The rate of dissolution of akaganéite in HCl increased with time over the bulk of the reaction leading to a sigmoid dissolution vs. time curve. The bulk of the dissolution of lepidocrocite could be described by the cube root law. Transmission electron microscopy examination of partly dissolved crystals of akaganéite showed that acid attack proceeded mainly along the [001] direction. Initially, the tapered ends of the crystals became squared, and as dissolution continued the lengths of the crystals decreased steadily. At the same time, the crystals were gradually hollowed out. Acid attack was most pronounced at the edges of the crystals of lepidocrocite and appeared to involve a disruption of the hydrogen bonds that link the sheets of octahedra making up the structure. Defects also acted as sites for preferential acid attack. Dissolution of multi-domainic crystals involved preferential attack along the domain boundaries, as well as at the edges of the crystals. Single-domain crystals were well developed, but appeared to contain internal imperfections, which promoted the formation of holes on the otherwise unreactive (010) faces.

The solubilities of HCl-treated samples of corundum, gibbsite, boehmite, and diaspore in aqueous solutions at 298 K and one atmosphere pressure were determined from undersaturated and supersaturated initial conditions. Solution characteristics at apparent equilibrium were measured and used to calculate equilibrium constants (Kr) for mineral dissolution reactions:

$$\begin{array}{l} A{l_2}{O_3}\left( {corundum} \right) + 3{H^ + } = A{l^3} + 1.5\,{H_2}O,\\ Al{\left( {OH} \right)_3}\left( {gibbsite} \right) + 3{H^ + } = A{l^3} + 3\,{H_2}O,\\ and\\ AlOOH\left( {boehmite\,or\,diaspore} \right) + 3{H^ + } = A{l^3} + 2{H_2}O, \end{array}$$

Polynuclear hydroxy-Al cations were prepared by partially neutralizing dilute solutions of aluminum chloride. These cations were introduced in the interlayer space of montmorillonite by cation exchange, which formed heat-stable pillars between the silicate layers. Polynuclear hydroxy-Al was preferentially adsorbed on montmorillonite compared with monomer-Al; the maximum amount adsorbed was ∼400 meq/100 g of montmorillonite. Of this amount 320 meq was non-exchangeable. The 001 X-ray powder diffraction reflection of the polynuclear hydroxy-Al-montmorillonite complex was at 27 Å, with four additional higher-order basal reflections, giving an average d(001) value of 28.4 Å. This complex was thermally stable to 700°C. An analysis of the basal reflections by the Fourier transform method indicated that the 28-Å complex had a relatively regular interstratified structure of 9.6- and 18.9-Å component layers with a mixing ratio of 0.46:0.54. This ratio implies that the hydroxy-Al pillars occupied every second layer. Considering the relatively small amount of Al adsorbed and the thermally stable nature of the structure, the hydroxy-Al pillars must have been sparsely but homogeneously distributed in the interlayer space.

Due to their unique polarity, pore-size distribution, and high surface areas, pillared and delaminated clays are potentially useful materials for the adsorption of environmental toxicants. To determine their properties for adsorption of chlorinated phenols, alumina-pillared montmorillonite (APM), chromia-pillared montmorillonite (CPM), and alumina-delaminated Laponite (ADL) were reacted with aqueous pentachlorophenol (PCP) solutions in batch equilibrium experiments. An hydroxy-Al Laponite (HAL) in which the Na+ exchange ions were replaced by ions of the type Al13O4(OH)(24+x)(H2O)(12-x)(7-x)+ was included in the study. With ADL as the adsorbent, the extent of PCP adsorption increased with decreasing pH, and then became constant at pH ≤ pKa. Thus, the neutral phenol was preferred over the phenolate form. Binding of neutral PCP at pH 4.7 to all adsorbents never reached saturation values, and the loadings achieved were limited by the water solubility of the adsorbate. Among the pillared and delaminated clays investigated, ADL exhibited the largest capacity for physical adsorption of PCP at pH 4.7. Differences in the PCP binding capacities for APM, CPM, and ADL suggested that adsorption was dependent on the pore structure and surface composition of the modified clay adsorbent, not on surface area alone. HAL exhibited quantitative uptake of PCP at the 8 µmole/g level, indicating that a chemi-sorption mechanism may operate for PCP binding to this adsorbent. Adsorption of 3-chlorophenol, 3,5-dichlorophenol, and 3,4,5-trichlorophenol by ADL at pH 7.4 increased as the degree of hydrophobicity and chlorination of the phenol increased; hence, the binding capacity was not limited by the molecular size of the adsorbate. In contrast to the adsorption properties observed for pillared, delaminated, and hydroxy-interlayered clays, Na+-montmorillonite and Na+-Laponite did not adsorb PCP from aqueous solution.

Hypothetical model structures for magadiite and sodium octosilicate, based on the structure of the zeolite dachiardite, are proposed that consist of layers of 6-member rings of tetrahedra and blocks containing 5-member rings attached to both sides of the layers. The infrared (IR) and nuclear magnetic resonance spectra of magadiite and sodium octosilicate have features in common with spectra of zeolites in the ZSM-5 and mordenite groups. A peak at 1225 cm-1 in the IR spectra of magadiite and sodium octosilicate is characteristic of zeolites containing 5-member rings, such as ZSM-5- and mordenite-type zeolites. The defect structures of pentasil zeolites may therefore be akin to layered alkali metal silicates containing zeolite-like domains, in which part of the silanol groups from adjacent silicate layers are condensed (cross-linked) forming siloxane linkages.

Cacoxenite having the composition (Al4.0Fe22.5O7.1(OH)14.3(PO4)17(H2O)23.7)·50.3H2O was identified in a bed of mature quartz sand in the Miocene Calvert Formation near Popes Creek, Maryland. This is the first reported occurrence of this mineral in Atlantic Coastal Plain sediments north of Florida. The cacoxenite occurs as silt-size to sand-size grains, both as irregularly shaped aggregates and as radiating arrays of delicate acicular crystals. The presence of discrete cores and overgrowths in some grains indicates at least two generations of crystal growth. Electron microprobe analyses reveal excess Si and Al (relative to the ideal composition), which is believed to reflect ultra-fine clay particles within the cacoxenite grains. Admixed clays probably served as a substrate for the formation of ferric oxyhydroxides, which were subsequently converted to cacoxenite through the addition of dissolved phosphorus.

A green, Lithic Torriorthent soil derived from a celadonite-rich, hydrothermally altered basalt immediately north of the Mojave Desert region in southern California was studied to investigate the fate of the celadonite in a pedogenic weathering environment. Celadonite was found to be disseminated in the highly altered rock matrix with cristobalite, chalcedony, and stilbite. X-ray powder diffraction (XRD) showed the soil material to contain celadonite having a d(060) value of 1.510 Å, indicative of its dioctahedral nature. Very little smectite was detected in the parent material, whereas Fe-rich smectite was found to be abundant in the soil. The Fe-smectite and celadonite were identified as the sole components of the green-colored clay fraction (<2 µm) of all soil horizons. The soil clay showed a single d(060) value of 1.507 Å, indicating that the smectite was also dioctahedral and that its b-dimension was the same as that of the celadonite. Mössbauer spectroscopy showed that the chemical environments of Fe in the rock-matrix celadonite and in the smectite-rich soil clay were also nearly identical. These data strongly suggest a simple transformation of the celadonite to an Fe-rich smectite during soil formation.

Supporting evidence for this transformation was obtained by artificial weathering of celadonite, using sodium tetraphenyl boron to extract interlayer K. The intensity of the 001 XRD peak (at 10.1 Å) of celadonite was greatly reduced after the treatment and a peak at 14.4 Å, absent in the pattern of the untreated material, appeared. On glycolation of the sample, this peak expanded to 17.4 Å, similar to the behavior of the soil smectite. The alteration of celadonite to smectite is a simple transformation requiring only the loss of interlayer K. The transformation is apparently possible under present-day conditions, inasmuch as the erosional landscape position, shallow depth, and lack of significant horizonation indicate that the soil is very young.

Changes in hydraulic conductivity (HC) and clay dispersion of smectite-sand mixtures as a function of exchangeable Na in Na-Ca and Na-Mg systems were measured. The charge density on the smectites had no effect on Na-Ca and Na-Mg equilibrium, and the affinity of the clays for Na was similar in both systems. A decrease in HC at 0.01 M concentration was found to be due to clay swelling. Mg was found to be less effective than Ca in preventing the breakdown of the packets by low concentrations of exchangeable Na, and Na-Mg-smectite swelled more than Na-Ca-smectites.

Na-Mg-clay particles dispersed more readily than Na-Ca-clay particles when the mixtures were leached with distilled water; however, if the electrolyte concentration in the clay-sand mixture was controlled by the leaching solutions, no difference between the Na-Mg- and Na-Ca-clays was noted. Thus, the effect of Mg on clay mixtures leached with distilled water was apparently due to the effect of Mg on the hydrolysis of the clays. Increase in charge density increased the stability of the R2+ clay packets, and higher concentrations of Na were needed to break the packets. Mg was less effective than Ca in stabilizing the packets, and lower concentrations of Na were needed to break the Mg-packets.

During the epigenetic alteration of boehmitic karstic bauxite in the Vlasenica region of Yugoslavia, which was caused by siliceous water descending through the deposit by means of cracks, fissures, etc., oolites were less altered compared with the coexisting matrix material, which was intensely kaolinized. The following zonal alteration pattern of the oolites was identified: a diaspore enrichment zone, followed by a diaspore-boehmite enrichment zone, and then the original bauxite. Considering this alteration pattern and that determined previously for the matrix material, the following overall pattern of alteration was established: a kaolinite-diaspore zone, followed by a boehmite-diaspore zone, and then the original bauxite. The alteration solutions reacted with the bauxite to form solution-matrix and solution-oolite subsystems, which were characterized by different types of diffusion and geochemistry.

In the kaolinite-diaspore zone Si-metasomatism kaolinized the matrix, and excess Al partly migrated into the oolites, forming diaspore, and outward into the bauxite. The latter Al-remobilization resulted in a transition zone, in which new boehmite was formed in both the matrix and the oolites, and diaspore only in the oolites. Thermodynamic models of oolites and whole bauxite alterations were established, on the basis of stability diagrams calculated for the mineral assemblages of both the oolites and the matrix, in the alteration zones and in the deposit as a whole. Based on these models, the genesis of the diaspore and the relationship of diaspore-boehmite-kaolinite assemblages in natural systems at low temperature and low pressure can be described.

Although numerous, small, manganese oxide deposits associated with dolomite in the Eastern Transvaal escarpment, Republic of South Africa, have been known for many years, their mineralogical make-up is somewhat controversial. Chemical, mineralogical, and morphological properties of the weathering products of dolomite and the coexisting manganese oxide material in the Graskop area were therefore determined. Mn and Fe occur only in minor accessory minerals in the original rock; however, in the weathering residue, these elements are concentrated and occur as separate mineral phases, chiefly birnessite, nsutite, and goethite. Thin veins of pure muscovite and quartz traverse the residua. Rare, pure calcite and maghemite nodules were noted throughout the residual manganese material. The properties of this weathering sequence suggest that the manganese wad deposits were formed in situ as a result of the congruent dissolution of dolomite, leaving a porous, sponge-like structure, highly enriched in Mn and Fe oxides.

The adsorption of n-octane and water vapor on natural kaolinite was measured. From adsorption isotherms film pressures were determined which were then used to calculate the dispersion and nondispersion components of the kaolinite surface free energy. In addition, thermodesorption of water from the kaolinite surface was determined. These results suggest that physically adsorbed water remained on the kaolinite surface, even at temperatures as great as 125°C. Therefore, experimentally determined dispersion and nondispersion components appear to relate to the surface precovered with a film of water. These values are: γSf(w)d = 34.4 mJ/m2 for dispersion interactions and γSf(w)n = 60.2 mJ/m2 for nondispersion interactions. Assuming a kaolinite surface precovered with a film of water, which decreased the free energy by the work of spreading, the following components of the energy for the bare surface were calculated: γSd = 67.6 mJ/m2 and γSn = 103.4 mJ/m2, for dispersion and nondispersion components, respectively.

This paper presents thermal conductivity data for highly compacted Ca-smectite, Na-smectite, illite, and palygorskite as a function of density (i.e., compaction pressure), water content, and temperature. All the clays behaved similarly: thermal conductivity increased directly with density and water content. Specifically, the thermal conductivity increased from 0.63 to 1.32 W/m·K as the dry density increased from 1.2 to 1.8 g/cm3 (for a water content of 17%). An increase of water content from 6 to 17% resulted in an increase in thermal conductivity from 0.63 to 1.22 W/m·K (for a dry density of 1.6 g/cm3). Differences from one clay to the other were less important. The thermal conductivity (in W/m·K) for constant conditions of 12% of water and a dry density of 1.6 g/cm3 were: Ca-smectite 0.80, Na-smectite 0.74, palygorskite 0.71, and illite 0.69. Heating to 188°C produced only a 10% increase in the thermal conductivity.

The influence of manganese oxide minerals (cryptomelane, hausmannite, and pyrolusite) on the formation of iron oxides was studied in the FeCl2-NH4OH system at different Mn/Fe molar ratios (0, 0.01, 0.1, and 1.0) and pHs (3.0, 4.0, 5.0, and 6.0) by X-ray powder diffraction, infrared absorption, transmission electron microscopic, and chemical analyses. In the absence of Mn minerals, lepidocrocite (γ-FeOOH) precipitated at pHs 5.0 and 6.0; however, no precipitate formed at lower pHs. All the Mn minerals studied promoted the precipitation of iron oxides and oxyhydroxides. In the presence of Mn oxides, Fe2+ was oxidized to Fe3+, which hydrolyzed and precipitated as noncrystalline and/or different crystalline iron oxides and oxyhydroxides, depending on the nature of the Mn oxides present in the system. Simultaneously, Mn2+ was detected in solution after the reaction by electron spin resonance spectroscopy. The presence of cryptomelane and hausmannite resulted in the formation of åkaganeite (β-FeOOH) and magnetite (Fe3O4), respectively. Thus, the effect of Mn oxides on the formation of Fe oxide minerals in the weathering zone merits attention.