The adsorption of DL-alanine at pH 4, 6 and 8 by a soil allophane has been determined. Two sets of experiments were carried out: (1) in which the allophane had been kept in a moist state throughout; and (2) in which the mineral had previously been dried at 50°C. In both instances, the adsorption isotherms showed three distinct regions as the concentration of alanine in solution was increased: (1) an initial, nearly linear, rise at low equilibrium concentrations; (2) a levelling off to a plateau at intermediate concentrations; and (3) a steep linear increase at high concentrations. For comparable concentrations of alanine in solution, adsorption decreased in the order pH 6 > pH 8 > pH 4. Irrespective of pH, however, more alanine was adsorbed by the ‘wet’ allophane than by its ‘dry’ counterpart. These observations are interpreted in terms of the morphology and aggregation of allophane unit particles together with the pH-dependent charge characteristics of allophane and alanine. The results are compared with published data on the adsorption of alanine by montmorillonite.

The unique properties of clays make them suitable for a large number of applications. Among the procedures that can be used to characterize clayey materials, the assessment of the abrasion and the abrasiveness index can be employed to predict the mechanical behaviour of clay samples. However, only a limited number of references to these testing procedures are available in the literature. Several Portuguese clayey samples were collected and the <63 μm fraction was analysed. The main clay minerals present are kaolinite, illite and smectite. The abrasiveness index depends on the granulometric and mineralogical compositions. A lower abrasiveness is induced by the presence of a high abundance of the <2 μm fraction, small mean particle size and a large phyllosilicate content . Kaolinite and illite show good correlation with the abrasiveness index, while smectite decreases abrasion.

The distribution of 2:1-2:2 intergrade clays has been investigated in some podzolized soils from Norway. In some of the profiles the intergrade clay mineral appears to be concentrated in the A2 horizon; in others, where smectite is predominant in the surface horizon, the maximum accumulation of the intergrade is observed in the B2 horizon. Smectite and vermiculite have been found to be the precursors of the intergrades of the A2 and B2 horizons respectively. A possible explanation to account for the observed variable pattern of occurrence of intergrades in soils is suggested.

The optical properties of oriented montmorillonite aggregates were measured in both non-complexing and complexing media. The changes observed lead to the following conclusions. Preparing oriented aggregates of clays for optical examination requires considerable care to avoid spurious orientation effects. In determining the optical constants of montmorillonite aggregates the medium must wet and enter the aggregate readily and displace the air, particularly from the smaller pores, otherwise large form birefringence effects of uncertain magnitude will occur. A suitable medium is likely to be one that complexes montmorillonite. The complex it forms must have relatively isotropic interlamellar layers and this is more likely with isodimensional molecules. Consideration of complexes with simple compounds suggests that the intrinsic birefringence of aggregates is overestimated by conventional techniques.

Forming complexes with aromatic compounds usually results in the birefringence of the aggregate being essentially determined by the orientation and anisotropy of the intercalated molecules.

Different types of dioctahedral smectites (nontronite, beidellite, montmorillonite) were investigated by X-ray fluorescence analysis (XRF) and Fourier transmission infrared spectroscopy (FTIR). Starting with the chemical composition of the octahedral sheet, the occupancies within the octahedral sheet were adjusted by computer simulations to fit the occupancies derived from FTIR. For both cis-and trans-vacant smectites the AlAl and FeFe pairs are mainly randomly distributed but seem to be aligned along OH-bonded directions. Relative to the chemical composition, AlFe pairs are enriched in cis-vacant smectites and depleted in nontronites. This behaviour can be explained by the necessity to dehydrate and hydrolyse cations when they become incorporated into the structure during crystal growth. The first and second hydrolysis steps are necessary for incorporating cations in trans-vacant smectites, whereas only the first hydrolysis step is necessary for cis-vacant smectites. The corresponding difference in energy may explain why mostly cis-vacant smectites occur in low-temperature environments.

Two iron ore samples from Nigeria have been examined using TG, DTA, EGA, XRD, and optical and electron microscopy. Itakpe iron ore is hematite-rich, this mineral being intergrown with magnetite, and silica is the major impurity. Agbaja ore is an acidic oölite ore consisting of goethite and magnetite, with alumina, silica and phosphorus as major impurities. Itakpe is typical of a rich ore formed by magmatic segregation whilst Agbaja is a lean ore of sedimentary origin. Isothermal mass-change measurements in hydrogen and carbon monoxide in the range 800–1100°C show Agbaja to be less reducible than Itakpe; in particular, Agbaja is very irreducible at 1100°C because of sintering of the ore. Characterization and reducibility experiments were also carried out on Corby (Northamptonshire, UK) iron ore for comparison.

Phosphorites occur throughout the Negev, southern Israel, within the upper part of the Mishash Formation of Late Campanian age. These phosphorites are part of the Upper Cretaceous-Eocene Tethys phosphatic province. Two units can be differentiated in the Mishash Formation: a lower chert unit and an upper phosphatic unit (Nathan et al., 1979). In the upper unit, rich, economic phosphorite beds with more than 25% P2O5 alternate with chert beds and so-called ‘sterile intercalations’ which contain about 15% P2O5.

Clinoptilohte (Mumpton, 1960), a zeolite of the heulandite-clinoptilolite family, was identified from XRD patterns of air-dried and heated samples of the clay fraction from the insoluble residue (1-20% of the rock) of selected phosphatic samples from the Hor Hahar field, Negev, southern Israel. Clinoptilohte occurred mainly in the ‘sterile intercalations’. Inasmuch as clinoptilohte has not been identified in older formations in the Negev, it was presumed to be authigenic in the Mishash Formation.

Ultramarine pigments were synthesized successfully from Na-A zeolite derived from kaolin waste. Na-A zeolite encapsulates the sulfur species formed and which act as chromophores, which circumvents their oxidation and the subsequent liberation of high levels of toxic gases during the reaction. Different Na-A zeolite matrices with various grain sizes (fine to coarse) were mixed with sulfur and sodium carbonate in various proportions to study the influence of these variables on the pigments’ colours and hues. After calcination at 500°C for 5 h, the products were characterized by X-ray diffraction, X-ray fluorescence and Raman spectroscopy and were classified by the Munsell system (colour and hue). Products with colour ranging from blue to green with various hues were obtained. Both colour and hue were affected by the amount of additives and by the particle size.

The present study investigates the use of magnesium sulfate (MgSO4) instead of (NH4)2SO4 as a lixiviant in the recovery of rare earth elements (REEs) from clays. Experiments were carried out to investigate the influence of leaching conditions such as leaching time, lixiviant concentration and liquid:solid ratio on the leaching efficiency. The optimum leaching conditions, leading to 75.48% of total REE leaching efficiency, required a stirring speed of 500 rpm, a leaching time of 30 min, a lixiviant concentration of 3 wt.% and a liquid:solid ratio of 3:1. After extension of the leaching process by a second stage, the leaching efficiency may reach up to 96.19%, which is slightly higher than that obtained by (NH4)2SO4. Leaching varies from element to element, with Ce presenting the lowest leaching efficiency, and the partition in leaching solution is in agreement with that in raw ore other than for Ce. Based on these findings, MgSO4 lixiviant is an excellent alternative leaching agent for a sustainable REE industry because it reduces or eliminates NH4+–N pollution.

On a étudié les transformations minéralogiques des argiles et des biotites isolées d'un sol cryptopodzolique humifère du Plateau de Millevaches, France. Pour les argiles, la diffraction de rayons X fait apparaître un comportement intergrade de plus en plus prononcé de l'horizon C vers l'horizon A1. La nature des éléments extraits par les traitements citratedithionite et Tamura indique que ce comportement est lié à la présence d'aluminium interfoliaire pour les argiles de l'horizon A1Bh, mais également à des résidus de chlorite altérée pour celles de l'horizon A1. Pour les biotites, on observe un comportement aux RX très voisin de celui de la fraction argileuse. On peut mettre en évidence dans l'espace interfoliaire des biotites altérées la présence d'ions alumineux et de composés organiques.

An understanding of the behaviour of contaminants in compacted clays is important in assessing the effectiveness of clay-based barrier materials used in many waste containment strategies. Here the diffusion and sorption behaviour of I− with selected compacted clays is examined (129I is a relatively long-lived radioisotope present in high-level nuclear fuel waste.) Diffusion coefficients, D, and distribution coefficients, Kd, were measured for I− with four clays: bentonite, Lake Agassiz clay (a glacial lake clay composed mainly of smectite, illite, kaolinite, and quartz), interstratified illite-smectite, and kaolinite. For the diffusion experiments the clays were compacted to a dry bulk density, ρ, of ∼1.2 Mg m−3. The mean measured D values, Dm, were as follows: bentonite, 310 µm2 s−1; Lake Agassiz clay, 0.62 µm2 s−1; illitesmectite, 190µm2s−1; and kaolinite, 74µm2s−1. The measured values were compared with those calculated, Dc, from the following model: D=Doτan/(n + ρKd), where Do is the diffusion coefficient in pure bulk water, τa the apparent tortuosity factor, and n the solution-filled porosity of the clay. Except for the Lake Agassiz clay, where Dm was about an order of magnitude lower than Dc, the Dm and Dc values agreed within a factor of about two. The Lake Agassiz clay has a markedly higher organic carbon content than the other three clays, and this could affect τa, which may be overestimated in the model.

A theoretical mechanism for the oxidation of ferrous iron in hydroxylated silicates is described. The reaction is represented by the general equation 4Fe2+ + 2nOH− + O2→4Fe3+ + (n + 2)O2− + nH2O, where n can vary. Oxidation occurs only at the surface of the mineral and is sustained by the migration of protons and electrons through the crystal. Non-oxidizable ions, such as Mg2+, and water formed during oxidation inhibit the reaction. The experimental evidence for the theory is derived, from a study of the oxidation of amphiboles.

The synthesis of clay composites modified with magnetite and Co ferrite magnetic nanoparticles is described. The synthetic method relies on the adsorption of colloidal magnetite or Co ferrite particles onto the external surfaces of a Na-saturated clay mineral to give magnetic clay composites that can be converted easily, through ion exchange reactions, to valuable clay derivatives, e.g. organoclays, which maintain the magnetic properties of the parent composite. The magnetic solids were characterized by XRD, EPR, Mössbauer, magnetic measurement and TEM techniques.

Study of sandstone diagenesis provides information about the origin, texture, distribution and composition of clay minerals, which in turn is used in reservoir description. Three examples of the use of clay mineralogy in reservoir description are given. (1) Kaolinite commonly forms pore-filling cements which are pervasive in specific sandstone intervals. It is shown that water-zone kaolinization homogenizes and lowers the porosity and permeability relative to the oil zone; in a reservoir model different Ø/K relationships are defined above and below the oil-water contact. (2) An occurrence of chlorite in dish-structured horizons is shown to increase horizontal permeability and decrease formation resistivity. The sensitivity of the neutron porosity log to the chlorite cement reduces the usefulness of the log for porosity evaluation. Uncritical application of wireline logs to define reservoir parameters can give pessimistic reservoir evaluation. (3) Sand production can be related to wettability, which in turn is strongly influenced by clay mineralogy. A perforation strategy to minimize sand production may then be based on knowledge of the clay mineralogy of a reservoir.

The chemisorption of methylene blue by kaolinite crystals increased as the aqueous suspensions changed from acid to alkaline because, at high pH values, not only the basal pinacoids but the edge-faces were negatively charged. The inability to calculate acceptable specific surfaces or cation exchange capacities from the chemisorption data is discussed, with special reference to the orientation of adsorbed dye cations, the covering of more than one exchange site by a monomer or polymer, the different concentrations of exchange sites on the basal pinacoids and edge-faces respectively, the possibility that such sites occur on the tetrahedral rather than on the octahedral basal pinacoid, and the incomplete replacement of inorganic cations.

L-cysteine (Cys) was adsorbed by bentonite (Ben) from aqueous solutions of variable concentrations and pHs. The raw materials and the adsorbed molecules (Ben-Cys) were characterized using X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analysis methods (TG, DTG and DSC). The results indicated that the adsorption process depended strongly on pH, temperature and concentration of amino acid. Cysteine is specifically adsorbed on bentonite surface sites, probably through its NH3+ moiety. The pH dependence suggests that these sites may be silanolate groups (≡Si-O–). It is presumed that ion exchange interaction governs the adsorption process. The experimental data of adsorption isotherms obtained and analysed with the Langmuir model showed that this model fitted the adsorption data. Calculated thermodynamic parameters (ΔHº, ΔSº, and ΔGº) indicate that the adsorption processes were exothermic.

Nine muscovite samples from different localities were analysed for all major chemical elements and examined by infrared spectroscopy in the range of 4000–250 cm−1. Iron in the octahedral positions was found to cause an intensity decrease and shifting of some absorption bands. Other structural cations were found not to be effective in producing intensity and frequency changes due to the narrow variations in their amounts. Heating studies indicated that at about 800°C muscovite transforms into a dehydroxylated phase which is stable at least up to 1000°C. Particle size studies showed that 5 µm is the upper size limit for a representative spectrum.

Few reports exist on the use of Diffuse Reflectance Infrared Fourier Transform Spectrometry coupled with Mass Spectrometry (DRIFTS-MS) in situ to monitor the dehydroxylation of kaolinitic clays. The use of DRIFTS-MS in situ allows study of the effect of heat treatment on the dehydroxylation, identifying intensities and temperatures at which the hydroxyl groups are released, forming metakaolinite and meta-alunite. The effluent gases from the infrared cell were analysed by mass spectrometry. The decrease in intensity of the bands at 3694, 3669, 3650 and 3621 cm−1 associated with the −OH stretching vibration modes of AlVI−OH−AlVI of kaolinite began at 450°C. Two additional bands at 3513 and 3485 cm−1 are associated with the vibration of AlVI−OH of alunite that also began to disappear during thermal treatment. Monitoring of the fractions m/e 17 and 18 using a mass spectrometer revealed that the intensity of these fractions increased starting at 450°C. Therefore, it is possible to study the dehydroxylation process of clays during thermal treatment.Chemical and mineralogical characterization of a kaolinitic clay (KN) fromMexico showed that the clay consists of 64.8% kaolinite, 11.0% alunite and 24.4% quartz based on PXRD, EDS, TG/DTA, TEM and FTIR results, and suggested that the material might have potential for use in the manufacture of ceramics, refractory bricks or geopolymers.

The <2 µm clay fractions from low-grade metabasalts of eastern North Greenland are mixtures of mafic phyllosilicates and celadonite that show complex X-ray diffraction (XRD) patterns. Interpretation of such patterns is difficult and subjective using only visual examination of peak positions and shapes. Deconvolution analysis offers a less subjective means of identifying peak positions for overlapping peaks and is applied to several composite peaks in a pattern; the peaks identified are then rationalized in terms of specific mixed-layer phases. Comparison against NEWMOD patterns of the identified clay mixture provides an additional constraint on the phases identified. Three mafic phyllosilicates, discrete chlorite and two chlorite-smectites with 60:40 and 80:20 proportions are demonstrated in the same XRD pattern. Modelling using NEWMOD of a mechanical mixture between these mineral shows an excellent match to the observed XRD pattern. The recognition in low-grade metabasalts of chlorite and random and different varieties of regular mixed-layer chlorite-smectite offers support for the classical model of a tri-smectite to chlorite transition. This is in contrast to an alternative model proposing smectite and chlorite end-members with corrensite as a discrete phase crystallizing directly without intervening mixed-layer chlorite-smectite.

The interlayer structures in one- and two-layer hydrates of Na-vermiculite are described by presenting the positional parameters of their constituent atoms, including protons.

The revision of these structures has been accomplished by: (1) determining accurate water contents of the two hydrates by thermoanalysis (TG, DSC); (2) using earlier X-ray diffraction data published by Slade et al.(1985) and de la Calle et al. (1984) as a reference; and (3) applying least-squares refinements when considering the constraints for atomic distances and bond angles between interlayer constituents.

In the 1.485 nm hydrate of Na-vermiculite (nH2O/nNa ≈ 4), sharing edges of Na(OH2)6 octahedra cause their chainlike arrangement. The chains are aligned along [100] and are stabilized by H-bonds between interlayer water molecules and oxygens of the silicate layer. The partial loss of these bonds during dehydration forces the stacking order to change from V3 to Vc in the resulting 1.185 nm (nH2O/nNa ≈ 2) hydrate.

This new understanding may help to explain differences in the rotational correlation time of water molecules between one- and two-layer hydrates of vermiculite as observed by quasielastic neutron scattering (Swenson et al., 2000).