Hydroxymetal-clay complexes, which contain reactive surface hydroxyl groups, have a strong affinity for both heavy-metal cations and oxyanions and hence can serve as efficient sorbents for ionic contaminants. The co-sorptive behavior of heavy-metal cations and oxyanions on the surface of hydroxymetal-clay complexes is not well understood, however. The objective of the present investigation was to help bridge that gap by determining the feasibility of co-sorbing Cd cations and phosphate from aqueous solution to a hydroxyiron-montmorillonite complex (HyFe-mont). A montmorillonite-rich clay from Inner Mongolia, China, was the starting material. The results showed that Cd and phosphate could be sorbed, simultaneously and synergistically, to HyFe-mont without a change in solution pH. Similarly, when phosphate was sorbed before Cd, the sorption capacities were comparable to those obtained in the simultaneous sorption experiment, and the solution pH did not change.When Cd was pre-sorbed, however, the subsequent sorption of both Cd and phosphate decreased as did solution pH. X-ray photoelectron spectroscopy (XPS) indicated that the binding energies of P2p, Cd3/2, and Cd5/2 were of similar magnitude for both the simultaneous sorption system and the phosphate pre-sorbed system. In addition, the single Cd and Cd pre-sorbed systems had similar Cd3/2 and Cd5/2 binding energies. The combined sorption and XPS results suggested that sorbed phosphate and Cd formed P-bridged ternary complexes on the HyFe-mont surface, contributing to the synergistic uptake of the contaminants in the simultaneous sorption system.

The formation conditions of the ferric smectite nontronite are not fully understood. The present study couples experimental and analytical data with field observations in an attempt to constrain the rate and temperature of formation of naturally occurring nontronites from Columbia River Basalt flows. Synthetic Fe-Al-Si gels were incubated at temperatures ranging from 4 to 150°C for 4 weeks. Samples were analyzed using Fe K-edge X-ray fluorescence spectroscopy (XAFS). Spectra of the synthesized nontronites were compared with spectra of natural samples collected from weathered Columbia River Basalt flows. Cation ordering in the synthetic samples increased with incubation temperature, but the synthetic clays did not approach the degree of crystal ordering of the natural nontronite samples. These observations suggest that highly ordered natural nontronites require longer crystallization times than are typically used in laboratory experiments. The natural samples were found filling open cracks near flow surfaces, indicating that the clays formed at temperatures below the boiling point of water. A comparison of experimental and field timescales with other estimates of nontronite growth rates suggests that natural nontronite crystallization in the region must have occurred at ambient, near-surface temperatures over timescales of up to millions of years.

Because relatively little information about the crystal-growth process of smectite is available, the process was assessed here by studying the size and shape of nontronite particles synthesized at six different temperatures from 75 to 150°C over a period of 4 weeks.

The morphology of nontronites was studied using low-pressure isotherms of argon adsorption at 77 K, a method which enables the measurement of the basal and edge surface areas of the nontronite particles and of their mean diameter and thickness. During the crystal growth of nontronite, the mean particle length increased whereas their thickness (and the number of stacked layers) did not vary significantly.

A specific two-dimensional crystal-growth process was observed for smectite via the lateral extension of the layers. This process also appears to occur during the growth of neoformed natural smectite.

The hypothesis that chemical remanent magnetization (CRM) in argillaceous rocks may be due to release of Fe during smectite illitization has been tested by study of spatial and temporal relationships of CRM acquisition, smectite illitization, and organic-matter maturation to deformation in the Montana Disturbed Belt. New K-Ar ages and stacking order and percentages of illite layers in illite-smectite (I-S) are consistent with conclusions from previous studies that smectite illitization of bentonites in Subbelts I and II of the Disturbed Belt was produced by thrust-sheet burial resulting from the Laramide Orogeny. Internally concordant, early Paleogene, K-Ar age values (55–57 Ma) were obtained from clay subfractions of thick bentonites which were significantly different in terms of their ages (i.e. Jurassic Ellis Formation and late Cretaceous Marias River Shale), further supporting a model of smectite illitization as a result of the Laramide Orogeny. Internally concordant K-Ar ages were found also for clay sub-fractions from a thick bentonite at Pishkun Canal (54 Ma) and from an undeformed bentonite near Vaughn on the Sweetgrass Arch (48 Ma). In Subbelts I and II, a greater degree of smectite illitization corresponds to increased thermal maturation, increased natural remanent magnetization intensity, and increased deformation (dip of beds). A dissolution-precipitation model over a short duration is proposed for the formation of illite layers in Subbelts I and II. A characteristic remanent magnetization was developed before or just after folding began in the early Paleogene. More smectite-rich I-S, low thermal maturity, and the absence of a CRM were noted in one outcrop of an undeformed rock on the Sweetgrass Arch. Strontium isotope data allow for the possibility that internal or externally derived fluids may have influenced illitization, but the K-Ar age values suggest that illitization was probably in response to conductive heating after the overthrusting had occurred. The differences in K-Ar dates among the bentonites studied herein may be due to differences in the timing of peak temperature related to differences in distance below the overthrust slab, in rates of burial and exhumation, and in initial temperature.

A number of chemical reactions (mass-action expressions) have been proposed to describe serpentinization of olivine in terrestrial serpentinites. Some have been applied to interpreting the formation of serpentine-group minerals in CM carbonaceous chondrites. The widely used olivine + pyroxene → serpentine (ol + px → srp) reaction is quantitatively inconsistent with observed ratios of olivine to pyroxene and olivine to serpentine in CM carbonaceous chondrites. The reaction of 5ol → 2srp is most consistent with constraints from textural observations at the scale of individual partial and complete pseudomorphs of serpentine after coarse olivine in CM chondrites, observed co-variations in modal abundances of reactant and product minerals in CM chondrites, and experimental geochemical kinetics. Furthermore, the 5ol → 2srp reaction provides insight into the mobility of solute species in the aqueous alteration environment of CM carbonaceous chondrites.

Different changes in the structural and thermal properties of various types of talc have been reported in the literature which have made comparison of analytical results difficult. The objective of the present study was to obtain some fundamental insights into the effects of the thermal behavior of talc and to carry out kinetic analyses of the decomposition of talc under high temperature. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetry-differential scanning calorimetry (TG-DSC) were used to study the thermal decomposition mechanism. The Coats-Redfern decomposition model was used to determine the decomposition mechanism of talc samples. The results showed that the decomposition of talc commenced at ~800°C, peaking at ~895°C, with the formation of enstatite and amorphous silica. An isothermal treatment at 1000°C caused the complete dehydroxylation of talc. The XRD and FTIR results indicated that the enstatite and amorphous silica phases were transformed into clinoenstatite and paracrystalline opal phases, respectively, after the decomposition stage at 1200°C. Good linearity in the Coats-Redfern model was observed from room temperature to 1300°C and the activation energy was calculated to be 69 kcal/mol.

The iron chemistry of aluminosilicates can markedly affect their adsorption properties due to possible changes in surface charge upon exposure to a variety of processes in the environment. One of these processes is chemical leaching, but to date little has been reported on the susceptibility of structural Fe to chemical leaching. The purpose of the current study was to determine the effects of solution pH on the stability of structural Fe in kaolinites, illite, and bentonite and the potential for formation of ancillary (oxyhydr)oxides. Structurally bound Fe does not participate in sorption properties but Fe that is released and phase transformed during leaching could take part in adsorption processes and form complexes and/or covalent bonds via Fe ions. Five different Fe-bearing clay minerals were treated in 0.5 M and 2 M HCl, distilled H2O, 0.1MKCl, and 0.5MKHCO3 for 24 h. The amount of Fe leached varied from 10 μg g-1 (for 0.1 M KCl) to 104 μg g-1 (for 2 M HCl) depending on the leaching agents. Acidic and water treatments indicated a relative independence of leached Fe on the initial Fe content in the clay and, conversely, a heavy dependence on the crystallinity of initial Fe phases. Well crystallized Fe(III) was stable during the leaching process, while poorly crystallized and amorphous Fe(III) phases were less stable, forming new ion-exchangeable Fe3+ particles. Under alkaline conditions, no relation between Fe crystallinity and mobility was found. The structural and surface changes resulting from leaching processes were identified by equilibrium adsorption isotherms. In kaolinite, the specific surface area (SBET) and porosity changed independently of Fe leaching due to the stability and crystallinity of Fe. In bentonite, the number of micropores was reduced by their partial saturation with Fe3+ particles caused by poorly crystallized and more reactive Fe forms during the leaching process. Potential phase transformations of Fe were characterized by the voltammetry of microparticles; well crystallized Fe(III) oxides remained stable under leaching conditions, while poorly crystallized and amorphous Fe(III) phases were partially dissolved and transformed to reactive Fe3+ forms.

The capture and storage of carbon dioxide (CO2) have considerable potential for mitigating climate change. Adsorption is one of the most popular methods for the storage of CO2. The adsorption of CO2 molecules on the hydroxylated (001) surface of kaolinite was investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics was studied systematically for a wide range of coverage, Θ [from 0.11 to 1.0 monolayers (ML)], and adsorption sites. The CO2 was adsorbed on the two-fold bridge-x (see the text for a definition) and the one-fold top-x sites in the bent, recumbent configuration, and on the three-fold hollow-z, two-fold bridge-z site, and the one-fold top-z sites in the vertical configuration. The surface-adsorbed binding site of CO2 was strongest at the bridge-x site and weakest at the top-z site. The adsorption energy increased with coverage, thus indicating the greater stability of surface adsorption and a tendency to form CO2 islands (clusters) with increasing coverage. The other properties of the CO2/kaolinite (001) system, including the different charge distribution, the lattice relaxation, and the electronic density of states, were also studied and are discussed in detail.