Liquid-Liquid Extraction of Zirconium(1V) with Mesityl Oxide SIR: Mesityl oxide (4-methyl-3penten-2-one) has been used for the extraction of uranium(V1) (2). Extension of these studies to zirconium(1V) revealed that zirconium(1V) can be quantitatively extracted from solutions containing 4 M nitric acid and 4M sodium nitrate. Zirconium(1V) is backextracted from the organic phase with water and is spectrophotometrically determined in the aqueous phase with alizarin. This provides the basis for the liquid-liquid extraction of zirconium (IV) at the milligram level. The method, although not specific, is applicable for the rapid separation of zirconium(1V). Early work on the solvent extraction of zirconium(1V) has been summarized by Morrison and Freiser (6). A recent method includes the extraction of the alizarin complex of zirconium(1V) in butanol (3).
RESULTS AND DISCUSSION
9.0
Effect of Acidity. T h e study of the extraction of zirconium(1V) with mesityl oxide from 0.5-6M nitric acid concentration showed t h a t the maximum extraction occurs a t 4 M nitric acid concentration. T h e partition coefficient ( D )was computed from the ratio of the concentration of zirconium(1V) in the organic phase t o t h a t in the aqueous phase. Zirconium(1V) content in the mesityl oxide phase was determined as described above, and that in the aqueous phase by difference from the total amount of zirconium(1V) initially taken. The maximum partition value was 100, corresponding to a n acid concentration of 4M containing 4M sodium nitrate (Table I). Salting-Out Agent. T h e effect of varying concentrations ( 1 - 4 x ) of ammonium and sodium nitrate as the
I-
*
5 1.0
: I&
8
5
E 2 6 P
b o
s
EXPERIMENTAL - 1.0
Apparatus and Reagents. A Cambridge p H meter (Marshall Model) and a Russian Type C94 quartz spectrophotometer with 1-cm. cells were used. A stock solution of zirconium nitrate (E. Merck and Co.) was prepared by
Table I.
Partition Coefficient as the Function of Acidity
Zirconium( IV), 130 pg. ; salting agent NaN03, 4M Partition coefficient, Mesityl oxide "01, k D 19%, (1.62M)
50%, (4.35M)
0 0 0.132 0,546 1.42 0,063 0.54 1.42 2.39 4.66
1
2 3 4 5 1 2 3 4
'
5
(8.70~) 1007,,
5 1 2 3 4 5
lOO7,, (8.7OM)
without salting agent
1 158
0.5 1. 0 1.25 1.5 2.5 4 6
7.40 0.137 0,699 7.4 100 7.4 0.132 0,416 0,546 0.546 0,699 1.12 4.66
ANALYTICAL CHEMISTRY
0.5 1.0 1.5 9.0 L O G OF MESITYL OXIDE CONCN.
9.9
c
Table II.
Figure 1 . Partition coefficient as function of mesityl oxide concentration A, 8.
Diverse Ions
Zirconium(IV), 130 pg. Tolerance limit,
Aqueous phase 5 M "01 Aqueous phase 3M "01
dissolving 1.6024 grams of zirconium nitrate in 500 ml. of water containing 1% nitric acid. The solution was standardized gravimetrically as an oxide. It contained 1.08 mg. of zirconium per milliliter. The test solutions (10.8 pg. of zirconium per ml.) were prepared by 10-fold dilution. Mesityl oxide (B.D.H., b.p. 128.7' C.) and alizarin (G. T. Gurr Ltd., London, 0.05% solutions) were used. General Procedure. T h e experimental outline was similar to t h a t reported earlier (2). An aliquot of zirconium nitrate solution containing 130 pg. of zirconium(1V) was mixed with sodium nitrate and nitric acid to a volume of 25 ml. so that the concentration of the salting-out agent and acid would be 4J9. It was then introduced into a separatory funnel and extracted with 10 ml. of 100~o mesityl oxide. For acidity studies, suitable nitric acid concentrhtions were used in place of 4M nitric acid, phereas tor the study of the effect of salting-out and diverse ions, suitable concentrations of saltingout agent and foreign ion were added to the aqueous phase before extraction. At the end of extraction the layers were allowed to settle and separate. The aqueous layer was removed first; then the zirconium(1V) was removed from the organic layer by back-extraction with two 20-ml. portions of water, and was spectrophotometrically determined with alizarin a t 525 mp (6).
Fo!eign ion Hg +z Pb + 2 T1+ Pt Pd +2 Cu +z Cd + 2 Bi + 3 Sn Th c4 Ce +4 Fe + 3 Cr +3 +)
~ 1 + 3
U +e +6
Zn +2 Mn + 2
c o +2 Xi + 2
Mood-' P04C3
sod-'
Source
rg. 205 457 510 30 150"
20b
500 520 150a 500 50 450 150b 230 240 150b 750 750 640 500 15OC
None
CN -
500 25Oe 5OC
Tartrate-'
120
c1-
SCN -
5OC
Kone Citric acid None Oxalic acid Acetic acid 50e Ascorbic acid None EDTA (disoNone dium salt) Foreign ion masked by sequestering agent as KI, HZOZ Tolerance limit increased by preliminary extraction with TTA c Anion removed by passing on anion exchange resin column Citrate-$
Oxalate-2 CHICOOAscorbate-2 EDTA-4
'
salting-out agent on extraction of zirconium(1V) with lOOyo mesityl oxide was studied in the acid range of 2.54J1. Their presence in t h e aqueous phase increased t h e extraction of zirconium(IV), because less mesityl oxide is combined with acid and hence more of it is available for the extraction. The optimum concentration of saltingout agent is 4M sodium nitrate in 4M nitric acid. A higher concentration of nitric acid was avoided because of the slight dissolution of the mesityl oxide layer. The extraction of Zr(1V) with 1 0 0 ~ mesityl o oxide was also studied in the acid range of 2.5-4M to determine the effect of varying concentrations (14M)of NH,NOa and NaN03 as the salting-out agent. Mesityl Oxide Concentration. T h e concentration of mesityl oxide was varied from 19 t o rooyo with methyl isobutyl ketone as the diluent. T h e effect of the extraction was noted a t different acidities (Table I) in t h e presence of 4 J I sodium nitrate. Dilution of mesityl oxide lowers the extraction. A plot of log D us. log C
mesityl oxide (Figure 1) a t 3 and 5 M nitric acid indicates slopes of 2.4 and 1.6, showing the extractable species to be Zr(N0-J4 2 M e 0 and H[Zr(h’Os)4(MeO)z], respectively. The system conforms to the limiting square law (1) in the case of zirconium(1V). The optimum reagent concentration is 100%. Diverse Ions. A number of representative ions were tested for interference (Table 11). Lead, thallium, cadmium, bismuth, iron, aluminum, zinc, manganese, cobalt, nickel, uranium, thorium, chloride, and sulfate do not interfere, even if present in the ratio of 1: 5. Ions which can easily form anionic complexes with zirconium(1V) -e.g., oxalate, citrate, ascorbate, E D T A strongly interfere. The tolerance limit ( 2 ) of ions such as copper, cerium, chromium, and palladium can be increased by preliminary extraction of these ions with 2-thenoyltrifluoroacetone ( 4 ) . Interferences due to anions can be eliminated by anion exchange; whereas those due to certain cations can be removed by masking with suitable sequestering agents. The
tolerance limits of the ions are listed in Table IT. From 10 runs with 130 pg., of zirconium(IV), using a general procedure, the average recovery was 96.4 f 1.2% with a standard deviation of 2.0%. LITERATURE CITED
( 1 ) Alcock. K.. Bedford. F. C.. Hardwick. W. H., &lcKay, H. A.’C., J . Inorg. Nucl: Chem. 4, 100 (1957). ( 2 ) Dhara, S. C., Khopkar, S. ST.,Mikrochim. Acta (in press). (3) Dragulescu, C., Simonescu, T., Policec, S., Talanta 11, 747 (1964). ( 4 ) Khopkar, S. hI., De, A. K., J . Scz. Ind. Res. ( I n d i a ) , 21A, 131 (1962). ( 5 ) Morrison, G. H., Freiser, H., ANAL. CHEM.36, 106R, (1964). ( 6 ) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed., p. 970, Interscience, New York, 1959.
S. 31.KHOPKAR S. C. DHARA
Department of Chemistry Indian Institute of Technology Bombay 76, India WORKsupported by a financial grant from the Council of Scientific and Industrial Research, India.
Modification of Flask Method of Sulfur Determination Determination of Sulfates with Sulfonazo 111
SIR: The flask method ( 2 ) is the most convenient method for determination of organic sulfur. The modification of this method by Wagner (S), who used titration with barium perchlorate and visual indication with thorin, is considered the best. Airecent investigation ( I ) of the color reaction of sulfonazo I11 [2, 7-bis(0-sulfopheny1azo)chromotropic acid] with barium ions resulted in excellent sensitivity and selectivity. Sulfonazo I11 can also be used for visual indication in the barium perchlorate titration of sulfate ions. Compared to the use of thorin, the end point is much sharper and is unaffected by pH changes. The
Table 1.
Determination of Sulfur in Various Samples
%S
Std. dev., %
Sample Calcd. Founda Chromotropic acid (dihy18 00 17 84 f O 16 drate) 1-Cysteine 26 47 26 41 3ZO 17 Potassium sulfate 18 40 18 40b fO 08 Sulfanilic acid 18 52 18 48 f0 16 Taurine 25 62 25 46 f O 18 Thiosemicarbazide 3 5 . 1 9 35,22 f0,20 Thiourea 4 2 . 1 3 4 1 . 9 7 3ZO.24 Average value from 5 determinations. b Average value from 10 determinations.
reaction should be carried out in a homogeneous aqeuous-nonaqueous solution, because a n aqueous medium permits formation of the sulfonazo 111-barium complex. Water and acetone appear to be the best medium. The aprotic solvent acetone decreases the dissociation of sulfonazo 111, and in this way the formation of the sulfonazo 111-barium complex is hindered. Organic sulfur can also be determined by using the flask method and sulfonazo I11 indicator. EXPERIMENTAL
For combustion and titration, 250-ml. or 300-ml. Schoniger flasks were used. Barium perchlorate (0.01M) was prepared by dissolving 2.37 grams of reagent grade barium perchlorate in distilled water and making up to 1 liter. The solution was standardized by titration with reagent grade potassium sulfate, previously dried a t 110’ C. Sulfonazo I11 (0.1%) was prepared by dissolving 0.1 gram of sulfonazo I11 in 100 ml. of distilled water. This solution is stable for many months. Medical grade oxygen wv~bsused directly from the cylinder, and all other chemicals used were reagent grade. Procedure. A 0.15-ml. sample of 30% hydrogen peroxide and 4 ml. of distilled water are placed in a Schoniger flask. The flask is filled with oxygen, and a 4- to 7-mg. sample is combusted and then absorbed by shaking in the absorption solution for 15 minutes.
The flask is opened, 3 ml. of acetone and 3 drops of sulfonazo I11 solution are added, and the solution is titrated with barium perchlorate solution. The red color of the solution changes sharply to blue a t the end point. A blank solution is unnecessary if Schleicher-Schuel filter paper No. 58g2 is used for the combustion step. For calculations, 1 ml. of barium perchlorate solution is the equivalent of 0.32066 mg. of sulfur. Other salts, such as potassium chloride and sodium perchlorate, interfere when present in excess of 0.1 mmole. Primary potassium phosphate interferes in excess of 0.01 mmole. RESULTS
Typical results from the determinations are given in Table I. Work in this laboratory indicates that the titration can be used for the determination of inorganic sulfur if a quartz combustion tube and a spiral absorber are used in place of the Schoniger flask. LITERATURE CITED
( 1 ) BudBBinsk9, B., Yrzalovit, D., Z. Anal. Chem., 210, 161 (1965). ( 2 ) Schoniger, W., Zbid., 181, 28 (1961). (3) Wagner, H., Mikrochim. Acta ( W i e n ) 1957, p. 19.
BRETTSLAV BCDESINSKY Department of Analytical Chemistry Xuclear .Research Institute Czechoslovak Academy of Sciences Rzhezh near Prague, Czechoslovakia VOL. 37, NO. 9, AUGUST 1965
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