Hydrometallurgical stepwise separation of alumina and recovery of aluminum fluoride from waste anode cover material of aluminum electrolysis

Anode cover material holds marked importance owing to its effect of maintaining the thermal balance of aluminum reduction cells, and is categorized as solid waste because of its continuous accumulation. However, cover materials contain large amounts of alumina and fluoride; thus, can be considered for strategic resource recovery. This research has developed a process for separating alumina and recovering aluminum fluoride from anode cover materials by aluminum salt solution leaching. In the present work, the effects of different factors on the leaching behaviors of sodium and fluoride during aluminum salt solution leaching were investigated. The results showed that 98.1 % sodium and 95.1 % fluoride were extracted when the Al3+ concentration was 2.5 mol/L, the liquid to solid ratio was 20 mL/g, and the stirring speed was 300 rpm at 90 °C for 2 h. Aluminum and fluoride were then precipitated as aluminum hydroxyfluoride hydrate (AHF) from the leachate. The aluminum fluoride (AlF3) product with high purity was obtained by calcining AHF precipitation, and the average particle size was 66.1 μm. This work demonstrates significant application potential on green recycling of anode cover materials and realize a high-value utilization of aluminum and fluoride resources. This plays a crucial role in the life cycle assessment (LCA) of the anode cover material.