Water balance analysis and wastewater recycling investigation in electrolytic manganese industry of China — A case study

A water balance investigation was performed for a representative electrolytic manganese metal (EMM) enterprise to study the details of water consumption and generation in the production process. A new integrated wastewater treatment approach was put forward to recover useful chemicals from the process wastewater, which contained high concentrations of Mn2 +, Cr(VI), Cr3 +, and NH4+. Cr(VI) was recovered from the wastewater by ion exchange techniques and reused as EMM passivant. The remaining wastewater containing Mn2 + and NH4+ was returned to the leaching section before the impurity removal procedure to prepare electrolytes. Complete wastewater recycling was achieved after water balance regulation and optimization. Final demonstration line results proved that the proposed process is feasible and exhibits significant advantages of better treatment effects, lower costs and lower environmental impact compared to the traditional reduction–neutralization–sedimentation treatment method. With the adoption of the proposed approach, solid waste disposal cost and the required area for the landfill yard were decreased by 80%. Operating costs for wastewater treatment were lowered by 85%. Around 4.8 kg/t EMM of Mn2 +, 5.2 kg/t EMM of NH4+ and 0.24 kg/t EMM of Cr(VI) were recovered. The recycled wastewater proportion was increased from 6.2% to 100.0%. 1.168 m3/t EMM of fresh water was saved and the equivalent amount of discharging wastewater was reduced to the environment.