Separation and recovery of heavy metals from hydrometallurgical effluents by solvent extraction

The possibility of separating and recovering heavy metals from hydrometallurgical effluents by successive solvent extractions has been investigated by two different procedures with liquid waste from the Espindesa Zn process. The waste (pH value approx 1.5) includes significant amounts of Zn ( approx 1.35), Cu ( approx 0.12), cobalt ( approx 0.32) and Mn ( approx 0.6 g/l) in the presence of big concentrations of macroconstituents (sulphate, chloride, Na) and Fe ( approx 8.8 g/l, mostly as Fe(II) salts). As extractants, Amberlite La-2 (a secondary ammine, as chlorohydrate), and DEPHPA (di-2-ethylhexyl-phosphoric acid) at 25 vol.% in kerosene were selected. The first method includes two extraction stages with LA-2 for Zn and Cu separation (the last one with 60 g/l of chloride ions) and three stages with DEPHA at pH values near to 1.5, 2.0, and 3.5 for isolating Fe, Mn, and Co. The second method separates firstly Fe (as ferric salts) with DEHPA. Afterwards, one stage with LA-2 isolates Zn and three stages with DEHPA at pH values near to 2.0, 3.0, and 3.5 lead to fractions rich in Mn, Cu, and Co. Reextractions from organic layers with water or HCl at different concentrations lead to purer solutions of the isolated metals. With both methods, the liquid waste can be converted into a saline solution with lesser problems for disposal. Graphs. 5 ref.--AA