Characterization of waste clay from the Sardes (Salihli) placer gold mine and its utilization in floor-tile manufacture

The aim of this work was to evaluate the use of Sardes waste clay (SC) from the Pomza Export placer gold mine at Sardes (Salihli), Turkey, as secondary raw materials in ceramic floor tiles. To obtain consistent quality, we monitored the physical and chemical properties of SC and fabrication conditions. Once SC was demonstrated to be acceptable as a secondary raw material, laboratory and industrial tests were conducted to understand the reaction mechanisms during firing and to determine the chemical, mineralogical, and technical properties of the reagents and products. The mineralogical composition of SC is dominated by quartz, plagioclase, K-feldspar, hematite, calcite, and clay minerals (muscovite–illite, chlorite, kaolinite, and smectite). Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis (TGA) analyses of SC from Aksay (Aksay, E.K., 2005. Determination of the technological properties of the İzmir-Menderes Pumice Ores as an industrial mineral. Ph.D. Thesis, Dokuz Eylül University, The Graduate School of Natural and Applied Sciences, Mining Engineering Department, Izmir, Turkey) show comparable peaks and curves to those obtained for illitic clays. We compared the chemical compositions of the waste clay with those of other red-firing Aegean clays. The physical properties (water absorption and contraction) of SC were assessed after firing separately at temperatures of 950, 1000, 1050, 1100, and 1150 °C. Ceramic characteristics were determined from pressed bodies, using four elevated firing temperatures (1140, 1160, 1180, and 1200 °C) for samples with 5, 10, 15, and 20 wt.% SC additions to a commercial floor-tile batch. We also assessed the physical properties of the fired and the unfired tiles, including water absorption, drying and fired shrinkage, and bending strength. Based on the technological characteristics of the resulting ceramic material, the batch with 10 wt.% SC addition was the most promising composition.