Processing of Secondary Raw Materials by Hydrometallurgical Methods for the Recovery of Zinc

The main purpose of this research was to find a suitable, economical and simple way to recover mainly zinc from waste Zn-Mn batteries. The most feasible way can be leaching the soluble zinc content in diluted sulphuric acid after a proper physical separation of the raw material. The leachate however contains an equally high concentration of manganese, and the residual iron content – not removed by magnetic separation – goes also into solution. Other significant impurities may be copper, nickel and cadmium, by experience. Electrolytic deposition of technically pure zinc is made possible by an efficient hydrolytic separation of iron at the end of the leaching step, followed by the oxidative precipitation of the manganese content. The practically neutral and pure zincsulphate solution can be utilized advantageously for electrowinning zinc. The procedure is still hardly economical, which shortcoming can be improved by the admixing of the easily available centrally stored electric arc furnace dust, containing comparable amounts of zinc, but very low concentration of other soluble metals. Experimental results have proved the viability of this combined processing, although complete recovery of the zinc content is not achieved from the added dust, which results in a basically zinc-ferrite type residue. It can be however recycled to ferrous metallurgy together with the manganese dioxide precipitate and the carbon-iron hydroxide – manganese dioxide containing residue from the battery waste leaching step. The other large scale source of secondary zinc is the electric arc furnace (EAF) dust, which is produced and stored at high quantities in a centralized manner. It is an interesting proposition to improve the availability of zinc by introducing the less soluble, but more accessible and less complex EAF dust into the processing scheme of the better leachable but more complex and less available Zn-Mn battery waste. The latter material represented a collected amount of 164 000 tons in 2003 in Europe consisting of ~30% Zn-carbon and ~60% Zn-Mn varieties [1].