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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
PREPARATION OF BLACK OXIDE OF URANIUM
(no31
By CHARLES L. PARSONS Received April 6, 1917
Val. 9, NO.
Hillebrand,’ when, in a study of uranium compounds, he fused uranyl chloride with a mixture of ammonium and sodium chlorides, obtaining thereby a reduction of the uranium chloride t o uranyl oxide. It is of course evident a t once t h a t sodium uranate, if -treated with hydrochloric acid, would give a mixture of salt and uranyl chloride and if this were fused with more salt and ammonium chloride, uranium oxide would probably result. This was found t o be true, but the process worked successfully only in small quantities with a large excess of ammonium chloride and could not be applied commercially. Based, however, on the principle t h a t a reducing agent acting on uranyl chloride should give, in a fused salt bath, uranium oxide, a series of experiments led t o the final simple result t h a t it was necessary only to fuse sodium uranate itself in a salt bath in the presence of carbon to yield the desired product. As soon as this was determined the method was applied on a plant scale. For some months now, the production of uranium oxide has been going on almost daily in the plant of the National Radium Institute and a purer uranium oxide than has ever been made in quantity heretofore has been turned out in lots of several tons. The method first adopted and still used is as follows: A cast steel pot, made of pure low-carbon steel, 19 in. deep by 16 in. wide with walls 3/4 in. thick, is filled with a mixture containing 35 parts salt, 2 0 parts sodium uranate and I part ground charcoal. The whole is heated by a n oil burner in a crucible furnace. In first starting the run the pot is filled with a carefully mixed charge. Under the influence of the heat, reaction begins on t h e bottom and sides and the carbon monoxide bubbles u p through the thick, pasty melt. The material should not be stirred during the operation but the reaction should be allowed t o continue to completion, more charge being added from the pot from time t o time as it settles down under the reaction. I n this manner about one-third more material than the pot would ordinarily hold can be added and the melt when finished leaves the pot approximately four-fifths full. Reaction takes place a t a red heat and is allowed to continue until no more gas escapes from the mass. The oxide should then be dipped (not poured) from the bottom of the pot with a long-handled iron ladle and ladeled together with the salt melt into an iron pot or trough where the mixture can cool. Approximately 4 runs per day per furnace can be made. The following figures represent the quantities used during a month’s run with two furnaces:
I n the extraction of uranium from its ores, the uranium is almost invariably obtained in the form of sodium uranate, Na2U20,. This material is sold to the trade as “yellow oxide of uranium” and is used chiefly t o give t o glass the rich, yellow tint characteristic of uranium and its salts. Sodium uranate of course does not lend itself readily to the production of alloys of uranium and for this purpose i t is desirable t o obtain the material in the form of oxide. Indeed, there can be little doubt t h a t t h e more concentrated form which t h e pure oxide offers would render this material more desirable even for use in glass works. There have been rumors of some two years’ standing t h a t uranium steel is being used in Germany in some of the larger cannon. These rumors have recently been corroborated and there appears t o be no question t h a t in Germany uranium steel has been developed which softens a t a temperature higher than any steel heretofore used in cannon. Some of the larger guns have a rigidity under repeated fire and high temperature which allows them t o be used through a longer period of intense firing without impairing their accuracy than was formerly possible. Uranium has also been proposed and, indeed, used t o replace tungsten in tool steel-the claim being t h a t I per cent uranium can successfully replace from 6 t o 1 2 per cent tungsten. I t has accordingly become important t o be able to procure uranium oxide cheaply, in order t h a t ferro-uranium might be readily produced. A report on the production of ferrouranium has already appeared2 in THIS J O U R N A L . Uranium oxide has now been prepared t o the amount of several tons in the Denver plant of the National Radium Institute. The details of its early production have already been e ~ p l a i n e d . ~The method first used t o make i t was b y precipitating as ammonium uranate. This required too many precipitations t o separate the sodium entirely, and, accordingly, on ignition of the ammonium uranate a considerable amount of sodium uranate remained with the uranium oxide. As t h e method was also very costly, it was abandoned. I n like manner the attempt t o volatilize sodium oxide from t h e uranium oxide a t the high temperature of t h e electric arc was not successful commercially owing t o t h e dangerous explosions t h a t took place. The cause of these explosions was never satisfactorily explained but they were probably due to the production of metallic sodium. Fortunately, some simple experi~ CHLORIDE CARBON ments which I carried out in the laboratory led t o a n No. OF CHARQBSSODIUMU K A N A TSODIUM 17,776 lbs. 485 lbs. 174 9680 lbs. immediate and easy solution of the problem. These experiments were suggested b y a reaction first mentioned by Wohler‘ and made use of analytically by The steel pot is but little attacked on the inside but scales off on the outside from the action of the flame 1 Published by permission of the Director of the Bureau of Mines. and accordingly lasts for only 3 5 to 40 charges. a H. W. Gillett and E. L. Mack, “Feno-Uranium,” THIS JOURNAL, 0 The reaction is practically quantitative and no (1917). 342. * Parsons, Moore, Lind and Schaefer, “Extraction and Recovery of uranium oxide is lost in the flux. Owing to the light Radium, Uranium and Vanadium from Carnotite.” Bull. Bur. Mines. 104. 4 Gmelin Kraut, 6 Ed., Vol. 2. Part 2, p. 372.
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W. D. Hillebrand. Z. anmg. Chem., 3 (1893),243.
May 1
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
character of the charge a small amount of sodium uranate is apparently lost in the flues. After cooling, the salt mass containing the uranium oxide is readily broken with a hammer and easily dissolves in water. I n practice the material for the day’s run is put, a t the end of the day, in a large box with an iron sieve bottom and placed in the top of a tank containing water. During the night t h e salt dissolves and the fine powdered uranium oxide passes through the sieve and settles in the bottom of the tank. By bringing the water to the boiling temperature with steam and stirring the contents of the tank, the uranium oxide is quickly and thoroughly washed and, as it is very heavy, i t can be almost immediately separated by decantation. The oxide so obtained generally contains some iron and some aluminum. These can, for the main part, be separated by washing the uranyl oxide with a 5 per cent solution of hydrochloric acid, in which it is not soluble. The acid dissolves the main part of the iron and aluminum compounds. I n this way it is a simple matter t o obtain uranyl oxide almost pure. I n commercial practice a purity equivalent t o 97 per cent U308is obtained, no attempt being made t o separate all of the iron as its presence is not deleterious in the production of ferro-uranium. One of the advantages of t h e process is that vanadium, if present, is easily separated and recovered a t the same time Sodium uranate made from carnotite always contains vanadium in some quantity. I n the procedure described above the vanadium stays in the salt as sodium vanadate, dissolves with the salt, and can be readily precipitated therefrom, in a high degree of purity, by iron sulfate. Indeed, the recovery of the vanadium will about half pay for the whole operation. The cost of producing “black oxide” of uranium from sodium uranate by this method varies with conditions. The average cost of conversion during the last 4 months of operation has been slightly less than 1 1 cents per lb. This might be made considerably lower by running the furnace continuously, or it might be increased if the furnace were run more intermittently. I t will, of course, also vary with the cost of fuel oil. I n the operations of the National Radium Institute the cost of conversion has varied from around 9 to 13 cents per lb., depending upon conditions. BUREAU OF
MINES.
WASHINGTON
THE EXTRACTION OF POTASH FROM SEICATE ROCKS-I1 By WILLIAHH. Ross Received March 5, 1917
I n a previous publication1 an account has been given of a preliminary investigation on the possibilities of recovering potash from insoluble silicates. It was shown t h a t when I part of feldspar and 3 parts of calcium carbonate were ignited for about an hour a t a temperature of I ~ O O - I ~ O Ot ~h e, potash in the feldspar was completely volatilized and the clinker which remained had a composition which fell between the limits required for Portland cement. 1
Eighth Intern. Congress of Applied Chemisfry, 16 (1912). 217.
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It was also observed t h a t when part of the lime was replaced with a quantity of calcium chloride equivalent t o t h e alkalies in the feldspar, volatilization took place in about half the time required when the ‘ignition was made with lime alone. As a result of these experiments i t was concluded t h a t potash could be set free from feldspar by substituting t h e latter for clay in the manufacture of cement; t h a t the potash would be volatilized to a greater or less extent, and could be recovered in the flue dust; and that it should be possible to obtain raw materials which on ignition would form a residue of the composition required for Portland cement clinker. Since potash silicates occur in the raw materials used in the manufacture of cement and as the temperature of clinkering is equal to t h a t used in the feldspar experiments, it might be expected t h a t complete volatilization of the potash would also take place in t h e burning of cement. The heating zone of a rotary kiln constitutes, however, only a comparatively short proportion of its length and while the charge occupies more than an hour in passing through the kiln, the time t h a t it is subjected t o a clinkering temperature is less than t h a t required t o bring about complete volatilization of the potash. The length of the kilns has also a retarding effect on t h e evolution of t h e potash. While complete volatilization for these reasons does not take place in any case, it is now known that the escape of potash from cement plants is considerable, and from analyses which have recently been made in this laboratory it has been found t h a t the percentage of the total potash in t h e raw mix which is volatilized in different cement plants in this country varies from about 2 5 t o 95 per cent. I n several cement plants this potash is now being collected with t h e flue dust by electrical precipitation and is used directly in the manufacture of fertilizers, or t h e potash is leached from the dust and disposed of separately. Recent developments have thus confirmed the conclusions previously reached t h a t one of the most promising methods of recovering potash from potash silicates was by the use of the latter in the manufacture of cement. Since the publication of the preliminary report referred to, a great deal of attention has been given in this laboratory t o the further investigation of this subject, particularly along the lines suggested in the numerous patents which have been granted on processes for the extraction of potash from insoluble silicates. It was soon concluded t h a t owing t o the limited percentage of potash occurring in any insoluble potash silicate, no process for recovering potash from these silicates can prove economical unless there is recovered a t the same time some other product of value in addition to the potash. The patented processes which relate to this subject now exceed I O O in number, Almost one-third of the total number make no claims t o recover any product other than t h e potash.1 I n the remaining processes, 1 U. S. Patents 5,384, 49,943, 513,001, 641,406, 772,206, 789.074, 851,922, 910,662, 952,278, 959,841, 987.436. 993,463. 1,011,172, 1,029,378. 1,076,508, 1,083,553, 1,091,034, 1,091,230, 1,148,850, 1,150,815, 1,159,464, 1,176,613, 1,194,464, 1,197,556, 1,201,396, 1,209,201, 1,217,388, 1,217,390; British Patents 1,211 (1854), 4,750 (1908); French Patent 409,513 (1910).
