IRON CONTROL IN ZINC PLANT RESIDUE LEACH SOLUTION

In the hydrometallurgical production of zinc through the conventional 'roast-leach-electro-win' process, zinc ferrite is formed together wit h zinc oxide during roasting of zinc sulphide concentrate. This ferrit e is not leached under normal conditions and separates out as residue. Zinc from this residue is recovered in high-temperature acid leaching , which yields a zinc sulphate solution containing high levels of iron . This imposes process constraints, because of high iron level, on rec ycling the solution to the neutral leaching stage. Investigations into the control of iron levels in residue leach solution by optimizing ac idity with zinc hydroxide-gypsum cake are presented in this paper. The plant implementation of this work is also illustrated.