Patent ID: 6893474

Claim:
A method of purifying a metal salt from inorganic impurities in an aqueous solution thereof, said metal salt being crystallized from said aqueous solution of said metal salt when supersaturated with the same and said inorganic impurities are dissolved therein, crystals of said metal salt subsequently being separated from said aqueous solution, wherein said aqueous solution is a non-saturated or saturated solution of said metal salt and is provided with an inorganic component, which is more easily soluble in said aqueous solution than said metal salt, said more easily soluble component being sulphuric acid, which inorganic component is added in such an amount that said aqueous solution becomes supersaturated with said metal salt, crystals of said metal salt as the more sparingly soluble component being displaced from said aqueous solution, wherein a first aqueous metal salt solution of a raw material containing impurities of salts of at least one more noble metal than the metal dissolved therein, is reduced adding metallic aluminium to said first aqueous aluminium salt solution, adding at least one chloride salt in order to activate said metallic aluminium, said at least one more noble metal salt being reduced to its metallic form; and separating said reduced at least one more noble metal from said first mixture, to form an aqueous metal salt solution, which forms the basis for the supersaturation step.