OBSERVATIONS ON THE RARE EARTHS. VII. THE SEPARATION OF HOLMIUM
Journal of the American Chemical Society
A large part of the rare earth work which has been in progress in this laboratory during the past three years has been concerned with that portion of the Yttrium Group which includes dysprosium, holmium, yttrium and erbium. These four elements form salts whose solubilities i,n general increase slightly in the order given. The general plan of separation has been to carry out a thorough series of fractional crystallizations of the bromates as suggested by James and Bisse1,l then to select those
... n to select those fractions which contain mainly two elements and to continue the separation by means of methods dependent upon some characteristics other than differences in solubilities. This plan has worked well for the more abundant of the rare earth elements like yttrium and erbium. But when applied to holmium the problem becomes more difficult because of the fact that it is one of the least abundant of the rareearthelements. Kremers and Balke2 have shown that it was possible to obtain bromate fractions containing holmium and yttrium only. The bromate fractionation, however, fails to concentrate all the holmium, as is shown by the fact that Kremers, Hopkins and EngleS did not succeed in removing all the holmium from their dysprosium material. In addition to the scarcity of holmium and the difficulty of concentrating it, the purification of this element is hard to control since the last impurity, yttrium, has no absorption lines in the visible spectrum. Hence the progress of purification must be judged by means of the equivalents of the fractions, which consumes both time and material. The purpose of the present investigation was to continue the study of the purification of holmium, in an effort to find methods of separation by which the material could be obtained in a high degree of purity. In general, only those yttrium-holmium fractions were used which were free from all but traces of other rare earths. Most of the material used in this work came originally from gadolinite, the preliminary treatment being described by Engle and Balke4, and Kremers and Balkens Fractional Hydrolysis of the Phthalates. Urbain" suggested that the best method for separating holmium and yttrium would depend on the difference in basicity of the two elements.