Physicochemical Behaviour of Complexants in Actinide Separation Processes

  • Richard Blundell

Student thesis: Phd


With the implementation of future recycling concepts and their associated contacting techniques, processes must be robustly evaluated to ensure the design and operation of safe and efficient liquid- liquid extraction processes. This relies on the characterisation of both the extraction performance and physicochemical behaviour between the organic and aqueous phases. This was achieved in this project through small-volume extractions and physicochemical studies performed using identified techniques (both commercially procured and developed in-house). This work has implemented a thorough evaluation of the first Group Actinide Extraction (GANEX-1) cycle through high concentration uranium extraction studies and the resulting impact of acid and metal extraction on the physicochemical behaviour and has tied mass transfer and separation fundamentals to these exhibited physical properties. The work undertook an assessment of experimental techniques and equipment for the purpose of physicochemical measurements of radioactive liquids and provided a recommendation for techniques within a laboratory environment. An empirical expression was derived to allow for the density and viscosity of any molar composition of DEHiBA or TBP in n-dodecane between 278 – 333 K for the use in modelling strategies. Proposed process conditions of the 1st GANEX cycle involving the bulk extraction of uranium from 2 -6 M nitric acid by 1 M DEHiBA in n-dodecane between 293 – 333 K. Obtained uranium distribution ratios showed that at acidic aqueous concentrations between 4 – 6 M HNO3 provided the most favourable extraction conditions for the DEHiBA containing solvent. However, at 6 M HNO3 and high uranium concentrations, 1 M DEHiBA in n-dodecane formed third phase at 293 K, highlighting an unfavourable operating regime. The studied properties of this third phase have shown that the density of the organic phase can be used to detect and avoid maloperation regimes. Radiolytic degradation of the GANEX and EURO-GANEX extractant systems with 60Co γ-radiation up to 750 kGy showed relatively minor changes to the density and viscosity of the systems. However, the negative trend between interfacial tension and total dose illustrated the requirement for a solvent regeneration technique to remove surface-active degradation products that could impair the effective separation of the aqueous and organic phases after mixing.
Date of Award31 Dec 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorAndrew Masters (Supervisor) & Clint Sharrad (Supervisor)

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