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Title: Modelling colloidal facilitated radionuclide filtration in porous media
Author: Tudor, Daniel
ISNI:       0000 0004 9358 4286
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2020
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The behaviour of colloidal particles within porous media is an active area of intense study within the nuclear industry, as colloidal particles can act as vectors for the transportation of radionuclides. Thus, modelling the behaviour of these particles helps better understand the likelihood of radionuclide transportation as well as, exploring the principle mechanisms that result in deposition and what conditions are required to retain colloidal particles within a porous media matrix. There are a number of different modelling conditions explored both macro, whereby porous media dynamics are investigated from a continuum point of view, and a more microscopic system where individual particles are modelled and their behaviours understood. These models allow for a full picture of particle behaviour and bed dynamics to be developed. The aim of this research is to analyse the use of agent based modelling method as an alternative way to further understand particle deposition and aggregation within porous media Within the model, colloidal behaviours were simplified into key statements addressed as rules, where particle interactions with each other, were maintained within the parameters set by these rules. This allowed for a large number of particles to be modelled in comparison to current microscopic techniques, and addressing shortcomings of some of these techniques, such as the use of the primary minimum well depth from the standard DLVO equation. This model was validated against both current experimental values and analytical solutions, where it was found to perform well in the estimation of colloidal aggregation rates and sizes. Furthermore, it was found that the behaviour of colloidal aggregation is not just limited to irreversible aggregation but indeed can be found to be influenced by the introduction of reversible aggregation, the rate of which was established by analysing the likelihood of aggregation under varying chemical conditions. Extensions of the models were then produced, in which a lattice Boltzmann flow field was constructed and validated along with particle trajectory equations. Allowing for particles to be investigated within an advective-diffusive environment. The behaviour of particle deposition within varying chemical regimes was analysed where the ability for particles to deposit is heavily influenced by the role of the secondary minima. Without the incorporation of the secondary minima, particles where rejected from the system in opposition to the same experimental conditions. With the introduction of the secondary minima, breakthrough and deposition behaviour more closely matched experimental observations. Finally, the influence of surface chemistry and flow dynamics were addressed in which growth size and rates were seen to change dramatically under differing flow and surface conditions implying an inherent sensitivity to these parameters. The behaviour of colloidal dynamics both in aggregation and deposition was accurately represented within the agent-based model allowing for an alternative modelling paradigm to be used in exploring the behaviours of colloidal particles within porous media.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral