Electrorefining of Metallurgical Grade Silicon in Molten CaCl₂Based Salts

Electrorefining of metallurgical grade silicon was studied in molten CaCl 2 -NaCl-CaO-SiO 2 (80:10:5:5 mol%) at temperatures from 1123 to 1223 K. A liquid anode prepared by alloying the metallurgical grade silicon with copper (31 mol% Si and 69 mol% Cu) was used to prevent the anode passivation problems and improve the purity of the produced silicon. Electrochemical studies of silicon deposition were performed, and the diffusion coefficient of Si (IV) was calculated. Analysis results indicated that the contents of boron and phosphorus in the refined silicon obtained by potentiostatic electrolysis were reduced from 36 ppmw and 25 ppmw to 0.27 ppmw and 0.89 ppmw respectively. The corresponding current efficiency and energy consumption were estimated to be 72% and about 2 kWh (kg of Si) −1 . These promising results show that the present electrorefining process is an alternative way to produce high purity silicon for solar cell applications.