GB849010A - Method for manufacture of aluminium fluoride - Google Patents

Abstract

Oxidic aluminium - containing material is reacted at 38-88 DEG C with phosphate-contaminated fluosilicic acid, solids are removed from the reaction mixture, a quantity of a strong mineral acid sufficient to provide a normality of at least 0.5 is added and aluminium fluoride trihydrate low in phosphate content crystallised and removed from the solution. The alumina-containing material may be solid hydrated alumina or bauxite and may be added as a slurry; the phosphate-contaminated fluosilicic acid may be that obtained as a by-product of the reaction of phosphate rock with sulphuric acid or in the concentration of wet process phosphoric acid by absorbing the evolved gases in water or aqueous hydrofluosilicic acid. The aluminium to fluoride ion ratio in the reaction mixture is preferably at least 1:3 and up to 20% Al2O3 in excess of that required for this ratio may be added. If desired, a water-soluble ferric salt such as the sulphate may be added to the fluosilicic acid to precipitate some of the phosphate present, prior to the precipitation of fluoride. Acids mentioned are sulphuric, hydrochloric and nitric; the acid is preferably first used to wash the solids filtered from the reaction mixture. The crystallisation may be performed by allowing the solution to stand, or it may be maintained at 10-79 DEG C., and may be assisted by seeding. The recovery of aluminium and fluorine may be improved by reacting the mother liquor from the crystallisation with a further quantity of the aluminabearing reactant and crystallising the resultant aluminium fluoride directly by allowing to stand, with or without seeding. This second product is not as pure as the first. The trihydrate may be dehydrated by calcining at 232-316 DEG C. Reference has been directed by the Comptroller to Specification 643,379.