Solutions obtained from soils in the Galicia Region of NW Spain had considerably lower activities of Al3+ when obtained by a speciation procedure (fractionation with an ionic column and application of specific software) than when obtained from concentrations of reactive Al (colorimetry with pyrocatechol violet) by a calculation that only considers simple hydroxylated species. Using the speciation method, many of the solutions obtained from surface horizons are unsaturated for most minerals, especially in granitic areas.

Complexes formed between 0·034 m dimethyltin dichloride solutions and Na-montmorillonite at pH 2·4 and 4·0 have been characterized using 119Sn Mössbauer spectroscopy, X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and water sorption isotherms. The dominant exchange cation at pH 2·4 is Me2Sn2+ characterized by an isomer shift, δ, and quadrupole splitting, Δ values of 1·25 and 3·80 mm s−1, respectively. The major exchange cation at pH 4·0 is the dimer, [Me2SnOH]22+, (δ = 1·38, Δ = 3·34 mm s−1) although the monomer, Me2Sn(OH)+, (δ = 0·95, Δ = 3·29 mm s−1) is also present. These complexes have basal spacings of 15·0 and 16·0 Å, respectively, which are stable up to 200°C. Mössbauer spectroscopy has shown that these ions are converted to SnO2 via Me2SnO upon thermal degradation. The temperature at which these oxides appear coincides with the collapse of the basal spacing. Both complexes display BET Type IV isotherms for the adsorption of water, following thermal pretreatment at 150°C, but the complex prepared at pH 4·0 has a lower sorption capacity. Both complexes, contrary to the normal behaviour of layer-silicates, have a definite pore volume and no further uptake occurs when this is filled.

The use of clay materials as selective sorbents for different contaminants requires very efficient methods. A natural kaolinite was calcined to metakaolinite and than rehydrated at different temperatures to produce a highly porous sorbent. The kinetics of this process were measured, with subsequent IR characterization of the phases formed. The surface and pore distribution of new phases were also assigned. In addition, the kaolinite obtained was pre-treated with Fe3+ ions to improve its sorption affinity for anionic particles. The rehydrated kaolinite and its Fe-modification were used for the adsorption of toxic cations (Zn, Cd, Pb) and anions (As, Se). Adsorption capacities depending on the physical chemical properties of the initial solution (pH, concentration of toxic ions) and the surface properties of the sorbent (specific surface area, modification method) were investigated. The adsorption properties of the sorbents were defined by the Langmuir model.

This study focuses on the main factors determining the apparent porosity of porous bioceramics prepared using small organic foam spheres as the pore-making reagent, in order to determine the best technical parameters for preparing porous bioceramics. In every experiment, only one of these factors (the time of heating, the sintering temperature, the mass ratio between small organic foam spheres and beta-tricalcium phosphate (β-TCP) powder, and the rate of the temperature rise) was changed, while the others were kept constant. In each case the apparent porosity was tested and the relation between the specific variable and apparent porosity was observed. Finally, the optimum technical parameters were deduced. The apparent porosity shows an inverse linear relation to the time of heating and the sintering temperature, and is approximately proportional to the mass ratio between the small organic foam spheres and the β-TCP powder and the rate of temperature rise. These factors have important influences on the apparent porosity. The optimum conditions were: heating time (soak time) 120 min, sintering temperature 850ºC, mass ratio 0.25, and a rate of temperature increase of 120ºC h–1.

Magnetite-rich waste from a niobium mine near Araxá, State of Minas Gerais, Brazil, was heated to 500°C and 1000°C under an O2 atmosphere. The original waste and its oxidized products were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), room-temperature 57Fe Mössbauer spectroscopy, thermogravimetric analysis (TG) and temperature-programmed reduction (TPR).

Semiquantitative analyses by EDS and quantitative chemical analyses showed the waste to be constituted primarily of Fe with minor amounts of Ti, Ba, Al, Si, Nb, Mn, S and P. Mössbauer and XRD showed the waste to consist predominantly of magnetite and hematite. The magnetite content decreases when the temperature increases due to its direct conversion to hematite. However, at 500°C only 10 wt.% of original magnetite was converted to hematite, confirming the high stability of this magnetite, which could still be detected at 1000°C. The TG profile shows no significant weight gain on heating, indicating a high stability of the magnetite. The TPR profiles show that the hematite in the waste is sintered after treatment at 1000°C and the reduction peaks are consequently shifted to higher temperatures. This high thermal stability is attributed to a moderate isomorphous replacement of Fe by other cations present in the Nb mining waste.

Lors de l'étude du gonflement des smectites par analyse de la diffusion des rayons X aux petits angles, Pons et al. (1981) et Ben Rhaiem (1983) ont obtenu des diagrammes de diffusion caractérisés dans le domaine étudié par des modulations plus ou moins prononcées de la courbe d'intensité.

L'analyse quantitative des courbes de diffusion, et en particulier de ces modulations, permet alors de remonter à une description de la structure du gel ou de la pâte et aux relations existant entre texture et structure (Pons et al., 1981; Pons et al., 1982). La méthode générale d'interprétation proposée par Pons et al. (1981) repose sur une comparaison entre intensité expérimentale et intensité théorique calculée à partir de modèles.

The occurrence of metahalloysite ‘nodules’ in the silica sand pocket deposits near Brassington, Derbyshire, is recorded for the first time. The geological surroundings are briefly described in an attempt to arrive at an explanation of the genesis of the ‘nodules.’ The history of attempts to work the deposits as china clay in the 18th century is included.

The purpose of this study was to develop a simple and efficient method for manufacturing porous bioceramics, in which small organic foam spheres were taken as the poremaking reagent and green bodies were made by hot die-casting in moulds. The raw materials (small organic foam spheres, paraffin, oleic acid and β-TCP powder) were mixed into a slurry at 30–120ºC and moulded into green bodies using a hot die-casting machine at 30–90ºC; the green bodies were then sintered and the porous bioceramics obtained. The main characteristics (structure and size of pores, water permeability, apparent porosity and shrinkage) were tested. The results indicated that the apparent porosity was high and directly proportional to the mass ratio between the small organic foam spheres and the β-TCP powder. The pores connected with each other in three dimensions; the size, distribution of the shapes and structures of the pores were clearly related to the dimensions of the small organic foam spheres. The water permeability was proportional to the hot die-casting pressures and the shapes of the samples could easily be controlled by selecting different moulds. This study indicated that the method can be used to manufacture porous bioceramics with controlled pore structures and different shapes effectively and easily by adding different amounts and sizes of small organic foam spheres, mixing the raw materials evenly, and by selection of the hot die-casting pressure and by the use of different moulds.

This study focused on the mineralogical and physico-chemical properties of heulandite/clinoptilolite (Heu/Cpt)-rich zeolitic tuffs SE of Ankara (Turkey) and evaluated their potential for use as adsorbents. The main Heu/Cpt minerals correspond to the intermediate type and the Cpt-type of the heulandite series. Minor chabazite, erionite and rarely analcime and accessory feldspars, mica, smectite, and quartz were also detected. Three types of Heu were recognized according to their thermal behaviour. Cpt (type-III Heu) was thermally stable at 600°C, whereas type-I Heu collapsed and type-II Heu partially collapsed. The Si/Al ratios of the Hul/Cpt ranged from 3.54 to 5.03, the Γ parameter (Γ = Ca/Al + 0.115*Al) varied between 0.78 and 1.85 and Al + Fe3+ varied between 6.27 and 8.00. The Na, K and Ca contents of Heu/Cpt varied widely and the Heu had an intermediate composition between types II and III. The Mg + Ca content is greater than the Na + K content in Heu-type II and smaller in Heu-type III zeolites. The BET surface area and the pore-size of the samples varied between 10.15 and 194.27 m2/g, and between 1.41 and 12.42 nm, respectively. The N2 adsorption and desorption isotherms were comparable, but the adsorption/desorption capacity is greater in type III than in type II Heu zeolites. The cation exchange capacities of the Heu/Cpt-rich samples ranged from 185 to 280 meq/100 g.

The catalytic influence of a Spanish kaolin and bentonite on the vapour phase oxidation of 96% ethyl alcohol has been studied, using different temperatures and varying proportions of air. Consideration has also been given to the changes produced in the activity of these minerals by previously saturating with different exchange cations or subjecting them to the action of acids.

The possibility of the identification by X-ray diffraction of montmorillonite and swelling chlorite, in the presence or absence of each other, is discussed. Swelling chlorite or montmorillonite, even in mixture with normal chlorite, but in the absence of mica, can be identified by heating to 500°C with immediate sealing of the tube, or by acid treatment followed by solvation with ethylene glycol. If mica is present, however, only the latter procedure will usually ensure positive identification. The same procedures will differentiate montmorillonite and swelling chlorite in mixture only when normal chlorite is absent.

Size graded fractions of ground quartz and other silica minerals are prepared by gravity settling for particles greater than 2 microns Stokes' diameter and by centrifugal methods for smaller sizes. The size distributions of the prepared fractions are determined by counting and sizing with an optical microscope or with an electron microscope. The volume-surface diameter ΣND3/ΣND2 is used both for calculating the specific surface of the fractions and for comparing the projected area diameters used in counting, with the Stokes' diameters.

Kaolin, or china clay, unlike most of the other clays mined in the United Kingdom, is residual in character, not sedimentary, being formed in situ in the mass of granite by decomposition of the original felspar. Granite occurs over a very considerable area of Great Britain but only in the granite bathylith of S.W. England, in Devon and Cornwall, does sufficient kaolinisation occur to justfy extensive exploitation which has been proceeding now for over 180 years. The granite intrusion welled up from great depths under a cover of sedimentary rocks of much greater age, which cover had already undergone great tectonic stresses prior to the granite's arrival.

The sorption properties of two layered minerals of the hydrotalcite supergroup – hydrotalcite and stichtite – were investigated with the aim of determining their kinetic parameters of sorption and their adsorption isotherm type. Pristine hydrotalcite and stichtite were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive Х-ray analysis and laser diffraction analysis of the particle-size distribution. The ‘memory effect’ of the sorbents was examined after calcination at 650°C. Slight indications of reconstructed hydrotalcite were observed, while the stichtite dehydration–rehydration cycle was irreversible. The hydrotalcite and stichtite were used to remove Congo Red from the aqueous solution. The pseudo-second order kinetic model described the process adequately. Mixed external and internal diffusion was confirmed for both minerals. The sorption of Congo Red on stichtite fits the Langmuir model. Stichtite demonstrated a maximum adsorption capacity of 2.5 mmol g–1 at 35°C. Increasing temperature increased the adsorption rate of Congo Red on stichtite but did not affect the adsorption rate constant for hydrotalcite.

The retreat of the Dead Sea and the lowering of the base level in recent decades have led to the exposure of the littoral clay sediments on the shore, the occurrence of exposed mudflats and the development of ground subsidence along strips (‘subsidence strips’) and clustered sinkholes. Based on field observations and laboratory analyses, the present study characterizes the clayey sediments in the environment of the exposed mudflats on the western Dead Sea shore. The clayey sediments of the exposed mudflats (‘mudflat sediments’) consist of fine-grained laminated calcareous clays. The mineral composition of the bulk mudflat sediments consists of clay and carbonate minerals (calcite, aragonite and dolomite) with some quartz and feldspar, and frequently gypsum and halite. The clay mineral composition of these samples is smectitic illite–smectite and kaolinite with some discrete illite and palygorskite. The smectitic illite–smectite is randomly interstratified (1.7 nm illite–smectite type R = 0). Although the detrital smectitic illite–smectite in the mudflat sediments is situated in the saline environment of the Dead Sea shore, no significant illitization is observed in the depositional detrital clay. Subsidence strips with clustered sinkholes were formed in the exposed mudflats as part of the adjustment of the Dead Sea periphery to the lowering of the base level as a result of the retreat. The field observations in the studied area reveal that the subsiding of mudflat sediments in the formation of the subsidence strips usually involves mud sagging of wet clayey sediments in the subsurface and sediment collapse of dry clayey sediments near the surface.