Simultaneous stripping recovery of ammonia-nitrogen and precipitation of manganese from electrolytic manganese residue by air under calcium oxide assist

Abstract

Leaching tests of electrolytic manganese residue (EMR) indicated that high contents of soluble manganese and ammonia-nitrogen posed a high environmental risk. This work reports the results of simultaneous stripping recovery of ammonia-nitrogen and precipitation of manganese by air under calcium oxide assist. The ammonia-nitrogen stripping rate increased with the dosage of CaO, the air flow rate and the temperature of EMR slurry. Stripped ammonia-nitrogen was absorbed by a solution of sulfuric acid and formed soluble (NH₄)₂SO₄ and (NH₄)₃H(SO₄)₃. The major parameters that effected soluble manganese precipitation were the dosage of added CaO and the slurry temperature. Considering these two aspects, the efficient operation conditions should be conducted with 8 wt.% added CaO, 60°C, 800 mL min⁻¹ air flow rate and 60-min reaction time. Under these conditions 99.99% of the soluble manganese was precipitated as Mn₃O₄, which was confirmed by XRD and SEM-EDS analyses. In addition, the stripping rate of ammonia-nitrogen was 99.73%. Leaching tests showed the leached toxic substances concentrations of the treated EMR met the integrated wastewater discharge standard of China (GB8978-1996).

Keywords:

• Ammonia-nitrogen
• calcium oxide
• electrolytic manganese residue
• manganese precipitation
• stripping recovery

Funding

The work was financially supported by the National Natural Science Foundation of China (Grant no. 51274261) and the Natural Science Research Project of the Education Department of Guizhou Province, China (Grant no. Qianjiaohe KY[2013]202).