EVALUATING MICROBIALLY MEDIATED IMMOBILIZATION OF VANADIUM IN A SHALE ORE

Vanadium (V) has a number of industrial uses but its primary use is in steel alloys. Global demand is increasing, which can be expected to increase the volume of V cycled in water and soil. Solubility of this metal is a function of oxidation state (V(V) > V(IV) > V(III)). The reduction of V to a lower oxidation state can therefore immobilize this metal. Research has shown that some bacteria are capable of reducing V(V) to V(IV). However, there have been no studies on the impact of bacterial V respiration on the mobility of V associated with a mineral phase.

We investigated V biogeochemistry in batch and column incubation studies in order to track the mobility of V associated with a shale ore in the presence of Shewanella putrefaciens CN-32, a dissimilatory metal-reducing bacteria. This ore was obtained from a vanadium mine in Nevada. Vanadate salts were used for comparison in each study.

In batch treatments, soluble sodium vanadate and V-ore treatments were incubated under anaerobic conditions for ~30 days. Na-vanadate treatments with bacteria showed a blue colour change within 24 hours, while controls without bacteria remained colourless. This was indicative of bacterial mediated V reduction. The ore masked colour changes that could be associated with reduction. However, soluble V decreased in the presence of bacteria, but increased in solution without bacteria. Transmission electron microscope images coupled with energy dispersive spectra also indicated that V was sorbed to the bacteria.

For column studies, glass columns were either packed with coarse sand and relatively insoluble calcium vanadate, which gave columns a yellow hue, or were packed with the V ore. S. putrefaciens CN-32 in suspension was introduced to the columns. Ca-vanadate columns with bacteria showed a colour change to greenish-blue after several hours, indicating V reduction. Controls without bacteria retained their yellow hue and had a higher V mobilization than treatments with bacteria. Results are pending for column treatments with V-ore. The outcome of these studies can be used to help predict V mobility through soil, sediment and ore tailings.