COMPARISON OF DIFFERENT HYBRID MEMBRANE SYSTEMS
FOR REMOVAL OF Zn(II) AND Cu(II)
Grażyna Szczepańska, Piotr Szczepański, Marek Świątkowski, and Romuald Wódzki
Nicholas Copernicus University, Faculty of Chemistry
87-100 Toruń, 7 Gagarina St., Poland
E-mail: wodzki@chem.uni.torun.pl
1. INTRODUCTION
Purification of drinking and industrial water contaminated by toxic heavy metal ions
(e.g. Zn(II) and/or Cu(II)) can be carried out by applying some membrane methods. In
general, two membrane methods are nowadays considered as feasible in the recovery of
metals from dilute aqueous solutions, i.e. Donnan dialysis (DD- exploiting cation-exchange
membranes) [1], and pertraction with use of the selective liquid membranes (LM). However,
the industrial use of LM is limited due to its instability and short lifetime [2] whereas the DD
method sometimes appears to be unselective in respect to cations of similar valence. This can
be overcome by constructing hybrid polymer-liquid-polymer membrane systems [3,4] MHS
(or MHS[FLM] where FLM denotes the flowing liquid membrane) which combine the both
techniques. Additionally, the system with a liquid membrane can be coupled to a
pervaporation unit (MHS[FLM-PV]) that allows removal of water absorbed by the organic
phase (LM). Furthermore, in the same way, such different process as Donnan dialysis and
pertraction in the MHS can be arranged in series as a new integrated hybrid system: DDMHS[FLM-PV]. The aim of this study was to compare and develop the process of removal
and separation of Zn(II) and Cu(II) as performed in the systems with D2EHPA (di-(2ethylhexyl)phosphoric acid), Cyanex 302 (di-(2,4,4-trimethylpenthyl) thiophosphinic acid),
Acorga PT-5050 (5-nonylsalicyl-aldoxime) or newly synthesised macromolecular carriers.
2. EXPERIMENTAL
The first membrane system (A: MHS in Tab.1) consisted of three chambers in which
dense, hydrophilic, cation-exchange membranes (CEM) separated the liquid organic
membrane with a dissolved mobile carrier, from the external aqueous solutions. The second
one (B: MHS[FLM-PV], in Tab.1) exploited a flowing liquid membrane (FLM), i.e. an
organic liquid is continuously flowing between two cation-exchange membranes and two
additional pervaporation membranes (PV). The third system (C': DD-MHS[FLM-PV], in
Tab.1) integrates the MHS with classic Donnan dialysis technique (DD) and consists of a DD
module, pertraction module (MHS) and pervaporation unit (PV). The part of a cell
corresponding with DD contained mediating solution acting simultaneously as the stripping
solution for the DD process and the feed solution for the pertraction process. The external
aqueous solutions were sampled in time and the concentration of metals has been determined
with an atomic absorption spectrophotometer (Varian 20 ABQ). The operation conditions for
each system are specified in Tab.1. The aqueous feed solution in each case was prepared by
dissolving an appropriate amount of reagent grade Zn2+, Cu2+, Ca2+, Mg2+, K+ and Na+ nitrates
in twice distilled water. The fluxes (stripping rates) of ionic species have been determined
from the primary data in the form of the strip concentration vs. time dependence as a slope of
a linear part of the Q s  f ( t ) plot:
J M  Q s / t [eqv/cm2s]
(1);
(2)
Q s  z M M s , t Vs / 1000A s [eqv/cm2]
Qs denotes the amount of metal species of valence zM transported to the receiver after the time
t, through 1 cm2 of the stripping CEM area (As, cm2), Vs (cm3) is the volume of the stripping
solution, [M]s,t (mol/dm3) is the concentration of metal species at the time t. The separation of
cations was evaluated by standard separation coefficients α MΣM and fractional fluxes N:
k
z M k [ M ] k ,s
 MMk

z M k [ M ] k ,f
z
z
j k
j k
M i [ M ] j,f
(3);
N
M i [ M ] j,s
J Mk
J
 100 ,
[%]
(4)
M
Tab.1. Membrane systems and their operation conditions
System
Conditions
A
MHS
V
Composition
500 cm3
110-2 mol/dm3
V
Composition
-
V
Solvent
30 cm3
0,011 mol/dm3
D2EHPA, CYANEX 302,
ACORGA PT-5050
technical kerosene
distilled kerosene
V
Composition
30 cm3
1 mol/dm3 H2SO4
400 cm3
1 mol/dm3 H2SO4
Area
Type
13 cm2
FKS
Area
Type
-
Carrier
B
MHS[FLM-PV]
Feed solution
2,5 dm3
210-3 mol/dm3
Mediating soln.
-
C
MHS[FLM-PV]
C
DD-MHS[FLM-PV]
50000 cm3
110-3 mol/dm3
50000 cm3
110-3 mol/dm3
-
400 cm3
Liquid membrane
90 cm3
500 cm3
3
12 g/dm
0,010,1 mol/dm3
macromolecular
D2EHPA
carriers
1,2 dichloroethane
distilled kerosene
Stripping solution
50 cm3
400 cm3
0.5 mol/dm3 H2SO4
1 mol/dm3 H2SO4
Cation exchange membrane
28,3 cm2
200 cm2
NAFION 117
FKS
Pervaporation membrane
72,6 cm2
23 cm2
PERVAP 2201
PERVAP 2201
0,010,3 mol/dm3
H2SO4
500 cm3
0,1 mol/dm3
D2EHPA
200 cm2
FKS
23 cm2
PERVAP 2201
3. RESULTS AND DISCUSSION
System A
In order to check the MHS effectiveness, the dependence of system performance on
the carrier concentration in the liquid membrane was studied. Some representative results are
presented in Fig.1. High separation coefficients were found for Zn2+ in the MHS with Cyanex
302 and for Cu2+ with Acorga PT-5050. The use of Cyanex 302 instead of D2EHPA
considerably lowers the flux of calcium and leads to the effective separation of Zn 2+ over
Ca2+. In view of the results, the MHS can be considered as a basic unit for the removal of
Zn(II) and Cu(II) from liquid solution such as domestic water. The system can be applied in
order to diminish the concentration of Zn2+ and Cu2+ or other harmful heavy metals according
to pro-ecological requirements.
1.0e-9
1.0e-10
2
Flux [eqv./cm s]
2
Flux [eqv./cm s]
1.0e-10
1.0e-11
1.0e-12
a)
b)
1.0e-11
1.0e-12
1.0e-13
1.0e-13
1.0e-14
0.0
1.0e-14
0.0
0.2
0.4
0.6
0.8
1.0
3
D2EHPA concentration [mol/dm ]
0.1
0.2
0.3
0.4
0.6
0.5
3
Acorga PT-5050 concentration [mol/dm ]
Fig.1. Fluxes vs carrier concentration in MHS-BLM (system A) with D2EHPA (a) and Acorga PT-5050 (b) as a
carrier:  Cu(II),  Zn(II),  Ca(II),  Mg(II),  Na(I),  K(I),
System B
The experiments in the system B, were carried out using macroionophore of the
composition presented in Fig.2. The polymer [star shaped polymer: I arm(POE Mn=3370)[DGEEG]-II arm (POE, Mn=5440) with CH3O-(I) and –OP(O)(OH)2 (II) end-groups] has
been synthesized in Polish Academy of Science in Łódź [5]. The pertraction properties of this
carrier were compared with the properties of poly(ethylene glycol) (PEG6000, Mn=6000
g/mol)and poly(oxyethylene) bisphosphates (BFPEG6000, Mn= 6200 g/mol)
R
a:
P
P
R
P
R
R
P
R -CH3O
end groups
P -OP(O)(OH)2
end groups
PEG chain:
b: (HO)2P(O)O-(CH2CH2O)n-P(O)(OH)2
c:
HO-(CH2CH2O)n-H
Fig.2. Scheme of composition of STAR-SHAPED macroionophore (a), BFPEG6000 (b) and PEG6000 (c).
Data in Tab.2 show that the use of ionizable carriers results in overall fluxes higher
than PEG600. This indicates the counter-transport mechanism to be dominant in the case of
star shaped and BFPEG macroionophores.
Tab. 2. Stationary fluxes J of cations in the MHS[FLM-PV] system with various macroionophores
Carrier
Star shaped
BFPEG
PEG
Zn(II)
8,110-12
35,410-12
0,1610-12
Cu(II)
1,1610-12
16,1 10-12
0,04 10-12
Flux, Js  1012 (eqv./cm2s)
Ca(II)
Mg(II)
0,410-12
0,2210-12
0,9410-12
0,9710-12
-12
Nd.
0,0810
K(I)
3,410-12
3,1510-12
0,9910-12
Na(I)
0,4210-12
0,2110-12
0,0610-12
The separation characteristics for studied macroionophores indicate high separation
ability of the star-polymer towards Zn(II) and K(I) cations. Selectivity for Zn(II) is caused by
phosphate groups, as observed also for the simpler macroionophore (BFPEG6000). On the
other hand, both side arms: with –OCH3 and –OP(O)(OH)2 end groups of the star shaped
macroionophore can facilitate the pertraction of K+ similarly to PEG6000 when applied as a
selective carrier for K+ cation.
System C
The results (Tab.3.) indicate the preferential transport of Zn2+ cations, according to the
properties of D2EHPA used as the carrier in a liquid membrane. The fluxes decrease in the
following order: Zn2+ >> Ca2+ > Cu2+> Mg2+ > K+ > Na+, in all cases. Thus, the final effect of
the MHS[FLM-PV] system operation is the separation of Zn2+ from a multication mixture.
Tab.3. The effect of carrier concentration in system C: pH f=2,5; 1M H2SO4 in the strip solution
Concentration
of D2EHPA
[mol/dm3]
0,01
0,05
0,1
Striping rates, J (eqv./cm2s)
Fractional fluxes N (%)
Ca2+
Mg2+
Zn2+
Cu2+
5,3910-12
3,2010-14
6,7610-14
96.96
2,4010-10
67.74
1,6310-10
51.59
0.58
1,5810-11
4.46
3,5710-11
11.30
1.21
9,7110-11
27.40
1,1410-10
36.08
Na+
K+
3,1610-14
1,0010-14
2,8010-14
0,57
7,2710-13
0.21
3,0310-12
0.96
0.18
3,3710-14
0.01
1,0110-13
0.03
0.50
6,5610-13
0.18
1,1310-13
0.04
System C’
In order to check the influence of sulphuric acid concentration in the mediating acid
solution, its initial concentration was varied in the range from 0,01 to 0,3 mol/dm3. The values
of resulting fluxes are collected in Tab.4. It was found that separation ability of the system
towards Zn2+ depends highly on the concentration of mediating solution - the optimal results
are achieved at 0,05M H2SO4.
Tab.4. The effect of mediating solution concentration in system C’: pH f=2,5; 0,1M D2EHPA; 1M H2SO4 in the
strip solution
Concentration
of H2SO4 in
mediating sol.
0,3
0,1
0,05
0,03
0,01
Striping rates, J (eqv./cm2s)
Zn(II)
Cu(II)
-11
1,6410
9,2910-11
2,0310-10
1,7710-10
7,6710-11
-13
1,3110
1,6210-12
1,5110-11
2,9910-11
7,3510-12
Ca(II)
Mg(II)
-12
1,3510
1,4710-11
9,8610-11
1,4410-10
6,1310-11
-13
1,1810
1,8110-13
1,3710-12
2,2510-12
1,1910-12
Na(I)
K(I)
-13
1,2210
3,6210-14
4,3910-14
6,6710-14
4,0110-14
3,6310-13
5,2310-14
1,6110-13
1,6910-13
1,4110-13
4. CONCLUSION
The experiments proved that the cation exchange membranes applied in the MHS, and
in more advanced hybrid systems, prevent a loss of a carrier and contamination of external
aqueous solutions by an organic solvent of LM. The MHS system is easy to reconstruct,
resize and regenerate, without the loss of stability and ability to work over a long time period.
The MHS system enables the removal of Zn(II) and/or Cu(II) from dilute aqueous solutions
using the standard carriers (D2EHPA, Acorga PT-5050, Cyanex 302) or a new star-shaped
macroionophore. A moderate scale application, especially for the removal of Zn(II) and
Cu(II) from solutions in food industry and pharmacy can be recommended.
5. REFERENCES
[1] Wódzki R., Szczepański P., Sep. Purif. Technol., 22-23, 697, (2001).
[2] Wijers M. C., Wessling M., Strathmann H., J. Memb. Sci., 147, 117, (1998).
[3] Wódzki R., Sionkowski G., Sep. Sci. Technol., 30, 2763, (1995).
[4] Wódzki R., Sionkowski G., Poźniak G., Sep. Sci. Technol., 34, 627, (1999).
[5] Wódzki R., Świątkowski M., Łapienis G., React.Funct.Polym., 52, 149, (2002).