In the context of deep-sea mining activities or submarine mine tailings disposal, dissimilatory iron reducing bacteria may play an important role in biogeochemical reactions concerning iron oxides placed on the sea bed. Toxic effects on coastal sediments may result from the release of different metals (e.g., Cr, V, Cu, Zn, Ni) and metalloids (e.g. As) contained in the iron oxides (e.g., magnetite) in the tailings. At the moment, we have little knowledge on the microbial reductive dissolution of iron oxides under marine conditions and the related potential release of trace elements. The goal of this work was to study the extent and kinetics of this process under marine conditions and the potential release of trace elements. To this end, batch experiments were performed using a number of iron ore samples from Chilean and Swedish mines and a mine tailings sample. The determined elemental composition of the Fe-oxides in the tailings showed relatively high amounts of trace elements (e.g. Mn, Zn, Co) compared with those of the iron ore samples (LA-ICP-MS and EMPA analyses). This enrichment of trace elements in the tailings oxides might occur during the separation process at the iron ore processing plant. The batch experiments prepared with artificial seawater (pH 8.2), a marine microbial strain (Shewanella loihica) and lactate as electron donor and carbon source, were conducted at 10 ○C in the dark for up to 113 days. Samples were collected at different times to measure lactate, acetate, Fe(II) and trace element concentrations in solution. Based on the consumption of lactate and production of acetate and aqueous Fe(II), the magnitude of microbial reduction of Fe(III) was calculated using a geochemical model including Monod kinetics. Furthermore, the model was used to simulate and evaluate the release of the trace elements detected in solution (e.g., Mn, V, Ga, Cu and As).

Bioreductive dissolution of Fe(III) oxides from metal mine tailings disposal offshore

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.