Jean-Louis Lacout

Synthesis of phosphate-silicate apatites at atmospheric pressure

Natural silicate-containing apatites (called britholites) are found in rare geological areas and contain large amounts of actinide and lanthanide elements [1–3]. Such compounds can be synthetised by a solid state reaction at high temperatures. As for the well-known fluoroapatite Ca10(PO4)6F2 and oxyapatite Ca10(PO4)6O□ (□ = vacancy) these compounds were prepared by the substitution pair (La3+, SiO44 −) for (Ca2+, PO43 −). The general formula of the compounds are given by Ca10 − xLax(SiO4)xPO4)6 − xF2, 0≤ χ ≤6, and Ca10 − xLax(SiO4)x(PO4)6 − xO□, 0 ≤ χ ≤ 6. They were analysed by X-ray diffraction and infrared spectroscopy. The synthesis has to be performed accurately to avoid the formation of poorly reactive intermediate phases.

Elaboration of an iodine-bearing apatite : Iodine diffusion into a Pb3(VO4)2 matrix

In the context of a scientific program on long-lived radionuclide conditioning, a matrix for iodine 129 immobilization has been synthesized and characterized. A lead vanado-iodoapatite Pb 10 (VO 4 ) 6 I 2 was prepared from the melt of Pb 3 (VO 4 ) 2 and PbI 2 in stoichiometric amounts. Iodine is volatile and it is necessary to use a closed system to synthezise the compound. In the context of the iodine conditioning program, iodine contamination must be avoided, and we have developed a method to prepare an iodoapatite without gas release. Lead vanado-iodoapatite was synthezised directly as a core of PbI 2 included in an external matrix of Pb 3 (VO 4 ) 2 . Otherwise, the thermal behaviour of the ceramic (250°C) was studied by iodine diffusion analysis.

Apatitic Waste Forms: Process Overview

Our study is concerned with the different apatitic waste forms which can be produced with processes ranging from high-temperatures to ambient temperature synthesis. The different processes developped allow to take into account the nature of the waste and the application targeted, from specific conditioning of separated wastes, encapsulating of mixed wastes, solid or liquid wastes, to filling materials for direct storage of spent fuel, interim storage, surface storage or deep repository.

Ca2+, PO43−⇌Ln3+, SiO44− coupled substitution in the apatitic structure: stability of the mono-silicated fluor-britholite

Abstract Synthetic crystals of mono-silicated fluor–britholite doped with rare earth elements have been prepared. The stoichiometry of the compound has been determined by means of microprobe analyses. Single crystal Laue diffraction and luminescence measurements reveal the covalent character of the rare-earth channel anion bond, thus explaining the stability of such compounds in the natural environment.