Selenium and tellurium concentration by organic materials

Selenium (Se) and Tellurium (Te) are scarce (semi)metallic elements usually recovered as by-products of the chemical extraction of other metals. The proposal will exploit close relationships between these elements and organic materials to target additional resources, and extract resources in a more sustainable, environmentally sensitive manner.

Se/Te are most concentrated in rocks containing organic matter (e.g. coals, carbon-rich shales, sandstones containing oil residues or coaly matter). We also know that microbial (bacterial) activity can concentrate Se/Te. We seek to use that knowledge to predict previously unrecognized concentrations of Se/Te by study of metal sulfide ores which are known to have been formed by microbial sulfate reduction, on the basis that these microbes could have also engendered Se/Te concentration. More significantly, we will try to advance our knowledge of how microbes interact with Se/Te in rocks and soil, to develop a strategy for the microbial concentration of Se/Te on a valuable scale. To achieve this the project combines interdisciplinary expertise on Se/Te from geology, soil science, chemistry and microbiology.

The catalyst stage involves data gathering, and pilot sampling from two field sites, one in SW Ireland where some of the most Se-rich soils in the world occur, and in Scotland where a gold mine and its environs have elevated levels of Te, and the Te needs to be exploited to ensure financial viability. We have the support of Scotgold Resources, who own the gold mine, and Stantec, an international company whose portfolio includes management of metal resources.

Selenium and Tellurium concentration by organic materials: Pathways to Impact

The catalyst stage proposal is focused on improving our understanding of how organic matter and Se(+Te) are linked, in preparation for a full grant proposal. It will yield information that has an impact on exploration strategy;
(i) Understanding the residence of Se in rocks and soils (i.e. distribution between organic and inorganic fractions) will influence the chemistry that might be used to extract Se in the most efficient manner.
(ii) Residence data will also help to predict the degree to which Se is bioavailable, to microbial processing or phytoaccumulation.
(iii) Bulk Se concentration data will help us assess if exploitation of Se-rich rock and soil would be competitive in comparison with other sources such as fossil fuel by-products (note the latter is a major consequence of the organic-selenium association but the SoS programme excludes us from study of it. We do, however, hold data on them directly pertinent to Se supply).
(iv) Microbiological studies will help us assess if microbial upgrading is a viable strategy to pursue in developing new Se resources, as has been commercially successful in gold/copper/uranium recovery (note Se is generally in anionic, not cationic, form so new approaches need to be developed), and encouraged by results from the EC BioShale project.
(v) If Se is shown to become enriched in soil over bedrock in some circumstances, this could help develop a bioaccumulation strategy.

The output from the catalyst stage will be summarized as a briefing document which will be distributed to potential industry partners using the SoS Network, the Selenium and Tellurium Development Association, and our catalyst stage partners (Scotgold, Stantec). We also plan to publish data from the SW Ireland pilot field study.

This data will be incorporated into a full grant proposal directed towards optimizing the choice of protolith and microbial processing of the protolith to maximize Se/Te extraction. We will deliver:
1. A conclusion about whether selected bedrock and/or soil could represent a product sufficiently rich in Se/Te to be a valuable commodity suitable for further upgrading.
2. Identification of any sulfide ore types produced by microbial sulfate reduction (MSR) which might have associated Se/Te enrichment (also due to MSR) that have not been recognized and exploited.
3. A plan for the optimization of Se/Te concentration by microbial activity. Existing bio-exploitation studies show that the microbial community has to be fine-tuned to the metal/metalloid concerned.

The implications of this research are:
(i) Reducing environmental impact via bio-processing/in situ leaching etc.
(ii) Maximizing recovery of resource, and hence sustainable development.
(iii) Development of an extraction strategy which can be applied within UK/Europe.

We also note that Se-respiring microbes are known to produce elemental selenium nanospheres with unique properties that cannot be replicated synthetically (Oremland et al. 2004. Applied Environ. Microbiol. 70, 52-60), indicating it will be worthwhile to explore their potential in nanotechnology .

We have a potential collaborator in Brazil (Ronaldo Santos, Center for Mineral Technology, Federal University of Rio de Janeiro, on advice of Alexandre Roccatto, Area Director - Engineering and Exact Sciences, FAPESP - State of São Paulo Research Foundation) whose involvement can be introduced at the main grant stage.