Mineralogical and geochemical characteristics of Belevi clay deposits at Denizli, SW Turkey: industrial raw material potential

Abstract

The present article addresses the potential usability of the Belevi clay from the Denizli region as a raw material in different ceramic applications and industrial products by investigating their mineralogical (X-ray diffraction), chemical (X-ray fluorescence), thermal (differential thermal analyzer-thermogravimetry), physical, firing, and geotechnical characteristics. For this context, cylindrical samples have been prepared and fired from 700 to 1200 °C; the mineralogical transformations during the firing process were obtained by X-ray diffraction. After that, linear firing shrinkage, bulk density (BD), water absorption (WA), unconfined compression strength (UCS), and ultrasonic pulse velocity (Vp) values of all of the samples were measured. In mineralogical point of view, samples were considered smectitic clays (56%) and rarely chlorite, illite, and kaolinite. In addition, calcite, quartz, feldspar, and dolomite minerals are observed in small quantities. Chemically, the major oxides of Belevi clay consist of SiO2, Al2O3, and Fe2O3 and characterized by higher CaO contents. The studied samples are generally composed of fine particles (clayey-silty). The plasticity indices (PI) are determined with a high value as 19%; this suggests that the studied clays are highly plastic raw materials. Samples with the particle size < 2 μm are abundant in clay deposits (∼ 20%), which is suitable for the ceramic applications. The presence of silt fraction in Belevi clay material can be eliminated by crushing and sieving. The main transformations during firing processes of the samples were determined at 900 °C together with the appearance of new crystalline phases especially anorthite, diopside, gehlenite, and hematite. An increase in the firing shrinkage and bulk density values with decrease in water absorption values is determined at 1000 °C and above. UCS and Vp values are also started to increase significantly from 900 °C due to mineralogical transformation. Technical tests show that Belevi clays are suitable in manufacturing of porous structural ceramic products such as brick and tiles, and also in pottery production.