Mineralogical study of kaolinitic clays from Sidi El Bader in the far north of Tunisia

The study concerns kaolinitic clay deposits occurring at Sidi El Bader, near Tabarka, north of Tunisia. At this site, clay is mined for the manufacture of the renowned Nabeul pottery. Two clay samples, SB1 and SB19, were selected that represent the lower and upper part of the quarry section, respectively. The clay deposits at the base of the quarry are brown whereas the clay deposits at the top are white to beige. These clays are associated with the Numidian Flysch of the Kroumiries mountain chain. The data from several analytical techniques (XRD, chemical analysis, SEM, infrared absorption spectroscopy, thermal analysis (TG/DTA) and optical proprieties) reveal that kaolinite and illite are the dominant clay minerals. Quartz and trace amounts of titanium oxide are also present. The size of clay particles of sample SB1 is about 2 mu m and their shape is sub-rounded, which suggests low crystallinity. In contrast, the size of clay particles of sample SB19 is up to 6 mu m and particles are elongated pseudo-hexagonal flakes consistent with higher crystallinity. This sample contains a lower content of Fe(2)O(3) and TiO(2) compared with the SB1 clay sample. The higher amounts of impurities including illite, titanium oxide and iron affect the whiteness and may also reduce the size and the crystallinity of the clay platelets from the clay deposits of the lower part of the quarry. The lowermost poorly crystalline kaolinite could be used for the fabrication of various ceramics (pottery and binding materials, as bricks and tiles). This clay may also be useful in environmental protection by immobilizing pollutants. The uppermost more crystalline kaolinite may be suitable for processing to produce a kaolin that meets specifications for industry fillers and other uses that demand high whiteness and low impurity contents. (C) 2007 Published by Elsevier B.V.