Fractionate as Bromates.
1 Gd, Tb, Dy. For separation of Terbium group.
2 Tb, Dy, Ho, Yt. Transform to Ethylsulphates.
3 Dy, Ho, Er, Yt. Fractionate by Nitrate Fusion.
4 Yt, Er, and Sc? Fractionate by Nitrate Fusion.
5 Tm, Yb, Lu, etc. Continue.
Terbium Group.
6 Tb, Dy. Continue Ethylsulphate Fractionation.
7 Dy. Ethylsulphate.
8 Ho, Yt. Fractionate by Nitrate Fusion.
9 Yt. Nitrate.
10 Yt, Er. Continue.
11 Er. Nitrate.
12 Tm. Bromate.
13 Yb. Bromate.
14 Lu. Bromate.
Yb, Lu. Bromates.
Ct? Bromate.
Ho. Basic Nitrate.
Ho, Yt.
Fig. 9.—Separation of the Yttrium Elements
The more modern methods of separation combine the above processes with the methods of fractional crystallisation, for which the bromates and alkylsulphates of these elements are well adapted. The procedure[361] which experience shows will lead to a fairly rapid separation is roughly represented in [Fig 9]. The double sulphates (B), left in solution after removal of the cerium and part of the terbium group, are transformed into the bromates, which are separated by fractional crystallisation into five main fractions. The least soluble portion, fraction 1, contains the terbium elements with some dysprosium; in the fractionation of the terbium group by means of the nitrates and double nitrates, the dysprosium, with some terbium, collects in the final fractions (fraction 6). Fraction 2 contains terbium, dysprosium, holmium, and yttrium as the bromates; these are converted into the anhydrous chlorides, from which, by treatment with sodium ethylsulphate in alcoholic solution, the ethylsulphates are obtained. By fractional crystallisation, dysprosium may be obtained in a fairly pure condition (fraction 7), the least soluble part (fraction 6) containing the terbium with some dysprosium. Holmium and yttrium collect in the most soluble part (fraction 8), from which pure holmium can be obtained by the method of nitrate fusion. Fraction 3 contains yttrium and erbium, with small quantities of dysprosium and holmium; the latter are readily separated by the nitrate fusion, which will also allow of a fairly complete separation of yttrium (fraction 9). Fraction 4 contains yttrium and erbium; scandium if present will also collect here. Erbium can be obtained pure by the nitrate fusion; the second fraction from this process contains both yttrium and erbium, and may be further worked up with the fraction of similar composition (fraction 10) from fraction 3.
[361] James, J. Amer. Chem. Soc. 1912, 34, 757.
The mother-liquors from the bromate separation (fraction 5) contain thulium and the ytterbium elements; the crystallisation is continued, and allows of complete separation of thulium and ytterbium, and probably of lutecium, though the most soluble fractions do not seem to have been fully separated.