Deposits of sepiolite, trioctahedral smectite (mixed-layer kerolite/stevensite), calcite, and dolomite, found in the Amargosa Flat and Ash Meadows areas of the Amargosa Desert were formed by precipitation from nonsaline solutions. This mode of origin is indicated by crystal growth patterns, by the low Al content for the deposits, and by the absence of volcanoclastic textures. Evidence for low salinity is found in the isotopic compositions for the minerals, in the lack of abundant soluble salts in the deposits, and in the crystal habits of the dolomite. In addition, calculations show that modern spring water in the area can precipitate sepiolite, dolomite, and calcite following only minor evaporative concentration and equilibration with atmospheric CO2. However, precipitation of mixed-layer kerolite/stevensite may require a more saline environment. Mineral precipitation probably occurred during a pluvial period in shallow lakes or swamps fed by spring water from Paleozoic carbonate aquifers.

The use of neutron diffraction to determine some of the structural properties of montmorillonite-water systems at low water concentrations is described. The samples were prepared by compression or suction to give clay samples with between one and three molecular layers of water between the plates.

About 10% of the platelets in the clay are randomly oriented. The remainder are partially oriented in the plane of the sample, with an angular spread of 40° about the mean orientation. It is suggested that these oriented domains are formed from the larger platelets present in the system. The Bragg diffraction pattern is better explained by a disordered lattice model rather than by a mixture model with small particles having a well-defined lattice spacing. We have fitted both the intensities of (00l) reflections and the shape of the (001) reflection quantitatively to a model which allows for a Gaussian spread of platelet spacing about a mean value. The half width of the spread is about 10% of the lattice spacing.

No significant structural differences are found between Li, Na, K, and Cs montmorillonites. The method of preparation has no effect on the structural properties of the large platelet particles but does affect the randomly oriented fraction. The lattice spacing of the latter appears to be better defined for samples prepared by compression.

Experiments on the variation of lattice spacing with humidity indicate that the structural model we have used is adequate except at humidities where the system is changing over from one to two, or two to three water layers.

The term ‘montmorillonite’ encompasses a wide range of chemical compositions and structures. Comprehensive and reliable characterization is essential for unambiguous classification. Twenty eight purified, Na-exchanged smectites (<0.2 µm) were characterized by layer-charge measurement using the alkylammonium method, by cation exchange capacity (CEC) measurement with Cu-triethylenetetramine, by determination of the chemical composition using X-ray fluorescence analysis, by calculation of the structural formula following determination of the octahedral structure (trans-vacant vs. cis-vacant) by simultaneous thermal analysis, and by X-ray diffraction analysis. Mössbauer spectroscopy was applied to determine the oxidation state and coordination of Fe and changes thereof during purification of the source materials.

The charge derived from chemical composition was considerably greater (by up to 30%) than the measured layer charge. The independently measured layer charge was used to calculate the structural formula. The measured CEC values, comprising the permanent charges and the pH-dependent edge charges, were consistent with measured layer charge but not with layer charge derived from the chemical composition. Therefore, the structural formula of smectites should be calculated using the measured layer charge.

The dehydroxylation temperature, which conveys information about the structure of the octahedral sheet, was correlated to the amount of Mg and Fe3+ and the location of charges. No relationship was found among the dehydroxylation temperature and the mean layer charge or the Mg content. In contrast, a clear relationship was observed between the Fe content and the dehydroxylation temperature. Montmorillonites with an Fe content <0.3/f.u. are cis-vacant and those containing Fe3+ > 0.3 mol/f.u. are trans-vacant, mostly with additional cis-vacancies. Tetrahedral substitution also appeared to be a function of the number of trans-vacancies.

The parameters analyzed provide the basis for a new descriptive classification system.

Stable organomineral derivatives are formed by reaction of organochlorosilanes with certain phyllosilicates. Organosiloxyl functions are grafted on silanol groups present at external mineral surfaces.

Water molecules adsorbed on external mineral surfaces may cause hydrolysis of the reactant organosilicon products, with liberation of HCl. This, in turn, may react with the silicate: octahedral cations are extracted from the lattice and fresh Si-OH groups, capable of further grafting, are formed on the mineral surface.

On the other hand, when difunctional reagents such as methylvinyldichlorosilane are used and if the ratio of adsorbed water to added reactive is adequate, then polymeric species with polysiloxane chains are grafted on the mineral.

Because of its high content of silanol groups, sepiolite forms organomineral compounds having a relatively high organic matter content. With chrysotile, the amount of organic matter grafted to the silicate, is considerably smaller, but it increases appreciably if water is added to the reacting products. This is attributed to hydrolysis of the organic reactant and subsequent destruction of external “brucitic” layers by acid attack.

Solutions containing hydroxy-SiAl (HSA) oligocations were prepared by two procedures: (1) treatment of a mixture of orthosilicic acid and AlCl3 with aqueous NaOH, followed by aging of the product; and (2) preliminary preparation and aging of hydroxy-Al13 oligocations followed by reaction of the latter with orthosilicic acid. Ion exchange of Na,Ca-montmorillonite with HSA oligocations yielded pillared, cross-linked montmorillonites (designated as HSA-CLM) showing a maximum d(001) value of 19.5 Å for air-dried samples, and maximum surface areas of ~500 m2/g after outgassing at 250°C/10−3 torr. Corresponding ion exchange of Li-fluorhectorite yielded HSA fluorhectorites (HSA-CLFH) showing a maximum d(001) value of 19.0 Å and a surface area of 355 m2/g. Calculated structural formulae for the HSA-CLM and HSA-CLFH products, based on elemental analysis, showed a gradual increase in the Si/Al ratio in the intercalated HSA oligocations with increasing Si/Al ratio in the pillaring solution. Optimum d(001) values and surface areas of HSA-CLM and HSA-CLFH products were obtained using method 2 and applying a ratio of 1.6–2.5 mmole (Si)Al/g smectite.

The thermal stabilities of HSA-CLM and HSA-CLFH products were determined by heat treatment between 250° and 700°C and subsequent measurement of the d(001) values and surface areas. HSA-CLFH products showed the unusual behavior of increase of d(001) with increase in temperature from 400° to 500°C, and essential constancy of d(001) from 500° to 600°C. The HSA-CLM products showed a gradual decrease in surface area, whereas the HSA-CLFH products prepared with a Si/Al ratio of 1.04–2.18 in the pillaring solution showed constant surface areas with increasing temperature from 250° to 600°C. HSA-CLM and HSA-CLFH show sharply higher acidities compared with those of reference Al-CLM and Al-CLFH samples obtained by pillaring with hydroxy-Al13 oligocations. This increased acidity is probably due to the presence of acidic, surface silanol groups in the HSA oligocations.

The nature of Cu2+ adsorption by boehmite, gibbsite, and noncrystalline alumina was studied over a range of equilibrium pH (4.5–7.5) and Cu2+ concentration (10−3–10−8 M) by electron spin resonance (ESR). Available chemisorption sites at pH 4.5 were the most numerous for noncrystalline alumina (~1 mmole/100 g), less for boehmite, and least for gibbsite as indicated by the relative strength of the rigid-limit ESR signal attributed to Cu2+ adsorbed at discrete sites. The chemisorption process involved immobilization of Cu2+ by displacement of one or more H2O ligands by hydroxyl or surface oxygen ions, with the formation of at least one Cu-O-Al bond. As the pH was raised from 4.5 to 6.0, essentially all of the solution Cu2+ appeared to be adsorbed by the solids. However, the noncrystalline alumina and boehmite chemisorbed much of the total adsorbed Cu2+ (10 mmole/100 g), whereas precipitation or nucleation of Cu(OH)2 in the gibbsite system was indicated. Precipitated Cu2+ was more readily redissolved by exposure to NH3 vapor than chemisorbed Cu2+.

Deferration by reduction of free Fe2O3 with Na2S2O4 in the presence of Na citrate and NaHCO3 caused a change in valence state of 10 to 35 per cent of the total structural iron in micaceous vermiculites, soils, nontronite, and muscovite. An increase in Fe2+ on deferration was accompanied by an equivalent decrease in Fe3+. Subsequent treatment with H2O2 reoxidized the structural Fe2+ previously formed.

Sesquioxide coatings on micaceous vermiculites were examined electron microscopically. These coatings were composed predominantly of Fe2O3 with approximately 10 per cent by weight of Al2O3 and small amounts of SiO2, as determined by chemical analysis of the deferration extracts.

The cation exchange capacity (CEC) increased 10–60 per cent as a result of deferration of micaceous vermiculites and soils. Treatment of the deferrated sample with H2O2 restored the Fe3+ content to approximately the original value but the CEC was not affected. Consequently, the increase in CEC on deferration was attributed to the removal of the positively charged sesquioxide coating. The reversible change in valence of structural iron without an equivalent change in CEC was attributed to deprotonation-protonation of the structure (OH− ⇄ O2−) simultaneous with the oxidation-reduction of iron (Fe2+ ⇄ Fe3+) in the phyllosilicate layer.

In alkaline media and at 70°C dilute suspensions of ferrihydrite transformed to goethite between pH 11.2 and 14 and to a mixture of goethite and hematite above and below this pH range. Increasing the temperature of the transformation or the concentration of the suspension reduced the pH range in which goethite alone formed. The morphology of goethite was chiefly a function of the pH of the system. Acicular crystals formed at all pHs and exclusively above pH 12.2. Epitaxial twinned crystals predominated at pHs below 11, and twins free from hematite formed at higher pHs. Increasing the suspension concentration, ionic strength, or temperature extended the pH range over which twinned crystals formed. Electron micrographs showed that twins formed mainly during the initial stage of the transformation, whereas acicular crystals formed over a longer period. Thus, the twins appeared to nucleate in the ferrihydrite; nucleation of acicular particles took place in solution.

The hydrolysis of aluminum-tri-(sec-butoxide), ASB, in ionic and nonionic media is shown to be a useful method for the synthesis of aluminum minerals. Infrared and X-ray analysis were used to identify the reaction products. Pseudoboehmite is formed at low water to aluminum ratios. At higher water content, transformation of pseudoboehmite occurs with bayerite as the final phase. Dawsonite-type minerals are produced when ASB is hydrolyzed in the presence of sodium, potassium, or ammonium bicarbonate. Infrared evidence suggests that the carbonate group is more perturbed than indicated by the proposed crystal structure. A compound with a structure like the pyoaurite-sjögrenite group was obtained when ASB reacted with a lithium carbonate solution. The infrared spectrum indicates the possible existence of bicarbonate and carbonate ions between the brucite-like layers.

The 001 spacing of Na-smectite was found to vary from 9.6 Å at 0% relative humidity (RH) to 12.4 Å at 60-65% RH. The 9.6-Å spacing corresponds to dehydrated Na-smectite, and the 12.4-Å corresponds to Na-smectite with one water layer. A regular series of intermediate values resulted from ordered interstratification of the 9.6- and 12.4-Å units. Ordered interstratification was confirmed by the presence of a 001 spacing of 9.6 + 12.4 Å = 22 Å. This peak appeared under experimental conditions at about 35% RH. It appeared for calculated simulations of ordered stacking of 50/50 mixtures (±10%) of 9.6- and 12.4-Å units. The 004 peak of this 22-Å spacing interacted with the 002 of the 9.6-Å spacing of ordered mixtures of more than 50% 9.6-Å units and with the 002 of the 12.4-Å spacing of ordered mixtures of more than 50% 12.4-Å units. The result of this interaction was a complex peak, the position of which was a function of the ratio of 9.6- and 12.4-Å units. This complex peak was noted for experimental and for calculated conditions. Calculated tracings assuming ordered stacking matched the experimental tracings closely, whereas those assuming random stacking did not.

Ordering was apparently due to the interaction of the positive charge of the interlayer cation repelling the positive charge of the hydrogens of the hydroxyl ions, one above and one below, closest to the interlayer space. The collapse of a single interlayer space (dehydration) brought the interlayer cation closer to the hydrogens of the hydroxyls causing the hydroxyls to rotate such that the hydrogens shifted toward the adjacent interlayer spaces. Collapse of these two interlayer spaces was therefore more difficult. This same mechanism helps explain ordering in illite/smectite. The difference is that hydration/dehydration is quick and reversible, whereas the change from smectite to illite is slow and irreversible.

The objective of this paper is to present flow sheets for a system of quantitative minera-logical analysis of clays of soils and sediments and to show representative results. Selective dissolution analysis by the Na2S2O7-HCl-NaOH procedure yields the quartz and feldspar contents (0 to 63%) and differentiates feldspar K from mica K. The NaOH-thermal system of selective dissolution yields the allophane plus gibbsite, kaolinite plus halloysite, and dickite contents (0 to 84% for the sediments; 1 to 25% for soil clays) Mica contents (0 to 92% for the rock specimens, 7 to 43% for soil clays) are determined by nonfeldspathic K (and Na). Vermiculite contents (1 to 97% of specimens; 3 to 21% for soil clays) are measured by blocking of interlayer CEC by drying at 110°C while K saturated and replacing with NH4Cl. Montmorillonite (and palygorskite) contents (0 to 85% of specimens; 3 to 36% of soil clays) are determined by the CEC not blocked by the K and NH4 sequence for vermiculite. Chlorite contents (0 to 85% for specimens; 0 to 37% for soil clays) are determined by thermal gravimetric analysis, after allocation of OH water lost between 300 and 950°C to other hydrous minerals determined.

The best evidence of the accuracy of the system of analysis lies in the consistent total recovery of 24 standard mineral samples averaging 100.4 ± 1.3 (± standard error of means) and of 22 soil clay samples averaging 99.5 ± 0.8. The different constituents were present in widely different proportions in the various samples, and were determined by independent methods. The complementary total of near 100% (maximum range 95 to 105% for specimens; 95 to 103% for soil clays) for the analyses is a significant measure of the specificity of the several determinations.

Three montmorillonites and a nontronite were reduced by sodium dithionite to obtain different amounts of Fe2+ in their octahedral sites. The mass ratio of water to clay, mw/mc was determined as a function of Fe2+ at several values of the swelling pressure, π. The value mwmc decreased markedly with increasing Fe2+ at each value of π for each clay. Moreover, curves of π vs. mwmc for the different clays were displaced downwards as Fe2+ increased. A straight line was obtained when In(π + 1) was plotted against 1/(mw/mc) however, at some oxidation states of three of the samples this line exhibited a sharp break at a specific value of 1/(w/mc. The slope of the line decreased for each clay as Fe2+ increased, and an increase in Fe2+ was accompanied by an increase in the cation exchange capacity. These observations are thought to be due to a collapse or partial collapse of the superimposed clay layers resulting from the increase in cation-exchange capacity.

Glauconite has been synthesized at low temperature by precipitation of Fe-hydroxides from Si-, Fe-, Al-, and K-containing solutions under reducing conditions. The compositions favorable for the synthesis at 20°C and pH 8.5 are 1 ppm Fe, 0.15 ppm Al, 13 ppm Si02, 1000 ppm KC1, and 1000 ppm dithionite. The K-content of the solutions must be sufficiently high to fix K in the precipitate.

Under special early diagenetic conditions glauconite is formed in marine sediments, probably at the interface between reducing and oxidizing zones in the muddy sediments. The silica content of pore waters seems to control the formation of glauconite or chamosite rather than depth or temperatures of the bottom waters.

Interlayer K in muscovite, biotite, phlogopite, illite and vermiculite-hydrobiotite samples was replaced by cation exchange with Na. The rate and amount of exchange varied with the mineral and the level of K in solution.

Essentially, all the K in muscovite, biotite, phlogopite and vermiculite was exchangeable when the mass-action effect of the replaced KT was reduced by maintaining a very low level of K in solution. The time required for this exchange varied from < 10 hr with vermiculite to > 45 weeks with muscovite. Only 66% of the K in the illite was exchangeable under these conditions. When the replaced K was allowed to accumulate in the solution, the amount of exchange was determined by the level of K in solution required for equilibrium. These levels decreased with the degree of K-depletion and with the selectivity of the mica for K. The order of selectivity was muscovite > illite > biotite > phlogopite > vermiculite. Decreasing the K in solution from 10 to 7 ppm increased the exchangeable K in biotite from 30 to 100%. A K level of only 0.1 ppm restricted the exchange of K in muscovite to 17%.

A decrease in layer charge was not required for K exchange, but a decrease did occur in K-depleted biotite and vermiculite. Muscovite with the highest layer charge (247 meq/100 g), least expansion with Na (12.3Å), and least sensitivity to solution pH had the highest selectivity for K and the slowest rate of exchange. The K in vermiculite was the most readily exchangeable.

Theoretical models of the mechanical properties of hydrated smectites, saturated with a variety of cations, are of much value in determining the potential for their use in various applications, including clay-polymer nanocomposites, but the development of such models is still in its infancy. The purpose of this study was to calculate the effects of divalent cations on the structural and mechanical elasticity of montmorillonite under different degrees of hydration. A theoretical study of the swelling and hydration behavior of montmorillonite was, therefore, undertaken using density functional theory (DFT) to investigate the basal spacing behavior of the homoionic montmorillonite with varying amounts of water in the interlayer space. The effect of the degree of the hydration of divalent interlayer cations (Mg2+/Ca2+/ Sr2+/Ba2+) on the structure expansion of the interlayer space was analyzed. In addition, the results obtained were compared to calculations performed on the montmorillonite model with a monovalent cation (Na+). The basal spacing (d001) is governed by the size and the degree of hydration of the countercations. The structures containing divalent cations are more compact than structures with monovalent cations. Ba-exchanged montmorillonite was found to have the largest d001 value for any degree of hydration (‘dry,’ one water layer, or two layers). The basal spacings of ‘dry’ montmorillonite exchanged with small cations, Mg2+ and Ca2+, are very similar. In hydrated models, the d001 expansion correlates with the ionic radius of the interlayer cation. The dependence of the total electronic energy on the volume expansion was calculated. From the energetic curves, bulk modulus (B0) was obtained by fitting in order to show how the compliance of the material depends on the type of interlayer cation and on the degree of hydration. With increasing water content in the interlayer space, the bulk modulus decreased, suggesting that the c-axial compression becomes easier with increasing hydration of the clay mineral. The values of the bulk modulus in hydrated systems are less sensitive to the type of the interlayer cation.

Kaolin-group clay minerals can be modified to form nanotubular and mesoporous structures with interesting catalytic properties, but knowledge of the best methods for preparing these structures is still incomplete. The objective of this study was to investigate intercalation/deintercalation as a method for the delamination and rolling of kaolinite layers in relation to structural order. To prepare nanotubular material, kaolinites of different crystallinities and halloysite (all from Polish deposits) were chosen. The experimental procedure consisted of four stages: (1) preparation of a dimethyl sulfoxide precursor intercalate; (2) interlayer grafting with 1,3-butanediol; (3) hexylamine intercalation; and (4) deintercalation of amine-intercalated minerals using toluene as the solvent. Structural perturbations and changes in the morphology of the minerals were examined by X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and transmission electron microscopy (TEM). The number of rolled kaolinite layers depended heavily on the efficiency of the intercalation steps. An increase in the structural disorder and extensive delamination of the minerals subjected to chemical treatment were recorded. Kaolinite particles which exhibited tubular morphology or showed rolling effects were observed using TEM. The nanotubes formed were ∼30 nm in diameter, with their length depending on the particle sizes of the minerals.

Due to the importance of clay minerals in metal sorption, many studies have attempted to derive mechanistic models that describe adsorption processes. These models often include several different types of adsorption sites, including permanent charge sites and silanol and aluminol functional groups on the edges of clay minerals. To provide a basis for development of adsorption models it is critical that molecular-level studies be done to characterize sorption processes. In this study we conducted X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) spectroscopic experiments on copper (II) sorbed on smectite clays using suspension pH and ionic strength as variables. At low ionic strength, results suggest that Cu is sorbing in the interlayers and maintains its hydration sphere. At high ionic strength, Cu atoms are excluded from the interlayer and sorb primarily on the silanol and aluminol functional groups of the montmorillonite or beidellite structures. Interpretation of the XAFS and EPR spectroscopy results provides evidence that multinuclear complexes are forming. Fitting of extended X-ray absorption fine structure spectra revealed that the Cu-Cu atoms in the multinuclear complexes are 2.65 Å apart, and have coordination numbers near one. This structural information suggests that small Cu dimers are sorbing on the surface. These complexes are consistent with observed sorption on mica and amorphous silicon dioxide, yet are inconsistent with previous spectroscopic results for Cu sorption on montmorillonite. The results reported in this paper provide mechanistic data that will be valuable for modeling surface interactions of Cu with clay minerals, and predicting the geochemical cycling of Cu in the environment.

The distribution of clay minerals in Recent sediments can be explained by the relative stability of the clays. The rates of particle aggregation for three clays were determined in the laboratory in synthetic estuarine solutions; from the kinetic studies stability values were calculated. The results indicate that illite is more stable than kaolinite which is more stable than montmorillonite. The distribution of the clays in the Pamlico River Estuary can be explained on the basis of relative clay stability where kaolinite which aggregates rapidly (relatively unstable clay) is found upstream of illite.

Saponite, hectorite, and laponite have been pillared with cationic Al clusters, and special attention has been given to the solution chemistry or Al. Pillared saponite is obtained after exchange with refluxed Al solutions; while for hectorite, Al solutions treated with ammonium acetate give a pillared product with 1.8–1.9 nm spacing and thermal stability up to 873 K. In both types of solutions, the Keggin ion Al cluster is a minority species or totally absent. The typical 1.8–1.9 nm spacing is only obtained after washing. The quality of the pillared material can be judged from its thermal stability, its surface area, and the width of the d001 line before and after pillaring. The width should not exceed 0.3 nm before calcination and 0.5 nm after calcination. The latter criterion reflects the importance of the crystallinity of the parent clay for successful pillaring. Pillaring in concentrated conditions occurs by a combination of ion exchange and precipitation of Al and gives materials that exhibit poor thermal stability.

White saponite occurs in joints and open fracture zones in metamorphosed dolomitic limestone near Ballarat, California. The saponite appears to have formed by hydrothermal alteration, possibly during Pliocene times. The material shows a 06l X-ray powder diffraction peak at 1.529 Å, A12O3 and MgO contents of about 4.4 and 23.5%, respectively, and a half-cell octahedral atoms summation value of about 2.82. The saponite appears to consist of a single, uniform clay species; the main impurities are fine shards of diopside and tremolite. The infrared and thermal properties of the Ballarat saponite are similar to those of the Allt Ribhein saponite. It has a lower water-holding capacity than montmorillonite and is characterized by lower Atterberg limits and expansion pressures and higher compaction densities. The apparent density of the saponite, 2.865 g/cm3, is greater than that of montmorillonite. This saponite is available from the Source Clays Repository of The Clay Minerals Society.