Preparations and Properties of Ammonium Diuranatel HURD W. SAFFORD and A. KUEBEL2 Department of Chemistry, University of Pittsburgh
T
HIS paper describes a commercial method and a laboratory method for the preparation of that ammonium compound of uranium usually called "ammonium diuranate" or "ammonium uranate" and represented by the formula (NH&JPOI. Certain of its chemical and physical properties are also presented. Commercially, the compound is sometimes known as "uranium yellow" although this name is more frequently applied to the corresponding sodium compound of uranium, sodium diuranate. Both the ammonium and the sodium diuranates are used as coloring agents in glass, and they are prepared on a commercial basis from pitchblende ore. A procedure which may be used for the industrial extraction of uranium from pitcbblende ore and which has been duplicated on a laboratory scale in this investigation follows. Pitchblende concentrate was given a preliminary roast in air a t approximately 750°C. to decompose any organic material which might have been present and also to decompose metallic sulfides and carbonates. These last two constituents, if left in the ore, would have caused undesirable effervescence in the sulfuric acid leach which was the first step in wet treatment of the ore. A second roast was then carried out after the ore had been mixed with sodium chloride. The purpose of this heating was to convert all silver which might have been present in the free or combined state to silver chloride. For the removal of uranium, which is usually present in the ore as an oxide, the product of the salt roast was boiled with 1:1sulfuric acid solution. (Sodium nitrate may be added a t this stage to oxidize any uranium left in the quadrivalent state to the sexavalent state.) The crude uranium sulfate solution was then separated from the residual ore by filtration. The ore residue, which contained radium as well as silver, was treated for the extraction of these two elements by a process described in an earlier paper.8 The steps for the purification of the crude uranium sulfate solution and for the production of the salt, ammonium diuranate, are outlined in the accompanying flow sheet. This is very similar to the process followed in the radium refinery of the Eldorado Gold Mines, Ltd., a t Port Hope, Ontario, where pitchblende ore from the Great Bear Lake deposits is treated. For the laboratory production of ammonium diuranate it is, of course, much easier to begin the prepara1 Contriubtion No. 488 from the Department of Chemistry, University of Pittsburgh. 2 Present address: JOURNAL OF CHEMICAL EDUCATION, Metcalf Chemical Labaratorv. Brown University. Providence, R. I.
Air r-t
I
Salt roast I Sulfuric meid leach I
Residue containing A g and Ka
Filtrate of mvde vranivm sulfate
I
Filtrate of crudesodium urany1 carbonate
ReridW of metallic impurities (Fe, Cu. Co, r t c )
I
I + NaOH
+
Precipitation of sodium divranatc r-Filtration-
1
Residue of NazU*OdWJ
Filtrate of soluble hydroxides
I + HsSOa
+
Solution of uranyl svlfate
I + NnaS
+
precipitation of metallic impurities
Filtrate of -my1 sulfate
Residue ot iorol. sulfide3
I + NaOR I
7 Residue of Na,UaO,rH~O
I
+
i KzSO.
Filtrate of soluble sulfides and hydroxide.,
Sdlltion Of U02S0,
I + NHaOH
+
Precipitation of
(NI~)S~O~ZH~O I
Residue of (N&hU.OrxH.O
I Filtrate of soluble rvlfides and hydroxide3
tion with a chemically pure uranium salt rather than with pitchblende ore. Uranyl nitrate, UOz(N0&6&0, is a convenient compound to use because it is one of the commonest and least expensive uranium salts and because i t is readily soluble in water. This material was employed in the laboratory investigation described below. Hydrated ammonium diuranate was precipitated from an aqueous solution of uranyl nitrate by addition of concentrated ammonium hydroxide. The precipitate, which was bright yellow in color and which settled out of solution readily, was exceedingly difficult to filter even by suction because it tended to cake. For this reason, the compound was washed by decanting the supernatant liquor and replacing i t with distilled water a total of eight times. As the coucentration of excess ammonium hvdroxide in the surface liquor decreased, the precipitate settled less readily; by the time this liquor was decantedfor the eighth time. it was quite turbid. This may indicate that the precipitate was a positively charged colloid and that the removal of OH- ions. which c o a d a t e d the narticles in basic solution, permitted a re&spersion of'the colloid. The wet precipitate was transferred to a sintered glass suction cup and was washed with absolute alcohol and then with ethyl ether. Finally, air was drawn throngh the precipitate until the last traces of ether were rcmoved. To determine whetherdning thecompound at 10O0C. in an O\WI had any effect upon its composition, i. e., to determine whether hrating it t i t that temperature could climinatc NHI in addition to water and lr;i\.e the uranium in the form of an oxide (possibly UOa), samples of oven-dried material and of material desiccated a t room temperature with anhydrous calcium sulfate were taken for x-ray analysis. Diffraction patterns of each were made under similar conditions with Cu-Ka radiation, using a current of 18 milliamperes a t 42 kilovolts (Figure 1 ( A ) and ( B ) ) . The lines in the patterns of the samples were in correspondingly identical positions, a fact indicating that drying ammonium diuranate in an oven a t 100°C. does not alter its structural composition appreciably. But there is definite evidence of a change in structure when decomposition takes place
Condilianr Dried in air a t room tempera-
PorriUc Producl (NHd~UsOixHaO )
ture Dried in desiccator over anhyd. CaSOa at room temper=tuie lor three weeks
(NHhUnGrHnO (yellow)
~ e a t e dto approximately 350" C. in air over Meeker burner Heated at approximately ?SOD C. in =ir in mume furnace for two hours Heated at approximately 1000° C. in dry hydrogen
(~dlow)
Rcsulls af X-Roy A nolyrir
I
Diffraction patterns practically identical
u01
Nodefinitepattern
(reddi~hbrown) Uz0.
Fairly good pattern
wive.green) UO, black
Goodpattern. Interpianar cai. c*=ted agreed with published values lor
uo:
'- ?
--
5 :a
~ G U R E 1.-X-RAY DIFFRACTION PATTERNS: (A) OVENDRIEDSAMPLE OF AMMONIUM DIURANATE; (B)SAMPLE DESICCATED OVER CaSO.: (C) URANOSICOXIDE. UxOa: AND (D)
a t higher temperatures. When ammonium diuranate was heated above 100°C., its color changed from orange to brown or reddish brown. This reddish brown product was probably an oxide, but its structure was not well defined since it seemed to be amorphous as far as x-ray and microscopical methods of analysis were concerned. The color of the material changed continuously as the temperature was increased. At 750% the product was the olive-green oxide of uranium called "uranosic oxide" and represented by the formula UaOs. When this decomposition in air a t 750°C. was carried out on a quantitative basis, it was found that the loss in weight on decomposition amounted to 13.2'% of the weight of the original sample of ammonium diuranate. When, however, the diuranate was heated t o 750°C. in dry hydrogen, the loss in weight amounted to 14.4% of the weight of the original sample. The differences in loss in weight in the two experiments are accounted for by the fact that when ammonium diuranate was de-
composed in hydrogen, the product formed was the pound were dissolved in dilute nitric acid to produce lowest stable oxide of uranium - uranium dioxide, solutions of uranyl nitrate whose absorption of @ rays UOz, instead of the higher oxide, U308. X-ray photo- would be approximately the same as the absorption of B grams of U30s and UOz are shown in Figure 1 (C) and rays by the standard solution of uranyl nitrate. If C.P. (D). Although data for the former do not appear in uranyl nitrate is 47.47, by weight of uranium, then the the literature, the interplanar spacings calculated for percentage of uranium determined by the counter UOz agreed with published values. The dioxide, UOz, analysis for the sample was G4.7y0. The accuracy of produced when ammonium diuranate was decomposed this experiment was limited by two factors: (1) the in hydrogen was either grayish black or bluish black in possibility that U02(N0&liHz0 was not the exact forcolor, depending upon the temperature at which de- mula for the nitrate which was used as a standard and composition took place, the length of heating, etc. (2) mechanical variations within the Geiger counter A diagram of the apparatus used for the hydrogen de- itself which might have influenced its counting rate composition is shown in Figure 2. Ordinarily, the and thus produced irregularities. Certain aualitative experiments with ammonium di~~ranate prodt~ced a~mrrvh:,~ more definite r e s ~ ~ l t s tlluti tlw quantitati\.e ~ m c s \I1itli rripcx't to the solubility 11f the compou~~d in \xrious retigents :~ndsollltions, the following positive results were obtained: it was readily soluble in the common acids including hydrochloric, sulfuric, nitric, acetic, phosphoric, and oxalic. The only common acid in which ammonium diuranate was found to be insoluble was boric acid. It was also soluble in aqueous solutions of certain salts such as aluminum sulfate, aluminum chloride, aluminum nitrate, ferric chloride, and ferrous chloride. It dissolved in solutions of copper salts with the production of a very light-colored precipitate. It was found to be insoluble in aaueous solutions of most of the salts of the alkaline earth group, and practically insoluble in Drl Ah,Frcuna 2.-APPARATUS USED FOR DECOMPOSITION MONIUM DIURANATB I N HYDROGEN. SHOWN (Right to Lefl): salt solutions of aluminum acetate, ammonium acetate, HYDROGEN TANK,CONC.HISOl TOWER. CaSO, DRYING Tuee, ammonium sulfate, ammonium nitrate, zinc chloride, A N D QUARTZ COMBUSTION TUBE. THESAMPLE WASPLACED IN A QUARTZBOAT INSIDE THE TWE. ALTHOUGH A MERER zinc nitrate, zinc acetate, zinc sulfate, cobalt chloride, BURNER1.3 SHOWN, AN OXYGEN TORCH SUPPLIED MOSTO F THE cobalt acetate, cobalt nitrate, etc. HEAT. The results of this investigation of the properties of ammonium diuranate do not make it possible to ascribe bluish black oxide was the one produced at higher tem- a definite formula to it. I n addition to a possible variperatures. Although some difficulty was encountered ation in the number of molecules of water of hydration, in obtaining an x-ray photogram of the ammonium the formula of the anhydrous salt itself may not be compound,' a relatively sharp diffraction pattern of uranium dioxide resulted when using Cu-Ka radiation. In one experiment, ammonium diuranate was decomposed in dry hydrogen a t a white heat and an x-ray pattern of the product was made; the interplanar spacings computed from the lines in this particular pattern were in close agreement with the d-spacings found for metallic uranium by Jacob and Warren.5 But this is not proof that metallic uranium can be prepared by heating ammonium diuranate in an atmosphere of hydrogen because no check results were obtained in later experiments. I n an effort to determine the dercentage of uranium in ammonium diuranate. a samole was analvzed bv a Geiger counter using C.P. uranyl nitrate, UOz(NOa)27 6H20, as a standard for comparison of radioactivity. Carefully weighed amounts of the ammonium com-
-
"ither a large part of the x-ray beam was reflected backward instead of passing through the sample, or secondary x-radiations were emitted from the sample itself, as evidenced by a considerable fogging of the film. J~corrAND WARREN,"The crystalline structure of uranium." J A m . Chenr. Sor.. 59,258R (1937).
Frcuna 3.-GEIGERCOUNTEREQUIPMENT WHICHITASL'seo MnAsunrNG THE RADIOACTIVITY OF AMMONIUM DIURANATE. THESAMPLE WAS PLACED IN THE SMALL VIAL (INDICATED BY ARROW),AND THE COUNTS WERERECORDED BY A STYLUS ON THE
FOR
DRUM.
(NH&UZOI, but perhaps (NH&UO1 or UOa with ammonia of crystallization. It is hoped that from the studies planned a t the present time, it may be possible to establish the exact composition of this uranium compound.
The authors wish to express their appreciation to Dr. David Halliday of the Department of Physics,
University of Pittsburgh for the time and effort he spent in making the x-ray patterns and Geiger counter analysis. They wish also to thank Dr. L. A. Goldblatt, formerly of the Department of Chemistry, University of Pittsburgh, now of the Department of Agriculture in Washington, for his suggesting the problem originally and for his many helpful comments. They are also indebted toDr.Frank Day, Jr., of thecorning Glassworks for his assistance during the initial progress'of the investigation.
