Fig. 1. LiF-BeF₂ and REF₃-LiF-BeF₂ mixed molten salts (color online)(a) LiF-BeF₂, (b) NdF₃-LiF-BeF₂, (c) CeF₃-LiF-BeF₂, (d) SmF₃-LiF-BeF₂, (e) YbF₃-LiF-BeF₂

Fig. 2. Gibbs free energy (Δ_rG_m) change of REF₃-Na₂S reaction

Fig. 3. Removal ratios when the ratio of NdF₃ to Na₂S∙5H₂O content is 1:2 under different temperatures for 5 h

Fig. 4. Photograph of Salt after adding Na₂S·5H₂O to REF₃-LiF-BeF₂ at 600 °C (a) NdF₃, (b) CeF₃, (c) SmF₃, (d) YbF₃

Fig. 5. XRD patterns of the precipitates after adding Na₂S·5H₂O to REF₃-LiF-BeF₂(a) NdF₃, (b) CeF₃, (c) SmF₃, (d) EuF₃

Fig. 6. SEM images of the precipitates after adding Na₂S·5H₂O to NdF₃ (a), SmF₃ (b)-LiF-BeF₂ molten salt

Fig. 7. EDS images of precipitates after adding Na₂S·5H₂O to EuF₃-LiF-BeF₂ molten salt

Fig. 8. S 2p XPS spectra of precipitate after adding Na₂S∙5H₂O to NdF₃-LiF-BeF₂

Fig. 9. Removal ratio comparison of two systems for RE elements (Nd, Ce, Sm, and Eu)

Fig. 10. Snapshots of distillation equipment (a) and quartz tube with nickel foil collection device (b)^[28]

Fig. 11. Photograph of ThF₄-LiF-BeF₂ salt (a) and mixed molten salt after adding Na₂S∙5H₂O (b)

Fig. 12. XRD patterns of precipitates after adding Na₂S·5H₂O to ThF₄-LiF-BeF₂