The Pleistocene Olorgesailie Formation in the southern Kenya Rift has yielded a remarkable assemblage of Acheulean artifacts and vertebrate fossils, including hominin specimen KNM-OG 45500. Members 1 and 7 both contain clay-rich deposits that have been pedogenically modified into paleosols (UM1p and UM7p, respectively). This study provides the first detailed mineralogical and geochemical analyses of the clays of this important Pleistocene basin. The smectitic clays, which show abundant evidence for pedogenesis, were apparently originally deposited under lacustrine conditions. They have an average structural formula of (Ca0.01Na0.32K0.26)(Si3.76Al0.24)(Al0.86Ti0.04Fe0.68Mg0.42)O10(OH)2. The high layer charge clays indicate diagenetic alteration of detrital clay derived from the volcanic drainage basin, probably involving alkaline waters of variable salinity. Despite overall lower salinity compared to other Plio–Pleistocene basins of the region (e.g. Olduvai Gorge), the basin still shows evidence for authigenic clay mineral precipitation. Clay chemistry and bulk geochemical indicators of pedogenesis imply that UM1p clays more closely reflect depositional paleo-waters, whereas UM7p clays have been more pedogenically altered due to subaerial exposure. UM1p smectites show some Mg enrichment near the western Lava Hump locality, consistent with discharge of Mg-bearing paleo-waters from a volcanic aquifer into a siliceous and alkaline (though not highly saline) paleo-lake. UM7p smectites were deposited in a more saline paleo-lake, but have lost substantial amounts of Mg due to post-depositional weathering. Locally abundant artifacts and vertebrate fossils found in these deposits accumulated at times following deposition of the lacustrine clay, probably concurrent with pedogenesis. The limnological conditions associated with initial clay deposition, therefore, preceded hominin occupation of the exposed surfaces.

Acid-activated bentonites are utilized in many applications, including those that depend on their rheological properties and behavior, but little information is available regarding the rheological characteristics of this important industrial material. The purpose of this study was to investigate the effects of solids concentration, salt concentration, and pH value on the shear rate, shear stress, and other flow parameters of acid-activated bentonite suspensions. Activated Na-bentonite was prepared using sulfuric acid. Flow curves of the suspensions were modeled using the Herschel-Bulkley equation, which performed well for this system. The Herschel-Bulkley yield stress increased with the solids concentration and showed a maximum and minimum at the NaCl concentrations of 0.001 M and 0.01 M, respectively, and increased again slightly with further increases in NaCl concentration. The yield stress was at a maximum and a minimum at pH values of ≈5 and ≈7, respectively, followed by a slight increase with pH under alkaline conditions. The variations in dispersion rheological properties can be attributed to the change in the particle-association modes under different conditions.

NEWMOD was developed by R.C. Reynolds, Jr., for the study of two-component interstratifications of clay minerals. One-dimensional X-ray diffraction (XRD) profiles of an interstratified system of two clay minerals can be simulated using NEWMOD, given a set of parameters that describes instrumental factors, the chemical composition of the system (e.g. the concentration of Fe and interlayer cations), and structural parameters (e.g. proportions of the two components, the nature of ordering, and crystallite size distribution). NEWMOD has served as the standard method for quantitatively evaluating interstratified clay minerals for >20 y. However, the efficiency and accuracy of quantitative analysis using NEWMOD have been limited by the graphical user interface (GUI), by the lack of quantitative measures of the goodness-of-fit between the experimental and simulated XRD patterns, and by inaccuracies in some structure models used in NEWMOD. To overcome these difficulties, NEWMOD+ was coded in Visual C++ using the NEWMOD architecture, incorporating recent progress in the structures of clay minerals into a more user-friendly GUI, greatly facilitating efficient and accurate fitting. Quantitative fitting parameters (unweighted R-factor, Rp, weighted R-factor, Rwp, expected R-factor, Rexp, and chisquare, χ2) are included, along with numerous other features such as a powerful series generator, which greatly simplifies the generation of multiple simulations and makes NEWMOD+ particularly valuable for teaching.

The contamination of aquatic environments by toxic metals such as radionuclides is of great concern because of the tendency of those metals to accumulate in the vital organs of humans and animals, causing severe health problems. The objective of this study was to investigate the use of natural and modified magadiite clay as an adsorbent to remove Th(IV), U(VI), and Eu(III) from aqueous solutions. Magadiite from the Amazon region, Brazil, was modified chemically with 5-mercapto-1-methyltetrazole (MTTZ) using a multi-step or heterogeneous synthesis pathway. The natural and modified materials were characterized using 29Si and 13C nuclear magnetic resonance, scanning electron microscopy, nitrogen gas adsorption, and elemental analysis. The physical-chemical properties of the chemically modified magadiite sample were modified, e.g. the specific surface area changed from 35.0 to 678.9 m2 g−1. The ability of the magadiite to remove Th(IV), U(VI), and Eu(III) from aqueous solution was then tested by a series of adsorption isotherms adjusted to a Sips equation. The effects of properties such as pH, contact time, and metal concentration on the adsorption capacity were studied. The adsorption maxima were determined to be 7.5 × 10−3, 9.8 × 10−3, and 12.9 × 10−3 mmol g−1 for Th(IV), U(VI), and Eu(III), respectively. From calorimetric determinations, the quantitative thermal effects for all these cations/basic center interactions gave exothermic enthalpy, negative Gibbs free energy, and positive entropy, confirming the energetically favorable conditions of such interactions at the solid/liquid interface for all systems.

The morphology of hydrotalcites determines their use in catalysis, biomedicine, or adsorption as they may work as anion exchangers or as drug deliverers. In catalysis, reagents need access to as much surface area as possible; in biomedicine, drugs have to be encapsulated. However, the parameters and the mechanisms which direct the synthesis towards a certain morphology are not well understood. Precipitating agents or crystallization conditions are expected to play a crucial role. In the present study, hydrotalcites were synthesized in the presence of two precipitating agents (NaOH or NH4OH) under three different crystallization conditions (conventional, microwave, or ultrasound irradiation) which determined the morphology of the final product, layered or vesicular. The features are explained through the template effect of the liberated gases on the co-precipitation and crystallization processes and consequently on the final structure/morphology of the synthesized solids. Indeed, the nodular particles crystallize using the effluent gases as templates. Fractal dimension and particle-size distributions, determined by small-angle X-ray scattering (SAXS) and gas adsorption are compared and correlated to the presence of ammonium. Although the materials obtained are heterogeneous, it is possible to propose a microscopic geode model.

Chemically modified bentonites are being developed with the aim of preserving low hydraulic conductivity in the presence of potentially aggressive permeants in pollutant-containment applications. ‘Multiswellable’ bentonite (MSB) has been obtained by treating standard sodium bentonite with propylene carbonate. Research on the engineering properties of MSB has focused mainly on permeability and chemical compatibility. Solute diffusion and membrane behavior in MSB have not yet been investigated. A combined chemico-osmotic/diffusion test was performed on a MSB specimen using a 5 mM CaCl2 solution. Permeability with distilled water and with the 5 mM CaCl2 solution was measured prior to and after the chemico-osmotic/diffusion tests. The material exhibited time-dependent membrane behavior with a peak osmotic efficiency value (ω) of 0.172 that gradually shifted to zero upon breakthrough of calcium ions. Effective diffusion coefficients of calcium and chloride ions were in the range commonly described for untreated bentonite at similar porosities. After the chemico-osmotic/diffusion stage and permeation with 5 mM CaCl2, the hydraulic conductivity of MSB increased from 1.1 × 10−11 m/s to 7.0 × 10−11 m/s. The MSB was apparently converted into a calcium-exchanged bentonite at the end of the test. Prehydration and subsequent permeation might have contributed to elution of the organic additive from the clay. Further investigation is recommended to clarify the effect of prehydration on the hydraulic performance of MSB in the presence of potentially aggressive permeants.

The objective of this paper is to describe the new serpentine group mineral, guidottiite, which is analogous to cronstedtite. Guidottiite has an ideal chemical composition of (Mn2Fe3+)(SiFe3+)O5(OH)4. The sample is from the N’chwaning 2 mine, Kalahari manganese field, Republic of South Africa, and apparently forms from hydrothermal solutions. Grains are optically near opaque [average index of refraction 1.765, with variable extinction on the (001)], vitreous, and black, with perfect {001} platy cleavage. A non-separable fibrous substructure exists perpendicular to cleavage that results in a silky luster under optical examination. The average chemical analysis determined from electron microprobe based on four grains with ten analyses each resulted in a structural formula of (Mn1.86Fe0.613+Mg0.54)Σ=3.01(Si1.36Fe0.643+)Σ=2.00O5(OH)4, with calculated density of 3.236 g/cm3. Analysis from another area of the sample showed a slightly different chemical composition and resulted in a formula of (Mn1.70Fe0.963+Mg0.24Σ=2.89(Si1.26Fe0.743+)Σ=2.00O5(OH)4, with calculated density of 3.291 g/cm3. The measured density on a bulk sample (with impurities) was 3.33 g/cm3. Thermal analysis suggested a dehydroxylation temperature of 535°C, a decomposition/recrystallization temperature of 722°C, and weight loss (= H2O loss) of 9.4%. The derived Mohs hardness from nano-indentation is H = 4.25.

The sample is mostly the 2H1 polytype with minor amounts of the 2H2 polytype. Using a predominantly 2H2 crystal, which has better crystallinity, the strongest observed X-ray peaks are: 7.21 Å (Io/Io = 100%), 3.543 (50), 2.568 (39), 1.982 (26), and 2.381 (25). All Gandolfi simulations, even with three crystal remountings, showed preferred orientation effects. Transmission electron microscope (TEM) analysis showed stacking disorder within Group D serpentine polytypes. Thus, a regular alternation of the occupancy of octahedral sets within each layer along the stacking exists, but disorder of the layer displacements of 0 and ±b/3 (b defined here as the orthohexagonal cell) exists. Ordered 2H1 (no layer displacement) and 2H2 (alternating + and —b/3 displacement) domains were also frequently observed. X-ray diffraction analysis showed that even apparent single crystals contain impurity phases, presumably Mn-rich and Ca phases that were detected in the microprobe study. The single-crystal structure refinement used a well (stacking) ordered apparent 2H2 crystal with little to no streaking in the diffraction pattern. Results showed that the crystal has a random interstratification of 2H2 and 2H1. The 2H2 polytype is hexagonal, space group P63, with a = 5.5472(3), c = 14.293(2) Å, and Z = 2, and was refined to R1 = 0.072 and wR = 0.108 from 656 unique reflections. Because the two polytypes in the composite have only small differences in the lower 1:1 layer, a large displacement parameter for the basal oxygen atom results, which was constrained to B = 1.5 Å2 (Ueq = 0.0190) in the refinement. Half of the tetrahedral sites in the 2H1 upper layer superpose over half of the tetrahedral sites in the 2H2 upper layer (T1 sites only) per unit cell. This superposition produces an apparent excess of electron densities of the T1 site relative to the T2 site (T1 = 21.9 electrons, T2 = 15.8). Comparison with the microprobe data indicates that observed tetrahedral bond lengths are generally not affected by this intergrowth. Tetrahedral bond lengths indicated that the tetrahedral sites contain T1 = Si0.678 Fe0.3223+ and T2 = Si0.631Fe0.3693+. This excess of electron densities and other refinement problems associated with the guidottiite single-crystal refinement closely parallel all single-crystal cronstedtite-2H2 refinements to date, suggesting that these refinements also involve random interstratifications of 2H2 and 2H1 polytypes.

Secondary Fe(III) oxyhydroxides play a key role in controlling the mobility and bioavailability of trace metals in acidic, sulfate-rich soils, such as mining and smelter sites. Schwertmannite, jarosite, goethite, and ferrihydrite are the most common mineral phases identified in such soils. A good understanding of the precipitation and transformation of these minerals in soils is very important for predicting the mobility and long-term stability of trace metals associated with them. In the present study, bulk powder X-ray diffraction (XRD), scanning electron microscopy (SEM), synchrotron based micro- X-ray diffraction (µ-XRD), and micro X-ray fluorescence (µ-SXRF) spectroscopy were used to investigate precipitates fromthe surface horizon of an organic soil (Histosol) at a site that once contained a lead smelter. Soil samples were collected from 0 to ≈10 cm depth during both wet and dry seasons. Goethite and akaganeite were identified as the major mineral phases in this soil. Schwertmannite and jarosite were also occasionally identified, particularly in the soil samples from dry periods. The peaks in the akaganeite XRD pattern were significantly broadened and the relative intensities of some major peaks were distinctly different compared with the diffraction pattern of synthetic akaganeite, possibly due to the effects of pH and the incorporation of sulfate. The SEM and µ-XRD data support the hypothesis that the goethite in the precipitates is not the product of direct precipitation froms olution but the transformation of previously precipitated schwertmannite or akaganeite.

The mineralogical characteristics of Ordovician and Silurian K-bentonites in the Baltic Basin were investigated in order to understand better the diagenetic development of these sediments and to link illitization with the tectonothermal evolution of the Basin. The driving mechanisms of illitization in the Baltic Basin are still not fully understood. The organic material thermal alteration indices are in conflict with the illite content in mixed-layer minerals. The clay fraction of the bentonites is mainly characterized by mixed-layered illite-smectite and kaolinite except in the Upper Ordovician Katian K-bentonites where mixed-layer chlorite-smectite (corrensite) occurs. The variation in expandability plus other geological data suggest that the illitization of Ordovician and Silurian K-bentonites in the Baltic Basin was controlled by a combination of burial and fluid driven processes. The illitization in the south and southwest sectors of the basin was effected mainly by burial processes. The influence of the burial process decreases with decreasing maximum burial towards the central part of the basin. The advanced illitization of the shallowburied succession in the north and northwest sectors of the basin was enhanced by the prolonged flushing of K-rich fluids in relation to the latest phase of development of the Scandinavian Caledonides ≈420–400 Ma.

Methods for predicting the volume change and swelling-pressure behavior of expansive clays require detailed understanding of coupled interactions between clay microstructure and macrostructure under hydraulic, thermal, and mechanical loads. In this study a suite of water-vapor sorption experiments was conducted using compacted bentonites hydrated in controlled relative humidity (RH) environments maintained under free and constrained volume-change boundary conditions. Emphasis was placed on examining the influences of compaction and predominant exchange cation on the water uptake, volume change, and swelling pressure response. Densely compacted specimens exhibited greater volume changes under free swelling conditions and greater swelling pressures under fully confined conditions. Water uptake, volume change, and swelling pressure were all more significant for Colorado (Ca2+/Mg2+) bentonite than forWyoming (Na+) bentonite. Plastic yielding, evident as a peak in the relationship between swelling pressure and RH, was more evident and occurred at lower RH for the Colorado bentonite. This observation was interpreted to reflect the limited capacity for interlayer swelling in Ca2+/Mg2+ bentonites and corresponding structural collapse induced by the onset of water uptake in larger intra-aggregate and inter-aggregate pores. A semi-quantitative model for the evolution of clay microstructure resulting from interlayer hydration was considered to attribute the experimental observations to differences in the efficiency with which transitions in basal spacing translate to bulk volume changes and swelling pressure. Results provide additional insight and experimental evidence to more effectively model the mechanical behavior of compacted bentonites used as buffer or barrier materials in waste repository applications.

The morphology, dehydroxylation, and dissolution properties of single- and multi-metal (Cr, Zn, Cd, and Pb)-substituted goethites prepared using hydrothermal methods are reported. The crystal morphology varied with the nature and the number of metals present in the system. The presence of Cr produced broader crystals while Zn, Cd, and Pb produced narrower crystals than pure goethite. The presence of multiple metals retards the crystal growth of the mineral. Metal substitution caused changes in the unit-cell parameters and the infrared (IR) spectra of the samples. The IR spectra were also sensitive to the morphology of the crystals. The separation of γO and δOH bending frequencies increased with increase in area and aspect ratio of the (100) crystal face. The dissolution-kinetics studies (1 M HCl, 40ºC) of single-metal-substituted goethite provided the following dissolution rate order: Zn- > Pb(II)- ≥ Pb(IV)- > unsubstituted > Cd- > Cr-goethite. More complex results were obtained for the multi-metal-substituted samples. In the di-metal-substituted goethites, incorporation of Cr suppressed the dissolution rate of Zn-substituted goethite by 85% and Cd suppressed the dissolution rate of Zn-substituted goethite by 53%. Similarly, incorporated Cr and Cd suppressed the dissolution rate of Pb(II)-substituted goethite by 50%. The dissolution rates of multi-metal-substituted goethite were linearly related to the steric strains derived from the lattice parameters of the mineral. Dissolution studies also showed that Cr, Zn, Cd, and Pb(IV) were distributed homogeneously throughout goethite crystals while Pb(II) was enriched in the near-surface regions of the crystals. Incorporation of Cr and Pb(II) increased, while Zn and Pb(IV) decreased the dehydroxylation temperature of single-metal-substituted goethites. Incorporation of Zn suppressed the effect of Cr on the dehydroxylation temperature in multi-metal-substituted goethites.

As advances in technology have led to increased use of bentonites, more high-quality bentonite has been sought. The volume of high-quality bentonites available is shrinking and use of bentonite reserves containing impurities is inevitable. The aim of this study was to apply Box–Behnken experimental design and response surface methodology to model and optimize some operational parameters of a hydrocyclone to produce three groups of bentonite concentrates. The four significant operational parameters of hydrocyclones are feed solid ratio, inlet pressure, vortex diameter, and apex diameter, and these parameters were varied and the results evaluated using the Box–Behnken factorial design. In order to produce bentonite concentrates using a hydrocyclone, mathematical model equations were derived by computer simulation programming applying a least-squares method, using Minitab 15. Second-order response functions were produced for the swelling and to establish the quantity of smectite in the bentonite concentrates. Predicted values were found to be in good agreement with the experimental values (R2 values of between 0.829 and 0.999 for smectite and three different swelling groups for the bentonites). Although in natural states these bentonites are not suitable for industrial use, enhancements were obtained giving up to 81.45% smectite and by increasing swelling by 194% for the three bentonite groups. The swelling properties of the bentonites are improved by increasing the proportion of smectite content. The graphics were designed to relate swelling and smectite content according to the two-dimensional hydrocyclone factors, and each factor was evaluated in itself. The present study revealed that the Box–Behnken and response surface methodology can be applied efficiently to model the hydrocyclone for bentonite; the method is economical and provides the maximum amount of information in a short period of time and with the smallest numberof experiments.