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THE CHEMICAL NEWS

VOL XCIX., No. 2570.

SCANDIUM.*

PART I.-THE SEPARATION OF SCANDIUM FROM WOLFRAMITE FROM ZINNWALD.

By R. J. MEYER. (Concluded from p. 87).

B.-Precipitation with Hydrofluoric Acid. VERY little is known of the properties of the fluorides of the rare earths. It is only known that, with the exception of zirconium fluoride, they separate as difficultly soluble precipitates from neutral solutions of the salts. It has been shown that scandium fluoride is almost insoluble in a fairly strongly acid solution, a property which it shares with thorium fluoride, while the fluorides of the other earths are considerably more soluble in acids, but they can be almost completely precipitated if a large excess of hydrochloric acid is added to a solution of their salts. In order to prepare scandium in the pure state it is essential that the fluoride precipitate obtained from a solution rich in manganese and iron should be quite free from manganese, and that the accompanying cerium and yttrium earths should mostly remain in solution.

The oxide obtained after the concentration process with oxalic acid is dissolved in hydrochloric acid, the solution is evaporated to dryness on the water-bath, and the residue is taken up with water and some hydrochloric acid. The solution is placed in a lead dish, and hydrofluoric acid is added in the cold until the precipitate, which at first dissolves, remains; the whole is then heated for some time on the water-bath. The slimy precipitate then settles well, and it is best to aspirate it on a Nutschen filter into an oiled filter flask, and to wash with hot water. The precipitate consists of calcium fluoride, lead fluoride, a little iron fluoride, and the fluorides of the rare earths. It is then decomposed by concentrated sulphuric acid in a platinum dish; the solution is evaporated until a damp mass is obtained, and is then boiled with water. The calcium is removed by repeated precipitation with ammonia, and the hydroxides free from calcium are boiled with oxalic acid solution. In this way a finely crystallised oxalate is obtained, while the last traces of iron remain in the solution. The oxides obtained on ignition must be perfectly white. In different experiments the yield from 1 kilogrm. of wolframite was 1'4 to 16 grms. of oxide, and 30 to 3'3 grms. of oxide from 1 kilogrm. of technical wolframite

oxides.

Owing to the success of the experiments with the fluoride purification, it seemed feasible to give up the preliminary concentration with oxalic acid and to precipitate the original solution at once with hydrofluoric acid. This was found to be perfectly satisfactory as long as only small quantities, i.e., about a kilogrm., of wolframite oxides were being treated. With larger quantities it was difficult to get suitable vessels for the precipitation of large volumes of liquid with hydrofluoric acid; moreover, a very con. siderable amount of hydrofluoric acid is used, because the greater part of the aluminium, in which the solutions obtained from impure material are very rich, must be precipitated as fluoride in order to be sure of completely precipitating the rare earths. For this reason it is usually best to perform the preliminary concentration with oxalic acid.

By this combination of methods 30 kilogrms. of wolframite oxides were worked up in several portions. The yield amounted to 75 grms. of a raw scandium containing always over 95 per cent of scandium oxide. As the oxides • Zeitschrift für Anorganische Chemie, lx., 134, November 17, 1908.

97

on extraction with hydrochloric acid left 6 grms. of insoluble residue, the result corresponds to a yield of 0.25 per cent of the raw, and o‘29 per cent of the pure material. (When smaller quantities were used the yield rose to 0.3 to 0.33 per cent of the raw material. The losses are due to the difficulty of treating such large quantities in a scientific laboratory).

C.-Methods with Hydrofluosilicic Acid.

The combined oxalate and fluoride method, as we have seen, gives good results, but certain definite instructions have to be very carefully followed; moreover, it is very tedious when large quantities of raw material have to be worked up. In addition, exceedingly large quantities of oxalic acid are absolutely necessary to precipitate the small quantities of the rare earths, and finally there are inconveniences attached to the use of hydrofluoric acid, due to its attack upon the apparatus, and also to its bad effects upon the health. It therefore seemed desirable to try to find a more convenient, less lengthy, and at the same time economical method. This was accomplished by replacing the hydrofluoric acid by hydrofluosilicic acid or sodium silicofluoride. It was first observed that the different groups of the rare earths behave very differently towards hydrofluosilicic acid. In neutral solution all rare earths are precipitated when hydrofluosilicic acid is added and they are boiled; on the other hand, in acid solution no precipitate is formed in solutions of the yttrium earths even on boiling, while with the cerium earths-cerium, lanthanum, praseodymium, neodymium, samarium-very striking differences are observed in their precipitability; I shall discuss these more fully later. Scandium, even in strongly acid solution, is gradually completely precipitated on boiling, and it is thus obtained quite free from foreign earths. These reactions merit a more thorough study, especially in relation to the possibility of successfully separating the rare earths with their help. The scandium is not precipitated as silicofluoride, but as fluoride, the silicofluor ions, SiF6", being decomposed on boiling, yielding silicon fluoride and F" ions:

Sc2(SiF6)3=3SiF4 + 2ScF3.

As