Improving flotation separation of micro Si/SiC particles from silicon sawing waste by surface hydrophilic modification

Abstract

Silicon sawing waste (MSW) produced by mortar cutting causes serious environmental issues and a waste of high-purity silicon. The major obstacle in the recovery of high-purity silicon (Si) is the separation of microscale Si and silicon carbide (SiC) in MSW. In this study, micro Si/SiC in silicon sawing waste was separated effectively by bulk-oil flotation after surface hydrophilic modification of Si particles. The structural evolution of micro Si surface after wet oxidization in water and acid was characterized by FT-IR, TEM, and XPS. Specifically, the wet oxidization process reduced the contact angle from 63 ± 0.3° to 18.5° of Si surface for the coating of an amorphous oxide with hydroxy groups on Si particles enhanced the wettability. The amorphous oxide layer with hydroxy coated on Si particles played a key role in enhancing the wettability of Si particles. The wet oxidization is essential to the subsequent flotation separation for the contact angle of SiC keeping at around 60.3°. The wettability of silicon sawing waste was further examined by the absorption of diesel. The effects of pH value and solid concentration on separation efficiency were studied. The best result obtained was 95% in Si recovery and 97.1 wt% in Si purity.