Patent ID: 6231822
Filing Date: 2001-05-15
Classification: C01B,C01C,C01F,C03C,C04B,C22B,Y02P,Y02W

Abstract:
A method of recovering chloride salts including at least one of calcium chloride, iron chloride and magnesium chloride from spent potliner material from aluminum reduction cells, which spent potliner material includes a material selected from the group consisting of fluoride compositions, cyanide compositions, iron compositions, calcium compositions, magnesium compositions, alumina, carbon, silica and sodium sulfate, the method comprising the steps of:(a) contacting the spent potliner with acid in an acid digester to produce a gas component containing at least one gas selected from the group consisting of HF and HCN and a slurry component comprised of solids and an acid solution containing soluble salts of at least one of Ca, Fe and Mg, the solids comprised of alumina, carbon and silica;(b) removing said gases from said digester;(c) separating said acid solution from said solids;(d) mixing said acid solution with an alcohol to precipitate soluble salts contained therein to provide a salt precipitate and alcohol solution;(e) filtering said salt precipitate from said alcohol solution to provide a filtered salt precipitate;(f) adding water to said filtered salt precipitate to dissolve said filtered salt precipitate to provide a dissolved salts liquid;(g) adjusting the pH of said dissolved salts liquid by adding sodium hydroxide thereto to form soluble sodium aluminate, and an insoluble material comprised of Ca(OH).sub.2, Fe(OH).sub.2, and Mg(OH).sub.2 ;(h) separating soluble sodium aluminate from said insoluble material to provide a sodium aluminate solution; and(i) treating said insoluble material with hydrochloric acid to recover CaCl.sub.2, FeCl.sub.2 and MgCl.sub.2 from said spent potliner.