The layer charge is perhaps the single most significant characteristic of 2: 1 layer phyllosilicates. Layer charge affects cation-retention capacity and adsorption of water, and various polar organic molecules. The effects of layer charge on the sorptive properties of organo- clays were illustrated by Lee et al. (1990). It is generally agreed that the classification of 2: 1 silicate clays, which is a continuing problem, may be resolved by taking into account the magnitude of the layer charge (Bailey et al., 1971; Malla and Douglas, 1987). Studies on structural chemistry also confirm the importance of the layer charge for the characterization of the 2:1 phyllosilicates (Newman and Brown, 1987).

An improved regression method for the evaluation of standard free energies of formation (ΔG°f) of clay minerals is here proposed in an attempt to remove some of the limitations of the earlier method (Chen, 1975). Particularly, this method suggests a procedure for the assignment of rankings for Σ ΔG°f, i values. Moreover, an iterative least-squares fitting technique is applied to solve the exponential equation to obtain the estimated ΔG°f. The estimated ΔG°f data for the various standard clay minerals are derived and compared with data available in the literature; in general, there is good agreement between the values. It is also shown how the regression method can be extended to clay minerals of variable composition. The ΔG°f's for several such minerals have been evaluated; a large number of combination equations required for such computations have been listed, so that for other similar minerals the process of evaluation of ΔG°f is greatly simplified.

This paper examines the ion-exchange properties of synthetic zeolite Na-Pc, which was produced from perlite-waste fines and has a SiO2:Al2O3 ratio of 4.45:1 and a cation-exchange capacity (CEC) of 3.95 meq g−1. Although equilibrium is attained rapidly for all three metals, exchange is incomplete, with Ac(max) (maximum equilibrium fraction of the metal in the zeolite) being 0.95 for Pb, 0.76 for Zn, and 0.27 for Ni. In both Na → ½Pb and Na → ½Zn exchange, the normalized selectivity coefficient is virtually constant for NAC (normalized equilibrium fraction of the metal in the zeolite) values of ≤0.6, suggesting a pronounced homogeneity of the available exchange sites. The Gibbs standard free energy, ΔG°, of the Na → ½Pb exchange calculated from the normalized selectivity coefficient is −3.11 kJ eq−1 and, for the Na → ½Zn exchange, it is 2.75 kJ eq−1.

Examination of the solid exchange products with X-ray diffraction (XRD) revealed a possible decrease in crystallinity of zeolite Pb-Pc as suggested by the significant broadening and disappearance of diffraction lines. This decrease is associated with a reduction of pore opening, as indicated from Fourier-transform infrared analysis (FTIR), which in turn results in a decrease of the amount of zeolitic water. Thermogra-vimetric-differential thermogravimetric (TG-DTG) analysis showed that water loss occurs in three steps, the relative significance of which depends on the type of exchangeable cation and subsequently on the type of complex formed with the cation and/or the zeolite channels. Zeolite Na-Pc might be utilized in environmental applications, such as the treatment of acid-mine drainage and electroplating effluents.

Color variations from brown to yellow of synthesized goethite have been studied colorimetrically and spectroscopically. Goethite with various colors was synthesized at pH 13 and 40°C by varying the incubation time. Colorimetry revealed that the b* value (yellowish chroma) in L*a*b* color space was a quantitative indicator of color variations of the diluted samples. From UV-VIS-NIR spectra, the increase in the b* value was found to be caused by the increase in crystal field absorptions due to goethite formation around 500 nm. The b* value was a good indicator of the relative proportion of goethite in the precipitates including ferrihydrite. X-ray diffraction patterns and infrared spectra revealed that crystallization of goethite was associated with loss of water from the proto-ferrihydrite.

Sorption parameters are important components of models used to predict mass transport through dense or compacted earthen materials. These parameters are, however, generally determined in batch tests with loose, unconsolidated materials. Here we directly measure, using a specially designed cell, the extent of Cs+ sorption on bentonite compacted to a series of densities ranging from 0.50 to 1.50 Mg/m3, and compare the results with those obtained from batch tests with loose bentonite. The clay was saturated with a Na-Ca-Cl-dominated solution with an effective ionic strength of 220 mol/m3. The sorption data were expressed as distribution coefficients, Kd. Over the clay density range examined, Kd values for Cs+ with compacted clay are about one-half to one-third the value of those with loose clay. The lower sorption on compacted clay is attributed to small and occluded pores that Cs+ cannot enter; thus it cannot access the entire volume, or all the sorption sites, of compacted clay. The data suggest that reasonable estimates of Kd with compacted clay can be obtained by scaling down the Kd values measured on loose clay by a factor na/n, where na is the accessible porosity and n the total porosity of compacted clay.

X-ray diffraction (XRD), Rb-Sr isotope analysis, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FTIR) methods were used to study diagenetic illite and illite-smectite (I-S) in Lower Cambrian unlithified clays of shallow depth of burial in the northern part of the intercratonic Baltic paleosedimentary basin of the East-European Platform. The studies focused on the <0.06-µm size fraction of the clay. This fraction consists of a highly illitic illite-smectite (I-S) and a poorly crystalline illite (PCI), with some traces of Fe-rich chlorite also present. Rb-Sr isotopic data for the <0.06-µm size fractions suggest that the illitic I-S and PCI have different formation ages. No precise isotopic ages were derived directly owing to the composite illite mineralogy and retention of radiogenic Sr. This retention occurred because of imperfect isotopic homog-enization at low water/rock ratios. The age of burial diagenesis is proposed to coincide with the time of maximum burial depth, which was achieved during the Middle to Late Devonian and continued until Permian-Triassic erosion. Because of the shallow depth of burial (<2 km), diagenesis was probably a low-temperature (<50°C) transformation process. The resident time of 100–150 million years at maximum burial had a major influence in the process.

A combined powder X-ray diffraction (XRD) and X-ray absorption (XAS) study of Fe(III) cation ordering within pyroaurite is described. It is concluded that there is no correlation between Fe(III) cation positions over distances of a few tens of angstroms, but that there is a very high level of local ordering, involving the absence of Fe(III)-Fe(III) neighbors. These observations are rationalized in terms of a significant frequency of lattice defects in the form of cation vacancies or Mg for Fe(III) substitutions. These results are expected to be generalizable to other M(II)/M(III) layered double hydroxides (LDHs), but are in contrast to the long-range cation ordering observed in Li/Al LDHs. This raises the interesting possibility of differing properties and stabilities based on the degree of cation ordering.

A method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.

Recent evidence of the occurrence of beidellite in many soils around the world necessitates a better understanding of the role of charge location on the colloidal behavior of this smectite as compared to the more frequently studied montmorillonites. Clay suspension stability and sorption of an organic polymer, two properties sensitive to surface charge characteristics, were selected to examine the differences in colloidal behaviors of these smectites. The Otay montmorillonite was shown to have a higher charge than either the beidellite or the SWy-1 montmorillonite. Even though structural formulae resulted in a higher permanent charge for the beidellite as compared to the SWy-1, effective charge of these two smectites is the same. The pH dependency of the critical coagulation concentration of the smectites could not be explained based only on edge charge considerations, and it is proposed that tetrahedral charge location enhances the pH effect on the CCC. Decreased poly(vinyl) alcohol sorption with either increasing surface charge or tetrahedral charge location was observed. Both parameters affect the ease of replacement of water molecules by PVA on the surface of smectites.

The relative growth rates of the three joint chains of silica tetrahedra and metal octahedra in the [100], [1̅10] and [1̅1̅0] directions within the mica layer (referring to the 1M unit-cell) seem to control the morphology of mica crystallites. Laths and fibers are the products of relatively fast growth along the [100] direction compared to growth along the [1̅10] and [1̅1̅0] directions. The (010) growth front in 1M micas with trans-octahedral vacancies exposes a pair of reactive OH ions that can form organic or inorganic complexes and ‘poison’ the growth on the (010) face.

Authigenic illite fibers in two sandstones with contrasting lithologies are found to have grown on mica or kaolinite cores. Illite fibers appear in single sets or in multiple sets, 120° apart. This texture seems to be related to the stacking sequence of the layers in mica or kaolinite in the core of these fibers.

Although wildlife management models across the world have since the early 1980s shifted from top-down fortress conservation to different labels of people-friendly community-based conservation, their outcomes remain contested. This paper explores how, and in whose interests, approaches to wildlife conservation in Malawi have been reconfigured from fortress conservation to market–community collaborative management. Based on qualitative field data, we demonstrate how varying levels of community participation in the processes of wildlife conservation transformed the identities and interests of powerful groups of people regarding wildlife conservation in the Majete Wildlife Reserve. We highlight how commodification and monetarization of wildlife conservation served the interests of the emergent powerful groups whilst marginalizing those of the weak. The work indicates how new community identities with regard to wildlife conservation mask the power hegemonies that dictate mechanisms of inclusion and exclusion regarding natural resource use.

Oxygen-isotope data were obtained for synthetic aluminum-hydroxide phases precipitated over 65–125 mo and have been compared to results from similar experiments conducted for 3–56 mo. The Al(OH)3 polymorphs, gibbsite, nordstrandite, and bayerite, were synthesized, but gibbsite was dominant in most samples, and commonly the only phase present. Using pure gibbsite samples, the following oxygen-isotope fractionation factors, ${\alpha }_{gibbsite-H_{2}O}$, were obtained: 1.0167 ± 0.0003 (9 ± 1°C), 1.0147 ± 0.0007 (24 ± 2°C), 1.0120 ± 0.0003 (51 ± 2°C). These values, and the associated equation for an oxygen-isotope geothermometer for the interval 0–60°C 103ln ${\alpha }_{gibbsite-H_{2}O}=2.04\times {10}^6/T^2-3.61\times {10}^3/T+3.65$ (T in K), are not significantly different from those obtained from experiments of much shorter duration. These results, and the good agreement with ${\alpha }_{gibbsite-H_{2}O}$ values obtained for well-constrained natural systems, suggest that the experimentally determined fractionation factors describe equilibrium conditions for gibbsite that has precipitated directly from solution.

As also proposed by others using a modified-increment calculation, our synthesis experiments suggest that ${\alpha }_{Al(OH{)}_3-H_{2}O}$ is polymorph-dependent at low temperatures and that a significant temperature-dependent trend exists in the values of ${\alpha }_{Al(OH{)}_3-H_{2}O}$. However, previously calculated fractionation factors obtained using the modified-increment method are higher than those obtained from the experiments, with this discrepancy becoming larger as temperature decreases.

The intercalation complex of a low-defect dickite from Tarifa, Spain, with hydrazine was studied by high-temperature X-ray diffraction (HTXRD) differential thermal analysis (DTA), and ther-mogravimetry (TG). The X-ray diffraction (XRD) pattern obtained at room temperature indicated that the intercalation of hydrazine and H2O into dickite caused an increase of the basal spacing from 7.08 to 10.24 Å, which is slightly lower than the 10.4-Å spacing commonly observed after intercalation into kaolinite. Heating between 25–50°C produced a structural rearrangement of the complex, which decreased the basal spacing from 10.24 to 9.4 Å, and the resulting 9.4-Å complex was stable between 50–90°C. Heating between 90–300°C caused a gradual reduction in spacing, which occurred through a set of intermediate phases. These phases were interpreted to be interstratifications of intercalated and non-intercalated layers. These changes were also observed by DTA and TG. Two main endothermic reactions and two main stages of mass loss, respectively, were indicated in the DTA and the TG curves in the temperature range 25–200°C. This behavior suggests that intercalated molecules, hydrazine and H2O, occupied well-defined sites in the interlayer of the dickite. The intercalated molecules were lost in an ordered fashion as confirmed by the infrared analysis of the decomposition products; H2O was lost in the first stage and ammonia was identified in the second stage. Above 300°C, complete removal of the intercalated molecules restored the basal spacing of the dickite. However, the basal reflections were broadened, the relative intensities were changed, and changes in the dehydroxylation temperature indicated that the intercalation-desorption process induced some stacking disorder in the dickite structure.

The terms “hydrophobic” and “hydrophilic” are typically used in a non-specific sense and, as such, they have a limited utility. Surface thermodynamic theory, as described here, allows a natural and potentially powerful definition of these terms. The boundary between hydrophobicity and hydrophilicity occurs when the difference between the apolar attraction and the polar repulsion between molecules or particles of material (1) immersed in water (w) is equal to the cohesive polar attraction between the water molecules. Under these conditions, the interfacial free energy of interaction between particles of 1, immersed in water (ignoring electrostatic interactions), exactly zero. When is positive, the interaction of the material with water dominates and the surface of the material is hydrophilic; when is negative, the polar cohesive attraction between the water molecules dominates and the material is hydrophobic. Thus, the sign of defines the nature of the surface and the magnitude of may be used as the natural quantitative measure of the surface hydrophobicity or hydrophilicity.

Single-crystal, X-ray examination of Mg,Fe-rich chlorites that were heated at 650°C for 24 hours in air and have undergone dehydroxylation of the interlayer shows that two product phases result with a topotactic relationship, with the c axis of both phases parallel. One phase (“modified chlorite” or “14-A phase”) has relatively sharp reflections with a 14-A c-axis repeat, indicating that it is well crystallized and maintains the 2:1 layer from the parent. Cell parameters are a = 5.368(1)A, b = 9.297(2)A, c = 14.215(6)A, a = 89.86(3)°, ß = 97.15(3)°, γ = 89.98(2)°, and it crystallizes in CĪ symmetry. A structure refinement, details of which will be reported later, indicates that the interlayer consists of two planes, each containing (M + O), where M is the interlayer cation species. These planes show about ±0.5A positional disorder along the [001] direction. There is no evidence for scattering material at z = 0.5 between the 2:1 layers. The second phase in the topotactic relationship is based on a 27-A unit c axis (“27-A phase”). The diffraction data are limited with about 15 diffuse reflections observed, indicating that it is poorly crystallized. The 27-A spacing suggests that both octahedral sheets in the parent chlorite contribute to the formation of this phase.

Heating Mg,Fe-rich chlorite powder in a closed system to 550°C, under either reducing or oxidizing conditions, prevents the formation of the 27-A phase. Because the 27-A phase forms in an open system, we infer that water fugacity is an important factor in its formation. Heating experiments involving samples with different polytypes and octahedral “type” (dioctahedral vs trioctahedral) of the 2:1 layer suggests that these two variables are important. However, the results are equivocal, and an ill-defined B-rich chlorite from Madagascar breaks the observed trends for both variations in stacking sequence and octahedral type. However, B-content may be a factor in the transformation also for those chlorites that contain B.

The lithium form of taeniolite served as the molecular template for carbon nanocomposites. It was intercalated with hydroxy aluminum and hydroxy aluminum-zirconium cations. Aliquots of the inorganic matrices were saturated by furfuryl alcohol followed by its interlayer polymerization. The structures were heated at 973 K in nitrogen to carbonize the polymeric precursor. Additional materials were mixed with polypropylene glycol which was then carbonized within the mineral layers. The surface properties of the nanocomposites were studied by X-ray diffraction (XRD), DTA, SEM and sorption experiments (sorption of nitrogen). The results showed that structural properties of the derived materials depend on the inorganic matrix and organic precursor. The carbon-taeniolite nanocomposites derived from polyfurfuryl alcohol as a precursor were characterized by high carbon content and a high percentage of its surface area in micropores. A broad spectrum of surface characteristics of the final products were found, depending on the history of the sample.