On Cadmium (II) Membrane-Based Extraction Using
Cyanex 923 as Carrier
A.M.Sastrea,*, F.J.Alguacilb,
M.Alonsob, F.Lopezb, A.Lopez-Delgadob
a,*
Department of Chemical Engineering, Universitat Politecnica de Catalunya,
E.T.S.E.I.B., Diagonal 647, E-08028 Barcelona, Spain.
E-mail: ana.maria.sastre@upc.edu
b
Centro Nacional de Investigaciones Metalúrgicas (CSIC), Avda. Gregorio Del Amo 8,
Ciudad Universitaria, 28040 Madrid, Spain. E-mail: fjalgua@cenim.csic.es
ABSTRACT
The facilitated transport of cadmium (II) from HCl medium by Emulsion Pertraction
Technique (EPERT), using Cyanex 923 (phosphine oxides mixture) as ionophore, is
investigated as a function of various experimental variables: hydrodynamic conditions,
concentration of cadmium (II) (5-100 mg L-1) and HCl (0.2-5 M) in the source phase,
carrier concentration (5-40 % v/v) and diluent in the organic phase. A model that
describes the transport mechanism is derived, consisting of diffusion through a source
aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and
the metal complexes through the membrane. The thickness of the source phase
boundary layer was calculated as 2.2x10-3 cm. The organic membrane diffusional
resistance (Δorg) and aqueous diffusional resistance (Δaq) were calculated from the
model, and their values were 1.0x107 s cm-1 and 347 s cm-1, respectively, whereas the
values of the bulk diffusion coefficient (Dorg,b) and diffusion coefficient (Dorg) also
calculated from the model were 4.8x10-9 cm2 s-1 and 1.3x10-9 cm2 s-1. The separation of
Cd(II) against Zn(II), Fe(III), Cr(VI) and Cu(II) and also the performance of the system
in relation with other extractants were evaluated.
Key Words: Emulsion pertraction technique; Transport; Cadmium (II); Cyanex 923.
INTRODUCTION
Cadmium is widely dispersed in the environment. This element occurs naturally in the
geosystem, and though, sometimes cadmium is a by-product in the production of metals
such as zinc and lead, cadmium is mostly found as chemical compounds of elements
2
such as oxygen, fluorine, chlorine and sulfur. The element and some of its compounds
have been widely used in the industry: plating, alloys, photography, photoengraving,
paints, batteries, etc. Besides of its uses, cadmium is considered as toxic.
Human exposures occur principally as inhalation of Cd-containing dust in industry
and orally as Cd-containing food and water in the general population. After uptake,
cadmium in blood is initially taken up by the liver and subsequently slowly redistributed
to the kidney where it is accumulate, resulting in various diseases; also Cd is considered
carcinogenic to humans.[1] Because of its toxicological properties, legislation implying
considerable restrictions in its use and in the discharge of Cd-bearing effluents has been
passed in a number of countries.
Several technologies can be used to remove this toxic metal from liquid effluents,
including precipitation, solvent extraction, ion exchange, etc., among these, liquid
membrane techniques have acquired an importance for its use in separation,
concentration or even analytical application. Though this technology is still in the
research or development stage, it holds a deserving position in the field of membrane
separations due to its advantages over conventional separation operations. Including in
the liquid membrane characteristics are their high specificity, low energy utilisation,
ease of installation, etc.
The different types of liquid membranes had been reviewed in the literature.[2,3]
Supported liquid membranes (SLMs) and emulsion liquid membranes (ELMs) are the
most commonly used. In SLMs, the extraction, stripping and regeneration of the organic
phase are combined in a single stage. Moreover, from the engineering and practical
standpoint, SLMs are of particular interest because of their simplicity.
3
The transport of Cd(II) from different aqueous solutions using these liquid membrane
technologies is reported in previous investigations (Table 1).[4-26]
Though these processes are normally effective, their use have been hampered by their
relatively instability, however, the introduction of the supported liquid membranes with
strip dispersion or emulsion pertraction technique (EPERT) apparently have solved the
stability problem. In this operation mode, the aqueous source solution, containing the
species to be extracted is into contact with one side of the support, whereas the aqueous
strip solution is dispersed in an organic solution, containing the corresponding carrier
and diluent, in a mixer and the emulsion formed is put into contact with the other side of
the microporous support. The continuous organic phase of the emulsion readily wets the
pores of the hydrophobic support and a stable liquid membrane supported in the pores
of the microporous support, similarly to that found in conventional SLMs, is formed.
Thus, this type of membrane can be considered as a conventional SLM with a constant
supply of the organic solution into the pores. Upon the operation is finished, the mixer
for the strip dispersion is switch off, and the dispersion is separated into the two phases,
the organic solution and the strip solution, which now contained the species, which was
extracted from the source solution, concentrated and separated from undesiderable
species. This strip solution can be now processed to obtain the final product of the
corresponding process.
Before scaling-up the technology in the form of other liquid membrane system (LMs)
configuration, i.e.hollow fiber modules, which is more adequate for industrial use since
it provides higher surface area to volume ratio, first laboratory studies which could
include a theoretical model of the LMs, are needed in order to design a more efficient
4
recovery process. In this role, flat-sheet SLMs configuration it is recognized as useful
for previous laboratory data.
Using this technique, this investigation presents a kinetic model of active transport of
Cd(II), from HCl aqueous medium, using Cyanex 923 (a commercially available
phosphine oxides mixture) dissolved in Solvesso 100. The organic membrane
diffusional resistance (Δorg) and the aqueous diffusional resistance (Δaq) were calculated
from the proposed model. The influence of hydrodynamic conditions and chemical
parameters were investigated in order to obtain efficient EPERT operation mode.
EXPERIMENTAL
Reagents and Solutions
The extractant Cyanex 923 was used as supplied by the manufacturer (CYTEC Ind.),
it contains different phosphine oxides.[27] The average molecular weight is 348 and the
density (20º C) is 800 kg m-3. The other extractants (Table 2) used in this work were
also used as supplied by the manufacturer. Solvesso 100 diluent was also used as
supplied by the manufacturer (ExxonMobil Chem. Iberia) and contains >99%
aromatics, boiling range 167-178º C and flash point 48º C; all other chemicals were of
AR grade.
A 1000 mg L-1 stock solution of Cd(II) was obtained by dissolving CdCl2 (Fluka) in
distilled water. The working solutions, containing various cadmium (II) concentrations
in 5 M HCl, were prepared by dilution of the stock cadmium solution in HCl-water
solution.
5
Apparatus and Procedure
The characteristics of the cell used in the present investigation were similar to those
described in a previous work.[28] The source and the organic/stripping phases emulsion,
though in fact is a pseudo emulsion, were mechanically stirred at 1100 and 750 rpm,
respectively, at 20±1ºC. The main characteristics of the supports used in the present
investigation were summarized in Table 3, once the membrane support was placed in
the cell, the source solution (200 mL) and the organic (100 mL) and stripping (100 mL)
phases were placed in their corresponding chambers and the operation begins. From the
initial moment of mixing (continuous organic phase and dispersed stripping phase), an
organic/stripping phases emulsion was formed, and providing adequate stirring speeds
in the source phase and in the emulsion phase, the membrane stabilizes similarly to
conventional flat-sheet supported liquid membrane operation, i.e. the organic phase
wets and it is retained into the micropores of the hydrophobic support by capillarity.
Membrane permeabilities were determined by monitoring metal concentration by
AAS in the source (or the stripping) phase as a function of time. The cadmium
concentration in the source phase was found to be reproducible within ±3%. The
permeation coefficient (P) was computed using
ln
CdIIt
CdII0

A
Vsource
Pt
(1)
where A is the effective membrane area (11.3 cm2), Vsource is the volume of the source
phase, [Cd(II)]t and [Cd(II)]0 are the concentration in the source phase at elapsed time t
6
and time zero, respectively. For the calculations of the cadmium metal-accompanying
permeabilities, the same eq. (1) was used.
The percentage of cadmium recovered in the stripping phase was determined using
%R 
Vsource
Vstripping
CdIIs
 100
CdII 0  CdII t
(2)
by analyzing the cadmium concentration in the stripping solution ([Cd(II)]s, after the
operation was stopped (typically 3 h) and the organic and the stripping phases were
separated.
RESULTS AND DISCUSSION
Influence of the stirring speed of the source solution
Previous experiments were carried out to establish adequate hydrodynamic conditions,
using the next phases and support, source phase: 10 mg L-1 Cd(II) and 2 M HCl;
membrane support: GVHP 4700; organic phase: 20% v/v Cyanex 923 in Solvesso 100;
stripping phase: water. The permeability of the membrane was studied as a function of
the stirring speed on the source solution side. The agitation of the organic/stirring
phases (O/S) emulsion was kept constant at 750 rpm. Constant permeabilities (P=
1.9x10-3 cm s-1) for stirring speeds in the range 800-1200 rpm was obtained.
Consequently, the thickness of the aqueous diffusion layer and the aqueous resistance to
mass transfer were minimized and the diffusion contribution of the aqueous species to
7
mass transfer process is assumed to be constant. Above 1200 rpm, the membrane phase
becomes unstable and the organic phase is loss from the membrane to the source phase
due to the excess of stirring speed.
Influence of HCl concentration in the source phase
To study the influence of the hydrochloric acid concentration in the source phase on
cadmium transport, a series of experiments were carried out at various HCl
concentrations, keeping other variables constant. Thus, the single metal transport
through the membrane of 10 mg L-1 Cd(II) from an aqueous source phase of varying
HCl concentrations was studied using water as strippant. Figure 1 shows that the
cadmium permeation increased as the HCl concentration of the phase was increased up
to 5 M (P= 3.0x10-3 cm s-1), whereas at HCl concentrations above 5 M the cadmium
permeation decreases, and this can be attributable to a competition between cadmium
and HCl. It is known that Cyanex 923 extracted mineral acids.[29]
Influence of cadmium (II) concentration in the source phase
The influence of Cd(II) concentration on the membrane permeation was also
investigated and the results are presented in Table 4. The results obtained revealed that
the metal permeation coefficient decreased with the increased of the initial metal
concentration up to 10 mg L-1 and then becomes constant, though the initial metal flux,
calculated as
J  PCd(II)TOTAL
(3)
8
increases with the increase of the cadmium concentration in the feed phase, being this in
accordance with the expected trend, since the flux of a solute varies in direct proportion
with solute concentration,[28,30] and hence, in this range of metal concentrations, the
permeation process is controlled by diffusion of cadmium species.
From experimental results, it is observed that from near 75 min, cadmium (II) was
being transported uphill against its concentration gradient, driven by the co-current
coupled transport of protons and chloride ions from the feed to the stripping phase.
Influence of the membrane diluent on the transport of cadmium
The characteristics of the organic phase diluent have an influence on the performance
of liquid-liquid extraction systems,[31] thus a similar effect may be observed in liquid
membranes.[32-35] A membrane diluent must fulfil a number of requirements, which are
described in the literature.[36,37]
Various commercial diluents for Cyanex 923 were investigated in the present EPERT
system. Figure 2 shows that the change in the diluent has little or no effect on metal
transport, and only when using xylene, a very slightly better cadmium transport is
achieved. Thus, in the present system, and against it what found in other various
systems, the change of the diluent of the organic phase which wets the membrane
support had apparently no influence on the transport of cadmium.
Influence of carrier concentration
9
The influence of the carrier concentration on cadmium transport was also investigated.
Table 5 shows the variation in the permeation coefficient when organic solutions
containing 5-40% v/v Cyanex 923 in Solvesso 100 were used. Lower concentrations of
carrier were investigated, and near no-transport was observed. The metal permeation
increased with the phosphine oxide concentration up to 20% v/v and then levels off, this
being typical of a process controlled by diffusion in the stagnant film of the source
phase.
Evaluation of the mass transfer resistances
In this EPERT operational device, the mass transfer of Cd(II) crossing the membrane
is described considering only diffusional parameters. The interfacial flux due to the
chemical reaction is neglected, as the chemical reactions seem to take place at the
interface source phase/membrane, whereas the membrane/receiving phase interface had
not been considered since this no exists as a such, and it has been suggested that
chemical reactions can be considered as occurring instantaneously relative to the
diffusional process.[30] Thus, a model of the mass transfer of cadmium (II) may be
derived by considering various steps:
i) diffusion of metal species from the bulk of source solution to the aqueous source
boundary layer,
ii) diffusion of protons and chloride ions from the bulk of source solution to the aqueous
source boundary layer,
iii) reaction between metal species, protons and chloride ions and carrier at the sourcemembrane interface,
10
iv) diffusion of metal-carrier complexes from the source-membrane interface through
the membrane,
v) stripping of metal species at the membrane-stripping phases pseudo emulsion and
diffusion of them to the bulk of the stripping solution,
vi) diffusion of the regenerated carrier back through the membrane to the feed –
membrane interface, after which the process is repeated.
Figure 3 shows a possible transport scheme for cadmium (II) using this EPERT. Such
a process is called coupled co-transport, where the difference in the counterion (protons
and chloride ions) concentrations between the source and stripping solution are used as
the driving force for metal transport.
The extraction of cadmium (II) by Cyanex 923 dissolved in Solvesso 100 has been
studied and described elsewhere.[38] The extraction equilibria at 5 M HCl (where
maximum cadmium extraction is achieved) can be described by the following reactions
and extraction constants
2

Cd aq
 2Cl aq
 2L org  CdCl 2  2L org
2


Cd aq
 H aq
 3Cl aq
 2L org  HCdCl 3  2L org
2


Cd aq
 2H aq
 4Cl aq
 2L org  H 2 CdCl4  2L org
K1 
CdCl2  2Lorg
Cd 2 aq Cl  aq2 Lorg2
 7.9  101
K1
(4)
K2
(5)
K3
(6)
(7)
11
K2 
HCdCl 3  2Lorg
Cd  H  Cl  L
2

aq
K3 
aq
 3
aq
2
org
H 2 CdCl3  2Lorg
Cd 2 aq H  aq2 Cl  aq4 Lorg2
 2.5x101
(8)
 7.9
(9)
where L is the extractant.
The cadmium (II) transport rate is determined by the rate of diffusion of cadmiumcontaining species through the source phase diffusion layer and the rate of diffusion of
these species through the membrane. Then, the flux of cadmium (II) crossing the
membrane may be first derived by applying Fick´s first diffusion law to the diffusion
layer in the feed phase side and to the membrane. The diffusional fluxes at the source
phase boundary layer, Jaq, and at the membrane phase, Jorg, can be expressed by the
following equations
J aq  aq1 Cd(II)TOT  Cd(II)i,TOT 




(10)

1
CdCl2  2Li,s  org1 HCdCl3  2Li,s  org1 H 2 CdCl4  2Li,s
J org  org

(11)
If the chemical reactions expressed by eqs. (4), (5) and (6) are assumed to be fast
compared to the diffusion rate, local equilibria at the interface are reached and
concentrations at the interface are related by eqs. (7), (8) and (9). At steady state,
12
Jaq=Jorg=J and by combination of Eqs. (7), (8), (9), (10) and (11), the next expression is
obtained
K L Cl   K L H  Cl   K L H  Cl  Cd(II)
J
   K L Cl   K L H  Cl   K L H  Cl  
1
 2
aq
2
org
org
aq
1
2
org
2
 2
aq
2
org
 3
aq

aq
2
3

2
org
aq
2
org
 3
aq
 2
aq
3
 4
aq
 2
aq
2
org
TOT
 4
aq
(12)
where Δorg and Δaq are the transport resistances due to diffusion through the membrane
and to diffusion by the source phase boundary layer, respectively, and [Cd(II)]TOT is the
total metal concentration in the feed phase. The permeability coefficient can be written
as
P
K L Cl   K L H  Cl   K L H  Cl  
  K L Cl   K L H  Cl   K L H  Cl  
1
 org
aq
2
org
1
 2
aq
2
org
2
 2
aq
2
org
2
 3
aq

aq
2
org

aq
3
 3
aq
2
org
3
 2
aq
2
org
 4
aq
 2
aq
 4
aq
(13)
This expression combines the equilibrium and diffusion parameters involved in the
cadmium (II) transport process through a supported liquid membrane containing
Cyanex 923 in Solvesso 100 as carrier.
From the above, and to determine the value of the resistances to the mass transfer, the
next expression, derived from eq. (13), has been used
1
  aq 
2
P
K 1 Lorg Cl 
 
2
aq
 org
  Cl 
 K 2 Lorg H 
2
aq
 3
aq
  Cl 
 K 3 Lorg H 
2
2
aq
 4
aq
(14)
or
 org
1
  aq 
P
ABC
(15)
13
Thus, by plotting 1/P versus 1/A+B+C for different carrier concentrations and 5 M
HCl, a straight line should be obtained with slope Δorg and intercept Δaq. From data
obtained in the present work, the values of Δorg and Δaq calculated from the proposed
model are 1x107 and 347 s cm-1, respectively. Assuming a value of 6.5x10-6 cm2 s-1 for
Daq, a value of 2.2x10-3 cm is obtained for daq (thickness of the aqueous boundary
layer). On the other hand, the calculated value of the diffusion coefficient (membrane
phase) was 1.3x10-9 cm2 s-1.
The diffusion coefficient of the cadmium-complexes in the bulk of the membrane
contained-organic phase (Dorg,b) can be evaluated from the diffusivity in the membrane
(Dorg) with micropores from the following expression[39]
D org 

D org,b
2
(16)
The value of Dorg,b was found to be 4.8x10-9 cm2 s-1. It should be noted that in the
present system, Dorg presents a lower value than that of the bulk diffusion coefficient,
this is attributable to diffusional resistance caused by microporous thin membrane
placed between the source and emulsion phases.
Influence of the membrane support
Three membranes (Table 3) with different characteristics were experimented in order
to study their influence on cadmium transport. In Table 6, the obtained flux (eq. (3)) are
14
given, it can be seen that the fluxes values are of the same magnitude order, though a
slightly better cadmium transport is achieved when FGLP support is used.
Selectivity of Cd-Cyanex 923 system against other metals
Since cadmium-bearing effluents are produced in a number of industries, it is
interesting to compare the performance of the present system against the presence of
other heavy metals in the wastewater. Table 7 shows results obtained in the transport of
cadmium (II) when the source phase also contained other accompanying metals. It can
be seen that within the experimental conditions, cadmium (II) is not always transported
preferably against the other metals presented in the initial source phase. The separation
factor cadmium-metal, βCd/M, defined as the ratio of permeabilities cadmium-metals:
 Cd / M 
PCd
PM
(17)
shows the possibilities of the separation of cadmium from other metals presented in the
source phase, using Cyanex 923 dissolved in Solvesso 100 as carrier, with cadmium (II)
transported in preference to Cu(II) and Cr(VI), whereas Fe(III) and Zn(II) are better
transported that Cd(II).
Cadmium transport using other carriers: a comparison
The performance of the system Cyanex 923-Solvesso 100 on cadmium transport has
been compared against other commercially available extractants (Table 2) using the
15
same experimental conditions. Table 8 shows the results of this study. It can be seen
that a slight better transport is achieved when Aliquat 336 and Cyanex 923 extractants
are used, though their performance is comparable to that of Hostarex A327. On the
other hand, when Primene 81R is the extractant presented in the organic phase,
cadmium is poorly transported through the membrane.
Cadmium stripping
As it has been noted along the work, water was used as stripping solution for this
system, and some of the results obtained from this study are summarized in Table 9,
along with the experimental conditions used in any case. It can be seen that in most of
the investigation more than 90% cadmium is recovered in the stripping phase with a
two-fold concentration factor, though it should be noted here, the poorly stripping yield
presented by Aliquat 336 in comparison with that of Cyanex 923, being this probably
attributable to the different cadmium-extraction mechanisms that both reagents
presented: ion exchange versus solvation, respectively.
ACKNOWLEDGEMENT
To the CSIC (Spain) for Project 2006CL0001.
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Zn2+ and Cd2+ from sulfate media using organophosphorous acids as mobile carriers. J.
Chem. Technol Biotechnol. 2004, 79, 140.
24. Swain, B.; Sarangi, K.; Das, R.P. Effect of different anions on separation of
cadmium and zinc by supported liquid membrane using TOPS-99 as mobile carrier. J.
Membr. Sci. 2006, 277, 240.
25. Huynh, H.; Tanaka, M. Removal of Bi, Cd, Co, Cu, Fe, Ni, Pb and Zn from an
aqueous nitrate medium with bis (2-ethylhexyl)phosphoric acid impregnated Kapok
fiber. Ind. Eng. Chem. Res. 2003, 42, 4050.
26. Luo, F.; Li, D.Q.; Wu, Y.L. Extraction and separation of cadmium (II), iron (III),
zinc (II) and europium (III) by Cyanex 302 solutions using hollow fiber membrane
modules. Solvent Extr. Ion Exch 2004, 22, 105.
27. Dziwinski, E.; Szymanowski, J. Composition of CYANEX 923, CYANEX 925,
CYANEX 921 and TOPO. Solvent Extr. Ion Exch. 1998, 16, 1515.
19
28. Alguacil, F.J.; Alonso, M. Separation of zinc (II) from cobalt (II) solutions using
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29. Alguacil, F.J.; López, F.A. The extraction of mineral acids by the phosphine oxide
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1984.
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correlation with transport data obtained from supported liquid membrane studies.
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mobile carrier. J. Chem Technol. Biotechnol. 1988, 42, 3.
21
Table 1. Selected carriers and aqueous systems used in liquid membranes for cadmium
transport.
a
Carrier
Aqueous feed
Reference
Tricaprylamine
chloride
[4]
Tri-n-octylamine
chloride
[5-7]
Cyanex 302
phosphoric acid
[8,9]
Aliquat 336
HCl
[10-12]
TBP
chloride
[13]
TBP
phosphoric acid
[14]
Kelex 100
pH>6
[15]
Cyanex 923
HCl/H3PO4
[16]
Polycyclic-carboxyl poliether derivative
acidic
[17]
DIPSA and TIBPS mixturea
pH 2-5
[18]
Cyanex 923
HCl
[19,20]
D2EHPA
sulfate
[21-24]
D2EHPA
nitrate
[25]
Cyanex 302
acidic
[26]
DIPSA= 3,5-diisopropylsalicylic acid, TIBPS= triisobutylphosphate sulfide.
22
Table 2. The extractants used in EPERT for cadmium transport.
Type of carrier
Name
Active substance
Manufacturer
Basic
Aliquat 336
Quaternay ammonium salt
Fluka
Hostarex A324
Tertiary amine
Hoechst
Amberlite LA2
Secondary amine
Fluka
Primene 81R
Primary amine
Rohm and Haas
Tributylphosphate
Phosphoric ester
Fluka
Neutral
Table 3. Characteristics of the support used in EPERT for cadmium transport.
Thickness (dorg)
Porosity (ε)
μm
%
GVHP04700
125
75
1.67
0.22
HVHP04700
125
75
1.67
0.45
FGLP04700
175
70
1.86
0.22
Support
Tortuosity (τ)
Pore size
μm
23
Table 4. Influence of initial cadmium (II) concentration on metal transport.
[Cd(II)] mg L-1
Px103 cm s-1
Jx107 mol cm-2 s-1
5
4.6
0.41
10
3.0
0.54
50
3.0
2.7
100
3.0
5.4
Source phase: Cd(II) in 5 M HCl. Membrane support: GVHP04700. Organic phase: 20 % v/v Cyanex 923
in Solvesso 100. Stripping phase: water.
Table 5. Influence of carrier concentration on cadmium transport.
[Cyanex 923] % v/v
Px103 cm s-1
5
0.17
10
0.62
15
0.70
20
3.0
40
3.0
Source phase: 10 mg L-1 Cd(II) in 5 M HCl. Membrane support: GVHP04700. Organic phase: Cyanex
923 in Solvesso 100. Stripping phase: water.
24
Table 6. Influence of membrane support on cadmium transport.
Support
Px103 cm s-1
GVHP04700
3.0
HVHP04700
3.4
FGLP04700
3.7
Source phase: 10 mg L-1 in 5 M HCl. Organic phase: 20 % v/v Cyanex 923 in Solvesso 100. Stripping
phase: water.
Table 7. Cadmium (II) transport in presence of different metals (binary solutions).
System
Px103 cm s-1
Cd(II)
3.0
Cd(II)
2.8
Zn(II)
3.2
Cd(II)
3.0
Cr(VI)
0.41
Cd(II)
2.7
Fe(III)
3.7
Cd(II)
3.2
Cu(II)
0.28
ΒCd/M
0.88
7.3
0.73
11.4
Feed phase: 10 mg L-1 each metal in 5 M HCl. Membrane support: GVHP04700. Organic phase: 20% v/v
Cyanex 923 in Solvesso 100. Stripping phase: water.
25
Table 8. Results on the transport of cadmium (II) using various extractants.
Extractant
Px103 cm s-1
Aliquat 336
3.0
Hostarex A327
2.8
Amberlite LA2
1.3
Primene 81 R
0.09
Cyanex 923
3.0
Tributylphosphate
0.97
Source phase: 10 mg L-1 Cd(II) in 5 M HCl. Membrane support: GVHP04700. Organic phase: 20 % v/v
extractant in Solvesso 100. Stripping phase: water.
26
Table 9. Cadmium recovery in the stripping phase under various experimental
conditions.
Source phase
Organic phase
% Cd (Metal)
stripped
10 mg L-1 Cd in 2 M HCl
20 % v/v Cyanex 923b
92
10 mg L-1 Cda
20 % v/v Cyanex 923b
98
50 mg L-1 Cda
20 % v/v Cyanex 923b
99
100 mg L-1 Cda
20 % v/v Cyanex 923b
60
10 mg L-1 Cda
20 % v/v Cyanex 923 in n-heptanec
93
10 mg L-1 Cda
20% v/v Cyanex 923 in n-decanec
93
10 mg L-1 Cda
20% v/v Cyanex 923 in xylenec
99
10 mg L-1 Cda
20 % v/v Cyanex 923 in cumenec
99
10 mg L-1 Cda
10 % v/v Cyanex 923b
99
10 mg L-1 Cda
40 % v/v Cyanex 923b
87
10 mg L-1 Cda
20 % v/v Amberlite LA2b
99
10 mg L-1 Cda
20 % v/v Hostarex A324b
99
10 mg L-1 Cda
20 % v/v Aliquat 336b
30
10 mg L-1 Cda
20 % v/v Cyanex 923d
97
10 mg L-1 Cda
20 % v/v Cyanex 923e
98
10 mg L-1 each Cd and Fea
20 % v/v Cyanex 923b
99 (4 Fe)
10 mg L-1 each Cd and Zna
20 % v/v Cyanex 923b
99 (70 Zn)
10 mg L-1 each Cd and Cra
20 % v/v Cyanex 923b
98 (4 Cr)
10 mg L-1 each Cd and Cua
20 % v/v Cyanex 923b
99 (29 Cu)
a
In 5 M HCl.
b
In Solvesso 100 and membrane GVHP04700. c Membrane GVHP04700.
100 and membrane FGLP04700. e In Solvesso 100 and membrane HVHP04700.
d
In Solvesso
27
Figure 1. Influence of HCl concentration (source phase) on cadmium transport. Source
phase: 10 mg L-1 Cd(II) in HCl. Membrane support: GVHP04700. Organic phase: 20 %
v/v Cyanex 923 in Solvesso 100. Stripping phase: water.
Figure 2. Influence of the diluent of the organic phase on cadmium transport. Source
phase: 10 mg L-1 Cd(II) in 5 M HCl. Membrane support: GVHP04700. Organic phase:
20 % v/v Cyanex 923 in the diluent. Stripping phase: water.
Figure 3. Schematic view of EPERT using Cyanex 923 as carrier. L: Cyanex 923.
28
Fig.1
29
Fig.2
30
Fig.3