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Overview

Project Highlights:

  • Gain expertise in novel methods of processing minerals in high ionic strength media.
  • Visit industry to gain insight into current hydrometallurgical mineral processing techniques.
  • Design and build prototype bench-top reactors for processing minerals with optimal space-time yield.

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 and a new method of mineral solubilisation which will use less energy, and will 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 (Abbott et al., 2015). Ionic liquids (in the case of this project deep eutectic solvents will be used) can also increase the selectivity and efficiency of metal extraction and winning (Abbott et al., 2011). 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 in 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.

One particular issue for hydrometallurgy is the processing of sulfidic ores. Reaction in strong mineral acids can yield H2S, whereas roasting prior to leaching can produce SO2. This project will focus on chalcopyrite CuFeS2 which is one of the main copper ores. It will use both electrocatalytic and electrochemical approaches to oxidise, and therefore solubilize, the mineral. 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.

 

3D Colour optical microscopic images of anodically polarised pyrite gains with an applied voltage of 1.2V

Methodology

You will characterise the structure and chemistry of chalcopyrite samples supplied by industrial collaborators. You will look at the synthesis of deep eutectic solvents including their manufacture in pilot plant scale. The reactivity of the chalcopyrite samples will be characterised using optical profiling (Fig 1), 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 the samples. This methodology has already been shown to be a successful approach with minerals (Jenkin et al., 2016). A bulk sample will be made and characterised from which all subsequent tests will be performed. This is the first time that bulk electro-chemical/catalytic processing will have been used for mineral processing. It has been shown to enable effective separation of copper from iron on the gram scale but this project will endeavour to test the kilogram scale and explore the issues with scaling up this innovative technology.

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.

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Timeline

Year 1: Training in research techniques. Visit processing operations to observe current practices, obtain samples and liaise with metallurgical staff. Obtain additional samples and characterise these mineralogically. Carry out bench top heap-leach on a 1 kg sample with static electrodes to determine the space time yield. Publication and presentation at national conference.

Year 2: Design and build a separated cell using a mineral paste anode with a cellulosic membrane. Measure separation efficiency as a function of current efficiency and electrode configuration. Bulk testing of concentrates and investigation of recovery. Presentation at international conference.

Year 3: Design a cell to allow counter flow of lixiviant and mineral which would be the first step towards a continuous flow process. Write publication on design and initial test. Presentation at international conference. Write and submit thesis.

Partners and collaboration (including CASE)

Prof Abbott developed DESs and their application to metal processing. He has worked on scale-up and 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