Efficiently enriched Ni, Co, and Zn with (NH4)2S-SDD combined system in MnSO 4 electrolyte

In the electrolytic manganese process, efficient sulfidation enrichment of Ni, Co, and Zn is essential for resource recovery. This study uses (NH₄)₂S and SDD as composite sulfiding agents and employs a batch addition method to achieve high enrichment of Ni, Co, and Zn. When the temperature is 45 °C, the ammonium sulfide dosage is 40% of the theoretical value, the SDD dosage is 160% of the theoretical value, the pH is 5.60, the reaction time is 30 min, and the stirring speed is 650 rpm, the enrichment rates of Ni, Co, and Zn exceed 99%, with a manganese impurity ratio of 1475.3. Under these conditions, the sulfidation of Ni, Co, and Zn is controlled by chemical reactions, with apparent activation energies (Ea) of 30.29, 35.30, and 38.73 kJ/mol, respectively. First-principles calculation results show that the bond length of $C_3$H₆NS₂-Me${}^{2+}$ and the Gibbs free energy during the sulfidation reaction are key factors contributing to the selective enrichment of Ni, Co, and Zn. The life cycle assessment (LCA) indicates that the treatment cost for 1 L of electrolytic manganese solution is 5.95 ¥, demonstrating good environmental and economic benefits. This study provides an efficient enrichment method for the recovery of strategic metals Ni, Co, and Zn, while also offering an electrolyte with low Ni, Co, and Zn impurities for the electrolytic manganese system.