Microbial reduction of metalloid oxyanions: significance of geochemical factors

Background and rationale
Fungi and bacteria are the major geoactive agents in terrestrial habitats and can transform Se and Te oxyanions by reduction, which reduces mobility and toxicity (Gadd, 2010; Glasauer et al. 2013). Se/Te reduction appears to be a widely found property, and has the potential to immobilize substantial amounts of these metalloids as elemental Se or Te (Gadd, 1993; Gharieb et al. 1995) which can be deposited intracellularly or extracellularly in nanoparticulate, -crystalline and -rod morphologies (Hockin and Gadd, 2003, 2006; Oremland et al. 2004; Baesman et al. 2007). However, almost all detailed research has been carried out with anaerobic selenate-respiring or sulfate-reducing bacteria (Hockin and Gadd, 2003, 2006). Surprisingly little information is available for Se or Te reduction in aerobic organisms although the capability seems ubiquitous (Gharieb et al. 1995). Further, almost nothing is known about geochemical influences and limitations on metalloid reduction in aerobic habitats. How can metalloid reduction proceed in such a complex environment as soil or sediment in the presence of multiple mineral phases, other redox-sensitive metal(loid)s, e.g. Fe, As, varying nutrient levels and organic content, and other organisms?

Workplan
The aim of this project is to examine geochemical influence on Se/Te reduction by aerobic microbes, using model systems of simple to intermediate complexity, in order to identify and understand what limitations there are to the process, and their importance. The influence of other metal and mineral components, organic components and nutrients on metalloid reductive capabilities of geoactive bacterial and fungal strains will be characterised, together with the abilities of strains to effect other metal-mineral transformations. Simple pure culture systems as well as mixed bacterial-fungal microcosms and simulated soil matrices will be used. Abiotic influence on the form and location of precipitated metalloids will also be investigated. The project will therefore produce fundamental scientific information regarding aerobic Se/Te reduction and its significance, and therefore add to our current understanding of Se/Te biogeochemistry. This project will use an interdisciplinary approach and the student will receive training in geomicrobiology and environmental mineralogy with associated analytical and preparative techniques, including growth and manipulation of experimental organisms, and techniques including atomic absorption spectrophotometry (AAS), X-ray powder diffraction (XRPD), and advanced light and electron microscopy, X-ray element analysis and mapping.

We have fully engaged with stakeholders and beneficiaries from the outset, and used the catalyst stage to develop relationships with industrial, governmental and NGO partners. They have helped shape the research plan by exchange of knowledge, strategic plans, and problems. Key issues they raised have allowed us to identify knowledge gaps addressed in the Case for Support:
* Identification of potential resources (lack of data & predictive models)
* Low current value requires low cost production
* Lack of rapid analytical capability with the requisite detection limits
* Dependence on energy intensive smelting and refining of base metals as the dominant source of supply
* How to process alternative ores for recovery
* Lack of well understood mass flows in recovery operations, and thus a lack of optimisation
* Their deleterious role in the recovery of gold from ores
Our research covers four areas of impact outside the scientific community:
1 Identification and discovery of alternative sources of Se and Te. Beneficiaries will include BGS, USGS, Geological Survey of Cyprus and Geological Institute of Romania - NATIONAL AGENCIES with the responsibility to advise government on resource statistics and policy and to provide impartial advice to industry, academia and the public. Our research will enable them to provide improved Te and Se resource statistics and more realistic estimates of future supply to manufacturers, qualified by a sound understanding of the feasibility of extraction and processing. PRIVATE SECTOR COMPANIES who will benefit include those who are already mining Se and Te-rich material but with little understanding of the location of these elements in their deposits and how to recover them; and those actively exploring for new deposits that could include Se and/or Te as a co-product. Our partners include Platina, Vale, Glencore, AngloGold Ashanti and Scotgold. Our research will provide: a) data on the occurrence of Te and Se in crustal systems; b) data for companies to perform a cost-benefit analysis for recovery of Te and Se currently mined, and c) process-based predictive models for the efficient discovery of new economic deposits of Te and Se. One of our UK study sites is a SSSI owned by Leicester City Council and managed by Natural England. These PUBLIC SECTOR ORGANISATIONS will benefit through enhanced scientific understanding of the site, helping them promote its value to the general public.
2 Improved analytical and geometallurgical characterisation techniques. Beneficiaries will be PRIVATE SECTOR COMPANIES who are mining Se and/or Te bearing ore, including AngloGold Ashanti, Mandalay Resources, and Glencore, who will use our results to develop geometallurgical models for Se and Te to improve their recovery along with associated metals. Olympus will benefit through becoming a world-leader in the use of portable instruments for Te and Se determination in grade and mill control.
3 Environmentally benign, low-cost extraction techniques. This will benefit PRIVATE SECTOR COMPANIES who process ores, including partners 5NPlus, Mandalay Resources, AngloGold Ashanti and Scotgold. They will gain economic advantage through our research on new low-energy, low-environmental impact, locally-based extraction, demonstrated at pilot plant scale. The WIDER PUBLIC gain through continued access to, and reduced CO2 footprint of, modern technologies.
4 Strategic knowledge of security of supply. Beneficiaries will be GOVERNMENT AGENCIES who advise on resource strategy (BGS, SOPAC and especially through integration with USGS parallel programs), and POLICY MAKERS IN INTERNATIONAL GOVERNMENT planning future clean energy strategies. PRIVATE SECTOR end-users of Se and Te will benefit through improved integration of their supply chain, security of supply confidence, and direct contact with producers. The WIDER PUBLIC gain through development of sustainable environmental technologies to support a low-carbon society.