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Ti(IV) extraction by tri-n-butylphosphate from sulphuric acid solutions
J inorg nucl. Chem. VoL 42, pp, 1033-[036 ,~'>Pergamon Press l,td., 1980 Printed in Grea! Brilain
0022-190218010701-1033t$~,2.0010
Ti(IV) EXTRACTION BY TRI-n-BUTYLPHOSPHATE FROM SULPHURIC ACID SOLUTIONS P. H. TEDESCO and V. B. DE RUMI Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
(Received 9 July 1979; receivedfor publication 8 November 1979) Abstract--Extraction of Ti(IV) from aqueous sulphuric acid solutions using TBP (tri-n-butylphosphate)undiluted and in carbon tetrachloride solution has been studied. Water and sulphuric acid extractions were previously considered. On the basis of chemical data some extraction mechanismsare proposed. INTRODUCTION In spite of the huge amount of information about solvent extraction of acids and metals by TBP (tri-n-butylphosphate) there are only a few references about metals extraction from sulphuric acid solutions [1] and we did not find any about titanium extraction from this medium. Even sulphuric acid extraction has been treated in a few papers of which the most comprehensive is that of Brauer and Hrgfeldt[2]. Neither in this paper nor in others[3-5] a coherent proposition of extraction mechanism using undiluted TBP is available. Moreover, no paper has been found regarding sulphuric acid extraction by TBP carbon tetrachloride solutions. So, as a part of our studies on the chemistry of titanium [6,7], we decided to investigate its extraction from sulphuric acid solutions using pure TBP and solutions in carbon tetrachloride. Previously, the extraction of sulphuric acid and water at the same conditions has been considered. EXPERIMENTAL TBP was obtained from the Comisi6n Nacional de Energia At6mica de la Reptiblica Argentina and purified according to standard procedures [8]. Titanium solutions were prepared dissolvingthe pure metal in hydrochloricacid, adding sulphuric acid and hydrogen peroxide and evaporating to sulphuric acid fumes. Solutions were standardised against normal ferrous sulphate solutions. Equilibrium experiments were done agitating in separating funnels equal volumes of organic and aqueous phases during three minutes at room temperature, time predetermined as sufficient to attain equilibrium. In "saturation" tests the contact was repeated with fresh aqueous solution until a limit concentration in the organic phase was obtained. Titanium in the diluted solution was determined by spectrophotometry (peroxide method). Water in the organic phase was determined by Karl Fisher titration.
same point which corresponds to a ratio of 1.2 at sulphuric acid concentration 13M. These results are confirmed by data in Fig. 3 in which log Eo~2so4>. (Eo~H2so4) is the distribution coefficient of sulphuric acid) is plotted against TBP concentration at sulphuric acid concentrations 7.5 and 11-12 M. It is seen that when sulphuric acid concentration is l l-12M the plot is a straight line with a slope 1.1-1.2 and when the acid concentration is 7.5 M the slope is 1.5. These results are consistent with two competing mechanisms:
H2SO4(aq) + TBP,,~ . . . . . .
H2SO4"TBP,,,,
(1)
H2SO,u,,,) + 2TBEo~ . . . . . .
H2SO~,'2TBP~,,
(2)
In these equations water has not been considered although, as will be seen, sulphuric acid is probably extracted as an hydrated complex, at least in some cases. It is assumed that with concentrated sulphuric acid reaction (1) predominates and at low concentration reactions (1) and (2) are both produced. In "saturation" tests, several samples of pure and diluted TBP were repeatedly treated with fresh portions of sulphuric acid solutions of different concentrations. When sulphuric acid 11 M was used with TBP 0.5 M .or lower the molar concentration ratio was 1 : 1.2 confirming the equilibrium results and showing that at these conditions the organic phase was saturated with only one
Z RESULTS AND DISCUSSION Extraction of sulphuric acid. In Fig. 1 it can be seen that sulphuric acid extraction by TBP I M in carbon tetrachloride increases with its concentration in the aqueous phase until 13 M; beyond this value decomposition of the organic phase is noticeable. Figure 2 shows the molar concentration ratio of sulphuric acid to TBP in the organic phase as a function of the sulphuric acid concentration in the aqueous phase at several TBP concentrations. As can be seen all curves converge to the J~¢ voL 42,No. 7---(3
I
TBP
2
10
IM
~4 [H2504] aq
Fig. I. SulphUric acid concentration in the organic phase as a function of the aqueous acid concentration in experiments with T B P ! M.
1033
1034
P.H. TEDESCO and V. B. DE RUMI
1,2
o [T,P]c.,c0s, o
1.0
0.3
•
n rn F- 0.8
.
0.8 M
x
.
2.0M
®
,
2.,M
a_ m
o
A
0.2
o
0,6
o
E 0.1
0.4
0.2 i
2 :......
I
10 ~ H2SO43
I 6
/
/
&/' /
y'
=o x
g
L
I
I
I 14 l]rH2s04' aq.
10
Fig. 4. Mole of water per mole of TBP in the organic phase as a function of sulphuric acid concentrationin the aqueous phase.
oq.
Fig. 2. Sulphuricacid to TBP concentrations ratio in the organic phase vs sulphufic acid concentration in the aqueous phase at several TBP concentrations.
•
/,,,i / "
-I
l
I 15
//
--
•
-'-- H2SO 4
H z S O 4 11-12 M 7.S M
0
I
log [T BP]ci4 C
Fig. 3. Log of the distributioncoefficientof sulphurieacid vs log of TBP concentrationsplots at two sulphuric acid concentrations in the aqueous phase. contact; with pure TBP this ratio was 3.5-3.8 which cannot be explained by a simple mechanism and suggests the possibility of aggregates formation (polymerization reaction). This has too been suggested by Brauer and H/~gfeldt. Extraction o[ water. This was studied as a function of TBP and sulphuric acid concentration. All experiments made with undiluted TBP or at concentrations higher than 0.5 M in carbon tetrachloride showed that no detectable water was extracted at any sulphuric acid concentration from 4 to 13 M. In Fig. 4 it is shown that with TBP 0.5 M water is extracted from aqueous sulphuric acid solution and extraction increases with the acid concentration until 13 M. The amount of extracted water is from 0.08 to 0.3 g per 100 g organic phase. This maximum concentration was obtained in "saturation" tests and corresponds to 0.3 mole of water per mole of TBP. In the same experiments no less than 1 mole of sulphuric acid per mole of TBP was extracted. These experiments were confirmed by density measurements which showed that the density of the organic phase after the extraction was equal to the calculated density assuming only sulphuric acid extrac-
tion when pure TBP or concentrated solutions were used and that the density after the extraction was lower than the calculated density on that assumption when TBP solutions 0.5 M or lower were used. In some experiments we could verify that when the aqueous phase contains Ti(IV) at about 0.05 M, water is less extracted that when Ti is absent. All these results suggest that water is probably extracted as an hydrated complex of the sulphuric acid when using diluted TBP and when pure or concentrated TBP is used an anhydrous complex is extracted. Moreover water seems to be partially displaced from the organic phase by a titanium anhydrous complex. Extraction of Ti(IV). The most important aspects of the extraction of Ti(IV) from sulphuric acid solutions, with TBP are indicated in Figs. 5-8. All experiments were made with Ti(IV) solutions 0.01 M. Preliminary experiments showed that titanium extraction is a function of TBP and sulphuric acid concentrations. When the acid concentrations in the aqueous phase is below 8 M titanium extraction is negligible. The maximum extraction is obtained from sulphuric acid solutions 13 M. As it was said, at higher acid concentrations decomposition of the organic phase is noticeable, after several contacts.
o uJ o
/•O/•o [.2so,] 10.
/ i -1.0
I
x
.
11 M
•
If
12 M
0
,
13M I
.
Fig. 5. Log. of Ti(IV) distribution coefficient vs log of TBP concentrations at several sulphuricacid concentrations.
Ti(IV) extraction by TRl-n-butylphosphatefrom sulphuricacid solutions
oj.O,t
In Fig. 5 the plot log Eomj vs TBP concentration shows straight lines with the same slope 1.5 for sulphuric acid concentrations between 10 and 13 M. At lower acid concentrations consistent results could not be obtained because extraction was poor. So, for the range 10-13 M it is possible to postulate two mechanisms: TBP(o} + TiOSO,~q} . . . . . .
~
f ® [TBP]cI4 C OBN 1 , 1.0 M 0
I,
®
"
2.0 M
x
,,
1,5 M
2.5 M
ITBP puro
1
10
15 [HzSO4] aq.
Fig. 6. Titanium to sulphuric acid concentrations ratio in the organic phase as a function of sulphuricacid concentrationin the aqueous phase at several TBP concentrations.
0.02
,_e, o
'!c''c °'' ,o '.
0.01 o
2.0M
x
2.5M TBP
I
II
I 15
10
puro
[HzSO4]aq.
Fig. 7. Titanium to TBP concentrations ratio as a function of sulphuric acid concentrationin the aqueous phase at several TBP concentrations.
!
I F
0.S~-[
0,f°'
1035
I
I
l
I
01
0.2
0.3
0,4
o.TiP O.S
[Ti]aq
Fig. 8. Titaniumconcentration in the organic phase per mole of TBP vs titanium concentration in the aqueous phase using pure and carbon tetrachloridesolutions of TBP.
2TBP(o~ + TiOSO4(aq). . . . . .
TBP.TiOSO4~o,
(1)
(TBP)2.TiOSOa~o~. (2)
Figure 6 shows the molar concentration ratio of titanium to sulphuric acid in the organic phase a,~ a function of the sulphuric acid concentration in the aqueous phase, obtained in equilibrium experiments. It is seen that the maximum value is obtained at sulphuric acid concentration about 11 M and is higher when the TBP concentration decreases. This indicates that over 11 M the rate of extraction of the acid is higher than tlhat of the titanium complex. In Fig. 7 the ratio of molar concentrations of titanium to TBP in the organic phase is plotted vs the sulphuric acid concentration in the aqueous phase at several TBP concentrations, It shows that this ratio increases as the acid concentration increases and is higher at lower TBP concentration. The ratio titanium concentration per mole of TBP as a function of titanium concentration in the aqueous phase was obtained in saturation tests for undiluted TBP and solutions 2 and 2.5 M in carbon tetrachloride; results are indicated in Fig. 8. This shows too that more relative titanium extracion is obtained when the organic phase is more diluted. Tests were not made at lower TBP concentrations because a third phase appeared. According to all this information it can be postulated the formation of 1:1 and 1:2 complexes TI:TBP in equilibrium experiments when the concentration of sulphuric acid is between 10 and 13 M. These complexes are anhydrous when the TBP concentration is above 0.5 ld. In saturation experiments titanium to TBP molar concentration ratio in the organic phase is lower than 1:2 which can be explained by the preferential extraction of sulphuric acid. As it is indicated in Fig. 2, sulphuric acid to TBP molar concentration ratio is higher at higher TBP concentration and in Fig. 7 it can be seen that titanium to TBP molar concentration ratio is lower at higher TBP concentrations, so it must be deducted that titanium to sulphuric acid molar concentration ratio is lower at higher TBP concentrations and this is precisely confirmed by the results indicated in Fig. 6. This ratio is lower beyond sulphuric acid concentration I1 M, which suggests, as well as the saturation tests, a preferential extraction of the acid. No additional information could be obtained through some infrared spectra runned with the organic pha:~e previously contacted with sulphuric acid solution with and without titanium. So, we can summarise in this way our experimental results: (l) TBP extracts sulphuric acid, water and Ti(IV) from an aqueous solution of the metallic ion at sulphuric acid concentrations higher than 7 M when the organic phase is a carbon tetrachloride solution of TBP 0.5 M or lower; (2) at higher TBP concentrations or with undiluted extractant no water can be detected iin the organic phase after contact with aqueous sulphufic acid solutions 10 M or higher with or without titanium, which indicates extraction of anhydrous complexes; (!3) in equilibrium experiments at sulphuric acid concen-
1036
P. H. TEDESCO and V. B. DE RUMI
trations higher than 11 M and in the saturation tests there is a preferential extraction of acid (lower relative extraction of titanium) and the sulphuric acid to TBP molar concentration ratio reaches a maximum value of 3.8, which is probably due to polymerization reactions and (4) slopes of lOgEoH2SO4 vS log [TBP]o and log EoTi vs Iog[TBP]o plots suggest that the acid is extracted through sulphuric acid to TBP 1:1 and 1:2 complexes, and the metal by an independent mechanism including TiOSO4:TBP 1 : 1 and 1 : complexes. Acknowledgements--Thanks are due to the Consejo Nacional de Investigaciones Cientificas y T6cnicas de la Repfiblica Argentina and to the Comisi6n de Investigaciones Cientfficas de la provincia de Buenos Aires for financial support.
RE~T.RENCES 1. Y. Marcus and A. S. Kertes, Ion exchange and solvent extraction of Metal Complexes, Wiley Interscience, (1969). 2. E. Brauer and E. H6gfeldt, J. Inorg. Nucl. Chem. 23, 115 (1961). 3. P. Biddle, A. Coe, H. A. C. McKay, J. H. Mils and M. I. Waterman, J. lnorg. Nucl. Chem. 13, 156 (1960). 4. E. Hesford and H. A. Mc Kay, J. Inorg. Nucl. Chem. 13, 156 (1960). 5. H. A. Mc Kay, Ind. Chim. Beige, T 29 12, 1278 (1964). 6. P. H. Tedesco and V. B. de Rumi, Industria y Qu(mica, 224, 32 (1977). 7. P. H. Tedesco and J. Martfnez, An. de la Asoc. QuEm.Arg. 65, 115 (1977). 8. A. De, D. Khopkar and R. Chalmers, Solvent Extraction of Metals. Van Nostrand Reinhold, London (1970).
0022-190218010701-1033t$~,2.0010
Ti(IV) EXTRACTION BY TRI-n-BUTYLPHOSPHATE FROM SULPHURIC ACID SOLUTIONS P. H. TEDESCO and V. B. DE RUMI Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
(Received 9 July 1979; receivedfor publication 8 November 1979) Abstract--Extraction of Ti(IV) from aqueous sulphuric acid solutions using TBP (tri-n-butylphosphate)undiluted and in carbon tetrachloride solution has been studied. Water and sulphuric acid extractions were previously considered. On the basis of chemical data some extraction mechanismsare proposed. INTRODUCTION In spite of the huge amount of information about solvent extraction of acids and metals by TBP (tri-n-butylphosphate) there are only a few references about metals extraction from sulphuric acid solutions [1] and we did not find any about titanium extraction from this medium. Even sulphuric acid extraction has been treated in a few papers of which the most comprehensive is that of Brauer and Hrgfeldt[2]. Neither in this paper nor in others[3-5] a coherent proposition of extraction mechanism using undiluted TBP is available. Moreover, no paper has been found regarding sulphuric acid extraction by TBP carbon tetrachloride solutions. So, as a part of our studies on the chemistry of titanium [6,7], we decided to investigate its extraction from sulphuric acid solutions using pure TBP and solutions in carbon tetrachloride. Previously, the extraction of sulphuric acid and water at the same conditions has been considered. EXPERIMENTAL TBP was obtained from the Comisi6n Nacional de Energia At6mica de la Reptiblica Argentina and purified according to standard procedures [8]. Titanium solutions were prepared dissolvingthe pure metal in hydrochloricacid, adding sulphuric acid and hydrogen peroxide and evaporating to sulphuric acid fumes. Solutions were standardised against normal ferrous sulphate solutions. Equilibrium experiments were done agitating in separating funnels equal volumes of organic and aqueous phases during three minutes at room temperature, time predetermined as sufficient to attain equilibrium. In "saturation" tests the contact was repeated with fresh aqueous solution until a limit concentration in the organic phase was obtained. Titanium in the diluted solution was determined by spectrophotometry (peroxide method). Water in the organic phase was determined by Karl Fisher titration.
same point which corresponds to a ratio of 1.2 at sulphuric acid concentration 13M. These results are confirmed by data in Fig. 3 in which log Eo~2so4>. (Eo~H2so4) is the distribution coefficient of sulphuric acid) is plotted against TBP concentration at sulphuric acid concentrations 7.5 and 11-12 M. It is seen that when sulphuric acid concentration is l l-12M the plot is a straight line with a slope 1.1-1.2 and when the acid concentration is 7.5 M the slope is 1.5. These results are consistent with two competing mechanisms:
H2SO4(aq) + TBP,,~ . . . . . .
H2SO4"TBP,,,,
(1)
H2SO,u,,,) + 2TBEo~ . . . . . .
H2SO~,'2TBP~,,
(2)
In these equations water has not been considered although, as will be seen, sulphuric acid is probably extracted as an hydrated complex, at least in some cases. It is assumed that with concentrated sulphuric acid reaction (1) predominates and at low concentration reactions (1) and (2) are both produced. In "saturation" tests, several samples of pure and diluted TBP were repeatedly treated with fresh portions of sulphuric acid solutions of different concentrations. When sulphuric acid 11 M was used with TBP 0.5 M .or lower the molar concentration ratio was 1 : 1.2 confirming the equilibrium results and showing that at these conditions the organic phase was saturated with only one
Z RESULTS AND DISCUSSION Extraction of sulphuric acid. In Fig. 1 it can be seen that sulphuric acid extraction by TBP I M in carbon tetrachloride increases with its concentration in the aqueous phase until 13 M; beyond this value decomposition of the organic phase is noticeable. Figure 2 shows the molar concentration ratio of sulphuric acid to TBP in the organic phase as a function of the sulphuric acid concentration in the aqueous phase at several TBP concentrations. As can be seen all curves converge to the J~¢ voL 42,No. 7---(3
I
TBP
2
10
IM
~4 [H2504] aq
Fig. I. SulphUric acid concentration in the organic phase as a function of the aqueous acid concentration in experiments with T B P ! M.
1033
1034
P.H. TEDESCO and V. B. DE RUMI
1,2
o [T,P]c.,c0s, o
1.0
0.3
•
n rn F- 0.8
.
0.8 M
x
.
2.0M
®
,
2.,M
a_ m
o
A
0.2
o
0,6
o
E 0.1
0.4
0.2 i
2 :......
I
10 ~ H2SO43
I 6
/
/
&/' /
y'
=o x
g
L
I
I
I 14 l]rH2s04' aq.
10
Fig. 4. Mole of water per mole of TBP in the organic phase as a function of sulphuric acid concentrationin the aqueous phase.
oq.
Fig. 2. Sulphuricacid to TBP concentrations ratio in the organic phase vs sulphufic acid concentration in the aqueous phase at several TBP concentrations.
•
/,,,i / "
-I
l
I 15
//
--
•
-'-- H2SO 4
H z S O 4 11-12 M 7.S M
0
I
log [T BP]ci4 C
Fig. 3. Log of the distributioncoefficientof sulphurieacid vs log of TBP concentrationsplots at two sulphuric acid concentrations in the aqueous phase. contact; with pure TBP this ratio was 3.5-3.8 which cannot be explained by a simple mechanism and suggests the possibility of aggregates formation (polymerization reaction). This has too been suggested by Brauer and H/~gfeldt. Extraction o[ water. This was studied as a function of TBP and sulphuric acid concentration. All experiments made with undiluted TBP or at concentrations higher than 0.5 M in carbon tetrachloride showed that no detectable water was extracted at any sulphuric acid concentration from 4 to 13 M. In Fig. 4 it is shown that with TBP 0.5 M water is extracted from aqueous sulphuric acid solution and extraction increases with the acid concentration until 13 M. The amount of extracted water is from 0.08 to 0.3 g per 100 g organic phase. This maximum concentration was obtained in "saturation" tests and corresponds to 0.3 mole of water per mole of TBP. In the same experiments no less than 1 mole of sulphuric acid per mole of TBP was extracted. These experiments were confirmed by density measurements which showed that the density of the organic phase after the extraction was equal to the calculated density assuming only sulphuric acid extrac-
tion when pure TBP or concentrated solutions were used and that the density after the extraction was lower than the calculated density on that assumption when TBP solutions 0.5 M or lower were used. In some experiments we could verify that when the aqueous phase contains Ti(IV) at about 0.05 M, water is less extracted that when Ti is absent. All these results suggest that water is probably extracted as an hydrated complex of the sulphuric acid when using diluted TBP and when pure or concentrated TBP is used an anhydrous complex is extracted. Moreover water seems to be partially displaced from the organic phase by a titanium anhydrous complex. Extraction of Ti(IV). The most important aspects of the extraction of Ti(IV) from sulphuric acid solutions, with TBP are indicated in Figs. 5-8. All experiments were made with Ti(IV) solutions 0.01 M. Preliminary experiments showed that titanium extraction is a function of TBP and sulphuric acid concentrations. When the acid concentrations in the aqueous phase is below 8 M titanium extraction is negligible. The maximum extraction is obtained from sulphuric acid solutions 13 M. As it was said, at higher acid concentrations decomposition of the organic phase is noticeable, after several contacts.
o uJ o
/•O/•o [.2so,] 10.
/ i -1.0
I
x
.
11 M
•
If
12 M
0
,
13M I
.
Fig. 5. Log. of Ti(IV) distribution coefficient vs log of TBP concentrations at several sulphuricacid concentrations.
Ti(IV) extraction by TRl-n-butylphosphatefrom sulphuricacid solutions
oj.O,t
In Fig. 5 the plot log Eomj vs TBP concentration shows straight lines with the same slope 1.5 for sulphuric acid concentrations between 10 and 13 M. At lower acid concentrations consistent results could not be obtained because extraction was poor. So, for the range 10-13 M it is possible to postulate two mechanisms: TBP(o} + TiOSO,~q} . . . . . .
~
f ® [TBP]cI4 C OBN 1 , 1.0 M 0
I,
®
"
2.0 M
x
,,
1,5 M
2.5 M
ITBP puro
1
10
15 [HzSO4] aq.
Fig. 6. Titanium to sulphuric acid concentrations ratio in the organic phase as a function of sulphuricacid concentrationin the aqueous phase at several TBP concentrations.
0.02
,_e, o
'!c''c °'' ,o '.
0.01 o
2.0M
x
2.5M TBP
I
II
I 15
10
puro
[HzSO4]aq.
Fig. 7. Titanium to TBP concentrations ratio as a function of sulphuric acid concentrationin the aqueous phase at several TBP concentrations.
!
I F
0.S~-[
0,f°'
1035
I
I
l
I
01
0.2
0.3
0,4
o.TiP O.S
[Ti]aq
Fig. 8. Titaniumconcentration in the organic phase per mole of TBP vs titanium concentration in the aqueous phase using pure and carbon tetrachloridesolutions of TBP.
2TBP(o~ + TiOSO4(aq). . . . . .
TBP.TiOSO4~o,
(1)
(TBP)2.TiOSOa~o~. (2)
Figure 6 shows the molar concentration ratio of titanium to sulphuric acid in the organic phase a,~ a function of the sulphuric acid concentration in the aqueous phase, obtained in equilibrium experiments. It is seen that the maximum value is obtained at sulphuric acid concentration about 11 M and is higher when the TBP concentration decreases. This indicates that over 11 M the rate of extraction of the acid is higher than tlhat of the titanium complex. In Fig. 7 the ratio of molar concentrations of titanium to TBP in the organic phase is plotted vs the sulphuric acid concentration in the aqueous phase at several TBP concentrations, It shows that this ratio increases as the acid concentration increases and is higher at lower TBP concentration. The ratio titanium concentration per mole of TBP as a function of titanium concentration in the aqueous phase was obtained in saturation tests for undiluted TBP and solutions 2 and 2.5 M in carbon tetrachloride; results are indicated in Fig. 8. This shows too that more relative titanium extracion is obtained when the organic phase is more diluted. Tests were not made at lower TBP concentrations because a third phase appeared. According to all this information it can be postulated the formation of 1:1 and 1:2 complexes TI:TBP in equilibrium experiments when the concentration of sulphuric acid is between 10 and 13 M. These complexes are anhydrous when the TBP concentration is above 0.5 ld. In saturation experiments titanium to TBP molar concentration ratio in the organic phase is lower than 1:2 which can be explained by the preferential extraction of sulphuric acid. As it is indicated in Fig. 2, sulphuric acid to TBP molar concentration ratio is higher at higher TBP concentration and in Fig. 7 it can be seen that titanium to TBP molar concentration ratio is lower at higher TBP concentrations, so it must be deducted that titanium to sulphuric acid molar concentration ratio is lower at higher TBP concentrations and this is precisely confirmed by the results indicated in Fig. 6. This ratio is lower beyond sulphuric acid concentration I1 M, which suggests, as well as the saturation tests, a preferential extraction of the acid. No additional information could be obtained through some infrared spectra runned with the organic pha:~e previously contacted with sulphuric acid solution with and without titanium. So, we can summarise in this way our experimental results: (l) TBP extracts sulphuric acid, water and Ti(IV) from an aqueous solution of the metallic ion at sulphuric acid concentrations higher than 7 M when the organic phase is a carbon tetrachloride solution of TBP 0.5 M or lower; (2) at higher TBP concentrations or with undiluted extractant no water can be detected iin the organic phase after contact with aqueous sulphufic acid solutions 10 M or higher with or without titanium, which indicates extraction of anhydrous complexes; (!3) in equilibrium experiments at sulphuric acid concen-
1036
P. H. TEDESCO and V. B. DE RUMI
trations higher than 11 M and in the saturation tests there is a preferential extraction of acid (lower relative extraction of titanium) and the sulphuric acid to TBP molar concentration ratio reaches a maximum value of 3.8, which is probably due to polymerization reactions and (4) slopes of lOgEoH2SO4 vS log [TBP]o and log EoTi vs Iog[TBP]o plots suggest that the acid is extracted through sulphuric acid to TBP 1:1 and 1:2 complexes, and the metal by an independent mechanism including TiOSO4:TBP 1 : 1 and 1 : complexes. Acknowledgements--Thanks are due to the Consejo Nacional de Investigaciones Cientificas y T6cnicas de la Repfiblica Argentina and to the Comisi6n de Investigaciones Cientfficas de la provincia de Buenos Aires for financial support.
RE~T.RENCES 1. Y. Marcus and A. S. Kertes, Ion exchange and solvent extraction of Metal Complexes, Wiley Interscience, (1969). 2. E. Brauer and E. H6gfeldt, J. Inorg. Nucl. Chem. 23, 115 (1961). 3. P. Biddle, A. Coe, H. A. C. McKay, J. H. Mils and M. I. Waterman, J. lnorg. Nucl. Chem. 13, 156 (1960). 4. E. Hesford and H. A. Mc Kay, J. Inorg. Nucl. Chem. 13, 156 (1960). 5. H. A. Mc Kay, Ind. Chim. Beige, T 29 12, 1278 (1964). 6. P. H. Tedesco and V. B. de Rumi, Industria y Qu(mica, 224, 32 (1977). 7. P. H. Tedesco and J. Martfnez, An. de la Asoc. QuEm.Arg. 65, 115 (1977). 8. A. De, D. Khopkar and R. Chalmers, Solvent Extraction of Metals. Van Nostrand Reinhold, London (1970).