An improved process methodology for extracting cobalt from zinc plant residues

Abstract

Zinc plant residue contains valuable metals that can be reused as a source for obtaining these metals. This paper describes the use of sodium thiosulfate (Na2S2O3) in leaching of Co and Mn from zinc plant residue, and purifying the leach solution in order to obtain a pure solution of Co(II). After dissolution of zinc using sulfuric acid, Co and Mn were dissolved in H2SO4 in the presence of a reducing agent. The effects of temperature, acid percentage, type and concentration of reducing agent on dissolution were studied. The results for sodium thiosulfate showed the dissolution of 90.7% and 87.6% Co and Mn, respectively at 65 °C, with an acid concentration of 5% and sodium thiosulfate concentration of 6 g/L. The corresponding results in the presence of H2O2 as a reducing agent are 94.7% Co, 96.3% Mn at 50 °C with the same acid and reagent concentration. An analysis of variation (ANOVA) on the corresponding data was performed. A new correlation as a function of reducing agent yielding the recovery for Co and Mn was derived. Moreover, the purification process of metals was investigated which was a combination of the precipitation method for removing iron, and the solvent extraction for separating Co(II) and Mn(II). The factors influencing solvent extraction i.e., pH, organic concentration, and organic/aqueous ratio were optimized. Finally, two processes for extracting Co and Mn from the hot filter cake (HFC) were proposed and compared.