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CHAPTER 3
LIQUID – LIQUID EXTRACTION AND
COMPLEXATION PROPERTIES OF
THORIUM (IV) WITH TETRA
FUNCTIONALIZED
AZO-CALIX[4]PYRROLE DERIVATIVES
Liquid Extraction of Th[IV]
Chapter 3 Page 110
RESUME
A new series of calix[4]pyrrole derivatives bearing azo-moiety at the meso-
position of the macrocycles have demonstrated the ability for liquid-liquid extraction,
preconcentration and transport of Th(IV) across a liquid membrane. Various
significant extraction parameters such as effect of pH, effect of solvent and effect of
reagent concentration were investigated, which showed high affinity and selectivity
towards Th(IV) in the presence of large quantities of associated metal ions. The
wavelengths of maximum extraction (λmax) and molar absorptivity (ε) have also been
determined. The stoichiometry of complex was evaluated by Job’s plot method, linear
concentration range obeying Beer’s law, effect of diverse-ions have also been studied.
Liquid membrane transport studies of Th(IV) were carried out from source to the
receiving phase under controlled conditions and a mechanism of transport is
proposed. The validity of the proposed method was checked by determination of
analyte ions in certain standard and natural geological samples.
Liquid Extraction of Th[IV]
Chapter 3 Page 111
TABLE OF CONTENTS
1. Introduction 112
2. Experimental Section 114
2.1. Instruments and measurements 114
2.2. Chemicals and reagents 115
2.3. UV/Vis titrations for preliminary complexation study 117
2.4. General procedure for the liquid-liquid extraction of Th(IV) 118
2.5. Liquid membrane transport studies 118
3. Results and Discussion 120
3.1. Preliminary complexation study 120
3.2. Spectral characteristics of Th(IV)–azo-calix[4]pyrrole complex 121
3.3. Effect of variables on the extraction 121
3.3.1. pH and shaking time for extraction
3.3.2. Effect of solvent
3.3.3. Reagent (DHPDPCP) concentration
3.4. Stoichiometry of complex 122
3.5. Liquid membrane transport studies 123
3.6. Preconcentration of Th(IV) 124
3.7. Effect of diverse ions 124
3.8. Applications 125
Conclusion 138
References 139
Liquid Extraction of Th[IV]
Chapter 3 Page 112
1. INTRODUCTION
Considerable effort has been focused on the preparation of supramolecular
host systems with the capability of recognizing specific chemical species through
weak, non covalent interactions [1]. The design and synthesis of a variety of host
molecules is a challenging topic in the field of molecular recognition chemistry
because of the promising new functions of these novel compounds or the fantastic
features attainable by forming supramolecular complexes from the host and guest
molecules [2]. Among representatives of a class of compounds that are the subject of
supramolecular chemistry, calixpyrroles are gaining increasing interest as new
macrocyclic receptor molecules [3]. Pioneering work in the area of calix[4]pyrroles
has been done by Sessler and co-workers, has evidenced that calix[4]pyrroles can
effectively be employed as suitable anion binding agents and may be used for the
detection and sensing purposes in new separation technologies [4-10]. The above
statement is furthered by the availability of various post macrocyclization
modifications [11, 12]. Synthetic chromo-ionophores that give rise to specific colour
changes on selective complexation with cations and anions, have attracted
considerable attention as efficient spectrophotometric analytical reagents for the
detection of particular species as well as the design of supramolecular devices having
recognition and optical sensing functions [13, 14]. Generally, the development of
most chromogenic reagents based on calixarenes have been achieved by attaching a
chromogenic moiety/chelating moiety. There have been few reports wherein
macrocycles such as calix[4]arene [15], calix[4]resorcinarene [16], thiacalix[4]arene
[17] and crown ether [18] are used as components for the preparation of azo dyes, but
the research in the area of calix[4]pyrrole based dyes [19] is still in infancy.
Liquid Extraction of Th[IV]
Chapter 3 Page 113
Detection and sensing of heavy, transition and rare earth metal ions via
synthetic receptors are topics of recent interest in supramolecular chemistry because
of their significant value in chemical, biological and environmental assays [20]. The
main source of Thorium Th(IV) is monazite sand, mainly associated with cerium,
lanthanum, yttrium and iron etc. Thorium is used in a wide array of products and
processes, for example in the production of ceramics, carbon arc lamps, alloys, in
mantles and also as a source of nuclear energy [21]. For all of these purposes,
development of analytical methodologies for separation and determination of these
elements becomes essential. Several analytical methods ranging from classical
methods to modern instrumental analytical techniques were developed for extraction
and determination of Th(IV) [22]. Although several preconcentration techniques are
available for the enrichment of thorium, the two most common traditional methods
are liquid–liquid extraction and ion exchange. Liquid–liquid extraction offers the
advantages of fast kinetics, high capacities and high selectivity [23]. There are several
reagents (thoron-I, arsenazo-III, arsenazo-I, p-bromochlorophosphoazo,
tribromoarsenazo etc.) that have been reported for spectrophotometric determination
of Th(IV) [24-26]. A large number of extranctants such as tributyl phosphate (TBP),
trioctyl phosphine oxide (TOPO), cyanex923 (a mixture of four trialkyl phosphine
oxides), tris-(2-ethyl hexyl) phosphate (TEHP)6 and triphenyl phosphine oxide
(TPPO) were reported for extraction of thorium [27].
The macrocycles can form the host-guest complex and can be used for the
complexation with several metal ions, however the complexation with Th(IV) is very
little [28]. Although a lot of chromogenic reagents [29] for detection of transition
metals have been reported, none of the reagents were prepared by attaching a
chromogenic moiety (–N=N–) at the meso-position of a macrocyclic compound, such
Liquid Extraction of Th[IV]
Chapter 3 Page 114
as calix[4]pyrrole. Recently, Chauhan et al. [30] have developed two novel octa
methyl calix[4]pyrroles by introducing the chromogenic group at two different
positions and studied them as potential anion binders due to their rich and unique
complexation behaviour.
In the present work, a preliminary complexation study of synthesized azo
calix[4]pyrrole dyes towards various metal ions [U(VI), Th(IV), La(III) and Ce(III)]
have been investigated by UV/Vis spectrophotometry. It was observed that only
Th(IV) to a larger extent and other metal ions to a smaller extent showed
complexation behaviour with all the dyes and out of all the dyes used, only meso-
tetra(methyl) meso-tetra{(3, 5-dihydroxy phenyl)- 4(2-diazenyl phenol)} calixpyrrole
2f (DHPDPCP) exhibit best sensitivity and selectivity for Th(IV). Therefore,
(DHPDPCP) was selected for the development of sensitive and selective
spectrophotometric method for the determination of Th(IV) by liquid-liquid
extraction. The extracted thorium complexes have been determined simultaneously by
spectrophotometry/ICP-AES. Various parameters for the extraction have been
studied. The validity of the proposed method was tested by analysing this Th(IV) in
certain natural and geological samples.
2. EXPERIMENTAL SECTION
2.1. Instruments and measurements
Inductively coupled plasma-atomic emission spectrophotometer Arcos model
by Spectro, Germany, with the plasma scan multitasking computer and a peristaltic
pump was used under optimum working conditions: R.F. Generator : Maximum of 1.6
KW, 27.12 MHz; Plasma: Radial plasma, having capability to analyse aqueous
solutions with high dissolved solid content; Spectrometer : Wavelength Range : 10
Liquid Extraction of Th[IV]
Chapter 3 Page 115
nm to 770 nm, Resolution : approx. 9 pico meter, having capability to scan full
spectrum; Detector : Charge Coupled Devices (CCD); Vertical Torch assembly
having fully demountable quartz torch with individual tubes; Nebulizers : Concentric,
cross flow, organic nebulizer (hydrocarbons, solvents) ; Spray Chambers : HF
Resistant cyclonic chamber and hydrocarbon solution spray chamber. UV/Vis
absorption studies were carried out on a JASCO 570 UV/VIS/NIR spectrophotometer
using 10 mm quartz cells. All pH measurements were performed using an Elico
digital pH meter, model L1 614, equipped with a combined pH electrode.
2.2. Chemicals and reagents
All the chemicals used were of analytical grade from E. Merck or BDH. All
aqueous solutions were prepared with quartz distilled deionized water, which was
further purified by a Millipore Milli-Q water purification system (Millipack 20, Pack
name: Simpak 1, Synergy) throughout the entire study. The pH was adjusted with the
following buffer solutions [31] : PO4-3/HPO4
-2 buffer for pH 2.0 and 3.0; CH3COO-1
/CH3COOH buffer for pH 4.0 and 6.0; HPO4-2/H2PO4
-1 buffers for pH 7.0 and 7.5.
Standard stock solutions (1000 μg mL-1) of U(VI), Th(IV), La(III) and Ce(III) were
prepared as given below.
Standard Stock Solutions
U(VI): Dissolve 0.2109 gm UO2(NO3)2.6H20 in water containing 1 mL
concentrated HNO3 and dilute upto 100 mL with water in volumetric flask.
Th(IV): Dissolve 0.25 gm Th(NO3)4.4H2O in water containing 1 mL
concentrated H2SO4 and dilute upto 100 mL with water in volumetric flask.
La(III): Dissolve 0.2345 gm La(NO)3.6H2O in water containing 1 mL
concentrated HNO3 and dilute upto 100 mL with water in volumetric flask.
Liquid Extraction of Th[IV]
Chapter 3 Page 116
Ce(III): Dissolve 0.4541 gm Ce(NO3)3.6H2O in water containing 1 mL
concentrated HNO3 and dilute upto 100 mL with water in volumetric flask.
Working solutions were subsequently prepared by appropriate dilution of the
stock solutions. Their final concentrations were then standardized
spectrophotometrically [32].
The six azo-calix[4]pyrrole dyes (Figure 1) were synthesized and
characterized as described in Chapter 2 and their stock solutions (0.1%) were
prepared in Iso-amyl alcohol and DMSO. Working solutions were subsequently
prepared by appropriate dilution of the stock solutions.
Figure 1. Synthesized azo-calix[4]pyrrole dyes :
NH
CH3
CH3 A
OH OHN
NR1
R2
4
Azo-calix[4]pyrrole dyes
a : R1= H , R2= -CH3
b : R1= -NO2 ,R2= -NO2
c : R1= H ,R2= -OH
d : R1= H , R2= -Cl
e : R1= H , R2= -NO2
f : R1= -OH , R2= H
Liquid Extraction of Th[IV]
Chapter 3 Page 117
Figure 2. Cyclic structure of dye 2f (DHPDPCP) used for liquid–liquid extraction of
Thorium.
2.3. General Procedure for preliminary complexation study by UV/Vis
spectrophotometer
Preliminary complexation studies for various azo-calix[4]pyrrole dyes with
rare earth metal ions were carried out at 25ºC using a JASCO 570 UV/VIS/NIR
spectrophotometer. Metal solutions [U(VI), Th(IV), La(III) and Ce(III)] were directly
injected by a precise syringe (Hamilton, 10 μL) into the cuvette having the solution of
azo-calix[4]pyrrole dyes in DMSO (2a-2f). The resulting solutions were allowed to
attain equilibrium for one minute before recording the spectra. Usually, 0.02 M (10
μL) metal solutions were added to 10-5 M solutions (3 mL) of azo-calix[4]pyrrole dyes
(2a-2f). The spectrophotometric data were collected over the range 200-800 nm for all
azo-calix[4]pyrrole dyes .
NHNH
NH
CH3
CH3
CH3
CH3
OHHOOH
HO
OHHOOH
HON
N
N
NN
N
N
NOH
OH OH
OH
Liquid Extraction of Th[IV]
Chapter 3 Page 118
2.4. General procedure for the liquid-liquid extraction of Th(IV)
An aqueous phase containing not more than 50 µg of Th(IV) was transferred
into a 25 mL separatory funnel and desired pH, 5.5 was adjusted with the appropriate
buffer solutions in a total volume of 10 mL. The mixture was shaken with 6 mL of
0.015 % reagents (azo-calix[4]pyrrole dyes) in Iso-amyl alcohol. The metal-reagent
complex was extracted into the organic phase. To ensure complete recovery, the
extraction was repeated with 2 mL of reagent solution; the organic extract was
separated, dried over anhydrous sodium sulphate and transferred into a 10 mL
volumetric flask. The combined extracts and washings were diluted to the mark (10
mL) with Iso-amyl alcohol. The absorbance of the organic phase was measured at 498
nm.
The concentration of the metal ion extracted into the organic phase [Th+4](org)
as complex was estimated by [Th+4](org) = [Th+4](aq, int) - [Th+4](aq), where [Th+4](aq, int)
is the initial concentration of the metal ion in the aqueous phase.
The percent extraction (%E), was calculated by
%E = 100
int),(4
)(4
aq
org
ThTh
The extracted thorium complex with azo-calix[4]pyrrole dye in Iso-amyl
alcohol after appropriate dilution was determined by spectrophotometry/ICP-AES.
2.5. Liquid membrane transport studies
Transport of Thorium was carried out in a specially fabricated glass assembly
as shown in Figure 3. The reaction cell was 6.6 cm in inner diameter and 9.0 cm in
height with a total capacity of 305 mL. U-tube (2.0 cm diameter, 20 cm length) was
fused from the base of the cell. The height of the tube inside the cell was 4.0 cm from
Liquid Extraction of Th[IV]
Chapter 3 Page 119
the basal plane. The transport experiments were performed with 50.0 mL of 1.0 10-5
M Th(IV) solutions at pH 5.5 from the source phase to the 50.0 mL, 0.1 M, HCl as the
receiving phase. The liquid membrane consisted of 75 mL of 1.0 10-5 M reagent (2f)
in Iso-amyl alcohol. A synchronous motor (200 rpm) provided constant reproducible
stirring from the top. The amount of thorium transported from the source phase to the
receiving phase was measured by spectrophotometry/ICP-AES. The transport data
were the average of 5 runs with an experimental error of less than 2%.
Figure 3. Apparatus for transport studies
Source Phase (SP) : 50.0 mL, pH 5.5, 1.0 x 10-5 M Th (IV)
Liquid Membrane Phase (LMP) : 75.0 mL, 1.0 x 10-5 M reagent (2f)
in Iso-amyl alcohol
Receiving Phase (RP) : 50.0 mL, 0.1 M HCl
Liquid Extraction of Th[IV]
Chapter 3 Page 120
3. RESULTS AND DISCUSSION
3.1. Preliminary complexation study
To examine the complexation of newly synthesized azo dyes with various rare
earths like U(VI), Th(IV), La(III) and Ce(III), titrations were carried out using
UV/Vis spectrophotometer.
The spectral bands (λmax) of the reagents (2a-2f) and their complexes were
measured using UV-Vis spectrophotometer. The spectra of the reagents are
characterized by an intense band in the range at 380-450 nm attributed to a n - π*
transition (–N=N–). In the spectra of their metal complexes, a new conspicuous
absorption band appears in the range of 400-500 nm. The results obtained for optical
response (∆λ) = [λmax(complex) - λmax(reagent)], are summarized in Figure 4.
The experimental results showed that the synthesized azo-calix[4]pyrrole dyes
exhibited optical response for each metal ion used for complexation study but it was
found maximum for Th(IV). To further check the selectivity for Th(IV), out of all
azocalixpyrrole dyes, used for complexation, only, azo dye 2f (DHPDPCP) gave
exceptional results and showed clear selectivity for Th(IV). These results indicated
that azo groups which may be circularly arranged on the meso-position of
calix[4]pyrrole cavity, construct novel cyclic metal receptors. These reasons were
sufficient to study the selective behaviour of reagent 2f (DHPDPCP) for Th(IV) by
liquid-liquid extraction.
In order to obtain the optimum conditions for the maximum extraction of
Th(IV) by 2f (DHPDPCP), different factors affecting this process have been studied
Liquid Extraction of Th[IV]
Chapter 3 Page 121
3.2. Spectral characteristics of Th(IV)-azo-calix[4]pyrrole complex
The synthesized azo-calix[4]pyrrole dyes (2a-2f) were used for the extraction
and spectrophotometric determination of Th(IV). It was observed that among all of
the synthesized azo-calix[4]pyrrole dyes (2a-2f), 2f (DHPDPCP) was most sensitive
for the Th(IV) (Table 1). The complexation of Th(IV) with DHPDPCP was studied
under optimum conditions of pH, shaking time, solvent and reagent (DHPDPCP)
concentration. The maximum absorbance of the dark red coloured complex was
measured at 498 nm and showed a bathochromic shift of 80 nm from that of the
reagent blank (Figure 5). The molar absoptivity (ε) was found to be 22,000 L mol-1
cm-1. The system obeys Beer’s law in the range of 0.5-10 µg mL-1 of Th(IV).
3.3. Effect of variables on the extraction
3.3.1. pH and shaking time for extraction
The pH of the medium is a significant factor in extraction process. A series of
experiments were carried out to study the effect of pH on the liquid-liquid extraction
of Th(IV), by DHPDPCP in Iso-amyl alcohol and the results are presented in Table
2. Maximum extraction of Th(IV) complex was obtained in range of pH 5.0 - 5.5
(Figure 6); at the lower and higher pH the extraction was incomplete. This may be
because the reagent remains protonated at pH lower than 4.5 and hydrolysis of
Thorium ions at pH higher than 6.5. So, pH 5.5 was chosen for the extraction of
Th(IV).
The extraction of Th(IV) was examined for various times of equilibration. The
extraction with 5, 10, 15 and 20 minutes of shaking was 96.0%, 99.1 %, 99.1 % and
99.3% respectively, hence, a 10 minute time of equilibrium was used in all the
Liquid Extraction of Th[IV]
Chapter 3 Page 122
experiments. The extraction was not affected by further shaking, indicating that the
equilibrium state had been attained.
3.3.2. Effect of diluents
The Th(IV)-DHPDPCP complex was extracted with various solvents like
ethyl acetate, chloroform, toluene, benzene, dichloromethane, carbon tetrachloride
and Iso-amyl alcohol. As compared to other solvents the molar absorptivity in Iso-
amyl alcohol was found to be maximum therefore it was chosen to be the solvent for
quantitative extraction (Table 3).
3.3.3. Reagent (DHPDPCP) concentration
The influence of DHPDPCP was studied by extracting a fixed amount of
Th(IV) with varying amounts of reagent (DHPDPCP) at 5.5 pH. A 6 mL, of 0.015%
DHPDPCP was found to be sufficient for the quantitative extraction of Th(IV)
whereas, the extraction was incomplete at the lower concentration of DHPDPCP
(Table 4). The excess of the reagent had no adverse effect on the extraction of
Th(IV).
3.4. Stoichiometry of complex.
The stoichiometric ratio of the Th(IV) complex was determined by the
modified Job’s method of continuos variation. The absorbance of complex Ac of a
series of solution having different concentration ratios of thorium ion (Th)(IV) a and
DHPDPCP b, keeping total concentration (a+b) constant, was measured at 498nm.
The absorbance of b was substracted from the observed absorbance Ac to obtain the
true absorbance ΔA.
ΔA = Ac-Ab
Liquid Extraction of Th[IV]
Chapter 3 Page 123
ΔA values were plotted against the molar ratio of Th(IV) ion a/a+b (Figure
7) . The maximum value for ΔA was clearly obtained at a/a+b = 0.65, indicating 2 : 1
stoichiometric ratio of Th (IV) and DHPDPCP. The accuracy of this result is possible
only if a single complex is formed. To verify this, measurements were taken at
different selected wavelength, which gave same value for a/a+b ratio.
To get more information about the nature of the extracted complex, the extract
was evaporated to dryness. A known weight of the dry complex was digested with a
nitric acid. It was centrifuged and after appropriate dilution the thorium content was
determined by ICP-AES, which also confirmed 2:1 (M : L) complex.
3.5. Liquid membrane transport studies
The transport of Th(IV) through the membrane containing 1.0 X 10-5 M,
DHPDPCP from source phase containing 1.0 x 10-5 M, Th(IV) to the receiving phase
of 1.0 M HCl was carried out. As evident from the Figure 8 the concentration of
Th(IV) in the source phase starts decreasing continuously and it took about 25
minutes to transport half of the Th(IV) from source phase to receiving phase (curve
A). On the other hand, concentration of Th(IV) in the receiving phase starts increasing
as shown in the (curve B). Therefore, it is clear that Th(IV) moved from the source to
receiving phase through the liquid membrane. Based on these facts and knowledge
obtained by the extraction equilibria, the proposed mechanism of transport of thorium
through the liquid membrane of DHPDPCP is as shown in Figure 9. The carrier in
the membrane reacts with Th(IV) in the source phase at the interface of these phases
and forms a complex [H4(Th+4)2L-8] while releasing 8 moles of proton into the source
phase. On the other hand, interface of the membrane and the receiving phase of the
Liquid Extraction of Th[IV]
Chapter 3 Page 124
complex reacts with 8 moles of protons while releasing 2 moles of Th(IV) in the
receiving phase.
3.6. Preconcentration factor of Th(IV)
The concentration of Th(IV) in natural water samples is too low for its direct
determination. Therefore, preconcentration or enrichment step is necessary to bring
the sample to the detectable limits of existing instrument method. The method was
studied for the preconcentration of Th(IV) in terms of its preconcentration factors.
The preconcentration study was carried out by extracting 20 μg Th(IV) in
1000 mL aqueous phase with 10 mL of 0.015% DHPDPCP in Iso-amyl alcohol . To
evaluate the efficiency of preconcentration, expressed as recovery, the concentration
of Th(IV) in organic phase and the aqueous phase was determined by ICP-AES .
Quantitative determination was possible with recovery up to 97-98% with a
preconcentration factor 100.
3.7. Effect of diverse ions
The extraction of single metal ion under controlled condition gives an
indiciation of potential sensitivity of the proposed method. In order to examine the
sensitivity and selectivity of the present method, the influence of alkali, alkaline
earths, transition metals and rare earths on the extraction of Th(IV) under its optimum
extraction conditions was studied. The tolerance limit was set as the amount of
foreign ion causing not more than ±2% change in the recovery of Th(IV). The results
presented in Table 5 indicate that Th(IV) can be quantitatively extracted in the
presence of large number of foreign ions including rare earth elements. Thus, the
method developed is specific for Th(IV).
solutionfeedinmetalofionconcentratInitialsolutionstrippinginmetalofionConcentratPF
Liquid Extraction of Th[IV]
Chapter 3 Page 125
3.8. Applications
Determination and Recovery of Th(IV) from Standard samples
Standard rock samples obtained from United States Geological Survey
(USGS), monazite sand, rocks were analysed to test the reliability of the present
method results are presented in Table 6. Matrix interference was verified by
comparison of the slopes of the calibration graphs with that using standard addition
method. The precision of preconcentration procedure when combined with ICP-AES
was expressed as relative standard deviation of 1.4 % with a recovery up to 98%.
.
Liquid Extraction of Th[IV]
Chapter 3 Page 126
Table 1. Spectral characteristics of azo-calix[4]pyrrole dyes for the
extraction of Th(IV).
Th(IV) : 4 mL, 25 μg mL-1
pH : 5.5
Reagent : 0.015 % Azo-calix[4]pyrrole dyes
Solvent : Iso-amyl alcohol
No Azo-calix[4]pyrrole based dyes λ max nm
Colour of
Complex
Molar absorptivity
(L mol-1 cm-1)
2a meso-tetra(methyl) meso-tetra{(3, 5-dihydroxy phenyl)- 4-(4-methyl
phenyl diazene)} calixpyrrole 450 Red 14,385
2b
meso-tetra(methyl) meso-tetra{(3, 5-dihydroxy phenyl)- 4-(2,4-
dinitrophenyl diazene)} calixpyrrole
473 Red 11,634
2c meso-tetra(methyl) meso-tetra{(3,
5-dihydroxy phenyl)- 4-(4-diazenylphenol)} calixpyrrole
481 Dark Red 18,987
2d
meso-tetra(methyl) meso-tetra{(3, 5-dihydroxy phenyl)- 4-chlorophenyl diazene)}
calixpyrrole
468 Red 14,305
2e
meso-tetra(methyl) meso-tetra{(3, 5-dihydroxy phenyl)- 4-nitrophenyl diazene)}
calixpyrrole
479 Red 16,846
2f meso-tetra(methyl) meso-tetra{(3,
5-dihydroxy phenyl)- 4-(2-diazenyl phenol}) calixpyrrole
498 Light Pink 22,000
Liquid Extraction of Th[IV]
Chapter 3 Page 127
Table 2. Effect of pH on the extraction of Th(IV) with DHPDPCP complex.
Th(IV) : 4 mL, 25 μg mL-1
Reagent : 0.015 % DHPDPCP
Solvent : Iso-amyl alcohol
λmax : 498 nm
pH % of Extraction Molar absorptivity
(L mol-1 cm-1)
2.0 11 2,420
2.5 24 5,280
3.0 36 7,920
3.5 47 10,340
4.0 61 13,420
4.5 70 15,400
5.0 78 17,160
5.5 100 22,000
6.0 63 13,860
6.5 45 9,900
7.0 13 2,860
Liquid Extraction of Th[IV]
Chapter 3 Page 128
Table 3. Effect of diluents on the extraction of Th(IV)-DHPDPCP complex.
Th(IV) : 4 mL, 25 μg mL-1
Reagent : 0.015 % DHPDPCP
pH : 5.5
λmax : 498 nm
Solvent Dielectric constant Molar absorptivity
(L mol-1 cm-1)
Extraction
(%)
Toluene 2.30 - -
Benzene 2.28 - -
Carbon tetrachloride 2.20 - -
Dichloromethane 8.90 7,040 32
Chloroform 4.80 11,220 51
Ethyl acetate 6.40 14,080 64
Iso-amyl alcohol 15.3 22,000 100
Liquid Extraction of Th[IV]
Chapter 3 Page 129
Table 4. Effect of reagent (DHPDPCP) concentration for the extraction of Th(IV)
Th(IV) : 4 mL, 25 μg mL-1
Reagent : 0.015 % DHPDPCP
pH : 5.5
Solvent : Iso-amyl alcohol
λmax : 498 nm
DHPDPCP
(0.015%)(mL) Colour of Complex
Molar absorptivity
(L mol-1 cm-1)
1 yellow 11,634
2 yellow 14,560
3 Red 18,653
4 Red 20,865
5 Red 22,000
6 Red 22,000
7 Red 21,980
8 Red 21,973
9 Red 21,973
10 Red 21,972
Liquid Extraction of Th[IV]
Chapter 3 Page 130
Table 5. Effect of diverse ions on the extraction of DHPDPCP – Th(IV) complex.
Th(IV) : 10 mL, 3 µg mL-1
pH : 5.0
Reagent : 0.015% DHPDPCP
Solvent : Iso-amyl alcohol
λmax : 498 nm
Ions Added as Amount Added (mg)
Recovery of Thorium (ppm)
Spectrphotometry ICP-AES
Ag+ AgNO3 65 3.0 3.0
Be+ BeCl2 70 2.94 2.95
Pb+2 Pb(NO3)2 70 2.93 2.92
Mn+2 MnCl2 65 2.98 2.99
Ni+2 NiCl2 75 2.97 2.97
Cu+2 CuCl2 75 2.98 2.98
Zn+2 ZnCl2 80 2.99 2.98
Cd+2 CdCl2 75 2.98 2.99
Hg+2 HgCl2 60 3.00 3.00
Pd+2 PdCl2 65 2.98 2.99
Al+3 AlCl3 65 2.97 2.98
Sn+2 SnCl2 70 2.99 2.98
Zr+4 Zr(NO3)4 80 2.98 2.99
Mo+6a (NH4)6Mo7O24 60 3.00 2.99
UO2+2 UO2(NO3)2 75 2.90 2.91
V+5b NH4VO3 80 2.98 2.97
Fe+3 FeCl3 85 2.99 2.98
Cr+3 Cr2O3 75 2.98 2.97
Mg+2 MgCl2 65 2.98 2.99
Liquid Extraction of Th[IV]
Chapter 3 Page 131
Table 6. Analysis of Th(IV) in standard samples from the United States
Geological Survey (USGS) and monazite sand.
Metal Ions Th(IV)
Sample Certified Amount(µg L-1)
Amount Found(µg L-1)
Natural geological samples
Monazite Sand, 8.41±0.009 8.40±0.011
Travancore, India (%)
USGS:BCR-1 (µg.gm-1) 6.1 ±0.009 6.1 ±0.007
USGR:GSP-1 (µg.gm-1) 105 ±0.01 104 ±0.025
Liquid Extraction of Th[IV]
Chapter 3 Page 132
Figure 4. Preliminary complexation of cations as a function of the
nature of the ligands.
Liquid Extraction of Th[IV]
Chapter 3 Page 133
Figure 5. Comparative spectra of reagent (DHPDPCP) and its complex
with Th(IV) in Iso-amyl alcohol
0
0.4
0.1
0.2
0.3
280 400 600
Abs
DHPDPCP
Th(IV) - DHPDPCP
Liquid Extraction of Th[IV]
Chapter 3 Page 134
Figure 6. Effect of pH on the extraction
0
20
40
60
80
100
120
0 1 2 3 4 5 6 7 8
(%) E
xtra
ctio
n
pH
Effect of pH
Liquid Extraction of Th[IV]
Chapter 3 Page 135
Figure 7. Job’s plot for the mixture of DHPDPCP and Th[IV]
00.010.020.030.040.050.060.070.08
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
∆A
Mole fraction
Stoichiometry
Liquid Extraction of Th[IV]
Chapter 3 Page 136
Figure 8. Transport profile of Th(IV) through the liqiud membrane
containing DHPDPCP at 30°C.
00.5
11.5
22.5
33.5
4
0 20 40 60 80
µg/m
L
Time (minutes)
Transport Profile
RPSP
Liquid Extraction of Th[IV]
Chapter 3 Page 137
Figure 9. Proposed mechanism for transport of Th(IV) through a liquid membrane
containing DHPDPCP.
SP LMP RP
2 Th+4
8H+
H12 L
H4(Th+4)2L-8
2 Th+4
8H+
SP : Source phase;
LMP : Liquid membrane phase;
RP : Receiving phase
Liquid Extraction of Th[IV]
Chapter 3 Page 138
CONCLUSION
Six reagents synthesized by the introduction of azo (-N=N-) functionality on
the calix[4]pyrrole macrocycle resulted in a chelating system which was used
successfully for the liquid-liquid extraction and transport of Th(IV) across a liquid
membrane of iso-amyl alcohol. The described solvent extraction method is simple,
sensitive and specific for the determination of Th(IV) ion in presence of large
quantities of associated metal ions. The binding of Th(IV) with azo-calix[4]pyrrole in
the ratio 2:1 (Metal : Ligand) indicates the greater utility of the reagent. The results
obtained from the determination of analyte ions in certain standard and natural
geological samples established the reliability, simplicity and robustness of the
method.
Liquid Extraction of Th[IV]
Chapter 3 Page 139
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Recommended