Recovery and Purification of Silicon From Diamond Wire Saw Wasted Silicon Powder by a Technique of Induction Smelting Followed by Directional Solidification

Abstract

A technique of induction smelting followed by directional solidification to recover and purify silicon from diamond wire saw waste silicon powder without the use of additives is presented herein. The silicon reaction and the effect of smelting time on the removal of impurities from silicon powder waste were investigated using a simple induction smelting and directional solidification method. Through the detection of byproducts and condensed volatiles, it is inferred that Si is volatilized and removed as silicon monoxide during smelting. Byproducts containing Si, SiC, or SiO2 phases can be generated by the reaction between silicon monoxide and graphite crucible after volatilization. Because the crucible is sealed with byproducts, the flow of volatile materials in the crucible disrupts the mass transfer balance in the silicon melt. The amount of residual impurities in silicon ingot trends downwards with the extension of smelting time. A 99 pct oxygen removal rate was obtained after the material was smelted three times. The silicon ingot achieved the lowest impurity content after smelting for 4 hours. The silicon powder waste can be potentially used as a metallurgical-grade silicon product after a simple one-step induction smelting process. Further purification of the silicon ingot by directional solidification can reduce residual impurities to 74 ppmw.