Mutual Separation Characteristics For The Yttium Oxide And Lanthanide Oxides Through Stepwise Slective Chorination-Chemical Vapour Transport Reaction

Rare earth elements are strategic resource for all world, which especially the single highly purity rare earths are the necessarily elements in the field of advanced materials. But there are very similar characteristics of rare earth elements and usually coexistent together in minerals. Thus, separation of rare earth has been one of the most difficult problems in rare earth chemistry or in inorganic chemistry.Recently, a dry method has been developed for separating or extracting rare earth elements from mixed oxides or concentrate ore using Chemical vapor transport reaction mediated by vapor complexes method, so called CVT method. It was based on that rare earth chlorides reacted with AlCl3 or alkali metals chlorides and formed vapor phase complexes that could easily volatilize and decompose to primary rare earth chloride and complex former chlorides at lower temperature by carrier gas. It offered separation possibility that chlorinating ability of different rare earth and thermodynamic characteristic of complex enlarge the difference between rare earths. There were a lot of factors which affected rare earth separation efficiency, such as selective chlorination temperature, temperature gradient, kinds and amounts of complex formers, ionic structure, ionic radii, electronic configuration of rare earth elements, stability of vapor phase complexes and so on.In this study, It was investigated that the separation characteristics of mixed rare earth oxides using stepwise selective chlorination-chemical vapor transport reaction (SC-CVT), which used rare earth oxides mixed with proper amounts of active carbon and complex former KCl as raw material. In this method, chlorination of rare earth oxide mixture and chemical vapor transport of chlorides could be realized in different condition. One was the selective chlorination of rare earth oxide mixture by Cl2 gas at temperature 800K for 2h and another was the chemical vapor transport of the resulted rare earth chlorides, Ar gas as a carrier gas at 1300K within 6h. The results of this study can provide theory support and experiment data for rare earth separation by dry process and rare earth vapor complexes. The separation of binary mixed rare earth oxides Y₂O₃-Ln₂O₃, Ho₂O₃-Ln₂O₃, Er₂O₃-Ln₂O₃ (Ln were Sc, La, Nd, Sm) and triple mixed ones Y₂O₃-Er₂O₃-Ho₂O₃ were investigated in this study.The results showed that separation characteristic of La₂O₃ are different from that of Y₂O₃, which showed that ionic framework and electronic configuration played very important role in this method. In compared to different separation characteristics of Y₂O₃-Ln₂O₃,Ho₂O₃-Ln₂O₃,Er₂O₃-Ln₂O₃(Ln = Sc, La, Nd, Sm), it is found that both Y and Sc displayed particularity in deposition temperature region, separative efficiency and transport amounts, which showed that the separative rule of Y and Sc didn't follow the relation of the ionic radii and vapor phase complexes stability. The largest deposit region of rare earth oxide had been changed from the higher temperature region to the lower temperature region with the contraction of the lanthanide ionic size of Ln3+ from La to Lu, while the total transported amounts of lanthanide oxide increased with the contraction of the ionic size of Ln3+, but both Nd₂O₃-Sm₂O₃ and Ho₂O₃-Er₂O₃ were not followed this rule. The difference of ionic radii between two rare earth elements determined the separative efficiency of two rare earth chlorides. At the same time, it is found that La transmission characteristic had prominent difference with Y and Sc in the same family, and had similarly characteristics with lanthanide ones, which proved that La3+ contained 4f mixed electron because of electron mixing of electronic configuration.