Stepwise separation of Co, Mn, Zn, and Cd from Co purification residue (CPR) in Zn hydrometallurgy

Co purification residue (CPR) is a byproduct of the Zn hydrometallurgy process, primarily comprising complex and hazardous combinations of Co, Mn, Zn, and Cd. The comprehensive separation and recovery of the four metals from CPR holds significant importance in resource recycling and environmental conservation. In this work, an integrated hydrometallurgy process comprises the acid leaching for preferential Zn and Cd extraction, the Cd separation by Zn replacement, the reduction acid leaching for Mn and Co extraction, and the Co separation from Mn-Co and Zn-Co solutions were proposed. It has been demonstrated that Zn and Cd as the forms of oxide and sulfide in CPR are rapidly dissolved in an H2SO4 solution. High-valence insoluble Mn and Co oxides in the Co-Mn residue are converted to soluble in the reductive H2O2-H2SO4 solution. Co in the Co-Zn and Co-Mn solutions can be selectively precipitated by the 1-nitroso-2-naphthol (1N2N). The effects of the main parameters on the metal recovery in the leaching and separation procedures were symmetrically investigated. Various characterizations including the XRD, XPS, SEM-EDS, FTIR, and thermodynamics analyses were carried out to determine the selective leaching and chelation precipitation mechanisms. Eventually, the four metals can be successfully separated step by step from CPR with a favorable comprehensive metal recovery.