Abstract: The invention provides a process for the separation of a strong mineral acid from other species present in an aqueous solution and the recovery thereof. The process comprises the steps of: (a) bringing an aqueous solution containing the mineral acid to be separated into contact with a substantially immiscible extractant phase, whereupon the mineral acid to be separated selectively and reversibly transfers to the extractant phase; (b) separating the two phases; and (c) backwashing the extractant phase with an aqueous system to recover substantially all the mineral acid contained in the extractant phase. The special extractant phase used comprises a strong organic acid which acid is oil soluble and substantially water immiscible both in free and in salt form, an oil soluble amine which amine is substantially water insoluble both in free and in salt form and a carrier solvent for the organic acid and amine, the molar ratio of the organic acid to amine in the extractant phase being between about 0.5:2 and 2:0.5.