Synthesis and kinetics of titanium silicides from photovoltaic industry waste and steelmaking slag for silicon and titanium recovery

The increasing amount of silicon waste generated from the rapid developing photovoltaic industry calls for an economical silicon recycling process. The present work proposes a facile process with which silicon waste and ironmaking slag containing TiO₂ were used as raw materials to produce titanium silicides, a promising high added value material. The process was experimentally investigated in lab scale. The result shows that a high CaO/SiO₂ ratio in slag promotes the reaction. TiSi₂ and Ti₅Si₃ could be synthesized as principal products within 0.5 and 3 h with CaO/SiO₂ = 1.31 in mass, respectively. CaO-SiO₂ slag was produced as byproducts. Kinetic analysis indicates that silicon diffusion in slag is the rate-determining step of the reaction process. The reaction rate constant is around 1.0 × 10^-4 s, and the effective diffusion film thickness in slag side is around 10^-3 cm at the silicon-slag interface. Slag basicity is suggested to increase to 1.31 for a faster silicon diffusion and further promotion of the reaction rate.