| Vitrification is currently the only kind of high level liquid waste immobilization treatment technology that has achieved industrial application.At present,the vitrification technology（Joule-Heated Ceramic Melter）also uses to immobilize the existing high sulfur and high sodium high level liquid waste.During the operation of Joule-Heated Ceramic Melter,the occurrence of uncontrolled crystalline phase can result in both processing problems and glass performance issues.The problem of crystallization has become a key technical limitation of nuclear waste glass vitrification in China,and has become a current research hotspot in the field of nuclear waste immobilization.In this study,the crystallization behavior of the original waste glass was analyzed,and the effects of glass components on the anti-crystallization performance of the waste glass were investigated.The relationship between the formation of diopside in the waste glass and the content and ratio of alkaline earth metal oxides was investigated,and an optimization scheme based on the composition of the original glass vitrification formulation was proposed.（1）The crystallization behavior of waste glass under different heat treatment process was investigated by the gradient furnace method.The results show the waste glass precipitates diopside phases after heat treatment at 700～900℃,and the crystallinity reaches 20～25 vol.%after holding at 750℃for 28 d.The high content of alkaline earth metal oxide in the waste glass formulation plays an accumulation role in the glass network structure,and causes phase separation,which is the main reason for the precipitation of diopside.（2）The effects of glass components on the anti-crystallization performance of the waste glass were investigated,and the purpose of inhibiting crystal precipitation was achieved by adjusting the glass components.Firstly,the effect of different alkaline earth metal oxide content on crystallization behavior of simulated waste glass was investigated.The results show that the maximum crystallization temperature and the crystallinity of diopside of the waste glass gradually decrease with the decrease of alkaline earth metal oxide content（CaO+Mg O+Ba O）.The increase in the degree of polymerization of the glass network is beneficial to improve the anti-crystallization performance of the waste glass.However,when the alkaline earth metal oxide content is lower than 11 wt.%,the solubility of sulfate has a significant decrease,based on the requirement of inclusion of 0.7 wt.%SO3,the appropriate composition of alkaline earth metal oxide content is around 11 wt.%.Secondly,the effect of different CaO/Mg O on crystallization behavior of simulated waste glass was investigated.The results show that CaO/Mg O is the key factor affecting the type of predominant phase.With the increase of CaO/Mg O,the crystallinity of waste glass decreases and then increases.The maximum crystallization temperature and crystallinity of the waste glass are the lowest when CaO/Mg O=4.Finally,the crystallization behavior of simulated waste glass modified by Zn O replacing Mg O was investigated.The results show that the glass forming ability enhances first with Zn O increasing from 0～4 wt.%,and then weakens with further addition of Zn O.Zn O could enter the glass network structure in the form of[Zn O4]tetrahedra,which improve the stability of the waste glass and enhance the anti-crystallization performance.（3）Based on the characteristics of high sulfur and high sodium waste and the performance requirements of waste glass,a glass formulation on high sulfur and high sodium high level liquid waste with lower crystallinity was prepared,by controlling the total alkaline earth metal oxides at 11 wt.%and Zn O addition at 3 wt.%.The optimized glass vitrification formulation has substantially better anti-crystallization performance than the existing glass vitrification formulation and is expected to be applied in high sulfur and high sodium waste glass vitrification project. |
