Sustainable Immobilization of Cadmium, Lead, and Arsenic in Contaminated Soils Using Iron–Phosphorus–Thiol-Functionalized Trachycarpus fortunei Hydrochar

Simultaneously stabilizing cadmium, lead, and arsenic in contaminated soils is challenging due to their significant differences in physical and chemical properties. This study developed a composite material by modifying hydrochar with iron (Fe), phosphorus (P), and sulfur (S) to address this issue. The iron–phosphorus–thiol-modified Trachycarpus fortunei hydrochar (H-PAL-Fe2-P-T) effectively stabilized these metals. Experimental results showed that the H-PAL-Fe2-P-T achieved over 90% stabilization for DTPA-extracted cadmium, lead, and arsenic. Characterization by XRD, SEM, and FTIR revealed structural and functional changes in the hydrochar. Column leaching tests simulating acid rain showed that the composite material maintained stable stabilization effects, with the fluctuations in the stabilization rates remaining below 20%. Additionally, the composite-modified hydrochar enhanced the stabilization of water-soluble, DTPA-extracted, and TCLP-extracted heavy metals in soil, demonstrating good stability and durability for long-term use. These findings suggest that Fe-, P-, and S-modified hydrochar is a promising and sustainable approach for the remediation of soils contaminated with cadmium, lead, and arsenic.