Investigation of secondary zinc oxides as an alternative feed to the Skorpion Zinc process: Part 1-leaching alternative zinc oxides

Skorpion Zinc processes zinc oxide ore using a sulphuric acid leaching, solvent extraction, and electrowinning process to produce Special High Grade zinc. The company investigated the possibility of supplementing ore with alternative zinc oxide sources to extend the life of mine and maximize zinc production. In part 1 of this two-part communication we report on experimental investigations to assess the technical feasibility of recovering zinc from electric arc furnace (EAF) dust, zinc dross, and zinc fume under the current Skorpion Zinc leaching conditions. The metal dissolution and acid consumption were determined at temperatures between 40 and 70 degrees C and pH values between 1.2 and 2.1 for slurries containing 20% solids. With the current Skorpion Zinc operating conditions of 50 degrees C and pH 1.8, zinc dissolution from the EAF dust, zinc dross, and zinc fume was 93, 96.9. and 98.5 %, respectively. The rate of zinc leaching from dross and from zinc fume decreased as the pH was increased to 1.5 and 1.8, respectively. The rate-determining step for zinc leaching from zinc dross gradually changed with an increase in pH from porous layer mass transport to chemical reaction and/or boundary layer mass transport. In the case of EAF dust, increasing the temperature to 70 degrees C significantly reduced the zinc leaching rate due to the precipitation of calcium sulphate, which inhibited the zinc leaching reactions. The overall acid consumptions for all three alternative oxides investigated were below the current target consumption of 1.5 t acid per ton of Zn in the feed. It would be technically feasible to use EAF dust, zinc dross, and/or zinc fume as supplementary feed to the Skorpion Zinc process.