冷指结晶法去除LiCl熔盐中的碱土金属Sr、Ba

Removal of Sr and Ba from molten LiCl salt using cold finger crystallization method

快堆乏燃料干法后处理中会产生含多种金属元素的LiCl废盐,分离废盐中的金属杂质既可净化熔盐,有利于盐的循环利用,又可减小废盐量,实现废物最小化。利用自行研制的冷指结晶装置,探索了LiCl熔盐中Sr、Ba两种碱土金属的分离和分离中的影响因素,并结合Fluent软件模拟确定较佳的分离工艺,进一步明确LiCl分离碱土金属的规律。研究表明,影响冷指结晶法分离效果的主要因素为熔盐初始温度,当熔盐温度高于660℃时,Sr、Ba去除率较佳;同时发现熔盐中Sr、Ba含量低于0.55%(w/w)时,其去除效率均可超过80%。进一步研究发现熔盐晶体不同部位的Sr、Ba去除效果不同,其中结晶盐顶部的杂质分离效果最佳,底部及内层的熔盐分离效果较差。含有Sr、Ba的LiCl熔盐较佳分离条件为温度660~670℃,气体流速10 L·min^(−1),生长时间20 min,此时LiCl盐中Sr、Ba的去除率可达90%。实验结果证实了冷指结晶法从电解质废熔盐中纯化溶剂盐的可行性,可为纯化废盐、实现熔盐的重复利用提供参考。

[Background]An electrolyte waste salt containing LiCl and various products is generated during the pyroprocessing of spent nuclear fuel in metal fast reactors.Separating metal impurities from waste salt can purify molten salt,facilitate salt recycling,and reduce the amount of waste salt,achieving waste minimization.[Purpose]This study aims to investigate the effects of key factors on the application of the cold finger crystallization method used for removal of Sr and Ba from molten LiCl salt.[Methods]A homemade cold finger experimental apparatus was applied to the experimental removal of two alkaline earth metals,Sr and Ba,from molten LiCl salt,and Fluent software was employed to simulate the application of cold finger crystallization equipment during dry reprocessing.The effects of crystal growth time,initial crystallization temperature,and initial SrCl_(2)/BaCl_(2) concentrations on the removal ratio of the crystalline salt during the process were analyzed.[Results]The initial temperature of molten salt is a critical factor that influences cold finger separation efficiency.When the initial temperature reaches 660℃,the removal efficiency improves.Moreover,when the impurity contents of Sr and Ba in molten salt are lower than 0.55%(w/w),the removal efficiency of the cold finger crystallization method can exceed 80%.Further analysis shows that the removal effects of different parts of molten salt crystals differ.The solvent salt at the top of the molten salt crystal is better,and the removal ratio of the bottom and inner salts is lower.Therefore,the optimal conditions for removing Sr and Ba from LiCl crystalline salt require an initial temperatures of 660~670℃,an airflow intensity of 10 L·min^(−1),and a growth time of 20 min.Under these optimal conditions,the removal ratio can reach 90%.[Conclusions]The proposed approach is feasible for purifying solvent salts from electrolyte waste molten salt via cold finger crystallization.This study provides a reference for purifying waste salt and reusing molten salt.