Uranium immobilization via sulfur-modified Fe⁰ nanoparticles: U(VI) trapping kinetics and long-term stability...

The modification of nanoscale zero-valent iron (nZVI) by loading or incorporating sulfur into the iron crystal lattice can augment their efficacy in the removal of hydrophobic contaminants from wastewater. Nevertheless, the reactivity of sulfur-embedded nZVI (SnZVI) in immobilizing hydrophilic uranyl ions and the long-term stability of the sequestered uranium has received little attention. This study employed Na₂S₂O₄ to modify the nZVI with different S/Fe molar ratios (0.1 and 0.3), following one-step and two-step approaches to create SnZVI-1 and SnZVI-2, respectively. Both experimental and theoretical calculation results revealed that the U(VI) ions exhibited low affinity for the surface of SnZVI. Additionally, the hindered electron transfer between the electron donors of SnZVI and U(VI) led to a diminished U(VI) reduction efficiency for SnZVI-1 (50.71 %∼67.74 %) and SnZVI-2 (68.03 %∼86.89 %), inferior to that of nZVI (78.63 %∼90.78 %). Consequently, the uranium detachment ratios of SnZVI (0.04 %∼0.85 %) during the 210-day stability assessment were higher compared to those of nZVI (0.04 %∼0.34 %). Hence, this study offered novel insights into how sulfur affected the adsorptive and redox properties of nZVI for U(VI) immobilization through solid and aqueous samples analyses, complemented by theoretical calculations. The findings are instrumental in designing SnZVI for effective and environmentally sound treatment of uranium-contaminated radioactive wastewater.