Radiocesium was deposited on the soils of Fukushima Prefecture in Japan after the meltdown of the Fukushima Daiichi Nuclear Power Plant in 2011. The radiocesium bound to 2:1 clay minerals, such as vermiculite, common in the soil of that region and became non-exchangeable due to the strong affinity of these clay minerals for the Cs+ adsorbed. The current study generated adsorption envelopes for Cs+ on three zeolite minerals: zeolite Y, ZSM-5, and ferrierite. Two of these (ZSM-5 and ferrierite) caused monovalent cations to adsorb via a strong inner-sphere mechanism. A comparison of Cs+ adsorption on these zeolites to Na+ adsorption on the same zeolites showed that Cs+ adsorbs much more strongly than Na+, which is explained by its atomic properties. Despite the inner-sphere adsorption of Cs+ on ZSM-5 and ferrierite, the affinity of vermiculite for Cs+ is even stronger. An adsorption envelope for Cs+ on vermiculite failed to show a low-pH adsorption edge even at a pH of 1.01, with adsorption remaining at ~65% of the maximum even at this low pH. The adsorption envelopes for Cs+ on ZSM-5 and ferrierite minerals did show low-pH adsorption edges centered at pH 3.5 and 3.0, respectively, where Cs+ adsorption dropped to zero. The greater affinity of vermiculite for Cs+, even when compared with that for two zeolite minerals known to have significant affinities for monovalent ions, highlights the difficulty in removing Cs+ from contaminated Fukushima soils.

Mineral chabazite has shown the unusual ability to surface template nanometal particles, especially Ag. A chabazite analog was synthesized from delaminated metakaolin. The chabazite formed retained the platy morphology of the base clay. This morphology is ideal for displaying surface-supported nanometal particles. The synthetic chabazite analog demonstrated the ability to form and support large concentrations of Ag nanoparticles, as observed in the related natural mineral. Due to greater Al content, the synthetic chabazite manifests significantly improved capacity for the formation of such Ag nanoparticles. As in the case of the mineral chabazite, surface Ag nanoparticles of high uniformity were observed in the range of 5–6 nm.

Four natural bentonites, from Texas, Wyoming, Mexico, and Puerto Rico, have been fractionated by use of a super-centrifuge. The fractions have been investigated for base exchange capacity, apparent density, X-ray diffraction character and gel strengths of their suspensions.

Based on (001) spacings from X-ray diffraction and cation composition from ammonium acetate base exchange data, it was found that upon fractionation, clays of heterogeneous cation composition divide into two groups. Fractions larger than 0.150 micron contain the divalent cations Ca2+-Mg2+, while the finer fractions contain the monovalent cation Na+. Based on indirect evidence provided by X-ray diffraction, particle size fractionation, and gel strength, and correlation of the data with the literature, it is concluded that Na+ clays exist as unit layers in suspensions while Ca2+-Mg2+ particles are aggregates of a few layers.

Base exchange capacity and density were found to be independent of particle size.

A new structure is postulated and proposed for aqueous montmorillonite gels. This structure, descriptively called “hinge,” comprises clay particles oriented randomly to form a network in which each particle is hinged to other particles through sharing of bound particle-water.

Developing low cost and effective phosphate adsorbents is crucial to prevent eutrophication of natural waters. Here, phosphate removal by a natural and abundant shale from the Ivory Coast was investigated in both batch and column experiments with special attention devoted to understand the adsorption process. Batch experiments were carried out to assess the influence of initial phosphate concentration, sorbent dosage, contact time, and pH on phosphate removal. The phosphate removal efficiency increased with increased shale dosage while phosphate uptake decreased. Aqueous Ca, Mg, Al, and Fe species concentrations decreased in the presence of phosphate. Additionally, phosphate uptake strongly decreased with pH increases in the range 2–11, but then increased at pH 12. The kinetics were well described using a pseudo-second order model, and Langmuir adsorption isotherms were used for the equilibrium surface reactions. Adsorption to nanoparticles of goethite was hypothesized to be the major phosphate removal mechanism in the pH range 4–10. Column experiments with a flow rate of 1 mL min−1 and an initial phosphate concentration of 25 mg L−1 showed a breakthrough point at a V/Vp value of ~17, where Vis the volume of phosphate solution added to the column and Vp is the pore volume. A V/Vp value of ~17 corresponded to a phosphate uptake of 0.17 mg/g, which was in agreement with the batch experiments. Column experiments revealed a strong correlation between the aqueous concentrations of Ca, Mg, Al, and Fe species and phosphate removal and, thus, suggest that phosphate removal by the shale occurred by aqueous dissolution/precipitation.

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.

A fine-grained kaolinite-illite clay, in which planar particle orientation resulted from filtration or plastic deformation, swelled differentially when liquid water was imbibed by test pieces already in the plastic state. Swelling was greater perpendicular than parallel to the plane in which the clay platelets tended to be arranged. Filtration, in contrast to deformation, gave test pieces that swelled more rapidly and extensively. The slipbands, present only in plastically deformed test pieces, restricted the swelling. They were arranged diagonally to the plane in which the clay platelets tended to lie. The plastically deformed test pieces showed enhanced expansion perpendicular to this plane when they were made successively thinner by compression under a cylindrical roller. This was attributed to improved planar orientation of the clay platelets.

The chemistry of Al transformation has been well documented, though little is known about the mechanisms of structural perturbation of Al precipitates by carbonates at a molecular level. The purpose of the present study was to investigate the structural perturbation of Al precipitates formed under the influence of carbonates. Initial carbonate/Al molar ratios (MRs) used were 0, 0.1, and 0.5 after aging for 32 days, then the samples were analyzed by X-ray absorption near edge structure spectroscopy (XANES), X-ray diffraction (XRD), Fourier-transform infrared absorption spectroscopy (FTIR), and chemical analysis. The XRD data were in accord with the FTIR results, which revealed that as the carbonate/Al MR was increased from 0 to 0.1, carbonate preferentially retarded the formation of gibbsite and had relatively little effect on the formation of bayerite. As the carbonate/Al MR was increased to 0.5, however, the crystallization of both gibbsite and bayerite was completely inhibited. The impact of carbonate on the nature of Al precipitates was also evident in the increase of adsorbed water and inorganic C contents with increasing carbonate/Al MR. The Al K- and L- edge XANES data provide the first evidence illustrating the change in the coordination number of Al from 6-fold to mixed 6- and 4-fold coordination in the structural network of short-range ordered (SRO) Al precipitates formed under the increasing perturbation of carbonate. The fluorescence yield spectra of the O K-edge show that the intensity of the peak at 534.5 eV assigned to σ* transitions of Al-O and O-H bonding decreased with increasing carbonate/Al MR. The XANES data, along with the evidence from XRD, FTIR, and chemical analysis showed clearly that carbonate caused the alteration of the coordination nature of the Al-O bonding through perturbation of the atomic bonding and structural configuration of Al hydroxides by complexation with Al in the SRO network of Al precipitates. The surface reactivity of an Al-O bond is related to its covalency and coordination geometry. The present findings were, therefore, of fundamental significance in understanding the low-temperature geochemistry of Al and its impacts on the transformation, transport, and fate of nutrients and pollutants in the ecosystem.

The nomenclature of phyllosilicates is discussed in relation to structural variations of layers and interlayers. Some discrepancies in the nomenclature which arose due to historical reasons and different viewpoints may be reconciled if the choice of the construction units (layers or their parts) is related to definite sets of structures for which these units are common. Features of idealized models approximating real structures should be considered for classification and derivation of nomenclature sets, whereas priority is given to structural variations before lattice and symmetry characteristics. Layer polymorphs, pseudo-polytypes, polytypes (both simple and complex), and OD structures are distinguished. Particular results obtained for micas as a model example of phyllosilicates in relation to modular structures in general are considered in an Appendix.

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.

X-ray diffraction techniques were used to identify the clay mineral assemblages of Pennsylvanian underclay samples taken mainly from beneath the Colchester (No. 2) and Herrin (No. 6) Coals of Illinois and the Middle Kittanning Coal of Ohio. The clay minerals present are kaolinite, illite, chlorite, vermiculite, montmorillonite, and mixed-layer clay minerals. The minerals are not restricted to any particular stratigraphic unit, and their areal distribution is related to paleogeographic position in the original basin of deposition. Kaolinite shows a decrease in abundance from near shore to more basinward areas; illite is not present in near shore regions, becomes common basinward, and then shows a decrease with increasing distance from shore; chlorite is not found in near shore or in extreme basinward areas but is most common slightly basinward of the illite maximum; montmorillonite is fairly rare but is prominent in the most basinward positions; vermiculite is uncommon but usually occurs where kaolinite is the dominant mineral; mixed-layer clay minerals are present in all samples, constituting a small fraction of the clay minerals in the near shore regions but increases to the major constituent in the most basinward areas.

Clay minerals entering the basin of deposition during underclay formation were mainly kaolinite and mixed-layer clay minerals. As the mixed-layer clays were carried basinward into waters of increasing salinity, some of the mixed-layer clays, formed from weathered illite and chlorite, preferentially adsorbed potassium and magnesium and were regraded. Mixed-layer clay minerals that had undergone severe structural damage during weathering were not regraded and were deposited further basinward.

Maps showing lateral variation of clay minerals in an underclay also show the paleogeography. These maps may be used in outlining positive areas and deltas, or specific types of clay deposits.

With the use of a BaCl2 solution containing radioactive Ba2+ ions, kinetics of cation exchange have been done on a Kenya vermiculite, natural on one hand and previously oxidized either by 50°C water or oxygenated water on the other hand. Correlatively, the quantity of ferric iron in the layer has been determined by E.P.R. These two methods have shown that during an oxidation the proportion of iron which stays in the octahedral layer depends upon the nature of the oxidizing agent. During a weak oxidation, the iron stays entirely in an octahedral layer and the exchange capacity of the vermiculite decreases; on the other hand, during an oxidation by oxygenated water, part of the iron is extracted from the octahedral layer and the exchange capacity of the vermiculite is not changed, as established by the studies of Farmer (Farmer et al., 1971). Kinetic data for Llano vermiculite also are reported and compared with those for the Kenya vermiculite.

The use of electron diffraction contrast to detect local concentrations of interlayer cations in mica-vermiculites was examined. Cs and Mg, because of their contrasting atomic scattering amplitudes for electrons, were chosen as exchange ions for Ca. Cs was absorbed to the near exclusion of Mg by the clays from the three soils and by weathered clay-size muscovite and phlogopite. The presence of Cs in addition to the other interlayer cations, K and Ca, caused bending and perhaps splitting of the mica-verrmculite layers. Extinction bend contours were common in Cs-treatea specimens but not those Ca-treated. After freeze-drying of specimens of Cs-Ca Nason clay, differential destruction by the electron beam of the central core in clay-size vermiculite containing hydrated Ca ions may indicate the edge location of Cs.

Molecular dynamics (MD) simulations provide an accurate description of the mineral–fluid interface from the perspective of the atomistic level taking into account all atom interactions. This simulation approach is computationally expensive if applied to large molecular systems. Classical Fluid Density Functional Theory (f-DFT) delivers structural and thermodynamic information at comparatively small computational costs. Numerous applications of f-DFT for electrolytes neglect an explicit consideration of solvent. In this work, an unrestricted three-component model (3CM) of f-DFT was applied, which incorporates Lennard-Jones (LJ) attractions for the description of the short-range interactions of fluid–fluid and fluid–wall rather than the hard sphere repulsions, named DFT/LJ-3CM. The DFT/LJ-3CM model considers ions as charged LJ particles and treats solvent molecules as neutral LJ particles. To validate the performance of the DFT/LJ-3CM, the f-DFT calculations were compared with atomistic simulations for montmorillonite (Mnt) with various hydrated states in electrolyte solutions. This benchmarking was used to assess critically the advantages and limitations of the f-DFT model. The calibrated DFT/LJ-3CM model for Na and Ca Mnt was applied to calculate cation selectivity for the ion exchange equilibrium with effective ion radius and swelling behavior of Mnt. The predictions of the DFT/LJ-3CM model were found to be in good agreement with the atomistic simulations and experimental data under a wide range of conditions. At the same time, the DFT calculations were 3–4 orders of magnitude faster than conventional MD simulations. Thus, the DFT/LJ-3CM model can be a computationally effective alternative to atomistic simulation in providing structural and thermodynamic properties of fluid–clay mineral interfaces. The DFT/LJ-3CM model provides a robust approach, which can be used for upscaling in reactive transport simulators and modeling ion migration taking place under more complex thermo-chemo-hydro-mechanical conditions.

Clay soils are very useful as liners in geotechnical structures such as landfill sites, dams, water channels, etc. Swelling is a common problem in clay liners, however. To better understand swelling properties, in the present study clay nanocomposites were produced by means of the sol gel method, using a hydrophobic clay, polymers (locust bean gum, latex, glycerine, vinyl acrylic copolymer), and rubber powder. The study focused on the swelling and dynamic properties (secant shear modulus and damping ratio) of the clay nanocomposites researched experimentally in laboratory conditions. The dynamic tests were conducted on samples compacted using two different compaction energy levels. The test results were compared with those of natural clay and hydrophobic organo-clay. The test results revealed that the damping ratios and secant shear modulus of clay nanocomposites without rubber (CNC) and with rubber (CNCr) that were compacted with both the E1 and E2 energy levels were increased and decreased, respectively. In addition, with increasing percentage of vinyl acrylic in nanoclay composites, the secant shear modulus values were decreased and damping ratio values were increased. Consequently, the test results found that the swelling and dynamic properties of clay nanocomposites can be optimized in order to attenuate the negative effects of dynamic loads on clay liners.

Potentiometric measurements using commercially available cationic glass electrodes, electrical conductance and self-diffusion measurements of cations and water were made in electrolyte-free 3–5 per cent Li, Na, K, Cs, Ca and Sr bentonite-water systems and bi-ionic systems with varying ratios of K and Ca. Activation energies for conductance in the homoionic clays were calculated using the Arrhenius equation.

The agreement between cation mobilities measured by diffusion and conductance indicates that the underlying mechanism is essentially the same for the two processes. But the activation energies for ion movement determined for conductance measurements do not explain the observed reduction in mobility. Only two clays, Li and Cs, gave values significantly higher than for the measured solution conductance and only the Cs clay gave a value higher than those calculated for ion conductance at infinite dilution.

Increasing Ca saturation in K-Ca clays from 1 to 99 per cent increased the self-diffusion coefficient or mobility of K by a factor of about 1.7 and Ca by a factor of about 30 reflecting the effect of the predominate accumulation of the divalent cation in regions of highest negative potential. The reduction in activity of monovalent cations calculated from the potentiometric measurements, although of the same order of magnitude, was consistently less than the corresponding reduction in mobility in both the homoionic and bi-ionic clays. This difference became greater with increasing mobility of K in the bi-ionic clays.

Ferric-iron stilpnomelane is triclinic, space group Pl, a = 21.724 Å, b = 21.724 Å, c = 17.740 Å, α = 124.14°, β = 95.86°, γ = 120,0°, Z = 16. The structure is dominated by a subcell for which as = 1/4a, bs = 1/4b, cs = 1/4c, αs = α, βs = β, γs = γ. The subcell reflections have h-k = 3n, and have a trigonal intensity distribution. The structure was determined from Patterson projections and by trial and error. Three-dimensional refinement by least squares gave an it! factor of 14.4 per cent for 296 reflections.

Stilpnomelane is a layer structure, having five anion and five cation planes parallel to (001). An iron-rich octahedral sheet is flanked by two tetrahedral sheets. The tetra-hedral sheets differ from those found in the common layer silicates in that adjacent tetrahedra point in opposite directions. Each tetrahedral sheet has 1.25 tetrahedra pointing toward the octahedral sheet, and 0.75 tetrahedra pointing away. Detail in the tetrahedral sheet cannot be determined from the subcell reflections only.