Thulium bromate

The classical methods used to separate the lanthanides from aqueous solutions depended on (i) differences in basicity, the less-basic hydroxides of the heavy lanthanides precipitating before those of the lighter ones on gradual addition of alkali (ii) differences in solubility of salts such as oxalates, double sulfates, and double nitrates and (iii) conversion, if possible, to an oxidation state other than -1-3, e g. Ce(IV), Eu(II). This latter process provided the cleanest method but was only occasionally applicable. Methods (i) and (ii) required much repetition to be effective, and fractional recrystallizations were sometimes repeated thousands of times. (In 1911 the American C. James performed 15 000 recrystallizations in order to obtain pure thulium bromate). 

Thulium in a fairly pure state may be obtained by the long-continued fractionation of a bromate series. The separation of erbium and thulium is fairly satisfactory by this method alone. According to Welsbach 1 thulium is a mixture of three elements which he designated as thulium I, II, and III. Probably no better thulium material has ever been obtained than that prepared by James2 using the bromate method, which gave a homogeneous product after 15,000 operations. 

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