Investigation of the system ThO2–NpO2–P2O5. Solid solutions of thorium–neptunium (IV) phosphate–diphosphate

Chemistry of tetravalent actinide phosphates—Part I

Publisher Summary This chapter presents an overview of the crystal structures of inorganic compounds in which actinide polyhedra are directly coordinated by phosphate or arsenate tetrahedra. Arsenates are considered for comparative purposes, because of the very similar structural roles played by arsenate and phosphate ions. Structural data are taken mainly from the Inorganic Crystal Structure Database and the published literature. In natural settings, uranium phosphate species are among the most numerous, widespread, abundant and insoluble of actinide-bearing minerals and largely control the mobility of actinides in groundwater and in actinide contaminated soils and sediments. The structures and behavior of uranium-bearing and thorium-bearing phosphate minerals thus provide a basis from which to predict the long-term behavior of actinide-bearing phosphates. Data are tabulated for a given structure type, with phosphates separated from arsenates, and organized in order of increasing atomic number of the actinide present.

Chapter 6 – Crystal chemistry of actinide phosphates and arsenates

Studies on phosphates of tetravalent uranium and thorium published by the authors in the 1990s are briefly overviewed. Methods of synthesis, properties, and structures of new phosphates of these elements are described. The chemical formulas of a number of already known uranium, thorium, and neptunium phosphates are critically analyzed. Special attention is given to thorium phosphate diphospate and solid solutions containing uranium, neptunium, and plutonium. These are suggested as ceramics for storage of radioactive wastes of actinides. The suitability of thorium phosphate diphosphate for immobilization of nuclear fission products is discussed.

M.F. Le Cloarec

Papers

Preparation and properties of tetravalent protactinium phosphates

Phosphates de protactinium pentavalent

Phosphates of pentavalent protactinium