November, 1924
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A Modified Method for the Determination of Uranium in Carnotit e’ By P. H. M.-P. Brinton and R. B. Ellestad UNIVERSITY OF
MINNESOTA, MINNEAPOLIS,
HE determination of uranium in carnotite as ordinarily carried out is somewhat tedious in operation, involving many precipitations and resolutions. The point of’ main difficulty is the separation from vanadium. Volumetric methods are not regarded with favor, because of the difficulty in adjusting the end point of the reduction exactly to the UOZ stage. The method usually considered the most accurate is the so-called Ledoux & Company method.2 This is based on solution of the ore in suitable acids: removal of lead, etc., by hydrogen sulfide; oxidation with hydrogen peroxide ; precipitation of iron and a part of the aluminium with sodium carbonate, solution and reprecipitation in the same way; Precipitation of vanadium by lead acetate, solution and reprecipitation in the same way; removal of most of the lead by precipitation with sulfuric acid; co-precipitation of uranium and the rest of the lead by ammonia and ammonium sulfide, solution in nitric acid and fuming with sulfuric acid to remove the last of the lead; removal of the rest of the aluminium by precipitation with ammonium carbonate; final precipitation of uranium by ammonium hydroxide, after expulsion of carbonate; and then testing the weighed precipitate for vanadium and aluminium by solution in nitric acid. There is no criticism of the accuracy of this method, and it may well be regarded as standard when carried out with skilled manipulation. A shorter method is given by LOW,^ but even this abbreviation leaves the method a little long. The same may be said of a method by Scholl14which is perhaps also open to criticism owing to final precipitation of ammonium uranate in presence of large quantities of sodium s a h 5 I n this paper is presented a method which, while using in general the principles of the long Ledoux method, accomplishes the determination of uranium in carnotite with a very great saving of time and chemical steps, and this a t slight cost in the degree of attainable accuracy. It was a t first hoped that by the successive use, without intervening filtration, of lead acetate, hydroxylamine hydrochloride, and ammonium carbonate, a complete separation of uranium from iron, aluminium, and vanadium could be accomplished in one operation, but it was found that the boiling necessary for good filtration decomposed the hydroxylamine, owing to the catalytic action of the iron. It was found possible, however, after first removing any iron, to precipitate vanadium as lead vanadate and then to remove practically all the excess lead along with it by the addition of ammonium carbonate under certain well-defined conditions, the prin-e requisite being precipitation under slight pressure. Many operators object to the use of a pressure flask because of the element of danger, so a determination of the pressure developed in the operation of this method was made by connecting the flask, closed with a rubber stopper in which was a glass tube connected to a mercury manometer. It
T
Received July 22, 1924. Low “Technical Methods of Ore Analysis,” 1922, p. 242. John Wiley & Sons, Inc., New York. BUY.Mznes, Bull. 212, 224 (1923). 3 O p . c t t , p. 239. ‘ T H I S JOURNAL, 11, 842 (1919). 6 Hillebrand and Ransome, A m . J. S c i , 10, 120 (1900); Kern, J . Am. Chem. Soc., 23, 685 (1901). 1
2
MI”.
was found that after the addition of ammonia and ammonium carbonate the pressure in the closed flask first fa& to about half an atmosphere. This is due to absorption of ammonia gas and carbon dioxide. On heating the pressure gradually increases, but never exceeds 1.5 atmospheres. It is therefore entirely safe to use ordinary 500-cc., Pyrex Erlenmeyer flasks, with rubber stoppers lightly wired on.
METHOD A sample of the ore (enough to yield from 0.1 to 0.2 gram of u308) is treated with 30 cc. of 1:1nitric acid and evaporated to dryness on the hot plate, with care to avoid loss by spattering. The residue is taken up with 10 cc. of concentrated nitric acid and 100 cc. of water, and heated until everything but the silicious gangue is in solution. The solution is nearly neutralized with ammonia, 1 gram of lead nitrate in solution is added, and then sufficient powdered ammonium carbonate to neutralize the free acid, followed by enough ammonium carbonate to make the total amount added about 10 grams. Then 25 cc. of strong ammonium hydroxide are added, and the flask is stoppered tightly with a‘rubber stopper and shaken thoroughly. The flask is heated over a low flame, or in a water bath, to about 80’ C. for 5 minutes, with frequent shaking, and then cooled to room temperature. The precipitate is filtered on close-grained paper, and well washed, a t first by decantation, with water containing a little ammonium carbonate. About 0.5 cc. of strong ammonium sulfide is added to the filtrate, followed by several cubic centimeters of ether. The solution is heated gently, with stirring, until any lead sulfide present coagulates and settles out. This is filtered off. The filtrate is boiled to remove most of the ammonium sulfide, then acidified with hydrochloric acid, and boiled to remove carbon dioxide. Any free sulfur which separates out here can be oxidized by adding nitric acid and boiling. The solution is neutralized with ammonia, acidified with an excess of several cubic centimeters of concentrated nitric acid, heated again to boiling, and the uranium then precipitated with 3 per cent ammonjum hydroxide, which is added slowly and with stirring until the solution smells faintly of ammonia, followed by 1 cc. in excess. The precipitate is allowed to settle, and is filtered off and washed with a 2 per cent ammonium nitrate solution. The precipitate is ignited gently in an uncovered porcelain crucible, and weighed as U308. The weighed oxide is dissolved in hot nitric acid, diluted somewhat, and the solution neutralized with an excess of ammonium carbonate. Any insoluble residue, together with any aluminium hydroxide found, is filtered off. If there is an appreciable amount of precipitate here, it is advisable to dissolve and reprecipitate. This residue is ignited and weighed in the original crucible, and the weight of the residue is deducted from the weight of the crude U308. The filtrate from the aluminium can be tested for vanadium by acidifying with hydrochloric acid and adding hydrogen peroxide. A faint brownish red color can be neglected, as it indicates an almost unweighable amount of vanadium. NOTES The amount of lead to be removed by ammonium sulfide is usually very small. The addition of a little ether has been
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found to aid coagulation of the lead sulfide-which a t first appears more of a coloration than a precipitation-and to facilitate filtration. It is desirable to boil off most of the ammonium sulfide while the solution is ammoniacal, as this greatly diminishes the amount of sulfur formed on acidification. Ammonium diuranate,.precipitated as here directed, should filter quite well. Occasionally, however, the precipitate a t first r i m through the paper. It must then be refiltered until clear. Failure to watch the filtrate from the ammonium diuranate closely is probably a common source of error in gravimetric uranium determinations. The ammonia used in uranium precipitations should be freshly distilled over slaked lime, as any ammonium carbonate renders the precipitation of uranium incomplete. The aluminium which is always found in the ignited uranium oxide is due to the large excess of strong ammonia used in the precipitation of lead, vanadium, etc. However, in any gravimetric method it is necessary to examine the ig-
American Potash-A
Vol. 16, No. 11
nited uranium oxide for alumina, and invariably a small amount of it is found.
TESTANALYSES A sample of Colorado carnotite which had been very carefully analyzed by the long standard method contained 16.9 per cent U,Os. The following results were obtained by five different analysts, using the short method here described, on the standard ore:
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While the method is not ideal for the most accurate umpire work, its rapidity and convenience make it well suited to routine determinations of uranium.
Progress Report’
By J. W. Turrentine BUREAU O F SOILS, DEPARTMENT O F AGRICITLTURE, WASHINGTON, D. C.
T
HE wide attention attracted by the American potash
industry as developed during the war years on the basis of unstable war-time prices and the complete deflation of that industry when that basis was removed left by contrast the impression that the industry was wholly unsound and had nothing more real as a foundation than those highly abnormal conditions. War-time activities in connection with potash have been regarded in certain quarters as nothing more than an effort to make war-time profits. The war-time industry was something much more worthy than that. It was to a large degree an effort to take advantage of the high prices obtainable for potash to finance the establishment of permanent industries from which potash would be produced as a major product or to improve already established industries by the development of potash production as a by-product. Particular reference is made to the labors of certain of the great fertilizer companies to establish industries based on the raw materials, alunite and kelp, of the borax industries better to utilize desert lake brines, of the explosives industry to utilize kelp, of the cement and blast furnace industries to utilize their dust, of the beet sugar industry to utilize Steffens waste, of the alcohol industry to utilize distillery waste, and of other industries to utilize other raw materials. However, money to finance research is not the only prerequisite. Time is also required, and there was not enough of this essential to accomplish the solution of the many problems which arose in connection with the profitable production of potash from the many materials from which it was recoverable. So as the result of these valient emergency labors, because of the shortness of time, disappointments followed and were given more emphasis in summarizing the results than the successes. I t has been the writer’s task, in reorganizing the potash investigations of the Department of Agriculture, to salvage the wreckage, to assort the values, to take the good and to discard the worn-out from among the experimental results a t hand; to save from the virtual junk heap of inaccessible private files t h e great mass of data there locked up, secured through the labors 1 Presented before the Division of Fertilizer Chemistry a t the 68th Meeting of the American Chemical Society, Ithaca, N. Y.,September S t o 13. 1924.
of scores of investigators a t the expense of scores of thousands of dollars; to reassemble and to use them as materials of construction wherewith to build the foundation on which the edifice of future potash investigations can be erected. He is glad t o report that he finds much that is excellent.
BY-PRODUCT POTASH The outstanding result of American activities with respect t o potash is that we now have an American potash industry producing 25,000 tons KzO annually. Of greater importance than the quantity produced is the fact that this industry is based on three different raw materials and the potash in all three instances is by-product potash. It has long been believed that there is no present known source of potash in America from which t h a t commodity can be produced alone; that to give its manufacture economic stability it must be produced as a by-product or with by-products. Furthermore, the foregoing instances of potash production, as shown by surveys, by a natural process of growth within the industries where they are now established, can be made to yield 150,000tons KzO per annum instead of the present 25,000 tons. Reference is made to the cement, the borax, and the alcohol industries. At the cement plant of the Santa Cruz Portland Cement Co., Davenport, Calif., a t the borax plant of the American Trona Corp., Searles Lake, Calif., and a t the alcohol plant of the United States Industrial Chemical Co., Baltimore, Md., potash of excellent grade is now being produced by processes so efficient and so economical that the output is able t o meet the competition of the European product placed on our seaboard a t the lowest price realized since the days of the Schmidtman controversy and representing the most severe competitive conditions ever experienced in that industry. I t will be noted that this considerable output is produced from a single plant in each of the respective industries mentioned. This is taken as evidence of the substantial nature of the industry’s foundation, that it can successfully meet this type of competition. Surveys have been completed of the three industries named and also of the blast furnace industry, which show a total tonnage of potash there producible of 225,000 tons. Omitting the borax industry, we are now throwing away as a waste product of
