Beyond Biorecovery: environmental win-win by biorefining of metallic wastes into new functional materials

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The last 30 years' research on metal biorecovery from wastes paid scant attention to the strong CONTEMPORARY demands for (i) conservation of dwindling vital resources (e.g platinum group metals (PGM) and, recently rare earth elements, (REE), base metals and uranium) and (ii) the unequivocal need to extract and refine them in a non-polluting, low-energy way. On the other hand, 21stC technologies increasingly rely on nanomaterials as these have novel properties not seen in bulk materials. Bacteria can fabricate nanoparticles, bottom up, atom by atom, with exquisite fine control offered by enzymatic synthesis and bio-scaffolding that chemistry cannot emulate. Bio-nanoparticles have proven applications in green chemistry, low carbon energy, environmental protection and in, potentially, photonic applications (e.g. nano-Au). Bacteria can be grown scalably and cheaply, i.e. step changes in facile production, scalability and price. Recent work showed the ability of bacteria to make these nanomaterials from primary and secondary wastes, yielding, in some cases, a metallic mixture which can show better activity than 'pure' nanoparticles. Fabrication of structured bimetallics can be hard to achieve by chemical means. For some metals like REEs and uranium their biorecovery from wastes (U) and scraps (REE) into bulk crystalline minerals can make 'enriched' solids for delivery into further commercial refining to make new magnets (REEs) or nuclear fuel (U). Biofabricating these solids is beyond the ability of living cells although biogenic nano-uranium phosphate can be used to 'hoover' base metals (and radionuclides) with a capacity several orders of magnitude greater than commercial ion exchangers.This project will operate at several levels of complexity, maturity and risk. Base metal mining wastes (e.g. Cu, Ni) will be biorefined into concentrated sludges for chemical reprocessing or alternatively for evaluating the scope to make base metal-bionanoproducts. U-mining waste will be biorefined into phosphate minerals for commercial fabrication into nuclear fuels. Precious metal wastes will be converted into bionanomaterials for catalysis and energy applications. In all of these examples the environment will be spared the dual impact of both the primary source pollution and the high energy demand of processing from primary 'crude'.Metallic scraps present problems as they require strong acids for dissolution. Approaches will include the use of acidophilic bacteria, use of alkalinizing enzymes or using bacteria to first make a chemical catalyst (under benign conditions) which can then convert the target metal of interest from the waste leachate into new nanomaterials (a hybrid living/nonliving system, already proven). The interface between biology, chemistry, mineralogy and physics, exemplified by nanoparticles in their unique 'biochemical nest', will receive special attention as this is where major discoveries are to be made; hence cutting edge technologies (e.g. X ray microscopy with nanoscale elemental mapping) will be applied in order to relate structure to function, and validate the contribution of upstream waste amendment, doping or 'blending' to these, as well as novel materials processing already shown to increase bio-nanoparticle efficacy.Secondary wastes to be 'scoped' for biorefining will include magnet scraps (REEs), spent automotive catalysts, road dusts (precious metals, Fe,Ce) and electronic scrap (Cu, precious metals). Their complexity and refractory nature makes for a higher 'risk' than with mine wastes but the 'payoff' compensates, in that the volumes tend to be lower, and the potential for 'doping' or 'steering' to fabricate/steer engineered nanomaterials is correspondingly higher. The B3 project will have an embedded significant (~15%) Life Cycle Analysis assessment of the systems chosen for special focus, and end-user trialing following scoping studies in conjunction with an industrial platform.