Selective Extraction and Complexation Studies for Thorium(IV) with Bis-triamide Extractants: Synthesis, Solvent Extraction, EXAFS, and DFT

Abstract

Three octyl-extended bis-triamide extractants (L1–L3) were designed and synthesized for the selective solvent extraction of Th­(IV) over U­(VI) in a kerosene–HNO3 system. L1 and L2 exhibited good extraction property and selectivity toward Th­(IV) over U­(VI) and reached extraction equilibrium within 10 min. In a wide range of a HNO3 concentration from 0.1 to 3.0 M, the separation factor of Th­(IV) over U­(VI) (SFTh/U) of L1 and L2 ranged from 12.1 ± 1.6 to 123.0 ± 20.2 and 15.2 ± 2.4 to 88.1 ± 14.9, respectively. Slope analysis indicated that Th­(IV) was extracted as different species under different HNO3 concentrations, in which the slopes were 2.08 ± 0.20, 1.61 ± 0.03, and 1.54 ± 0.03 for L1 and 2.37 ± 0.22, 2.07 ± 0.17, and 1.76 ± 0.18 for L2 under 0.1, 1.0, and 3.0 M HNO3, respectively. A continuous variation method (Job plot) illustrated a 1.5:1 ligand/thorium (L/Th) ratio in a methanol phase, indicating that L1/L2 and Th­(IV) could form mixed 1:1 and 2:1 L/Th extracted complexes. Extended X-ray absorption fine structure (EXAFS) and density functional theory (DFT) calculations revealed that the extracted complexes of L1 and L2 with Th during the extraction process at 0.1 M HNO3 were [2L1·Th·3­(NO3)]+ and [2L2·Th·3­(NO3)]+.

Selective Complexation and Separation of Uranium(VI) from Thorium(IV) with New Tetradentate N,O-Hybrid Diamide Ligands: Synthesis, Extraction, Spectroscopy, and Crystallographic Studies

“…However, the efficient and selective separation of uranium remains a formidable task because of the similar physicochemical properties as well as the invariable oxidation state of thorium. 8 To address this issue, extensive endeavors have been devoted to uranium/thorium separation, and different technologies have been developed, such as solvent extraction, 9 adsorption, 10 precipitation, 11 ion exchange, 12 etc. Of them, solvent extraction plays a dominating role in the nuclear industry, benefiting from its facile process and high sample throughput.…”

“…To address this issue, extensive endeavors have been devoted to uranium/thorium separation, and different technologies have been developed, such as solvent extraction, adsorption, precipitation, ion exchange, etc. Of them, solvent extraction plays a dominating role in the nuclear industry, benefiting from its facile process and high sample throughput. , The thorium-uranium extraction (Thorex) process, based on the solvent extraction technique with tri- n -butyl-phosphate (TBP, Figure ) in a hydrocarbon diluent, represents one of the most promising methods for separating uranium and thorium from fission products and from each other. , However, it is well known that TBP suffers from drawbacks of high water solubility and formation of the third phase .…”

Selective Extraction of Thorium(IV) from Uranium and Rare Earth Elements Using Tetraphenylethane-1,2-diylbis(phosphoramidate)

“…Thorium is the most abundant naturally occurring actinide element, and its reserve is estimated to be over three times more abundant than uranium in the Earth’s crust. With the development of liquid fluoride thorium reactors (LFTR) near commercialization, thorium is tagged to be the next-generation nuclear fuel. − LFTR, a part of the generation IV molten salt reactor system, can produce ∼250 times more energy, compared to the uranium-fueled light water reactors, using the same weight of nuclear fuel. − Thorium is less radioactive than uranium due to its naturally abundant 232 Th isotope (99.98%, half-life of 14.05 billion years). No isotope enrichment is required for LFTR fuel, as the fertile 232 Th can be converted to fissile 233 U in a reactor.…”

“…No isotope enrichment is required for LFTR fuel, as the fertile 232 Th can be converted to fissile 233 U in a reactor. The thorium fuel cycle also produces much less long-lived radioactive nuclear waste products compared to the uranium fuel cycle. − It has been estimated that the existing reserves of thorium can contribute to clean energy for several hundreds of years and that too at a fraction of the cost compared to the combustion of fossil fuels in thermal power plants. − , In addition, the nuclear power plants do not release CO 2 into the environment like thermal power plants do.…”

Aggregation Behavior of Nitrilotriacetamide (NTAmide) Ligands in Thorium(IV) Extraction from Acidic Medium: Small-Angle Neutron Scattering, Fourier Transform Infrared, and Theoretical Studies

“…Nitrilotriacetamide (NTAmide) ligands, with soft N -donor atoms, have been studied by several authors for the extraction of lanthanide (Ln)/actinide (An) ions for their potential application toward An 3+ /Ln 3+ separation. − However, higher extraction of tetravalent actinide compared to the trivalent or hexavalent actinides by NTAmide was also reported by others. − The involvement of the central nitrogen of the NTAmide in the extraction of softer trivalent actinides was suggested by Bhattacharyya et al, , whereas interaction of amidic oxygen of lignad for tetravalent ion extraction was shown by Huang et al The long alkyl chain derivatives of NTAmide , such as the one with n -octyl groups (HONTA­( L II ), Figure ), show high extraction ability and selectivity for Th­(IV) compared to trivalent Ln ions from pH 1 to 10.0 M HNO 3 with separation factors ( SF Th – Ln = D Th / D Ln ) ranging from 2.5 × 10 2 to 10 3 . The high relative extraction of Pu 4+ compared to U­(VI) and Am­(III) from 3 M HNO 3 solution was also suggested by others. ,,,− The separation factor of Pu 4+ was found to be greater than10 3 and 5 × 10 3 for UO 2 2+ and Am 3+ , respectively, at 3 M HNO 3 for HONTA dissolved in n -dodecane +10% isodecanol.…”