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

Abstract

A new uranium (IV) phosphate of proposed formula U 2(PO 4) 2HPO 4·H 2O, 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(HPO 4) 2· nH 2O. The new product appears similar to the previously published thorium phosphate-hydrogenphosphate hydrate Th 2(PO 4) 2HPO 4·H 2O (TPHPH). From preliminary studies, it was found that UPHPH crystallizes in monoclinic system ( a = 2.1148 ( 7 ) nm , b = 0.6611 ( 2 ) nm , c = 0.6990 ( 3 ) nm , β = 91.67 ( 3 ) ° and V = 0.9768 ( 10 ) nm 3 ). Heated under inert atmosphere, this compound is decomposed above 400 °C into uranium phosphate-triphosphate U 2(PO 4)P 3O 10, uranium diphosphate α -UP 2O 7 and diuranium oxide phosphate U 2O(PO 4) 2. Crystallized cerium (IV) phosphate-hydrogenphosphate hydrate Ce 2(PO 4) 2HPO 4·H 2O (CePHPH) was also synthesized from (NH 4) 2Ce(NO 3) 6 and phosphoric acid solutions by the same method (monoclinic system: a = 2.1045 ( 5 ) nm , b = 0.6561 ( 2 ) nm , c = 0.6949 ( 2 ) nm , β = 91.98 ( 1 ) ° and V = 0.9588 ( 9 ) nm 3 ). When heating above 600 °C, cerium (IV) is reduced into Ce (III) and forms a mixture of CePO 4 (monazite structure) and CeP 3O 9.