solution. Tne average plutonium recovery was 98.8% with a coefficient of variation of 0.8. Figure 1 shows the decontamination associated with each step in the proposed procedure for 1-month- and 1.5year-cooled fission product mixtures. The differences shown for the over-all decontamination of zirconium and/or niobium and of ruthenium are undoubtedly dependent upon the past history of each sample. The 1-month-cooled material \vas obtained by irradiating about 2 mg, of enriched uranium oxide in a thermal neutron flux and dissolving in nitric acid. The older fission product mixture was obtained from a plant process stream of a nitric acid dissolu-
elective Prec
LITERATURE CITED
tion of an enriched uranium, aiuminumclad, fuel element. That the ruthenium and zirconium and/or niobium are in different forms in each sample is highly probable. The over-all decontamination of lo4 to 106 for ruthenium and zirconium-niobium is adequate to permit an alpha pulse height analysis with a Frisch grid chamber with no interference from beta-gamma activity. The uranium activity carried through was less than 0.05%.
(1) Maeck, W. J., Booman, G. L., Elliott, M. C., Rein, J. E., ANAL. CHEY. 3Q,
1902 (1968). (2 Ibid., 31, 1130 (1959). (3j I bid., 32, 605 (1960). (4) Moore, F. L., Ibid., 30, 1368 (1958). ( 5 ) Moore, F. L., Hudgens, J. E., Ibid., 29, 1767 (1957). (6) Murray, B. B., U. S. Atomic Energy Commission Rept. DP-316(1958). (7) Schneider, R. A, Harmon, K. &I., Ibad., HW-53368(1957). RECEIV~D for review May 16, 1960. Accepted August 17, 1960. Division of Snalytical Chemistry, 138th Meeting, ACS, iYew York, N. Y., September 1960. The Idaho Chemical Procesaing Plant la operated by Phillips Petroleum Co. for the U. S. Atomic Energy Commisaion under Contract No. AT(10-1)-205.
ACKNOWLEDGMENT
The authors thank James A. Merrill for advice on statistical design of experiments.
n of Silver Halides Solution
Separation of Iodide, romide, and Chloride Using Volatilization of Ammonia F. H.
FiRSCHlNG
Department of Chemisfry, Universify of Georgia, Athens, Ga. Silver iodide, silver bromide, and silver chloride are selectively precipitated from homogeneous solution using controlled evolution of ammonia. All three silver halides are soluble in concentrated ammonia, because of the formation of the silver-ammonia cornplex. As ammonia escapes from the solution, the silver iodide precipitates first, then the silver bromide, and finally the silver chloride. The solution i s filtered in three suitable pH ranges, thus separating the three silver halides.
N
methods have been developed for determining the halides in the presence of each other. However, no precipitation method for determining one of the halides in the presence of another has been available. Previous methods for precipitating silver halides from homogeneous solution have been limited to the chloride (9). Britton (1) studied the silver halides in concentrated ammonia. Hayek et al. (3) precipitated insoluble silver compounds from ammoniacal solution by volatilization of ammonia. The method described in this paper is based on the different solubilities of the silver halides and on the formation of the silver-ammonia complex. The concentration of free silver ion is held to a very small value in concentrated amWMEROWB
1876
a
ANALYTICAL CHEMISTRY
ion concentration gradually increases and silver bromide precipitates. At the point where the silver bromide is almost quantitatively precipitated, the chloride is still soluble. Silver bromide is filtered off and ammonia is again allowed to escape from the solution. The silver ion concentration increases until the silver chloride precipitation is complete. Thus a separation and determination of iodide, bromide, and chloride can be made from the same solution using but one reagent, the silver-ammonia complex. The silver halide precipitates are crystalline and easily filtered and washed.
monia, in which all three silver halides are soluble. As ammonia escapes from the solution, the silver ion concentration gradually and uniformly increases, causing silver iodide, the most insoluble halide, to precipitate selectively in the presence of both bromide and chloride. The solubility products for the silver halides are: AgI = 1.6 X 1 P 8 , AgBr = 7.7 X l V 3 ,AgCl = 1.6 X 10-10. At the point where the silver iodide is quantitatively precipitated, the bromide and chloride are still soluble. The eilver iodide precipitate is filtered off and ammonia is again allowed to escape from the eolution. The silver
b Figure 1 . Influence of pH on precipitation of silver halide
5
P
I
\
PROCEDURE
Add a soluble sample containing about 0.2 mmole of iodide (about 30 mg. of sodium iodide) to a 400-ml. beaker. Add 30 mmoles of ammonium nitrate, dissolve in about 20 ml. of water, and dilute to about 200 ml. with concentrated ammonium hydroxide. Prepare the precipitant solution by adding about 0.4 mmole of silver nitrate to 100 ml. of concentrated ammonium hydroxide, Add the precipitant solution directly to the iodide solution in one portion. A clear uniform solution results. Add 3 drops of thymolphthalein indicator solution and place on a low temperature hot plate for about 2 hours until the blue color fades noticeably. K h e n the p H of the solution, a t room temperature, is in the range 9.8 to 10.2, filter the cooled solution through a tared glass or porcelain filtering crucible. mash the precipitate with several small portions of distilled water, dry a t 110" C. for at least an hour, and weigh as silver iodide. Place the filtrate and washing in a 400-ml. beaker, and add silver nitrate solution (pH 10 or higher), in amount approximately equivalent to the suspected bromide content of the sample. Add 5 drops of phenolphthalein solution, and place on a low temperature hot plate for about an hour until the pink color of phenolphthalein is completely discharged. The pH of the solution is nom approximately 9. Carefully continue the gentle heating for about 20 minutes until the solution, a t room temperature, is in the p H range 8.6 to 8.7. Filter the cooled solution, wash and dry the precipitate as above, and weigh as silver bromide. Place the filtrate and washings in a 400-ml. beaker, and add silver nitrate solution (pH 8.7 or higher), in amount approximately equivalent to the suspected chloride content of the sample. Place on a low temperature hot plate until the solution is below p H 7.3. Filter the cooled solution, wash and dry the precipitate as above, and weigh as silver chloride.
Table I.
(0.2 mmole of iodide, 25.4 mg., taken) PH 10.1 10.1 10. 1 10. 1 10.0 9 .8 10.0 9 .8 9 .7 9 3
Bromide, Mmoles
Chloride, Mmoles
Iodide Found, M g .
0.2 2.0 2.0 6.0 0.8 0.2
...
24.8 23.5 23.9 36.6 24.6 25.1 24.8 24.5 25.7 26.3 25.2 24.6 25.2 25.3 26.0 25.1
...
... ..*
... ...
... ...
0.8
30 9.0 21 0.2 0.2 0.2 0.2 0.2 0.2
,..
...
i0.i
0.2 0.2 0.2 0.2 0.2 0.2
9.8 9.8 9.8 9.7 9.7
bromide can be separated from silver chloride in the p H range 8.6 to 8.7. Table I shows that iodide can be separated and determined in the presence of 10 times the molar concentration of bromide and 150 times the molar concentration of chloride, in the p H range 9.8 to 10.2. Results using iodine-131 as a tracer, given in Table 11, show that silver iodide is quantitatively precipitated near p H 10. Table I11 shows that bromide can be determined reasonably well in the presence of an equal molar concentration of chloride. The interference of chloride increases markedly as the p H decreases. The p H range of 8.6 to 8.7 should be measured with a pH meter,
Table 111.
yo Error
-
2.4 7.5 5.9 +44 3.2 1.2 2.4 3.5
-
+4- 31 .. 52
- (3.8 -
3.2 0.8
+- 0.4 2.4 1.2
Table II. Precipitation ob.Silver Iodide Using Iodine- 1 3 1 as Tracer
(0.2 mmole of iodide, 25.4 mg., taken)
Iodide in Filtrate (Radiometric), PH
70
Iodide Found (Gravimetric),
9 4 9.8 9.8 9 9 10 3
0.4 1 1 1.0 0 6 2.1
23.3 25.1a 24.6 25.0 24 6
5
Gravimetric % Error
Mg.
-0.4 -1.2 -3.2 -1.6 -3.2
0.2 mmole bromide present.
Precipitation of Silver Bromide in the Presence of Chloride
(0.20 mmole of bromide, 16.0 mg., taken)
DISCUSSION
Preliminary experimental work required the preparation of a graph (Figure 1) showing the percentage of silver halide precipitated at various p H values. Each solution contained 0.2 mmole of halide, 0.4 mmole of silver nitrate, and 30 mmoles of ammonium nitrate in 300 ml. The large concentration of ammonium ion is necessary, so that the presence or absence of ammonium ealts in any sample will not noticeably affect the p H measurements. The p H of the solution is used as an indicator for the ammonia concentration. This is possible when a large concentration of ammonium ion is present, because changes in hydroxyl ion concentration will then correspond to changes in ammonia concentration. Figure 1 shows that silver iodide can be separated from silver bromide in the p H range 9.8 to 10.2. Silver
Precipitation of Silver Iodide in the Presence of Bramide and Chloride
PH 8.9
8.7 8.5 8.5 8.2
Chloride, bImole
Bromide Found (Grav.), Mg.
Bromide
0.20 0.22 0.22 0.40 0.22
15.6 15.6 16.5 17.0 17.8
++- 236 ... 125
using either a high temperature glass electrode in the warm solution or a regular glass electrode in the cooled solution. This p H range was selected because the solubility loss resulting from the incomplete precipitation of silver bromide is compensated by the coprecipitation of chloride. These compensated errors are only several per cent in this p H range. I n the separation of bromide and chloride the excess silver reagent must be controlled. If the excess is too lotv,
% Error
-
2.5
+11.2
Table IV.
Chlorine in Ppt. Corrected (Radiometric), Bromide, % FourLd,Mg.
...
...
4.7 7.9
15.0 15.4
...
...
21
15.0
Precipitation of Silver Chloride
(Chlorine-36 as tracer, 0.21 mmole of chloride taken) Chloride PH in Filtrate 7.3 6.6 6.5 6.4
1.4 1.4 1.2 1.2
VOL. 32, NO. 13, DECEMBER 1960
1877
incbmplete bromide precipitation is expected. If the cxcess is too high, the chloride co;?recipitation increases. This means that the general Iange of the halides in the sample must be known; otherwise a double precipitation would be necessary to establish the purity of the bromide and chloride precipitates. R,esults given in Table IV show that chloride is quantitatively precipitated below piE 9.3, and that solubility losses are slight. Iodide can be determined in the presence of an equal molar c o n c e n h tion of bromide and chloride (Table V). Bromide and chloride can also be determined reasonably well on the same sample. The range of errors is of the same order of magnitude as in the potentiometric method (4) for analyzing mixed halides. However, the potentiometric method requires a set of correction equations t o achieve this accuracy. It can be applied to a wider range of halide mixtures than the method described here. A survey of passible anion inter-
Table V.
Precipitation of Silver Halides
(Average of four determinations) Taken, Found, Mg. Mg. iodide 25.4 25.2 Q 0 . 2 Bromide 16.0 15.9 Q 0 . 5 Chloride 7.1 7 . 3 f 0.5" Corrected for reagent contamination of 0.5 mg. 5
ferences showed that anions forming silver salts more soluble than silver bromide will not interfere in the determination of iodide, and that anions forming silver salts more soluble than silver chloride will not interfere in the determination of bromide. Anions such as cyanide and thiocyanate, which form silver salts with a solubility close to silver bromide, would be expected to interfere in the determination of bromide. Anions such as phosphate and carbonate, which form silver salts with a solubility close to silver chloride,
would be expected to interfere in the determination of chloride. Experimental results using the described procedure show that equal molar concentrations of cyanide and thiocyanate did not interfere in the determination of iodide. Equal molar concentrations of arsenate, carbonate, iodate, oxalate, and phosphate did not interfere in the determination of either iodide or bromide. Equal molar concentrations of sulfate did not interfere in the determination of iodide, bromide, or chloride. LITERATURE CITED
(I) Britton, H. T. S., AnaEysl 50, 601 (1925). (2) Gordon, L., Peterson, J. I., B u t t , B. P., ANAL.CHEM.27,1770 (1955). (3) Hayek, E., Hohenlohe-Profanter, Hohenlohe-Profanter M., Marcic, IB., Beetz, E., Angew. &hem. 70.307 fimx). 70,307 (1958). (4) Martin, A. J., ANAL. CHEM.30, 233 (1958). RECEIVEDfor review April 11, 1960. Accepted August 1, 1960. Presented in part before the Division of Anal ical Chemistry, 137th Meeting, ACS, 8eveland, Ohio, April 1960.
rialkyl Selective
xtractants for Silver and Mercury
T. H. HANDLEY Analyfical Chemisfry Division, Oak Ridge Nafional Laboratory, Oak Ridge, Tenn. JOHN A. DEAN Department o f Chemistry, University of Tennessee, Knoxville, Tenn.
fx- Triiso-octyl thiaphosphate and tsi-nbutyl thiophosphate, neutral esters of monothiophosphoric acid which contain an isolated P=S group, are Isighiy selective extractants for silver and mercury(l1) ions in nitric acid medium from the 35 elements tested. The extracted species are formed rapidly and the partition is easily reversed. From aqueous solutions 6M in nitric acid, and for a 0.67M solution of the reagent in carbon tetrachloride, the partition coefficient at room temperature for silver exceeds 100; for mercury it ie 90. The influence of a wide range of nitric acid, reagent, and silver concentrations, and the e of temperature, diverse acids, and salting agents upon the partition equilibrium have bean investigated. Struciwres are postdated for the soivaree formed between rke reagent molecules and nitric acid und the metai nitrates. e
ANALYTECAL CHEMISTRY
contains numerous references to nonionic phosphoryiated reagents, such as tributyl phospkate, as extractants for metallic salts (3, 5, 7, 9 ) . Their application t o the purification of uranium and other metals by solvent extraction has been well established. The extraction properties of the phosphorylated reagents are influenced by the nature of the substituents attached to the phosphoryl group, P=O (a, 4). However, it was not known in what manner the properties of nonionic phosphorylated reagents would be influenced by the replacement of the isolated P=O group by a P=S group. The semipolar sulfur atom is the sole structural difference between the phosphates and the monothiophosphates. The employment of triiso-octyl thiophosphate or of tri-nbutyl thiophosphate, neutral esters of monothiophosphoric acid, as the extracting reagent has revealed a high HE LITERATURE
degree of selectivity for silver and mercury(I1) from a nitric acid medium. Earlier Pishchimuka (8) had found few solid salts capable of forming complexes with trialkyl thiophosphates. EQUILIBRIUM DISTRIBUTION STUDIES
Materials. TWOthiophosphates were tested: tri-n-butyl thiophosphate (TBPS) briefly, and triiso-octyl thiophosphate (TOTP) extensively. Both were obtained from Peninsular ChemResearch, Inc., Gainesville, Fla. The butyl compound was used without further purification. However, the octyl derivative was found t o contain approximately 0.00095N amount of an acidic component, pTesumably a dialkyl monohydrogen thiophosphate. Consequently, the reagent was purified by passing a solution of the reagent in carbon tetrachloride through a column of Fisher chromatographicgrade alumina. No acidic component was detected after purification; the
