Study on the mechanism and mechanical properties of magnesium oxychloride cement for blocking pollutants migration from electrolytic manganese residue

Electrolytic manganese residue (EMR) is a hazardous solid waste, which contains a large amount of soluble manganese and ammonia nitrogen, and improper disposal will pollute the environment and affect human health. In this paper, the magnesium oxychloride cement (MOC) was used to stabilize/solidify the heavy metals in EMR, and the leaching toxicity, compressive strength, phase composition and microstructure of the solidified body were studied under the conditions of different MOC dosage and MgO/MgCl₂ molar ratio. The research showed that the leaching of Mn²⁺ and NH₄⁺–N of EMR solidified by MOC were lower than the integrated wastewater discharge standard of China, and each group showed good compressive strength. When the molar ratio of MgO/MgCl₂ was equal to 5 and MOC dosage was 50%, the compressive strength of the solidified body reached 82.26 Mpa. The microscopic experiment showed that the insoluble salts NH₄H(PO₃)₂, K₄MnCl₆, and Mn(MgMn)Zn₂(OH)₁₀(H₂O)₂ generated in solidified body could stabilize Mn²⁺ and NH₄⁺–N. In addition, the needle-rod phase 5 and phase 3 generated in EMR-solidified body were the main providers of mechanical strength and barrier pollutants, and the waste EMR can be recycled as a green cementitious material.