Sorption of aniline and its derivatives by montmorillonite substituted by cations of widely different acidity depends upon the polarizing power of the interlayer cations. Infra-red spectra indicate that the anilines are mostly bound to the interlayer cations through water molecules, except in Cs montmorillonite, where bonding to the oxygen surfaces of the alumino-silicate sheets seems to predominate. Anilines are weak bases, which compete with the oxygen surfaces for protons of acidic interlayer water. Consequently, the tendency of anilines to act as proton donors in the clay interlayers increases with the polarizing power of the exchangeable cation. The concept of ‘basic’ water is introduced to account for some of the features of the spectra of Cs montmorillonite treated with the organic ligands.

The < 1-μm fraction of 17 bentonite samples from Kinnekulle, southwest Sweden, were studied by chemical analysis, X-ray powder diffraction, and cation-exchange capacity. The bentonites are interbedded with undeformed, flat-laying Ordovician and Silurian sediments and were formed by the transformation of volcanic ash (dated at about 450 Ma) into smectite, which later converted to mixed-layer illite/smectite (I/S). The reaction, possibly driven by heat from an overlaying diabase intrusion (about 300 Ma), stopped at different stages of conversion, as evidenced by the I/S which ranges in composition from 60 to 10% smectite layers. A 2-m-thick bed shows zonation, with decreasing smectite proportions towards the upper contact. The zonation is not symmetrical towards the lower contact. In thin beds the illite proportion is higher and the regularity of ordering is inversely proportional to the thickness of the bed. K:Sr and K:Rb ratios follow the illite pattern; the ratios are highest at the contact and in thin beds. The inhibiting effect of Ca and Mg on the smectite-to-illite conversion probably was the cause of less-reacted smectite in the center of the thick bed.

The formation of illite through the smectite-to-illite (S-I) reaction is considered to be one of the most important mineral reactions occurring during diagenesis. In biologically catalyzed systems, however, this transformation has been suggested to be rapid and to bypass the high temperature and long time requirements. To understand the factors that promote the S-I reaction, the present study focused on the effects of pH, temperature, solution chemistry, and aging on the S-I reaction in microbially mediated systems. Fe(III)-reduction experiments were performed in both growth and non-growth media with two types of bacteria: mesophilic (Shewanella putrefaciens CN32) and thermophilic (Thermus scotoductus SA-01). Reductive dissolution of NAu-2 was observed and the formation of illite in treatment with thermophilic SA-01 was indicated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). A basic pH (8.4) and high temperature (65°C) were the most favorable conditions forthe formation of illite. A long incubation time was also found to enhance the formation of illite. K-nontronite (non-permanent fixation of K) was also detected and differentiated from the discrete illite in the XRD profiles. These results collectively suggested that the formation of illite associated with the biologically catalyzed smectite-to-illite reaction pathway may bypass the prolonged time and high temperature required for the S-I reaction in the absence of microbial activity.

Hydroxy-Al and -Fe interlayers were prepared in “mono-mineralic” fine and coarse clay montmorillonite and coarse clay and silt vermiculite at 3°C and 21°C. The formation of hydroxy interlayers was evaluated by X-ray diffraction, cation exchange capacity, and chemical analyses.

At comparable particle size and regardless of temperature, the amounts of hydroxy-Al and -Fe interlayers in montmorillonite exceeded by far those formed in vermiculite. Likewise, the aluminum systems exhibited a higher degree of interlayering than iron systems.

Within montmorillonite, the amount of hydroxy-Al and -Fe interlayers increased as the particle size decreased, regardless of temperature. The aluminum interlayered montmorillonite equilibrated at 3°C was characterized by basal spacings of about 17 Å after Ca-saturation plus 54 per cent relative humidity. These spacings are larger than those normally observed for smectites.

Within vermiculite systems equilibrated at 3°C, more hydroxy-Al interlayers were recorded in coarse clay than in silt fraction, whereas at 21°C about equal amounts of interlayers were formed. By contrast, hydroxy-Fe interlayer was favored by the silt fraction at both temperature levels.

The formation of aluminum interlayers in both minerals increased with increasing temperature. The formation of hydroxy-Fe interlayers in montmorillonite was generally not temperature dependent, whereas the formation of such interlayers in vermiculite increased slightly with increasing temperature.

These data may partially explain the formation of chloritic intergrades in soils as a function of type of minerals, kind of ions, and thermal variations.

Quantitative measurements are made of the adsorption of benzidine and aniline from aqueous hydrochloride solutions by Na-, Li-, and Ca-montmorillonite and of the displaced inorganic cations. From these data, the ionic states of the adsorbed organic species are determined. Under conditions of controlled pH, the adsorption of benzidine increases as the pH increases, and involves mainly divalent species at pH<3·2, and increasing proportions of monovalent and neutral species at pH> 3·2. With aniline, monovalent and neutral species are adsorbed, and hydrogen ions also appear to participate in the reactions.

Color developments of benzidine and aniline complexes of montmorillonite and hectorite are considered qualitatively in relation to the adsorption data, to various experimental conditions including the nature of the inorganic exchangeable cations, the pH, and the presence or absence of oxygen in the system, and to relevant previous work. It is hypothesized that the blue color of the benzidine complex is due to semiquinone formation by oxidation on montmorillonite by the clay itself, and on hectorite by dissolved oxygen or H2O2, and that the yellow color under acid conditions arises from reversible formation of quinoidal cations from semiquinones. The color developments of the aniline complex are due probably to oxidation of aniline by atmospheric oxygen.

A 14-Å mineral coexisting with kaolin minerals, mica, and gibbsite in a Korean Ultisol and showing X-ray powder diffraction features of “chloritized” vermiculite was studied by a combination of methods. The 14-Å mineral collapsed on saturation with K+ after extraction with hot 1/3 M sodium citrate, but the Si/Al ratio of the extracted material was close to 1.0 and kaolin minerals dissolved, as indicated by difference infrared spectroscopy. The 14-Å mineral was also collapsed by heating at or above 350°C. The difference infrared spectra and the X-ray powder diffraction patterns indicated that two forms of kaolin mineral are present that differ in thermal stability; one decomposed by heating at or below 375°C and the other by heating above 375°C. The former kaolin mineral is probably associated with vermiculite and the latter is present as a discrete form. The 14-Å mineral was inferred to be an intergradient vermiculite-kaolin mineral, in which most vermiculite layers each partially transform into double kaolin layers, and to represent an intermediate phase during the transformation of 2:1 to 1:1 layer silicates in acid soils.

Organoclays were prepared by exchanging Ca2+ in a Ca2+-saturated smectite partially or fully with trimethylphenylammonium (TMPA) cations. The mechanistic function of these organoclays as adsorbents for neutral organic compounds in aqueous solution was examined. TMPA cations were found to take a random distribution on the surfaces of mixed Ca/TMPA-smectites. The presence of TMPA, and its random distribution, resulted in water associated with the clay surfaces being held more weakly. Apparently, the interspersing of TMPA and Ca2+ ions prohibits the formation of a stable network of water molecules around Ca2+. Water molecules associated with the siloxane surface in mixed Ca/TMPA-clays are removed during the adsorption of neutral organic compounds from bulk water, leaving only ∼11 strongly held water molecules around each Ca2+, as opposed to ∼58 water molecules in homoionic Ca2+-smectite. These results demonstrate that the amount of water associated with the clay surfaces and interlayers depends on the nature of the exchange cation(s), and not on the amount of available siloxane surface area by itself. We conclude that in TMPA-smectites the TMPA cations function as nonhydrated pillars, and sorption of organic solutes occurs predominantly on the adjacent siloxane surfaces, which are hydrophobic in nature. The water molecules around Ca2+ in mixed Ca/TMPA-smectites obscures some of the siloxane surfaces. This diminishes sorption capacity, in an amount roughly equivalent to the fraction of the CEC occupied by Ca2+, because organic solutes cannot displace the waters of hydration of Ca2+.

A specimen montmorillonite (Arizona bentonite) was treated with hydroxy-aluminum solutions of various basicity. The cation exchange sites of this clay were found not to be homogeneous in their strength of retaining hydroxy-aluminum polymers; this strength varied from very weak, with which the Al polymers were only loosely held, to very strong, with which stable interlayer Al-clay complexes were formed. When a large amount of clay was treated with a small amount of solution, the polymers were held only in positions of strong affinity; the polymers were difficult to extract with neutral salt solutions and did not change to crystalline Al(OH)3 during prolonged aging. When a small amount of clay was treated with a large amount of solution, the exchange sites were completely occupied by polymers; a portion of these polymers was easily extractable with neutral salt solutions and, during aging, changed to Al(OH)3. This contrast is significant in any attempt to compare results obtained under different experimental conditions and to correlate laboratory experimentation with the occurrence of gibbsite and interlayer Al-clay complexes in nature.

Structure, morphology, and chemical composition of illite/smectite (I/S) containing 30–50% smectite layers (% S) from Kinnekulle bentonites, Sweden, of diagenetic origin were examined using X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Interlayer arrangements of I/S changed from random interstratification to short-range ordered at about 40% S. The transition from random to ordered structure proceeded continuously as reflected by the gradual decrease in probability of two smectite neighbors (Pss) towards zero. TEM observations of water-dispersed samples that had not been cation-exchanged showed that the I/S consisted dominantly of flakes coexisting with laths having a length/width ratio of about 4, regardless of % S. The thickness of the I/S particles ranged from 30 to 100 Å, and no systematic variation in thickness was detected with decreasing % S. The chemical composition of the I/S also changed continuously with decreasing % S. These observations suggest no dissolution of smectite layers and no recrystallization of illite layers during the formation of the I/S in these bentonites; rather, cationic substitutions occurred within a smectite precursor (termed a solid-state transformation mechanism). A comparison of interlayer order, particle texture, and chemistry of the I/S from various types of rocks suggests that the mechanism of smectite-to-illite conversion in the range 100% S-30% S was related to the porosity and permeability of original rocks. The solid-state transformation mechanism appears to have predominated in rocks of low porosity and permeability.

Recent sediments of the Niger delta contain the detrital clay minerals kaolinite, mont-morillonite and a small amount of illite. The montmorillonite content increases with water depth and distance from the shore, and the results of laboratory experiments on natural Niger delta clay support the assumption that this is due to differential floc-culation and sedimentation.

The easterly Guinea Current, transporting montmorillonite-rich floccules in suspension, may cause an increase in the montmorillonite content of the clays in the ©cistern part of the delta.

Mineralized faecal pellets are present in most marine sediment samples. Chamosite occurs authigenically in coastal water shallower than 35 fathoms, as brown and dark-green pellets. Green pellets, composed of highly expandable, montmorillonite-type glauconite, are particularly common around the 100 fathom isobath. Both chamosite and glauconite have a high magnesium content, which seems to be usual during their early stages of formation.

The formation of chamosite and glauconite is governed by redox potential and the availability of iron. If no reduction takes place, the pellets remain grey and their composition is similar to that of the clay matrix. Grey pellets are less restricted to a particular depth than are the chamosite and glauconite pellets, but distinct maxima occur around the 250 fathom isobath.

An X-ray diffraction method for determining quartz in sediments is described which is both rapid and precise, with a coefficient of variation of 1·9 per cent. Samples are ignited at 950°C prior to X-ray analysis. This removes the interference of clay peaks, increases the relative intensity of the quartz peaks and reduces the initial matrix variation of samples. The peak area ratio of quartz (4·26Å) to an added standard boehmite (6·18 Å) is measured. Quartz content is obtained from a working curve constructed using similar rocks of known free silica content, which were analysed by the method of Trostel and Wynne (1940).

Under closed geochemical conditions, the weathering of a serpentinite rock composed of serpentine (70–85%) and magnesian chlorite (10–15%) associated with magnetite and chromite leads to the complete replacement of serpentine and chlorite by 2:1 layer silicates and produces new Fe oxides. The serpentine minerals crystallize under different habits issued from the serpentinization processes: mesh and hourglass pseudomorphic textures were formed from olivine, and thin-bladed pseudomorphic textures from pyroxene and amphibole crystals. Serpentine veins crosscut the whole rock with locally non-pseudomorphic interpenetrating and interlocking serpentines.

Specific weathering microsystem habits with specific clay mineral crystallizations originate from these different habits: a poorly aluminous saponite in thin-bladed textures, two Fe-rich montmorillonites in mesh and hourglass (MH) textures, and in veins (V) which differentiate on Al, Mg and Fe contents. Magnesian chlorites, isolated from serpentine by hand-picking under a stereomicroscope, are found to weather to trioctahedral vermiculite. Magnetite and chromite extracted from the bulk samples are replaced by newly formed Fe oxides, maghemite, goethite and hematite, which give way to specific Fe accumulation habits in the regolith zone of the weathering profile.

The effect of heat treatments on the swelling, dispersion, particle charge and particle aggregation of Li-, Na-, K-, Mg-, Ca- and Al-Wyoming bentonite was investigated. Before thermal treatment, unheated (25 °C) Li-, Na- and K-clays showed increased d001 spacing on glycerol solvation and dispersed spontaneously in water. Mg-, Ca- and Al-clays did not disperse spontaneously in water, but the d001 spacing increased upon glycerol solvation. After heating at 300 °C or above, none of these clays dispersed spontaneously. However, swelling varied with the type of cation and the temperature of heating.

The results generally suggested that swelling and dispersion of homoionic Wyoming bentonite after heating at various temperatures depended upon the nature of bonding between clay particles and the cations. Enhanced swelling and dispersion of clays indicated the more ionic character of the cationic bonding than cases where heating resulted only in swelling, with polar covalent bonding of cations to clay surfaces allowing limited hydration. It is also suggested that, when both swelling and dispersion as a result of thermal treatment are absent, a covalent bond is formed between cation and clay surface.

Thermal treatment apparently affects the bonding in different ways. It appears that the smaller cations (ionic radius <0.7 Å) Li, Mg and Al migrate to octahedral vacant sites and form covalent bonds after heating at 400 °C; this drastically reduces the negative charge. This process for Li-clays occurred even at 200 °C. The larger cations (ionic radius > 0.9 Å) Na, K and Ca apparently did not migrate into the lattice sites after heating to 400 °C; a high proportion of them were exchangeable. The data for exchangeable cation, particle charge and clay particle size were consistent with the postulated effect of the nature of cationic bonding upon swelling and dispersion properties.

Electron spin resonance (ESR) spectroscopy is used to investigate the nature of exchange sites on kaolinite. ESR spectra of exchangeable Cu2+ and Mn2+ on kaolinite indicate that divalent exchange ions are about 11–12Å apart on kaolinite surfaces and that planar Cu (H2O)42+ ions are oriented parallel to the surfaces. Solution-like spectra for exchangeable Cu2+ and Mn2+ are observed at high relative humidities, suggesting a high degree of mobility of exchange cations on kaolinite surfaces. The evidence seems to eliminate edge sites as being active in cation exchange at least in the acidic range of pH. Similar conclusions are derived from ESR studies of Cu2+-saturated talc and pyrophyllite. It is proposed that most exchange sites arise from ionic substitutions or mineral impurities in phyllosilicates.

The structure and behavior of homoionic bentonites was markedly affected by a grinding procedure often applied to clays. The main changes observed on clay powders were the breakage of weakly bound large aggregates, the reduction in the tactoids’ thickness by delamination, the reduction in the plates’ area, and the formation of colloidal matter. The tendency of clays to form secondary aggregates in aqueous suspensions is probably due to the exposure of active broken edges following grinding.

The mild mechanical stress applied increased both the rate and the amounts of parathion sorbed by clays from an apolar solvent. The effect of grinding on parathion adsorption in aqueous clay suspensions seems to be a rate effect.

Mineralogical (XRD), morphological (transmission electron microscopy), chemical (major, rare-earth elements, and scanning-transmission electron microscopy), and isotope (Sr, O, H) measurements were made of marine detrital smectite from shales to study their reactions during early diagenesis. Albian, Aptian, and Palaeogene smectite samples were selected from Deep Sea Drilling Project drill cores taken in the Atlantic Ocean and from outcrops and drill cores from Belgium and northern France. Detrital, fake-like smectite particles seem to have adapted to their depositional environment by isochemical dissolution and subsequent crystallization of authigenic, lath-like particles. The major-element and rare-earth element compositions of both types of particles are similar. The Sr isotope chemistry suggests that the dissolution-crystallization process occurred soon after deposition in an almost closed chemical system. Except for slight changes in the amount of Fe and the oxygen isotope composition, the reaction took place without noticeable chemical exchange with the interstitial or marine environment. Such closed-system recrystallization of clay minerals may be a common diagenetic process if the water/rock ratio is small, as in shales.

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.

Kaolins and clays are important raw materials for production of supplementary cementitious materials and geopolymer precursors through thermal activation by calcination beyond dehydroxylation (DHX). Both types of clay contain different polytypes and disordered structures of kaolinite but little is known about the impact of the layer stacking of dioctahedral 1:1 layer silicates on optimum thermal activation conditions and following reactivity with alkaline solutions. The objective of the present study was to improve understanding of the impact of layer stacking in dioctahedral 1:1 layer silicates on the thermal activation by investigating the atomic structure after dehydroxylation. Heating experiments by simultaneous thermal analysis (STA) followed by characterization of the dehydroxylated materials by nuclear magnetic resonance spectroscopy (NMR) and scanning electron microscopy (SEM) together with first-principles calculations were performed. Density functional theory (DFT) was utilized for correlation of geometry-optimized structures to thermodynamic stability. The resulting volumes of unit cells were compared with data from dilatometry studies. The local structure changes were correlated with experimental results of increasing DHX temperature in the following order: disordered kaolinite, kaolinite, and dickite, whereupon dickite showed two dehydroxylation steps. Intermediate structures were found that were thermodynamically stable and partially dehydroxylated to a degree of DHX of 75% for kaolinite, 25% for disordered kaolinite, and 50% for dickite. These thermodynamically stable, partially dehydroxylated intermediates contained AlV while metakaolinite and metadickite contained only AlIV with a strongly distorted coordination shell. These results indicate strongly the necessity for characterization of the structure of dioctahedral 1:1 layer silicates in kaolins and clays as a key parameter to predict optimized calcination conditions and resulting reactivity.