Synthesis and Borate Uptake of Two Novel Chelating Resins

We examined the synthesis and borate uptake of novel chelating resins, named MGR and HMR, derived from the functionalization of macroporous poly(glyci...
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Ind. Eng. Chem. Res. 2002, 41, 133-138

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APPLIED CHEMISTRY Synthesis and Borate Uptake of Two Novel Chelating Resins Tao Qi, Akinari Sonoda, Yoji Makita, Hirofumi Kanoh, Kenta Ooi, and Takahiro Hirotsu* National Institute of Advanced Industrial Science and Technology, 2217-14 Hayashi-cho, Takamatsu 761-0395, Japan

We examined the synthesis and borate uptake of novel chelating resins, named MGR and HMR, derived from the functionalization of macroporous poly(glycidyl methacrylate-co-trimethylolpropane trimethacrylate) matrixes with N-methyl-D-glucamine (MG) and 2-amino-2-(hydroxymethyl)-1,3-propanediol (HM), respectively. The structures of free matrixes, resins, and borateloaded resins were confirmed by infrared spectroscopy. The borate uptake depends significantly on the proton capacity, which is proportional to the GMA fraction in matrixes, but little on the pore structure of macroporous matrixes. The ion-exchange isotherms of borate on MGR and HMR follow the Langmuir equation. MGR shows a larger uptake capacity toward borate than does HMR, comparable to that of Diaion CRB 02, because the tetradentate coordination mode of the former is more stable than the bidentate one of the latter. MGR exhibits a higher rate of borate uptake than does Diaion CRB 02, and the uptake kinetics are explained from a macropore diffusion model. Introduction The development of new boron-specific chelating resins with large capacity, high selectivity, and high uptake rate has held much interest both for the separation of boron isotopes in nuclear-related fields and for the recovery and removal of borate from geothermal waters and boron-containing wastewaters. Bicak et al. found that two cross-linked polymers derived from N-glucidol-N-methyl-2-(hydroxypropyl) methacrylate show a high uptake of borate and are effective in removing borate at ppm levels.1 Matsumoto et al. prepared a chitosan resin modified with saccharides and found that the uptake mechanism of boric acid on the resin is based on the complex formation of boric acid with the vicinal diol groups of the branched saccharide.2 Suzuki et al. demonstrated from 11B, 1H, and 13C NMR spectroscopy that an ion exchanger consisting of chromotropic acid and strongly basic anion-exchange resin binds boric acid very firmly, because of the formation of a stable bis-chelate-type complex.3 Maeda et al. reported that macroporous poly(GMA) (GMA: glycidyl methacrylate) modified by 2-amino-2-(hydroxymethyl)1,3-propanediol (HM) exhibits a high affinity for borate and binds borate selectively from the waste solution of geothermal power stations.4 The uptake capacity, however, decreases markedly with an increase in the molar fraction of divinylbenzene (DVB) in the copolymer, poly(GMA-co-DVB), because of the steric hindrance due to the formation of networks cross-linked with DVB.4 From the screening of 46 kinds of inorganic adsorbents and 12 kinds of organic adsorbents with a residual brine after salt production from seawater, Ooi et al. confirmed * To whom correspondence should be addressed. E-mail: [email protected].

that glucamine-type resins, particularly commercial Diaion CRB 02, exhibit the highest uptake capacity for borate in a dilute solution.5 Our interest has been much focused on the development of novel chelating polymers for the separation of boron isotopes.6-8 The fractionation of boron isotopes is due to a change in the coordination geometry of complexes between the solution phase and resin phase.7 A chelating resin with diethanolamine groups possesses a high boron-isotope separation factor because 10B is more fractionated to boron complexes with a tetrahedral coordination structure than to those with a planar triangular coordination structure.7 A unique pH dependence of the fractionation of boron isotopes with a glucamine-type resin results from the competitive fractionation of 10B isotopes to boron species bound to the resin as well as B(OH)4- in solution, both of which have a tetrahedral coordination geometry.8 Recently, we have synthesized successfully a porous copolymer of GMA with trimethylolpropane trimethacrylate (TRIM), poly(GMA-co-TRIM), with a large pore volume at a high fraction of GMA, using toluene as a porogen by suspension polymerization.9 Poly(GMA-coTRIM) is at least as mechanically stable as poly(styreneco-DVB) gel.10 In this study, we describe the synthesis and the borate uptake properties of chelating resins, MGR and HMR, obtained from functionalizing poly(GMA-co-TRIM) with N-methyl-D-glucamine (MG) and HM as ligands, respectively. The dependences of borate uptake on the GMA molar fraction and the pore structure of poly(GMA-co-TRIM) matrixes and on the pH value and the borate concentration of solution were investigated. The ion-exchange isotherms of borate on MGR and HMR and the uptake kinetics of borate on MGR were compared with those of borate on Diaion CRB 02, a commercial boron-specific chelating resin

10.1021/ie0104417 CCC: $22.00 © 2002 American Chemical Society Published on Web 12/28/2001

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Ind. Eng. Chem. Res., Vol. 41, No. 2, 2002 Scheme 1

Table 1. Porous Properties of Poly(GMA-co-TRIM) Matrixes surface pore pore GMA M:Pa areab volumec sized 2 3 matrix (mol %) (v/v) (m /g) (cm /g) (nm) MGRe P1 P2 P3 P4 P5 P6

46 72 72 72 79 84

1:2 1:2 1:1 1:3 1:2 1:2

419 147 115 127 86 59

1.07 1.14 0.47 1.66 1.37 1.11

74 75 38 147 117 67

MGR-1 MGR-2 MGR-3 MGR-4 MGR-5 MGR-6

HMRe HMR-1 HMR-2 HMR-3 HMR-4 HMR-5 HMR-6

a The volumetric ratio of monomer (M) to porogen (P). b Determined by N2 adsorption according to the Brunauer-EmmettTeller method. c Determined by mercury porosimetry. d The most frequent pore size determined by mercury porosimetry. e MGR-n and HMR-n prepared from the corresponding matrix Pn.

with N-methyl-D-glucamine as a ligand. The uptake kinetics of borate on MGR and Diaion CRB 02 were successfully simulated with a macropore diffusion model. Experimental Section Synthesis of Chelating Resins MGR and HMR. Porous beads of poly(GMA-co-TRIM) (0.25-0.5 mm) with different pore structures were prepared with toluene as a porogen by suspension polymerization.9 The particle size distribution of the resin beads was measured by a LMS-24 laser sizer (Seishin, Tokyo, Japan). Porous parameters of the resultant poly(GMA-co-TRIM) (P1-P6) are shown in Table 1. One gram of matrix beads was swelled in a solution of MG (3.75 g) or HM (4.6 g) and N,N-dimethylformamide (20 cm3) at 40 °C for more than 100 h in a three-necked flask and then stirred at 80 °C for 8-14 h. The resulting product was washed with hot deionized water until the washings became neutral. Then, the product was purified with acetone for 24 h in a Soxhlet extractor and dried under vacuum at 60 °C for more than 48 h. The sample number n of the chelating resins, MGR-n and HMR-n, relates to that of poly(GMA-co-TRIM), Pn, as shown in Table 1. Infrared Measurement. FT-IR spectra were recorded on a Perkin-Elmer model 2000 spectrophotometer at a resolution of 4 cm-1 for 300 scans. The polymer matrix and chelating resin samples were pulverized with liquid nitrogen freezing. The borate-loaded resins were filtered and centrifugated at 10 000 rpm for 20 min to remove the free boron solution in resins. The resins were dried in a microwave oven for about 20 min until the weight of resins was constant and then conditioned under vacuum at 50 °C for more than 5 days. The IR tablets were prepared from 0.5 mg of the pulverized resins and 200 mg of dried potassium bromide.11 Uptake of Protons. Samples of 0.2 g of MGR or HMR and 50 cm3 of 0.05 mol/dm3 hydrochloric acid were shaken in a 100 cm3 glass-stopper Erlenmeyer flask at 25 °C for 24 h. The hydrochloric acid concentration in the supernatant was measured by titration with a 0.05 mol/dm3 standardized sodium hydroxide solution. The proton uptake capacity was determined from the difference between the proton concentrations in the aqueous phase before and after the uptake of protons. Uptake and Elution of Borate. The batchwise uptake of borate was accomplished by shaking 50 mg of MRG or HMR with 10 cm3 of a 0.009 25 mol/dm3 borate solution containing 0.1 mol/dm3 KCl in a plastic flask at 30 °C for 48 h. The pH value of the borate solution was adjusted with hydrochloric acid and sodium

hydroxide solutions to avoid the effect of buffers. Ionexchange isotherms of borate were obtained with the different weight/volume ratios of MGR-6, HMR-6, or Diaion CRB 02 (Mitsubishi Chemicals, Tokyo, Japan) to a borate solution at pH values of 5.66 ( 0.48 (MGR-6 and CRB 02) and 6.70 ( 0.36 (HMR-6). For the kinetic experiments, 0.5 g of MGR-6 or Diaion CRB 02 was shaken with 100 cm3 of a 0.009 25 mol/dm3 borate solution at a pH value of 5.70 ( 0.25 at 30 °C. Aliquots of 1 cm3 were collected from the solution phase at approximate intervals and were diluted to 100 cm3. In the batchwise elution of borate, 0.5 g of borateloaded MGR was shaken in 100 cm3 of a hydrochloric acid eluant at 30 °C for 14 h. The borate concentration of the solution phase was measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES; SPS 7800, Seiko Instruments Inc., Chiba, Japan). The uptake capacity of borate was calculated from the difference between the borate concentrations before and after the load of borate. Results and Discussion Preparation of MGR and HMR. Poly(GMA-coTRIM) was functionalized by a ring-opening reaction of oxirane with the amino groups of MG and HM, as shown in Scheme 1, to yield chelating resins MGR and HMR, respectively. The functionalization of P6 into MGR-6 brings about not only the disappearance of the peaks due to epoxy groups at 2996, 1340, 993, 908, and 847 cm-1 but also the appearance of the new peaks at 1088 cm-1 (δOH) and 880 cm-1 (δCN), suggesting the complete conversion of the epoxy groups by the reaction with MG and in part by hydrolysis.11-13 A strong peak at 3415 cm-1 is due to the hydroxy groups in MG groups. The IR spectrum of HMR-6 shows that the peaks of the epoxy groups vanish and new peaks appear at 1636 (δNH), 1570 (δNH), 1052 (δCN), and 870 cm-1 (δCN). A broad peak in the region of 3730-3050 cm-1 indicates the overlap of the strong peak of hydroxy groups at 3500 cm-1 with the absorption band at 3200 cm-1(νNH). The new bands at 966 cm-1 for borate-loaded MGR-6 and at 986 cm-1 for borate-loaded HMR-6 are probably assigned to vibrations of tetrahedral B-O bonds in the tetradentate and bidentate complexes as shown in Scheme 2, respectively.14 This assignment is consistent with the fact that the B-OH bonds (1.40 Å) in the bidentate mode are stronger than the ester B-O bonds (1.46 Å) in the tetradentate mode.15 As for MGR-6 and HMR-6, the absorption bands at 2952 (νCH2), 1464 (δCH2),

Ind. Eng. Chem. Res., Vol. 41, No. 2, 2002 135

Figure 1. Effects of functionalization time on the uptake capacities of proton and borate. Proton uptakes with MGR-4 (O) and HMR-4 (4); borate uptakes with MGR-4 (b) and HMR-4 (2) under conditions T ) 30 °C, pH ) 7.8, C0 ) 0.009 25 mol/dm3, uptake time ) 48 h, and P4 as a matrix.

Figure 2. Effects of the molar fraction of GMA in poly(GMA-coTRIM) on the uptake capacities of proton and borate. Proton uptakes with MGR (O) and HMR (4); borate uptakes with MGR (b) and HMR (2) under conditions T ) 30 °C, pH ) 7.8, C0 ) 0.009 25 mol/dm3, and uptake time ) 48 h.

Scheme 2

1389 (δCH3), and 759 cm-1 (γCH), as well as those at 1730 (νCdO ester), 1260 (νCO ester), and 1150 cm-1 (νCO ester), remain unchanged, indicating no change of the polymer matrix by functionalization and borate uptake. To determine optimum conditions for the synthesis of MGR and HMR, the dependences of the uptake capacities for proton and borate on the functionalization time and temperature were investigated using P4 as a matrix. Figure 1 shows the results on MGR-4 and HMR-4 synthesized at 80 °C. The uptake capacities for borate and proton on MGR-4 increase markedly within 2 h and to a plateau before 5 h, while the uptake capacities on HMR-4 exhibit their maximum values at 14 h. MGR-4 and HMR-4 synthesized at 100 °C showed lower proton uptakes of 1.4 and 1.5 mmol/g than those at 80 °C (1.5 and 1.6 mmol/g in Figure 1), respectively, probably because the higher reaction temperature induces hydrolysis of epoxy groups in the matrix. Consequently, MGR and HMR were synthesized at 80 °C for 8 and 14 h, respectively, for the remainder of the experiments. From Figure 2, uptakes of borate on MGR and HMR depend significantly on the number of functional groups introduced, which is proportional to the molar fraction of GMA in the matrix. On the other hand, the uptake capacities for borate as well as proton on MGR and HMR depend little on the pore structure of macroporous poly(GMA-co-TRIM) in Figure 3, showing a very slight increase around the most frequent pore size of 75 nm. Consequently, MRG-6 and HMR-6 have been selected as the most suitable resins for borate uptake in the remainder of the studies. The significance of the cross-linker TRIM on the borate uptake of HMR is worth noting, compared with the relevant chelating resin cross-linked with DVB

Figure 3. Effects of the pore size of poly(GMA-co-TRIM) on the uptake capacities of proton and borate. Proton uptakes with MGR (O) and HMR (4); borate uptakes with MGR (b) and HMR (2) under conditions T ) 30 °C, pH ) 7.8, C0 ) 0.009 25 mol/dm3, uptake time ) 48 h, and GMA molar fraction ) 72%.

under similar experimental conditions: an initial concentration of 0.009 25 mol/dm3 and an uptake time of 48 h.4 HMR-5 and HMR-6 with molar GMA fractions of 79 and 84% have borate uptakes of 0.31 and 0.38 mmol/g (corresponding proton uptakes were 1.96 and 2.14 mmol/g), respectively, while the relevant chelating resins from poly(GMA-co-DVB) with greater GMA molar fractions of 95 and 97% show borate uptakes of 0.26 and 0.39 mmol/g (corresponding proton uptakes were 1.25 and 1.53 mmol/g), respectively.4 HMR with the lower GMA fraction exhibits a higher borate uptake capacity than the relevant chelating resin from poly(GMA-coDVB), probably because of the higher proton uptake of HMR, the higher hydrophilicity of poly(GMA-co-TRIM), and less steric hindrance in the cross-linked networks formed by TRIM.4,9 Accordingly, MGR and HMR with a higher cross-linking degree of TRIM, exhibiting greater compression moduli and strengths, are very suitable for practical application to column operations and chromatography.10 Effect of pH. The borate uptakes and the distribution coefficients Kd on MGR-6 and HMR-6 are plotted against pH in Figure 4. The distribution coefficient Kd, i.e., the molar ratio of borate bound on the resin to free borate in the solution inside the resin particles, is expressed as16

Kd ) (c0 - ce)V/cemvp

(1)

where c0 is the initial concentration of borate in solution (mmol/ dm3); ce is the concentration of borate at the equilibrated solution (mmol/dm3); m is the resin weight

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Figure 4. Effect of equilibrium pH on borate uptakes of MGR-6 (b) and HMR-6 (2) and on Kd of MGR-6 (O) and HMR-6 (4). Conditions: T ) 30 °C, C0 ) 0.009 25 mol/dm3, and uptake time ) 48 h.

(g); V is the volume of the borate solution used (cm3); and νp is the inner volume of the resin considered as the pore volume of the relevant poly(GMA-co-TRIM) in Table 1 (cm3/g). In Figure 4, the borate uptake and the distribution coefficient Kd exhibit maximum values at about pH ) 7.7 for MGR-6 and around pH ) 8.2 for HMR-6. Because the complexation of boric acid with hydroxyl groups in MGR-6 and HMR-6 liberates protons, the borate uptakes increase significantly with an increase in the pH value up to 8. The decrease in the borate uptake in the pH range above 10 is due to the hydrolysis of boric acid (pKa1 ) 9.27 at 20 °C).17 In the bonding of borate on MGR and HMR, the dominant structures for complexes of borate with the functional groups are the tetradentate mode (a related IR band at 966 cm-1) and the bidentate mode (a related IR band at 986 cm-1), respectively, as shown in Scheme 2. Generally, the tetradentate complex with a high formation constant of 104 is more stable than the bidentate complex because MG containing vicinal diol groups are the most efficient for the chelation to borate.16,18,19 Furthermore, the number of combinations to form a complex between the boron and OH groups in a ligand group increases with an increase in the number of OH groups in the ligand group. Accordingly, MGR shows a higher borate uptake capacity than does HMR, as shown in Figures 1-4. Ion-Exchange Isotherms. Ion-exchange isotherms of borate on MGR-6 and HMR-6 are shown in Figure 5, compared with those on Diaion CRB 02, a commercial borate-specific chelating resin. The isotherms of borate on MGR-6, HMR-6, and Diaion CRB 02 follow well the Langmuir equation at 30 and 10 °C, with a slight dependence on the uptake temperature. The Langmuir equation is expressed as

ce ce 1 ) + qe Kqs qs

(2)

where K is the equilibrium constant (dm3/mmol); qe is the borate uptake at the equilibrium (mmol/g); and qs is the saturated borate uptake capacity on the resin (mmol/g). The K and qs values, obtained by the leastsquares method with correlation coefficients of more than 0.989, are listed in Table 2. The binding constant K of MGR-6 is more than 2 times greater than that of HMR-6 in Table 2, consistent with the formation of the more stable complex of borate with MGR-6 as discussed above. MGR-6 shows a high borate uptake of 0.85

Figure 5. Ion-exchange isotherms of borate on MGR-6, HMR-6, and Diaion CRB 02. Temperatures: 30 (b) and 10 °C (O) for MGR6, 30 (2) and 10 °C (4) for HMR-6, and 30 (9) and 10 °C (0) for Diaion CRB 02. Equilibrium pH values: 5.66 ( 0.48 for MGR-6 and CRB 02 and 6.70 ( 0.36 for HMR-6. Solid lines represent the best fit according to the least-squares method. Table 2. Langmuir Constants for Borate Uptake on MGR-6, HMR-6, and Diaion CRB 02 at 30 and 10 °C resin

K (dm3/mmol)a

qs (mmol/g)a

r2 a,b

MGR-6 HMR-6 CRB 02

1.36 (1.13) 0.47 (0.57) 2.10 (3.40)

1.38 (1.36) 0.72 (0.75) 1.32 (1.34)

0.997 (0.997) 0.989 (0.996) 0.997 (0.999)

a The values in parentheses are the results at 10 °C. b The correlation coefficient regressed by the least-squares method.

mmol/g even at a borate concentration of 0.000 58 mol/ dm3 ()6.3 ppm of boron), suggesting a potential application for the removal of borate at ppm levels. It follows from Figure 5 and Table 2 that MGR-6 exhibits the isothermal uptake capacity of borate equivalent to Diaion CRB 02, which is the most effective for uptake of borate from a dilute solution.5 Uptake Kinetics. A detailed knowledge of the uptake kinetics of a borate-specific resin is very important for its practical use in laboratory and in industry. For this reason, some authors have investigated the borate uptake kinetics of newly synthesized or commercial resins on the basis of Vermeulen’s approximation expressed in eq 3,1-3,20 where t is uptake time (s); De is

ln[1 - (qt/q∞)2] ) -π2Det/R2

(3)

the effective diffusivity (cm2/s); qt and q∞ are the uptake capacities of borate on a resin at time t and t f ∞, respectively (mmol/g); and R is the particle radius (cm).20,21 Although the effective diffusivity De can be obtained by analyzing the experimental data by eq 3, it is not always easy to make an accurate a priori prediction of De because this is strongly dependent on the details of the pore structure. The pore diffusivity Dp, however, has been accurately measured by many experimental methods and approximately evaluated by diffusivity correlations.22 It was very interesting to obtain the pore diffusivity Dp for borate uptake on macroporous MGR. In the borate uptake with MGR-6, the uptake kinetics are mainly controlled by particle diffusion because the chelation is a fast reaction and the film diffusion can be neglected by the effective mixing of the resin beads with solution. The most frequent pore size of the P6 matrix is in the macropore region. Accordingly, we analyzed tentatively the kinetics of borate uptake on macroporous MGR-6 from a macropore diffusion model with the matrix physical parameters and the linear

Ind. Eng. Chem. Res., Vol. 41, No. 2, 2002 137 Table 4. Batchwise Elution of Borate Loaded on MGR at 30 °C

Figure 6. Uptake kinetics of borate on MGR-6 (b) and Diaion CRB 02 (2). Conditions: T ) 30 °C, pH ) 5.70 ( 0.25, and C0 ) 0.009 25 mol/dm3. Dotted (- - -) and solid lines (s) were obtained from eqs 3 and 4, respectively. Table 3. Analysis of Uptake Kinetics of Borate on MGR-6 and Diaion CRB 02 at 30 °C resin MGR-6

eq

3 4 CRB 02 3 4

π2De/R2 (1/s) 0.001 22 0.001 25 0.000 304 0.000 318

R (cm) dq/dca 0.0173 0.0173 0.0186 0.0186

pb

De (cm2/s)

Dp (cm2/s)

3.7 × 0.59 3.8 × 10-8 6.0 × 10-7 1.0 × 10-8 0.49 1.1 × 10-8 2.1 × 10-7 10-8

21.2 17.2

r2 c 0.973 0.988 0.993 0.995

a

Local slope calculated from the ion-exchange isotherm considered to be the linear equilibrium isotherm. b Porosity of a resin particle calculated from the equation p ) 1/(1 + 1/νpF), where νp is the pore volume of the corresponding backbone polymer and F is the real density of the resin. The real density of the resin was measured in heptane at 25 °C.9 c The correlation coefficient regressed by the least-squares method.

equilibrium isotherm (q ) fc).22 The approximate analytical solution is given by eq 4, which holds in the range of fractional uptake greater than 0.7 with a deviation of less than 2%:22

(

ln 1 -

) ()

qt π2Dp 6 t) ) ln 2 - 2 q∞ π R [1 + (1 - p)f/p] ln

()

π2De 6 t (4) π2 R2

where Dp is the macropore diffusivity (cm2/s); f is the dimensionless Henry’s law equilibrium constant; p is the porosity of a resin particle calculated from the pore volume and the real density of the resin; and the effective diffusivity De ) Dp/[1 + (1 - p)f/p] (cm2/s). Because the borate uptake rate was measured over a small differential step, the equilibrium constant f can be replaced by the local slope of the isotherm (dq/dc).22 Thus, De can also be written as De ) Dp/{1 + [(1 - p) (dq/dc)]/p}. MGR-6 possesses a higher borate uptake rate than Diaion CRB 02 in Figure 6 with a shorter uptake halftime t1/2 of 12 min than that for Diaion CRB 02 (24 min), because of the greater hydrophilicity and the larger surface area of MGR-6 (46 m2/g for MGR-6 and 30 m2/g for Diaion CRB 02). The effective diffusivities De of MGR-6 and Diaion CBR 02 calculated by eqs 3 and 4 are of almost the same magnitude (Table 3). As shown in Table 3, the macropore diffusivities Dp calculated from eq 4 are 6.0 × 10-7 cm2/s for MGR-6 and 2.1 × 10-7 cm2/s for Diaion CRB02, which are reasonably focused around 1/24-1/70 of the boric acid diffusivity 1.41 × 10-5 cm2/s in aqueous solution at a borate concentration of 0.009 25 mol/dm3.22,23 Accordingly, the marked

resin

HCl (mol/dm3)

elution (%)

resin

HCl (mol/dm3)

elution (%)

MGR-1 MGR-2 MGR-3

0.1 1.0 0.5

90.0 92.9 93.9

MGR-4 MGR-5 MGR-6

0.1 0.1 0.1

95.5 90.0 93.1

enhancement in the borate uptake rate on MGR-6 is due to the increase in Dp as well as hydrophilicity. We will later describe the effects of the pore structure and the nonlinearity of the ion-exchange isotherm on the uptake kinetics of borate on MGR based on the macropore diffusion model elsewhere. Elution of Borate Loaded on MGR. The batchwise elution in Table 4 demonstrates that the borate loaded on MGR can be eluted with 0.1-1.0 M hydrochloric acid. The chemical stability of MGR was investigated by immersing MGR-6 in 1 mol/dm3 hydrochloric acid at room temperature for 7 days. The treated MGR-6 exhibited the same borate uptake capacity as the original sample, confirming the chemical stability of MGR. Conclusions Novel chelating resins, MGR and HMR, have been synthesized through functionalization of macroporous poly(GMA-co-TRIM) with MG and HM, respectively. The uptake of borate on MGR and HMR depends significantly on the capacity, which is proportional to the GMA fraction in poly(GMA-co-TRIM), but little on the pore structure of macroporous poly(GMA-co-TRIM). The ion-exchange isotherm of borate on MGR-6 and HMR-6 follows the Langmuir equation. MGR-6 shows the larger uptake capacity toward borate than HMR-6, comparable to that of commercial Diaion CRB 02, because the tetradentate coordination mode of the former is more stable than the bidentate one of the latter. MGR-6 exhibits a higher rate of borate uptake than Diaion CRB 02; their kinetics are explained by a macropore diffusion model. Therefore, MGR-6 is expected to be promising for the separation of boron isotopes by a column operation that requires a chelating resin with a higher rate as well as a larger capacity of boron uptake. Literature Cited (1) Bicak, N.; Ozbelge, H. O.; Yilmaz, L.; Senkal, B. F. Crosslinked Polymer Gels for Boron Extraction Derived from N-glucidolN-methyl-2-hydroxypropyl Methacrylate. Macromol. Chem. Phys. 2000, 201, 577. (2) Matsumoto, M.; Matsui, T.; Kondo, K. Adsorption Mechanism of Boric Acid on Chitosan Resin Modified by Saccharides. J. Chem. Eng. Jpn. 1999, 32 (2), 190. (3) Suzuki, T. M.; Tanaka, D. A. P.; Yokoyama, T.; Miyazaki, Y.; Yoshimura, K. Complexation and Removal of Trace Boron from Aqueous Solution by an Anion Exchange Resin Loaded with Chromotropic Acid (Disodium 2,7-dihydroxynaphthalene-4,5-disulfonate). J. Chem. Soc., Dalton Trans. 1999, 1639. (4) Maeda, H.; Egawa, H.; Jyo, A. Preparation of Chelating Resins Selective to Boric Acid by Functionalization of Macroporous Poly(glycidyl methacrylate) with 2-Amino-2-hydroxymethyl-1,3propanediol. Sep. Sci. Technol. 1995, 30 (18), 3545. (5) Ooi, K.; Kanoh, H.; Sonoda, A.; Hirotsu, T. Screening of Adsorbents for Boron in Brine. J. Ion Exchange 1996, 7 (3), 166. (6) Sonoda, A.; Takagi, N.; Ooi, K.; Hirotsu, T. Complex Formation between Boric Acid and Triethanolamine in Aqueous Solutions. Bull. Chem. Soc. Jpn. 1998, 71, 161. (7) Hirotsu, T.; Sonoda, A.; Makita, Y.; Kanoh, H.; Takagi, N.; Ooi, K.; Seno, M. Fractionation of Boron Isotopes to Bis(2-

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Received for review May 16, 2001 Revised manuscript received October 26, 2001 Accepted October 29, 2001 IE0104417