Processes governing semi-metal - PGE linkage in crustal magmatic systems: opportunities for discovery and recovery

A low carbon future for the UK depends on new and evolving technologies such as solar power and hydrogen fuel cells; these in turn are reliant on rare raw materials previously only mined in small quantities such as tellurium (Te), selenium (Se) and platinum group elements (PGE) - so called "E-tech" elements. However, at present there is considerable risk of supply shortages as the PGE can currently only be mined economically in a few countries; Te and Se are by-products of other commodities and supply risk is compounded by the historical lack of demand and an informal market ill-prepared for the predicted demand surge. Our research will tackle the security of supply of these E-tech elements by improving: i) our understanding of the processes that govern how and where these elements are concentrated in the Earth's crust; and ii) our ability to recover them with minimal environmental impact and economic cost.

To do this we are taking advantage of their behaviour in the crust - the PGE are sulphur-loving, so readily concentrate in sulphide melts in magma bodies and form minerals with sulphur, whereas Se and Te also concentrate in sulphide melts, but become sulphur-replacers in minerals. Thus their behaviour and occurrence in natural systems are strongly controlled by the same processes; in fact Te and Se may be as important as sulphur in determining PGE behaviour, which leads to differences in the actual mineralogy of the ores. This then affects how they can be best processed in order to minimise energy usage and environmental impact.

We propose to bring together researchers and industrial partners from academia, mining, mineral exploration, processing, solar panel production and fuel cell design, with the driving principle that better understanding the linkage between semi-metals and PGE in magmas will:

a) provide new insight into the key processes that determine the cycling and concentration of Te, Se and PGEs in and through crustal systems;

b) better quantify crustal fluxes and processes affecting sulphur (fractionation, contamination, melt immiscibility and volatile loss) and the related sulphur-loving elements;

c) enable the development of existing and novel ore processing techniques to improve recovery of combined semi-metal and PGE, whilst mitigating the environmental footprint of extraction and processing.

Our research covers three main areas in terms of impact, outside of the scientific community. These can be summarised within the 'discovery', 'recovery', and 'end user' categories.

In terms of discovery, future supply of PGEs are threatened by the limited geographical occurrence of economic deposits, with around 90% of production coming from South Africa, Russia and Zimbabwe, whereas Se and Te are limited to recovery as minor by-products of other commodities (chiefly copper porphyries), and are not explicit exploration targets. Both element groups have low crustal abundances, further complicating their discovery.

In terms of recovery, around 3% of the world's energy (up to 7% in Australia, and over 10% in Chile) is used in the extraction and processing of rocks. Any advances in geometallurgical understanding can have significant cost and energy savings in mineral processing.

In terms of end use, the semi metals Te and Se, and the PGE are vital for sustaining and building low carbon energy and transport infrastructure. Primary end-users of Te, Se and PGE are the producers of photovoltaic cells and automotive catalytic convertors and fuel cells. These end-users are the ultimate target of the Security of Supply initiative.

Therefore, the main beneficiaries of this research will be:

1. Companies currently exploring for PGE and/or semi metal ores.
This research will provide information on: (1) the occurrence of PGEs and semi-metals in crustal systems; (2) the distribution and preferred concentration of those elements within minerals as framework and substitution elements; and (3) process-based predictive models for the discovery of prospects for the mining of PGE and semi-metals on a wide geographical basis. Sound scientific understanding of the natural deposits of these resources is essential in developing sustainable supply through the discovery of new deposits and cost and energy efficient exploration

2. Mining companies currently extracting and processing PGE and/or semi metal ores.
In helping to identify key metallurgical characteristics of these platinum ores, the research directly impacts on recovery and processing strategies, and contributes towards enhancing the efficiency, performance and economic prosperity of the companies involved. By enhancing efficiency, this also reduces the environmental impact of mineral processing in terms of energy, resources and costs. Furthermore, the development of novel extraction methods, such as non-hydrous ionic liquids helps to reduce carbon emissions (embedded within pyrometallurgical processing such as smelting) and water usage (embedded within hydrometallurgical processing such as cyanidation/solvent-extraction electro-winning)

3. Companies that refine and market the PGE, Te and Se for green energy end-products
Potential impacts to end-users are that future supply issues are eased; processing can be designed to deliver product in the most amenable form and most efficient manner to end-users; and that networks with producers (from Discovery and Recovery) are built and facilitate knowledge exchange regarding projections of supply and demand.

We will ensure impact is delivered across these groups during the catalyst by using the Environmental Sustainability KTN, trade associations (such as the British Photovoltaic Association and the Selenium-Tellurium Development Association) and topical publications (e.g. Metal Bulletin, Mining Magazine, Platinum Metals Review) to disseminate review articles, invite additional partners and promote awareness of the SoS initiative. We plan to work closely with organisations such as the Mineral Industry Research Organisation and AMIRA International, collaborative research and technological development facilitators that will expand the range of links between our consortium and industrial partners.