Analysis of Samples Containing Uranium, Niobium, and Zirconium PHILIP 1. ELVING and EDWARD C . OLSON University o f M i c h i g a n , A n n Arbor, M i c h .
I.
Ihe importance to the atomic energy program of reasonably rapid, simple, and accurate methods for the analysis of mixtures containing uranium, niobium, and zirconium prompted an inr estigation of polarographic and amperometric procedures for this purpose. Rlixtures containing uranium and zirconium can be analyzed by polarographing an aliquot of a 10% sulfuric acid solution between 0.0 and -0.5 volt to determine uranium, and titrating another aliquot amperometrically with standard cupferron solution at -1.0 volt to determine zirconium. In mixtures containing uranium, niobium, and zirconium, the zirconium is separated as the phosphate from h j drogen peroxidesulfuric acid solution, and the suspended phosphate is titrated amperometrically with cupferron. The uranium and niobium are determined simultaneously from the polarogram of their solution in concentrated hydrochloric acid. Errors are about 1% for uranium and niobium, and about 0.5% for zirconium. The procedure was successfully applied to the assay of a niobium ore.
pared daily from a purified sample of cupferron (16). Nitrogen was purified and equilibrated in the usual fashion (1.5). All other chemicals were reagent, or C.P. grade and were used without furth6.r purification. EXPERI.MENT4L
Polarographic Determination of Group IVB Metals. The polarography of titanium has been summarized by Kolthoff and Lingane (9) ; titanium is grnerally determined in strongly acidic solution by reduction of titanirim(IS-) to titanium(II1). S o wave is observed for the titanate ion in strongly alkaline solution. I n solutions containing high concent,rations of oxalate, tartrate, or citmtr! titanium gives a well-defined wave over the p H range from 0.5 to 11.8 (ID).
B
ECAUSE of the relatively common natural occurrence of uranium, zirconium, and niobium, as well as their occurrence
in mixtures useful for the utilization of atomic energy, it seemed highly desirable to develop fairly rapid and simple procedures for the analysis of samples containing uranium and zirconium, and uranium, niobium, and zirconium. Hafnium, while not specifically studied, would follow zirconium in the proposed schemes of analysis. Titanium is separated from zirconium and hafnium by the phosphate-hydrogen peroxide isolation of the latter two elements. Tantalum produces no polarographic wave under the conditions used t o determine niobium and may thus be present in considerable quantities without causing any interference.
c
e
z
a V
I
APPARATUS kYD REAGEYTS
-0.4
Apparatus. A Sargent Model XXI Polarograph was used in conjunction with a thermostated H-type cell containing a saturated calomel reference electrode (10). Potentials were checked with a Type K potentiometer. The capillary used had an m 2 ' 3 t 1 ' 6 value (25" C., open circuit, distilled water) of 2.04 mg.2'3 sec. -l'2, Reagents. A standard uranium solution (0.0398 millimole or 9.47 mg. of uranium per milliliter) was prepared by dissolving reagent grade uranyl nitrate in sulfuric acid and heating until sulfur trioxide was evolved. The resultant solution was diluted to contain 10% sulfuric acid by volume; i t was standardized by reduction with zinc amalgam, aerated for 5 minutes, and titrated with standard permanganate. Uranium(1V) solutions were prepared daily from t h r uranium(V1) solution by reduction with zinc amalgam. A standard niobium solution was prepared by dissolving reagent grade potassium niobate in water, adding 50 ml. of saturated oxalic acid solution, warming the resulting suspension gently until solution m-as complete, and then adding 5 ml. of hydrochlor& acid. This solution was diluted t o 250 ml. and standardized gravimetrically ( 1 7 ) ; it contained 0.0124 millimole (1.05 mg.) of niobium per milliliter and remained unchanged in composition throughout the investigation. When this solution Kas used, the ovalate present was first destroyed by fuming with sulfuric acid and then adding, as necessarv, a few drops of dilute permanganate. Standard zirconium solution, prepared by dissolving the pure metal in boiling concentrated hydrochloric acid, contained 0.0757 millimole (6.905 mg.) of zirconium per milliliter. Standard cupferron solutions in oxygen-free water were pre-
I
I
-0.5 Potential
,
- 0.6
v.
I
- 0.7
Figure 1. Polarographic curves for 1.16mM niobium(\;) 1. In 12M hydrochloric acid 2. In 9M sulfuric acid
The polarographic reduction of zirconium in 1.11 hydrochloric acid solution containing potassium chloride has been reported (1%);however, it is preceded by the reduction of hydrogen and is therefore of little use. AIore recently the polarographic reduction of zirconium in methanol solutions has been described (1) and may prove t o be useful after further study. The polarographic reduction of hafnium and thorium has not been achirved as yet. Reaction of Group IVB Metals with Cupferron. Previous studies (5, 6, 14>16) have established the optimum conditions for the rapid quantitative precipitation of the Group IVB metals with cupferron. The amperometric titration of titanium, zirconium, and hafnium with cupferron has been described (5, 1 5 ) . Polarography of Niobium and Tantalum. Siobium gives a polarographic wave in 11f nitric acid ( 2 0 ) : although the limiting current is proportional to niobium concentration, the wave is artually due t o the catalytic reduction of nitrate ion in the
338
V O L U M E 28, NO. 3, M A R C H 1 9 5 6
3.2 4.0
339 acid, a bright orange color resulted, indicating that reaction had occurred. Consequently, solutions of uranyl sulfate in 10yo sulfuric acid were titrated amperometrically with standard cupferron sohti6n a t a potential of -0.4 volt us. S.C.E. (Figure 3 ) . The curves obtained indicated no relationship between the amount of uranium(V1) present and the volume of cupferron
t -0.4
-0.5
-0.7
-0.6
Potential ,v. Figure 2. Effect of hydrochloric acid concentration on polarographic wave of 1.16m.W niobium(\-) 1. 2. 3.
4.
a.
12M hydrochloric acid 9.6M hydrochloric acid 7.2M hydrochloric acid 4.8M hydrochloric acid Residual current in 12M hydrochloric acid
presence of niobium ( 3 ) . I n concentrakd hydrochloric acid niobium(\') is reduced to niobium(1V) by a reversible l-elect,ron process (El/?of -0.455 volt us. S.C.E.; the wave height is proport,ional to concentration and reproducible in 9- t o 12M hydrochloric acid); a second wave appears but merges with the I I I I I hydrogen discharge wave (2, 4 ) . The polarographic reduction of I 2 3 4 niobium in sulfuric acid solution has also been reported (11)) Cupferron Solution, ml. hut details are not available. Consequently, a brief study was made of the polarographic behavior of niobium in sulfuric and hydrochloric acid solutions. Figure 3. Amperometric titration of uraniumSiobium gives a well-defined wave in very strongly acidic solu(VI) and uranium(1V) with 0.0672M cupferron in 50 ml. of 2 M sulfuric acid tions of both sulfuric and hydrochloric acids (Figure I ) ; thr wave in hydrochloric acid is not quite as sharp but is better de1. 0.0769 millimole of uranium(V1) 2. 0.1990 millimole of uranium(VI), run at one half the fined brcause of the larger diffusion current plateau. The minisensitivity of curve 1 3. 0.0199 millimole of uranium(1V) mum hydrochloric acid concentration necessary t,o obtain the full wave height is about 11.6L11(Table I, Figure 2 ) . ,4n increasing Tyndall effect appears on decreasing the hydrochloric acid concentration: in fact, after standing for several hours, a considrr:thle amount of niobic acid had precipitated from the i . 2 J I and Table I. Effect of Hydrochloric Acid Concentration upon 4.811 hydrochloric acid solutions. All of the polarographic test Height of Polarographic Ware of 1.16m.M Niobium(\-) solutions were prepared at the same time and m r e run in order, HC1 Concn., Niobium, HC1 Concn., Siobiuni, Avf ~ d pa. . .If Zd, Ha. starting with the 12Jf solution. -4hout 15 minutes was required 12.0 3.95 10.8 3.60 for each run, so that the last sample (4.831) n-ould have been run 11.6 4.00 9.6 2.80 ahout 2 hours after preparation. T h r 123r solution n-as rerun 11.5 3.90 7.2 0.63 11.4 3 80 4 8 0.33 after the last samole had been run: no decrease in current was found. It there__ ~ ~ _ _ -__ fore apprars that the decrease in the Table 11. Half-Wale Potentials and Currents of Uranium and Cupferron in niohiuni wave is the result of the hydroPresence of Each Other in 2 M Sulfuric Acid lytic formation of niobic acid, even in (Ciipferron Concentration 9.6M hydrochloric acid. (Uranyl Concentration 4 X lo-3.M) 4.5 x 10-3.11) Cupferron Under the conditions described, tanCupferron Uranium Uranyl talum does not uroduce a polarographic JI X 1OJ Ei/z. volt id, pa. E I , z , volt I d . pa. -M X IO3 - E L / %volt , td, p a . -~ 0.00 0.18 24.0 0.00 0.52 27.8 wave. 0.64 0 62 6.6 0.19 22 4 0.08 0.61 27.8 Polarographic Behavior of Uranium in 0.92 0.63 8.8 0.18 21.6 0.1 0.63 27.6 0.64 11.6 0.21 30.4 0.2 0.65 28 0 1.28 Presence of Cupferron. It had pre1 60 0.66 13.8 0.29 19.8 0.4 0 65 28.0 1.92 0.66 14.6 0.40 20.6 0.8 0.66 28.6 viously been noticed that, when cupfer2.56 0.66 18.0 8.48 21.4 3.20 0.66 20.0 0.52 22.0 ron was added in sufficient excess to a solution of uranyl ion in lOYc sulfuric ~
~~~
~
~
340
ANALYTICAL CHEMISTRY
required to reach the apparent end point. Consequently, the rapid decrease in uranium current found on adding cupferron was investigated polarographically by observing the effects of varying uranium or cupferron concentrations at a constant concentration of the other. The results of this study, summarized in Table I1 and Figure 4, indicate that the apparent decrease in current is due to thr shifting of the uranium wave to more negative potentials as cupferron is added; this shift in E112 of uranyl ion is not accompanied by an appreciable decrease in id. The cupferron wave ia also slightly shifted t o more negative potentials. This shift of naves occurs a t cupferron concentrations much too low t o cause complete complexation of t h e uranium present; therefore, it should be accompanied by a wave split. However, no w.tves other than the two attributable to uranyl ion and cupferron appear on the polarograms.
A28
-
0.6
-20 0
--t. .-0
>' 0.4
4
- 12
Lt'
0.2
-4
I
2 Cupferron, mM.
3
Figure 4. Half-wave potentials and diffusion currents of uranium and cupferron as a function of cupferron concentration E+ of cupferron i d of uranium(V1) 3. E + of uranium(V1) 4. id of cupferron
1. 2.
These studies indicated the desirability of performing titrations employing cupferron in the presence of uranyl ion a t an applied potential of -1.0 volt us. S.C.E., because the shift in E112 of cupferron is sufficiently small t o enable the wave to attain its full height at this potential. If the titration is performed a t -0.84 volt ( l j ) , the current increase after reaching the equivalence point will not be as rapid as before, because the potential of -0.84 volt occurs on the steeply rising portion of the wave rather than on the limiting current plateau. Recent polarographic studies on the uranium(S-I)-cupferron system a t lower acidities (16) indicate that complexation occurs in solutions approximately O . l J 1 in hydrogen ion. Hovr-ever, no such complexation in solutions 2.11 in sulfuric aFid was found in the present investigation.
Table 111. Titration of Zirconium in 10% IIrSOa in Presence of Uranium(IY), Cranium(\-I), and Kiobium(V) -~
Siieci+-
Added AIilliiiide
Taken
Zirconium. I\Iilliinole ~Found Deviatiun
0,0737 0,0757 0.04
0 08 0.12 0.20 0 08 0 20 0 04 0 04 0.08 0 08 0,022 0.01:'"
0.02.5" 0 0020 O.OL'5h 0.0::1 b 0 OOL'b
0.0737 0.075i 0.0757 0.0757
0,0757 0,0757 0 0000 0 0000 0 07.57 0,0757 0 0757 0,0757 0,073: 0.0737
O.Oi5i 0,075;
O.Oi5S
T O 0001
0.0765 0,0739 0,0757 0,0756 0.07SR 0.0759 0,0732 0. 000il
-0 0002 +0 0001
0.0000 0.1001 0.097D 0 1172 0.1191 0.0900 0 0794 0 0815 0.0851'
0 -0 -0 -0 -0
0000 0001 0001
0002 0005
+ o 0?$4 -0 0219 + O 0415 -0 0434 +O 0149 +O 0037 t o 0061 -0 0095 -0 0001 t o 0001 - 0 0003 +O 0141 + o 0131
0.0737 0,0755 0.07.57 0,0759 0.0757 0.0754 0.025c 0,0757 0,0897 0.0?3 C 0,073 0.0888 fl S i o h i u m precipitated b y hydrolysis: resulting suspension titratpd h Zirriiniuiii separated as pliospliate in iire8ence of H202. Zirconiuus separated as phosphate in absence of H202.
Attempted Amperometric Titration of Uranium. The amperometric titration of uranium(IV), which is precipitated quantitxtively by cupferron ( B ) , was att,empted. From a typical titratiou curve (Figure 3j, it is apparent that a considerable excess of cupferron must be present to initiate precipitation: direct titration of uranium(1V) is not possible. The instability of cupferron in acid solution effectively precludes a back-titration procedure. Moreover, the data in Table I J I show that it is not possible to tit,rate zirconium in the presence of uranium(IT*) rrithout precipitating the uranium. The fact that the uranium is more nearly completely precipitated when the uranium to zirconium ratio is small, rather than when it is large, also indicates that this is a case of coprecipitation. Because uranium(IS-) is readily oxidized t o uranium(YI), its presence does not affect the zirconium determination. Polarography of Uranium in Concentrated Hydrochloric Acid. Kolthoff and Harris ( 7 , 8) have described the polarographic hehavior of uranium(1-I) in 0.01 to 0.2.11 and in 1.0 to 2.0A.1 hydrochloric acid solutions. The fact that niobium gave a welldefined polarographic wave a t moderately negative potential iu 12J1 hydrochloric acid solution prompted a brief study of uranium in this medium. .4t 25.0" C., uranium(V1) gave a well-defined wave, whose E1/2cannot' be precisely evaluated because the toe of the wave merges with the anodic wave from mercury. Values of i J C were 9.2 f 0.1, which corresponds to I equal to 4.51. Prolegomena to the Analysis of Mixtures of Uranium, Niobium, and Zirconium. It Tyas first thought that the best method for analyzing mixtures of niobium and zirconium n-ould he to determine the sum of zirconium and niobium by titration with cupferron, and then determine one of these elements. ITOWever, titration of niobium under various conditions rerealed that, although niobium is quantitatively precipitated, it does not form a stoichiometric cupferrate. The ratio of cupferron to niobium varied from 2.7 to 3.8, depending upon the conditions of precipitation-e.g., acidity and rate of reagent addition. This indicates formation of a mixture of nioliium cupferrates. Typical titration curves of niobium with cupferron in 0.131 and in 2.11 (log,) sulfuric acid (Figure 5 ) show a sharp initial increase ill current when the first milliliter or P O of cupferron solution is added. Hoxever, when zirconium and niohium are titrated in the presence of each other, the niobium coprecipitates, so that satisfactory results for zirconium cannot be obtained (Table 111). Table I11 also s h o w the effects of various means of separating zirconium and niobium upon the titration results. Hydrolysis of
34 1
V O L U M E 28, NO. 3, M A R C H 1 9 5 6 niobium to niobic acid and titration of the resulting suspension is an attractive possibility because no separations are involved; however, an appreciable positive error results when this method is applied. Hoxyever, it is possible to titrate accurately 5 suspension of zirconium phosphate lvith cupferron (15); the method finally developed uses prior separation of zirconium by precipitation as the phosphate in the presence of hydrogen peroxide, followed by titration of the rcsuspc,nded phosphate. The fact that hydrogen peroxide is necessary to prevent precipitation of consideriihlc quantities of niobium is also shoivn in Table 111.
70
/
60
Cupterron Added,
Using another aliquot of the gelatin-containing solution arid the procedure previously described ( 1 5 ) , titrate the zirconium amperometrically with standard cupferron solution at - 1.O volt, us. S.C.E. Uranium, Niobium, and Zirconium. Transfer a solution of thr sample to a 150-ml. beaker; add sufficient Concentrated sulfuric acid to make the total amount of acid present 10 nil.; if oxalate is present, add 25 ml. of concentrated nitric acid. Evaporate until sulfur trioxide is evolved vigorously. Cool and dilute to 100 ml. in a volumetric flask. Pipet an aliquot of this solution (containing about 0.1 millimole of zirconium) into a 125-ml. centrifuge tube; add 50 ml. of 10% sulfuric acid, 3 ml. of 30% hydrogen peroxide, and 25 ml. of 10% sulfuric acid saturated with ammonium dihydrogen phosphat,e (about 25 grams per 100 ml. of acid). hIiv and centrifuge, then wash the zirconium phosphate SCVera1 times by centrifugation wit,h a solution prepared by mixing 50 ml. of the sulfuric acid-ammonium phosphate solution, 50 ml. of 10% sulfuric acid, and 3 ml. of 30% hydrogen peroxide. After xashing, suspend t'he zirconium hosphate precipitate in about 50 ml. of 10% sulfuric acid an$ titrate with cupferron (15). Alternatively, filter the zirconium phosphate on a small rapid filter paper such as Whatman KO.41, and, after washing, suspend the paper and precipitate in 10% sulfuric acid. Pulverize the paper v i t h a stirring rod and titrate the resulting SUBpension. Measure a second portion of the original sample solution into a 150-ml. beaker, add 5 ml. of concentrated sulfuric and 25 ml. of concentrated nit,ric acid, and heat unt,il sulfur trioxide is e v o l v d . Dissolve the residue in concentrated hydrochloric acid, transfer to a 100-ml. volumetric flask containing 1 ml. of 0.1% gelatin solution, and dilute to 100 ml. with concentrated hydrochloric acid. Add a portion of the latter solution to the polarographic cell, and, aft'er the removal of oxygen, record the polarogram.
ml.
Figure 5 . Amperometric titration of 0.0730 millimole of niobium(V) with 0.0648M cupferron 1. 2.
In 0.1M sulfuric acid In 2 M sulfuric acid
T h e determination of uranium and niobium in admixture was achieved simultaneously by a direct polarographic method. Calibration Data. The data in Figure 6 establish the direct proportionality to concentration of the wave heights of niobium( V ) and uranium( VI) in concentrated hydrochloric acid, and of uranium(V1) in 1070 sulfuric acid.
Concentration, mM. Figure 6.
PROCEDURES
Uranium and Zirconium. Transfer a sulfuric acid solution of the sample containing the equivalent of 10 ml. of sulfuric acid (add acid if necessary) to a platinum dish, and cautiously add 10 ml. of Tvater. While the solution is still hot, add dilute permanganate solution (about 0.001h') until the permanganate color persists. Add 2 ml. of concentrated hydrochloric acid and heat the solution until copious fumes of sulfur trioxide are evolved. Cool and dilute the residue to 100 ml. in a volumetric flask containing 1 ml. of 0.1% gelatin solution. Transfer a portion of this solution to the polarographic cell, and, after the removal of oxygen, record the uranium polarogram betn-een 0.0 and -0.5 volt, us. S.C.E. Determine the uranium concentration in the test solution by comparing the uranium wave height (determined geometrically or using a residual current correction) n i t h a standard curve. Calculate the amount of uranium in the original sample on the basis of the dilutions employed
Calibration curves
1. 2.
Uranium(V1) i n 12M hydrochloric acid Niobium(V) i n 1241 hydrochloric acid 3. Uranium(V1) i n 2.M sulfuric acid
Determine the height of the uranium wave between -0.3 and -0.4 volt vs. S.C.E. by com arison n-ith the residual current curve of concentrated hy%ochloric acid. Determine the niobium wave height directly without correction for the residual current polarogram. From the i d values thus obtained, determine the niobium and uranium concentrations from standard curves (Figure 6). Niobium Ores. Fuse the sample with potassium carbonate in a platinum dish; dissolve the reaidue in water with the aid of a little potassium hydroxide (18). After solution is complete, filter through a medium glass fritted funnel and transfer to a 400-ml. beaker. Add 10% sulfuric acid dropwise until the ~ o l u -
342
ANALYTICAL CHEMISTRY
-
Table I v .
..inalysis of Zirconium, -Millimole Taken Found
Saingle No.
0.0303 0.0303 0.0303 0.0303 0,0757 0.0757 0.0757 0 0757
Uranium-Zirconium hIixtures Cranium, Eiror, Millimole Error, c, 70 Taken Found IC
0.0306 0.0301 0,0300 0.0301 0.0759 0.0759 0.0751 0 0755
+0.99 -0.66 -0.99 -0.66 + O , 26 +0.26 -0.79 -0.26 .4v . 1 0 . 6 oxidized t o Con++with
-1.73
+l.Ol -0.75 -1.38 +1.25 -1.51 L0.63 -0.50 lt1.1
Assays of a Niobium Ore. The polarographic determination of niobium was aDDlied to the anal\,& of a niobium ore Rrhich .I had the following chemical analysis: 5%
Si02 FeO MnO SbnOa TanOs Sn0n
3 42 9.24 21.42 34.93 29,50 0.20
A1203
Ti02 CaO
Polarographic analysis gave 35.3, 34.9, 35.1, and 31.8% niobium pentoxide, or an average value of 35.1 f 0.3’%, xhich sis. is in good agreement with the knon-n -~ . ~... value of 34.9%. The alkaline fusion procedure was chosen for solution of Table V. Analysis of IIixtures of Uranium, Niobium, and Zirconium the sample because it prevented the iron Zirconium K i obi um Uranium and titanium in the sample from disMillimole E ~ ~ Millimole ~ ~ , E ~ ~ ~ ~ , Sample JIillimole Error, solving. Both of these would interXo. Taken Found ‘Z Taken Found % Taken Found yo 1 0.755 0.755 -0.3 0.464 0.458 -1.3 0,199 0.202 +1.5 fere in the polarographic determinat,ion 2 0.757 0.759 ~ 0 . 3 0.464 0.461 +0.6 0,199 0.199 0.0 of niobium. 3 0.757 0.754 -04 0.464 0.470 +1.3 0,398 0,392 -1.5 4 0.757 0.754 -0 4 1.160 1.170 +O 9 0.398 0,393 -1.3 The small amount of tin in the ore was .5 0.757 0.761 ~ 0 . 5 1.160 1.143 -1.5 0.597 0.604 +l.2 determined as niobium, because Ell2 for fi 0.757 0.751 -0.8 1.160 1.156 -0.3 0.597 0,600 C0.5 .4v. 1 0 . 4 3kl.O lt1.0 tin(1V) in concentrated hydrochloric acid solution is almost the same as for nicbiumiV). If an aDDreciabk :tmount of tin is present, it would be necessary tion is acidic; then add 5 ml. of concentrated sulfuric and 5 ml. to perform a preliminary separation or t o correct i, of niobium of concentrated hydrochloric acid (the latter reduces any mangafor that of the tin present; the tin in the sample could be readily nese oxidized during the dissolution process). Evaporate until determined polarographically ( I S ) . sulfur trioxide is evolved; cool and dilute to 100 ml. with concentrated hydrochloric acid in a volumetric flask containing 1 ml. The determination is rapid after solution of the sample has of 0.1% gelatin solution. Introduce the resulting test solution been achieved. However, largely because of the timc nrccssary into the polarographic cell, and record the polarogram after the for complete solution, about 4 hours are required t o perform an removal of oxygen. From t h e Zd obtained and a standard curve, anal yei s, calculate the niobium concentration and then the niobium percentage. a
.4dded as U’4 and ~
~~
~~
~
permanganate during analy-
~~~
~
~
~~~~
~
__
DISCUSSION
ACKNOWLEDGMENT
Mixtures Containing Uranium and Zirconium. The results of the analysis of mixtures of both oxidation states of uranium with zirconium are given in Table IV. These results were obtained by the procedures described, using direct polarographic determination of the uranium as uranyl ion and amperometric titration of the zirconium in the presence of uranyl ion. The foro uranium, are of the errors, 2 ~ 0 . 6 7for ~ zirconium and = t l , l ~ order of magnitude expected from the methods used. Although the sample ranges cover only 0.03 to 0.075mM zirconium and 0.04 to 0.08mX uranium solutions, these limits probably could be safely extended by a factor of 10 from either end. Although interferences were not specifically investigated, the titration of zirconium is carried out under conditions similar t o those previously used (16), where iron(III), vanadium(T’), and large amounts of tin(1V) mere found to interfere; titaniuni(IT’), hafnium(IV), and niobium(V) would also interfere. .4ny ion which is reduced in sulfuric acid solution in the potential region of about -0.1 t o -0.4 volt us. S.C.E. would interfere in the polarographic determination of uranium. Mixtures Containing Uranium, Niobium, and Zirconium. The results of the procedures described, when applied to mixtures of uranium, niobium, and zirconium, indicate good agreement \\ith the theoretical values (Table V). The average errors of f l . O , f l 0, and ~ t 0 . 5 for 7 ~ uranium, niobium, and zirconium, respectively, are perhaps somewhat lower than expected. Starting with a liquid sample, the procedure requires between 1 and 1.5 hours t o carry out a duplicate analysis for all three elements. The sample composition can vary within rather wide limits, except that the volume of the phosphate precipitate limits the upper end of the usable zirconium concentration range. Because the procedure employs the phosphate-hydrogen peroxide separation of zirconium, only hafnium would precipitate with zirconium. It would be determined along with zirconium by the cupferron titration.
The authors nish to thank the Atomic Energy Commission which helped support this n-ork. LITERATURE CITED
(1) Colichman, E. L., Ludewig, IT’, H., ASAL. CHEir. 25, 1909 (1953). (2) Coaai, D., Vivarelli, S.. Ricerca sci. 23, 2244 (1953). (3) Coaai, D., Vivarelli, S., Z . Elektmchem. 57, 406 (1953). (4) Ibid.,58, 177 (1954). (5) Elving, P. J., Olson, E . C . , ASAL. CHEM.28, 251 (1986). (6) Furman, N. H . , lIason, 11’. B., Pekola. J. S., Ibid., 21, 1328 (1949). (7) Harris, W. E., Kolthoff, I. AI,, J . Am. Chem. SOC.6 7 , 1484 (1945). (8) Kolthoff, I. A I . , Harris, TV. E., Ibid.,68, 1175 (1940). (9) Kolthoff, I. l I . , Lingane, J. J., “Polarography,” 2nd ed., Interscience, New York, 1952. (10) Komyathy, J. C., hlalloy, F., Elring, P. J., - 4 s . k ~ . (-HEMI. 24, 431 (1952). (11) Krylov, E. I., Kolevatova, V. S., Samarina, V. d.,Doklady Akad. SaukS.S.S.R. 98,593 (1954). (12) Laubengayer, A . W., Eaton, R . B., J . A m . Chem. SOC.62, 270 (1949). (13) Lingane, J. J.,Ibid.,67, 919 (1945). (14) Olson, E. C., Ph.D. thesis, University of lfichigan, 1955. (15) Olson, E. C., Elving, P. J., =INAL.CHEX. 26, 1747 (1984). (16) Rulfs, C. L., Elving, P. J., J . Am. Chem. SOC.77, 5502 (1955). (17) Schoeller, W. R., “Analytical Chemistry of Tantalum and Xiobium,” Chapman & Hall, London, 1937. (18) Simpson, S . G., Schumb, W ,C., J . Ani. Chem. SOC.53, 921 (1931). (19) Vandenhosch, IT., Bull. SOC. chim. Belges 58, 532 (1949). (20) Zeltzer, S., Collection Czechoslor. Chem. Communs. 4, 319 (1932). RECEIVEDfor review October 19, 1955, Accepted December 5 , 1955.
