Modelling bubble-particle interactions for solids separation

Bubble-particle systems are encountered in a wide range of industrial and environmental applications (flotation, bioreactors, slurry bubble columns) but the complex dynamics and interactions make the design and operation of such systems particularly challenging. This collaborative project between the University of Birmingham and McGill University (Montreal, Canada) aims at better understanding bubble-particle dynamics for novel applications in recycling.

This project is in collaboration with Professor Kristian Waters at McGill University, with the possibility of a research placement in his laboratories during the PhD. The student will also benefit from association with the EPSRC PREMIERE Programme Grant (https://premiere.ai) and be part of the PREMIERE research team including researchers from Birmingham, UCL and Imperial College.

Froth flotation is an established method of separating minerals in a slurry based upon the relative hydrophobicity of the particles and while it has been used for decades in the minerals industry to recover high value materials, less attention has been paid to ridding water of low value ones (e.g. plastics). Surface active agents known as collectors are used to enhance the particle separation with the polar part of the molecule becoming attached to surface of the target particles, with the hydrophobic part forming a surface which is attracted to bubbles in the liquid. The target particles rise with the bubbles to form a froth, which overflows the cell to be recovered. To maintain stable, small bubbles, frothing agents known as frothers are added. The froth flotation principle has the potential to be used in a variety of novel applications outside its original use in the minerals industry, for example in the recycling of plastics or battery materials. However, there are many aspects of its operation which are still poorly understood which affect the overall efficiency of the process.

This project will aim at investigating:

– the dynamics of the frothing agent with the forming bubble interfaces: how the surface-active molecules alter the local interfacial tension and how Marangoni stresses may impact the performance of the froth and the attachment of the particles;

– the interaction of the particles in the wake of the bubbles, where recent research has shown that this may be an important feature affecting the process selectivity, therefore efficiency. Both are critical to understanding the overall potential and efficiency of separation in novel applications.

The research will involve a series of experimental work involving visualisation of particle and bubble dynamics in small-scale test cells and measurements of interfacial properties including dynamic interfacial tension. These will feed into a finite volume numerical model based on open-source libraries (OpenFOAM or Basilisk). The interfacial properties measured in the lab will be implemented and 3D numerical simulations of bubbly flows will be performed. The dynamics of the solid particles will also be coupled to the bubble dynamics and will be compared to the experiments in terms of flow structure, entrainment in the wake and adhesion to the interface. The understanding of these phenomena at reduced scale will help in developing empirical or data-driven models for improving larger scale models and the design of flotation columns.

Funding: EPSRC DTP/College studentship in support of EPSRC PREMIERE Programme Grant (EP/T000414/1).

Applicant: Applicants should have a first-class degree or good 2:1 (or equivalent) in Chemical Engineering, Mechanical Engineering, Computing, Mathematics, or related areas. We are looking for an enthusiastic and self-motivated person with a keen interest in conducting numerical simulations, as well as experimental work in the lab.

Deadline: The position will be filled as soon as a suitable person has been found; hence you are encouraged to apply as soon as possible (by email to t.abadie@bham.ac.uk or online https://www.birmingham.ac.uk/schools/chemical-engineering/postgraduate/phd-research.aspx). PhD Starting October 2024 or soon after.