Specimen samples of Crook County montmorillonite and Silver Hill illite, purified and prepared in the Na-form, were imaged under 80% relative humidity using an atomic force microscope. The direct images showed clearly the hexagonal array of hexagonal rings of oxygen ions expected for the basal planes of 2:1 phyllosilicates. Fourier transformation of the digital information obtained by the microscope scanning tip led to an estimate of 5.1 ± 0.3 Å for the nearest-neighbor separation, in agreement with the ideal nearest-neighbor spacing of 5.4 Å for hexagonal rings as derived from X-ray powder diffraction data. The atomic force microscope should prove to be a useful tool for the molecular-scale resolution of clay mineral surfaces that contain adsorbed macromolecules.

A series of hydrothermal experiments was performed to determine the effect of fluid abundance on the reaction of smectite to illite. Experiments were conducted on K-saturated montmorillonite (<0.1-µm fraction) in a closed system at 250° to 400°C using run times of 1, 7, 14, 30, and 60 days at 100 MPa (1 kbar) pressure. In fluid-deficient systems (pore spaces not saturated), the rate and extent of illitization was significantly inhibited. A rock: water ratio of 20:1 (mass: mass) produced an R0 illite/smectite (I/S) having 82% smectite layers after 60 days at 250°C, whereas a rock: water ratio of 1:1 produced an I/S having 57% smectite layers under the same conditions. The effect became less pronounced at higher temperatures, with the 20:1 and the 1:1 experimental products differing by only 11% expandability at 400°C after 60 days. In addition, the low-fluid experiments produced fewer crystalline byproducts (quartz, cristobalite, chlorite) than did the fluid-rich runs, and the I/S was more difficult to disperse and orient in the fluid-deficient samples, suggesting enhanced cementation at grain contacts or the production of particle morphologies that did not lend themselves to orientation. The difference in reactivity of the smectite and I/S as a function of water content appears to be attributable to the reduced capacity for low volumes of water to mediate the dissolution, solute transport, and precipitation reactions that make up the series of reactions collectively termed illitization. Of these variables, solute transport is likely to be affected most by reduction of fluid.

The characterization of cations associated with clay materials has generally been approached by the sequential use of specific chemical reagents. To avoid the disturbing effect of the chemical reagents on the state and location of compensating cations of clays and to get information in situ, far-infrared spectroscopy was used. The far-infrared vibrational spectra of the potassium cation in muscovite, phlogopite, and biotite were recorded before and after heating at the dehydroxylation temperature. The vibrational frequency of K in micas before dehydroxylation was found to be a function of the di- or trioctahedral character and of the Fe content. After dehydroxylation or deprotonation, shifts of the K absorption band to lower frequencies were observed for the heated muscovite, in which K exchangeability increased, and to higher frequencies for the heated biotite, in which K exchangeability decreased. These results suggest that the vibrational frequency of potassium is characteristic of the state of K in these minerals and of its ability to be exchanged.

The surface charges and the zeta potential of a Na-montmorillonite (Na-mont) and two pillared montmorillonite (MP1 and MP2) samples with different aluminum contents were determined by Potentiometric titrations and electrophoretic measurements. At pH >9 the two pillared montmorillonite samples showed zeta potentials similar to those of Na-mont, but at pH <8, the negative zeta potential shifted to lower negative values as the aluminum content increased. Sample MP1, which had a greater Al content, showed an isoelectric point (IEP) of 5.0–5.5. Titration curves obtained by acid-base Potentiometrie titration for sample MP1 showed a well-defined cross-over point at pH = 5.0, whereas this point was not observed for sample MP2 in the pH range studied. The results indicate, in principle, that both techniques can be used to characterize surface charges in this type of material. An attempt was also made to relate the data obtained from electrophoretic mobility and Potentiometrie titrations.

A montmorillonite exchanged with large hydroxy-Al cations was thermally treated to convert the hydroxy cations to oxide pillars and to generate permanent microporosity in the interlayers. The pillared clay products were characterized by X-ray powder diffraction (XRD) and water-sorption measurements to delineate the effect of aging of the pillaring solutions, the methods of drying and concentration of clay-water suspensions, and the temperatures of calcination on micropore volumes. Although samples prepared at different conditions gave d(001) reflections of 17–17.5 Å, at least to 500°C, the concentrations of clay-water suspensions and the temperatures of calcination significantly changed the pore-size distribution and the volume of micropores present in the sample, as calculated from the water-sorption isotherms. A narrow pore-size distribution having little or no macroporosity or external surface condensation was observed in samples prepared by the addition of the pillaring solution directly to the clay (solid) without first making a clay-water suspension and calcining the sample at ≥400°C. About 87% of the total volume was found to be micropores of ≤14–17 Å in the sample calcined at 600°C. Aging the pillaring solution, however, did not influence either the water-sorption isotherms or the XRD patterns significantly under the conditions specified. Essentially the same results were obtained for samples prepared from both hydroxy-Al polymer (OH/Al = 2) and aluminum chlorohydrol (ACH) solutions.

Although alumina-pillared clays exhibited an extreme type-I isotherm (Langmuir type) for nitrogen adsorption, the sorption of water vapor gave an isotherm of unusual shape that fit neither a BET nor a Langmuir equation. This latter behavior has previously been attributed to a unique pore size and hydrophobicity and is apparently common to all pillared montmorillonite materials. The hydrophobicity of the pillared clay apparently developed on calcination by the migration of protons from the interlayers to the octahedral sheets, in which sites of cationic substitution (negative charge) were located. Protons migrated back to the interlayers by treatment with NH3, which subsequently converted to NH4+ in the interlayers. The exchange of the NH4+ by Ca2+ introduced hydrophilicity to the alumina-pillared clay, which was reflected both in the shape of the water isotherm (close to moderate Brunauer type I), the heat of sorption, and the total sorption capacity.

Samples of mixed-layer illite/smectite were investigated from a single bentonite bed zoned with respect to expandability from 90 to 30%. Chips of natural rocks were embedded in a resin, using a procedure designed to preserve the original fabric, cut with an ultramicrotome, and observed by high-resolution transmission electron microscopy (HRTEM). These observations confirmed the X-ray powder diffraction (XRD) model of mixed-layer clays, i.e., that illite/smectite grains in natural rocks are built of mixed-layer crystals, from 1 to as many as 15 silicate layers thick (4–6 interlayers per crystal on average). These crystals are present either as individual particles (loose crystals) or, typically, they form nearly parallel face-to-face groupings called here quasi-crystals. Free fundamental smectite and illite particles as defined by Nadeau and coworkers were essentially absent.

Illite and smectite interlayer spacings were 10 and 13.5 Å, respectively. Crystal thickness and number of interlayers were measured for 35–100 mixed-layer crystals per sample. Illite/smectite expandabilities were calculated from these data in two ways: either neglecting the crystal edges or accounting for them. The former determinations agree well with XRD estimates of expandability and the latter, with expandabilities calculated from the distributions of fundamental particle thickness measured by a shadowing technique in the TEM. This result explains the systematic discrepancy between XRD and TEM measurements of illite/smectite expandability.

Quasi-spherical particles (7-µm mean diameter) were prepared from cross-linked hydroxy-Al-montmorillonite (basal spacing =15.3 and 18.6 Å) by spray-drying. These particles (SP-CLM) were used as a packing material for columns in high-pressure liquid chromatography (HPLC). Aromatic phosphate esters, chlorosubstituted phenyl-ureas, monosubstituted benzenes, and the o-, m-, and p-isomers of disubstituted benzenes were separated on the columns, using isopropanol and hexane. Alkyl and alkoxy groups in the solute molecules sterically hindered the interaction of these molecules with the solid phase. The retention of the isomers of disubstituted benzenes that possess one electronegative (or dipolar) and one nonpolar substituent increased in the order: o- < m- < p-. In contrast, for all investigated disubstituted benzenes containing two electronegative (or dipolar) substituents, the o-isomer was retained on the 18.6-Å SP-CLM more strongly than the m- and p-isomers. The chromatographic data suggest that the strength of the interaction of phenolic groups with the solid phase increased with the acidity of these groups. The o-isomers of phenols that contained an additional electronegative (or dipolar) substituent displayed an exceptionally strong adsorption. The capacity of the o-isomers of disubstituted benzenes containing two electronegative (or dipolar) substituents to form chelates with Al probably was responsible for the strong retention of such o-isomers compared with the retention of the corresponding m- and p-isomers.

Cross-linked hydroxy-Al-montmorillonite acted as a strong and selective adsorbent for many families of organic compounds. It was used successfully as the solid phase in HPLC separations with eluents ranging from nonpolar (e.g., hexane) to highly polar (e.g., water).

Clay-modified electrode research indicates that adsorbed complexes are electroactive if the adsorption sites are clay edges. Interlayer adsorbed complexes may be electroactive if a charge shuttle is added or if interlayer swelling is large. Conductivity of the film towards anionic species depends upon the swelling of the clay, which depends on the electrolyte concentration and speciation. The diffusion coefficients measured by electrochemical experiments agree well with alternative measurements.

The feasibility of transforming palygorskite from two localities to smectite hydrothermally at temperatures ranging from 22° to 160°C was investigated in a series of laboratory experiments, in which alkalinity was maintained in the pH range of 11.4 to 12 by adding NaOH. The smectite formed was characterized by chemical, spectroscopic, and electron microscopic techniques. Smectite formed rapidly at > 100°C; the transformation was slow, however, at 22°C. The introduction of MgCO3 accelerated the alteration process, but changes in alkalinity at pH > 12 and the difference in elemental composition of the palygorskite samples did not significantly affect the alteration. A pressure of one atmosphere and a temperature of 22°C were sufficient for some transformation to occur within a few months, provided the alkalinity was maintained close to pH 12. X-ray powder diffraction characterization of the product indicated a smectite, and infrared spectroscopy indicated saponite. The alteration to smectite was appreciable even at room temperature, which suggests that the reaction can take place without any external heating.

Na-beidellite, a member of the smectite group, was grown hydrothermally from a gel of composition 0.35Na2O·2.35Al2O3·7.3SiO2 in NaOH solutions at a pH between 7.5 and 13.5, a pressure of 1 kbar, and a temperature of 350°C. The synthetic Na-beidellite was characterized by means of scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, electron microprobe, inductively coupled plasma-atomic emission spectroscopy, and thermogravimetric analysis. The unit-cell parameters of the orthorhombic cell are: a = 5.18, b = 8.96, and c = 12.54 Å. The cation-exchange capacity was determined to be 70 meq/100 g. A maximum of 40 wt. % water was present and reversibly lost by heating to about 55°C. The loss of water caused a decrease of the basal spacing to 9.98 Å. At temperatures ≥600°C, the Na-beidellite started to dehydroxylate, reaching its maximum in the range 600°–630°C. At 1100°C the remaining solid recrystallized to Al6Si2O13 (mullite) and SiO2 (cristobalite).

A mixed-layer kaolinite/smectite (K/S) containing trace amounts of quartz, discrete kaolinite, goethite-hematite, and calcite was hydrothermally reacted with deionized water at 150°, 200°, and 250°C for 1 to 12 months. The starting K/S contained 50% smectite consisting of 15% low-charge and 35% high-charge layers. The X-ray powder diffraction and chemical analyses of the reacted products indicated a progressive reaction from high-charge to low-charge smectite as a function of time and temperature. The reaction reached completion after 4 months at 250°C, at which point high-charge smectite layers entirely reacted to low-charge smectite layers, the latter maintaining a constant proportion of about 90% for longer run durations. For long reaction times, discrete kaolinite totally reacted, whereas quartz showed only partial dissolution and iron oxides remained stable. Thus, the reaction of high-charge to low-charge smectite layers may be expressed as: high-charge smectite + kaolinite (both interstratified and discrete component) + quartz → low-charge smectite.

Montmorillonite and K-feldspar deposits of potential economic interest occur in the Late Oligocene-Miocene tuffs of the Vizcarra Formation in the state of Durango, Mexico. The two minerals were formed separately from rhyodacitic to rhyolitic pyroclastic deposits in a closed hydrologie system and diagenetically altered following two different patterns. In material deposited on dry land the glass was completely replaced by K-feldspar, and the interstices between the replaced glass bubbles and shards were filled with chalcedony, quartz, and albite. Pyroclastic material deposited in an alkaline lacustrine environment were diagenetically altered to montmorillonite, which formed the bentonitic tuffs widely exposed beneath the K-feldspar-rich tuff. These bentonitic tuffs contain as much as 85% montmorillonite plus authigenic chalcedony and quartz. Pyrogenic sanidine, quartz, and oxybiotite, coarse glass shards, and clastic grains make up about 8% of the clay-rich tuffs. The composition of the montmorillonite corresponds to the formula (Si3.88Al0.12)(Al1.41Mg0.59)O10(OH)2(Ca0.07Mg0.11,Na0.28K0.06). The montmorillonite is dioctahedral, the surface acidity is of the Lewis type, and the clay swells to one- and two-layer complexes. The cation-exchange capacity is 64 meq/100g; base exchange is Ca2+, 15; Mg2+, 20; Na+, 4.1; and K+, 1.0 meq/100 g. Its interlamellar charge is 18.6 microcoulombs/cm2. Dacitic pyroclastics were deposited later at higher elevations along the margins of the basin. Percolating solutions apparently removed a siliceous leachate from the dacitic glass and partially altered it to clinoptilolite.

Adsorption calorimetry was used to develop a method for determining the surface area of low-surface-area materials (<1 m2/g), which required no pretreatment of the surface, such as outgassing at elevated temperatures. The method involved flowing heptane through a small amount of sample (0.15 to 1.0 g) in the flow cell of a commercial microcalorimeter. When thermal equilibrium was reached at the powder-heptane interface, pure heptane was replaced with a heptane carrier-solution containing 0.6 volume % n-butanol (n-BuOH) as the preferential adsorbate. The integral enthalpy of preferential saturation adsorption, ΔHsat, of n-BuOH on the surface was found to be a function of the BET surface area of the sample. An empirical relationship between ΔHsat and BET surface area was determined over a surface area range of about three orders of magnitude (0.095 to 81 m2/g) by performing adsorption experiments on five α-alumina standard reference powders. The technique was applied to the determination of surface areas of untreated rock and mineral powders.