Polyamine functionalised ion exchange resins: Synthesis, characterisation and uranyl uptake

A series of linear polyamine functionalised weak base anion exchange resins have been synthesised using the Merrifield resin and characterised using infra-red spectroscopy, thermogravimetry, elemental analysis and solid state 13 C nuclear magnetic resonance spectroscopy. Uptake behaviour towards uranium (as uranyl) from sulfuric acid media has been assessed as a function of pH and sulfate concentration, with comparison to a commercially available weak base anion exchange resin, Purolite S985. Synthetic polyamine resins were seen to outperform the commercial resin at industrially relevant uranyl concentrations, with a trend of increased uptake being seen with increasing polyamine chain length. Uranium loading isotherm studies have been performed and fit with the Langmuir and Dubinin-Radushkevich isotherm models, with a maximum loading capacity observed being 269.50 mg g −1 for the longest polyamine chain studied. Extended X-ray absorption fine structure experiments have been used to determine uranium coordination environment on the resin surface, showing a [UO 2 (SO 4 ) 3 ] 4− species. This coordination knowledge was employed to develop an extraction mechanism and derive an isotherm model based on the law of mass action

New Materials for Selective Separations at the Back End of the Nuclear Fuel Cycle

Storage and recycling of nuclear waste are important issues that will increase in importance if nuclear power becomes more widely adopted worldwide. Recycling of used nuclear fuel is of benefit both in terms of increasing the nuclear lifetime (ie the number of years nuclear power will be a viable option for power generation) and decreasing the hazards (radiotoxicity, volume and longevity) of nuclear waste. Currently, most reprocessing of used nuclear fuel is performed using liquid-liquid extraction. However, use of solid sorbent materials has many advantages such the lack of organic solvent wastes. This research involves development of materials that are able to selectively remove specific target elements from solutions of used nuclear fuel. Once loaded with radionuclides, these materials may be utilised as transmutation matrices or wasteforms. Therefore, radiolytically and hydrolytically stable materials able to withstand the conditions of nuclear separations, such as titania and zirconia, have been targeted. Further, ordered porosity has been introduced into these titania and zirconia framework materials to improve their sorption capacity and kinetics. In order to impart selectivity to these materials, organic ligands are incorporated. Functional groups, including phosphonates, amines and peptides, have been chosen or designed based on their selectivity for elements relevant to the nuclear fuel cycle. Elements of interest include uranium, which constitutes >96% of used nuclear fuel and can be recycled; minor actinides, which contribute significantly to the radiotoxicity of nuclear waste and can also be recycled in fast neutron reactors; and lanthanides, which are targets for separation from the minor actinides as their high neutron absorption cross sections prevent transmutation of the minor actinides. Novel hybrid materials have been synthesized and their sorption characteristics, including selectivity, capacity and kinetics, evaluated

Separation of actinides from spent nuclear fuel: A review.

This review summarises the methods currently available to extract radioactive actinide elements from solutions of spent nuclear fuel. This separation of actinides reduces the hazards associated with spent nuclear fuel, such as its radiotoxicity, volume and the amount of time required for its’ radioactivity to return to naturally occurring levels. Separation of actinides from environmental water systems is also briefly discussed. The actinide elements typically found in spent nuclear fuel include uranium, plutonium and the minor actinides (americium, neptunium and curium). Separation methods for uranium and plutonium are reasonably well established. On the other hand separation of the minor actinides from lanthanide fission products also present in spent nuclear fuel is an ongoing challenge and an area of active research. Several separation methods for selective removal of these actinides from spent nuclear fuel will be described. These separation methods include solvent extraction, which is the most commonly used method for radiochemical separations, as well as the less developed but promising use of adsorption and ion-exchange materials. This review summarises the methods currently available to extract radioactive actinide elements from solutions of spent nuclear fuel. This separation of actinides reduces the hazards associated with spent nuclear fuel, such as its radiotoxicity, volume and the amount of time required for its’ radioactivity to return to naturally occurring levels. Separation of actinides from environmental water systems is also briefly discussed. The actinide elements typically found in spent nuclear fuel include uranium, plutonium and the minor actinides (americium, neptunium and curium). Separation methods for uranium and plutonium are reasonably well established. On the other hand separation of the minor actinides from lanthanide fission products also present in spent nuclear fuel is an ongoing challenge and an area of active research. Several separation methods for selective removal of these actinides from spent nuclear fuel will be described. These separation methods include solvent extraction, which is the most commonly used method for radiochemical separations, as well as the less developed but promising use of adsorption and ion-exchange materials. © 2016 Elsevier B.V

The impact of structural variation in simple lanthanide binding peptides

A series of di-, tri- and tetra-peptides were synthesised using L- and D-glutamic acid in order to determine the effects of peptide length and stereochemistry on lanthanide binding affinity. Binding studies with Eu were performed at neutral pH, which is relevant to biological applications, and also under industrially relevant acidic conditions. Increasing peptide length resulted in higher binding affinity but the effect of stereochemistry was dependent on the peptide length. Modelling and experimental characterisation of the peptide[thin space (1/6-em)]:[thin space (1/6-em)]Eu complexes formed suggested that multiple modes of binding were present, with the Eu cation coordinated by the terminal and side chain carboxylic acids of the peptides as well as by backbone carbonyl groups. The peptide with the strongest binding affinity was the tetra-peptide with alternating L- and D-glutamic acid residues, which was able to bind Eu at pH values as low as 4. This peptide was appended with a long-chain alkene and used to covalently functionalise titania nanoparticles. The resulting peptide functionalised titania demonstrated selective sorption of lanthanides over Ca, Ni, Sr and Cs ions. Overall, a deeper understanding of how peptide structure affects lanthanide binding affinity has been gained and the potential of these peptides as selective ligands for separations at acidic pH has been demonstrated. © 2016 The Royal Society of Chemistr

Effective Am(III)/Eu(III) separations using 2,6-bis(1,2,4-triazin-3-yl)pyridine (BTP) functionalised titania particles and hierarchically porous beads

Hybrid materials which selectively extract Am(III) over Eu(III) from 0.01 M nitric acid solutions with fast kinetics and separation factors up to 160 have been synthesised. The materials consist of titania functionalised with a modified organic 2,6-bis(1,2,4-triazin-3-yl)pyridine (BTP) derivative. Both particles and hierarchically porous beads have been prepared and provide advantages over conventional solvent extraction separations. © 2015 The Royal Society of Chemistr

Effects of precursor solution aging and other parameters on synthesis of ordered mesoporous titania powders

Evaporation-induced self-assembly (EISA) of ordered mesoporous titania powders using block copolymer templates Brij 58 and F127 has been studied as a function of the precursor solution composition and age as well as the evaporation conditions. Small-angle X-ray scattering was used to monitor the degree of order in the mesoporous structure of materials synthesized under these varying conditions. Also, for the first time, the time-dependent formation of Ti structures in precursor solutions and the effect of those structures on the creation of mesostructural order have been demonstrated. The interactions of the Ti precursor with Brij 58 and F127 were investigated and showed that the different templates caused formation of Ti oligomers of unique sizes and structures. Precursor solution composition and evaporation conditions were also shown to affect the order and stability of the mesoporous titania produced. Overall, this systematic study has provided fundamental insights into the synthesis conditions that maximize the degree of order and thermal stability of the final materials. These “optimal” conditions are highly dependent on the choice of template. As a result of this improved understanding, the synthesis of ordered mesoporous titania powders using the block copolymer F127 as a template has been achieved without the use of stabilizing agents for the first time. © 2015 American Chemical Societ

Selective sorption of actinides by titania nanoparticles covalently functionalized with simple organic ligands

Although current and proposed reprocessing of used nuclear fuel is performed predominantly by solvent extraction processes, solid phase sorbent materials have many advantages including the ability to avoid production of large volumes of organic waste. Therefore, three titania nanoparticle based sorbent materials have been developed, functionalized with organic ligands designed to impart selectivity for elements relevant to important separations at the back end of the nuclear fuel cycle. A novel, simplified method of covalent functionalization to the titania surface has been utilized, and the resulting materials have been shown to be hydrolytically stable at pH 2. The sorption behavior of these organofunctionalized titania materials was investigated over a wide pH range with a selection of elements including fission products and actinides. Titania nanoparticles functionalized with an amine or phosphate moiety were able to demonstrate exclusive extraction of uranium under optimized conditions. Titania nanoparticles functionalized with a picolinamide moiety exhibited superior minor actinide sorption properties, in terms of both efficiency and selectivity, to solvent extraction processes using similar organic moieties. As such, organo-functionalized titania materials as solid phase sorbents show promise as a future alternative to solvent extraction processes for nuclear separations. © 2013, American Chemical Society

Effects of Precursor Solution Aging and Other Parameters on Synthesis of Ordered Mesoporous Titania Powders

Evaporation-induced self-assembly (EISA) of ordered mesoporous titania powders using block copolymer templates Brij 58 and F127 has been studied as a function of the precursor solution composition and age as well as the evaporation conditions. Small-angle X-ray scattering was used to monitor the degree of order in the mesoporous structure of materials synthesized under these varying conditions. Also, for the first time, the time-dependent formation of Ti structures in precursor solutions and the effect of those structures on the creation of mesostructural order have been demonstrated. The interactions of the Ti precursor with Brij 58 and F127 were investigated and showed that the different templates caused formation of Ti oligomers of unique sizes and structures. Precursor solution composition and evaporation conditions were also shown to affect the order and stability of the mesoporous titania produced. Overall, this systematic study has provided fundamental insights into the synthesis conditions that maximize the degree of order and thermal stability of the final materials. These “optimal” conditions are highly dependent on the choice of template. As a result of this improved understanding, the synthesis of ordered mesoporous titania powders using the block copolymer F127 as a template has been achieved without the use of stabilizing agents for the first time

Selective Sorption of Actinides by Titania Nanoparticles Covalently Functionalized with Simple Organic Ligands

Although current and proposed reprocessing of used nuclear fuel is performed predominantly by solvent extraction processes, solid phase sorbent materials have many advantages including the ability to avoid production of large volumes of organic waste. Therefore, three titania nanoparticle based sorbent materials have been developed, functionalized with organic ligands designed to impart selectivity for elements relevant to important separations at the back end of the nuclear fuel cycle. A novel, simplified method of covalent functionalization to the titania surface has been utilized, and the resulting materials have been shown to be hydrolytically stable at pH 2. The sorption behavior of these organofunctionalized titania materials was investigated over a wide pH range with a selection of elements including fission products and actinides. Titania nanoparticles functionalized with an amine or phosphate moiety were able to demonstrate exclusive extraction of uranium under optimized conditions. Titania nanoparticles functionalized with a picolinamide moiety exhibited superior minor actinide sorption properties, in terms of both efficiency and selectivity, to solvent extraction processes using similar organic moieties. As such, organo-functionalized titania materials as solid phase sorbents show promise as a future alternative to solvent extraction processes for nuclear separations