UC Riverside

Exposure to vanadium (V) results in adverse health outcomes in humans and a plethora of species in the environment across trophic levels. V is released from rock, slag and mine tailings, where it is able to oxidize to vanadate (VV) (HnVO4 −3+n), which poses the greatest risk to human health. Vanadate is highly soluble unlike its VIII or VIV, and is readily taken up by well systems, resulting in human exposure in areas where water treatment is minimal. However, the geochemical controls that determine the mobility of V in the environment are poorly understood, making the behavior of V in the subsurface difficult to predict. This dissertation addresses this knowledge gap by investigating the abiotic reactions of V with common iron and manganese mineral phases. These mineral phases are already known to play an important role in the fate and transport of similar contaminants, but many aspects of their specific reactivity towards V are unknown. To address this knowledge gap, their surface capacity, adsorption affinity and their ability to retain vanadate via surface complexation is investigated. The vanadate adsorption capacity and surface affinity are both found to be inversely proportional to the crystallinity of the oxide examined. One manganese oxide, birnessite is also known to promote the oxidation of many trace metal contaminants. The oxidative capacity of birnessite towards VIV is much greater than its surface capacity for VV. At the aggregate scale, birnessite, V and Fe oxides coexist in close spatial proximity where rates of diffusion limit the transport of solutes. In such an environment, birnessite effectively oxidizes VIV and retains more VV than adjacent Fe oxide phases. Further, FeII-bearing oxides can reduce VV back to VIV. However, this pathway is slow compared to the oxidation rate of VIV by birnessite. This suggests that surface complexation of vanadate, even by birnessite is a greater attenuation pathway than abiotic FeII-mediated reduction. The result of this research emphasizes the role of abiotic surface processes in constraining the mobility of V within the soil matrix which will improve the reliability of models implemented in the management and reclamation of V contaminated sites.