Hydrothermal Method of Preparation of Actinide(IV) Phosphate Hydrogenphosphate Hydrates and Study of Their Conversion into Actinide(IV) Phosphate Diphosphate Solid Solutions

Abstract

Several compositions of Th2-x/2AnIVx/2(PO4)2(HPO4).H2O (An=U, Np, Pu) were prepared through hydrothermal precipitation from a mixture of nitric solutions containing cations and concentrated phosphoric acid. All the samples were fully characterized by X-ray diffraction, UV-vis, and infrared spectroscopies to check for the existence of thorium-actinide(IV) phosphate hydrogenphosphate hydrates solid solutions. Such compounds were obtained as single phases, up to x=4 for uranium, x=2 for neptunium, and x<4 for plutonium, the cations being fully maintained in the tetravalent oxidation state. In a second step, the samples obtained after heating crystallized precursors at high temperature (1100 degrees C) were characterized. Single-phase thorium-actinide(IV) phosphate-diphosphate solid solutions were obtained up to x=0.8 for Np(IV) and x=1.6 for Pu(IV). For higher substitution rates, polyphase systems composed by beta-TAnPD, An2O(PO4)2, and/or alpha-AnP2O7 were formed. Finally, this hydrothermal route of preparation was applied successfully to the synthesis of an original phosphate-based compound incorporating simultaneously tetravalent uranium, neptunium and plutonium.

Linear Alkyl Diamine-Uranium-Phosphate Systems: U(VI) to U(IV) Reduction with Ethylenediamine

“…The Raman spectrum confirms the presence of PO 4 groups in C2UP2. All the deformation and elongation modes of the P−O bond were assigned considering the data previously reported: − (δ s (380−472 cm −1 ), δ as (556−627 cm −1 ), υ s (950 and 960 cm −1 ), and υ as (1016−1072 cm −1 )) (Figure a). The additional bands located at 1000, 1120, 1246−1339, and 1435−1475 cm −1 were attributed to the various vibrations (stretching, scissoring, wagging, and bending) of the C−C, C−N, NH 3 + , and CH 2 bond belonging to the (CH 2 ) 2 (NH 3 ) 2 2+ cations.…”

Deviation Between the Chemistry of Ce(IV) and Pu(IV) and Routes to Ordered and Disordered Heterobimetallic 4f/5f and 5f/5f Phosphonates

“…When surrogates are actually compared with transuranium elements, it has been found in many cases that they are not proper mimics of transuranium elements both in solution and in the solid state. − The foremost example of this that impacts the modeling of plutonium in the environment is that the primary hydrolysis product for U(VI) is a trimer, whereas for Pu(VI), it is a dimer . Raymond and co-workers have demonstrated with both complex octadentate chelating agents and more simple homoleptic chelates of Ce(IV) and Pu(IV) that these two cations can yield substantially different coordination geometries even if they possess the same coordination number .…”

“…Diphosphonates were selected as a ligand for this study in order to probe potential differences between Ce(IV) and Pu(IV), and the effects of mixing Np(IV) and Pu(IV) with both each other and with Ce(IV). Phosphonates have wide-ranging applications in the nuclear waste remediation and actinide separation processes and are also relevant to the functional groups on the cell walls of the bacteria that are believed to bind actinides under natural conditions. , In previous reports, we demonstrated that both Np(IV) and Pu(IV) phosphonates and diphosphonates can be prepared via in situ hydrothermal reduction of Np(VI) and Pu(VI), which allows for slow kinetics of crystal growth. − This synthetic methodology is broadly applicable to the crystallization of many tetravalent actinide oxoanion systems. − ,− Herein, we disclose routes to both ordered and disordered heterobimetallic 4f/5f and 5f/5f compounds and a rare example of the incorporation of Pu(VI) into a U(VI) material.…”

New insights into phosphate based materials for the immobilisation of actinides

“…The very low solubility of TPHPH and the derived solid solutions allow for a quantitative precipitation of actinides from solution [110]. An actinidebearing TPHPH (Th 2−x/2 An IV x/2 (PO 4 ) 2 (HPO 4 ) · H 2 O; An IV = U, Np, Pu) was reported by Dacheux et al [112] for x = 4 for U IV , x = 0.8 for Np IV and x = 1.6 for Pu IV .…”