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552 IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH
Volume : 5 | Issue : 4 | April 2016 • ISSN No 2277 - 8179 | IF : 3.508 | IC Value : 69.48 Research Paper
Jewel Hossen Department of Applied Chemistry and Chemical Engineering, University of Rajshahi,
Md. Moynul Islam Department of Chemistry, BAUET, Qadirabad, Natore-6431, Bangladesh.
Siddhartha Sankar Saha Department of Chemistry, Rajshahi University of Engineering and Technology,
Solvent Extraction of Ti(IV) From Aqueous
Sulphate Solution By Cyanex301 Dissolved in
Kerosene : Equilibrium Studies.
KEYWORDS : Titanium, Solvent extrac-
tion, cyanex301, equilibrium.
ABSTRACT Cyanex301 dissolved in kerosene is found to be a good extractant for the extraction of Ti(IV) from aqueous sul-
phate medium. e equilibration time has been determined to be ~30 min. e extent of extraction is found to in-
crease with increasing Ti(IV) concentration in the aqueous phase, though the extraction ratio is decreased with increasing Ti(IV) concentra-
tion. e extraction is found to increase with increasing pH and cyanex301 concentration. e sulphate ion concentration has little eect on
the extraction of Ti(IV) by Cyanex301. e system is found to be endothermic in the lower temperature region (<30o C) and exothermic over
30o C. e pH dependence of 1 and the Cyanex301 dependence of 1 in its lower concentration region as well the sulphate ion dependence of
almost zero suggests the following reaction for extraction at lower concentration region of Cyanex301(HR):
[TiOHSO4R](0) + H+
On the other hand, the extractant dependence of 5 at higher concentration region of the extractant suggests the following mechanism:
[TiOHSO4R.4HR](0) + H+
satisfying the dependences of other parameters. Finally the equilibrium constants for the extraction reactions suggested have been calculated
to be 54.97 and 282.50 respectively.
Introduction: Titanium is known as a space-age metal because
it has high tensile strength and its weight is comparatively low.
Moreover, metal titanium is inert to many corrosive media. Pres-
ently, the applications of titanium include canister for nuclear
plant waste, casting for pace maker, medical implant, high per-
formance automobile and ordnance armor. ough highly pure
TiO2 is mainly being utilized as a white pigment, it can also be
used as a photocatalyst for the treatment of anthropogenic com-
pounds present in water. Titanium is an important constituent
for various alloys and catalyst and that’s why- the future applica-
tions of titanium could include single-crystal electrode of TiO2,
catalyst for u-gas denitrication, and for the manufacture of
thermistor such as barium- titanate. As titanium is being used
frequently for many purposes, the primary sources of titanium
are going to be nished and ecient methods should be devel-
oped to recover titanium from low-grade secondary sources. For
this reason, to get high purity and quantity, solvent extraction is
attractive and a good alternative.
Solvent extraction of Ti (IV) by Cyanex301 has been reported
Biswas et al (1) as well as with Cyanex302 (2) from sulphate so-
lution. Sole (3,4) also reviewed the extraction of Ti(IV) from sul-
phate medium using some acidic and neutral organo-phospho-
rus extractants, concluding tri-octylphosphine oxide as the best
for Ti(IV) extraction. Some other researchers have also reviewed
the extraction of Ti (IV) from sulphate solution (5-7), on the
other hand, Some other reported its extraction procedure from
chloride solution (8-17).
(C16H34PS2H) acid is an acidic extractant produced by Ameri-
can Cyanamide Co. e supplied sample contains 77.2 % of Cy-
anex301 having pKa in water = 2.61, viscosity = 7.8 kg m-1 s-1, mo-
lar mass = 322 g mol-1, density = 950 kg m-3, aqueous solubility =
7 mg dm-3, ash point = 146 oC, auto ignition temperature = 297
oC and decomposition temperature = 220 oC and it is monomeric
in nature  Cyanex301 as a good extractant is also being used
for the extractions of Zn(II) by Rickelton et al(19); In(III) by Avila
et al(20); Fe(III), Zn(II), Cu(II), and Ni(II) by Sole et al (21); Co(II)
and Ni(II) by Tait (22); Sb(III), Bi(III), Pb(II), and Sn(IV) by Facon
et al (23) Cu(II) by Sole and Hiskey(18); Ag(I) by Sole et al(24).
A Mettler- Toledo 320 pH meter (England), Stuart Flask Shaker
machine (220V, 50Hz), Mettler- Toledo balance (AB 204-S) and
WPA5104 Spectrophotometer (UK) were used for experimental
The stock solution was prepared by digesting appropriate 50g of
TiO2 in concentrated H2SO4 with continuous heating and constant
stirring and then ltered to remove insoluble residue dissolving
it in 15% H2SO4. The standard solution was prepared roasting
0.50g of TiO2 with 10g of KHSO4 and calibration line was t-
ted (30% 1 ml H2O2 and 1 ml H3PO4). The extractant Cyanex301
(bis-(2,2,4-trimethylpentyl)-di thiophosphinic acid) was analytical
grade and 2.0M solution was prepared using kerosene as a dilu-
ent and all other chemicals used were analytical grade.
General Extraction Procedure
Extraction experiments were carried out by taking 20ml of aque-
ous solution containing TiOHSO4
+ with 20ml of Cyanex301 solu-
tion dissolved in kerosene at an O/A ratio of one and shacked for
40 min to reach equilibrium state at room temperature and then
the aqueous phase was separated to determine the concentration
of aqueous phase by spectro photometer and the value of distri-
bution co-efcient (D) was determined.
Result and discussion:
The experimental data and graph shows that the value of con-
centration ratio increases almost exponentially with increasing
the phase contact time up to 30 min and then the curve levels
off when Ti(IV) is extracted from SO-2
4 medium by analytical
grade Cyanex301. It is therefore concluded that the equilibrium
time for this system is 30 min. In subsequent experiments phase
contact time of 40 min have been used to ensure equilibration for
other parameters. Previously, the equilibration time of about 3
hours and 2 hours have been reported for extractions of Ti(IV) by
IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH 553
Volume : 5 | Issue : 4 | April 2016 • ISSN No 2277 - 8179 | IF : 3.508 | IC Value : 69.48
D2EHPA from sulphate (5) and chloride (13) medium, respective-
ly. So, Cyanex301 can extract Ti(IV) faster than does D2EHPA.
Fig-1: Dependence of extraction ratio on time for the extrac-
tion of Ti(IV) by Cyanex301. pH = 1.60, Temperature = 25oC
,[Ti(IV)] = 0.5 g dm-3, [SO4
2- ] = 1.0 mol dm-3 [Cyanex-301] =
0.05 mol dm-3
Effect of Ti(IV) concentration in the aqueous phase on the extrac-
tion ratio(D) of Ti(IV) during extraction by Cyanex301 shows
that plot is a straight line with slope equaling to -1.0. This is con-
trary to the general principle of solvent extraction of metal ions.
The Eq. (4) deduced latter shows that the values of D should be
independent of metal ion concentration provided the equilibrium
pH and extractant concentration are kept constant. The deviation
from this statement indicates the non ideality of phases in the
system. The log D vs. log [Ti(IV)]eq plot is also shown in Fig.2.
This plot is also a straight line but with a slope of -0.5. One rea-
son for this dependency may be due to the change of equilibri-
um pH to different extent from the initial pH value and also the
change in equilibrium extractant concentration.
Fig-2: Eect of Ti(IV) concentration in the aqueous phase
on the extraction ratio(D) of Ti(IV) during extraction by Cy-
anex301. pH = 1.60, Time = 40 min, [Cyanex-301] = 0.1 mol
2-] = 1.0 mol dm-3, Temperature = 24o C
The logD vs. pHeq plot in Fig.3 shows that the extraction
of Ti(IV) with analytical grade Cyanex301 is a straight line
with slope approximately one both for extractant concentra-
tio n 0.1 mol dm-3 and 0.25 mol dm-3 (the least squares slopes
being 0.95 and 0.965 respectively ), so that the extraction
ratio (D) increases with increasing equilibrium as well as
initial pH values of aqueous solution of Ti(IV). The straight
line has least squares intercept of -0.673 and -0.915. In
case of extraction with D2EHPA, the pH dependence is
about 2 . Consequently Cyanex301 can extract Ti(IV)
-3.8 -3.6 -3. 4 -3.2 -3.0 -2. 8 -2.6 -2.4
-2.7 -2.6 -2. 5 -2.4 -2.3 -2.2 -2.1 -2. 0 -1.9
, mol dm
, mol dm
over a wide range of aqueous pH than does D2EHPA.
However, in the present case, the extraction at higher pH
values is often encountered with emulsion formation. It is
therefore suggestible to carry out this extraction system in
presence of a modifier (higher alcohol-emulsion inhibitor)
as done for the ditolylphosphoric acid extraction of Ti(IV)
Fig-3: Dependence of extraction ratio (D) on equilibrium pH
in the aqueous phase in the case of extraction of Ti(IV) by
Cyanex301. [Ti(IV)](ini) = 0.5 g dm-3, Shaking time = 40 min,
2-] = 1.0 mol dm-3 and series1[Cyanex-301] = 0.1 mol dm-3,
series2[Cyanex-301] = 0.25 mol dm-3, Temperature = 30o C.
The equilibrium pH values in both series of extractions are found
to very within ± 0.01 pH units. The data have been displayed in
Fig.-4 as log D vs. log [Cyanex301] for pH values of 1.6 and
1.8. In both cases, curves rather than straight line are obtained.
The curves have a limiting slope of unity at lower concentration
region of Cyanex301, whereas it is increased to about 5 in the
higher concentration region.
Fig-4: Dependence of extraction ratio (D) on extractant
(Cyanex301) concentration in the organic phase. Time = 40
min, Temperature = 24o C, [Ti(IV)] = 0.5 g dm-3, [SO4
2-] = 1.0
mol dm-3 pH = 1.60 and pH =1.80
Fig.-5 shows log D vs. log [SO-2
4] plot. e log D vs. log [SO-
4] plot is a straight line with slope of about 0.16. From this
plot, it is clear that there is little eect of sulphate ion con-
centration in the aqueous phase on the extraction ratio.
-1.4 -1.2 - 1.0 -0.8 -0. 6 -0.4
log ([Cyanex 301], mol dm
0.0 0.1 0.2 0.3 0.4 0. 5
], mol dm
554 IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH
Volume : 5 | Issue : 4 | April 2016 • ISSN No 2277 - 8179 | IF : 3.508 | IC Value : 69.48 Research Paper
Mechanism of extraction:
An acidic extractant, HR can extract a metal ion, Mz+ according
to the following reaction:
Mz+ + nHR(0)
MRz. (n-z)HR (0) + zH+ …………….... (1)
e equilibrium constant, Kex of the above reaction can be repre-
sented as follows:
On taking logarithm of both sides
log Kex = log D + z log H+ - n log [HR](0) ……………. (3)
Where, D = [MRz . (n-z) HR](0) / [Mz+] = [Mz+](0) / [M z+](a).
From equation (3)
logD = log Kex + z pH + n log [HR](0) ………………….. (4)
Equation (4) states that the slope of the plot of log D vs. pH
gives the value of z (the number of H+ releases due to extraction
reaction) and slope of the plot of log D vs. log [HR](0) gives the
value of n (the number of HR molecule consumes to form the
extractable species due to extraction reaction.)
In the present case, the value of n (in lower concentration re-
gion of Cyanex301) and z are both unity. erefore, n-z = 0, so
that no solvated complex is formed in the lower concentration
region of Cyancex301. However in the higher concentration
region of Cyanex-301, the value of n becomes almost 5 and so
solvated species is formed at higher concentration region of
TiO2+ can form strong complex with bisulphate ion. e acid dis-
sociation constant of H2SO4 are Ka1~ 1000  and Ka2 = 10-2 at
zero ionic strength . ese values indicate that if in an acidic
solution, sulphate ion is added, all sulphates converts into bisul-
The stability constant of TiOHSO+
4 is 102.2 . Simple cal-
culation shows that in 0.5 g dm-3 Ti(IV) and 1 mol dm-3 sul-
phate medium, the percentage of TiOHSO+
4 is 98.88; whereas
in 0.5 g dm-3 Ti(IV) and 3 mol dm-3 sulphate medium, the
percentage of TiOHSO+
4 is 99.84%. It is therefore obvious
that the extractable TiO2+ species in the aqueous phase is
4 and its concentration is not so much varied
when sulphate ion concentration is varied within 1 - 3 mol
dm-3. For this reason, the log D vs. log [SO-2
4] plot has a very
Considering all these facts, the proposed extraction equilib-
rium reaction in the case of extraction of Ti(IV) from sul-
phate medium by Cyanex301 in its lower concentration re-
4 + HR (0)
[TiOHSO4R](0) + H+ ……………… (5)
On the other hand, the extraction reaction at higher concentra-
tion region of Cyanex301 is:
TiOHSO4 + 5HR (0)
[TiOHSO4R.4HR](0)+H+ ……………… (6)
Calculation of Extraction Equilibrium Constant, Kex:
Equation (5) indicates that the intercept of the plot of log D vs.
pH will be equal to log Kex + n log [Cyanex301]. e value of n
depends on the Cyanex301 concentration region. It is 1 in the
concentration region of 0.05-0.15 mol dm-3 and above concentra-
tion region up to 2 mol dm-3 of cyanex301 for eq.-5
Intercept = -0.91=log Kex +1.0 log 0.1
log Kex = 0.09
So that Kex = 100.09 = 1.23
And also for eq.-6
Intercept = -0.673=log Kex +5.0 log 0.25
Equation (4) also indicates that the intercept of log D vs. log
[Cyanex301] plot is log Kex + z pH. Here ‘z’ is 1. e intercepts at
lower Cyanex-301 region of log D vs. log [Cyanex-301] plots are
1.28 and 1.50, respectively, at equilibrium pH 1.5 and 1.7. It fol-
(i) Intercept = 1.28 = 1.0log Kex + 1× 1.5
log Kex = -0.22
or, Kex =10-0.22 = 0.60
(ii) Intercept = 1.5 = log Kex + 1× 1.7
or, log Kex = -0.2
or, or, Kex = 10-0.2 = 0.63
erefore, the average Kex value for the reaction given in Eq. (4)
e equilibrium constant Kex for the reaction given by Eq. (6)
which is valid at higher concentration region of Cyanex301, can
be derived as follows:
Intercept = 3.98 = log Kex +1.5 (eq.pH)
giving log Kex = 2.48 or Kex = 301.99
and intercept = 4.12 = log Kex + 1.7 (eq. pH)
giving log Kex = 2.42 or, Kex = 263
erefore, Kex value at the higher concentration region is 282.50.
Dependence of extraction on temperature:
e log D vs 1/T × 103 plot is shown in Fig. 6. e extraction of
Ti(IV) increases with increasing temperature below 30oC and
above 30oC, the reverse trend is observed.
Since the extraction ratio, D is proportional to extraction equi-
librium constant, Kex, the Vant Ho equation in the following
modied form can the applied for the solvent extraction study:
Log D = - H /2.303 RT ……………….. (7)
Where, H is the enthalpy change during extraction and R
is the molar gas constant. According to this equation, the
slope of the log D Vs 1/T plot should be equal to -H /
In the present case, the slopes at lower and higher tempera-
ture regions are -5236.16 and 4000, respectively which give
respective H values of 100.28 kj and -76.61 kj mol-1. The
extraction process is therefore endothermic at lower temper-
ature region whereas it is exothermic at higher temperature
IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH 555
Volume : 5 | Issue : 4 | April 2016 • ISSN No 2277 - 8179 | IF : 3.508 | IC Value : 69.48
Fig-6: Dependence extraction of Ti(IV) by Cyanex301 on
temperature pH = 1.6, Time = 40 min [SO4
2-]=1.0 moldm-3 ,
[Ti(IV)] = 0.5 g dm-3 [Cyanex-301] = 0.05 mol dm-3
1. e Ti(IV)-SO4-cyanex301-kerosene system takes about 30
min for equilibration.
2. e slopes of the logD vs. log [Ti(IV)]ini and logD vs. log
[Ti(IV)]eq plots are -1 and -0.5 respectively. Although with
increasing Ti(IV) concentration in the aqueous phase, D
is found to decrease, the amount of Ti(IV) extracted in the
organic phase is increased.
3. e slope of logD vs. pH plot shows that the aqueous acid-
ity dependence is minus unity.
4. e logD vs. log [cyanex301] plots show that extractant de-
pendences are 1 and 5 in the lower and higher concentra-
tion regions of extractant respectively.
5. e extraction ratios are varied little with increasing sul-
phate ion concentration. e slope of logD vs. log[SO4
plot is 0.16.
6. e temperature dependence study shows that the reaction
is endothermic up to 30oC and in the higher temperature
region, the extraction process seemed to be exothermic in
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