Abstract: A process for treating an aqueous acidic solution containing a large amount of ferric ion and other metal ions such as a hydrochloric acid solution of manganese nodules, which includes contacting the aqueous solution with an organic extractant to selectively extract the ferric ion therefrom. The extractant is comprised of a dialkylphosphoric acid having 6-12 carbon atoms and a hydrocarbon solvent such as kerosene. The aqueous phase obtained after the extraction is then added with a pH-controlling agent to increase the pH thereof to a value so that unextracted ferric ion remaining therein may precipitate as ferric hydroxide while the other metal ions may be prevented from precipitating. Solid-liquid separation of the resulting mixture gives a solution having a ferric ion concentration of about 0.1 g/l or less. The pH-controlling agent is preferably an industrial waste containing a metal oxide or hydroxide such as a sludge from plating industries.

Abstract: A method for separating gold etc. from acid aqueous solution comprising a first step in which a silver amalgam with high silver content is added to acid aqueous solution containing gold to precipitate metallic gold, a second step in which silver amalgam with low silver content is added to the mother liquor from the first step to thereby separate silver amalgam in the mother liquor and a third step in which amalgam of base metal other than mercury is added to the mother liquor from the second step to thereby separate residual silver and mercury present in the mother liquor as a silver amalgam, or alternatively the mother liquor from the second step is electrolyzed by using mercury as a cathode to thereby precipitate residual silver and mercury present in the mother liquor as a silver amalgam on the cathode.