Preparation of erbium-oxide in pure state by Craig-distribution in the system tributylphosphate-nitric acid

In recent years K. Rossmanith introduced the method of Craig-distribution in the system tributylphospate-11M nitric acid for the separation of rare earth mixtures on a preparative scale. It was not possible, however, to separate the elements Y and Er under this strong acid conditions. It could be shown that in a weak acid medium the distribution coefficients of these two elements become different. So it was possible to obtain yttrium oxide with a purity over 99.9% by Craig-distribution. The aim of the present work was the preparation of erbium oxide by the method described above. The starting material was 1.66 kg earth-oxide which contained 4-6% Er2O3. After elimination of the cerium group, the excess of yttrium was separated by using weak acid (approx= 4M HNO3). During these 'weak-acid-distributions' it was possible to get informations on the influence of variable distribution-conditions, on the effective distribution coefficients and the effctive separation factors. After finding the best conditions for purification of Er2O3 by this method, alternative distribution in weak (Y-separation) and strong (Dy, Ho, Tm, Yb-separation) acid medium was performed. It was necessary to carry out 18 Craig-distributions with 11M HNO3 and 28 Craig-distributions with approx= 4M HNO3 for getting 19.48 g erbium oxide with a purity of better than 99.9%. (Author)