Fractional removal of manganese and ammonia nitrogen from electrolytic metal manganese residue leachate using carbonate and struvite precipitation.

A comparative investigation of hydroxide precipitation, sulfide precipitation, carbonate precipitation and the struvite formation process for removing manganese and ammonia nitrogen from electrolytic metal manganese residue leachate (EMMRL) was investigated. Chemical equilibrium model-Visual MINTEQ was applied to simulate the chemical reactions and optimize chemical dosages in manganese and ammonia nitrogen removal. Phase transition, morphology, and valence state of the precipitates were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS). Results indicated that carbonate precipitation prior to the other two methods for removal of manganese and ammonia nitrogen. The removal efficiency of manganese was 99.9%, when molar ratio of C to Mn was 1.1:1 at pH 9.5, and manganese was removed in the form of MnCO3. When molar ratio of P to N was 1.1:1 at pH 9.5, the removal efficiency of ammonia nitrogen was 97.4%, and ammonia nitrogen was removed in the form of struvite. Economic evaluation reveals that the treatment cost was 9.316 $ m-3 when carbonate and phosphate was used to remove manganese and ammonia nitrogen from EMMRL.