The effects of Mg²⁺ concentration, (NH₄)₂SO₄ concentration and current density on electrolytic manganese process

Abstract In this paper, the effects of Mg2+ concentration, (NH4)2SO4 concentration and current density on the current efficiency, cell voltage and morphology of electrolytic manganese metal were studied. The current efficiency of electrolytic manganese decreased with the increase of Mg2+ concentration in the electrolyte; Increasing the concentration of (NH4)2SO4 , the current efficiency of electrolytic manganese showed a gradually increasing trend. By changing the current density, the current efficiency of electrolytic manganese increased first and then decreased. When the current density was 400 A·m−2, the current efficiency was the highest, it was about 66.63%. The cell voltage in the process of manganese electrolysis was independent of Mg2+ concentration and (NH4)2SO4 concentration, but only positively related to current density. Through the macroscopic analysis of the cathode plate, the greater the current efficiency was, the brighter the color of the metal manganese sheet was, it shew a silver white, and the dendritic growth of metal manganese was less. From the microscopic morphology of the manganese metal sheet, the electrolytic manganese metal was formed by stacking metal manganese sheets, each metal manganese sheet exhibited a regular hexagonal structure, the shape was similar to a ‘pyramid’, it had a better compactness, in which the better the current efficiency was, the better the compactness of the electrolytic manganese metal was. Under different experimental conditions, crystal plane (330,411) was the strongest and best orientation for the growth of electrolytic manganese. Cyclic voltammetry experiments showed that Mg2+ was not beneficial to electrodeposition of manganese, the increase of (NH4)2SO4 was beneficial to improve the current efficiency, and it was consistent with the conclusion of electrolysis experiment.