I
NOTES
Mesityl Oxide as an Extracting Agent for Beryllium P. V. Dhond and S. M. Khopkar Department of Chemistry, lndian lnsfitute of Technology, Bombay-400076, lndia
Mesityl oxide (4-methyl-3-pentene-Z-one) can be used for the solvent extraction of beryllium. It quantitatively extracts beryllium from 0.5M hydrochloric acid containing 5M potassium thiocyanate. The metal can be stripped from the organic phase with water and determined photometrically a t 530 nm, as its complex with aluminon. The reagents useful for the quantitative extraction of beryllium are very limited in number. Acetylacetone ( I , 2) was used as an extractant but a t pH > 7.0 the reagent showed ionization to form a water soluble metal complex. In addition, excess of reagent showed serious interference in absorptiometric measurements. In extractions with dibenzoylmethane (2), ammonia showed strong interference and hydrolysis of metal was prevented by using EDTA as the masking agent. The extracted complex with thenoyltrifluoroacetone (1, 2) was so stable that for back-stripping, the solution was equilibrated for a t least 80 hours with concentrated hydrochloric acid. The concentration of reagent used was also too high. The method of extraction with tributyl phosphate ( 3 ) had no practical utility. The extractions with diethyl ether ( 4 ) from fluoride were incomplete while those from thiocyanate media with diethyl ether ( 5 ) or amylacetate (6) were not quantitative in spite of using very high thiocyanate concentration. Thus, in all extractions sequestering agents like EDTA or tartaric acid ( 2 ) were used to prevent hydrolytic precipitation of beryllium. In many instances, a large volume of organic phase was used to ensure complete extraction; the period of equilibration was unusually long, and many ions showed strong interferences. The method we propose is simple, sensitive, selective, and applicable at microgram concentration of beryllium. It is not essential to use a masking agent or a large reagent volume. The extractions and stripping operations are fast.
EXPERIMENTAL Apparatus and Reagents. A type FEK-57 photoelectric filter photometer and a Cambridge p H meter with glass electrodes were used. Mesityl oxide ( b p 127-132 "C) was B.D.H. Anal R. About 11.4 grams of beryllium nitrate (B.D.H. Anal. R) was dissolved in 100 ml of distilled water. Then 0.5 ml of hydrochloric acid was added to preserve the solution for longer duration. The solution was standardized gravimetrically (7). It was found to contain 5 mg/ml of beryllium. The diluted solution containing 20 pg/ml of beryllium was prepared from stock solution by appropriate dilution. Korkische. "Modern Methods for the Separation of Rare Metal Ions," Pergarnon Press, London, 1969, p 300. A . K . D e , S. M . Khopkar, R . ' A . Chalrners, "Solvent Extraction of Metals," Van Nostrand Reinhold Co., London, 1970, p 58. D . F. C. Morris and M . W. Jones, J. Inorg. Nucl. Chem.. 27, 2454
J.
(1965). R. Bock and M. Herrrnann. Z.Anorg. Allg. Chem.. 284, 288 (1956). R. Bock, Fresenius' Z.Anal. Chem.. 133, 110 (1933). A . V . Novosselow, T. I . Pochkuera, N . S. Tarnrn, G . A. Trubachera, Vest Mosk Univ. Khim., 44 (1969);Anal. Absfr.. 19. 76 (1970). A . I . Vogei "The Text Book of Quantitative Inorganic Analysis," Longrnans and Green, London, 1962, p 518.
Sodium aurintricarboxylate (Aluminon): 0.1% aqueous solution was prepared from the tested product. The solution was allowed to stand for a t least a day before use. General Procedure. An aliquot of the solution containing 20 pg of beryllium was taken. Then enough hydrochloric acid and potassium thiocyanate were added t o make their concentrations 0.5M and 5M, respectively, in a total volume of 25 ml. The aqueous phase was then transferred into the separatory funnel. It was then extracted with 10 ml of 100% mesityl oxide for 3 minutes. The two layers were allowed to settle and separate. Beryllium was stripped from the organic phase by shaking it once with 10 ml of distilled water. To the aqueous phase, 2 ml of 20% sodium acetate was added. The p H of the resulting solution was adjusted to about 6.6 with 0.1M sodium hydroxide or 0.1M acetic acid. Then 3 ml of 0.1% aluminon solution was added. The volume of the aqueous phase was made u p to 25 ml. Then the solution was allowed to stand for 20 minutes. Finally absorbance of the reddish brown colored complex was measured photometrically at 530 nm (8).
RESULTS AND DISCUSSION Effect of Acidity and Mesityl Oxide Concentrations. The concentration of hydrochloric acid was varied from 0.1 to 2M and that of mesityl oxide from 19 to 100% (1.62 to 8.70M). Toluene was used as a diluent. All the extractions were carried out in the presence of 5M potassium thiocyanate and the distribution ratio was calculated as described earlier (9). It was observed (Table I) that the extraction was incomplete with diluted mesityl oxide in any acid range, but it was quantitative with pure mesityl oxide at 0.6M hydrochloric acid concentration. Further, a t this acidity the presence of the chloro complex has no effect on the extent of extraction, when any of the concentrations of mesityl oxide were used. The optimum acid concentration was 0.5M hydrochloric acid in the presence of 5M potassium thiocyanate. Beyond this acidity, there was a slight decrease in extraction, presumably on account of the presence of the excess of chloride ion concentration, as, with the excess of chloride, competition is between metal ion and anions such as chloride and thiocyanate to form a complex which can be extracted into mesityl oxide. Dilution of mesityl oxide lowered the extraction. It was possible to strip the complex back into the aqueous phase by equilibration with distilled water as it reverses the conditions of extraction and thereby beryllium returns to aqueous phase. An attempt was made to ascertain the composition of extractable species by extracting beryllium a t a fixed acid concentration of 0.5M with varying concentrations of mesityl oxide using toluene as diluent. A plot of log of distribution ratio against log of mesityl oxide concentration indicated the slope of 2.24. This shows the probable nature of extractable species as Be(SCN)Z.ZMeO where M e 0 = mesityl oxide. This shows that the system conforms to the and Y . Kakita. Sci. Rep. Res. Insf. Tohoku Univ.. Sei. A . 5, 163 (1953);Chem. .4bstr., 48. 38411' (1954). (9) S. M . Khopkar,Anal. Chem.. 38, 360 (1966). (8) H. Goto
ANALYTICAL CHEMISTRY, VOL. 45, NO. 11, SEPTEMBER 1973
1937
limiting squares law. A further study of the infrared spectra in the region of 4000-600 cm-1 of the extracted species Table I . Distribution Ratio as the Function of Acidity Mesityl oxide Extraction YO Distribution concn Initial HCI, M E ratio, D 19% (1.62M)
0.1 - 0.3 0.4
... 5.00
0.5
12.50 5.00 5.00
0.75 1.oo 25% (2.17)
50% (4.35)
7.50 10.00
0.1 0.2 0.3 0.4 0.5 0.75 1.oo
15.00 15.00 20.00 15.00 7.50
0.1 0.2 0.3 0.4
20.00
0.5
50.00 30.00
20.00 22.50 35.00
0.75 1 .oo 75% (6.53)
17.50
0.1 0.2 0.3 0.4
52.50 57.50 65.00 70.00 75.00
0.5
100% (8.7M)
0.75 1.oo
50.00
0.1 0.2 0.3 0.4
75.00 75.00 77.50 80.00 100.00
35.00
0.5
70.00
0.75 1 .o 1.5 2.0
57.50
50.00
... 0.132 0.357 0.132 0.132
0.255 0.280 0.442 0.442 0.62 0.442 0.255 0.62 0.62 0.75 1.34 2.50 1.07 0.53 2.76 3.38 4.64 5.83 7.5 2.50 1.34 7.50 7.50 8.61 10.00 >2.5 x 103 5.83 3.75 2.50
0.950
27.50
Table I t . Effect of Diverse Ionsa Tolerance limit,
1
x 103pg
Added ions
5.0
sod2-, C N - ,
2.5 2.0
Co3+,N i 2 + , M g z + , As3+,Cit3-, oxalz-, tart3-, malont2-, CH3COO-, EDTA4C u 2 + , Cr3+. U6+, Ca2+,Ba2+,Rb', Zn2+,
1.o
TI+, Sb3+, Bi3+, Fe3+,A u 3 + , V 0 3 -
Nos-
CS+,M070246-, wo42-, P043-,
0.5
S Z O ~ ~F-- , P b 2 + , H g 2 + , Ag+, Flu3+. Rh3+, Pd2+, p i 4 + , C e 4 + , SeOs2-, TeO32--,Reo4C d 2 + , Th4+, Zr41
0.25 Be(l1) = 20 fig, O . 5 M HCI
1938
I - , Br-
+ 5 M KSCN
100% mesityl oxide
revealed the absence of characteristic bands representing water molecules. This showed absence of water molecules directly linked to beryllium in its coordination sphere. The characterization of the spectra of the species in the ultraviolet region showed absorption maxima a t 235 nm with molar absorptivity 1.2 x lo4 indicating that the conjugated arrangement of unsaturated groups in 3-positions remains undisturbed during the process of extractions. Thus,.it can be concluded that beryllium is extracted as a disolvated species in the presence of thiocyanate as complexing anion. Effect of Thiocyanate Concentrations. The concentration of thiocyanate was varied from 1.0-5.OM in the presence of 0.5M hydrochloric acid. Pure mesityl oxide was used as an extractant. The results showed that when the concentration of potassium thiocyanate was 1.0, 2.0, 3.0, and 4.0M, the corresponding percentage extraction was 25, 65, 70, and 80. However, the extraction was quantitative when 5M, potassium thiocyanate was used. Thus, the optimum concentration of thiocyanate was 5M. The extraction remained constant even at a high concentration of 8M. For all practical work, use of 5M potassium thiocyanate was recommended. Period of Extraction. The extraction was carried out for various times of shaking. The period of equilibration was varied from 1, 2, 3, 5 , 10, and 20 minutes. The corresponding percentage extraction was 82.5, 90, 100, 100, 100, and loo%, respectively. This showed the optimum period of equilibration as 3 minutes. All other existing methods needed a much higher period of shaking for complete extraction ( I , 2 ) . Diverse Ions. The effect of diverse ions on the solvent extraction of beryllium (20 p g ) from 0.5M hydrochloric acid containing 5M potassium thiocyanate with mesityl oxide was studied. The tolerance limit was calculated as described earlier (9). The results (Table 11) showed that the common inorganic anions were tolerated in the ratios of 1:250. The common organic complexing agents which were generally used as the masking agents were well tolerated in the ratio of 1:125. Copper, chromium, zinc, alkali, and alkaline earth metals, molybdate, tungstate, and halides were tolerated in the ratios of 1:lOO. Other ions including those belonging to noble metals were tolerated in smaller ratios of 1:25, but manganese showed strong interference. The tolerance limit of silver and mercury was enhanced by masking them with alkali cyanide. Thus, it was possible to separate beryllium from large excess of copper, nickel, and magnesium which were associated with it in light alloys. Beryllium is used as the moderator and source for neutron in the atomic reactor; hence, its separation from fission product elements such as zinc, arsenic, selenium, strontium, zirconium, molybdenum, platinum metals, antimony, and tellurium has special significance in reactor chemistry. From ten experiments, the average recovery of beryllium was 99.5 f 0.5%. Each determination took a total of 30 minutes. The standard deviation was 3~1.12%. Received for review July 17, 1972. Accepted March 16, 1973.
ANALYTICAL C H E M I S T R Y , VOL. 45, NO. 11, SEPTEMBER 1973
