SEPARATION OF ZINC FROM MANGANESE BY SOLVENT EXTRACTION FROM ACIDIC LEACHATES OF SPENT ZINC-MnO2 DRY CELLS USING NEUTRAL ORGANOPHOSPHORUS EXTRACTANTS

This paper describes a route for recovering manganese and zinc from spent zinc-MnO 2 dry cells via acid leaching using sulfuric or hydrochloric acids as leachants. Hydrogen peroxide was added as reductant. Experiments were run at 25-40 o C for 1-3 h. Under the best optimal conditions, over 97.5 wt.% of zinc and manganese were leached by both acids. Zn(II) was best extracted at high free acidity ( 1 mol L -1 ) with tributylphosphate (TBP) or trialkylphosphine oxides (Cyanex 923) diluted in n-heptane. Cyanex 923 was a better extractant than TBP, and the extraction was better performed in hydrochloric leachates. Mn(II) was more co-extracted from hydrochloric leachates and when Cyanex 923 was the extractant, but was easily scrubbed with dilute leachant (~1-2 mol L -1 ). Zn(II) striping was possible using 5 mol L -1 HCl or H 2 SO 4 . Manganese was precipitated as oxalate (MnC 2 O 4 .2H 2 O), free of leached contaminants. High-purity sodium salts of the anions of the leachants were recovered after slow evaporation of the final solution.