From waste to resource: development of selenium-enhanced iron-carbon galvanic materials from landfill leachate for efficient mercury and thallium detoxification in contaminated waters

Landfill leachate, characterized by high concentrations of organic pollutants, ammonia nitrogen (NH₃-N), and heavy metals (HMs), impacts ecosystems and human health threats. Conventional treatment technologies exhibit significant efficiency limitations in addressing such complex pollution, necessitating innovative remediation strategies that integrate pollutant removal with resource recovery. This study proposes the development of a novel in-situ selenium-modified iron-carbon (Se-Fe-C) galvanic material derived from landfill leachate. The core objective is to establish an efficient detoxification system for Hg²⁺/Tl⁺ contaminated water, while elucidating the material's adsorption mechanisms and reaction pathways through systematic characterization. A homogeneous Fe-C matrix was engineered via Se doping and pyrolysis optimization following an orthogonal experimental design. Key preparation parameters were systematically evaluated, including Se dosage and thermal treatment conditions. To investigate physicochemical properties and adsorption behaviors, comprehensive material characterizations were performed using XPS, BET analysis, FTIR, TGA, SEM-EDS, and elemental mapping. The optimized Se-Fe-C composites demonstrated exceptional adsorption capacities, achieving Hg²⁺ removal efficiencies of 325.79-542.96 mg/g and Tl⁺ uptakes of 43.65-75.21 mg/g. These capacities surpass most Fe-C or biochar adsorbents reported in the past five years by 40-370 % and are comparable to Se-functionalized activated carbons produced from pure precursors. Kinetic analyses revealed distinct mechanisms: Hg²⁺ adsorption followed complex electrochemical interactions involving galvanic corrosion, while Tl⁺ removal exhibited heterogeneous surface-driven characteristics. Post-adsorption XPS confirmed redox-mediated transformations of Hg⁰/Hg²⁺ to Hg⁴⁺ and Tl⁺ to Tl³⁺, validating electron transfer between contaminants and the Se-Fe-C matrix. This work advances the understanding of galvanic-driven HM adsorption mechanisms and establishes a scalable material engineering strategy for Hg/Tl remediation. The developed Se-enhanced Fe-C material provides a sustainable solution for simultaneous HM removal and resource recovery, offering new perspectives for landfill leachate management and environmental protection.