氧化物沉淀-减压蒸馏耦合分离FLiNaK熔盐中的NdF_3

利用氧化物沉淀-减压蒸馏耦合法研究FLiNaK熔盐体系中氟化物的蒸发行为及稀土Nd的分离。高温下氧化物CaO与稀土氟化物NdF_3反应形成难溶于熔盐的稀土氧化物,通过减压蒸馏蒸发、收集冷凝FLiNaK熔盐,提高稀土与熔盐的分离度,促进熔盐的回收利用。研究表明,含有NdF_3(w=3%)的FLiNaK熔盐中加入CaO,730°C下反应6 h,n(NdF_3):n(CaO)=1:3时NdF_3的转化率达95%。X射线衍射(X-ray Diffraction,XRD)分析表明生成的Nd_2O_3主要沉淀在熔盐的底部。经730°C高温沉淀、930°C熔盐蒸馏,冷凝盐中稀土Nd的去污因子达9.4′105,而未经沉淀处理Nd的去污因子为3.1′104,表明高温沉淀蒸馏耦合法使稀土NdF_3转化为氧化物Nd_2O_3,显著增大稀土与FLiNaK的分离度,提高收集盐的纯度。

Separation of NdF3 using precipitation-distillation coupled method in FLiNaK molten salt

Background:Low pressure distillation is a promising technology for the recovery and purification of carrier salts (LiF-BeF2) in the thorium based molten salt reactors (TMSR).Purpose:This study aims to compare the separation behavior of NdF3 before and after adding the oxidant CaO in FLiNaK molten salt.Methods:Precipitation-distillation coupled method was employed in purification of molten salt.Then the X-ray Diffraction (XRD) was applied to the analysis of the produced NdF3 in the molten salt.Results:At high temperature,CaO was confirmed to react with NdF3 and form rare earth oxide Nd2O3 insoluble in molten salt.At 730 ℃,the conversion rate for Nd was up to 95％.After the precipitation reaction,the separation rate under low pressure distillation was compared with the preceding one.The decontamination factor of Nd was deduced to 9.4×105 whilst the value was 3.1 × 104 without adding CaO.Meanwhile,the evaporation rate also was improved after precipitation.Conclusion:The combination of the precipitation and distillation treatment is an effective way to achieve the high throughput performance in the salt separation process.