Optimisation of biomineral precipitation in chemoorganotrophic systems for metal recovery

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BackgroundBiologically-induced mineralization is common in microbes (1). Fungi are capable of precipitating minerals including oxides, carbonates, phosphates and oxalates by differing mechanisms but all dependent on chemoorganotrophic metabolism, and varying nutritional and environmental conditions (2-4). Such processes receive little attention in the contexts of metal biogeochemistry or biorecovery. Through manipulation of growth conditions, it is possible to promote metal bioprecipitation which provides a means of biorecovery of metals. Further, biominerals can be of nanoscale dimensions in spherical, nanocrystalline, rod and tube-like forms (1). This provides further applied interest in view of the very high surface area to volume ratio and reactivity of such preparations. Oxalates and carbonates, for example, are important in many industrial contexts including as precursors of other useful compounds, e.g. oxides. Industry seeks improved means of making nanoscale preparations of such substances (5,6). There is a dearth of information in this area and this PhD project therefore provides an excellent opportunity to obtain fundamental data and increase understanding of biomineralization in the biogeochemistry of Co and other metals, and applied significance in bioprocessing and production of useful biomineral products.WorkplanThis project will investigate the ability of selected geoactive fungal species to biomineralize Co as insoluble biominerals (primarily oxalates, phosphates, carbonates) with the aim being characterisation and optimisation of each process for maximum yield. A range of nutritional and physico-chemical variables, e.g. carbon and nitrogen source, and pH, will be investigated for the different biomineral systems, along with the mechanisms involved in biomineral precipitation. The overall objective is to optimise the maximal yield of desired biominerals, and to understand conditions that enable bioprecipitation at various scales including nano- and microscale. Conditions necessary for selective recovery of Co from metal mixtures in leachates will be determined, as well as the possibility of obtaining other precipitates from liquors, such as those of Ni. The student will work alongside the PDRA, and will directly interact with other research groups through receipt of materials and leachates, chemical analyses of ores and leachates, and comparison of results with chemolithotrophic metal leaching and bioprecipitation studies. The student will receive cross-disciplinary training in geomicrobiology and geomycology, environmental geochemistry and mineralogy, and will interact with other ongoing research projects and training networks, e.g. Geo-Rep-Net, Geomicrobiology Network, that are concerned with metal mobility in the environment.References(1) Gadd, G.M. Metals, minerals and microbes: geomicrobiology and bioremediation. Microbiology 156, 609 - 643 (2010).(2) Gadd, G.M. Geomycology: biogeochemical transformations of rocks, minerals, metals and radionuclides by fungi, bioweathering and bioremediation. Mycological Research 111, 3-49 (2007).(3) Rhee, Y.J., Hillier, S. & Gadd, G.M. Lead transformation to pyromorphite by fungi. Current Biology 22, 237-241 (2012).(4) Wei, Z., Liang, X., Pendlowski, H., Hillier, S., Suntornvongsagul, K., Sihanonth, P. & Gadd, G.M. Fungal biotransformation of zinc silicate and sulfide mineral ores. Environmental Microbiology 15, 2173-2186 (2013). (5) Aimable, A., Torres Puentes, A. & Bowen, P. Synthesis of porous and nanostructured particles of CuO via a copper oxalate route. Powder Technology 208, 467-471 (2011).(6) Zhang, S., Wang, F., He, D. & Jia, R. Batch-to-batch control of particle size distribution in cobalt oxalate synthesis process based on hybrid model. Powder Technology 224, 253-259 (2012).