Our everyday technology and current and future clean energy technologies critically depend on 14 “critical” or “strategic” raw materials – as identified by the European Commission - which are economically important but currently at high supply risk. These materials include the Platinum Group Elements (PGE), the Rare Earth Elements (REE), and elements like Germanium, Gallium, Indium and Cobalt.
In recent years, interest in polymetallic nodules has soared because of economical Manganese, Copper, Nickel and Cobalt concentrations, but polymetallic nodules are also enriched in REE and PGE compared to most rocks. REE concentrations and PGE’s (in particular Pd) are present in concentrations similar to or higher than those in worked mine tailings, marine clays, electronics scrap and recycled road pavement, which are all currently being investigated as economic sources of REE and PGE. These critical elements can potentially be recovered economically from polymetallic nodules as a by-product of processing. Previous studies have largely focused on bulk concentrations of REE and PGE in processed nodules, but little is known about the chemistry and mineralogy of these elements of interest. This is critical, as the feasibility of their recovery will be strongly dependent on their mode of occurrence, for instance, as adsorbed elements onto Mn-oxide or Fe-oxide-hydroxide surfaces, or in more stable oxide, sulfide or alloy (PGE) phases with much higher concentrations.
Overall objectives and approaches
In this project, we propose an integrated approach centered on advanced imaging methods and microbeam analysis, primarily using scanning electron microscopy, to fully determine and quantify the texture and mineralogy of polymetallic nodules, with a focus on REE-rich and PGE-rich phases. This project would make use of the high-resolution Field Emission Gun Scanning Electron Microscope (FEG-SEM) at the Electron Microscopy Centre at Plymouth University. This microscope is equipped with a fast Silicon Drift Large Area EDS detector, which allows for ultrafast X-ray spectrum acquisition and fast high-resolution large-area chemical mapping. In addition, it is equipped with a WDS detector which allows fully quantitative analysis on micron-sized spots of minor, and in some cases, trace elements. In our pilot study we already identified the presence of REE-rich clay bands within test nodules using these techniques. The FEG-SEM is also equipped with state of the art software that allows for automated mineralogical scanning for minerals or elements of interest. For instance, by a method referred to as ‘bright phase search’, we were able to locate and image a micron-sized Au particle in a polymetallic nodule in a 90 minute automated scan. For comparison, we will use these in-situ microbeam techniques in combination with bulk analytical techniques such as XRF (for major and minor elements), and ICP-MS (for trace elements, including the REE and the PGE), all available in-house at Plymouth University.
The project will also include a feasibility study of innovative leaching and recovery of REE, PGE, but possibly also Co, Ni and Cu, using ‘green’ biogeochemistry, as an alternative to smelting and roasting. Clearly, increased use of strategic elements for future clean technologies is not sustainable if the environmental costs of recovery outweigh the gains. Energy-efficient and clean bioextraction of REE is currently being developed at Plymouth University, together with partners at Birmingham University, and trials using PGE are also being carried out. We aim to test the range of promising ‘rock eating’ bacteria mixtures available and licensed to PU and partners to investigate their suitability for REE and PGE recovery.
The candidate will receive extensive training to become a specialist in scanning electron microscopy (imaging, EDS and WDS analysis), whole rock major and trace element geochemistry. There is a major role in the project for using and further developing our existing automated mineralogy techniques on our scanning electron microscopes. Previous experience in some of these advanced techniques is not a requirement but would of course be an advantage. It is likely that the student will be asked to take part in a seagoing expedition to recover samples. Other training aspects include strengthening scientific writing and presentation skills, and general training in working in an ISO accredited laboratory. The Earth Science department at Plymouth University also hosts the world’s only full professor in Geoscience Communication, Professor Iain Stewart, who is well known for his programmes on BBC television about all aspects of Geosciences, and the student will take part in specialist short courses about communication taught by Professor Stewart.
The student will be expected to write a standard thesis following Plymouth University regulations and produce papers which can be submitted to high-impact journals in the relevant field, such as Chemical Geology, Contributions to Mineralogy and Petrology, and Earth and Planetary Science Letters. The student is also likely to contribute to reports for industry partners, and will be encouraged to engage with outreach activities and communication with the general public.
Make up of supervisory team
Coordinators: Dr Arjan Dijkstra (Igneous Petrologist/Geochemist), Dr Natasha Stephen(Mineralogist/Petrologist/Electron Microscopy Specialist), Dr Colin Wilkins (Economic Geologist/Mineralogist), Dr Uwe Balthasar (Paleontologist/Seawater Chemistry Specialist)