稀土氟化物在硝酸中溶解性质的研究

Solubility of rare earth fluorides in nitric acid

采用微波消解-电感耦合等离子体原子发射光谱(Inductively Coupled Plasma Atomic Emission Spectroscopy,ICP-AES),系统研究了钍铀燃料循环后处理中4种典型稀土氟化物(Nd F3、Eu F3、Gd F3、Ce F3)在硝酸中的溶解性质。结果表明,在10 m L、浓度为16 mol·L-1的硝酸中,微波消解2 h,190oC下,4种稀土氟化物的最大溶解量可达2.5-3.9 g·L-1,均比文献报道的数值高2-3个数量级;采用ICP-AES测试溶解液,线性范围0.999 47-0.999 96,标准偏差SD≤4.2%(n=3),该溶解方法旨在为核燃料后处理流程中含有难溶稀土氟化物的熔盐固溶体样品分析前处理提供参考。

Background： A varity of rare-earth fluorides can be produced with thorium uranium fuel circulating post-processing. These fluorides need to be dissolubled in solvent for seperation and contents measurement.Purpose： This paper aims to develop a fast and efficient pretreatment method to dissolve slightly soluble rare earth fluorides in nitric acid.Methods： Rare earth fluorides related to the thorium molten salt reactor （TMSR） fuel circulating post-processing including NdF3, EuF3, GdF3 and CeF3 were studied by using Inductively Coupled Plasma Atomic Emission Spectrometry （ICP-AES）. After 2-h microwave digestion at temperature of 190 oC, the maximum solubility of these fluorides in 10 mL nitric acid （16 mol·L-1） is determined by ICP-AES.Results： The saturated concentration varies from 2.5 g·L-1 to 3.9g·L-1, which are two or three orders of magnitude higher than their solubility reported in previous literature. The standard deviation （n=3） of measurement by ICP-AES is under 4.2% and the linear correlation coefficient （r） is in the range of 0.999 47？0.999 96.Conclusion：An efficient chemical procedure for dissolving some rare earth fluorides has been developed. It provides a reference for pretreatment of insoluble rare earth fluorides in the solid molten salt samples of thorium uranium fuel circulating post-processing.