Solvent Extraction Research and Development, Japan, Vol. 25, No 1, 23 36 (2018) A Kinetic Study of Copper(II) Extraction using LIX84-I Impregnated Polymeric Particles with Different Structures Nov Irmawati INDA 1, Masaya FUKUMARU 2, Takashi SANA 2, Shiro KIYOYAMA 3, Takayuki TAKEI 4, Masahiro YOSHIDA 4, Akira NAKAJIMA 5 and Koichiro SHIOMORI 2,* 1 Department of Environment and Resource Sciences, Interdisciplinary Graduate School of Agriculture and Engineering, University of Miyazaki, 1-1 Gakuenkibanadai-nishi, Miyazaki 889-2192, Japan; 2 Department of Applied Chemistry, University of Miyazaki, 1-1 Gakuenkibanadai-nishi, Miyazaki 889-2192, Japan; 3 Department of Chemical Science and Engineering, National Institute of Technology, Miyakonojo College, 473-1 Yoshio-cho, Miyakonojo 885-8567, Japan; 4 Department of Chemical Engineering, Graduate School of Engineering, Kagoshima University, 1-21-40 Korimoto, Kagoshima 890-0065, Japan; 5 Department of Biotechnology, Frontier Science Research Center, University of Miyazaki, 5200 Kihara, Miyazaki 889-1692, Japan (Received February 3, 2017; Accepted September 25, 2017 ) Polymeric particles impregnated with LIX84-I having different structures, such as large interconnected -spherical pores (PDVB), small pores (XAD-4) and multi cores (PVA/NaAlg-GA crosslinked gel), were used for copper(ii) extraction from an aqueous phase. The extraction kinetics of copper(ii) from the aqueous solution into three different types of polymeric particles was influenced by the amount of LIX84-I impregnated in the polymeric particles and also their structures. The amount of copper(ii) adsorbed into all types of the polymeric particles increased with time and reached a plateau after a longer contact time. The extraction mechanism of copper(ii) into all types of polymeric particles impregnated with LIX84-I was found to obey Pseudo-second order kinetics. It is suggested that complex-formation and mass-transfer diffusion is the predominant rate-determining step in the copper(ii) extraction process from aqueous solution into the polymeric particles. 1. Introduction Polymeric particles have been widely employed for metal ion recovery by impregnating then with ligands [1-7]. Polymeric particles are considered to be easily usable in metal ion separation processes because the selection of ligands is possible [8]. Polymeric particles as supporting materials have several advantages: (1) large specific interfacial area, (2) the core and semipermeable membranes of the polymeric particle can be used as independent phases which can then support the different ligands, (3) easy separation - 23 -
of the two phases [9]. Several types of polymeric particle have been identified, including chitosan/sporopollenin [10], P(St-EGDMA) [11-14], P(APP-EGDMA) [15], P(Divinylbezene) [16-23], polysulfone [24-26], alginate [27-30], and XAD-4 [31]. There are a few types of polymeric particle such as single-core, multicore, and matrix type [8]. Recently, we prepared three types of polymeric particles containing an extractant: (1) small pore type (XAD-4), (2) multi core type (PVA/Alg-GA) [32] and (3) large interconnected spherical pore type (PDVB) [33]. Commercial XAD particles are hard and insoluble particles, and provide differences in surface properties [34]. These polymeric particles show a wide range of adsorption (via van der Waals forces) behavior, a highly porous structure with a diameter of 0.5 mm, and many small micro-pores exist whose diameters are 10-7 m [31]. Multi-core type particles, PVA/Alg-GA, were prepared through O/W emulsion gelation then crosslinked with glutaraldehyde [32]. The interconnected spherical pore type polymeric particles were prepared from an W/O/W emulsion wherein NaCl aqueous solution was added as an inner aqueous phase in order to form large interconnected spherical pores [5]. Furthermore, these types of polymeric particles were impregnated with LIX84-I (1-(2-hydroxy-5-nonylphenyl) ethanone oxime) for copper(ii) ion extraction [33]. Polymeric particles can act as supporting material containing LIX84-I, so they would have the characteristics of both an ion exchange resin and a ligand used in a liquid-liquid extraction system [8]. In hydrometallurgy, polymeric particles would present an effective adsorbent in separation, removal and recovery of metal ions from aqueous solutions [12]. Several researchers have focused on producing polymeric particles using a common monomer and polymerization initiators [1-2]. Meanwhile, other researchers have focused on the extraction rate behavior of metal ions into polymeric particles by using different kinetic models [8, 12, 17, 35]. In this work, we studied the extraction rate behavior of copper(ii) ion using three different types of polymeric particles impregnated with LIX84-I. In most cases, the extraction process includes a chemical reaction between the adsorbent and the metal ions to remove the metal ions by a mechanism called chemiextraction [12]. Kamio et al. [8] reported that the overall metal ion extraction process into the polymeric particles would be ruled by a mass transfer process accompanied by a chemical reaction that allows the metal ions to be separated and concentrated from the aqueous feed solution toward the acceptor. On the other hand, Araneda et al. reported that the rate of extraction of metal ions (cadmium(ii) and copper(ii)) into the polymeric particles fitted well with a pseudo-second order kinetic model [12]. Based on the kinetic study conducted by Araneda et al. [12] and Kamio et al. [8], we employed the pseudo-second order model as the kinetic model and the mass transfer as the diffusion model. 2. Experimental procedures 2.1 Reagents 1-(2-hydroxy-5-nonylphenyl) ethanone oxime (LIX84-I, Cognis Co. Ltd.) was used as the extractant. Monomeric divinylbenzene (DVB) was purchased from Wako Pure Chemical Industries, Ltd. and washed - 24 -
with 10wt% NaOH aqueous solution to remove the polymerization inhibitor. The monomers were stored in a refrigerator until use. Tri-n-octylamine (TOA), 2,2 - azobis (4-methoxy- 2,4-dimethylvaleronitrile) (ADVN), polyvinyl alcohol (PVA, polymerization degree about 500), sodium dodecylsulphate (SDS), ammonium sulfate, copper sulfate hexahydrate, hexane, ethanol, sodium alginate (Viscosity 500 600 mpa s), glutaraldehyde, calcium chloride and hydrochloric acid were purchased from Wako Pure Chemical Industries, Ltd. Hexaglycerin ricinoleic acid (818SX) was purchased from Taiyo Kagaku Co. The commercial Amberlite XAD-4 was purchased from Sigma-Aldrich Chemicals. It was washed with ethanol three times to remove the aqueous solution from the wetted XAD-4 and dried under vacuum. 2.2 Preparation of PDVB polymeric particles The PDVB polymeric particles were prepared by the same procedure as given in the previous paper [33] and were immersed in a hexane solution of LIX84-I overnight. Hexane was removed from the polymeric particles using a rotary evaporator and the polymeric particles containing LIX84-I were obtained after drying under vacuum. 2.3 Preparation of XAD-4 polymeric particles A defined amount of commercial XAD-4 particles immersed in 100 ml of ethanol in the 200 ml Erlenmeyer flask for 24 hrs, then filtrated, and dried. The XAD-4 (3 g) were then immersed in 60 ml hexane with various weights of LIX84-I in the eggplant shaped flask for 72 hrs. A rotary evaporator was used for hexane removal. The XAD-4 particles impregnated with LIX84-I were then dried under vacuum overnight. The pore size and pore volume of the commercial XAD-4 were 100 Å and 0.98 ml/g, respectively. 2.4 Preparation of PVA/Alginate-Glutaraldehyde crosslinked gel polymeric particles The PVA/Alg-GA multi core type polymeric particles were prepared as reported in the previous paper using LIX84-I [32]. The organic phase, which is LIX84-I (5, 10 and 20wt%), was added to an aqueous solution containing PVA (5wt%), Na-Alginate (1wt%) and distilled water (89, 84 and 74wt%), then homogenized to obtain an (O/W) emulsion. The (O/W) emulsion was fed by peristaltic pump onto a CaCl 2 aqueous solution (10wt%) through a tube having a diameter of 1 mm, stirred for 30 mins and allowed to solidify. Thus, PVA/alginate gel polymeric particles were obtained. The obtained PVA/alginate gel polymeric particles were transferred to HCl 0.1 M containing glutaraldehyde and stirred for 2 hrs. The PVA/Alginate-glutaraldehyde crosslinked gel polymeric particles containing LIX84-I were washed with water and stored in distilled water until used. 2.5 Measurement of the LIX84-I content of the polymeric particles In order to determine the amount of LIX84-I impregnated in the polymeric particles, the polymeric particles were added to ethanol to elute the LIX84-I from the polymeric particles, and the amount of LIX84-I in the ethanol solution was measured using the weight measurement method [33]. The molar content of LIX84-I, E based on LIX84-I purity was calculated from Eq. (1); - 25 -
,, x purity 100 mmol 1 g where W pp+lix84-i,ini, W pp+lix84-i, and Mw LIX84-I are the total initial weight of the polymeric particles and LIX84-I (before impregnation), the total weight of polymeric particles and LIX84-I (after impregnation), and the molar mass of LIX84-I, respectively. 2.6 Observation and analysis of the polymeric particle The morphologies of the polymeric particles containing LIX84-I were observed by scanning electron microscopy (Hitachi, TM-1000 or SU3500, SEM) and a digital microscope (KEYENCE, VHX-600 system). The diameter of the polymeric particles was measured using the digital microscope. 2.7 Extraction properties of copper(ii) using PDVB, XAD-4 and PVA/Alg-GA gel polymeric particles impregnated with LIX84-I A defined amount of the polymeric particles impregnated with LIX84-I was added to 200 mg/l of copper(ii) sulphate in 0.5 mol/l (NH 4 ) 2 SO 4 at 303 K. A small amount (3 ml) of the aqueous solution was collected using a plastic pipet, which has a welded Millipore filter (0.22mm) at its tip, at given time intervals. The concentrations of copper(ii) in the collected and the feed solutions were measured by ICP-AES (Shimadzu, ICPS-8100). The amount of copper(ii) extracted into the polymeric particles, q t, was calculated from Eq. (2); (,,, ) [mmol/g] (2) where C Cu,aq,ini, C Cu,aq, V aq, M Cu and W PP are the initial concentration of copper(ii) in the aqueous phase, the equilibrium concentration of copper(ii) in the aqueous solution after extraction, the volume of the aqueous phase, the atomic weight of copper(ii) and the weight of the polymeric particles used for the extraction, respectively. 3. Results and Discussions 3.1 Observation of PDVB, XAD-4 and PVA/Alg-GA crosslinked gel polymeric particles The surface and cross section images of PDVB, XAD-4 and PVA/Alg-GA polymeric particles impregnated with LIX84-I are shown in Figure 1. SEM images show the spherical structure of all the various types of polymeric particle. PDVB has a rough surface and inner aqueous droplets are observed on the surface Figure 1. SEM photographs of PDVB, XAD-4 and PVA/Alg-GA crosslinked gel polymeric particles impregnated with LIX84-I. - 26 -
of the particle and in the cross section of the SEM images. The inner aqueous droplets formed large spherical pores which are interconnected. XAD-4 has a dense structure observed on the surface and in the cross section of the SEM images. Because of the long contact time of LIX84-I and the polymeric particles in hexane for PDVB and XAD-4, we assume that the LIX84-I would exist on the surface of the polymeric particle wall and in the pores of the polymeric particles. On the other hand, PVA/Alg-GA has a dense surface and some small depressions can be seen on the surface of the SEM image. It is considered the depressions were caused by the droplets of LIX84-I which were released from the surface of the particle during the crosslinking of the alginate. The cross section image shows the rough structure which contains a lot of round shaped particles, empty spaces between the particles and many isolated spherical pores with dense shells surrounded by the particles. The particles and the shell wall are considered to be the hydrophilic polymer of PVA/Alg-GA. The spherical pores are considered to be the traces of the droplets of LIX84-I which were released during the sample preparation under SEM observation. These droplets of LIX84-I in the spherical pores would act as an organic extraction media in the PVA/Alg-GA polymeric particle. According to Crotts and Park, 1995, porosity is a critical factor for the extraction rate due to the viscosity of the LIX84-I liquid phase entrapped in the surface portion of the polymeric particle. Polymeric particles with very small pores or without pores would hinder the diffusion process, meanwhile, polymeric particles with large pores would present little diffusional resistance due to their high interfacial area [36]. 3.2 Extraction rate of copper(ii) into PDVB, XAD-4 and PVA/Alg-GA polymeric particles Figure 2 shows the effect of the amount of LIX84-I immobilized in the PDVB polymeric particles on the rate of uptake of copper(ii) at different contact times from a 200 mg/l solution of copper(ii). It can be seen that the amount of copper(ii) uptake increased with contact time, and at some point in time reached an almost constant value where the amount of copper(ii) being removed from the aqueous solution onto the polymeric particles is in a state of dynamic equilibrium with the amount of copper(ii) desorbed from the polymeric particles. For the range of contact time under which the experiments were conducted, the amount of copper(ii) extracted from the solution was higher depending on the amount of LIX84-I present in the Figure 2. Rate of copper(ii) extraction with PDVB polymeric particles at different amount of LIX84-I content in the polymeric particles and the different amounts of polymeric particles used. - 27 -
polymeric particles. However, the copper(ii) uptake rate using the various types of polymeric particles was different as shown in Figure 3. For the PDVB polymeric particles, the copper(ii) uptake rate was found to be extremely rapid at the initial stage, slowed down as the extraction proceeds and reached an almost constant value after 60 minutes of contact time. Otherwise, for the XAD-4 polymeric particles, the copper(ii) uptake rate slowly increased initially and reached an almost constant value after 360 minutes. On the other hand, the PVA/Alg-GA polymeric particles also show initially a slow uptake rate of copper(ii) and slowly reached an almost constant value after 120 minutes. The higher initial extraction rate may be due to a large number of vacant sites available initially, which results in an increased concentration gradient between the adsorbate in solution and the adsorbate on the adsorbent surface [37]. The PDVB polymeric particles present a larger surface area for the extraction due to the small particle size and the existence of interconnected spherical pores, which tend to rapidly increase the initial copper(ii) extraction rate. As time proceeds the concentration gradient is reduced due to the accumulation of copper(ii) in the vacant sites, leading to a decrease in extraction rate at the later stage of the extraction. For the XAD-4 polymeric particles, a slow extraction rate of copper(ii) was observed with the large number of vacant sites on the surface of the polymeric particles because of the morphology of the polymeric particles which are dense, with a smooth surface and really small pores as shown in Figure 1. The dense structure and small pores could be hindering the diffusion of copper(ii) onto the active sites of the polymeric particles [36]. On the other hand, the copper(ii) uptake rate into the PVA/Alg-GA polymeric particles also slowly increased at the initial stages due to the particle size of the polymeric particles. According to Ofomaja [37], a small particle size presents a larger surface for extraction and leads to a rapidly increase in the extraction rate at the initial stages. The particle size of the PVA/Alg-GA polymeric particles is approximately 3 mm. These results reveal that the PDVB polymeric particles impregnated with LIX84-I are preferable for copper(ii) extraction from aqueous solution due to the morphology of the PDVB polymeric particles compred with that of the other two types of polymeric particles. For further investigation, a kinetic study of copper(ii) extraction with the different types of Figure 3. Rate of copper(ii) extraction with various types of polymeric particles. - 28 -
polymeric particles has also been employed to analyze our experimental data. Based on the kinetic study of Kamio et al. [8,35] and Araneda et al. [12], we prefer to employ the pseudo-second order kinetic and the mass-transfer diffusion models to fit our experimental data. 3.2.1 Analysis of the extraction rate by the pseudo-second order kinetic model Many adsorption kinetic models have been proposed to clarify the mechanism of metal ion sorption from aqueous solution onto an adsorbent. In most cases, the metal ion adsorption process involves a chemical reaction between the metal ion with the adsorbent by a mechanism called chemisorption through sharing or exchanging of electrons. The adsorbent contains functional groups and/or active sites, which are negatively charged and therefore will bond to the metal ions through coordination compound formation, salt formation and ion-pair formation, thereby extracting them from the aqueous solution. Ho (2006) has thoroughly reviewed the pseudo-second order kinetic models of metal ion extraction using solid adsorbents [38]. A pseudo-second order kinetic model can be used to describe very well chemisorption involving valency forces through sharing or exchanging of electrons between the adsorbent and the metal ion, as covalent forces, and ion exchange. The rate of the second-order reaction is dependent on the amount of divalent metal ions on the surface of the adsorbent and the amount of divalent metal ions adsorbed at equilibrium [38]. Kamio [8,35] reported that the sorption behavior of Ga(III) and In(III) and lanthanides into microcapsules loaded with an alkylphosphonic acid extractant involve both chemical reaction and diffusion processes as the rate-determining step. Based on Araneda [12] who considers that, practically, the extractant would be present in a pure state and at high concentration on the surface of the polymeric particle through an evaporation process and, as reported by Sobkowsk [39], that second-order models could be applied to higher concentrations of the extractant on the surface of the adsorbent, the pseudo-second order kinetic model was applied to analyze our experimental data. Our previous paper reported that the overall reaction of copper(ii) ion in the polymeric particles can be written as follows [40]: Cu 2+ + 2 (HR) CuR 2 + 2H + HR:LIX84-I (3) In the polymeric particles, LIX84-I is present at high concentrations on the surface and inside the pores of the polymeric particles [12] and the extraction rate is dependent on the amount of copper(ii) on the surface of the polymeric particles and the amount of copper(ii) adsorbed at equilibrium. Thus, the driving force, (q e q t ), is proportional to the available fractions of active sites. The kinetic rate equations can be rewritten as follows:, (4) where k 2 is the rate constant of copper(ii) ion extraction, q e and q t are the amounts of copper(ii) ion sorbed at equilibrium and time, t. Integrating Eq. (4) for the boundary conditions t = 0 to t = t and q t = 0 to q t = q t gives: - 29 -
which has a linear form of, (5). (6) The constants can be determined experimentally by plotting t/q t against t and the initial extraction rate is. (7) Figure 4. Experimental data and pseudo-second order kinetic model for copper(ii) ion extraction. - 30 -
Figure 4 shows the applicability of the pseudo-second order kinetic model to the experimental data generated for the extraction of copper(ii) from aqueous solution using polymeric particles impregnated with LIX84-I. The initial extraction rate, h, the pseudo-second order rate constant, k 2, the amount of copper(ii) extracted at equilibrium, q e, and the corresponding linear regression R 2, for copper(ii) ions are given in Table 1. It shows the amount of LIX84-I impregnated in the polymeric particles influence the amount of copper(ii) sorbed onto the polymeric particles. For a large amount of LIX84-I impregnated in the polymeric particles, the amount of copper(ii) sorbed also increased and reached a constant value after a long contact time. The experimental data was found to fit the pseudo-second order kinetic model well. The pseudo-second order kinetic model assumes that the rate-determining step is chemical extraction or chemiextraction involving covalent forces through sharing or the exchange of electrons between the sorbent and sorbate. LIX84-I is a phenolic oxime which has phenol and oxime as functional groups. In contact with water and with increasing ph, these groups become negatively charged and are likely sites for chemical reaction on the polymeric particle surface. According to Kamio et al. [8], a monomolecular layer of extractant would be formed on the surface of the polymeric particles. LIX84-I exists as a monomolecular layer on the surface of the polymeric particles. Table 1. Pseudo-second order kinetic parameters obtained from experimental data analysis. Polymeric particle types D pp Pseudo-second order kinetic ( 10-3 ) k 2 h q e R 2 PDVB 0.200 2.71 10-1 3.68 10-2 3.68 10-1 0.9999 XAD-4 0.500 4.34 10-2 1.56 10-2 5.99 10-1 0.9979 PVA/Alg-GA 3.000 3.40 10-1 1.63 10-3 6.93 10-2 0.9967 k 2 = g/mmol min; h = mmol/g min; q e = mmol/g; D pp = diameter of the polymeric particle (m) 3.2.2 Analysis of extraction rate using the mass-transfer diffusion model Sorptive removal of copper(ii) from aqueous solution involves solute transfer, which is usually characterized by either external mass transfer (boundary layer diffusion) or intraparticle diffusion or both. The extraction process can be described by four consecutive steps [41]: (1) Transport in the bulk of the solution; (2) Diffusion across the liquid film surrounding the sorbent particle; (3) Particle diffusion in the liquid contained in the pores and in the sorbate along the pore walls; and (4) Extraction within the particle in and on the external surface (This step is considered to be an equilibrium reaction and is assumed to be rapid and considered negligible). The overall rate of extraction will be controlled by the slowest step, which would be either film diffusion or pore diffusion. According to Boyd [42], if film diffusion is rate-determining, the rate constant will vary inversely with the particle size and film thickness; if the exchange is chemically rate-determining, the rate constant - 31 -
will be independent of particle diameter and flow rate and it will depend only on the concentrations of the ions in solution and the temperature. By considering that extractants exist inside the pores of the polymeric particles, the global mechanism also includes the diffusion of metal ions through the aqueous film and diffusion of metal complexes through the pores of the polymeric particles, so any of these may be the rate-determining step of the overall process [12]. In order to characterize what the actual rate-controlling step involved in the copper(ii) extraction process is, the experimental data were further analyzed by the kinetic expression given by Boyd [9]: 1 exp (8) Substituted n = 1 and n = 2, Eq. (8) can be rearranged and simplified as in Eqs. (9) and (10), respectively: ln 1. (9) ln 1. (10) where k MD is the overall rate constant as follows: (11) where q t, q e and k MD represent the amount sorbed (mmol/g) at any time, infinite time and the mass-transfer diffusion rate constant, respectively. The slope obtained from the straight line plot of ln(1-q t /q e ) versus t and ln(1-(q t /q e ) 2 ) is defined as the film/surface diffusion and intraparticle/pore diffusion rate constant, respectively. Figures 5 and 6 shows the relationship between t against ln(1 q t /q e ) and t against ln(1-(q t /q e ) 2 ) for different types of polymeric particles, respectively. In both Figures 5 and 6, PDVB polymeric particles are not fitted with Eq. (9) and Eq. (10) at an early stage. However, PDVB polymeric particles fit quite well at the later stage with Eq. (9) and Eq. (10). It is assumed that intraparticle/pore diffusion becomes the rate-determining step for the copper(ii) ion adsorption process at the later stage (after 180 minutes of contact time). PDVB polymeric particles have large interconnected spherical pores on the surface and in the body of the PDVB polymeric particles thus giving the metal ion easy access for reaction with the free active sites in the polymeric particles. When the LIX84-I on the surface of the polymeric particle reacted with copper(ii) ions, forming a complex and accumulating on the surface of the polymeric particle, the complex molecules would diffuse through the organic phase in the polymeric particle to offset the accumulation of the complex on the surface of the polymeric particle. Hence, we consider that complex-formation is the predominant rate-determining step for the extraction of copper(ii) in the PDVB polymeric particle. Otherwise when the complex molecules accumulate on the surface of the polymeric particle, film and intraparticle diffusion become the rate-determining step for copper(ii) extraction. The XAD-4 and PVA/Alg-GA polymeric particles fit well with Eq. (9) as shown in Figure 5. We - 32 -
suggest that film diffusion is the rate-determining step in copper(ii) ion adsorption from aqueous solution onto the polymeric particles. For the XAD-4 polymeric particles, LIX84-I would form a boundary layer on the surface of particle. Copper(II) ion adsorbed from aqueous solution would form a complex in the interface area of the particle and diffuse through the boundary layer to offset the accumulation of the copper(ii) complex on the surface of the polymeric particles. In order to equilibrate accumulation of complex formation on the surface and at the boundary layer, the copper(ii) complex would diffuse through the organic phase in the polymeric particles. Hence, the intraparticle/pore diffusion has become the rate-determining step for copper(ii) adsorption at the later stage as shown in Figure 6. Figure 5. Relationship between t against ln(1-q t /q e ) for different types of polymeric particles. a) PDVB, b) XAD-4 and c) PVA/Alg-GA particles. Figure 6. Relationship between t against - ln(1-(q t /q e ) 2 ) for different types of polymeric particles. a) PDVB, b) XAD-4 and c) PVA/Alg-GA particles. - 33 -
Therefore, for the PVA/Alg-GA polymeric particles, LIX84-I would exist as a droplet in the particle pore. Copper(II) ions would diffuse from the aqueous solution into the particles through the particle wall and form a complex on the surface of the LIX84-I droplets existing in the pore. The complex molecule would diffuse to fill the internal pore. Therefore, film diffusion is the rate-determining step in copper(ii) adsorption. When the copper(ii)-lix84-i complex filling the internal pores of the polymeric particle becomes saturated, the copper(ii) ions adsorbed from aqueous solution would slowly increase and have to pass the microdoplets of the complex. Hence, intraparticle/pore diffusion is the rate-determining step at the later stage (slowest step) as shown in Figure 6. In order to provide an effective diffusion coefficient, D i (m 2 /s), the calculated K MD value in Eq. (11) is used, where r represents the radius of the particles obtained by digital microscopy. The D i values of the XAD-4 and PVA/Alg-GA polymeric particle are 1.21 10-12 m 2 /s and 6.39 10-11 m 2 /s, respectively for n = 1. The intraparticle diffusion coefficient of the PVA/Alg-GA polymeric particles is higher by considering the water content in the polymeric particles. As reported by Krys, et al. (2013), the intraparticle diffusion coefficient of wet beads is higher than for dried beads [43]. Overall, in PDVB and XAD-4 polymeric particles, copper(ii) ions react on the surface of the polymeric particles loaded with LIX84-I, HR, [8], which exists in its dimerized form [44]. Reaction (3) itself proceeds through a four-step mechanism in which (1) copper(ii) ions in aqueous solution diffuse through the aqueous solution up to the polymeric particle surface; (2) LIX84-I loaded on the surfaces of the polymeric particles dissociates into a proton and an anion, (3) copper(ii) ions will react with the anion and form a complex on the surface of the polymeric particle (interface interaction), (4) the complex of copper(ii)-lix84-i will diffuse through the organic phase in the polymeric particles to offset its accumulation on the surface of the polymeric particles. Whereas, in PVA/Alg-GA polymeric particles, (1) copper(ii) ion will diffuse through the aqueous solution and the particle wall, (2) LIX84-I which exist in the spherical pores of the particles dissociates into a proton and anion, (3) formation of the copper(ii)-lix84-i complex molecule on the surface of the LIX84-I droplets and diffusion of the complex molecule through the organic phase to fill the internal pores (LIX84-I droplet), (4) the remaining copper(ii) ions from the aqueous solution have to pass the microdroplets of the complex molecule at the later stage. For the fourth step mechanism, mass-transfer diffusion becomes the rate-determining step. In other words, the copper(ii) extraction rate in the polymeric particles will be controlled by either complex-formation reaction or mass-transfer diffusion. 4. Conclusion The present study used three types of polymeric particles: PDVB, XAD-4 and PVA/Alg-GA polymeric particles impregnated with LIX84-I for copper(ii) extraction from aqueous solution. These types of polymeric particles have a spherical structure and show a good performance in copper(ii) extraction. The amount of copper(ii) ions extracted from the aqueous solution into the polymeric particles increased with - 34 -
time and reached a plateau at longer contact times. A pseudo-second order kinetic model was employed in modeling the extraction mechanism of the copper(ii) ions in various types of polymeric particles. It was found that the experimental data obeyed the pseudo-second order kinetic model which assumes that complex-formation is the predominant rate-controlling step for copper(ii) ion extraction in the polymeric particles. A mass-transfer diffusion model was found to be involved in the rate-controlling step for copper(ii) extraction at the later stage. In conclusion, the extraction mechanism for copper(ii) from aqueous solution into the polymeric particles was found to be surface extraction (complex-formation reaction) and the copper(ii) diffusion rate was governed by the existence of the pores. A further study will focus on the diffusivity of metal ion extraction rate in polymeric particles with pores, without pores and interconnected spherical pores. References 1) S. Nishihama, G. Nishimura, T. Hirai, I. Komasawa, Ind. Eng. Chem. Res., 43, 751-757 (2004). 2) K. Shiomori, H. Yoshizawa, K. Fujikubo, Y. Kawano, Y. Hatate, Y. Kitamura, Sep. Sci. Technol. 38, 4057-4077 (2003). 3) K. Minamihata, S. Kiyoyama, K. Shiomori, M. Yoshida, Y. Hatate, Ars Sep. Acta, 5, 55-67 (2007) 4) K. Kondo, M. Ishihara, M. Matsumoto, Solvent Extr. Res. Dev. Jpn, 17, 139-149 (2010). 5) A. Matsushita, T. Sana, S. Kiyoyama, M. Yoshida, K. Shiomori, Solvent Extr. Res. Dev. Jpn., 18, 123-135 (2011). 6) K. Kondo, Y. Nishiguchi, T. Matsuo, M. Matsumoto, J. Chem. Chem. Eng., 5, 1074-1082 (2011). 7) K. Kondo, M. Sawada, M. Matsumoto, J. Water Process Eng., 1, 115-120 (2014). 8) E. Kamio, M. Matsumoto, F. Valenzuela, K. Kondo, Ind. Eng. Chem. Res., 44,2266-2272 (2005) 9) H. Watarai, S. Hatakeyama, Anal. Sci., 7, 487-489 (1991). 10) I. Sargin, M. Kaya, G. Arslan, T. Baran, T. Ceter, Bioresour. Technol., 177, 1-7 (2015). 11) S. Fujii, D.P. Randall, S. P. Armes, Langmuir, 20, 11329-11335 (2004). 12) C. Araneda, C. Fonseca, J. Sapag, C. Basualto, M. Yazdani-Pedram, K. Kondo, E. Kamio, F. Valenzuela, Sep. Purif. Technol., 63, 517-523 (2008). 13) H. Yan, Y. Chen, Y. Zhang, W. Wu, e-polymers, 30, 1-12 (2010). 14) A. Alcazar, A. Perez, A. De Lucas, M. Carmona, J. F. Rodriguez, J. Chem. Sci. Technol., 2, 25-38 (2013). 15) J. Wilsno, J. Yoeza, N. Philip, J. Epiphan, G. Mdoe, Org. Polym. Materials, 4, 29-36 (2014). 16) M. Matsumoto, K. Kondo, Solvent Extr. Res. Dev. Jpn., 8, 113-119 (2001) 17) E. Kamio, K. Kondo, Ind. Eng. Chem. Res., 41, 3669-3675 (2002). 18) E. Kamio, M. Matsumoto, K. Kondo, Ind. Eng. Chem. Res., 46, 255-265 (2007). 19) K. Shiomori, K. Fujikubo, Y. Kawano, Y. Hatate, Y. Kitamura, H. Yoshizawa, Sep. Sci. Technol., 39, 1645-1662 (2004). - 35 -
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