A theoretical model describing the interaction between crystalline swelling and cation exchange selectivity is proposed for expanding 2:1 phyllosilicates. The model is based on the assumption that changes in basal spacing of a clay are phase changes, and that each phase of a clay has a different selectivity constant for a particular cation exchange reaction. Energy barriers stabilize the various phases over a limited range of interlayer ionic composition. These energy barriers cause hysteresis in crystalline swelling, which in turn causes hysteresis in cation exchange. Results are presented for an experiment involving Ba-Mg exchange on a synthetic fiuoro-hectorite. The results demonstrate key aspects of the proposed model, including a correlation between measured selectivity coefficients and basal spacings (R2 = 0.85), an abrupt change in basal spacing that corresponds with an abrupt change in selectivity and corresponding hysteresis in crystalline swelling and cation exchange selectivity. The results also demonstrate increased selectivity for the preferred cation (Ba) at high solution mole fraction of the preferred cation. This trend is opposite of that observed for heterogeneous natural smectites but consistent with predictions of the model for a homogeneous smectite.

Experimental alteration of obsidian was performed in 0.001 to 0.5 N NaOH and KOH solutions at 150 and 200 °C for 1 to 30 d. The products were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). Changes in chemical composition and pH value of solutions during the reactions were also measured. As the pH of reacting solutions was increased, smectite, phillipsite and rhodesite crystallized progressively in NaOH solutions, while smectite, merlinoite and sanidine grew successively in KOH solutions. In addition, a small amount of less-soluble, poorly ordered boehmite was present as products of all the experiments. Smectite mainly appeared at slightly high pH, Si/Al and Na/K conditions, whereas rhodesite should be produced in extremely high pH, Na/K and Si/Al conditions. Sanidine was also formed in conditions of very high pH and Si/Al and very low Na/K. In intermediate conditions of pH and Si/Al, crystallization of phillipsite was stimulated in solutions of Na/K > 10, while formation of merlinoite was favored in conditions of Na/K < 1.

An Fe-berthierine occurs in a buried laterite from the Late Cretaceous (Cenomanian) in southwestern Minnesota. It formed beneath a lignitic horizon in which reducing solutions percolated through a laterite comprising gibbsite, kaolinite and goethite. Morphologic differences suggest 2 separate conditions of Fe-berthierine formation. Early forms of Fe-berthierine include radial bladed or radial blocky crystallites coating pisoids, along with alteration of kaolinite at crystal boundaries. These morphologies formed in the vadose zone. Later forms precipitated under subaqueous conditions as macroscopic, pore-filling cement. The large size of the later-formed Fe-berthierines enabled microprobe characterization. This 1st reported occurrence of Mg-free berthierine has a structural formula close to an idealized Fe-berthierine: Fe2Al2SiO5(OH)4. Apart from their chemistry, the unique feature of the Minnesota Fe-berthierines is their formation in an exclusive nonmarine depositional environment. They formed in situ as part of a lateritic weathering profile developed on a broad, low relief peneplain. Physical evidence of formation under nonmarine conditions includes the presence of 1) scattered lignitic fragments; 2) concretions forming casts and molds of woody material; and 3) a nonmarine fossil (Unio sp. undet). Chemical evidence includes siderites collected from the berthierine-bearing horizon having stable isotope values indicating freshwater formation.

The thermal decomposition behavior of hydrotalcite-like compounds (HTlcs) prepared by reconstruction of calcined HTlcs is described. From the results of X-ray diffraction (XRD), it seems that dicarboxylate intercalates of HTlc calcined at 500 °C are completely reconstructed to Mg-Al-CO3 HTlc by exposure to aqueous Na2CO3. However, the Mg-Al-CO3 HTlc reconstructed under particular conditions yields spinel (MgAl2O4) at 400 °C. This temperature is very low, because Mg-Al-CO3 HTlc that has been reported yields spinel at 900 °C after forming a Mg-Al double oxide. The reconstructed Mg-Al-CO3 HTlc that yields spinel at 400 °C is obtained when the following conditions are fulfilled: the crystallites of the starting dicarboxylate intercalates are coagulated tightly and the calcined HTlcs and reconstructed materials are not ground. The Mg-Al-CO3 HTlc reconstructed under these conditions contains only 55–70% of carbonate anions required by stoichiometry. Therefore, we conclude that the transformation of reconstructed Mg-Al-CO3 HTlc to spinel at 400 °C is the result of a reaction occurring between edges of crystallites.

Divalent tin has been intercalated into montmorillonite by reacting partially hydrolyzed solutions of SnCl2 under aerobic conditions at pH = 2.8 with aqueous dispersions of the smectite mineral. The precursor tin solution contains mainly the cationic trimeric ion Sn3(OH)42+, which is shown to take part in the exchange reactions with the surface cations of the mineral. Variable temperature Mössbauer spectroscopy was used in order to: 1) directly probe changes in the oxidation state and coordination environment of Sn2+ in the process of intercalation; 2) examine the nature of tin atoms on the external surfaces and in the interlayer space of the clay platelets; and 3) study the dynamics of motion of tin atoms on the clay surfaces.

The main conclusion from these studies is that about 75% of the Sn2+ ions undergo extensive oxidation to the +4 state with concomitant hydrolysis and condensation that lead to the precipitation of SnO2 on the external surfaces of the clay. The rest of the Sn2+ ions are introduced into the lamellar zone, as evidenced by the detailed Mössbauer analysis of the dynamics of motion of tin atoms on the clay surfaces.

In the Tertiary lacustrine sediments of the Jbel Rhassoul (Morocco), stevensite and sepiolite, confined to the dolomitic facies, are commonly mixed at lower parts of the so-called “Formation Intermédiaire”. Transmission electron microscopy (TEM) observations reveal a relation between these 2 magnesian clay minerals. One can observe the different transition steps, from the initial folded layers of stevensite to the fibers emerging from the layers, and finally to the complete replacement of stevensite by sepiolite. That transition can also be observed by scanning electron microscopy (SEM), where the fibers seem to grow at the expense of stevensite. Thermodynamic calculations have been applied to provide geochemical conditions for the formation of sepiolite after stevensite. Early deposition of the “Formation Intermédiaire” occurred under climatic conditions varying between dry and wet. During dry periods, the relative silica enrichment and the pH decrease in the lake water should destabilize stevensite, leading to the formation of sepiolite. Subsequently, a perennial wet climate would lead to the formation of pure stevensite without any trace of sepiolite.

The formation and structure of hematite aggregates were examined by dynamic and static light scattering techniques. A large range in coagulation kinetics was studied by varying either indifferent electrolyte (KCl) concentration or surface complexing anion (H2PO4-) concentration, PT, at pH 6.0 ± 0.1. Diffusion limited aggregation (DLA) was induced by counterion screening at [KCl] > 80 mM or by surface charge neutralization at P T = 31 μM (and ionic strength =1.0 mM). In DLA, the fractal dimension, df, of aggregates formed by either surface charge neutralization or counterion screening was 1.7 ± 0.1. A reduction in the rate of coagulation in KCl for [KCl] > critical coagulation concentration (CCC) produced an increase in df to 2.1 ± 0.1. For aggregation induced by phosphate adsorption at constant ionic strength, there was no apparent trend in df with coagulation rate. The value of df was consistently less than 1.8 when reaction limited aggregation (RLA) resulted from surface charge neutralization rather than counterion screening. TEM observations of aggregates formed in the presence or absence of phosphate confirm that, when RLA is induced by phosphate adsorption, resulting aggregates are much looser in structure than those formed by counterion screening. The results suggest that the high-affinity binding of phosphate to hematite may result in a nonrandom distribution of surface charge that facilitates the coalescence of positive and negative charge crystal faces.

The formation of layer silicates on capsuled bacterial cell walls was studied in freshwater microbial mats. The trends associated with Al, Si, Mn and Fe deposits with capsules are consistent with occurrence of layer silicates with 14, 10 and 7 Å X-ray diffraction (XRD) patterns. Scanning electron microscope and transmission electron microscope (SEM and TEM) observations of the microbial mats revealed the presence of microcolonies of rod- and coccus-shaped bacteria with layer-silicate thin films. Field measurements of pH, temperature and Eh indicated that these conditions for bacterial crystallization of layer silicates and hydrated Fe/Mn oxides in freshwaters are as follows: pH 6.3 to 7.8, 12 to 20 °C and Eh −24 to +200 mV. Glass slides kept for 3 weeks in the beakers with natural freshwater and river sediments were coated with brown materials. These materials were identified as layer silicates and colonized bacteria formed under photosynthetic conditions. The well-developed holdfasts on Leptothrix discophora bacterial cells are mainly associated with poorly crystalline layer silicates and hydrated Fe-Mn oxides. Semiquantitative elemental analyses of holdfasts using energy-dispersive X-rays (EDX) indicated that layer-silicate crystallization covers the cell at an early stage. Iron and manganese crystallization develops at a later stage, where aluminum substitution occurs in crystal structures. Laboratory experimental results indicated that layer silicates grew from a biochemical origin, rather than from inorganic origins in freshwater. Layer-silicate formation is linked with bacteria in microbial mats.

Transgression by the Western Interior Sea during the Late Cretaceous in southwestern Minnesota caused swampy conditions to be imposed upon a laterite consisting of gibbsite, goethite and kaolinite. Reducing conditions overprinted upon the laterite reduced ferric Fe in goethite for incorporation of ferrous Fe into Fe-berthierine. Attendant oxidation of organic matter provided CO2 for siderite's formation. Thermodynamic calculations indicate that berthierine, gibbsite, goethite, kaolinite and siderite were in equilibrium with a solution whose pH was 5.2 and whose pCO2 was on the order of 0.3 atm. Formation of Fe-berthierine is favored by solutions having: 1) low silica concentration; 2) low [Mg2+]/[Fe2+] ratio; 3) high pCO2; 4) extremely low sulfate content before reduction takes place; and 5) moderate reducing conditions (Eh around −0.05 V).

Pennsylvanian underclay from Illinois is characterized by well-developed mineral zonation: towards the coal bed, marly limestone gradually evolves into carbonate-free clay, chlorite becomes undetectable and illite/smectite changes from ordered and illite-dominated into random and smectite-dominated, with both types present in the middle of the profile. Transmission electron microscopy (TEM) observations of the bulk material imply that disappearance of calcite is due to dissolution. Movement of SiO2 in the upper part of the profile is evidenced by quartz cementation of clay aggregates; crystallization of kaolinite, by the presence of vermicular aggregates absent from less-altered samples. Illitic material in unaltered (limestone) samples consists of rare, large, Al-rich crystals of mica, interpreted as detrital, and abundant thin crystals of illite/smectite intimately mixed in approximately equal proportions with even thinner crystals of discrete illite. Both are more Mg- and Fe-rich than the large mica crystals and are interpreted as diagenetic, based on their 1Md polytype and the correlation with coal rank. Illitic material of the upper, carbonate-free section of the profile contains the same 3 types of crystals, but in different proportions: illite/smectite crystals dominate and their composition is more smectitic. Two distinct morphologies of the aggregates of crystals with different proportions of the component layers are observed. It explains why 2 different illite/smectites are detectable by X-ray diffraction (XRD) in these samples. The analysis of chemical data suggests that the underclay is a residue after dissolution of all of the calcite and half of the quartz from the original limestone (paleosol and/or telogenetic process). The TEM observations are not decisive regarding the origin of variation within the illitic material. It may result from burial diagenetic illitization of more-smectitic material, similar to the composition preserved in the center of underclay profile, or it may represent telogenetic alteration of illitic clay by acid waters penetrating down from the coal bed. The aggradation model explains the increase in percent K2O, MgO and illite layers in the uppermost part of the profile. Whichever is the direction of reaction, it proceeds on an aggregate-by-aggregate basis and not fundamental particle-by-particle, and cannot be explained by simple opening or collapse of interlayers.

The acidic properties of acid-modified montmorillonite and vermiculite were determined by pyridine and ammonia adsorption to correlate with the alkylating and dehydrating activity of the activated samples. Treatment of the minerals with different concentrations of hydrochloric acid results in the variation of overall acidity and density of acidic sites. Infrared (IR) spectral and differential scanning calorimetric analyses have revealed the presence of Bronsted and Lewis acid sites on the activated samples. The catalytic activity towards the above reaction has been correlated to the acid strength and density of Lewis acid sites. Treatment of montmorillonite with hydrochloric acid in the range of 0.1 and 0.3 M and vermiculite with 0.2 to 0.3 M seemed to be suitable for the conversion of methanol into olefin-rich hydrocarbons. Acid-activated montmorillonite catalyzed the isopropylation of benzene to a maximum extent of 16%, whereas acid-activated vermiculite gave a maximum conversion of only 4%.

The orientation of rhodamine 6G (R6G) in the 22-Å basal-spaced complex with Li-fluor-taeniolite has been studied using X-raypowder diffraction, 1-dimensional Fourier analysis, polarized infrared (IR) spectroscopy, carbon analysis and thermal analysis. The R6G was adsorbed by cation exchange in aqueous solution. In the range of 0.086 to 0.46 molar ratio of R6G to taeniolite, the basal spacings of the complex were nearly constant at 21.7 to 22.2 Å. From X-raydiffraction (XRD) data, it was confirmed that R6G in the complex orients with its longest xanthene ring axis perpendicular to the ab plane of the host. The pleochroism of IR absorption bands at 1331, 1517, 1537 and 1621 cm−1 supports the vertical orientation. The wide stability range of the vertical configuration is consistent with the strong coulombic force between the highly negatively charged silicate layer of the host [cation exchange capacity (CEC) = 157 ± 9 meq/100 g] and the positively charged nitrogen bonded to both sides of the R6G xanthene ring.

The adsorption-condensation of olefins was studied on 7 adsorbents: 2 commercial clays, a natural clay and its protonated form, γ-alumina and porous and nonporous silicas. These adsorbents were characterized by X-ray diffraction (XRD), chemical analysis, thermogravimetric analysis (TGA), differential thermal analysis (DTA) and determination of specific surface area measurement by the BET method. The experiments were carried out gravimetrically, in gas- or vapor-solid systems, at 25 °C and on adsorbents dried at 120 °C. Adsorption-condensation of olefins are fast processes, diffusion controlled. Alumina and silicas adsorb olefins and paraffins only reversibly, but are unable to condense olefins. The water polarized by the countercations is the source of Brønsted acid sites. When the gas phase is evacuated or swept with inert gas, the condensation terminates. On clays, paraffins are reversibly adsorbed but no condensation was observed.

The uptake of Sr and Cs by 2 types of aluminum pillared layered clays (Al-PILC), a reference sample (AZA) and a specially tailored sample (FRAZA), were investigated. The AZA sample was prepared from air-dried precursors and the FRAZA sample from freeze-dried precursors. X-ray diffraction (XRD), pore and grain size measurements revealed that freeze-drying leads to a very fine-grained material with substantial mesoporosity. In contrast, air-drying results in coarse grains and an essentially microporous material. Four different methods were tested for restoring the cation exchange capacity (CEC) of the prepared PILCs. The most effective method proved to be exposing the material to ammonia fumes, then soaking it in a NaCl solution at pH =10. Strontium and Cs kinetic experiments were carried out with PILCs after restoring their CEC by this method. The results revealed 1 fast uptake component in both materials but with different relaxation times for each PILC.

The surface charge components of 2 Georgia kaolinites of differing degrees of crystallinity (KGa-1 and KGa-2) were determined using procedures based on charge balance concepts. Permanent structural charge density (σ0) was determined by measuring the surface excess of Cs, which is highly selective to permanent charge sites. The values of σ0 determined were -6.3 ± 0.1 and -13.6 ± 0.5 mmol kg−1 for kaolinites KGa-1 and KGa-2, respectively. The net proton surface charge density (σH) was determined as a function of pH by Potentiometrie titration in 0.01 mol dm-3 LiCl. Correction from apparent to absolute values of σH was made by accounting for Al release during dissolution, background ion adsorption and charge balance. Lithium and C1 adsorption accounted for the remainder of the surface charge components. Changes in surface charge properties with time were measured after mixing times of 1, 3 and 15 h, the latter representing “equilibrium”. Time-dependent behavior is believed to be caused by mineral dissolution followed by readsorption or precipitation of Al on the mineral surface. Both the point of zero net charge (p.z.n.c.) and the point of zero net proton charge (p.z.n.p.c.) changed with mixing time, generally increasing. The “equilibrium” p.z.n.c. values were approximately 3.6 for KGa-1 and 3.5 for KGa-2, whereas the corresponding p.z.n.p.c. values were about 5.0 and 5.4. The p.z.n.c. results were in good agreement with previous studies, but the values of p.z.n.p.c. were higher than most other values reported for specimen kaolinite.

When Li-saturated montmorillonite is heated to 200–300 °C, the Li ions migrate from interlayer positions to sites in the layer structure. However, the identity of these sites has not been clearly established. Here we have investigated the migration of Li ions in montmorillonite, after heat treatment at 250 °C, using chemical and instrumental analyses. The latter include X-ray diffractometry (XRD), 7Linuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Heating causes a large reduction in cation exchange capacity (CEC) and an almost complete loss of interlayer expansion with glycerol as shown by XRD. Static and magic angle spinning (MAS) 7Li-NMR spectroscopy shows that the quadrupole coupling constant of Li increases markedly over the corresponding value for unheated Li-montmorillonite (where Li occupies exchange sites in the interlayer space) and for hectorite (where Li is located in the octahedral sheet). This would indicate that, in heated montmorillonite, Li occupies structural sites of low symmetry which, however, cannot be identified with octahedral vacancies in the layer structure as is commonly assumed. XPS shows that the binding energy (BE) for Li in unheated montmorillonite is comparable to that for other exchangeable cations. Heating broadens the Li 1s band and decreases the BE. The BE for Li in heated montmorillonite is significantly higher than that in either spodumene or lepidolite, where Li is known to occupy octahedral sites. The combined data suggest that heating induces Li to migrate from interlayer sites to ditrigonal cavities in the tetrahedral sheet, rather than into vacancies in the octahedral sheet, of montmorillonite.

Samples containing spherical kaolinite, synthesized under hydrothermal conditions (T = 200 °C; t = 24 h, 192 h, 720 h) from gel with Si/Al = 0.84, were studied by differential thermal analysis/thermogravimetry (DTA/TG) to provide a contribution to the mineralogical characterization of this unusual morphology. The data clearly show that dehydroxylation temperature of spherical kaolinite is lower than that of platy/lath kaolinite. It can also be used to detect the presence of spheres in the presence of the other morphologies. A rough estimation of its quantity can be obtained by TG data if spheres are present in appreciable concentrations. The results also confirm microscopic observations previously reported in the literature: spherical morphology is a discrete and metastable phase, and it is gradually dissolved along hydrothermal treatments of gels.

The adsorption of olefins at 25 °C in gas- or vapor-solid systems on 4 clays dried at 120 °C was studied by infrared spectroscopy. Products of condensation have the spectra of paraffinic oligomers. Paraffins are adsorbed onto the same structural surface hydroxyls that adsorb olefins, confirming the physical unspecific character of this adsorption. These hydroxyls do not participate in the condensation reaction. The reappearance of these hydroxyl bands after evacuation suggests that product molecules are not adsorbed onto the surface but remain on it because of its low vapor pressure. The reversible adsorption sites participate in feeding the condensation sites. Double-bond isomerization of olefins was not observed, at room temperature, on clays, alumina and silicas dried at 120 °C. When the gas-phase is evacuated or swept with inert gas, reaction does not proceed with a new monomer. Paraffins are only physically adsorbed.

Vermiculite crystals from Santa Olalla, Spain, were intercalated with tetramethylammonium (TMA) after Na saturation. The resulting TMA-vermiculite showed near perfect 3-dimensional stacking order with cell parameters of a = 5.353(1) Å, b = 9.273(2) Å, c = 13.616(6) Å, β = 97.68(3)°, and space group C2/m, which indicated a 1M polytype. Single crystal X-ray refinement (R = 0.073, wR = 0.082) located the central atom (N) of the TMA (occupancy at 0.418) and the C atom of 1 methyl group (occupancy at about 0.35). The TMA is offset from the center plane between 2 silicate layers by 1.52 Å, and the methyl group is keyed into the silicate ring of the adjacent silicate layer. This arrangement constrains the positions of the C atoms of the other methyl groups to an opposing plane parallel to the oxygen basal plane. Associated H2O is randomly located between the TMA pillars, and no scattering from these molecules was observed. The calculated height of the TMA molecule is shown to be 4.15 Å.

Steric and electrostatic arguments suggesting that adjacent TMA molecules must alternate apex directions (±c) allow for a description of the local TMA arrangement. This model involves the keying of TMA molecules laterally, thereby explaining why perfect 3-dimensional stacking occurs. The offset of TMA from the center of the interlayer region produces a cavity suitable as an adsorption site for small molecules, such as benzene, which is consistent with the higher than expected adsorption of these molecules in TMA-smectites of high layer charge. This offset also explains the easy expandability of TMA-clays, since only very weak interactions occur between TMA and 1 adjacent silicate layer, thereby allowing molecules to enter the interlayer.

Altered perthites from a weathered pegmatite in the Spruce Pine District, North Carolina, were characterized by electron microprobe as a K-rich microcline host with lesser Na-rich plagioclase having a lamellar morphology. Light-optical and transmission electron microscopy (TEM) show microtextural elements such as phase boundaries, holes and microfractures that could serve as potential nucleation sites for alteration to clay minerals.

The host microcline contains albite and pericline twinning textures that vary in character; the amount of each twinning type and/or the size of twin individuals changes on a μm scale. Plagioclase ranges from large lamellar vein and film albite (visible in the light microscope) to cryptoperthite whose size ranges from μm to perhaps 100 Å. The smallest-scale albite appears to be a late-stage phase of exsolution in which lamellae have nucleated heterogeneously on albite-twin composition planes in the microcline.

Alteration is concentrated in vein and film albite, especially along grain boundaries with microcline. Powder X-ray diffraction (XRD) patterns of intensely altered pegmatite show halloysite. Holes, microfractures, vein albite/host microcline boundaries and microcline/halloysite boundaries trend parallel to the traces of (010) and {110}, suggesting that these directions are pathways along which fluids migrate. Cleavage and microfractures occur along, and holes are bounded by, these directions. Holes are associated with dislocations and the latter are observed at feldspar/clay boundaries. Twin domains and cryptoperthitic albite are less susceptible to alteration than coarse lamellar albite and regions containing negative crystals and microfractures. However, microtextures in some areas containing halloysite suggest that once fluids penetrate the crystal, alteration may proceed preferentially in more strongly twinned regions.