Study on the kinetics of iron removal from silicon diamond-wire saw cutting waste: Comparison between heterogeneous and homogeneous reaction methods

Silicon powder waste (SPW) from diamond-wire saw cutting process has a very low content of boron and phosphorus. Therefore, it is a promising and precious raw material for producing SoG-Si. The SPW also contains iron impurities which were from the worn of cutting wire during the silicon wafer producing process. Since the presence of iron will affect the quality of the silicon products, it is essential to remove the iron from SPW. In this paper, the removal of iron from SPW by acid leaching was researched and its kinetics were investigated by the heterogeneous and homogeneous reaction methods. Diluted sulfuric acid was selected as the leaching agent. The leaching parameters were optimized, i.e., temperature 60 °C, acid concentration 12%, liquid-solid ratio 10 mL/g and stirring speed 200 rpm. Under the optimized conditions, the removal rate of iron could reach 94.34%. It was found that the iron removing process can be divided into two stages. In both of the stages, the leaching process was controlled by second order rate of homogeneous reaction model, and the activation energy are 10.78 kJ/mol and 35.97 kJ/mol, respectively.