X-ray superlattice reflections, infrared spectroscopy, and chemical analyses have established that cetylpyridinium bromide (CPB) is highly ordered when adsorbed on vermiculite. The molecules, which stand at about 57° to the silicate surface, form close-packed arrays. Full surface coverage is achieved only for the most highly charged vermiculites. The packing within the arrays accounted for the superlattice observed and each adsorbed molecule had an area of 18.4 Å2 at the surface. The implications of these findings for the CPB method used in soil surface area studies are discussed.

Kaolinites of all kinds (fine, ‘fireclay,’ ‘type IV,’ etc.), some of which do not expand or expand incompletely with the usual intercalation methods used for comparison, are expanded completely by treatment of dry (110°C) clay with dry CsCl salt, followed by contact with hydrazine for 1 day at 65°C and then with DMSO overnight at 90°C. Comparison treatments were grinding in KOAc, soaking in hydrazine, and Li-DMSO, as well as combination of these. Following the Cs-hydrazine-DMSO treatment, the 7.2 Å spacing of 1:1 dioctahedral layer silicates shifts to 11.2 Å and the 11.2 Å/(7.2 + 11.2 Å) ratio ≃1.0. The trioctahedral 1:1 layer silicates and chlorite are not expanded by the Cs-hydrazine-DMSO procedure.

Using a simple ionic model, the energy necessary to expand a layer structure by a certain distance can be calculated. This has been done for a series of 15 structures including hydroxides, 2:1 and 1:1 structures of various types. Plots of energy versus separation distance show three major groups which have common bonding properties. For large separations, the group with the strongest interlayer bonds contains the brittle micas, the hydroxides, and the 1:1 structures. Intermediate bonding structures are the normal micas and the weakest bonds occur in the zero layer charge 2:1 structures. The relative energies needed for a given separation are not constant so that for small separations the zero layer charge structures such as talc and pyrophyllite are more strongly bonded than the normal micas. These groupings correlate very well with the expandability of the structures by water and other substances. It is proposed that this approach to the study of the layer structures will provide a simple theory explaining the expansion properties of layer silicates.

Dehydroxylated sericites were stirred in the various salt solutions, or washed several times with various salt solutions using a centrifuge. By these treatments a seriate of the 2M type was easily transformed into an interstratified mineral of the rectorite type when a sericite was treated with sodium salts, and random mixed-layer mineral was formed from 1M sericite. The formation of a rectorite-type mixed-layer mineral from 2M sericite can be explained by the (OH) bond direction after the extraction of the potassium ions.

From swelling and surface area measurements, it was found that the swelling of a montmorillonite depends linearly on the fraction of its layers that fully expand in water and that this fraction, in turn, depends linearly on the b dimension of the unit cell. Therefore, swelling is a linear function of the b dimension. However, the specific surface area of a montmorillonite is a linear function of its b dimension only if no partially expanded layers exist. It was also found that the distance between fully expanded layers at a given applied pressure is the same for all montmorillonites.

Infrared spectroscopic, X-ray powder diffraction, diffuse reflectance, and electron-spin resonance examination of homoionic bentonite from Sardinia treated with diazomethane indicates that poly-methylene was formed in the interlayer position. Polymerization can be attributed to the acidic properties of the residual water in the interlamellar space, depending on the nature of the exchanged ion. The presence of an interlayer polymer causes the clay to assume strong hydrophobic properties.

The adsorption of butanol, hexanol, and octanol on alkylammonium clays of different chain length is studied. The adsorption at infinite dilution compares to the distribution of alcohol between alkane and water in bulk solution. The interlamellar phase of the montmorillonite acts as a solvent even more reactive than carbon tetrachloride. Hydrogen bonds probably occur between the OH group of the alcohol and the NH3+ group. The exchange of water by alcohol on the interlamellar alkylammonium ion is the major factor in the transfer process.

Nickel nitrate solution is potentiometrically titrated (a) with montmorillonite, (b) without montmorillonite, in the nitrate solution. X-ray powder diffraction and chemical analyses are made of the products formed by the clay at various stages of titration. The pH values of the titration curve (a) are lower than those of curve (b) until the brucite-like hydroxynickel interlayer is more or less complete. The resulting product then closely resembles a chlorite. The preferential precipitation of hydroxide in the interlayer region is explained in terms of the acidic character of montmorillonite interlayers.

The basal spacings of montmorillonites with Li, Na, K, Cs, Mg, Ca, Sr, Ba, and Pb interlayer cations were measured after immersion in dimethylsulfoxide (DMSO) and in water-DMSO mixtures. In DMSO alone, the spacings were in the range 18.3–19.3 Å and fell on or near a single curve when plotted against ionic field strength, q/r2, where q = valence and r = ionic radius. These spacings correspond to double layers of DMSO molecules between the silicate layers. Water had practically no effect on the spacings when the mole fraction of DMSO exceeded about 35–45%. Osmotic swelling of Li-, Na-, and K-mont-morillonite occurred up to mole percentages of DMSO 45%, 30%, and 10%, respectively. K- and Cs-mont-morillonite formed single-layer complexes in appropriate water-DMSO mixtures with spacings of 14.3 Å prior to development of double-layer complexes when the mole fraction of DMSO exceeded 35% and 15%, respectively.

Several new salt intercalation complexes of halloysite have been prepared and characterized using X-ray powder diffraction techniques taking into account both the position and the shape of the d001 peaks. The amount of intercalated ion in some fully complexed halloysites has been directly determined using conventional analytical techniques. The results show that less than half of the theoretical amount of salt is intercalated into the clay; the amount of salt depending on its nature and, where hydrolyzable ions are present, on the pH. Infrared spectra taken of some complexes give an indication of the nature of the interaction within interlayer space and elsewhere. The interactions are weak and are either dipolar attractions or hydrogen bonds. The ions which show the greatest tendency to intercalate with halloysite are water structure-breaking cations or hydrogen-bonding anions.

The cation-exchange capacity (CEC) of Na-Al- and Ca-Al-montmorillonite after neutralization with NaOH or Ca(OH)2 was studied at three Al levels: 10, 25, and 50% of the CEC. Hydroxy-Al polymers were effective in reducing the CEC of Na-montmorillonite (by more than 46%), the exact effectiveness being dependent on the hydroxy-Al content. The hydroxy-Al polymers were less effective in reducing the CEC of Ca-montmorillonite (less than 26%). The CEC reduction was equal to or larger than the amount of the untitrated Al. The electrostatic charges of the clay which were blocked by the hydroxy-Al polymers were compensated for by both the positive charge of the hydroxy-Al polymers and the trapped cations on the clay surfaces. These cations remained on the clay even after extensive washing with 0.1 M KCl.

Several new minerals, structurally and chemically similar to the hydrotalcite-manasseite group, have been found in the saline deposits of the central pre-Caspian depression and in those of Middle Asia. Their structures consist of layers of (Mg1-xAlx)(OH)2 plus interlayers of anions and molecular water. In addition to manasseite itself, [(Mg4Al2)(OH)12][(CO3)-3H2O], having unit-cell parameters of a = 3.042, c = 2 × 7.56= 15.12 Å and a calculated density of Dc = 2.15 g/cm3, other varieties were identified whose interlayers contain alternately SO42− or SO42− and CO32− anions. The following new phases were recognized: (1) an 8.85-Å phase having the composition [(Mg4Al2)(OH)12][(SO4)·3H2O], subcell dimensions of a' = 3.04, c' = 8.85 Å, and Dc = 1.96 g/cm3; (2) an 11-Å phase having the composition [(Mg3.96Fe0.06Al1.98)(OH)12][Na0.56(SO4)1.30·7.3H2O], hexagonal unit-cell parameters of a = √3 · 3.042 = 5.28 Å, c = 11.16 Å, and Dc = 1.90 g/cm3; (3) a 16.5-Å mixed-layer phase having the composition [(Mg4Al2)(OH)12][(SO4)0.5(CO3)0.5·3H2O] and an ordered ABAB... alternation of 7.56-Å layers (i.e., a brucite-like layer + a CO32−-containing interlayer) and 8.94-Å layers containing SO42− anions in interlayers; this phase has unit-cell dimensions of a' = 3.05, c' = 16.5 Å and Dc = 2.06 g/cm3; and (4) an 18.5-Å ordered mixed-layer phase having the ideal composition [(Mg8Al4)(OH)24][M+0.5(SO4)1.25(CO3)1.0·9H2O] and an alternation of 7.56-Å, CO3-containing layers and 11-Å layers having SO42− anions and Na and Mg cations in interlayers (M+0.5 corresponds to interlayer cations). This last phase has unit-cell dimensions of a = 3.046, c = 3 × 18.54 = 55.62 Å and Dc = 1.99 g/cm3. Some of the varieties containing SO42− in the interlayers swelled with ethylene glycol or glycerol.

For this diverse family of minerals whose structures are based on brucite-like layers of the composition (R2+1-xR3+x)(OH)2, a unifying system of nomenclature is offered for consideration. In describing these brucite-like structures intercalated with anion- and cation-containing interlayers, the composition of the hydroxide sheet and the interlayers, the periodicity of the layers, and the mixed-layer nature of the material should be described. By means of symbols, a single term might be used to describe the crystal chemistry of any member of the group having a given cation composition for the brucite-like layers, for example, manasseite, a 2H polytype of hydrotalcite that has a repeat distance of 7.56 Å and CO3-containing interlayers, might be designated as 7.56-Å CO3-hydrotalcite-2H.

Hydroxychromium montmorillonites were prepared from solutions containing chromium nitrate and varying amounts of NaOH. The reactant Cr ions were hydrolyzed and, in some experiments, were dimerized to a significant extent. The extent of polymerization in the product formed from a solution containing a maximum amount of [Cr2(H2O)8(OH)2]4+ was compared with that in products obtained from solutions containing monomer, [Cr(H2O)5OH]2+, and lesser amounts of the dimer. Despite the uncertainty about the nature and amounts of product interlamellar species, the catalytic effect of the montmorillonite interlayer on the hydrolysis and polymerization of Cr(III) appears to be independent of the nature of the reactant species. The validity of this conclusion depends to a large extent on the reliability of water determination in the clay mineral species, which is estimated to be no better than 5%. The assumption that H2O+ is 'combined’ and H2O— is 'free’ water is shown to be partially true, thereby causing some uncertainty in the interpretations of interlayer compositions.

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.

To better predict the fate and mobility of surfactants in the environment, sorption and desorption of a nonionic polyoxyethylene lauryl ether surfactant (Brij 35) by two smectites (Wyoming montmorillonite and Panther Creek smectite) and two interstratified mica-vermiculites (IMVs) were investigated by batch techniques, X-ray diffraction, and infrared spectroscopy. Maximum surfactant sorption by smectites ranged from 196 to 256 g kg−1, whereas the maximum sorption by the IMVs was indeterminate over the range of concentrations employed. Sorption by smectites was best described by the Langmuir model, but sorption by the IMVs showed an S-shaped isotherm, suggesting that cooperative sorption occurred. The surfactant was more readily desorbed from the IMVs than from the smectites in an initial wash with water. After two water washes, 65–75% of the initially sorbed surfactant was retained by the smectite, and 44–51% of the surfactant sorbed to the IMVs remained with the solid phase. In this study, basal spacing of the smectites increased to ≈17.5 Å near the sorption maximum, suggesting intercalation of surfactant molecules in the interlamellar regions of the clay. X-ray data also suggested that the surfactant molecules were oriented horizontally in the interlayer spaces. Greater surfactant sorption by the Casmectites gradually diminished the intensity of the 1630 cm−1 infrared band dues to hydration water, indicating that some water had been displaced by the surfactant. The surfactant was also sorbed by the IMV clays, but only on external surfaces and probably via interactions of micelles with the solid phase.

Water-vapor sorption experiments were conducted to quantify bulk volume change of compacted expansive clay specimens resulting from interlayer hydration and dehydration in the crystalline swelling regime. Effects of interlayer cation type and pore fabric are examined by comparing results for natural Na+-smectite and Ca2+-smectite specimens compacted over a range of initial bulk densities. Transitions in interlayer hydration states are reflected in the general shape of the sorption isotherms and corresponding relationships between humidity and volume change. Hysteresis is observed in both the sorption and volume-change response. Volume change for Ca2+-smectite specimens is significantly greater than for Na+-smectite over the entire range of packing densities considered. Loosely compacted specimens result in less volume change for both clays. Results are interpreted in light of a conceptual framework based on previous SEM and TEM observations of particle and pore fabric for Na+ and Ca2+ smectite at high suctions. A pore-scale microstructural model is developed to quantitatively assess changes in interlayer and interparticle void volume during hydration. Modeling suggests that the relatively small volume changes observed for Na+-smectite are attributable to a reduction of interparticle void volume as expanding quasicrystals encroach into surrounding larger-scale pores. Volume change hysteresis is attributed to unrecovered alterations in interparticle fabric required to accommodate the swelling process. The results provide new insight to address volume change upscaling, hysteresis, and the general evolution of bi-modal pore fabric during crystalline swelling.

The aqueous chemistry of water films confined between clay mineral surfaces remains an important unknown in predictions of radioelement migration from radioactive waste repositories. This issue is particularly important in the case of long-lived anionic radioisotopes (129I-, 99TcO4-, 36Cl-) which interact with clay minerals primarily by anion exclusion. For example, models of ion migration in clayey media do not agree as to whether anions are completely or partially excluded from clay interlayer nanopores. In the present study, this key issue was addressed for Cl- using MD simulations for a range of nanopore widths (6 to 15 Å) overlapping the range of average pore widths that exists in engineered clay barriers. The MD simulation results were compared with the predictions of a thermodynamic model (Donnan Equilibrium model) and two pore-scale models based on the Poisson-Boltzmann equation under the assumption that interlayer water behaves as bulk liquid water. The simulations confirmed that anion exclusion from clay interlayers is greater than predicted by the pore-scale models, particularly at the smallest pore size examined. This greater anion exclusion stems from Cl- being more weakly solvated in nano-confined water than it is in bulk liquid water. Anion exclusion predictions based on the Poisson-Boltzmann equation were consistent with the MD simulation results, however, if the predictions included an ion closest approach distance to the clay mineral surface on the order of 2.0 ± 0.8 Å. These findings suggest that clay interlayers approach a state of complete anion exclusion (hence, ideal semi-permeable membrane properties) at a pore width of 4.2 ± 1.5 Å.

Sets of replicate hydraulic conductivity tests were conducted using 100 mM KCl and 20 and 40 mM CaCl2 solutions to evaluate how changes in hydraulic conductivity are related to changes in the exchange complex and physical properties (water content and free swell) of prehydrated and non-prehydrated bentonite used for geosynthetic clay liners (GCLs). Essentially no change in hydraulic conductivity and water content (or void ratio) occurred during tests with the 100 mM KCl solution even though K+ was replacing Na+ on the exchange complex. In contrast, for the CaCl2 solutions (20 mM and 40 mM), the hydraulic conductivity increased and the free swell and water content decreased as exchange of Ca2+ for Na+ occurred. Faster changes in hydraulic conductivity and the exchange complex occurred in the tests with the 40 mM CaCl2 solution and the non-prehydrated bentonite (i.e. the hydraulic conductivity changed more rapidly when exchange occurred more rapidly). Even though exchange of Ca2+ for Na+ was essentially complete at the end of testing, the hydraulic conductivity obtained with the 20 mM CaCl2 solution was less and the water content greater than obtained with the 40 mM CaCl2 solution (2.6 × 10−8 cm/s vs. 6.7 × 10−8 cm/s, 122% vs. 111%, and 3.2 vs. 2.9). Similarly, the prehydrated bentonite had lower hydraulic conductivity (1.9 × 10−8 cm/s vs. 6.7 × 10−8 cm/s) and greater water content (167% vs. 111%) than the non-prehydrated bentonite at the end of testing, even though Ca-for-Na exchange was essentially complete.

Compacted Na-bentonite clay barriers, widely used in the isolation of solid-waste landfills and other contaminated sites, have been proposed for a similar use in the disposal of high-level radioactive waste. Molecular diffusion through the pore space in these barriers plays a key role in their performance, thus motivating recent measurements of the apparent diffusion coefficient tensor of water tracers in compacted, water-saturated Na-bentonites. In the present study, we introduce a conceptual model in which the pore space of water-saturated bentonite is divided into ‘macropore’ and ‘interlayer nanopore’ compartments. With this model we determine quantitatively the relative contributions of pore-network geometry (expressed as a geometric factor) and of the diffusive behavior of water molecules near montmorillonite basal surfaces (expressed as a constrictivity factor) to the apparent diffusion coefficient tensor. Our model predicts, in agreement with experiment, that the mean principal value of the apparent diffusion coefficient tensor follows a single relationship when plotted against the partial montmorillonite dry density (mass of montmorillonite per combined volume of montmorillonite and pore space). Using a single fitted parameter, the mean principal geometric factor, our model successfully describes this relationship for a broad range of bentonite-water systems, from dilute gel to highly-compacted bentonite with 80% of its pore water in interlayer nanopores.