Hydrophobic MOF-modified graphite tailings–red mud mixtures for pavement bases: Heavy metal stabilization and drying shrinkage control

The utilization of industrial solid waste for the preparation of pavement base materials is an effective pathway toward sustainable development. However, graphite tailings exhibit a low plasticity index, leading to difficulties in compaction and a high tendency to crack when used in base layers. Although red mud can be introduced to improve plasticity, its large-scale application is restricted by the leaching risk of Pb(II). To overcome this contradiction, a hydrophobic metal–organic framework (MOF), MIL‑101‑NH 2 ‑H, was designed and synthesized in this study with the dual aim of stabilizing heavy metals and improving the drying shrinkage behavior of the composite base material. The results show that MIL-101-NH 2 -H exhibits excellent Pb(II) adsorption performance. The lead concentration in the leachate of the mixture treated with 0.1 wt% MIL-101-NH 2 -H is below 0.1 mg/L, meeting the Class IV groundwater standard for agricultural water in GB/T 14848–2017, while that of the control group (3.64 mg/L) far exceeds the limit. For engineering properties, the control group shows a 7 days UCS of 3.3 MPa and a drying shrinkage strain of 706 × 10 −6 . At 0.1 wt% dosage, MIL-101 and MIL-101-NH 2 present comparable mechanical and shrinkage behaviors to the control, whereas MIL-101-NH 2 -H increases the 7 days water-immersed UCS by 26.5% and reduces the drying shrinkage strain by 38.7%. This improvement is attributed to the hydrophobic functional groups of MIL-101-NH 2 -H, which hinder water transport, thereby suppressing the development of capillary tension and reducing the surface tension of the pore solution-fundamental factors in mitigating drying shrinkage. In addition, the chelation/coordination interaction between amino groups in MIL‑101‑NH 2 ‑H and Pb(II) provides abundant active adsorption sites, effectively decreasing the leaching of Pb(II) ions. Overall, this study indicates that MIL-101-NH 2 -H, as a multifunctional additive, can synergistically enhance the mechanical properties, volumetric stability, and environmental safety of solid waste-based pavement base materials, offering an innovative strategy for the high-value utilization of industrial solid waste.