Stepwise chlorination-chemical vapor transport reaction for rare earth separation from ternary oxide mixtures Y 2O 3–Ho 2O 3–Er 2O 3 mediated by vapor complexes KLnCl 4

Abstract

Mutual separation characteristics for ternary oxide mixtures Y 2O 3–Ho 2O 3–Er 2O 3, in which these three kinds of rare earth ion (III) have very similar ion radius values, have been investigated using a stepwise chlorination-chemical vapor transport (SC-CVT) reaction mediated by vapor complexes KLnCl 4 in different temperature gradients. Both the main deposition temperature region tendency and total transport amounts of chlorides for YCl 3 with respect to the ion radius of Y (III) were exceptional compared with those of LnCl 3 (Ln = Ho and Er), which were observed both in the degressive temperature gradient and the wave type temperature gradient. All the three chlorides produced from the oxide mixtures concentrated in the middle temperature range from 1150 to 1000 K (FN = 5–9) in degressive temperature gradient. The deposition temperature of the largest chlorides amounts was at FN = 6 for YCl 3 and FN = 8 for HoCl 3 and ErCl 3, which in the order of YCl 3 > HoCl 3 ≈ ErCl 3. Total transported yields of the chlorides was in the order of HoCl 3 > ErCl 3 > YCl 3 in the two type temperature gradients. The largest separation factors 7.48 for Ho:Y, 5.10 for Er:Y and 7.58 for Ho:Er in the lower temperature region were observed in the degressive temperature gradient, respectively. Furthermore, the improved separation factor values of 23.8 for Ho:Y and 19.2 for Er:Y were obtained in the wave type temperature gradient due to variation of the dynamic conditions of CVT. The results were discussed on the difference between the ionic structure of Y and 4f lanthanoid elements of Ho and Er and verified that the ionic radius of the rare earth is one of the decisive factors of CVT reaction only for lanthanoid elements, not for Y. On the other hand, the cooperate effect among the three elements and the variation of the dynamic conditions of CVT have been the important factors to influence the separation efficiency of the three elements.