The use of a soaking procedure combined with the sintering process to reach a high cerium content in a cerium-bearing Y-britholite
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A Y-britholite loaded with Ce, with the chemical composition (19.12 % SiO2, 7.53 % P2O5, 15.87 % CaO, 46.77 % Y2O3, 0.67 % CaF2, 0.95 % H2O, 9.09 % CeO2) was synthesized by two methods: a dry route and a combined route of natural sintering/soaking procedure. In the first synthesis method, all the milled reagents are pressed in pellets at 340 MPa and then sintered for 20 h in air at 1473 K. In the second method, the Ce-free mineral was first obtained by the dry route described above. Then, it was unfiltered by a cerium nitrate solution to incorporate Ce in the Y-britholite crystalline structure. The powder is calcined at 1223 K and sintered in air at 1473 K for 20 h. These last two steps are repeated twice to allow a good incorporation of Ce in the material, as well as reaching a good homogeneity of the mineral. A physical characterization of the materials coming from the two synthesis methods, by both XRD and EDX analyses, gives a total Ce incorporation into the mineral obtained by the combined dry/wet synthesis process, namely 7.40 wt. % , against a 5 wt. % of Ce incorporation rate in the Y-britholite obtained by the dry route process. The XRD analysis identified crystalline phases were a major hexagonal crystalline phase of Y-britholite in both Y-britholites. To assess the chemical durability of the synthesized minerals, a water static leach test was performed at 298 K for the dry way obtained Y-britholite, and at 298, 323 and 363 K for the dry/wet way obtained Y-britholite. The tests were based on the release of cerium in water. UV analysis was used to follow the evolution of Ce concentrations in the leachates. The Ce mean diffusion coefficients were of the order of magnitude of 10−7 m2 s−1, and the mineral water altered layers were lower than 220 μm (22 × 10−5 m). This demonstrated the superficial phenomenon of leaching. The diffusional model of leaching was validated, proving the chemical durability of the mineral, even at high leaching temperatures for the dry/wet way obtained Y-britholite. This synthesis method has proved the possibility to confine higher amounts of Ce, an actinide surrogate, into the crystal of Y-britholite, with the combined synthesis method of sintering/soaking procedure, compared with the dry route of synthesis.