Abstract
A zero emission process was established by treatment of a spent liquor resulting from frequent pickling of copper alloy rods in sulfuric acid. The spent liquor contains 35 g l(-1) copper. 25 g l(-1) zinc, 1.1 g l(-1) chromium, 35 g l(-1) sulfuric acid, and 135 g l(-1) total sulfate. These pollutant materials, if discharged directly into water bodies, pose acute environmental and ecological problems. Recovery and separation of these metals have been studied. The solvent extraction technique was applied to separate copper selectively using 10% Acorga 5640 in kerosene, at pH 2.0 for 10 min. Three extraction stages with an organic/aqueous (O/A) phase ratio of 4/1 were applied for efficient removal of copper from the aqueous phase. A copper-loaded organic solution was stripped using 3 M sulfuric acid. Pure copper was obtained from the strip solution by electrowinning. From the raffinate. chromium was recovered as chromic III hydroxide at pH 5-6 by adding ammonium buffer solution (NH4OH/NH4Cl). Zinc was precipitated from the resulting solution either as carbonate or as sulfide by using ammonium carbonate at pH 7.6 or ammonium sulfide at pH 9, respectively. Ammonium sulfate by-product was crystallized from the final solution. At the optimum conditions, almost all contents of metals were recovered. (C) 2001 Elsevier Science Ltd. All rights reserved.