Lead (Pb) and arsenic (As) contaminated soil poses severe threats to human health. This study proposes a novel approach for synchronous stabilisation/solidification (S/S) of Pb and As contaminated soil and explains the immobilisation mechanisms in red mud-modified magnesium phosphate cement (MPC). Experimental results show that incorporation of red mud in MPC binder retarded over-rapid reaction and enhanced compressive strength via the formation of (Al,Fe,K)PO₄·nH₂O compounds as indicated by X-ray diffractometer (XRD) and elemental mapping. The presence of Pb had a marginal effect on the MPC reaction; however, the presence of As suppressed the generation of MgKPO₄·6H₂O, leading to a significant delay of setting time and a reduction of compressive strength. Extended X-ray absorption fine structure (EXAFS) analysis proved that Pb²⁺ strongly coordinated with the PO₄^3–, whereas AsO₂– gently coordinated with K⁺. The MPC binder displayed an excellent immobilisation efficiency for Pb (99.9%), but was less effective for As. The use of red mud enhanced the As immobilisation efficacy to 80.5% due to strong complexation between AsO₂– and Fe³⁺. The treated soils fulfilled requirements of metal(loid) leachability and mechanical strength for on-site reuse. Therefore, red mud-modified MPC can be an effective binder for sustainable remediation of Pb and As contaminated soil.

铅（Pb）和砷（As）污染的土壤对人类健康构成了严重威胁。这项研究为铅和砷污染土壤的同步稳定/固化（S / S）提供了一种新方法，并解释了红泥改性磷酸镁水泥（MPC）的固定机理。实验结果表明，通过X射线衍射仪（XRD）和元素分析表明，通过形成（Al，Fe，K）PO ₄ ·nH ₂ O化合物，在MPC粘结剂中掺入赤泥可延缓过快反应并提高抗压强度。映射。Pb的存在对MPC反应影响很小；但是，As的存在抑制了MgKPO ₄ ·6H ₂的生成O，导致凝固时间的显着延迟和抗压强度的降低。扩展的X射线吸收精细结构（EXAFS）分析证明，Pb ²⁺与PO ₄ ^3–具有强配位作用，而AsO ₂ –与K ⁺具有适度配位作用。MPC粘合剂对Pb的固着效率极高（99.9％），但对As的有效性较低。由于AsO ₂ –与Fe ³⁺之间的强络合作用，赤泥的使用将As的固定效率提高到80.5％。。处理后的土壤满足现场重复使用的金属（胶体）浸出性和机械强度的要求。因此，赤泥改性的MPC可以有效地修复受Pb和As污染的土壤。