A novel process for producing Al-Si alloy utilizing aluminum-silicon oxide extracted from coal fly ash

Abstract

As a kind of solid waste rich in aluminum and silicon resources, the comprehensive utilization of coal fly ash (CFA) will be of great significance to reduce environmental pollution and improve economic benefits. This work proposed a facile and environmentally friendly cleaning process for producing Al-Si alloy by molten salt electrolysis from CFA extract, aluminum-silicon oxide (ASO). The dissolution behavior and dissolution reaction mechanism of ASO were studied by high temperature visual dissolution experiment, thermodynamics analysis and phase analysis. Due to the chemical reaction between ASO and cryolite-based melt, ASO powder dissolves rapidly in melt and the dissolution rate of ASO is not determined by the phase compositions but by the mass ratio of Al2O3/SiO2. For replenishing the oxide concentration in the electrolyte as quick as possible, the proper mass ratio of Al2O3/SiO2 is in the range of 0.75–7.5. The electrochemical co-reduction behavior of Si (IV) and Al (III) ions on the W electrode was performed by cyclic voltammetry and square wave voltammetry. The results indicated that the reduction of Si (IV) ion in the melt was a two-step irreversible process. Hypoeutectic Al-Si alloy and eutectic Al-Si alloy were prepared by galvanostatic electrolysis using ASO as raw material. This innovative technology can realize high-value recycling of CFA resources and low carbon emission, low energy consumption production of Al-Si alloy.