Utilization of solutions obtained after magnesium removal from sphalerite concentrates with spent electrolyte derived from winning of cathode zinc

As domestic zinc and lead deposits occur in dolomite rocks, the sphalerite concentrates obtained from these ores contain an admixture of dolomite. These concentrates should be characterized by a high content of zinc and low levels of impurities such as magnesium, arsenic, iron, and others. The domestic process of cathode zinc winning from this raw material consists of roasting of sphalerite concentrates (in order to obtain zinc in the oxide form), leaching of the oxide concentrate with sulfuric acid, purification of the zinc sulfate obtained, and a final stage - zinc electrodeposition. During chemical treatment of the oxide concentrate with sulfuric acid,magnesium is added to the solution of zinc sulfate. A high magnesium concentration in the solution is undesirable, and causes deterioration of zinc cathode quality, and technical as well as economical indexes of the process. The required content of magnesium in a solution amounts to less than 0.3%MgO; therefore,MgO should be removed before the electrodeposition of zinc. One of the methods of magnesium removal is decreasing its content in a sphalerite concentrate by means of pre-leaching, using sulfuric acid as a leaching agent. The aim of this study was the recovery of certain components from solutions after magnesium removal with zinc concentrates by means of pre-leaching. Spent electrolyte deriving from the zinc electrodeposition process was used as the pre-leaching agent. The study consisted of two major measuring series, namely leaching of raw sphalerite concentrate with spent electrolyte and removal of components from the solutions after pre-leaching. Leaching was carried out in three stages. After the first stage of the two-hour leaching, the extent of magnesiumleaching was almost 84%. After the second and third stages of the leaching steps, magnesium content was slightly lower respectively 81.5 and 70.4%. Magnesium content in the concentrate was below the maximum permissible value, i.e. 0.30%. After the third stage, the content of this component was 0.40%. Zinc losses were highest after the first leaching stage at 2.6%, and were acceptable from a technological point of view.The results confirmed that the pre-leaching process with spent electrolyte is an effective method for the removal of magnesium and other impurities from zinc concentrate. The described procedure for purification and separation of components from a solution is an effective method of recovering some components. The resulting products can be utilized in various technological processes; for example, for the production of magnesium compounds, recycling of zinc product, winning of zinc, etc.