- Email: [email protected]
Emulsion liquid membrane stability in the extraction of ionized nanosilver from wash water
G Model
JIEC-1734; No. of Pages 8 Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Emulsion liquid membrane stability in the extraction of ionized nanosilver from wash water Raja Norimie Raja Sulaiman a,b, Norasikin Othman a,*, Nor Aishah Saidina Amin b a
Centre of Lipid Engineering and Applied Research (CLEAR), Faculty of Chemical Engineering, Universiti Teknologi Malaysia (UTM), Skudai, 81310 Johor Bharu, Malaysia b Chemical Reaction Engineering Group (CREG), Faculty of Chemical Engineering, Universiti Teknologi Malaysia (UTM), Skudai, 81310 Johor Bharu, Malaysia
A R T I C L E I N F O
Article history: Received 5 September 2013 Accepted 3 December 2013 Available online xxx Keywords: Emulsion liquid membrane Ionized nanosilver Wash water Removal Ionic liquid
A B S T R A C T
The discharge of ionized nanosilver into environment triggers a great concern owing to the toxicity problem for aquatic organism. In this study, emulsion liquid membrane used to extract the ionized nanosilver from wash water. Variables like carrier, stripping agent and surfactant concentrations, emulsifying time, homogenizer and agitation speed, pH feed phase, and effect of ionic liquid [BMIM]+[NTf2]were investigated. The membrane phase containing Cyanex 302, Span 80, acidic Thiourea, and kerosene as carrier, surfactant, stripping agent, and diluent respectively. Results demonstrated that 99.89% of silver ion was extracted and ionic liquid show good performance on emulsion stability with 10% swelling. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Nanosilver has been extensively used in various consumer products, medicines, and food applications owing to the high prospects of its antimicrobial properties. For instance, this nanoparticle can act as an anti-HIV drug by inhibiting the human immunodeficiency virus (HIV) replication [1]. Besides, they are also coated with the medical devices in order to avoid the occurrence of infection [2]. United States Environmental Protection Agency (USEPA) indicates silver as a priority pollutant in natural waters in 1977. USEPA also regulates a guideline of less than 0.10 ppm of total silver in drinking water due to the potential effects of silver ingestion specifically argyria disease. USEPA, however, prescribes maximum concentrations of 3.2 ppb silver in fresh water and 1.9 ppb in salt water based on acute toxicity of silver to macroinvertebrates and fish [3]. These standards are enforced through the issuance of discharge permits at the state level. With respect to the chronic water quality to protect aquatic life, a few states have set the threshold concentrations for example the North Carolina Division of Water Quality has proposed a criterion of 0.06 ppb [4]. Oregon also has established a 0.12 ppb criterion in its administrative rules based on chronic toxicity to rainbow trout and minnows in fresh water and to mysids in salt
* Corresponding author. Tel.: +607 5535561; fax: +607 5581463. E-mail address: [email protected] (N. Othman).
water [5]. Texas, New York, and several regions in California have established maximum contaminant levels for silver between 5 and 10 ppb. Nanosilver used in some products can enter the environment as individual nanoparticles, small clusters, or potentially dissolve into ions. The ionization behavior of nanosilver in the ionic form has been reported by several researchers via clothing, textiles, washing machine, and home application [6–9]. According to Benn et al. [6], about 1.30 ppm of nanosilver ions have been leached into distilled water from the six types of commercial socks containing nanosilver. Another study also observes as much as 11 ppb of nanosilver ions have been released from washing machine (Samsung brand) which contain ion generating devices for nanosilver ions release in order to protect our clothing from bacteria during the washing process [9]. To date, Benn et al. [10] have found that about 3.2 and 7.6 ppm of silver ion was released from silver nanoparticles coming from the detergent and the toothpaste, respectively. The presence of nanosilver in the natural water environment is of great concern due to its small size, which can create toxicity effect to aquatic organism, especially when it is in the free ionized form [11]. The toxicity effect occurred when the silver ions have massively associate with the other chemicals organic or colloidal, hence influencing the bioavailability and the bioacccumulation of nanoparticle into the cell of aquatic organism. The observation shows that the exposure of nanosilver ions with concentration of 5 ppm can increase the mortality and heart malformation in zebra fish [12].
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.12.005
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 2
R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Therefore, the removal of this nanoparticle from the waste water is very positive for environmental safety. In the past, several numbers of methods were reported for nanosilver ion extraction including electrowinning [13], electrochemical method [14], solvent extraction [15,16], electrodialysis [17], and liquid membrane separation [18,19]. The disadvantage of electrochemical method is the deposition rate and the composition of the solution, in some cases, can cause the production of dendrites and loose or spongy deposits and interference from the hydrogen evolution reaction. In addition, this process also involves a large capital investment with expensive electricity supply. Besides, electrowinning also is a suitable process for the treatment of effluents with a silver concentration between 2 and 12 ppm. The recovery of silver down to concentrations of less than 0.2 ppm enables the formation of the precipitate silver sulfide on the cathodic surface. However, a second treatment is required by cementation or chemical precipitation. Solvent extraction also involves high consumption of chemical reagents. The electrodialysis is an advance technology, which does not lend itself readily to small-scale applications due to its high capital and operational costs, and requirement for highly trained people with supervision. Liquid membrane technology is regarded as one of the effective method, which combines the extraction and recovery process thus making this technique more advantageous and profitable over other separation methods. Therefore, this method does not need the second treatment like electrowinning, which need the other treatment, which is cementation or chemical precipitation process [13]. The extraction chemistry is basically the same as that found in solvent extraction, but the transport is governed by kinetic rather than equilibrium parameters, that is, it is governed by a non-equilibrium mass transfer. This process also provides low cost and energy because not much chemicals and equipments are used if compared with the electrochemical deposition method, which involve large capital investment with expensive electricity supply [14]. On the other hand, this method also provides the low consumption of chemicals which is the use of carrier is ten times lower than that used in solvent extraction method [15]. Principally, emulsion liquid membrane involves a dispersion of emulsion containing of organic and aqueous stripping phase into the aqueous feed phase containing solutes. The solute from the feed phase permeates into the membrane phase and chemically reacts with the stripping agent present in the stripping phase, which impenetrates in the membrane phase and remains confined in stripping phase. The transportation of solute in the emulsion liquid membrane is chiefly motivated by the concentration gradient and pH. Based on the ELM system, which involves the mass transfer mechanism of metal ions from the external into the internal phase have proven that the silver ion have been ionized from the silver nanoparticles and react with the carrier and stripping agent. However, the main drawback experienced with this method is the emulsion stability problem which influences the extraction efficiency. The emulsion liquid membrane stability problem which take place in emulsion liquid membrane system are swelling and breakage phenomena. Swelling occurs when the water molecules from the external phase is transferred inside the internal phase, diluting the solute and reducing the solute concentration. Emulsion swelling can increase in emulsion volume during operation and trigger the breakdown of the globules which finally decrease the extraction efficiency. In the meantime, the membrane breakage occurs when portions of the internal phase spill into the external phase. During breakage, the stripping agent and previously extracted solute is leaked into the external phase [20]. The most stable emulsion was obtained when there was neither swelling nor breakage or emulsion with minimum of swelling occurrence.
The application of ionic liquid in the liquid membrane has become the other alternative in order to develop emulsion stability as well as the extraction efficiency. The unique characteristic of ionic liquid such as low melting point, insignificant vapor pressure, and low flammability have successfully drawn a great attention of many researchers in order to improve the membrane stability. Room temperature ionic liquids, which are constituted by salts comprising organic anions and cations have provided great potential application as an alternative candidate in membrane separation. They have been reported by a number of researchers as a carrier, diluent, and stabilizer in liquid membrane procedure for various types of metal removal [21–23]. In the presence of ionic liquid, the robust membrane barrier has been produced in order to stabilize the emulsion in the emulsion liquid membrane process. The emulsion stability is due to the Coulombic interactions of the charges on the ions of ionic liquids [BMIM]+[NTf2] with carrier, surfactant, diluent, and stripping agent. The Coulomb interaction also called Coulomb force or electrostatic force between two or more charged. If the particles are both positively and negatively charged, the force is repulsive and if they are of opposite charge, it is attractive. The attractive interaction between the opposite charges of ionic liquid can create the strong van der Waals interactions, which can avoid the coalescence of the internal droplets [24]. This ionic liquid also is capable of developing a polymeric structure with large cavities when they are used as a solvent. These polymeric structures of ionic liquid also act as barrier in membrane phase thus enhancing emulsion stability [25]. The properties such as high hydrophobicity of [BMIM]+[NTf2]also prevent the reaction with water in the stripping phase, hence enhancing the emulsion stability [26]. In this research, the main focus was to study the extraction of ionized nanosilver from the wash water using emulsion liquid membrane process. Several parameters such as effect of carrier, stripping agent and surfactant concentration, emulsifying time, homogenizer and agitation speed, pH of feed phase, extraction time, and treat ratio were investigated. In addition, the effect of ionic liquid [BMIM]+[NTf2]has also been attempted as well. The ranges of parameters studied are illustrated in Table 1. 2. Extraction mechanism of ionized nanosilver The mechanism for the extraction of ionized nanosilver is exhibited in Fig. 1. The extractant, Cyanex 302 act as a carrier in this process. The structure of Cyanex 302 is shown in Fig. 2(a). Silver ion chemically reacts with the carrier to form the silvercarrier complexes, Ag(RH)2 on the external interface as illustrated by Eq. (1). Then, these complexes diffuse through the liquid membrane to the internal interface. AgðTEAÞ2 OH þ H3 Oþ þ ðRHÞ2 ! AgðRHÞ2 þ 2½TEAHOH
(1)
Table 1 The range of parameters used in the extraction of ionized nanosilver. Operating conditions
Ranges
Volume of acidic Thiourea (ml) Volume of Cyanex 302 in kerosene (ml) Emulsifying time (min) Span 80 concentration (% w/v) Cyanex 302 concentration (M) Homogenizer speed (rpm) Agitation speed (rpm) pH of wash water Thiourea concentration (M) Sulfuric acid concentration (M) Ionic liquid concentration (% w/v) Treat ratio (emulsion to external ratio) Extraction time (min)
5 5 5, 10, 15, 20 1, 3, 5, 7 0.0003, 0.0005, 0.0007, 0.001 8000, 10000, 12000, 13000 200, 250, 300, 350 2, 4, 5, 8 0.5, 1.0, 1.5, 2.0 1 1–6 3, 5, 7, 10 5, 10, 15, 20
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
3
3.2. Nanosilver ionization study
Fig. 1. Extraction mechanism of silver ion by ELM using Cyanex 302 as carrier from the wash water solution; (HR)2 is a dimer of Cyanex 302.
At this interface, silver ion from the silver-carrier complexes are stripped by the acidic Thiourea into stripping phase to form stable complexes of Ag–Thiourea which cannot penetrate reversibly into the membrane phase and the carrier diffuse back to the external interface. The reaction at stripping phase can be expressed by Eq. (2): AgðRHÞ2 þ CSðNH2 Þ2 Hþ $ ðRHÞ2 þ AgðCSðNHÞ2 Þ2 Hþ
(2)
The wash water containing silver–triethanolamine complexes, Ag(TEA)2OH as illustrated in Fig. 1, are derived from Eqs. (3)–(5). Triethanolamine is a common surfactant used in liquid detergent and has been found to be chemically react with silver ions [27]. The structure of triethanolamine is shown in Fig. 2(b). TEA þ H2 O ! TEAHþ þ OH
(3)
Ag þ ½TEAHOH ! AgOH þ TEAHþ
(4)
AgOH þ 2½TEAHOH ! AgðTEAÞ2 OH þ 2H2 O
(5)
where, TEA represents NR30 and R0 represent ethanol group of TEA
This research focused on the ionization of nanosilver during washing machine process. To make simulated wash water containing nanosilver ion, about 0.001 g of nanosilver powder was added in 100 ml wash water and mixed together with 1–4% w/ w surfactant of detergent, triethanolamine. Then the solution was put in the water bath and the temperature was setting up from 30 to 60 8C with speed from 200 to 350 rpm, respectively. The ionization process was carried out for 45 minand represents the operation time of real washing machine. The ionized nanosilver in the simulated solution was analyzed using Atomic Absorption Spectrometry (AAS). The amount of nanosilver ionized will be recorded. 3.3. Emulsion preparation An equal volume of 5 ml of organic liquid membrane solution (Cyanex 302 and Span 80 in kerosene) and an aqueous stripping solution (acidic Thiourea) was emulsified constantly at 12,000 rpm by employing motor driven homogenizer for 5 min to achieve a stable primary emulsion. For the study of the ionic liquid effect, 1–5% w/v of ionic liquid was added appropriately. The emulsion needs to be freshly prepared each time before the experiments. 3.4. Extraction process The primary emulsion was dispersed into the 250 ml beaker with 70 ml of wash water containing nanosilver solution as a feed phase. The mixture of water and water in oil emulsion was agitated using a motor stirrer with an extraction speed of 250 rpm for 15 min. Then the mixture was separated by pouring into the separation funnel about half an hour for phase separation. The apparent swelling and breakage of the emulsion was determined by measuring the volume of emulsion before and after the extraction process while the aqueous phase was measured using Atomic Absorption Spectrometry (AAS). The schematic diagram of the emulsion liquid membrane process is shown in Fig. 3.
3. Experimental 3.5. Analytical method 3.1. Materials Cyanex 302 (85% purity) as a carrier, kerosene (78% purity) as diluent, Span 80 (99% purity) as a surfactant, and Thiourea (99% purity) in sulfuric acid (98% purity) as stripping agent were obtained from Sigma–Aldrich. Ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide [BMIM]+[NTf2] (98% purity) was used as a stabilizer in ELM system also was acquired from Sigma–Aldrich. Nanosilver in the range less than 100 nm in size was procured from one of the company in Malaysia. Wash water containing triethanolamine was taken from the laundry service. All these materials were used directly as received from the manufacturer.
The apparatus used in the study include homogenizer Heidolph Silent Crusher for emulsion preparation, portable smart pH meter 108 (Milwaukee Model) for pH measurement, viscometer for viscosity measurement, and Perkin Elmer Flame Atomic Absorption Spectrometer (AAS) for the measurement of silver ion concentration, 3.6. Determination and calculation The percentage of ionized nanosilver extraction and emulsion swelling and breakage was determined by using Eqs. (6) and (7), respectively. Co Ct 100 ð%Þ Co
(6)
V i;t V i;o 100 ð%Þ V i;o
(7)
Percentage of extraction; Ex ¼
Percentage of swelling; Sw ¼
Fig. 2. (a) Structure of Cyanex 302; R = bis(2,4,4-trimethylpentyl) group (b) structure of triethanolamine (TEA).
Where Co is the initial concentration of silver in feed phase, whereas Ct represents the concentration of silver after extraction; V i;o is the initial volume of the volume before extraction and V i;t is volume of emulsion after extraction.
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
4
Fig. 3. Schematic diagram of emulsion liquid membrane process for ionized nanosilver extraction process.
is reduced which have a high tendency to destabilize the emulsion. Thus, the acidic medium, pH 2 was used in the feed phase in order to enhance the extraction efficiency of silver ion.
4. Results and discussion 4.1. Nanosilver ionization study Table 2 shows nanosilver ionization study at favorable condition. Almost 70% of nanosilver have been ionized which was confirmed by Atomic Absorption Spectrometry (AAS) analysis. During the process, triethanolamine as a surfactant was added in order to help the ionization of nanosilver which chemically reacts with the silver forming silver–TEA complexes. This is in line with Benn et al. [6] who claimed about 90% of nanosilver was ionized in water. Hence, it is proven that nanosilver can potentially ionized into the water especially wash water. 4.2. Effect pH of feed phase Fig. 4 shows the effect pH of feed phase towards the performance of ionized nanosilver extraction. As can be observed, 76.47% of silver ion was extracted and no extraction occurred at pH 2 and 8, respectively. The facilitated transfer of silver ion occurs when the pH of the stripping phase is lower than the pH of the feed phase. Besides, acidic medium provides the stronger complexation between the solute and the carrier hence increasing the extraction efficiency. Besides, the higher hydrogen ions concentration in the feed phase will induce the transportation the silver ion from feed phase into the stripping phase. However, it can drive more transportation of water molecules by hydration surfactant to the stripping phase which leads to the emulsion swelling. This finding is supported by Peng et al. [28] who indicated that at low pH in the stripping phase, the solute molecule partly transforms into an ionic state while at high pH, the properties of the surfactant as stabilizer
4.3. Effect of carrier concentration The influence of carrier concentration towards the performance of silver ion extraction and emulsion swelling is depicted in Fig. 5. The result shows that 99.89% of silver ion was extracted when using carrier concentration from 0.0003 to 0.001 M. However at 0.0003 M, 20% of the emulsion swelling was observed. Basically Cyanex 302 molecule has structural characteristics much like a surfactant, a nonpolar hydrophobic end (bis(2,4,4-trimethypentyl) groups) and a polar hydrophilic end (the phosphate group) and thus showing an affinity for the water interface [29]. This hydrophilic part can encourage the transportation of water molecules into the internal phase. In contrast, the emulsion swelling decreased by increasing the carrier concentration from 0.0003 to 0.0005 M. This can be attributed that at the higher carrier concentration, the membrane phase tends to be more viscous as shown in Fig. 6. This condition creates the resistance for the
Table 2 Nanosilver ionization study. Variables
Percent ionization (%)
Agitation speed (350 rpm) Triethanolamine concentration (4% w/w) Temperature (50 8C)
69.13
Fig. 4. Effect on pH of feed phase towards the performance of ionized nanosilver extraction (emulsifying time = 5 min; [Cyanex 302 in kerosene] = 0.0005 M; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Span 80] = 3% w/ v; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min and emulsion/ feed = 1/7).
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Fig. 5. Effect of carrier concentration towards the performance of silver ion extraction and emulsion swelling (emulsifying time = 5 min; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
Fig. 6. Membrane viscosity at different carrier concentration.
transportation of water molecules from the feed phase into the internal phase, hence decreasing the emulsion swelling. This is supported by Lee et al. [30] who observed that the higher concentration of carrier leads to the high viscosity effect which resists the mass transfer of water molecules into the internal phase [30]. Nevertheless, further increase in the carrier concentration up to 0.001 M has slightly increased the emulsion swelling. This is in agreement with Tang et al. [20] who observed that in excess carrier concentration lead to high osmotic swelling and high rates of membranes breakdown. Then, there exists a trade-off between these two effects. Thus, 0.0005 M Cyanex 302 concentration was selected as the best condition with the lowest percentage of swelling. 4.4. Effect of stripping agent concentration Fig. 7 illustrates the effect of various stripping agent concentrations towards the performance of silver ion extraction and emulsion swelling. The result shows that 99.89% of silver ion was extracted and it was observed that the emulsion swells during the extraction process. At 0.5 M Thiourea concentration, 60% of the swelling was observed. This can be explained by the fact that the concentration of 0.5 M Thiourea in 1.0 M H2SO4 would increase the concentration of hydrogen ion in stripping phase, hence enhancing the ionic strength of stripping phase. This condition has led to the occurrence of osmotic pressure gradient between both the phases, which allow the transportation of more water molecules from the feed phase into stripping phases. This finding is in agreement with Teresa et al. [31] who found that the differences of ionic strength between the two aqueous phases promoted water transfer from feed phase into stripping phase. In contrast, by increasing the concentration up to 1.0 M Thiourea, the swelling effect significantly dropped to 5%. This indicates that 1.0 M Thiourea in 1.0 M
5
Fig. 7. Effect of stripping agent concentrations towards the performance of silver ion extraction and emulsion swelling (emulsifying time = 5 min; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Cyanex 302 in kerosene] = 0.0005 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
H2SO4 is strong enough to strip the silver ions due to an appropriate stoichiometry of one to one molar ratio Thiourea and H2SO4. There is also the saturation of the driving force for diffusion through ELM owing to an increase of metal complexes concentration at the membrane-stripping solutions interface [32]. Therefore, further increase in the Thiourea concentration from 1.0 to 2.0 M only significantly increased the swelling percentages. According to Othman et al. [18], increasing Thiourea concentration above the optimum condition might lead to the salt formation which has a high tendency for membrane breakage. Another observation also reported by Goyal et al. [33] who indicated that the higher concentration of stripping agent will lead to the reaction with surfactant and reduces the number of surfactant in the membrane which causes emulsion destabilization. Based on the result obtained, 1.0 M Thiourea was selected as the most stable concentration with minimum 5% of swelling occurrence. 4.5. Effect of emulsifying time Fig. 8 shows the effect of emulsifying time on the performance of silver ion extraction and emulsion stability. It was demonstrated that by increasing an emulsifying time from 5 to 20 min, 99.76% of silver ion was extracted. At 5 min of emulsifying time, the lowest swelling was observed. Nevertheless, further increase of emulsifying time up to 10 min increased the emulsion swelling. It is because longer emulsifying time provides great exposure of stripping phase to the high internal shearing speed which leads to a high number of smaller droplets. Thus, the interfacial areas available for mass transfer of solutes increase and promote water molecules transfer between the two aqueous phases. Similar observation is reported by Chiha et al. [34] who found that when the emulsification time increases, the swelling percentage also
Fig. 8. Effect of emulsifying time towards the performance of silver ion extraction and emulsion stability ([Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; [Cyanex 302 in kerosene] = 0.0005 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
6
gradually increases because of the high internal shearing, producing a high number of smaller globules, which is conducive to their diffusion into feed phase. However, when increasing the emulsifying time up to 20 min, there is not much difference in swelling occurs. This is due to the production of smaller globules that tend to coalesce, hence resulting in larger sizes which lead to the breakage. At the same time, swelling is also increasing. There exists a trade-off between these two effects. The swollen particles can break down induced by shear. Thus, an emulsification time of 5 min was chosen throughout the study. 4.6. Effect of homogenizer speed The effect of homogenizer speeds towards the performance of silver ion extraction and emulsion stability are exhibited in Fig. 9. The result illustrates that 99.76% of silver ion was extracted. It was observed that the emulsion swelling also increased by increasing the homogenizer speed from 8000 to 10,000 rpm. This can be attributed to the high dispersion rate of the internal phase into the membrane phase which leads to the production high number of smaller emulsion globules which create the larger interfacial area of membrane-internal interface. This condition results to the more diffusion of water molecules from the external into the internal phase. However, further increase the homogenizer speeds up to 12,000 rpm decreased the emulsion swelling. At this stage, the higher speed has led to the formation of a higher number of smaller emulsion droplets which tend to swell and break simultaneously. However, in this condition, the emulsion breakage is highly dominated, hence decreasing the emulsion swelling. This is in line with Othman et al. [19] who observed that the higher speeds provide the emulsion breakage which decrease the emulsion stability. On the other hand, the smaller droplets also are conducive for their coalescence, thus providing larger emulsion droplets. This condition decreases the interfacial area of membrane-internal interface, hence decreasing the water diffusion into the internal phase which reduces the swelling occurrence. With further increasing the speed up to 13,500 rpm, emulsion swelling increased again. This indicates that the rapid coalescence provide the higher emulsion breakage. However, the swelling which take place among the other smaller emulsion globules were occurring simultaneously. Then, there exists a trade-off between these two effects. Therefore in this study, 12,000 rpm was selected as the best homogenizing speed for further experiment. 4.7. Effect of agitation speed Fig. 10 illustrates the effect of agitation speed on the extraction of silver ion performance and emulsion stability. The result shows
Fig. 9. Effect of homogenizer speeds towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; Span 80 = 3% w/v; agitation speed = 250 rpm; [Cyanex 302 in kerosene] = 0.0005 M; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
Fig. 10. Effect of agitation speeds towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; Span 80 = 3% w/v; [Cyanex 302 in kerosene] = 0.0005 M; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
that 99.86% of silver ion was extracted during the extraction process. It was observed that when increasing the speed from 200 to 250 rpm swelling percentages significantly decreased because high numbers of smaller globules are produced which lead to higher emulsion stability. However, the emulsion swelling increased with further increase of agitation speed from 250 to 300 rpm. At this stage, an entrainment swelling occurs which is caused by the entrainment of feed phase into the stripping phase due to the repeated coalescence emulsion globules during the dispersion time, thus increasing the volume of the internal phase. This finding is strongly supported by Wan et al. [35], who found that entrainment swelling occurs at the beginning of the dispersing operation and remains unchanged under stable mixing conditions and increases the volume of the stripping phase. There is not much increment in swelling occurrence when increasing the speed up to 350 rpm. The higher mixing speed may result in breaking the emulsion droplets. However, some globules also tend to swell at the same time. Higher mixing speed is in favor of improving the dispersion of emulsion in the treated feed solutions and then decreases the thickness of membrane phase, which promotes the diffusing process, thus leading to the swelling [20]. Thus, 250 rpm is an appropriate speed for the further extraction process. 4.8. Effect of Span 80 concentration Fig. 11 exhibits the effect of surfactant concentration on the performance of silver ion extraction and emulsion stability. The result presents that 99.85% of silver ion was extracted. It is observed that 5% of emulsion breakage occurred at low concentration of Span 80 (1% w/v). This can be attributed that at low surfactant concentration, only a small number of internal water droplets appear in the dispersed emulsion globules which are insufficient to
Fig. 11. Effect of Span 80 concentration towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; [Cyanex 302 in kerosene] = 0.0005 M; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
stabilize the emulsion, thus leading to the emulsion breakage. This is in agreement with Malik et al. [36], who found that an insufficient surfactant concentration cannot be a tough barrier, protecting the internal and feed phase from emulsion breaking. An increase the amount of surfactant concentration from 3 to 5% w/v increased the emulsion swelling. This can be explained by the fact that at the higher concentrations of surfactant, the surface tension of membrane phase was reduced. This condition has led to the formation of a high number of smaller emulsion droplets which tend to coalesce, thus leading to the emulsion breakage. At the same time, the hydrophilic part of surfactants promotes the transportation of water molecules into the internal phase hence increasing the emulsion swelling. There would be a trade-off between the two effects of breakage and swelling phenomena. Beyond 5–10% w/v Span 80 concentrations, the swelling becomes increasingly high due to the more surfactants which have high potential for the transportation of water molecules from the feed phase into the internal phase. On the other hand, the molecules of surfactant may exist as inverse micelles which can transport large quantities of water from external phase into the internal phase [37,38]. Thus, 3% w/v of Span 80 concentration is enough for the production of the stable emulsion with minimum swelling occurrence. 4.9. Effect of emulsion to feed ratio (treat ratio) Fig. 12 exhibits the effect of treat ratio on the extraction of silver ion and emulsion stability. The treat ratio is varied by changing the amount of feed phase and keeping the volume of the membrane constant. The treat ratio controls the interfacial mass transfer across emulsion liquid membrane. The result observes that 99.89% of silver ion was extracted. At a low treat ratio of 0.10, emulsion swelling was observed. This is due to the emulsion phase did not disperse very well and the contact area between both phases significantly decreased. At the same time, the surfactant would also provide the co-transport of water, thus diluting the internal phase. A further increase in the treat ratio up to 0.14 has slightly decreased the emulsion swelling. This indicates that at this ratio, ELM system has achieved the effectiveness of the stability. In addition, increasing treat ratio also increased the emulsion phase hold up which simultaneously increased in the extraction capacity [39]. At higher treat ratio provides higher space for the emulsion dispersion, hence increasing the contact area between the two phases [40–42]. Further increase treat ratio up to 0.33, the emulsion gets breakage. This condition might lead to the increment of the surface area for mass transfer owing to the formation of a high number of emulsion globules. However, there is continuous movement of water molecules into the internal phase with the help of hydration surfactant which lead to the emulsion breakage. Therefore, treat ratio of 0.14 was used as an optimum condition for silver ion extraction.
Fig. 12. Effect of treat ratio towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; [Cyanex 302 in kerosene] = 0.0005 M; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2).
7
Fig. 13. Effect of extraction time towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; [Cyanex 302 in kerosene] = 0.0005 M; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; pH 2 and emulsion/feed phase = 1/7).
4.10. Effect of extraction time The effect of extraction time on the performance of nanosilver ion extraction and emulsion stability is depicted in Fig. 13. The result demonstrates that 99.84% of silver ion was extracted. Emulsion breakage was observed at the first 5 min. This indicates that at the short contact time, mass transfer of solutes increases rapidly once it comes in contact with the carrier in ELM system. At the same time, the hydration surfactant also significantly increases the co-transport of water molecules into the internal phase, hence leading to the emulsion breakage. As the extraction time increased up to 10 min, emulsion swelling slightly increased due to the surfactant which carried water molecules continuously into internal phase. At 15 min of extraction time, swelling decreased. It seems that this period of contact time is adequate for satisfactory extraction efficiency. Besides, Mortaheb et al. [42] also observed that by increasing the mixing intensity of emulsion and feed phases, the contact area for mass transfer is increased due to a reduction in the size of the globules, thus enhancing emulsion stability. With further increasing the extraction time up to 20 min, emulsion swelling slightly increased. This is due to the instability of the emulsion over longer extraction times. Thus 15 min of extraction time were the best condition for silver ion extraction. 4.11. Effect of ionic liquid concentration Fig. 14 exhibits the effect of ionic liquid concentration on the extraction performance and emulsion stability. From the result
Fig. 14. Effect of ionic liquid concentration towards the performance of ionized nanosilver extraction and emulsion swelling (emulsifying time = 5 min; pH of feed phase = 2; [Cyanex 302 in kerosene] = 0.0005 M; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; pH 2 and emulsion/feed phase = 1/7).
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 8
R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
obtained, 95% of ionized nanosilver was extracted by increasing the concentration of ionic liquid [BMIM]+[NTf2] from 1 to 5% w/v. It was observed that from 1 to 3% w/v of ionic liquid concentration, the extraction significantly increased by 10% of swelling occurrence. It is because the low concentration of ionic liquid is still not strong enough to inhibit the water transport into the internal phase. However, there is no swelling or breakage observed with the additional of 4–5% w/v of ionic liquid concentration. This indicates that the higher concentrations of ionic liquid are enable to restrict the transport of water into the membrane interface, thus increasing the emulsion stability. This finding is consistent with Goyal et al. [33] who found that the polymeric structure of this ionic liquid can form polymeric surfactant and produces a repulsive barrier in order to avoid the rupture of membranes. The properties such as high hydrophobicity of this ionic liquid also prevent the reaction with water in the stripping phase hence enhancing the emulsion stability [25]. 5. Conclusions As a conclusion, 99.89% of silver ions were extracted under the favorable conditions which are pH 2, 0.0005 M Cyanex 302, 1.0 M acidic Thiourea, 5 min of emulsifying time, 12,000 rpm of homogenizer speed, 250 rpm of agitation speed, 3% w/v Span 80, 15 min of extraction time, and 0.14 of treat ratio. The ionic liquid [BMIM]+[NTf2] also provide a good performance on emulsion stability during the extraction of ionized nanosilver with around 10% of the swelling. Acknowledgement The authors would like to acknowledge the Ministry of Science Technology and Innovation (Vot 4H009) and Universiti Teknologi Malaysia for making this research possible. References [1] J.L. Elechiguerra, J.L. Burt, A. Morones, H.H. Gao, M.J. Lara, M.J. Yacaman, J. Nanobiotechnol. 3 (2005) 1. [2] X. Chen, H.J. Schluesener, Toxicol. Lett. 176 (2008) 1.
[3] U.S. EPA (U.S. Environmental Protection Agency) (2009) http://www.epa.gov/ waterscience/criteria/wqctable/nrwqc-2009.pdf.(Accessed September 2013). [4] North Carolina Department of Environment Health (2007) http://hero.epa.gov/ index.cfm?action=search.view&reference_id=597412.(Accessed September 2013). [5] Oregon Department of Environmental Quality (2004) http://hero.epa.gov/ index.cfm?action=search.view&reference_id=597421.(Accessed September 2013). [6] T.M. Benn, P. Westerhoff, Environ. Sci. Technol. 42 (2008) 4133. [7] Y. Yan, H. Yang, J. Li, X. Lu, C. Wang, Text. Res. J. 0 (00) (2012) 1. [8] J. Fabrega, S.N. Luoma, C.R. Tyler, T.S. Galloway, J.R. Lead, Environ. Int. 37 (2011) 517. [9] J. Farkas, H. Peter, P. Christian, J.A.G. Urrea, M. Hassellov, J. Tuoriniemi, S. Gustafsson, E. Olsson, K. Hylland, K.V. Thomas, Environ. Int. 37 (2011) 1057. [10] T. Benn, B. Cavanagh, K. Hristovski, J.D. Posner, P. Westerhoff, J. Environ. Qual. 39 (2010) 1875. [11] S.W.P. Wijnhoven, W.J.G.M. Peijnenburg, C.A. Herberts, W.I. Hagens, A.G. Oomen, E.H.W. Heugens, B. Roszek, J. Bisschops, I. Gosens, V.D. Meent, D. Dekkers, S.D. Jong, W.H.V. Zijverden, M. Sips, R.E. Geertsma, Nanotoxicology 3 (2) (2009) 109. [12] P.V. Asharani, Y.L. Wu, Nanotechnology 19 (2008) 1. [13] M. Chatelut, E. Gobert, O. Vittori, Hydrometallurgy 54 (2) (2000) 79. [14] J.P. Chen, L.L. Lim, Chemosphere 60 (2005) 1384. [15] S.G. Sarkar, P.M. Dhadke, J. Chin. Chem. Soc. 47 (2000) 869. [16] N. Othman, H.B. Mat, M. Goto, J. Solvent Extr. Res. Dev. Jpn. 12 (2005) 27. [17] A. Gfiveng, B. Karabacako, Desalination 172 (2005) 7. [18] N. Othman, H. Mat, M. Goto, J. Membr. Sci. 282 (2006) 171. [19] N. Othman, R. Djamal, N. Mili, S.N. Zailani, J. Appl. Sci. 11 (7) (2011) 1406. [20] B. Tang, G. Yua, J. Fang, T. Shi, J. Hazard. Mater. 177 (2010) 377. [21] A.L. Ahamed, A. Kusumastuti, C.J.C. Dereka, B.S. Ooi, Chem. Eng. J. 171 (2011) 870. [22] R.K. Goyal, N.S. Jayakumar, M.A. Hashim, J. Hazard. Mater. 195 (2011) 55. [23] S. Venkatesan, K.M.M.S. Begum, Chem. Eng. J 148 (2009) 254. [24] T. Mandai, M. Imanari, K. Nishikawa, Chem. Phys. Lett. 543 (2012) 72. [25] A. Balasubramanian, S. Venkatesan, Desalination 289 (2012) 27. [26] Y.S. Ng, N.S. Jayakumar, M.A. Hashim, Desalination 278 (2011) 250. [27] T. Kocareva, I. Grozdanov, B. Pejova, Mater. Lett. 47 (2001) 319. [28] W. Peng, H. Jiao, H. Shi, C. Xu, Desalination 286 (2012) 372. [29] D. Wu, Y. Xiong, D. Li, Hydrometallurgy 82 (2006) 176. [30] S.C. Lee, J. Membr. Sci. 381 (2011) 237. [31] M. Teresa, A. Reis, M.R. Carvalho, Chem. Eng. Technol. 17 (1994) 242. [32] R.A. Kumbasar, Sep. Purif. Technol. 64 (2008) 56. [33] R.K. Goyal, N.S. Jayakumar, M.A. Hashim, Desalination 278 (2011) 5. [34] M. Chiha, Q. Hamdaoui, F. Ahmadchekkat, C. Petrier, Ultrason. Sonochem. 17 (2010) 318. [35] Y. Wan, X. Zhang, J. Membr. Sci. 196 (2002) 185. [36] M.A. Malik, M.A. Hashim, F. Nabi, J. Dispersion Sci. Technol. 33 (3) (2012) 346. [37] S. Venkatesan, K.M.M.S. Begum, Desalination 236 (2009) 65. [38] B.S. Chanukya, N.K. Rastogi, Sep. Purif. Technol. 105 (2013) 41. [39] R.A. Kumbasar, Sep. Purif. Technol. 68 (2009) 208. [40] R.A. Kumbasar, O. Tutkun, Desalination 224 (2008) 201. [41] H.R. Mortaheb, H. Kosuge, B. Mokhtarani, M.H. Amini, H.R. Banihashemi, J. Hazard. Mater. 165 (2009) 630. [42] H.R. Mortaheb, M.H. Amini, F. Sadeghian, B. Mokhtarani, H. Daneshyar, J. Hazard. Mater. 160 (2008) 582.
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
JIEC-1734; No. of Pages 8 Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Emulsion liquid membrane stability in the extraction of ionized nanosilver from wash water Raja Norimie Raja Sulaiman a,b, Norasikin Othman a,*, Nor Aishah Saidina Amin b a
Centre of Lipid Engineering and Applied Research (CLEAR), Faculty of Chemical Engineering, Universiti Teknologi Malaysia (UTM), Skudai, 81310 Johor Bharu, Malaysia b Chemical Reaction Engineering Group (CREG), Faculty of Chemical Engineering, Universiti Teknologi Malaysia (UTM), Skudai, 81310 Johor Bharu, Malaysia
A R T I C L E I N F O
Article history: Received 5 September 2013 Accepted 3 December 2013 Available online xxx Keywords: Emulsion liquid membrane Ionized nanosilver Wash water Removal Ionic liquid
A B S T R A C T
The discharge of ionized nanosilver into environment triggers a great concern owing to the toxicity problem for aquatic organism. In this study, emulsion liquid membrane used to extract the ionized nanosilver from wash water. Variables like carrier, stripping agent and surfactant concentrations, emulsifying time, homogenizer and agitation speed, pH feed phase, and effect of ionic liquid [BMIM]+[NTf2]were investigated. The membrane phase containing Cyanex 302, Span 80, acidic Thiourea, and kerosene as carrier, surfactant, stripping agent, and diluent respectively. Results demonstrated that 99.89% of silver ion was extracted and ionic liquid show good performance on emulsion stability with 10% swelling. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Nanosilver has been extensively used in various consumer products, medicines, and food applications owing to the high prospects of its antimicrobial properties. For instance, this nanoparticle can act as an anti-HIV drug by inhibiting the human immunodeficiency virus (HIV) replication [1]. Besides, they are also coated with the medical devices in order to avoid the occurrence of infection [2]. United States Environmental Protection Agency (USEPA) indicates silver as a priority pollutant in natural waters in 1977. USEPA also regulates a guideline of less than 0.10 ppm of total silver in drinking water due to the potential effects of silver ingestion specifically argyria disease. USEPA, however, prescribes maximum concentrations of 3.2 ppb silver in fresh water and 1.9 ppb in salt water based on acute toxicity of silver to macroinvertebrates and fish [3]. These standards are enforced through the issuance of discharge permits at the state level. With respect to the chronic water quality to protect aquatic life, a few states have set the threshold concentrations for example the North Carolina Division of Water Quality has proposed a criterion of 0.06 ppb [4]. Oregon also has established a 0.12 ppb criterion in its administrative rules based on chronic toxicity to rainbow trout and minnows in fresh water and to mysids in salt
* Corresponding author. Tel.: +607 5535561; fax: +607 5581463. E-mail address: [email protected] (N. Othman).
water [5]. Texas, New York, and several regions in California have established maximum contaminant levels for silver between 5 and 10 ppb. Nanosilver used in some products can enter the environment as individual nanoparticles, small clusters, or potentially dissolve into ions. The ionization behavior of nanosilver in the ionic form has been reported by several researchers via clothing, textiles, washing machine, and home application [6–9]. According to Benn et al. [6], about 1.30 ppm of nanosilver ions have been leached into distilled water from the six types of commercial socks containing nanosilver. Another study also observes as much as 11 ppb of nanosilver ions have been released from washing machine (Samsung brand) which contain ion generating devices for nanosilver ions release in order to protect our clothing from bacteria during the washing process [9]. To date, Benn et al. [10] have found that about 3.2 and 7.6 ppm of silver ion was released from silver nanoparticles coming from the detergent and the toothpaste, respectively. The presence of nanosilver in the natural water environment is of great concern due to its small size, which can create toxicity effect to aquatic organism, especially when it is in the free ionized form [11]. The toxicity effect occurred when the silver ions have massively associate with the other chemicals organic or colloidal, hence influencing the bioavailability and the bioacccumulation of nanoparticle into the cell of aquatic organism. The observation shows that the exposure of nanosilver ions with concentration of 5 ppm can increase the mortality and heart malformation in zebra fish [12].
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.12.005
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 2
R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Therefore, the removal of this nanoparticle from the waste water is very positive for environmental safety. In the past, several numbers of methods were reported for nanosilver ion extraction including electrowinning [13], electrochemical method [14], solvent extraction [15,16], electrodialysis [17], and liquid membrane separation [18,19]. The disadvantage of electrochemical method is the deposition rate and the composition of the solution, in some cases, can cause the production of dendrites and loose or spongy deposits and interference from the hydrogen evolution reaction. In addition, this process also involves a large capital investment with expensive electricity supply. Besides, electrowinning also is a suitable process for the treatment of effluents with a silver concentration between 2 and 12 ppm. The recovery of silver down to concentrations of less than 0.2 ppm enables the formation of the precipitate silver sulfide on the cathodic surface. However, a second treatment is required by cementation or chemical precipitation. Solvent extraction also involves high consumption of chemical reagents. The electrodialysis is an advance technology, which does not lend itself readily to small-scale applications due to its high capital and operational costs, and requirement for highly trained people with supervision. Liquid membrane technology is regarded as one of the effective method, which combines the extraction and recovery process thus making this technique more advantageous and profitable over other separation methods. Therefore, this method does not need the second treatment like electrowinning, which need the other treatment, which is cementation or chemical precipitation process [13]. The extraction chemistry is basically the same as that found in solvent extraction, but the transport is governed by kinetic rather than equilibrium parameters, that is, it is governed by a non-equilibrium mass transfer. This process also provides low cost and energy because not much chemicals and equipments are used if compared with the electrochemical deposition method, which involve large capital investment with expensive electricity supply [14]. On the other hand, this method also provides the low consumption of chemicals which is the use of carrier is ten times lower than that used in solvent extraction method [15]. Principally, emulsion liquid membrane involves a dispersion of emulsion containing of organic and aqueous stripping phase into the aqueous feed phase containing solutes. The solute from the feed phase permeates into the membrane phase and chemically reacts with the stripping agent present in the stripping phase, which impenetrates in the membrane phase and remains confined in stripping phase. The transportation of solute in the emulsion liquid membrane is chiefly motivated by the concentration gradient and pH. Based on the ELM system, which involves the mass transfer mechanism of metal ions from the external into the internal phase have proven that the silver ion have been ionized from the silver nanoparticles and react with the carrier and stripping agent. However, the main drawback experienced with this method is the emulsion stability problem which influences the extraction efficiency. The emulsion liquid membrane stability problem which take place in emulsion liquid membrane system are swelling and breakage phenomena. Swelling occurs when the water molecules from the external phase is transferred inside the internal phase, diluting the solute and reducing the solute concentration. Emulsion swelling can increase in emulsion volume during operation and trigger the breakdown of the globules which finally decrease the extraction efficiency. In the meantime, the membrane breakage occurs when portions of the internal phase spill into the external phase. During breakage, the stripping agent and previously extracted solute is leaked into the external phase [20]. The most stable emulsion was obtained when there was neither swelling nor breakage or emulsion with minimum of swelling occurrence.
The application of ionic liquid in the liquid membrane has become the other alternative in order to develop emulsion stability as well as the extraction efficiency. The unique characteristic of ionic liquid such as low melting point, insignificant vapor pressure, and low flammability have successfully drawn a great attention of many researchers in order to improve the membrane stability. Room temperature ionic liquids, which are constituted by salts comprising organic anions and cations have provided great potential application as an alternative candidate in membrane separation. They have been reported by a number of researchers as a carrier, diluent, and stabilizer in liquid membrane procedure for various types of metal removal [21–23]. In the presence of ionic liquid, the robust membrane barrier has been produced in order to stabilize the emulsion in the emulsion liquid membrane process. The emulsion stability is due to the Coulombic interactions of the charges on the ions of ionic liquids [BMIM]+[NTf2] with carrier, surfactant, diluent, and stripping agent. The Coulomb interaction also called Coulomb force or electrostatic force between two or more charged. If the particles are both positively and negatively charged, the force is repulsive and if they are of opposite charge, it is attractive. The attractive interaction between the opposite charges of ionic liquid can create the strong van der Waals interactions, which can avoid the coalescence of the internal droplets [24]. This ionic liquid also is capable of developing a polymeric structure with large cavities when they are used as a solvent. These polymeric structures of ionic liquid also act as barrier in membrane phase thus enhancing emulsion stability [25]. The properties such as high hydrophobicity of [BMIM]+[NTf2]also prevent the reaction with water in the stripping phase, hence enhancing the emulsion stability [26]. In this research, the main focus was to study the extraction of ionized nanosilver from the wash water using emulsion liquid membrane process. Several parameters such as effect of carrier, stripping agent and surfactant concentration, emulsifying time, homogenizer and agitation speed, pH of feed phase, extraction time, and treat ratio were investigated. In addition, the effect of ionic liquid [BMIM]+[NTf2]has also been attempted as well. The ranges of parameters studied are illustrated in Table 1. 2. Extraction mechanism of ionized nanosilver The mechanism for the extraction of ionized nanosilver is exhibited in Fig. 1. The extractant, Cyanex 302 act as a carrier in this process. The structure of Cyanex 302 is shown in Fig. 2(a). Silver ion chemically reacts with the carrier to form the silvercarrier complexes, Ag(RH)2 on the external interface as illustrated by Eq. (1). Then, these complexes diffuse through the liquid membrane to the internal interface. AgðTEAÞ2 OH þ H3 Oþ þ ðRHÞ2 ! AgðRHÞ2 þ 2½TEAHOH
(1)
Table 1 The range of parameters used in the extraction of ionized nanosilver. Operating conditions
Ranges
Volume of acidic Thiourea (ml) Volume of Cyanex 302 in kerosene (ml) Emulsifying time (min) Span 80 concentration (% w/v) Cyanex 302 concentration (M) Homogenizer speed (rpm) Agitation speed (rpm) pH of wash water Thiourea concentration (M) Sulfuric acid concentration (M) Ionic liquid concentration (% w/v) Treat ratio (emulsion to external ratio) Extraction time (min)
5 5 5, 10, 15, 20 1, 3, 5, 7 0.0003, 0.0005, 0.0007, 0.001 8000, 10000, 12000, 13000 200, 250, 300, 350 2, 4, 5, 8 0.5, 1.0, 1.5, 2.0 1 1–6 3, 5, 7, 10 5, 10, 15, 20
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
3
3.2. Nanosilver ionization study
Fig. 1. Extraction mechanism of silver ion by ELM using Cyanex 302 as carrier from the wash water solution; (HR)2 is a dimer of Cyanex 302.
At this interface, silver ion from the silver-carrier complexes are stripped by the acidic Thiourea into stripping phase to form stable complexes of Ag–Thiourea which cannot penetrate reversibly into the membrane phase and the carrier diffuse back to the external interface. The reaction at stripping phase can be expressed by Eq. (2): AgðRHÞ2 þ CSðNH2 Þ2 Hþ $ ðRHÞ2 þ AgðCSðNHÞ2 Þ2 Hþ
(2)
The wash water containing silver–triethanolamine complexes, Ag(TEA)2OH as illustrated in Fig. 1, are derived from Eqs. (3)–(5). Triethanolamine is a common surfactant used in liquid detergent and has been found to be chemically react with silver ions [27]. The structure of triethanolamine is shown in Fig. 2(b). TEA þ H2 O ! TEAHþ þ OH
(3)
Ag þ ½TEAHOH ! AgOH þ TEAHþ
(4)
AgOH þ 2½TEAHOH ! AgðTEAÞ2 OH þ 2H2 O
(5)
where, TEA represents NR30 and R0 represent ethanol group of TEA
This research focused on the ionization of nanosilver during washing machine process. To make simulated wash water containing nanosilver ion, about 0.001 g of nanosilver powder was added in 100 ml wash water and mixed together with 1–4% w/ w surfactant of detergent, triethanolamine. Then the solution was put in the water bath and the temperature was setting up from 30 to 60 8C with speed from 200 to 350 rpm, respectively. The ionization process was carried out for 45 minand represents the operation time of real washing machine. The ionized nanosilver in the simulated solution was analyzed using Atomic Absorption Spectrometry (AAS). The amount of nanosilver ionized will be recorded. 3.3. Emulsion preparation An equal volume of 5 ml of organic liquid membrane solution (Cyanex 302 and Span 80 in kerosene) and an aqueous stripping solution (acidic Thiourea) was emulsified constantly at 12,000 rpm by employing motor driven homogenizer for 5 min to achieve a stable primary emulsion. For the study of the ionic liquid effect, 1–5% w/v of ionic liquid was added appropriately. The emulsion needs to be freshly prepared each time before the experiments. 3.4. Extraction process The primary emulsion was dispersed into the 250 ml beaker with 70 ml of wash water containing nanosilver solution as a feed phase. The mixture of water and water in oil emulsion was agitated using a motor stirrer with an extraction speed of 250 rpm for 15 min. Then the mixture was separated by pouring into the separation funnel about half an hour for phase separation. The apparent swelling and breakage of the emulsion was determined by measuring the volume of emulsion before and after the extraction process while the aqueous phase was measured using Atomic Absorption Spectrometry (AAS). The schematic diagram of the emulsion liquid membrane process is shown in Fig. 3.
3. Experimental 3.5. Analytical method 3.1. Materials Cyanex 302 (85% purity) as a carrier, kerosene (78% purity) as diluent, Span 80 (99% purity) as a surfactant, and Thiourea (99% purity) in sulfuric acid (98% purity) as stripping agent were obtained from Sigma–Aldrich. Ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide [BMIM]+[NTf2] (98% purity) was used as a stabilizer in ELM system also was acquired from Sigma–Aldrich. Nanosilver in the range less than 100 nm in size was procured from one of the company in Malaysia. Wash water containing triethanolamine was taken from the laundry service. All these materials were used directly as received from the manufacturer.
The apparatus used in the study include homogenizer Heidolph Silent Crusher for emulsion preparation, portable smart pH meter 108 (Milwaukee Model) for pH measurement, viscometer for viscosity measurement, and Perkin Elmer Flame Atomic Absorption Spectrometer (AAS) for the measurement of silver ion concentration, 3.6. Determination and calculation The percentage of ionized nanosilver extraction and emulsion swelling and breakage was determined by using Eqs. (6) and (7), respectively. Co Ct 100 ð%Þ Co
(6)
V i;t V i;o 100 ð%Þ V i;o
(7)
Percentage of extraction; Ex ¼
Percentage of swelling; Sw ¼
Fig. 2. (a) Structure of Cyanex 302; R = bis(2,4,4-trimethylpentyl) group (b) structure of triethanolamine (TEA).
Where Co is the initial concentration of silver in feed phase, whereas Ct represents the concentration of silver after extraction; V i;o is the initial volume of the volume before extraction and V i;t is volume of emulsion after extraction.
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
4
Fig. 3. Schematic diagram of emulsion liquid membrane process for ionized nanosilver extraction process.
is reduced which have a high tendency to destabilize the emulsion. Thus, the acidic medium, pH 2 was used in the feed phase in order to enhance the extraction efficiency of silver ion.
4. Results and discussion 4.1. Nanosilver ionization study Table 2 shows nanosilver ionization study at favorable condition. Almost 70% of nanosilver have been ionized which was confirmed by Atomic Absorption Spectrometry (AAS) analysis. During the process, triethanolamine as a surfactant was added in order to help the ionization of nanosilver which chemically reacts with the silver forming silver–TEA complexes. This is in line with Benn et al. [6] who claimed about 90% of nanosilver was ionized in water. Hence, it is proven that nanosilver can potentially ionized into the water especially wash water. 4.2. Effect pH of feed phase Fig. 4 shows the effect pH of feed phase towards the performance of ionized nanosilver extraction. As can be observed, 76.47% of silver ion was extracted and no extraction occurred at pH 2 and 8, respectively. The facilitated transfer of silver ion occurs when the pH of the stripping phase is lower than the pH of the feed phase. Besides, acidic medium provides the stronger complexation between the solute and the carrier hence increasing the extraction efficiency. Besides, the higher hydrogen ions concentration in the feed phase will induce the transportation the silver ion from feed phase into the stripping phase. However, it can drive more transportation of water molecules by hydration surfactant to the stripping phase which leads to the emulsion swelling. This finding is supported by Peng et al. [28] who indicated that at low pH in the stripping phase, the solute molecule partly transforms into an ionic state while at high pH, the properties of the surfactant as stabilizer
4.3. Effect of carrier concentration The influence of carrier concentration towards the performance of silver ion extraction and emulsion swelling is depicted in Fig. 5. The result shows that 99.89% of silver ion was extracted when using carrier concentration from 0.0003 to 0.001 M. However at 0.0003 M, 20% of the emulsion swelling was observed. Basically Cyanex 302 molecule has structural characteristics much like a surfactant, a nonpolar hydrophobic end (bis(2,4,4-trimethypentyl) groups) and a polar hydrophilic end (the phosphate group) and thus showing an affinity for the water interface [29]. This hydrophilic part can encourage the transportation of water molecules into the internal phase. In contrast, the emulsion swelling decreased by increasing the carrier concentration from 0.0003 to 0.0005 M. This can be attributed that at the higher carrier concentration, the membrane phase tends to be more viscous as shown in Fig. 6. This condition creates the resistance for the
Table 2 Nanosilver ionization study. Variables
Percent ionization (%)
Agitation speed (350 rpm) Triethanolamine concentration (4% w/w) Temperature (50 8C)
69.13
Fig. 4. Effect on pH of feed phase towards the performance of ionized nanosilver extraction (emulsifying time = 5 min; [Cyanex 302 in kerosene] = 0.0005 M; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Span 80] = 3% w/ v; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min and emulsion/ feed = 1/7).
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Fig. 5. Effect of carrier concentration towards the performance of silver ion extraction and emulsion swelling (emulsifying time = 5 min; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
Fig. 6. Membrane viscosity at different carrier concentration.
transportation of water molecules from the feed phase into the internal phase, hence decreasing the emulsion swelling. This is supported by Lee et al. [30] who observed that the higher concentration of carrier leads to the high viscosity effect which resists the mass transfer of water molecules into the internal phase [30]. Nevertheless, further increase in the carrier concentration up to 0.001 M has slightly increased the emulsion swelling. This is in agreement with Tang et al. [20] who observed that in excess carrier concentration lead to high osmotic swelling and high rates of membranes breakdown. Then, there exists a trade-off between these two effects. Thus, 0.0005 M Cyanex 302 concentration was selected as the best condition with the lowest percentage of swelling. 4.4. Effect of stripping agent concentration Fig. 7 illustrates the effect of various stripping agent concentrations towards the performance of silver ion extraction and emulsion swelling. The result shows that 99.89% of silver ion was extracted and it was observed that the emulsion swells during the extraction process. At 0.5 M Thiourea concentration, 60% of the swelling was observed. This can be explained by the fact that the concentration of 0.5 M Thiourea in 1.0 M H2SO4 would increase the concentration of hydrogen ion in stripping phase, hence enhancing the ionic strength of stripping phase. This condition has led to the occurrence of osmotic pressure gradient between both the phases, which allow the transportation of more water molecules from the feed phase into stripping phases. This finding is in agreement with Teresa et al. [31] who found that the differences of ionic strength between the two aqueous phases promoted water transfer from feed phase into stripping phase. In contrast, by increasing the concentration up to 1.0 M Thiourea, the swelling effect significantly dropped to 5%. This indicates that 1.0 M Thiourea in 1.0 M
5
Fig. 7. Effect of stripping agent concentrations towards the performance of silver ion extraction and emulsion swelling (emulsifying time = 5 min; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Cyanex 302 in kerosene] = 0.0005 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
H2SO4 is strong enough to strip the silver ions due to an appropriate stoichiometry of one to one molar ratio Thiourea and H2SO4. There is also the saturation of the driving force for diffusion through ELM owing to an increase of metal complexes concentration at the membrane-stripping solutions interface [32]. Therefore, further increase in the Thiourea concentration from 1.0 to 2.0 M only significantly increased the swelling percentages. According to Othman et al. [18], increasing Thiourea concentration above the optimum condition might lead to the salt formation which has a high tendency for membrane breakage. Another observation also reported by Goyal et al. [33] who indicated that the higher concentration of stripping agent will lead to the reaction with surfactant and reduces the number of surfactant in the membrane which causes emulsion destabilization. Based on the result obtained, 1.0 M Thiourea was selected as the most stable concentration with minimum 5% of swelling occurrence. 4.5. Effect of emulsifying time Fig. 8 shows the effect of emulsifying time on the performance of silver ion extraction and emulsion stability. It was demonstrated that by increasing an emulsifying time from 5 to 20 min, 99.76% of silver ion was extracted. At 5 min of emulsifying time, the lowest swelling was observed. Nevertheless, further increase of emulsifying time up to 10 min increased the emulsion swelling. It is because longer emulsifying time provides great exposure of stripping phase to the high internal shearing speed which leads to a high number of smaller droplets. Thus, the interfacial areas available for mass transfer of solutes increase and promote water molecules transfer between the two aqueous phases. Similar observation is reported by Chiha et al. [34] who found that when the emulsification time increases, the swelling percentage also
Fig. 8. Effect of emulsifying time towards the performance of silver ion extraction and emulsion stability ([Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; [Cyanex 302 in kerosene] = 0.0005 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
6
gradually increases because of the high internal shearing, producing a high number of smaller globules, which is conducive to their diffusion into feed phase. However, when increasing the emulsifying time up to 20 min, there is not much difference in swelling occurs. This is due to the production of smaller globules that tend to coalesce, hence resulting in larger sizes which lead to the breakage. At the same time, swelling is also increasing. There exists a trade-off between these two effects. The swollen particles can break down induced by shear. Thus, an emulsification time of 5 min was chosen throughout the study. 4.6. Effect of homogenizer speed The effect of homogenizer speeds towards the performance of silver ion extraction and emulsion stability are exhibited in Fig. 9. The result illustrates that 99.76% of silver ion was extracted. It was observed that the emulsion swelling also increased by increasing the homogenizer speed from 8000 to 10,000 rpm. This can be attributed to the high dispersion rate of the internal phase into the membrane phase which leads to the production high number of smaller emulsion globules which create the larger interfacial area of membrane-internal interface. This condition results to the more diffusion of water molecules from the external into the internal phase. However, further increase the homogenizer speeds up to 12,000 rpm decreased the emulsion swelling. At this stage, the higher speed has led to the formation of a higher number of smaller emulsion droplets which tend to swell and break simultaneously. However, in this condition, the emulsion breakage is highly dominated, hence decreasing the emulsion swelling. This is in line with Othman et al. [19] who observed that the higher speeds provide the emulsion breakage which decrease the emulsion stability. On the other hand, the smaller droplets also are conducive for their coalescence, thus providing larger emulsion droplets. This condition decreases the interfacial area of membrane-internal interface, hence decreasing the water diffusion into the internal phase which reduces the swelling occurrence. With further increasing the speed up to 13,500 rpm, emulsion swelling increased again. This indicates that the rapid coalescence provide the higher emulsion breakage. However, the swelling which take place among the other smaller emulsion globules were occurring simultaneously. Then, there exists a trade-off between these two effects. Therefore in this study, 12,000 rpm was selected as the best homogenizing speed for further experiment. 4.7. Effect of agitation speed Fig. 10 illustrates the effect of agitation speed on the extraction of silver ion performance and emulsion stability. The result shows
Fig. 9. Effect of homogenizer speeds towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; Span 80 = 3% w/v; agitation speed = 250 rpm; [Cyanex 302 in kerosene] = 0.0005 M; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
Fig. 10. Effect of agitation speeds towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; Span 80 = 3% w/v; [Cyanex 302 in kerosene] = 0.0005 M; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
that 99.86% of silver ion was extracted during the extraction process. It was observed that when increasing the speed from 200 to 250 rpm swelling percentages significantly decreased because high numbers of smaller globules are produced which lead to higher emulsion stability. However, the emulsion swelling increased with further increase of agitation speed from 250 to 300 rpm. At this stage, an entrainment swelling occurs which is caused by the entrainment of feed phase into the stripping phase due to the repeated coalescence emulsion globules during the dispersion time, thus increasing the volume of the internal phase. This finding is strongly supported by Wan et al. [35], who found that entrainment swelling occurs at the beginning of the dispersing operation and remains unchanged under stable mixing conditions and increases the volume of the stripping phase. There is not much increment in swelling occurrence when increasing the speed up to 350 rpm. The higher mixing speed may result in breaking the emulsion droplets. However, some globules also tend to swell at the same time. Higher mixing speed is in favor of improving the dispersion of emulsion in the treated feed solutions and then decreases the thickness of membrane phase, which promotes the diffusing process, thus leading to the swelling [20]. Thus, 250 rpm is an appropriate speed for the further extraction process. 4.8. Effect of Span 80 concentration Fig. 11 exhibits the effect of surfactant concentration on the performance of silver ion extraction and emulsion stability. The result presents that 99.85% of silver ion was extracted. It is observed that 5% of emulsion breakage occurred at low concentration of Span 80 (1% w/v). This can be attributed that at low surfactant concentration, only a small number of internal water droplets appear in the dispersed emulsion globules which are insufficient to
Fig. 11. Effect of Span 80 concentration towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; [Cyanex 302 in kerosene] = 0.0005 M; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2 and emulsion/feed phase = 1/7).
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
stabilize the emulsion, thus leading to the emulsion breakage. This is in agreement with Malik et al. [36], who found that an insufficient surfactant concentration cannot be a tough barrier, protecting the internal and feed phase from emulsion breaking. An increase the amount of surfactant concentration from 3 to 5% w/v increased the emulsion swelling. This can be explained by the fact that at the higher concentrations of surfactant, the surface tension of membrane phase was reduced. This condition has led to the formation of a high number of smaller emulsion droplets which tend to coalesce, thus leading to the emulsion breakage. At the same time, the hydrophilic part of surfactants promotes the transportation of water molecules into the internal phase hence increasing the emulsion swelling. There would be a trade-off between the two effects of breakage and swelling phenomena. Beyond 5–10% w/v Span 80 concentrations, the swelling becomes increasingly high due to the more surfactants which have high potential for the transportation of water molecules from the feed phase into the internal phase. On the other hand, the molecules of surfactant may exist as inverse micelles which can transport large quantities of water from external phase into the internal phase [37,38]. Thus, 3% w/v of Span 80 concentration is enough for the production of the stable emulsion with minimum swelling occurrence. 4.9. Effect of emulsion to feed ratio (treat ratio) Fig. 12 exhibits the effect of treat ratio on the extraction of silver ion and emulsion stability. The treat ratio is varied by changing the amount of feed phase and keeping the volume of the membrane constant. The treat ratio controls the interfacial mass transfer across emulsion liquid membrane. The result observes that 99.89% of silver ion was extracted. At a low treat ratio of 0.10, emulsion swelling was observed. This is due to the emulsion phase did not disperse very well and the contact area between both phases significantly decreased. At the same time, the surfactant would also provide the co-transport of water, thus diluting the internal phase. A further increase in the treat ratio up to 0.14 has slightly decreased the emulsion swelling. This indicates that at this ratio, ELM system has achieved the effectiveness of the stability. In addition, increasing treat ratio also increased the emulsion phase hold up which simultaneously increased in the extraction capacity [39]. At higher treat ratio provides higher space for the emulsion dispersion, hence increasing the contact area between the two phases [40–42]. Further increase treat ratio up to 0.33, the emulsion gets breakage. This condition might lead to the increment of the surface area for mass transfer owing to the formation of a high number of emulsion globules. However, there is continuous movement of water molecules into the internal phase with the help of hydration surfactant which lead to the emulsion breakage. Therefore, treat ratio of 0.14 was used as an optimum condition for silver ion extraction.
Fig. 12. Effect of treat ratio towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; [Cyanex 302 in kerosene] = 0.0005 M; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; extraction time = 15 min; pH 2).
7
Fig. 13. Effect of extraction time towards the performance of silver ion extraction and emulsion stability (emulsifying time = 5 min; [Cyanex 302 in kerosene] = 0.0005 M; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; pH 2 and emulsion/feed phase = 1/7).
4.10. Effect of extraction time The effect of extraction time on the performance of nanosilver ion extraction and emulsion stability is depicted in Fig. 13. The result demonstrates that 99.84% of silver ion was extracted. Emulsion breakage was observed at the first 5 min. This indicates that at the short contact time, mass transfer of solutes increases rapidly once it comes in contact with the carrier in ELM system. At the same time, the hydration surfactant also significantly increases the co-transport of water molecules into the internal phase, hence leading to the emulsion breakage. As the extraction time increased up to 10 min, emulsion swelling slightly increased due to the surfactant which carried water molecules continuously into internal phase. At 15 min of extraction time, swelling decreased. It seems that this period of contact time is adequate for satisfactory extraction efficiency. Besides, Mortaheb et al. [42] also observed that by increasing the mixing intensity of emulsion and feed phases, the contact area for mass transfer is increased due to a reduction in the size of the globules, thus enhancing emulsion stability. With further increasing the extraction time up to 20 min, emulsion swelling slightly increased. This is due to the instability of the emulsion over longer extraction times. Thus 15 min of extraction time were the best condition for silver ion extraction. 4.11. Effect of ionic liquid concentration Fig. 14 exhibits the effect of ionic liquid concentration on the extraction performance and emulsion stability. From the result
Fig. 14. Effect of ionic liquid concentration towards the performance of ionized nanosilver extraction and emulsion swelling (emulsifying time = 5 min; pH of feed phase = 2; [Cyanex 302 in kerosene] = 0.0005 M; [Span 80] = 3% w/v; agitation speed = 250 rpm; homogenizer speed = 12,000 rpm; [Thiourea] = 1.0 M; [H2SO4] = 1.0 M; pH 2 and emulsion/feed phase = 1/7).
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005
G Model
JIEC-1734; No. of Pages 8 8
R.N.R. Sulaiman et al. / Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
obtained, 95% of ionized nanosilver was extracted by increasing the concentration of ionic liquid [BMIM]+[NTf2] from 1 to 5% w/v. It was observed that from 1 to 3% w/v of ionic liquid concentration, the extraction significantly increased by 10% of swelling occurrence. It is because the low concentration of ionic liquid is still not strong enough to inhibit the water transport into the internal phase. However, there is no swelling or breakage observed with the additional of 4–5% w/v of ionic liquid concentration. This indicates that the higher concentrations of ionic liquid are enable to restrict the transport of water into the membrane interface, thus increasing the emulsion stability. This finding is consistent with Goyal et al. [33] who found that the polymeric structure of this ionic liquid can form polymeric surfactant and produces a repulsive barrier in order to avoid the rupture of membranes. The properties such as high hydrophobicity of this ionic liquid also prevent the reaction with water in the stripping phase hence enhancing the emulsion stability [25]. 5. Conclusions As a conclusion, 99.89% of silver ions were extracted under the favorable conditions which are pH 2, 0.0005 M Cyanex 302, 1.0 M acidic Thiourea, 5 min of emulsifying time, 12,000 rpm of homogenizer speed, 250 rpm of agitation speed, 3% w/v Span 80, 15 min of extraction time, and 0.14 of treat ratio. The ionic liquid [BMIM]+[NTf2] also provide a good performance on emulsion stability during the extraction of ionized nanosilver with around 10% of the swelling. Acknowledgement The authors would like to acknowledge the Ministry of Science Technology and Innovation (Vot 4H009) and Universiti Teknologi Malaysia for making this research possible. References [1] J.L. Elechiguerra, J.L. Burt, A. Morones, H.H. Gao, M.J. Lara, M.J. Yacaman, J. Nanobiotechnol. 3 (2005) 1. [2] X. Chen, H.J. Schluesener, Toxicol. Lett. 176 (2008) 1.
[3] U.S. EPA (U.S. Environmental Protection Agency) (2009) http://www.epa.gov/ waterscience/criteria/wqctable/nrwqc-2009.pdf.(Accessed September 2013). [4] North Carolina Department of Environment Health (2007) http://hero.epa.gov/ index.cfm?action=search.view&reference_id=597412.(Accessed September 2013). [5] Oregon Department of Environmental Quality (2004) http://hero.epa.gov/ index.cfm?action=search.view&reference_id=597421.(Accessed September 2013). [6] T.M. Benn, P. Westerhoff, Environ. Sci. Technol. 42 (2008) 4133. [7] Y. Yan, H. Yang, J. Li, X. Lu, C. Wang, Text. Res. J. 0 (00) (2012) 1. [8] J. Fabrega, S.N. Luoma, C.R. Tyler, T.S. Galloway, J.R. Lead, Environ. Int. 37 (2011) 517. [9] J. Farkas, H. Peter, P. Christian, J.A.G. Urrea, M. Hassellov, J. Tuoriniemi, S. Gustafsson, E. Olsson, K. Hylland, K.V. Thomas, Environ. Int. 37 (2011) 1057. [10] T. Benn, B. Cavanagh, K. Hristovski, J.D. Posner, P. Westerhoff, J. Environ. Qual. 39 (2010) 1875. [11] S.W.P. Wijnhoven, W.J.G.M. Peijnenburg, C.A. Herberts, W.I. Hagens, A.G. Oomen, E.H.W. Heugens, B. Roszek, J. Bisschops, I. Gosens, V.D. Meent, D. Dekkers, S.D. Jong, W.H.V. Zijverden, M. Sips, R.E. Geertsma, Nanotoxicology 3 (2) (2009) 109. [12] P.V. Asharani, Y.L. Wu, Nanotechnology 19 (2008) 1. [13] M. Chatelut, E. Gobert, O. Vittori, Hydrometallurgy 54 (2) (2000) 79. [14] J.P. Chen, L.L. Lim, Chemosphere 60 (2005) 1384. [15] S.G. Sarkar, P.M. Dhadke, J. Chin. Chem. Soc. 47 (2000) 869. [16] N. Othman, H.B. Mat, M. Goto, J. Solvent Extr. Res. Dev. Jpn. 12 (2005) 27. [17] A. Gfiveng, B. Karabacako, Desalination 172 (2005) 7. [18] N. Othman, H. Mat, M. Goto, J. Membr. Sci. 282 (2006) 171. [19] N. Othman, R. Djamal, N. Mili, S.N. Zailani, J. Appl. Sci. 11 (7) (2011) 1406. [20] B. Tang, G. Yua, J. Fang, T. Shi, J. Hazard. Mater. 177 (2010) 377. [21] A.L. Ahamed, A. Kusumastuti, C.J.C. Dereka, B.S. Ooi, Chem. Eng. J. 171 (2011) 870. [22] R.K. Goyal, N.S. Jayakumar, M.A. Hashim, J. Hazard. Mater. 195 (2011) 55. [23] S. Venkatesan, K.M.M.S. Begum, Chem. Eng. J 148 (2009) 254. [24] T. Mandai, M. Imanari, K. Nishikawa, Chem. Phys. Lett. 543 (2012) 72. [25] A. Balasubramanian, S. Venkatesan, Desalination 289 (2012) 27. [26] Y.S. Ng, N.S. Jayakumar, M.A. Hashim, Desalination 278 (2011) 250. [27] T. Kocareva, I. Grozdanov, B. Pejova, Mater. Lett. 47 (2001) 319. [28] W. Peng, H. Jiao, H. Shi, C. Xu, Desalination 286 (2012) 372. [29] D. Wu, Y. Xiong, D. Li, Hydrometallurgy 82 (2006) 176. [30] S.C. Lee, J. Membr. Sci. 381 (2011) 237. [31] M. Teresa, A. Reis, M.R. Carvalho, Chem. Eng. Technol. 17 (1994) 242. [32] R.A. Kumbasar, Sep. Purif. Technol. 64 (2008) 56. [33] R.K. Goyal, N.S. Jayakumar, M.A. Hashim, Desalination 278 (2011) 5. [34] M. Chiha, Q. Hamdaoui, F. Ahmadchekkat, C. Petrier, Ultrason. Sonochem. 17 (2010) 318. [35] Y. Wan, X. Zhang, J. Membr. Sci. 196 (2002) 185. [36] M.A. Malik, M.A. Hashim, F. Nabi, J. Dispersion Sci. Technol. 33 (3) (2012) 346. [37] S. Venkatesan, K.M.M.S. Begum, Desalination 236 (2009) 65. [38] B.S. Chanukya, N.K. Rastogi, Sep. Purif. Technol. 105 (2013) 41. [39] R.A. Kumbasar, Sep. Purif. Technol. 68 (2009) 208. [40] R.A. Kumbasar, O. Tutkun, Desalination 224 (2008) 201. [41] H.R. Mortaheb, H. Kosuge, B. Mokhtarani, M.H. Amini, H.R. Banihashemi, J. Hazard. Mater. 165 (2009) 630. [42] H.R. Mortaheb, M.H. Amini, F. Sadeghian, B. Mokhtarani, H. Daneshyar, J. Hazard. Mater. 160 (2008) 582.
Please cite this article in press as: R.N.R. Sulaiman, et al., J. Ind. Eng. Chem. (2013), http://dx.doi.org/10.1016/j.jiec.2013.12.005