Synthesis of Highly Porous Chitosan Microspheres Anchored with 1,2

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SEPARATIONS Synthesis of Highly Porous Chitosan Microspheres Anchored with 1,2-Ethylenedisulfide Moiety for the Recovery of Precious Metal Ions Yuki Kanai, Tatsuya Oshima, and Yoshinari Baba* Department of Applied Chemistry, Faculty of Engineering, UniVersity of Miyazaki, 1-1 Gakuen-Kibanadai Nishi, Miyazaki 889-2192, Japan

The highly porous chitosan microspheres (HPCM) with throughpores were performed by mixing the oil-inwater-in-oil (chitosan O/W/O) emulsions containing chitosan in the water phase with the NaCl W/O emulsions containing 15% sodium chloride in the aqueous phase. The difference of the osmotic pressure between these emulsions causes the transportation of water from chitosan O/W/O emulsions to NaCl W/O emulsions to make HPCM. Both introduction of 1,2-ethylenedisulfide moiety and cross-linking were performed at the same time by activating HPCM with 2-(chloromethyl)oxirane, followed by introducing 1,2-ethylenedisulfide moiety with 1,2-ethanedithiol. These chitosan microspheres (EDSC) had an average diameter of 143 µm and average pore size of 2-6 µm. EDSC exhibited high selectivity for precious metals such as palladium(II), gold(III), and platinum(IV) over base metal ions in hydrochloric acid solutions. The adsorbed palladium(II) was completely desorbed using aqueous thiourea solution. Furthermore, the adsorption kinetics was investigated to elucidate the effect of large pores on the adsorption of palladium(II) with EDSC from acidic chloride media. The adsorption mechanism indicated that the mass transfer rate in the laminar film in the aqueous phase and the chemical reaction of palladium(II) with sulfur ligand in EDSC were the rate-determining steps at low and high concentrations of hydrochloric acid, respectively. This suggests that adsorption of palladium(II) on EDSC is very fast, which is due to the decrease in mass transfer resistance of intraparticle diffusion by the effect of large pores. Introduction Precious metals such as gold(III), palladium(II), and platinum(IV) are the most important rare metals indispensable in the high-technology industries as raw materials of catalysts, electronic materials, and other components.1 Therefore, the recovery of precious metals from acidic solutions that leached out these metals from spent catalysts and industrial wastes is very important because of the increasing industrial needs for these metals and their limited resources. Thus, it is necessary to develop new adsorbents with high adsorption ability for these metals. In recent years, much attention has been paid to the adsorption of metal ions using low-cost natural adsorbents such as agricultural wastes, clay materials, biomasses, and seafood processing wastes.2-7 Among them, chitin and chitosan, which are the second most abundant polysaccharides in nature and are obtained from shells of crustacean such as shrimp, crabs, and lobsters, are waste products from the seafood processing industries.8 Chitosan has great potential for the adsorption of metal ions due to an amino group and hydroxyl groups in its chemical structure. In particular, the amino groups are responsible for the adsorption of metal cations, and the protonated amino groups in acidic solution are responsible for the electrostatic attraction with anionic metal complexes. The amino groups also make many chemical modifications possible for the purpose of improving the affinity of adsorbents for metals. Muzzarelli et al. carried out a series of studies on the * Corresponding author. Tel.: +81-985-58-7307. Fax: +81-98558-7323. E-mail: [email protected].

chromatographic separations of metal ions with some chitosan derivatives from an analytical point of view since the 1980s.9-11 Thus far, the authors have also developed a number of chitosan derivatives for the recovery of metal ions and reported their adsorption properties for metal ions.12-24 One of the most important problems in adsorption of precious metal ions is its slow adsorption kinetics. The adsorption kinetics is controlled not only by the chemical interactions between the metal ions and adsorption sites but also by the mass transfer of the metal ions from the bulk of the liquid phase to the adsorption sites inside the particles. In general, mass transfer of adsorbates includes several steps such as film diffusion in the aqueous phase, intraparticle diffusion, and chemical reaction in the adsorbents. Intraparticle diffusion is frequently considered to be a limiting step in the adsorption process with porous materials. Modifying the porous structure of adsorbents is an efficient way for improving diffusion properties. Chitosan can readily be modified physically by preparing different polymer forms such as powder, nanoparticles, beads, membranes, sponges, and fibers for application in various fields. This paper reports on how the highly porous chitosan microspheres with large pores were prepared by a new method using chitosan O/W/O emulsions that we presented earlier.24 The highly porous chitosan microspheres can be expected to show superior adsorption properties because the adsorption kinetic rate increases by increasing the intraparticle diffusion due to large “throughpores” that penetrate through the diameter of the particles. Therefore, this makes it possible to utilize it for

10.1021/ie070235k CCC: $40.75 © 2008 American Chemical Society Published on Web 04/16/2008

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Figure 1. Scheme for preparation of highly porous chitosan microspheres.

perfusion chromatography, which is a separation system for high-speed separation of metal ions.25 In this study, the highly porous chitosan microspheres with large pores were prepared through chitosan oil-in-water-in-oil (O/W/O) emulsions. Furthermore, the new chitosan derivative (EDSC) with 1,2-ethylenedisulfide moiety as a sulfur ligand has been synthesized to examine its ability to adsorb precious metal ions such as gold(III), palladium(II), and platinum(IV). The introduction of chelating ligands and the cross-linking reaction have been performed at the same time. In addition, measurements of the adsorption kinetics of palladium(II) with EDSC have been carried out in order to elucidate the effect of large throughpores on the adsorption kinetics. The adsorption mechanism of palladium(II) has been revealed by examining the effects of the reaction species on the adsorption kinetics. Experimental Section Reagents. The aqueous metal solutions were prepared by dissolving the corresponding reagent-grade metal chlorides in hydrochloric acid. Chitosan (trade name, Chitosan 100 L, 100% deacetylation), produced and marketed by Katokichi Co. Inc., Japan, was used without further purification. The molecular weight of chitosan used was 80 000-100 000. Tetraglycerin condensed ricinoleic acid ester (TGCR) of a surfactant for food additives was purchased from Sakamoto Co., Inc., Japan. Other reagents of reagent grade were used without further purification. All aqueous solutions were prepared with distilled and deionized water. Preparation of Highly Porous Chitosan Microspheres. The preparation of highly porous chitosan microspheres is shown in Figure 1. Chitosan (16 g) was dissolved in 250 mL of 3 wt % aqueous adipic acid solution containing Tween60 emulsifier, and then it was emulsified with 50 mL of hexane to form chitosan O/W emulsion containing chitosan in the aqueous phase. The chitosan O/W emulsion was added to 500 mL of hexane containing TGCR emulsifier to form chitosan O/W/O emulsion. On the other hand, 250 mL of hexane containing TGCR emulsifier was emulsified with 200 mL of 15 wt % aqueous sodium chloride solution, and it was added to the chitosan O/W/O emulsion. The highly porous chitosan microspheres were prepared through dehydration caused by the difference in their osmotic pressures. The highly porous chitosan microspheres were filtrated and thoroughly washed with ethanol. Preparation of a Chitosan Derivative Containing 1,2Ethylenedisulfide (EDSC). The scheme for preparation of EDSC is shown in Figure 2. Chitosan derivative precursor anchoring intact epoxy or chloromethyl groups was obtained

by the reaction of the porous chitosan microspheres (8 g, 50 mmol of monomeric units) and 100 mL of 2-(chloromethyl)oxirane in 50 mL of dimethylformamide (DMF) at 60 °C for 2 h with sodium hydroxide as a catalyst. EDSC was synthesized by adding the chitosan derivative precursor and 1,2-ethanedithiol (47 g, 500 mmol) into 100 mL of DMF at room temperature under nitrogen atmosphere, where triethylamine was used as a catalyst. After stirring for 48 h, the product was filtered off and thoroughly washed with ethanol, aqueous sodium hydroxide solution, hydrochloric acid, and deionized water. A quantity of 10.5 g of EDSC was obtained. Characterization of EDSC. The shape and surface of the EDSC microspheres were observed with scanning electron microscope (SEM, Hitachi S-4100M). The pore structure of the EDSC microspheres was examined with a mercury porosimeter (Shimadzu Micromeritics Pore Sizer 9320). The values of the contact angle of mercury on the surface of the microspheres and the mercury surface tension used in this study were 140° and 480 dyne cm-1 to calculate the pore size, respectively.26 The size distribution was determined by measuring 700 dried EDSC microspheres with an optical microscope (Olympus). The total sulfur content of the EDSC microspheres was measured using fluorescence X-ray spectroscopy. The quantitative determination of the thiol groups on the EDSC microspheres was carried out by Ellman method using 5,5′-dithiobis-(2-nitrobenzoic acid).27 Adsorption Equilibrium. About 0.05 g of dried EDSC and 15 mL each of 0.01-5 mol dm-3 hydrochloric acid solutions containing 1 × 10-3 mol dm-3 of metal chloride were shaken at 120 rpm for 24 h in a stoppered 30 mL glass flask immersed in a water bath thermostated at 303 K. The initial and equilibrium metal concentrations in the aqueous solutions were determined by ICPS-7000 sequential plasma spectrometer (Shimadzu). Equilibrium concentrations of hydrochloric acid in the aqueous solutions were determined by titration with standardized aqueous NaOH solution. The adsorption percentage and the amount of adsorbed metal ion [qe (mol kg-1)] were calculated from the initial and equilibrium concentrations in the aqueous solution [Cinit and Ce (mol dm-3)], the volume of the aqueous solution [V (dm-3)], and the weight of the dry EDSC microspheres [W (kg)].

adsorption % ) (Cinit - Ce)/Cinit qe ) (Cinit - Ce)V/W In the desorption experiment, ammonia, aqueous ammonium thiocyanate solution, aqueous thiourea solution, and aqueous thiourea solution containing hydrochloric acid were used as eluents of palladium(II) by a batchwise method. The contact time for desorption was 24 h. The desorption percentage was defined as the ratio of the amount of palladium(II) desorbed to the amount of palladium(II) adsorbed multiplied by 100. Adsorption Kinetics of Palladium(II) from Hydrochloric Acid Solutions. About 0.1 g of EDSC was stirred together with 100 mL of the aqueous phase containing 0.25 × 10-3 mol dm-3 palladium(II) in a flask equipped with a speed controller, which was situated in a water bath maintained at 303 K. The hydrogen ion and chloride ion concentrations of the aqueous phase were adjusted by changing the mixture mole ratio of hydrochloric acid and sodium chloride. The aqueous palladium(II) solution was introduced into the flask after 2 mL of distilled water was added to eliminate air in EDSC. Aliquots of samples of 1 mL were taken at time intervals. The palladium(II) concentration

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Figure 2. Synthetic scheme for EDSC.

Figure 4. Pore size distribution of EDSC.

Figure 3. SEM images of EDSC: (a) surface and (b) cross section.

in the sample was determined by using ICPS-7000 sequential plasma spectrometer (Shimadzu). Results and Discussion Characteristics of the EDSC Microspheres. SEM images of the EDSC microspheres are shown in Figure 3. A considerable number of large pores can be observed on the surface of and inside the EDSC microspheres, and their inside pore structure resembles a sponge. In addition, it is confirmed that the EDSC microspheres are highly porous, with large pores and throughpores. These large pores were presumably formed by aggregation and coalescence of many internal small droplets of hexane in the aqueous chitosan droplets of the O/W/O emulsions.

Figure 5. Particle size distribution of EDSC.

The pore size distribution of the EDSC microspheres is represented in Figure 4, where Vp is the pore capacity and D is the average pore diameter. The pore size range of the microspheres was 2-6 µm, which agrees with the pore size estimated by the SEM images as shown in Figure 3. Therefore, it is expected that the large pores and throughpores of the EDSC microspheres will improve the adsorption kinetics of palladium(II) by increasing the intraparticle diffusion rate. Figure 5 shows the size distribution of the EDSC microspheres with an average particle diameter of 143 µm. The total sulfur content (thioether group (-S-) and thiol group (-SH)) was determined to be 1.84 mol kg-1 by a fluorescence X-ray spectroscopy. The thiol group (-SH) content in EDSC was much smaller in value (3.6 × 10-3 mol kg-1) compared to the

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Figure 6. Effect of hydrochloric acid concentration on adsorption percentage of metal ions with EDSC.

total sulfur content. Consequently, the 1,2-ethaneditiol content of EDSC was estimated to be 0.92 mol kg-1, indicating that almost all sulfur atoms exist in 1,2-ethylenedisulfide groups (-CH2-S-CH2CH2-S-CH2-) through the reaction of 1,2ethanedithiol and 2-(chloromethyl)oxirane. Adsorption Selectivity for Metal Ions. Figure 6 shows the effect of concentration of hydrochloric acid on the adsorption percentage of metal ions. Palladium(II), gold(III), and platinum(IV) were preferentially adsorbed over the base metal ions, copper(II), nickel(II), cadmium(II), iron(III), cobalt(II), and zinc(II). EDSC was found to be an effective adsorbent for the separation of palladium(II), gold(III), and platinum(IV) from these base metal ions. Palladium(II) was selectively adsorbed in the hydrochloric acid concentration range used. Although gold(III) and platinum(IV) were completely adsorbed in the low concentration region of hydrochloric acid, their adsorption percentages slightly decreased with an increase in concentration of hydrochloric acid. The separation of palladium(II) from nickel(II) was investigated. Palladium(II) was adsorbed selectively using the EDSC microspheres from its solution containing nickel(II) of about 650 times the molar quantity of palladium(II) as shown in Figure 7. EDSC is found to be an effective adsorbent for the selective separation of palladium(II) from nickel(II). Adsorption Isotherm of Palladium(II). The adsorption equilibria of palladium(II) on EDSC were conducted from 0.1 mol dm-3 hydrochloric acid at temperatures of 283, 303, and 323 K. Figure 8 shows the adsorption isotherms of palladium(II) with the EDSC microspheres at different temperatures. The relationship between the amount of palladium(II) adsorbed on the EDSC microspheres and the remaining palladium(II) concentration in the aqueous solution at equilibrium was fitted by the Langmuir isotherm model. Consequently, the maximum adsorption capacity [qm (mol kg-1)] and the adsorption equilibrium constant [KL (m3 mol-1)] at different temperatures were estimated from the slope and intercept of the Langmuir equation:

Ce 1 1 ) C + qe qm e KLqm Their values are given in Table 1, and they indicate that the temperature effect in the range studies is insignificant. Therefore, we carried out a thermodynamic discussion as follows. The free energy change (∆G), enthalpy change (∆H), and entropy change (∆S) in the adsorption of palladium(II) are

Figure 7. Selective adsorption of palladium(II) over nickel(II) from their mixed solution on EDSC at 0.1 mol dm-3 hydrochloric acid.

Figure 8. Adsorption isotherms of palladium(II) on EDSC from 0.1 mol/ dm3 hydrochloric acid at different temperatures. Table 1. Adsorption Capacity, Langmuir Constants, and Thermodynamic Parameters in the Adsorption of Palladium(II) on EDSC at 283, 303, and 323 K temp qm KL ∆G ∆S ∆Hav (K) (mol kg-1) (m3 mol-1) (kJ mol-1) (J K-1 mol-1) (kJ mol-1) 283 303 323

2.34 2.33 2.41

14.48 13.98 13.24

-6.29 -6.65 -6.94

16.28 16.38 16.27

-1.68

calculated by the following equations.

∆G ) -RT lnKL ln KL ) -

∆H + constant RT

∆G ) ∆H - T∆S The thermodynamic parameters of the adsorption of palladium(II) with EDSC are also summarized in Table 1 using these equations. The enthalpy change was obtained from the slope of the ln KL versus 1/T plot as -1.68 kJ mol-1. This low value indicates that the adsorption is an exothermic process. The negative values of the free energy change indicate that adsorp-

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Figure 9. Effect of the chloride ion concentration on the adsorption rate of palladium(II) adsorbed on EDSC.

Figure 10. Plots of ln(Ct/Cinit) versus t.

Table 2. Eluents and Desorption Percentage of Palladium(II) eluent 1 mol dm-3 ammonia aqueous solution 1 mol dm-3 ammonium thiocyanate aqueous solution 1 mol dm-3 tiourea aqueous solution 1 mol dm-3 tiourea aqueous solution containing 1 mol dm-3 hydrochloric acid

desorption % 2.7 2.6 100 100

tion of palladium(II) is spontaneous and a favorable process. Positive values of the entropy change suggest that the disorder of the system increased through the chelating formation of palladium(II) with 1,2-ethylenedisulfides of EDSC. These thermodynamic parameters demonstrate that the adsorption of palladium(II) on EDSC is controlled by the entropy change because there is almost no enthalpy change in the adsorption of palladium(II) on EDSC. Desorption Isotherm of Palladium(II) Adsorbed onto EDSC. The experimental results for the desorption of palladium(II) by a one-time batch method are shown in Table 2. The adsorbed palladium(II) was completely desorbed with an aqueous thiourea solution and the aqueous thiourea solution containing hydrochloric acid to recover and concentrate palladium(II), indicating that EDSC can be regenerated with these reagents and reused for recovery of palladium(II). Adsorption Kinetics of Palladium(II) from Hydrochloric Acid Solutions. Next, in order to elucidate the effect of large throughpores on the adsorption kinetics, the adsorption kinetics of palladium(II) with EDSC from hydrochloric acid were measured by a batchwise method at 303 K. We examined the effects of concentrations of the hydrogen ion and the chloride ion, and the stirring speed on the adsorption kinetics of palladium(II) to elucidate the adsorption mechanism. Figure 9 shows the effect of the chloride ion concentration on the time-course of changes of palladium(II) concentration in the aqueous phase. The effect of chloride ion concentration was investigated by keeping the concentration of the hydrogen ion at 0.01 mol dm-3 and the stirring speed at 350 rpm. The concentration change of palladium(II), (Cinit - Ct) (mol dm-3), was calculated from the mass balance of palladium(II) in the aqueous phase. Here, Ct and Cinit are the concentration of palladium(II) in the aqueous phase at contact time (t) and the initial concentration of palladium(II), respectively. It is obvious from Figure 9 that the adsorption kinetics is rapid at low concentration of the chloride ion, and then it reaches equilibrium after about 10 min. The adsorption kinetics decreased with increasing concentration of the chloride ion. In order to analyze the adsorption kinetics, a pseudo-firstorder rate equation with respect to the palladium(II) concentra-

Figure 11. Effect of the concentration of the chloride ion on the pseudofirst-order rate constant in the initial adsorption of palladium(II).

tion (eq 1) was applied to the experimental data describing at the initial adsorption. The pseudo-first-order rate equation was represented by

ln(Ct/Cinit) ) -k1t

(1)

where k1 (s-1) is the pseudo-first-order rate constant of initial adsorption. The value of k1 was obtained from the slopes of the ln(Ct/Cinit) versus t plot, as shown in Figure 10. Figure 11 shows the effect of the concentration of the chloride ion on the pseudo-first-order rate constant at 0.01 mol dm-3 hydrogen ion concentration and at 350 rpm. As you can see from these results, the pseudo-first-order rate constant is independent of the concentration of the chloride ion at low concentration of the chloride ion, while it decreases with increasing concentration of the chloride ion at high concentration of the chloride ion. The relationship between ln(Ct/Cinit) versus t at high chloride concentration is described by a straight line with a slope of -1. Therefore, it can be assumed that the adsorption mechanism in the high concentration of chloride ion is different from that at low concentration. Figure 12 shows the effect of the concentration of the hydrogen ion on the pseudo-first-order rate constant at high and low concentrations of the chloride ion, while keeping stirring speed at 350 rpm. As is seen from Figure 12, the pseudo-firstorder rate constant is almost independent of the concentration of the hydrogen ion at both concentrations of the chloride ion studied, suggesting that the hydrogen ion has not participated in the adsorption of palladium(II) from hydrochloric acid.

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the following equation,

R0 ) kR[PdCl3 ] (kR ) k′R[RSSR]) ) kRa3CPdi

(3)

where CPdi (mol dm-3) is the interfacial concentration of palladium(II) in the aqueous phase, R3 ) β3[Cl-]/(1 + Σβn[Cl-]n) (n ) 1-4), β1 ) 5.01 × 104 (mol dm-3)-1, β2 ) 5.01 × 107 (mol dm-3)-2, β3 ) 2.00 × 1010 (mol dm-3)-3, and β4 ) 7.94 × 1011 (mol dm-3)-4.28 Equation 3 can be approximated to eq 4 at high concentrations of the chloride ion. Therefore, the pseudo-first-order rate constant is expressed by eq 5. Equation 5 shows the inverse first-order dependence on the concentration of chloride ion, being in accordance with the experimental results in Figures 10 and 11. Figure 12. Effect of the concentration of the hydrogen ion on the pseudofirst-order rate constant in the initial adsorption of palladium(II).

R0 ≈ kRβ3/β4 × [Cl-]-1 × CPdi

(4)

k1 ) kRβ3/β4 × [Cl-]-1

(5)

Under steady-state conditions, the mass transfer of palladium(II) in the aqueous-phase film (JM) is balanced with its adsorption kinetics (R0) as described by eq 6.

R0 ) JM ) kRCPdiR3 ) apkM(CPd0 - CPdi)

(6)

where CPd0 (mol dm-3) is the initial concentration of palladium(II) in the aqueous bulk phase and apkM (s-1) is the volumetric coefficient of mass transfer. On the basis of eq 6, the initial adsorption kinetics can be expressed as follows:

R0 ) Figure 13. Effect of the stirring speed on the pseudo-first-order rate constant in the initial adsorption of palladium(II).

The effect of the stirring speed was investigated by keeping the concentration of hydrochloric acid at 0.01 and 3 mol dm-3, respectively. The relationship between the pseudo-first-order rate constant and the stirring speed is shown in Figure 13. It can be observed that the rate constant is almost independent of the stirring speed at the higher concentration of hydrochloric acid; however, it depends on the stirring speed at the lower concentrations of hydrochloric acid. From the results mentioned above, it may be concluded that the initial adsorption kinetics is strongly controlled by mass transfer in the aqueous-phase film at low concentrations of hydrochloric acid, while it is probably controlled by the chemical reaction processes in the high concentration range. Adsorption Kinetics Mechanism. From the experimental results outlined above, the adsorption mechanism of palladium(II) onto EDSC microspheres is considered to be explained by diffusion in the aqueous-phase film or the chemical interaction between the palladium(II) ion and the functional group (-SC2H4-S-) in EDSC. We assumed that the chemical reaction of palladium(II) with EDSC ()RSSR) (eq 2) is the ratedetermining step. k′R

PdCl3(H2O)- + RSSR 98 RSPdCl2SR + Cl- + H2O

(2)

where kR′ (s-1) is the rate constant of adsorption of palladium(II). Under the experimental conditions in this study, the initial adsorption kinetics [R0 (mol dm-3 s-1)] can be expressed by

kRR3apkM × CPd0 kRR3 + apkM

(7)

The pseudo-first-order rate constant can be ultimately expressed as follows:

logk1 ) log

kRR3apkM kRR3 + apkM

(8)

The rate constant and the volumetric coefficient of mass transfer were determined to be kR ) 0.25 (s-1) and apkM ) 0.80 × 10-2 (s-1) by a curve-fitting method based on eq 8. The theoretical curves using kR and apkM are in good agreement with the experimental results, as shown in Figures 11 and 12. Conclusions The highly porous chitosan microspheres (EDSC) with large pores anchoring 1,2-ethylenedisulfide as a ligand were synthesized for perfusion chromatography by means of O/W/O emulsion method. EDSC was found to be a selective adsorbent for palladium(II), gold(III), and platinum(IV) over base metals in hydrochloric acid. The obtained thermodynamic parameters demonstrate that the adsorption mechanism of palladium(II) on EDSC is predominantly controlled by the entropy change, indicating that palladium(II) is adsorbed by forming a chelating compound with 1,2-ethylenedisulfide in EDSC. In addition, 100% desorption of palladium(II) adsorbed onto EDSC was achieved by a batch method using an aqueous thiourea solution. The adsorption kinetic studies revealed that the mass transfer rate in the aqueous-phase film and the chemical reaction are the rate-determining steps in the adsorption of Pd(II) at low and high concentrations of hydrochloric acid, respectively. These adsorption mechanisms indicate that the adsorption rate of

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palladium(II) on EDSC is very high, which is due to a decrease in the mass transfer resistance of the intraparticle diffusion due to the large pores and throughpores in EDSC. Acknowledgment The authors wish to thank The Ministry of Environment of Japan for providing a Grant for Research and Technology Development on Waste Management. Literature Cited (1) Junji, S.; Akihiko, O. Recycling Technology of Precious Metals. Shigen to Sozai 2002, 118, 1-3. (2) Yang, T. C.; Zall, R. R. Adsorption of Metals by Natural Polymers Generated from Seafood Processing Wastes. Ind. Eng. Chem. Prod. Res. DeV. 1984, 23, 168-172. (3) Onsoyen, E.; Skaugrud, O. Metal Recovery using Chitosan. J. Chem. Technol. Biotechnol. 1990, 49, 395-404. (4) Volesky, B.; Holan, Z. R. Biosorption of Heavy Metals. Biotechnol. Prog. 1995, 11, 235-250. (5) Feng-Chin, W.; Ru-Ling, T.; Ruey-Shin, J. Comparative Adsorption of Metal and Dye on Flake- and Bead-types of Chitosans Prepared from Fishery. J. Hazard. Mater. 2000, 73, 63-75. (6) Galo, C.; Parra, O.; Taboada, E. Synthesis and Applications of Chitosan Mercaptanes as Heavy Metal Retention Agent. Int. J. Biol. Macromol. 2001, 28, 167-174. (7) Ruey-Shin, J.; Huey-Jen, S. A Simplified Equilibrium Model for Sorption of Heavy Metal Ions from Aqueous Solutions on Chitosan. Water Res. 2002, 36, 2999-3008. (8) Tanja, B.; Michael, S.; Henry, S. Adsorption of Nickel(II), Zinc(II) and Cadmium(II) by New Chitosan Derivatives. React. Funct. Polym. 2000, 44, 289-298. (9) Muzzarelli, R. A. A. Removal of Uranium from Solutions and Brines by a Derivative of Chitosan and Ascorbic Acid. Carbohydr. Polym. 1985, 5, 85-89. (10) Muzzarelli, R. A. A.; Tanfani, F.; Emanuelli, M.; Mariotti, S. N-(Carboxymethylidene)chitosans and N-(Carboxymethyl)chitosans: Novel Chelating Polyampholytes Obtained from Chitosan Glyoxylate. Carbohydr. Res. 1982, 107, 199-214. (11) Muzzarelli, R. A. A.; Zattoni, A. Glutamate Glucan and Aminogluconate Glucan, New Chelating Polyampholytes Obtained from Chitosan. Int. J. Biol. Macromol. 1986, 8, 137-141. (12) Guibal, E.; Sweeney, N. V. O.; Zikan, M. C.; Vincent, T.; Tobin, J. M. Competitive Sorption of Platinum and Palladium on Chitosan Derivatives. Int. J. Biol. Macromol. 2001, 28, 401-408. (13) Guibal, E.; Sweeney, N. V. O.; Vincent, T.; Tobin, J. M. Sulfur Derivatives of Chitosan for Palladium Sorption. React. Funct. Polym. 2002, 50, 149-163. (14) Merrifield, J. D.; Davids, W. G.; MacRae, J. D.; Amirbahman, A. Uptake of Mercury by Thiol-grafted Chitosan Gel Beads. Water Res. 2004, 38, 3132-3138.

(15) Vieira, E. F. S.; Cestari, A. R.; Santos, E. de B.; Dias, F. S. Interaction of Ag(I), Hg(II), and Cu(II) with 1,2-Ethanedithiol Immobilized on Chitosan: Thermochemical Data from Isothermal Calorimetry. J. Colloid Interface Sci. 2005, 289, 42-47. (16) Yoshinari, B.; Hiroyuki, H. Selective Adsorption of Palladium(II), Platinum(IV), and Mercury(II) on a New Chitosan Derivatives Possessing Pyridyl Group. Chem. Lett. 1992, 1905-1908. (17) Yoshinari, B.; Hiroyuki, H.; Yoshinobu, K. Selective Adsorption of Precious Metals on Sulfur-Containing Chitosan Derivatives. Chem. Lett. 1994, 117-120. (18) Yoshinari, B.; Hiroyuki, H.; Kazuharu, Y.; Katsutoshi, I.; Yoshinobu, K. Adsorption Equilibria of Silver(I) and Copper(II) Ions on N-(2Hydroxylbenzyl)chitosan Derivative. Anal. Sci. 1994, 10, 601-605. (19) Yoshinari, B.; Koichi, M.; Yoshinobu, K. Selective Adsorption of Copper(II) over Iron(III) on Chitosan Derivative Introducing Pyridyl Group. Chem. Lett. 1994, 2389-2392. (20) Yoshinari, B.; Yoshinobu, K.; Hiroyuki, H. Highly Selective Adsorption Resins I. Preparation of Chitosan Derivatives Containing 2-Pyridylmethyl, 2-Thienylmethyl, and 3-(Methylthio)propyl Groups and Their Selective Adsorption of Precious Metals. Bull. Chem. Soc. Jpn. 1996, 69 (5), 1255-1260. (21) Yoshinari, B.; Naohiko, M.; Koichiro, S.; Yoshinobu, K. Selective Adsorption of Mercury(II) on Chitosan Derivatives from Hydrochloric Acid. Anal. Sci. 1998, 14, 687-690. (22) Yoshinari, B.; Koichi, M.; Yoshinobu, K. Synthesis of a Chitosan Derivative Recognizing Planar Metal Ion and its Selective Adsorption Equilibria of Copper(II) over Iron(III). React. Funct. Polym. 1998, 36, 167172. (23) Yoshinari, B.; Youji, A.; Kaoru, O.; Sigeo, N.; Tatsuya, O. Adsorption Removal of Copper(II) on N-Methylene Phosphonic Chitosan Derivative. J. Chem. Eng. Jpn. 2005, 38, 887-893. (24) Yoshinari, B.; Kaoru, O.; Tatsuya, O. Preparation of Pd(II)Imprinted Chitosan Derivative and Its Selective Adsorption for Palladium(II). In CHEMECA 2006, Auckland, New Zealand, 2006; pp 17-20. (25) Garcı´a, M. C.; Marina, M. L.; Torre, M. Perfusion Chromatography: An Emergent Technique for the Analysis of Rood Proteins. J. Chromatogr. 2000, 880A, 169-187. (26) Washburn, E. W. Note on a Method of Determining the Distribution of Pore Sizes in a Porous Material. Proc. Natl. Acad. Sci. U.S.A. 1921, 7, 115-116. (27) Fernandez Diez, M. J.; Osuga, D. T.; Feenay, R. E. The Sulfhydryls of Avian Ovalbumins, Bovine β-Loctoglobulin, and Bovine Serum Albumin. Arch. Biochem. Biophys. 1964, 107, 449-458. (28) Gel’fman, M. I.; Kiseleva, N. V. Stability Constants of Palladium Chloride Complexes. Zh. Neorg. Khim. 1969, 14, 502-504.

ReceiVed for reView February 12, 2007 ReVised manuscript receiVed February 9, 2008 Accepted February 9, 2008 IE070235K