Efficient recovery of manganese and ammonia nitrogen from filter-pressing electrolytic manganese residue by organic complexation

Abstract

Filter-pressing electrolytic manganese residue (F-EMR) contains large amounts of NH4+–N and Mn2+, causing serious environmental issues. Therefore, it is of great significance to reduce the Mn2+ and NH4+–N content. In this work, complexing agents are employed to efficiently recover Mn2+ and NH4+–N from the F-EMR by organic complexation. Firstly, the NTA is identified as the optimal one among different complexing agent candidates, and then experimental conditions are optimized to improve the leaching performance. As it turns out, the NTA significantly promotes the leaching of Mn2+ and NH4+–N. Optimal recovery efficiencies of Mn2+ and NH4+–N reach 97.06% and 28.47% under the NTA concentration of 0.015 mol/L, solid/liquid ratio of 1:4 g/mL, stirring speed of 400 rpm, and leaching time of 20 min. X-ray diffraction (XRD) and Fourier-transformed infrared (FTIR) spectroscopy analyses demonstrate the advantage of NTA in improving the leaching performance, and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) analysis proves low contents of both Mn2+ and NH4+–N in the leaching residue. Additionally, based on density functional theory calculation and mechanism analysis, it is discovered that NTA and manganese ions in the F-EMR can form a stable mononuclear multi-ring product structure, promoting the leaching of Mn2+ and NH4+–N.