Industrial & Engineering Chemistry Research, Vol.51, No.25, 8366-8377, 2012
Leaching of Spent Pot-Lining with Aluminum Anodizing Wastewaters: Fluoride Extraction and Thermodynamic Modeling of Aqueous Speciation
The cotreatment of spent pot-lining (SPL), a high fluoride (20 wt %), and cyanide (up to 1 wt %) waste generated in aluminum smelting, and Al3+ wastewaters generated by the aluminum anodizing industry was identified in this work as a treatment alternative that holds the potential to virtually remove the need for purchasing chemical reagents while keeping carbon dioxide emissions to a minimum. The process proposed involves fluoride leaching with anodizing wastewaters and precipitation of AlF2OH by treatment with caustic waste from the aluminum anodizing industry. AlF2OH can be directly injected into fluidized beds that are used to convert Al(OH)(3) to AlF3. Since AlF3 is used in primary aluminum smelting, aluminum and fluoride from aluminum industry wastes such as SPL and anodizing wastewaters are recovered in a form that can be readily used as a feedstock in the aluminum industry. In this paper, the results of SPL leaching studies using aluminum anodizing waste are presented together with a model of the solution equilibria, which has been used to interpret experimental observations. Mild leaching temperatures were used and no chemical reagents other than anodizing waste were necessary to extract the soluble fluoride.