Actinide Phosphate Research Articles

Thermochemical studies of X(NpO2)(PO4)(H2O)3 (X = K+, Rb+), neptunium analogs of the autunite/meta-autunite group

Actinide phosphate materials with autunite or meta-autunite type sheets consisting of vertex-sharing actinyl square bipyramids and phosphate tetrahedra have low aqueous solubility and potential applications for actinide immobilization in the environment. Neptunyl phosphates, X(NpO2)(PO4)(H2O)3, X ​= ​K+ and Rb+, have been synthesized by hydrothermal reactions and characterized for their structures and purities. Direct thermochemical studies were performed using high temperature oxide melt drop solution calorimetry. After correcting for the presence of residual fluorapatite from the synthesis, the formation enthalpies of K(NpO2)(PO4)(H2O)3 and Rb(NpO2)(PO4)(H2O)3 are determined to be −3235 ​± ​21 ​kJ/mol and −3270 ​± ​11 ​kJ/mol, respectively. The thermodynamic data presented here may be important for understanding neptunium mobility after disposal of nuclear waste in a geological repository.

A 3,2-Hydroxypyridinone-based Decorporation Agent that Removes Uranium from Bones In Vivo

Searching for actinide decorporation agents with advantages of high decorporation efficiency, minimal biological toxicity, and high oral efficiency is crucial for nuclear safety and the sustainable development of nuclear energy. Removing actinides deposited in bones after intake is one of the most significant challenges remaining in this field because of the instantaneous formation of highly stable actinide phosphate complexes upon contact with hydroxyapatite. Here we report a hydroxypyridinone-based ligand (5LIO-1-Cm-3,2-HOPO) exhibiting stronger affinity for U(VI) compared with the reported tetradentate hydroxypyridinone ligands. This is further revealed by the first principles calculation analysis on bonding between the ligand and uranium. Both in vitro uranium removal assay and in vivo decorporation experiments with mice show that 5LIO-1-Cm-3,2-HOPO can remove uranium from kidneys and bones with high efficiencies, while the decorporation efficiency is nearly independent of the treatment time. Moreover, this ligand shows a high oral decorporation efficiency, making it attractive for practical applications.

Actinide solubility-controlling phases during the dissolution of phosphate ceramics

Phosphate ceramics (britholites, monazite/brabantite solid solutions, thorium phosphate diphosphate, i.e. β-TPD, and associated β-TPD/monazite composites) are often considered as potential candidates to immobilize tri- and tetravalent actinides. In order to study the properties of such materials on the retention of actinides during aqueous alteration, phosphate-based neoformed phases were prepared using under- and over-saturation processes then extensively characterized (involving grazing XRD, EPMA, μ-Raman, IR or SEM). In over-saturation conditions, lanthanides (used as surrogates of trivalent actinides) are quickly precipitated as three hydrated forms (monazite, rhabdophane or xenotime) depending on the temperature, the heating time and the ionic radius of the element. Moreover, as already described for thorium, tetravalent actinides (Th, U, Np, Pu) are more often immobilized as phosphate hydrogenphosphate compounds. However, samples of (Ln,Ca,Th)-rhabdophane can also precipitate in the presence of large concentrations of calcium. Such neoformed phases were also precipitated at the surface of leached phosphate-based ceramics during under-saturation experiments. The associated thermodynamic solubility constants at infinite dilution were estimated. Due to their rapid precipitation and their very low solubility constants, these actinide phosphate solubility-controlling phases appear of significant interest in the field of the evaluation of the long-term performance of actinide-doped phosphate ceramics.

Hydrothermal Methods as a New Way of Actinide Phosphate Preparation

AbstractPrecipitation processes driven in hydrothermal conditions were applied to the preparation of phosphate-based ceramics. Three systems composed by a crystallized precursor linked with a high temperature compound were particularly examined: M(OH)PO4 / M2O(PO4)2 (M = Th, U), MPO40.5 H2O / MPO4 (M = La - Dy) and Th2-x/2Anx/2(PO4)2(HPO4) H2O / β-Th4-xAnx(PO4)4P2O7 (M = U, Np, Pu). A significant improvement of several physico-chemical properties of the powders, especially in the sintering capability and the homogeneity of the final solids was evidenced when starting from the precursors. Furthermore, these phases were also found to control the solubility of lanthanides and actinides during leaching experiments when reaching the saturation conditions in the solution.

Anhydrous Lanthanide and Actinide(III) and (IV) Orthophosphates Mem(PO4)n. Synthesis, Crystallization, Structure, and Properties

Anhydrous orthophosphates Mem(PO4)n, where Me is an element in the oxidation state +1 (A), +2 (B), +3 (R), +4 (M), or +5 (C), containing f elements(III) and (IV), are systematized. Their crystallographic characteristics are described, and the common and specific features of structure formation are discussed. The main structural (mineral) types realized in lanthanide and actinide phosphates are revealed: eulytite, zircon, monazite, NaZr2(PO4)3 (NZP), NaTh2(PO4)3 (NThP), rhabdophane, Sb0.5Bi1.5(PO4)3 (SbBi), whitlockite, arcanite, glaserite, langbeinite, scheelite, Sc2(WO4)3 (ScW). The crystal-chemical factors determining the stability of structures, polymorphism of cations, morphotropy in the series, and possibility of formation of solid solutions on the basis of iso- and heterovalent isomorphism and isodimorphism are analyzed. The possibility of predicting new compounds of f elements of the expected structure is demonstrated.

Chemistry of tetravalent actinide phosphates—Part I

The chemistry and crystal structure of phosphates of tetravalent cations, including that of actinides was reviewed several times up to 1985. Later, new compounds were synthesized and characterized. In more recent studies, it was found that some of previously reported phases, especially those of thorium, uranium and neptunium, were wrongly identified. In the light of these new facts an update review and classification of the tetravalent actinide phosphates is proposed in the two parts of this paper. Their crystal structure and some chemical properties are also compared to non-actinide cation phosphates.

Rhombohedral Actinide Phosphates A I M 2 IV(PO 4 ) 3 (MIV = U, Np, Pu; A I = Na, K, Rb)

Double orthophosphates of actinides and alkali metals AIM2IV(PO4)3, where MIV = U, Np, or Pu; AI = Na, K, or Rb, are studied by X-ray diffraction. Rhombohedral modifications (β-forms) formed from the low-temperature monoclinic modifications (α-forms) on heating in the range 600-1650°C are examined. The α → β transition temperature depends on particular alkali metal and actinide. The crystallographic parameters of the complexes are tabulated. The trends in variation of the unit cell parameters in relation to the ionic radii of alkali metals and actinides are discussed.

The synthesis and characterization of crystalline phosphates of thorium, uranium and neptunium

The high temperature synthesis and stability of phosphates of thorium, uranium and neptunium have been studied by Raman spectroscopy, X-ray diffraction and chemical analyses. For these actinides, the only orthophosphate An3(PO4)4 (An ≡ actinide) that could be prepared was thorium orthophosphate. The high temperature (α, cubic) forms of all three metal pyrophosphates were synthesized. For the oxypyrophosphate compounds (AnO)2P2O7, only the thorium compound was not obtained and (NpO)2P2O7 is reported here for the first time. The results of these studies are discussed and compared with published data on actinide phosphates.

Synthesis and characterization of actinide phosphates

The immobilization of actinides by incorporation into synthetic monazite is an attractive concept for the long term storage of actinides. This stems from the known stability, over geological age, of natural monazites (which contain uranium and thorium) toward radiation and sea water. In seeking methods for the preparation of metal phosphates from insoluble metal compounds by simple reactions, we have identified both BPO 4 and SiP 2O 7 as convenient reagents for such a task. a large variety of reactions, involving compounds of Th, U, Np, Pu, Am and all the lanthanides were studied. The results obtained, based mainly on Raman spectroscopy and X-ray powder diffraction, allowed for postulating reaction mechanism and for optimizing conditions for the preparation of ortho-, pyro- and trimeta-phosphates and actinide oxide phosphates. Some of the ternary phosphates thus prepared were used to prepare other phosphate, e.g., Pu(PO 3) 3 and sodium -containing quaternary phosphates, e.g. Na 3Pu(PO 4) 2 and Na 3Ln(PO 4) 2 Ln is a lanthanide element). Raman spectroscopy proved to be a very sensitive technique for identifying most of the compounds and for establishing their purity.

Search for high energy alpha emitters in monazite minerals

We have attempted to find evidence for high energy alpha particles from Malaysian, Madagascan and Indian monazite minerals (rare earth and actinide phosphates) which might indicate the presence of naturally occurring superheavy elements in nature. A silicon surface barrier detector was used to detect alpha particles in conjunction with a cosmic-ray anti-coincidence detector. The results are consistent with no alphas above 12.5 MeV. This agrees with results of Fireman and Brandt 1978 but does not agree with results of Chevalier et al. 1978.