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The rheological and filtration properties of a Tunisian clay are presented and compared with those of Wyoming bentonite. The study was part of an evauation of Tunisian mining resources in general, and of the bentonitic deposits in particular. Qualitatively, the two clays exhibit the same rheological and filtration behaviour but quantitatively the properties of purified Wyoming bentonite are distinctly better at the same concentration. The difference can be related to the mineralogical structure and the presence of 13% illite in the Tunisian clay. Standard tests show that the rheological behaviour of the purified Tunisian clay is close to that of the raw Wyoming bentonite and conform to the American Petroluem Institute (A.P.I.) standards for medium-depth drilling formulations.
A clayey soil from southern Tunisia has been studied in order to assess its possible use as an anti-pollution barrier. The soil has been characterized from both geotechnical and physicochemical points of view. The physicochemical characterization was carried out using X-ray diffraction, thermogravimetric and differential thermal analyses, specific surface area and cation exchange capacity measurements. Hydration tests were carried out using oedometers to determine the swelling behaviour of compacted specimens under different stress conditions. The large swelling pressure (420 kPa) is in agreement with the mainly smectitic character of the soil highlighted by the physicochemical tests. The changes in the fabric of the soil and in its porosity after the hydration tests were investigated using the same physicochemical methods, and related to the macroscopic hydro-mechanical properties. X-ray diffraction and mercury intrusion measurements show that there are changes in the interlayer spacing, particle size and inter-aggregate pore distribution. Comparing the properties of the soil with the Belgian guidelines for the construction of anti-pollution barriers showed that the material was suitable for that use.
The behaviour of clays is not still well understood. Most information
concerning clays has been obtained by techniques which give statistical
information on the structure and chemistry. However papers have reported
results from scanning and high resolution electron microscopy. This work
presents a nanoscopic approach, using electron energy loss spectroscopy
(EELS), of different purified clays. EELS permitted to detect all the
elements found by classical chemistry at a macroscopic level. In particular
it made it possible to determine the Si/Al ratio in kaolinite (Si/Al ~ 1), smectite and illite (Si/Al ~ 2). In all the cases, the K edge
oxygen energy loss near edge structure (ELNES) is often similar to that of
other clays we studied, but a strong heterogeneity has been observed. It was
also possible to highlight an influence of the presence of iron on the
profile of the oxygen peak.
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