Uncovering the Critical Metal Concentrations in Mine and Metal Processing Wastes: A data driven microstructural approach

The transition to a low carbon future, relies heavily on an increased usage of metals. Examples include rare earth elements for the permanent magnets used in wind turbines, to platinum group elements leveraged for catalysis and most notably lithium for battery technologies. These example metals are just part of a broader class called critical metals or energy critical elements. Most of these metals, are extracted as by-product or ‘companion’ metals (Nassar et al. 2015; Mudd et al. 2017). Often this means these metals are not recovered at either the initial extraction or during refinement process (especially in legacy waste materials). This leads to many of these elements getting left in tailings and slags. Additionally, as extraction technologies have advanced the overall composition of waste materials will have changed in time. As the waste materials are exposed to weathering conditions, these by-product critical metals will mobilise and potentially localise in anthropogenic minerals (Lottermoser 2002; Kierczak et al. 2009; Werner et al. 2017). Further, while these elements have low bulk concentrations, they are expected to concentrate as sub-micrometre phases due to the heterogenous nature of the materials at the nanoscale. In general, both tailings and slags are poorly characterised and understood in the context of these critical metals and could potentially be economically viable for recovery. Re-working and further refining them would also lead to more sustainable approaches to mineral extraction.

This studentship will:

1. Explore the distribution and concentration of companion critical metals in slags, as a function of age and

2. Characterise the microstructural relationships observed in these phases to assess viability for extraction and utilisation.

3. We will explore these questions examining tailings from the Talnotry mine Galloway(Stanley et al. 1987; Power et al. 2004), and slags from Warton Slag Bank, Lancashire. Other historical mining and processing locations could be considered.


The above questions will be explored using a combination of microanalytical techniques combined with machine learning methods(Tominaga et al. 2021) acquired from the legacy waste sites noted above. Large area automated chemical (energy dispersive spectroscopy) and crystallographic (electron back scatter diffraction) mapping will be used to produce quantitative mineral phases maps. These data sets will be examined using machine learning tools such as clustering and manifold learning to identify regions of interest for high resolution characterisation using focused ion beam nano-tomography and / or transmission electron microscopy. These datasets will be further combined to refine our understanding of the economic and environmental potential for these industrial waste products.

Project Timeline

Year 1

Getting started and understanding the project

Literature review

Scoping our field sites and fieldwork planning

basic training in electron microscopy and microanalysis

introduction to coding skills required for machine learning data analysis.

Fieldwork and sample collection

Year 2

Processing and working up field data

Sample preparation

Laboratory analysis (Optical petrology, Modal Mineralogy)

Year 3

Laboratory analysis (High-res SEM EDS, EBSD and FIB)

Data processing and interpretation

Development of conceptual model

Year 3.5

Any final data collection/processing

Thesis and paper writing

& Skills

This project will equip the student a range of analytical and transferable skills which are desirable for careers in research or industry.

Research Methods

Fieldwork at the case study sites will be conducted with the supervisory team. Full training will be given in all of the laboratory and machine learning techniques to be used in the project, mainly at the University of Glasgow but also in collaboration with some external facilities.

Researcher Development

Technical & personal skills development will be undertaken with guidance from doctoral advisors and within the framework of the DTP Researcher Development Statement. Researcher developmental training will be provided by IAPETUS2 and supplemented by the University of Glasgow. The School of Geographical and Earth Sciences at the University of Glasgow (GES) has a large research student cohort (currently ~60 PhD students) that will provide peer-support throughout the research program. The scholar will participate in GES’s annual progression assessment and post-graduate research conference, providing an opportunity to present their research to postgraduates and staff within the School, and to also learn about the research conducted by their fellow postgraduate peers. Additionally, skills in NERC’s ‘most wanted’ list for PhD student training will be developed, including in multi-disciplinarity, data management, numeracy, and fieldwork, in addition to principles and practice of various other laboratory analytical techniques. Training and experience in national and international conference presentations, and preparation and submission of papers to international peer-reviewed journals will also be provided.

References & further reading

Kierczak, J., Néel, C., Puziewicz, J., and Bril, H. (2009) The mineralogy and weathering of slag produced by the smelting of lateritic ni ores, Szklary, Southwestern Poland. Canadian Mineralogist, 47, 557–572.

Lottermoser, B.G. (2002) Mobilization of heavy metals from historical smelting slag dumps, north Queensland, Australia. Mineralogical Magazine, 66, 475–490.

Mudd, G.M., Jowitt, S.M., and Werner, T.T. (2017) The world’s by-product and critical metal resources part I: Uncertainties, current reporting practices, implications and grounds for optimism. Ore Geology Reviews, 86, 924–938.

Nassar, N.T., Graedel, T.E., and Harper, E.M. (2015) By-product metals are technologically essential but have problematic supply. Science Advances, 1.

Power, M.R., Pirrie, D., Jedwab, J., and Stanley, C.J. (2004) Platinum-group element mineralization in an As-rich magmatic sulphide system, Talnotry, southwest Scotland. Mineralogical Magazine, 68, 395–411.

Stanley, C.J., Symes, R.F., and Jones, G.C. (1987) Nickel-copper mineralization at Talnotry, Newton Stewart, Scotland. Mineralogy and Petrology, 37, 293–313.

Tominaga, M., Ortiz, E., Einsle, J.F., Ryoichi Vento, N.F., Schrenk, M.O., Buisman, I., Ezad, I.S., and Cardace, D. (2021) Tracking subsurface active weathering processes in serpentinite. Geophysical Research Letters, e2020GL088472.

Werner, T.T., Mudd, G.M., and Jowitt, S.M. (2017) The world’s by-product and critical metal resources part III: A global assessment of indium. Ore Geology Reviews, 86, 939–956.

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