Chapter 5
Equilibrium study for
TBP-HNO3-diluent
system
5. Equilibrium study for TBP-HNO3-diluent system
5.1. Introduction:
5.1.1. Phase rule:
In a liquid-liquid system, the minimum number of components is three and
two phases are in equilibrium. For a ternary system, the number of degrees of freedom
is three, as calculated by the phase rule (F = C- P + 2 = 3 - 2 + 2 = 3). There are six
variables: temperature, pressure, and four concentrations. If the pressure and
temperature are specified, then setting one concentration will fix the system. The
other three concentrations are calculated from the phase equilibrium. Therefore for
three components system, the equilibrium data are often expressed in equilateral
triangular coordinates as shown in Fig. 5.1.
5.1.2. Phase equilibrium:
The three corners represent three pure components, A, B and C. The point M
is a mixture. The perpendicular distance from the point M to any base line is the mass
fraction of the component at the corner opposite to that base line. For example, the
distance from M to base AB is the mass fraction of C (x C = 0.40).
Fig 5.1. Coordinates of a triangular diagram
The simplest extraction system comprises three components: the solute or the
material to be extracted; the solvent, which must not be completely miscible with the
other liquids; and the carrier, or nonsolute portion of the feed mixture to be separated.
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The simplest ternary system called Type I, for one immiscible pair is shown in
Fig. 5.2. For such a system the carrier and the solvent are essentially immiscible,
while the carrier-solute and solvent-solute pairs are miscible. The diagram shows a
single-phase region and a two-phase region; for extraction to be feasible,
compositions must be such as to fall within the two-phase envelope. The tie lines
connect equilibrium phase compositions. The Plait point is the intersection of the
raffinate phase and the extract phase boundary curves, and no separation can be made
at that point.
Fig. 5.2. Phase diagram of Type I system
Fig. 5.3 shows Type II ternary liquid-liquid system, one where there are
immiscibilities between solvent and solute, and between solvent and carrier. The tie
lines are indicated, and there is no plait point. With this type of system it is possible to
obtain an extract that is essentially free of carrier, which is not possible with the Type
I system shown in Fig. 3. For all systems, temperature influences the locations of the
phase envelopes, and a normally immiscible system can become completely miscible
if the temperature is raised sufficiently.
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Fig. 5.3. Phase diagram of Type II system
Reliable liquid-liquid equilibrium data are crucial for the rational and
economic design of extraction processes. Such data can be measured with less
difficulty than vapour-liquid equilibria, when the phases are brought to equilibrium in
a suitable container and then allowed to separate completely before they are sampled
for analysis.
5.1.3. Importance of equilibrium study for TBP-diluent-nitric acid system:
Equilibrium study plays a very important role in liquid-liquid extraction
studies. It is an important factor which decides the distribution of solute between two
liquid phases. A system is said to be in equilibrium when no mass transfer takes place
between two phases and all the physical properties of each phase becomes uniform.
TBP is the most frequently used solvent in liquid – liquid extraction for fuel
reprocessing. It is also used widely as a solvent in nuclear chemistry for recovery of
the actinides elements like Th, U, Np and Pu. As the density and viscosity of TBP is
very much similar to that of water, the separation of TBP from water becomes
difficult. This problem can be solved by diluting TBP with a light, saturated
hydrocarbon, such as n-dodecane, NPH, kerosene, etc which reduces the density of
TBP and aid phase separation (Schulz and Navratil 1984).
TBP dissolves in NPH by dimerization and in nitric acid due to stable
equimolar i.e. 1:1 complex formation by hydrogen-bonding (Collopy and Cavendish
1960). The two-phase system can be represented by an equilibrium reaction (1) in the
organic phase
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xTBP org. + NPH org . ↔ (TBP) x .NPH org.
(1)
an equilibrium reaction (2) in the aqueous phase
TBP aq. + HNO 3aq. ↔ TBP.HNO 3aq.
(2)
and the equilibrium distribution constant (K d ) for associated TBP between the two
phases is represented by eq.(3)
K d = TBP org. / TBP aq.
(3)
The similar type of distribution also takes place for nitric acid. The extraction
of nitric acid from aqueous solutions by TBP in NPH can be explained by following
reaction:
H+ aq. + NO3- aq. + TBP
org.
↔ HNO 3. TBP org.
while its distribution in the aqueous phase takes place as
HNO 3aq + H 2 O aq ↔ H 3 O+ aq + NO3- aq
The above equations explain that when TBP in NPH is contacted with nitric
acid two types of mass transfer takes place. TBP distributes itself between NPH and
nitric acid but simultaneously nitric acid is also distributed between TBP and water.
In the PUREX process, the spent fuels are typically dissolved in nitric acid and
30% TBP in a paraffinic diluent is used as an extracting solvent. The diluents like ndodecane, NPH, kerosene etc. affect the solubility of TBP in aqueous phase. It is
therefore of fundamental importance to study the equilibrium diagram of the ternary
system TBP-diluent-nitric acid. The equilibrium study of this TBP-diluent-nitric acid
system will aid in finding out the amount of TBP in different concentration of nitric
acid in presence of diluent.
The work done by different investigators on the equilibrium and extraction
study related to TBP-diluent-nitric acid system is explained in detail in the literature
survey section below.
5.2. Literature survey:
Number of extraction studies of nitrates with TBP has been done in past.
Alcock et al. (1956) have studied TBP-diluent-water-HNO 3 system and measured the
mutual solubility of TBP and water in the presence of nitric acid and also in presence
of various diluents like kerosene, heptane, hexane, cyclohexane, toluene and benzene.
The partition of nitric acid between water and TBP in kerosene at various TBP
concentrations has also been determined. They have reported that the extraction of
nitric acid in the organic phase takes place due to 1:1 compound formation with TBP.
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Siddall and Parker (1957) have presented in their report the equilibrium
distribution of uranium, thorium, and nitric acid between solutions of tri-n-butyl
phosphate in kerosene and the various aqueous solutions encountered in the
separation of plutonium and uranium for the recovery of U-235 from spent reactor
fuel.
Collopy and Cavendish (1960) have published the results on equilibrium
distribution curve for nitric acid between TBP and water where the concentration of
nitric acid is ranging from 0-12M in the aqueous phase. The equilibrium distribution
constant and the equilibrium reaction constant for the partition of associated nitric
acid into TBP and the reaction of this acid in TBP to form a complex was calculated
as 0.19 and 19.9 ± 0.5, respectively. The equilibrium constants obtained were used to
determine the values of the concentration of associated nitric acid in diluted aqueous
nitric acid solutions.
Davis (1962) has reported thermodynamics studies for extraction of nitric acid
by TBP-diluent hydrocarbon system using mathematical model. It was observed that
HNO 3 reacts with both TBP and TBP.H 2 O to form TBP.HNO 3 and TBP.HNO 3 .H 2 O
complex. Since the water concentration did not appear as a variable except in
calculation of the TBP concentration, the presence of water in the organic phase not
affected the reaction of HNO 3 with TBP or TBP.H 2 O.
Burns and Hanson (1964) have studied the distribution of nitric acid between
TBP and water at 20°C and 25°C. 20% and 30% TBP in odourless kerosene was used
as the organic phase while the concentration of the aqueous phase was upto 10 moles
per litre.
Hardy et al. (1966) have also obtained data on partition of nitric acid and water
between aqueous nitric acid and pure TBP solutions and have also analyzed these data
in the terms of Gibbs-Duhem equation.
Baldwin and Higgins (1974) have extracted TBP using different diluents viz.,
dipropylene glycol, methyl carbitol, 1,2-propanedioI and hexane. Distribution ratios
greater than one were observed when hydrocarbons and tributyl amine were the
diluents but in the aromatic solvents and some others, the K d ’s were less than one.
Sagert and Lee (1980) have measured the distribution of lower trialkyl
phosphates like trimethyl, triethyl, tripropyl and tributyl phosphate between water and
dodecane as a function of temperature and trialkyl phosphate concentration. The
thermodynamic functions associated with the transfer of each
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5. Equilibrium study for TBP-HNO3-diluent system
trialkylphosphates from water to dodecane were also calculated. It was found that the
free energies of transfer changed by -3.5 kJ/mol with addition of each methylene
group to the solute. The enthalpies of transfer for all the trialkylphosphates were in
the range of 26 to 30 kJ/mol.
Hoh and Wang (1980) have carried out rate studies on the acid extraction
(denitration) and stripping (acid recovery) for the nitric acid-TBP system. The
optimum conditions for extraction of nitric acid by 75% TBP in kerosene were
agitation rate of 520 rpm and 3 min of liquid mixing, while for stripping of nitric acid
from TBP loaded with nitric acid by water were agitation rate of 750 rpm and 3 min
of liquid mixing.
Maimoni (1980) has examined the liquid-vapor equilibrium data for nitric acid
and nitric acid-plutonium nitrate-water solutions. For the nitric acid-water system and
plutonium nitrate-water solutions correlations of activity co-efficients were obtained
over limited temperature ranges. The estimation of vapor pressures for plutonium
nitrate solutions at temperatures other than the normal boiling point could be made
from the approximate value of activity co-efficient obtained from the above
correlations.
Horng (1984) has developed an extraction model based on the extraction
kinetics for UO 2 (NO 3 ) 2 -TBP-kerosene system in the acidic medium by assuming that
the extraction rate of uranyl nitrate is pseudo first order with respect to its
concentration in aqueous phase and concentration of free TBP and that the rate of
stripping is also pseudo first order with respect to the concentration of TBP
complexed by uranyl nitrate. The values of Be
ΔH/RT
determined for the case of 20%
TBP in kerosene could be used to predict the equilibrium values for the system of
30% TBP. The extraction equilibrium isotherms were characterized by the Langmuir
type. The absolute errors in the correlation coefficients between the experimental data
and the predicted values were in the ranges from 2.68% to 6.73%.
Petkovic (1988) have clarified the stoichiometry of thorium nitrate extraction
with TBP and determined the thermodynamic equilibrium constant of the extraction
process. Formation of a 1:3 adduct of thorium nitrate with the phosphate has been
established. The influence of different diluents on this constant was also considered.
Kopenchi and Petkovic (1994) have proposed a chemical model for the
extraction of uranyl nitrate with TBP. The model utilizes the chemical activities of the
extraction species in the aqueous phase. A chemical model was developed based on
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the chemical reaction where a neutral extractant interacts with an inorganic salt
present in the aqueous phase to form an uncharged complex which is extracted into
the organic phase. The model fits well the distribution results over the whole
concentration range of the extraction isotherm. Extraction and dimerization constants
obtained by means of the model are in agreement with literature data within
acceptable error bar.
Naganawa and Tachimori (1997) have determined hydration of nitric acid in
dodecane on the basis of acid and water distribution between aqueous acid solutions
and dodecane at 298K. The equilibrium data of mono- and decahydrate of nitric acid
which are regarded as molecular and ionized acid alongwith anhydrous nitric acid in
dodecane has been calculated. The influence of solvent in formation of acid hydrates
in dodecane was also compared with the results obtained in benzene.
Barnes et al. (1999) obtained the phase diagram of the water -oxalic acid tributyl phosphate ternary system at 303.15K. A multistage cross-flow extraction
process was performed in order to verify the accuracy of the basic equilibrium data
and to calculate the number of stages required to extract oxalic acid from its aqueous
solutions. This number was also graphically determined by using a distribution
diagram in Bancroft’s coordinates and analytically calculated by assuming virtual
immiscibility between the feed and the extraction solvents. The number of theoretical
stages obtained graphically was similar to the experimental value, which confirms that
the equilibrium in each stage was achieved during the extraction process.
Xun et al. (2002) have investigated the phase behaviour and phase
composition of TBP-kerosene-H 3 PO 4 -H 2 O three-phase extraction system and
compared with the TBP-H 3 PO 4 -H 2 O two-phase system without the diluent. In TBPkerosene-H 3 PO 4 -H 2 O system, the formation of the third phase is related only to the
equilibrium concentration of H 3 PO 4 in the bottom phase. The composition of the
middle phase is not a function of only the C H3PO4 but also related to the initial
concentration of TBP.
Ayedi et al. (2002) have presented the phase equilibrium diagram for the
ternary system H 2 O-H 3 PO 4 -TBP at 298.15 and 323.15K. The bimodal curves, tie
lines and distribution curves alongwith plait point by Hand’s method have also been
determined.
Sahnoun et al. (2002) have presented liquid-liquid phase equilibria for the
ternary system water-phosphoric acid-tributyl phosphate at 298.15 and 323.15 K. The
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5. Equilibrium study for TBP-HNO3-diluent system
binodal curves, tie lines, and distribution curves have been determined. The plait point
compositions have been calculated by Hand’s method. The extraction power of TBP
for phosphoric acid has been compared to those of methyl isobutyl ketone, dibutyl
ether, isoamyl alcohol, and diethyl ketone. The extraction chemistry of H 3 PO 4 by
TBP was also discussed.
Ziat et al. (2004) have studied the liquid–liquid equilibria of the system
H 3 PO 4 –KCl–H 2 O–TBP experimentally in the concentration range 0–6 mol/kg. The
obtained data has been modelled using the Pitzer equation for the aqueous phase and
the Sergievskii–Dannus relationship for the organic phase. A fairly good agreement
was observed between the model and the experimental data.
Alibrahim (2007) extracted phosphoric acid from different aqueous solutions
using 80% TBP in kerosene as an extractant. The effect of the nature of the diluents
on the extraction of phosphoric acid with TBP has been studied and correlated with
the dielectric constant. Kerosene gave the highest extraction yield compared with the
other diluents tested. Results demonstrated that H 2 SO 4 enhanced the extraction yield
of H 3 PO 4 to a large extent compared with HCl, HNO 3 , or HClO 4 . McCabe and
Thiele method was used to calculate the extraction stages needed to extract H 3 PO 4
from H 2 SO 4 solution.
Keshav et al. (2008) have carried out equilibrium studies for the extraction of
propionic acid using TBP in different solvents viz. 1-dodecanol, benzene, toluene,
heptane, hexane, butyl acetate, petroleum ether, and paraffin liquid to check their
effectiveness.
Equilibrium parameters such as distribution ratios, loading ratio,
degree of extraction and equilibrium complexation constants have also been
presented. However, it was observed for diluents of similar type, e.g., inerts (hexane
and n-heptane) or aromatics (benzene and toluene), the increase in molar mass,
boiling point, and specific gravity resulted in the lowering of the equilibrium
extraction coefficient. The successful relationship was obtained using dipole moment
and extraction parameter.
Comor et al. (2010) have developed a mathematical for the simultaneous
extraction of nitric acid and uranyl nitrate with TBP in alkane diluents. The model
uses chemical activities of nitric acid and uranyl nitrate in the aqueous phase and the
stoichiometric concentrations of their TBP solvates in the organic phase. This model
fits well the distribution results over the whole concentration range of the extraction
isotherms, extractant concentrations 5-100 % TBP and in the extraction of uranyl
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5. Equilibrium study for TBP-HNO3-diluent system
nitrate with TBP concentrations up to about 60 % TBP. The deviation of distribution
ratio of nitric acid to uranyl nitrate calculated using this model is 8.7% from
experimental values.
Guohua et al. (2010) have studied three-phase extraction system of TBPkerosene- HClO 4 -H 2 O and compared it with two-phase system of TBP-HClO 4 -H 2 O.
The results indicate that the composition of the middle phase and its change with the
increasing aqueous acidity are almost the same as that of the organic phase in twophase system.
All the above authors have mainly focused on the distribution of nitric acid
between TBP and water at different temperatures and in presence of various inert
diluents but the data on distribution of TBP between nitric acid and diluent are still
not available and the equilibrium diagram for the TBP-diluent-nitric acid system has
not yet been published.
The main objective of this study was to find the equilibrium concentration of
TBP at various concentration of nitric acid ranging from 0.3-3N by using different
percent of diluent in TBP as the organic phase. This study will help in finding out the
distribution of TBP in both organic and aqueous phase at equilibrium. The solubility
of TBP in nitric acid has been measured as a function of diluent in this work. The
diluent used in the present study is NPH. It has been found that the distribution ratio
value varies with the concentration of TBP, nitric acid and NPH. Nitric acid partitions
between TBP and water have also been studied. The concentration of nitric acid in
both the phases is determined by titration method. It has also been proved that the
concentration of nitric acid varies during this equilibrium study due to 1:1 complex
formation with TBP by hydrogen bonding. This study will be useful in nuclear waste
management generated by spent fuels of reprocessing origin.
5.3. Experimental section:
5.3.1. Materials:
TBP and nitric acid was supplied by SD fine chemicals. NPH was supplied by
Bhabha Atomic Research center (BARC). All the reagents used were of A.R. grade.
5.3.2. Mixing Vessel:
A 100ml baffle reactor with glass stirrer was used as mixing vessel. An
electrically driven motor was used for stirring the solution as shown in Fig.5.4. The
speed of the motor was adjusted using speed regulator.
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5. Equilibrium study for TBP-HNO3-diluent system
Fig.5.4: Schematic of the reaction assembly for equilibrium study
5.3.3. Equilibration and phase separation:
Partition experiments were performed by equilibrating 50 ml of TBP in NPH
with 50 ml nitric acid for around 3 h at 500 rpm. in mixing vessel. The phases were
allowed to separate for overnight at room temperature to ensure complete separation
before analysis. The settling technique was preferred over centrifugation since the
latter technique might invariably result in an increase in the temperature of the
solution and hence disturb the solution equilibrium. The same procedure was repeated
for different percent of TBP in NPH contacted with nitric acid of different normality.
5.3.4. TBP Concentration Determinations:
TBP concentration in organic phase was determined by gas chromatography
(GC) and in aqueous phase by high performance liquid chromatography (HPLC).
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5.3.4.1. Analysis of TBP on GC:
The ThermoFisher model GC-8 gas chromatograph with flame ionization
detector (FID) was used. A 10% OV-17 SS column with 80/100 mesh and 1/8’’x 2 m
in length was used for separation. The operating conditions were as follows: column
temperature, 235°C, injector port and detector temperatures, 300°C and nitrogen was
used as the carrier gas. 2-µl of the organic sample was injected into the column using
a borosilicate glass syringe. Calibration curve was plotted for quantifying amount of
TBP in NPH after equilibrium.
5.3.4.2. Analysis of TBP on HPLC:
The Jasco make HPLC system equipped with, a R.I detector Model RI-2031,
an isocratic pump Model PU-2080, a Rheodyne manual sample injector Model
77251and LC NET II AD box with Borwin DV software was used. A HPLC column
oven Model HCO- 02 was used to maintain the temperature constant throughout the
analysis. The HiQ sil C18HS 4.6mm x 250mm in size was used as an analytical
column. The mobile phase was a mixture of acetronitrile and water.
5.3.5. Nitric acid partitions:
The concentration of nitric acid in both the phases after equilibration was
determined by titration method. The NaOH solution was used as a base and
phenolphthalein as an indicator during titration. The color change at endpoint was
from colourless to pale pink.
5.4. Results and discussion:
The distribution ratio was generated by varying the concentration of TBP,
nitric acid and NPH in the solution. The effect of concentration of TBP, nitric acid
and NPH on the equilibrium data for TBP-NPH-nitric acid system has been
determined and discussed below.
5.4.1. Effect of TBP concentration:
The effect of TBP concentration on the equilibrium data of TBP-NPH-HNO 3
system has been investigated. The partition of TBP between nitric acid and NPH is
shown in Fig.5.5. The equilibrium curve was generated by varying the concentration
of TBP in organic phase ranging from 0.1% to 100%. It has been observed that the
distribution ratio values increases sharply with the concentration of TBP in organic
phase as shown in Fig 5.6. It is found that as the concentration of TBP in organic
phase increases, more amount of TBP is transferred into the aqueous phase and hence,
the solubility of TBP in aqueous phase increases. The distribution ratio values of TBP
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5. Equilibrium study for TBP-HNO3-diluent system
increases with increasing aqueous phase TBP concentration because of dimerization
of TBP. The results obtained are in agreement with that reported by Schulz and
Navratil (1984). They have measured distribution ratio of TBP as a function of TBP
concentration in aqueous phase. Germain and Plout (1980) have also obtained
equilibrium data for TBP-2M nitric acid-diluent system. They have also found that the
distribution ratio value of TBP increases sharply with the concentration of TBP in
aqueous phase. Sagert and Lee (1980) have also reported that distribution ratio
increases with concentration of TBP due to aggregation of TBP in dodecane. Hence, it
is confirmed from the equilibrium study that the distribution ratio for this system
depends upon the concentration of TBP in both the phases and is a function of TBP
Conc. of TBP in extract phase
(104 mg/l)
concentration in organic phase.
120
100
80
60
40
20
0
0
200
400
600
Conc. of TBP in raffinate phase(mg/l)
0.3M nitric acid
1M nitric acid
3M nitric acid
Fig.5.5: Graphical representation of equilibrium data for TBP-Diluent-Nitric
acid system
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5. Equilibrium study for TBP-HNO3-diluent system
4000
3500
3000
Kd
2500
2000
1500
1000
500
0
0
20
40
60
TBP in organic phase(%)
80
100
0.3M nitric acid
1M nitric acid
3M nitric acid
Fig.5.6. Effect of nitric acid on K d values of TBP
5.4.2. Effect of nitric acid concentration:
The effect of nitric acid concentration on the equilibrium data of TBP-NPHnitric acid system has also been studied. The concentration of nitric acid in aqueous
phase has been varied from 0.3M to 3M during the equilibrium study. It is observed
that the distribution ratio values increases with the concentration of acid as shown in
Fig.5.6. This is because of the decrease in the solubility of TBP in nitric acid with the
concentration of nitric acid in aqueous phase. Hence, the distribution ratio value was
found to be maximum for 3M HNO 3 and minimum for 0.3M HNO 3 . The results
obtained are in agreement with that reported by Germain and Plout (1980). They have
reported that the solubility of TBP in the nitric acid is due to complex formation by
hydrogen bonding and the distribution ratio value rises with HNO 3 concentration due
to lower solubility of TBP in the concentrated range of nitric acid.
5.4.3. Effect of Diluent:
The influence of diluent i.e. NPH on the equilibrium data for TBP-NPHHNO 3 system has also been investigated. It is found that the distribution ratio value
increases with increase in concentration of TBP in NPH in organic phase when
contacted with different concentrations of nitric acid as shown in Fig.5.6. NPH is a
non-polar diluent which affects the solubility of TBP in nitric acid. Hence, the
presence of NPH lowers the solubility of TBP in nitric acid as shown in Fig.5.7. Many
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5. Equilibrium study for TBP-HNO3-diluent system
authors like Schulz and Navratil (1984), Germain and Plout (1980) and Sagert and
Lee (1980) have also reported the same results. They have found that the distribution
of TBP in the organic phase is because of dimerization of TBP rather than the
association between TBP and the diluent NPH. The distribution ratio value increases
TBP in aqueous phase(ppm)
with increase in TBP in NPH due to lower dimerization constant.
450
400
350
300
250
200
150
100
50
0
0
50
100
150
TBP in organic phase (%)
0.3 M nitric acid
1M nitric acid
3M nitric acid
Fig. 5.7: Effect of NPH on solubility of TBP in aqueous phase
5.3.4. Nitric acid partitions:
The change in the concentration of nitric acid at equilibrium when contacted
with different percent of TBP in NPH is shown in Fig.5.8. The distribution ratio for
nitric acid has been determined by measuring the amount of nitric acid in aqueous and
organic phase and result obtained is summarized in Table 5.1. It is observed that
concentration of nitric acid in aqueous phase decreases with concentration of TBP in
aqueous phase. The concentration of 0.3M, 1M and 3M HNO 3 reduces to 0.24M,
0.603M and 1.716M HNO 3 respectively at equilibrium after pure TBP contact. This is
due to extraction of nitric acid by TBP into the organic phase. Acids are soluble in
TBP and form strong bonds with the P=O group of TBP. Collopy and Cavendish
(1960) reported that TBP forms equimolar complex with nitric acid due to hydrogen
bonding which has resulted in the transfer of nitric acid into the organic phase. Hoh
and Wang (1980) have also studied the distribution of nitric acid between water and
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TBP and have observed the same reason for this partition. Alock et al. (1956) have
also agreed with this complex formation mechanism and have determined the
solubility of nitric acid in TBP. It has also been found that the distribution ratio value
for nitric acid increases with the concentration of nitric acid due to more complex
formation. Burns and Hanson (1960) have also observed the same trend for the
distribution ratio at higher nitric acid concentration in the aqueous phase. Hence, the
results obtained are in good agreement with that observed by various other
investigators.
Table 5.1.: Effect of TBP concentration on distribution ratio of nitric acid
Conc. Of TBP in
K d for nitric acid
org. phase (%)
0.3 M
1M
3M
0.1
0
0
0
0.2
0
0
0
0.5
0
0
0
1
0
0
0
3
0
0
0
5
0
0
0
10
0
0
0.06
20
0
0.05
0.13
30
0.02
0.07
0.2
40
0.02
0.16
0.28
50
0.04
0.23
0.33
60
0.04
0.3
0.37
70
0.08
0.39
0.47
80
0.13
0.53
0.54
90
0.19
0.59
0.67
100
0.25
0.65
0.75
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5. Equilibrium study for TBP-HNO3-diluent system
3.5
Concentration of nitric acid(N)
3
2.5
2
1.5
1
0.5
0
0
50
100
Conc. of TBP in NPH (%)
0.3M nitric acid
1M nitric acid
3M nitric acid
150
Fig.5.8: Variation in concentration of nitric acid at equilibrium
5.4. Conclusions:
The equilibrium data has been successfully generated for TBP-NPH-nitric acid
system for three different concentrations of nitric acid i.e. 0.3M, 1M and 3M. The
effect of concentration of TBP, nitric acid and diluent on distribution ratio was
studied. It was found that the distribution ratio increases with TBP concentration in
NPH and nitric acid. It has also been proved that the concentration of nitric acid varies
during this equilibrium study due to complex formation with TBP. The results
obtained will be of prime importance in the reprocessing of spent fuels from PUREX
process and will be helpful in nuclear waste management.
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