Biohydrometallurgy as a remediation strategy for marine sediments contaminated by heavy metals

This paper deals with biohydrometallurgy applied for the remediation of sediments contaminated by heavy metals. Both metal mobilization by bioleaching and metal stabilization by sulfate reducing bacteria stimulation have been investigated. In the first case, leaching experiments were performed with different microbial strains: i) autotrophic Fe/S-oxidizing bacteria, ii) heterotrophic Fe reducing bacteria, and iii) a mix of them. The highest extraction yields were 90% for Cu, Cd, Hg and Zn and were achieved with a consortium of the autotrophic and the heterotrophic strains. In the second case, anaerobic microcosm experiments were performed according to a full factorial experiment where the main factors were: i) acetate, ii) inoculum Of alloctonous sulfate-reducing bacteria and iii) treatment time. Significant changes on metal partitioning were observed in all the investigated treatments: in particular, Cu, Pb and Zn concentrations in the mobile fraction were reduced and the ones in the oxidizable fraction significantly increased. Anaerobic processes where hypothesized to lead to the formation of metal sulfides, relatively stable and less bioavailable than mobile fractions. The obtained results open new perspectives for biohydrometallurgy applied in the context of remediation strategies for sediments contaminated by heavy metals.