Electrorefining of Silicon Using Molten Salt and Liquid Alloy Electrodes

Abstract

A new Si refining process, which employs molten salt electrolysis and precipitation steps, is proposed and tested. In this process, impure Si is added to a Cu-Si liquid alloy anode, and the electrorefining of Si is conducted using an Al-Si liquid alloy cathode in a fluoride-based molten salt. From the obtained Si-enriched Al-Si alloy, purified Si is obtained by precipitation. A glow discharge mass spectrometry analysis revealed that the proposed process can effectively remove the dominant impurities such as Fe, Mn, Ti and V from metallurgical grade Si (98–99% purity). A preliminary electrolysis using Si cells recovered from a commercial photovoltaic module, of which the dominant impurities are Ag, Al and Na, showed that the present process is also applicable for Si recycling from waste photovoltaic modules.