Coupled environmental behaviors of vanadium and organic matter during Fe(II)-induced ferrihydrite transformation in mining areas.

Vanadium (V), as a heavy metal, has different valence states that impose potential risks to ecosystems, and its occurrence is closely associated with organic carbon (OC), but it is still ambiguous how V and OC interact and influence their environmental behavior, especially in mining regions. We selected humic acid and simple organic acids as model OC compounds to synthesize Fh-organominerals, and then conducted the Fe(II)-induced transformation experiments in the presence of V to investigate the redistribution of V(IV) and V (V) and OC. The results show that V(V) is more easily encapsulated within the mineral or in interstitial spaces of Fe mineral particles than V(IV). The presence of OC could reduce more V(V) to V(IV), chelate with V(IV), and then decrease the fixation of V(IV) inside Fe minerals, where the suppression of V fixation increases with OC contents. During the Fe mineral transformation, the presence of V (especially V(IV)) could facilitate the translocation of high-molecular-weight condensed aromatic compounds from weakly-bounded pool into the strongly-bounded pool, probably preserving OC over longer time scales. These findings offer a deeper mechanistic insight into the processes responsible for the migration and fixation of V with different valence and organic carbon in the natural environment.