Sixty-five bauxite samples of different ages and origins were studied by scanning electron microscopy. Only broken surfaces of the specimens were investigated. Size and form of individual crystals and of grain aggregates were studied as were different types of microtextures and space-fillers.

Grain size varies from 0.05 μm to 1 mm. Smallest is the grain size of young karstic bauxite deposits that is explained by a physicochemical retardation effect of the carbonate environment. Significant differences were found by comparing the space-filling of karstic and lateritic bauxite deposits. High-level and low-level lateritic deposits show differences as well.

A combined use of macroscopic observations, petrographie microscopy, electron microprobe, SEM, and TЕM furnishes the best clues for any genetic interpretation of bauxites. SEM studies are useful in solving technological problems of bauxite processing.

The different types of iron oxide phases associated with the surfaces of two suites of kaolins from Georgia, U.S.A., and from the Southwest Peninsula of England, have been identified using electron spin resonance (ESR) spectroscopy combined with magnetic-filtration, thermal, and chemical treatments. It has been shown that the English kaolins are coated with a lepidocrocitelike phase, which is readily removed by de Endredy's method of deferrification, while the Georgia kaolins are coated with a hematite- or goethitelike phase, which is not removed by this treatment. Throughout the course of this study, the effects of the various physical and chemical treatments on the brightness values of the kaolins were examined.

The i.r. spectra (4000-1200 cm-1) are obtained for several homoionic montmorillonite films on which various amounts of dimethyl sulfoxide (DMSO) were adsorbed. Analyses of these spectra indicate that H- and natural-montmorillonite-DMSO complexes contain an intercalated layer of physisorbed DMSO while transition metal cation substituted-montmorillonite-DMSO complexes possess both physi- and chemisorbed DMSO in their interlamellar spaces. The latter species involve coordination of DMSO molecules with the exchangeable cations by their oxygen atoms. Most of the interlamellar water is replaced by DMSO as the latter molecules penetrate the interlamellar spaces. Heat-treating transition metal cation substituted-montmorillonite-DMSO complexes at 120°C for 48 hr results in both the desorption of physisorbed DMSO and the retention of intercalated monolayers involving DMSO-transition metal cation coordination. A water-sensitive, reversible color change (tan to light purple) is produced by either desiccating over P2O5 or heat-treating at 120°C the cobalt-montmorillonite-DMSO complex. Interpretation of the visible spectra suggests that Co2+-cations undergo changes from octahedral to tetrahedral coordination during desiccation or heating. Band assignments are made for the clay complexes using the assignments for related gases, liquids, and crystals.

The exchange of various alkylammonium cations from aqueous solution by sodium laponite has been studied. The affinity of the clay for these organic cations was linearly related to the molecular weight, molecular size or chain length of the alkylammonium ions. The affinity for the clay increases regularly with increasing chain length of the primary amines. A comparison of primary, secondary, and tertiary amines, containing the same alkylgroups shows that the affinity increases in the order R1NH3+ < R2NH2+ < R3NH+. These affinity sequences were attributed to important van der Waals contributions and changes in ion hydration states. The thermodynamic excess function, ΔGmE, was calculated and indicated that with respect to the pure homoionic forms the heterogeneous Na+-alkylammonium surface phases were more stable than they would be if the mixing were ideal.

Oxidation of acetaldehyde molecules adsorbed on Na- and Mg-Wyoming montmorillonite at room temperature (20-25°C) and in N2 atmosphere has been studied by I.R. spectroscopy, A comparison between clay-acetic acid complex and that prepared from acetaldehyde is given. The influence of the nature of the saturating cation as well as the clay pretreatment on this oxidation process are discussed and reaction pathways are proposed. Acetic acid directly adsorbed on the clay surface is almost removed at 110°C, while that produced from the oxidation of the adsorbed acetaldehyde appears to be strongly held. Within a temperature range 180-230°C, the fixed acetic acid molecules dissociate to acetate form; then occurs an interaction of the acetate and the residual acid with the lattice OH of the clay at 200–300°C. This interaction involves the loss of the structural OH and deposition of carbon on the clay surfaces. The thermal decomposition of the residual complex is almost completed at 500–600°C

The recent determination of the three-dimensional crystal structure of a dickite:formamide intercalate allows insight into the clay:organic bonding schemes of amides and other small organic molecule intercalates of the kaolin minerals. It is demonstrated that the observed basal spacings of intercalates with these molecules are consistent with hydrogen bonding schemes in which, if possible, triple hydrogen bonds from the clay hydroxyls to 0=C< are formed. Variations in basal spacing within a series of amides can be explained by considering the maximization of hydrogen bonding while avoiding close van der Waals contacts.

X-ray intensity ratios of Si/Al, Si/Fe, and Al/Fe in micron-sized particles of geochemical standards were found to vary linearly with the composition ratio. The same linear relationship was found for samples of the clay minerals kaolinite and illite.

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.