An Economical Approach for the Recycling of High-Purity Silicon from Diamond-Wire Saw Kerf Slurry Waste

Large amounts of solar-grade silicon were wasted as silicon powder waste (SPW) during the diamond-wire saw slicing process. In this paper, the SPW was purified by acid leaching, and the purified SPW was pelletized. Then the pellets were melted in induction furnace in air atmosphere to produce high-purity silicon ingots. Firstly, the SPW as raw material was characterized. The results show that the particle size of the powder is mainly in the range of 0.14 approximate to 8.71 m, the powder has a shape of thin flake, the contents of SPW are Si 83.99 wt%, silicon oxide 13.5 wt%, others 2.51 wt%, of which B (boron) 0.2 ppmw, P (phosphorus) 4.32 ppmw, and metallic impurities 16412 ppmw, respectively. Secondly, the SPW was purified by acid leaching and the leaching parameters were optimized, i.e. leaching time 80 min, temperature 60 degrees, acid concentration 25%, liquid-solid ratio 10 mL/g and agitation speed 200 rpm. Thirdly, the purified SPW was pelletized and then melted in induction furnace in air atmosphere. High-purity silicon ingots with Si 99.99%, B 0.16 ppmw and P 1.1 ppmw were produced. The slag mainly consists of 48.63 wt% Si, 43.51 wt% SiO2 and 7.86 wt% SiC. The high-purity silicon ingots can be used to produce aluminum silicon alloy and silicon nitride. And it is prospective to use the high-purity silicon ingots as the feedstock to produce solar grade silicon (SoG-Si).