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Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell
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Chemical Engineering Research and Design journal homepage: www.elsevier.com/locate/cherd
Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell Kahina Annane a , Amar Sahmoune a , Patrice Montels b , Sophie Tingry b,∗ a
Equipe de Recherche Matériaux et Procédés pour l’Environnement, Université Mouloud Mammeri Tizi-Ouzou, Algeria b Institut Européen des Membranes – ENSCM/UM2/CNRS 5635, IEM/UM2, CC 047, Place Eugène Bataillon, F-34095, Montpellier Cedex 5, France
a b s t r a c t In this work, membrane transport of cadmium ion was explored through a polymer inclusion membrane (PIM) in micro-system. The system was composed of a flat sheet membrane sandwiched between donor and acceptor aqueous phases that flow in serpentine microchannels built in Teflon plates. The PIM was composed by cellulose triacetate as polymer base, Aliquat 336 as carrier and o-nitrophenyl octyl ether as plasticizer. The potential of the system was demonstrated from continuous measurement of Cd(II) collected in the aqueous phases and analyzed by atomic absorption spectroscopy. The reported on-chip PIM extraction focused on proof-of-principle studies based on the system optimization from operational parameters affecting the performance. Enrichment factors (EF) were close to 11% and 100% for 1 h and 8 h of extraction experiment, respectively, at flow rates of 3 mL min−1 . Compared with conventional cell, our results showed the feasibility of PIM in micro device to achieve efficient Cd ions extraction. The applicability of the device was briefly illustrated by extraction of metal ions mixture from aqueous solutions. © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Microchip; Polymer inclusion membrane; Aliquat 336; Cadmium(II) extraction
1.
Introduction
The advantages of micro devices are based on their small dimensions and enhanced interfacing area/volume ratios that contribute both
studied. Several authors have described the efficient use of the Aliquat
to the reduction of solvent and chemicals consumption and of extraction time of the analysis. The integration of membranes into micro channel-based devices
336 in emulsion membrane extraction (ELM) (Kumbasar, 2008), in bulk liquid membrane (Dalali et al., 2012), in supported liquid membrane
has been recently reviewed (Jong et al., 2006). Membranes are nowadays involved in a wide range of industrial applications as selective barriers
The extraction and the separation of numerous metals by liquid and affinity membranes containing Aliquat 336 as carrier have been widely
(SLM) (Bhatlurietal et al., 2014; Lv et al., 2007; Fontàs et al., 2005), and
between fluid flows for separation, concentration and removal of ana-
in plasticized membrane (PPM) (Gherasim and Bourceanu, 2013; Fontàs
lytes, the driving-force of the separation being a difference in activity (Nath, 2008; Strathmann, 1981). Membrane extraction systems based on liquid membranes have been down-scaled to be implemented into
et al., 2007; Kebiche-Senhadji et al., 2008; Nghiem et al., 2006; Wang et al., 2000, 2005; Juang et al., 2004) for separating or recovering cadmium ions from mixture of metal ions. In order to strip efficiently metal ion species from the membrane to the receiving phase and to avoid low transport time and instability of membrane, several issues have been considered such as the integration of the membranes in microchips for
microchip devices to control, manipulate, and analyze flows in submillimeter dimensions. Several groups have developed micro-devices for effective extraction of organic compounds (Surmeian et al., 2002)
carrying out extractions, separations and detections with high resolution and sensitivity (Jayawardane et al., 2013; Zhang et al., 2011, 2012;
and metal ions (Maruyama et al., 2004), from a three-layer of immiscible fluids (water/organic solvent/water) formed in a microchannel. The separation of the components was based on a difference in sol-
Wang et al., 2005).
ubility in the liquid membrane phase, and could be enhanced by the
∗
Corresponding author. Tel.: +33 04 67 14 91 57; fax: +33 04 67 14 91 19. E-mail address: [email protected] (S. Tingry). Received 23 June 2014; Received in revised form 19 September 2014; Accepted 5 October 2014 http://dx.doi.org/10.1016/j.cherd.2014.10.004 0263-8762/© 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: Annane, K., et al., Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.10.004
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presence of complexing agents to reach high selectivities (Maruyama et al., 2004). To avoid the instability of liquid–liquid interfaces, membrane based-micro systems have been also developed from solid membranes. These devices were based on a three-phase system containing a supported liquid membrane (SLM) in contact with both donor and acceptor solutions flowing through microchannel structures. SLMs consisted of commercial microporous polymeric support impregnated with an organic solution that may contain extractants as selective complexing agents (Parhi, 2013). These membranes have been widely used in macrosystems for transport and extractions of metal ions (Parhi, 2013; Danesi, 1984) and neutral organic species (Hassoune et al., 2009; Di Luccio et al., 2002; Rios et al., 2002) from aqueous phases. However, a few works have reported on SLM based micro-chips, applied to the enrichment of haloacetic acids from water (Wang et al., 2005), to the arsenic (V) extraction (Hylton and Mitra, 2008), and to the recovery of nonpolar basic drugs (Payan et al., 2012; Petersen et al., 2010, 2011). In such systems, the membrane was clamped between two microchannels, and sample solutions were delivered continuously to the microchannels by micro syringe pumps. Due to the specific design of these systems, the performances of the analysis were affected by operational parameters such as phase flow rates and microchannel dimensions (Petersen et al., 2011; Wang et al., 2005). As demonstrated by Wang et al. (2005), micro-devices designed with shallower acceptor channels (100 m) provided more concentrated extract that enhanced the enrichment factor of haloacetic acids to 65. In another works, Petersen et al. (2010, 2011) have designed on-chip electro membrane extractions based on the control of the electrical potential to adjust the magnitude and the direction of the transport across the membrane, and have shown the crucial role of the flow rate of the fluids to increase the extraction recoveries to 65–86% for the different analytes. To avoid the short lifetime of SLMs caused by the progressive leakage of both solvent and extractant from the membrane, polymer inclusion membranes (PIMs) are a good alternative (Nghiem et al., 2006). These membranes are obtained by casting a solution containing a selective extractant, a plasticizer and a base polymer such as poly(vinyl chloride) (PVC) or cellulose triacetate (CTA) to form a thin, flexible and stable film (Hayashita et al., 1995). The resulting selfsupporting membrane can be used to selectively separate the solutes of interest in a similar fashion to that of SLMs with the advantage of excellent stability over the time (Vázquez et al., 2014; Cho et al., 2011; Kebiche-Senhadji et al., 2008; Fontás et al., 2005; Juang et al., 2004). These membranes seem homogeneous at the macro level although it
2.
Experimental
2.1.
Reagents preparation
Cadmium(II) chloride (CdCl2 ), sodium chloride (NaCl), perchloric acid (HClO4 ), chloroform (CHCl3 ), cellulose tri acetate (CTA) and 2-nitro phenyl octyl ether (NPOE) were purchased from Fluka of analytical grade reagents and were used without further purification. The commercial carrier Aliquat 336 (tricaprylmethyl ammonium chloride R4 N+ Cl− ) was from Aldrich and used as received. All the aqueous solutions were prepared by dissolving the reagents in distilled water.
2.2.
Membrane preparation
The polymer inclusion membrane (PIM) was prepared by a procedure already described (Fontás et al., 2005). Amounts of CTA (200 mg), NPOE plasticizer (0.3 mL) and extractant Aliquat 336 (32 mmol L−1 equivalent to 34% weight to the total PIM weight) were dissolved in chloroform (20 mL) and stirred during 5 h in order to ensure the complete dissolution. The solution was poured in 9.5 cm diameter covered circular glass Petri dish and the solvent was allowed to evaporate over 24 h at 25 ◦ C. The resulting polymer film was then separated from the bottom of the glass Petri dish by immersion in cold water. The membrane was cut into small pieces of approximately 4.6 cm2 that were placed between two microchannels. The membrane sample was viewed using scanning electron microscopy at 500× magnification (HITACHI S4500 analyzer). As observed in Fig. 1, the membrane presents a homogenous appearance and thickness approximately of 84 m.
2.3.
Fabrication of the PIM micro device
The membrane extraction device (Fig. 1) was composed of two rectangular serpentine microchannels micromachined in our laboratory (European Institute of Membrane) on two separate Teflon blocks using a vertical numerical milling machine (HAAS TM2). The two blocks with the microchannels were face
has been suggested that they are composed of liquid micro-domains, at optimized extractant concentration, creating continuous channels connected between the two interfaces (Fontàs et al., 2007). The first use of a PIM in a flow injection analysis (FIA) has been reported for on-line separation of Zn(II) in the presence of other metals by Zhang et al. (2011). The PIM was obtained from the base polymer PVC and with the di(2-ethylhexyl) phosphoric acid (D2EHPA) as extractant. The FIA system was optimized with respect to flow rates and compositions of donor and acceptor streams. The system was further studied as function of the temperature and sonication effect to enhance mass transfer process in the PIM extraction (Zhang et al., 2012). This study reports on cadmium extraction under flow conditions by a PIM-based micro-chip. The PIM is composed by cellulose triacetate as polymer base, Aliquat 336 as carrier and o-nitrophenyl octyl ether as plasticizer. The micro-device is a dynamic system with a sandwiched flat sheet PIM between donor and acceptor aqueous phases that flow in serpentine microchannels built in Teflon plates. The solutions flow continuously and are recycled with a peristaltic pump. Aqueous phases are collected and analyzed by atomic absorption spectroscopy for the determination of Cd(II). The extraction performances have been optimized with respect to operational parameters and compared with a conventional membrane device. Finally, the micro-PIM device is briefly evaluated toward membrane stability and applied to competitive extraction of metal ions mixture containing Cd(II), Zn(II) and Pb(II) ions.
Fig. 1 – Representation of the membrane extraction micro-device based on the PIM sandwiched between two serpentine microchannels built in Teflon plates. SEM micrograph of the PIM cross section.
Please cite this article in press as: Annane, K., et al., Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.10.004
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2.4.
100
Cd concentraon %
to face to clamp the PIM. At the ends of the microchannel, holes were drilled through the blocks serving as inlet and outlet for acceptor and donor solutions. The microchannel was 164 mm long, 1 mm wide, 1 mm deep with a volume of 164 L. The PIM was clamped between the two microchannels to form the PIM based-micro module. The membrane surface area in contact with the microchannel was 1.64 cm2 .
Extraction experiments
C0 donor − Ct donor C0 donor
Cdacceptor =
Ct acceptor = enrichment factor (EF) C0 donor
(1)
(2)
where C0 donor is the initial concentration of Cd(II) in the donor phase, and Ct donor and Ct acceptor are the concentration of Cd(II) in the donor phase and acceptor phase at time t, respectively.
3.
Results and discussion
3.1.
Mechanism of Cd2+ extraction by PIM
Donor phase
80
Acceptor phase
70
Membrane phase
b
60 50 40 30
a
20 10
The extraction membrane experiments were carried out at 25 ◦ C. The aqueous donor phase contained cadmium metal ions 0.1 mM in 1 M sodium chloride (NaCl) at pH 5.5 and the aqueous acceptor phase contained specified concentration of perchloric acid (HClO4 ). The solutions (15 mL) were delivered separately into the microchannels located on both sides of the micro-cell and recycled by two separate peristaltic pumps (Gilson Miniplus 3). The tygon tubings, connected to the reservoirs of donor and acceptor phases, were characterized by 1.02 mm of inlet diameter and 400 mm of length. Flow rates of aqueous solutions in the microchannels located on both sides of the membrane were varied from 0.1 to 3 mL min−1 . Aliquots of 0.3 mL of both donor and acceptor phases were withdrawn periodically and analyzed by atomic absorption with a Varian spectrophotometer AA 220 FS at wavelength of 228.80 nm to determine cadmium(II) concentration. Each experiment was repeated 3 times. The Cd(II) concentration in the donor and acceptor phases was defined respectively as: Cddonor =
90
The transport process across PIM involves essentially the exchanging of ionic species between two compartments separated by a membrane phase (Nghiem et al., 2006). Due to the specific PIMs structure, the membrane diffusion coefficients of metal cations are low and set by the membrane composition (Zhang et al., 2012). In this study, the transport experiments of Cd(II) were conducted across a PIM using the specific extractant Aliquat 336. The Aliquat concentration is a dominant factor that affects the extraction ratio of metals, and thus was fixed to 34% (w/w), according to previous works on Cd and Pt extraction by PIMs containing Aliquat 336 PIM (KebicheSenhadji et al., 2008; Fontás et al., 2005). Cd(II) is known to readily complex with chloride to form negatively charged chloro metal complexes (Kavitha and Palanivelu, 2012; Wang et al., 2000), extracted via anion-exchange mechanism by Aliquat 336. This mechanism involves the formation of a 1:1 metal-ion complex from the aqueous phase that can enter the membrane. In chloride solutions, different chloro complexes can be formed depending on both the metal and chloride concentration. Assuming that trichloro metal complex
0
c 0
1
2
3 Time (h)
4
6
8
Fig. 2 – Concentration profile of Cd(II) % in the donor phase (a), acceptor phase, (b) and in the membrane phase (c) during extraction experiment (8 h) with the PIM micro-channel cell. Donor phase: 15 mL of CdCl2 10−1 mM in 1 M NaCl at pH = 5.5; acceptor phase: 15 mL of 0.5 M HClO4 . Flow rate of the two phases: 1 mL min−1 . CdCl3 − is the main species involved in the extraction process (Kavitha and Palanivelu, 2012; Pont et al., 2008), the extraction between the metal and Aliquat (R4 N+ Cl− ) at the interface membrane/donor phase can be described as follow: R4 N+ Cl− (membrane) + CdCl3 − (aq) → R4 N+ CdCl3 − (membrane) + Cl− (aq) In this study, a proof-of-principle extraction experiment was conducted with the micro-channel cell from a solution containing 0.1 mM Cd(II) in 1 M NaCl to a solution 0.5 M HClO4 , the flow rate of the solutions being adjusted to 1 mL min−1 . In Fig. 2, the concentration profile of Cd(II) in the donor and acceptor phases is shown. Cd(II) is transported in the acceptor phase with increasing time. In one hour, 43% of cadmium are removed from the donor phase and only 11% are recovered in the acceptor phase. If the experiment is carried on beyond 1 h, 90% of the metal recovery is achieved in 8 h. This experiment confirmed that on-chip membrane extraction is possible. However, as shown in Fig. 2, an important amount of Cd is retained in the membrane, reaching a maximum of 33% after 2 h of transport and decreasing slowly as Cd(II) discharge progress into the acceptor phase. This phenomenon, is comparable with that reported by Kavitha and Palanivelu (2012) for Cu(II) extraction through the PIM with the carrier di(2-ethylhexyl)phosphoric acid. The following objective was to study the influence of the operational parameters on Cd% recovery in the acceptor phase in one hour.
3.2.
Investigation of principal operational parameters
3.2.1.
Influence of donor and acceptor composition
To study the influence of chloride concentration in the donor phase on metal extraction, experiments were carried out with the micro-device with solutions containing 10−1 mM Cd(II) at various chloride concentrations (0, 0.5, 1 and 2 M of NaCl, pH 5.5). The flow rate of the two solutions was 1 mL min−1 . Results were summarized in Table 1. One can observe that the absence of NaCl in the donor phase inhibited the metal extraction that agrees with the inexistence of the extractable species CdCl3 − to form a complex with the Aliquat 336. The forward extraction of Cd(II) was only efficient in the presence of NaCl and especially from high concentrations that enhanced the formation
Please cite this article in press as: Annane, K., et al., Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.10.004
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Table 1 – Influence of NaCl concentration in the donor phase on Cd(II) extraction efficiency with the PIM micro-channel cell after one hour. The flow rate of the donor and acceptor phases was 1 mL min−1 . [NaCl] (M)
0 0.5 1 2
[Cd(II)] (%) extracted from donor phase 0 20 43 43
[Cd(II)] (%) recovered in acceptor phase 0 4 11 11
of the complex at the interface membrane/donor phase. As the increase of NaCl from 1 to 2 M resulted in identical extracted Cd(II) % and recovered Cd(II) %, the concentration of NaCl was fixed to 1 M for the following experiments. A similar influence of NaCl concentration, in the range 0–3 M, was also reported by Adelung et al. (2012) for the extraction of Cd(II) by PVC/Aliquat PIMs in conventional device. The nature of the acceptor phase is a factor affecting the enrichment factor, defined as Eq. (2). Fig. 3 shows the enrichment factor obtained for an extraction time of 60 min with different acceptor phases such as H2 O, HCl (0.5 M), HClO4 (0.5 M) and HNO3 (0.5 M). The results confirmed that the extraction of cadmium could only occur in acidic or neutral conditions and that the presence of chloride, in the case of HCl, is unfavorable for the recovery process as the recovery of cadmium generated chloride in the acceptor phase. The enrichment factor was in the order: HClO4 (11%) > HNO3 (5%) ≈ H2 O HCl (0%). The efficiency of HClO4 was attributed to its higher tendency to protonate tertiary amines than that of other acid anions as Cl− , NO3 − , and SO4 2− , due to its smaller hydrated radii size (Mahmoud, 2012). However, the increase of HClO4 concentration from 0.5 to 2 M (results not shown) had no influence on the enrichment factor. For the following experiments, the acceptor phase was fixed to HClO4 0.5 M. It was also observed that the variation of the nature of the acceptor phase did not impact the amount of Cd(II) extracted from the donor phase to the membrane during the first hour of the experiment due to the accumulation of the Cd ions in the membrane as observed in Fig. 2.
3.2.2.
Influence of the flow rate
In membrane separation techniques, the flow rate of the phases in contact with the PIM is a variable that can influence the performances of the extraction. The investigation of the
Fig. 3 – Enrichment factor versus different acceptor phases (15 mL): H2 O, HClO4 (0.5 M), HCl (0.5 M), HNO3 (0.5 M). Extraction time: 60 min. Donor phase: 15 mL of CdCl2 10−1 mM in 1 M NaCl at pH = 5.5; flow rate of the two phases: 1 mL min−1 .
Fig. 4 – (A) Cd2+ % extracted from the donor phase and Cd2+ % recovered in the acceptor phase versus flow rate varied simultaneously for the donor and acceptor phases in the range 0.1–3 mL min−1 . (B) Enrichment factor versus flow rate in the range 0.1–3 mL min−1 : (a) identical flow rate for the donor and acceptor phases, (b) variation of the donor flow rate, and (c) variation of the acceptor flow rate. Donor phase: 15 mL of CdCl2 10−1 mM in NaCl 1 M at pH = 5.5; acceptor phase: 15 mL of 0.5 M HClO4 . Extraction time t = 1 h.
principal operational parameters was thus completed with a study of the phase flow rate. In a first experiment, the sample flow rate of the two phases was simultaneously varied in the range 0.1–3 mL min−1 for an extraction time of 1 h (Fig. 4A). In the donor phase, the Cd % decreased as the amount extracted by the membrane increased regularly from 20 to 53% with variation of the flow rate in the range 0.1–2 mL min−1 . Between 2 and 3 mL min−1 , the extracted amount was constant, indicating a saturation of the active sites contained in the membrane. For the acceptor phase, the flow rate 0.1 mL min−1 was not optimal for Cd(II) extraction in 1 h. As the flow rate increased, EF increased because more Cd(II) ions came in contact with the PIM per unit of time and could complex with Aliquat at the membrane interface. However, from 1 mL min−1 , EF was 11% and remained constant while the flow rate increases up to 3 mL min−1 . The constant value of EF resulted mainly to a high degree of interaction between Cd(II) and Aliquat 336 in the PIM that limited the efficiency of the extraction. This was consistent with the important retention of Cd(II) observed in the membrane (see Fig. 2) that is maximal during the first hours of the extraction experiment. Further experiments were thus conducted by varying the flow rate ratio between the two phases. In a first set of experiments, the acceptor flow rate was kept constant at 1 mL min−1 while the donor flow rate was varied between 0.1 and 2 mL min−1 . In a second set of experiments, the donor flow was kept constant to 1 mL min−1 , while the acceptor flow rate was varied between 0.1 and 2 mL min−1 . EF was measured
Please cite this article in press as: Annane, K., et al., Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.10.004
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100 90
Microfluidic cell
80
Conventional cell
70
EF %
60 50 40 30 20 10 0
0
1
2
3
4
5
6
7
8
Time (h)
Fig. 5 – Enrichment factor versus time obtained for the PIM micro-channel and the conventional cells. Donor phase: 15 mL of CdCl2 10−1 mM in NaCl 1 M at pH = 5.5; acceptor phase: 15 mL of 0.5 M HClO4 . Flow rate of two phases in the micro-channels = 3 mL min−1 . and presented in Fig. 4B for each experiment. Apart from a slight variation of EF in the range 0–1 mL min−1 , when the flow rate of one phase exceeded the other one, the efficiency of the extraction procedure was not improved. The variation of the operational parameters (NaCl concentration, nature of the acceptor phase, flow rate) did not impact on EF for extraction experiments conducted in 1 h, indicating that the efficiency of the extraction is thus limited by the membrane diffusion coefficient of Cd(II), governed by its dense morphology.
3.2.3. Comparative PIM performances between micro-channel cell and conventional devices The efficiency of the PIM micro-channel cell was compared with the one obtained with a conventional cell performed with solutions of 25 mL and identical conditions: the donor phase contained Cd(II) 0.1 mM in 1 M chloride sodium (NaCl) at pH 5.5 and the acceptor phase contained HClO4 0.5 M. The conventional cell consisted of two plexiglass compartment separated by the PIM and clamped together (the area of the PIM in contact with the solution was 3.14 cm2 ). Transport experiments were conducted at room temperature (25 ◦ C) and the aqueous phases were stirred at 900 rpm with two mechanical stirrers (Heidolp RZR 2101). For the conventional device, the concentration profile of Cd(II) in the phases and in the membrane showed also an important amount of Cd retained in the membrane, reaching a maximum of 30% in one hour (results not shown). EF was calculated for the two devices (Fig. 5). When the extraction experiment was conducted for one hour, with the conventional cell the enrichment factor was 5%, whereas with the micro-device, it was twice higher (11%). Besides, with the micro-device, EF was 90% after an extraction time of 6 h and 100% after 8 h (at flow rate = 3 mL min−1 ), whereas EF was only 80% after 8 h with the conventional cell. Although the comparison between the two devices is not straightforward (due to differences in cell design and operating variables), these results demonstrated the versatile use of PIM in micro devices for metal ions extraction, that resulted in higher EF and shorter extraction process, as well as reduced amounts of solvent and chemicals. Besides, another micro channel cell, characterized by the same footprint but with a lower surface area in contact with the membrane (1.5 cm2 ), was tested. When operating in the same experimental conditions, the Cd % extracted decreased by 25%.
5
Under the optimum extraction conditions of cadmium, a preliminary study was conducted to evaluate competitive extraction of metal ions mixture containing Cd(II), Zn(II) and Pb(II) at concentrations of 10−1 mM in NaCl (1 M) at pH = 5.5. The flow rate of the donor and acceptor phases was 3 mL min−1 . After an extraction time of 60 min, results showed that Cd(II) was favorably transported and EF were found to be of 11%, 5% and 3% for Cd(II), Zn(II) and Pb(II), respectively, with the selectivity order Cd > Zn > Pb. Maximum EF reached at the transport time of 6 h were 90% for Cd(II), 79% for Zn(II) and 75% for Pb(II). It was observed that a same EF value (90%) of cadmium was obtained for both the tertiary mixture Cd–Zn–Pb solutions and the individual metal ion.
3.3.
Stability of the PIM
The long term stability of the PIMs in the micro-cell was evaluated by carrying out repeated Cd(II) extraction experiments. After each experiment, the membrane was washed with water for several hours to remove any Cd(II) ions present in the membrane. Results showed that the PIM presented a long-term stability and can be reused up to 16 times without loss of its performance with a standard deviation of 1.5%. This result corroborates the high stability of the PIMs (Adelung et al., 2012; Zhang et al., 2011; Nghiem et al., 2006).
4.
Conclusions
The present work demonstrated the feasibility of continuous Cd(II) extraction with a PIM-based micro-system containing Aliquat 336 as carrier. Donor and acceptor solutions were delivered continuously to the device by peristaltic pumps. The results of the transport experiments pointed out the versatile use of PIM in micro devices for efficient extraction of Cd(II). The extraction of Cd(II) from individual metal ion and tertiary mixture Cd–Zn–Pb chloride solutions was achieved with an EF of 90% after a transport time of 6 h. The stability tests showed that the membrane can be reused up to 16 times without any loss of extraction efficiency. The transport time of cadmium ions in this system is considerably dependent on the diffusion of the ions through the PIM and can be performed by reducing the membrane thickness. Work is in progress to prepare thinner membranes to improve the sampling rate and the ability to selectively separate metal ions.
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Chemical Engineering Research and Design journal homepage: www.elsevier.com/locate/cherd
Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell Kahina Annane a , Amar Sahmoune a , Patrice Montels b , Sophie Tingry b,∗ a
Equipe de Recherche Matériaux et Procédés pour l’Environnement, Université Mouloud Mammeri Tizi-Ouzou, Algeria b Institut Européen des Membranes – ENSCM/UM2/CNRS 5635, IEM/UM2, CC 047, Place Eugène Bataillon, F-34095, Montpellier Cedex 5, France
a b s t r a c t In this work, membrane transport of cadmium ion was explored through a polymer inclusion membrane (PIM) in micro-system. The system was composed of a flat sheet membrane sandwiched between donor and acceptor aqueous phases that flow in serpentine microchannels built in Teflon plates. The PIM was composed by cellulose triacetate as polymer base, Aliquat 336 as carrier and o-nitrophenyl octyl ether as plasticizer. The potential of the system was demonstrated from continuous measurement of Cd(II) collected in the aqueous phases and analyzed by atomic absorption spectroscopy. The reported on-chip PIM extraction focused on proof-of-principle studies based on the system optimization from operational parameters affecting the performance. Enrichment factors (EF) were close to 11% and 100% for 1 h and 8 h of extraction experiment, respectively, at flow rates of 3 mL min−1 . Compared with conventional cell, our results showed the feasibility of PIM in micro device to achieve efficient Cd ions extraction. The applicability of the device was briefly illustrated by extraction of metal ions mixture from aqueous solutions. © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Microchip; Polymer inclusion membrane; Aliquat 336; Cadmium(II) extraction
1.
Introduction
The advantages of micro devices are based on their small dimensions and enhanced interfacing area/volume ratios that contribute both
studied. Several authors have described the efficient use of the Aliquat
to the reduction of solvent and chemicals consumption and of extraction time of the analysis. The integration of membranes into micro channel-based devices
336 in emulsion membrane extraction (ELM) (Kumbasar, 2008), in bulk liquid membrane (Dalali et al., 2012), in supported liquid membrane
has been recently reviewed (Jong et al., 2006). Membranes are nowadays involved in a wide range of industrial applications as selective barriers
The extraction and the separation of numerous metals by liquid and affinity membranes containing Aliquat 336 as carrier have been widely
(SLM) (Bhatlurietal et al., 2014; Lv et al., 2007; Fontàs et al., 2005), and
between fluid flows for separation, concentration and removal of ana-
in plasticized membrane (PPM) (Gherasim and Bourceanu, 2013; Fontàs
lytes, the driving-force of the separation being a difference in activity (Nath, 2008; Strathmann, 1981). Membrane extraction systems based on liquid membranes have been down-scaled to be implemented into
et al., 2007; Kebiche-Senhadji et al., 2008; Nghiem et al., 2006; Wang et al., 2000, 2005; Juang et al., 2004) for separating or recovering cadmium ions from mixture of metal ions. In order to strip efficiently metal ion species from the membrane to the receiving phase and to avoid low transport time and instability of membrane, several issues have been considered such as the integration of the membranes in microchips for
microchip devices to control, manipulate, and analyze flows in submillimeter dimensions. Several groups have developed micro-devices for effective extraction of organic compounds (Surmeian et al., 2002)
carrying out extractions, separations and detections with high resolution and sensitivity (Jayawardane et al., 2013; Zhang et al., 2011, 2012;
and metal ions (Maruyama et al., 2004), from a three-layer of immiscible fluids (water/organic solvent/water) formed in a microchannel. The separation of the components was based on a difference in sol-
Wang et al., 2005).
ubility in the liquid membrane phase, and could be enhanced by the
∗
Corresponding author. Tel.: +33 04 67 14 91 57; fax: +33 04 67 14 91 19. E-mail address: [email protected] (S. Tingry). Received 23 June 2014; Received in revised form 19 September 2014; Accepted 5 October 2014 http://dx.doi.org/10.1016/j.cherd.2014.10.004 0263-8762/© 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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presence of complexing agents to reach high selectivities (Maruyama et al., 2004). To avoid the instability of liquid–liquid interfaces, membrane based-micro systems have been also developed from solid membranes. These devices were based on a three-phase system containing a supported liquid membrane (SLM) in contact with both donor and acceptor solutions flowing through microchannel structures. SLMs consisted of commercial microporous polymeric support impregnated with an organic solution that may contain extractants as selective complexing agents (Parhi, 2013). These membranes have been widely used in macrosystems for transport and extractions of metal ions (Parhi, 2013; Danesi, 1984) and neutral organic species (Hassoune et al., 2009; Di Luccio et al., 2002; Rios et al., 2002) from aqueous phases. However, a few works have reported on SLM based micro-chips, applied to the enrichment of haloacetic acids from water (Wang et al., 2005), to the arsenic (V) extraction (Hylton and Mitra, 2008), and to the recovery of nonpolar basic drugs (Payan et al., 2012; Petersen et al., 2010, 2011). In such systems, the membrane was clamped between two microchannels, and sample solutions were delivered continuously to the microchannels by micro syringe pumps. Due to the specific design of these systems, the performances of the analysis were affected by operational parameters such as phase flow rates and microchannel dimensions (Petersen et al., 2011; Wang et al., 2005). As demonstrated by Wang et al. (2005), micro-devices designed with shallower acceptor channels (100 m) provided more concentrated extract that enhanced the enrichment factor of haloacetic acids to 65. In another works, Petersen et al. (2010, 2011) have designed on-chip electro membrane extractions based on the control of the electrical potential to adjust the magnitude and the direction of the transport across the membrane, and have shown the crucial role of the flow rate of the fluids to increase the extraction recoveries to 65–86% for the different analytes. To avoid the short lifetime of SLMs caused by the progressive leakage of both solvent and extractant from the membrane, polymer inclusion membranes (PIMs) are a good alternative (Nghiem et al., 2006). These membranes are obtained by casting a solution containing a selective extractant, a plasticizer and a base polymer such as poly(vinyl chloride) (PVC) or cellulose triacetate (CTA) to form a thin, flexible and stable film (Hayashita et al., 1995). The resulting selfsupporting membrane can be used to selectively separate the solutes of interest in a similar fashion to that of SLMs with the advantage of excellent stability over the time (Vázquez et al., 2014; Cho et al., 2011; Kebiche-Senhadji et al., 2008; Fontás et al., 2005; Juang et al., 2004). These membranes seem homogeneous at the macro level although it
2.
Experimental
2.1.
Reagents preparation
Cadmium(II) chloride (CdCl2 ), sodium chloride (NaCl), perchloric acid (HClO4 ), chloroform (CHCl3 ), cellulose tri acetate (CTA) and 2-nitro phenyl octyl ether (NPOE) were purchased from Fluka of analytical grade reagents and were used without further purification. The commercial carrier Aliquat 336 (tricaprylmethyl ammonium chloride R4 N+ Cl− ) was from Aldrich and used as received. All the aqueous solutions were prepared by dissolving the reagents in distilled water.
2.2.
Membrane preparation
The polymer inclusion membrane (PIM) was prepared by a procedure already described (Fontás et al., 2005). Amounts of CTA (200 mg), NPOE plasticizer (0.3 mL) and extractant Aliquat 336 (32 mmol L−1 equivalent to 34% weight to the total PIM weight) were dissolved in chloroform (20 mL) and stirred during 5 h in order to ensure the complete dissolution. The solution was poured in 9.5 cm diameter covered circular glass Petri dish and the solvent was allowed to evaporate over 24 h at 25 ◦ C. The resulting polymer film was then separated from the bottom of the glass Petri dish by immersion in cold water. The membrane was cut into small pieces of approximately 4.6 cm2 that were placed between two microchannels. The membrane sample was viewed using scanning electron microscopy at 500× magnification (HITACHI S4500 analyzer). As observed in Fig. 1, the membrane presents a homogenous appearance and thickness approximately of 84 m.
2.3.
Fabrication of the PIM micro device
The membrane extraction device (Fig. 1) was composed of two rectangular serpentine microchannels micromachined in our laboratory (European Institute of Membrane) on two separate Teflon blocks using a vertical numerical milling machine (HAAS TM2). The two blocks with the microchannels were face
has been suggested that they are composed of liquid micro-domains, at optimized extractant concentration, creating continuous channels connected between the two interfaces (Fontàs et al., 2007). The first use of a PIM in a flow injection analysis (FIA) has been reported for on-line separation of Zn(II) in the presence of other metals by Zhang et al. (2011). The PIM was obtained from the base polymer PVC and with the di(2-ethylhexyl) phosphoric acid (D2EHPA) as extractant. The FIA system was optimized with respect to flow rates and compositions of donor and acceptor streams. The system was further studied as function of the temperature and sonication effect to enhance mass transfer process in the PIM extraction (Zhang et al., 2012). This study reports on cadmium extraction under flow conditions by a PIM-based micro-chip. The PIM is composed by cellulose triacetate as polymer base, Aliquat 336 as carrier and o-nitrophenyl octyl ether as plasticizer. The micro-device is a dynamic system with a sandwiched flat sheet PIM between donor and acceptor aqueous phases that flow in serpentine microchannels built in Teflon plates. The solutions flow continuously and are recycled with a peristaltic pump. Aqueous phases are collected and analyzed by atomic absorption spectroscopy for the determination of Cd(II). The extraction performances have been optimized with respect to operational parameters and compared with a conventional membrane device. Finally, the micro-PIM device is briefly evaluated toward membrane stability and applied to competitive extraction of metal ions mixture containing Cd(II), Zn(II) and Pb(II) ions.
Fig. 1 – Representation of the membrane extraction micro-device based on the PIM sandwiched between two serpentine microchannels built in Teflon plates. SEM micrograph of the PIM cross section.
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2.4.
100
Cd concentraon %
to face to clamp the PIM. At the ends of the microchannel, holes were drilled through the blocks serving as inlet and outlet for acceptor and donor solutions. The microchannel was 164 mm long, 1 mm wide, 1 mm deep with a volume of 164 L. The PIM was clamped between the two microchannels to form the PIM based-micro module. The membrane surface area in contact with the microchannel was 1.64 cm2 .
Extraction experiments
C0 donor − Ct donor C0 donor
Cdacceptor =
Ct acceptor = enrichment factor (EF) C0 donor
(1)
(2)
where C0 donor is the initial concentration of Cd(II) in the donor phase, and Ct donor and Ct acceptor are the concentration of Cd(II) in the donor phase and acceptor phase at time t, respectively.
3.
Results and discussion
3.1.
Mechanism of Cd2+ extraction by PIM
Donor phase
80
Acceptor phase
70
Membrane phase
b
60 50 40 30
a
20 10
The extraction membrane experiments were carried out at 25 ◦ C. The aqueous donor phase contained cadmium metal ions 0.1 mM in 1 M sodium chloride (NaCl) at pH 5.5 and the aqueous acceptor phase contained specified concentration of perchloric acid (HClO4 ). The solutions (15 mL) were delivered separately into the microchannels located on both sides of the micro-cell and recycled by two separate peristaltic pumps (Gilson Miniplus 3). The tygon tubings, connected to the reservoirs of donor and acceptor phases, were characterized by 1.02 mm of inlet diameter and 400 mm of length. Flow rates of aqueous solutions in the microchannels located on both sides of the membrane were varied from 0.1 to 3 mL min−1 . Aliquots of 0.3 mL of both donor and acceptor phases were withdrawn periodically and analyzed by atomic absorption with a Varian spectrophotometer AA 220 FS at wavelength of 228.80 nm to determine cadmium(II) concentration. Each experiment was repeated 3 times. The Cd(II) concentration in the donor and acceptor phases was defined respectively as: Cddonor =
90
The transport process across PIM involves essentially the exchanging of ionic species between two compartments separated by a membrane phase (Nghiem et al., 2006). Due to the specific PIMs structure, the membrane diffusion coefficients of metal cations are low and set by the membrane composition (Zhang et al., 2012). In this study, the transport experiments of Cd(II) were conducted across a PIM using the specific extractant Aliquat 336. The Aliquat concentration is a dominant factor that affects the extraction ratio of metals, and thus was fixed to 34% (w/w), according to previous works on Cd and Pt extraction by PIMs containing Aliquat 336 PIM (KebicheSenhadji et al., 2008; Fontás et al., 2005). Cd(II) is known to readily complex with chloride to form negatively charged chloro metal complexes (Kavitha and Palanivelu, 2012; Wang et al., 2000), extracted via anion-exchange mechanism by Aliquat 336. This mechanism involves the formation of a 1:1 metal-ion complex from the aqueous phase that can enter the membrane. In chloride solutions, different chloro complexes can be formed depending on both the metal and chloride concentration. Assuming that trichloro metal complex
0
c 0
1
2
3 Time (h)
4
6
8
Fig. 2 – Concentration profile of Cd(II) % in the donor phase (a), acceptor phase, (b) and in the membrane phase (c) during extraction experiment (8 h) with the PIM micro-channel cell. Donor phase: 15 mL of CdCl2 10−1 mM in 1 M NaCl at pH = 5.5; acceptor phase: 15 mL of 0.5 M HClO4 . Flow rate of the two phases: 1 mL min−1 . CdCl3 − is the main species involved in the extraction process (Kavitha and Palanivelu, 2012; Pont et al., 2008), the extraction between the metal and Aliquat (R4 N+ Cl− ) at the interface membrane/donor phase can be described as follow: R4 N+ Cl− (membrane) + CdCl3 − (aq) → R4 N+ CdCl3 − (membrane) + Cl− (aq) In this study, a proof-of-principle extraction experiment was conducted with the micro-channel cell from a solution containing 0.1 mM Cd(II) in 1 M NaCl to a solution 0.5 M HClO4 , the flow rate of the solutions being adjusted to 1 mL min−1 . In Fig. 2, the concentration profile of Cd(II) in the donor and acceptor phases is shown. Cd(II) is transported in the acceptor phase with increasing time. In one hour, 43% of cadmium are removed from the donor phase and only 11% are recovered in the acceptor phase. If the experiment is carried on beyond 1 h, 90% of the metal recovery is achieved in 8 h. This experiment confirmed that on-chip membrane extraction is possible. However, as shown in Fig. 2, an important amount of Cd is retained in the membrane, reaching a maximum of 33% after 2 h of transport and decreasing slowly as Cd(II) discharge progress into the acceptor phase. This phenomenon, is comparable with that reported by Kavitha and Palanivelu (2012) for Cu(II) extraction through the PIM with the carrier di(2-ethylhexyl)phosphoric acid. The following objective was to study the influence of the operational parameters on Cd% recovery in the acceptor phase in one hour.
3.2.
Investigation of principal operational parameters
3.2.1.
Influence of donor and acceptor composition
To study the influence of chloride concentration in the donor phase on metal extraction, experiments were carried out with the micro-device with solutions containing 10−1 mM Cd(II) at various chloride concentrations (0, 0.5, 1 and 2 M of NaCl, pH 5.5). The flow rate of the two solutions was 1 mL min−1 . Results were summarized in Table 1. One can observe that the absence of NaCl in the donor phase inhibited the metal extraction that agrees with the inexistence of the extractable species CdCl3 − to form a complex with the Aliquat 336. The forward extraction of Cd(II) was only efficient in the presence of NaCl and especially from high concentrations that enhanced the formation
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Table 1 – Influence of NaCl concentration in the donor phase on Cd(II) extraction efficiency with the PIM micro-channel cell after one hour. The flow rate of the donor and acceptor phases was 1 mL min−1 . [NaCl] (M)
0 0.5 1 2
[Cd(II)] (%) extracted from donor phase 0 20 43 43
[Cd(II)] (%) recovered in acceptor phase 0 4 11 11
of the complex at the interface membrane/donor phase. As the increase of NaCl from 1 to 2 M resulted in identical extracted Cd(II) % and recovered Cd(II) %, the concentration of NaCl was fixed to 1 M for the following experiments. A similar influence of NaCl concentration, in the range 0–3 M, was also reported by Adelung et al. (2012) for the extraction of Cd(II) by PVC/Aliquat PIMs in conventional device. The nature of the acceptor phase is a factor affecting the enrichment factor, defined as Eq. (2). Fig. 3 shows the enrichment factor obtained for an extraction time of 60 min with different acceptor phases such as H2 O, HCl (0.5 M), HClO4 (0.5 M) and HNO3 (0.5 M). The results confirmed that the extraction of cadmium could only occur in acidic or neutral conditions and that the presence of chloride, in the case of HCl, is unfavorable for the recovery process as the recovery of cadmium generated chloride in the acceptor phase. The enrichment factor was in the order: HClO4 (11%) > HNO3 (5%) ≈ H2 O HCl (0%). The efficiency of HClO4 was attributed to its higher tendency to protonate tertiary amines than that of other acid anions as Cl− , NO3 − , and SO4 2− , due to its smaller hydrated radii size (Mahmoud, 2012). However, the increase of HClO4 concentration from 0.5 to 2 M (results not shown) had no influence on the enrichment factor. For the following experiments, the acceptor phase was fixed to HClO4 0.5 M. It was also observed that the variation of the nature of the acceptor phase did not impact the amount of Cd(II) extracted from the donor phase to the membrane during the first hour of the experiment due to the accumulation of the Cd ions in the membrane as observed in Fig. 2.
3.2.2.
Influence of the flow rate
In membrane separation techniques, the flow rate of the phases in contact with the PIM is a variable that can influence the performances of the extraction. The investigation of the
Fig. 3 – Enrichment factor versus different acceptor phases (15 mL): H2 O, HClO4 (0.5 M), HCl (0.5 M), HNO3 (0.5 M). Extraction time: 60 min. Donor phase: 15 mL of CdCl2 10−1 mM in 1 M NaCl at pH = 5.5; flow rate of the two phases: 1 mL min−1 .
Fig. 4 – (A) Cd2+ % extracted from the donor phase and Cd2+ % recovered in the acceptor phase versus flow rate varied simultaneously for the donor and acceptor phases in the range 0.1–3 mL min−1 . (B) Enrichment factor versus flow rate in the range 0.1–3 mL min−1 : (a) identical flow rate for the donor and acceptor phases, (b) variation of the donor flow rate, and (c) variation of the acceptor flow rate. Donor phase: 15 mL of CdCl2 10−1 mM in NaCl 1 M at pH = 5.5; acceptor phase: 15 mL of 0.5 M HClO4 . Extraction time t = 1 h.
principal operational parameters was thus completed with a study of the phase flow rate. In a first experiment, the sample flow rate of the two phases was simultaneously varied in the range 0.1–3 mL min−1 for an extraction time of 1 h (Fig. 4A). In the donor phase, the Cd % decreased as the amount extracted by the membrane increased regularly from 20 to 53% with variation of the flow rate in the range 0.1–2 mL min−1 . Between 2 and 3 mL min−1 , the extracted amount was constant, indicating a saturation of the active sites contained in the membrane. For the acceptor phase, the flow rate 0.1 mL min−1 was not optimal for Cd(II) extraction in 1 h. As the flow rate increased, EF increased because more Cd(II) ions came in contact with the PIM per unit of time and could complex with Aliquat at the membrane interface. However, from 1 mL min−1 , EF was 11% and remained constant while the flow rate increases up to 3 mL min−1 . The constant value of EF resulted mainly to a high degree of interaction between Cd(II) and Aliquat 336 in the PIM that limited the efficiency of the extraction. This was consistent with the important retention of Cd(II) observed in the membrane (see Fig. 2) that is maximal during the first hours of the extraction experiment. Further experiments were thus conducted by varying the flow rate ratio between the two phases. In a first set of experiments, the acceptor flow rate was kept constant at 1 mL min−1 while the donor flow rate was varied between 0.1 and 2 mL min−1 . In a second set of experiments, the donor flow was kept constant to 1 mL min−1 , while the acceptor flow rate was varied between 0.1 and 2 mL min−1 . EF was measured
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100 90
Microfluidic cell
80
Conventional cell
70
EF %
60 50 40 30 20 10 0
0
1
2
3
4
5
6
7
8
Time (h)
Fig. 5 – Enrichment factor versus time obtained for the PIM micro-channel and the conventional cells. Donor phase: 15 mL of CdCl2 10−1 mM in NaCl 1 M at pH = 5.5; acceptor phase: 15 mL of 0.5 M HClO4 . Flow rate of two phases in the micro-channels = 3 mL min−1 . and presented in Fig. 4B for each experiment. Apart from a slight variation of EF in the range 0–1 mL min−1 , when the flow rate of one phase exceeded the other one, the efficiency of the extraction procedure was not improved. The variation of the operational parameters (NaCl concentration, nature of the acceptor phase, flow rate) did not impact on EF for extraction experiments conducted in 1 h, indicating that the efficiency of the extraction is thus limited by the membrane diffusion coefficient of Cd(II), governed by its dense morphology.
3.2.3. Comparative PIM performances between micro-channel cell and conventional devices The efficiency of the PIM micro-channel cell was compared with the one obtained with a conventional cell performed with solutions of 25 mL and identical conditions: the donor phase contained Cd(II) 0.1 mM in 1 M chloride sodium (NaCl) at pH 5.5 and the acceptor phase contained HClO4 0.5 M. The conventional cell consisted of two plexiglass compartment separated by the PIM and clamped together (the area of the PIM in contact with the solution was 3.14 cm2 ). Transport experiments were conducted at room temperature (25 ◦ C) and the aqueous phases were stirred at 900 rpm with two mechanical stirrers (Heidolp RZR 2101). For the conventional device, the concentration profile of Cd(II) in the phases and in the membrane showed also an important amount of Cd retained in the membrane, reaching a maximum of 30% in one hour (results not shown). EF was calculated for the two devices (Fig. 5). When the extraction experiment was conducted for one hour, with the conventional cell the enrichment factor was 5%, whereas with the micro-device, it was twice higher (11%). Besides, with the micro-device, EF was 90% after an extraction time of 6 h and 100% after 8 h (at flow rate = 3 mL min−1 ), whereas EF was only 80% after 8 h with the conventional cell. Although the comparison between the two devices is not straightforward (due to differences in cell design and operating variables), these results demonstrated the versatile use of PIM in micro devices for metal ions extraction, that resulted in higher EF and shorter extraction process, as well as reduced amounts of solvent and chemicals. Besides, another micro channel cell, characterized by the same footprint but with a lower surface area in contact with the membrane (1.5 cm2 ), was tested. When operating in the same experimental conditions, the Cd % extracted decreased by 25%.
5
Under the optimum extraction conditions of cadmium, a preliminary study was conducted to evaluate competitive extraction of metal ions mixture containing Cd(II), Zn(II) and Pb(II) at concentrations of 10−1 mM in NaCl (1 M) at pH = 5.5. The flow rate of the donor and acceptor phases was 3 mL min−1 . After an extraction time of 60 min, results showed that Cd(II) was favorably transported and EF were found to be of 11%, 5% and 3% for Cd(II), Zn(II) and Pb(II), respectively, with the selectivity order Cd > Zn > Pb. Maximum EF reached at the transport time of 6 h were 90% for Cd(II), 79% for Zn(II) and 75% for Pb(II). It was observed that a same EF value (90%) of cadmium was obtained for both the tertiary mixture Cd–Zn–Pb solutions and the individual metal ion.
3.3.
Stability of the PIM
The long term stability of the PIMs in the micro-cell was evaluated by carrying out repeated Cd(II) extraction experiments. After each experiment, the membrane was washed with water for several hours to remove any Cd(II) ions present in the membrane. Results showed that the PIM presented a long-term stability and can be reused up to 16 times without loss of its performance with a standard deviation of 1.5%. This result corroborates the high stability of the PIMs (Adelung et al., 2012; Zhang et al., 2011; Nghiem et al., 2006).
4.
Conclusions
The present work demonstrated the feasibility of continuous Cd(II) extraction with a PIM-based micro-system containing Aliquat 336 as carrier. Donor and acceptor solutions were delivered continuously to the device by peristaltic pumps. The results of the transport experiments pointed out the versatile use of PIM in micro devices for efficient extraction of Cd(II). The extraction of Cd(II) from individual metal ion and tertiary mixture Cd–Zn–Pb chloride solutions was achieved with an EF of 90% after a transport time of 6 h. The stability tests showed that the membrane can be reused up to 16 times without any loss of extraction efficiency. The transport time of cadmium ions in this system is considerably dependent on the diffusion of the ions through the PIM and can be performed by reducing the membrane thickness. Work is in progress to prepare thinner membranes to improve the sampling rate and the ability to selectively separate metal ions.
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Please cite this article in press as: Annane, K., et al., Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.10.004
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Please cite this article in press as: Annane, K., et al., Polymer inclusion membrane extraction of cadmium(II) with Aliquat 336 in micro-channel cell. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.10.004