Recovery of silicon powder from kerfs loss slurry using phase-transfer separation method

The recovery of silicon powder from the kerfs loss slurry, which consists of Si and SiC particles, metal fragments, and a glycol solution, produced in the silicon wafer slicing process was studied using the phase-transfer separation method. Two stages of phase-transfer separation, which take advantage of the difference in a surface property between the Si and SiC particles after acid washing, were carried out to recover the Si particles from the powder mixture. In either stage of separation, an oil was added to an aqueous slurry of the two particles. The larger SiC particles were removed in the first stage to obtain a Si-rich powder, which was then subject to a second-stage operation to remove the submicron SiC particles. The effects of the operating variables on the purity and recovery of the Si product were investigated, including the pH value of the water phase, oil/water volume ratio, and solid concentration. The best result obtained was 71.1% in overall recovery and 99.1 wt% in Si purity.