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

摘要

Several compositions of Th_(2-x/2)An~(IV)_(x/2)(PO4)2(HPO4) centre dot 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 °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,An20(P04)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.