Bio-reduction of Co and Ni bearing Manganese Minerals

Laterites and Mn-nodules are potential new sources of Co that can be extracted by microbial processes. The key to exploiting these resources and optimising processing pathways is an understanding of the redox reactions at the microbial-Fe and Mn mineral interfaces. Determining the mechanisms of the interaction between microbes and Co-bearing Fe and Mn hydroxyoxide phases is critical to understanding the natural biogeochemical cycling of cobalt, and also the release of this technologically important metal from potential ores during bioprocessing. The Fe and Mn mineralogy of these, often poorly crystalline, ferruginous concentrations comprises the ferri- and mangano-hydroxyoxides with cobalt present as both Co(II) and Co(III). Dissimilatory Fe(III) and Mn(IV) reduction by microorganisms provides a pathway to extract Co from these sources; the controls on the electron transfer processes in the key microbial-mineral interactions of Mn is less well known than Fe, and that of Co and Ni are little studied. Extracellular polymeric substances including lipopolysaccharides are thought to have varying importance in microbial-mineral interactions, and cytochromes, pili and secreted flavins may play a key role in electron transfer [1,2].
The student will elucidate the role of microbial reduction of Mn hydroxyoxides in controlling Co fate by examining the interaction between Geobacter species and Mn and Mn/Fe oxyhydroxides; Co and Mn are positively correlated in laterites while Ni correlates with MnO2 in Mn-hydroxides in Mn-nodules. A suite of microcosms containing potential ores will be studied using a range of state of the art microbial and geochemical techniques. Synchrotron radiation is crucial to exposing the mechanisms of behaviour of these transition metals by determining the redox process involved and the spatial relationship between the organic and inorganic components. In particular, scanning transmission X-ray microscopy (beamline I08, DLS) provides, at a scale of 40nm, elemental distributions, metal oxidation states and structural information. Measurement the C K-edge and Mn L2.3, Co L2.3 and Fe L2,3 edge will identify the relationship between microbial species and the oxidation states of the products of different microcosms [3,4]. This will lead to a better understanding of how Co is cycled in the environment, and also help optimise the leaching processes and mineral processing scale-up development.