Cao Qiuxiang, Burakov B. E., Liu Xiangton, Detailed study of natural fully metamict minerals and products of their thermal recrystallization Cao Qiuxiang, Burakov B. E., Liu Xiangton,

Outline Introduction Experimental Procedure Sample description Products of its thermal Recrystallization 5. Conclusions

1. Introduction A lot of studies have been carried out to understand properties of metamict minerals in the past. Metamict minerals are characterized by amorphous states but initially they were crystalline. Due to admixture of natural radioactive elements such as U and Th, their crystal structures were destroyed. Metamict minerals can be considered as natural analogues of ceramic nuclear waste-forms affected by radiation damage. Therefore, the study of metamict minerals helps to understand behavior of waste forms under geological conditions.

2. Experimental Procedure

3. Sample description A mineral found as a large grain (2 x 3 x 2 cm in size) in granite pegmatites of Karelia, Russia It is assumed that initially it was single crystal.

3. Sample description Y-Fe-niobate Micrograph of electron microscope

3. Sample description Chemical Composition Empirical formula: (Y0.33Fe0.56U0.03Th0.01Ca0.01Mn0.04) ∑= 0.98(Nb0.73Ta0.05Ti0.26) ∑=1.04 O4

XRD after annealing in air 4.Products of their thermal Recrystallization XRD after annealing in air “Columbite” “FeNb2O6” “ Fergusonite-beta-(Y)” “YNbO4” “Tapiolite” “Fe (Ta,Nb)2O6” “Uranium niobium oxide”? “U3O8·1.5 Nb2O5”

“Fergusonite-beta-(Y)”. 4.Products of their thermal Recrystallization “Fergusonite-beta-(Y)”. PDF№: 01-083-1319 Ce “Columbite” PDF№: 01-074-7356 after decay + caused by hetaing Fe o “Tapiolite” -(Fe)” PDF№: 01-074-2182

XRD after annealing in Vacuum 4.Products of their thermal Recrystallization XRD after annealing in Vacuum “Tapiolite-(Fe)” “Fe (Ta,Nb)2O6” “ Fergusonite-beta-(Y)” “YNbO4” “Ishikawaite” “ (U,Fe,Mn,Y)(Nb,Fe,Ta)O4” “Iron niobim oxide” “Fe Nb O4” “Columbite-(Fe)” “Fe Nb2O6” o “Samarskite-(Y)” “ (Y,Fe,U)( Nb,Ti,Ta)O4” “Fergusonite-(Y)” “ ( Y,Er)(Nb,Ta,Ti)O4”

XRD after annealing in Argon 4.Products of their thermal Recrystallization XRD after annealing in Argon “Tapiolite” “Fe (Ta,Nb)2O6” “ Fergusonite-beta-(Y)” “ YNbO4” o “Samarkite-(Y)” “ (Y,Fe,U)( Nb,Ti,Ta)O4”

4.Products of their thermal Recrystallization 12 SEM Micrograph Homogeneous matrix After annealing in air (400оС, 1h) After annealing in vacuum (400оС, 3 h)

4.Products of their thermal Recrystallization 13 SEM Micrograph After annealing in air (700оС, 1h) After annealing in vacuum (700оС, 3 h)

4.Products of their thermal Recrystallization 14 SEM Micrograph After annealing in air (1000оС, 1h) After annealing in vacuum (1000оС, 1h)

4.Products of their thermal Recrystallization 15 SEM Micrograph：Redistribution of U and Th (wt.%) “Fergusonite-beta-(Y)” U: 5.9 Th: 2.9 “Fergusonite-beta-(Y)” U: 3.7 Th: 0.2 “Tapiolite-(Fe)” U: 20.1 Th: 2.6 “Tapiolite-(Fe)” U: 12.5 Th: 4.6 After annealing in air (1200оС, 1h) After annealing in vacuum (1200оС, 1h)

16 5. Conclusion The temperature-induced structural recovery of metamict minerals is a complex process. The essential redistribution of radionuclids was observed in the course of high-temperature recovery of initially metamict Y-Fe-niobate. No formation of separate actinide-oxides was observed in matrices of the Y-Fe-niobate recrystallized in a broad range of annealing temperature.

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