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Ind. Eng. Chem. Res. 2004, 43, 2222-2227
Collagen-Fiber-Immobilized Tannins and Their Adsorption of Au(III) Xuepin Liao, Mina Zhang, and Bi Shi* The Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, Chengdu 610065, P. R. China
Novel adsorbents that have an excellent adsorption capacity for Au(III) were prepared by immobilization of bayberry tannins and larch tannins onto collagen fiber matrixes. When the initial concentration of Au(III) was 478 mg/L and the amount of adsorbent was 20.0 mg, the adsorption capacities at equilibrium of immobilized bayberry tannins and larch tannins were 877 and 784 mgAu(III)/g respectively at 303 K. As the temperature was increased, the adsorption capacities were further increased. At a temperature of 323 K, the adsorption capacities at equilibrium of the immobilized tannins were as high as 1.50 × 103 and 1.36 × 103 mgAu(III)/g, respectively. The adsorption equilibrium data for Au(III) on the immobilized tannins can be well fitted by the Langmuir model, and the mechanism of the adsorption was found to be chemical adsorption. Furthermore, the adsorption isotherms of Au(III) in buffer solutions with different pH values could also be described by the Langmuir model, and the adsorption capacities increased at lower pH values. The kinetics of the adsorption can be well described by a pseudo-secondorder rate model, and the adsorption capacities calculated by the pseudo-second-order rate model were close to the values actually measured at higher temperatures. It was found that the breakthrough point of the adsorption column was at 223 bed volumes for the experimental system, indicating that the immobilized tannins have an outstanding ability to concentrate Au(III). The mass-transfer coefficient of Au(III) adsorption in the adsorption column determined by the Adams-Bohart equation was 3.34 × 10-5 L/(mg‚min). 1. Introduction Adsorption is the most cost-efficient and effective way of recovering gold from wastewater, and numerous adsorbents have been developed for this purpose. Activated carbon,1,2 mineral materials,3,4 and ion-exchange resins5,6 have been reported to be used as adsorbents for gold recovery. In recent years, attention has been focused on the use of various forms of biomass, such as microorganisms7-10 and plant polyphenols,11 as adsorbents for the recovery of Au(III). Tannins, which are natural polyphenols, are widely distributed in root, bark, stalk, and fruits of plants as metabolism products.12 According to the chemical structures of tannins, they can usually be classified as hydrolyzable tannins, condensed tannins, and complex tannins. Hydrolyzable tannins yield gallic acid or ellagic acid when they are hydrolyzed by acids, bases, or some enzymes.13 Tannic acid is a representative of hydrolyzable tannins. Condensed tannins are the polymerized products of flavan-3-ols and/or flavan-3,4-diols. Black wattle tannin is a representative of condensed tannins. Complex tannins simultaneously have both the structures of condensed tannins and hydrolyzable tannins, such as bayberry tannins. Precipitating proteins and precipitating metal ions are the two characteristic capabilities of tannins. The ability of tannins to precipitate metal ions is due to their multiple adjacent phenolic hydroxyl groups, which can form stable com* To whom correspondence should be addressed. Address: The Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, Chengdu 610065, P. R. China. Tel.: +86-028-85405508. Fax: +86-028-85405237. E-mail:
[email protected].
plexes with many metal ions.14,15 Thus, tannins can probably be used as alternative, effective, and efficient adsorbents in Au(III) recovery. However, tannins are water-soluble compounds. Therefore, tannins have to be modified or immobilized for practical use. It has been reported that adsorbents based on tannins exhibited high adsorption capacities compared to other adsorbents.16-18 Two approaches have been used to prepare adsorbents based on tannins. One method is to immobilize tannic acid on cellulose, aminopolystyrene, or agarose by means of epichlorohydrin activation, diaminohexane expansion of the chain length, and epichlorohydrin reactivation.16,18,19 The immobilization procedures of this method are complicated, and the tannins on the matrixes are easily leached out by water because they are linked with the matrixes by ester bonds. Another technique is to prepare tannin resins through interactions of condensed tannins and aldehyde compounds.20,21 However, tannin resins offer no more benefits than immobilized tannins, and the disadvantage of being leached by water still remains. Tannins have traditionally been used as tanning agents in leather making because of their high reactivity with collagen fibers in animal hides. In this study, cattle collagen fiber was selected as the matrix for the immobilization of tannins. Bayberry tannins and larch tannins (the molecular structures of which are shown in Figure 1) were first allowed to interact with collagen fibers through hydrophobic bonds and hydrogen bonds and were then covalently immobilized on the collagen fibers by a cross-linking agent. The adsorption isotherms, adsorption kinetics, and column adsorption kinetics of the immobilized tannins to Au(III) were investigated in detail.
10.1021/ie0340894 CCC: $27.50 © 2004 American Chemical Society Published on Web 03/27/2004
Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 2223
Figure 1. Chemical structures of tannins and primary amino acid sequence of cattle hide collagen.
2. Experimental Section 2.1. Materials. (a) Preparation of Collagen Fibers. Cattle hide powder, prepared according to standard procedures,22 was used as the collagen fibers. A cattle pelt was cleaned, limed, splitted, and delimed according to the standard techniques of leather processing to remove the noncollagen components. Then, the pelt was treated with an aqueous solution of acetic acid (concentration ) 16.0 g/L) three times to remove mineral substances. After the pH of pelt had been adjusted to 4.8-5.0 with an acetic acid-sodium acetate buffer solution, the pelt was dehydrated by absolute ethyl alcohol, dried in a vacuum to a moisture content of e10.0%, grinded, and sieved. As a result, 10-20 mesh hide powder with a moisture content of e12.0%, an ash content of e0.3%, and a pH of 5.0-5.5 was obtained. (b) Preparation of Tannins. Bayberry tannin extract and larch tannin extract were obtained from the barks of Myrica esculenta and Larix gmeli, respectively, by extraction with an acetone-water solution (1:1, v/v) and then spray dried. The tannin contents of the extracts were 76.3 and 72.7%, respectively. Auric chloride (AuCl3‚4H2O) and other chemicals were all analytical reagents. 2.2. Methods. (a) Preparation of Immobilized Tannins. The immobilization procedure was performed according to the authors’ patent.23 Briefly, 9.0 g of each kind of tannin was dissolved in 300 mL of distilled water and mixed with 15.0 g of collagen fiber. The mixture was stirred at 25 °C for 24 h. After the intermediate products had been collected by filtration and washed with distilled water, 300 mL of 2 wt % oxazolidine E (Guanghong Merchandising Ltd. Corp., Taiwan) crosslinking agent solution at pH 6.5 was added. The mixture was first stirred at 25 °C for 1 h and was then continuously stirred at 50 °C for 4 h. When the reaction was complete, the product was washed with 2000 mL of distilled water and vacuum-dried at 60 °C for 12 h,
after which the immobilized tannins were obtained. The DSC determination indicated that the decomposition temperatures of the collagen fibers after the immobilization reactions with the bayberry tannins and larch tannins were increased to 90-95and 93-98 °C, respectively, compared to 60-65 °C for raw collagen fibers, which shows an additional advantage of this approach. The higher thermal stability comes from the so-called tanning effect. (b) Study of Adsorption Equilibrium. Immobilized tannin adsorbent (20.0 mg) was suspended in 100 mL of Au(III) solution. The concentrations of Au(III) used were 96, 191, 287, 383, and 478 mg/L. The initial pH’s of the Au(III) solutions were adjusted to 2.5 with 0.1 M NaOH or 0.1 M HCl. The adsorption experiments were conducted under constant stirring at controlled temperatures for 24 h. The concentration of Au(III) in the residual solution was analyzed by means of TMK (thioMichler’s ketone)-Tween-20 spectrophotometry.24 The adsorption capacities were calculated according to a mass balance of Au(III) in the solution and are represented in units of milligrams of Au(III) per gram of adsorbent. For comparison, the anion-exchange resin D301G (weakly basic anionic resin, Chemical plant of Nan Kai University, P. R. China) was also used for the adsorption of Au(III). (c) Study of Adsorption Equilibrium in Buffer Solutions. A 50-mL portion of buffer solution was mixed with Au(III) solution, and the total volume was scaled to 100 mL. The concentrations of Au(III) were controlled to 96, 191, 287, 383, and 478 mg/L. The other experimental procedures were the same as in the study on adsorption equilibrium. The preparation methods of the buffer solutions are described in Table 1. (d) Study of Adsorption Kinetics. A 20.0-mg sample of immobilized tannins was suspended in 100 mL of Au(III) solution. The initial concentration of Au(III) was 287 mg/L. The initial pH of the Au(III)
2224 Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 Table 1. Preparation Methods Used for Buffer Solutions pH
preparation method
4.0
20.0 g of NaAc‚3H2O was dissolved in distilled water 134 mL of 6 M HAc solution was added solution was then scaled to 500 mL 32.0 g of NaAc‚3H2O was dissolved in distilled water 68 mL of 6 M HAc solution was added solution was then scaled to 500 mL 50.0 g of NaAc‚3H2O was dissolved in distilled water 34 mL of 6 M HAc solution was added solution was then scaled to 500 mL 77.0 g of NaAc‚3H2O was dissolved in distilled water solution was then scaled to 500 mL
4.5 5.0 7.0
solution was adjusted to 2.5 with 0.1 M HCl. The adsorption experiment was conducted under constant stirring at a controlled temperature for 3 h, and the concentration of Au(III) during the adsorption process was analyzed at regular intervals. The adsorption capacity at time t was calculated by a mass balance of Au(III) in solution and is reported in units of milligrams of Au(III) per gram of adsorbent. (e) Study of Column Adsorption Kinetics. A 1.5-g sample of immobilized bayberry tannin adsorbent was soaked in distilled water for 12 h. Then, the adsorbent was filled into a column with an 11-mm diameter. The height of the bed was 205 mm. A solution of 239 mgAu(III)/L was pumped into the column at a constant volume velocity of 1.93 BV/h (BV ) bed volume). The effluent was collected by an automatic collector, and the content of Au(III) in the effluent was analyzed by means of TMK-Tween-20 spectrophotometry. 3. Results and Discussion 3.1. Immobilization of Tannins by Collagen Fiber. The chemical structures of bayberry tannins and larch tannins, whose basic structures consist of flavan3-ols, are illustrated in Figure 1. On the other hand, the collagen molecule is composed of three polypeptide chains with a triple helical structure, and many such molecules are aggregated through hydrogen bonds to form collagen fibers.25 Collagen fibers with abundant functional groups are more suitable for use as matrixes for the immobilization of tannins compared to most synthetic polymers and other biomasses. However, because the interactions between tannins and collagen fibers occur through hydrogen bonds and hydrophobic bonds12,13 that can be easily broken by organic solvents, tannins might be easily leached out in practical applications. Therefore, it is necessary to carry out cross-linking reactions. The 6 and 8 positions of the A rings of bayberry tannins and larch tannins molecules exhibit high nucleophilic reaction activities; therefore, these locations can be covalently bonded to amino groups of collagen molecules by reactions with aldehydes. The immobilized tannins prepared according to the method described in the Experimental Section can withstand organic solvent and urea solution extraction, as indicated in Table 2. 3.2. Adsorption Equilibrium of Au(III) on Immobilized Tannins. The adsorption capacities of immobilized tannins at equilibrium are reported in Table 3. It was found that, under the experimental conditions investigated here, the adsorption capacity of immobilized bayberry tannins is larger than that of immobilized larch tannins. For example, when the initial concentration of Au(III) was 478 mg/L, the adsorption capacities of immobilized bayberry tannins and larch tannins at
Table 2. Concentration of Tannins in Extract Solution (mg/L)a extraction solution urea solution
immobilization method
water
95% (v/v) ethanol
1M
3M
8M
tannins + collagen fibers tannins + collagen fibers + aldehyde
44 -b
260 8.1
245 8.2
355 9.0
535 9.0
a Immobilized bayberry tannins, 0.500 g; organic solvent and urea solution, 100 mL; extraction conditions, stirring at room temperature for 4 h; detection, UV spectrophotometry. b No tannins were detected.
equilibrium were 877 and 784 mgAu(III)/g, respectively, at 303 K. The difference in adsorption capacity between these two kinds of immobilized tannins is related to their molecular structures. In bayberry tannins, the B ring is a pyrogallol structure, and the C rings are partly attached with galloyl groups that can improve the tannins’ ability to chelate to metal ions; in contrast, the B ring of larch tannins is a catechol structure. Therefore, bayberry tannins are easier to chelate with metal ions than larch tannins.26 This is consistent with the metalion-precipitation ability of tannins.11 In contrast, the adsorption capacity of the weakly basic anionic resin D301G was 483 mgAu(III)/g at the same experimental conditions. The adsorption capacities of different kinds of ion-exchange resins (including weakly and strongly basic anionic resins) have been reported to fall in the range of 158-335 mgAu(III)/mL of resin.5 It was also found that the adsorption capacities at equilibrium of both types of immobilized tannins increased with increasing temperature, as shown in Table 3. For an initial Au(III) concentration of 478 mg/L, the adsorption capacities of immobilized bayberry tannins and larch tannins at equilibrium were as high as 1.50 × 103 and 1.36 × 103 mgAu(III)/g, respectively, at 323 K. The experimental data were further analyzed with respect to the Langmuir and Freundlich models, and it was observed that the experimental data fit well to the Langmuir model (eq 1 below), as illustrated in Figure 2. 3.3. Adsorption Mechanism. It was proposed that the adsorption of metal ions on immobilized tannins occurred through chemical adsorption, led by a chelation reaction between the metal ions and the O-dihydroxyphenyl groups of the tannin molecules.2,11 To further understand the adsorption mechanism of Au(III) on immobilized tannins, a thermodynamic analysis was carried out. The maximum Au(III) adsorption (qmax) at each temperature and the enthalpy change (∆H) of the adsorption process were obtained according to the Langmuir model and the van’t Hoff equation (eqs 1 and 2, respectively)
Ce Ce 1 + ) qe qmaxb qmax log b )
-∆H + constant 2.303RT
(1) (2)
where qe and ce are the amount adsorbed (mgAu(III)/g) and the bulk concentration (mgAu(III)/L) at equilibrium, respectively; qmax is the maximum gold adsorption (mgAu(III)/g); b is a coefficient related to the strength of adsorption, b ) ka/kd (where ka is the rate constant of adsorption and kd is the rate constant of desorption);
Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 2225 Table 3. Adsorption Capacities (qe, mg/g) of Au(III) on Immobilized Tannins at Equilibrium immobilized bayberry tannins
immobilized larch tannins
Ci (mg/L)
293 K
303 K
313 K
323 K
293 K
303 K
313 K
323 K
96 191 287 383 478
433 610 656 662 731
474 743 779 823 877
477 926 1.14 × 103 1.01 × 103 1.23 × 103
478 956 1.38 × 103 1.33 × 103 1.50 × 103
413 532 710 741 708
477 632 704 747 784
478 798 874 985 993
478 954 1.18 × 103 1.27× 103 1.36 × 103
Figure 2. Langmuir isotherms of Au(III) adsorbed on immobilized tannins (303 K).
Figure 3. Adsorption isotherms of Au(III) on immobilized bayberry tannins in buffer solutions (303 K).
Table 4. Langmuir Constants and Enthalpy Changes for Au(III) Adsorption by Immobilized Tannins
verified that AuX4- ions [X ) O(H) or Cl] bind to the surface of goethite via a bidentate inner-sphere mechanism. However, Berrodier et al.29 used the same technique and found that, at low pH and high Cl concentration, mixed chloro-hydroxo complexes (AuCl2O23- or AuClO34-) are present around Au adsorbed on ferrihydrite and, at high pH or low Cl concentration, the local environment around Au on ferrihydrite exhibits only the presence of O (OH, H2O) ligands. These different results indicate that the nature of Au(III)-chloride speciation remains unclear. If one assumes that AuCl4- is the main state of Au(III) in the solution, then the reaction between tannins and Au(III) can be described as follows
immobilized tannins
T (K)
qmax (mgAu(III)/g)
b
bayberry
293 303 313 323 293 303 313 323
732 875 1.15 × 103 1.46 × 103 759 791 1.01 × 103 1.35 × 103
0.076 0.135 0.355 0.718 0.057 0.098 0.146 0.355
larch
∆H (kJ/mol) -60.4
-40.3
∆H is the change in enthalpy (kJ/mol); T is the temperature (K); and R is the gas universal constant (8.314 J/Kmol). The results listed in Table 4 indicate that the enthalpy change of the adsorption process was significant and that qmax increased with incresing temperature, which confirms the conclusion that the mechanism of Au(III) adsorption by immobilized tannins is chemical adsorption. 3.4. Adsorption Equilibrium of Au(III) in Buffer Solutions. The adsorption isotherms of Au(III) in different buffer solutions are illustrated in Figure 3. In general, the adsorption isotherms of Au(III) in buffer solutions were well fitted by the Langmuir model. It is clear that pH value had a significant effect on the adsorption capacity of immobilized bayberry tannins. As the pH increased, the adsorption capacity at equilibrium decreased, that is, acidic conditions were more suitable for the adsorption of Au(III). However, the effects of other ions in solution on the adsorption capacity and selectivity of Au(III) should be further investigated. 3.5. Adsorption Kinetics of Au(III) on Immobilized Tannins. It was confirmed in section 3.3 that the mechanism of Au(III) adsorption by immobilized tannins is chemical adsorption. In general, the adjacent phenolic hydroxyl groups of tannins can chelate with metal ions to form five-memberred rings.11,27 Heasman et al.28
2(-OH) + AuCl4- ) AuCl2O23- + 2H+ + 2Cl- (3) The experimental data indicate that the adsorption is very fast at beginning and then slows as equilibrium is approach. Therefore, the adsorption rate can be described by a pseudo-second-order rate model
dqt ) k2(qe - qt)2 dt
(4)
where k2 is the pseudo-second-order rate constant [g/(mmol‚h)], qe is the adsorption capacity at equilibrium (mgAu(III)/g), and qt is the adsorption capacity at time t (mgAu(III)/g). Separating the variables in eq 4 and integrating gives
1 1 t ) + t 2 qt k q qe
(5)
2 e
According to the experimental data on qt, the equilibrium adsorption capacity, qe, and the pseudo-secondorder rate constant, k2, can be determined from the slope and intercept, respectively, of a plot of t/qt vs t.
2226 Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004
Figure 5. Breakthrough curve of Au(III) on immobilized bayberry tannins column.
Figure 4. Adsorption kinetics of Au(III) on immobilized tannins (pH 2.5). Table 5. Adsorption Kinetics Parameters of Au(III) Adsorbed on Immobilized Tanninsa T (K)
k2 × 105 (g/mg‚min)
303 313 323
5.03 5.48 6.36
immobilized bayberry tannins 1.15 × 103 0.997 779 1.25 × 103 0.998 1.14 × 103 1.14 × 103 0.999 1.39 × 103
-47.6 -9.6 18.0
303 313 323
4.47 9.35 8.95
immobilized larch tannins 1.08 × 103 0.994 704 1.10 × 103 0.999 874 3 1.17 × 10 0.999 1.18 × 103
-53.4 -25.9 -0.8
qe(calc) (mg/g)
R2
qe(meas) (mg/g)
errorb (%)
a C ) 287 mg/L; pH ) 2.5. b Error ) [q (meas) - q (calc)]/ i e e qe(meas) × 100.
It was found that the pseudo-second-order model gives an excellent fit to all of the experimental data, as shown in Figure 4. In general, the equilibrium adsorption capacities calculated according to the pseudo-secondorder rate model were close to the actual measurements reported in section 3.2 of this paper at higher temperatures, as compared in Table 5. However, the deviation was considerable at lower temperatures, probably due to the fact that multiple basic reactions are involved in the overall reaction between Au(III) and immobilized tannins. 3.6. Column Adsorption Kinetics. Figure 5 is the breakthrough curve of the adsorption column. It can be seen that the breakthrough point was at 223 BV (bed volumes), which indicates that Au(III) can be greatly concentrated by a column of immobilized tannins. The concentration of Au(III) in the effluent was increased rapidly after the breakthrough point, meaning that the adsorption column has a high availability. The column adsorption kinetics was further specified by determining the mass-transfer coefficient according to the Adams-Bohart equation8
ln(Ct/Ci) ) kCit - kqV(Z/ui)
(6)
Figure 6. Determination of the mass-transfer coefficient in column adsorption by plotting ln(Ct/Ci) vs t.
where Ct is the concentration of Au(III) (mg/L) in the eluant at time t (min), Ci is the initial or inlet Au(III) concentration (mg/L), qV is the volume of Au(III) taken up by the immobilized bayberry tannins (mg/L), Z is the height of the column (m), ui is the linear flow rate of the solution (m/min), and k is the mass-transfer coefficient (L/mg‚min). A straight line was attained for this system by plotting ln(Ct/Ci) against t, as illustrated in Figure 6, which gives the value of k from the slope of the line. The range of t considered should be from the beginning to the end of breakthrough. The masstransfer coefficient for the experimental system was found to be 3.34 × 10-5 L/(mg‚min). 3.7. Desorption. Solutions of sodium bicarbonate (1.0 mol/L), sodium carbonate (1.0 mol/L), hydrochloric acid (1.0 mol/L), urea(1.0 mol/L), and thiourea (1.0 mol/L) and combinations of these solutions were used to desorb the Au(III) adsorbed onto the immobilized tannins. None of these solutions was found to be effective in regenerating the immobilized tannins. This issue needs to be studied further. However, the recovery of Au(III) adsorbed on immobilized tannins by burning is considerable. Thus, considering the value of gold and the advantage of the high adsorption capacity of immobilized tannins, this might be a possible alternative route to the recovery of gold adsorbed on immobilized tannins.
Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 2227
4. Conclusion The experimental data of this study lead us to conclude that tannins immobilized on collagen fiber matrixes function as novel adsorbents that are effective in the recovery of Au(III) from aqueous solutions. Because the B ring of bayberry tannins is a pyrogallol structure whereas the B ring of larch tannins is a catchol structure, bayberry tannins have a higher reaction activity with Au(III). Therefore, immobilized bayberry tannins have a higher adsorption capacity for Au(III) than immobilized larch tannins. A thermodynamic study reported herein supported the conclusion that the mechanism of Au(III) adsorption onto immobilized tannins is chemical adsorption. The Langmuir equation gave a satisfactory description of the measured adsorption isotherms. However, many factors significantly affect the adsorption of gold by immobilized tannins, such as the form of gold in the solution and the different anions chelating with the gold. Therefore, further investigations should be undertaken to develop a better understanding of the adsorption mechanism of immobilized tannins. An adsorption kinetics study indicated that a pseudosecond-order rate model provides an excellent fitting of the experimental data. The mass-transfer coefficient in the adsorption column could be determined by the Adams-Bohart equation. Compared with ion-exchange resin and activated carbon, immobilized tannins have excellent adsorption capacities. In addition, their preparation is convenient and cost-effective. Therefore, the burning method of recovering Au(III) adsorbed on immobilized tannins is acceptable. Acknowledgment This research was financially supported by The Research Fund for the Doctoral Program of Higher Education (Grant 20020610010) and The Key Science and Technology Research Project of Sichuan Province, China (Grant 01ZQ052-52) Literature Cited (1) Jia, Y. F.; Steele, C. J.; Hayward, I. P.; Thomasa, K. M. Mechanism of adsorption of gold and silver species on activated carbons. Carbon 1998, 36, 1299. (2) Nakbanpote, W.; Thiravetyan, P.; Kalambaheti, C. Comparison of gold adsorption by Chlorella vulgaris, rice husk and activated carbon. Min. Eng. 2002, 15, 549. (3) Ran, Y.; Fu, J.; Rate, A. W.; Gilkes, R. J. Adsorption of Au(I, III) complexes on Fe, Mn oxides and humic acid. Chem. Geol. 2002, 185, 33. (4) Lukey, G. C.; Van Deventer, J. S. J.; Shallcross, D. C. Equilibrium model for the selective adsorption of gold cyanide on different ion-exchange function groups. Min. Eng. 2000, 13, 1243. (5) Zhang, H. G.; Dreisinger, D. B. The adsorption of gold and copper onto ion-exchange resins from ammoniacal thiosulfate solution. Hydrometallurgy 2002, 66, 67. (6) Liu, C. P.; Qu, R. J.; Sun, L.; Wang, C. H.; Sun, R. Z.; Cheng, G. X. Adsorption properties of polyphenol formaldehyde resin containing polyamine for Au(III). Lizhi Jiaohuan Yu Xihu 2001, 17, 339. (7) Khoo, K. M.; Ting, Y. P. Biosoprption of gold by immobilized fungal biomass. Biochem. Eng. J. 2001, 8, 51.
(8) Pethkar, A. V.; Paknikar, K. M. Recovery of gold from solution using Cladosporium cladosporioides biomass beads. J. Biotechnol. 1998, 63, 121. (9) Zhao, J. Z.; Shi, D. J.; Zhang, Y. Bioaccumulation of Au(III) by Cyanobacteria Anabaena azollae. Kexue Tongbao 1997, 42, 2205. (10) Liu, Y. Y.; Fu, J. K.; Hu, H. B.; Tang, D. L.; Lin, Z. Y.; Ni, Z. M.; Yu, X. S. Properties and characterization of Au3+ by mycelial waste of streptomyces aureofaciences. Kexue Tongbao 2001, 46, 1179. (11) Mcdonald, M.; Mila, I.; Scalbert, A. Precipitation of metal ions by plant polyphenols: Optimal conditions and origin of precipitation. J. Agric. Food Chem. 1996, 44, 599. (12) Shi, B.; Di, Y. Priniciple of using vegetable tannins in leather manufacturing. Pege Kexue Yu Gongcheng 1998, 8, 5. (13) Shi, B.; Di, Y. Plant Polyphenols, China Science Press: Beijing, 2000. (14) Vasconcelos, M. T.; Azenha, M.; Freitas V. Role of polyphenols in copper complexation in red wine. J. Agric. Food Chem. 1999, 47, 2791. (15) Yamguchi, H.; Higasida, R.; Higuchi, M.; Sakata, I. Adsorption mechanism of heavy-metal ion by microspherical tannins resin. J. Appl. Polym. Sci. 1992, 45, 1463. (16) Chibata, I.; Tosa, T.; Mori, T.; Watanabe, T.; Sakata, N. Immobilized tannins-a novel adsorbent for protein and metal ion. Enzyme Microb. Technol. 1986, 8, 129. (17) Sakaguchi, T.; Nakajima, A. Recovery of uranium from seawater by immobilized tannins. Sep. Sci. Technol. 1987, 22, 1609. (18) Nakajima, A.; Sakaguchi, T. Recovery of uranium by tannins immobilized on matrices which have amino group. J. Chem. Technol. Biotechnol. 1990, 47, 31. (19) Nakajima, A.; Sakaguchi, T. Recovery of uranium by tannins immobilized on agarose. J. Chem. Technol. Biotechnol. 1987, 40, 223. (20) Yamguchi, H.; Higuchi, M.; Sakata I. Methods for preparation of absorbent microspherical tannins resin. J. Appl. Polym. Sci. 1992, 45, 1455. (21) Nakajima, A.; Sakaguchi, T. Uptake and removal of iron by immobilized persimmon tannins. J. Chem. Technol. Biotechnol. 2000, 75, 977. (22) Lu¨, X. Y. A brief discussion on manufacture of hide powder for tannins analysis. Linchan Huaxue Yu Gongye 2000, 20, 71. (23) Liao, X. P.; Shi, B. Vegetable tannins immobilized by collagen fibres and their adsorption to metal ions. P. R. China Patent 02134174.5, 2002. (24) Tie, A. N.; Deng, Y. J. Spectrophotometric determination of gold by TMK-tween-20. Yejin Fenxi 1991, 11, 47. (25) Friess W. Collagen-biomaterial for drug delivery. European. J. Pharm. Biopharm. 1998, 45, 113. (26) Sykes, R. L.; Hancock, R. A.; Orszulik, S. T. Tannage with aluminium salts. Part II. Chemical basis of the reactions with polyphenols. J. Soc. Leather Technol. Chem. 1980, 64, 31. (27) Tiwari, D.; Mishra, S. P.; Mishra, M.; Dubey, R. S. Biosorptive behaviour of Mango (Mangifera indica) and Neem (Azadirachta indica) bark for Hg2+, Cr3+, and Cd2+ toxic ions from aqueous solution: a radiotracer study. Appl. Radiat. Isot. 1999, 50, 631. (28) Heasman, D. M.; Sherman, D. M.; Ragnarsdottir, K. V. An EXAFS study of the adsorption of Au3+ from aqueous chloride solutions to goethite (R-FeOOH). Min. Magn. 1998, 62, 589. (29) Berrodier, I.; Farges, F.; Benedetti, M.; Brown, G. Adsorption of Au ferrihydrites using Au-LIII edge XAFS spectroscopy. J. Synchrotron Radiat. 1999, 6, 651.
Received for review August 23, 2003 Revised manuscript received January 24, 2004 Accepted February 9, 2004 IE0340894
