| Chinese high-level nuclear waste which contain large amounts of zirconium and sodium,and glass has a low solubility for these elements.Zirconium and sodium can as the raw material of zirconium phosphate glass-ceramics waste forms.It is easy to form glass-ceramics waste forms with sodium zirconium phosphate?NaZr2?PO4?3?as the main crystal phase,which can stabilize various nuclides and has excellent chemical stability.Based on B2O3-ZrO2-Na2O-P2O5-Fe2O3 system,the zirconium phosphate glass-ceramics waste forms contain NaZr2?PO4?3 were prepared by method of melting-quenching-annealing.The effects of the zirconia?ZrO2?substituted for sodium oxide?Na2O?,melting temperature,melting time and boron oxide?B2O3?content on the crystallization type and content,thermal stability,structure,and chemical stability of glass-ceramics waste forms were systematically studied.The effect of cerium oxide?CeO2?content on the structure and chemical stability of zirconium phosphate glass-ceramics waste forms was also discussed.The“one step method”preparation technology and properties of glass-ceramics waste forms were systematically studied.The conclusions as follows:?1?The 20Na2O-80?36Fe2O3-10B2O3-54P2O5?as the base glass,ZrO2 substituted for Na2O is conducive to the formation of NaZr2?PO4?3,ZrP2O7,FePO4 microcrystalline phases in the waste forms.When the content of ZrO2 substitution was less than 10 mol%,the main crystal phase of the waste forms was NaZr2?PO4?3.The thermal stability was best when the content of ZrO2 substitution was 6 mol%,and the glass formation ability of remaining components was also better.With the increase of ZrO2 content,the Q0 phosphate units increased and then decreased,and the Q1 phosphate units decreased and then increased.Glass-ceramics wasteforms with NaZr2?PO4?3 as the main crystal phase soaked in the 90? deionized water for 28 days,and the normalized leaching rates of Zr,Fe,Na and P element were 2.5?10-6 g×m×-2×d-1,3.3?10-6 g×m×-2×d-1,2.5?10-3 g×m×-2×d-1 and 6.2?10-4g×m×-2×d-1,respectively.Glass-ceramics waste forms had good chemical stability.?2?The extension of melting time,the increase of melting temperature or the increase of B2O3 content promoted the formation of NaZr2?PO4?3 crystal phases,inhibited the production of other phosphate microcrystalline phases such as ZrP2O7 and FePO4,and facilitated the preparation of glass-ceramics waste forms with a single NaZr2?PO4?3 crystal phase.As the content of B2O3 increases,the[BO4]units increased and then decreased,and the[BO3]units gradually increased when the content of B2O3 exceeds 10 mol%.The glass-ceramics waste forms had the maximum valve of glass transition temperature?Tg?and the difference between initial crystallization temperature and transition temperature?Tr-Tg?when the content of B2O3 was 10 mol%.The glass-ceramics waste forms with a single NaZr2?PO4?3 crystal phase soaked in the 90? deionized water for 56 days,and the normalized leaching rates of P and Fe element were about 2.0?10-4 g·m-2·d-1 and 2.0?10-6 g·m-2·d-1,respectively.There was almost no zirconium in the leaching liquid.Glass-ceramics waste forms had excellent chemical stability.?3?The glass-ceramics of 10ZrO2-10Na2O-28Fe2O3-10B2O3-42P2O5 can doped with5 wt%of CeO2.The obtained glass-ceramics waste forms had no crystal phase related to cerium.CeO2 and ZrO2 promote the precipitation of the secondary crystal phase?FePO4,ZrP2O7,NaFe3?PO4?3 and Na7Fe4?PO4?3?.The main structural units of the glass-ceramics containing CeO2 were Q0 phosphate units and Q1 phosphate units,a small number of[BO4]units,[BO3]units and Q2 units.With the increase of CeO2,[BO3]units and density increased.Ce was not detected in 90? deionized water,and the glass-ceramics waste forms had excellent chemical stability. |
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