Efficient removal of impurities from electrolytic manganese anode slime enhanced by ammonium chloride

Electrolytic manganese anode slime （EMAS） has become one of the major challenges hindering the development of China’s electrolytic manganese industry. Although existing technologies can achieve efficient leaching of manganese from the EMAS, impurities such as Ca and Mg also simultaneously enter the leaching solution, resulting in manganese-based products with low added value and unstable performance. Therefore, developing efficient source removal technologies for eliminating impurities such as Ca and Mg from EMAS has become the key to achieving high-value utilization of manganese resources in EMAS. This study proposes a method using an NH₄Cl system to efficiently remove impurities such as Ca and Mg from EMAS. The effects of NH₄Cl dosage, reaction pH value, reaction time, and reaction temperature on impurity removal efficiency are investigated. The results show that under conditions of pH=2.0 and a reaction temperature of 30 ℃, using a 16% NH₄Cl solution for 2 hours achieves Ca and Mg removal efficiency of 95.00% and 98.59%, XRF analysis shows that the MnO content in the EMAS obtained under the optimal leaching conditions increases from 83.33% to 89.17% before leaching; BET analysis shows that the adsorption capacity, specific surface area and pore volume of the leaching slag under optimal conditions are greater than those of the original EMAS, indicating that the NH₄Cl leaching process improved the pore structure of the EMAS. The analysis of TEM, HRTEM and SAED shows that compared with the original EMAS, the leaching slag shows more obvious lattice fringes, the crystallization product is intact, and the crystal plane spacing belonged to the α-MnO₂ crystal plane. The leaching mechanism of NH₄Cl shows that NH₄Cl converted the insoluble Ca and Mg and other impurities in the EMAS into soluble chloride, so as to achieve the efficient removal of Ca and Mg in the EMAS, and the Mn element is mainly enriched in the form of α-MnO₂. This study provides a novel approach for the efficient removal of Ca, Mg, and other impurities from EMAS.