Recovery of zinc from waste material using hydrometallurgical processes

A lead-zinc ore deposit in Balikesir/Balya, Turkey, was mined and abandoned almost 70 years ego. Nearly 1, 000, 000 tons of flotation tailings and 300, 000 tons of slag, which contain considerable amounts of zinc remain. In this study, an assessment of the technical feasibility of an acidic leach process for the recovery of zinc from slag was considered. The slag contained approximately 29% Fe, 13% Zn, 3% Pb and 2% S. Preliminary leach tests showed that it was not possible to achieve a selective and efficient extraction of Zn from the slag using low concentrations of H2SO4 and low temperatures. this result can be attributed to the proportions of zinc present as oxide and ferrite (Zn Fe2O4). This slag composition has a significant effect on treatment options because the oxide is soluble to a varying degree in most leachants, whereas ferrites tend to be insoluble. In order to increase the recovery using extraction, leaching tests were performed in two stages. Slag was first subjected to leaching, and residue was contacted with a hot and more concentrated sulfuric acid solution in order to dissolve the ferrite. The dissolved iron was then recovered from solution by ammonium jarosite precipitation. The optimum conditions to leach the slag were determined: 1.85 Nand 4.07 N H2SO4 at 1/10 solids ratio, at a temperature of 55degreesC and 95degreesC in the first and second stages, respectively. Results show that the 77.45% Zn extraction could be achieved by atmospheric leaching. Compared to other processes, such as pressure leaching, ammonia, and NaOH leaching, pressure leaching bad the highest extraction efficiency of 87% Zn and 80% Fe, but may have extremely high investment and operation costs.