Immobilization of “Mo6+” in Monazite Lattice: Synthesis and Characterization of New Phosphomolybdates, La1−xCaxP1−yMoyO4, Where x=y=0.1-0.9

Abstract

In the process of high-level nuclear waste (HLW) disposal, monazite, LaPO4 is considered as one of the potential phosphate ceramics to immobilize lanthanides and actinides. HLW along with hazardous long-lived nuclides contains elements such as Zr, Mo, etc. in higher wt%. In the current investigation, an attempt was made to introduce “Mo” into the monazite lattice. The phosphomolybdates of the formula La1−xCaxP1−yMoyO4, x, y=0.1–0.9 were synthesized by a solution route and characterized by powder X-ray diffraction, FT-IR, TGA/DTA, and scanning electron microscopic techniques. The phases with compositions La0.9Ca0.1P0.9Mo0.1O4, La0.8Ca0.2P0.8Mo0.2O4, and La0.7Ca0.3P0.7Mo0.3O4 were found to be crystallized in monazite structure. The composition La0.1Ca0.9P0.1Mo0.9O4 with X=Y=0.9 crystallized in the scheelite structure. The compositions indicate the immobilization of ∼4.1, 8.5, 12.9, and 42.5 at. wt% of “Mo.” With x, y=0.6, 0.5, 0.4, 0.3, and 0.2, along with the monazite phase, formation of a secondary phase LaP3O9 was observed.