This could undoubtedly be improved by increasing the ligand to metal ratio. Extraction of the Chelate. I n previous work with hydroxamic acids, advantage has been taken of the fact t h a t some chelates are considerably more soluble in organic solvents t h a n in aqueous solution. I n some cases the color of the chelate is more intense in the organic phase t h a n in the aqueous phase. Thus, Wise and Brandt (5) have developed a method for determining vanadium(V) by extracting vanadium benzohydroxamate with 1-hexanol and measuring the absorbance. The molar absorptivity for the chelate in the aqueous solution is 1 x l o 3 while in 1-hexanol it is 3.5 X 103. Since nicotinylhydroxamic acid is quite similar to benzohydroxamic acid, an attempt was made to find an appropriate organic solvent for extracting
the chelate. Visual examination revealed that none of the organic solvents tried would extract the chelate. Those solvents tried were: benzene, bromoethane, carbon tetrachoride, chloroform, diethyl ether, diisobutyl ketone, ethyl acetate, ethyl benzoate, heptaldehyde, n-hexanol, isoamyl alcohol, skelly B, and toluene. This is in keeping with Feigl's rule. Effect of Foreign Ions. T h e interfering ionu have been studied quite extensively by Dutta (S) with regards to the &In system. It should be pointed out that uranium(V1) and Ti(1S') interfere a t all concentrations employed. This is in addition to Dutta's work. Stability Constants. The stability constants were determined by the method of Bjerrum ( I ) . The K n of the ligand, was found to be 8.2 X at an ionic strength of 0.1. Kai and Kaz for the Mo(V1) chelate were 5 X
and 2 X These values are also for an ionic strength of 0.1. The calculations aere made with an 113111 1620 programmed for a constant pH increment. The experimental conditions employed were a 10: 1 ligand to metal ratio, 0.01JI solutions, 25' C.. and ionic strength adjusted with SaC104. LITERATURE CITED
( I ) Bjerrum, "Metal A4mmineFormation in *Aqueous Solution," P. Haase and Son, Copenhagen, 1941. ( 2 ) Dhar, S. K., Das Gupta, A. K., J . Sci. Ind. Res. (Indiu) 11C 500 (1953). (3) I h t t a , R. L., J . Indian ('hem. SOC. 34, 311-16 (1957); Ibid., 35, 243-50
ij 19581. -.-_, ( 4 ) Job, P., Ann. Chim. 10, 113 (1928). ( 5 ) Wise, W. M., Brandt, W. W., AXAL. CHEM.27, 392 (1955).
RECEIVEDfor review A n d 29. 1963. Resubmitted July 1, 1664. '4ccepted July 1, 1964.
Determination of Cesium and Rubidium after Extraction with 4-sec- Butyl-2(a-met hylbe nzyl) phen01 W. J. ROSS and J. C. WHITE Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b Methods have been developed for radiochemical and flame photometric determinations of cesium and rubidium. These elements are selectively extracted from basic tartrate solutions, after removal of the alkaline earth elements, with 1M solutions of 4-sec 2(a methylbenzy1)phenol butyl (BAMBP) in cyclohexane. Cesium and rubidium can be measured directly in the organic solution or after being back-extracted into 1 M HCI.
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in the recovery of heavy alkali metals from their ores and in the separation of radioactive Cs'3' from spent nuclear fuels has resulted in additional attention being given t,o analytical methods for isolating and determining cesium and rubidium. Cronther and Moore (4) have recently discussed the advantages of liquidliquid extraction as a means of separating cesium and presented a method based on the extraction of cesium with t'henoyltrifluoroacetone (TTA). C r h l this time gravimetric ( 5 ) and extraction (8) methods using tetraphenylboron have been t'he most popular means for isolating cesium. Recently, Horner et al. (1,1, 6 ) demonstrat)ed the feasibility of extracting cesium from alkaline solutions with substituted phenols, especially with 4 - sec - butyl - 2 - ( a - methylbenzyl) NCREASED INTEREST
1998
ANALYTICAL CHEMISTRY
phenol or BAMBP. Subsequently, Arnold (3) has efficiently separated cesium from other alkali metals through a continuous extraction process employing BAMBP. The novelty and efficiency of the separations reported by these workers have given impetus to an investigation of the analytical potentialities of BAMBP. This paper describes a rapid and efficient method for extracting tracer and milligram amounts of cesium and rubidium from all other elements that interfere either in radiochemical or flame photometric determinations of these alkali metals. EXPERIMENTAL
Apparatus. A\ll extractions were performed manually in glass extraction funnels. The gamma activities of single radionuclides were measured with a single-channel pulse-height analyzer coupled with a well-type XaI(T1) crystal. The gamma activities of multicomponent system? were resolved and measured with a multichannel pulse-height analyzer equipped with a 3-inch X 3-inch NaI(T1) crystal. Flame photometric measurements were made with a Jarrell-Ash spectrophotometer with flame attachment. Reagents. Radiotracers of X a z 4 , K4*, Ca47, Srs5, RbS6, and Cs13' were obtained in aqueous solutions from the Isotopes Division of the Oak Ridge Kational Laboratory.
Gamma-emitting radionuclides of and all other elements were produced by activating microgram amounts of the natural element for 16 hours in a reactor neutron flux of 8 X 10" neutron per sq. cm. per second. Solutions of 1 M BAMUP were prepared by dissolving 25 grams of the phenol in 100 ml. of cyclohexane. This reagent, 4-sec-butyl-2(a.methylbenzyl) phenol, was obtained from Dow Chemical Co. and was used without further purification. Radiochemical Procedure. Pipet an aliquot of a neutral, aqueous sample into a 50-ml. centrifuge tube. Add 1 ml. of 5% N a O H and evaporate to incipient dr) ness to expel ammonia. Add 1 ml. of 1'11 tartaric acid and dilute to -3 ml. with HzO. Add 1 ml. of strontium carrier (10 nig. of Sr) and 1 ml. of 1 X ?;azCOs solution. Precipitate SrC03 by warming the solution in a water bath (50' to 70" C.) for 10 minutes. Separate the precipitate by centrifugation and decant the supernatant liquor into a 25-ml. separatory funnel. Add 5 ml. of 1JI BXMBP and extract for 1 minute. Repeat the extraction with 5 ml. of fresh E h M B P solution if quantitative separation of rubidium is desired. Combine the extracts. Remove an aliquot of the organic phase and count the activity of cesium and rubidium. If interference from radionuclides of sodium or potassium is observed, backwash the organic phase with 5 ml. of 131 S a O H solution and recount an aliquot of the organic phase.
The extraction of sodium is very slight when the S a O H concentration is 15y0 less than 0.5.lf but increases to in >251 S a O H solutions. The reduction in extraction of Cs, Rb, and K from >1M solutions is indicative of competitive equilibria between the extractable species of these elements and the increasing concentration of sodium in the aqueous phase. The extraction of lithium is slight and is not appreciably affected by high S a O H concentrations. The investigations of Horner and Arnold were performed in less basic (pH 11 to 13) systems. Continuous countercurrent techniques were employed to achieve quantitative separation of cesium from the other alkali metals. Effect of Sodium and Ammonium Salts. T h e extraction of cesium, rubidium, and potassium from 1.1f K a O H solutions is decreased when t h e concentration of sodium is increased by the addition of sodium salts (Figure 2 ) . Sodium salts have a less deleterious effect than S a O H although the type of anion (Cl-, C03+, c104-,P04C2, c204-') appears to be significant only in the relative solubilities of the sodium salts. Thus, the concentrations of sodium salts that result from the neutralization of acid samples or from the precipitation of the alkaline earth elements must be limited if quantitative separation is to be achieved with a single extraction. The extractability of cesium and rubidium is drastically reduced by ammonium or quarternary ions so that these ions must be removed before extraction. Extraction Capacity of BAMBP. T h e degrees t o which various amounts of cesium, rubidium, and potassium are extracted bv 5 ml. of 1-21 B A M R P are presented in Figure 3. Sixty milligrams of cesium are 99.2y0 extracted while the extraction of 80 mg. is 98.370 complete. T h e loading capacity of 5 mmoles of B;\MBP is approached when the initial aqueous solution contains >300 mg. of cesium. The combining ratio of BAMBP to cesium in the organic extract has not been established absolutely, but is 4 to 5 moles of BAX'IBP per mole of cesium in a highly loaded system. Although rubidium is not extracted quantitatively in a single equilibration, as much as 26 mg. can be 90% extracted by 5 inmoles of BL4M131'. Saturation of 5 mmoles of BAAM13Pis approached when the system contains >IO0 mg. of rubidium, and the mole ratio of extractant to rubidium in the organic phase is approximately 5 . Effect of Contact Time. Equilibration is achieved within a very short period when 1 M K a O H solutions of N a , K , R b , and Cs are con-
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NaOH , M Figure 1 . Effect of sodium hydroxide concentration
Nonradiochemical, Procedure. The procedure for radiochemical separation is followed with the exception t h a t precipitation of strontium carrier with N a r C 0 3is unnecessary unless t h e concentration of alkaline earth elements is > l o 4 that of cesium or rubidium. If the precipitation step is eliminated, the ammonia-free sample solution is transferred to a separatory funnel and extracted with 5 ml. of 1Jf BAMBP. The extracted cesium aud rubidium can be transferred back to an aqueous solution by equilibrating the organic phase with 5 ml. of 1.11 HCl for 1 minute. -In aliquot of thf. organic (or HC1 phase) is analyzed for cesium and rubidium by flame photometric methods. DlSCUSS'lON
Effect of NaOH: Concentration. .is shown in Figu:re 1, the alkali metals are not extracted from neutral or acidic solutions. T h e extractability of tracer and m i l l i p m amounts of cesium is very s i n d a r and increases rapidly as the concentration of NaOH is increased t'o 0.3.1f. Extraction of cesium is essentially complete in 0.3 to 1.531 NaOH but dec:reases as the concentration of NaOH is increased > 1.5.1f. The optimum NaOH concentration for the extract'ion of rubidium is 0.5 to 1.0.11. Only 93% of both timer and milligram amounts of rubidium is extracted by a single equilibration with 1.11 13AlI13P. &uant,itative separation is achieved, however, with a double extracttion. The extraction characteristics of potassium are similar to those of rubidium; however, less i;han 50% of the potassium present is ext'racted during a single equilibration with 1X BAMBP.
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tacted with 1.11 cyclohexane solutions of BAMBP. Actually, there is a slight decrease (0.1-0.4%) in extraction when the equilibration time is extended from 1 to 10 minutes. T h e organic phase remains slightly turbid for approximately 1 hour after extraction; however, complete clarification is not necessary before a test portion can be removed. Back Extraction. T h e alkali metals are quantitatively back-extracted into a n aqueous solution when the BXkIBP-cyclohexane phase is contacted with a n equal volume of 0.1 to 1 M H C l or H?r;03. .I single, 1minute equilibration suffices except when t h e BAMBP phase is saturated. Extraction of Diverse Elements with BAMBP. X survey of the extraction characteristics of microgram amounts of 49 elements was made with activated radiotracers. Of the naturally occurring metallic elements only B, Be, M g , Al, Ti, V, A h , Os, and R h were not investigated. Some elements precipitated from 1.M N a O H b u t could be retained in solution by the addition of 1 ml. of 1JI tartaric acid. When the tested elements existed in their most common oxidation states [usually the highest except for Cr(III), hs(III), Sb(III), and Ce(III)], only Ca, Sr, and Ba were extracted from such a basic tartrate solution. Separation of Alkaline Earth Elements. Radiotracer concentrations of C a , Sr, and Ba are precipitated quantitatively on strontium carrier when lL14N a 2 C 0 3solution is added to a N a O H solution of these elements. Precipitation is slow and incomplete when tartrate is present unless t h e mixture is heated. T h e degree to which alkali metal are coprecipitated was determined by the use of cesium VOL. 36, NO. 10, SEPTEMBER 1964
1999
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CARBONATE PRECIPITATE
Figure 3. Effect of concentration of cesium, rubidium, and potassium
tracer, 40 mg. of cesium carrier, and 20 mg. of strontium carrier. Less than 0.2y0 of the cesium activity was found in the SrC03 precipitate after a single washing of the precipitate with 5 ml. of 1Jf S a O H . Extraction of Cesium and Rubidium in the Presence of Ca, Sr, and Ba. T h e effect of large amounts of alkaline earth elements on the extraction of tracer and milligram amounts of Cs and R b was established with synthetic solutions t h a t contained 10 mg. of Sr and 15 mg. of Ua. T h e extraction of Cs and R b is not affected, even though 60 to 70% of the Sr and Ba are also extracted. Cesium and rubidium can be determined accurately by flame photometric methods in the presence of as much as 104J excess of alkaline earth elements (9). Therefore, the alkaline earth elements need not be separated if the determination of Cs and R b is to be made by flame photometric methods. APPLICATIONS
The nonradiochemical procedure has been used to determine cesium and rubidium in several samples of siliceous and carbonate ores after dissolution of the samples in HF-HN03-H2S04 and HC1, respectively. Double extractions were performed to extract rubidium quantitatively. Typical results obtained by flame photometric analysis of the BARIBP-cyclohexane phase are shown in Table I. Cesium-134 and cesium-137 have been extracted from aqueous solutions of extraneous gamma-emitting nuclides and determined by the radiochemical
Sample Silicate Carbonate
2000
GAMMA ENERGY, MeV
Figure 4. Extraction of cesium- 1 37 from fission product solution
method. This method can be readily applied to the determination of cesium in burn-up analysis. This application is shown in Figure 4 by the gamma spectra of a solution of fission products and of the nuclides isolated by the carbonate precipitation and BAZIBP extraction steps. The concentration of cesium produced during fission is readily determined by comparing the activity of the Cs13’ in the extract with that of a standard source of Cs1S7.
by substituting N H 4 0 H for XaOH or when ammonium ions are present in 1Jf KaOH solutions. The extracted ions are readily back-extracted into mineral acid solution. Use of B;IMUP to separate and isolate both cesium and rubidium appears to be equivalent to the best methods now available and to offer a rapid way of achieving accurate analyses of ores or solutions that contain these constituents.
CONCLUSIONS
ACKNOWLEDGMENT
The extent to which the alkali and alkaline earth metals are extracted by BAMBP increases with atomic weight. Only cesium is extracted quantitatively from NaOH solution. The detrimental effect of high sodium content has been tentatively explained by Horner ( 7 ) as being caused by loss of reagent through formation of a relatively water-soluble sodium species of high reagent/ion ratio (approximat,ely 5 ) . The variation in this effect from one element to another reflects the relative competition of each element us. sodium for the BAZIBP molecules. The metal-BA4MBP species have not been identified but are formed rapidly and have combining ratios of approximately 5 moles of BA4R1UPper mole of cesium or rubidium. The extraction is most effective when the system contains 0.5 to 1JI hydroxyl ions. This degree of basicity cannot be achieved
The author thanks T. C. Rains for the flame photometric analyses performed during this studj- and D. E. Horner and W. D. Arnold, Jr., for discussions pertaining to their continuous extraction work.
Table I. Analysis of Ores Rubidium, % Cesium, r0 Present Found Present Found 22.9 1.99
ANALYTICAL CHEMISTRY
23.6 i0 . 2 2.02 i0 . 0 3
0.64 18
0.70 i0.05 1 7 . 7 i0 . 2
LITERATURE CITED
(1) Brown, K. B., U. S. htomic Energy Comm. Rept. ORNL TM-181, pp. 17-32 (July 1962). 12) , , Ibid..Rent. ORNL TM-265,. DP. _ - 7-16 (August 1962). ( 3 ) Ibid., Rept. ORNL-3496, p. 8 (October 1963). ( 4 ) Crowther, P., Moore, F. L., ANAL. CHEY.35, 2081 (1963). ( 5 ) Handley, T. H., Burros, C. L., Ibid., 31, 332 (1959). (6) Horner, I>. E., Croye, D. J., Brown,
K. B., Weaver, B., Fission Product Recovery from Waste Solutions by Solvent Extraction,” presented at American Instihte of Mechanical Engineers Meeting, Dallas, Texas, February 1963. ( i )Horner, D. E., ORSL, Oak Ridge, Tenn..,~Drivate communication, April 1963. (8) Morrison, G. H., Freiser, H., “Solvent Extraction in Analytical Chemistry,” pp, 200-1, Wiley, Sew York, 1937. ( 9 ) Rains, T. C., ORSL,, Oak Ridge, Tenn., private communlcation, April 1963.
RECEIVEDfor review April 20, 1964. Accepted June 19, 1964. Research sponsored by the C . S. Atomic, Energy Co,nimission under contract wlth the Union Carbide Corp.
