Recycling of carbonized rice husk for producing high purity silicon by the combination of electric arc smelting and slag refining

Abstract

In this study, the combination of electric arc smelting and slag refining was employed to produce high purity silicon from Carbonized rice husk (CRH) and silica sand. CaO-SiO₂-CaF₂ were selected as the slagging agents. Firstly, the CRH was mixed with silica sand and slagging agents. Secondly, the mixed raw materials were pelletized and then melted in an experimental electric arc furnace. Thirdly, the cooling graphite crucible was dissected and divided into four parts, i.e., the loose granular zone, skull zone, cavity zone and product zone. Samples were taken from these four parts and analyzed to study the silicon producing mechanism. It was found that the silicon was produced mainly in the skull zone, and silicon with a purity of 96.97% was obtained at the product zone. By adding slagging agents during the smelting process, the impurities in silicon, i.e., Fe, Al and P were reduced thoroughly from 2.06%, 1.33%, 0.09% to 1.04%, 0.08%, and 0.04%, respectively. The results indicate that adding slagging agents CaO-SiO₂-CaF₂ can remove the impurities effectively from silicon. After acid leaching, the purity of the silicon can reach up to 99.9%.

Keywords: Carbonized rice husk; Carbothermal reduction; Electric arc smelting; High-purity silicon; Slag refining.