ThF4 Research Articles

Sorption of Protactinium, Thorium, and Other Actinides from the LiF–NaF–KF Melt by Activated Carbon

The sorption of uranium and thorium fluorides by activated carbon from the eutectic was studied. The sorption isotherms of both fluorides at a temperature of 650°C have a pronounced convex character and are described by the Langmuir equation. Experiments were carried out on the sorption of protactinium by activated carbon AG-3 at 650°С from a melt of alkali metal fluorides LiF–NaF–KF containing thorium and neodymium fluorides. It was found that with an increase in the concentrations of neodymium or thorium fluorides, the value of protactinium sorption diminishes, and in the case of thorium fluoride, the decrease occurs to a greater extent. When protactinium is sorbed by activated carbon with metallic sodium, the sorption enhances by a factor of 20 at the 30% sodium content in the carbon. The separation factors of protactinium from other actinides rise with increasing sodium content in the carbon.

Reactions of Atomic Thorium and Uranium Cations with SF6 Studied by Guided Ion Beam Tandem Mass Spectrometry.

The fundamental chemistry of the thorium and uranium fluorides continues to be an area of interest because of the use of thorium and uranium fluoride compounds in nuclear fuel systems. Here, we study the reaction of thorium cations with sulfur hexafluoride for the first time and revisit the reaction of uranium cations with sulfur hexafluoride. By using guided ion beam tandem mass spectrometry, we explore the reaction pathways that become accessible well above thermal energies (E ∼ 0.04 eV). Overall, we find that both Th+ and U+ react very efficiently with SF6, approaching the collision limit at both thermal and elevated energies. The primary products observed at low energies include Th1-3+, UF1-4+, and SF1-4+, all of which are formed in barrierless, exothermic processes. SF5+ was also observed, although the pressure dependence of this channel reveals that SF5+ forms exothermically through secondary reactions, which the energy dependences suggest result from reactions between ThF2+ and UF3+ with SF6. At higher energies, both AnF3+ products are observed to decay to AnF+ + F2, and both SF4+ and SF2+ exhibit cross sections with endothermic features. For both systems, the rise in SF4+ can be attributed to a secondary collision between AnF+ with SF6 on the basis of the pressure dependence of the SF4+ channel at higher energies, and the rise in SF2+ appears to result from the decomposition of SF3+ to SF2+ + F.

Effect of process parameters on the recovery of thorium tetrafluoride prepared by hydrofluorination of thorium oxide, and their optimization

Liquid fueled molten salt reactors (MSRs) have seen renewed interest because of their inherent safety features, higher thermal efficiency and potential for efficient thorium utilisation for power generation. Thorium fluoride is one of the salts used in liquid fueled MSRs employing Th–U cycle. In the present study, ThF4 was prepared by hydro-fluorination of ThO2 using anhydrous HF gas. Process parameters viz. bed depth, hydrofluorination time and hydrofluorination temperature, were optimized for the preparation of ThF4 in a static bed reactor setup. The products were characterized with X-Ray diffraction and experimental conditions for complete conversion to ThF4 were established which also corroborated with the yield values. Hydrofluorination of ThO2 at 450 °C for half an hour at a bed depth of 6 mm gave the best result, with a yield of about 99.36% ThF4. No unconverted oxide or any other impurity was observed. Rietveld refinement was performed on the XRD data of this ThF4, and Chi2 value of 3.54 indicated good agreement between observed and calculated profiles.

Sorption of NdF3 and ThF4 from the LiF\u2013NaF\u2013KF Melt

The sorption of neodymium and thorium fluorides by AG-3 activated carbon from molten alkali metal fluorides LiF–NaF–KF has been studied. The sorption isotherm of neodymium fluoride at 650°C has a pronounced convex and is adequately described by the Langmuir equation. The sorption of thorium fluoride under the same conditions is much weaker than that of neodymium fluoride, which is determined by the size of the neodymium and thorium fluoride complexes. The kinetic dependence of the sorption of neodymium fluoride at a temperature of 650°С is adequately described by a first-order equation for a reversible reaction. The temperature dependence of sorption capacity in the range 550–750°С passes a maximum within 600–650°С.

Bismuth and thorium fluorides as efficient X-ray radiation shielding materials

Composite materials (CM) consisting of polysiloxane rubber filled with lanthanide acetylacetonates, acetates, carboxylates and bismuth (III) and thorium (IV) fluorides were tested as X-ray shielding materials. It has been established that materials containing bismuth and thorium fluorides are superior in protective properties to the other studied materials, as well as to the convenient composites based on lanthanide oxides. The values of half value layer (HVL) of the materials based on BiF3(H2O) (79% wt) and ThF4(H2O) (69% wt) at X-ray irradiation with photon energy range 10–45 keV reach 0.20 mm. The obtained materials are flexible and thermally stable up to 300 °C.

On the Structures of Thorium Fluoride and Oxyfluoride Anions in Molten FLiBe and FLiNaK.

The structures of thorium fluoride and oxyfluoride ions in molten FLiBe-ThF4 and FLiNaK-ThF4 were investigated by Raman spectroscopy and density functional theory calculations. Thorium fluorides are present in the form of ThF62- (Oh) and ThF73- (C2v) in molten FLiNaK-ThF4. Similar speciation was identified in FLiBe-ThF4, and the thorium fluoride anions are in equilibrium with free F- ions and beryllium fluoride anions, which are responsible for the red shift of the beryllium fluoride bands in the Raman spectra. With the addition of Li2O into the FLiNaK-ThF4 and FLiBe-ThF4 melts, the Th2OF104- anion with a linear Th-O-Th geometry was formed at the expense of thorium fluoride anions. The beryllium fluoride bands in the Raman spectra of FLiBe-ThF4 exhibit a blue shift upon Th2OF104- formation, which results from the release of free F- ions that can further react with beryllium fluoride. Insoluble thorium oxides were found in the FLiNaK and FLiBe melts at a Li2O concentration of 15 mol %, and the Th2OF104- anion is, therefore, a bridge connecting the soluble thorium fluorides and insoluble thorium oxides in molten fluorides.

Thorium tetrafluoride analyzed by XPS

X-ray photoelectron spectroscopy was performed on a freshly exposed thorium tetrafluoride (ThF4) granule surface. The sample surface exhibits stoichiometric ThF4 with hydrocarbon contamination and an oxide impurity which is tentatively attributed to thorium oxyfluoride.

Isobaric Heat Capacity of Solid and Liquid Thorium Tetrafluoride

The isobaric heat capacity of solid and liquid thorium tetrafluoride was determined by two calorimetry methods: drop calorimetry to obtain the enthalpy increments in the range from 430 to 1600 K an...

In situ high-temperature EXAFS measurements on radioactive and air-sensitive molten salt materials.

The development at the Delft University of Technology (TU Delft, The Netherlands) of an experimental set-up dedicated to high-temperature in situ EXAFS measurements of radioactive, air-sensitive and corrosive fluoride salts is reported. A detailed description of the sample containment cell, of the furnace design, and of the measurement geometry allowing simultaneous transmission and fluorescence measurements is given herein. The performance of the equipment is tested with the room-temperature measurement of thorium tetrafluoride, and the Th-F and Th-Th bond distances obtained by fitting of the EXAFS data are compared with the ones extracted from a refinement of neutron diffraction data collected at the PEARL beamline at TU Delft. The adequacy of the sample confinement is checked with a mapping of the thorium concentration profile of molten salt material. Finally, a few selected salt mixtures (LiF:ThF4) = (0.9:0.1), (0.75:0.25), (0.5:0.5) and (NaF:ThF4) = (0.67:0.33), (0.5:0.5) are measured in the molten state. Qualitative trends along the series are discussed, and the experimental data for the (LiF:ThF4) = (0.5:0.5) composition are compared with the EXAFS spectrum generated from molecular dynamics simulations.

Synthesis of thorium tetrafluoride (ThF4) by ammonium hydrogen difluoride (NH4HF2)

Abstract The present study aims to investigate the fluorination of thorium oxide (ThO2) by ammonium hydrogen difluoride (NH4HF2). Fluorination was performed at room temperature by mixing ThO2 and NH4HF2 at different molar ratios, which was then left to react for 20 days. Next, the mixtures were analyzed using X-ray diffraction (XRD) at the intervals of 5, 10, 15, and 20 days, followed by the heating of the mixtures at 450–750 °C with argon gas flow. The characterization of ThF4 was established using X-ray diffraction (XRD) and scanning electron microscopy–dispersion X-ray spectroscopy (SEM–EDX). In this study, ammonium thorium fluoride was synthesized through the fluorination of ThO2 at room temperature. The optimum molar ratio in synthesizing ammonium thorium fluoride was 1.0:5.5 (ThO2:NH4HF2) with 5 days reaction time. In addition, the heating of ammonium thorium fluoride at 450 °C was sufficient to produce ThF4. Overall, this study proved that NH4HF2 is one of the fluorination agents that is capable of synthesizing ThF4.

Insight into the Crystalline Structure of ThF4 with the Combined Use of Neutron Diffraction, 19F Magic-Angle Spinning-NMR, and Density Functional Theory Calculations.

Because of its sensitivity to the atomic scale environment, solid-state NMR offers new perspectives in terms of structural characterization, especially when applied jointly with first-principles calculations. Particularly, challenging is the study of actinide-based materials because of the electronic complexity of the actinide cations and to the hazards due to their radioactivity. Consequently, very few studies have been published in this subfield. In the present paper, we report a joint experimental-theoretical analysis of thorium tetrafluoride, ThF4, containing a closed-shell actinide (5f0) cation. Its crystalline structure has been revisited in the present work using powder neutron diffraction experiments. The 19F NMR parameters of the seven F crystallographic sites have been modeled using an empirical superposition model, periodic first-principles calculations, and a cluster-based all-electron approach. On the basis of the atomic position optimized structure, a complete and unambiguous assignment of the 19F NMR resonances to the F sites has been obtained.

Immobilization of Alkali Metal Fluorides via Recrystallization in a Cationic Lamellar Material, [Th(MoO4)(H2O)4Cl]Cl·H2O.

Searching for cationic extended materials with a capacity for anion exchange resulted in a unique thorium molybdate chloride (TMC) with the formula of [Th(MoO4)(H2O)4Cl]Cl·H2O. The structure of TMC is composed of zigzagging cationic layers [Th(MoO4)(H2O)4Cl]+ with Cl- as interlamellar charge-balancing anions. Instead of performing ion exchange, alkali thorium fluorides were formed after soaking TMC in AF (A = Na, K, and Cs) solutions. The mechanism of AF immobilization is elucidated by the combination of SEM-EDS, PXRD, FTIR, and EXAFS spectroscopy. It was observed that four water molecules coordinating with the Th4+ center in TMC are vulnerable to competition with F-, due to the formation of more favorable Th-F bonds compared to Th-OH2. This leads to a single crystal-to-polycrystalline transformation via a pathway of recrystallization to form alkali thorium fluorides.

Synthetic Strategies for the Synthesis of Ternary Uranium(IV) and Thorium(IV) Fluorides.

A series of new U(IV) and Th(IV) fluorides, Na7U6F31 (1), NaUF5 (2), NaU2F9 (3), KTh2F9 (4), NaTh2F9 (5), (H3O)Th3F13 (6), and (H3O)U3F13 (7), was obtained using hydrothermal and low-temperature flux methods. Mild hydrothermal reactions with uranyl acetate as a precursor yielded 1, 7, and the monoclinic polymorph of NaU2F9, whereas direct reactions between UF4 and NaF led to the formation of 2 and orthorhombic NaU2F9 (3). This highlights an unexpected difference in reaction products when different starting uranium sources are used. All seven compounds were characterized by single-crystal X-ray diffraction, and their structures are compared on the basis of cation topology, revealing a close topological resemblance between fluorides on the basis of the layers observed in NaUF5(H2O). Phase-pure samples of 1, 2, and both polymorphs of NaU2F9 were obtained, and their spectroscopic and magnetic properties were measured. The UV-vis data are dominated by the presence of U4+ cations and agree well with the electronic transitions. Effective magnetic moments of the studied compounds were found to range from 3.08 to 3.59 μB.

Single crystal structures of thallium (I) thorium fluorides and crystal chemistry of monovalent tetravalent cation pentafluorides

Two thallium (I) thorium (IV) fluorides, TlTh3F13 and TlThF5 were obtained by solid state synthesis and their crystal structures determined from single crystal X-ray diffraction data recorded at room temperature with an APEX-II CCD diffractometer. TlTh3F13 is orthorhombic, space group Pmc21, with a=8.1801(2)Å, b=7.4479(2)Å, c=8.6375(2)Å, V=526.24(2)Å3, Z=2 and TlThF5 is monoclinic, space group P21/n, with a=8.1128(5)Å, b=7.2250(4)Å, c=8.8493(6)Å, β=116.683(3)°, V=463.46(5)Å3, Z=4.The structure of TlTh3F13 comprises layers of corner and edge-sharing ThF9 polyhedra further linked by chains of trans connected tricapped trigonal prisms ThF9 through corners and edges. The three dimensional thorium frameworks delimits channels parallel to [0 0 1] where the 11-coordinated Tl+ ions are arranged into double columns located in mirror planes of the structure. TlTh3F13 is isotypic with RbTh3F13, RbU3F13 and with one of the two polymorphs of CsTh3F13. The structure of TlThF5 may be regarded as a layer structure built up from the regular succession of ∞2[M′F5]− corrugated layers further held by the Tl+ ions along the [1 0 1̅] direction. The layers are built up from edge and corner-sharing thorium polyhedra where each (ThF9)5− monocapped square antiprism is connected to five others by sharing three edges and two corners. TlThF5 is isostructural with β-NH4UF5 and with one of the polymorphs of CsThF5. A comparison of the different structural types of MM′F5 pentafluorides is presented and a diagram of repartition of their structures is given.From the comparison of the Tl structures with their Rb or Cs homologs, where very similar monovalent cation environments are observed it should be concluded to a stereochemically inactivity of the 6s2 lone pair of Tl(I) in both TlTh3F13 and TlThF5, contrary to what is observed in richer Tl(I) content Tl3ThF7 fluorothorate.

Joint solubility of PuF3 and CeF3 in ternary melts of lithium, thorium, and uranium fluorides

Joint solubility of PuF3 and CeF3 in melts of the molar composition 78LiF-7ThF4-15UF4 and 72.5LiF-7ThF4-20.5UF4 in the temperature range 550°-800°C was studied. Anhydrous PuF3 and CeF3 spiked with 144Ce, and also anhydrous ThF4 were synthesized. Isothermal saturation method was used for studying the solubility of pressed PuF3 and CeF3 pellets in these melts in an inert (argon) atmosphere. The dependence of the joint solubility of PuF3 and CeF3 on the melt temperature was determined.

Hydrothermal Synthesis and Crystal Chemistry of Novel Fluorides with A7B6F31 (A = Na, K, NH4, Tl; B = Ce, Th) Compositions

Two new monovalent metal thorium fluorides and three new monovalent metal cerium fluorides have been synthesized hydrothermally and structurally characterized. The structures of the five compounds are described in space group $${\text{R}}\bar{3}$$ : Tl7Th6F31 with a = 15.598(2) and c = 10.893(2), (NH4)7Th6F31 with a = 15.5979(2) and c = 10.952(2), K7Ce6F31 with a = 15.013(2) and c = 10.295(2), (NH4)7Ce6F31 with a = 15.232(2) and c = 10.749(2), and Na7Ce6F31 with a = 14.567(2) and c = 9.6921(19). Comparison of these materials was made based on their structures and synthesis conditions. The formation of these species in hydrothermal fluids appears to be largely dependent upon the concentration of the monovalent fluoride mineralizer solution and thus, the ratio of monovalent ions to thorium or cerium in the system. The crystal chemistry of the A7B6F31 (A = Na+, K+, Rb+, Tl+, NH4 +; B = Zr4+, Ce4+, Th4+) structure type is described by examining the title compounds alongside other isomorphs to gain a broader understanding of the crystallization of complex fluorides. Structural subtleties are also discussed, including substitutional disorder of Na+ and Ce4+ cations in Na7Ce6F31. The hydrothermal synthesis of fluorides having compositions A7B6F31 (A = Na, K, NH4, Tl; B = Ce, Th) is described. Structural comparisons are made to discuss the crystal chemistry within this family of compounds in terms of the combinations of A and B cations supported by the structure type. The study introduces Tl+ and NH4 + as new A-site building blocks, and Ce4+ as a new B-site building block for this structure type.

UF4, ThF4 Solubility in LiF–NaF–KF Melt

The results of measurements of the solubility of UF 4 and ThF 4 in the eutectic 46.5LiF‐11.5NaF‐42KF are presented. Isothermal saturation of the salt melt by the experimental compounds is used. The UF 4 and ThF 4 solubility in the experimental salt system is experimentally shown to be high (45 and 41 mol. %, respectively, at 700°C) and temperature-dependent in the interval 550‐700°C. The available data on the solubility of heavy-element fluorides in LiF‐NaF‐KF are limited and the systematic errors are not known. A few theoretical estimates, obtained using a thermodynamic approach, exist [1, 2]. The measured values of the solubility in salt with the composition 45LiF‐12NaF‐43KF at 600, 650, and 700°C are 4.7, 9.7, and 11.7 for UF 4 and 4.5, 6.8, and 7.6 for ThF 4 [3]. The present work is devoted to measuring the solubility of UF 4 and ThF 4 in a salt system with eutectic composition 46.5LiF‐11.5NaF‐42KF (T melt = 454°C) in the interval 550‐700°C by a method of isothermal saturation of melt, differing somewhat from the one used in [3]. Experiment. A schematic diagram of the setup for measuring solubility is presented in [4]. The initial reagents were factory products of depleted uranium tetrafluoride and thorium nitrate. Thorium nitrate was dissolved in distilled water followed by precipitation of hydrated ThF 4 by concentrated hydrofluoric acid. The precipitate obtained was separated from the solution, washed with a dilute 0.001 M solution of hydrofluoric acid and dried over a long period of time to a powder. Hydrated thorium tetrafluoride ThF 4 ·H 2 O was dewatered in a special hermetic cell in an argon (high purity grade 5.5) stream in a nickel boat, adding ammonium bifluoride NH 4 F·HF to the cell and boat. ThF 4 ·H 2 O was processed repeatedly at 350°C until phase-pure anhydrous thorium tetrafluoride was obtained. Pellets were produced from uranium and thorium tetrafluoride using a 5-mm in diameter die-casting mold under pressure 200 MPa. The quality of the preparations was monitored by x-rays in a RKU-114M Debye‐Scherrer chamber with a copper anti-cathode and nickel filter as well as a DRON-3N x-ray diffractometer. The interpretation of the x-ray diffraction patterns and calculations of the functions of the scattering angles were performed in the PIKAR laboratory measuring complex taking account of the main systematic errors (absorption and uncertainty of the film radius) [5, 6]. The intensity of the reflections was evaluated visually according to the blackening marks on a 100 unit scale with step 2 1/4 . The JCPDS diffraction data library was used to identify the phase composition of the products [7]. The eutectic was prepared using the initial reagents lithium, sodium and potassium fluorides manufactured by the Sigma-Aldrich Company (USA). Weighed portions of anhydrous Li, Na, and K fluorides were placed into a box with a dry

ChemInform Abstract: Thorium Fluorides ThF, ThF2, ThF3, ThF4, ThF3(F2), and ThF5‐ Characterized by Infrared Spectra in Solid Argon and Electronic Structure and Vibrational Frequency Calculations.

AbstractLaser‐ablated Th atoms are reacted with different F2 concentrations to produce ThFx (x = 1, 2, 3, 4), ThF3(F2) and ThF5‐.

Crystal structures and stability of K2ThF6 and K7Th6F31 on compression

K2ThF6 and K7Th6F31 were prepared hydrothermally as single crystals. Their structures were investigated with single-crystal X-ray diffraction at ambient conditions and at high pressures using diamond anvil cells. The results of this study indicate that the two materials, with chains of face-sharing tricapped trigonal prisms ThF9 and with layers of square antiprisms ThF8 sharing their edges in Th2F14 doublets, respectively, are structurally stable at least to about 9GPa at room temperature. This observation suggests that, in general, moderate high pressure has no effect on the coordination polyhedra around the Th atoms and the topology of the structure of complex thorium fluorides. The bulk compressibility of the thorium fluorides entirely depends on the alkali metal present in the structure.

The Crystal Structures of CsTh6F25 and NaTh3F13

Two new alkali thorium fluorides have been synthesized hydrothermally and structurally characterized. The structures of CsTh6F25 and NaTh3F13 are each described in space group P63 /mmc (No. 194) with a = 8.3507(12) and c = 16.914(3) A, and a = 8.2570(12) and c = 16.891(3) A, respectively. Both structures exhibit a framework structure containing pores, unlike most of their alkali metal thorium fluoride analogs. The significant structural difference between the two compounds, however, is the arrangement of the alkali metal within the pores formed in the framework. Accordingly the pores exhibit differing degrees of distortion depending on their contents. Two new alkali thorium fluorides, CsTh6F25 and NaTh3F13, have been synthesized hydrothermally and found to crystallize in space group P63 /mmc (No. 194) with both having an interesting structural difference in the contents of the pores formed from their framework structures.