Efficient capture of U(VI) by Fe-doped biochar derived from agricultural waste

Fe@PBC was synthesized via facile pyrolysis and in-situ reduction using pig manure as low-cost biomass precursor. • Fe@PBC exhibits ultrahigh U(VI) adsorption capacity of 623.7 mg/g and fast equilibrium within 60 min. • Excellent anti-interference ability is achieved with removal efficiency >93% under coexisting cation interference. • U(VI) immobilization is dominated by Fe-mediated reduction coupled with O/N functional group complexation. • Surface chemical properties outweigh physical structure in governing U(VI) adsorption performance. The oxidized pig manure biochar doped with reduced iron species (Fe@PBC) was fabricated through facile pyrolysis and in-situ reduction to overcome the drawbacks of conventional carbon-based adsorbents for U(VI) adsorption, including agglomeration, insufficient active sites, weak reducibility and poor anti-interference capacity. An ultra-high adsorption capacity of 623.7 mg/g, fast adsorption equilibrium within 60 min and excellent selectivity toward U(VI) even under interference of coexisting cations were achieved by Fe@PBC. The high removal efficiencies were maintained in tap water and surface water and the stable adsorption performance was retained for at least 6 cycles. Notably, although the coconut shell-derived biochars exhibited significantly higher specific surface areas and more developed mesopores, they showed markedly inferior U(VI) uptake relative to the pig manure-derived counterparts, confirming that surface chemical functionalities, rather than physical pore structures, governed the adsorption process. Besides, the U(VI) immobilization mechanism was attributed to surface complexation by oxygen- and nitrogen-containing functional groups, with the possible participation of iron oxides and iron (oxy)hydroxides in the adsorption process. The column experiments further demonstrated that the breakthrough curves were well described by the Thomas and Yoon-Nelson models, with the breakthrough time being prolonged at lower flow rates, higher adsorbent dosages, and lower influent U(VI) concentrations, confirming the practical applicability of Fe@PBC for continuous wastewater treatment. The low-cost and eco-friendly adsorbent derived from agricultural waste was demonstrated to hold promising potential for efficient remediation of U(VI)-contaminated wastewater. Download: Download high-res image (186KB) Download: Download full-size image