaCl concentration in the pore waters was found to range from the values typical for seawater in shales to the freshwater level in clean sandstones.

Phenol and its derivatives are regarded as ‘priority pollutants’ and p-nitrophenol (p-NP), in particular, is of great interest due to its toxicity and frequent presence in waste waters and fresh waters. Straightforward, inexpensive methods to identify p-NP in water, however, is lacking. In the present study, an electrochemical technique using clay-modified electrodes to measure p-NP was investigated as a potentially promising method to fill that gap. A glassy carbon electrode (GCE) was modified with a thin layer of Na-enriched bentonite and a series of benzyltrimethylammonium (BTMA+)-bentonites (BTMA+-B) in order to confirm these materials as p-NP electrosensitive. A series of organobentonites was synthesized using different BTMA+/bentonite ratios. The materials obtained were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, and a low-temperature nitrogen adsorptiondesorption method. A monolayer arrangement of BTMA+ within the interlamellar region of beidellite-rich smectite was confirmed. Deterioration of the textural properties was observed with increase of BTMA+ loading. The electro-oxidation of p-NP in an acidic medium on BTMA+-B-modified GCE was investigated. The cyclic voltammetry method with a three-electrode cell was used. The reference electrode was Ag/AgCl in 3 M KCl and a Pt foil was the counter electrode. For each electrochemical measurement, a different BTMA+ loading in BTMA+-B was used as the material for GCE coating and applied as the working electrode. The electrochemical activity of BTMA+-B-based electrodes increased with BTMA+ loading. The results confirmed that the organophylic character of the BTMA+-B-modified surface was the main influence on the electrochemical activity of the BTMA+-B-based GCE; the influence of textural properties was almost negligible. The increased electrode activity toward p-NP was achieved by the adsorption of p-NP on the electrode surface, the process that commonly precedes the electro-oxidation. The present study showed that synthesized materials could potentially be used in an electrochemical test for the presence of p-NP in water solutions.

Synthesized zeolites are extremely important as industrial minerals and are most commonly prepared using organic templates. Because these organic templates present undesirable environmental hazards, a synthesis method which avoids their use is desirable. The objective of the current study was to develop such a synthesis method. Zeolite NaY was synthesized hydrothermally starting from a mixture of 1.0 Al2O3:10 SiO2:4.6 Na2O:180 H2O molar gel composition, without adding any organic additives. Experiments were carried out to investigate the effects of molar compositions including water content (H2O/SiO2), crystallization conditions including temperature, and time on the crystal size and yield of NaY-type zeolite. The results showed that increasing the crystallization time from 5 to 12 h increased the crystal size, while increasing the crystallization temperature from 80 to 100°C also increased crystallinity. The crystal species of zeolite NaY were characterized by X-ray diffraction, X-ray fluorescence, and scanning electron microscopy analysis. Zeolite NaY crystals in the size range 25–150 nm were synthesized successfully over a period of 8 h at 100°C.

Recognizing weathering effects is significant for any work carried out on glauconites at the surface. The mineralogy and chemistry of glauconite grains exposed to weathering in a hot arid climate for a maximum of 42 y were studied here. The objective of the study was to find the mineralogical and chemical differences between weathered glauconite from the surface and fresh glauconite from the subsurface.

One specific glauconite-bearing layer at the surface (Layer 16) of the Abu Tartur phosphate mine, located in the Western Desert of Egypt, was studied in detail and compared to a fresh, subsurface glauconitic sandstone from the underground mine.

Even within this single surface layer, the brownish-green glauconite grains vary in color and chemical composition. From top to bottom, the grains show an increase in Fe and K and a decrease in Al and S. In addition, the grains show an internal color zonation caused by variation of Fe and K contents between the center and rim of the grains. The differences in color and chemical composition are even more pronounced between the weathered-glauconite grains from the surface and the fresh glauconite grains from the subsurface which are dark green and enriched in Fe and K.

The clay fractions consisted of mixed-layer glauconite (illite)-smectite, with the surface samples containing more expandable smectite (50%) than the subsurface samples (20%). In the charge-distribution diagram for muscovite-pyrophyllite-celadonite, the weathered glauconites at the surface showed a clear trend from smectitic glauconite at the top to illitic glauconite at the bottom of the layer, whereas the fresh subsurface sample plotted exactly in the glauconite field.

The color, mineralogy, and chemistry indicate that the surface samples were strongly altered by weathering processes and that glauconite transformed progressively into Fe-rich mixed-layer illite-smectite and then into smectites.Weathering can thus completely reverse the glauconitization process. For any chemical and mineralogical characterization of glauconites at the surface, these weathering effects must be taken into consideration.

X-ray diffraction patterns of oriented mounts of clay minerals are often used in clay mineralogy for qualitative and quantitative purposes. Fequently occurring stacking defects, in particular, can be characterized by this technique. Modeling of these diffraction profiles has become an important tool in obtaining structural information about the nature of stacking order. Manual matching of calculated and observed patterns is time consuming and user dependent. Automatic refinement procedures are, therefore, desirable. An improved approach for the treatment of disordered layer structures within a Rietveld refinement is presented here. The recursive calculation of structure factors, similar to that of the simulation program DIFFaX, was introduced in the Rietveld code BGMN. Complete implementation is formulated within the interpreter language of the Rietveld code and is transparent as well as flexible. Such a method has opened the application of Rietveld refinement to patterns of oriented mounts where only basal reflections of stacking disordered structures were recorded. The DIFFaX code was used to simulate basal reflections of illite-smectite mixed layers (I-S) with different ratios of illitic and smectitic layers and with different degrees of long-range ordering (Reichweite). Rietveld refinements with these simulated patterns were used to evaluate the application of this new approach. Several I-S with different degrees of ordering were also chosen as tests for the refinement of basal reflections. The samples were prepared as standard airdried and ethylene glycol-solvated, oriented specimens. Realistic structural parameters were obtained for the composition and ordering of the I-S.

Bentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proven to be one of the most sensitive parameters for detecting changes in mineral properties in bentonite-alteration experiments. An interlaboratory study of CECs and exchangeable cations for three reference bentonite buffer materials that were used in the Alternative Buffer Material test (ABM) project in Äspö, Sweden, was conducted to create a suitable database. The present study focused on CEC accuracy and compared CEC methods where care was taken to prevent dissolution of soluble minerals such as calcite and gypsum. The overall quality of the CEC and exchangeable cation values measured using non-Cu-trien CEC methods were good, with CECs of 74–91±0.5–3.3 meq/100 g and exchangeable cation values of 22–61±1.2–3.9 meq/100 g Na+, 7–23±0.8–1.5 meq/100 g Mg2+, and 19–39±0.8–1.6 meq/ 100 g Ca2+. The precision was comparable to the standard Cu-trien method even for exchangeable Ca2+, although the laboratories used different solution/solid ratios and reaction-time parameters for Cu-trien which affect carbonate dissolution. The MX80 and Dep.CAN bentonite exchangeable Ca2+ values were more accurate than standard-Cu-trien values. Using the optimized methods of this study, MX80 and Dep.CAN exchangeable Ca2+ values averaged 20.2±1.6 and 38.8±1.4 meq/100 g which amounts to ~70% of the inflated Cu-trien values. A more complex analysis of the CEC data using different methods, anion analyses, and mineralogical analysis is necessary to obtain plausible and accurate CEC values. Even with a more complicated analytical procedure, the CEC and exchangeable cation values were still not accurate enough because of excess anions. Chloride, sulfate, and dolomite might have increased the exchangeable Na+, Mg2+, and Ca2+ values.

Attempts at optical resolution and asymmetric syntheses using smectite clay minerals are described. Use of the method was prompted by the discovery that the saturated adsorption of a tris(chelated) metal complex, [Ru(1,10-phenanthroline)3]2+, by Na-montmorillonite depended heavily on the stereochemical properties. The pure enantiomer was adsorbed by cation exchange at negative surface sites of the clay mineral, while the racemic mixture was adsorbed to two times excess of the cation exchange capacity. The chelate takes a uniform orientation on a clay mineral surface due to the matching between the molecular symmetry and the two-dimensional network of a phyllosilicate layer. On a clay mineral surface covered with the enantiomeric chelates, a vacant space capable of chiral discrimination was generated. Based on this, an ion-exchange adduct of smectite and the chiral chelate was used as an adsorbent for separating racemic mixtures or selectively producing either one of the optical isomers.