Kaolinite aggregates are the major alteration product in the strongly deformed areas of a shear zone developed in contact-metamorphosed slates from the Southern Iberian Massif near Jaén (SE Spain). Muscovite and Fe-rich chlorite in strain shadows of broken andalusite crystals were observed in slates from less deformed areas. The presence of phyllosilicate packets nearly perpendicular to each other and veinlets parallel to {110} of andalusite reveal the importance of cleavage-controlled fracturing of andalusite to the mineral reactions. The compositional similarity between kaolinite and andalusite suggests a direct transformation of andalusite to kaolinite in the strongly altered area. The absence of clear preferred orientation of phyllosilicates relative to andalusite, and the compositional differences of andalusite with muscovite and chlorite from the less altered samples, indicate andalusite dissolution and chlorite-muscovite precipitation during a first mineral-growth stage. Muscovite-kaolinite and chlorite-kaolinite intergrowths indicate a later retrograde replacement stage.

High-resolution synchrotron X-ray diffraction recorded on a collection of palygorskites with different chemical compositions (obtained by analytical electron microscopy) permits unambiguous correlation of the crystallographic parameters a (or a sin β if a monoclinic phase is considered) with the nature of the octahedral sheet, i.e. with both the number of octahedral positions that are occupied and the type of octahedral cation. No significant changes in the lattice parameters b and c are observed. The unit cell modification consists essentially of an expansion in a as the number of cations with larger ionic radii (Mg2+ and Fe3+) predominates over smaller cations (Al3+). A linear dependency of a (or a sin β) on the chemical composition of the octahedral sheet was obtained that can be used for classifying palygorskite into compositional groups, using only conventional diffraction data, without the need for chemical analyses.

Alternative Fenton and Fenton-like systems based on natural Fe oxides are described. The collected materials were modified through controlled reduction with H2 and were characterized by chemical analysis, X-ray diffraction, saturation magnetization measurements, and Mössbauer spectroscopy at 298 and 110 K. The catalytic activities of these original and modified materials were tested by studying the decomposition of H2O2 and the discolouration of methylene blue. Iron oxides present in the samples were mainly hematite and subordinate goethite which, after controlled reduction, were converted to metallic iron and magnetite. The mixture of Fe0 and magnetite in one of these materials was significantly more efficient at H2O2 decomposition and the discolouration of methylene blue than the original Fe3+ oxides. These results suggest that Fe2+ is essential to produce an active Fenton system.

Green rusts, GRs, can act as both sorbents and reductants towards selected pollutants. Organo-GRs are expected to combine these properties with a high affinity for hydrophobic substances. A novel organo-GR, GRLAS, was synthesized by incorporating a mixture of linear alkylbenzenesulphonates (LAS) into the interlayer space of synthetic sulphate green rust, GRSO4 . Mössbauer analysis of GRLAS indicates that the structure of the organo-GR is very similar to that of the initial GRSO4 with regard to the FeII/FeIII ratio and local coordination of Fe atoms. X-ray diffraction demonstrates that the GRLAS formed was well ordered, although a mixture of surfactant was used for intercalation. The basal spacings of the GRLAS and the kinetics of the ion-exchange process were dependent on the initial surfactant loading; basal spacings of ~2.85 nm were obtained at LAS solution concentrations >10 mM. The ratio LASadsorbed/SO42–desorbed significantly exceeded the stoichiometric ratio of 2 during the initial part of the ion-exchange process (t = 5 h). However, this ratio was reached progressively with time. GRSO4 preferentially sorbed LAS homologues with long alkyl chains over short ones. Carbon tetrachloride was successfully adsorbed into GRLAS. The adsorption isotherm was linear with a distribution coefficient, Kd, of 505±19 litre kg–1.

The rheological and filtration properties of a Tunisian clay are presented and compared with those of Wyoming bentonite. The study was part of an evauation of Tunisian mining resources in general, and of the bentonitic deposits in particular. Qualitatively, the two clays exhibit the same rheological and filtration behaviour but quantitatively the properties of purified Wyoming bentonite are distinctly better at the same concentration. The difference can be related to the mineralogical structure and the presence of 13% illite in the Tunisian clay. Standard tests show that the rheological behaviour of the purified Tunisian clay is close to that of the raw Wyoming bentonite and conform to the American Petroluem Institute (A.P.I.) standards for medium-depth drilling formulations.

Adsorption of the polycation chitosan on montmorillonite was studied at different pH values from 4.5 to 6.5 and at temperatures of 25, 50 and 75ºC. The amount of chitosan adsorbed increased with temperature, indicating that temperature is a decisive factor. At pH 5.0 and 25ºC the amount adsorbed was 1.18 molc kg–1, whereas it was 1.5 times higher (1.79 molc kg–1) at 75ºC. The uptake of chitosan increased significantly at higher pH. This can be attributed to the decrease in the degree of protonation. Surface charge and X-ray diffraction measurements indicate that most of the chitosan is adsorbed in the interlayer, where mono- and bilayer structures are formed.

The kinetics of chitosan adsorption also depend on temperature and pH. At ⩾ 50ºC, the adsorption mechanism of chitosan on montmorillonite is closest to the intraparticle diffusion model, whereas at lower temperature (25ºC) the adsorption process is closer to the pseudo-second order model. The pH of the solution affects the protonation degree of chitosan and the mode of adsorption on montmorillonite, but not the adsorption rate.

For chitosan-montmorillonite prepared at pH 5.0 and 75ºC, the effective anion exchange capacity (AEC) was found to be 80% (0.36 molc kg–1) of the calculated value. The relatively large AEC and the location of most of the anion exchange sites in the interlayer make chitosan-montmorillonite an interesting prospect as an adsorbent for water-purification procedures.

A geochemical and mineralogical study has allowed us to address the factors controlling distribution pattern, residence and behaviour of rare earth elements (REE) during kaolinization of Variscan granitoids in NW Spain. Mineral composition of the deeply weathered samples is dominated by kaolinite, with minor amounts of quartz, muscovite-illite, alkaline feldspar and traces of resistant minerals (rutile, ilmenite, zircon and monazite). Variable amounts of Si, Na, Ca, K, Rb, Cs, Ba, U and P were lost from the weathering profile, as a result of feldspars, mica and apatite breakdown, whereas Al, Fe, Ti, Zr, Th, Hf and REE were concentrated in the residual kaolin. Chondrite-normalized REE patterns of the kaolins show an overall enrichment of light REE (LaN/SmN = 1.22–2.53), heavy REE depletion (GdN/YbN = 2.42–15.10) and a strong negative Eu anomaly (Eu/Eu* = 0.11–0.25), probably inherited from the parent granite. Nevertheless, the normalization to the parent granite reveals some REE fractionation and increasing positive Eu anomalies with advancing weathering, in response to the breakdown of feldspars. Different grain-size fractions show similar REE distribution patterns, but differ in concentration levels. Although the fine fractions are the most important REE reservoir, there is no positive correlation with clay mineralogy. The correlative behaviour among P2O5, Th and REE in the <2 mm fraction suggests that monazite plays a dominant role controlling the REE budget in the weathering profile.

This study characterizes the effects of fluid migration into a predominantly shale cover which seals the active geothermal system of Mt. Amiata (Tuscany, Italy). During Alpine orogenesis the shale unit was affected by regional metamorphism at the limit of the diagenesis-anchizone. Subsequently, the phyllosilicate clay minerals of the shales underwent significant alteration at diagenetic temperatures (175±25ºC as determined by the geochemical model) by the pervasive circulation of fluids activated by the geothermal field. The overall mineralogical assemblages indicate that the main transformations consisted mostly of destabilization of illite and formation of kaolinite together with large amounts of I-S mixed layers, with higher smectite content and decreased Reichweite I-S ordering (from R3 to R1) with respect to the original, unaltered phases. Application of computer modelling indicates that the circulation of CO2-rich geothermal fluids into the shale unit was responsible for the observed phyllosilicate clay mineral transformations.

Two soil profile sequences on paragneiss debris in the Val di Rabbi (Northern Italy) along an altitude gradient ranging from 1200 to 2400 m a.s.l. were studied to evaluate the effect of aspect on the weathering of clay minerals. All the soils had a coarse structure, a sandy texture and a low pH. Greater weathering intensities of clay-sized phyllosilicates (greater content of smectites) were observed in soils on the north-facing slope. On the south-facing slope, smectite was found only in the surface horizon of the soil profile at the highest altitude. Hot citrate treatment of north-facing soils revealed the presence of low-charged 2:1 clay minerals, the expansion of which was hindered in the untreated state by interlayered polymers. However, the hot citrate treatment encountered some problems with the samples of the south-facing soils: as confirmed by Fourier transform infrared spectroscopy, the hot citrate treatment was unable to remove all interlayer Al polymers. The 2:1 phyllosilicates were not expanded by ethylene glycol solvation in several samples, although thermogravimetric analyses indicated the presence of clay minerals with interlayer H2O. At the same time, the collapse of clay minerals to 1.0 nm following K-saturation was evident. Theoretically, this should indicate that 2:1 phyllosilicates had no evident substitution of trioctahedral cations (Mg2+, Fe2+) by dioctahedral cations (Al3+ and Fe3+). X-ray diffraction analysis of the d060 region and determination of the layer charge of clay minerals by the long-chain (C18) alkylammonium ion, however, did not confirm this. A transformation from trioctahedral to dioctahedral species was observed and low-charge clay minerals (ξ ~0.30) were identified in the surface horizons of the south-facing sites. In the south-facing soils, the podzolization process was less pronounced because of a lower water flux through the soil and probably less complexing organic molecules that would remove the interlayer polymers. Besides the eluviation process, clay minerals underwent a process of ionic substitutions in the octahedral sheet that led to the reduction of the layer charge. This process was more obvious in the north-facing sites.

The bentonite deposits in Başören Kütahya, W Anatolia, Turkey were formed by alteration of Pliocene perlite and pyroclastic rocks. Two types of bentonites are distinguished in this area on the basis of their physical properties, chemistry and occurrence. Bentonites were examined to determine their mineralogical, chemical and physical properties. Analytical methods include X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analysis and measurement of cation exchange capacity (CEC), swelling volume, water adsorption, bleaching capacity, and firing shrinkage. Bentonites consist mainly of dioctahedral smectite. They also contain zeolite, opal-CT, cristobalite, quartz, feldspar, dolomite and calcite. The ‘Type 2’ bentonites had greater CEC, swelling volume, water adsorption and bleaching capacity than ‘Type 1’. The variation in the physical properties of the two bentonites is attributed to the differences in the non-clay mineralogy and to the chemical composition and nature of interlayer cation.