Potential use of the lower cretaceous clay (Kef area, Northwestern Tunisia) as raw material to supply ceramic industry

The aim of this study is to evaluate the potential use of clay deposits from northern Tunisia (Albian system) for the manufacture of bricks and ceramic tiles. Clay samples were collected from the Slata study site to the north of the Kef district, Tunisia. Chemical composition by atomic absorption spectrometry (AAS) showed that these clays were mainly composed of silica (33%), alumina (15%), iron oxide (6%) and minor amount of potassium oxide (3%). Mineralogical analysis by X-ray diffraction (XRD) confirmed the results of AAS; it showed reflections of quartz, calcite, kaolinite (65-70%) and illite (15%) associated with low percentage of interstratified illitesmectite (5%). After firing near 900 degrees C, new mineralogical species such as mullite, anortite and spinel appeared due to several temperature-dependent transformations. Further analysis indicated that plasticity index (PI) ranged between 16 and 20%. Geotechnical and thermal tests have shown acceptable values of drying shrinkage (3%), firing shrinkage (10%), water absorption (8.9-15.9%) and a very high mechanical bending strength (17-20 MPa) indicating non refractory clays. Those results further confirmed the potential application of the Albian clays from Slata site in ceramics.