Structure-Modulated Complexation of Actinides with Phosphonates: A Combined Experimental and Quantum Chemical Investigation

Crystalline versus Amorphous: High-Performance Hafnium Phosphonate Framework for the Separation of Uranium and Transuranium Elements

Metal phosphonate frameworks (MPFs) consisting of tetravalent metal ions and aryl-phosphonate ligands feature a large affinity for actinides and excellent stabilities in harsh aqueous environments. However, it remains elusive how the crystallinity of MPFs influences their performance in actinide separation. To this end, we prepared a new category of porous, ultrastable MPF with different crystallinities for uranyl and transuranium separation. The results demonstrated that crystalline MPF was generally a better adsorbent for uranyl than the amorphous counterpart and ranked as the top-performing one for uranyl and plutonium in strong acidic solutions. A plausible uranyl sequestration mechanism was unveiled by using powder X-ray diffraction in tandem with vibrational spectroscopy, thermogravimetry, and elemental analysis.

Thorium as an abundant source of nuclear energy and challenges in separation science

Today about 440 nuclear power plants, with total installed capacity of 390 GW(e) are in operation worldwide generating around 10% of global electricity which are largely fuelled by enriched uranium oxide [Nuclear Power in the World Today. https://world-nuclear.org/information-library/current-and-future-generation/nuclear-power-in-the-world-today.aspx]. Thorium is 3–4 times more abundant than uranium and needs to be exploited by countries with limited stock of uranium. Historically, there have been several attempts to develop Th based reactors, but none has reached commercial scale. In recent years, High Temperature Reactor based on thorium has gained prominence for production of hydrogen with long term goal of complete carbon neutrality. However, unlike natural uranium, which contains ∼0.7% fissile 235U isotope, natural thorium does not contain any ‘fissile’ material and is made up exclusively of the ‘fertile’ 232Th which can be converted to ‘fissile’ 233U, thereby enlarging the fissile material resources. However, there is a need to develop robust closed fuel cycle to address to the challenges of high gamma dose due to the presence of decay products of 232U. It is necessary to gain more experience with promising THOREX process to achieve the desired recovery and D.F. of 233U from the irradiated 232Th. There is also scope to have a close look at some of the alternative extractants and emerging separation techniques for the reprocessing of spent Th based fuels. In view of the distinct advantages of non aqueous reprocessing over aqueous reprocessing, there is need to intensify the efforts to develop the former on a commercial scale. Molten Salt Breeder Reactor (MSBR) is particularly promising in this context. There is a need to investigate Th as energy amplifier under Accelerator Driven Sub-critical System (ADSS) which has potential to burn long lived radio nuclides, considered as a threat to environment over million of years.