Immobilization of 'Mo~(6+)' in Monazite Lattice: Synthesis and Characterization of New Phosphomolybdates, La_(1-x)Ca_xP_(1-y)MO_yO_4,Where x=y= 0.1-0.9

摘要

In the process of high-level nuclear waste (HLW) disposal, monazite, LaPO_4 is considered as one of the potential phosphate ceramics to immobilize lanthanides and actinides. HLW along with hazardous long-h'ved nuch'des 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 La_(1-x)Ca_xP_(1-y),Mo_yO_4, 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 La_(0.9)Ca_(0.1)P_(0.9)Mo_(0.1)O_4, La_(0.8)Ca_(0.2)P_(0.8)Mo_(0.2)O_4, and La_(0.7)Ca_(0.3)P_(0.7)Mo_(0.3)O_4 were found to be crystallized in monazite structure. The composition Lao_(0.1)Ca_(0.9)P_(0.1)Mo_(0.9)O_4 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 LaP_3O_9 was observed.