Energy efficient electrodeposition of metallic manganese in an anion-exchange membrane electrolysis reactor using Ti/IrO2–RuO2–SiO2 anode

Manganese electrodeposition experiments were performed in an anion-exchange membrane (AEM) electrolysis reactor using Ti/IrO2–RuO2–SiO2 anode. The influence of Mn2+ concentration, cathode current density (CCD), (NH4)2SO4 concentration, SeO2 concentration and electrolysis time on the cell voltage (CV), cathode current efficiency (CE) and specific energy consumption (SEC) of manganese electrodeposition was investigated. The crystalline structure, chemical composition and morphology of the deposited manganese metal and the generated dark mass were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) measurements. The obtained results reveal that the crystalline structure of the deposited manganese metal was α-Mn. The dark mass of MnOOH would be generated and precipitated on the surface of the cathode, inhibiting the electrodeposition of manganese metal when the operating condition was not well controlled. Considering the CE, SEC and environmental aspect, the operating condition of Mn2+ concentration = 30 g L−1, CCD = 350 A m−2, (NH4)2SO4 concentration = 110 g L−1 and SeO2 concentration = 0.03 g L−1 was regarded as the best condition for manganese electrodeposition. Under this condition, the CE was 78.3% and the SEC was 4346–4433 kW h t−1 after electrolyzing for 24 h. Compared with the traditional approach, the CE increased by about 10% and the SEC decreased by about 27%. In addition, the electrolytic manganese anode slime was not generated during the manganese electrodeposition process. This approach is recommended as it will reduce the energy consumption and the quantities of solid waste discharge of manganese electrodeposition.