Separative treatment of zinc-bearing flue dust

Abstract

A hydrometallurgical process is provided for separative treatment of zinc-bearing metallurgical flue dust containing significant amounts of lead, chlorine, and iron. The process is especially suited for extraction of zinc sulfate from blast furnace white dust resulting in the smelting of secondary copper. According to the process, the flue dust is leached in sulfuric acid solution for substantially complete dissolution of soluble constituents, notably zinc, leaving insoluble residue consisting principally of lead oxide. At completion of leaching, pH is selectively adjusted corresponding to the desired extent of subsequent chloride removal. Second, the loaded leach solution is treated for chloride removal wherein chloride ion concentration is substantially and selectively reduced by precipitation of cuprous chloride, cuprous ions being provided by pH regulated reduction of cupric ions. Third, the dechlorinated leach solution is treated by pH regulated cementation with zinc to remove residual cupric copper from the previous step along with other metal impurities more noble than zinc. Fourth, iron is precipitated from the acidic leach solution by oxidation of acid-soluble ferrous ions to the relatively insoluble ferric state. Finally, the purified leach solution is subjected to evaporative crystallization to recover commercial grade zinc sulfate.