J. Serb. Chem. Soc. 71 (3) 223–234 (2006)
JSCS – 3413
UDC 546.834+543.5:66.061
Original scientific paper
Solvent extraction separation of zirconium(IV) from succinate
media with N-n-octylaniline
M. M. RAJMANE, B. M. SARGAR, S. V. MAHAMUNI and M. A. ANUSE*
Analytical Chemistry Laboratory, Department of Chemistry, Shivaji University,
Kolhapur 416004, India (e-mail: [email protected])
(Received 10 November 2004, revised 13 June 2005)
Abstract: The extraction behavior of zirconium(IV) from succinate (0.01 – 0.03 M)
medium (25 mL) with 10 mL 3 % N-n-octylaniline in xylene was investigated. The
pH range 3.7 – 5.0 was effective for the quantitative extraction of zirconium(IV).
Zirconium(IV) was back extracted with 0.5 M HNO3 (3 ´ 5 mL). The method was
free from interferences of a large number of cations and anions. Zirconium(IV) was
separated from associated elements in its binary mixture with Mo(VI), Nb(V),
Re(VII), La(III), Ti(IV), Th(IV) and Al(III). The proposed method was applied to
synthetic mixtures. The results of analysis indicate that trace amounts of zirconium(IV) could be separated effectively from higher amounts of other elements. The
method is simple, selective, rapid and eco-friendly.
Keywords: solvent extraction, zirconium(IV) determination, N-n-octylaniline, succinate.
INTRODUCTION
Zirconiuim is one of the abundant elements (162 ppm) and is widely distributed in the Earth’s crust.1 World production of zirconiuim(IV) minerals was
808,000 tonnes in 1992. Most of the zirconium is used as compounds for the ceramic industry, refractories, glazes, enamels, foundry mold and abrasive grits and
compounds for electrical ceramics. The incorporation of zirconium oxide in glass
significantly increases its resistance to alkali. Zirconium metal is used almost entirely for cladding uranium fuel elements for nuclear power plants. Another significant use is in photo flash bulbs. Some chemical processing industries use zirconium metal for corrosion-resistant vessels and piping, particularly for withstanding hydrochloric and sulphuric acid.
A literature survey revealed that trioctylamine (TOA) has been used for extraction of zirconium(IV).2–8 The method involved extraction of zirconium(IV)
from hydrochloric acid solution with TOA in benzene. The extraction efficiency
depended on the chain length of the amine.2 Higher reagent concentrations were
*
Corresponding author. Tel: +91-231-2690571, Ext-5164; fax: +91-0231-2692333.
doi: 10.2298/JSC0603223R
223
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RAJMANE et al.
required.4 The trioctylamine reagent was not so effective for the mutual separation
of elements when they were present as congeneric pairs in aqueous solutions. A solution of Alamine 336 in an appropriate diluent was used to extract zirconium(IV)
from 1 M sulphuric acid9 and 7 ´ 10–4 M malonic acid10 media. The methods suffer from being multistage extractions and from emulsion formation.
Extraction of zirconium(IV) from hydrochloric acid solution with di-n-octylamine in benzene was investigated under different conditions.11 The extraction efficiency depended on the type of the group present in the amine. A method for the separation and determination of zirconium(IV) in a mixture containing zirconium(IV)
and hafnium(IV) was outlined. However, a long equilibration time was required.
Various organophosphorus reagents have been reported for the extraction separation of zirconium(IV) from associated elements. The solvent extraction of zirconium(IV) with cyanex 272,12 cyanex 302 and cyanex 30113 from sulphuric acid
solutions has been investigated systematically. However, the reagents show poor
selectivity. Zirconium(IV) was effectively extracted from nitric and hydrochloric
acid solution with tri-n-butyl phosphate (TBP) in kerosene. The method required
multiple extraction and depended on the phase ratio.14 The behaviour of a third
phase for the solvent extraction of zirconium(IV) by TBP has also been studied.15
Some other phosphorus-containing extractants were reported for the extraction of
zirconium(IV) from acid media, such as tritolyl phosphate (TTP),16 dibutyl hydrogen phosphate (HDBP),17,18 di-o-tolylphosphoric acid19 and tri-isoamyl phosphate (TAP).20 The extraction of zirconium(IV) decreased remarkably with increasing
sulphate ion concentration in the aqueous phase,19 and also the extraction was
found to be incomplete.20
The species involved in the solvent extraction of zirconium(IV) from aqueous
hydrochloric acid by mixtures of thenoyltrifluoroacetone (HTTA) and dipentyl
sulfoxide (DPSO) in benzene as diluent appeared to be Zr(OH)2 (TTA)2 (DPSO) as
a synergism.21 Synergetic solvent extractions of zirconium(IV) from thiocyanate
and hydrochloric acid solutions by LIX-26 and dioctyl sulfoxide (DOSO) have
been reported.22 The extraction of zirconium(IV) depends greatly on the thiocyanate concentration.
Zirconium(IV) was determined with xylenol orange after liquid–liquid extraction by tri-n-butylacetohydroxamic acid (TBAH) from 6 M HCl.23 Hafnium interfered and the method required the prior extraction of zirconium(IV) with TOA, in
order to avoid interference by Th(IV).
Methyl isobutyl ketone (MIBK) has been reported for the extraction of the zirconium(IV)-thiocyanate complex from hydrochloric acid media24 but the method
was not very selective. The extraction of zirconium(IV) from nitric acid solution
with amido podands PA II and PA V was studied.25 The extractant PA II was satisfactory for the extraction of zirconium(IV), but there was a serious emergence of a
third phase when the concentration of the desalting agent (NaNO3) and the concen-
SEPARATION OF ZIRCONIUM(IV) FROM SUCCINATE MEDIA
225
tration ratio of extractant to zirconium(IV) was over the range. PA V was not suitable for the extraction of zirconium(IV). The extraction separation of zirconium(IV) from associated elements with the liquid–solid extraction system poly(vinyl pyrrolidone)–Tween 40 was studied.26 The recovery of zirconium(IV)
was found to be icomplete. The extraction of zirconium(IV) from an aqueous solution of constant ionic strength with versatic acid-10 dissolved in benzene was studied as a function of pH and concentration of zirconium(IV) and organic acid.27 The
extraction depended on the sulphate and chloride ion concentration. Even though
extensive work has been performed on the extraction and separation of zirconium(IV), in many instances the available methods are found to be inadequate for effective extraction. It was therefore felt worthwile to evolve an entirely new procedure which facilitates the extraction and separation of zirconium(IV) from associated elements with a minimum amount of manipulation.
The extraction of zirconium(IV) was carried from weak organic acid media,
i.e., sodium succinate. It is worthwhile here to stress the advantages of organic acid
media over mineral acid media. One distinct advantage of organic acid media is the
facility of controlling the concentration of complexing ligand, the ease of pH adjustment and the widely differing pH values at which various metals form anionic
complexes. Stripping the complexes from the organic phase can be achieved comparatively easily by fully exploiting the differences in the reactivity of various metals to backwash in the aqueous phase by a mineral acid. It is known that organic
acid media offer better separation of metals, possibly due to the high stability of
metal–organic acid complexes.
EXPERIMENTAL
Apparatus
An Elico digital spectrophotometer, Model SL-171, with a 1 cm quartz cell was used for the
absorbance measurements; the pH measurements were carried out using an Elico digital pH meter,
Model LI-120.
Reagents
Standard zirconium(IV) solution. A stock solution of zirconium(IV) was prepared by dissolving 1.0 g of zirconium(IV) nitrate hydrate in 20 mL of hot concentrated nitric acid and diluting to
100 mL with distilled water. The solution was standardized complexometrically.28 A working solution of 50 mg/mL was made by diluting the stock solution with distilled water.
N-n-octylaniline was prepared by the method of Gardlund29 and its soltuions were prepared in
xylene.
All reagents were of analytical reagent grade and doubly distilled water was used throughout
this study.
General procedure for the extraction and determination of zirconium(IV)
A solution containing 150 mg of zirconium(IV) was mixed with 0.01 M sodium succinate (27
mg), adjusted to pH 4.0 with sodiuim hydroxide and hydrochloric acid and diluted to 10 mL. The solution was then transferred into a 125 mL separatory funnel and shaken with 10 mL 5 % N-n-octylaniline in xylene for 3 min. The aqueous phase was discarded. The organic phase was shaken with 0.5
226
RAJMANE et al.
M nitric acid (3 ´ 5 mL) to strip the zirconium(IV). The acid layer was withdrawn and shaken with
xylene (2 ´ 5mL) in order to remove traces of dissolved amine.
To the aqueous phase, 1 mL gum arabic was added, followed by the addition of 5 ml of 0.05 %
Alizarin Red S.30 The solution was diluted upto 25 mL with 0.5 M nitric acid. After waiting for 15
min, the absorbance was measured at 520 nm using a regent blank as the reference. The amount of
zirconium(IV) was computed from a calibration curve.
RESULTS AND DISCUSSION
Extraction as a function of pH
The pH ranges for the extraction of zirconium(IV) were ascertained by carrying out
the extraction between pH 1.0 to 10.0 with a 5 % solution of N-n-octylaniline in xylene
at a fixed concentration of 0.01 M sodium succinate. The optimum pH for the quantitative extraction of zirconium(IV) was found to be in the range 3.7 to 5.0 (Fig. 1).
Fig. 1. Extraction of zirconium(IV) with 5 % N-n-octylaniline from 0.01 M sodium succinate as a function of pH.
Effect of various diluents
Solutions of 5 % N-n-octylaniline in various diluents, such as benzene, xylene,
toluene, kerosene, chloroform, carbon tetrachloride, MIBK, amyl alcohol, amyl
acetate and n-butanol were studied. The extraction of zirconium(IV) was quantitative with hydrocarbon diluents, such as benzene, xylene and toluene, because the
distribution ratio of the ion pair complex is high in these solvents, whereas kerosene (90.8 %), chloroform (93.6) %, carbon tetrachloride (91.5 %), methyl isobutyl
ketone (22.1%), amyl alcohol (7.1 %), amyl acetate (11.7 %) and n-butanol (26.4
%) were found to be poor solvents. However, benzene and toluene are more toxic
than xylene, which also provides a better phase separation, hence xylene was preferred as the diluent for the further studies.
227
SEPARATION OF ZIRCONIUM(IV) FROM SUCCINATE MEDIA
Extraction as a function of N-n-octylaniline concentration
In order to optimize the conditions for the extraction of zirconium(IV), xylene
solutions of N-n-octylaniline of varying concentration (0.1 % to 15 %) were employed. It was found that 10 mL of 3 % N-n-octylaniline was sufficient for the
quantitative extraction of 150 mg zirconium(IV) from 0.01 M sodium succinate at
pH 4. However, in the recommended procedure, 5 % N-n-octylaniline in xylene
was used to ensure complete extraction of the metal ions. There was no adverse effect if an excess of N-n-octylaniline (15 %) was used. However, decreasing the
concentration of the extractant below the recommended value resulted in a lowering of the distribution ratio for zirconium(IV).
Effect of weak organic acid concentration
The extraction of zirconium(IV) was carried out at pH 4.0 with 5 % N-n-octylaniline in xylene in the presence of various concentrations of sodium succinate,
sodium malonate, sodium salicylate, sodium oxalate and ascorbic acid as the weak
acid media.
TABLE I. Extraction behaviour of zirconium(IV) as a function of the concentration of various acids.
Zirconium(IV) = 150 mg; Equilibration period = 3 min; Extractant = 5 % N-n-octylaniline in xylene;
pH = 4.0; Aq : Org = 1 : 1, Strippant = 0.5 M HNO3 (3 ´ 5 ml)
Conc. of
acid
Sodium
succinate
Sodium
malonate
Sodium
salicylate
Sodium
oxalate
Ascorbic
acid
%E
D
%E
D
%E
D
%E
D
%E
D
0.005
70.0
2.33
57.3
1.35
32.3
0.48
19.8
0.24
5.7
0.07
0.01
99.9
999.00
73.2
2.73
47.3
0.89
32.1
0.47
31.6
0.46
0.02
99.9
999.00
75.0
3.00
52.4
1.10
34.7
0.53
54.7
1.21
0.03
99.9
999.00
72.5
2.63
69.0
2.22
19.2
0.23
68.3
2.15
0.04
89.7
8.70
57.3
1.34
79.3
3.84
17.2
0.21
67.8
2.11
0.05
74.2
2.88
42.7
0.75
78.4
3.62
13.2
0.15
66.5
1.98
0.06
61.5
1.60
34.6
0.53
63.3
1.72
9.3
0.10
60.0
1.50
0.07
42.8
0.75
22.5
0.29
34.5
0.52
9.3
0.10
33.3
0.49
0.08
34.2
0.52
18.2
0.22
29.7
0.42
6.2
0.07
28.5
0.29
0.09
23.3
0.30
18.0
0.21
14.8
0.17
6.2
0.07
13.3
0.15
0.10
21.5
0.27
18.0
0.21
11.6
0.13
6.2
0.07
13.0
0.15
% E = percentage extraction; D = distribution ratio
The extraction of the ion pair complex of zirconium(IV) was found to be quantitative in the range of 0.01 – 0.03 M sodium succinate (Table I). With increasing concentration of sodium succinate, there was decrease in the extraction of zirconium(IV). The decrease in the extraction at high acid concentrations is presumably due to the preferential
formation of the succinate of N-n-octylaniline. Therefore, 0.01 M sodium succinate was
228
RAJMANE et al.
used throughout this work. The extraction of zirconium(IV) was found to be incomplete
in sodium malonate, sodium salicylate, sodium oxalate and ascorbic acid.
Period of extraction
The period of equilibrium was varied from 10 s to 15 min. The minimum shaking
time was 2 min. However, it was found that prolonging the shaking (> 4.5 min) had an
adverse effect on the extraction of metal ions and it should be avoided (Fig. 2).
Fig. 2. Extraction of zirconium(IV) at pH 4 with 5 % N-n-octylaniline from 0.01 M sodium
succinate as a function of time.
The decrease in the extraction of zirconium(IV) with shaking time might be due to
the involvement of the ion-pair complex in a parallel equilibrium with other species
present in the organic phase. At pH 4.0, the optimum pH chosen for the extraction,
succinic acid exists mainly as the succinate ion and to a lesser extent as undissociated
succinic acid. The undissociated succinic acid will also be extracted into the organic
phase, along with the ion-pair formed. Since the concentration of undissociated succinic
acid is small in the aqueous phase its concentration in the organic phase is smaller still.
Therefore, the interaction between the ion-pair and the undissociated succinic acid occurs after prolonged shaking, this causing the observed decrease in the extraction.
Effect of stripping agents
The zirconium(IV) was stripped with two 5 mL portions of various stripping
agents at different concentrations. The stripping was found to be complete with nitric acid (0.5 – 2.0 M), while it was found to be incomplete with hydrochloric acid.
There was no recovery of zirconium(IV) with stripping agents such as sulphuric
acid, perchloric acid, acetic acid, ammonia, and water. In this work three 5 mL portions of 0.5 M nitric acid was used as the strippant.
SEPARATION OF ZIRCONIUM(IV) FROM SUCCINATE MEDIA
229
Effect of the aqueous to organic volume ratio on the extraction of zirconium(IV)
The effect of contacting different volume ratios of organic to aqueous phase
was studied. The results indicate that the preferred aqueous/organic (A/O) phase
ratio in this study was 4:1, or less. This was evident from the sharp increase in the
separation efficiency, as well as of the distribution ratio of zirconium(IV) when the
phase ratio (A/O) was changed from 20:1 to 5:1. This may simply be due to the unavailability of the reagent for metal extraction and hence a crowding effect occurs
at low phase ratios. However, in the recommended procedure, the phase ratio was
maintained at 1:1, in order to avoid a large consumption of sodium succinate.
Nature of the extracted species
A log–log plot of the distribution ratio versus the succinate concentration at a
fixed pH and a fixed concentration of N-n-octylaniline or a log–log plot of the distribution ratio versus the N-n-octylaniline concentration at a fixed pH and a fixed
concentration of succinate yielded a molar ratio of 1 : 2 with respect to both
succinate and extractant (Figs. 3 and 4). Hence, the extracted species was thought
to be an ion association complex with the probable composition:
[(RR’NH2+)2 ZrO (succinate2–)2]org
Fig. 3. Log–log plot of distribution ratio log DZr(IV) versus
log c[sodium succinate] at pH 1 and
pH 2.
which was subsequently extracted into the organic phase. The ZrO (succinate)22–
ion1,5,10,31 in the aqueous solution associates to form an ion pair with the cationic
species RR’NH2+ from the organic phase. The mechanism of the formation of the
ion-pair complex is as follows:
230
RAJMANE et al.
Fig. 4. Log–log plot of distribution ratio log DZr(IV) versus
log c[N-n-octylaniline] at pH 1
and pH 2 at a constant succinate concentration (0.01 M).
RR’NH(org) + H+(aq) D RR’NH2+(org)
ZrO2+(aq) + 2 succinate 2– D ZrO (succinate)22–(aq)
2 RR’NH2+(org) + ZrO (succinate)22–(aq) D [(RR’NH2+)2 ZrO (succinate2–)2](org)
Effect of metal loading
Zirconium(IV) was extracted quantitatively in the concentration range 50 – 500 mg
in a single extraction with 10 mL 5 % N-n-octylaniline in xylene. The average recovery
was 99.9 %. It was possible to quantitatively extract higher concentrations of zirconium(IV) by using a larger volume and a higher concentration of N-n-octylaniline.
Effect of various foreign ions on the percentage extraction of zirconium(IV)
Various cations and anions were investigated to study their interference on the extraction and determination of zirconium(IV) with N-n-octylaniline as the extractant. The
tolerance limit was defined as the amount of foreign ion required to cause a ± 2 % error
in the recovery of zirconium(IV) using the proposed method. The results presented in
Table II indicate that many cations and anions did not interfere. However, significant interferences were caused by anions such as tartarate, acetate, oxalate and malonate.
APPLICATIONS
Separation and determination of zirconium(IV) from binary mixtures
The difference in the extraction behaviour of each of the metals was fully exploited to provide a complete separation of the metals from zirconium(IV) in vari-
231
SEPARATION OF ZIRCONIUM(IV) FROM SUCCINATE MEDIA
ous mixtures. Binary mixtures of metals, such as Mo(VI), Nb(V), Re(VII), La(III),
Ti(IV), Th(IV) and Al(III) with zirconium(IV) when extracted by the above
method remained unextracted, leading to the separation of zirconium(IV), because
they do not form a succinate complex at pH 4.0 (Table III).
TABLE II. Effect of foreign ions on the extraction of 150 mg of zirconium(IV) at pH 4.0 in 0.01 M
sodium succinate with 5 % N-n-octylaniline dissolved in xylene
Ratio of ions, zirconium(IV) : ions
Amount tolerated/mg
Foreign ion
1 : 200
30.0
Thiocyanate
1 : 133
20.0
Thiourea
1 : 67
10.0
Citrate, iodide, ascorbate
1 : 26
4.0
Ba(II), Mg(II), Al(III)
1 : 20
3.0
U(VI), Ni(II)
1: 13
2.0
Sr(II), Zn(II), Se(IV), Te(IV)
1:7
1.0
Ca(II), V(V), Fe(II), Fe(III),
La(III), Ga(III), Nb(V), Th(IV),
Tl(III)
1:3
0.5
Mo(VI), W(VI), V(V), Re(VII),
Y(V), Sn(II), Ta(IV), In(III)
–
0.0
Tartarate, acetate, oxalate,
malonate
The separation of zirconium(IV) from Y(III) was made possible by selective
stripping. Zirconium(IV) from the organic phase was stripped first with 0.5 M nitric acid (3 ´ 5 mL) followed by the stripping of Y(III) with 0.05 M hydrochloric
acid (3 ´ 5 mL). The added metal ions were determined by standard methods30,32,33 while zirconium(IV) was estimated by the recommended procedure.
TABLE III. Extraction separation and determination of zirconium(IV) and added metal ions from
binary mixtures
Amount of metal ion / mg
Average* recovery / %
Zr(IV) 150;
Mo(V) 30
Zr(IV) 150;
Nb(V) 50
Zr(IV) 150;
Re(VII) 30
Zr(IV) 150;
La(III) 40
Zr(IV) 150;
Ti(IV) 20
Zr(IV) 150;
99.9
99.8
99.8
99.9
99.9
99.7
99.8
99.8
99.9
99.8
99.9
Chromogenic ligand
Ref. No.
Thiocyanate
30
PAR
32
Thiocyanate
33
Arsenazo III
49
PAR
48
232
RAJMANE et al.
TABLE III. Continued
Amount of metal ion / mg
Average* recovery / %
Chromogenic ligand
Ref. No.
Th(VI) 30
99.9
Arsenazo III
49
Zr(IV) 150;
99.8
Al(III) 6
99.7
Eriochrome Cyanin R
49
*Average
of five determinations
Determination of zirconium(IV) in synthetic mixtures
TABLE IV. Separation of zirconium(IV) from synthetic mixtures
Composition/mg
Zr, 150;
Mo, 500;
Re, 500
Zr, 150;
W, 500;
Re, 500
Zr, 150;
Nb, 500;
La, 500
Zr, 150;
U, 500;
Th, 500
Zr, 150;
Tl, 500;
Ta, 500
Zirconium(IV) found/mg
149.8
149.7
149.8
149.9
149.8
149.8
149.8
149.8
149.7
149.7
149.8
149.7
149.5
149.5
149.6
149.7
149.7
149.6
149.5
149.5
149.5
149.5
149.5
149.8
149.6
Mean/mg
Recovery/%
R.S.D./%
149.8
99.86
0.13
149.8
99.86
0.13
149.6
99.73
0.26
149.6
99.73
0.26
149.5
99.66
0.33
The method was extended to the determination of zirconium(IV) in some
synhtetic mixtures of associated metal ions. The zirconium(IV) was extracted using the proposed method and the results are presented in Table IV.
SEPARATION OF ZIRCONIUM(IV) FROM SUCCINATE MEDIA
233
CONCLUSION
The highlights of the proposed method are given below:
– The method is simple, quantitative and requires a single step.
– It permits the separation of zirconium(IV) from associated elements Mo(VI),
Nb(V), Re(VII), Al(III), Ti(IV), Y(III), La(III), Th(IV).
– Pre-equilibrium, multiple extraction of the organic phase is not required.
– There is no emulsion formation.
– The method is suitable for the determination of zirconium(IV) in synthetic
mixtures.
– The extraction of zirconium(IV) was found to be quantitative at room temperature.
– The method is eco-friendly.
Acknowledgement: Thanks are due to the University Grants Commission, New Delhi, for providing a teacher fellowship to one of the authors (MMR). The authors thank Hon’ble Vice-Chancellor Professor M. M. Salunkhe, Shivaji University Kolhapur and Professor G. S. Gokavi for fruitful
discussion in the research work.
IZVOD
RAZDVAJAWE CIRKONIJUMA(IV) IZ SUKCINATNE SREDINE
EKSTRAKCIJOM RASTVARA^EM SA N-n-OKTILANILINOM
M. M. RAJMANE, B. M. SARGAR, S. V. MAHAMUNI i M. A. ANUSE
Analytical Chemistry Laboratory, Department of Chemistry, Shivaji University, Kolhapur 416 004, India
Ispitivana je ekstrakcija cirkonijuma(IV) iz sukcinatne (0,01–0,03 M) sredine
(25 mL) sa 10 mL 3 % N-n-oktilanilina u ksilenu. Efektivni pH opseg za kvantitativnu ekstrakciju cirkonijuma(IV) bio je 3,7–5,0. Cirkonijum(IV) je re-ekstrahovan sa 0,5
M HNO3 (3 ´ 5 mL). U kori{}ewu metode nema interferencije velikog broja katjona i
anjona. Cirkonijum(IV) je odvajan od elemenata prisutnih u wegovim binarnim sme{ama sa Mo(VI), Nb(V), Re(VII), La(III), Ti(IV), Th(IV) i Al(III). Predlo`ena metoda
primewena je na sinteti~ke sme{e. Rezultati analiza ukazuju da tragovi cirkonijuma(IV) mogu efikasno da se razvoje od ve}ih koli~ina drugih elemenata. Metoda je
jednostavna, selektivna, brza i nije ekolo{ki {tetna.
(Primqeno 10. novembra 2004, revidirano 13. juna 2005)
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