A novel approach for recovery of manganese from on-site manganese-bearing wastewater

Acid leaching of rhodochrosite will generate electrolytic manganese residue together with emission of carbon dioxide (CO2). Wastewater containing highly concentrated manganese is being generated when treating electrolytic manganese residue. Although carbonate precipitation has been identified as an effective process for manganese removal, this conventional approach is limited by heavy use of alkaline solution and the obtained MnCO3 precipitates have low purity. In this study, an electrolytic manganese plant in Guangxi, China was selected as the study site. CO2 generated from flue gases was carefully chosen as the potential reagent for the recovery of manganese from wastewater. The effects of operational modes including batch mode, batch mode with external recirculation, continuous mode and continuous mode with external recirculation on the performance of wastewater treatment were systematically investigated in pilot scale, and the obtained precipitates were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and the thermal gravity-differential thermal analysis (TG-DTA). It was found that batch mode with external recirculation is optimal as over 99.99% of Mn2+ can be selectively recovered from Ca2+, Mg2+ and Mn2+-containing wastewater by bubbling with CO2, and the obtained MnCO3 precipitates met the industrial standard in China (grade I). The pH value of the effluent is 6.6 and the concentration of Mn2+ is 1.0 mg L-1, which can be recycled within this system. The present study provides a sustainable technique to solve the problems of treating industrial wastewater containing heavy metals. (C) 2019 Elsevier Ltd. All rights reserved.