Effect of oxidizing agents on the hydrometallurgical purification of metallurgical grade silicon

The effects of two different oxidizing agents viz. ferric chloride and ammonium persulfate on the purification of metallurgical grade silicon (MGSi) by leaching with hydrochloric acid were investigated as a function of temperature, particle size and hydrochloric acid concentration. It was found that the addition of oxidizing agent improved the extraction of impurities from the MGSi as compared to that in the absence of any oxidizing agent. The extraction of impurities from the MGSi increased with a decrease in particle size and increase in temperature and hydrochloric acid concentration. By leaching MGSi with 10 M hydrochloric acid in the presence of 0.1 M ferric chloride and at 90 °C a maximum of 66% Ca, 92% Cr, 27% Fe, 98% Cu, 98% Ni and 89% Zn were removed. The unleachable Si-Fe and Si-Fe-Ti phases in the grain boundaries of MGSi hindered the extraction of Fe and Ti.