Preparation of aluminium fluoride

Abstract

The paper describes a method for preparation of aluminium fluoride using fluorspar as starting material. Fluorspar is digested with sulphuric acid, ammonium sulphate and boric acid when fluoboric acid and gypsum are formed. Fluoboric is separated from the resulting gypsum slurry and neutralized with hydrated alumina and ammonium carbonate. The double salt ammonium aluminium fluoride separates out. This is filtered and dried. The dried double salt is then reacted with ignited alumina to convert it fully to aluminium fluoride in dry state. The boric acid liberated during the neutralisation with hydrated alumina is cycled back to the leaching stage. The carbon dioxide evolved during neutralisation and ammonia released during reaction of the double salt with ignited alumina may be recovered to form ammonium carbonate to be recycled to neutralisation stage. Calcium sulphate is obtained as a by-product from the digestion of fluorspar. The process is applicable to metallurgical grade fluorspar low in iron. (Shri M.L. Dey, Senior Technical Assistant and Shri Gurdial Singh, Scientist, National Metallurgical Laboratory)