Comparative yield stress determination for pure and interstratified smectite clays.

Different experimental devices and operative procedures were used to obtain the main properties of suspensions of two purified clays, a pure smectite and an interstratified illite-smectite natural clay, at different concentrations. The yield stress values derived from flow and creep tests were found to be very consistent, while those derived from dynamic tests were observed to be much more sensitive to experimental conditions. Qualitatively, the two clays exhibit the same rheological behaviour, which can be modelled using the Herschel-Bulkley model; their yield stress increases with clay concentration and they present a thixotropic character for low concentrations, with an inversion of the curves when the clay concentration increases. However, significant differences were observed when considering numerical values. For the same clay concentration in the suspension, the yield stress of the pure smectite is distinctly higher than that of the interstratified one. The rheological properties of the pure smectite clay can be related to the swelling properties and the organisation of the minerals in water, leading to three-dimensional strong but deformable structures. On the other hand, the presence of a small percentage of illite in the natural clay gives it a brittle behaviour which collapses more easily under stress

Fe-rich smectites from Gafsa (Tunisia): Characterization and pillaring behaviour

Three raw samples of Fe-rich smectites from Gafsa (Jebels Shemsi and Hammadi, Tunisia) have been characterized by different techniques which indicate that they contain (15-20%) illite, probably interstratified and to a lesser extent they also contain kaolinite, calcite, quartz and Fe oxides. These samples present a relatively high Fe content (∼9%) in the <2 ♂m fraction. From EPR and Mössbauer spectroscopy it is deduced that Fe is mainly present as Fe(III) in the octahedral environment of smectites and also in Fe-oxyhydroxides associated with the clays. Aluminiumpillared clays have been prepared from the Na+-purified samples, and their thermal stability and acidity have been studied

Physico-Chemical Characterizations of Tunisian Organophilic Bentonites

International audienceOrganoclays were prepared from two tunisian purified Na-bentonites using benzyltetradecyldimethylammonium chloride (C14) and benzyldodecyldimethylammonium chloride (C12). The added quantities of organic salts, expressed as a function of the clay's cationic exchange capacity (CEC), have been varied from 0.3 to 4 CEC. Two different methods were investigated in order to determine the influence of the preparation method on the adsorption properties:  on one hand, dry powder clay (method I) and, on the other hand, aqueous clay suspensions (method II) were mixed with the organic salt solutions. The adsorption of organic cations on clays was studied by adsorption isotherms, FTIR spectroscopy and X-ray diffraction. It appears that more salts are adsorbed in the clay interlayer space when using method II. The arrangement of salts within clay is rather complicated. It depends on clay composition, nature of tensioactive molecules, CEC of the clay, and preparation method. According to these parameters, the inserted surfactants can be arranged in monolayer, paraffin, or admicelles structures