The palygorskite-sepiolite group of clay minerals has a wide range of industrial applications derived mainly from its sorptive, rheological and catalytic properties which are based on the fabric, surface area, porosity, crystal morphology, structure and composition of these minerals. For assessing potential industrial uses, the mineralogical and chemical composition of the clay and its basic physical and physico-chemical parameters must be determined. Then some particular properties of commercial interest can be modified and improved by appropriate thermal, mechanical and acid treatments, surface active agents, organo-mineral derivatives formation, etc. In this paper, a revision of the principal characteristics of commercial palygorskite-sepiolite clays is presented, and potential uses are suggested according to these data. New products and applications are being investigated and those concerning environmental protection in particular, are noted. Finally, possible health effects of these elongate clay minerals are discussed.

Two sets of natural Al-substituted goethites from contrasting surface environments (24 tropical and subtropical soils vs. ten lake iron ores from Finland) were characterized by Mössbauer spectra obtained at room temperature and 4.2 K. A negative correlation between Bhf and Al substitution (R2 = 0.751) was found by combining the data of all the samples, which was slightly improved (R2 = 0.779) by taking the mean coherence length perpendicular to 111 (MCL111) into account. The effect of Al on lowering Bhf was, however, stronger for the tropical soil goethites than for those of the lake ores. This is parallelled by a corresponding difference in the unit-cell decrease per unit Al substitution. These differences are believed to result from the crystallization conditions in the two different environments.

Isomorphic substitution in goethites is common in nature and the properties of goethites generally change as a function of the degree of substitution (e.g. Al-goethites). In synthetic goethites, substitution by other elements such as Co is also known. Recent literature indicates that the influence of Al and Co on the unit-cell dimensions of goethite is similar. In contrast to Al-goethites, however, little is known about other properties of Co-goethites and in this study some properties of synthetic Co-goethites were investigated by XRD, IR, TEM, TGA and reductive dissolution techniques. Eight goethite samples (S1 to S8) with varying Co concentrations were synthesized from mixed alkaline solutions of Fe(III) nitrate and Co(II) nitrate, aged at 63°C and ambient pressure. The goethites contained up to 9.5 mol.% Co. Their redness increased with Co concentration, e.g. 0.5 Y 6.0/6.4 for S1 and 6.4 YR 3.3/3.2 for S8. Surface area ranged from 46 to 88 m2/g. Unit-cell parameters a, b, c and v all showed a negative linear dependency on the Co concentration of the goethites. Transmission and diffuse reflectance IR spectrometry showed the presence of strong bands which were interpreted as v-OH, δ-OH and γ-OH vibrations. The δ-OH and γ-OH band positions showed a positive linear dependency on the Co concentration of the samples. Dehydroxylation occurred between 280 and 315°C and dehydroxylation peak positions tended to decrease with increasing Co concentrations. As with Al-goethites, Co-goethite reductive dissolution rates decreased parabolically with increasing substitution. X-ray diffraction and IR analyses, TGA and congruent reductive dissolution suggest the existence of single phases, i.e. Co-goethites of varying degrees of isomorphic substitution.

Two smectites with different layer charge localization were used to characterize the chemical and structural aspects of minerals treated with 1.9 × 10−2m and 1 m heavy metal solutions (Zn2+ and Pb2+). Natural and treated smectites were analysed by: (1) X-ray powder diffraction first at 25°C and relative humidity of 60% and then at increasing temperature up to 400°C; (2) thermo-gravimetric and differential thermal analysis; (3) X-ray fluorescence; (4) atomic absorption and UV visible spectrophotometries. The sorption of both metals depends on 2:1 layer features and is enhanced when the total layer charge is mostly due to substitution in the octahedral sheet. The variability between Zn2+- and Pb2+-treated smectites in the interlayer water content depends both upon cation electrostatic features and upon smectite layer charge localization. The greatest water content was observed in [Zn2+]1 m-treated smectite showing charge imbalance in the octahedral sheet. In smectites treated with [Zn2+]1 m solutions, an additional thermal reaction occurs at a temperature of ∼380°C, and the d(001) spacing, which is 10 Å at a temperature of ∼200°C, gradually decreases in the temperature range 200–400°C. In smectites treated with 1 m [Pb2+] solutions this value is reached at a temperature of ∼150°C and remains quite constant up to 400°C.

The adsorption of Cd and Zn on a standard montmorillonite (SAZ-1) in the presence of the cationic pesticide chlordimeform, both in solution (simultaneous adsorption) and when the pesticide is previously adsorbed on the clay (successive adsorption) has been studied. The adsorption of Zn decreases when the chlordimeform concentration increases in both simultaneous and successive adsorptions, following the sequence: chlordimeform-free solutions > successive > simultaneous. In the adsorption of Cd the sequence is different: successive > chlordimeform-free solutions > simultaneous, indicating that a small amount of pesticide adsorbed favours Cd adsorption. In all cases, the apparent affinity of the metal for adsorption on montmorillonite, on the basis of distribution coefficients, KD, is higher for lower metal surface coverage, and decreases largely with the amount of the metal adsorbed. This indicates the existence of high affinity sites on the clay, probably those of variable charge edge regions. The contribution of edge and interlamellar positions to adsorption of Zn and Cd on SAZ-1 has been studied.

Complexes of Cu(lysine)2+2 and Cu(histidine)2+2 have been intercalated between the layers of saponite clays by a simple cation exchange procedure from aqueous solutions of preformed Cu(amino acid)2-complexes. Successful immobilization was obtained with an amino acid: Cu2+ ratio of 5, and a pH of 10 and 7.3 for lysine and histidine, respectively. The synthesized materials were investigated as powders and as thin films by electron spin resonance (ESR), diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD). The light blue clays are characterized by an axially symmetric ESR spectrum with A//= 192 G, g//= 2.23 and g⊥ = 2.07, and a d-d absorption band around 600 nm, due to the intercalated planar Cu2+-complexes. Ammonia interacts reversibly with these intercalated complexes, suggesting the presence of a free coordination site. The novel synthesized materials are active in various oxidation reactions with t-butyl hydroperoxide as oxidant.

The preparation and characterization of Ti-pillared acid-activated clays (designated Ti PAACs) and conventional Ti-pillared clays (designated Ti PILCs) are described. Preliminary catalytic results show that these materials possess remarkably enhanced abilities to catalyse the dehydration of pentanol compared with their Al counterparts (in excess of 200% in the case of the PILCs and up to 82% for the PAACs). These activities approach those previously reported for non-pillared acid-activated clays.

The interaction between interlamellar Lu(III) cations and the layered silicate structure has been studied by means of MAS-NMR, XRD and EDX. Irreversible fixation of exchangeable Lu(III) cations upon hydrothermal treatment at 300°C of Lu-saturated montmorillonite is reported, through the formation of the crystalline phase Lu2Si2O7. It is shown that the lowest temperature previously described for this reaction, 400°C, does not indicate a thermodynamic boundary. This basic solid-state finding is relevant for some clay applications such as those related to the safety of nuclear waste repositories with engineering barriers.

Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy has been used to determine the nature of acid sites present in Na+-, Ni2+- and Al3+-exchanged montmorillonite using the diagnostic base, pyridine. The pyridine additions were performed in situ at 25°C in the presence of liquid benzene or deuterated 1,4-dioxan to ascertain whether the acidity profile was influenced by the presence of either the non-polar or oxygenated solvent. Pyridine treated Ni2+-montmorillonite exhibited absorption bands characteristic of Lewis bound base in both benzene and deuterated 1,4-dioxan indicating that the Lewis acid sites were present at low temperature and were accessible in both solvents. The presence of a strong 1537 cm−1 band in pyridine-saturated Al3+-montmorillonite confirmed that this clay acted as a Brønsted acid in benzene. However, this diagnostic band was significantly reduced in the presence of deuterated 1,4-dioxan.

Mudrocks and sandstones from the Palaeocene of the central North Sea have been studied to assess the petrology, diagenesis and extent of any chemical interaction between the two lithologies. Authigenic and detrital minerals have been distinguished using a variety of electron microscope techniques. Small but significant quantities of authigenic minerals, which would not be detected by conventional petrographic tools, have been detected through the use of high-resolution electron beam techniques. Sandstone mineralogy has been quantified by point counting, and mudrock mineralogy semi-quantified by XRD. The detrital and authigenic mineralogy in the sandstone is almost identical to that found in the mudrock. The principal difference is in the relative proportions. Qualitative mass balance suggests that cross-formational flow has not been significant in either clay or quartz diagenesis.

Experimental studies of reactions between water and kaolinite, kaolinite + quartz, kaolinite + quartz + muscovite and natural kaolinitic mudstones (Jurassic Draupne Formation; Norwegian North Sea; Rhaetic Westbury Formation, SW England; Tertiary ball clay, SW England) at 50 MPa and 150°C or 200°C have demonstrated that quartz saturation can be achieved readily at 200°C At 150°C quartz saturation is achieved for natural mudstones, but not for mineral mixtures because of slow reaction kinetics. Geochemical solution modelling demonstrates coincidence between observed fluid compositions and those expected for the solid mineral assemblage. In addition to inorganic solutes, organic acid anions including citrate are reported as products in experiments with natural mudstones (especially the Draupne Formation). Fluids supersaturated with respect to quartz are unlikely to be developed from mudstones which lack smectites or amorphous silica.

The growth and decay rates of rapid, induced electro-optical phenomena in dilute colloidal suspensions are characteristic of the geometry of the solute particles. The speed of measurement renders such methods especially relevant for fast, in situ analyses of the size and size distribution of colloids in practical, industrial situations where these properties may be undergoing continuous change. The principles of the measurement of electrically induced birefringence using pulsed fields is outlined and used to study vermiculite suspensions as they undergo size reduction in an ultrasonic field. The high sensitivity of the method to both the particle size range and the form of the distribution function is indicated. The use of the method for on-line monitoring of dilute mineral suspensions for the indication and control of aggregated, dissolving or growing media is discussed.

Porrenga (1968) described the green clays from the Lower Oligocene of Aardebrug, east of Leuven (Louvain) in Belgium as glauconitic illite, a mineral intermediate in chemistry between glauconite and illite, and presumed this clay to be neoformed, though the mode of origin is not discussed. Notably, most of the section from which Porrenga obtained his sample of 'glauconitic illite' is nonmarine. Non-marine glauconites are rare in the literature and there is no standard terminology. Parry and Reeves (1966) reported green pellets of 10 Å clay from recent sediments at Lake Mound, Texas, but with no detrital green clay as source and an authigenic origin is assumed. Green clays described as Fe-rich mica occur in lacustrine environments in the Oligocene of Cantal (Jung, 1954), and the Massif Central (Gabis, 1963) in France. These deposits are derived from altered crystalline basement.