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Previous investigations have demonstrated the influences of interlayer cation composition, relative humidity, temperature, and magnitude of interlayer surface charge on the interlayer hydration of montmorillonites and vermiculites. It has been suggested that the sites of layer charge deficiencies may also have an influence upon the amount of hydration that can take place in the interlayers of expandable clay minerals, if the interlayer cation-to-layer bonds are considered as ideally electrostatic, the magnitude of the forces resisting expansion may be expressed as a form of Coulomb’s law. If this effect is significant, expandable structures in which the charge-deficiency sites are predominantly in the tetrahedral sheet should have less pronounced swelling properties than should structures possessing charge deficiencies located primarily in the octahedral sheet.
Three samples that differed in location of layer charge sites were selected for study. An important selection criterion was a non-correlation between tetrahedral charge sites and high surface-charge density, and between octahedral charge sites and low surface-charge density.
The effects of differences in interlayer cation composition were eliminated by saturating portions of each sample with the same cations. Equilibrium (001) d values at controlled constant humidities were used as a measure of the relative degree of interlayer hydration.
Although no corrélation could be made between the degree of interlayer hydration and total surface-charge density, the investigation does not eliminate total surface-charge density as being significant to the swelling properties of three-sheet clay-mineral structures. The results do indicate a correlation between more intense expandability and predominance of charge deficiencies in the octahedral sheet. Conversely, less intense swelling behavior is associated with predominantly tetrahedral charge deficiencies.
A white clay from the Jatoba talc mine, Castro, Paraná, Brazil, is shown by chemical analysis, X-ray and electron diffraction, and by thermal analysis to be essentially pure antigorite in the strict sense of the term. Single crystal electron diffraction patterns give various values for the long a parameter, with 43·5 Å perhaps the most commonly occurring, b = 9·25 Å, d(001) = 7·25 Å. X-ray powder diffraction gives d(001) = 7·26 Å and b = 9·23 A. Electron micrographs show irregular platy and lath-like crystals of about 0·5–2 μ size with large development of (001) planes and with b in the direction of elongation. Other crystals are observed with very unusual forms, some having holes through them. They show mainly 0kl diffraction patterns and lie with the basal (001) planes normal to the stage of the instrument. The chemical analysis agrees closely with the ideal serpentine composition and the differential thermal analysis curve is consistent with antigorite.
The physical and chemical interactions between organic amines and mineral surfaces are of considerable importance in many industrial applications. For example, the preparation of organophilic minerals often involves the adsorption of organic amines, or the ion exchange of the minerals with quaternary ammonium salts (Jordon, 1951; Miller and Faust, 1972). Chemical interactions occurring in these systems have been studied because of their relevance to an understanding of the chemical nature of the clay surface. A number of these studies have reported on the decomposition of adsorbed amines and alkylammonium-mineral complexes at elevated temperatures, usually in excess of 100°C (Chaussidon and Calvet, 1965; Weiss and Roloff, 1963; Durand, Pellet and Fripiat, 1972; Chou and McAtee, 1969). It is now well established that under these conditions the mineral may have potential strong-acidity, and these reactions have been explained in terms of acid-induced decomposition or rearrangement of the adsorbed amines or their derivatives. However, there have been few studies of the reactions of organo-mineral complexes at temperatures below 100°C, under conditions where retention of adsorbed water could be expected to moderate the mineral surface acidity.
Dissolution data on five of the six illites reported by Reesman and Keller (1968) indicate that these illites are more stable than was previously thought. The revised Gibbs free energies of formation (ΔGf0) with respect to the ‘ideal’ illite formula and the muscovite formula are
Use of muscovite formula as an indirect comparator provides a means of predicting the relative stabilities of these chemically complex materials.
The response of illite-equilibrated solution to a kaolin ΔGf0 was found in all samples in which a 7 Å mineral phase was detected by X-ray diffraction. Stability diagrams based upon the ΔGf0 with respect to ideal muscovite and kaolin formulas show a rather wide range in chemical conditions through which illites and kaolin minerals with differing ΔGf0 would be stable. However, in carbonate rocks and sea water illite is stable relative to kaolin. During the weathering of carbonates the lower pH zones in the clay-rich residuum above the carbonates favor the transformation of illite to kaolin minerals.
Various dehydroxylated micas and rectorites were acid-treated. Rectorite-type mixed-layer mineral was formed from 2M1 and 2M2 mica and random mixed-layer mineral from 1M and 1Md mica. Rectorite was formed again from dehydroxylated rectorite. The rehydration and rehydroxylation properties of dehydroxylated rectorite and 2M sericites were found to be similar.
The structure and hydration status of attapulgite clay after heating at elevated temperatures and the stability of parathion on these clays was studied. Using infrared spectroscopy and scanning electron microscopy it was found that the bound water was lost in two steps, at 250° and 450° with the first step being largely reversible. At 650°C the structure began to dissolve releasing significant amounts of Mg, and a decrease in aggregate porosity was noted. At 850°C an amorphous phase was formed bearing little resemblance to the original attapulgite. Parathion was stable on all of the preheated clays when kept at 25°C for 190 days. The reactions of parathion on the preheated clays was studied at 110°C Hydrolysis of parathion was found to be minimal. Isomerization was the main reaction occurring on the Ca-attapulgite, whereas on an organo-clay no isomerization was observed. A mechanism for the isomerization reaction is proposed which entails a distortion of the phosphate moiety of the pesticide by the oxygen of the ligand water resulting in the conformational changes necessary for the isomerization to take place. On the organo-clay such a conformation was not possible; hence no isomerization occurred.
A 1–0·2 μm fraction from a soil in the Dominican Republic was studied by X-ray diffraction combined with solvation, cation saturation, and heat treatments. I.R., thermal (DTA, TGA) and chemical analyses were also made. This soil is saline and alkaline and its mineral composition is greatly influenced by the lacustrine parent material and poor drainage.
In addition to swelling chlorite, illite, kaolinite, carbonates and quartz are present in the 1–0·2 μm fraction. The swelling chlorite expanded to over 18 Å when Mg saturated and solvated with glycerol or water. Lower spacings with other cations and ethylene glycol were observed. 1 N HCl treatment partially removed the interlayer hydroxides in the chlorite and 6 N HCl destroyed the mineral. The mineral gave a reflection close to 14 Å up through 600°C but collapsed at higher temperatures to 10·2 Å.
Neutron diffraction measurements for a preferentially oriented aggregate slab sample of deuterated Na-montmorillonite from Upton, Wyoming, are described for a series of clay-water contents ranging from 0 to 500 mg/g. A neutron wavelength of 2.39 Å was used with extended detectors to collect much of the “out of plane” component of the diffraction peak intensities.
The diffraction pattern intensities from the 00ℓ planes of the clay, corresponding to a reflection geometry, are a strong function of sample water content and show a variation in basal spacing from 9.8 to 19.0 Å. The hk reflections from transmission geometry measurements show, however, that the lattice a and b axes are constant within experimental uncertainty (0.02 Å) over the range in water content and their intensities vary only by a few percent. In this geometry, a broad, water-like diffraction pattern was noted as a background under the usual hk peak intensity series. This underlying water-like pattern varies in proportion to the sample water content.
Data reduction steps included consideration of background removal, multiple scattering, flux normalization, and attenuation of scattering due to sample thickness. Analysis of the reduced data revealed that the clay-water has a “liquid-like” ordering, with a density increase of approximately 5% over bulk water. An association between a few interlayer water molecules and the silicate superstructure is indicated by the slight change in the hk band intensities, but this change seems to be complete at water contents below 100 mg/g. Fourier analysis of the basal peak series from the dry clay shows that the hydrogens of the lattice hydroxyl groups lie in the same basal plane as their associated oxygen atoms.
A laboratory study of cadmium exchangeability revealed large differences in extractable cadmium which are dependent on the exchange solution being utilized. The standard exchange solutions employed in this study were: N NaNO3, N NaOAc, N NH4OAc, NCaCl2, and 2N CaCl2, in order of increasing Cd removal. An interpretation of the chemical behavior of Cd and an experiment with mixed sodium nitrate and acetate solutions suggest that cadmium carbonate, octavite, was precipitated when the sediments were saturated with Cd prior to the exchange experiments and that the quantities of Cd recovered in the acetate solutions were erroneously high because of the dissolution of the carbonate material. Dissolution of solid phases, the lack of pH buffering, and the possible formation of a complex hydroxyl chloride salt also made the Cd values obtained with the chloride solutions too high. Sodium nitrate exchange solutions minimize these problems and are thought to best represent the exchangeable cadmium in the sediment.
The adsorption of the cationic oxidized safranine S+ by a Na+, Ni2+ and Fe3+ montmorillonite has been studied with X-ray powder diffraction, u.v., visible and i.r. spectroscopy. In solution S+ may be protonated: S+, SH2+ and SH23+ have characteristic spectra in the 500–600 nm region where the clay structure does not absorb. In the Na+ as well as in the Ni2+ and Fe3+ clays, the adsorption of S+ is a cation exchange process accompanied by the protonation of the adsorbed dye such as variable concentrations of M+ (Na+, Ni2+ or Fe3+), S+ and SH2+ are simultaneously present. Protonation activity decreases from Fe3+ to Ni2+ and Na+, being the protonation site the amine group as shown by i.r. In the interlamellar space it seems that a SH2+.. S+ association exists that could be described as a sandwich structure 6.5 Å thick.
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).