Hydrometallurgical Processing of Spent Carbon Lining to Extract Valuable Components for Cryolite Production

Abstract

The technique of mathematical modeling using the Selector software package has been applied to study the leaching of fluorine from the carbon part of the aluminum electrolysis cell spent lining. Based on the model obtained, the effects of the solvent (caustic soda Na2Oку) concentration and the ratio of liquid and solid phases in the pulp on the fluorine extraction have been assessed. The research object was the lining samples by the RUSAL Krasnoyarsk JSC. A thermodynamic assessment of the spent carbon lining components behavior during the alkaline processing has been performed with the introduction of three solvent concentrations into the model: 12.5, 17.5, and 25.0 g/dm3. According to the model solutions, the maximum fluorine extraction (up to 90 %) is achieved when using a reagent with the Na2Oку concentrations of 12.5 and 17.5 g/dm3 and a liquid to solid ratio of 8.5÷10:1. Using the model, the phase composition of the cake and the forms, in which fluorine remains in the solid residue (cake), have been determined. Laboratory studies confirm the convergence of the simulation results with the experimental data: solutions have been obtained to crystallize out cryolite (with fluorine and silica content of 50–53 % wt. and 0.11÷0.53 % wt., respectively), which is in demand in the electrolysis of cryolite-alumina melts.