Sb(III) removal from groundwater using Fe-carbon composites derived from CO2-pyrolyzed livestock and industrial wastes

Abstract

Industrial discharge of antimony (Sb) presents a critical factor to groundwater (GW) contamination, where its strong affinity to biomolecules poses public health threats. However, Sb remediation is technically challenging due to its persistence under GW conditions. To address this, this study proposes the synthesis of Fe-carbon composites from swine manure (SM) and pipe sludge (PS) via CO2-assisted pyrolysis, aiming to leverage Fe as adsorption and/or redox sites. Cofeeding PS during SM pyrolysis enhanced syngas generation and produced composites with Fe3O4 as the dominant phase. Thermochemical analysis confirmed that syngas served as a reducing agent to convert Fe oxides into zero-valent iron (Fe0), simultaneously supported by carbon-based porous structures. Sb(III) removal performance of the Fe0-carbon composite was evaluated under simulated GW conditions. The Fe0-carbon composite exhibited superior Sb(III) removal capacity of 22.78 mg g-1 compared with other Fe-based composites. Mechanistic investigations revealed two superoxide-mediated pathways: (i) surface adsorption followed by oxidation and (ii) solution-phase oxidation followed by adsorption. Computational simulations further demonstrated the feasibility of the produced composite for field-scale applications. These findings demonstrate the simplified procedures to synthesize the fully reduced Fe-carbon composites using SM and PS, highlighting their potential for effective Sb remediation in GW systems.