Hydrotalcite-like layered double hydroxides (LDH), of the formulation M2Al(OH)6(CO3)0.5.H2O, where M = Mg, Zn, Co, Ni, have been prepared, the products characterized and their solubility products measured at ionic strengths of 0.0065 and 0.0128 M and at 25°C. Steady-state solubility was reached after 100 days. The solubility products have been formulated according to the following reaction: $M_2\text{Al}{\left(\text{OH}\right)}_{6}0.5{\text{CO}}_3\cdot {\text{H}}_2\text{O}+6{\text{H}}^{+}\to 2M^{2+}+{\text{Al}}^{3+}+0.5{\text{CO}}_3^{2-}+{\text{H}}_2\text{O}$ where

$K_{\text{SO}}=\frac{{\left[M^{2+}\right]}^2\left[{\text{Al}}^{3+}\right]{\left[{\text{CO}}_3^{2-}\right]}^{0.5}}{{\left[\text{H}\right]}^6}$

Average values of Kso for I = 0, estimated using the Davies equation, are 25.43, 20.80, 22.88 and 20.03 for Mg, Zn, Co and Ni, respectively. Model calculations reveal that the thermodynamic stability of the LDHs is greater than that of the corresponding divalent hydroxides for Zn, Co and Ni below a pH of ∼10, 9 and 8, respectively, and at least up to pH 12 for Mg.

In water-rich smectite gels, bound or less mobile H2O layers exist near negatively-charged clay platelets. These bound H2O layers are obstacles to the diffusion of unbound H2O molecules in the porespace, and therefore reduce the H2O self-diffusion coefficient, D, in the gel system as a whole. In this study, the self-diffusion coefficients of H2O molecules in water-rich gels of Na-rich smectites (montmorillonite, stevensite and hectorite) were measured by pulsed-gradient spin-echo proton nuclear magnetic resonance (NMR) to evaluate the effects of obstruction on D. The NMR results were interpreted using random-walk computer simulations which show that unbound H2O diffuses in the gels while avoiding randomly-placed obstacles (clay platelets sandwiched in immobilized bound H2O layers). A ratio (volume of the clay platelets and immobilized H2O layers)/(volume of clay platelets) was estimated for each water-rich gel. The results showed that the ratio was 8.92, 16.9, 3.32, 3.73 and 3.92 for Wyoming montmorillonite (⩽ 5.74 wt.% clay), Tsukinuno montmorillonite (⩽ 3.73 wt.% clay), synthetic stevensite (⩽ 8.97 wt.% clay), and two synthetic hectorite samples (⩽ 11.0 wt.% clay), respectively. The ratios suggest that the thickness of the immobilized H2O layers in the gels is 4.0, 8.0, 1.2, 1.4 and 1.5 nm, respectively, assuming that each clay particle in the gels consists of a single 1 nm-thick platelet. The present study confirmed that the obstruction effects of immobilized H2O layers near the clay surfaces are important in restricting the self-diffusion of unbound H2O in water-rich smectite gels.

Particle-size analysis (obtained by Galai CIS 1) was used to determine the following statistical parameters of aqueous suspensions of Na-, Ca- and Mn-montmorillonite: the size distributions, the diameters of the largest and of the median and mean particles, and the percentage of particles with diameters <1.5 µm. Dilution or shaking had almost no effect on the particle-size distribution curves and statistical parameters of Ca- and Mn-montmorillonites but the curves and the statistical parameters of Na-montmorillonite were very much affected by these treatments. The median and mean diameters of Na-montmorillonite range from 0.8 to 10.5 µm and 0.8 to 11.6 µm, respectively, the median and mean diameters of Ca-montmorillonite range from 1.5 to 3.6 µm and 2.12 to 4.2 µm, respectively, and those for Mn-montmorillonite from 1.2 to 2.3 µm and 1.5 to 2.5 µm, respectively. The presence of large particles of Na-montmorillonite was attributed to the extensive swelling of this clay in aqueous suspensions by osmotic water adsorption. The median and mean diameters of aged Na-montmorillonite suspensions indicate that swelling increases with dilution. The swelling of Ca- and Mn-montmorillonite, on the other hand, is limited and their particle size does not increase with dilution.

Al-hydroxy intercalated clays (ALHICs) obtained from different parent clays were used to investigate the interactions between oligomers and clay surface layers.

The thermal stability of ALHICs obtained from natural, Cs-, Ca-, Ba-, Fe-, Cu- or Ce-montmorillonites has been investigated by studying the relationship between basal spacing and calcination temperature. X-ray diffraction has shown that the basal spacing of ALHICs obtained from Cu-montmorillonite calcined at 550°C is 13.4 Å, different from basal spacings of ALHICs obtained from Fe-montmorillonite (16.0 Å) and other parent clays (16.7 Å). Thermograms for AlHICs obtained from natural, Fe- and Ce-montmorillonites displayed distinct steps at 225 and 650°C, attributed to the dehydration of Al13 oligomers, and the dehydroxylation of the surface layer, respectively. By contrast, thermograms of ALHICs obtained from Cu-montmorillonite displayed one step between 250 and 700°C for both dehydration and dehydroxylation. Mössbauer parameters showed that Fe3+ octahedra in octahedral sheets are distorted in pillared interlayered clay (PILC) obtained from Cu-montmorillonite and undistorted in that obtained from Fe-montmorillonite. The difference in thermal stability for the various ALHICs is attributed to the retention of some of the original cations after intercalation with Al13 oligomers, which induces several interactions between the oligomers and the clay surface layers.

Titanium was introduced into the clay structure by cation exchange with polymeric Ti cations which were formed by partial hydrolysis of Ti alkoxide in HCl. X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperature-programmed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Ti-pillared clays (Ti-PILCs). Titanium methoxide allows the synthesis of a solid with a large basal spacing (26 Å), a large surface area (360 m2/g), a significant amount of micropore surface area (90%), and notable acidity. Moreover, Ti-PILCs obtained from methoxide were found to be thermally stable up to 500°C. A correlation between the increase in acidity and the increases in both microporosity and Ti content was observed. The surface area, the micropore volume, the acidity and the d001 peak intensity all increased upon increasing the amount of Ti added to the preparation (up to ∼15 mmoles of Ti/g clay). The use of an aqueous suspension of 0.13 wt.% of clay yielded the best structural and textural properties in terms of subsequent use of the clay as a catalyst.

De-tert-butylation of 2-tert-butylphenol was carried out over thermally-treated and acid-treated Jordanian bentonite clay samples. This reaction was found to follow first-order kinetics for all clay samples with different pretreatment procedures. The apparent rate constant, k, was also determined, and found to depend on the pretreatment. Thermal pretreatment at temperatures up to 250°C has an enhancing effect on surface acid sites. The total surface acidity (Ho <4.8) and the concentration of strong acid sites peaked at 250°C. Also, as a result, the maximum catalyst activity was obtained with samples treated at this temperature. Acid pretreatment with 0.10 M HCl, 1.0 M H2SO4 or 1.0 M H3PO4, followed by thermal treatment at 250°C produced the best enhancement effect on the surface acidity and catalytic activity.

The grafting, by chemical adsorption, of molecular 1.10-phenanthroline (OP) onto some Brazilian bentonite (montmorillonites) was studied to improve their adsorptive capacities to remove Cu ions from synthetic wastewater. The quantity of OP adsorbed was 112 mg g−1 of bentonite at pH 8.5 and no significant desorption was detectable in acidic or basic solutions. X-ray diffraction (XRD) spectra show that a complex type-β is formed in which the OP molecules lay inclined in the clay interlayer. After the intercalation of OP, the adsorptive capacities of the natural bentonites increased by a factor of ten. Thus, adsorption of Cu ions, at optimal pH of 8.0±0.5, showed saturation values, which, calculated by the Langmuir model, yielded 110 mg of Cu ions g−1 of bentonite (3.5 meq g−1). The mechanisms of Cu uptake are ion-exchange adsorption onto untreated bentonite and ion exchange plus Cu2+ phenanthroline complexation (chemisorption) on the modified pillared clay. The desorption of Cu ions from OP clay revealed high uptake irreversibility and physical stability (of the adsorbent) either in strongly acidic or basic solutions. Thus, after acid treatment ∼90% of the adsorbed Cu ions continued to be bound onto the OP-modified bentonite surface.

The effect of humic acid (HA) adsorption on the hydrophilicity of two different montmorillonite samples (Na-montmorillonite, NaMt, and a Na-fluorinated Na-montmorillonite, FNaMt, or ‘Rassoul’) was investigated. The changes in the wettability of clays were discussed in terms of the non-electrostatic free energy of interaction between the clay particles immersed in aqueous humic acid solutions (ΔG121), using the van Oss-Chaudhury-Good (vOCG) model. The surface free energy components (both non-polar or Lifshitz-van der Waals, and polar or acid-base) of clays were obtained from contact angle measurements, after adsorption of humic acid, at acid or basic pH, in 10−2 M NaCl solutions. It was found that: (1) at acid pH, a progressive decrease in the hydrophilic character of both clays was observed when the humic acid concentration was increased; (2) at basic pH, the hydrophilic character of both samples studied increased with HA concentration; (3) the effect of humic acid adsorption on the wettability of model edge surfaces of the laminar montmorillonite particles was estimated from a parallel study on silica and alumina surfaces, and only a slight decrease in the hydrophilicity was observed, whatever the pH of the liquid media. The ζ potentials of both clays in the absence and presence of humic acid were determined and the linkage between ζ potential and the electron-donor character of the materials is discussed.

The loss of K-bearing clay minerals has been observed over an 80 y cultivation period in Chinese rice paddies despite the use of NKP fertilizers. Clay mineral determinations were made in flood-irrigated paddies cultivated for 3, 10, 15, 30 and 80 y in clayey (45 wt.%), red soils derived from red Quaternary sediments. Three clay minerals are initially present in these soils: illite-mica, magnesian chlorite and an interstratified mica-aluminous chlorite mineral. This last phase was identified using computer simulations. The K-bearing phases (discrete mica and illite as well as interstratified mica layers) are to a large extent lost while the Fe content decreases in the soil as a whole and increases in the chlorite. The mica component in the mixed-layer mineral decreases also. These changes in clay mineralogy and relative abundance suggest a loss of potassic minerals and an increase in the formation of less siliceous, more ferro-magnesian chlorite. These changes occur over 30 y or less, a rather rapid, irreversible transformation of soil clay minerals. Such loss of potassic minerals renders the cultivation more dependent on fertilizer amendment.

The formation of siderite and magnetite by Fe(III)-reducing bacteria may play an important role in C and Fe geochemistry in subsurface and ocean sediments. The objective of this study was to identify environmental factors that control the formation of siderite (FeCO3) and magnetite (Fe3O4) by Fe(III)-reducing bacteria. Psychrotolerant (<20°C), mesophilic (20–35°C) and thermophilic (>45°C) Fe(III)-reducing bacteria were used to examine the reduction of a poorly crystalline iron oxide, akaganeite (β-FeOOH), without a soluble electron shuttle, anthraquinone disulfuonate (AQDS), in the presence of N2, N2-CO2(80:20, V:V), H2 and H2-CO2 (80:20, V:V) headspace gases as well as in -buffered medium (30–210 mM) under a N2 atmosphere. Iron biomineralization was also examined under different growth conditions such as salinity, pH, incubation time, incubation temperature and electron donors. Magnetite formation was dominant under a N2 and a H2 atmosphere. Siderite formation was dominant under a H2-CO2 atmosphere. A mixture of magnetite and siderite was formed in the presence of a N2-CO2 headspace. Akaganeite was reduced and transformed to siderite and magnetite in a -buffered medium (>120 mM) with lactate as an electron donor in the presence of a N2 atmosphere. Biogeochemical and environmental factors controlling the phases of the secondary mineral suite include medium pH, salinity, electron donors, atmospheric composition and incubation time. These results indicate that microbial Fe(III) reduction may play an important role in Fe and C biogeochemistry as well as C sequestration in natural environments.

Lithiophorite is a naturally occurring phyllomanganate which has been identified in soils and ores. Studies on a synthetic version have shed light on the conditions required for the formation of lithiophorite. In this study, we successfully prepared lithiophorite under highly alkaline conditions. In addition, we found that Li+, Al3+ and hydrothermal treatment are all necessary for the formation of lithiophorite. Lithiophorite, birnessite and Li-intercalated gibbsite were examined by infrared (IR) spectroscopy. The Mn oxide sheets of lithiophorite and birnessite were found to have quite similar structural environments. On the other hand, the LiAl2(OH)6 sheets are affected more markedly by the Mn oxide sheets. After intercalation, the symmetry of the six interlayer OH groups of LiAl2(OH)6 is reduced and they are divided into two groups occupying different sites, corresponding to the IR absorption bands at 3480 and 3312 cm−1, respectively.

The aim of this paper was to define the nature and the relative chronology of the diagenetic clay bearing assemblages within sandstones of the Middle Proterozoic Kombolgie formation (Northern Territory, Australia). The detrital minerals of these rocks comprise quartz, accessory zircon, tourmaline, rutile and rare phengitic white micas. Diagenetic features consist of pore-sealing secondary quartz overgrowths, strong compaction shown by interlocked structures and stylolith joints, local hematization and the occurrence of two distinct clay parageneses. Blocky crystals of dickite constitute the earlier diagenetic clays. Their FTIR spectra and their DTA curves, with a sharp dehydroxylation endothermic peak near 680°C, are characteristic of the well-ordered dickite already encountered in many deeply-buried sandstones. Quartz overgrowth may be contemporaneous with the crystallization of dickite. Illite occurred during a subsequent stage as grain coatings and as pseudomorphs of dickite in the residual pores of the sandstones. Illite seems to be contemporaneous with the major deformation features associated with compaction phenomena at the maximal burial conditions experienced by the sandstone formation. These illites are essentially of 2M1 polytype. They display pseudohexagonal platy crystals with average diameters ranging from 2 to 10 µm. Their chemical composition is Al-rich (Ca0.01Na0.02K1.72) ()(Si6.27IVAl1.73)O20(OH)4. These Proterozoic rocks provide a natural reference for the illite end-member occurring as a replacement of kaolin subgroup minerals during burial diagenesis of sandstones The textural properties of the Kombolgie sandstones (absence of fracture network, low porosity, well-developed macroscopic stylolith joints…) and the crystal structure of both the diagenetic dickite and illite would tend to indicate that the Kombolgie sandstones were buried at a depth exceeding 5 km.