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Liquid-liquid extraction of gallium(III) complex ion from aqueous oxalic acid solutions with high molecular weight amine
J. inorg, nucl. Chem., 1977, Vol. 39, pp. 871-875. Pergamon Press. Printed in Great Britain
LIQUID-LIQUID EXTRACTION OF GALLIUM(Ill) COMPLEX ION FROM AQUEOUS OXALIC ACID SOLUTIONS WITH HIGH MOLECULAR WEIGHT AMINE K. YAKABE, H. KATO and S. MINAMI The OsakaInstituteof Technology,Omiya-5-16-1,Asahi-ku,Osaka,Japan
(First received 22 December 1975;in revisedform 20July 1976) Abstract--Theextractionof gallium(III)complexion from aqueous oxalic acid solutionswith tri-n-octylaminein xylene has been investigatedand the effects of pH, of a mole ratio of oxalate to gallium(III)and of amineand gallium(III)concentrationson the gallium(III)extractionhave been measured. Also,gallium(III)species in aqueous oxalic acid solutionshave been examinedusingthe amineextractionmethod. A mechanismfor the extractionof gallium(III)complex ion was discussed on the basis of the results obtained.
INTRODUCTION
The solvent extraction of gallium(HI) complex ion from aqueous chloride media with high molecular weight substituted alkyl ammonium and quaternary salts has been studied by Good et al. [1, 2] and they have reported R3NH+GaCIF and R4N+GaCL- as extracted gallium(Ill) species. Isopropyl ether has been used as extractant for the extraction of HGaC1, by Nachtried et a/.[3] and diethyl ether for the extraction of NH4GaCL by Friedman et al. [4]. In the extraction of metal complex ion from aqueous oxalic acid solutions with high molecular weight amine, one of the factors considered is the distribution ratio of oxalic acid between aqueous and organic phase. The distribution of oxalic acid between the aqueous solution and the organic one of methyldioctylamine has been studied by Bullock et a/.[5] and Funaki et al. have reported the extraction of oxalic acid from aqueous solutions with organic solution of Amberlite LA-2[6]. Pushkov et al. have obtained the distribution coefficient of oxalic acid between aqueous solution of nitric acid and solution of tri-n-octylamine in xylene[7]. The extraction of other metal ions from aqueous oxalic acid solutions with high molecular weight amines has been reported by several investigators[6, 8-10]. The stability constant of trioxalatogallium(III) complex (log/33 = 18.0) was reported[ll]. The authors previously investigated the effect of organic acids on the extraction of zirconium [12] and the extraction of hafnium from aqueous oxalic acid solutions with tri-n-octylamine in xylene[13]. No reference on the extraction of the gallium(Ill) complex ion from aqueous oxalic acid medium has been found. The present paper describes the extraction of the gallium(Ill) complex ion from aqueous oxalic acid solutions with tri-n-octylamine in xylene.
Determination of gaUium(IlI) ion and oxalate After the oxalate included in aqueous solutionswas decomposed with ammoniumpersulfate, gallium(III)ion was standardized against ethylenediaminetetra-aceticacid (EDTA) and the determination of oxalate was carried out by the potassium permanganatemethod. The gallium(III)ion concentrationin the organic phase was obtained as the difference between the concentrations of gallium(III)ion in equalaliquotsof the aqueousphase before and after the extraction. The oxalate concentrationin the organic phase was found by a similarmethod as described above. Extraction procedure Extractions were carried out by the followingprocedure; 25 ml of the aqueous solution containing a definite volume of the gallium(III)stock solution, various amounts of oxalic acid and 25 ml of the TOA xylene solution in a 100ml glass stoppered separating funnel were shaken for 5 min at room temperature. RESULTS AND DISCUSSION
Effect of extraction time on the gallium (III) extraction In order to investigate the effect of extraction time on the gallium(HI) extraction, the extractions of gallium(HI) complex ion from the various systems with 4.70 x 10-2 M TOA xylene solution were carried out. The results obtained are shown in Table I. These results indicate that 5 min extraction time is sufficient to reach equilibrium in this work.
Determination of gaUium(III) species in aqueous oxalic acid solution Investigation of gallium(HI) species in aqueous oxalic acid solutions were carried out using Job's method, the mole ratio and the slope ratio ones[14] and the results obtained are given in Figs. 1-3 respectively. In Fig. 1, gallium(HI) complex ion was extracted into 5.80 x 10-2 M TOA xylene solution from aqueous solution consisting of various molar fractions of gallinm(HI) ion. EXPERIMENTAL The value of pH of the aqueous phase at equilibrium was Reagents and preparation of stock solution in the range of 2.9-3.0. The concentrations of gallium(HI) High purity tri-n-octylamine(TAO) (obtained from Tokyo species in the organic phase were plotted against molar Kashei Kashei Co., Ltd) was used without further purification. fractions of gallium(HI) ion and oxalate in the aqueous The TOA was diluted with xylene. Other chemicals were of phase. The maximum concentration of gallium(HI) analyticalgrade. A stock solution was prepared by dissolvinggallium metal species in the organic phase appeared at the molar (purity is 99.99%)in boilingoxalic acid solutionand the aqueous fraction of gallium(HI) ion of 0.25. In Fig. 2, the results obtained in the extractions of solutionsof gallium(III)chloride(purityis 99.999%)were usedfor gallium(HI) complex ion from 1.22x 10-2 M gallinm(HI) Job's method, the mole ratio and the slope ratio ones. 871
872
K. YAKABE, H. KATe and S. MINAMI Table 1. Effect of extraction time on the gallium(III)extraction Mole rafter (C2042-/Ga
Time (rain)
pH
0.50 1.00 2.00 4.00 6.00 8.00
2.53 2.52 2.52 2.52 2.52 2.52
Mole radar
3+)
2.78 E~(o~) E~(o.)§ 2.34 2.38 2.38 2.38 2.38 2.38
Mole ratios (C20,2-/Ga3+) 4.11 4.66 E:(o.> E~°(o~)§ pH E°(o~ E:(o~§
(C2042-1Ga3 +)
pH
2.93 3.14 3.14 3.16 3.14 3.16
1.49 1.48 !.47 1.47 1.47 1.47
4.96 5.43 5.41 5.43 5.41 5.41
1.22 1.26 1.26 1.26 1.26 1.26
1.19 1.18 1.17 1.17 1.17 1.17
3.32 3.39 3.40 3.41 3.40 3.41
1.01 1.03 1.03 1.03 1.03 1.03
#Gallium--oxalatesystem. ~:Galliumchloride--oxalatesystem. §Oxalate.
r
i
i
i
1.2
el o
o a.
g
u -~0.8
o E cm
L o 0.6 ._=
(.9o c
0.4
H~C~O,: / /so0 i2
"6 0 0
i
1.0
0!2 I 014 I 01.6 I 01,8 f M o l a r f r a c t i o n of Ga in aq. p h a s e 0.8 0.6 0,4 0.2 Molar f r a c t i o n o f o x a l a t e i n o q p h a s e
IO 0
Fig. 1. Determinationof gallium(III)complex species in aqueous oxalic acid solution with Job's method. TeA: 5.80x 10-2 M.
c co 0.2 0
0
0.2 0.4 Concns. of Ga
0.6 0.8 1.0 1,2 and H~C204 i n a q phase (mMol/25ml)
Fig. 3. Determinationof gallium(III)complex species in aqueous oxalic acid solution with slope ratio method. (a) TeA: 3.24x 10-' M; oxalate: 1.92x 10-1M. (b) TeA: 4.80x 10-2 M; gallium: 1.60 x 10-2 M.
o
g •
¢
0.3
¢
.7.
¢
0.2
g o
O0
I
I
I
2 Initial mole ratio
I
I
4 in aq. p h a s e
I
6
(C~O~-/Go)
Fig. 2. Determinationof gallium(III)complex species in aqueous oxalic acid solution with mole ratio method. TeA: 3.24x 10-2 M; gallium: 1.22x 10-2 M. chloride solution containing various amounts of oxalic acid into 3.24 x 10-'M T e A xylene solution in which T e A is a large excess of gallium(III) complex ion give two straight lines with a point of intersection at the mole ratio of oxalate to gallium(Ill) of 3.05 in the aqueous phase. The value of pH of aqueous phase at equilibrium was in the range of 2.7-3.3. In Fig. 3, gallium(Ill) complex ion was extracted from the 1.92 x 10-I M aqueous oxalic acid solution containing various amounts of gallium(Ill) ion and from the 1.60× 10-2M gallium(III) chloride solution containing various amounts of oxalic acid into 3.24x 10-1M and 4.80x 10-2M T e A xylene solutions respectively. The value of pH of aqueous phase at equilibrium was in the range of 2.5-1.3.
The plots of the concentration of gallium(III) species in the organic phase versus the concentrations of gallium(Ill) chloride and of oxalic acid in the aqueous phase give straight lines with the slopes equal to 1.0 and 1/3 respectively. These results obtained from Figs. I-3 show that gallium(Ill) species is presented as a trioxalatogallium(III) complex anion in the aqueous oxalic acid solution and this agrees with the results reported by Kurnakov[15]. Effect of the p H on the gallium (III) extraction Gallium(III) complex ion was extracted into 1.21 x 10-1M T e A xylene solution in which T e A is a large excess to gallium(Ill) complex ion from aqueous oxalic acid solutions containing 1.70 x 10-2 M gallium(Ill) complex ion and 7.43 x 10-2 M oxalate in the pH range from 1.10 to 3.84 adjusted with aqueous ammonium solution and the extraction coefficient of gallium(Ill) complex ion (Eo° = equilibrium concentration of material in the organic phase/that of material in the aqueous phase) were plotted against the value of the pH of equilibrated aqueous phase in Fig. 4. It was found by the titration using EDTA that no detectable amount of gallium(Ill) ion in the equilibrated aqueous pha~e remained at pH 2.3. The E, ° of gallium(III) complex ion is shown by eqn (1), if T e A exists excessively in the organic phase,
log Ea° = n x pH + constant
(1)
where n is an association number of amine to each
Extractionof gallium(III)complexion from aqueousoxalicacid solutions 4
organic phase increased sharply within the extent in which the Eo° of gallium(Ill) complex ion increased linearly and then increased, slowly in contrast to the behavior of gallium(Ill) complex ion. This result suggests that the sharp increase in the Eo° can be attributed to the increase of the amount of the extractable gallium(Ill) species formed with increasing mole ratios in the aqueous phase in the mole ratio region from 1.4 to 2.5 and above this region, the decrease of Eo° for gallium(II) complex ion and the increase of concentration of oxalate in the organic phase appear to be due to the competitive reaction between gallium(III) complex ion and oxalate with TOA.
i
2
~o ,
.J
2
i
i
3
4 oH
Fig. 4. The extraction of gallinm(iII) complex ion with 1.21x 10-~M TOA xylene solution from aqueous solution containing 1.70x 10-2 M gallium(Ill)ion, 7.43x 10-2 M oxalate and various amounts of hydrogenion. gallium(Ill) complex ion. The plot of log Eo° vs pH give slope n, when large excess amine exists and its concentration keeps constant value. The slope of log E~° vs pH of aqueous solution at equilibrium is about -3.0 shown in Fig. 4. Effect of a mole ratio o[ oxalate to gaUium(III) in aqueous phase on the gallium(Ill) extraction The extraction of gallium(Ill) complex ion from aqueous solution containing 2.09x 10-2M gallium(III) complex ion and various amounts of oxalate with 2.91 x 10-2 M TOA xylene solution was carried out. These results are presented in Fig. 5. The Eo° of gallium(III) complex ion increased linearly with increasing equilibrium mole ratios of the aqueous phase in the mole ratio region from 1.4 to 2.5 and attained maximum value at an equilibrium mole ratio of about 3.0 and then gradually decreased with increasing equilibrium mole ratios, while the concentration of oxalate in the .
O~
.
.
.
.
873
Determination of the concentration o[ extracted gallium(Ill) species Gallium(Ill) complex ions were extracted with 2.80 x 10-2 M TOA xylene solution from aqueous oxalic acid solutions containing various amounts of gallium(III) complex ion at a constant mole ratio of oxalate to gallium(Ill) complex ion. The gallium(Ill) and oxalate extracted into the organic phase were determined analytically. The results are shown in Fig. 6. In Fig. 6, the extraction curves (a), (b), (c) and (d) correspond to the extractions carried out with a mole ratio (C2042-/Ga3*) of 1.65, 2.74, 3.25 and 12.7 respectively, at the equilibrium concentration of 8.0 x 10-3 M gallium(Ill) complex ion in the aqueous phase. The value of pH of aqueous solution at equilibrium was present in the range of 1.12-2.76 in each extraction. In the curve (a), it is suggested that the formation of easily extractable gallium(Ill) complex ion is unsatisfactory at the low mole ratio (C2042-/Ga++= 1.65), since the concentration of gallium(Ill) complex ion and oxalate in the organic phase continuously increased over the gallium(Ill) concentration range used in this work. In the curves (b) and (c), however, the concentrations of gallium(III) complex ion and oxalate in the organic phase gradually increased in the range of the equilibrium concentration of gallium(III) complex ion of 4.0 x 10-32.0 x 10-2 M in the aqueous phase. In the curve (d), these concentrations attained a definite value above 2.0x 10-3 M gallium(III) complex ion in the aqueous phase at equilibrium. In the curves (b), (c) and (d), the mean mole .......
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i
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0
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Fig. 5. The extraction of gallium(llI) complex ion with 2.91x 10-2 M TOA xylene solution from aqueous solution containing 2.09 x 10-2 M gallium(Ill)ion and various amounts of oxalate. 0, Extraction coefficient of gallium(Ill); &, extracted oxalate into organicphase. JINC Vol. 39, No. 5--I
0.01 0.1 c o n c h , o f G a in aq. p h a s e
(mMol/25ml)
Fig. 6. The extraction of gallium(III)complex ion from aqueous solution containingvarious amounts gallium(Ill)ion and oxalate with 2.80x 10-2 M TOA. The concentrationsof gallium(Ill)and of oxalatein organicphase are plotted againstequilibriumconcentration of gallium(Ill)ion in aqueous phase. Curves (a; O, O), (b; [], 1), (c; A, &) and (d; <>,@)correspondto moleratio (C20+2-/Ga3+) of 1.65,2.74,3.25 and 12.7at equilibriumrespectively.O, r-l,A, <>, Extracted gallinm(iII)ion; 0, II, A, @,extracted oxalate.
874
K. YAKABE, H. KATO and S. MINAMI
ratios of oxalate to gallium(Ill) in the organic phase obtained in the equilibrium concentration range of gallium(IIl) complex ion of 4.0 × 10-3-2.0 × 10-2 M in the aqueous phase were 3.02, 3.02 and 3.43 for the equilibrium mole ratio (C20~2-/Ga~÷) of 2.74, 3.25 and 12.7 in the aqueous phase respectively. The mole ratios of oxalate to gallium(Ill), of TOA to gallium(IIl) and of TOA to oxalate in the organic phase are plotted against the equilibrium mole ratios of oxalate to gallium(Ill) in the aqueous phase at 8.0 × 10-3M of gallium(III) complex ion in Fig. 7. The mole ratios of TOA to gallium(Ill) and of oxalate to gallium(III) in the organic phase increase with increasing the mole ratio of oxalate to gallium(Ill) in the aqueous phase in the range of the aqueous equilibrium mole ratio (C2042-/Ga~÷) of 3.25 to 12.7, while the mole ratio of TOA to oxalate in the organic phase decreases. It appears that the mole ratio of TOA to gallium(Ill) in the organic phase decreases with increasing amount of extractable gallium(Ill) complex ion in the range of the aqueous equilibrium mole ratio (C20~2-/Ga 3+) of 1.65-3.25 but increases above this range. From Fig. 7, it is supposed that the trioxalatogallium(III) amine salt, amine oxalate and amine bisoxalate may be formed in the organic phase by the competitive reactions between the gallium(Ill) complex ion and oxalic acid with TOA according to the following equations; 3R3N(o~+ 3H+~,)+ Ga(C20,)~-~o) = (R3NH)~Ga(C20,)~o)
(2)
other gallium(IIl) oxalate complex ions and/or the formation of amine oxalates. Therefore, the concentration of oxalate extracted into the organic phase was investigated. On the assumption that unassociated amine is negligible in the flat parts of the extraction curve (d) in Fig. 6, the total concentrations of amine and of oxalate in the organic phase are represented by the following eqns (5) and (6) respectively. [YR3N]¢o)= 2[(R3NH)2C204](o)+ [R3NH2C204](o)+ (2n - 3) x [Ga]¢o) (5) [~-C2042-](o) = [(R3NH)2C204](o)+ [R3NH2C204](o
+ n [Ga]¢o)
where n is an association number of oxalate to each gallium(III) ion. In a previous paper[13], furthermore, the relation between eqns (3) and (4) was investigated and it was found that the following relationship was obtained between [R3NH2C204](o), [(R3NH)2C204](o) and [H2C204](a)
~
[R3NH2C204]~o)/[(R3NH)2C204](o)= 412[H2C204]t°).
(7) Assuming that the association number n is three, from eqns (5-7) the total concentration of oxalate in the organic phase is presented by eqn (8);
2RaNto)+ H2C204ta) = (R3NH)2C204~o>
(3)
A
(R3NH)2C204to)+ H2C204ta)= 2R3NH2C20~o)
(4)
+ 3[Ga]¢o)
where (a) and (o) represent aqueous phase and organic phase respectively and R is n-octyl group and H2C20~=~ represents undissociated oxalic acid in the aqueous phase. At low mole ratios of oxalate to gallium(Ill) in the aqueous phase such as 2.74 and 3.25, gallium(III) complex ion appears to be extracted as the type of trioxalatogallium(III) anion mainly according to eqn (2), since the mole ratio of oxalate to gallium(Ill) in the organic pMse is nearly 3.0. However, the value of the mole ratio of oxalate to gallium(Ill) in the organic phase becomes progressively greater as the equilibrium mole ratio of oxalate to gallium(III) in the aqueous phase increases. This result may be attributed to the formation of the
~3.5C
1 2B_
3] (8)
where A and B are 103[H2C20,]t,> and 3[Ga]to~- [R3N]to~ respectively. From eqns (5-7), the association number n is also represented by eqn (9);
n=3÷ X--~Y X2+(2Y-3Z)(2X-2Y+3Z) Z 4AZ
(9)
where X, Y and Z are observed [C2042-]
u
(6)
3(2Y-3Z) 4A
X2 4AZ"
(10)
The observed concentrations of oxalate in the organic phase were compared with those calculated using eqn (8) and the association number n of oxalate to each o gallium(Ill) complex ion was calculated using eqn (10) and these results are shown in Table 2. In Table 2, the concentration of H2C20~ is calculated using the value of .ao o ¢ pH of the aqueous phase at equilibrium. The accordance o between data observed and calculated is satisfactory and I.IO the value of association number n calculated is nearly 0 three. I-- 3 . 0 0 LO0 i i i i i i From these results and the result described below in the 2 4 6 8 IO 12 investigation of solvent dependence of extraction coeffiEquilibrium mole ratio of aq. ph(Ise ( c=o~./(3o ) cient for gallium(III) complex ion, it is concluded that Fig. 7. Mole ratios of (C2042-/Ga3+), (TOA/Ga3÷) and three molecules of oxalate are associated with each (TOA/C20,2-) in organic phase are plotted against aqueous mole gallium atom; three molecules of oxalate occupy 6ratio of oxalate to gallium(Ill)at equilibrium.@,(C20,2-/Ga3÷)co); coordination positions of gallium atom as bidentate @,(TOA/Ga3+)
Extraction of gallium(Ill)complexion from aqueous oxalic acid solutions
875
Table 2. The observed concentrations of oxalate in organic phase were compared with those calculated by use of eqn (8) and the association number n were calculated by use of eqn (10) Initial concn. of Ga (minnie/L) 10.6 15.9 16.0 16.1 16.1 19.8 21.2
ConCh. of Ga Conch.of oxalate in org. phase pH HzC20~°~ in org. phase Calculated data Observeddata at equilibrium (minnie/L) (minnie/L) (minnie/L) (minnie/L) 1.38 1.30 1.44 1.17 1.12 1.13 1.22
30.6 36.3 23.6 52.9 65.0 54.5 52.9
7.72 9.26 8.24 7.83 7.64 8.19 9.56
complex ion appears to be extracted as the trivalent anion of trioxalatogallium(III) ion, which is formed by the following eqn (11), together with amine bisoxalate mainly formed according to eqn (4), since the value of the mole ratio of TOA to oxalate in the organic phase comes close to 1.0 and the value of the mole ratio of oxalate to gallium(Ill) in the organic phase increases continuously. Ga 3+ + 3H2C20~ = Ga(C204)33- + 3H +.
(I I)
Effect of the amine concentration on the extraction coefficient o[ gallium (III) complex ion The results of the extraction experiments in which gallium(Ill) complex ion was extracted from aqueous oxalic acid solutions containing gallium(Ill) ion and oxalate into xylene solutions containing various amounts of TOA are shown in Fig. 8. The value of pH of aqueous phase at equilibrium are about 2.2, 1.4 and 1.3 for curves (a), (b) and (c) respectively. The equilibrium concentration of TOA in Fig. 8 is defined as the concentration of TOA not associated with gallium(Ill) complex ion and is calculated by subtracting three times of the organic gallium(Ill) concentration from the total concentration of TOA. The extracted gallium(III) complex ion seems to be one
2.¢
28.2 28.2 29.0 28.8 28.8 29.1 28.2
27.8 27.8 29.1 28.3 28.2 28.2 28.7
Association number n 2.98 2.99 2.98 2.99 2.99 2.99 3.00
species which consist of three tri-n-octylammonium cations and one trioxalatogallium(III) anion, since the extraction coefficient of gallium(Ill) complex ion depends on third power of the equilibrium concentration of TOA and the slope of the plot of log E=° vs pH of the aqueous phase at equilibrium was about - 3.0 under the conditions used in this work (Fig. 4), i.e. three tri-n-octylammonium cations associate with each extractable trivalent trioxalatogallium(III) anion. Alternatively, the presence of mixed complex or partially ionized complex acid, e.g, [Ga(C204)3-(HC204),] ¢"+3)- or [H, Ga(C204),+~] ~"+~)- instead of [Ga(C20~)3]3- may be considered but in Fig. 8 it appears that extractable gallium(III) complex anion associates with three ammonium cations. Therefore, the mechanism for the extraction of gallium(Ill) complex ion from aqueous oxalic acid solutions with tri-n-octylamine in xylene in high acidity is represented mainly according to eqn (2). Acknowledgement--The authors are indebted to Mr. M. Oue for his experimental assistance. REFERENCES
1. M. L. Good and F. F. Holland, Jr., J. lnorg. Nucl. Chem. 26, 321 (1963). 2. M.L. Good and S. C. Srivastva,J. lnorg. Nucl. Chem.27, 2429 (1965). 3. N. H. Nachtried and R. E. Frvxell, J. Am. Chem. Soc. 71,4039
(1949).
o
-,.0
/ s l o p e = 3.0
-,i0
0
Log Amine
Fig. 8. The extractions of gallium(liDcomplex ions from aqueous oxalic acid solution containing 2.01 × 10-2 M gallium(HI)complex ion at a constant mole ratio (C20,2-/Ga~+) with xylene solution containing various amounts of TOA were carried out. Curves (a), (b) and (c) correspond to mole ratio (C2042-/Ga3÷) of 3.53, 4.06 and 4.97respectively.
4. H. L. Friedman and H. Taube, J. Am. Chem. Soc. 72, 3362 (1950). 5. J. I.Bullock,S. S. Choi, D. A. Goodrick, D. G. Tuck and E. J. Woodhouse, J. Phys. Chem. 68, 2687 (1964). 6. K. Funaki, I. Ishijima and H. Seki, Kogyo Kagaku Zasshi 71, 339 (1968). 7. A. A. Pushkov, V. S. Schmidt and V. N. Shesterikov, Trudy MKhTI ira. D. I. Mendeleeva No. 43, 13 (1963). 8. H. J. deBruin, D. Kairaitis and R. B. Temple, Austral. J. Chem. 15, 457 (1962). 9. J. I. Bullock and D. G. Tuck, J. lnorg. Nucl. Chem. 33, 3891 (1971). 10. F. L. Moore, Anal. Chem. 37, 1235 (1965). II. J, Stary, Solvent Extraction Chemistry, p. I. North-Holland, Amsterdam 0967). 12. K. Yakabe, S. Kato, H. Uda and S. Minami, Kogyo Kagaku Zasshi 72, 2343 (1969). 13. K. Yakabe and S. Minami, J. lnorg. Nucl. Chem. 37, 1973 (1975). 14. Yu. A. Zolotov, Extraction o/Chelate Compounds, p. 119. Ann Arbor (1970). 15. N. S. Kurnakov, Inst. Obshcheii Neorg. 3, 57 (1957).
LIQUID-LIQUID EXTRACTION OF GALLIUM(Ill) COMPLEX ION FROM AQUEOUS OXALIC ACID SOLUTIONS WITH HIGH MOLECULAR WEIGHT AMINE K. YAKABE, H. KATO and S. MINAMI The OsakaInstituteof Technology,Omiya-5-16-1,Asahi-ku,Osaka,Japan
(First received 22 December 1975;in revisedform 20July 1976) Abstract--Theextractionof gallium(III)complexion from aqueous oxalic acid solutionswith tri-n-octylaminein xylene has been investigatedand the effects of pH, of a mole ratio of oxalate to gallium(III)and of amineand gallium(III)concentrationson the gallium(III)extractionhave been measured. Also,gallium(III)species in aqueous oxalic acid solutionshave been examinedusingthe amineextractionmethod. A mechanismfor the extractionof gallium(III)complex ion was discussed on the basis of the results obtained.
INTRODUCTION
The solvent extraction of gallium(HI) complex ion from aqueous chloride media with high molecular weight substituted alkyl ammonium and quaternary salts has been studied by Good et al. [1, 2] and they have reported R3NH+GaCIF and R4N+GaCL- as extracted gallium(Ill) species. Isopropyl ether has been used as extractant for the extraction of HGaC1, by Nachtried et a/.[3] and diethyl ether for the extraction of NH4GaCL by Friedman et al. [4]. In the extraction of metal complex ion from aqueous oxalic acid solutions with high molecular weight amine, one of the factors considered is the distribution ratio of oxalic acid between aqueous and organic phase. The distribution of oxalic acid between the aqueous solution and the organic one of methyldioctylamine has been studied by Bullock et a/.[5] and Funaki et al. have reported the extraction of oxalic acid from aqueous solutions with organic solution of Amberlite LA-2[6]. Pushkov et al. have obtained the distribution coefficient of oxalic acid between aqueous solution of nitric acid and solution of tri-n-octylamine in xylene[7]. The extraction of other metal ions from aqueous oxalic acid solutions with high molecular weight amines has been reported by several investigators[6, 8-10]. The stability constant of trioxalatogallium(III) complex (log/33 = 18.0) was reported[ll]. The authors previously investigated the effect of organic acids on the extraction of zirconium [12] and the extraction of hafnium from aqueous oxalic acid solutions with tri-n-octylamine in xylene[13]. No reference on the extraction of the gallium(Ill) complex ion from aqueous oxalic acid medium has been found. The present paper describes the extraction of the gallium(Ill) complex ion from aqueous oxalic acid solutions with tri-n-octylamine in xylene.
Determination of gaUium(IlI) ion and oxalate After the oxalate included in aqueous solutionswas decomposed with ammoniumpersulfate, gallium(III)ion was standardized against ethylenediaminetetra-aceticacid (EDTA) and the determination of oxalate was carried out by the potassium permanganatemethod. The gallium(III)ion concentrationin the organic phase was obtained as the difference between the concentrations of gallium(III)ion in equalaliquotsof the aqueousphase before and after the extraction. The oxalate concentrationin the organic phase was found by a similarmethod as described above. Extraction procedure Extractions were carried out by the followingprocedure; 25 ml of the aqueous solution containing a definite volume of the gallium(III)stock solution, various amounts of oxalic acid and 25 ml of the TOA xylene solution in a 100ml glass stoppered separating funnel were shaken for 5 min at room temperature. RESULTS AND DISCUSSION
Effect of extraction time on the gallium (III) extraction In order to investigate the effect of extraction time on the gallium(HI) extraction, the extractions of gallium(HI) complex ion from the various systems with 4.70 x 10-2 M TOA xylene solution were carried out. The results obtained are shown in Table I. These results indicate that 5 min extraction time is sufficient to reach equilibrium in this work.
Determination of gaUium(III) species in aqueous oxalic acid solution Investigation of gallium(HI) species in aqueous oxalic acid solutions were carried out using Job's method, the mole ratio and the slope ratio ones[14] and the results obtained are given in Figs. 1-3 respectively. In Fig. 1, gallium(HI) complex ion was extracted into 5.80 x 10-2 M TOA xylene solution from aqueous solution consisting of various molar fractions of gallinm(HI) ion. EXPERIMENTAL The value of pH of the aqueous phase at equilibrium was Reagents and preparation of stock solution in the range of 2.9-3.0. The concentrations of gallium(HI) High purity tri-n-octylamine(TAO) (obtained from Tokyo species in the organic phase were plotted against molar Kashei Kashei Co., Ltd) was used without further purification. fractions of gallium(HI) ion and oxalate in the aqueous The TOA was diluted with xylene. Other chemicals were of phase. The maximum concentration of gallium(HI) analyticalgrade. A stock solution was prepared by dissolvinggallium metal species in the organic phase appeared at the molar (purity is 99.99%)in boilingoxalic acid solutionand the aqueous fraction of gallium(HI) ion of 0.25. In Fig. 2, the results obtained in the extractions of solutionsof gallium(III)chloride(purityis 99.999%)were usedfor gallium(HI) complex ion from 1.22x 10-2 M gallinm(HI) Job's method, the mole ratio and the slope ratio ones. 871
872
K. YAKABE, H. KATe and S. MINAMI Table 1. Effect of extraction time on the gallium(III)extraction Mole rafter (C2042-/Ga
Time (rain)
pH
0.50 1.00 2.00 4.00 6.00 8.00
2.53 2.52 2.52 2.52 2.52 2.52
Mole radar
3+)
2.78 E~(o~) E~(o.)§ 2.34 2.38 2.38 2.38 2.38 2.38
Mole ratios (C20,2-/Ga3+) 4.11 4.66 E:(o.> E~°(o~)§ pH E°(o~ E:(o~§
(C2042-1Ga3 +)
pH
2.93 3.14 3.14 3.16 3.14 3.16
1.49 1.48 !.47 1.47 1.47 1.47
4.96 5.43 5.41 5.43 5.41 5.41
1.22 1.26 1.26 1.26 1.26 1.26
1.19 1.18 1.17 1.17 1.17 1.17
3.32 3.39 3.40 3.41 3.40 3.41
1.01 1.03 1.03 1.03 1.03 1.03
#Gallium--oxalatesystem. ~:Galliumchloride--oxalatesystem. §Oxalate.
r
i
i
i
1.2
el o
o a.
g
u -~0.8
o E cm
L o 0.6 ._=
(.9o c
0.4
H~C~O,: / /so0 i2
"6 0 0
i
1.0
0!2 I 014 I 01.6 I 01,8 f M o l a r f r a c t i o n of Ga in aq. p h a s e 0.8 0.6 0,4 0.2 Molar f r a c t i o n o f o x a l a t e i n o q p h a s e
IO 0
Fig. 1. Determinationof gallium(III)complex species in aqueous oxalic acid solution with Job's method. TeA: 5.80x 10-2 M.
c co 0.2 0
0
0.2 0.4 Concns. of Ga
0.6 0.8 1.0 1,2 and H~C204 i n a q phase (mMol/25ml)
Fig. 3. Determinationof gallium(III)complex species in aqueous oxalic acid solution with slope ratio method. (a) TeA: 3.24x 10-' M; oxalate: 1.92x 10-1M. (b) TeA: 4.80x 10-2 M; gallium: 1.60 x 10-2 M.
o
g •
¢
0.3
¢
.7.
¢
0.2
g o
O0
I
I
I
2 Initial mole ratio
I
I
4 in aq. p h a s e
I
6
(C~O~-/Go)
Fig. 2. Determinationof gallium(III)complex species in aqueous oxalic acid solution with mole ratio method. TeA: 3.24x 10-2 M; gallium: 1.22x 10-2 M. chloride solution containing various amounts of oxalic acid into 3.24 x 10-'M T e A xylene solution in which T e A is a large excess of gallium(III) complex ion give two straight lines with a point of intersection at the mole ratio of oxalate to gallium(Ill) of 3.05 in the aqueous phase. The value of pH of aqueous phase at equilibrium was in the range of 2.7-3.3. In Fig. 3, gallium(Ill) complex ion was extracted from the 1.92 x 10-I M aqueous oxalic acid solution containing various amounts of gallium(Ill) ion and from the 1.60× 10-2M gallium(III) chloride solution containing various amounts of oxalic acid into 3.24x 10-1M and 4.80x 10-2M T e A xylene solutions respectively. The value of pH of aqueous phase at equilibrium was in the range of 2.5-1.3.
The plots of the concentration of gallium(III) species in the organic phase versus the concentrations of gallium(Ill) chloride and of oxalic acid in the aqueous phase give straight lines with the slopes equal to 1.0 and 1/3 respectively. These results obtained from Figs. I-3 show that gallium(Ill) species is presented as a trioxalatogallium(III) complex anion in the aqueous oxalic acid solution and this agrees with the results reported by Kurnakov[15]. Effect of the p H on the gallium (III) extraction Gallium(III) complex ion was extracted into 1.21 x 10-1M T e A xylene solution in which T e A is a large excess to gallium(Ill) complex ion from aqueous oxalic acid solutions containing 1.70 x 10-2 M gallium(Ill) complex ion and 7.43 x 10-2 M oxalate in the pH range from 1.10 to 3.84 adjusted with aqueous ammonium solution and the extraction coefficient of gallium(Ill) complex ion (Eo° = equilibrium concentration of material in the organic phase/that of material in the aqueous phase) were plotted against the value of the pH of equilibrated aqueous phase in Fig. 4. It was found by the titration using EDTA that no detectable amount of gallium(Ill) ion in the equilibrated aqueous pha~e remained at pH 2.3. The E, ° of gallium(III) complex ion is shown by eqn (1), if T e A exists excessively in the organic phase,
log Ea° = n x pH + constant
(1)
where n is an association number of amine to each
Extractionof gallium(III)complexion from aqueousoxalicacid solutions 4
organic phase increased sharply within the extent in which the Eo° of gallium(Ill) complex ion increased linearly and then increased, slowly in contrast to the behavior of gallium(Ill) complex ion. This result suggests that the sharp increase in the Eo° can be attributed to the increase of the amount of the extractable gallium(Ill) species formed with increasing mole ratios in the aqueous phase in the mole ratio region from 1.4 to 2.5 and above this region, the decrease of Eo° for gallium(II) complex ion and the increase of concentration of oxalate in the organic phase appear to be due to the competitive reaction between gallium(III) complex ion and oxalate with TOA.
i
2
~o ,
.J
2
i
i
3
4 oH
Fig. 4. The extraction of gallinm(iII) complex ion with 1.21x 10-~M TOA xylene solution from aqueous solution containing 1.70x 10-2 M gallium(Ill)ion, 7.43x 10-2 M oxalate and various amounts of hydrogenion. gallium(Ill) complex ion. The plot of log Eo° vs pH give slope n, when large excess amine exists and its concentration keeps constant value. The slope of log E~° vs pH of aqueous solution at equilibrium is about -3.0 shown in Fig. 4. Effect of a mole ratio o[ oxalate to gaUium(III) in aqueous phase on the gallium(Ill) extraction The extraction of gallium(Ill) complex ion from aqueous solution containing 2.09x 10-2M gallium(III) complex ion and various amounts of oxalate with 2.91 x 10-2 M TOA xylene solution was carried out. These results are presented in Fig. 5. The Eo° of gallium(III) complex ion increased linearly with increasing equilibrium mole ratios of the aqueous phase in the mole ratio region from 1.4 to 2.5 and attained maximum value at an equilibrium mole ratio of about 3.0 and then gradually decreased with increasing equilibrium mole ratios, while the concentration of oxalate in the .
O~
.
.
.
.
873
Determination of the concentration o[ extracted gallium(Ill) species Gallium(Ill) complex ions were extracted with 2.80 x 10-2 M TOA xylene solution from aqueous oxalic acid solutions containing various amounts of gallium(III) complex ion at a constant mole ratio of oxalate to gallium(Ill) complex ion. The gallium(Ill) and oxalate extracted into the organic phase were determined analytically. The results are shown in Fig. 6. In Fig. 6, the extraction curves (a), (b), (c) and (d) correspond to the extractions carried out with a mole ratio (C2042-/Ga3*) of 1.65, 2.74, 3.25 and 12.7 respectively, at the equilibrium concentration of 8.0 x 10-3 M gallium(Ill) complex ion in the aqueous phase. The value of pH of aqueous solution at equilibrium was present in the range of 1.12-2.76 in each extraction. In the curve (a), it is suggested that the formation of easily extractable gallium(Ill) complex ion is unsatisfactory at the low mole ratio (C2042-/Ga++= 1.65), since the concentration of gallium(Ill) complex ion and oxalate in the organic phase continuously increased over the gallium(Ill) concentration range used in this work. In the curves (b) and (c), however, the concentrations of gallium(III) complex ion and oxalate in the organic phase gradually increased in the range of the equilibrium concentration of gallium(III) complex ion of 4.0 x 10-32.0 x 10-2 M in the aqueous phase. In the curve (d), these concentrations attained a definite value above 2.0x 10-3 M gallium(III) complex ion in the aqueous phase at equilibrium. In the curves (b), (c) and (d), the mean mole .......
0.8
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i
, i i i i 3 5 7 E q u i l i b r i u m m o l e r a t i o o f aq. phase
0
(C=O~'/G a )
Fig. 5. The extraction of gallium(llI) complex ion with 2.91x 10-2 M TOA xylene solution from aqueous solution containing 2.09 x 10-2 M gallium(Ill)ion and various amounts of oxalate. 0, Extraction coefficient of gallium(Ill); &, extracted oxalate into organicphase. JINC Vol. 39, No. 5--I
0.01 0.1 c o n c h , o f G a in aq. p h a s e
(mMol/25ml)
Fig. 6. The extraction of gallium(III)complex ion from aqueous solution containingvarious amounts gallium(Ill)ion and oxalate with 2.80x 10-2 M TOA. The concentrationsof gallium(Ill)and of oxalatein organicphase are plotted againstequilibriumconcentration of gallium(Ill)ion in aqueous phase. Curves (a; O, O), (b; [], 1), (c; A, &) and (d; <>,@)correspondto moleratio (C20+2-/Ga3+) of 1.65,2.74,3.25 and 12.7at equilibriumrespectively.O, r-l,A, <>, Extracted gallinm(iII)ion; 0, II, A, @,extracted oxalate.
874
K. YAKABE, H. KATO and S. MINAMI
ratios of oxalate to gallium(Ill) in the organic phase obtained in the equilibrium concentration range of gallium(IIl) complex ion of 4.0 × 10-3-2.0 × 10-2 M in the aqueous phase were 3.02, 3.02 and 3.43 for the equilibrium mole ratio (C20~2-/Ga~÷) of 2.74, 3.25 and 12.7 in the aqueous phase respectively. The mole ratios of oxalate to gallium(Ill), of TOA to gallium(IIl) and of TOA to oxalate in the organic phase are plotted against the equilibrium mole ratios of oxalate to gallium(Ill) in the aqueous phase at 8.0 × 10-3M of gallium(III) complex ion in Fig. 7. The mole ratios of TOA to gallium(Ill) and of oxalate to gallium(III) in the organic phase increase with increasing the mole ratio of oxalate to gallium(Ill) in the aqueous phase in the range of the aqueous equilibrium mole ratio (C2042-/Ga~÷) of 3.25 to 12.7, while the mole ratio of TOA to oxalate in the organic phase decreases. It appears that the mole ratio of TOA to gallium(Ill) in the organic phase decreases with increasing amount of extractable gallium(Ill) complex ion in the range of the aqueous equilibrium mole ratio (C20~2-/Ga 3+) of 1.65-3.25 but increases above this range. From Fig. 7, it is supposed that the trioxalatogallium(III) amine salt, amine oxalate and amine bisoxalate may be formed in the organic phase by the competitive reactions between the gallium(Ill) complex ion and oxalic acid with TOA according to the following equations; 3R3N(o~+ 3H+~,)+ Ga(C20,)~-~o) = (R3NH)~Ga(C20,)~o)
(2)
other gallium(IIl) oxalate complex ions and/or the formation of amine oxalates. Therefore, the concentration of oxalate extracted into the organic phase was investigated. On the assumption that unassociated amine is negligible in the flat parts of the extraction curve (d) in Fig. 6, the total concentrations of amine and of oxalate in the organic phase are represented by the following eqns (5) and (6) respectively. [YR3N]¢o)= 2[(R3NH)2C204](o)+ [R3NH2C204](o)+ (2n - 3) x [Ga]¢o) (5) [~-C2042-](o) = [(R3NH)2C204](o)+ [R3NH2C204](o
+ n [Ga]¢o)
where n is an association number of oxalate to each gallium(III) ion. In a previous paper[13], furthermore, the relation between eqns (3) and (4) was investigated and it was found that the following relationship was obtained between [R3NH2C204](o), [(R3NH)2C204](o) and [H2C204](a)
~
[R3NH2C204]~o)/[(R3NH)2C204](o)= 412[H2C204]t°).
(7) Assuming that the association number n is three, from eqns (5-7) the total concentration of oxalate in the organic phase is presented by eqn (8);
2RaNto)+ H2C204ta) = (R3NH)2C204~o>
(3)
A
(R3NH)2C204to)+ H2C204ta)= 2R3NH2C20~o)
(4)
+ 3[Ga]¢o)
where (a) and (o) represent aqueous phase and organic phase respectively and R is n-octyl group and H2C20~=~ represents undissociated oxalic acid in the aqueous phase. At low mole ratios of oxalate to gallium(Ill) in the aqueous phase such as 2.74 and 3.25, gallium(III) complex ion appears to be extracted as the type of trioxalatogallium(III) anion mainly according to eqn (2), since the mole ratio of oxalate to gallium(Ill) in the organic pMse is nearly 3.0. However, the value of the mole ratio of oxalate to gallium(Ill) in the organic phase becomes progressively greater as the equilibrium mole ratio of oxalate to gallium(III) in the aqueous phase increases. This result may be attributed to the formation of the
~3.5C
1 2B_
3] (8)
where A and B are 103[H2C20,]t,> and 3[Ga]to~- [R3N]to~ respectively. From eqns (5-7), the association number n is also represented by eqn (9);
n=3÷ X--~Y X2+(2Y-3Z)(2X-2Y+3Z) Z 4AZ
(9)
where X, Y and Z are observed [C2042-]
u
(6)
3(2Y-3Z) 4A
X2 4AZ"
(10)
The observed concentrations of oxalate in the organic phase were compared with those calculated using eqn (8) and the association number n of oxalate to each o gallium(Ill) complex ion was calculated using eqn (10) and these results are shown in Table 2. In Table 2, the concentration of H2C20~ is calculated using the value of .ao o ¢ pH of the aqueous phase at equilibrium. The accordance o between data observed and calculated is satisfactory and I.IO the value of association number n calculated is nearly 0 three. I-- 3 . 0 0 LO0 i i i i i i From these results and the result described below in the 2 4 6 8 IO 12 investigation of solvent dependence of extraction coeffiEquilibrium mole ratio of aq. ph(Ise ( c=o~./(3o ) cient for gallium(III) complex ion, it is concluded that Fig. 7. Mole ratios of (C2042-/Ga3+), (TOA/Ga3÷) and three molecules of oxalate are associated with each (TOA/C20,2-) in organic phase are plotted against aqueous mole gallium atom; three molecules of oxalate occupy 6ratio of oxalate to gallium(Ill)at equilibrium.@,(C20,2-/Ga3÷)co); coordination positions of gallium atom as bidentate @,(TOA/Ga3+)
Extraction of gallium(Ill)complexion from aqueous oxalic acid solutions
875
Table 2. The observed concentrations of oxalate in organic phase were compared with those calculated by use of eqn (8) and the association number n were calculated by use of eqn (10) Initial concn. of Ga (minnie/L) 10.6 15.9 16.0 16.1 16.1 19.8 21.2
ConCh. of Ga Conch.of oxalate in org. phase pH HzC20~°~ in org. phase Calculated data Observeddata at equilibrium (minnie/L) (minnie/L) (minnie/L) (minnie/L) 1.38 1.30 1.44 1.17 1.12 1.13 1.22
30.6 36.3 23.6 52.9 65.0 54.5 52.9
7.72 9.26 8.24 7.83 7.64 8.19 9.56
complex ion appears to be extracted as the trivalent anion of trioxalatogallium(III) ion, which is formed by the following eqn (11), together with amine bisoxalate mainly formed according to eqn (4), since the value of the mole ratio of TOA to oxalate in the organic phase comes close to 1.0 and the value of the mole ratio of oxalate to gallium(Ill) in the organic phase increases continuously. Ga 3+ + 3H2C20~ = Ga(C204)33- + 3H +.
(I I)
Effect of the amine concentration on the extraction coefficient o[ gallium (III) complex ion The results of the extraction experiments in which gallium(Ill) complex ion was extracted from aqueous oxalic acid solutions containing gallium(Ill) ion and oxalate into xylene solutions containing various amounts of TOA are shown in Fig. 8. The value of pH of aqueous phase at equilibrium are about 2.2, 1.4 and 1.3 for curves (a), (b) and (c) respectively. The equilibrium concentration of TOA in Fig. 8 is defined as the concentration of TOA not associated with gallium(Ill) complex ion and is calculated by subtracting three times of the organic gallium(Ill) concentration from the total concentration of TOA. The extracted gallium(III) complex ion seems to be one
2.¢
28.2 28.2 29.0 28.8 28.8 29.1 28.2
27.8 27.8 29.1 28.3 28.2 28.2 28.7
Association number n 2.98 2.99 2.98 2.99 2.99 2.99 3.00
species which consist of three tri-n-octylammonium cations and one trioxalatogallium(III) anion, since the extraction coefficient of gallium(Ill) complex ion depends on third power of the equilibrium concentration of TOA and the slope of the plot of log E=° vs pH of the aqueous phase at equilibrium was about - 3.0 under the conditions used in this work (Fig. 4), i.e. three tri-n-octylammonium cations associate with each extractable trivalent trioxalatogallium(III) anion. Alternatively, the presence of mixed complex or partially ionized complex acid, e.g, [Ga(C204)3-(HC204),] ¢"+3)- or [H, Ga(C204),+~] ~"+~)- instead of [Ga(C20~)3]3- may be considered but in Fig. 8 it appears that extractable gallium(III) complex anion associates with three ammonium cations. Therefore, the mechanism for the extraction of gallium(Ill) complex ion from aqueous oxalic acid solutions with tri-n-octylamine in xylene in high acidity is represented mainly according to eqn (2). Acknowledgement--The authors are indebted to Mr. M. Oue for his experimental assistance. REFERENCES
1. M. L. Good and F. F. Holland, Jr., J. lnorg. Nucl. Chem. 26, 321 (1963). 2. M.L. Good and S. C. Srivastva,J. lnorg. Nucl. Chem.27, 2429 (1965). 3. N. H. Nachtried and R. E. Frvxell, J. Am. Chem. Soc. 71,4039
(1949).
o
-,.0
/ s l o p e = 3.0
-,i0
0
Log Amine
Fig. 8. The extractions of gallium(liDcomplex ions from aqueous oxalic acid solution containing 2.01 × 10-2 M gallium(HI)complex ion at a constant mole ratio (C20,2-/Ga~+) with xylene solution containing various amounts of TOA were carried out. Curves (a), (b) and (c) correspond to mole ratio (C2042-/Ga3÷) of 3.53, 4.06 and 4.97respectively.
4. H. L. Friedman and H. Taube, J. Am. Chem. Soc. 72, 3362 (1950). 5. J. I.Bullock,S. S. Choi, D. A. Goodrick, D. G. Tuck and E. J. Woodhouse, J. Phys. Chem. 68, 2687 (1964). 6. K. Funaki, I. Ishijima and H. Seki, Kogyo Kagaku Zasshi 71, 339 (1968). 7. A. A. Pushkov, V. S. Schmidt and V. N. Shesterikov, Trudy MKhTI ira. D. I. Mendeleeva No. 43, 13 (1963). 8. H. J. deBruin, D. Kairaitis and R. B. Temple, Austral. J. Chem. 15, 457 (1962). 9. J. I. Bullock and D. G. Tuck, J. lnorg. Nucl. Chem. 33, 3891 (1971). 10. F. L. Moore, Anal. Chem. 37, 1235 (1965). II. J, Stary, Solvent Extraction Chemistry, p. I. North-Holland, Amsterdam 0967). 12. K. Yakabe, S. Kato, H. Uda and S. Minami, Kogyo Kagaku Zasshi 72, 2343 (1969). 13. K. Yakabe and S. Minami, J. lnorg. Nucl. Chem. 37, 1973 (1975). 14. Yu. A. Zolotov, Extraction o/Chelate Compounds, p. 119. Ann Arbor (1970). 15. N. S. Kurnakov, Inst. Obshcheii Neorg. 3, 57 (1957).