The isothermal solid state reactions of Na2CO3 and other salts at 550°C with montmorillonite and with 1:1 mixtures of montmorillonite-illite and montmorillonite-chlorite were investigated. At a concentration of 20 wt. %, Na2CO3 caused the complete destruction of the X-ray powder diffraction (XRD) pattern of montmorillonite alone and in mixtures with other clays. Less deterioration of the XRD pattern was found for NaOH, NaF, K2CO3, and Li2CO3. NaCl, Na2SO4, Na3PO4, MgCO3, and CuCO3 had no effect on the XRD traces of montmorillonite. The time dependence of the Na2CO3-montmorillonite interaction at 550°C suggested that the reaction is diffusion controlled in three dimensions, i.e., diffusion was directed from the surface of the particle towards its center.

The influence of adsorbed H+, Na+, K+, Ca2+, Mg2+, Ba2+, and Al3+ ions on the wettability of a kaolinite surface was determined from contact angles, which were measured in kaolinite-water drop-air (saturated water vapor) and kaolinite-diiodomethane drop-air systems. From the results and using a modified Young equation, the dispersion and nondispersion components of the free energy of the kaolinite hydrated surface were determined. The dispersion component of all the tested samples was between 32.8 and 38.9 mJ/m2, but the nondispersion component changed almost linearly from 53 to 95.9 mJ/m2 with the change of the entropy of hydration of the adsorbed ions, except for K+ and Ba2+. The latter ions were exceptions, probably due to their large ionic radii.

The resolution of the infrared spectra of structural OH in kaolin-group minerals increases with decreasing temperature. Poorly crystalline kaolinite gives typical infrared spectra, which suggest the existence of kaolinite-, dickite-, and nacrite-like configurations. The relative amount dickite- and nacrite-like configurations compared with kaolinite-like configurations increases with decreasing crystallinity. Low-temperature infrared spectroscopy is a more sensitive means of estimating the degree of order of poorly crystalline kaolinite than is X-ray powder diffraction.

The structure of sepiolite from a piston core obtained on Ninetyeast Ridge in the Indian Ocean was modified by exposure to ethylene glycol vapor. With ethylene glycol, the sepiolite Oil X-ray powder diffraction peak expanded from 12.4 to 12.8 Å, and the 130 peak contracted from 4.53 to about 4.45 Å. The cell modification is consistent with concomitant expansion along the c-axis and contraction along the b-axis. This structural distortion is not permanent, however, inasmuch as the sepiolite returned to its original state 6 to 12 hr after it was removed from the ethylene glycol-saturated atmosphere.

The mechanisms of palygorskite and sepiolite alteration to smectite under mild hydrothermal conditions were investigated by solid-state 27Al and 29Si magic-angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopy, X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Palygorskite altered to smectite in the presence of NaOH at 150°C. 27Al MAS-NMR spectroscopy showed that the Al coordination changed from chiefly octahedral in palygorskite to chiefly tetrahedral in the smectite product. 29Si MAS-NMR spectroscopy showed that the nearest neighbor environment of Si also changed when palygorskite altered to smectite. The XRD data showed that the synthetic smectite is trioctahedral in nature with tetrahedral charge. The TEM results revealed that the needle-like morphology of palygorskite was preserved in the product smectite. The MAS-NMR results in conjunction with the above XRD and TEM studies suggest that the mechanism of palygorskite alteration was a dissolution and recrystallization process rather than a solid-state reorganization to form 2:1 layer silicate units from the preexisting chain structure. Sepiolite altered to smectite in the presence of 2 N salt solutions at 300°C. The trioctahedral nature of the product smectite as detected by XRD and the foil-like morphology of product smectite as shown by TEM suggest that the mechanism of sepiolite transformation to smectite was also a dissolution and recrystallization process. The tetrahedral Al coordination detected by 27Al MAS-NMR in the smectite altered from sepiolite corroborated the XRD and TEM results.

The transformation of ferrihydrite to goethite and/or hematite, as influenced by the presence of co-precipitated Si, was investigated by infrared spectroscopy (IR), X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). Ferrihydrite samples having Si/Fe molar ratios ranging from 0 to 1 were synthesized by reacting Fe2(SO4)3 with NaOH to an equilibrium pH of 8.2 in the presence of Na2SiO3. The XRD pattern of the Si-free sample contained five distinct but weak peaks, whereas the patterns of ferrihydrite samples containing Si had only two broad bands. With an increase of the Si/Fe molar ratio from 0.10 to 1.0, the 2.54-Å XRD peak shifted to 2.97 Å, and broad IR bands were observed at 990 cm−1 (Si-O stretching region) and 450 cm−1 (silicate bending region). The intensities of both IR bands increased with increasing Si/Fe molar ratio.

Ferrihydrite samples were incubated at room temperature in sodium acetate/acetic acid buffer solutions at pH 3, 5, 7, and 10 and in CaCO3 suspension at pH 8.3 for 10 months. Additional samples were incubated at pH 12.5 at 24°, 40°, 60°, and 91°C for 36 hr. Room-temperature incubation of ferrihydrite samples having Si/Fe molar ratios ≥0.1 at pH 3 for one week resulted in the dissolution of Fe and the precipitation of silica gel. Ferrihydrite samples having Si/Fe molar ratios ≤0.05 transformed to poorly crystalline goethite during room-temperature incubation at pH 5. The rate of transformation and the degree of crystallinity of the product were inversely related to Si/Fe molar ratio, and, with heat treatment, were also dependent on incubation temperature. Siliceous ferrihydrite samples having Si/Fe molar ratios ≥0.10 did not transform to phases having greater crystallinity during incubation at either room temperature in buffered solutions at pH ≥7 for as long as 10 months or at pH 12.5 at 91°C for 36 hr. The XRD peak at 2.97 Å did not shift significantly during incubation procedures, providing evidence that the structure of the high-Si ferrihydrite was not significantly altered.

The adsorption of D-glucosamine (2-amino-2-deoxy-D-gIucose) in the protonated or neutral form on homoionic Cu2+-bentonite was investigated by infrared (IR) and electron spin resonance (ESR) spectroscopy and chemical analyses of solution. The results show that the interaction of the glucosamine hydrochloride with the clay complexed a small fraction of interlayer metal ions with neutral amino sugar molecules. In contrast, the adsorption of free glucosamine was much more favorable and resulted in interlayer copper(II) complexes, mainly those in which the ligand was coordinated through amino and deprotonated hydroxyl groups. Part of the amino sugar molecules, however, were transformed into glucosammonium, replacing copper as the saturating ion.

The osmotic swelling of an n-butylammonium vermiculite in a 0.1 M solution of n-butylammonium chloride has been studied as a function of temperature and hydrostatic pressure by neutron diffraction. On application of a pressure of 1050 bar the vermiculite swelled macroscopically at 20°C, the c-axis spacing changing from 19.4 to 126 Å. The phase transition was completely reversible with respect to both pressure and temperature, and a complete study of the temperature-pressure phase diagram was made at pressures as high as 2000 bar. The heat capacity change with temperature across the swelling transition was measured at atmospheric pressure, and the enthalpy and entropy of the change from crystalline to osmotic phases were found to be, respectively, 5.2 J/g and 0.0183 J/K·g of dry clay. The combination of the entropy change with the gradient of the pressure-temperature phase boundary gave the volume change accompanying the transition. The total volume of the swollen phase was less than that of the crystalline phase plus the appropriate amount of solution, corresponding to a fractional decrease of about 0.1% in the water volume from bulk solution to between the plates.

The rate and extent of oxidation of dihydroxybenzenes (DHB) to quinones in acetate-buffered suspensions of synthetic birnessite were studied using Mn dissolution to monitor reaction progress. Concentration of free Mn2+ in the aqueous phase was continuously monitored by electron spin resonance, and ultraviolet-visible (UV-VIS) spectroscopy was utilized to quantify dihydroxybenzene and quinone concentrations. Although dissolution of the oxide and release of Mn2+ to solution generally accompanied phenol oxidation, a threshold oxidation level had to be exceeded before Mn2+ appeared in solution. Once this threshold was surpassed, the mole quantity of Mn2+ dissolved equaled the mole quantity of organic oxidized for 1,4-DHB, but exceeded the quantity of organic oxidized for 1,2-DHB. Thus, the latter phenol was more efficient in dissolving the oxide. Soluble phosphate suppressed Mn2+ release without influencing the degree of organic oxidation, suggesting that phosphate chemically interacted with reduced Mn to hinder its dissolution. UV spectra provided tentative evidence for the transitory existence of Mn3+-1,4-DHB complexes in the solution phase.

Infrared spectra of the birnessite after reaction with 1,4-DHB indicated some new features, which may have been a result of the reduction of surface Mn atoms to the 3+ oxidation state. These features were not present after reaction with 1,2-DHB, confirming that the latter phenol efficiently dissolved the oxide to release Mn2+. Although the initial Mn dissolution was very rapid and was attributed to a surface reaction, further slow Mn release accompanied by more complete oxidation of the phenols suggests a process limited by the rate of dissolution of the solid.

The treatment of smectites with a hydroxy-Al polymer produced chemically modified clays that had much greater affinities for chlorinated dioxins and biphenyls than untreated clays. For hydroxy-Al-treated kaolinite, the high affinity for chlorinated dioxins is thought to have arisen from an interaction between the hydroxy-Al polymer bound to the clay and the chlorinated dioxin in solution. Thus, the adsorption of dioxins from aqueous solution by hydroxy-Al-treated clays is similar to the adsorption of reactants from the gas phase by metals supported on mineral oxides during catalysis. In both systems, the essentially inert mineral oxide support effectively disperses the active adsorptive agent. At the concentrations of octachlorodioxin used in this study (≤5 ppb), hydroxy-Al-montmorillonite had a distribution coefficient of 90,000 (ml/g), corresponding to about 95% removal efficiency of the dioxin from solution per batch. For hexachlorohiphenyl, the distribution coefficient was 30,000 (ml/g), and the removal efficiency was 85%.