Synergistic leaching process and mechanism of manganese and ammonia nitrogen from electrolytic manganese residue by malonic acid-ascorbic acid

The high concentration of manganese (Mn) and ammonia nitrogen (NH+4 - N) in electrolytic manganese residue (EMR) represents a constraint on its potential for resource utilization. However, the synergistic use of malonic acid (MA) and ascorbic acid (AA) in the leaching process can effectively extract Mn2+ and NH+4 -N from manganese residue. In this paper, the effects of process parameters on the leaching efficiency of Mn2+ and NH+4 in EMR were investigated. Mn2+ and NH+4 -N leaching models were constructed, and the leaching mechanisms were explored through microscopic characterization and kinetic analysis. Results showed that the leaching efficiency of Mn2+ and NH+4-N was 91.54 % and 95.42 %, respectively, under the conditions of 400 r/min leaching by electric stirring, MA concentration of 6 %, AA concentration of 12 %, liquid-solid ratio (L/S) of 5 mL/g and temperature of 45 degrees C. In the leachate, Mn2+ mainly formed soluble complexes with MA through chemical bonding, while NH+4 formed soluble complexes with MA and AA through chemical bonding and hydrogen bonding. The stability of the complexes formed by MA and Mn2+ in a 2:1 coordination was slightly greater than that of the complexes formed by 1:1 coordination, and that of the complexes formed by AA and NH+4 was the most stable, NH+4 forming 1:1 coordination complexes with the greatest stability. The leaching of Mn2+ and NH+4 -N is controlled by a mixture of chemical reactions and internal diffusion.