Immobilization and stabilization of heavy metals in coastal sediments using polycrystalline silicon-aluminum biochar-based material GBMSS: Mechanisms and performance

Coastal sediments contaminated by heavy metals (HMs) pose significant ecological risks due to their high mobility under saline and dynamic hydrological conditions. Traditional stabilization/solidification (S/S) materials (e.g., cement, sodium silicate) often fail under these challenges, while biochar alone lacks mechanical strength. This study develops a polycrystalline silicon-aluminum biochar composite (GBMSS) derived from dragon fruit peel, metakaolin, and sodium silicate to address these limitations. Through orthogonal experiments, we optimized the ratio of components (DPC:MK: SS = 2:3:3, modulus M =1.3) and demonstrated that 5% GBMSS enhanced sediment dry density (1.43 g/cm3) and reduced plasticity index by 32%, transforming high-plasticity sediment (MH) into medium-plasticity soil (ML). Under a 28-day curing period, the unconfined compressive strength of the stabilized sediment reached 2.81 MPa at the optimized ratio. Mechanistic studies revealed that GBMSS adjusted sediment surface charge (zeta potential:-31.1 mV), compressing the diffuse double layer and improving particle cohesion. Compared to conventional materials, GBMSS increased the residual fraction of HMs (Zn, Pb, Cu) by 3-10 times and reduced leaching concentrations below EPA limits even under acidic conditions (pH 2-4). While this study focused on short-term stabilization, future work should incorporate dynamic hydraulic simulations to assess long-term field performance. This work offers a green, multifunctional approach for HM immobilization and sediment reuse in coastal remediation.