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Synergic effects in the solvent extraction of hafnium (IV)
INORG.
NU et .
CHEM.
LETTERS
Vol.
4.
pp.
67-72,
1968.
Peqlamu
Press,
Printed
In
Great
Britain.
SYNERGIC EFFECTS IN THE S O L V ~ T EXTRACTION OF HAFNIUM (IV) J. H~la Department of Physical Kotlarska 2,
Chemistry, University of Brno, Czechoslovakia
( R ~ v e d ~ Oc~ber 1967)
In the metal cation/ 1,3-diketone extraction systems, low concentrations (<10 -2 M) of neutral phosphate esters cause synergic enhancement of the metal distribution ratio due to the extraction of mixed complexes of various types (1).
These are, however, destroyed (2) at higher concentrations
because of the increasing water content in the organic phase (3), which causes the metal distribution ratio again to decrease.
In this contribution,
we report some preliminary results on Hf (IV) extraction by 2-thenoyltrifluoroacetone (TTA)/tri-n-butyl phosphate (TBP) and N-benzoyl-N-phenylhydroxylamine (BPHA) / TBP mixtures from 1 - 4 M solutions of mineral acids; the extraction behaviour of these systems at high TBP concentrations differs considerably from those described in the literature.
Solven~ extraction of
Hf (IV) by various mixtures of two chelating extracting ligands is also described.
Experimental
Preparation of the
175+181 Hf tracer in perchloric acid solution,
extraction technique, radioactivity measurement, and other details were described elsewhere (4).
The phases (4.0 ml. each) were contacted in
stoppered test-tubes for two days, and the distribution ratios, DHf ' were expressed as the organic to aqueous count rate ratios.
When extracting
from other than perohlorate media the re-extraction technique (5) was used to avoid the interfering influence of the perchlorate anion from the tracer 67
68
SOLVENT EXTRACTION OF HAFNIUM (IV)
stock solution.
¥ol. 4~ N*. 2
Benzene was used as the organic diluent throughout.
Re@~its
FIG. i shows the log DHfVS log [TBP]tot plots for 0.O5 M TTA and various perchloric acid concentrations.
It can he seen that
10-3 - IO-
TBP concentrations are without any influence on DHf; higher concentrations cause antagonism and, still higher [TBP] values, an increase in DHf. The curving of these plots upwards depends on the perchlorate (as HCIO 4) concentration in the aqueous phase. It becomes more pronounced
21
i
V
-3
'
,
-2 ~elmpJ.
l
i
-~
o
FIG. 1.
Distribution ratio of Hf (IV) as a function of TBP concentration in benzene. 0.05 M TTA. Aqueous HCI04 concentrations: @ 4.0; ~
1.O;
Q
2.0; O
3.Q;
6.0 M.
with increasing perchlorate concentration.
This can be seen from the shift
of the minimum position (given in TBP molarity), i.e., 1.32, O.83, 0.56 and 0.25 M TBP for l, 2, 3 and 4 M HC104, respectively.
Higher acidities have not
been applied .because the extraction of Hf(TTA)3Cl~(4) and Hf(C104)4.2 TBP (log DHf= - 1.4 for pure TBP and 7.0 M HG104) complicate the situation. Similar though less pronouced effects were observed in nitrate media
Vol. 4~ N*, 2
SOLVENT
EXTRACTION
I
I
OF HAFNIUM
(IV)
69
I
0
-f
.~
i
-2
i
I
1~a~Ti~Pj-f
0
FIG. 2.
Distribution ratio of Hf (IV) as a function of TBP concentration in benzene. 0.05 M TTA. Aqueous acidities: HC1; O
2.0
O
2.0 M KNO3:
•
4.0 M HN03;
~
2.0
M HBr.
I
I
I
f
0
~o
|
-3
I
-f
-2
i
0
FIG. 3.
Distribution ratio of Hf(IV) as a function of TBP concentration in benzeme. 2.5x10 -3 M BPHA. Aqueous acidities; •
2.0 M HCI;
•
2.0 M HBr.
O
1.O M HC104;
O
2.0 M HC104;
70
SOI.YEHT EXTRACTION OF HAFNIUM (IY)
(FIG. 2).
V.l. 4, He. |
The minimum positions are at 1.86 and 1.2 M TBP for 2 and 4 HN03,
respectively.
When extracting from HC1 and HBr solutions, antagonism occured
over the whole (TBP)range investigated (FIG 2).
In FIG. 3, the results of similar extractions with 2.5 x 10-3M BPHA are shown.
The extraction from 1.O M HC104Proceeds in the same way as with
TTA. The minimum is, however, much more shallow and disappears completely in 2.0 M HC104.
Contrary to TTA, similar effects have been observed even with
extractions from HC1 and HBr solutions. In nitric acid, BPHA is decomposed.
The extraction mechanism in the high [TBP] range of the systems described remains still unexplained. Attempts to deduce the composition of the complexes extracted by means of slope analysis failed, obviously because of the mutual interaction of extracting agents in the organic phase.
The governing role
of the type of inorganic anion in the aqueous phase is, however, certain and it is likely that inorganic anions are involved in the extraction process in the ranges of DHfincreasing with TBP concentration.
It is noteworthy
2+ that Zangen (6) observed similar effects with UO 2 extraction by mixtures of some acidic (H2Y 2) and neutral (B) phosphate esters and explained them in terms of extraction of mixed complexes such as UO2(HY2)CIB2.
The higher
tendency of BPHA towards the synergism described may be connected with its easier formation of mixed complexes with inorganic anions (5).
In the course of these studies we also found synergic enhancement of DHfwhen extracting with mixtures of two chelating agents.
Some preliminary
results obtained for 2.0 M aqueous HC104and chloroform as the organic diluent are summarized in Table 1. Except for the presence of perchlorate anion in the complexes extracted by BPHA (4) and dialkyl phosphoric acids (7), these effects may be of similar origin as those recently found with di- and trivalent metal cations (8, 9).
V*l. 4j He. 2
SOLVENT EXTRACTION OF HAFNIUM (.IV)
71
TABLE 1 Extraction of Hf (IV) by Mixtures of Two Chelating Agents
Extracting agent (a)
a)
DHf,found
Cc)
DHf,exp
C0)
Dfoun d
DZPA b)
1.56
TTA
0.93
BPHA
0.73
DBPA + TTA
5.44
2.49
2.2
DBPA + BPHA
88
2.29
38
TTA + BPHA
14.1
1.66
8.5
Dexp
Concentrations used : DBPA: 2 x 10 -4M; TTA: 5 x 10-2M; BP}~: ~ IO-3M
b)
di-n-butyl phosphoric acid
c)
mean value of at least three measurements
d)
values expected considering both agents to act additi~ely in their mixture References
1. H.M.N.H. Irving,"Solvent Extraction Chemistry", Rorth-Holland Publ. Comp., i~nsterdam, 1967, p. 91. 2. S.M. Wang, W.R. Walker and b.C. Li, J. Inor~. Nucl. Chem., 28, 875 (1966). 3. T.V. Healy, D.F. Peppard and G.W. Mason, J. Inorg. Nucl. Chem., 24 , 1429 (1962. ) 4. J. Hala, J. Inor~. Nucl. Chem., 2_~ 187"(1967). 5. J. Hala, J. Inorg. Nucl. Chem., 2_~ 1317 (1967). 6. M. Zangen, J. Inorg. Nucl. Chem., 25, 581 (1963). 7. O. Navratil, J. Inorg. Nucl Chem., 29.2007 (1967).
72
SOLVENT EXTRACTION OF HAFNIUM (IV)
Vol. ~ He. 2
8e T. Sekine and D. Dyrssen, ~. Inor~. Nucl. Chem., 26, 2013 (1964); 29, 1489 (1967). 9. H. Yoshida, Bull. Chem. Soc. Japan, 39, 1810.(1966).
NU et .
CHEM.
LETTERS
Vol.
4.
pp.
67-72,
1968.
Peqlamu
Press,
Printed
In
Great
Britain.
SYNERGIC EFFECTS IN THE S O L V ~ T EXTRACTION OF HAFNIUM (IV) J. H~la Department of Physical Kotlarska 2,
Chemistry, University of Brno, Czechoslovakia
( R ~ v e d ~ Oc~ber 1967)
In the metal cation/ 1,3-diketone extraction systems, low concentrations (<10 -2 M) of neutral phosphate esters cause synergic enhancement of the metal distribution ratio due to the extraction of mixed complexes of various types (1).
These are, however, destroyed (2) at higher concentrations
because of the increasing water content in the organic phase (3), which causes the metal distribution ratio again to decrease.
In this contribution,
we report some preliminary results on Hf (IV) extraction by 2-thenoyltrifluoroacetone (TTA)/tri-n-butyl phosphate (TBP) and N-benzoyl-N-phenylhydroxylamine (BPHA) / TBP mixtures from 1 - 4 M solutions of mineral acids; the extraction behaviour of these systems at high TBP concentrations differs considerably from those described in the literature.
Solven~ extraction of
Hf (IV) by various mixtures of two chelating extracting ligands is also described.
Experimental
Preparation of the
175+181 Hf tracer in perchloric acid solution,
extraction technique, radioactivity measurement, and other details were described elsewhere (4).
The phases (4.0 ml. each) were contacted in
stoppered test-tubes for two days, and the distribution ratios, DHf ' were expressed as the organic to aqueous count rate ratios.
When extracting
from other than perohlorate media the re-extraction technique (5) was used to avoid the interfering influence of the perchlorate anion from the tracer 67
68
SOLVENT EXTRACTION OF HAFNIUM (IV)
stock solution.
¥ol. 4~ N*. 2
Benzene was used as the organic diluent throughout.
Re@~its
FIG. i shows the log DHfVS log [TBP]tot plots for 0.O5 M TTA and various perchloric acid concentrations.
It can he seen that
10-3 - IO-
TBP concentrations are without any influence on DHf; higher concentrations cause antagonism and, still higher [TBP] values, an increase in DHf. The curving of these plots upwards depends on the perchlorate (as HCIO 4) concentration in the aqueous phase. It becomes more pronounced
21
i
V
-3
'
,
-2 ~elmpJ.
l
i
-~
o
FIG. 1.
Distribution ratio of Hf (IV) as a function of TBP concentration in benzene. 0.05 M TTA. Aqueous HCI04 concentrations: @ 4.0; ~
1.O;
Q
2.0; O
3.Q;
6.0 M.
with increasing perchlorate concentration.
This can be seen from the shift
of the minimum position (given in TBP molarity), i.e., 1.32, O.83, 0.56 and 0.25 M TBP for l, 2, 3 and 4 M HC104, respectively.
Higher acidities have not
been applied .because the extraction of Hf(TTA)3Cl~(4) and Hf(C104)4.2 TBP (log DHf= - 1.4 for pure TBP and 7.0 M HG104) complicate the situation. Similar though less pronouced effects were observed in nitrate media
Vol. 4~ N*, 2
SOLVENT
EXTRACTION
I
I
OF HAFNIUM
(IV)
69
I
0
-f
.~
i
-2
i
I
1~a~Ti~Pj-f
0
FIG. 2.
Distribution ratio of Hf (IV) as a function of TBP concentration in benzene. 0.05 M TTA. Aqueous acidities: HC1; O
2.0
O
2.0 M KNO3:
•
4.0 M HN03;
~
2.0
M HBr.
I
I
I
f
0
~o
|
-3
I
-f
-2
i
0
FIG. 3.
Distribution ratio of Hf(IV) as a function of TBP concentration in benzeme. 2.5x10 -3 M BPHA. Aqueous acidities; •
2.0 M HCI;
•
2.0 M HBr.
O
1.O M HC104;
O
2.0 M HC104;
70
SOI.YEHT EXTRACTION OF HAFNIUM (IY)
(FIG. 2).
V.l. 4, He. |
The minimum positions are at 1.86 and 1.2 M TBP for 2 and 4 HN03,
respectively.
When extracting from HC1 and HBr solutions, antagonism occured
over the whole (TBP)range investigated (FIG 2).
In FIG. 3, the results of similar extractions with 2.5 x 10-3M BPHA are shown.
The extraction from 1.O M HC104Proceeds in the same way as with
TTA. The minimum is, however, much more shallow and disappears completely in 2.0 M HC104.
Contrary to TTA, similar effects have been observed even with
extractions from HC1 and HBr solutions. In nitric acid, BPHA is decomposed.
The extraction mechanism in the high [TBP] range of the systems described remains still unexplained. Attempts to deduce the composition of the complexes extracted by means of slope analysis failed, obviously because of the mutual interaction of extracting agents in the organic phase.
The governing role
of the type of inorganic anion in the aqueous phase is, however, certain and it is likely that inorganic anions are involved in the extraction process in the ranges of DHfincreasing with TBP concentration.
It is noteworthy
2+ that Zangen (6) observed similar effects with UO 2 extraction by mixtures of some acidic (H2Y 2) and neutral (B) phosphate esters and explained them in terms of extraction of mixed complexes such as UO2(HY2)CIB2.
The higher
tendency of BPHA towards the synergism described may be connected with its easier formation of mixed complexes with inorganic anions (5).
In the course of these studies we also found synergic enhancement of DHfwhen extracting with mixtures of two chelating agents.
Some preliminary
results obtained for 2.0 M aqueous HC104and chloroform as the organic diluent are summarized in Table 1. Except for the presence of perchlorate anion in the complexes extracted by BPHA (4) and dialkyl phosphoric acids (7), these effects may be of similar origin as those recently found with di- and trivalent metal cations (8, 9).
V*l. 4j He. 2
SOLVENT EXTRACTION OF HAFNIUM (.IV)
71
TABLE 1 Extraction of Hf (IV) by Mixtures of Two Chelating Agents
Extracting agent (a)
a)
DHf,found
Cc)
DHf,exp
C0)
Dfoun d
DZPA b)
1.56
TTA
0.93
BPHA
0.73
DBPA + TTA
5.44
2.49
2.2
DBPA + BPHA
88
2.29
38
TTA + BPHA
14.1
1.66
8.5
Dexp
Concentrations used : DBPA: 2 x 10 -4M; TTA: 5 x 10-2M; BP}~: ~ IO-3M
b)
di-n-butyl phosphoric acid
c)
mean value of at least three measurements
d)
values expected considering both agents to act additi~ely in their mixture References
1. H.M.N.H. Irving,"Solvent Extraction Chemistry", Rorth-Holland Publ. Comp., i~nsterdam, 1967, p. 91. 2. S.M. Wang, W.R. Walker and b.C. Li, J. Inor~. Nucl. Chem., 28, 875 (1966). 3. T.V. Healy, D.F. Peppard and G.W. Mason, J. Inorg. Nucl. Chem., 24 , 1429 (1962. ) 4. J. Hala, J. Inor~. Nucl. Chem., 2_~ 187"(1967). 5. J. Hala, J. Inorg. Nucl. Chem., 2_~ 1317 (1967). 6. M. Zangen, J. Inorg. Nucl. Chem., 25, 581 (1963). 7. O. Navratil, J. Inorg. Nucl Chem., 29.2007 (1967).
72
SOLVENT EXTRACTION OF HAFNIUM (IV)
Vol. ~ He. 2
8e T. Sekine and D. Dyrssen, ~. Inor~. Nucl. Chem., 26, 2013 (1964); 29, 1489 (1967). 9. H. Yoshida, Bull. Chem. Soc. Japan, 39, 1810.(1966).