Cored specimens of several commercial bentonite beds were preserved at field moisture levels for laboratory examination. Green strength, water content, and x-ray diffraction character of undisturbed material were found to conform substantially to the relation that strength is proportional to the solid fraction.

The viscosity of clay-water suspensions is an important factor in determining commercial uses of Georgia Kaolins. Impurities, such as montmorillonite type minerals, in these basically kaolinite clays play a part in causing variations in viscosity. However, seemingly pure kaolinite clays also show variations which seem to be related to morphology and degree of crystallinity. Studies are underway to determine the various factors involved.

The electrical state of the interface between a kaolinite-dominated clay sample and aqueous electrolyte solutions was characterized using low-frequency conductance measurements. From these measurements, the ζ-potential and surface conductivity contributions from the diffuse and non-diffuse parts of the electrical double layer were obtained. The suspensions were studied as a function of volume fraction, electrolyte concentration, and electrolyte type (LiCl, NaCl, KCl, CsCl, CaCl2, SrCl2, and BaCl2). Interpretation in terms of the surface conductance revealed that a substantial part of the surface conductivity originates in the inner part of the double layer. Electrokinetic potentials and related diffuse double layer properties are highly dependent on the nature of monovalent counterions, whereas divalent counterions do not show such clear dependencies. Further presented was a simple way to estimate the order of magnitude of counterion mobilities in the inner part of the electrical double layer. All counterions were shown to have a substantial mobility in the inner part of the double layer. Finally, we suggest that the apparent ion-specific effects observed in the diffuse part of the double layer are at least in part related to the finite size of the counterions. Our findings are relevant to scenarios where fluid flow in porous media is accompanied by charged species transport, e.g., in electro-osmotic remediation, spectral-induced polarization, or permeability measurements.

The present paper represents an extension of recent work that considered the partitioning response of binary solvents placed into contact with charged, expandable clays. Previous theoretical work yielded a model of partitioning by performing a thermodynamic analysis, involving the work of polarization, on a binary solvent, treated as a continuum and residing within the interlayer space of a layered aluminosilicate clay. Partitioning, or the tendency for sorbed and bulk phases to have different compositions, was shown to be sensitive to the dielectric properties of the 2 solvents of the binary mixture and to the surface charge density on the clay, among other factors. Although previous experimental work has helped to validate the theory, additional work is reported here that looks at hysteresis effects, the role of the exchangeable cation (usually organic), the prediction of adsorption isotherms and the contribution that partitioning, or sorption, makes to the disjoining pressure that develops in binary solvent systems. In this current study, 3 different organo-clays were considered: Cetyltrimethylammonium (CTMA), Isopropanolammonium (IPA), and Benzylammonium (BA) montmorillonite. Solvent systems under study included: acetone/chloroform (a-c), acetone/quadricyclane (a-q) and acetonitrile/chloroform (an-c). While partitioning of the a-c system on CTMA-clay follows theory quite well, theory tends to over-predict partitioning for the a-q system on the same clay and under-predict partitioning for the an-c system on all clays. Predicted adsorption isotherms range from highly nonlinear to nearly linear. Finally, the delamination and subsequent swelling processes of BA-clay in a water/acetonitrile binary solvent system are very sensitive to composition, a result that is directly linked to the partitioning process.

The employment of clay minerals in the transport of water, nutrients, and contaminants depends on a few factors, including permeability, hydration behavior, ion-exchange efficiency, and more. With the application of external stress, it is still difficult to understand how clay particles swell and collapse, how water is retained, how hydration heterogeneities are formed within crystallites, and how interlamellar space is organized. The present work studied the link between geochemical, thermal, kinetic constraints (established at the laboratory scale), and intrinsic clay features by exchanging Na-rich montmorillonite (SWy2) with Ni2+, Mg2+, or Zn2+ cations. By comparing the experimental 00l reflections with the calculated reflections obtained from the structural models, quantitative X-ray diffraction (XRD) analysis has enabled the building of a theoretical profile describing the layer stacking mode (LSM) and allowed the description of interlayer space (IS) configuration along the c* axis. Regardless of the type of the exchangeable cations (EC), XRD modeling revealed that all samples exhibited interstratified hydration behavior within the crystallite size, which probably indicates partial or incomplete saturation of the IS. This theoretical result was defined by the appearance of two hydration states (1W and 2W), which were unrelated to the strain strength creating a higher degree of structural heterogeneity. Using the theoretical decomposition of the observed XRD patterns, the identification of all distinct layer populations and their stacking mode was achieved. The segregated LSM are, therefore, obviously superior as a function of stress strength.

In order to gain a better understanding of clay and Fe (oxyhydr)oxide minerals formed during pedogenesis of basalts in tropical monsoonal Hainan (southern China), a basalt-derived lateritic soil at Nanyang, Hainan, was investigated comprehensively. The results show that the lateritic regolith consists uniformly of kaolinite and Fe (oxyhydr)oxide minerals, with trace gibbsite only in the AE horizon. Abundant dioctahedral smectite in the basalt bedrock formed due to primary hydrothermal alteration, and transformed to kaolinite rapidly in the highly weathering saprolite horizon. The ‘crystallinity’ of kaolinite is notably low and its Hinckley index fluctuates along the soil profile, resulting from intense ferrolysis due to fluctuations between wet/dry climate conditions. From the base to the top of the profile, maghemite shows a decreasing trend, whereas magnetite, hematite, and goethite exhibit a slightly increasing trend, indicating that maghemite formed as an initial product of basalt weathering. Formation of Fe (oxyhydr)oxide species in basalt-derived soil is mainly controlled by local environmental conditions such as soil moisture, redox, and acidic conditions; thus, iron mineral-based paleoclimatic proxies could not be used for subtropical to tropical soils. The highly weathered saprolite has a similar δ56Fe value (+0.06‰) to that (+0.07‰) of the parent rock, while the AE to middle E horizons have greater δ56Fe values of +0.12‰ to +0.19‰. Fe isotopic signatures correlate positively with the Fe mass transfer coefficient (R2=0.77, n=6, ρ<0.05), indicating repetitive weathering and relative accumulation of isotopically heavier Fe in the upper soil horizons, which occurred by reductive dissolution of organic matter under oxic conditions, as reflected by the greater U/Th.

Various fractions, ranging in size from 5 to 0·05 μ of natural clays from Mexico and Wyoming, occurring as heterogeneous or multicomponent cationic systems, were studied under specific equilibrium conditions of salt concentrations in the range found in many drilling fluids and formation waters.

Glass electrodes were utilized in this study. A Tektite electrode was found to have specific sensitivity to divalent cations.

Gypsum deposits of Mississippian age in southwestern Indiana contain several argillaceous partings. A study of these partings was made to find out what clay minerals are present in such an evaporite association.

The most abundant minerals in the clay partings are dolomite, gypsum, quartz, illite, chlorite and mixed-layer illite-montmorillonite. No kaolinite was found in any of the samples.

One potential solution to the rising threat of antibacterial drug resistance is the application of therapeutic clays to treat wound infections. Clays with antibacterial activity have been identified from a range of sources with their antibacterial properties often attributed to the release of toxic metal ions such as Fe(II) and Al(III). Here, clays from Afghanistan, Azerbaijan and Bangladesh that are utilized for washing and healing purposes were examined. Their antibacterial activities were assessed in suspension and as aqueous leachates against representative Gram-negative, Escherichia coli, and Gram-positive, Bacillus subtilis, bacteria. The majority of the clays conferred no deleterious effect and, in fact, tended to promote bacterial growth, likely as a result of released organic and inorganic nutrients. However, one of the clays, obtained from the Dhaka region of Bangladesh, displayed significant bactericidal activity against E. coli and B. subtilis as a clay suspension but not as an aqueous leachate. Further experiments confirmed that contact between clay and the bacteria was necessary for most of the antibacterial effects. Detailed analysis of bulk and <2 μm clay fraction mineralogy and geochemistry revealed no single defining parameter or mineral component that could be used to easily distinguish natural clays with antibacterial properties from those without. Overall, the results suggest a mechanism of antibacterial action of the Dhaka clay that arises from acidic conditions, likely enabled by the absence of calcite in the bulk clay, metal release, the presence of interstratified chlorite-smectite, and direct clay–bacteria interactions.

Clays are extremely variable materials with different mineral compositions, and they are the main ingredients in ceramics applications. Their properties play specific roles in influencing the technological properties and performance of ceramics products. Evaluating the various properties can help to determine the best way to utilize clay materials, such as the locally available Bombawuha (BC) and Denkaka (DC) clays mined from Ethiopia's Bombawuha and Denkaka areas, respectively. The objective of this study was to examine these materials for the purpose of using them to produce quality electrical porcelain insulators. The clay samples were characterized for their chemical composition, mineralogy, thermal properties, plasticity, and particle-size distribution, using atomic absorption spectrometry (AAS), X-ray diffractometry (XRD), differential thermal analysis coupled with thermogravimetric analysis (DTA-TGA), the Atterberg plasticity test, and sieve hydrometer analysis. Based on the characteristics, suitable clay materials were selected and mixed with feldspar and quartz to formulate various porcelain body compositions which were fired at three different temperatures (1200, 1250, and 1300°C) and dwell times (1.5, 2.0, and 2.5 h). The mineralogy, water adsorption, apparent porosity, bulk density, dielectric strength, flexural strength, and microstructure of the fired bodies were measured. The results revealed that, compared to DC, BC contains kaolinite as the major mineral with appreciable amounts of silica (46.72 wt.%), alumina (35.32 wt.%), and fluxing oxides but smaller amounts of CaO. BC contains greater clay fractions (20.58 wt.%); and has a middle-range plasticity index (PI = 11.2 wt.%), thus making BC suitable for producing porcelain insulators. A test-body composition of 40 wt.% BC, 40 wt.% feldspar, and 20 wt.% quartz, fired at 1250°C for 2 h, exhibited water adsorption of 0.17 wt.%, apparent porosity of 0.42 wt.%, bulk density of 2.45 g/cm3, a dielectric strength of 8.22 kV/mm, and flexural strength of 43.63 MPa and, thus, satisfied the required properties for quality porcelain insulators.

Fe is a common substituent in palygorskites (Plg), but its effect on the microscopic properties is unclear. In the current study, molecular dynamics (MD) simulations were carried out to investigate the effect of Fe on the properties of the nano-pores in Plg. The structures and dynamics of water and Na+ ions in the pores were computed by analyzing the MD trajectories. The results revealed that for both Fe-containing and ordinary Plg, zeolitic water molecules can diffuse into the pores with very low mobility whereas Mg-coordinated water fails to escape. Na+ ions show no obvious diffusivity because they are fixed above the Si–Osix-membered rings. Detailed comparison indicates that Fe-substitution has no significant influence on the pore properties of Plg.

Clay minerals occur most commonly as constituents of sedimentary rocks and nearly all the clay mineral species, with the possible exception of nacrite, have been found in sediments. Different clay minerals occur in different kinds of sediments and may be used as one criterion for classifying sediments and interpreting their genesis.

At the Desmoinesian-Missourian disconformity in southeastern Kansas a fossil soil zone is recognized by variations in clay mineralogy in the uppermost Desmoinesian Holdenville shale, which underlies basal Missourian Hepler sandstone. The clay fraction of the overlying basal Missourian Hepler sandstone contains kaolinite, slightly hydrated illite, quartz, and vermiculite. Chlorite (rather than vermiculite) is present in shaly portions of the basal Hepler sandstone. Clay-size minerals of the typical Holdenville shale (marine) are predominantly illite, chlorite, quartz, feldspar, and a very small quantity of kaolinite. The clay-mineral assemblages in samples from the upper part of the Holdenville shale indicate hydration of illite, sporadic increase in kaolinite, possible decrease in feldspar, and progressive modification and destruction of chlorite resulting in production of mixed-layer minerals.

The exchange of Rh(NBD)(Pϕ3)2+, Rh(NBD)(PMe2ϕ)3+, Rh(COD)(Pϕ3)2+, and Rh(PMe2ϕ)4+ on hectorite was studied in methanol/dichloromethane, acetone, dimethylformamide, and acetonitrile. At low initial Rh+ concentration and short contact times, ion exchange was the predominant process, and its selectivity and maximum capacity were solvent-dependent. High initial Rh+ concentrations, long contact times, and the most polar solvents favored intersalation and salt precipitation. In all experiments monolayers of complex formed in the interlamellar space and were very tightly held. The complexes retained their integrity on the surface even after removal of all solvent molecules.

Ion-exchange modeling is used widely to describe and predict ion-adsorption data on clay minerals. Although the model parameters are usually optimized by curve fitting experimental data, this approach does not confirm the identity of the adsorption sites. The purpose of the present study was to extend to divalent cations a previous study on the retention of monovalent cations on Na-saturated montmorillonite (NaMnt) which optimized some of the model parameters using density functional theory (DFT) simulations. The adsorption strength of divalent cations increased in the order Mg2+ < Cd2+ < Ca2+ < Sr2+ < Ba2+. After adding adsorption of metal hydroxide species (MOH+), the three-site ion-exchange model was able to describe adsorption data over a wide pH range (pH 1–10) on NaMnt. X-ray diffraction (XRD) analyses were conducted to investigate the interlayer dimension of clay samples under various conditions. The cation retention strengths of divalent cations did not correlate with interlayer dimensions. The XRD analyses of the Mnt showed a d001 value of 19.6 Å when saturated with alkaline earth cations, 22.1 Å with Cd2+, 15.6 Å with Na+, and 15.2 Å with H+. In the case of Na+, the 15.6 Å peak decreased gradually and disappeared, and new peaks at 22.1 and 19.6 Å appeared when the percentages of Mg2+ and Ba2+ adsorbed increased on NaMnt. The peak shifted from 22.1 to 20.3 and 19.6 Å when the pH increased for all cations except Cd2+, which stayed constant at 22.1 Å. The coexistence of multiple d001 peaks in the XRD patterns suggested that the interlayer cations were segregated, and that the interlayer ion–ion interactions among different types of ions were minimized.