Choosing the Reagent to Leach Fluorine from Spent Pot Lining of Aluminum Electrolysis Cells

Abstract

The production of aluminum by electrolysis of cryolite-alumina melts is associated with generation of process waste including gas cleaning sludge, electric filter dust, coal flotation tailings, and spent pot lining (SPL). Most of this waste is then stored in sludge fields, deteriorating the environment near aluminum works. 30 to 50 kg of spent pot lining is produced per ton of Al. The authors’ research was dedicated to finding the best reagent for solvent extraction of valuable components (fluorine in particular) in the process of SPL hydrometallurgy. To that end, the research team sampled carbon parts of lining at the RUSAL Bratsk facility in Shelekhov, Irkutsk Oblast. The following reagents were tested: 2 wt.% solutions of sulfuric acid and sodium hydroxide. Leaching lasted 60 minutes in each experiment. 2% H2SO4solution was found to release fluorine at a higher rate. However, the resulting liquors contained sulfates, which might negatively affect the service life of equipment; for this reason, 2% NaOH solution was chosen for further leaching of fluorine from spent carbon parts of lining.