Adsorption Kinetics of Boron by Anion Exchange Resin in Packed Column Bed

Transcription

1 J. Ind. Eng. Chem., Vol. 13, No. 3, (2007) Adsorption Kinetics of Boron by Anion Exchange Resin in Packed Column Bed Ki-Won Baek, Sang-Hun Song, Seok-Hwan Kang, Young-Woo Rhee, Chang-Soo Lee, Bum-Jae Lee**, Sam Hudson*, and Taek-Sung Hwang School of Applied Chemistry and Biological Engineering, College of Engineering, Chungnam National University, Daejeon , Korea *Fiber and Polymer Science Program, Non-h Carolina state University, Raleigh, NC , USA **Department of Fine Chemical Engineering & Chemistry College of Engineering, Chungnam National University, Daejeon , Korea Received July 6, 2006; Accepted February 6, 2007 Abstract: In this paper, we present a novel application of Amberlite IRA 743 resin that has glucamine functional groups for specific boron exchange. The boron removal efficiency from seawater was examined through the packed column experiment. The efficiency of boron removal was investigated with respect to several key experimental parameters, including the ph of the solution, the initial concentration of boron, the bed volume of the resin, and the temperature. The performance of boron removal increased upon increasing the batch ratio of resin to boron and decreasing the initial concentration of boron in solution. Although the removal rate of boron increased at the initial state of increasing temperature, it was independent of temperature. Most of the boron in aqueous solution could be removed efficiently under the optimum operation conditions at ph 8.5. In addition, a kinetic study of boron removal under the optimum conditions fit Thomas s adsorption model well. The simple method presented could be applied to the efficient removal of boron from wastewater. Keywords: boron removal, ion exchange, glucamine group, wastewater, kinetics Introduction 1) Boron is widely distributed in the environment, occurring naturally (seawater) or from anthropogenic pollution, mainly in the form of boric acid (H 3 BO 3 ) or borate salts (NaBO 2, Na 2 B 4 O 7 10 H 2 O). Although it is an important micronutrient for plants, animals, and humans, the range between deficiency and excess is narrow [1]. Currently, boric acid and boron salts have extensive industrial use in the manufacturing of glass, porcelain, carpets, cosmetics, photographic chemicals, and fireproofing fabrics. Furthermore, boron compounds are used in certain fertilizers for the treatment of boron-insufficient soils, in welding and brazing of metals, hand-cleansing, high-energy fuels, cutting fluids, and catalysts [2]. For boron removal from aqueous solution or seawater, several methods have been suggested. Among those To whom all correspondence should be addressed. ( tshwang@ cnu.ac.kr) methods, the ion exchange processes have been the most extensively studied and reported in the literature [1-8]. Therefore, the development of chelating resins, containing functional groups for boron removal and recovery from natural waters and wastewaters, is a prerequisite for improving the capacity, selectivity, and sorption rates [9]. Most of the processes have utilized batch or continuous flow reactors, as fiber or bead types. In addition, membrane processes, such as the use of reverse osmosis [10,11], polymer-enhanced ultrafiltration [3,12], electrodialysis [13], and chromatographic column [5,7,8], have been also applied for boron removal. In this study, a packed bed column was employed to assess the efficiency of boron removal from seawater using Amberlite IRA 743 resin, which is highly selective for boric acid and borate. Several experimental parameters, such as the ph of the solution, the initial concentration of boron, the bed volume of the resin, and the temperature, were studied. Experimental data were collected statistically to find a model for the adsorption kinetics and the

2 Adsorption Kinetics of Boron by Anion Exchange Resin in Packed Column Bed 453 Table 1. Characteristics of Ion Exchange Resins Parameter Amberlite IRA 743 Exchange capacity, meq/ml Particle size, mm Effective size, mm Moisture content, % ph range Uniformity coefficient Max. operation Temp., K Ionic form True density (wet), g/cm OH 0.68 Table 2. Experimental Conditions Parameter Bed volume, ml Temperature, K ph of solution SV, h -1 C 0(boron), ppm Range 4, 6, 8 283, 293, , 7.0, 8.5, , 24, 40 5, 10, 20 to the column at a flow rate of SV 24 h -1 (SV: space velocity defined as bed volumes per hour) using a peristaltic pump (SMP-23, EYELA Co.). From the outlet of the column, the effluents were collected ca. 2 ml before boron was analyzed by ICP-MS. The ph of the solution was in the range The adsorption temperatures for kinetic analysis were 283, 293, and 313 K. Results and Discussion Boron in water or seawater is always present in the form of boric acid, which is a very weak acid, or borate salts. The adsorption of boron is mainly affected by the ph, because the ionization of boric acid is determined accordingly. The general mechanism for boron adsorption by glucamine-type resins is given as follows [14]: Figure 1. Schematic diagram of the adsorption column bed. capacity of Amberlite IRA 743 for boron removal. Experiments Materials The bead-type ion exchange resin, Amberlite IRA 743 is a macroporous styrenic resin with methyl glucamine functionality. It is commonly known that boron is retained, borate ion is complexed by two sorbitol groups, and a proton is retained by a tertiary amine site, which behaves as a weakly basic anion exchanger. The characteristics of Amberlite IRA 743 are listed in Table 1. The boric acid (Aldrich Co.) employed in this study had a purity of %. All other chemicals used were of GR grade. Water, distilled and deionized through a purification system, was used as the the solvent. Adsorption The resin having a mm particle size range was used. The resins of bead-type were immersed in deionized water for 12 h before being packed into the column. The columns were made of glass and had an internal diameter of 7 mm. The column was packed with 1, 1.5, or 2 g of wet-settled volume of resin. The aqueous solution containing boron was delivered from down-flow Breakthrough Curves for the Variables The effects of the ph and initial concentration on the boron removal is illustrated in Figure 2. In the experiments, the temperature, bed volume of the resin, and SV (Space Volume) were kept constant at 293 K, 6 ml, listed in 24 h -1, respectively. In general, boric acid bare dissociates at values of ph lower than 7. On the other hand, at values of ph higher than 11.5, boron occurs as dissociated borate [B(OH) 4 ] -. Thus, the greatest value of the breakthrough point was obtained at ph 8.5, while it was minimized at ph 11.0 [7-8]. At concentrations up to 1000 ppm around ph 9, the polyborate ions B 2 -, B 3 -, and B 4 - exist. For this reason, the adsorption rate of boron removal can decline substantially at concentrations > 1000 ppm [2]. These results can be seen in Figure 3, which displays (1)

3 454 Ki-Won Baek, Sang-Hun Song, Seok-Hwan Kang, Young-Woo Rhee, Chang-Soo Lee, Bum-Jae Lee, Sam Hudson, and Taek-Sung Hwang Figure 2. Breakthrough curves of boron plotted with respect to the initial concentration of boron for the ion exchange resin (ph = 8.5; resin amount = 1.5 g; SV = 24 h -1 ; T = 293 K). Figure 4. Breakthrough curves of boron plotted with respect to the temperature for the ion exchange resin (ph = 8.5; C 0 = 20 ppm; SV = 24 h -1 ; resin amount = 1.5 g). quickly for the low bed volume of resin because of an effect of increasing the glucamine group content with increasing the bed volume of resin. Moreover, increasing the glucamine group content, resulted in an increasing retention capacity. The effect of temperature also can be seen in Figure 4. With in the range of K, the removal of boron from wastewater increased with increasing temperature up to 313 K, as can be seen in Figure 4. The profile for the removal of boron did not change at temperatures above 313 K. Figure 3. Breakthrough curves of boron plotted with respect to the ph of solution for the ion exchange resin (C 0 = 20 ppm; SV = 24 h -1 ; T = 293 K; resin amount = 1.5 g). the effect of ph on the removal of boron in a batch reactor and shows that the optimum solution ph was ca for boron removal both in this work and the literature. The effect of the initial concentration for boron removal can also be seen in Figure 2. The breakthrough point for the 5-ppm solution appeared more quickly than that for the 20-ppm solution. The lower the boron initial concentration, the more the fronts spread. This result is attributed to mass transfer limitations and/or chemical kinetics. Such limitations are caused by the initial concentration of boron as well as the different flow rates [15]. Moreover, as could be seen from Fick s first law, the diffusivity at low concentration is larger than that at high concentration. The breakthrough curves for boron removal on the bed volume of resin and temperature under the experimental conditions (ph = 8.5; C 0 = 20 ppm; SV = 24 h -1 ) are given in Figure 4. The breakthrough point appeared more Kinetics Approach In the continuous flow reactor, the adsorption kinetics for boron removal are usually adopted using first-order reversible adsorption models, such as the equilibrium adsorption model or Thomas s model. In this work, Thomas s model was used, as follows: where C and C 0 are the concentration of an outward solution and its initial concentration, respectively. k is a rate constant, M is the weight of ion-exchange resin, Q is the flow rate of the solution, q 0 is the maximum concentration of boron ion-exchanged, and V is the volume of solution. Representative kinetic results are illustrated with the slope (kc 0 /Q) in Figures 5 and 6. The effect of temperature on the boron removal is shown in Figure 5. Upon increasing the temperature at ph 8.5, the rate constant (k) increased gradually. In terms of the effect of the bed vol- (2) (3)

4 Adsorption Kinetics of Boron by Anion Exchange Resin in Packed Column Bed 455 Table 3. Rate Constants (k) and Activation Energies (E) Determined Using Thomas s Adsorption Model ph Rate constant, mol min/l Activation energy T = 283 K T = 293 K T = 313 K J/mol K 4.0 1,262 1,370 1,589 5, ,589 1,711 1,957 5, ,694 1,821 2,073 4, ,315 Figure 5. Kinetic approach result plotted with respect to the temperature change in a continuous column (ph = 8.5; C 0 = 20 ppm; SV = 24 h -1 ; resin amount = 1.5 g). Figure 7. Arrhenius plot for the activation energy. of 8.5, as follows: (4) Figure 6. Kinetic approach result plotted with respect to the ph of the solution in a continuous column (C 0 = 20 ppm; SV = 24 h -1 ; T = 293 K; resin amount = 1.5 g). ume of resin, the slope is inversely proportional to the increase of bed volume because the flow rate (Q) changed until SV (24 h -1 ). This result indicates that the flow rate can confine mass transfer limitations and/or chemical kinetics. These results can be also predicted from Figure 2. The effect of ph on the kinetic approach is shown in Figure 6. According to the value of ph, boric acid could be undissociated or dissociated to borate ions. The highest value of k was obtained at ph 8.5 under the experimental conditions although it showed irregularity. From these results, we obtained the activation energy from the plot of lnk versus 1/T, which was a straight line with a slope equal to -E/R and an intercept equal to ln[a(1-x)n] (Figure 7). Table 3 summarizes the rate constant and activation energy at each value of ph of the solution. In addition, the kinetic model was obtained [Eq. (4)] at the optimum ph Conclusions In this study, the adsorption characteristics and kinetics of an anion exchange resin for boron removal were investigated in a packed bed column. The breakthrough point for boron removal appeared more quickly upon increasing the boron concentration, but it appeared more slowly upon increasing the amount of resin and the adsorption temperature. This finding is attributed from the increase in the glucamine group content with increasing the resin amount. On the other hand, the greatest value for breakthrough point was obtained at an optimum ph of 8.5 because boric acid was undissociated at lower ph (< 7) and borate was easily dissociated at higher ph (11.5). The adsorption kinetics for boron removal correlated well with Thomas s model. The rate constant (k) increased gradually with increasing temperature and boron concentration because change of the fronts spread result in the influence of mass transfer and chemical kinetics.

5 456 Ki-Won Baek, Sang-Hun Song, Seok-Hwan Kang, Young-Woo Rhee, Chang-Soo Lee, Bum-Jae Lee, Sam Hudson, and Taek-Sung Hwang The optimum ph was obtained rapidly using the kinetic model. Acknowledgment This research was supported by the Ministry of Maritime Affairs and Fisheries. References 1. R. Boncukcuoglu, A. E. Yllmaza, M. M. Kocakerimb, and M. Copurb, Desalination, 160, 159 (2004). 2. J. W. Na and K. J. Lee, Ann. Nucl. Energy, 20, 455 (1993). 3. B. M. Smith, P. Todd, and C. N. Bowman, Sep. Sci. Technol., 30, 3849 (1995). 4. N. Kabay, I. Yilmaz, S. Yamac, M. Yukse, U. Yuksel, N. Yildirim, O. Aydogdu, T. Iwanaga, and K. Hirowatari, Desalination, 167, 427 (2004). 5. M. O. Simonnot, C. Castel, M. Nicolai, C. Rosin, M. Sardin, and H. Jauffret, Water. Res., 34, 109 (2000). 6. S. Şahin, Desalination, 143, 35 (2002). 7. M. Dj. Ristic and Lj. V. Rajakovik, Sep. Sci. Technol., 31, 2805 (1996). 8. S. H. Yoon, J. Ind. Eng. Chem., 12, 877 (2006). 9. N. Kabay, I. Ylmaz, S. Yamac, S. Samatya, M. Yuksel, U. Yuksel, M. Arda, M. Saglam, T. Iwanaga, and K. Hirowatari, React. Funct. Polym., 60, 163 (2004). 10. M. Taniguchi, M. Kurihara, and S. Kimura, J. Membr. Sci., 183, 259 (2001). 11. J. Redondo, M. Busch, and J. P. DeWitte, Desalination, 156, 229 (2003). 12. C. Dilek, O. Ozbelge, N. Blcak, and L. Yilmaz, Sep. Sci. Technol., 37, 1257 (2002). 13. L. Melnik, O. Vysotskaja, and B. Komilovich, Desalination, 124, 125 (1999). 14. K. Ooi, H. Katoh, A. Sonoda, and T. Hirotsu, J. Ion Exchange, 7, 166 (1996). 15. J. Deson and R. Rosset, Bull. Soc. Chim. Fr., 8, 4307 (1968).