Use of manganese sulfide as a sustainable precipitant for the separation of Co(II) and Ni(II) by sulfide precipitation from spent lithium-ion battery leachates

The rising uptake for lithium-ion batteries (LIBs) requires the need for effective recycling methods to recycle critical metals like cobalt, nickel, and manganese while minimizing environmental harm. In general, hydrometallurgical treatments of spent LIBs result in leachates that contain Co(II), Mn(II) and Ni(II) with diverse concentration ratio. By utilizing the difference in the solubility products among CoS, NiS and MnS, it is possible to simultaneously precipitate CoS and NiS, leaving Mn(II) in the filtrate. This study employed MnS as a cost-effective and eco-friendly precipitant for selective precipitation of Co(II) and Ni(II) sulfide from simulated solution containing Mn(II). Among several factors, the influence of solution pH, MnS dosage and reaction time was found critical on the precipitation of Co(II) and Ni(II) at room temperature. Under optimized conditions: pH 2.0, a MnS/(Co + Ni) molar ratio of 10, agitation speed of 400 rpm at 25℃, use of MnS led to complete precipitation of CoS and NiS, leaving Mn(II) in the filtrate with minimal contamination. Moreover, common ion effect and encapsulation effect were observed to affect the dissolution behavior of MnS during the precipitation. Unlike traditional sulfide sources like Na₂S and NaHS, MnS provides a controlled release of sulfide ions, addressing challenges like the formation of colloidal particle. Our results indicated that MnS demonstrated its potential as a precipitant for the selective precipitation of Co(II) and Ni(II) from the acidic media containing Mn(II).