Pathways and mechanism of (NH4)2Me(SO4)2 formation during the process of (NH4)2S sulfide removal of Ni, Co, and Zn in MnSO4 electrolyte

Abstract

In the process of removing Ni, Co, and Zn from manganese sulfate electrolyte solution, the metal sulfides produced are mixed with ammonium metal sulfate. The reasons and roles behind the formation of ammonium metal sulfate are not fully understood, and this study explores this aspect. Experimental verification, density functional theory (DFT) calculations, and molecular dynamics simulations reveal that NH₄⁺ and SO₄^2- exhibit a stronger binding affinity to low-concentration metal ions compared to S^2-, which is crucial for the formation of ammonium metal sulfate. Furthermore, the formation order of ammonium metal sulfate is Zn, Ni, Co, and Mn. In the process of sulfurization and impurity removal of manganese sulfate electrolyte solution, the formation of ammonium metal sulfate is conducive to the removal of Ni, Co, and Zn impurities, which helps to purify the manganese electrolyte and increases the manganese impurity ratio from 48.51 to 75.05. This study clarifies the phase transition characteristics during the impurity removal process of manganese sulfate electrolyte, reveals the formation pathway and practical application of the metal ammonium sulfate mixture, and provides an optimized approach for sulfurization-based heavy metal removal.