Overview

Traditional ore processing is generally carried out using either hydrometallurgy (high cost, low volume, reasonable selectivity) or pyrometallurgy (lower cost, high volume, low selectivity). Both methods require a large energy input and produce large volumes of waste e.g. slags or waste water. This project will seek to use a new type of solvent process which will use less energy, and be more environmentally compatible.

It has already been shown that electrocatalytic and electrolytic methods can be used to solubilize metals and metallic compounds from complex matrices e.g. ore concentrates. Ionic liquids can also increase the selectivity and efficiency of metal extraction and winning. The main issue is that this approach necessitates a new approach to reactor design. The majority of processes use batch style tanks or heap leaching to extract metals from their ores. The majority use oxidizing acids or strong bases to change speciation is solution and increase solubility.

In this project methods of optimizing space-time yield will be characterized. Space-time yield is the amount of material which can be processed in a unit volume and unit time. Hydrometallurgy is often characterized by slow process kinetics. Heap leaching always uses aqueous solutions and evaporation is often an important factor in controlling process efficiency. The use of non-volatile lixiviants clearly minimizes this issue and this in itself will be a useful characteristic to quantify.

The project will address a diverse group of ore minerals commonly encountered in important hydrothermal deposit types such as epithermal gold and porphyry copper (including the world-class Lepanto deposit of one of our partners). These minerals, and the elements they host, pose both challenges and opportunities for mineral processing operations. Their variable compositions and complex structures (involving bonds between sulfur and semi-metals) make sulfosalt minerals notoriously difficult to process by conventional pyrometallurgy or hydrometallurgy (Sarfarzadeh et al. 2014). Sulfosalts such as tennantite-tetrahedrite and enargite are important ore minerals for copper, but the group’s capacity to host a wide range of metals and semi-metals means they are an important repository for potential by-products, including critical metals (Sb, Ge, Se and Te) and precious metals (Ag, Au). However, other contained elements such as As, Hg and Se pose an environmental risk if not properly disposed of or reused afterwards. Thus, the ability to characterise and properly process sulfosalts would be beneficial to the mining industry and wider society by increasing resource efficiency and reducing environmental impact.

This project will explore the electrochemistry of common sulfosalt minerals in ionic liquids to assess the potential for new environmentally-benign approaches to processing. It will suit a student, either with a degree in mineral processing/applied geology/geochemistry/mineralogy who is keen to develop skills in chemistry, or with a degree in chemistry who is keen to apply their skills in the mineral processing industry. Gaps in your skills and knowledge will be covered in our training programme.

Ionic liquids allow us to modify the reactivity of metals in solution – image shows copper chloride dissolved in 8 different ionic liquids.

Methodology

You will characterise the structure and chemistry of sulphosalt samples obtained from our collections, museums and from mining operations worldwide. You will assess the reactivity of these sulphosalts in deep eutectic solvents and their reaction products using optical profiling, cyclic voltammetry, UV-vis spectroscopy and electrochemical quartz crystal microbalance. These data will be correlated with the mineralogical information to derive general rules about the behaviour of these minerals. These will then be used to design bulk tests on concentrate samples from mining operations to assess the efficacy of dissolution and methods of recovery of the components from solution. There will be the opportunity to investigate routes to produce end-products of value as well as means of safe disposal of waste products (such as converting arsenic to scorodite). Based on results, a pilot scale test will be carried out to demonstrate the possible industrial application of your work. One aim will be to focus on a non-cyanide based method for extracting gold from ores which is an important issue in artisanal mining.

Training and Skills

CENTA students benefit from 45 days training through their PhD including a 10 day placement. In the first year, training will be a single cohort on environmental science, research methods and core skills. Training will progress from core skills sets to master classes specific to the student's projects and themes.

Geological training will include: reflected light microscopy and scanning electron microscopy (SEM) for mineralogical and textural characterisation of sample material, operation of the electron microprobe to determine the chemistry of samples and X-ray diffraction (XRD) to confirm crystal structures. Chemical training will include: electrochemical techniques such as cyclic voltammetry and chronocoulometry, advanced microscopy including SEM and 3D optical profilometry, and spectroscopy to determine speciation in the solid and solution states.

You will have the opportunity to take introductory modules in mineralogy, ore deposit geology, Advanced Analytical Chemistry or Sustainability of Materials to upgrade your knowledge as required.

Timeline

Year 1: Training in research techniques. Obtain additional samples (including museum visits) and characterise these mineralogically. Carry out experiments on selected samples to scope out the major controls on dissolution. Publication and presentation at national conference.

Year 2: Visit processing operations to observe current practices, obtain samples and liaise with metallurgical staff. Systematically investigate a range of samples with the aim of being able to predict reactivity across the group and write publication. Bulk testing of concentrates and investigation of recovery. Presentation at international conference.

Year 3: Completion of bulk testing and write publication. Presentation at international conference. Design and implementation of pilot demonstration. Final publication. Write and submit thesis.

Partners and collaboration (including CASE)

Prof Abbott developed deep eutectic solvents and their application to metal processing. He has worked on scale-up and chemical engineering aspects of reactor design through numerous EU and Innovate UK projects. He is a partner on a Marie Curie Training network on ionometallurgy.

Drs Jenkin and Smith have between them over 40 years experience in mineralogy and geochemistry and their application to mineral deposits. They are lead investigators on a £2.4M NERC consortium project “Tellurium and Selenium Cycling and Supply” (TeaSe).

Further Details

Prof Andrew Abbott;

Department of Chemistry, University of Leicester,

LE1 7RH, UK, 0116 252 2087, apa1@le.ac.uk