当前位置:首页 >> 材料科学 >>

Mechanism of lead adsorption from aqueous solutions using


ARTICLE IN PRESS

Water Research 37 (2003) 3905–3912

Mechanism of lead adsorption from aqueous solutions using an adsorbent synthesized from natural condensed tannin
Xin-Min Zhana,*, Xuan Zhaob
a

State Key Joint Laboratory on Environmental Simulation and Pollution Control, Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China b Environmental Technology Section, Institute of Nuclear Energy Technology, Tsinghua University, Beijing 100084, China Received 2 January 2003; received in revised form 2 May 2003; accepted 6 May 2003

Abstract Adsorption is a method for removing lead from wastewater. The adsorption of lead on a new adsorbent synthesized from natural condensed tannin has been investigated using a series of batch adsorption experiments. The study on the adsorption mechanism indicates that the adsorbent performed in aqueous solutions as an ionic exchanger whose end group was sodium ion (Na+). One lead (II) ion (Pb2+) was adsorbed onto the adsorbent by taking the place of two Na+ ions. The maximum exchangeable Na+ present on the adsorbent was measured with the proton titration experiments and it was up to 1.0 mmol Na+ g?1 dry adsorbent. To a signi?cant extent, pH in?uenced the extraction of lead from aqueous solutions. The lead removal ef?ciency was up to 71%, 87% and 91% with initial solution pH at 3.0, 3.6 and 4.2, respectively. The Langmuir equation ?tted the adsorption isotherm data well. The maximum adsorption capacity of lead calculated was 57.5, 76.9 and 114.9 mg lead g?1 dry adsorbent at initial solution pH of 3.0, 3.6 and 4.2, respectively. Therefore, the adsorbent does offer favorable characteristics in lead removal from acidic wastewater. r 2003 Elsevier Ltd. All rights reserved.
Keywords: Adsorption; Adsorption mechanism; Condensed tannin; Ion exchange; Lead removal

1. Introduction Many industries, such as the petrochemical, painting and coating, newsprint, smelting, metal electroplating, mining, plumbing and battery industries, discharge lead (Pb) into the environment without adequate puri?cation in some cases. Lead may be transported into water bodies by natural circulation and therefore threaten human life due to its well-known toxicity, accumulation in food chains and persistence in nature. Unlike organic compounds, lead is non-biodegradable, and, therefore, must be removed from wastewater.

When removing lead from wastewater, particular attention is given to effective and simple processes. Lead removal by low-cost adsorbent materials may be advantageous, compared with traditional processes, such as chemical precipitation, electrode deposition, ?ltration, reverse osmosis, evaporation recovery and solvent extraction. These low-cost adsorbent materials recently studied include: (1) Activated carbon [1–3] and modi?ed activated carbon [4,5]. Most recently, Li et al. extracted lead from aqueous solutions with carbon nanotubes [6]. But this adsorbent may be expensive. (2) Biosorbents. Fungal biomass is used as an adsorbent to treat heavy metals, including lead [7–9]. (3) Mineral adsorbents, such as goethite [10] and gibbsite [11]. (4) Biopolymer adsorbents. Carrillo-Morales et al. used natural adsorbent CACMM2 that was extracted

*Corresponding author. Department of Civil Engineering, National University of Ireland, Galway, Galway, Ireland. Tel: +353-91-524411x2762; fax: +353-91-750507. E-mail address: xinmin.zhan@nuigalway.ie (X.-M. Zhan).

0043-1354/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0043-1354(03)00312-9

ARTICLE IN PRESS
3906 X.-M. Zhan, X. Zhao / Water Research 37 (2003) 3905–3912

Nomenclature C0 Ce Dd ?H? ?e ?H ? ?0 K1 initial concentration of lead in aqueous solutions (mg L?1) equilibrium concentration of lead in the liquid phase (mg L?1) distribution coef?cient of adsorption between the solid and liquid phase, L g?1 equilibrium concentration of proton (H+) in the liquid phase (mol L?1) initial concentration of H+ in aqueous solutions before adsorption (mol L?1) apparent equilibrium constant of the ionic exchange process for lead adsorption (g L?1) apparent equilibrium constant of the ionic exchange process for proton adsorption ?rst-order hydrolysis constant of lead (mol L?1) second-order hydrolysis constant of lead (mol2 L?2) equilibrium constant of incomplete dissociation of lead nitrate, L mol?1 initial concentration of Na+ in aqueous solutions (mol L?1) equilibrium concentration of Na+ in the liquid phase (mol L?1) equilibrium concentration of NO? 3 in the liquid phase (mol L?1)

?Pb2? ?e ?PbNO? 3 ?e ?Pb?OH?? ?e ?Pb?OH?2 ?e ?Pb?e ?Pb?0 pH0 pHe Q ?RH?e ?RNa?e

K2

K3 K4 K5 ?Na? ?0 ?Na? ?e ?NO? 3 ?e

?R2 Pb?e ? RT ?

Xe Xm

equilibrium concentration of Pb2+ in the liquid phase (mol L?1) equilibrium concentration of PbNO+ 3 in the liquid phase (mol L?1) equilibrium concentration of Pb(OH)+ in the liquid phase (mol L?1) equilibrium concentration of Pb(OH)2 in the liquid phase (mol L?1) total concentration of lead in the liquid phase at the equilibrium (mol L?1) initial concentration of lead in aqueous solutions (mol L?1) initial pH of aqueous solutions ?nal solution pH at the adsorption equilibrium dosage of the adsorbent particles in aqueous solutions (g L?1) equilibrium concentration of proton adsorbed in the solid phase (mol g?1) equilibrium concentration of exchangeable sodium ion in the solid phase (mol g?1) equilibrium concentration of lead adsorbed in the solid phase (mol g?1) maximum exchangeable sodium ion present on the tannin adsorbent, mol g?1 amount of lead adsorbed in the solid phase at the equilibrium (mg g?1) maximum adsorption capacity of the adsorbent (mg g?1)

from a cactus to remove lead (II) ion (Pb2+) from aqueous solutions [12]. Jeon et al. studied characteristics of carboxylated alginic acid of lead removal [13]. (5) Wide-spread and cheap natural materials or reused waste, such as clay [14], slag [15], peat [16–18] and ?y ash [19]. A similar kind of lead elimination is possible by means of tannin adsorbents, which are made from natural condensed tannins. Condensed tannins are ubiquitous in species throughout the plant kingdom. They are not an isolated group of compounds, but a part of the vast collection of natural compounds and chemicals based on ?avan-3-ol units. Flavanoid units in tannin extracts are predominantly phloroglucinolic, resorcinolic or pyrogallolic A-rings and catecholic or pyrogallolic B-rings [20], which are shown in Fig. 1. Tannins are reactive with formaldehyde due to the strong nucleophilicity of their A-rings and are available to complex with metal ions because of the ortho-hydroxyls present in their B-rings.

R3 6' R2 OH 7 6 8 5 4 5' 4' OH B-ring 3' OH

O
1 2 3

1' 2' OH

A-ring R1

Fig. 1. Flavanoid unit in natural condensed tannins. To A-ring: R1=OH, R2=H, phloroglucinolic, R1=R2=H, resorcinolic; R1=H, R2=OH, pyrogallolic. To B-ring: R3=H, catecholic; R3=OH, pyrogallolic.

The study on the removal of heavy metals from wastewater by tannin adsorbents was almost from the application of barks in the similar aspects. In 1977, Randall observed that adsorption characteristics of barks for heavy metals rested on tannin structures

ARTICLE IN PRESS
X.-M. Zhan, X. Zhao / Water Research 37 (2003) 3905–3912 3907

present in the bark adsorbent [21]. Later, researchers synthesized adsorbents from commercial tannins and applied them to remove heavy metals from wastewater, such as uranium [22], americium [23], chromium [24,25] and copper [26]. These studies illustrate that it is possible to remove heavy metals from wastewater with tannin adsorbents. Zhan et al. developed a tannin adsorbent whose end group was proton and after a systematical study, it was found that ionic exchange was the main adsorption mechanism when the pH of the solution was not more than 6 [27]. However, its adsorption capacity was not as satisfactory as expected, only 30– 40 mg Pb g?1 dry adsorbent. Hence, it presents a challenge to develop another form of tannin adsorbent that is applicable in acidic wastewater and has a higher adsorption capacity. The speci?c objective of the present study is to investigate characteristics of lead adsorption on the newly developed tannin adsorbent, mainly the adsorption mechanism, adsorption isotherm and adsorption capacity.

and 90% of lead removal was completed in the initial 50 min.). The shaking speed was 100 rpm and the temperature was maintained at 20 C. After adsorption, the suspensions were ?ltered with 0.45 mm ?lters. The ?ltrates were acidi?ed with 10 M HNO3 to decrease pH below 3 in order to avoid lead precipitation before lead measurement. Then, the concentrations of lead and sodium in the ?ltrates were immediately measured by an inductively coupled plasma spectrometer (Pro?le, Leeman, USA). Solution pH was measured using a WTW SenTix 21 pH electrode and a WTW pH 320 digital meter. The electrode was calibrated in accordance with the manufacturer’s procedures. Some bottles containing lead solutions without adsorbent particles were used as the blank experiment to ?nd out the effect of lead precipitation, if any. 2.3. Proton titration experiment The proton titration experiments were carried out to determine the number of valid sites for adsorption present on adsorbent particles in two solutions that had different ionic strength, in which, one was deionized water and the other was 0.01 M KCl solution. 25 mL deionized water; (or 0.01 M KCl solution) with 0.025 g particles were placed in nine well-sealed glass beakers. Then, various amount of solutions of 0.025 M HClO4 (from 0 to 0.8 mL with an interval of 0.1 mL) were added to the beakers and the beakers were placed on the thermostatic shaker. The shaking speed was 100 rpm and temperature was 20 C. After 24 h, solution pH in each bottle was measured.

2. Methods and materials 2.1. Preparation of the novel adsorbent Wattle tannin, a kind of natural condensed tannins, was selected as the raw material to synthesize the adsorbent. A certain amount of wattle tannin powder was dissolved in 25% sodium hydroxide solution at room temperature. Then, tannin was gelated through polymerization with formaldehyde (37 wt%) at 80 C for 1 h in decahydronaphthalene solvent. Finally, the obtained tannin particles were completely washed with acetone and distilled water, dried at 40 C for 24 h. The particles passing through a 20 mesh sieve (opening size 0.833 mm) but retained on a 40 mesh sieve (opening size 0.417 mm) were chosen for the following experiments. 2.2. Batch adsorption experiment A series of batch experiments were conducted to study the adsorption mechanism, adsorption isotherm and adsorption kinetics. Lead stock solution (lead=1000 mg L?1) was prepared by dissolving lead nitrate in deionized water. The pH of the stock solution was around 1. The solution was further diluted to the required concentrations before use. pH adjustment was ful?lled by adding HNO3 or NaOH. 50 mL solutions with known initial lead concentrations and pH values were added into well-sealed 100 mL glass beakers with 0.05 g adsorbent particles. The bottles were set on a thermostatic shaker for 24 h (The shaking time was decided on after the study of adsorption kinetics. For this novel adsorbent, it took 5 h to arrive at the adsorption equilibrium at a shaking speed of 100 rpm

3. Results and discussion 3.1. Adsorption mechanism A series of batch adsorption experiments were conducted at different initial pH values and at different initial concentrations of lead. When the adsorption reached equilibrium, pHe, [Na+]e and [Pb]e in the liquid phase were measured. It is found that pHe values were higher than corresponding pH0 values, which indicates that protons were adsorbed onto adsorbent particles from the liquid phase along with lead removal. Meanwhile, the concentrations of Na+ in the liquid phase increased. The magnitude of sodium released ([Na+]e– [Na+]0), the adsorption of proton ([H+]0–[H+]e) and the adsorption of lead ([Pb]0–[Pb]e) were calculated. Fig. 2 presents the relationship between two variables, [Na+]e–[Na+]0 and [H+]0–[H+]e+2 ([Pb]0–[Pb]e). From Fig. 2, it may be inferred that ?Na? ?e ? ?Na? ?0 E1; ??H ?0 ? ?H? ?e ? ? 2??Pb?0 ? ?Pb?e ?
?

ARTICLE IN PRESS
3908 X.-M. Zhan, X. Zhao / Water Research 37 (2003) 3905–3912

0.001 0.0008

Pb2? ?H2 O ? Pb?OH?? ?H? ; hydrolysis constant?K3 ? ? 1:8 ? 10?8 mol L?1 Pb2? ?2H2 O ? Pb?OH?2 ?2H? ; ?6?

Y (mol L )

0.0006 0.0004 0.0002 Slope = 1:1 0 0 0.0002 0.0004 0.0006 0.0008 0.001

hydrolysis constant?K4 ? ? 7:5 ? 10?11 mol2 L?2 : ?7? K3 and K4 were estimated by the authors from the lead speciation diagram obtained by Reed et al. [2]. The inaccuracy in the estimation does not affect the following calculation because K3 5?H? ?e and K4 5?H? ?2 in the batch experiments. e The incomplete dissociation of lead nitrate in solution is described as
-1

-1

[Na ]e - [ Na ]0 (mol L )
Fig. 2. Relationship between released sodium and adsorbed proton and lead. In this ?gure, Y=[H+]0? [H+]e+2([Pb]0?[Pb]e).

+

+

? pb2? ? NO? 3 ? PbNO3 ;

equilibrium constant ?K5 ? ? 15:1 L mol?1 From Eqs. (6)–(8), [Pb ]e is calculated as ?Pb2? ?e ?
2

?8?

?Pb?e : ?9? ? 1 ? ?K3 =?H? ?e ? ? ?K4 =?H? ?2 e ? ? K5 ?NO3 ?e ?10?

implying that two Na+ ions present on the tannin adsorbent may be exchanged by one Pb2+ ion or two H+ ions. Hence, it can be reasonably assumed that ionic exchange may occur in the current adsorption process. The stoichiometric equation for ionic exchange occurring between Na+ and Pb2+ and between Na+ and H+ may be written in the form of Eqs. (1) and (2), respectively: 2RNa ? Pb2? ? R2 Pb ? 2Na? ; RNa ? H? ? RH ? Na? ; ?1?

At the adsorption equilibrium, ?RH?e ? ??H? ?0 ? ?H? ?e ?=Q:

In which, Q is the dosage of adsorbent particles. In this study, Q=1 g L?1. From Eqs. (3)–(5), (9) and (10), Eq. (11) is obtained: K1 2 K2 ?
? ? ? 2 ?H? ?2 e Dd ?1 ? ?K3 =?H ?e ? ? ?K4 =?H ?e ? ? K5 ?NO3 ?e ? : 2 ??H ? ?0 ? ?H ? ?e ?

?2?

?11? Equation (11) is rearranged to Eq. (12), ln Dd ? 2 ln??H? ?0 ? ?H? ?e ? ! K3 K4 ? ln 1 ? ? ? ? 2 ?H ?e ?H ?e   K1 ? 2ln?H? ?e : ? ? ? ln ? K5 ?NO? 3 e 2 K2

where R represents the immobile functional anion group attached to the exchangeable sodium ion. In this study, the ionic strength of the lead solutions was so small that activity coef?cients for the ions in solutions are assumed to be at unity. Meanwhile, the possibility of non-ideality in the solid phase is ignored. The apparent equilibrium constant K1 of Eq. (1) and K2 of Eq. (2) are expressed in Eq. (3) and Eq. (4), respectively: ?Na? ?2 e ?R2 Pb?e K1 ? ; ?Pb2? ?e ?RNa?2 e K2 ? ?Na? ?e ?RH?e : ?H? ?e ?RNa?e ?R2 Pb?e ?Pb?e ?R2 Pb?e ?5? ?Pb2? ?e ??Pb?OH?? ?e ??Pb?OH?2 ?e ??PbNO? 3 ?e ?3?

?12?

?4?

De?ne adsorption distribution coef?cient (Dd ) as Dd ? ?

In the aqueous phase, hydrolysis of lead occurs readily, as is written in Eqs. (6) and (7):

? The term ln?1 ? ?K3 =?H? ?e ? ? ?K4 =?H? ?2 e ? K5 ?NO3 ?e ? can be taken as zero because K3 =?H? ?e ; K4 =?H? ?2 and e K5 ?NO? 3 ?e were 5 1. K1, K2 can be assumed as a constant if the experimental condition is limited to a narrow range [28]. Therefore, Eq. (12) indicates that if Eqs. (1) and (2) are the proper stoichiometric equations, a linear relationship should exist between ln Dd ? 2 ln??H? ?0 ? ? ?H? ?e ? ? ln?1 ? ?K3 =?H? ?e ? ? ?K4 =?H? ?2 e ? ? K5 ?NO3 ?e ? and ln ?H? ?e and its slope should be –2. Calculated from the experimental data obtained at initial pH of 3.0 and 3.6, a linear relationship between ln Dd ? 2 ln??H? ?0 ? ? ?H? ?e ? ? ln?1 ? ?K3 =?H? ?e ? ? ?K4 =?H? ?2 e ? ? K5 ?NO3 ?e ? and ln?H ? ?e was established, which is shown in Fig. 3. The slope of the correlated line was 2.2, very close to 2.

ARTICLE IN PRESS
X.-M. Zhan, X. Zhao / Water Research 37 (2003) 3905–3912 3909

1

0.4

0 0 -1 0.5 1 1.5 2

0.3

Y

0.2

-2

Y = -2.2X + 1.26 R = 0.91
2

Y

0.1
in deionized water in 0.01 M KCl solution

-3
0

-4

0

100

200

300

400

500

X
Fig. 3. Plot of the linear relationship correlated between the two variables of X and Y. In this ?gure, X=ln[H+]e, Y ? lnDd ? 2ln??H? ?0 ? ?H ?e ? ? ln?1 ? ?K3 =?H ?e ? ? .
? ?

X
Fig. 4. Plot of the proton titration experiment results. In this ?gure, X? ?H ? ?e ; ?0:025x=?x ? 25? ? ?H? ?e ??10?3 x ? ?x ? 25??H? ?e =25? ? ?H ?e : Y? 0:025x=?x ? 25? ? ?H? ?e

?K4 =?H ? ?2 e?

?

K5 ?NO? 3 ?e ? :

Therefore, 2RNa ? Pb2? ? R2 Pb ? 2Na? can describe the ionic exchange. 3.2. Maximum exchangeable Na+ present on the adsorbent The total amount of exchangeable Na+ present on the tannin adsorbent, RT(mol g?1 dry adsorbent), corresponds to the ionic exchange capacity. In the present study, RT was calculated from the data of the proton titration experiment by using perchloric acid (HClO4). ?H ? ?e 0:025x=?x ? 25? ? ?H ? ?e ? ?H ? ?e 1 ?RT ? ? : K2 ?0:025x=?x ? 25? ? ?H ?e ??10?3 x ? ?x ? 25??H? ?e =25??H? ?e ?
?

According to Eq. (4),
K2 ? ?Na? ?e ?RH?e ?RNa?e ?H? ?e ?0:025x=?x ? 25? ? ?H? ?e ??10?3 x ? ?x ? 25??H? ?e =25? : ?H? ?e ??RT ? ? 10?3 x ? ?x ? 25?=?H? ?e =25?

?

?13? Eq. (13) is converted to

?14?

Calculations were performed using experimental data at which pHe was below 7. Assuming that when x mL 0.025 M HClO4 was added into the well-sealed beakers that were ?lled with 25 mL deionized water or 0.01 M KCl solution, the volume of the aqueous solution was changed to x+25 mL. The resultant pHe o7 implies that 0:025 ? 10?3 x ? ?H? ?e ? ?x ? 25? ? 10?3 mol proton had been consumed. On the other hand, the same amount of Na+ had been released from the adsorbent.

Then, a linear relationship between  ?H ? ?e  ; 0:025x ?x ? 25? ? 10?3 x ? ? ?H ? ?e ?H ?e x ? 25 25

and ?H ? ?e ; 0:025x ? ?H ? ?e x ? 25

ARTICLE IN PRESS
3910 X.-M. Zhan, X. Zhao / Water Research 37 (2003) 3905–3912 Table 1 Results of the proton titration experiment RT (mmol g?1 dry adsorbent) In deionized water In 0.01 M KCl solution 1.0 1.0 K2 286 66 Correlation coef?cient (R2)

100

80

Removal (%)

0.999 0.994

60

The blank experiment

40

may be established and ?RT ? and K2 can be obtained, respectively, from the slope and intercept of the line. Fig. 4 shows and proves the linear relationship in deionized water and in 0.01 M KCl solution. ?RT ? and K2 of the tannin adsorbent in solutions calculated from the plots in Fig. 4 are listed in Table 1. The value of ?RT ? shows that the theoretical ionic exchange capacity for the adsorbent particles was 1.0 mmol Na+ g?1 dry adsorbent. 3.3. Effect of solution pH on lead removal The uptake of lead was strongly affected by solution pH. At the initial lead concentration of 100 mg L?1, lead removal ef?ciency was zero at a solution pH of 2.0, but it increased sharply when solution pH rose from 2 to 6 (shown in Fig. 5). Further experiments at a solution pH above 6 were not conducted due to the precipitation of lead occurring in the solution. The blank experiment, which is also given in Fig. 5, indicates that lead removal through precipitation took place at pH about 5. Eqs. (2) and (3) show that a competition between proton adsorption and lead removal existed. Therefore, increasing the initial concentration of proton in aqueous solutions resulted in the decrease of lead removal. When initial solution pH was 3.6, 4.2 and 5.0, lead removal ef?ciency was up to 71%, 87% and 91% respectively. This is advantageous for lead removal and recovery from wastewater because wastewater containing lead is always found to be acidic in order to avoid lead precipitation. 3.4. Adsorption isotherm The Langmuir equation KL Ce Xe ? Xm 1 ? KL Ce and the Freundlich equation
1=n Xe ? KF Ce

20

0 0 2 4 6 8

Solution pH
Fig. 5. Dependence of lead removal on solution pH.

2.4 2 1.6 1.2 0.8 0.4 0 0 20 40 60
-1

pH = 3.0 pH = 3.6 pH = 4.2

Ce/Xe (g L )

-1

80

100

Ce (mg L )
Fig. 6. Adsorption isotherms expressed by the Langmuir equation. The correlation coef?cients of the three lines are 0.95 (pH=3.0), 0.99 (pH=3.6) and 0.98 (pH=4.2), respectively.

are often used to express adsorption isotherms in aqueous solutions (Xm, KL are the Langmuir coef?cients and KF, n are the Freundlich coef?cients). It is found that the adsorption isotherm of the novel tannin

adsorbent for lead removal can be expressed well using the Langmuir equation. Fig. 6 summarizes the adsorption isotherms measured at pH=3.0, 3.6 and 4.2. From the Langmuir equation, the maximum adsorption amount, namely Xm, can be calculated. When initial solution pH was 3.0, 3.6 and 4.2, the maximum adsorption capacity calculated was 57.5, 76.9 and 114.9 mg Pb g?1 dry adsorbent, respectively. These data are much higher than the adsorption capacity of the proton-end tannin adsorbent developed previously (30– 40 mg Pb g?1 dry adsorbent) [27].

ARTICLE IN PRESS
X.-M. Zhan, X. Zhao / Water Research 37 (2003) 3905–3912 3911

According to the results of the proton titration experiment, the maximum exchangeable Na+ present on the adsorbent was 1.0 mmol g?1 dry adsorbent, which means that the theoretical maximum lead removal by ionic exchange was 103.6 mg Pb g?1 dry adsorbent. The maximum adsorption capacity calculated from the Langmuir equation at pH=4.2 (114.9 mg g?1 dry adsorbent) is slightly higher than the theoretical value. A possible reason for this is lead removal through surface precipitation, though solution pH values at equilibrium varied in the range of 4.5–5.2, lower than the pH value at which lead precipitation occurs. Reed et al. have cited that surface pH may be higher than the solution pH and surface precipitation of lead may occur at pH values of 0.5–1 pH units lower than the pH at which solution precipitation occurs [2].

preparing the manuscript. Finally, thanks a lot to the reviewers for their comments in improving the manuscript.

References
[1] Reed BE, Arunachalam S. Use of granular activated carbon columns for lead removal. J Environ Eng—ASCE 1994;120:416–36. [2] Reed BE, Robertson J, Jamil M. Regeneration of granular activated carbon (GAC) columns used for removal of lead. J Environ Eng—ASCE 1995;121:653–62. [3] Akhtar S, Qadeer R. Active carbon as an adsorbent for lead ions. Adsorpt Sci Technol 1997;15:815–24. [4] Mostafa MR. Adsorption of mercury, lead and cadmium ions on modi?ed activated carbons. Adsorpt Sci Technol 1997;15:551–7. [5] Lee MY, Shin HJ, Lee SH, Park JM, Yang JW. Removal of lead in a ?xed-bed column packed with activated carbon and crab shell. Sep Sci Technol 1998;33: 1043–56. [6] Li YH, Wang SG, Wei JQ, Zhang XF, Xu CL, Luan ZK, Wu DH, Wei BQ. Lead adsorption on carbon nanotubes. Chem Phys Lett 2002;357:263–6. [7] Wang JL, Zhan XM, Ding DC, Zhou D. Bioadsorption of lead (II) from aqueous solution by fungal biomass of Aspergillus niger. J Biotechnol 2001;87:273–7. [8] Lo WH, Chua H, Lam KH, Bi SP. A comparative investigation on the biosorption of lead by ?lamentous fungal biomass. Chemosphere 1999;39:2723–36. [9] Kapoor A, Viraraghavan T. Removal of heavy metals from aqueous solutions using immobilized fungal biomass in continuous mode. Water Res 1998;32:1968–77. [10] Abdel-Samad H, Watson PR. An XPS study of the adsorption of lead on goethite (a-FeOOH). Appl Surf Sci 1998;136:46–54. [11] Weerasooriya R, Aluthpatabendi D, Tobschall HJ. Charge distribution multi-site complexation (CD-MUSIC) modeling of Pb(II) adsorption on gibbsite. Colloids Surf A: Physicochem Eng Asp 2001;189:131–44. [12] Carrillo-Morales G, Davila-Jimenez MM, Elizalde-Gonzalez MP, Pelaez-Cid AA. Removal of metal ions from aqueous solution by adsorption on the natural adsorbent CACMM2. J Chromatogr A 2001;938:237–42. [13] Jeon C, Park JY, Yoo YJ. Characteristics of metal removal using carboxylated alginic acid. Water Res 2002;36: 1814–24. [14] Papini MP, Bianchi A, Majone M, Beccari M. Equilibrium modeling of lead adsorption onto a ‘‘red soil’’ as a function of the liquid-phase composition. Ind Eng Chem Res 2002; 41:1946–54. [15] Dimitrova SV, Mehandgiev DR. Lead removal from aqueous soluitons by granulated blast-furnace slag. Water Res 1998;32:3289–92. [16] Blais JF, Mercier G, Durand A. Lead and zinc recovery by adsorption on peat moss during municipal incinerator used lime decontamination. Environ Technol 2002;23: 515–24.

4. Conclusion The objective of this paper was to investigate adsorption characteristics of lead removal of a newly developed tannin adsorbent synthesized from wattle tannin, a kind of natural condensed tannins. The following results have been obtained. (1) The adsorbent can be taken as an ionic exchanger whose end group was Na+. Two Na+ ions were exchanged by one Pb2+ ion. (2) The proton titration experiments show that the new adsorbent contained a maximum exchangeable Na+ of 1.0 mmol g?1 dry adsorbent. (3) pH of aqueous solutions affected lead removal signi?cantly and removal ef?ciency increased with increasing solution pH. Lead removal ef?ciency was up to 71%, 87% and 91% when initial solution pH was 3.6, 4.2 and 5.0, respectively. (4) Adsorption isotherms can be described by the Langmuir equation. When initial pH was 3.0, 3.6 and 4.2, the adsorption capacity calculated was 57.5, 76.9 and 114.9 mg Pb g?1 dry adsorbent, respectively.

Acknowledgements The authors are very grateful to the support of 985 Fund, Tsinghua University. Also, X.-M. Zhan would like to thank Prof. Yoshio Nakano (Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology) because he enlightened this research when X.-M. worked in his lab. X.-M. Zhan also wishes to thank Mr. John Mulqueen and Mr. Edmond Q’Reilly (Civil Engineering Department, National University of Ireland, Galway) for their kind help in

ARTICLE IN PRESS
3912 X.-M. Zhan, X. Zhao / Water Research 37 (2003) 3905–3912 [23] Matsumura T, Usuda S. Applicability of insoluble tannin to treatment of waste containing americium. J Alloy Compd 1998;271-273:244–7. [24] Yamaguchi H, Higuchi M, Sakata I. Methods for preparation of adsorbent microspherical tannin resin. J Appl Polym Sci 1992;45:1455–62. [25] Nakano Y, Takeshita K, Tsutsumi T. Adsorption mechanism of hexavalent chromium by redox within condensedtannin gel. Water Res 2001;35:496–500. [26] Yamaguchi H, Higasida R, Higuchi M, Sakata I. Adsorption mechanism of heavy-metal ion by microspherical tannin resin. J Appl Polym Sci 1992;45:1463–72. [27] Zhan XM, Miyazaki A, Nakano Y. Mechanisms of lead removal from aqueous solutions using a novel tannin gel adsorbent synthesized from natural condensed tannin. J Chem Eng Jpn 2001;34:1204–10. [28] Weber WJ. Ion exchange. In: Weber Jr WJ, editor. Physicochemical Process for Water Quality Control. New York: Wiley-Interscience; 1972. p. 268. [17] Chen B, Hui CW, McKay G. Film–pore diffusion modeling for the sorption of metal ions from aqueous ef?uents onto peat. Water Res 2001;35:3345–56. [18] Ho YS, Ng JCY, McKay G. Removal of lead (II) from ef?uents by sorption on peat using second-order kinetics. Sep Sci Technol 2001;36:241–61. [19] Woolard CD, Petrus K, van der Horst M. The use of a modi?ed ?y ash as an adsorbent for lead. Water SA 2000;26:531–6. [20] Hemingway RW. Structural variations in proanthocyanidins and their derivatives. In: Hemingway RW, Karchesy JJ, Branham SJ, editors. Chemistry and signi?cance of condensed tannins. New York, London: Plenum Pub Corp; 1989. p. 83–107. [21] Randall JM. Variations in effectiveness of barks as scavengers for heavy metal ions. For Prod J 1977;27:51–6. [22] Sakaguchi T, Nakajima A. Accumulation of uranium by immobilized persimmon tannin. Sep Sci Technol 1994;29:205–21.


相关文章:
Mechanism of lead adsorption from aqueous solutions using_....pdf
Mechanism of lead adsorption from aqueous solutions using_材料科学_工程科技_专业资料。ARTICLE IN PRESS Water Research 37 (2003) 39053912 Mechanism of ...
Removal of lead from aqueous solution by hybrid precursor ....pdf
Removal of lead from aqueous solution by hybrid precursor prepared by rice ...(1) The results show that the %adsorption is 95 from dilute solutions (...
Adsorption of heavy metal ions from aqueous solutions by ....pdf
which have been used for removal of heavy metals from aqueous solutions. ...Adsorption of zinc, cadmium, copper and lead ions on oxidised anthracite. ...
Removal of lead(II) from aqueous solutions by activated ....pdf
Removal of lead(II) from aqueous solutions by activated carbon developed ...s speciicf surface area and adsorption capacity for Pb were examined to ...
...of methylene blue from aqueous solutions by modi....pdf
Kinetics and mechanism o... 暂无评价 4页 2.... Adsorption of lead(II) i... 9页 2财富值 ...from aqueous solutions by modified expanded graphite...
...of cesium (I) from aqueous solution using oxidiz....pdf
Adsorption of lead(II) i... 9页 2财富值 ...The dominant mechanism of cesium adsorption on ...sorption of cations from aqueous solutions [33]....
Adsorption of Pb(II) and Cd(II) from aqueous solutions using ....pdf
Adsorption of Pb(II) and Cd(II) from aqueous solutions using titanate ... Mechanism of lead adso... 暂无评价 8页 1下载券 喜欢此文档的还喜欢 ...
...of cadmium(Ⅱ) and lead(Ⅱ) ions from aqueous solutions ....pdf
Biosorption of cadmium(Ⅱ) and lead(Ⅱ) ions from aqueous solutions onto dried activated slu_专业资料。维普资讯 http://www.cqvip.com SSNI O7 OOI42 ...
7Adsorption of Lead(II) Ion from Aqueous Solution Using Rice ....pdf
7Adsorption of Lead(II) Ion from Aqueous ...mechanism proposed by Daifullah et al.10 and ...Removal of Lead from Aqueous Solutions using Rice...
...of Copper(II) and Nickel(II) from Aqueous Solution Using ....pdf
cation. Aqueous metal solutions were prepared from analytical grade CuSO4 and...than nickel, so it leads to an increase in the selectivity of adsorption....
...for Determination of Lead(Ⅱ) in Aqueous Media_论文.pdf
Gold Nanoparticle-based Colorimetric Assay for Determination of Lead(Ⅱ) in Aqueous Media_专业资料。CHEM.RES.CHISUNWERSIES201NEE TI 0 , 2()141762, ...
...IN TO RICE STRAW FOR REMOVING LEAD FROM AQUEOUS SOLUTION_....pdf
desorption of Pb and sorption mechanism The main ...Removal of lead from aqueous solutions by ...Adsorption of hexavalent chromium from aqueous ...
Adsorption of Ni(II) from Aqueous Solution Using Ox....pdf
Ion exchange may be the predominant mechanism of ....903 of heavy metal ions from aqueous solutions....Q. Lead adsorption on carbon nanotubes. Chem. ...
...of Single-Layer Graphene Oxide and Graphene Using ....pdf
from aqueous solutions without surfactant has not ...Proposed Mechanism for GO Immobilization. Given ...adsorption that leads to nearly complete coverage ...
Adsorption of basic dye from aqueous solutions by m....pdf
Adsorption of lead(II) i... 9页 2财富值 ... Adsorption of basic dye from aqueous solutions ...mechanism of the adsorption process and to test ...
Hazarous07-Adsorption of methylene blue onto bamboo-based ....pdf
for removing organic contaminants and colored bodies from aqueous solutions. ...understand the adsorption mechanism of the dye molecules onto the activated ...
Adsorption of Cd(II) and Cu(II) from aqueous solution by ....pdf
Adsorption of Cd(II) and Cu(II) from aqueous ...In general, all stripping solutions lead to ...? From the results obtained, the mechanism of ...
...ions removal from synthetic aqueous solutions.pdf
Adsorption of lead(II) i... 9页 2财富值 ...aqueous solutions using by novel magnetic p(GMA-...mechanism is predominant and that chemisorption ...
adsorption equilibrium of zinc ions from aqueous solution by ....pdf
(II) ion from aqueous solutions using zeolite, ...adsorption mechanism based on the potential theory ...and Ismail T., Lead Removal from Aqueous ...
英语论文标题.doc
aqueous solutions using boron doped diamond anodes 3、Adsorption of lead ...solutions: Mechanism and evaluation method 10 、 Tuning of electrochromic ...