Dissolution of sphalerite (ZnS) in acidic ferric sulfate solution in the presence of manganese dioxide

Abstract

This paper describes a new approach for examining the kinetics and mechanism of zinc dissolution from sphalerite concentrate in acidic ferric sulfate solution in the presence of manganese dioxide. A literature search was performed to access the possible action of the two oxidizing agents, i.e., ferric ion and manganese dioxide. The possibility of galvanic coupling between ZnS and MnO2 and the cyclic action of the redox couple, Fe2+/Fe3+, on these two minerals were theoretically examined based on corrosion principles. Expressions for the mixed potential (E-m,) and the mixed current (i(m)), were derived for the relevant corrosion and galvanic couples. Leaching experiments were conducted to establish which of the above phenomena is operative during leaching. The results indicated that the dissolution mostly occurs by the action of ferric ion on ZnS producing ferrous ions. The presence of MnO2 enables a quick conversion of ferrous to ferric, which maintains the rate of Zn dissolution. The process has promising features for commercial exploitation.