Diluted Tributyl Phosphate as an Extractant for Beryllium as Its Thiocyanate Complex S. Kalyanaraman and S. M. Khopkar Department of Chemistry, Indian Institute of Technology, Powai, Bombay-400076, hdia
50% Tributyl phosphate-toluene was used for the quantitative extraction of beryllium from 0.5M hydrochloric acid containing 5M ammonium thiocyanate. Beryllium was stripped from the organic phase with 1 M sodium hydroxide and determined colorimetrically at 510 nm as its complex with Eriochrome Cyanine R. Although several extractants are available for the solvent extraction of beryllium, they have only limited applications ( I ) . The @-diketoneshad no special advantages (2). Diethyl ether was used in fluoride ( 3 ) and thiocyanate ( 4 ) media but the extraction was incomplete. Trioctylamine in methyl isobutyl ketone (5) was used for its separation from acidic solutions. Tributyl phosphate (6) was used for the extraction of beryllium but the method had no practical utility as the extraction was possible only from 0.1M hydrochloric acid and 14M lithium chloride. Further, the extraction was not quantitative. A similar attempt was made to use tributyl phosphate as an extractant ( 7 ) in the presence of salicylic acid with no advantage. Many transition elements were extracted as their thiocyanate complexes with tributyl phosphate as the extractant (2). Sekine (8) extracted americium from 5M sodium thiocyanate with 5% tributyl phosphate in hexane. Similarly, De and Sen (9) utilized the thiocyanato system for the solvent extraction of some transition elements such as cobalt, copper, and iron with tributyl phosphate. An attempt was made to extract beryllium from thiocyanate media with 50% tributyl phosphate, using toluene as the diluent. This paper describes such a method for the solvent extraction of beryllium. The method proposed is simple, rapid, selective, and applicable a t microgram concentrations. The procedure was extended for the analysis of beryllium in beryl.
EXPERIMENTAL Apparatus a n d Reagents. A Spektromom 204 spectrophotometer with 10-mm matched quartz cells, a Type FEK-57 photoelectric filter photometer, and Cambridge pH meter with glass and calomel electrodes were used. The tributyl phosphate, bp 143 "C, was from British Drug House, England (BDH). About 1.241 grams of beryllium nitrate tetrahydrate (BDH AnalaR) was dissolved in 100 ml of distilled water containing l ml of nitric acid. The solution was standardized gravimetrically (10). It contained 0.545 mg/ml of beryllium. The diluted solution containing 5.45 Gg/ml of beryllium was prepared from stock solution by appropriate dilution. Eriochrome Cyanine R. (E. Merck, Germany) was an 0.1% a ueous solution. General Procedure. An aliquot of the solution containing 10.9 wg of beryllium was taken. Then enough hydrochloric acid and ammonium thiocyanate were added to make their concentrations 0 . 2 4 and 5 M , respectively, in a total volume of 25 ml. The sample was then transferred to a separatory funnel and extracted with 10 ml of 50% tributyl phosphate in toluene for 5 minutes at room temperature. The two layers were allowed to settle and separate. Beryllium was stripped from the organic phase by shaking it twice with 15 ml of 1M sodium hydroxide. T o the aqueous phase, 3 ml of concentrated hydrochloric acid was added. Then 5 ml of 0.1% Eriochrome Cyanine R and 5 ml of 2.5% EDTA were added. The pH of the resulting solution was adjusted to 9.8 with 0.1M sodium hy-
droxide or hydrochloric acid. The solution was made up to 50 ml. Finally the absorbance of the red colored complex was measured a t 510 nm vs. a reagent blank prepared similarly (11, 12).
RESULTS AND DISCUSSION Effect of Acidity and Tributyl Phosphate Concentrations. The concentration of hydrochloric acid was varied from 0.1 to 2M and that of tributyl phosphate from 19 to 100% (0.70 to 3.66M). Toluene was used as a diluent. All the extractions were carried out in the presence of 5M ammonium thiocyanate, and the distribution ratio was calculated as described earlier (13). I t was observed (Table I) that the extraction was incomplete up to 40% tributyl phosphate in any acid range, but it was quantitative with 50% tributyl phosphate a t 0.4-0.6M hydrochloric acid, because a t this acidity the chloro complex has no effect on the extent of extraction. The optimum condition was 0.5M hydrochloric acid and 5M ammonium thiocyanate. Beyond this acidity, there was a decrease in the extraction, possibly due to the presence of an excess of chloride ion concentration which enters into competition with the thiocyanate ion to form a complex with the metal ion which can be extracted. Even with higher tributyl phosphate concentration, the extraction was not quantitative at acidities higher than 0.7M hydrochloric acid. It was possible to strip the complex back into the aqueous phase by equilibrating twice with 15 ml of 1 M sodium hydroxide, as it reverses the conditions of extraction and thereby beryllium returns to the aqueous phase. All the extractions were invariably carried out at room temperature of 25 OC. An attempt was made to ascertain the composition of the extractable species by extracting beryllium at a fixed acid concentration? of 0.3M with varying concentrations of tributyl phosphate using toluene as diluent and varying concentrations of thiocyanate at fixed concentration of tributyl phosphate and acidity. A plot of log of distribution ratio vs. log of tributyl phosphate concentration indicated a slope of 2.14. At the same time, the plot of log of distribution ratio vs. the log of thiocyanate ion concentration indicated a slope of 1.73. This shows the probable nature of the extractable species as Be(SCN)2.2 TBP. This indicates the system conforms to the limiting square law (14) by forming a disolvated species. It was further observed by Siddall ( 2 5 ) that Distribution ratio a [TBP]q where q is the solvation number. A further study of the infrared spectra in the region 4000-600 cm-l of the extracted species revealed the absence of characteristic bands representing water molecules, in its coordination sphere. Further the intensity of =P=O stretching decreased from 1275 cm-' to 1210 cm-l indicating that Be(SCN)2 is directly linked to the =P=O group of tributyl phosphate. Thus, it can be concluded that beryllium is extracted as a disolvated species in the presence of thiocyanate as complexing anion. Effect of Thiocyanate Concentration. The concentration of thiocyanate was varied from 1.0-7.OM in the presence of 0.5M hydrochloric acid. 50% tributyl phosphate-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
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Table I. Distribution Ratio as the Function of Acidity' TBP Concentration
[nitial HCI,!I
Extraction %. P I -
Table 11. Effect of Diverse Ionsa
Distribution ratio. D
Tolerance limit, 1 x 10.' iLg
19% (0.7061)
0.1
0.3 0.5
25cc (0.91JZ)
0.7 1.o 0.1 0.3 0.5
40% (1.46,11)
0.7 1.o 0.1 0.3 0.5
50% (1.8351)
0.7 1.o 0.1 0.3 0.4-0.6
0.7 1.o
7 0 7 (2.56.11)
1.5 2 .o 0.1
0.3 0.5-0.7 1.o 1.5 2 .o 100% (3.66.11)
0.1 0.3
0.5-0.7 1.o
a
1.5 2 .o Be*+ = 10.9p g , XH4SCN. 5M
21.81 21.81 52 -00 40.00 0 .oo 32.73 34.51 63.62 54.54
0.00 54.54 63.62 80.00 55.00 2 .oo 66.81 70.92 100.00 63.62 25 .OO 14.25 6.52 70.92 80.00 100.00 75 $00 38.14 26.85 80.00 80.00
100.00 90.90 74.42 56.18
0.69 0.69 2.79
7.5 5 .O
1.66
...
1.31 4.25 2.93
...
2.93 4.25 10.00 3.05 0.05 4.04 6.07 >2.50 x 103 4.25 0.83 0.41
0.17 6.07 10.00 >2.50 x 103 7.50 1.54 0.92 10.00 1 0 .oo >2.50 x 103 24.95 7.26 3.21
K', Li'. SI-'+, B a 2 + , Mg'' EDTA?-, NO,-. pod3-, so,?-
Ca",
c20d2-, s?oj2-, ~ 0
~ 3 -
C s + , Rb'. Cits-, C1Tart3-, CN'. t h i o u r e a , malonate'2.5 Ai3', Bi3+, Cr3'. Th". lJOzz+, y3+,pt'+ Fez+,Zn'+, Sb3' 2 .o 1.o Rh3', Tl', AsOll-, SeO,'-, Br-, 10.5 Hg", Ir'+, Ag', Pb" 0.25 cu2+,Co", Fe3+, Mn", Ni2+, Pd", Ru3', In", V02'+, Au3' a Be*+ = 10 9pg. 0 5-V HC1. 5.V NHISCS, 5 0 7 ~ TBP-toluene.
1.21
toluene was used as the extractant. The results showed that when the concentration of ammonium thiocyanate was 1.0, 2.0, 3.0, and 4.OM, the corresponding percentage extraction was 50.9, 76.2, 83.6, and 90.9. However, the extraction was quantitative when 5M ammonium thiocyanate was used. The extraction remained constant even a t a high concentration of thiocyanate. For all practical work, 5M ammonium thiocyanate was used. Period of Extraction. The extraction was carried out for various times of shaking. The period of equilibration was varied from 1, 2, 3, 4, 5 , and 10 minutes. The corresponding percentage extraction was 66.6, 80, 80, 88.4, 100, and 100, respectively. This showed the optimum period of equilibration as 5 minutes. All other existing methods needed a much higher period of shaking for complete extraction (2). Diverse Ions. The effect of diverse ions on the solvent extraction of beryllium (10.9 pg) from 0.5M hydrochloric acid and 5M ammonium thiocyanate using 50% tributyl phosphate was studied. The tolerance limit was calculated as described earlier ( 1 3 ) .The results are shown in Table 11. Alkali and alkaline earth metals were tolerated in the ratio of 1:1000. The common complexing organic reagents were tolerated in the ratio of 1:500. Cadmium, aluminium, bismuth, platinum, thorium, and uranium were tolerated in the ratio of 1:250. The tolerance limits of silver, mercury, gold, and palladium were enhanced by masking them with alkali cyanide (16). The interference of ions such as indium, manganese, vanadium, and copper ( I 7) was eliminat2042
10.0
Added ions
Cd",
ed by the selective extraction with thiothenoyltrifluoroacetone (18). Thus it was possible to separate beryllium from large excess of elements. Its separation from fission products has special significance in reactor chemistry. From ten experiments, the average recovery of beryllium was 99.6 f 0.4%. The standard deviation was f0.8%. Application to Analysis of Beryl. A known weight (0.1 g) of beryl was fused and brought into solution by the method described by Sankar Das and Athavale (19). An aliquot (1 ml) of the solution was taken and sodium acetate was added such that its concentration was 0.8M. The pH was adjusted to 4.8 and iron was extracted with 10 ml of 10-3M thiothenoyltrifluoroacetone (20) in carbon tetrachloride. The solution containing beryllium was adjusted such that it contained 0.5M hydrochloric acid and 5M ammonium thiocyanate. I t was then extracted with 10 ml of 50% tributyl phosphate-toluene and beryllium from it was determined spectrophotometrically as described earlier. The results from triplicate analyses of beryl found were 9.60 and 9.82, and 9.68% of beryllium as beryllium oxide. To an aliquot (50 ml) of the solution containing beryllium, 25 ml of 10% EDTA and 10 ml of 20% dihydrogen ammonium phosphate were added. After the addition of a drop of hydrogen peroxide, 5 g of urea was added and the mixture was boiled gently for 30 minutes. The precipitate of beryllium ammonium phosphate was allowed to settle in a water bath for one hour. The solution was cooled, filtered, dried, ignited, and weighed as beryllium pyrophosphate (19). The results of the duplicate analyses of the ore gave the percentage of beryllium oxide as 9.72 and 9.78. This showed that the extractive spectrophotometric method for the determination of beryllium in beryl compares favorably well with the pyrophosphate method.
LITERATURE CITED (1) P. V. Dhond and S. M. Khopkar, AnalCbem., 45, 1937 (1973). (2) A. K. De, S. M. Khopkar, and R. A. Chaimers, "Solvent Extraction of Metals", Van Nostrand-Reinhold Co., London, 1970, p 46. (3) R. Bock and M. Herrmann. Z. Anorg. Allg. Cbem., 284, 288 (1956). (4) R. Bock, Z.Anal. Cbem., 133, 110 (1933). (5) A. V. Novoselova, N. S. Tamm, T. I. Pochkaera, and N. V. Likhanskaya, Vestn. Mosk. Univ. Kbim., 14, 55 (1973). (6) D. F. C. Morris and M. W. Jones, J. lnorg. Nucl. Cbem., 27, 2454 (1965). (7) J. Aggett, U. Evans, and R. Hancock, J. lnorg. Nucl. Chem., 30, 2559 (1968). (8) T. Sekine. Bull Cbem. SOC. Jpn, 38, 1972 (1965). (9) A. K. De and A. K . Sen, Sep. Sci., 1, 641 (1966). (10) A. I. Vogel, "The Text Book of Quantitative Inorganic Analysis", Longmans and Green, London, 1962, p 5 18. (11) U. T. Hill, Anal. Cbem., 28, 1419 (1956). (12) U. T. Hili, Anal. Cbem., 30, 521 (1958). (13) S. M. Khopkar, Anal. Chem., 38, 360 (1966). (14) K. Aicock, F. C. Bedford, W. H. Hardwick, and H. A. C . McKay, J. lnorg. Nucl. Cbem., 4, 100 (1957). (15) T. H. J. Siddali, J. Inorg. Nucl. Cbem.. 28, 1919 (1964). (16) D. D. Perrin, "Masking and Demasking Agents of Chemical Reactions", Wiiey Interscience. New York, 1970, p 42.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
(17)V. M. Shlnde and S. M. Khopkar, Anal. Chem., 41,343 (1969). (18)K. R. Solanke, "Liquid-llquld extraction of metals wlth thlothenoyltrlfluoroacetone", Ph.D. Thesls, lndlan lnstltute of Technology, Bombay, 1973. (19) M. Sankar Das and V. T. Athavale, Anal. Chlm. Acta, 12,414(1955).
(20) R. R. Mulye and S. M. Khopkar, Fresenlus' 2. Anal. Chem.. 266, 348 (1973).
RECEIVEDfor review March 11, '1975. Accepted June 61 1975.
Extraction of Metal Ions with N,N-Disubstituted Amides James S. Fritz and Gene M. Orf Ames Laboratory-ERDA and Deparfment of Chemistry, Iowa State University, Ames lows 500 10
In this paper, liquid alkyl amides are studied as solvents for liquid-liquid extraction of metal ions. Feder first showed that N,N-dibutylacetamide is roughly comparable to tributylphosphate as an extractant for uranyl nitrate ( I ) . Siddall extended the work of Feder and studied the effects of altering the hydrocarbon substituents of the amide molecule on the extraction of U(VI), Pu(IV), Pu(VI), Np(VI), Th(IV), Zr(IV), and H N 0 3 from nitric acid solution (2). The thermal stability of amides was shown to be comparable to that of tributylphosphate and the hydrolytic stability of amides on solvent extraction about the same as T B P ( 3 ) .Several other brief reports (4-8) deal with substituent effects of amides on solvent extraction of several metal ions. All of the previous work with amides as extractants has been on the extraction of actinide metal nitrates, zirconium nitrate, and on the extraction of nitric acid itself. The purpose of the present work is to extend the study of the extracting power of amides to several other metal ions from nitrate solution, to study the extracting power of amides on several metal ions from perchlorate solution where the mechanism of extraction is entirely different from that in nitrate solution, and to examine the possible use of amides as reagents for analytical separations.
EXPERIMENTAL
Procedure. To 60-ml separators funnels were added exactly 5 ml of 0 . W metal ion in 0.02M "03, appropriate amounts of 4.OM sodium nitrate or sodium perchlorate, and water to make the volume 10 ml, and 10 ml of the appropriate amide in toluene. The mixture was placed on a Burrell Wrist-Action shaker and equilibrated for 1 hr. The lower aqueous phase was run off and analyzed for the amount of metal ion present after extraction.
RESULTS AND DISCUSSION Extractions from Nitrate Solution. Distribution ratios for metal ions extracted from aqueous nitrate solution with dibutylformamide (DBF), dihexylacetamide (DHA), and diethyldodecanamide (DED) are given in Tables I, 11, and 111, respectively. The acetamide (DHA) extracts uranium(V1) and thorium(1V) strongly, and iron(III), mercury(II), and zirconium(1V) to a lesser degree. Dibutylacetamide behaves much like DHA but has the disadvantage of a higher solubility in the aqueous phase. With the formamide (DBF), the distribution ratios for uranium and thorium are a little lower than with DHA under comparable conditions, but zirconium(1V) is more strongly extracted by DBF. The dodecanamide (DED) is a much less effective extractant; only uranium has a distribution ratio greater than 1.0 under the most favorable extraction conditions. The data show excellent possibilities for separation of uranium from all other metal ions studied, and for separation of thorium and zirconium from each other and from other metal ions using appropriate amide extractants. For example, comparison of extractions with 1.OM nitrate and 3.OM amide (3.5M for DHA) show the following separation factors:
Reagents. The standard solution of zirconium was prepared from hafnium-free ZrOC1&3H20 prepared with the Ames Laboratory of Energy Research and Development Administration. All other solutions of metal ions were prepared from reagent grade metal nitrates. N,N-Diethyldodecanamide (DED), mp 3-4 "C, was purchased from Eastman Organic Chemicals, and N,Ndibutylformamide (DBF), bp 120 "C a t 15 mm, n20D 1.4429, was purchased U/Th: DBF, 23.1; DHA, 9.4;DED, 41.3 from Aldrich Chemical Company. Both amides were used without Th/Zr: DBF, 11.9; DHA, 297; DED, 8.0 further purification. N,N-Dihexylacetamide (DHA) was prepared by overnight reaction of acetic anhydride with di-n-hexylamine, dissolved in ether. The solution was shaken with several portions At 1.OM nitrate and 5.OM DBF, the separation factor for of sodium bicarbonate solution to neutralize the acetic acid formed Zr/Fe is 34.3. in the reaction. Then the organic layer was shaken with 2.OM hyThe log distribution ratio was plotted vs. the amide condrochloric acid to remove any amine remaining in the solution. centration (at constant nitrate) and also vs. nitrate concenThe ether was removed from the product by fractional distillation, tration (at constant amide) to show the chemical nature of and the product was dried over magnesium sulfate. The final prodthe extracted species. For uranium, straight line plots were uct was purified by vacuum distillation a t 150 "C a t a pressure of 4 mm mercury. obtained for the log D vs. log amide plots with slopes of 2.1 The standard 0.05M EDTA solution was prepared from reagent for both DBF and DHA, and 1.6 for DED. At least for the grade disodium dihydrogen ethylenediaminetetraacetate dihyfirst two amides, this indicates clearly a 2:1 amide-uranium drate. Arsenazo I, 3-(2-arsonophenylazo)-4,5-dihydroxy-2,7-naphtha-ratio. Data for plots of log D vs. log nitrate were more erratic but suggest two nitrates for uranium. The extracted lene-disulfonic acid, was purchased from Eastman Organic Chemispecies is thus indicated to be U02(amide)2(N03)2. cals. Analytical Techniques. Uranium was determined colorimetriFor thorium extracted with DBF, a plot of log D vs. log cally with Arsenazo I. All other metal ions were determined by tiamide has a slope of 4.0; and log D vs. nitrate, a slope of 3.2. tration with EDTA. Calcium was determined with Calmagite at The corresponding plots for DHA show slopes of 3.2 and pH 10, and magnesium was determined with Eriochrome Black T 3.4, respectively. While these results are somewhat incona t pH 10. The other metal ions were determined with Xylenol Orclusive, a formula of Th(amide)4(N03)4 for extracted ange and Naphthyl Azoxine S (NAS), as specified by Fritz, Abspecies is likely. bink, and Payne (9). ANALYTICAL CHEMISTRY, VOL. 47, NO. 12, OCTOBER 1975
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