Although it is generally agreed that Fe and Al can act to bind soil particles, their relative efficiencies as aggregants are still disputed. In this work, the aggregating efficiencies of both aged and non-aged Fe and Al oxides precipitated on kaolin or quartz substrates were characterized by comparing their effects on particle size distributions (PSD). To facilitate comparison of PSD data, these were parameterized by fitting them with five different probability density functions (the normal, lognormal, Jaky, fractal and Rosin-Rammler functions). The best fits were given by the Rosin-Rammler function (R2 = 0.997), whose α parameter was used to compare the aggregating efficiency of Fe and Al oxides: in order of decreasing efficiency, non-aged Al > non-aged Fe ≈ aged Fe > aged Al-precipitates.

From measurements of dielectric losses as a function of frequency and temperature, as well as thermally stimulated depolarization currents, performed on a dry Na-montmorillonite, a qualitative description of the conduction mechanism has been proposed for this type of material. A representative approach related to the polarization phenomenon determined on this material led to the evaluation of the elementary energy Wj, connected with the reorientation of the dipoles during the hopping process. The results show the coherence between the polarization conductivity and the thermally stimulated currents methods.

Distribution coefficients and isotherms for the adsorption of radioiodide, caesium and strontium ions (125I−, 134Cs+ and 85Sr2+) were determined in untreated vermiculite and in vermiculite treated with the chloride salt of hexadecylpyridinium (HDPy+). Experimental data reveal that some of the alkylammonium ions were incorporated as HDPyCl ion pairs into the vermiculite. The fraction of ion pairs adsorbed is reflected by an increase in distribution coefficients with increasing saturation levels. Consequently, a considerable part of the iodide adsorption could be attributed to an anion exchange process. At smaller amounts of Cs+ and Sr2+ adsorbed, distribution coefficients of the modified clay mineral are significantly reduced in comparison with the original material. These differences are less pronounced when greater amounts of cations are adsorbed. Generally, larger distribution coefficients were found for the Cs+ compared with the Sr2+ ion in the untreated and modified samples.

A method has been developed to synthesize organo-hectorite clays directly from a Mg-silicate gel containing organic or organometallic molecules that are expected to be incorporated within the interlayer space. Complete crystallization occurs upon aqueous reflux for 48 h. The progress of clay layer formation was monitored by X-ray powder diffraction (XRD), differential thermal gravimetry (DTG), and infrared (IR) spectroscopy. Evidence of clay XRD peaks occurs after just 4 h of hydrothermal treatment, and Mg(OH)2 is no longer observable after 14 h. Observable changes in DTG and IR occur at about this time as well. Warren line-shape analysis of the 110 reflection indicates that when growth is complete the clay lamellae are on average ∼50% and 25% of the size of natural hectorites and montmorillonites, respectively. The N2 BET surface areas for all materials are also compared. Small angle neutron scattering shows that addition of tetraethyl ammonium (TEA) ions does not alter the structural integrity over that of the purely inorganic form of Li-hectorite, but that use of a cationic polymer does significantly alter the microstructure. The effect of temperature is critical, for at room temperature only the layered Mg hydroxide mineral brucite crystallizes unless very long time scales are used. The crystallizations carried out at room temperature show that clay will form after about 3 months, but that the presence of organics (at least TEA) acts to hinder this process greatly. The role of the organic molecules on silicate clay layer formation is compared with the role of organics in zeolite synthesis.

The characterization, pillaring ability and some catalytic properties of a saponite from the Vicálvaro deposit of Tolsa, located in Madrid have been studied. This mineral is associated with sepiolite in the same lacustrine environment. The raw saponite presents, as special characteristics, high specific surface area (>200 m2/g) and a high percentage of tetrahedral Al (90% of the total Al in the sample). Natural saponite gives rise to high conversions when used as a catalyst in the reaction of alkylation of benzene with 1-dodecene. Increased catalytic performances are obtained over the alumina-pillared saponite derivatives. These materials have also been tested in the cracking of gas-oil (microactivity test), giving good conversions and high selectivity towards the gasoline fraction, especially the pillared forms.

Mixed hydroxy Al-Fe-montmorillonite complexes (5 mmol of Al+Fe per g of clay) were prepared at pH 5.0 by mixing different amounts of Al(NO3)3 and Fe(NO3)3 to give initial Fe/Al molar ratios (R) of 0, 0.1, 0.25, 0.5, 1.0, 4.0, 10.0 or ∞. The effect of ageing on the interlayering, mineralogy, chemical composition, CEC and external surface area of the complexes was studied. The degree of interlayering of freshly prepared and aged complexes (up to 120 days at 50°C) was always greater in the samples with R ranging from 0.5 to 4. Gibbsite and hematite (with traces of goethite) formed in the samples with R ⩽ 1 and R∞, respectively. No crystalline Fe oxide was detected by XRD analyses in the complexes with R ranging from 0.1 to 10, whereas no crystalline Al and Fe oxides were formed in the complexes at R = 4–10. However, some evidence suggests the possible formation of a microcrystalline Fe oxide/oxyhydroxide undetectable by XRD analyses in the complexes richer in Fe. The CEC and the surface area of the freshly prepared mixed hydroxy Al-Fe-montmorillonite complexes increased with increasing R. Large quantities of Al+Fe were solubilized by oxalate in the complexes with R ⩾ 0.5, even after ageing for 120 days at 50°C, indicating that interlayering of Al-Fe species at certain Fe/Al molar ratios was particularly stable.

The Fourier transform Raman spectra of the kaolinite minerals have been measured in the 50–3800 cm−1 region using near infrared spectroscopy. Kaolinites are characterized by remarkably intense bands in the 120–145 cm−1 region. These bands, attributed to the O-Si-O and O-Al-O symmetric bending modes, are both polymorph and orientation dependent. The 200–1200 cm−1 spectral range is a finger-print region for clay minerals and each kaolinite clay has its own characteristic spectrum. The structure of clays is fundamentally determined by the position of hydroxyl groups. Fourier-transform Raman spectroscopy readily enables the hydroxyl stretching region to be examined allowing identification of the component bands. The advantages of FT-Raman spectroscopy are shown to enhance the study of the kaolinite structure.

An ion-exchange adduct of saponite with tetra-n-decylammonium cation ((n-decyl)4N+) was prepared and dispersed in chloroform. The material was spread on a water surface to form a thin film at the air-water interface. From the measurements of surface pressure vs. area, it was concluded that the film consisted of the very thin layer which was a mixture of single and double layers of saponite adduct. A clay-modified electrode was prepared by depositing the film on a glassy carbon substrate using the Langmuir-Blodgett method. When the electrode was soaked in an aqueous solution of [Fe(phen)3](ClO4)2 (phen = 1,10-phenanthroline), (n-decyl)4N+ cations were replaced by [Fe(phen)3]2+ ions from solution. This process was followed by measuring the cyclic voltammogram.

By means of transmission electron microscopy (TEM) and the gold decoration technique, the surface microtopography of rectorite (allevardite) crystals collected from Allevard, France was investigated. On the crystal surfaces, gold decoration successfully revealed growth steps of ∼20 Å in height. Only closed polygonal steps 20 Å high occur on the 001 surface of a thick platy crystal, although spiral growth patterns were not observed. Thick platy particles were easily split into thinner plates 20 Å thick in distilled water by means of ultrasonic vibration. No step patterns were observed on the surfaces of these thin plates which correspond to the cleavage plane. The growth of this rectorite, therefore, seems to be controlled by a layer nucleation mechanism.

Absorption and fluorescence spectroscopies were applied to study the adsorption of rhodamine 6G on several smectite-type clays in aqueous suspension. The dye can be adsorbed as the monomeric and the dimeric forms on both the external and the interlamellar surfaces of the clay. The presence of these species and their evolution with the stirring time of the sample and the relative dye/clay concentration depend on the nature of the smectite, the clay concentration and the particle size, factors that also affect the dispersion degree of the clay particles in water.

Structural formulae and other crystallochemical parameters were used to study different species of dioctahedral micas in clay and coarse gravel fractions of horizons from a red soil (Ultic Haploxeralf) in southern Spain. Mineralogical analyses using X-ray powder diffraction, and measurements of the b0 parameter revealed dioctahedral micas, illite and paragonite. Structural formulae established from electron microprobe analysis and energy dispersive X-ray analysis showed the illites to be K mica related in elemental composition and structure to muscovite and phengite. The paragonites were found to be closer to ideal mica. Structural formulae for Na-K dioctahedral micas were obtained with crystallochemical characteristics intermediate between those of Na micas and K micas. The possibilty of these micas representing individual mineral phases or intergrowths of Na and K micas is discussed. In the soil profile, micas from the Bt horizon showed the largest crystallochemical changes induced by pedogenesis.

The reactivity of an Al-pillared interlayered clay (PILC) (AZA) and a mixed Fe/Al-PILC (FAZA), used as references by the Concerted European Action-Pillared Layered Structure (CEA-PLS), was investigated in the selective catalytic reduction (SCR) of NO by NH3 or propane, as either catalysts or as supports of Cu ions. Both AZA and FAZA, either with or without Cu were found to be inactive in the reduction of NO with propane and oxygen. This is different from the behaviour with alumina with or without Cu, because of the different surface acidity properties. Good NO conversions were observed for both PILCs using NH3. The best catalytic performances were shown by FAZA, but the activity of AZA was also remarkable. The addition of Cu ions to both AZA and FAZA leads to an improvment in the activity in NO conversion and a reduction in the side formation of N2O. The catalytic behaviour was found to depend on the method of Cu addition, the Cu loading and the nature of the PILC. With AZA the best results were obtained for a Cu content up to 2 wt%, while further increases in the amount of Cu resulted in a considerable decrease in the conversion of NO. With FAZA, on the other hand, a high activity was observed at up to 3% of Cu introduced by ion exchange. By comparison with other Cu containing catalysts, Cu-FAZA allows operation in a wider range of reaction temperatures due to the reduced rate of side ammonia combustion. The surface acidity properties of AZA and FAZA were also characterized to interpret the above effects.

The interaction of the cationic hydroxo-bridged binuclear iron(III) complexes of the sevendentate ligands HPTP and HPTB with montmorillonite was studied. Both complexes can be introduced reversibly into the interlayer region of the smectite. The catalase active HPTP-complex preserves its activity in the smectite interlayers. The unstable peroxide adducts of both complexes can be introduced into montmorillonite interlayers from water/H2O2 at 273 K and can be stored there for months at 243 K. Adduct/montmorillonite compounds can also be prepared by direct reaction of H2O2 with the complexes already bound to montmorillonite. From IR spectra of the adduct/montmorillonite compounds it can be concluded that the adduct of the HPTP complex contains nitrate whereas the adduct of the HPTB complex does not. These results can help to decide whether structures of the adducts proposed in the literature are possible or not and may therefore open a new field of application of clay minerals in studies on unstable intermediates.

Clay minerals play an important role in the retention, transport and chemistry of organic micropollutants in soils. There has been considerable recent interest in modelling and designing modified clays as adsorbents and catalysts for the removal of contaminants from waste waters (McBride et al., 1977; Mortland et al., 1986; Boyd et al., 1988). Organo-clays have been used as chromatographic stationary phases over the past three decades. White (1957) and Barrer & Hampton (1957) used alkylammonium montmorillonites as stationary phases and determined the selective retention of aromatic hydrocarbons relative to paraffins, naphthalenes and xylenes. Until now only organo-clays have received attention as chromatographic stationary phases (McAtee & Robbins, 1980) while their pillared variants have been totally ignored.