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Understanding Cement-Superplasticiser Interactions in Geopolymer Encapsulants for Safe Disposal of Radioactive Waste


   Department of Chemical & Biological Engineering

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  Dr Brant Walkley, Prof Siddharth Patwardhan, Prof John Provis  No more applications being accepted  Funded PhD Project (UK Students Only)

About the Project

In the UK, over 150,000m3 of radioactive waste (enough to fill 60 Olympic size swimming pools) has been produced to date. Most of this radioactive waste needs conditioning by encapsulating it in cement to prevent release to the biosphere.

Geopolymer cements are ideally suited for this, providing low viscosity, increased tolerance to problematic wastes, and lower leach rates of fission products than other encapsulants. Geopolymer cements also have significantly lower CO2 emissions associated with their production compared to traditional Portland cement, reducing these by as much as 90%, and are critical in helping to reach Net Zero 2050.

Superplasticising dispersants can further improve flow characteristics at a given water content, and reduce the requirement for tight specifications on cement powders needed at encapsulation plants. However, superplasticiser behaviour in geopolymers differs significantly from that in common Portland cement encapsulants, due to extensive differences between aqueous and solid-state chemistry in each case. There is little information on what parameters are critical to reliable application.

Chemical differences between geopolymers and Portland cement encapsulants lead to different superplasticiser effects (exacerbated by variability in powder physical/chemical characteristics), and little is known about which superplasticisers are most suitable for geopolymers. It is essential that we understand the fundamental cement-superplasticiser interactions, and effect on geopolymer encapsulant performance, so that robust specifications can be developed, and encapsulant properties and performance can be predicted.

This PhD examines interactions between organic superplasticisers and inorganic cement particles in geopolymer encapsulants, benchmarked against common Portland cement-based encapsulants. It adopts a new in-situ characterisation approach (including surface-specific techniques, spectroscopic and microstructural characterisation) to investigate mechanisms and kinetics of organic-inorganic interactions, and effects on performance.

We will elucidate the fundamental processes controlling dispersion, fluidisation and reaction of these cements, and design, produce and test novel encapsulant formulations with enhanced performance.

Specifically, it will develop a mechanistic understanding of the interactions between the organic superplasticiser and the inorganic cement particles, in geopolymer cements, by experimentally assessing:

1)    Surface chemistry at the cement – superplasticiser interface;

2)    Fresh state physical characteristics of the grouts;

3)    Evolution of cement structure, phase assemblage and durability.

This will determine how interactions between organic superplasticisers and inorganic cement particles affect (i) dispersion and fluidisation, (ii) reaction and setting, and (iii) physical property development of geopolymers, benchmarked against Portland cement encapsulants. We will use this information to design, produce and test new encapsulant formulations with enhanced performance.

Based in the Departments of Chemical and Biological Engineering, and Materials Science and Engineering, the successful candidate will be joining a team of multidisciplinary researchers at The University of Sheffield to develop research and innovation for decarbonisation. The successful applicant will also benefit from industrial supervision by Sellafield Ltd. They will benefit from being a member of a friendly and collegial group with world-leading expertise and facilities.

The PhD researcher will also undertake a 3 to 6 month secondment in the Encapsulant Integrated Research Team (EIRT) at Sellafield’s Cumbria site and/or the National Nuclear Laboratory’s Workington R&D site. During this industrial secondment, the PhD researcher will evaluate their new encapsulant formulations and superplasticiser specifications in terms of their chemical stability at high ionic strength and pH, and performance as relevant to Sellafield’s encapsulant needs.

The Sustainable Materials at Sheffield group (in the Department of Chemical and Biological Engineering) and the Cements@Sheffield group (in the Department of Materials Science & Engineering) are world-leading research teams, located in highly-rated and very successful departments, building from over 100 years of history in cements research at Sheffield. We investigate interesting and important cements and related materials for applications in nuclear and infrastructure sectors, publish our work in the leading journals and conferences in the field, and take great pride in the fact that alumni have gone on to the highest levels of success in both academia and industry.

Both the Department of Chemical and Biological Engineering and the Department of Materials Science & Engineering rank among the top in the UK and have among the highest levels of research income.

Start Date of Studentship: 26th Sept 2022

Please see this link for information on how to apply: https://www.sheffield.ac.uk/cbe/postgraduate/phd/how-apply. Please include the name of your proposed supervisor and the title of the PhD project within your application.

This interdisciplinary project spans chemical engineering, materials engineering, and organic and inorganic chemistry. It is ideally suited to a mature, highly numerate graduate with good communication skills, a passion for scientific and engineering research, and enthusiasm to tackle globally relevant and uniquely challenging chemical engineering and chemistry problems.

Applicants should have a first or upper second class UK honours degree or equivalent in a related discipline (Chemical/Materials/Environmental/Civil Engineering, Materials/Inorganic/Organic Chemistry or Mineralogy/Geochemistry). A strong undergraduate background in organic/inorganic chemistry and chemical/materials engineering, with an interest in driving sustainability is desired. If English is not your first language then you must have an International English Language Testing System (IELTS) average of 6.5 or above with at least 6.0 in each component, or equivalent. Please see this link for further information: https://www.sheffield.ac.uk/postgraduate/phd/apply/english-language.

For more details contact Dr Brant Walkley at [Email Address Removed].


Funding Notes

This is a fully funded PhD studentship, funded by the Engineering and Physical Sciences Research Council and Sellafield Ltd. The funding covers the cost of tuition fees and provides an enhanced annual tax-free stipend for 4 years (£19,062 in 2021/22). The studentship is available for a student from the United Kingdom or from the European Union with 3 years residency in the UK.
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