Process for Solar Grade Silicon Production by Molten Salt Electrolysis Using Aluminum-Silicon Liquid Alloy

Abstract

A new process for solar grade silicon production by molten salt electrolysis has been proposed and its feasibility discussed. This process consists of an electrolysis step of SiO2 dissolved in a fluoride melt using an aluminum-silicon liquid alloy cathode and a precipitation step of silicon from the liquid alloy. According to the calculation based on literature data, the proposed process has the possibility to produce solar grade silicon in combination with directional solidification, even if the electrolysis step has no purification effect. A preliminary electrolysis using aluminum cathode and carbon anode in a NaF-AlF3-SiO2 melt at 1273 K revealed that silicon was formed by the electrolysis and that sub-reactions, such as the reduction of SiO2 by aluminum and metal fog formation, also took place. Especially, SiO2 reduction by aluminum was found to be fast compared to the reduction by the electrolysis, which made it difficult to evaluate the current efficiency. Thus, these sub-reactions were further investigated in order to measure the reaction rates, and their potential dependence. Based on the obtained data, the cathodic current efficiency during the preliminary electrolysis was evaluated to be greater than 46%.