Enhanced removal of Mn2+ and NH4+-N in electrolytic manganese metal residue using washing and electrolytic oxidation

[Display omitted] •NH4+-N and Mn2+ in EMMR were removed by washing and electrolytic oxidation.•The concentrations of NH4+-N and Mn2+ were 6.79 mg/L and 0.05 mg/L, respectively.•Mn2+ was mainly removed in the forms of MnO2, Mn2O3, MnOOH and Mn3O4.•NH4+-N was mainly oxidised to N2. In this study, a new combination method for Mn2+ and NH4+-N removal from electrolytic manganese metal residue (EMMR) using washing and electrolytic oxidation processes was studied. The effects of washing pH, the dosage of sodium hypochlorite, current density, reaction time and reaction temperature on the concentrations of Mn2+ and NH4+-N were investigated. The results showed that the concentrations of NH4+-N and Mn2+ were 6.79 mg/L and 0.05 mg/L, respectively, which were lower than the integrated wastewater discharge standard (GB8978-1996), when the current density was 35 mA/cm2, the sodium hypochlorite dosage was 2%, and the initial pH was 9.5 after reacting for 2 h at 20℃. Mn2+ was mainly removed in the forms of MnO2, Mn2O3, MnOOH and Mn3O4. NH4+-N was mainly oxidised to N2. This study provides a new harmless treatment technology for EMMR.