Purification of metallurgical grade silicon by electrorefining in molten salts

Abstract

Electrochemical studies on silicon deposition were performed in molten salt electrolytes. Purification of metallurgical grade silicon by electrorefining was carried out in molten Si–chloride salts at temperatures from 973 K to 1223 K. It was found that the use of a liquid alloy anode of silicon and copper was beneficial in molten CaCl2 with NaCl, CaO and dissolved Si. ICP-AES analysis results showed efficient removal of metal impurities, such as titanium, aluminum and iron, which are present in significant quantities in the feedstock. The contents of boron and phosphorus in the silicon after electrorefining were reduced from 36×10−6 and 25×10−6 to 4.6×10−6 and 2.8 ×10−6, respectively. The energy consumption of electrorefining was estimated to be about 9.3 kW·h/kg.