A green method for Mn2+ and NH4+-N removal in electrolytic manganese residue leachate by electric field and phosphorus ore flotation tailings

Abstract

• Electric field and POFTs were used for Mn 2+ and NH 4 + -N removal in EMRL firstly. • The treated EMRL can be discharged to the standard (GB8978–1996). • The phosphate precipitation obtained could be used as market fertilizer. • This study provided a new idea for EMRL harmless disposal and POFTs utilization. High concentrations of manganese (Mn 2+ ) and ammonia nitrogen (NH 4 + -N) in electrolytic manganese residue leachate (EMRL) have seriously polluted the environment. In this study, electric field and phosphorus ore flotation tailings (POFTs) were used for Mn 2+ and NH 4 + -N removal in EMRL firstly. The effects of the liquid acid ratios, reaction temperature, current density, initial pH and stable pH of the solution, characteristics of EMRL and POFTs, and removal mechanism of NH 4 + -N and Mn 2+ were investigated. The results indicated that an electric field enhanced the leaching of POFTs and promoted the adsorption and precipitation of Mn 2+ and NH 4 + -N. The concentrations of Mn 2+ , NH 4 + -N, PO 4 3− and F − in EMRL were 0.12 mg/L, 9.2 mg/L, 0.09 mg/L, and 0.24 mg/L, respectively, which were within the permitted level for the integrated wastewater discharge standard (GB8978-1996) after adjusting the second stable pH to 10.0. Mn 2+ was mostly remove in the form of Mn(OH) 2 , MnOOH, Mn 5 (OH) 4 (PO 4 ) 2 and MnO 2 . NH 4 + -N was mostly remove as NH 4 MgPO 4 ·6H 2 O. The phosphate precipitation obtained could be used as market fertilizer. This study provided a new research idea for EMRL harmless disposal and POFTs resource utilization.