Abstract
ABSTRACTThe reduction of Cr(VI) by the metal-reducing bacterium Shewanella oneidensis MR-1 was evaluated, to determine the potential for exploiting Cr(VI) bioreduction as a means of treating chromate conversion coating (CCC) waste streams. Inclusion of Cr(VI) at concentrations ≥1 mM inhibited aerobic growth of S. oneidensis, but that organism was able to reduce Cr(VI) at a concentration of up to 1 mM under anaerobic, nongrowth conditions. S. oneidensis reduced Cr(VI) in the presence of common CCC constituents, with the exception of ferricyanide, when these CCC constituents were included at concentrations typical of CCC waste streams. Ferricyanide inhibited neither aerobic growth nor metabolism under aerobic, nitrate- or iron-reducing conditions, suggesting that the ferricyanide-depended inhibition of Cr(VI) reduction is not due to broad metabolic inhibition, but is specific to Cr(VI) reduction. Results indicate that under some conditions, the activities of metal-reducing bacteria, such as S. oneidensis, could be exploited for the removal of Cr(VI) from CCC waste streams under appropriate conditions.
Highlights
Galvele’s critical acidification model first introduced in 1976 allows the estimation of a critical potential, Ecrit, if the concentration of aggressive species in pits or crevices is known[1]
Pits and crevices are treated as the same phenomenon from an electrochemical point of view, the sole difference being the diffusion length
As noted by Galvele[1,2], the critical potential can be estimated by measuring the anodic polarization behavior of the material of interest in pit- or crevice-like solutions prepared with reagent grade chemicals
Summary
Galvele’s critical acidification model first introduced in 1976 allows the estimation of a critical potential, Ecrit, if the concentration of aggressive species in pits or crevices is known[1]. In this model, pits and crevices are treated as the same phenomenon from an electrochemical point of view, the sole difference being the diffusion length. As noted by Galvele[1,2], the critical potential can be estimated by measuring the anodic polarization behavior of the material of interest in pit- or crevice-like solutions prepared with reagent grade chemicals. A brief review of the various proposed pitand crevice-like solutions in stainless steels is presented below
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