The first occurrence of Ni-rich stevensite found in the ophiolite complex of Othrys, Central Greece is described. The stevensite, which develops in cracks in a host serpentinite, formed at the expense of serpentine. Two varieties of stevensite have been described: a Mg-rich, Ni-poorer variety with 0.4–1.2 octahedral Ni atoms per half formula unit (p.h.f.u.) and a Ni-rich variety with >2 Ni atoms p.h.f.u. The layer charge in both varieties is −0.24 p.h.f.u.. Stevensite layers are completely separated when dispersed in dilute polyvinylpyrrolidone (PVP) solutions and begin to convert to talc after heating at 250°C for 90 min. Total conversion to talc is observed at 550°C. Formation of Ni-rich stevensite took place at ambient temperature during supergene processes. The scarcity of Ni-rich stevensite occurrences in nature is attributed to the metastability of smectite and to the analytical procedures used in previous studies. Stevensite is considered a phase containing domains with variable numbers of octahedral vacancies. A new experimental protocol is proposed for the determination of Ni-rich stevensite, based on a combination of XRD after solvation with various organic liquids and subsequent heating at 750°C.

Mg-rich kaolinite and Mg+Ni-rich kaolinite have been synthesized in hydrothermal experiments (200 and 400°C) from poorly crystalline kaolinite and Mg- and Mg+Ni-bearing solutions. Al-rich serpentine and Al-rich chlorite were obtained as sub-products of the reactions. The formation of these phases occurred through a dissolution-precipitation mechanism that led to spherical kaolinite after short reaction times. A morphological evolution towards platy particles and stacks occurred at increasing run times.

Identification of the several phases was carried out using a combination of X-ray diffraction and transmission/analytical electron microscopy. Analytical data indicate that the Mg content in kaolinite increased as a function of the reaction time and temperature, reaching up to 0.46 atoms per half formula unit (a.p.h.f.u.). The measured (Mg+Ni) content reached up to 0.56 a.p.h.f.u.. Both the gradual increase of the b-cell parameter of kaolinite at increasing Mg contents and the presence of new bands on the FTIR spectra of the synthesized kaolinite point to a Mg-for-Al replacement in the octahedral sheet rather than to the presence of serpentine-like layers interstratified in the kaolinite structure.

Zeolites and other open framework materials provide a powerful tool for remediation and solidification of a range of cationic wastes (e.g.${\text{NH}}_4^{+}$${\rm{NH}}_4^ + $, Pb2+) due to the combined properties of large surface area and cation exchange capacity. However, practical barriers exist to the continued expansion of their use, including handling issues related to the fine particle size, and continued ion exchange following waste adsorption. This study examines the synthesis and characterization of zeolites adhered to a muscovite mica wafer, in order to assess if practical benefit can be derived from the preparation of layered composite materials. The paper demonstrates that increased metal adsorption, as demonstrated by surface chemical composition, can be induced in regions by growth of zeolite on and within the lamellar structure of the matrix. X-ray diffraction studies suggest that a site-specific crystallization mechanism controls the zeolite type and extent of growth, thereby reducing control over the zeolites prepared. However, although increased adsorption has been introduced to the mica, the amount of zeolite added is small (<50 mg per gram of muscovite), and thus any adsorption is very limited.

A series of organoclays with monolayers, bilayers, pseudotrilayers, paraffin monolayers and paraffin bilayers were prepared from montmorillonite by ion exchange with hexadecyltrimethylammonium bromide (HDTMAB). The HDTMAB concentrations used for preparing the organoclays were 0.5, 0.7, 1.0, 1.5, 2.0 and 2.5 times the montmorillonite cation exchange capacity (CEC). The microstructural parameters, including the BET-N2 surface area, pore volume, pore size, and surfactant loading and distribution, were determined by X-ray diffraction, N2 adsorption-desorption and high-resolution thermogravimetric analysis (HRTG). The BET-N2 surface area decreased from 55 to 1 m2/g and the pore volume decreased from 0.11 to 0.01 cm3/g as surfactant loading was increased from Na-Mt to 2.5CEC-Mt. The average pore diameter increased from 6.8 to 16.3 nm as surfactant loading was increased. After modifying montmorillonite with HDTMAB, two basic organoclay models were proposed on the basis of HRTG results: (1) the surfactant mainly occupied the clay interlayer space (0.5CEC-Mt, 0.7CEC-Mt, 1.0CEC-Mt); and (2) both the clay interlayer space and external surface (1.5CEC-Mt, 2.0CEC-Mt, 2.5CEC-Mt) were modified by surfactant. In model 1, the sorption mechanism of p-nitrophenol to the organoclay at a relatively low concentration involved both surface adsorption and partitioning, whereas, in model 2 it mainly involved only partitioning. This study demonstrates that the distribution of adsorbed surfactant and the arrangement of adsorbed HDTMA+ within the clay interlayer space control the efficiency and mechanism of sorption by the organoclay rather than BET-N2 surface area, pore volume, and pore diameter.

Bentonite from the ‘Bogovina’ coal mine in Serbia, was characterized. The influence of acid treatment on its composition, as well as mathematical descriptions of this influence are reported. The purpose of this work was to correlate the concentration of the acid used for the treatment with the resulting bentonite composition. X-ray diffraction (XRD), infrared spectroscopy and quantitative chemical analysis were employed to define the changes caused by acid treatment.

The contents of all the cations, except Si, decreased exponentially with increasing concentration of the HCl used for the treatment of the bentonite. This approach was tested on previously published data and was shown to be valid.

The basal reflections of smectite decreased gradually and eventually disappeared after intense treatment, while the other reflections remained in the XRD patterns of all the samples, but decreased slightly with increasing acid strength. In addition, the amount of X-ray amorphous matter formed increased rapidly with increasing acid concentration up to 4.5 M. With further increase in the acid strength, the amount of X-ray amorphous matter remained virtually constant.

Many soils in southern Switzerland have a black color, contain a large amount of soil organic matter (SOM) and seem to have some andic properties although they did not develop on volcanic parent material. We investigated three typical ‘black’ soils to determine the mechanisms of (clay) mineral formation and transformation. We measured total element pools as well as the dithionite-, pyrophosphate-and oxalate-extractable fractions (Fe, Al, Si). The clay fraction (<2 µm) was analyzed using X-ray diffraction and FTIR spectroscopy. Iron speciation in the solid phase was determined by Mössbauer spectroscopy. With increasing weathering conditions, the plagioclase (albite) content decreases, trioctahedral species in the clay fraction such as biotite, chlorite or trioctahedral vermiculite either decompose or transform into a dioctahedral mineral such as dioctahedral vermiculite or hydroxy interlayered smectite (HIS). Typical weathering products were hydroxy interlayered vermiculite (HIV), HIS, interstratified minerals and kaolinite. The oxidation of Fe(II) into Fe(III) was evident and contributes to the transformation of trioctahedral mineral species into dioctahedral ones. In one soil, a large part of the Fe (up to 41%) was found in the form of Fe oxides. In the surface horizon, the poorly crystalline mineral ferrihydrite was dominant, while in the subsoil goethite prevailed. Maghemite (or maghemite/hematite mixture) was, furthermore, found in distinct concentrations down to a depth of ∼50 cm. The formation of this mineral requires high temperatures which means that a forest fire can influence soil mineralogy down to a considerable depth. The specific climatic conditions with periods of strong humidity alternating with periods of winter droughts, sporadic fire events and the relatively large content of poorly crystalline fractions of Fe and Al contributed to the stabilization of SOM.

Cryosols from Maritime Antarctica have been less studied than soils from continental areas of Antarctica. In this work X-ray diffraction, difference X-ray diffraction, differential thermal analysis, thermogravimetry, transmission electron microscopy/energy dispersive spectroscopy and selective chemical dissolution were used to characterize the clay fraction of basaltic, acid sulfate and ornithogenic Cryosols from ice-free areas of Admiralty Bay, King George Island. Non-crystalline phases are important soil components and reach >75% of the clay fraction for some ornithogenic soils. Randomly interstratified smectite-hydroxy-Al-interlayered smectite is the main clay mineral of basaltic soils. Kaolinite, chlorite and regularly interstratified illite-smectite predominate in acid sulfate soils. Jarosite is also an important component of the clay fraction in these soils. Crystalline Al and Fe phosphates occur in the clay at sites directly affected by penguin activity and the chemical characteristics of these ornithogenic sites are controlled by highly reactive, non-crystalline Al, Si, Fe and P phases. Chemical weathering is an active process in Cryosols in Maritime Antarctica and is enhanced by the presence of sulfides for some parent materials, and faunal activity.

This review is concerned with the synthesis and physical-chemical characteristics of a specific type of modified clay material: Ti-PILCs. The two general synthetic procedures and the main problems associated with the scale-up synthesis of these pillared materials are discussed in detail. The general characteristics of Ti-PILCs in terms of basal spacing, pillar homogeneity, surface area, microporosity, mesoporosity, pore size and distribution, thermal resistance and acidity are discussed in depth. Likewise, the most important synthesis parameters that have a clear and marked influence on the final characteristics of the materials are summarized.

Details of the quantitative techniques successfully applied to artificial rock mixtures distributed for the third Clay Minerals Society Reynolds Cup (RC) contest are presented. Participants each received three samples, two containing 17 minerals each and a third containing ten minerals. The true composition of the samples was unknown to all participants during the contest period. The results submitted were ranked by summing the deviations from the actual compositions (bias). The top three finishers used mainly X-ray diffraction (XRD) for identification and quantification. The winner obtained an average bias of 11.3% per sample by using an internal standard and modified single-line reference intensity ratio (RIR) method based on pure mineral standards. Full-pattern fitting by genetic algorithm was used to measure the integrated intensity of the diagnostic single-line reflections chosen for quantification. Elemental-composition optimization was used separately to constrain phase concentrations that were uncertain because the reference mineral standards were lacking or not ideal. Cation exchange capacity, oriented-sample XRD analysis, and thermogravimetric analysis were also used as supplementary techniques. The second-place finisher obtained an average bias of 13.9%, also by using an RIR method, but without an added internal standard and with intensity measured by whole-pattern fitting. The third-place finisher, who obtained an average bias of 15.3%, used the Rietveld method for quantification and identification of minor phases (using difference plots). This participant also used scanning electron microscopy (with X-ray microanalysis) to identify minor components and verify the composition of structures used in Rietveld analysis. As in the previous contests, successful quantification appears to be more dependent on analyst experience than on the analytical technique or software used.