The objective of this project is the development of SILPs containing radiation resistant ionic liquids that are suitable for the separation of lanthanides, and to apply these ionic liquids for the extraction and separation of radiolanthanides with a high separation yield. After a literature study, several lanthanide systems will be selected as target mixtures. Possible mixtures are the Yb/Lu and Sm/Eu systems in view of the 177Lu and 153Sm medical radioisotopes currently obtained via neutron irradiation of ytterbium and samarium respectively. Since the ionic liquids have to be used for extraction of metal ions from an aqueous phase to an ionic liquid phase, water-immiscible ionic liquids are required. The targeted ionic liquids consist of (substituted) imidazolium, benzimidazolium, pyridinium and (iso)quinolinium cations. Immiscibility with water will be achieved by making the alkyl chain of the ionic liquid cation sufficiently long and/or to use strongly hydrophobic anions. Examples of anions are bis(trifluoromethylsulfonyl)imide, higher branched alkanoates and dialkylphosphates. Some of these anions can acts as extractants themselves. Otherwise, molecular extractants (e.g. crown ethers) have to be dissolved in the ionic liquid phase. No hexafluorophosphate ionic liquids will be prepared because the hexafluorophosphate anion is not resistant to hydrolysis. Different porous solid supports (silica, alumina,...) will be investigated for the development of SILPs and the stability of the resulting SILPs against leaching of the ionic liquid phase from the support will be tested. For the separation of the Sm/Eu couple, advantage is taken of the fact that Eu3+ can easily be reduced to Eu2+, whereas reduction of Sm3+ to Sm2+ requires more drastic conditions. Divalent europium and trivalent samarium have quite different chemical properties, so that this facilitates the Sm/Eu separation. In the same way, advantage is taken of the fact that Yb3+ can be reduced to Yb2+ in organic solvents, whereas Lu3+ cannot. Separation of the couple Yb2+/Lu3+ is much easier than separation of the couple Yb3+/Lu3+.
This PhD project is envisaged as a first feasibility study to investigate the possible implementation of supported ionic liquid phases for separation for radiolanthanides. The development of a full separation and purification technology towards the production of pure medical radioisotopes is beyond the scope of this project.
In a first phase, ionic liquids will be developed and tested on non-radioactive lanthanide systems. In a second phase, the radiation stability of selected ionic liquids will be tested and extraction tests on radioactive systems will be performed. The radioactive lanthanide systems will be produced via irradiation of the respective target lanthanide oxide or nitrate in the BR1 reactor. Sample quantities and the required neutron fluxes are low to ensure further sample manipulations in a glove box environment. Such irradiation experiments in BR1 are common practice at SCK•CEN. However, the possibility and compatibility towards larger scale experiments in BR2 will be kept in mind. The irradiated targets will be dissolved in an acid aqueous solution (in the case when lanthanide oxides were used) or water (in the case when lanthanide nitrates were used) followed by dedicated extraction tests.
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