Résumé
Precipitation processes driven in hydrothermal conditions were applied to the preparation of phosphate-based ceramics. Three systems composed by a crystallized precursor linked with a high temperature compound were particularly examined: M(OH)PO4 / M2O(PO4)2 (M = Th, U), MPO40.5 H2O / MPO4 (M = La - Dy) and Th2-x/2Anx/2(PO4)2(HPO4) H2O / β-Th4-xAnx(PO4)4P2O7 (M = U, Np, Pu). A significant improvement of several physico-chemical properties of the powders, especially in the sintering capability and the homogeneity of the final solids was evidenced when starting from the precursors. Furthermore, these phases were also found to control the solubility of lanthanides and actinides during leaching experiments when reaching the saturation conditions in the solution.