Barium Borosilicate Glass-ceramic For Immobilization Of Simulation Of Trivalent Actinide Nuclide

Zirconolite–based glass–ceramics have attacted a great deal of interest for the immobilization of high-level radioactive wastes. In this work, neodymium ion was used as a surrogate to simulate the trivalent actinide ions, Zirconolite–based barium borosilicate glass–ceramics were prepared by melting–heat treatment method. The Si/Ba, Si/B, content of nucleating agents?Ca O, Ti O2, and Zr Si O4?, Nd₂O₃, Al₂O₃ and heat treatment process on crystalline phases, microstructure, and chemical durability of barium borosilicate glass–ceramics were mainly researched. The crystallization mechanism of zirconolite and tiranite was also researched.The homogeneous glass in Si O2-B₂O₃-Na2O-Ba O-Ca O-Ti O2-Zr O2-?Nd₂O₃? system can be obtained under the melting temperatures 1100¹250 ?, the glass transition temperature of barium borosilicate glass at about 580⁶60 ?, crystallization temperature at about 850 1050 ?; When the Si/Ba ratio is 2⁴ and Si/B=1², only Ca Zr Ti2O7 can be obtained; When calcium oxide?Ca O?, titanium dioxide?Ti O2? and zirconium silicate?Zr Si O4? content is 45⁵5 wt %, the samples possess Ca Zr Ti2O7 and Ca Ti Si O5 crystalline phases. The PCT experiment shows that the lower normalized leaching rates of B, Na and Nd in the sample contained 45 wt % Ca O, Ti O2 and Zr Si O4 at about 8.8×10-3 g·m-2·d-1, 7.7×10-3 g·m-2·d-1 and 7.5×10-6 g·m-2·d-1 after 28 days. From the research of crystallization mechanism in barium borosilicate glass, the activation energy E?Kissinger method? and Avrami constant n associated with zirconolite are 124.38 k J/mol and 3.4, respectively, indicating three-dimensional crystallization mechanism. The activation energy E?Kissinger method? and Avrami constant n associated with titanite are 166.13 k J/mol and 2.2, respectively, indicating two-dimensional crystallization mechanism. Only zirconolite phase is observed at crystallization temperatures between 750 °C and 850 °C, and the intensity of the diffraction peaks of titanite phase increases as the thermal treatment temperature increases from 900 °C to 1050 °C.The results show that the glass-ceramics with 2-6 wt% of Nd₂O₃ possess mainly zirconolite and titanite crystals in the bulk. Calcium titanate appears when the Nd₂O₃ content increases to 8 wt%, and the amount of quadrate calcium titanate crystals increases with further increasing content of Nd₂O₃. In the glass-ceramic with 6 wt.% Nd₂O₃, about 47 % of total amount of Nd₂O₃ distribute in zirconolite and titanite crystals. And it possesses high chemical durability which the LRB, LRCa and LRNd are about 6.79×10-3 g·m-2·d-1?1.61×10-3 g·m-2·d-1 and 4.8×10-6 g·m-2·d-1, respectively, after 42 days. Calcium titanate phase appears in the glass–ceramic with 2 wt% Al₂O₃, and calcium titanate phase increases with the increase of concentration of Al₂O₃. When the content of Al₂O₃ increase to 6 wt%, titanite crystalline phase disappear mostly, only strip–shape Ca Zr Ti2O7 and cubic Ca Ti O3 exist in glass–ceramics. The PCT experiment shows that the addition of Al₂O₃ has no significant influence on the leaching properties of glass–ceramics.