Insight into Plasma-Synthesized nZV Fe/Ni–BC Coupled with Sulfite Effect for Enhanced Removal of U(VI)

The presence of hexavalent uranium (U(VI)) in aqueous systems poses a severe environmental threat due to its high solubility and toxicity. Herein, we developed a synergistic strategy integrating plasma-synthesized nanoscale zerovalent Fe/Ni nanoparticles supported on biochar (nZV Fe/Ni-BC) with a sulfite (S(IV)) effect for highly efficient U(VI) removal. The nZV Fe/Ni-BC composite provided a highly active and stable scaffold, while S(IV) served a dual function as radical precursors (generating SO₃^•- and SO₄^•-) and antipassivation agents, inhibiting Fe⁰ surface oxidation. This synergy resulted in a U(VI) removal efficiency of 96.71% and a high capacity of 187.92 mg g^-1 under mild conditions (pH 6.0). Mechanistic investigations confirmed that the reduction of U(VI) to insoluble U(IV) was facilitated through multiple pathways, including direct electron transfer from Fe⁰, atomic hydrogen mediated by Ni, and S(IV) derived radicals. The composite exhibited excellent stability over five consecutive cycles, maintaining 88% efficiency, and its performance was significantly enhanced by humic acid up to 99.60%, demonstrating robustness in complex water matrices. This work provides a sustainable and highly effective remediation platform for uranium-contaminated water.