Imágenes de páginas
PDF
EPUB

III.

THE SEPARATION OF URANIUM.

SEPARATIONS FROM IRON.

By Acetates.—The separation of uranium from iron, by precipitating the latter as basic acetate, was referred to in a general way by Gibbs, but no particulars were given. Some phases of the process were studied by Rheineck,” who suggested that the operation was a delicate one, and observed that a crystalline precipitate is formed at once in concentrated, and, after some time, in more dilute solutions, when sodium acetate is added to any salt of the oxide of uranium.

The following experiments were made with the object of determining in which direction the weakness of the separation lay, rather than with the idea of improving it for regular service. Five grams of bar iron were dissolved in hydrochloric, and oxidized with nitric acid, 25 grams ammonium chloride and 150 c.c. standard uranium solution

1 Chemical News, xi. 102.

2 Chemical News, xxiii. 233.

added, and the mixture then neutralized and divided into five equal portions.

(a) Was diluted to 300 c.c., and boiled. The iron was almost entirely precipitated, and no acetate whatever was added :

added : 0'2055 gram uranium was found in the filtrate, instead of O'2045 gram.

(6) Five cubic centimetres strong ammonium acetate were added, which precipitated the iron immediately in the cold. The solution was then boiled three or four minutes. The filtrate contained only o‘0853 gram uranium.

(c) Treated like (6), but 10 c.c. acetic acid were added before the acetate. A precipitate formed after very little heating. The filtrate contained oʻ1994 gram uranium.

(d) Treated as (a), but added 0-5 c.c. acetate

the boiling solution, to completely precipitate the iron—0-2000 gram uranium in the filtrate.

(e) Treated as (a), but added 5 c.c. acetic acid to the cold solution, and 1 c.c. ammonium acetate to the boiling solution. The precipitation of the iron was complete; in fact, less acetate might have been used. The filtrate contained oʻ2048

to

gram uranium.

There is no doubt that when phosphoric acid

one.

is absent, and the proportion of uranium is large enough to yield a sufficient amount in the filtrate, without having to deal with unwieldy precipitates of basic ferric acetate, this separation is a reliable

The neutralized solution, however, should contain 1 or 2 per cent of free acetic acid, and no more acetate should be used than will comfortably precipitate all the iron. With these precautions the separation appears to be quite as easy as that of iron and nickel by the same process. It is probable, also, that others of the alkaline salts which have the power of precipitating neutralized ferric solutions might advantageously be substituted for ammonium acetate.

By Alkalis.- When ammonium carbonate is added to a solution containing iron and uranium, the former is precipitated, but may or may not be free from the latter. A separation, which is practically perfect, can be made by pouring a solution containing as much as 2 grams of iron into a solution, which is kept agitated, of ammonium or sodium carbonate or sodium bicarbonate. A little iron, however, is apt to remain in solution, and it is customary, if its presence is objectionable, to allow it to settle out after prolonged standing or to precipitate it with ammonium sulphide.

Separations made in this way gave the following results :-1

[merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small]

Caustic alkalis, of course, precipitate the uranium along with the iron, but, according to Walker, it remains in solution if hydrogen peroxide is also present. This separation appears to be quite successful only when the proportion of iron is not large and the total weight of the metals dealt with is small.

By Ether, etc.-Kern's valuable contribution to the quantitative separation and determination of uranium deals particularly with the separation of iron. His experimental work is confined to the ether-extraction process, which in other directions is already well known, and he finds that the most complete separations are obtained by using hydrochloric acid of 1'10 specific gravity. More than one extraction is

1 I am indebted to my friend, Fred Ibbotson, B.Sc., for these results.

2 Jour. Amer. Chem. Soc., xx. 513. 3 Four. Amer. Chem. Soc., xxiii., and Chemical News, vol. Ixxxiv.

necessary, and it is doubtful whether the process is a desirable one unless ether extractions in other directions are being regularly carried out.

A separation described by Rose depends on the precipitation of the two oxides by ammonia, ignition in a stream of hydrogen, and extraction of the metallic iron with hydrochloric acid. Or the iron may be volatilized from the mixture by heating it in an atmosphere of the gaseous acid.

The electro-deposition of iron from oxalate solutions is said to lead to a perfect separation.

The separation by means of alkaline acetates is trustworthy and convenient within the limitations already referred to.

Its value and accuracy is further attested by the following results ; nevertheless, some other alkaline salt instead of acetates could probably be used with advantage :

[blocks in formation]

When a minor constituent of any mixture is required to be estimated, it is generally best to

С

« AnteriorContinuar »