Multi-potential electropurification of a reusable CaCl2-CaF2 eutectic salt for solar-grade Si electrorefining

Molten-salt electrorefining is a promising technique for energy-efficient production of ultrapure solar-grade Si. This work focuses on electropurification to remove impurities from an eutectic CaCl2-CaF2 molten salt for solar-grade Si. Both an as-received salt and a salt used for Si electrorefining have been electropurified by a field-enhanced process and the impurity concentrations before and after purification have been characterized by inductively-coupled plasma mass spectrometry and cyclic voltammetry. More importantly, a new multi-potential electropurification process, enabled by the three-electrode electrolyzer, has been proposed and proven to be more effective in removing all the impurities in the molten salt than a single-potential process. The salt after Si electrorefining has been regenerated to its original purity level before Si electrorefining by the multi-potential process, demonstrating the feasibility of a reusable salt by electropurification.