Investigation of Na2CO3–CaO–NaCl (or Na3AlF6) additives for the remanufacturing of silicon from diamond wire saw silicon powder waste

Abstract

The demand for high-quality silicon for solar cell preparation will continue to grow due to shortages of silicon feedstock driven by the photovoltaic industry. Consequently, the silicon lost in diamond wire saw silicon powder waste during silicon wafer production must be recovered for silicon production. Depending on the current yield of silicon and level of residual impurities, an optimization treatment for the increase of the recovery rate and purity of silicon collected from diamond wire saw silicon powder should be further developed. In this study, NaCl and Na3AlF6 are designed as additives to optimize Na2CO3–CaO to increase the silicon recovery rate and purity. The action mechanisms of NaCl and Na3AlF6 for silicon recovery and the removal of metal during the direct smelting process are investigated. It is found that NaCl and Na3AlF6 improve the silicon migration channels and stabilize the impurities in slag by reducing the slag viscosity and tuning the slag composition. After induction smelting at 1823 K for 2 h with the furnace feed mass ratios of Na2CO3:CaO:NaCl = 12.8:1.7:8.6 and Na2CO3:CaO:Na3AlF6 = 12.8:1.7:8.6, the obtained silicon recovery rates were respectively 76.39% and 79.25%, and the silicon purities were respectively 99.985% and 99.986%. Therefore, NaCl and Na3AlF6 could be used as potential additives to promote the efficient remanufacturing of silicon collected from diamond wire saw silicon powder waste, and are technically and economically feasible for large-scale application.