Mechanochemical modification of electrolytic manganese residue: Ammonium nitrogen recycling, heavy metal solidification, and baking-free brick preparation

The increasing accumulation of electrolytic manganese residue (EMR) with high ammonium nitrogen and heavy metals has become the biggest obstacle restricting the sustainable development of electrolytic manganese industry. A novel method for efficient recovery of ammonium nitrogen as well as solidification of Mn and other heavy metals in the process of preparation of EMR based baking-free brick (B-EMR) was invented by mechanical milling in the coexistence of water and calcium oxide for the first time. It was demonstrated that the solidification/recovery efficiency of Mn and ammonium nitrogen can reach more than 98%. And the compressive of B-EMR was higher than 12 Mpa, which met the requirement of China's national industry standard of stronger than 9.6 Mpa (JC/T 239–2001). Mechanochemical action breaked the Si–O bond and promoted the calcium silicate-like cementitious structure, which contributed to the compressive strength of B-EMR and the solidification of heavy metals. CaO plays a key role in the conversion of ammonium nitrogen in EMR to NH3 and enhanced by mechanical milling. This study provided a feasible path for the resource disposal of EMR. And demonstrated a solution for the limitation of ammonium nitrogen and heavy metals in the large-scale utilization of EMR.