Reuse of hazardous electrolytic manganese residue: Detailed leaching characterization and novel application as a cementitious material

Electrolytic manganese residue (EMR) was characterized in detail. A pH-dependent leaching test in combination with geochemical modelling was used to reveal the leaching mechanisms and calculate the solubility-controlling phases of various elements. In addition, a novel EMR-activated cementitious material (EGCH) was developed based on the characteristic of EMR (namely, high gypsum content). The results show that Mn and NH3-N are the most predominant hazardous elements in EMR that pose environmental risks. Mn mainly exists as acid-extractable phases (Mg-bearing jacobsite and szmikite) in EMR, and its solubility is mainly controlled by sorptive phases, rhodochrosite and hausmannite. NH3-N leaching is virtually pH independent in acid regions, but NH3-N reacts with hydroxyl to form NH3 at pH values above 9. The simulated equilibrium concentrations from multi-element modelling match well with the measured results. In addition, hardened EGCH can achieve a 28-day compressive strength of 30 MPa, and its EMR utilization ratio can reach 45 wt.%. The encapsulation effect and strong alkaline buffering capacity provided by EGCH are beneficial for the stabilization of Mn and NH3-N. Overall, the EGCH cementitious material can meet the requirements for green construction.