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.