Halloysite with tubular morphology is formed in a wide range of geological environments from the alteration of various rock types. Intrusive acidic coarse-grained rocks, such as granites, pegmatites and anorthosite, with large potash and sodic feldspars contents, are subsequently altered to kaolinite, halloysite and other clay minerals by weathering or shallow hydrothermal fluid activity. Processing to separate the halloysite-kaolinite fraction from the altered host rock provides a product which can be used as a paper filler and in ceramics and fibreglass, among other uses, with various deposits in Brazil, China, Thailand and elsewhere. In the Kerikeri-Matauri Bay district of Northland, North Island, New Zealand, volcanic alkali rhyolite was extruded as domes and cooled rapidly with fine-grained feldspar subsequently altered to halloysite. The IMERYS plant in Matauri Bay separates the clay from the quartz-cristobalite matrix with an ∼20% yield of halloysite. The principal market is for high-quality porcelain and bone china that require low levels of Fe2O3 and TiO2. Deposits with high levels of halloysite occur in China, Turkey and the USA. The Dragon mine in Utah, USAwas recently reopened by Applied Minerals Inc. and now produces halloysite from zones of up to 100% white halloysite. Smaller occurrences of tubular halloysite are mined in China, Turkey and elsewhere from masses of comparatively pure clay that appear to have crystallized directly from solutions in which Al and Si were soluble.

Two kaolins containing kaolinites of different crystallinity, as confirmed by the Aparicio-Galán-Ferrell index, were treated in HCl and KOH solutions at 95º and 80ºC, respectively, for periods up to 36 h. Changes resulting from the treatments have been characterized by several methods. Fe occurs in the octahedral sheets of both kaolinites and dissolves similarly to Al. Lower structural ordering, more structural defects and particles of smaller average size and less regular shape are responsible for faster dissolution of KGa-2 in comparison to well ordered Gold Field (Tanzania) kaolinite. More Si than Al is dissolved in KOH from both kaolins after any dissolution time. An aluminosilicate (feldspathoid) phase is thought to occur in the material prepared from KGa-2 in KOH. Near-IR spectra provide very useful information on changes in the mineral structure upon the treatments, on the solid reaction products and on the adsorbed water molecules.

A study has been carried out on the influence of acid concentration, time and temperature of reaction, liquid to solid ratio and chemical composition of the mineral on the extension and selectivity of the octahedral cations extracted during acid leaching of palygorskite. The mechanism of the extraction of Mg2+, Al3+, and Fe3+ is discussed on the basis of kinetic models fitted for a reacting-shell model, taking into account particle shape and the rate controlling step. A model is given from which kinetics parameters and the activation energy of the process are calculated. The different behaviour observed for the two palygorskites could be explained on the basis of their differences in surface areas.

The electron microprobe has been used in petrographic research for almost 20 years and more recently as a tool for investigations of clay minerals. However, to the author's knowledge no information has been published concerning the reliability of such analyses―especially those of the alkali elements. Since the alkali contents of clays are often critical, e.g. in determining the smectite content of mixed-layered minerals, it is important to have some idea of the reliability of an analysis made using an electron microprobe.

Three variables can be controlled in electron microprobe analysis—time, beam-current intensity and beam size (the diameter of the beam which excites the sample). Exaggerated conditions of any one of these variables tend to diminish the signal received by the detectors for the alkali elements, especially sodium. As an example, the effect of varying two of these parameters on the intensity of sodium radiation for sodium-aluminumsilicon glass is shown in Fig. 1. The signal decreases (% loss Na) over a 200 s counting time. Beam intensity and beam diameter were varied in this example.

Ochre sediments from acid mine drainage in Cornwall have been investigated using X-ray diffraction, thermal methods, infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and chemical methods in order to determine their mineralogical and chemical composition. Fresh sediments consist of ferrihydrite and goethite. Large fractions of these minerals are dissolved by the ammonium oxalate treatment reflecting their poorly crystalline structure. Fresh sediments contain large amounts of surface-adsorbed SO4 (up to 9.3%) which is readily desorbed by the PO4 treatment. Goethite is the only mineral present in relatively older sediments and the mineral is well crystallized with rod-shaped morphology. Environmental conditions, such as pH and SO4 content, are not favourable for the presence of schwertmannite at the site. Iron minerals appear to be precipitating around filamentous algae and the shape of algae is preserved in the Fe oxide matrix. The ubiquitous presence of algae in close association with Fe minerals indicate their possible role in the crystallization of Fe oxides.

An investigation was carried out on the bioavailability of kaolinite and the role it plays in remediating oil-polluted seawater, since kaolinite is known to enable hydrocarbon-degrading bacteria to grow well. Experimental results revealed that significant amounts of Al and Si dissolved from kaolinite were not observed ((P > 0.05) in comparison with a control sample which contained no kaolinite) in the aqueous phase during the ~24 day experimental period. Transmission electron microscope observations and energy-dispersive spectroscope data revealed that some altered kaolinite particles appeared, connected to intact kaolinite and bacterial cells. Bacterial cells were associated and encrusted with intact and/or altered kaolinite clay particles, where mixed (C, O, Na and Si)-precipitates of kaolinite clays were formed on the surface of hydrocarbon-degrading bacterial cells. However, the uptake of Si (from kaolinite) by bacterial cells appeared to be more prevalent than Al, and there were no significant changes in basal spacings of kaolinite due to these altered kaolinite particles. Separate studies showed that hydrocarbon-degrading bacteria have a high resistance to Si. Thus, the present data suggest that Si from kaolinite may facilitate hydrocarbon-degrading bacterial growth as shown in our previous study (Chaerun et al., 2005), and the C-O-Na-Si complexes on the surfaces of bacterial cell walls may be the stimulator for hydrocarbon-degrading bacterial growth in seawater contaminated with oil spill.

The structure of an illite-smectite (I-S) sample (HSI) from the Tertiary–Cretaceous boundary layer at Stevns, Denmark, i.e. the so-called Fish Clay, is investigated in order to discuss the origin of this clay and its similarity to clays from Maastrichtian-Danian chalk of Denmark and the North Sea. The phase compositions and layer sequences have been determined by X-ray diffraction. The structural formulae are determined from chemical analysis and solid-state 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The octahedral vacancy pattern has been determined by thermal analysis and the particle shape by atomic force microscopy. The HSI sample I-S consists of two phases, a high-smectitic (HS) phase (70%) having 95% smectite and 5% illite (leucophyllite) layers, and a low-smectitic (LS) phase (30%) having 50% smectite and 50% illite (leucophyllite) layers. Both phases have trans-vacant dioctahedral sheets and contain only traces of IVAl, the charge of the illite (leucophyllite) layers being provided predominantly by octahedral Mg for Al substitution. The structure of the tetrahedral and octahedral sheets for the HSI are compared to the structure of an I-S sample (GRI) from the Maastrichtian chalk at Stevns below the Tertiary-Cretaceous boundary and to the standard smectite SAz-1 from Arizona. For all three samples the 27Al MAS NMR spectra show the presence of two resolved IVAl resonances, which indicate the presence of two different IVAl sites. The NMR, infrared spectroscopy and chemical data show that both HSI and GRI have highly ordered Mg for Al substitution in the octahedral sheet, each Al having one Mg and two Al neighbours, whereas substitution of Mg for Al in SAz-1 is random. For the HSI sample, both the HS and LS phases are probably formed from volcanic ash. The structural similarity of the phases in HSI and GRI shows that GRI formed from a material similar to HSI by illitization of the HS phase and chloritization of the LS phase.

Optical isomers deamination of L- and D-glutamic and aspartic amino acids and of their DL racemic mixtures has been achieved in the presence of Na-montmorillonite at pH = 6 and room temperature. The adsorption curves showed that the enantiomer adsorbed depends on the type of amino acid. Nevertheless, deamination reaction kinetics brought about a stereoselectivity of the clay mineral for the L-isomer and implicitly showed an unquestionable “structural chirality character” of the clay mineral.

The alteration and transformation behaviour of the Tertiary Hammerschmiede Smectite and the Jurassic Opalinus Shale in an alkaline solution was studied in column experiments. The Hammerschmiede Smectite is proposed as potential backfill material and the Opalinus Shale as host rock for the Swiss low-level nuclear waste storage site. Over a period of 18 months, the evolution of permeability, pH and solution concentrations were measured. After the experiment, the columns were cut into pieces to study the mineralogical and the chemical evolution of the clays. X-ray diffraction (XRD) revealed no significant appearance or disappearance of diffraction peaks at the end of the experiments. The scanning electron micrographs of the clays revealed that both clays exhibited a precipitation zone, which extends from 0 to 2 cm below the infiltration surface. Both clays showed significant differences in the evolution of pH and hydraulic conductivity. The solution front crossed the Opalinus Shale column entirely after only 11 weeks and the initial values for K+ and Na+ were conserved in the solution. For both clays, the salt concentrations in the percolating fluids mirror the evolution of pH.

The effect of temperature on the swelling of clay was studied by determining (1) the relation between the interlayer spacing, λ, and the swelling pressure,Π, at different values of the temperature, T, using the method of Viani et al. (1983) as modified by Wu et al. (1989); (2) the relation between λ and T at different values of Π; and (3) the relationship between Π and mw/mc, the mass ratio of water to clay, at different values of T using the method of Low (1980). The results showed that λ was essentially independent of T but that mw/mc decreased slightly with T at any value of Π. Such results are not consistent with electric double-layer theory. Therefore, it was concluded that the decrease in mw/mc with increasing T was due primarily to the thermal breakdown and consequent loss of water from the larger pores outside of the interlayer region.

La sépiolite chauffée à 300°C et 480°C sous vide a été étudiée avec un microscope électronique en haute-résolution. Les clichés donnent une photographie réelle des structures de la sépiolite naturelle et de la sépiolite anhydre, telles qu'elles ont été calculées par la cristallographie. Les résultats obtenus sont en accord avec ceux de la diffraction des rayons X et de la spectroscopie infrarouge.

L'étude expérimentale de l'adsorption d'ions La3+ sur une smectite, successivement saturée en ions K+, Na+ puis Ca2+, montre que la stoechiomérie de l'échange s'effectue dans le rapport des charges des cations participant à la réaction. Dans un domaine de force ionique suffisamment restreint, l'échange a lieu dans les rapports suivants: 1 La3+ pour 3 Na+ ou 3 K+, et 1 La3+ pour 1·4 Ca2+. L'adsorption de toutes les terres rares sur la smectite et une illite s'effectue sans ségrégation notable dans cette famille d'éléments, les terres rares les plus lourdes étant un peu plus adsorbées que les terres rares légères. La désorption des terres rares est plus difficile, leur charge trivalente devant les stabiliser en position interfoliaire dans les minéraux argileux.

A new method of measuring the layer charge of smectites by IR spectroscopy is proposed based on the integrated intensity measurement of the band assigned to the ammonium fundamental ν4 mode of NH+4-exchanged clays. Measurements are made before and after Li fixation (Hofman & Klemen effect). These allow the quantitative determination of the total charge, equivalent to CEC, and tetrahedral and octahedral charge distribution in both dioctahedral and trioctahedral smectites.

Chemical variations in individual chlorite crystals of diagenetic origin delineated by energy dispersive X-ray spectroscopy (EDS) in a transmission electron microscope (TEM) indicate a temperature dependent chemical zonation in each grain. Silicon decreases and Al increases with higher temperature resulting in a decreasing Si/Al ratio away from the crystal core reflecting the time and rate of the crystal growth. Chlorite particle-size distributions obtained by scanning electron microscopy (SEM) give steady state profiles which suggests that the chlorite growth is controlled by a grain coarsening process related to Ostwald ripening.

A thin (15–20 cm) Fe-rich intraformational conglomerate in the fresh- to brackish-water Early Cretaceous succession of south-east England contains pisoids and pseudo-ooids of a green clay mineral which has been identified as berthierine. The pisoids (up to 0·5 cm in size) are concentrically laminated, have complex structure, and are frequently nucleated around a sandstone fragment. They show evidence of weathering due to a change in their environment after formation. The ooids have well to moderately well developed concentric lamination, are very often multi-nucleated and do not always completely cover the nucleus. They suggest formation as a result of mineral precipitation as opposed to agitation and accretion. The climate and environment during the Wealden were suited to the formation of Fe-rich soils and it is likely that the pisoids and ooids were originally composed of iron oxyhydroxide and kaolinite, having formed in soil in the Weald Basin. They were then eroded and deposited in the base of a large scour structure as part of the conglomerate. On burial, and the attainment of low Eh conditions, berthierine formed by diagenetic transformation of the pre-existing minerals.

New chemical and structural data on sepiolite-falcondoite in garnierite veins from the Falcondo Ni-laterite deposits, central Dominican Republic, are reported. Samples of Ni-sepiolite-falcondoite vary in colour from whitish green to green depending on the NiO content (wt.%) and the amount of silica present. The texture is normally schistose and friable but samples with considerable quartz and/or amorphous silica are compact and hard. Back-scattered electron images indicate that the samples are composed of at least three generations of Ni-sepiolite-falcondoite. The extreme refined cell parameters for Ni-sepiolite-falcondoite vary from 13.400(2), 27.006(4), 5.273(1) Å to 13.340(3), 27.001(6), 5.267(1) Å (space group Pncn). As the Ni content increases there is a small reduction in the a parameter. Chemical compositions determined by electron probe microanalysis cover a large interval of the Ni-sepiolite-falcondoite solid solution (Fal3 and Fal77). Individual samples show a considerable range in composition with the widest range determined in one sample from 4.63 to 22.40 wt.% NiO.

The preparation of green rusts from sulphate solutions and representative Mössbauer spectra are described. As the samples oxidized readily, attention focused on the Mössbauer parameters at liquid nitrogen and helium temperatures. The spectra recorded at 77 K could be fitted satisfactorily with one ferrous iron quadrupole doublet with a separation of 2·93 mms−1 and one ferric iron quadrupole doublet with a separation of 0·45 mms−1. In some spectra a ferric iron magnetic hyperfine of strength 49·2 T was also apparent. At 4·2 K, the ferrous iron exhibited a hyperfine splitting with a field of 12·4 T whilst the ferric iron exhibited a hyperfine splitting with a field of strength 50·4 T. The ratio of ferrous to ferric ions was 2·25 ± 0·25 at 77 K and at 4·2 K, and ∼1·6 with a large variation at room temperature. The liquid helium spectra did not always give a good chi-squared fit, the main reason being attributed to relaxation. The line-width of the ferrous iron site at 77 K is slightly larger than that for iron metal and could be explained by a variation in the number of near Fe3+ neighbours at different Fe2+ sites, consistent with the assumption that the ferrous iron site is in the hydroxide sheet. The effect of different numbers of Fe2+ and Fe3+ neighbours probably contributed to the increase in line-widths at 4·2 K compared with those at 77 K. The ferrous iron doublet is marginally different to those of chloride and hydroxy-carbonate green rusts and the aluminium analogues.

The removal of gaseous mercury from flue gases from coal-fired power plants is currently an environmental challenge under investigation. Therefore, the main aim of this paper was to evaluate the suitability of faujasite group zeolites (Na-X) to adsorb mercury compounds. Previous, initial tests showed negligible Hg0 uptake by Na-X zeolite, but silver impregnation improved adsorption markedly. Therefore, the testing of mercury adsorption from flue gases into Ag+- impregnated Na-X synthetic zeolite (Ag-X zeolite) derived from coal fly ash was carried out. This material was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, X-ray fluorescence and nitrogen adsorption/desorption before being evaluated for mercury removal from exhaust gas. After preliminary mercury adsorption tests (fixed bed) under a nitrogen atmosphere, the adsorbent was examined with a simulated flue gas composition under various conditions, i.e. weight of zeolite, temperature of experiment and zeolite in powder and granulated forms. The removal of mercury was shown to depend on the sorbent texture (powder or granulate), exhaust gas flow rate and contact time, as well as the temperature of the experiment. The Ag-X zeolite tested reduced the level of mercury in the flue gas and, depending on the experimental conditions, long-time mercury breakthrough ranges from 15 to 40% were obtained. The best results for mercury capture were obtained for granulated material.

Una sepiolita procedente de Toledo (España) se ha activado por tratamiento con disoluciones 0·25, 0·50 y 0·75 n de NO3H, seguido de calentamiento durante 10 h a 110, 200, 300, 400 y 500°C. Para cualquier concentración ácida, un calentamiento de 110, 200 y, a veces, 300°C, produce un aumento del número de poros mientras que las temperaturas superiores significan un cierre de los mismos tanto mayor cuanto más elevada es la temperatura de tratamiento. El máximo desarrollo de la superficie accesible al N2 tiene lugar con una disolución 0·50 n de NO3Hy 200°C (449 m2/g, método de BET); la superficie específica de la sepiolita natural es de 321 m2/g.