This paper provides evidence of appreciable amounts of Zn (up to 0.52 a.p.f.u.) residing in the crystal structure of trioctahedral vermiculite; the results were obtained by a combination of experimental methods (X-ray diffraction, energy dispersive X-ray spectrometry, electron microprobe analysis and selective chemical extractions) and theoretical studies based on density functional theory (DFT). Vermiculite occurs in size fractions ranging from 10 to 40 μm of near-neutral soils naturally enriched in Zn (up to 8110 mg kg–1) due to the weathering of carbonate-hosted Zn-Pb deposits in SW Spain. Zinc was partitioned among the various pedogenic phases during soil formation, but the larger part (>80%) was concentrated in the residual silicate fraction. The soil exchangeable Zn pool was found to be virtually negligible. The DFT calculations support the hypothesis that the role of vermiculite is an effective sink for geogenic Zn; this is consistent, in terms of energetic stability, with the assumption that most Zn is structurally bound in octahedral sheets rather than in the interlayer exchange sites. The findings conclusively indicate that the potential mobility of Zn should remain low under the present soil conditions.

Alkali- and Ca-rich smectites occur in association with Neogene lacustrine sedimentary rocks and high-K calc-alkaline volcanic rocks with compositions ranging from andesite to rhyolite in western Anatolia (Turkey). Major clay occurrences are associated predominantly with the Foça and Akçaköy ignimbrites and with the ignimbrites within the Rahmanlar pyroclastics. Experimental studies indicate that the main clay minerals present are Na- and Ca-smectite and subordinate illite, associated with silica polymorphs, trace clinoptilolite and chlorite. The authigenic minerals formed by weathering and metasomatic reactions between hot volcanic material and lake water. Smectite was produced as a result of argillic alteration of the volcanic glass and feldspars of the ignimbrites, Rahmanlar pyroclastics and reworked volcaniclastic sediments through chemical weathering and dissolution-precipitation processes and formed as authigenic phases both in terrestrial and nearby shallow lacustrine environments under prevalent humid or semi-humid climate during the Neogene.

The chemical composition and structural characteristics of clays from samples of eight Tuscan soils were investigated. Using simple selective dissolution method (successive boiling in 1 N HCl and 0·5 N NaOH) it was possible to distinguish two types of low charge dioctahedral vermiculite; one easily HCl soluble the other practically insoluble.

Structural formulae for the soluble type were calculated from the chemical analysis of the dissolved material; for the insoluble type it was possible to calculate only an 'average' structural formula which included the micaceous material.

Since the HCl soluble vermiculites show a high content of Fe and Mg, they can be considered either as alteration products of glauconites or biotites, or as a result of a synthesis, at least in soils derived from basic rocks which do not contain mica.

The aluminous insoluble type, present also in parent material, may be the result of an incomplete 'illitization' in a marine environment.

The ease with which sorbed Cr(III) is released to solution via oxidation or cation exchange depends on its mode of complexation and the broader chemical environment in which it is held. This study was conducted to elucidate the chemical environment of hydrolysed Cr(III) sorbed onto montmorillonite, both alone and coprecipitated with Al. The 27Al MAS NMR revealed that Cr in the coprecipitated hydroxy interlayer created a second environment for AI, slightly more shielded than that of Al in the montmorillonite 2:1 layer. This observation is evidence for the presence of numerous Al-O-Cr linkages, thus revealing a uniform distribution of Al and Cr within the hydroxy polymers. The 29Si MAS NMR revealed a second environment for Si in the tetrahedral sheet of the Cr clays. This environment could be created only through a redistribution of electrons at the siloxane surface caused by inner-sphere complexation of Cr(III). Due to this inner-sphere complexation, sorbed Cr(III) is difficult to displace via simple exchange reactions and, consequently, its bioavailability is decreased.

The Georgia, USA, kaolins contain three major occurrences of Fe-sulphide minerals, namely (1) in burrow structures, (2) as nodules associated with lignite and (3) as finely disseminated material. We have used sulphur isotope analysis and X-ray powder diffraction to understand these three occurrences in order to gain insight into the diagenetic conditions and microbial influences affecting the kaolin mineralogy. Burrows and nodules are dominated by corroded marcasite with thin pyrite overgrowths. The δ34S composition of each sulphide sample has internal fractionations (δ34Shigh – δ34Slow) ranging from 22‰ to 67‰. The secondary pyrite phase tends to be the most 34S depleted, with a low δ34S value of –47‰, whereas marcasite displays a δ34S range from 30‰ to +33‰. Early acidic environments from organic acids could have facilitated the initial marcasite crystallization, with a pH increase during later diagenesis producing pyrite overgrowths. Sulphide formation would have continued until burial restricted the diffusion of sea-water sulphate. At this point, the metabolism of sulphate-reducing bacteria would have been retarded, producing δ34S values ranging from –30‰ (open sulphate supply) to +40‰ (highly restricted sulphate supply). Under the nutrient-starved conditions of later-diagenesis, disproportionate sulphur-reducing bacteria would likely have become more dominant, yielding additional δ34Ssulphide fractionation and producing the observed fractionation (δ34Ssulphate – δ34Ssulphide) values of +67‰.

Steam jet milling was applied for the first time to ultra-fine grind the filter cake (moisture content 23.80%) produced by a kaolin concentrator. The material was dehydrated and dried simultaneously during grinding, and the final ground sample met the moisture content requirement for powder products of <2%. The particle size of the ground kaolin samples decreased and the particle-size distribution was more concentrated, indicating that the steam jet milling was more effective for kaolin processing than the conventional dry grinding process. In addition, steam jet milling can improve the whiteness and decrease the crystal order of the samples, thus improving the kaolin properties in follow-up applications.

Two samples collected from the phosphogypsum deposits of the chemical products industry Elixir Prahovo (Serbia) were subjected to a recrystallization experiment performed over several repeated cycles. In these tests, phosphogypsum was separated into recrystallized (purified) gypsum, insoluble residue and supernatant. Both raw phosphogypsum and recrystallized gypsum were examined using inductively coupled plasma optical emission spectrometry, X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry. The activity concentrations of 238U, 235U, 226Ra, 210Pb, 232Th and 40K were investigated using γ-ray spectrometry. Based on the activity concentration results, a number of radiometric parameters were calculated for the original and recrystallized phosphogypsum (i.e. radium equivalent activity, γ indices for construction materials, α index and external and internal hazard indices). Raw phosphogypsum samples showed greater mean activity concentration levels of 238U and 226Ra than the international recommended limits, while the recrystallized gypsum demonstrated notably lower activity concentrations for these two isotopes. The activity concentration of 226Ra in recrystallized gypsum is ~6 times lower than in raw phosphogypsum. Therefore, recrystallized gypsum does not present a radiation hazard when used as a building material, while raw phosphogypsum meets the requirements only for road construction materials.

The two high-pressure water-retaining dams at the Ibbenbüren coalmine in Münsterland (Germany) have to perform reliably under the induced tension caused by further exploitation of the current mining area. The load-bearing and the sealing functions of the new barriers were separated and new sealing materials were developed. An innovative multilayer sealing system of bentonite and sandwiched equipotential layers (SANDWICH) supporting homogeneous swelling and sealing, independent of formation water (Nüesch et al., 2002), was applied in this project. A testing program of strain-controlled swelling pressure tests on compacted bentonite specimens and on a bentonite/sand mixture was conducted to ensure an adequate potential for swelling-pressure development.

The measurements under constant volume for dry densities between 1.45 g/cm3 and 1.67 g/cm3 showed an evolving swelling pressure between 1.04 and 1.8 MPa for 100% bentonite samples. Straincontrolled oedometer tests for zero strain and step-wise applied strain up to 2% revealed that a sufficient magnitude of swelling pressure existed at maximum applied strain.

Constructional details of the balance and methods to give maximum sensitivity in obtaining and presenting results are described. Examples of work on clay minerals include comparison of results from the balance with d.t.a. traces of kaolinite and halloysite, low temperature dehydration of various montmorillonites, and a series at different rates of heating showing the relation between the d.t.a. trace and the equilibrium isobaric dehydration curve of Li+-Wyoming bentonite.

Differential heat of water vapour adsorption for Cs+-saturated montmorillonite, kaolinite and allophane was measured over a low relative humidity range from 10−4 to 10−1. Two interactions (clay surface atom-water and counterion-water) are mainly involved in the water vapour adsorption process. To assess the affinity of water to the clay surface, the amounts of adsorbed water and the differential heat due to Cs+ were estimated from equilibrium constants in the gas phase reactions. It is tentatively concluded that (i) a dominant role of water adsorption due to the Cs+-water interaction in the adsorption process is evident only for montmorillonite; (ii) the affinity of water to the clay surface is strongest for allophane and weakest for montmorillonite.

The technique of neutron inelastic scattering has demonstrated the presence of longitudinal acoustic phonons in two layer-silicate minerals. Values of the elastic constants determined from the dispersion curves have established the validity of the technique for this class of materials.

This paper describes reactions occurring between the 25.5 Å ammonium propionate (AP) intercalate of a well-crystallized Georgia kaolinite with ethylene glycol, 1-6-diaminohexane and a quaternary amine (QA), namely

An ethylene glycol kaolinite complex is obtained with a strong d001 reflection at 10.9 Å. Seven 00l orders are observed easily. The IR spectrum shows bands at 3697, 3654 (weak shoulder) 3644 and 3622 cm−1, assigned to OH stretching of kaolinite and a strong OH band of E.G. at 3300 cm−1. No absorption band of AP is observed.

The 1.6-diaminohexane product is characterized by two broad reflections at 16.6 and 7.4 Å. Distinct Amide I and Amide II IR bands imply that the carboxyl group of the propionic acid has reacted with the amino group. By treating the AP complex with QA a very stable kaolinite-QA complex suspension in benzene was obtained. On drying an X-ray amorphous solid with no reflection at spacing & 20 Å was obtained. The hydroxyl stretching bands of the original kaolinite are drastically modified, a very strong band at 3560 cm−1, a strong doublet at 3620 and 3605 cm−1 were observed. A weak singlet is obtained at 3695 cm−1. The two OH bending bands are replaced by a single band at 912 cm−1. A complicated set of interactions results in the loss of stacking order about the C-axis, accompanied by some curling of layer packets. A prolonged treatment with water restores the X-ray and IR spectra of the original kaolinite.

The worldwide use of pharmaceuticals is of concern to those researchers who develop new techniques for the removal of these compounds from the aquatic medium. The objective of the present work was to characterize and evaluate the performance of a commercial, bentonite-based organophilic clay in removing ivermectin from aqueous solution. The adsorbent was characterized by nitrogen physisorption, thermogravimetric-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). Batch-scale adsorption experiments were performed to evaluate the kinetics, isotherms, thermodynamics and effect of pH on removal of this drug and reuse of the clay. The bentonite has a small specific surface area with an irregular surface. The Elovich kinetic model fits the experimental data better than other models, indicating that chemisorption contributes to drug removal in this case. The Langmuir and Sips isothermal models best fit the experimental equilibrium data. The process was shown to be favorable (ΔG°ads<0), endothermic (ΔH°ads>0), with an increase in the degrees of freedom at the solid–liquid interface (ΔS°ads>0), and with characteristics of a physical-chemical adsorption process (Ea = 11.065 kJ mol–1) under the study conditions. Adsorption was favored at the natural pH of the solution and the organophilic clay could be regenerated with water and reused in consecutive adsorption cycles. The amount of ivermectin adsorbed on the organophilic clay ranged from 1.78 to 3.88 mg g–1. The organophilic clay was shown to be a cost-effective potential adsorbent for ivermectin-contaminated water-treatment applications.

The translatory and rotatory diffusion coefficients, electrophoretic mobility, permanent dipole moment, electrical polarizability and optical anisotropy factor for a crocidolite sol have all been measured in a single optical apparatus. Electrophoretic light-scattering and electrically-induced birefringence were the methods used, these being rapid and well-suited to particles in the micron and sub-micron size-range, where conventional electrophoresis is difficult. Electric birefringence offers a fast means of sizing mineral particles in suspension and the electrical polarizability and electrophoretic mobility have a common origin in such sols. This is discussed in terms of the surface-charge and electric double-layer characteristics of the particles.

Luminescence, induced by dehydration and by wetting with hydrazine and unsymmetrically substituted hydrazine, and related ESR spectra have been observed from several kaolinites, synthetically hydrated kaolinites, and metahalloysites. The amine-wetting luminescence results suggest that intercalation, not a chemiluminescence reaction, is the luminescence trigger. Correlation between dehydration-induced luminescence and g = 2 ESR signals associated with O−-centres in several natural halloysites, and concurrent diminution of the intensity of both these signal types as a function of aging in two 8.4 Å synthetically hydrated kaolinites, confirm a previously-reported relationship between the luminescence induced by dehydration and in the presence of O−-centres (holes, i.e., electron vacancies) in the tetrahedral sheet. Furthermore, the ESR spectra of the 8.4 Å hydrate showed a concurrent change in the line shape of the g = 4 signal from a shape usually associated with structural Fe in an ordered kaolinite, to a simpler one typically observed in more disordered kaolinite, halloysite, and montmorillonite. Either structural Fe centres and the O−-centres interact, or both are subject to factors previously associated with degree of order. The results question the long-term stability of the 8.4 Å hydrate, although XRD does not indicate interlayer collapse over this period. Complex inter-relationships are shown between intercalation, stored energy, structural Fe, and the degree of hydration which may be reflected in catalytic as well as spectroscopic properties of the clays.

Caesium aluminium silicates, caesium aluminium fluoride and aluminium fluoride were identified in a mixture obtained through the evaporation of kaolinite aqueous suspension with CsF. The mixture was studied by X-ray powder diffraction and IR spectroscopy. Two types of intercalation complexes of kaolinite were identified (A and B) which were characterized by c-spacings of ∼0.99 and 0.83 nm, respectively. Complex A seems to be an hydrated CsF intercalation complex, whereas complex B is a water intercalation complex, probably containing H3O+ and F−. It showed an IR absorption band at 3518 cm−1. The c-spacings of similar CsCl and CsBr complexes depend on the ionic radii. The intercalated ions are keyed into the ditrigonal cavities of the oxygen plane. A straight line plot of the keying values versus the ionic size indicates that keying is high for F−and decreases with increasing ionic size.

Clay minerals in early Jurassic sequences of shales, siltstones and sandstones deposited in non-marine, transitional and shallow marine environments have been examined by X-ray diffraction, electron microscopy and chemical analysis to study the relationship between clay minerals, their environment of deposition and subsequent diagenetic modifications.

The inherited clay mineral composition of the fine-grained sediments reflects the influence of climate, relief, source rocks and depositional processes. Inhomogeneous clay mineral assemblages, comprising abundant kaolinite and varying proportions of illite, I-S, chlorite and vermiculite, characterize fine-grained sediments from the non-marine and transitional environments. In shallow marine depositional environments clay mineral assemblages are more uniform, dominated by illite+I-S with minor kaolinite and chlorite.

The principal diagenetic process affecting fine-grained sedimentary rocks is the smectite–illite transformation. In sandstones, the authigenic formation of kaolinite, chlorite and illite appears to have been primarily determined by the environment of deposition.

A tightly cemented series of marine sandstones, interbedded with shales and mudstones, occurs in the lower part of the Kimmeridge Clay Formation (Kimmeridgian to Ryazanian) of Arco Well 14/26-1 (Core No. 5, 8067–8085 ft). The well is on the northern flank of the Fraserburgh Spur Basement Ridge. The sediments are in the immature stage of hydrocarbon generation and are now at their maximum temperature and burial depth: the bottom hole temperature is 75°C. The sandstone diagenesis was complex, essentially of an intrinsic type, and took place under considerable overpressures. Initially a series of early cements was precipitated (minor chalcedony, quartz, feldspar, ferroan calcite, non-ferroan dolomite and major ferroan dolomite). A later phase of diagenesis embraced two periods of intrastratal solution (each affecting both the silicate and the carbonate components of the sediment) separated by a phase of calcite precipitation and followed by a phase of kaolinite cementation. The early cements are interpreted as being of the intrinsic miagenetic type. The later phase of diagenesis (alternating intrastratal solution and cement precipitation) resulted from the interaction of (i) the biotic breakdown of organic matter by thermophyllic micro-organisms and (ii) the abiotic thermal alteration of organic matter with the mineral components of the sediment: of particular importance were varying PCO2 and the generation of carboxylic and phenolic acids. The diagenetic pattern is closely comparable to that known from various Upper Jurassic sandy shelf sediments in other parts of the northern North Sea which have very different burial histories.