The influence of Al on the products formed by aerial oxidation at pH 5.5-7 and 20°C of Fe(II) chloride, sulfate and carbonate solutions, was examined. In all cases Al at levels Al/Al + Fe = 0.09−0.30 inhibited the formation of y phases (lepidocrocite and maghemite) in favor of goethite under conditions where, in the absence of Al, these y phases formed. The influence of Al in these laboratory studies was supported by field observations.

At higher levels of Al, ferrihydrite formation was favored. This effect of Al was seen to be the result of a slowing down in the hydrolysis/oxidation rate of the Fe(II) system.

The presence of Al not only changed the direction of mineral formation, but also caused the formation of Al substitued goethites which resembled in particle size and morphology the natural aluminiferous goethite extracted from a soil.

Scan electron micrographs are shown of (1) kaolinite and dickite which crystallized from solution within cavities, (2) kaolinite weathered from clastic primary silicate material, (3) residual kaolinite from primary silicate rock, (4) kaolinite above and below a basal unconformity on granitic rock, and (5) hydrothermally altered kaolinite. The texture of kaolin reflects the environment in which the clay was formed.

Euhedral crystals of kaolin minerals characterize cavity fillings. The weathering environment produces large crystal flakes of kaolinite, expanded books, mats of elongates, high porosity, and low bulk density (less than 2.0). The hydrothermal environment produces smaller crystals, singles, sheaves and packets of crystals, low porosity and high bulk density (2.0 and above).

The interrelationships of genetic environment of kaolin minerals and accompanying texture are discussed in light of available geochemical information.

This study was an investigation of the effects of sesquioxide constituents on some mineralogical and physiochemical properties of a Panamanian latosol.

Latosols are soils characterized by high concentrations of iron and aluminum oxides and a general absence of free silica and alkaline earths.

X-ray diffraction studies revealed sesquioxide coatings existed on the surfaces of the clay minerals. Mineralogically, the soil was composed of kaolin, amorphous minerals, hydrated iron and aluminum oxides, free silica, quartz grains, and magnetite. The results of DTA data suggested the presence of amorphous colloids in the soil. This suggestion was subsequently confirmed by selective dissolution analysis which revealed the unexpected presence of 17% amorphous silica in the coarse clay size fraction. Grain size analysis and scanning electron microscopy studies showed that the clay minerals are probably agglomerated by the sesquioxides into silt size clusters. CEC values obtained were primarily attributed to the amorphous colloids rather than the crystalline clay minerals because the sesquioxides probably partially blocked the exchange sites of the clays.

Removal of the iron and aluminum oxides by sodium dithionite citrate-bicarbonate procedures (Mehra and Jackson, 1960), (a) sharpened and exposed previously “masked” X-ray diffraction peaks, (b) disaggregated the clay clusters producing greater amounts of clay size particles, and (c) altered the Cation Exchange Capacity (CEC) and water retention characteristics of the soil constituents.

This investigation demonstrated that amorphous silica and iron and aluminum oxides greatly influence the properties of this latosol by coating and aggregating the clay minerals. These sesquioxide coatings suppress the ordinary behavioral characteristics of the indigenous clay minerals and consequently the observed behavior of the soil is dominated by the amorphous constituents.

This investigation was designed to integrate the quick-freeze technique for ion diffusion with two computer programs to permit the simultaneous measurement and calculation of the diffus-ivity of a variable number of ions in heteroionic soil system. Kaolinite clay was prepared so as to have the following percentage saturations of the CEC, Sr2+65, Mg2+15, Rb+10, Na+5 and H+5. A quadruplicate radioisotope tag consisting of 85Sr, 28Mg, 86Rb, and 22Na was used to measure the diffusivity of each ion. The complex spectra were resolved by use of Schonfeld’s revised Alpha-M computer program. A probit-transformation procedure was formulated into a computer program to enable the calculation of each diffusion coefficient. These programs are described and illustrated with the diffusivity of 86Rb in kaolinite clay.

An electro-optic birefringence technique was employed to study the orientation mechanism of montmorillonite in an electric field. The instantaneous reversal of the field polarity produced evidence of a low voltage permanent dipole and a high voltage induced dipole. This technique was used to study theeffect ofelectrolyte concentration on the rotational diffusion coefficient, a measure of the rate at which the particles rotate or relax, within the solution, from a preferred orientation. Thus, a measure of the immediate environment of the particles was obtained that is not an average effect for the whole system, yet allows for the full development of the clay-cation-water interactions under the experimental conditions. It was found that particle rotation could be accounted for using the measured particle size and normal water viscosity only when the double layer was fully developed, with no free ions or other perturbations. As soon as perturbations were applied, either by adding salts or applying an electric field, the measured particle size and normal viscosity would not account for the data. Either the rotating moiety has to be larger, that is, be a particle plus a water hull, or the viscosity greater, or in some cases both.

The electron spin resonance of some structural Fe3+ for montmorillonites having low Fe3+ content, is perturbed by electrostatic interaction between exchange cations and structural charge sites. The position of charge centers of organic and inorganic cations in the interlayer can thus be determined at various levels of solvation. Dielectric media between the silicate layers lower the electrostatic attraction between the silicate and the exchange cations. The silicate charge appears to be partially delocalized on structural oxygen atoms as shown by electron spin resonance and i.r. spectroscopy. There is also evidence that divalent exchange cations on dehydrated montmorillonites cause hydrolysis of water; the protons so produced migrate to structural charge sites.

A review of fabric studies of clays suggests the need for relating those fabric characteristics which are revealed at the two levels of magnification provided by optical and electron microscopy, and a technique to achieve this has been developed and is described within the context of the initial stages of a long term study of the interrelation between fabric and engineering behaviour. Two kaolinitic clays with contrived fabrics were prepared by controlling particle size, moisture content and pH of suspension, and consolidation load and were subjected to shear loading to failure. Resin impregnation techniques which permit the kaolinite to be cut into thin sections for transmission electron microscopy have been optimized with the object of minimizing fabric strain and damage during ultratomy.

The fabrics of the hard and soft ambient material are qualitatively compared by means of electron micrographs and are explained in terms of the preparatory procedures adopted for fabric control. The fabrics of the two types of shear induced structures are also qualitatively compared and explained in terms of the original fabrics and the subsequent shear loading.

An infrared method has been developed for estimating kaolinite in sediments. Hydroxyl stretching bands of kaolinite in sediments can be recorded by using a differential technique which eliminates the overlapping owing to other mineralic constituents present. By adding known amounts of an appropriate standard to the sample and by measuring intensities of the OH bands before and after the addition it is possible to calculate the proportion of kaolinite in the test sample. The choice of the added standard is made from characteristic features of the hydroxyl stretching bands.

The t-plot method has been applied to the results of nitrogen adsorption at 76°K on sepiolite first heated in vacuo at various temperatures. Heating sepiolite samples in vacuo at 427°K results in a large decrease in surface area compared with samples outgassed at 373°K. A change in structure and a consequent collapse of micropores is postulated. However, the t-plots indicate that some microporosity remains. Outgassing at 623°K appears to destroy completely the micropores.

Electrochemical treatment of kaolinite-glass bead plugs in the presence of water and CaCl2 solutions produces dissolution of the glass beads, corrosion of the anodes, and transport of the released elements toward the cathodic zone. In this area, new mineral phases (both amorphous and crystalline) are synthesized. Most of these new phases, and especially the calcium silicate hydrate (CSH-1), are well known to exhibit important cementing properties. The nature and the extent of the modifications brought about by the treatment are dependent on the nature of the electrodes, the pH and the ionic strength of the circulating electrolyte, and the duration of the treatment.

The composition and physical properties of three clay soils were altered by introducing aluminum under an electro-chemical gradient in order to evaluate the role of pH in controlling changes in soil composition and the feasibility of pH buffering during electrochemical treatment.

Both X-ray diffraction and selective chemical extraction methods were used to determine the distribution and mode of occurrence of aluminum in the treated samples. Aluminum was detected in the treated samples in both exchangeable form and as a hydroxy-aluminum interlayer. Aluminum oxide minerals such as gibbsite were not detected in any of the treated samples. Mineralization by aluminum ions was speeded and intensified in bentonite soils by buffering the catholyte with carbon dioxide.

Plasticity of bentonite soil samples from South Dakota was reduced markedly by electrochemical treatment, whereas the plasticity of an illite soil from Illinois and an illite-montmorillonite soil from Mississippi were relatively unaffected. Nearly all treated samples exhibited some degree of electrochemical induration or mineralization. Induration was most pronounced in bentonite soil samples with high water contents and alkaline pH largely because of hydroxy-aluminum interlayering in the ciay. On the other hand interlayering was negligible in illite soil samples with low pH; the main effect of electrochemical treatment in this case was the addition of aluminum in exchange sites.

Clay beds 1–2 m thick and interbedded with marine limestones probably of early Eocene age are composed of nearly pure mixed-layer kaolinite-montmorillonite. Particle size studies, electron micrographs, X-ray diffraction studies, chemical analyses, cation exchange experiments, DTA, and TGA indicate that clays from three different localities contain roughly equal proportions of randomly interlayered kaolinite and montmorillonite layers. The montmorillonite structural formulas average K0·2Na0·2Ca0·2Mg0·2(Al2·5Fe1·03+Mg0·5)(Al0·75Si7.25)O20+(OH)4−, with a deficiency of structural (OH) in either the montmorillonite or kaolinite layers. Nonexchangeable K+ indicates that a few layers are mica-like. Crystals are mostly round plates 1/10 to 1/20 μ across. The feature most diagnostic of the mixed-layer character is an X-ray reflection near 8 Å after heating at 300°C. The clays are inferred to have developed by weathering of volcanic ash and subsequent erosion and deposition in protected nearshore basins.

The rates of dehydroxylation of smectites intercalated with the decomposition products of Ni(phen)3SO4 are from 2 to 4 times greater than those of clays without the heat-stable intercalate. These results suggest that the intercalated material, in keeping the clay sheets separated, provides a more ready avenue for water loss during the dehydroxylation process.