Direct Leaching of Low-Grade Zinc Oxide Ore Containing High Amounts of Iron and Manganese

Consumption of zinc metal has been rapidly increased in the world. Zinc metal exists as oxide, sulfide, carbonate and silicate ores, among which zinc oxide ores have not been mined because it is very difficult to separate zinc from gangue or to concentrate using the conventional flotation processes. In the current study, a low-grade zinc oxide ore containing 5.9% Zn, 33.4% Fe and 13.7% Mn was selected to investigate direct leaching. Results of the direct leaching at conventional conditions showed that the Zn leaching efficiency was improved at high acidity, high temperature and grinding conditions and reached about 60% at temperature of 50 °C, d80 of 110 microns, leaching time of 120 min and sulfuric acid consumption of 3.3 kg/kg Zn. Results showed that between 20 and 30% of zinc is associated with other species containing manganese IV. In the reductive leaching experiments by using Na2SO3 as reductant, the maximum Zn and Mn leaching efficiencies are about 82.7% and 96.2%. Dissolving high manganese as impurity in the pregnant solution is a potential concern with the reductive leaching process that needs further investigation.