Comparison of separation of Mn(II), Co(II), and Ni(II) by oxidative precipitation between chloride and sulfate solutions

In hydrometallurgy, precipitation would be easier and simpler than solvent extraction as a separation operation. In this work, the separation performance of Co(II), Mn(II) and Ni(II) by oxidative precipitation was investigated. For this purpose, NaClO was employed as an oxidizing agent and the separation behavior of the three ions was compared between chloride and sulfate solutions by varying some factors such as the dosage of NaClO, solution pH and reaction temperature. By controlling the molar ratio of NaClO to Mn(II), manganese ions(II) were easily separated as MnO2 by oxidative precipitation from both chloride and sulfate solutions. At the same experimental conditions, precipitation percentage of Co(II) from chloride solution was higher than that from sulfate solution, which can be ascribed to the stronger tendency of Co(II) to form complexes with chloride ion than with sulfate ions. Addition of NaCl to sulfate solution and oxidative precipitation at high temperature enhanced the precipitation percentage of Co2O3 and thus separation degree between Co(II) and Ni(II) was improved. Under the optimum conditions, MnO2 and Co2O3 powders with 99.9% purity were completely recovered by oxidative precipitation from chloride solution. By contrast, the purities of the MnO2 and Co2O3 thus recovered from sulfate solution were only 76 and 91%, respectively. Our results indicated that chloride solution would be more effective than sulfate solution in separating Mn(II) and Co(II) by oxidative precipitation with NaClO. Therefore, the use of chloride-based leaching solutions such as HCl and FeCl3 might be better for the leaching medium of spent lithium-ion batteries.