In-situ seepage-type microwave-absorbing composite: Preparation and application for enhancing remediation of PAHs-contaminated soil

Enhanced microwave remediation via microwave-absorbing materials is one of the promising methods for remediating soils contaminated with polycyclic aromatic hydrocarbons (PAHs). To facilitate the large-scale in-situ implementation, a seepage-type microwave-absorbing composite (STMAC) capable of in-situ seepage distribution has been successfully developed by modulating viscosity regulators and flow rate improvers. The prepared STMAC was characterized via SEM, EDS, specific surface area/pore size analysis, and vector network analysis. Column migration and microwave-enhanced remediation tests were designed to investigate the material's fluidity and microwave-enhanced degradability. Characterization results revealed that the STMAC exhibits a uniform mesoporous structure and excellent electromagnetic loss capability. Based on these properties, formulation optimization showed that carboxymethyl cellulose (CMC) and glycerol (GLY) are the optimal viscosity control agent and flowability improver, with their optimal concentrations determined as 2 g·L⁻¹ and 5 g·L⁻¹, respectively. The material achieved 100% particle penetration and uniform distribution in unsaturated porous media. Under microwave remediation (600 W for 20 minutes), the removal rates for naphthalene (Nap), fluorene (Flu), and pyrene (Pyr) reached 69.8%, 92.5%, and 87.0%, respectively. Exhaust gas analysis confirmed that the material's 'hotspot effect' facilitates in-situ degradation of PAHs, reducing direct emissions of volatile PAHs by over 85%. This technology provides an efficient strategy for the in-situ remediation of PAHs-contaminated soil. • A flowable microwave absorbent (STMAC) was developed using magnetic walnut shell biochar as the substrate. • STMAC achieves 100% particle penetration and uniform dispersion in unsaturated porous media. • Synergistic coupling of microwave absorption and catalytic oxidation enables enhanced PAHs degradation. • This strategy eliminates soil excavation and mixing, enabling large-scale in-situ remediation.