Simultaneous removal of ammonia and manganese from electrolytic metal manganese residue leachate using phosphate salt

Abstract

Ammonia and manganese were simultaneously removed from electrolytic metal manganese residue leachate using phosphate salt. The influence of different N:P ratios and pH were investigated. Phase transition and decomposing behavior of precipitates and the characterization of the precipitates pyrolysis were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis, and scanning electron microscope. In the laboratory experiment, under the condition of 1:1.15 N:P ratio and 9.5 pH value, removal efficiencies of ammonia and manganese from the residue leachate were achieved 95.0% and 99.9%, respectively, and remaining concentration of orthophosphate was as low as 12 mg L−1. In the process, manganese was first removed as Mn3(PO4)2·7H2O, and then ammonia was removed as NH4MgPO4·6H2O. In addition, MgNaPO4, MgHPO4, Mg2P2O7, Na3PO4 and MnO2 were generated during precipitate pyrolysis process, and the ammonia removal efficiency decreased from 84.0% in the first cycle to 66.0% in the fifth, and manganese removal efficiency was approximately 99.0%. Economic evaluation shows that recycling the precipitates for three times could save 68.4% cost on average, compared to the use of pure chemicals.