Deuteration (H/D substitution at 200ºC) was performed on powders of two ground talcs of different particle shapes (different basal/lateral surface ratios). Results indicate that the deuteration process is only efficient on lateral talc surfaces, and suggest that the hydrogens located in the hexagonal ring of the talc basal surfaces are not exchanged. The FTIR spectra collected from the two talc samples show that it is possible to discriminate between particles with the same specific surface area but with different basal/lateral surface ratios using the deuteration process.

A series of organo-silicates was obtained from synthetic Na-fluorotetrasilicic mica (Na-TSM) by ion exchange with dodecyl-, tetradecyl-, hexadecyl- and octadecyltrimethylammonium (C12, C14, C16 and C18) bromides. When the concentration of the alkylammonium ions has varied from 0.43 to 3.4 mmol/g of the silicate, the maximum amount adsorbed on the mica was 0.92 mmol/g. As shown by 23Na MAS NMR, ∼0.30 mmol/g of Na+ ions were non-exchangeable, even if a large excess of the organic ions was used. The XRD patterns of all the samples obtained show that alkylammonium ions are distributed inhomogeneously within the mica interlayers. As a consequence, the organo-micas contain several phases consisting of randomly and regularly interstratified layers differing in terms of the amount of alkylammonium ions adsorbed. These different layers swell in ethylene glycol in the same manner and form new interlayers with identical spacings. The d001 values of individual organo-TSMs after glycolation suggest that the alkylammonium ions are oriented perpendicular or almost perpendicular to the mica layers. The Na-TSM layers were not detected in organo-TSMs by XRD. The presence of organic and inorganic (Na) mixed-ion interlayers with spacings controlled by the arrangements of the organic ions is consistent with the results obtained. These data also suggest that the alkylammonium/Na+ ion ratios vary in alternate interlayers.

The hydrothermal reaction of kaolinite in the system Na2O-K2O-(MgO)-Al2O3-SiO2- H2O has been investigated at 200 and 300ºC. The study of the solid products indicates that, at 200ºC, disordered illite was the first phase formed, which evolved at increasing run times towards well ordered illite and analcime. After longer reaction times illite and kaolinite were the sole phases identified by XRD. The b parameter of the illites increased at longer reaction times, from 9.05 to 9.08 Å. Study by TEM/AEM revealed the presence of surface chlorite-like layers, covering the illite packets, however. The trend observed in the products of the reaction at 300ºC was similar, except for the presence of boehmite or pseudoboehmite at the higher temperature. The values of the bparameter of illite, of the order of 9.12 –9.16 Å, indicate that illites formed at 300ºC have a more trioctahedral character. The results obtained also indicate that Mg determines which product will be formed, Kand Na-zeolites and Al-rich illites being the phases formed in the absence of Mg.

Aggregation of colloidal clay particles (Na-montmorillonite) by CaCl2 and anionic polysaccharide (succinoglycan) in turbulent conditions was investigated using time-resolved size measurements by laser diffraction on diluted (50 mg l –1) and stirred suspensions. Excess of Ca2+ ions promotes coagulation of the clay, reducing interparticle repulsions, and allows adsorption of succinoglycan, inducing bridging flocculation. Growth/breakage cycles, characteristic of the turbulent conditions, cause the macromolecules to be incorporated in the innermost of the flocs, where the morphological units are shown by confocal microscopy to be the micrometric Ca-clay particles. Such incorporation results in an increased floc tensile strength, depending on the amount of macromolecules adsorbed, with a maximum at polysaccharide concentrations of 2 wt.% with respect to clay mass.

The mineralogical and geochemical characteristics of Eocene continental sediments in south central Tunisia (Chebket Bouloufa and Jebel Hamri) and in north central Tunisia (Jebel Lessouda and Jebel Rhéouis), which contain considerable amounts of palygorskite, were studied. The clay fraction of the sediments also comprises illite, kaolinite, Mg smectite and Al smectite, together with carbonates (calcite and/or dolomite), quartz, gypsum and feldspars, all of which are present in extremely variable proportions.

The textural characteristics of the samples containing most palygorskite, as well as the chemical composition of the fibres and the contents of certain trace and rare earth elements suggest that the genesis of this fibrous clay is intimately linked to the diagenetic transformation of illite, mixedlayered minerals and/or Al smectite, as has also been observed in contemporaneous deposits in Morocco.

FTIR spectroscopy has been applied to NH4+-exchanged dioctahedral clay minerals to determine the molecular environment of NH4+ and to quantify N concentration. FTIR under vapourpressure control, coupled with heating and freezing treatments has shown that NH4+ ion symmetry varies with the nature of clay minerals. NH4+ has a perfect tetrahedral symmetry in hydrated or dehydrated smectites and belongs to the Td symmetry group. The NH4+-bending vibration is centred at 1450 and 1425 cm–1.

The Si4+-Al3+ substitution in dioctahedral clay minerals induces the loss of symmetry elements of the NH4+ tetrahedron which acquires a C2v symmetry. As a consequence, the Td –C2v transition can be used to characterize the smectite–illite transition. Quantification of NH4+ content per half unit cell is provided by nNH4 = k[NH4]/[OH] where [NH4]/[OH] is the band area ratio of the NH4+-bending vibration to the OH-stretching vibration. k = 1.1 for hydrated smectite, 0.9 for dehydrated smectite and 0.8 for illite or tobelite. The bending vibration of NH4+ is chosen for the calculation because it is not affected by superimposed contributions.

The evolution of textural properties of Na/Ca-bentonite from Wyoming (MX-80) was studied by adsorption of nitrogen, water vapour, and ethylene glycol monoethyl ether. Clay suspensions were heated at 80 and 300ºC for up to 9 months in the absence of or in the presence of Fe and/or Fe oxides. The treatment without Fe did not change the textural properties of the samples significantly. The treatment at 80ºC in the presence of Fe resulted in a considerable increase in the external surface areas of the samples. The total and external surface areas and swelling capacities of the samples decreased following the treatment at 300ºC in the presence of Fe and Fe oxides. In the case of larger additions of Fe, the treatment at 300ºC resulted in a considerable decrease in the total and external surface areas and swelling capacity of the sample and in the formation of a network of large-size pores, in which all the pores were connected.

The dehydration of hexadecyltrimethylammonium (HDTMA)-exchanged smectites has been studied using X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The basal spacing of hydrated HDTMA-smectites changed with temperature. The 2.5 HDTMA-smectite (i.e. smectite treated with HDTMA equivalent to 2.5 times the CEC) showed a continuous increase in its basal spacing during dehydration up to 200ºC, while the 1.2 HDTMA-smectite showed a significant decrease in basal spacing. It is assumed that the less ordered alkyl chains in the wet state in the interlayer region may be rearranged to ordered chains (e.g. all-trans conformation) during sequential dehydration. This results in a decrease in interlayer spacing in the phase with low organic packing density and a flat-lying array (i.e. 1.2 HDTMA-smectite), and a gradual increase in the basal spacing when the chains have a vertical configuration (2.5 HDTMA-smectite).

Kaolinite cation adsorption data are processed using recent gas adsorption concepts such as the undersaturation ∆m = ln (C/Cs) and the monolayer coverage y. This process shows that using the proper reference phase through its solubility Cs, it is possible to characterize adsorption sites that have the same adsorption energy regardless of the nature of the cation. Under mildly acidic conditions, a single ‘Langmuirian’ site category fits cation adsorption data whereas another family of sites is revealed in mildly alkaline conditions. These results suggest that at mildly acidic pH, only silanol sites are available to ion exchange and adsorption whereas at higher pH, a wider range of sites is made available, some of them displaying the same average adsorption energy and the others constituting a different category of sites with a much lower adsorption energy. This latter category is attributed to the aluminol sites.

In 1985, Dashidaira Dam, equipped with a flushing gate, was built on the Kurobe River in Toyama, Japan. Since the dam sediments were first flushed out in December 1991, benthic fish counts have decreased year by year due to repeated flushing of clay-rich dam sediments.

In June 2001, the flushed dam water contained a low oxygen concentration (1 to 2 mg/l) and high concentrations of smectite and vermiculite. To establish the cause of the death of the benthic fish, living flatfish were collected from Toyama Bay in order to examine their gills, which showed tissue damage and chemical changes caused by adherent expandable clays, derived from the flushed dam sediments. For comparison, exposure experiments on rainbow trout were carried out using smectite suspensions. Examination by optical microscopy revealed that the gills had shrunk because of the smectite concentrations. Low oxygen concentrations and large amounts of expanding clays have a significant effect on downstream benthic life.