2024-L12 Promoting pyrometallurgical slags as a critical metal resource: Geometallurgy and leaching behaviour with environmentally benign solvents

Project highlights

Develop skills in mineralogy and solvometallurgy and apply them to sustainably recover metals for the green transition from waste products instead of mining.
Opportunity to work with Industrial Partner Descycle www.descycle.com to develop real impact from your research.
Be part of the Centre for Sustainable Resource extraction to deliver vital solutions to the security of supply of metals for the 21st century.

Overview

Pyrometallurgical slags are the solidified waste products from the smelting of metals. These are dominantly composed of finely crystalline or glassy silicate and oxide minerals but contain small blebs of native metals or metal sulfides which reflect the original ore being smelted, such as Sn, Cu, Pb or Ag. Subsequent weathering may form new secondary oxide and carbonate minerals. Historically generated slags produced by inefficient smelting and slag separation often contain high contents of metals which may be a few % to sometimes >10% of base metals and 10s-100s ppm of silver or gold. These values well above modern ore values – and thus a potentially valuable metal resource if they can be recovered. Little is known about the critical metal content of slags but given that historical smelters used less “clean” ore than modern smelters, there is likely significant amounts of critical metals (e.g. Sb, Bi, Te) also contained in some historical slags.

Slag reprocessing is therefore tempting, but is challenging for a number of reasons: Poor knowledge of metal-bearing phases, variable oxidation of metal particles, some metals (such as Zn) partition to the silicate phase. Pyrometallurgical reprocessing is one option but has a high energy consumption and a smelter may no longer exist in the area. Alternatively, hydrometallurgy may use solvents such as sulfuric acid, although this may be inhibited by gelation of some slags and may not recover silicate-hosted metals.

This project aims to develop a fresh approach to reprocessing of historical slags. You will develop a geometallurgical workflow for characterising the mineralogy of target metals (including critical metals where they occur) using SEM-based automated mineralogy. This will be combined with the use of novel solvents, such as Deep Eutectic Solvents to selectively leach and recover the target metals in an environmentally friendly and low energy process, building on the extensive experience in this field at Leicester within the Centre for Sustainable Resource Extraction. This project will equip you for a career in mineral resource metallurgy.

Figure 1: Sample of historical copper slag from Cornwall, showing blebs of unrecovered metal. Could we sustainably reprocess these as a metal resource, and what critical metals are present?

Case funding

This project is suitable for CASE funding

Host

University of Leicester

Theme

Climate and Environmental Sustainability
Dynamic Earth

Supervisors

Project investigator

Prof Gawen Jenkin, University of Leicester (grtj1@le.ac.uk)

Co-investigators

Dr Phil Bird, DESCYCLE and University of Leicester

How to apply

Each host has a slightly different application process.
Find out how to apply for this studentship.
All applications must include the CENTA application form.
Choose your application route

Methodology

Samples of slag will be collected from known localities in the UK (e.g. Cornwall) and material from abroad donated by Descycle and their partner companies. These samples will be mineralogically and texturally characterised using transmitted and reflected light microscopy together with SEM-based automated mineralogy (Zeiss Mineralogic software). This will be augmented by other microbeam techniques such as µ-XRF and laser ablation ICP-MS where necessary to understand the mineralogical setting of critical elements.

The leaching behaviour of the metal-bearing target minerals with novel solvents will be assessed using both in situ and bulk leach techniques. For the latter leachates will be characterised by ICP-MS and solid residues by XRF and ICP-MS. You will work to optimise solvents to efficiently extract target metals and leave a non-hazardous waste.

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.

You will become proficient in the use of analytical equipment, especially SEM and automated-SEM, to derive geometallurgical information that informs leaching behaviour such as mineralogy and liberation in tandem with experience in the use of novel solvents such as DES. These skills are highly attractive to both industrial and academic employers for the green transition. You will join a thriving community of mineral resource researchers in as well as materials scientists and chemists within the Centre for Sustainable Resource Extraction.

Partners and collaboration

The student will benefit from a close relationship with Descycle, a thriving startup that is working to roll out commercial development of DES technology for mineral and metal processing. The company will provide materials for research, support the project as a CASE partner, and provide opportunities to meet industrial partners and attend relevant conferences.

Further details

Further details on how to contact the supervisor for this project and how to apply for this project can be found here:

For any enquiries related to this project please contact Gawen Jenkin ([email protected]).

To apply to this project:

You must include a CENTA studentship application form, downloadable from: CENTA Studentship Application Form 2024.
You must include a CV with the names of at least two referees (preferably three) who can comment on your academic abilities.
Please submit your application and complete the host institution application process via: https://le.ac.uk/study/research-degrees/funded-opportunities/centa-phd-studentships. Please scroll to the bottom of the page and click on the “Apply for NERC CENTA Studentship” button. Your CV can uploaded to the Experience section of the online form, the CENTA application form 2024 can be uploaded to the Personal Statement section of the online form. Please quote CENTA 2024-L12-CENTA2-SGGE4-JENK  when completing the application form.

Applications must be submitted by 23:59 GMT on Wednesday 10th January 2024.

Possible timeline

Year 1

Carry out a literature review of what is known about metallurgy of different types of metallurgical slags. Training in SEM and other microbeam analysis on the initial samples and carry out initial solvent leaching. Collect further samples from the UK and receive samples from abroad and plan and commence a more detailed analytical geometallurgy programme. Attend a national conference.

Year 2

Continue geometallurgical characterisation – presentation of results at international conference and initial publication. Plan and commence a larger programme of test leaching in light of the target element mineralogical deportment revealed by geometallurgy.

Year 3

Complete geometallurgy programme and optimise leaching conditions for target elements. Carry out basic cost-benefit analysis and life-cycle assessment of developed processes in collaboration with Descycle. Publish papers on research and present at international conference.