Effect of red mud and phosphate on water resistance and hydration mechanism of magnesium oxychloride cement

The proper disposal and utilization of red mud (RM) remains a challenge due to its substantial accumulation. This study attempted to employ magnesium oxychloride cement (MOC) to recycle RM, considering its low carbon footprint. KH2PO4 was used as a modifier to mitigate the negative impact of RM. Multi-scale performances were examined to evaluate the feasibility of using MOC as an environmentally sustainable medium for RM recycling. Results showed that RM and KH2PO4 significantly lengthened MOC's setting time, and KH2PO4 effectively delayed the scum formation of RM-MOC. The complex reactions among RM, KH2PO4, and MgO-MgCl2-H2O ternary systems facilitated the formation of more gel-like phases and effectively enhanced the water resistance of MOC. Additionally, KH2PO4 improved the stability of phase 5 in RM-MOC. The findings suggest that proper incorporation of RM benefits in improving the main performance of MOC and offers a promising approach to mitigate the environmental impact of RM.