Cation-exchange capacities determined by methylene blue adsorption (CEC MB) and by the amount of K displaced from a K-saturated clay by NH4 (CEC K//NH4) correlate closely in five soil clays from Pennsylvania, but differ greatly in two soil clays with a large content of amorphous material. CEC MB was found to provide a more precise distinction between montmorillonite and vermiculite than CEC K//NH4. Synthetic aluminosilicate gels showed CEC K//NH4 > CEC Ca/Mg > CEC MB, but no relation to the behavior of the two soil clays with a large content of amorphous material was found.

Smectite (from South Dakota, Wyoming, and Mississippi) and Vermiculite (Transvaal) were treated with solutions of Al(OH)B(3-B)+, with B varying from 0 to 2.5. The average basicity (OH/Al = B) of the Al adsorbed differed very much from the basicity of the Al added. The average basicity of the Al adsorbed by smectite was always above the average basicity of the Al added. In contrast to smectite, Vermiculite adsorbed smaller hydroxy-Al complexes. One reason for the different selective behavior was the difference in expansion between smectite (about 18 Å) and vermiculite (about 14 Å). Because of the adsorption of the relatively more basic OH-Al by smectite, smectite adsorbed considerably more Al than vermiculite. The total amount of aluminum in the interlayer generally could not be calculated by the difference between Al added and that remaining in solution after the reaction because of possible protonation of the clay mineral and adsorption of structural Al and other cations, which is more pronounced for vermiculite. The results in the present study demonstrated that neither the quantitative nor the qualitative composition of an Al(OH)B-treated exchanger can be deduced from B of the Al salts added. These points are frequently overlooked when cation exchangers are pretreated with Al of variable basicity and are used for further investigations, such as studies of CEC, surface area, interlayer spacing, anion reactions, the formation of gibbsite, etc. Before these kinds of investigations are conducted employing the pretreated OH-Al-exchangers, their composition should be known precisely.

Seven kaolins from Georgia (southeastern U.S.A.), ranging from high to low commercial grade, were characterized by X-ray powder diffraction and chemical techniques to establish that the variation in quality was caused by impurities. The Ca and Cs cation-exchange capacities (CEC) varied from 2.67 to 8.17 and from 3.29 to 8.77 meq/100g, respectively. Selective dissolution and correlation analyses strongly indicated that expandable 2:1 minerals, particularly smectite (1.2-5.9%), were responsible for most of the observed variations in Ca CEC (r = 0.85*). The external surface CEC of kaolinite ranged from 0 to 1 meq/ 100 g. The positive significant correlation (r = 0.90**) between the Ca CEC and the K-mica content (03.9%) suggested that Ca CEC may be related to the degree of mica weathering through an expandable mineral stage.

The Cs-retention capacity (0.19–1.14 meq/100 g) was closely related to Cs-measured vermiculite content (r = 0.80*), and this content plus specific surface (R = 0.93**) or mica content (R = 0.86*). The Cs retention appeared to be primarily related to the presence of interlayer wedges at mica/vermiculite XY interfaces.

X-ray superlattice reflections, infrared spectroscopy, and chemical analyses have established that cetylpyridinium bromide (CPB) is highly ordered when adsorbed on vermiculite. The molecules, which stand at about 57° to the silicate surface, form close-packed arrays. Full surface coverage is achieved only for the most highly charged vermiculites. The packing within the arrays accounted for the superlattice observed and each adsorbed molecule had an area of 18.4 Å2 at the surface. The implications of these findings for the CPB method used in soil surface area studies are discussed.

A regularly interstratified chlorite/vermiculite occurs in red beds of the East Berlin Formation (Early Jurassic age) in the Connecticut Valley. The mineral is restricted to a 2.5-m wide zone of contact metamorphosed strata adjacent to and underlying the Hampden Basalt. Chemical and X-ray powder diffraction data indicate that the chlorite/vermiculite formed in response to lava-induced elevated temperatures and the availability of magnesium in the muds during and shortly after emplacement of the lava flow. Near the contact, hydrothermal fluids originating from the lava and from the synchronal weathering of basalt fragments by superheated pore waters provided a source of Mg. Further from the contact, magnesium was primarily derived from the thermal dissociation of dolomite. K2O concentrations and the distribution of clay minerals in the red mudstone suggest that the interstratified chlorite/vermiculite formed from preexisting illite or vermiculite as potassium was released and brucitic sheets were incorporated into interlayer positions.

The effects of hydrothermal conditions on the sorption and fixation of cesium by various clay minerals and shales were investigated. Hydrothermal heating, which may be expected in a radioactive waste repository, altered the clay minerals and shales and led to a decrease in their cation-exchange capacity. Cesium sorption greatly decreased in micaceous vermiculite and in well-crystallized illites containing vermiculite upon hydrothermal treatment at 400°C and 300 bars pressure due to complete layer collapse. However, poorly crystallized illites heated as above showed either a small increase or only a slight decrease in Cs sorption because of partial layer collapse. These studies show that the decrease in Cs sorption is greater in well-crysallized illites than in poorly crystallized illites when treated similarly under hydrothermal conditions. Hydrothermal heating of Cs-sorbed and Cs-saturated samples increased the amount of Cs fixation in all minerals and shales as a result of collapse of the layers. For example, a sample of the Conasauga shale fixed only 18% of sorbed Cs before treatment but fixed 47% after hydrothermal treatment at 200°C and 300 bars pressure. Thus, hydrothermal conditions in a shale repository may be beneficial after leaked radioactive Cs ions are taken up by clay minerals in shales.

The adsorption-desorption of the cationic pesticide chlordimeform from aqueous solutions on montmorillonite, kaolinite, illite, and vermiculite appears to be a cation-exchange process coupled with the coadsorption of neutral molecules and the extraction of Al from the structure of the mineral. Chlordimeform adsorption on montmorillonite, illite, and vermiculite by cation exchange is an irreversible process, whereas chlordimeform adsorbed on kaolinite is weakly bonded to the clay and easily removed by washing with water. X-ray powder diffraction and infrared spectroscopic data show that chlordimeform cations are adsorbed in the interlamellar spaces of montmorillonite at charge sites, lying in a flat position in contrast to kaolinite, illite, and vermiculite, where they adsorb on external surfaces or charge sites close to the crystal edges.

When aqueous dispersions of Na+-smectite or n-butylammonium-vermiculite react with sulfate salts of Fe(II), Co(II), or Ni(II) bipyridyl or 1, 10-phenanthroline complexes in excess of the cation-exchange capacities, intersalated phases with spacings of about 29.5 Å are obtained. Thermal decomposition of the intersalated complex cations affords expanded phases with a d(001) spacing near 18 Å for the smectites and near 28 Å for the vermiculites. These phases are stable to temperatures of at least 550°C. Nitrogen surface areas of the fired products are as high as 400 m2/g.

Biotite in deeply weathered granitic rocks in southwestern Australia has altered to exfoliated grains composed of biotite, mixed-layer clay minerals, kaolinite, vermiculite, gibbsite, goethite, and hematite. Discrete vermiculite and vermiculite-dominant mixed-layer clay minerals are not major weathering products. Oxidation of octahedral iron in biotite is associated with ejection of octahedral cations, loss of interlayer K, and a contraction of the b-dimension of the biotite sheet. Si, Mg, Ca, Mn, K, and Na are lost from biotite during weathering, and Ti, Al, Ni, and Cr are retained. Fe and water have been added to the grains during weathering. Much Fe occurs as aggregates of microcystalline, aluminum-rich goethite particles on flake surfaces and within etchpits, with smaller amounts occurring as hexagonal arrangements of lath-shaped crystals of goethite on flake surfaces.

To identify mineral alterations which might occur in stream environments, predominantly illitic soil clays were equilibrated in bottom sediment environments under natural and laboratory conditions for 217 and 98 days, respectively. Changes occurring after 217 days on the bottom of the Auglaize River, Ohio, consisted of a reduction in carbonate content, a decrease in particle size, and a slight loss of Al and Si; however, no significant changes in basal spacings were observed.

Clays equilibrated in river water under laboratory conditions at 4° and 25°C in CO2, N2, or air atmospheres showed only an increase in oxalate-extractable iron. The concentrations of Al, Si, Fe, Mn, K, and Ca in solution above the clays varied with the atmosphere and temperature. The concentrations of Fe, Al, and Si in solution may have been influenced by the dissolution of amorphous Al-Fe-Si compounds. Therefore, the mineralogical differences between soils in the watershed and sediments in the drainage system can not be attributed to mineralogical transformations during residence in the drainage system.

Single grain X-ray and electron diffraction patterns of weathered biotite flakes exhibit groupings of 001 and hk reflections of biotite, vermiculite, mixed-layer clay minerals, and kaolinite indicating that the secondary minerals are in parallel crystallographic orientation to the parent biotite. Asterism of biotite reflections is enhanced by weathering. Gibbsite crystals developed in parallel basal orientation to biotite flakes. Most goethite in weathered biotite occurs as aggregates of randomly oriented crystals in cleavages and on grain surfaces. Some goethite is present on micaceous fragments as 0.05-μm size, lathlike crystals in a hexagonal arrangement with their (100) face resting on the (001) biotite face. Selected area electron diffraction patterns of aggregates of lathlike goethite crystals contain 0kℓ, 1kℓ, and 2kℓ reflections due to undulation of the aggregates and the extreme thinness of the crystals. These patterns indicate that the close packed anion layers in goethite coincide with the brucite-like layer of the micaceous minerals.

The effects of Na-citrate-dithionite (NaCD), ammonium oxalate in the dark (NH4Ox-D), and photolytic reaction under ultraviolet radiation (NH4Ox-P) on the mineralogy of <2-µm fractions of selected soils from Virginia were investigated. The NH4Ox-D treatment removed the smallest amounts of Al (<0.22%) and Fe (<0.50%) from all soils, indicating low levels of noncrystalline material in these materials. From the six soils examined, NH4Ox-P treatment extracted 5–62% more Fe and 12–300% more Al than the NaCD treatment. The NH4Ox-D and NaCD treatments revealed no X-ray diffraction detectable alterations to mineral phases present in <2-µm fractions of these soils. The NH4Ox-P treatment, on the other hand, produced considerable degradation of hydroxy-interlayered vermiculites in these soils, as evidenced by a shift of the 14-Å X-ray diffraction maxima to lower spacings with heat treatment of the sample. The NH4Ox-P treatment removed variable amounts of hydroxy-Al material from the interlayers of 2:1 layer silicates, depending on their stability and degree of development.

Silica has been intercalated in swelling clays by hydrolysis and/or oxidation of tris(acetylacetonato)siIicon(IV) cations, Si(acac)3+, and polychlorosiloxanes, (-SiOCl2-)n, in the interla-mellar regions of the minerals. The Si(acac)3+ ions have been placed on the interlamellar surfaces by ion exchange and by in situ reaction of the acetylacetone-solvated clays with SiCl4. The (-SiOCl2-)n polymers were formed in the interlayers by reaction of adsorbed benzaldehyde with SiCl4. The optimum (001) spacing observed after firing the clays in air at 500°C (12.6 Å) corresponds to the presence of a monolayer of siloxane chains. Nitrogen BET surface areas range from 40 to 240 m2/g, depending on the amount of internal surface covered by the intercalated silica. In some cases, highly ordered products were formed which exhibit four orders of (00ℓ) reflection. Interstratified products with d(001) values between 9.6 and 12.6 Å exhibit surface areas consistent with the presence of a random mixture of totally collapsed interlayers and interlayers containing siloxane monolayers. Attempts to achieve silica intercalation by hydrolysis of SiCl4 in the clay interlayers were not productive.

The effects of NaOAc removal of carbonates, H2O2 removal of organic materials, and sodium citrate-bicarbonate-dithionite (SCBD) removal of iron oxides upon the X-ray powder diffraction (XRD) characteristics of clay minerals present within weathered volcanic ash deposits were examined. All pretreatments of samples derived from the Ae and Bhf horizons containing volcanic ash resulted in dramatic increases in XRD peak intensities, while the treatment of IIC-horizon samples resulted in subdued XRD peak intensities. Also, the chemical treatments produced an apparent increase in the amount of expandable clay minerals within the Ae horizon, due probably to the hydrolysis and removal of interlayer Al3+ when H2O2 and SCBD were used. Hence, poorly ordered and pedogenically modified vermiculite or vermiculite/montmorillonite interstratifications became “weathered” by H+ attack and Al3+ removal in a manner similar to the natural processes which take place in the acid and eluvial A horizon. In addition, possible XRD peak modification due to the dilution of crystalline clay concentrations by amorphous clay-size material appeared to be subordinate to the laboratory-induced chemical alteration of the weathered clay minerals.

Statistical analyses of chemical data from the literature of corrensite minerals suggest a large compositional variability, more evident in octahedral than in tetrahedral coordination. Mg occupies 40–80% of the octahedral sites, with Al and Fe2+ making up the remainder. Approximately 15–30% of the tetrahedral sites are filled by Al. Despite this compositional variability, distinct fields for the several types of mixed-layer trioctahedral chlorite/trioctahedral swelling layer are not apparent. Statistical analyses of the composition of corrensite compared with saponite, vermiculite, and chlorite suggest that corrensite is an intermediate between trioctahedral chlorite and trioctahedral smectite. If Fe/(Fe + Mg) > 50%, chlorite alone is favored, but with increasing Mg, chlorite appears to transform into corrensite and then, by iron oxidation, into trioctahedral smectite. Despite the chemical variability between corrensite, chlorite, and saponite, corrensite appears chemically to be a well-defined species. On the other hand, corrensite cannot be characterized chemically on the basis of its swelling component. Thus, the current definition of corrensite as a regular 1:1 interstratification of trioctahedral chlorite and either trioctahedral smectite or vermiculite is appropriate.

The three-dimensional order shown by the two-layer hydrates of Na- and Ca-vermiculite, prepared from Mg-vermiculite from Llano, Texas, has enabled clear, two-dimensional Fourier projections of their interlayer structures to be obtained. Structure factor calculations were made in space group C2 and with unit-cell dimensions of a = 5.358 Å, b = 9.232 Å, and ß = 96.82°; for Na-vermiculite C = 14.96 Å and for Ca-vermiculite c = 15.00 Å. In Na-vermiculite the interlayer cations are octahedrally coordinated to water molecules with the sodium-water polyhedra only located between the triads of oxygen atoms forming bases to tetrahedra in adjacent silicate layers. In Ca-vermiculite the interlayer cations are in both octahedral and 8-fold (distorted cubic) coordination with water molecules. The octahedrally coordinated Ca ions are between the bases of tetrahedra in adjacent silicate layers, but the 8-fold coordinated Ca ions are between the ditrigonal cavities. In both Na- and Ca-vermiculite some water molecules are drawn from planar networks appreciably towards the ditrigonal cavities. The three-dimensional order observed for these vermiculites contrasts with the stacking disorder reported for Mg-vermiculite from Llano. The distinct crystallographic behavior of Na+, Ca2+, and Mg2+ in the hydration layers of Llano vermiculite probably depends on cation sizes and field strengths, together with the need to achieve local charge balance near the sites of tetrahedral Al-for-Si substitution.