Silicon Recovery Via the Acid Leaching of a Si-Ca-Al Alloy Produced by the SisAl Process

Abstract

The sustainable production of high-purity silicon is one of the greatest concerns in the solar industry. The SisAl process is an alternative and innovative approach to produce high-purity silicon based on aluminothermic reduction of silica in slags. In the present work, a Si-Ca-Al alloy was produced through SisAl aluminothermic reduction and further purified through acid leaching. The main precipitates of the Si-Ca-Al alloy were determined as CaSi2 and CaAl2Si2 with minor other metallic phases embedded inside. The alloy was further crushed and milled for leaching experiments using hydrochloric acid under magnetic stirring. The concentration of impurities before and after leaching experiments were measured by inductively coupled plasma mass spectrometry (ICP-MS). After 3 hours leaching, 97.5% Ca, 97.1% Al, and 79.8% P were removed, while the silicon purity was upgraded from 75% to over 99%.

Keywords: Silicon, Impurity, Acid leaching, Purification, Microstructure