Gas-solid chromatographic measurements of interaction energies were made for the systems ethanol and acetone with K-, Na-, Ba-, and Ca-montmorillonites. The results revealed an increased interaction energy in the order

K-mont. < Na-mont. < Ba-mont. < Ca-mont.

Interaction energies ranged from about 14 kcal/mole for K-montmorillonite to about 30 kcal/mole for Ca-montmorillonite. A very good agreement was observed between experimental heats of adsorption values and theoretical values for the electrostatic attractive energy between the respective cations and polar molecules.

These results confirm our earlier suggestions that complex formation takes place through cation-dipole interactions and that the polar molecules solvate the exchange cations in a manner similar to the hydration of cations in aqueous solutions.

X-ray analysis of Li+- and K+-saturated samples, differential thermal analysis (DTA), thermal gravimetric analysis (TGA), and chemical analysis of 83 samples enable a distinction to be made between Wyoming, Tatatilla, Otay, Chambers, and non-ideal types of montmorillonite, and between ideal and non-ideal types of beidellite. The Greene-Kelly Li+-test differentiates between the montmorillonites and beidellites. Re-expansion with ethylene glycol after K+-saturation and heating at 300°C depends upon total net layer charge and not upon location of the charge. Wyoming-type montmorillonites characteristically have low net layer charge and re-expand to 17 Å, whereas most other montmorillonites and beidellites have a higher net layer charge and re-expand to less than 17 Å.

Major differences in dehydroxylation temperatures cannot be related consistently to the amount of Al3+-for-Si1+ substitution, nor to the amount of Mg, Fe, type of interlayer cations, or particle size. The major factor controlling temperature of dehydroxylation seems to be the amount of structural (OH). Of 19 samples analyzed by TGA, montmorillonites and the one ideal beidellite that give dehydroxylation endotherms on their DTA curves between 650° and 760°C all contain nearly the ideal amount of 4(OH) per unit cell, but the non-ideal montmorillonites and beidellites that give dehydroxylation peaks between 550° and 600°C do not. Non-ideal beidellites contain more than the ideal amount of structural (OH) and non-ideal montmorillonites seem to contain less, although the low temperature of dehydroxylation of the latter could also be due to other structural defects. Change in X-ray diffraction intensity of the 001 reflection during dehydroxylation suggests that the extra (OH) of beidellite occurs at the apex of SiO4 or AlO4 tetrahedrons with the H+ of the (OH)− polarized toward vacant cation sites in the octahedral sheet.

Conductometric titrations of clay suspensions with surfactant solutions offer a rapid method of surface area determination of clay particles suspended in aqueous media. A cationic surfactant, dodecylamine hydrochloride, was used in this investigation. This surfactant was adsorbed by electrostatic bonding at cation exchange sites and by van der Waals forces. A monomolecular or bimolecular layer of the surfactant coats the particle and the completion of the layer is determined from a change in slope of the conductometric titration curve due to the formation of micelles. Good agreement between this method and BET determined values were obtained for kaolinite. The bentonite suspensions had a strong tendency to flocculate after the initial stage of adsorption causing the results to vary considerably. This method of surface area measurement of clay particles offers many advantages over the present techniques: (1) a dry particle is not required; (2) the equipment is inexpensive and available in many laboratories; (3) the method is rapid; (4) vacuum and high temperature are not required, and (5) the method measures the internal as well as external surface area.

A magnesium hydroxide-montmorillonite complex prepared at an OH/Mg molar ratio of 2 (16 meq Mg/g clay) and immediately cleaned of any free Mg(OH)2 behaves like magnesium-chlorite and shows no change during 3 months ageing. Magnesium hydroxide completely precipitates within the interlayer space of montmorillonite. X-ray diffraction analysis, thermal (DTA and TGA) studies, i.r. absorption analysis, polarographic reduction behaviour, and cation exchange capacity measurements confirm the transformation of montmorillonite to a chlorite-like structure. Further ageing of the complex results in the release of brucite from the interlayer space and expansion of the complex on glycerol treatment. X-ray analysis of the 6 months aged sample shows the presence of free brucite but not montmorillonite. A small but significant increase in CEC of the complex is observed on ageing. When the Mg(OH)2-montmorillonite complex is allowed to age in the presence of free Mg(OH)2 (external to montmorillonite unit layers) in a dry state, a “seeding” effect takes place and the “fixed” Mg(OH)2 starts coming out from the interlayer space after 10 days.

Centrifuged fractions, ranging in size from 2·0 to 0·05 μ of a Wyoming bentonite, Bentonita de Durango from Mexico, and Helms clay from Texas were studied. The variation in replacement of Na+, Ca2+, Mg2+, K+, and H+ from these heteroionic clay systems under specific equilibrium conditions of salt concentrations was measured.

The displacement cation distribution was monitored by using specific ion glass electrodes, such as a sodium ion electrode, a cationic glass electrode, a calcium ion electrode and a Tektite electrode. Some factors affecting the exchange reactions are discussed and application of findings to drilling and production techniques is indicated.

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.

The removal of titanium minerals from kaolin can be accomplished by treatment with dispersing agents in an amount in excess of that required to produce maximum deflocculation of the kaolinite particles. In this reflocculated state the kaolinite particles attain a high degree of suspensional stability, and the titanium mineral particles, primarily anatase, are liberated and can be separated by sedimentation. Substantial removal of anatase impurities can be achieved by this method.

If a series of rock samples with granitic composition in various stages of chemical weathering is ground in a mortar with distilled water and the pH of the slurry produced is determined, it will be evident that the pH declines as the weathering increases. This relationship can be made useful by plotting abrasion pH against some other index of weathering such as the percentage of clay mineral or the bulk density of the weathered rock. Factors controlling abrasion pH are the cations such as K, Na, Ca, and Mg and the amount of clay mineral present.

The mechanism of interaction between cationic organic molecules satisfying exchange sites in montmorillonite and organic molecules with carbonyl groups was investigated. Dialkyl amides adsorbed on trimethyl-ammonium- and tetramethylammonium-montmorillonite were studied by i.r. spectroscopy. The electronegativity or basicity of the amides, expressed as a summation of the Taft polar factors (Σσ*), was found to be linearly related to the C-O stretching frequency after adsorption on trimethyl-ammonium-montmorillonite. Furthermore, the changes in the C—O and N—H stretching frequencies of the amides and trimethylammonium ion respectively, exhibited a direct linear relationship. Thus, the dialkyl amides were shown to be hydrogen bonded through the oxygen of the carbonyl group to the hydrogen of the trimethylammonium. The (001) spacing of trimethyl-ammonium-montmorillonite was 12·9 Å Only after the adsorption of amide molecules of the size of N,N-diethylacetamide or larger did this spacing change. Dialkyl amides were adsorbed on tetramethylammonium-montmorillonite, but less energetically than on trimethylammonium-clay. The (001) spacing of tetramethylammonium-montmorillonite was 13·8 Å and remained the same after adsorption of the dialkyl amides. Evidence of hydrogen bonding between the hydrogen of trimethylammonium-ion and some other carbonyl compounds was also noted.

A series of organic ammonium ions were exchanged onto clay minerals montmorillonite and hectorite. Thermal effects on these surface modified organic-inorganic complexes were investigated by means of differential thermal analysis and heating-oscillating X-ray diffraction methods. It was found that the organo-clay complexes were dehydrogenated at temperatures from 180 to 350°C, depending on the organic cation used. Following the dehydrogenation, hydrolysis took place leaving a layer of “carbon” on the clay surface. The “carbon” was then oxidized at a temperature of about 550°C. Investigation of possible correlations between the activation energy of dehydrogenation and basicity, boiling point, ionization potential, molecular structure, and carbon-carbon bond distances of the organic cations showed that the geometric factors outweighed the acid, chemical and electronic factors in determining the effect of montmorillonite and hectorite toward the dehydrogenation of organic ions exchanged on the surfaces of these clay minerals.

Surface-area studies were made on several homoionic vermiculites with both nitrogen and carbon dioxide as adsorbates. These studies show that only very slight penetration occurs between individual vermiculite platelets. This is in contrast to an earlier investigation of montmorillonite where it was found that the degree of penetration between layers is quite high, particularly for carbon dioxide, and is governed by the size and charge of the interlayer cation. The inability of these adsorbates to penetrate substantially between vermiculite platelets is due primarily to this mineral’s high surface-charge density.

The extent of penetration of nitrogen and carbon dioxide at the edges of vermiculite platelets, though slight, is influenced by the coordinated water retained within the sample at a given degassing temperature. Forces between layers are weakened with increasing water content, which permits slightly greater penetration by adsorbate gases. Thus, the surface area of vermiculite, as determined by gas adsorption, is larger than the calculated external surface area based upon particle size and shape considerations. In addition, “extra” surface is provided by the lifting and scrolling of terminal platelets. These morphological features are shown in scanning electron micrographs of a naturally occuring vermiculite.

Previously reported deposits of kaolin of hydrothermal origin in Mexico have been described from igneous parent rocks dominantly extrusive in occurrence. Recently observed evidence from other localities confirms an intrusive mode of occurrence, however, for hydrothermally kaolinized agglomerate and tuff within limestone host rock. Three such occurrences have been recognized near Jasso-Calera, north of Mexico City, and near Coacoyula, Guerrero, and Sombrerete, Zacatecas.

The contacts of these clay deposits with limestone show regularly a concentration of iron-rich minerals such as red to brown oxides and/or nontronite, but less commonly an irregular development of grossularite, and bands or pockets of endellite. Silica gossans indicate that hypogene altering solutions were active into the current geomorphic cycle. Kaolinite at the center of the clay body and endellite at the border zones are interpreted as originating, respectively, from in situ alteration of solid rock and deposition from ambient solutions.

The acid dissolution of 8 chlorites in 2N Si-saturated HCl showed that there was no preferential dissolution of Al in octahedral positions and that the octahedral and tetrahedral sheets in the chlorite structure were equally attacked. An analysis of chemical data suggested a simple two-dimensional diffusion model in which the acid attack on the chlorite particles proceeded from the edges inward leaving a reacted layer which formed a diffusion barrier. Microscopic examination showed, however, that the acid attack was not simply an edge attack but started at any point where cracks, structural defects and weaknesses apparently predisposed sites to acid attack. It was also clear from the formation of etch figures and solution channels that the product layer at least partially dissolved or disintegrated during the progress of acid attack. The residue which remained after acid attack appeared to be an opaline amorphous hydrated silica as was indicated by index of refraction measurements. The orderly arrangement of etch figures on flakes of some chlorites reflected certain crystal symmetry elements. The results indicate that the acid dissolution technique to determine the ratio of Al in octahedral and tetrahedral positions can not be used as an aid in the calculation of structural formulae for chlorites.

Nevada has produced one-third million tons of montmorillonite clays; a major portion was natural adsorbent clay from the Ash Meadows district. Four properties, 3 with swelling and 1 with non-swelling montmorillonite, are currently producing.

Detailed geologic and laboratory studies were made of thirty Nevada montmorillonite deposits. Pyroclastic and other volcanic rocks, mainly Miocene and Pliocene in age, were the host for most of these. The montmorillonite deposits are believed to have been formed in four ways: (1) eleven deposits by alteration of volcanic ash shortly after it settled in lacustrine basins; (2) two deposits by deposition of fine-grained clastic materials; (3) eleven deposits by hydrothermal alteration of a variety of rock types near structural channelways; and (4) six deposits by partial leaching and alteration of glassy, rhyolitic volcanic rocks by ground water.

Montmorillonite is the predominant clay mineral in all the deposits except Ash Meadows, where saponite is present. Sodium is much more common as the exchangeable cation than calcium and/or magnesium. Kaolinite and illite are present in one-fifth of the samples; chlorite or mixed-layer material are rarely present. Quartz, cristobalite, feldspars, calcite, and gypsum are common impurities.

The tests performed on the clay samples were: color; texture; slaking reaction; percentage swelling in water; plastic viscosity, yield point and gel strength of clay-water slurry; colloid content; and pH. Some montmorillonites formed by incomplete alteration of pyroclastic rocks can be wet separated to yield a light-colored, — 2μ fraction with superior viscosity and thixotropy.