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Liquid-liquid extraction of hafnium complex ion from aqueous oxalic acid solution with high molecular weight amine
J. ino~t, ,lull Chem. 1975, Vol. 3"r, pp. 1973-1q76 Pergamon Press. Printed in Great Britain
LIQUID-LIQUID EXTRACTION OF HAFNIUM COMPLEX ION FROM AQUEOUS OXALIC ACID SOLUTION WITH HIGH MOLECULAR WEIGHT AMINE K. YAKABE and S. MINAMI The Osaka Institute of Technology,Omiya-5-16-1,Asahi-ku,Osaka, Japan
(First received 22 July 1974:in revisedfi)rm 21 October 1974) Abstract--Extraction of hafnium from aqueous oxalic acid solution with high molecular weight amine was studied. It was confirmed that the tetraoxalato complex ion of hafnium is extracted from aqueous oxalic acid solution with tri-n-octylamine in xylene solution. A mechanism for the extraction of hafnium complex ion was discussed on the basis of the results obtained. INTRODUCTION THE EXTRACTIONof hafnium complex ion from strongly acidic solution with N-benzoyl-N-phenylhydroxylamine has been studied by Hala[1, 2] and the extraction of tStHf tracer from hydrochloric acid solution with methyl-dioctylamine by Moore[3]. The distribution of oxalic acid between aqueous solution and organic solution of methyl-di-octylamine has been studied by Bullock et al. [4] and Funaki et al. [5] have reported the extraction of oxalic acid from aqueous solution with organic solution of Amberlite LA-2. The extraction of the other metal complex ions from aqueous oxalic acid solutions with high molecular weight amines in organic solvents has been studied by several investigators [5-7]. The authors have previously investigated the effect of organic acids on the extraction of zirconium ion[8]. The present paper describes the extraction of hafnium ion from aqueous oxalic acid solution with tri-n-octylamine in xylene solution. EXPERIMENTAL Reagents and preparation of stock solution The amine used was tri-n-octylamine (TOA) diluted with xylene. The other chemicals were analytical reagent grade. A stock solution of hafnium complex ion was prepared by dissolving hafnium hydroxide obtained from the alkali fussion of hafnium oxide in an aqueous oxalic acid solution.
Extraction procedure Extractions were carried out by the followingprocedure; 25 ml of aqueous solution containing a definite volume of hafnium stock solution and various amounts of oxalic acid and 25 ml of TOA-xylenesolution in a 100 ml glass stoppered separating funnel were shaken for 5 rain at room temperature. After the separation of an organic phase, both the hafnium complex ion and the oxalate ion extracted into the organic phase were stripped with 1.5 M nitric acid or 2.0 M hydrochloric acid. Hafnium was determined by the gravimetric method as pyrophosphate or oxide and the determination of oxalate and chloride was carried out by the titration methods. RESULTS AND DISCUSSION Effect of concentration of hydrogen ion on hafnium extraction Hafnium complex ion was extracted from aqueous
oxalic acid solution containing 0.012 M hafnium, 0.089 M oxalate and various amounts of hydrogen ion with 0.055 M TOA-xylene solution and the results are shown in Fig. 1. Figure 1 shows that the distribution coefficient (E~a= equilibrium concentration of hafnium in organic phase/equilibrium concentration of hafnium in aqueous phase) of the hafnium complex ion is 199 at a pH of about 1.7 at equilibrium but decreases sharply as the pH of the aqueous phase increases and reaches almost zero at a pH of about 4.4.
Effect of chloride ion on the hafnium extraction In order to investigate the effect of chloride ion on the extraction of hafnium complex ion, hafnium complex ion was extracted with 0.059 M TOA-xylene solution from the aqueous oxalic acid solution containing 0.012 M hafnium complex ion, 0.089M oxalate and various amounts of hydrochloric acid and these results are shown in Fig. 2. The E~ of the hafnium complex ion decreased with increasing equilibrium concentration of hydrochloric acid in the aqueous solution and became almost zero above I. 19 M of aqueous hydrochloric acid, while the concentration of chloride ion in the organic phase increased with increasing equilibrium concentration of hydrochloric acid in the aqueous phase and TOA was saturated with chloride above 1.19 M of aqueous hydrochloric acid. These results show that the decrease of E~ is due to the competitive reaction between hafnium complex ion and chloride ion with TOA. Effect of a mole ratio of oxalate to hafnium in aqueous phase on hafnium extraction Hafnium complex ions were extracted from aqueous phase containing 0.018M hafnium complex ion and various amounts of oxalate with 0.082 M TOA in xylene solution. These results are presented in Fig. 3. The E~ of hafnium complex ion increased linearly with increasing equilibrium mole ratios of aqueous phase in the mole ratio region from 1.58 to 8.58, but a third phase formed slightly between the aqueous and the organic phase below a mole ratio of about 2-00. This suggests that the increase in the E~ can be attributed to the increase in
1973
1974
K. YAKABEand S. MINAMI
/-
2
2 I
o~
o _J
o,o
I
-I
0 I
I
I
I
2
3
4
5
I
I
I
2
3
LO g (C~)~'/H f ) af equilibrium
pH
Fig. 1. Effect of pH on the extraction of hafnium with 1.38mmole/25ml TOA-xylene solution from aqueous phase containing 0.31 mmole/25ml of hafnium, 2.22 mmole/25ml of oxalate and various amounts of hydrogen ion. Log E is plotted against pH of equilibratedaqueous phase.
_-
I
~
1,5
2 E
¢) 04 ~' 0
I
f.o =E
E
Fig. 3. Effect of a moleratio of oxalate to hafniumon the extraction of hafnium with 2.05 mmole/25ml TOA-xylene solution from aqueous phase containing0.45 mmole/25ml of hafnium at various mole ratios. Log E is plotted against the mole ratio of equilibrated aqueous phase.
Determination of the concentration of extracted hafnium species Hafnium complex ions were extracted with 0.056 M TOA in xylene solution from aqueous oxalic acid solution containing various amounts of hafnium complex ion at a constant mole ratio of hafnium complex ion to oxalate. The hafnium and the oxalate extracted into the organic phase were determined analytically. These results are shown in Fig. 4. In Fig. 4, the curves (a), (b) and (c) correspond to extractions carried out with a mole ratio (C2042-/H0 of 3.56, 5.69 and 15.2 respectively at the equilibrium
n
-i
o.o _~ o
5
I ~ ./J'.~s-:-~----~--<~-<~--.~o U I
0
I
n
1.0
0 2.0
Cone. of HCI at equilibrium (M/L)
Fig. 2. Effect of chloride ion on the extraction of hafnium with 1.48mmole/25ml TOA-xylene solution from aqueous phase containing 0.31 mmole/25ml of hafnium, 2.22mmole/25ml of oxalate and various amounts of chloride ion, O, Hafnium complex ion; &, Chloride ion.
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i
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,,: //
, 0.01
the extractable hafnium species with increasing mole ratios in the aqueous phase. Above a mole ratio of about 70, the E~° attained a constant value, that is, 199. But below a mole ratio of about 1.6, the extraction of hafnium complex ion was impossible because of the formation of emulsion.
A'/I
/ ",' / l
1
5
~ 0.1
1.0
Equilibrium cone, o f Hf ( m M o l / 2 5 ml)
Fig. 4. Concentrations of hafnium and of oxalate in organic phase are plotted against equilibrium concentration of hafnium in aqueous phase. Curves (a-c) are mole ratios (C2042-/Hf)3.56, 5.69 and 15.2 at equilibriumrespectively. ©, A, O, Hafnium complex ion; O, i , e, Oxalate.
Liquid-liquidextraction of hafniumcomplexion
t975
concentration of 8.0x 10--3M hafnium complex ion aqueous phase. The concentrations of hafnium and oxalate in the organic phase increase with the equilibrium concentration of hafnium up to about 1.6 x 10-3M and then attain a definite value. In the flat parts of the curves (a) and (b) in Fig. 4, the mole ratios of oxalate to hafnium in the organic phase were 3.99 and 4-02 respectively. These results indicate that the extracted hafnium complex species consists of one atom of hafnium and four molecules of oxalate, and this conclusion agreed with that of X-ray analysis for crystal hafnium oxalate[9]. In the fiat parts of the curves (c) in Fig. 4, however, the mole ratio of oxalate to hafnium in the organic phase attained a value of 4-27. In Fig. 5, the mole ratios of oxalate to hafnium, of TOA to hafnium and of TOA to oxalate in organic phase are plotted against the mole ratio of oxalate to hafnium in aqueous phase at 8.0 x 10-~ M of hafnium complex ion. From Fig. 5, it is supposed that hafnium oxalate amine salt, amine oxalate and amine bisoxalate may be formed in the organic phase by the competitive reactions between the hafnium oxalate complex and oxalic acid with TOA according to the following equations;
(1) and at high mole ratio such as 15.2, the hafnium oxa|ate complex ion and amine bisoxalate appear to be extracted mainly according to the Eqns (1) and (3), since the mole ratio of TOA to oxalate in the organic phase attained a value of almost 1 : 1. Furthermore, in order to investigate the relation between Eqn (2) and (3), log [R3NH2C204]~,,)/ [(R~NH)2C_.O,].... is plotted against Iog[H2C20~]~,, in Fig. 6. Since the log-log plot in Fig. 6 gives a straight line and its slope is 1.00 -+0.03, the following relation is deduced;
4R3N(o) + 4H[,~+ Hf(C204)~., = (R3NH)4Hf(C204)4(o}
where n is an association number of oxalate to each hafnium atom. From Eqns (4-6), the total concentraction of oxalate in the organic phase is represented by Eqn (7):
(1)
2R3N~o~+ H2C204~.,= (R3NH)2C204~o~
(2)
(R~NH)2C204,o,+ H2C~O4,.,= 2R3NH2C~O~o~
(3)
where (o) and (a) represent organic phase and aqueous phase respectively and H2C204(o, represents undissociated oxalic acid in the aqueous phase. At low mole ratios of oxalate to hafnium in the aqueous phase such as 3.56 and 5.69, the hafnium oxalate complex appears to be extracted mainly according to the equation o °"430
[R 3NH2C204]~o)][(R 3NH)2C204],,,, = 412[H2C204],0, (4) On the assumption that unassociated amine is negligible in the fiat parts of the extraction curves (c) in Fig. 4, the total concentration of amine and oxalate in the organic phase are represented by the following Eqns (5) and (6) respectively. []~R3N]~o~= 2[(R3NH)2C:O4],o)+ [R3NH2C204](,,, + (2n - 4)[Hf],o,
(5)
[EC..O,z-],o, = [(R3NH)2C:O,],o,+ [R 3NH2C204](o) + n [Hf],,,
(6)
(7) where A and B are I03[C2042 ]<~ and n[Hf]~:,~--[R3N]~,,~ respectively. Assuming that the association number n is four, the observed concentrations of oxalate in the organic phase were compared with those calculated and these results are shown in Table 1.
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Equilibrium mole ratio of aq. phase (C20~-IH f)
Fig. 5. (C2042-/Hf),(TOA/Hf)and (TOA/C2042-)in organicphase are plotted against aqueous mole ratio of oxalate to hafnium at equilibrium. O, (C~O,~-/Hf) in organic phase; @, (TOA/Hf) in organicphase; A, (TOA/C20,2-) in organicphase.
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-z~
-zo
I
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[R.,NH2C20.d~,./I(R3NH)2C20.].,, is log H2C20,~,,,
plotted against
1976
K. YAKABE and S. MINAMI Table I. The observed concentration of oxaiate in organic phase was compared with those calculatedby use of the Eqn (7) Initial concn. HzCzO,(a) of Hf pH (mMol/L) at equilibrium (mMol/L)
Total concn. of TOA (mMol/L)
Concn. of Hf in org. phase (m~;ol/L)
Concn. of oxalate in org. phase Calculated data Observed data (mMol/L) (ml;ol/L)
25.5
q.15
49.3
57.5
q3.8
57.5
57.8
26.6
1 .q8
51.3
56.8
q3.5
56.8
56.6
27.8
1.07
88.2
57.3
1~.5
57.3
56.6
29.6
1.10
70.6
56.8
13.3
56.8
56.4
31.9
1.05
76.6
57.5
q3-6
57.5
57.6
In Table 1, the concentration of H2C2041a , is calculated by using the pH of the aqueous solution at equilibrium. According to these results, it is concluded that four molecules of oxalate are associated with each hafnium atom; four molecules of oxalate occupy eight of the coordination positions as bidentate ligand. The tetravalent anion of tetraoxaiatohafnium complex is formed by the following Eqn (8);
LO
O.5 o -J
e:4.O Hf(OH)4 + 4H2C204 = Hf(C20,)44- + 4H + + 4H20 (8) Effect of variation of amine concentration on distribution In order to investigate the solvent dependence of the distribution coefficient, hafnium complex ion is extracted from an aqueous solution containing 0.040 M of hafnium complex ion and 0.223M of oxalate with different concentrations of TOA xylene solution and these results are shown in Fig. 7. The equilibrated TOA concentration in Fig. 7 is defined as TOA unassociated with hafnium complex ion and is calculated by subtracting four times the organic hafnium concentration from the total TOA concentration. The slope of log E~° vs log TOA is very nearly 4 at the initial pH of 0.70 in the aqueous phase. This solvent dependence indicates that four tri-n-octylammonium cations associate with each extractable tetravalent tetraoxalatohafnium complex anion and the mechanism for the extraction of hafnium complex ion from the aqueous oxalic acid solution with tri-noctylamine in xylene solution in high acidity is represented mainly according to the Eqn (1). Acknowledgement--The authors are indebted to Mr. Y. Nasa for his experimental assistance.
O I -0.9
I -0.7
I
I -0.5
Log Amino
Fig. 7. Solvent dependence of distribution coefficientfor extraction of hafnium with organicphase containingvarious amountsof TOA from aqueousphase containing1.02mmole/25ml of hafnium and 5.82 minnie/25nil of oxalate. REFERENCES
I. 2. 3. 4.
J. Hala, J. Inorg. Nucl. Chem. 29, 187 (1967). J. Hala, J. Inorg. NucL Chem. 29, 1777 (1967). F. L. Moore, Anal Chem. 29, 1661 (1957). J. I. Bullock, S. S. Choi, D. A. Goodrick,D. G. Tuck and E. L Woodhouse, J. Phys. Chem. 68, 2687 (1964). 5. K. Funaki, I. Ishijima and H. Seki, Kogyo Kagaku Zasshi 71, 339 (1968). 6. F. L. Moore, Anal. Chem. 37, 1235 (1965). 7. J. I. Bullock and D. G. Tuck, J. Inorg. NucL Chem. 33, 3891 (1971). 8. K. Yakabe, S. Kato, H. Uda and S. Minami, Kogyo Kagaku Zasshi 72, 2343 (1969). 9. J. L. Hoard, G. L. Glen and J. V. Silverton,J. Am. Chem. Soc. 83, 4293 (1961).
LIQUID-LIQUID EXTRACTION OF HAFNIUM COMPLEX ION FROM AQUEOUS OXALIC ACID SOLUTION WITH HIGH MOLECULAR WEIGHT AMINE K. YAKABE and S. MINAMI The Osaka Institute of Technology,Omiya-5-16-1,Asahi-ku,Osaka, Japan
(First received 22 July 1974:in revisedfi)rm 21 October 1974) Abstract--Extraction of hafnium from aqueous oxalic acid solution with high molecular weight amine was studied. It was confirmed that the tetraoxalato complex ion of hafnium is extracted from aqueous oxalic acid solution with tri-n-octylamine in xylene solution. A mechanism for the extraction of hafnium complex ion was discussed on the basis of the results obtained. INTRODUCTION THE EXTRACTIONof hafnium complex ion from strongly acidic solution with N-benzoyl-N-phenylhydroxylamine has been studied by Hala[1, 2] and the extraction of tStHf tracer from hydrochloric acid solution with methyl-dioctylamine by Moore[3]. The distribution of oxalic acid between aqueous solution and organic solution of methyl-di-octylamine has been studied by Bullock et al. [4] and Funaki et al. [5] have reported the extraction of oxalic acid from aqueous solution with organic solution of Amberlite LA-2. The extraction of the other metal complex ions from aqueous oxalic acid solutions with high molecular weight amines in organic solvents has been studied by several investigators [5-7]. The authors have previously investigated the effect of organic acids on the extraction of zirconium ion[8]. The present paper describes the extraction of hafnium ion from aqueous oxalic acid solution with tri-n-octylamine in xylene solution. EXPERIMENTAL Reagents and preparation of stock solution The amine used was tri-n-octylamine (TOA) diluted with xylene. The other chemicals were analytical reagent grade. A stock solution of hafnium complex ion was prepared by dissolving hafnium hydroxide obtained from the alkali fussion of hafnium oxide in an aqueous oxalic acid solution.
Extraction procedure Extractions were carried out by the followingprocedure; 25 ml of aqueous solution containing a definite volume of hafnium stock solution and various amounts of oxalic acid and 25 ml of TOA-xylenesolution in a 100 ml glass stoppered separating funnel were shaken for 5 rain at room temperature. After the separation of an organic phase, both the hafnium complex ion and the oxalate ion extracted into the organic phase were stripped with 1.5 M nitric acid or 2.0 M hydrochloric acid. Hafnium was determined by the gravimetric method as pyrophosphate or oxide and the determination of oxalate and chloride was carried out by the titration methods. RESULTS AND DISCUSSION Effect of concentration of hydrogen ion on hafnium extraction Hafnium complex ion was extracted from aqueous
oxalic acid solution containing 0.012 M hafnium, 0.089 M oxalate and various amounts of hydrogen ion with 0.055 M TOA-xylene solution and the results are shown in Fig. 1. Figure 1 shows that the distribution coefficient (E~a= equilibrium concentration of hafnium in organic phase/equilibrium concentration of hafnium in aqueous phase) of the hafnium complex ion is 199 at a pH of about 1.7 at equilibrium but decreases sharply as the pH of the aqueous phase increases and reaches almost zero at a pH of about 4.4.
Effect of chloride ion on the hafnium extraction In order to investigate the effect of chloride ion on the extraction of hafnium complex ion, hafnium complex ion was extracted with 0.059 M TOA-xylene solution from the aqueous oxalic acid solution containing 0.012 M hafnium complex ion, 0.089M oxalate and various amounts of hydrochloric acid and these results are shown in Fig. 2. The E~ of the hafnium complex ion decreased with increasing equilibrium concentration of hydrochloric acid in the aqueous solution and became almost zero above I. 19 M of aqueous hydrochloric acid, while the concentration of chloride ion in the organic phase increased with increasing equilibrium concentration of hydrochloric acid in the aqueous phase and TOA was saturated with chloride above 1.19 M of aqueous hydrochloric acid. These results show that the decrease of E~ is due to the competitive reaction between hafnium complex ion and chloride ion with TOA. Effect of a mole ratio of oxalate to hafnium in aqueous phase on hafnium extraction Hafnium complex ions were extracted from aqueous phase containing 0.018M hafnium complex ion and various amounts of oxalate with 0.082 M TOA in xylene solution. These results are presented in Fig. 3. The E~ of hafnium complex ion increased linearly with increasing equilibrium mole ratios of aqueous phase in the mole ratio region from 1.58 to 8.58, but a third phase formed slightly between the aqueous and the organic phase below a mole ratio of about 2-00. This suggests that the increase in the E~ can be attributed to the increase in
1973
1974
K. YAKABEand S. MINAMI
/-
2
2 I
o~
o _J
o,o
I
-I
0 I
I
I
I
2
3
4
5
I
I
I
2
3
LO g (C~)~'/H f ) af equilibrium
pH
Fig. 1. Effect of pH on the extraction of hafnium with 1.38mmole/25ml TOA-xylene solution from aqueous phase containing 0.31 mmole/25ml of hafnium, 2.22 mmole/25ml of oxalate and various amounts of hydrogen ion. Log E is plotted against pH of equilibratedaqueous phase.
_-
I
~
1,5
2 E
¢) 04 ~' 0
I
f.o =E
E
Fig. 3. Effect of a moleratio of oxalate to hafniumon the extraction of hafnium with 2.05 mmole/25ml TOA-xylene solution from aqueous phase containing0.45 mmole/25ml of hafnium at various mole ratios. Log E is plotted against the mole ratio of equilibrated aqueous phase.
Determination of the concentration of extracted hafnium species Hafnium complex ions were extracted with 0.056 M TOA in xylene solution from aqueous oxalic acid solution containing various amounts of hafnium complex ion at a constant mole ratio of hafnium complex ion to oxalate. The hafnium and the oxalate extracted into the organic phase were determined analytically. These results are shown in Fig. 4. In Fig. 4, the curves (a), (b) and (c) correspond to extractions carried out with a mole ratio (C2042-/H0 of 3.56, 5.69 and 15.2 respectively at the equilibrium
n
-i
o.o _~ o
5
I ~ ./J'.~s-:-~----~--<~-<~--.~o U I
0
I
n
1.0
0 2.0
Cone. of HCI at equilibrium (M/L)
Fig. 2. Effect of chloride ion on the extraction of hafnium with 1.48mmole/25ml TOA-xylene solution from aqueous phase containing 0.31 mmole/25ml of hafnium, 2.22mmole/25ml of oxalate and various amounts of chloride ion, O, Hafnium complex ion; &, Chloride ion.
o~
/
=~ "-E
¢
-
0.4 /
" .
r
0
" .
c N
'"o"~" :/
o.20~-~'
j
o~
i
A
d
,,: //
, 0.01
the extractable hafnium species with increasing mole ratios in the aqueous phase. Above a mole ratio of about 70, the E~° attained a constant value, that is, 199. But below a mole ratio of about 1.6, the extraction of hafnium complex ion was impossible because of the formation of emulsion.
A'/I
/ ",' / l
1
5
~ 0.1
1.0
Equilibrium cone, o f Hf ( m M o l / 2 5 ml)
Fig. 4. Concentrations of hafnium and of oxalate in organic phase are plotted against equilibrium concentration of hafnium in aqueous phase. Curves (a-c) are mole ratios (C2042-/Hf)3.56, 5.69 and 15.2 at equilibriumrespectively. ©, A, O, Hafnium complex ion; O, i , e, Oxalate.
Liquid-liquidextraction of hafniumcomplexion
t975
concentration of 8.0x 10--3M hafnium complex ion aqueous phase. The concentrations of hafnium and oxalate in the organic phase increase with the equilibrium concentration of hafnium up to about 1.6 x 10-3M and then attain a definite value. In the flat parts of the curves (a) and (b) in Fig. 4, the mole ratios of oxalate to hafnium in the organic phase were 3.99 and 4-02 respectively. These results indicate that the extracted hafnium complex species consists of one atom of hafnium and four molecules of oxalate, and this conclusion agreed with that of X-ray analysis for crystal hafnium oxalate[9]. In the fiat parts of the curves (c) in Fig. 4, however, the mole ratio of oxalate to hafnium in the organic phase attained a value of 4-27. In Fig. 5, the mole ratios of oxalate to hafnium, of TOA to hafnium and of TOA to oxalate in organic phase are plotted against the mole ratio of oxalate to hafnium in aqueous phase at 8.0 x 10-~ M of hafnium complex ion. From Fig. 5, it is supposed that hafnium oxalate amine salt, amine oxalate and amine bisoxalate may be formed in the organic phase by the competitive reactions between the hafnium oxalate complex and oxalic acid with TOA according to the following equations;
(1) and at high mole ratio such as 15.2, the hafnium oxa|ate complex ion and amine bisoxalate appear to be extracted mainly according to the Eqns (1) and (3), since the mole ratio of TOA to oxalate in the organic phase attained a value of almost 1 : 1. Furthermore, in order to investigate the relation between Eqn (2) and (3), log [R3NH2C204]~,,)/ [(R~NH)2C_.O,].... is plotted against Iog[H2C20~]~,, in Fig. 6. Since the log-log plot in Fig. 6 gives a straight line and its slope is 1.00 -+0.03, the following relation is deduced;
4R3N(o) + 4H[,~+ Hf(C204)~., = (R3NH)4Hf(C204)4(o}
where n is an association number of oxalate to each hafnium atom. From Eqns (4-6), the total concentraction of oxalate in the organic phase is represented by Eqn (7):
(1)
2R3N~o~+ H2C204~.,= (R3NH)2C204~o~
(2)
(R~NH)2C204,o,+ H2C~O4,.,= 2R3NH2C~O~o~
(3)
where (o) and (a) represent organic phase and aqueous phase respectively and H2C204(o, represents undissociated oxalic acid in the aqueous phase. At low mole ratios of oxalate to hafnium in the aqueous phase such as 3.56 and 5.69, the hafnium oxalate complex appears to be extracted mainly according to the equation o °"430
[R 3NH2C204]~o)][(R 3NH)2C204],,,, = 412[H2C204],0, (4) On the assumption that unassociated amine is negligible in the fiat parts of the extraction curves (c) in Fig. 4, the total concentration of amine and oxalate in the organic phase are represented by the following Eqns (5) and (6) respectively. []~R3N]~o~= 2[(R3NH)2C:O4],o)+ [R3NH2C204](,,, + (2n - 4)[Hf],o,
(5)
[EC..O,z-],o, = [(R3NH)2C:O,],o,+ [R 3NH2C204](o) + n [Hf],,,
(6)
(7) where A and B are I03[C2042 ]<~ and n[Hf]~:,~--[R3N]~,,~ respectively. Assuming that the association number n is four, the observed concentrations of oxalate in the organic phase were compared with those calculated and these results are shown in Table 1.
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6
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i
9
12
I
1,5
_1
Equilibrium mole ratio of aq. phase (C20~-IH f)
Fig. 5. (C2042-/Hf),(TOA/Hf)and (TOA/C2042-)in organicphase are plotted against aqueous mole ratio of oxalate to hafnium at equilibrium. O, (C~O,~-/Hf) in organic phase; @, (TOA/Hf) in organicphase; A, (TOA/C20,2-) in organicphase.
I
-z~
-zo
I
-L.5
|
-,.o
LOg [H2Cz041(a) Fig. 6, Log
[R.,NH2C20.d~,./I(R3NH)2C20.].,, is log H2C20,~,,,
plotted against
1976
K. YAKABE and S. MINAMI Table I. The observed concentration of oxaiate in organic phase was compared with those calculatedby use of the Eqn (7) Initial concn. HzCzO,(a) of Hf pH (mMol/L) at equilibrium (mMol/L)
Total concn. of TOA (mMol/L)
Concn. of Hf in org. phase (m~;ol/L)
Concn. of oxalate in org. phase Calculated data Observed data (mMol/L) (ml;ol/L)
25.5
q.15
49.3
57.5
q3.8
57.5
57.8
26.6
1 .q8
51.3
56.8
q3.5
56.8
56.6
27.8
1.07
88.2
57.3
1~.5
57.3
56.6
29.6
1.10
70.6
56.8
13.3
56.8
56.4
31.9
1.05
76.6
57.5
q3-6
57.5
57.6
In Table 1, the concentration of H2C2041a , is calculated by using the pH of the aqueous solution at equilibrium. According to these results, it is concluded that four molecules of oxalate are associated with each hafnium atom; four molecules of oxalate occupy eight of the coordination positions as bidentate ligand. The tetravalent anion of tetraoxaiatohafnium complex is formed by the following Eqn (8);
LO
O.5 o -J
e:4.O Hf(OH)4 + 4H2C204 = Hf(C20,)44- + 4H + + 4H20 (8) Effect of variation of amine concentration on distribution In order to investigate the solvent dependence of the distribution coefficient, hafnium complex ion is extracted from an aqueous solution containing 0.040 M of hafnium complex ion and 0.223M of oxalate with different concentrations of TOA xylene solution and these results are shown in Fig. 7. The equilibrated TOA concentration in Fig. 7 is defined as TOA unassociated with hafnium complex ion and is calculated by subtracting four times the organic hafnium concentration from the total TOA concentration. The slope of log E~° vs log TOA is very nearly 4 at the initial pH of 0.70 in the aqueous phase. This solvent dependence indicates that four tri-n-octylammonium cations associate with each extractable tetravalent tetraoxalatohafnium complex anion and the mechanism for the extraction of hafnium complex ion from the aqueous oxalic acid solution with tri-noctylamine in xylene solution in high acidity is represented mainly according to the Eqn (1). Acknowledgement--The authors are indebted to Mr. Y. Nasa for his experimental assistance.
O I -0.9
I -0.7
I
I -0.5
Log Amino
Fig. 7. Solvent dependence of distribution coefficientfor extraction of hafnium with organicphase containingvarious amountsof TOA from aqueousphase containing1.02mmole/25ml of hafnium and 5.82 minnie/25nil of oxalate. REFERENCES
I. 2. 3. 4.
J. Hala, J. Inorg. Nucl. Chem. 29, 187 (1967). J. Hala, J. Inorg. NucL Chem. 29, 1777 (1967). F. L. Moore, Anal Chem. 29, 1661 (1957). J. I. Bullock, S. S. Choi, D. A. Goodrick,D. G. Tuck and E. L Woodhouse, J. Phys. Chem. 68, 2687 (1964). 5. K. Funaki, I. Ishijima and H. Seki, Kogyo Kagaku Zasshi 71, 339 (1968). 6. F. L. Moore, Anal. Chem. 37, 1235 (1965). 7. J. I. Bullock and D. G. Tuck, J. Inorg. NucL Chem. 33, 3891 (1971). 8. K. Yakabe, S. Kato, H. Uda and S. Minami, Kogyo Kagaku Zasshi 72, 2343 (1969). 9. J. L. Hoard, G. L. Glen and J. V. Silverton,J. Am. Chem. Soc. 83, 4293 (1961).