Separation studies of Pd(II) from acidic chloride solutions of Pt(IV), Ni(II) and Rh(III) by using 4-aroyl-3-phenyl-5-Isoxazolones

Article abstract of DOI:10.1155/2012/802621

This study examined the effectinfluence of various factors on the extraction of Pd(II) to develop a new liquid-liquid extraction mechanism for the selective separation of palladium(II) from its acidic chloride solutions using 4-aroyl-3-phenyl-5-isoxazolones (HA), such as 3-phenyl-4-(4-fluorobenzoyl)-5- isoxazolone (HFBPI), 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and 3-phenyl-4-(4-toluoyl)-5-isoxazolone (HTPI). The extraction strength of Pd(II) with HA were in the followingorder: HFBPI > HPBI > HTPI, which is opposite to that observed withtheir pK^avalues. HPBI was used to separatePd(II) from Pt(IV), Ni(II) and Rh(III) metal ions and calculated their separation factors (S.F.) were followed in the order: Pd/Ni (40±0.4) > Pd/Pt (25±0.2) > Pd/Rh (15±0.3 > Rh/Ni (2.7±0.3) > Pt/Ni ≈ Rh/Pt (1.7±0.2). The loading and striping of Pd(II) (1.12×10^-4 mol L^-1) were also examinedusing 1.0×10^-3 mol L^-1HPBI in CHCl³ and 1.0 mol L-1HCl, respectively. The results demonstrated that the maximum (97.5%) extraction and desorption(89%) of metal required at least 3.0 cycles. The developed method was applied successfully tothe separation of palladium from synthetic water samples.

Full text of DOI:10.1155/2012/802621

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.ejchem.net
2012, 9(2), 756-765
Separation Studies of Pd(II) from Acidic
Chloride Solutions of Pt(IV), Ni(II) and Rh(III) by
Using 4-Aroyl-3-Phenyl-5-Isoxazolones
KODURU JANARDHAN REDDY1, 2 and LEE KAP DUK1†
1Department of Nanomaterial Chemistry
College of Science & Technology, Dongguk University
707 Seokjang-Dong, Gyeongju, Gyeongbuk -780 714, Republic of Korea
2Department of Chemistry (GEBH)
Sreevidyanikethan Engineering College (Atonomous), Sri Sainath Nagar-517 501
A.Rangampet, Tirupathi, Andhrapradesh, India
kapduklee1@gmail.com, kdlee@dongguk.ac.kr
Received 25 October 2011; Accepted 30 December 2011
Abstract: This study examined the effect influence of various factors on the
extraction of Pd(II) to develop a new liquid-liquid extraction mechanism for the
selective separation of palladium(II) from its acidic chloride solutions using
4-aroyl-3-phenyl-5-isoxazolones (HA), such as 3-phenyl-4-(4-fluorobenzoyl)-5-
isoxazolone (HFBPI), 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and 3-phenyl-4-
(4-toluoyl)-5-isoxazolone (HTPI). The extraction strength of Pd(II) with HA were
in the following order: HFBPI > HPBI > HTPI, which is opposite to that observed
with their pKa values. HPBI was used to separate Pd(II) from Pt(IV), Ni(II) and
Rh(III) metal ions and calculated their separation factors (S.F.) were followed in the
order: Pd/Ni (40±0.4) > Pd/Pt (25±0.2) > Pd/Rh (15±0.3 > Rh/Ni (2.7±0.3) > Pt/Ni
≈ Rh/Pt (1.7±0.2). The loading and striping of Pd(II) (1.12×10-4 mol L-1) were also
examined using 1.0×10-3 mol L-1 HPBI in CHCl3 and 1.0 mol L-1 HCl, respectively.
The results demonstrated that the maximum (97.5%) extraction and desorption
(89%) of metal required at least 3.0 cycles. The developed method was applied
successfully to the separation of palladium from synthetic water samples.
Keywords: Palladium(II) extraction, Separation of precious metals, 4-Aroyl-3-phenyl-5-isoxazolones,
Acidic chloride solutions.
Introduction
Palladium group metals (PGMs) are used widely as catalysts in hydrogenation reactions in
chemical and automobile industries as well as in other organic syntheses1,2. These materials
are extremely useful in areas, such as electrical and electronic industries, extrusion devices,
in jewelry and dental and medical prostheses, owing to their high resistance to corrosion and
oxidation with high melting points, electrical conductivity and catalytic activity1-3. In

Separation Studies of Pd(II) from Acidic Chloride Solutions 757
addition, they are extremely important to the automotive industry because there is no other
metal substitute for PGMs.
Despite the limited supply of primary sources and limited availability for industry3,4, the
demand for PGMs is increasing continuously. Therefore, the recovery or recycling of PGMs
from secondary resources or from post-consumer scrap is needed to secure these metals. The
major secondary resource of PGMs is spent automobile catalysts and nuclear waste but the
amount of PGMs currently being recycled from spent auto catalyst is only ~20%5,6. An
efficient and selective extraction/separation technique is essential for the recycling of PGMs
from secondary resources.
There are some conventional methods for the separation of the PGMs3 but they have
inherent problems, such as high chemical consumption and high labor requirements in the
procuring process, slow kinetics, solid-liquid separation and increased environmental
pollution due to the use of toxic chemicals. In addition, the aqueous chemistry of these
metals is extremely complicated7-10. Therefore, it is important to develop a feasible
hydrometallurgical route in the place of the above conventional methods.
Liquid-liquid extraction is a versatile technique for the separation/concentration of
metal species from aqueous solutions and has also been used commercially in to separate
palladium/platinum using several extractants9-13. Nevertheless, there are limitations, such as
poor selectivity and difficult stripping. Recently, 4-aroyl-5-isoxazolones have been used to
separate Zr(IV) and Hf(IV) and some other lanthanides and actinides from its acidic
solutions with good selectivity between these metal ions14-19
.
The above factors prompted us to develop a selective liquid-liquid extraction method for the
extraction of palladium from its acidic chloride solutions using 4-aroyl derivates of 3-phenyl-5-
isoxazolones (HA) (Figure 1). Specifically, 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone
(HFBPI), 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and 3-phenyl-4-(4-toluoyl)-5-isoxazolone
(HTPI), were synthesized14,15 by introducing both electron-withdrawing (-F) and electron-
donating (-CH3) groups and their effects on the extraction behavior of Pd(II) from hydrochloric
acid solutions was investigated. In addition, a range of factors, such as the extractant
concentration in the organic phase and the acid and chloride concentration in the aqueous phase,
were examined to achieve a better selectivity of Pd(II) from Pt(IV), Ni(II) and Rh(III) metal ions.
R
N
O
O
O
H
R = H, F, CH3
Figure 1. 4-Aroyl-3-phenyl-5-isoxazolones (HA).
Experimental
A Varian SpectrAA 220 (AAS) (Varian Australia Pty., Ltd., Australia) was used to determine
the metal ion concentrations in aqueous solutions. An Orion (USA) 720A Ion Analyzer was
used for the pH measurements. A Nicolet FT-IR 560 Magna spectrometer using KBr (neat)
was used to obtain the infrared spectra of the synthesized ligands. C, H and N analysis were

758 K. J. REDDY et al.
performed using a Perkin-Elmer Series 2 Elemental Analyzer 2400. A Bruker 300 MHz
NMR spectrometer was used to obtain the 1H NMR spectra of the isoxazolones.
Chemicals
Palladium and platinum stock solutions were prepared using PdCl2 (Analytical reagent,
99%) and PtCl4 (Analytical reagent, 99%), which were purchased from Sigma Aldrich
Chemical Company Pvt. Ltd., Republic of Korea. NiCl2.6H2O (Merck, 98%) and RhCl3.nH2O
(Merck, 98.5%) were used to prepare the respective metal ion stock solutions. Suitably diluted
stock solutions of metal ions were used in the extraction and analytical studies. The ionic
strength was maintained at 1.0 mol L-1 using sodium chloride and hydrochloric acid
(Analytical reagent, Merck, Korea). Chloroform (Analytical reagent, Merck, Republic of
Korea) was used as the diluent. All other chemicals used were of analytical reagent grade.
Synthesis and characterization of various 3-phenyl-4-aroyl-5-isoxazolones
The synthesis of the various 4-aryol-3-phenyl-5-isoxazolones using Scheme 1 and 2 is
reported elsewhere14-16. The synthesis of the ligands and their characterizations are shown
below:
3-Phenyl-4-benzoyl-5-isoxazolone (HPBI)
HPBI was synthesized by the benzoylation of 3-phenyl-5-isoxazolone (Scheme 1)14-16. 3-Phenyl-
5-isoxazolone, benzoic anhydride and sodium benzoate were refluxed in dry 1, 4-dioxane for
3 h. The reaction mixture was cooled and filtered. The filtrate was diluted with distilled
water and acidified with HCl. The brown precipitate was filtered, dried and recrystallized
from ethyl acetate. FT-IR, 1H NMR and elemental analysis were used for characterization.
O
C6H5
C6H5
C
C
C6H5COONa
1,4-Dioxane
C6H5
+
N
O
N
O
O
O
O
O
O
H
Scheme 1. Synthesis of 3-phenyl-4-benzoyl-5-isoxazolone (HPBI).
1
HPBI : M.P. = 146 °C; H NMR data:  6.94 - 8.06 (m, 10H, phenyl); IR (KBr) data
( cm1) : 3052, 1699, 1613, 1489, 831; Elemental analysis: Calc. for C16H11NO3, C,72.45;
H,4.15; N, 5.28. Found: C, 72.27; H, 4.18; N, 5.17%.
3-Phenyl-4-aroyl-5-isoxazolones
3-Phenyl-4-(4-fluorobenzoyl)-5-isoxazolone (HFBPI) and 3-phenyl-4-(4-toluoyl)-5-
isoxazolone (HTPI) were synthesized from 3-phenyl-5-isoxazolone and the corresponding
acid chlorides (Scheme 2)14-16. The crude products were filtered, dried and recrystallized
from ethyl acetate. The synthesized 4-aroyl-3-phenyl-5-isoxazolones were confirmed by
FT-IR, 1H NMR and elemental analysis.
0
1
HTPI : M.P. = 145 C; H NMR (Figure S2) data:  6.93-7.37 (m, 9H, phenyl); 2.31
(3H, methyl); IR data ( cm1): 2600, 1699, 1613, 1600, 830; Elemental analysis: Calc. for
C17H13NO3, C, 73.12; H, 4.66; N, 5.02. Found: C, 73.52; H, 4.73; N, 5.31%.

Separation Studies of Pd(II) from Acidic Chloride Solutions 759
R
O
Cl
Ph
O
N
O
F
CH3 : HTPI
:
HFBPI
Ca(OH)2
N
O
R =
+
1,4-dioxane
O
O
H
R
Scheme 2. Synthesis of 3-phenyl-4-aroyl-5-isoxazolones.
0
1
HFBPI : M.P. = 149 C; H NMR data:  6.80-7.40 (m, 9H, phenyl); IR data ( cm1) :
2600, 1702, 1620, 1583; Elemental analysis: Calc. for C16H10NO3F, C, 67.84; H, 3.53; N,
4.95. Found: C, 67.56; H, 4.08; N, 4.95%.
The enolic –OH peaks observed at  5.90, 4.08 and 3.57 in the 1H NMR spectra of HPBI,
HTPI and HFBPI, respectively, were found to be exchanged upon the addition of D2O,14 which
confirms the existence of these compounds in the enolic form. The absence of a peak at  3.8
corresponding to the methylene proton at the fourth position of the isoxazolone ring, further
confirmed the existence of various 3-phenyl-4-aroyl-5-isoxazolones quantitatively in enolic form.
Liquid- liquid extraction and analytical procedure
Equal volumes of aqueous and organic phases were placed in a glass stopper vial and shaken for
45 min using a mechanical shaker at 303±1.0 K to determine the distribution of metal ions. The
solutions were allowed to settle and the phases were separated. The Pd(II) concentration in the
aqueous phase was determined using AAS. The concentration of metal ions in the organic phase
was then obtained by mass balance. The distribution ratio, D was taken as the ratio of the
concentration of metal ions in the organic phase to that in the aqueous phase. All experiments
were performed in duplicate and the general agreement between the distribution ratios values
obtained was within ±5%. Chloroform was chosen as the diluent due to the solubility limitations
of 4-aroyl-3-phenyl-5-isoxazolones in various industrially employed diluents. The ionic strength
was maintained at 1.0 mol L-1 using a sodium chloride and hydrochloric acid mixture.
Results and Discussion
Liquid-liquid extraction of Pd(II) from its acidic chloride solutions using 4-aroyl-3-
phenyl-5-isoxazolones (HA)
The metal ion distribution equilibrium studies were performed using equal volumes of the
aqueous phase (1.12×10-4 mol L-1 of Pd(II) at 0.1 mol L-1 [H+] and 1.0 mol L-1 Cl- was
maintained using HCl + NaCl mixture) and organic phase (1.0×10-3 mol L-1 HA in
Chloroform) at 303±1.0 K. The results obtained are shown in Figure 2. The maximum time
needed to reach the maximum metal ion extraction into the organic phase was 30 to 45 min.
Therefore, further studies were performed for 45 min, which is said to be a sufficient
equilibration time for Pd(II) extraction into the organic phases.
The effect of 4-aroyl-3-phenyl-5-isoxazolone (HA) (3-phenyl-4-benzoyl-5-isoxazolone
(HPBI), 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone (HFBPI) and 3-phenyl-4-(4-toluoyl)-5-
isoxazolone (HTPI)) concentrations (1.0×103 – 3.0×103 mol L-1 in chloroform) on the
extraction behavior of Pd(II) was investigated at constant metal ion (1.12104 mol L-1) and
hydrochloric acid (0.05 mol L-1) concentrations, and the results are depicted in Figure 3. The
extraction of metal ions increased linearly with increasing 4-aroyl-3-phenyl-5-isoxazolone
concentration. The log-log plots gave slopes of 2.0±0.22, indicating the involvement of two
molecules of extractant in complex formation.

760 K. J. REDDY et al.
80
HPBI
HFBPI
HTPI
60
40
20
0
20
40
60
Time/min
Figure 2. Kinetic equilibrium of Pd(II) with 4-aroyl-3-phenyl-5-isoxazolones(HA). [HA] =
1.0×10-3 mol L-1, Pd(II) = 1.12×10-4 mol L-1 at 0.1 mol L-1 H+ and 1.0 mol L-1 Cl-.
HPBI
HFBPI
HTPI
1.8
1.2
Slope = 2.0 ± 0.22
0.6
-3.2
-3.0
-2.8
Log[HA]free
-2.6
Figure 3. Effect of 4-aroyl-3-phenyl-5-isoxazolones (HA) on Pd(II) extraction. Aqueous
phase = 1.12×10-4 mol L-1 Pd(II) at 0.1 mol L-1 H+ and 1.0 mol L-1 Cl-, Organic phase =
1.0×10-3 mol L-1 in CHCl3, Equilibration time = 45 min.
The extraction of Pd(II) with HPBI, HFBPI and HTPI (1.0×10-3 mol L-1) in chloroform
was examined as a function of the hydrogen ion concentration at constant metal (1.1210-4 mol L-1)
and chloride ion (1.0 mol L-1) concentrations by employing HCl and NaCl mixtures. The
extraction behavior showed an inverse dependence on acidity. The log-log plots (Figure 4)
gave slopes of -2.0±0.11, indicating the release of two hydrogen ions into the aqueous phase.
The effect of the chloride ion concentration (0.1 to 1.0 mol L-1) was also studied using a
NaCl and HCl mixture at 0.05 mol L-1 [H+]. The results showed that the extraction/
distribution of Pd(II) ion is independent of the chloride ion concentration.

Separation Studies of Pd(II) from Acidic Chloride Solutions 761
0.8
0.0
Slope = -2.0 ± 0.11
HPBI
HFBPI
HTPI
-0.8
-1.2
-0.9
-0.6
Log[H+
Figure 4. Effect of the H+ concentration on Pd(II) extraction with 4-aroyl-3-phenyl-5-
isoxazolones(HA). Aqueous phase = 1.12×10-4 mol L-1 Pd(II) at 1.0 mol L-1 ionic strength,
Organic phase = 1.0×10-3 mol L-1 in CHCl3, Equilibration time = 45 min.
The effect of the metal ion concentration (0.510-4 – 2.810-4 mol L-1) on the extraction
process of Pd(II) from 0.05 mol L-1 hydrochloric acid solutions was examined using a range of
4-aroyl-3-phenyl-5-isoxazolones (1.0×10-3 mol L-1) in chloroform. The results showed that
extraction is independent of the metal ion concentration in the range investigated.
The log-log plots (Figure 5) of the equilibrium organic phase metal concentrations as a
function of the aqueous phase metal concentrations were linear with slopes of unity,
indicating the extraction of mononuclear species into the organic phase. Based on these
results, the extraction equilibrium of Pd(II) from hydrochloric acid solutions with 4-aroyl-3-
phenyl-5-isoxazolones (HA) can be represented as follows:
Kex,Pd(II)
2+
Pd + 2 HAorg
Pd2+A2org + 2 H+
aq
aq
(1)
(2)
Where Kex, Pd(II) denotes the conditional equilibrium constant and can be expressed as:
[Pd2+A2]org [H+]2aq
Kex,Pd(II)
=
[Pd2+ aq [HA]2org
]
HPBI
HFBPI
HTPI
-3.6
-3.8
-4.0
-4.2
-4.4
Slope = 1.0 ± 0.11
-5.4
-5.2
-5.0
-4.8
Log[M+]aq
-4.6
-4.4
-4.
Figure 5. Effect of the metal ion concentration on Pd(II) extraction with 4-aroyl-3-phenyl-5-
isoxazolones(HA).Aqueous phase = 0.5×10-4 - 2.8×10-4 mol L-1 Pd(II) at 0.05 mol L-1 H+ and 1.0 mol L-1
ionic strength, Organic phase = 1.0×10-3 mol L-1 in CHCl3, Equilibration time = 45 min.

762 K. J. REDDY et al.
The calculated Kex,Pd(II) values refer only to the concentration quotients, which are
calculated based on the assumption that the activity coefficients of the species involved do
not change significantly under the present experimental conditions. Table 1 lists the
equilibrium constants of Pd(II) with various 4-aroyl-3-phenyl-5-isoxazolones. A comparison
of the equilibrium constants of various 4-aroyl-3-phenyl-5-isoxazolones with their pKa
values14,17-20 showed that the equilibrium constants increase with decreasing pKa of HA. This
shows that the extraction efficiency of Pd(II) ions occurs in the following order HFBPI >
HPBI > HTPI. Interestingly, the substitution of electron-withdrawing fluorine in the fourth
position of the benzoyl moiety in the HPBI molecule improves the extraction efficiency of
these metal ions. On the other hand, the substitution of an electron-releasing, e.g. like methyl
(-CH3), reduces the extraction efficiency. Therefore, it is clear from the present study that the
extraction of Pd(II) with 4-aroyl-3-phenyl-5-isoxazolone vary in accordance with the
substituent on the benzoyl moiety of isoxazolone, which ultimately reflects the acidity of the
ligand (pKa ), which was supported by other reports14,15
.
Table 1. Relationship between the extractant pKa and equilibrium constants of Pd(II)
towards its extraction from acidic chloride solutions using isoxazolones in chloroform.
Extractant
HFBPI
HPBI
pKa
0.65
1.23
1.48
Log Kex,Pd(II)
4.39±0.06
4.26±0.05
4.15±0.04
HTPI
Loading and striping studies of 4-aroyl-3-phenyl-5-isoxazolones (HA)
Loading and striping studies of 4-aroyl-3-phenyl-5-isoxazolones were performed using
HPBI (1.0×10-3 mol L-1) as a representative of the above working isoxazolones. 1.12×10-4 mol L-1
Pd(II) at 0.05 mol L-1 H+ and 1.0 mol L-1 HCl were used for the loading and striping studies
of Pd(II), respectively and are shown in Figure 6. The results show that the maximum
loading (97.5%) and striping (89%) of Pd(II) was within 3.0 cycles of the above
experiments.
100
90
80
70
60
% Metal loading (1.12 x10-4 mol L-1 of Pd2+
% Metal striping(1.0 mol L-1 HCl)
)
50
40
1
2
3
4
5
No cycles
Figure 6. Loading and striping studies of Pd(II) with HPBI. Conditions for extraction =
1.12×10-4 mol L-1 Pd(II) in 0.05 mol L-1 H+ at 1.0 mol L-1 Cl-, 1.0×10-3 mol L-1 HPBI in
CHCl3; Conditions for desorption = 1.0 mol L-1 HCl.

Separation Studies of Pd(II) from Acidic Chloride Solutions 763
Separation of Pd(II) from acidic chloride solutions of Pt(IV), Ni(II) and Rh(II)
The separation of Pd(II) from Pt(IV), Ni(II) and Rh(III) ions present in acidic chloride
solutions were examined as a function of [H+] (0.05 – 0.3 mol L-1) and [HPBI] (1.0×10-3 mol L-1)
and the results shown in Figure 7 and 8. The results show that metal extraction decreases
linearly with increasing H+ ion concentration and Pd(II) shows maximum extraction at
0.05 mol L-1 [H+], with minimum extraction (< 35%) of the remain metal ions. An increase
in the HPBI concentration results in an increase in metal ion extraction and showed 99%
Pd(II) extraction at 3.0×10-3 mol L-1, whereas < 75% metal extraction was achieved by
remaining desired metal ions.
Pt(IV)
Rh(III)
Ni(II)
80
Pd(II)
60
40
20
0
0.05
0.10
0.15
0.20
0.25
0.30
[H+]/ mol L-1
Figure 7. Separation studies of Pd(II) from acidic chloride solutions of Pt(IV), Ni(II) and
Rh(III) as a function of the H+ concentration using HPBI as extractant. [M] = 1.12×10-4 mol L-1
at 0.05 mol L-1 H+ with 1.0 mol L-1 Cl-, [HPBI] = 1.0×10-3 mol L-1 in CHCl3.
100
80
60
40
Pd(II)
Pt(IV)
Rh(III)
Ni(II)
20
0.0010
0.0015
0.0020
0.0025
0.0030
[HPBI], mol L-1
Figure 8. Separation studies of Pd(II) from acidic chloride solutions of Pt(IV), Ni(II) and
Rh(III) as a function of the HPBI concentration. [M] = 1.12×10-4 mol L-1 at 0.05 mol L-1 H+
with 1.0 mol L-1 Cl-.

764 K. J. REDDY et al.
Table 2 lists the separation factors of these metal ions calculated from their distribution
ratios (D), which were obtained from the extraction of metal ions (1.12×10-4 mol L-1) at
0.05 mol L-1 H+ with various concentration of HPBI in chloroform. The results show that the
selective separation of Pd(II) from the desired metal ions was achieved, particularly in the
case of Pd(II) and Ni(II). Moreover, better separation (Pd/Ni = 40.0±0.30) was achieved.
Table 2. Separation of Pd(II) from Pt(IV), Rh(III), Ni(II)(1.12×10-4 mol L-1) chloride
(0.05 mol L-1 H+) solutions using HPBI.
HPBI/
mol L-1
0.001
D
Average Separation Factors
Pd(II) Pt(IV) Rh(III) Ni(II) Pd/Pt Pd/Rh Pd/Ni Pt/Ni Rh/Ni Rh/Pt
7.268 0.291 0.485 0.182
0.0015 16.452 0.654 1.0902 0.409 25.0± 15.0± 40.0± 1.70± 2.70± 1.70±
0.002
0.0025
0.003
29.072 1.163 1.938 0.727 0.22 0.15 0.30 0.40 0.35 0.42
45.43 1.817 3.028 1.136
65.46 2.616 4.361 1.635
The separation factors of among these metal ions were in the following order: Pd/Ni >
Pd/Pt > Pd/Rh > Rh/Ni > Pt/Ni ≈ Rh/Pt, which can be explained by their ionic radius as well
as by the hard and soft acid and base theory of metal ions. Pd(II) has a smaller ionic radius
than Ni(II) and slightly more hardness than Pt(IV). Rh(III) ions were extracted more
effectively using a hard ligand, HPBI19.
Application and validity of the present liquid-liquid extraction method
The developed method was applied to the separation and determination of Pd(II) in synthetic
water samples. Various amounts of palladium (0.012 g L-1 to 0.03 g L-1) were added to the
water samples, and the palladium was extracted and determined using the above developed
liquid–liquid extraction method, and the results are listed in Table 3. The standard deviation
(< 0.0004) and % RSD (< 2.11) indicates that the method was more precise and accurate.
The percentage metal recovery achieved was > 93.33%. The validity of the method was
checked by a direct AAS determination of the Pd(II) ion concentration in the synthetic water
samples, and the data is listed in Table 3. The data from the present method was close to that
determined using AAS, highlighting the validity of this method.
Table 3. Pd(II) concentration in the synthetic water samples.
Pd(II) added,
Pd(II) Found*, g L-1
Present method AAS method
S.D
R.S.D.
%
Recovery
98.33
94.66
95.01
g L-1
0.012
0.015
0.020
0.025
0.0118
0.0142
0.0190
0.0245
0.0280
0.0119
0.0145
0.0180
0.0240
0.0290
0.0002
0.0003
0.0002
0.0004
0.0002
1.69
2.11
1.05
1.63
0.71
98.02
93.33
0.030
*Average of five determinations.
Conclusion
This study examined the extraction of Pd(II) from acidic chloride solutions using 4-aroyl-
3phenyl-5-isoxazalones(HA), such as HPBI, HFBPI and HTPI in chloroform. The extraction
strength of the isoxazolones was in the following order: HFBPI > HPBI > HTPI, which
correlated with their pKa values. The metal extraction strength decreased with increasing pKa

Separation Studies of Pd(II) from Acidic Chloride Solutions 765
values of the isoxazolones. Interestingly, the substitution of electron-withdrawing fluorine in
the fourth position of the benzoyl moiety in the HPBI molecule improved the extraction
efficiency of these metal ions. On the other hand, the substitution of electron-releasing
groups, such as methyl (-CH3) decreased the extraction efficiency, which also reflects their
acidity (pKa). Loading and striping studies of HPBI were also performed using 1.12×10-4 mol L-1
Pd(II) at 0.05 mol L-1 as the loading conditions and 1.0 mol L-1 HCl as the striping agent.
The maximum metal extraction or desorption was achieved within 3.0 cycles.
The separation of Pd(II) from Pt(IV), Ni(II) and Rh(III) acidic chloride solutions was
examined as a function of the H+ and HPBI concentrations. The calculated separation factors
between these metal ions at 0.05 mol L-1 H+ using HPBI were in the following order: Pd/Ni
> Pd/Pt > Pd/Rh > Rh/Ni > Pt/Ni ≈ Rh/Pt, which correlated with their ionic radius as well as
the hard and soft acid base nature of these metal ions. A better separation factor was
achieved between Pd(II) and Ni(II) (Pd/Ni = 40.0) metal ions with HPBI.
The above liquid-liquid extraction method was applied successfully to the determination
of Pd(II) from its synthetic water samples and their precision and accuracy was checked by
the standard deviation, % RSD and recovery of metal ion. A comparison of the developed
method with a direct determination of Pd(II) using AAS confirmed that the present method
had high accuracy and can be applied successfully to real samples.
Acknowledgment
This work was supported by Dongguk University Research Grant-2011, Republic of Korea.
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