DISSOLUTION OF SPHALERITE (ZNS) IN ACIDIC FERRIC SULFATE-SOLUTION IN THE PRESENCE OF MANGANESE-DIOXIDE

This paper describes a new approach for examining the kinetics and mec hanism of zinc dissolution from sphalerite concentrate in acidic ferri c sulfate solution in the presence of manganese dioxide. A literature search was performed to access the possible action of the two oxidizin g agents, i.e., ferric ion and manganese dioxide. The possibility of g alvanic coupling between ZnS and MnO2 and the cyclic action of the red ox couple, Fe2+/Fe3+, on these two minerals were theoretically examine d based on corrosion principles. Expressions for the mixed potential ( E-m,) and the mixed current (i(m)), were derived for the relevant corr osion and galvanic couples. Leaching experiments were conducted to est ablish 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 expl oitation.