Synthesis and characterization of uranium (IV) phosphate-hydrogenphosphate hydrate and cerium (IV) phosphate-hydrogenphosphate hydrate

A new uranium (IV) phosphate of proposed formula U2(PO4)2HPO4·H2O, i.e. uranium phosphate-hydrogenphosphate hydrate (UPHPH), was synthesized in autoclave and/or in polytetrafluoroethylene closed containers at 150 °C by three ways: from uranium (IV) hydrochloric solution and phosphoric acid, from uranium dioxide and phosphoric acid and by transformation of the uranium hydrogenphosphate hydrate U(HPO4)2·nH2O. The new product appears similar to the previously published thorium phosphate-hydrogenphosphate hydrate Th2(PO4)2HPO4·H2O (TPHPH). From preliminary studies, it was found that UPHPH crystallizes in monoclinic system (image, image, image, image and image). Heated under inert atmosphere, this compound is decomposed above 400 °C into uranium phosphate-triphosphate U2(PO4)P3O10, uranium diphosphate image-UP2O7 and diuranium oxide phosphate U2O(PO4)2. Crystallized cerium (IV) phosphate-hydrogenphosphate hydrate Ce2(PO4)2HPO4·H2O (CePHPH) was also synthesized from (NH4)2Ce(NO3)6 and phosphoric acid solutions by the same method (monoclinic system: image, image, image, image and image). When heating above 600 °C, cerium (IV) is reduced into Ce (III) and forms a mixture of CePO4 (monazite structure) and CeP3O9.