Chlorine anion elimination from zinc sulfate solution by periodical current reverse electrolytic system

Almost 30% of steel in Japan is produced by electric are furnace (EAF) treatment of iron scrap. EAF dust includes approximately 20 wt % of Zn and 3-5 wt % of Cl and is treated by the pyrometallurgical processes to recover Zn as Zn oxide. Direct hydrometallurgical processing is one of the most effective methods to recover high purity Zn. In this case, Cl in the EAF dust is dissolved in the liquid phase by leaching, and the Cl anion in electrolyte attacks anodes which are commonly made of a lead base alloy. Several processes have been proposed to remove Cl anions from acidic sulfate solution. In this study, an electrolytic process was examined to eliminate Cl anions from Zn sulfate electrolyte. From our study it can be said that the elimination rate of Cl anion depends on the anode material (i.e., the elimination rate is Pb-Ag alloy congruent to Pb > DSE congruent to Pt). In industrial Zn electrowinning process, the electrolyte contains Mn, which means the influence of Mn should be considered in the elimination of Cl. Mn dioxide deposition on an anode plate reduces the efficiency of Cl removal. A periodical reverse current electrolytic system was examined to prevent this efficiency decrease, and deposited Mn dioxide could be removed very rapidly when the current is reversed. More than 95% of Cl anion could be removed by this method in a shorter period than direct current method.