APPLICATIONS
Table 11.
Effect of Foreign Cations on Recovery of Nickel
Amount, mg. 100 100 190 0.05 100
Complexing agent NHdAc, tironb NHdAc, tironb NHaSCN NaF; [Fel = [F-] 600 Tironb Tartaric acid Tironb Tironb Tartaric acid Tartaric acid Tironb
Recovery of 51 rg. of nickel, yo 100 101 99 101 100 99 101 100 98 101 99
Ion PH Cerium(1V)a 5 Chromium(111) 5 CoDDer(1I)c 7 Iron( 111) 7 XLlanganese( 11) 6 Rare earthsd ... 5 Thorium( IT) 100 5 Tin( IIT)n 100 11 100 Titanium(I T ) 8 Vanadium( V ) 100 8 Zirconium(IV) 100 11 Reduced with hydroxylammonium chloride. 4,5-Uihydroxy-m-benzenedisulfonicacid. Reduced with sulfite. d 19 mg. neodymium, 23 mg. of samarium, 6.5 mg. of praseodymium, 42 mg. of erbium, and 17 mg. of thulium.
__
anions on the determination of 51 r g . of nickel by extraction of the complex into xylene was investigated. A solution containing a suitable concentration of ion was taken and the p H was buffered at 7 with ammonium acetate. Ten milliliters of a saturated solution of 4 - tert - butyl - 1,2 - cyclohexanedionedioxime were added and the solution was equilibrated with xylene. Noninterfering anions in 100-mg. amounts are acetate, bromate, bromide, chloride, chromate, citrate, fluoride, iodate, nitrate, oxalate, perchlorate, sulfate, sulfite, and tartrate. I n the presence of citrate, complex formation is slower. Cations
~
r
which do not interfere in 100-mg. amounts are ammonium, arsenic(III), barium, cadmium, calcium, lead, lithium, magnesium, potassium, silver, sodium, and zinc. The effects of other diverse ions are listed in Table I. Lower recovery of nickel occurred in some instances when other foreign ions such as Ce(IV), Cr(III), Cu(II), hln(II), Sn(IV), Ti(IV), and V(V) were present. When suitable masking reagents were added, nickel was quantitatively recovered (Table 11). Nickel was separated from cobalt(I1) by using the hydrochloric acid anionic exchange method of Kraus (4).
This method is simple, sensitive, rapid, and accurate and has been used in this laboratory for the determination of traces of nickel in scandium, yttrium, and rare-earth samples. ACKNOWLEDGMENT
The authors express their appreciation to J. J. Richard for preparing 4tert- butyl- 1,2-cyclohexanedionedioxime and for the carbon and hydrogen analyses. LITERATURE CITED
(1) Banks, C. V., Hooker, D. T., Richard, J. J., J. Org. Chem. 21, 547 (1956).
(2)Dale, J. M., Banks, C. V., “Treatise on Analytical Chemistry,” I. M. Kolthoff, P. J. Elving, eds., Part 11, Vol. 2, Interscience, Sew York, 1962. (3) Hooker, D. T.,Banks, C. V., U . S. Atomic Energy Comm., ZSC-697, hlarch 1955. (4)Kraus, K. A., Xelson, F., A S T M Special Technical Publzcation Xo. 195 (1958). (5) McDowell, B. L., Meyer, A. S.,Jr., Feathers, A. E., Jr., White, J. C., ANAL.CHEM.31, 931 (1959). (6) Voter, R. C., Banks, C. V., Zbid., 21, 1320 (1949).
MARYM. BARLING CHARLES V. BANKS Institute for Atomic Research and Department of Chemistry Iowa State University Ames, Iowa WORKperformed in Ames Laboratory of U. S. Atomic Energy Commission.
Removal of Radioactive Actinides and Lanthanides from Aqueous Solutions with Calcium Fluoride Prior to Flame Photometric Determination of Lithium SIR: The Tramex ( 2 ) solvent extraction process is used to separate americium and curium from the lanthanide elements. The aqueous feed to the process contains about 11JP lithium chloride. The actinides are extracted into the solvent, which is a high molecular weight tertiary amine diluted with diethylbenzene. Because the extraction coefficients of americium and curium are strongly dependent on the lithium chloride concentration, the lithium concentration in the feed solution must be known to within +2% for adequate process control. Flame photometry is suitable for the analysis of lithium, but extensive shielding and containment facilities are needed to house the flame photometer and to filter the off-gases unless the lithium is first separated from the radioactive elements. A column of calcium fluoride absorbs trivalent lanthanide and actinide elements ( I ) , which are the 2360
ANALYTICAL CHEMISTRY
major source of alpha and beta radiation in the feed solution, while lithium is not retained. Thus, the lithium in the column effluent can be analyzed in a normal manner by flame photometry. EXPERIMENTAL
Pretreatment of calcium fluoride, pretreatment of glass beads, and preparation of the calcium fluoride column have been described ( I ) . Separation Procedure. Dilute the Tramex feed solution 1000-fold with 0.05M nitric acid. The alpha activity of the dilution should be 2 X 108 d.p.ni. (disintegrations per minute) per ml. or less and the lithium concentration approximately 0.01Ji. Into a 15-ml. centrifuge cone containing approximately 0.5 ml. of 0.05M nitric acid, pipet 500 ~ 1 of. the 1000-fold dilution and mix. To the cone add 1 drop of concentrated ammonium hydroxide and mix. Wash the calcium fluoride column
with 2 ml. of 0.121 ammonium hyl droxide-0.005M ammonium nitrate solution and discard the wash. Place a clean 15-ml. graduated centrifuge cone under the column and then carefully transfer the sample solution to the column. Adjust the flow through the column to approximately 1 drop per 15 seconds. Do not allow the liquid level to drop below the top surface of the calcium fluoride. Wash the centrifuge cone that contained the sample with three 2-ml. portions and a final 1-ml. portion of 0.1M ammonium hydroxide-0.005M ammonium nitrate solution; transfer the individual washes to the column. Collect the washes with the feed effluent. During the final wash, close the stopcock on the column just before the liquid level reaches the top of the calcium fluoride. Dilute the effluent and washes to 10.0 ml. with 0.1J1 ammonium hydroxide-0.005M ammonium nitrate. Stopper the cone and mix well. Verify the alpha and beta activity
of the solution by mounting an 10O-bl. aliquot for gross a- and gross @-counting. Determine the lithium concentration of the solution by flame photometry. (The working curve should be prepared by analyzing standard solutions of lithium in 0.1V ammonium hydroxide0.005N ammonium nitrate.) The calcium fluoride column may be used for a t least three more sample aliquots. RESULTS AND DISCUSSION
The mechanism for the removal of trivalent lanthanides and actinides from solution by calcium fluoride and the factors affecting the performance of the calcium fluoride column have been described ( I ) , The highest decontamination factors are obtained when the sample and washed are basic. The wash solution, 0.1N ammonium hydroxide, is made 0.005M in ammonium nitrate, which serves as an electrolyte to prevent peptization of calcium fluoride and breakthrough of radioactivity. Four synthetic samples, each containing 1.2 x 1 0 8 d.p.m. of americium-
241 alpha activity, were passed consecutively through a single calcium fluoride column. Because the respective decontamination factors, (a d.p.m. in feed)/(a d.p.m. in effluent), were 7.5 X lo6, 5.0 X lo6, 2.5 X lo6, and 7.5 X lo6, a column can be used for at least four samples. The degree of separation of lithium from the trivalent actinides and lanthanides was determined with 16 simulated Tramex feed solutions, each containing 1.2 x 108 a d.p.m. of americium-241. A separate calcium fluoride column was used for each sample. The average decontamination factor was 5 X 106. The effluent and wash solutions from seven of these samples contained less than detectable activity representing complete removal of activity by the calcium fluoride column. Twelve simulated Tramex feed solutionq were passed through four calcium fluoride columns (three samples per column) and were analyzed for lithium by flame photometry. Each of the synthetic samples was 11. O M in lithium.
The results of the twelve analyses averaged 10.7-11 lithium (97.3% recovery) with a relative standard deviation of 1.7% ( n = 12). One actual feed s d u tion containing 10' CY d.1i.m. and 1.5 X lo7 p d.1i.m. per sample aliquot was analyzed for lithium with a relative standard deviation of 1.8% ( n = 5). This method is being used routinely a t the Savannah River Laboratory. ACKNOWLEDGMENT
The author acknowledges the assistance of E. G. Orebaugh, who performed the flame photometric analyses. LITERATURE CITED
(1) Holcomb, H. P.,
A . v . 4 ~ . CHEM.36, 2329, (1964). ( 2 ) Leuze, R. E . , Bavbarz, R. I)., Weaver, Boyd, Yucl. Sci. Eng. 17, 252 (1963).
H. PERRY HOLCOMB Savannah River Laboratory E. I. du Pont de Semours & Co. Aiken, S. C. WORK done under contract AT(07-2)-1 with the U. S. Atomic Energy Commission.
Kinetic Inhibition of Cerium(lV) Reduction by Oxalic Acid SIR: I n a previous paper ( 2 ) we reported on a detailed kinetic study of the cerium(1V)-oxalic acid reaction in sulfate media t o provide basic information useful in choosing optimum reaction conditions for analytical titrations. Our study of this reaction has now been extended t o conditions which prevail a t the beginning of a titration-the situation where one of the reactants is present in great excess. The primary aim of the experiments reported here is to further confirm the proposed mechanism ( 2 ) and, if possible, to explain the anomalous induction period described by Rao, Mohan, and Sastri (3) for the first addition of cerium(1Vj to excess oxalate in sulfuric acid media. Using the classification scheme of Anbar ( I ) , 01 r data for the mechanism fit the sequence MX,+a (stable) Lj 2X J I X , - l L + ~ (unstable]+ MX,-l +h products where Ai', X, and L stand for cerium(IV), sulfate, and oxalate, respectively. According to Taube (4, 6), a likely consequence of this mechanism, if n > 1, is that the specific rate of the oxidationreduction reaction should increase, pass through a maximum, and again decrease as the ratio of I, t o JZX,+a is increased. We tested this hypothesis,
+
+
+
using the techniques described in the first paper ( 2 ) )by following the kinetics of cerium(1V) disappearance in solutions containing a 2- 120-fold excess of oxalate under otherwise identical conditions. The results are summarized in Table I and show that the specific rate constant for the cerium(IV)-oxalate react:on indeed passes t,hrough a maximum and then decreases as the ratio of oxalate to cerium(1V) is further increased.
Table I. Effect of Excess Oxalic Acid on Specific Rate Constant 4 08 x 10-4M Ce(IV), 0 5M H280r, 5.0 + 0.05" C.
Oxalic acid, M 0 0 0 0 0 0 0
050 025 020 010 005 002 001
Specific rate constant, sec. -l 0 0 0 0 0 0 0
022 043 093 093 085 049 021
The most probable mechanistic explanation for the observed trend involves the formation of higher
oxalato complexes of cerium(1V) by successive replacement of sulfate ligands by the reducing agent. In selective oxidations of this type such complexes tend to be less reactive than the 1 : l intermediate (5). The oxalate to ceriuin(1V) ratio a t maximum specific rate reflects the formation constant of t'he intermediate and is consistent with independent optical measurements ( 2 ) . The principal analytical consequence of this kinetic complication will be an apparent induction period a t the beginning of titrations where crrium(1V) is titrated into excess oxalate. R'e believe that the anomalous results described qualitatively by Rao, Mohan, and Sastri (3) are caused by t,his effect. LITERATURE CITED
( 1 ) Anbnr, XI., Surnnier Symposium on
Inorganic lfechanisms (ACS), Lawrence, Kan., June 1964. ( 2 ) El-Tantawy, Y. A., Ilechnitz, G.A , , ANAL.CHEM.36, 1774 (1964). ( 3 ) Rao, (>. P., lfohari, 1'. G.,Sastri, &I. S . , 2. =Lnal. C h e m . 156, 338 (1957). ( 4 ) Tauhe, H . , .J. L A t u . Chem. SOC. 69, 1418 (1947). (5) Ibid., 70, 1216 (1948).
G. A. RECHNITZ Y. A. EL-T.4NTAR.Y
Universit . of Pennsylvania Philadelpha, Pa. VOL. 36, NO. 12, NOVEMBER 1964
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