Electrolytic Production of Silicon Using Liquid Zn Alloy Cathode in Molten CaCl₂

Abstract

A new electrolytic production process for solar-grade Si has been proposed utilizing a liquid Si–Zn alloy cathode in molten CaCl₂. The process consists of three major processes: electrolysis, precipitation, and refining. One of the advantages of the process is the attainability of high purity by application of a solidification refining from the liquid Si–Zn alloy. The residual zinc is easily removed afterwards due to its high volatility. To establish this process, the behavior of liquid Zn metal in molten CaCl₂ at 1123 K was investigated. Evaporation of Zn metal was largely suppressed by immersion into the molten salt, which enabled the use of a Zn electrode despite its high vapor pressure. Based on the results of cyclic voltammetry, the reduction of SiO₂ on a liquid Zn cathode was conducted by potentiostatic electrolysis at 0.9 V vs. Ca²⁺/Ca. Precipitated Si particles were recovered in the solidified Zn matrix.