Liquid-liquid solvent extraction of rare earths from chloride medium with sec-nonylphenoxy acetic acid and its mixtures with neutral organophosphorus extractants

Article abstract of DOI:10.1134/S0036023611070321

In the present study, sec-nonylphenoxy acetic acid (CA100) and its mixtures with four neutral organophosphorus extractants, tri-butyl-phosphate (TBP), 2-ethylhexyl phosphonic acid di-2-ethyl ester (DEHEHP), Cyanex923, and Cyanex925 have been applied to the extraction of rare earths. Results show that all the four mixing systems do not have evident synergistic effects on the extraction of rare earths. The different extraction effects have been considered to the separation of rare earths. The four mixtures may be applied to the separation of yttrium from some certain lanthanoids at proper mole fractions of CA100. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S0036023611070321

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 7, pp. 1157–1161. © Pleiades Publishing, Ltd., 2011.
PHYSICAL CHEMISTRY
OF SOLUTIONS
LiquidꢀLiquid Solvent Extraction of Rare Earths from Chloride
Medium with SecꢀNonylphenoxy Acetic Acid and Its Mixtures
1
with Neutral Organophosphorus Extractants
Pengfei Xiao, Changli Bao, Naizhong Song, Cui Li, and Qiong Jia
College of Chemistry, Jilin University, Changchun 130022, China
eꢀmail: jiaqiong@jlu.edu.cn
Received December 30, 2009
Abstract—In the present study, secꢀnonylphenoxy acetic acid (CA100) and its mixtures with four neutral
organophosphorus extractants, triꢀbutylꢀphosphate (TBP), 2ꢀethylhexyl phosphonic acid diꢀ2ꢀethyl ester
(DEHEHP), Cyanex923, and Cyanex925 have been applied to the extraction of rare earths. Results show that
all the four mixing systems do not have evident synergistic effects on the extraction of rare earths. The differꢀ
ent extraction effects have been considered to the separation of rare earths. The four mixtures may be applied
to the separation of yttrium from some certain lanthanoids at proper mole fractions of CA100.
DOI: 10.1134/S0036023611070321
1
1
. INTRODUCTION
stants, and thermodynamic functions have also been
determined.
As a kind of organic carboxylic acid, naphthenic
In our previous work, the synergistic extraction of
REs with mixtures containing CA100 or another carꢀ
boxylic acid, secꢀoctylphenoxy acetic acid (CA12),
has been reported [6–8, 11, 12, 21]. The mixing sysꢀ
tems of CA100 or CA12 with di(2ꢀethylhexyl) phosꢀ
phoric acid (D2EHPA), 2ꢀethylhexyl phosphonic acid
monoꢀ(2ꢀethylhexyl) ester (HEHEHP), bis(2,4,4ꢀtriꢀ
methylpentyl) dithiophosphinic acid (Cyanex301)
acid has been widely used for the separation of rare
earths. Although carboxylic acid is easy to get and
cheap, it has some shortcomings such as complicated
composition, instability in technology, easy to emulsiꢀ
fication, etc. Secꢀnonylphenoxy acetic acid (CA100),
an extractant recently developed by Shanghai Institute
of Organic Chemistry, Chinese Academy of Sciences,
has several advantages including stable composition, have been applied to the extraction of REs. All the
low solubility, easy preparation, and uneasy emulsifiꢀ above organophosphorus extractants are acidic
cation during extraction [1]. The extraction of rare reagents. However, there are no reports about the
earths (REs) with CA100 has been reported in some extraction of REs with the mixing systems containing
previous papers [2–5], Wang et al. [3] have studied the these two carboxylic acids and neutral organophosꢀ
3+
extraction behavior of Eu from hydrochloric acid phorus extractants.
2
+
2+
2+
2+
2+
solutions together with Zn , Cd , Co , Ni , Cu ,
In the present study, CA100 and its mixtures with
four neutral extractants, triꢀbutylꢀphosphate (TBP),
2ꢀethylhexyl phosphonic acid diꢀ2ꢀethyl ester
2+
2+
3+
Mn , and Mg . It is proved that Eu can be effecꢀ
tively separated from the other metal ions.
(
DEHEHP), Cyanex923, and Cyanex925, have been
Synergistic extraction, i.e. the extraction with two
kinds of extractants, has been applied extensively in
order to enhance extractability and selectivity. Kinds
of mixing systems have been employed to the synergisꢀ
tic extraction of REs. Organophosphorus acids [6–
used for the extraction of REs. The extraction effects are
determined and considered for the separation of REs.
2. EXPERIMENTAL
1
6], neutral organophosphorus reagents [14–20],
amines [13, 15], and ꢀdiketones [18–21] are very
common extractants used in synergistic extraction sysꢀ
tems. For example, Sun et al. [10] have investigated Pr O (99.95%), Eu O (99.99%), Tb O (99.999%),
2.1. Reagents
β
Highꢀpurity La O (99.999%), Ce O (99.99%),
2
3
2
3
2
3
2
3
2
3
the synergistic extraction of REs using mixtures of Ho O (99.999%), Tm O (99.999%), Lu O (99.995%),
2
3
2
3
2
3
CA100 and bis(2,4,4ꢀtrimethylpentyl)phosphinic acid
Y O (99.99%) were obtained from Changchun Instiꢀ
2 3
in n
ꢀheptane. A cation exchange mechanism has been tute of Applied Chemistry, Chinese Academy of Sciꢀ
proposed. The equilibrium constants, formation conꢀ ences (Changchun, China), Stock solutions of REs
were prepared by dissolving their oxides in concenꢀ
1
The article is published in the original.
trated hydrochloric acid and diluting to the required
1157

1158
XIAO et al.
volume with distilled water. The stock solutions were
standardized by titration using EDTA standard solution.
0
.30
.25
.20
La
Eu
Tm
Ce
Tb
Lu
Pr
Ho
Y
–3
All the initial REs concentrations were
was added to keep the constant ionic strength (
.3 M). All other reagents were of AR grade.
CA100 and TBP were supplied by Shanghai Rareꢀ
5 × 10 M. NaCl
0
μ
=
0
0
Earth Chemical Co., Ltd. DEHEHP was purchased
from Tianjin Chemical Company. Cyanex923 and
Cyanex925 were obtained from Cytec Canada Inc. All
the extractants were used without further purification.
0.15
0.10
0.05
2.2. Experimental Procedures
Equal volumes (5 mL each) of aqueous and organic
0
0.01
0.02 0.03
CA100], mol L
0.04
0.05 solutions were mixed and shaken for 30 min at 293 ± 1 K.
–1
[
After the split of the phases, the concentration of REs
in the aqueous phase was determined by titration with
EDTA and that in the organic phase by material balꢀ
ance. The distribution ratio was calculated as the ratio
of the concentration of REs in the organic phase to
that in the aqueous phase.
Fig. 1. Extraction of RE3+ with CA100. [RE3+] = 5.0
×
–3
10
M, pH 3.0,
µ
= 0.3 M.
0
0
0
0
0
0
0
.07
.06
.05
.04
.03
.02
.01
La
Eu
Tm
Ce
Tb
Lu
Pr
Ho
Y
3. RESULTS AND DISCUSSION
3
.1. Extraction of Rare Earths with CA100
There have been some reports about the extraction
of REs with CA100 from chloride medium. The
extraction stoichiometry can be written as follows [3,
8
, 10]:
3
+
+
Eu + 4
(
NH A
)
ꢀ EuA3
(
NH A
)
+ 3NH , (1)
4 a
o
(
a
)
4
(o)
4
( )
( )
3+
a)
+
La( + 2H A2 ꢀ LaHA4(o) + 3H ,
(2)
3)
2
(
o
)
( )
a
3
a
+
–
a
Y( + 2OH( + 2H A2
2
)
)
( )
o
0
0.01
0.02
[
0.03
0.04
0.05
(
TBP], mol L–1
+
ꢀ
Y
(
OH 2
)
A
(
HA
)
+ H ,
a
3(o)
( )
Fig. 2. Extraction of RE3+ with TBP. [RE3+] = 5.0
×
10⎯ M,
3
where H A denotes CA100.
2 2
In the present work, the extraction of La, Ce, Pr,
Eu, Tb, Ho, Tm, Lu, and Y with CA100 in ꢀheptane
pH 3.0,
µ
= 0.3 M.
n
0.07
0.06
0.05
0.04
0.03
0.02
0.01
from chloride medium has been studied. Results are
shown in Fig. 1. It can be seen that the distribution
ratio decreases with increasing atomic numbers of
REs. Y locates between Ho and Tm. Such an order has
been reported by Sun et al. when Ho, Er, Tm, Yb, Lu,
and Y are extracted with CA12 [9]. The distribution
ratio values follow the order of Ho > Er > Tm > Yb >
Lu > Y. The authors have concluded that single CA12
system can be used to separate Y from light and middle
lanthanoids.
La
Eu
Tm
Ce
Tb
Lu
Pr
Ho
Y
3.2. Extraction of Rare Earths with Neutral
Organophosphorus Extractants
0
0.01
0.02 0.03
DEHEHP], mol L
0.04
0.05
There have been many reports about the extraction
of REs with neutral organophosphorus extractants,
e.g. TBP [15, 17], DEHEHP [18, 19, 22], Cyanex923
–1
[
Fig. 3. Extraction of RE3+ with DEHEHP. [RE3+] = 5.0
×
[
14, 16, 23–30], and Cyanex925 [15, 23, 31, 32]. For
example, the extraction of La and Sm from nitrate
–3
3+ 3+
10
M, pH 3.0,
µ
= 0.3 M.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 7 2011

LIQUIDꢀLIQUID SOLVENT EXTRACTION
1159
medium with Cyanex923 and Cyanex925 can be
expressed as follows according to ElꢀNadi et al.’s
work [23]:
0
.15
.12
La
Eu
Tm
Ce
Tb
Lu
Pr
Ho
Y
0
3
+
–
a
( )
RE(a + 3NO3 + 2Cyanex923(o)
)
(4)
ꢀ
RE
(
NO3
)
⋅ 2Cyanex923 ,
o
3
(
)
0.09
3
+
–
a
( )
RE(a) + 3NO3 + Cyanex925(o)
(
5)
0
.06
.03
ꢀ
RE
(
NO3
)
⋅ Cyanex925 .
o
3
( )
The following extraction stoichiometry has also
been obtained when REs are extracted with
Cyanex923 [25, 26]:
0
3
+
–
RE(a + 3NO3( + 3Cyanex923(o)
0
0.01
0.02 0.03 0.04
–1
Cyanex923], mol L
0.05
)
a
)
(6)
[
ꢀ
RE
(
NO3
)
⋅ 3Cyanex923 .
o
3
( )
Fig. 4. Extraction of RE3+ with Cyanex923. [RE3+] = 5.0
×
In the present work, the extraction of La, Ce, Pr,
Eu, Tb, Ho, Tm, Lu, and Y from chloride medium
with TBP, DEHEHP, Cyanex923, and Cyanex925 has
been investigated under the same experimental condiꢀ
tions. Results are shown in Figs. 2–5. It is evident that
the extraction of REs with the neutral reagents
increases with increasing atomic numbers. These
results are in accordance with previous papers [23, 33].
–3
1
0
M, pH 3.0,
µ
= 0.3 M.
0
.18
La
Eu
Tm
Ce
Tb
Lu
Pr
Ho
Y
0.15
0.12
0
0
0
.09
.06
.03
3
.3. Extraction of Rare Earths with Mixtures of CA100
and Neutral Organophosphorus extractants
The extraction of the above REs with mixtures of
CA100 and TBP, DEHEHP, Cyanex923, Cyanex925
has been carried out. All the four mixtures do not have
synergistic effects on the REs. However, different
extraction effects of the REs have been found in differꢀ
ent mixing systems. The reason why a mixing system
has synergistic or antagonistic effects is not clear so far.
In the four mixtures, the extraction of REs with single
CA100, single neutral organophosphorus extractant,
and the mixtures exists simultaneously. The three
extraction processes determine the final extraction
effects.
As a representative, the extraction of La with
CA100, TBP, and CA100 + TBP is shown in Fig. 6,
where XCA100 denotes the mole fraction of CA100 in the
organic phase.
It is evident that the mixing system has antagonistic
effects on La extraction from chloride medium.
Since the mixtures of CA100 and TBP, DEHEHP,
Cyanex923, Cyanex925 have different extraction
effects on REs, the separation of REs may be considꢀ
ered. If DA and DB represent the distribution ratios of
two metal ions (A and B) under the same extraction
conditions, the separation factor between A and B can
be expressed as:
0
0.01
0.02 0.03
Cyanex925], mol L
0.04
0.05
–1
[
Fig. 5. Extraction of RE3+ with Cyanex925. [RE3+] =
–3
5
.0
×
10 M, pH 3.0,
µ
= 0.3 M.
0.30
CA100
TBP
CA100 + TBP
0.25
0.20
0.15
0.10
0.05
0
0.2
0.4
0.6
XCA100
0.8
1.0
β
A/B
=
DA
/
DB
.
(7)
The further
metal ions be separated. The
CA100, CA100 + TBP, CA100 + DEHEHP, CA100 +
β
is from 1, the better can the two
3+
A/B
Fig. 6. Antagonistic extraction of La with CA100, TBP
3+
–3
β
values of REs in
A/B
and CA100 + TBP. [La ] = 5.0
×
10 M, pH 3.0, µ= 0.3 M,
[CA100] + [TBP] = 0.05 M.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 7 2011

1160
XIAO et al.
Separation factors between Y and lanthanoids with CA100 and its mixtures with TBP, DEHEHP, Cyanex923, Cyanex925a
Extractꢀ
CA100
CA100 + TBP
CA100 + DEHEHP CA100 + Cyanex923 CA100 + Cyanex925
ant
XCA100 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8
Y/La 0.3 0.5 0.5 0.6 1.7 1.6 1.1 0.6 8.2 3.9 0.8 0.5 1.9 3.1 2.0 1.3 1.9 3.0 3.8 1.2
Y/Ce 0.4 0.5 0.6 0.6 4.1 2.3 0.8 0.4 2.3 2.0 0.7 0.4 2.9 1.8 0.9 0.8 1.0 1.1 2.1 1.4
Y/Pr 0.6 0.6 0.6 0.7 2.8 1.5 0.6 0.5 4.5 1.7 0.6 0.5 4.1 2.9 1.8 1.5 2.2 3.6 3.7 1.5
Y/Eu 0.9 0.7 0.7 0.7 1.2 0.9 0.6 0.5 1.9 0.9 0.7 0.7 1.8 2.4 1.5 1.2 1.3 1.5 2.3 1.0
Y/Tb 1.0 0.9 0.8 0.9 5.4 6.0 3.1 2.3 1.4 1.3 1.3 1.3 2.2 2.7 1.9 2.0 1.8 1.9 1.6 1.6
Y/Ho 1.0 0.9 0.9 0.9 2.4 1.8 1.1 0.8 4.6 5.0 4.6 4.1 1.2 1.3 1.6 1.6 1.1 1.3 1.5 1.3
Y/Tm 1.1 1.1 1.1 1.1 1.0 1.1 0.6 0.7 0.9 0.9 0.6 0.5 1.1 1.4 1.6 2.2 0.9 1.0 1.4 1.8
Y/Lu 1.4 1.4 1.4 1.5 0.9 1.0 0.8 0.8 6.4 4.6 2.6 1.9 0.9 1.0 1.1 1.1 0.7 0.7 0.8 0.8
a
3+
10–3 M, pH 3.0,
[
RE ] = 5.0
×
µ
= 0.3 M. In single CA100 system, [CA100] = 0.05 M; In mixing system, [CA100] +
[neutral extractant] = 0.05 M.
Cyanex923, CA100 + Cyanex925 are shown in Table,
showing that the mixtures have some advantages when
used for the separation of REs compared with single
CA100 system. For instance, all the four mixtures have
higher separation abilities for Y/Tb and Y/Ho than
CA100, implying that the mixtures are feasible for the
separation of these rare earths.
ACKNOWLEDGEMENTS
The authors wish to thank Prof. Zhenfeng Cui and
Mr. Yunfeng Shi of Changchun Institute of Technoꢀ
logy.
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8
The extraction of rare earths, La, Ce, Pr, Eu, Tb,
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