The effects of exchanged cation and layer charge on the sorption of water and ethylene glycol monoethyl ether (EGME) vapors on montmorillonite have been studied on SAz-1 and SWy-1 source clays, each exchanged respectively with Ca, Na, K, Cs and tetramethylammonium (TMA) cations. The corresponding lattice expansions were also determined, and the corresponding N2 adsorption data were provided for comparison. For clays exchanged with cations of low hydrating powers (such as K, Cs and TMA), water shows a notably lower uptake than does N2 at low relative pressures (P/P0). By contrast, EGME shows higher uptakes than N2 on all exchanged clays at all P/P0. The anomaly for water is attributed to its relatively low attraction for siloxane surfaces of montmorillonite because of its high cohesive energy density. In addition to solvating cations and expanding interlayers, water and EGME vapors condense into small clay pores and interlayer voids created by interlayer expansion. The initial (dry) interlayer separation varies more significantly with cation type than with layer charge; the water-saturated interlayer separation varies more with cation type than the EGME-saturated interlayer separation. Because of the differences in surface adsorption and interlayer expansion for water and EGME, no general correspondence is found between the isotherms of water and EGME on exchanged clays, nor is a simple relation observed between the overall uptake of either vapor and the cation solvating power. The excess interlayer capacities of water and of EGME that result from lattice expansion of the exchanged clays are estimated by correcting for amounts of vapor adsorption on planar clay surfaces and of vapor condensation into intrinsic clay pores. The resulting data follow more closely the relative solvating powers of the exchanged cations.

Ferruginous beidellites with Al:Fe atomic ratios up to 2.36 were obtained when solutions containing Al, Fe2+ and H4SiO4 were adjusted to pH 8.5 with Ca(OH)2 and incubated at 95 °C in the presence of CaCO3 as a pH buffer. Incubation took place under cyclic reducing and oxidizing conditions achieved by adding 2 mM hydrazine at 14–15-d intervals over a period of 10–13 weeks. During the 14–15-d cycle, atmospheric oxygen slowly diffused through the high-density polyethylene bottles used, causing a slow oxidation of Fe(II) to Fe(III). The infrared (IR) spectra of the products approached that of natural beidellite, but indicated little change in octahedral Al:Fe ratio in the products for starting Al:Fe ratios from 2.5 up to 3.5, which was the highest Al:Fe ratio at which a well-crystallized product was obtained. Chemical analysis showed the presence of more Al+Fe in the products than could be incorporated into a dioctahedral formula. After the excess was assigned to a hydroxy-aluminium interlayer, the formula of the most Al-rich beidellite was calculated to be 0.575Ca(Si6.85A1.15)(Al2.47Fe1.53)O20(OH)4. This composition lay within the range recorded for the ferruginous beidellites that form in Vertisols.

Motion of the guest molecules in kaolinite/dimethyl sulfoxide (DMSO) intercalation compounds Al2Si2O5(OH)4∙(CH3)2SO has been studied by means of solid-state nuclear magnetic resonance (NMR) in the temperature range between 300 and 380 K, which is just below the evolution temperature. The 13C magic angle spinning (MAS) NMR spectra show 2 inequivalent methyl carbons: 1 methyl carbon is keyed in the ditrigonal hole of the silicate sheet, while the other is located parallel to the sheet. Above 320 K, the 2 peaks have different intensities, suggesting that the keyed methyl groups from some of the DMSO molecules are released from the hole. The 2H NMR spectra have been measured for kaolinite/DMSO-d6 intercalate. The methyl group of the interlayer DMSO molecule undergoes free rotation around its C3 axis over the temperature range studied. The axis of rotation is fixed at the low temperature (about 160 K), and the methyl group initiates a wobbling motion whose amplitude increases with temperature. The wobbling angles have an anisotropy, estimated from theoretical analysis of the 2H spectral line shapes. The DMSO molecules released from the silicate layer undergo anisotropic rotation of the whole molecule.

Yucca Mountain, Nevada, is being investigated to determine its suitability to host a potential high-level radioactive waste respository. An important reason for its choice as a potential repository site was the presence of thick zeolite-rich horizons in the altered volcanic tufts that compose the mountain. Clinoptilolite is the most abundant zeolite at Yucca Mountain and may be important in radionuclide retardation and in determining hydrologic properties. Therefore, it is necessary to understand the geochemical conditions affecting its long-term stability. For example, it has been suggested that long-term, repository-induced heating of the rocks at Yucca Mountain may lead to the transformation of clinoptilolite to analcime, thereby significantly affecting the hydrologic properties and retardation capabilities of the rock.

Thermodynamic modeling of clinoptilolite-analcime equilibria was conducted with the program Ge0-Calc PTA-SYSTEM using estimated thermodynamic data for measured chemical compositions of clinoptilolite and analcime at Yucca Mountain. Log[aK+)2/aCa2+] versus log[aNa+)2/aCa2+] diagrams were calculated to model the conditions under which clinoptilolite may transform to analcime. Temperature, relative cation abundances and silica activity are all important factors in determining clinoptilolite-analcime equilibria. Increased Na+ concentrations in either clinoptilolite or the fluid phase, increased clinoptilolite K+ concentration, increased temperature and decreased aqueous silica activity all stabilize analcime relative to clinoptilolite, assuming present-day Yucca Mountain water compositions. However, increased Ca2+ concentrations in either clinoptilolite or the fluid phase, increased aqueous K+ concentration and increased Al:Si ratios in clinoptilolite (heulandite) all stabilize clinoptilolite with respect to analcime.

Assuming well J-13 water as the analog chemistry for Yucca Mountain water, clinoptilolite should remain stable with respect to analcime if temperatures in the clinoptilolite-bearing horizons do not significantly exceed 100 °C. Even if temperatures rise significantly (for example, to 150 °C not all clinoptilolite should alter to analcime. Perhaps more importantly, thermodynamic modeling suggests that some Yucca Mountain clinoptilolites, particularly those rich in Ca and Al, will remain stable at elevated temperatures, even with an aqueous silica activity at quartz saturation.

Fifty-two Bidi-Koum bauxites from Guinea, Africa, of diversified chemical composition were characterized for their mineral composition. First, 14 element oxide concentrations were determined by X-ray fluorescence (XRF) using a fusion sample preparation technique. Loss of Mass (LOM) and organic carbon (OC) concentrations were also determined. The initial X-ray diffraction (XRD) phase quantification was carried out employing XDB software. This software allows for full interpretation of a sample diffractogram and helps generate initial concentrations of identified minerals based on a standardless approach. In the stage that followed, the mass balance procedure on the XDB software helped refine the final phase composition. Then, gibbsitic Al2O3 concentrations obtained by wet chemistry for all samples and kaolinitic SiO2 concentrations obtained for selected samples were compared with the concentrations obtained using the XDB software. Phases that were quantified are: gibbsite, boehmite, kaolinite, wavellite, goethite, hematite, quartz, anatase, rutile and illite. Phase concentrations were obtained for illite from K2O and for wavellite from P2O5 concentrations. The alumina substitution in the goethite lattice was also estimated.

Rehydration is shown to be straightforward for the reconstruction of polyoxometallate-pillared layered double hydroxides. Zn-Al hydrotalcite-like minerals were prepared with Zn/Al ratios of 1 to 5 by coprecipitation at pH 7. Good crystallinity was obtained for samples with Zn/Al ratios above 2. Thermal decomposition was achieved by calcining the samples at 300 to 900 °C. The calcined samples were exposed to decarbonated water, with or without hydrothermal treatment to evaluate reconstruction of the hydrotalcite-like minerals by rehydration. Restoration of the hydrotalcite-like structure was found to be independent of the Zn/Al ratios for samples calcined between 300 and 400 °C; however, asecond phase, aluminum hydroxide or zinc oxide, was generally detected. A spinel phase, formed during the calcination of samples at temperatures above 600 °C, inhibited reconstruction of the hydrotalcite-like phase. The rehydrated hydrotalcite-like minerals had Zn/Al ratios close to 2, irrespective of the chemistry of the starting material.

Utilizing high-resolution transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and X-raydiffraction (XRD) techniques, we have studied the transition from shallower smectite-rich mudrocks to deeper illite-rich mudrocks in Pliocene-age turbidite sediments from the northern Gulf of Mexico (GOM). Our objective in this work was to better understand how the smectite-illite transition may affect the onset of geopressuring in GOM sediments. The samples studied were sidewall cores from an offshore Louisiana well. In previous studies of GOM sediments, the smectite-to-illite reaction has mainly been documented in considerably older, Miocene-age sediments.

The results of this study elucidate the reaction mechanisms entailed in the transformation of clays in this sediment from smectitic to illitic. We found that illite formed at the expense of smectite in 2 ways: 1) growth of preexisting discrete illite flakes, and 2) creation of new illite layers within mixed-layer illite-smectite. Also, illitization apparently proceeded via a dissolution/precipitation, Al-conserving reaction rather than a solid-state, layer-conserving reaction. Smectite illitization is commonly believed to require input of K from feldspar dissolution. Our XRD results found little correlation between decreases in K-feldsparand increases of illite. However, in 1 instance TEM/EDS analyses indicated the presence of high-charge smectite, which suggests that insufficient K was available for illitization. TEM images also show small packets of authigenic chlorite in illite-rich mudrock. This chlorite may act as a sink for Fe liberated upon smectite illitization.

Fine kaolinite suspensions were mixed with unaged or aged FeCl3 in this experiment. The interaction between clay particles and Fe3+ hydrolysis products was studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The proportion of Fe adsorbed was measured and the electrical charge on the clay particles was determined by electrophoresis. The effect of this interaction on flocculation of clay suspensions was investigated in a series of sedimentation tests. The Fe3+ ions acted as counterions when their concentration was low and when unaged FeCl3 solution was used. Otherwise, their hydrolysis complexes acted as a bonding agent between kaolinite particles. The dispersion-flocculation behavior of kaolinite suspensions was found to be in agreement with the theory of Derjaguin, Landau, Verwey and Overbeek (DLVO), as the sedimentation behavior could be predicted from the data of zeta potentials (ζ).

There has been much interest in the rare specimen of beidellite from the Black Jack Mine, Florida Mountain, Idaho. A variety of aluminous clays exists along veins such as the Black Jack vein, in rhyolite and latite flows, and in near-surface ash beds, often containing less than 1.0% MgO and 0.5% Na20. Associated clays include beidellite, illite, kaolinite, 10-Å halloysite, dickite, nacrite, rectorite and a tarasovite-like mineral. The predominant clay is mixed-layer illite—beidellite. The beidellites have Al2O3 contents ranging from about 28 to 33%, and predominantly Ca and K as interlayer cations. The typical beidellite dehydroxylation temperatures of about 595 °C readily differentiate the beidellite from montmorillonite, which has a dehydroxylation temperature in the range of 735 °C. A modified differential thermal analysis (DTA) method is given for readily estimating the interlayer cation populations of smectites, including Mg++ and Al+++ cations. Chemical analyses and layer charges of II beidellites from mines around the Black Jack Mine are given. The beidellites have an American Society for Testing and Materials (ASTM) classification of CR, φ value, internal friction angle of about 8° and an expansion pressure of about 9 kgf/cm2 (88.3 kPa), similar to that of nontronite.

Iron-manganese concretions are common in upper sola of Alfisols in the Inner Bluegrass Region of Kentucky. Their nature and quantities appear to be related to the fluctuation of seasonal perched water tables above clayey argillic horizons. This study was conducted to examine changes in the macro-and micromorphology, chemistry and mineralogy of concretions as a function of size, color and soil depth. Total Mn and Fe contents increased, while SiO2 decreased with concretion size. Black concretions contained higher Mn, while brown concretions were higher in Fe. Crystalline Mn- and Fe-oxides fractionated with a sequential extraction procedure increased, but amorphous Mn and Fe decreased with concretion size. Goethite was the only crystalline Fe oxide mineral identified by X-ray diffraction (XRD) analysis. Manganese oxide minerals were very difficult to detect due to the diffuse nature of their XRD peaks and poor crystallinity. Examination of soil thin sections showed concretions of soil horizons overlying restrictive clayey layers to exhibit differentiated fabrics, sharp external boundaries and generally spherical shapes. Concretions found within clayey restrictive layers or above lithic interfaces usually had less structural organization, softer matrices and diffuse external boundaries due to longer term saturated conditions. Scanning electron microscopy (SEM) examinations suggested that the concretionary matrix, in spite of its density, has numerous cavities and an extensive micropore system within which dissolved plasmic Fe and Mn can diffuse and precipitate.

The use of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory in colloid science has continued to the present day in spite of the inability of this theory to explain, even qualitatively, numerous phenomena exhibited by clays and other colloidal materials. An alternative description of the fundamental forces involved in the formation of dispersions and gels was presented in 1938 by Langmuir, but was never widely accepted among colloid scientists. Recent experimental and theoretical work, particularly in Japan, has revived this alternative view, in which a long-range Coulombic attraction force appears to explain several phenomena, particularly transitions among ordered and disordered phases of colloidal particles in dilute salt solutions.

Examples are given from surface chemistry where rather complex models based on diffuse double layer theory are used to explain chemical adsorption behavior that often has a simpler explanation. It is argued that the rule of parsimony (Ockham's Razor) should be applied to complex models that appear to explain the data at hand before such models are taken to be generally valid. A satisfactory fit of model predictions to experimental data obtained under a very limited range of conditions does not prove the validity of the model. Thus, it is concluded that the DLVO theory and its modifications fail to meet the 2 criteria necessary to the acceptance of a theory: agreement with observations and simplicity.

Formation processes of weathering products of pumice collected from a rhyolitic pyroclastic flow deposit were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). SEM clearly showed the presence of some weathering products adhering to the surface of pumice. XRD showed that the products were composed mainly of noncrystalline materials with a relatively small amount of halloysite (10 Å). TEM and EDX revealed texture transformation sequences from the earliest weathering product to a final product of halloysite as follows: 1) precipitation of very thin flaky or film-like noncrystalline Al-hydroxide; 2) transformation into irregularly aggregated Al-Fe-Si-rich fibrous material; 3) morphological changes to rounded aggregates; 4) development of halloysite-like curled domains with successive decrease in Fe content; and 5) further development of curled domains in rounded aggregates. These materials must be metastable phases at early reaction stages with kinetics limiting formation of the stable equilibrium phase of kaolinite.

A 4-component clay-polymer-salt-water system was studied by neutron scattering. The clay-salt-water system consisted of n-butylammonium vermiculite, n-butylammonium chloride and heavy water, and the volume fraction of clay in the system was held constant, at r = 0.01. Three polymers in the molecular weight range 10,000 to 30,000 were studied, poly(vinyl methyl ether) (PVME), poly (ethylene oxide) (PEO) and poly(acrylic acid) (PAA), at a polymer volume fraction of v = 0.01. The addition of PAA suppressed the clay swelling, irrespective of the salt concentration, c. The addition of the neutral polymers had no effect on the phase transition temperature, Tc, between the gel and tactoid phases of the system, its value remaining at 14 °C for c = 0.1 M and 30 °C for c = 0.01 M. At c = 0.01 M, the neutral polymers also had a negligible effect on the lattice constant d along the swelling axis of the clay colloid, but at c = 0.1 M, the d-value was significantly lower than in the system without added polymer. For a PVME sample of molecular weight 18,000, both d and Tc were measured as a function of ν, for volume fractions between 0 and 0.04. The addition of polymer, up to v = 0.04, had no effect on Tc. However, even for v values as low as 0.001, the vermiculite layers in the gel phase were more parallel and more regularly spaced than in the system without added polymer. In the gel phase, d decreased exponentially as a function of v, from 12 nm at v = 0 to 8 nm at v = 0.04. In the tactoid phase, at T < 14 °C, the d-value in the crystalline regions was equal to 1.94 nm at v = 0 and v = 0.04, showing that the spacing between the vermiculite layers is not affected by the added polymer when they are collapsed by an increase in temperature. The addition of a PVME sample of molecular weight 110,000, at v = 0.001, had no noticeable effect on either d or Tc.

A thorough understanding of the capacity of clay minerals to adsorb radiocesium is essential in order to predict the fate of this pollutant in the environment and to interpret routine measurements, such as desorbability. We have investigated the adsorption of radiocesium onto 2 contrasting reference clay minerals in dilute suspensions after a 2-h contact period. The results have been expressed as the distribution coefficient, Kd, or the selectivity coefficient, Kc. The adsorption properties have been studied with respect to various parameters: nature of the charge compensating cation, ionic strength, concentration of Cs, concentration of K and concentration of a soil-extracted fulvic acid.

A Freundlich isotherm has been found to fit experimental data well for levels of adsorbed cesium in the range 10−7 to 1 mol kg−1. Evidence of surface heterogeneity is discussed, but it was not possible to deduce the exchange capacities of the groups of exchange sites with differing affinities for Cs, which are thought to exist in illites. The concentration dependence of adsorption upon montmorillonite is postulated to arise from a modification of the exchange complex with increasing presence of Cs, rather than from heterogeneity of exchange sites. Increasing ionic strength caused a decrease in the relative affinity for a trace amount of cesium on both minerals, although mass action led to a fall in Kd. This is thought to indicate a high covalent interaction between Cs and the clay surface.

Potassium caused a smaller decrease in adsorption than stable Cs, which suggests that neither K nor NH4 plays a decisive role in the immobilization of radiocesium by clay minerals. There was a small decrease in adsorption upon addition of soil organic matter, which may contribute to the poor fixation capacity observed for some soils with a high organic matter content.

Griffithite, a high Fe content saponite (Griffith Park, California) was pillared with Al polymeric solutions, using different Al/clay ratios. The cation exchange began when Al-polycation solutions were added, being completed during the dialysis of the samples. Pillared solids were obtained by calcination of intercalated precursors at 500 °C. The content of A12O3 increased from 7.35% in the natural griffithite to about 14% in the pillared samples, equivalent to the fixation of about 1.4 mmol Al per g of clay. The surface areas of the pillared griffithite were between 230–300 m2 g-1. The intercalation and pillaring of griffithite were easier than that of a less-crystalline nonferrous saponite.

This study characterizes various chemical and mineralogical properties of goethite and jarosite from a mine drainage environment using chemical extraction techniques, X-ray diffractometry (XRD), 57Fe Mössbauer spectroscopy and scanning electron microscopy (SEM). Goethite and jarosite precipitates were collected from leachate-contaminated soils and from groundwater samples that were stored for up to 3 y. The results indicate that the soil goethites have primarily microcrystalline morphologies with moderately large mean crystallite dimensions (MCD110 ∼ 40 nm), and are superparamagnetic at room temperature and magnetically ordered at 77 K. The substitution of Al for Fe in the goethites is less than 0.03 mol/mol, and there is consequently no measured contraction in the goethite unit cell volume. The jarosite unit cell dimensions, Mössbauer parameters and chemical compositions indicate that the precipitates are primarily well-crystallized K-Na-H3O solid solutions, although the presence of poorly crystalline H3O-rich jarosite is also identified in one sample.

A structural model for the geometry of Fe(III) octahedra near the surface of finely divided ferrihydrite was elaborated based on the bond-valence theory and by considering the interaction of water molecules in the 2 nearest hydration spheres. In contrast to bulk Fe atoms, which are bonded to bridging oxo (O) and hydroxo (OH) ligands, surface Fe atoms are also octahedrally coordinated to H2O ligands forming the 1st hydration shell ((H2O)I). In the wet state, external water molecules of the 2nd hydration shell ((H2O)II) are singly H-bonded to (H2O)I, while they are doubly coordinated in the dry state. Accordingly, wet ferrihydrite contains twice as many sorbed water molecules as dry ferrihydrite, and the structural difference due to the 2nd hydration shell accounts quantatively for the 15% increase of ferrihydrite weight experimentally measured in moist atmosphere. The interaction of surface Fe atoms with their 2 nearest hydration spheres modifies the geometry of surface Fe octahedra as compared to bulk octahedra, and idealized Fe-OH and Fe-H2O bond lengths in the wet and dry state were evaluated by the bond-valence theory. Our structural model provides a sound crystal-chemical basis to describe many apparent incongruities of Fe X-ray absorption near edge structure (K-XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopic data that have led to differing interpretations of the coordination environment of Fe in ferrihydrite by various investigators.