Available online at www.sciencedirect.com
Chinese Chemical Letters 22 (2011) 1095–1098
www.elsevier.com/locate/cclet
Study on supported combined liquid membrane containing
HEH(EH)P and HNO3 for trivalent gadolinium transfer
Liang Pei a,b,*, Li Ming Wang b
a
Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research,
Chinese Academy of Sciences, Beijing 100101, China
b
Faculty of Water Resources and Hydraulic Power, Xi’an University of Technology, Xi’an 710048, China
Received 27 December 2010
Abstract
A novel kind of supported combined liquid membrane (SCLM) has been studied for the Gd(III) transfer. SCLM contained
polyvinylidene fluoride membrane (PVDF) as the liquid membrane support and renewal solution including HNO3 solution as the
stripping solution and 2-ethyl hexyl phosphonic acid-mono-2-ethyl hexyl ester (HEH(EH)P) as the carrier dissolved in kerosene.
The mixed solution of carrier and kerosene was membrane solution. The optimum transport conditions of Gd(III) were that
concentration of HNO3 solution was 4.00 mol/L, concentration of carrier was 0.16 mol/L, and volume ratio of membrane solution to
stripping solution was 30:30 of the renewal phase, and pH value was 4.80 of the feed phase. Under the optimum condition studied,
when initial concentration of Gd(III) was 1.00 104 mol/L, the transfer rate of Gd(III) was 96.8% during 130 min.
# 2011 Liang Pei. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Supported combined liquid membrane; 2-Ethyl hexyl phosphonic acid-mono-2-ethyl hexyl ester; Renewal phase; Gadolinium
Rare earth metal has extensive applications in many respects [1]. As the applications became more and more
extensive in the production and life, it is very necessary to separate and enrich the rare earth element. Many
organizations at home and abroad have been conducting researches in recent years [2–6].
Transfer of rare earth metals with liquid membrane was characterized by a short process, high speed, great
enrichment ratio, little reagent-consuming and low cost, which has broad industrial application prospect. In china, the
research in this area began in the early 1980s. Organic solvents to extract liquid membrane system of rare earth metal
ions were carried with kerosene or common sulfonated kerosene, supporter used D2EHPA, PC-88A, TBP, etc., internal
phase used H2SO4, HCl, H3PO4, etc. Leaching liquid of rare earth can be grouped, purified, separated and other
operations according to the need [7].
This is a new liquid membrane process with several advantages: increased stability of the membrane, reduced costs,
increased simplicity of operation, extremely efficient stripping of the target species from the organic phase to obtain
high flux and a high concentration of the recovered target species in the aqueous stripping solution. The effect of
* Corresponding author at: Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural
Resources Research, Chinese Academy of Sciences, Beijing 100101, China.
E-mail address: [email protected] (L. Pei).
1001-8417/$ – see front matter # 2011 Liang Pei. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2011.03.020
[(Fig._1)TD$IG]
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L. Pei, L.M. Wang / Chinese Chemical Letters 22 (2011) 1095–1098
Fig. 1. Scheme of the SCLM process transfer experiments.
various experimental parameters on the transfer of rare earth gadolinium(III) ions was investigated. Although the
metal ions transfer by SLM containing the same carrier HEH(EH)P has been extensively studied, there were not many
researches about SCLM for transfer of rare earths.
1. Theoretical analysis
Fig. 1 is the apparatus of SCLM process. The co-transfer involves various (equilibrium) reactions, which are
described below: (a) Gd(III) diffuses from the feed phase to interface between feed phase and membrane. (b) In the
membrane phase near interface between feed phase and membrane, the extraction of Gd(III) from the feed solution
with carrier HEH(EH)P (such as (HR)2) in kerosene can be expressed as chemical equation I of Fig. 1 [3,8]. (c) The
metal-complex (GdR3(HR)3) diffuses through the membrane. (d) In the stripping side near interface between renewal
phase and membrane, GdR3(HR)3 dissolves in the membrane solution and Gd(III) are stripped by stripping agent. At
the drop interface, Gd(III) in the organic phase interchanges H+ in the stripping phase, then Gd(III) diffuses to the bulk
of the stripping phase and the extractant is regenerated. The stripping reaction can be written as chemical equation II of
Fig. 1. (e) Carrier HEH(EH)P returns from interface between renewal phase and membrane to interface between feed
phase and membrane.
The equation for permeability coefficient can be defined as [3]
Qjt ¼
eADe K ex ½ðHRÞ2 3 C f
tl½Hþ 3
l2
t
6De
(1)
In previous study, we obtained [8–11]
ln
Ct
A
¼ Pc t
Vf
C0
(2)
where Kex stands for extraction equilibrium constant, A stands for membrane surface, Vf represents the volume of feed
phase, Cf represents the concentration of Gd(III) of the feed phase, l stands for the thickness of the membrane, De
stands for the diffusion coefficient of Gd(III) in the membrane, t and e stand for the tortuosity and porosity of
membrane, respectively. C0 and Ct stand for the concentrations of Gd(III) of the feed phase at t = 0 and t = t,
respectively.
2. Experimental
2-Ethyl hexyl phosphonic acid-mono-2-ethyl hexyl ester (HEH(EH)P), Gd(III) acetate (Gd(CH3COO)34H2O),
acetic acid glacial and sodium acetate anhydrous(HAc-NaAc), arsenazo III (C22H18As2O14N4S2), hydrochloric acid
(HCl), sulfate acid (H2SO4), nitric acid (HNO3) and kerosene were dissolved by deionized water.
All the experiments were conducted using the self-designed systems, which consisted of two-compartment cells
and two motor stirrers that can shift gears. The volume of one cell was 80 cm3. The two cells were separated by the
polyvinylidene fluoride microporous film as porous support with porosity, pore size, tortuosity of 75, 0.65 mm and
1.67, respectively. The effective area of membrane was 12 cm2.
The metal solution was prepared by dissolving the required amount of Gd(CH3COO)24H2O. The renewal phase was
the mixture of aqueous solution containing HNO3 solution and membrane solution. The membrane solution was prepared
by dissolving of HEH(EH)P in kerosene. The PVDF support, which was made in Shanghai, China, was pre-wetted with
[(Fig._2)TD$IG]
L. Pei, L.M. Wang / Chinese Chemical Letters 22 (2011) 1095–1098
1097
-ln(ct/c0)
3
pH=3.0
pH=4.0
pH=4.8
2
pH=3.5
pH=4.4
pH=5.0
1
0
0
50
100
t/min
150
Fig. 2. Effect of pH of the feed phase on transfer of Gd (III).
the required amount of membrane solution more than 5 h in order to make the pores filled with carriers enough. The
experiments were performed in the pH range of 3.3–4.5. The pH value of each experiment of the feed phase was kept
constant by buffer solutions during other conditional experiment.
The Gd(III) concentration was analyzed with spectrophotometric method (652 nm), using arsenazo III as the
indicator. And a digital precision ionometer model PHS-3C with a combined glass electrode was used for pH
measurements (0.01 pH). The pH meter was standardized against 4.00, 6.86 and 9.14 standard buffer solutions.
3. Results and discussion
Based on mechanism of mass transfer process, the concentration difference between feed phase and renewal phase
is the driving power of mass transfer process. Stronger power will promote the transfer of Gd(III). Equally, the greater
the pH value of the feed phase is, the more efficient the effect of Gd(III) transfer is. The initial experimental conditions
were that ratio of membrane solution to stripping solution of the renewal phase was kept constant at 30:30, initial
concentration of Gd(III) was adjusted to 1.00 104 mol/L of the feed phase, concentration of HNO3 solution was
adjusted to 4.00 mol/L and concentration of carrier was adjusted to 0.16 mol/L of the renewal phase. The results are
shown in Fig. 2. So we chose pH of 4.80 as the optimum pH condition of the feed phase during the following
experiments.
The effect of volume ratio of membrane solution to stripping solution, HNO3 solution concentration, different
[(Fig._3)TD$IG]stripping agents and carrier concentration of the renewal phase on Gd(III) transfer were studied in this experiment.
b
3
2
10:50
20:40
40:20
50:10
1
0
3
2
5.0mol/L
6.0mol/L
1
0
0
50
2.0mol/L
3.0mol/L
4.0mol/L
30:30
-ln(ct/c0)
-ln(ct/c0)
a
100
150
0
nitric acid(4mol/L)
sulfate acid(2mol/L)
hydrochloric acid(4mol/L)
-ln(ct/c0)
-ln(ct/c0)
d
4
3
2
1
0
100
150
Time (min)
Time (min)
c
50
4
0.036mol/L
0.065mol/L
0.100mol/L
0.160mol/L
0.230mol/L
3
2
1
0
50
100
Time(min)
150
0
0
50
100
150
Time (min)
Fig. 3. Effect of other factors of the renewal phase on transfer of Gd(III): (a) volume ratio of membrane solution to stripping solution, (b)
concentration of HNO3 solution, (c) different stripping agents, (d) concentration of carrier.
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L. Pei, L.M. Wang / Chinese Chemical Letters 22 (2011) 1095–1098
These effects on transfer of Gd(III) is shown in Fig. 3. So we chose 30:30 as the optimum volume ratio of membrane
solution to stripping solution, 4.00 mol/L as the optimum concentration of HNO3 solution, HNO3 as the optimum
stripping agent and 0.16 mol/L as the optimum carrier concentration.
4. Conclusions
Supported combined liquid membrane (SCLM) with HEH(EH)P as carrier for transfer of Gd(III) has been
studied. The optimum conditions of Gd(III) transfer in the SCLM system were that the concentration of HNO3
solution was 4.00 mol/L, volume ratio of membrane solution to stripping solution was 30:30, the concentration of
carrier was 0.16 mol/L of the renewal phase, pH value was 4.80 of the feed phase. When initial concentration of
Gd(III) was 1.00 104 mol/L, the effect of transfer of Gd(III) was very obvious in the optimum condition and
the transfer rate of Gd(III) was up to 96.8% during the transfer time of 130 min.
Acknowledgments
This work is financially supported by the Foundation for Planning project of West Action of Chinese Academy of
Sciences (No. KZCX2-XB2-13), the National Natural Science Foundation of China for Young Scientists (No.
41001131; No. 51009126) and Research Fund for Excellent Doctoral Thesis of Xi’an University of Technology (No.
602-210805; No. 602-210804).
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