Comparative leaching of spent zinc-manganese-carbon batteries using sulfur dioxide in ammoniacal and sulfuric acid solutions

摘要

The non-magnetic fraction of spent zinc-manganese-carbon batteries containing 20.8% Zn, 22.7% Mn, 2.65% Fe, and <0.1% Hg, Ni, Co, Cu and Pb was leached in H_2SO_4, H_2SO_4/SO_2, NH_3 and NH_3/SO_2 at 30-60℃. In acid media the complete dissolution of zinc is unaffected by SO_2. However, the reductive role of SO2 increases the leaching of manganese in H_2SO_4 from 25% to 100% and iron from 1% to 25%. Literature results of leaching with other reductants are compared. The XRD analysis of leach residues from ammonia solutions shows the conversion of Zn_5(OH)_8Cl_2·H_2O in the feed to ZnO with low dissolution of zinc, manganese and iron. Low leaching of iron in NH_3/SO_2 is due to the formation of Fe(NH_4)_2(SO_3)_2 and Fe(NH_4)_2(SO4)_2 identified by XRD analysis of leach residues. However, the formation of Zn(NH_3)_4~(2+) facilitates the selective leaching of zinc in buffered SO_2/NH_3 solutions that contains NH_4~+. Complete dissolution of copper also occurs in both H_2SO_4/SO_2 and NH_3/SO_2. The dissolution of mercury by H_2SO_4 is retarded in the presence of SO_2, and enhanced by NH_3/SO_2. Lead remains insoluble in all media, whilst the partial dissolution of nickel and cobalt is retarded by NH_3/SO_2.