EPSRC DTP PhD studentship: CFD-DEM modelling of enhanced gravity separators to reduce the impact of bio-available heavy metals released to the environment

Location: University of Exeter, Penryn Campus, Cornwall

Project Description:

Mineral processing is a uniquely complicated field due to the heterogeneous nature of the minerals involved. It is an important area of industry as it is vital to produce feed material to metallurgical processes which is of suitable grade for efficient and feasible recovery of metals. Natural variability in the minerals present in different orebodies as well as variations in the mineral distribution, textures and associations means that mineral processing equipment cannot be universally optimised; this results in poor recovery of minerals as the orebody is ‘fitted’ to the equipment.

The release of bio-available heavy metals is generally associated with poor recovery of minerals within fine sized particles below 20-30 microns in diameter in mineral processing plants. These bio-available metals can accumulate in the environment with recognised deleterious effects to eco-systems. Examples of this are readily seen in the south-west due to historical processing such as in the Bissoe river and Carbon Valley.

Gravity separation enhanced by centrifugal force is an established technique for the recovery of fine particles containing heavy metals. Despite this fact the exact physical means of separation within these devices is poorly understood and historically only empirical models have been developed which are device and ore specific and so of limited use.

The continual improvement in computational power has led to increased abilities to simulate complex two and three phase dynamic systems, including densely populated particulate systems through the combination of computational fluid dynamics and discrete element modelling. This technique is ideally suited to investigating the fundamental physics of material flow in equipment designed to separate particles by differences in density. It is anticipated that this modelling will finally enable improved equipment design and manufacture allowing equipment to be ‘fitted’ to the specific requirements of an orebody. This will reduce the environmental impact of mining but also reduce energy costs per tonne of produced metal.

It is anticipated that this project will combine aspects of:

computational modelling alongside experimental validation
manufacture of process equipment
investigations into the chemical, biological and environmental impact of reducing heavy metals release in the environment.

The role of the successful candidate will cover a number of areas, reflecting the inter-disciplinary approach of the project. The student will generate models of centrifugal separation equipment using a combined CFD-DEM approach and validate these models experimentally. This willmainly be completed at the University of Exeter but also University of Birmingham (positron emission particle tracking - PEPT). The student will liaise with a manufacturer to implement changes to process equipment based on their modelling and test these changes experimentally. Modelling will also be used to determine the ideal particle size distribution (PSD) of material for equipment and the student will investigate means of producing material with this PSD using specialised ultra-fine grinding equipment available through links with local consultancy firms. Test material will be collected from currently operating mines and locations of historic mine waste. The student will assess the environmental impacts of the material and quantify the change in impact after processing.

The provisional timeline for this study is outlined below:

Year 1

- Familiarisation with CFD-DEM software
- Introduction to mineral processing by participation in UG and PGT modules (if required)
- Literature review
- Collection of samples and assessment of environmental impact using a combination of analytical techniques and bio-availability tests
- Design and execution of validation experiments.

Year 2

- Create CFD-DEM models of centrifugal gravity separation equipment
- Use models to optimise equipment design and find optimal material PSD
- Implement proposed equipment designs and validate.
- Begin experimentation to produce material with optimal PSD

Year 3

- Finalise experimentation and assess change in environmental impact under optimal conditions
- Complete write-up of thesis

The student will be exposed to a range of scientific areas from an applied perspective. They will:

- Gain knowledge in CFD-DEM which has relevance across all physical sciences and beyond as well as the principles and environmental impact of mineral processing
- Gain practical experience in the design of robust and statistically relevant experiments, collection of representative samples and use of analytical techniques
- Have the opportunity to work with specialised equipment such as PEPT, QEMSCAN and ultra-fine grinding equipment as well as working directly with manufacturers to design industrial equipment.