Immobilization and transformation behavior of V(IV) and V(V) by ferrihydrite and lepidocrocite

Ferrihydrite and lepidocrocite, as abundant iron oxides in vanadium-titanium (V-Ti) magnetite, play a crucial role in regulating the migration and transformation of V species, particularly V(IV) and V(V), in the environment. This study investigated the effects of pH, iron oxide dosage, and light exposure on the immobilization of these V species by ferrihydrite and lepidocrocite through batch experiments, and explored the transformation of iron oxides. The results indicated that the maximum adsorption capacities of ferrihydrite and lepidocrocite for V(IV) were 42.85 mg g- 1 and 36.76 mg g-1, respectively, and for V(V) were 32.18 mg g-1 and 27.64 mg g-1, respectively. Compared with V(V), ferrihydrite and lepidocrocite have a greater impact on the migration and transformation of V(IV). Mechanistically, ferrihydrite formed Fe-O-V via Fe-O bonds, while lepidocrocite formed Fe-V or complexed V ions via Fe-O-V through Fe-OH bonds. These findings deepen the understanding of the complexity of V(IV) and V(V) adsorption/desorption on the surfaces of iron oxides, providing theoretical support for utilizing iron oxides as geological adsorbents to regulate the immobilization and release of V in mining areas.