Adsorption of Cd(II) and Pb(II) onto functionalized formic lignin from sugar cane bagasse

blC C)UI C[ T III LC iY ELSEVIER

Bioresource Technology 68 (1999) 95-100

Adsorption of Cd(II) and Pb(II) onto functionalized formic lignin from sugar cane bagasse Wilson S. Peternele, Ana A. Winkler-Hechenleitner, Edgardo A. G6mez Pineda* Departamento de Quimica, Universidade Estadual de Manngtt, Av. Colombo 5790, 87020-090 Maring(z-PR, Brazil Received 5 September 1997; revised 15 December 1997

Abstract

The effects of temperature, pH and ionic strength on adsorption of Cd(II) and Pb(II) onto carboxymethylated lignin from sugar cane bagasse have been studied. Adsorption equilibrium data obtained using the batch technique were fitted to the Langmuir model. A factorial design showed that the most important variables are temperature and ionic strength for the Pb(II) adsorption in single and binary system respectively. For both metals, maximum binding capacity decreased with the ionic strength increase. Increasing pH the Pb(II) adsorption is enhanced. Carboxymethylated lignin adsorbed Pb(II) selectively at pH 6.0, 30°C and 0.1 mol dm -3 of ionic strength. © 1998 Published by Elsevier Science Ltd. All rights reserved. Keywords: Carboxymethylated lignin; Cadmium; Lead

1. Introduction

Heavy metals are nowadays among the most important pollutants in source and treated water, and are becoming a severe public health problem. Heavy metals removal from aqueous solutions has been traditionally carried out by chemical precipitation. However, metal removal in the precipitation-coagulation system does not generally allow strict regulatory requirements to be met. In the last few years, adsorption has been shown to be an economically feasible alternative method for removing trace metals from wastewater and water supplies (Huang and Ostovic, 1978; Gabald6n et al., 1996; L6pez et al., 1995; Allen and Brown, 1995). Activated carbon has been the most used adsorbent, nevertheless it is relatively expensive (Gabald6n et al., 1996; L6pez et al., 1995). In order to obtain cheaper adsorbents, lignocellulosics materials have been studied. Agricultural byproducts such as onion skins (Kumar and Dara, 1981; Asai et al., 1986), palm kernel husk (Omgbu and Iweanya, 1990), peanut skin (Randall et al., 1975), modified cellulosic materials (Shukla and Sakhardande, 1990; Okeimen et al., 1985), pinus bark (Freer et al., 1989), corn cobs (HawthorneCosta et al., 1995) etc., have received attention in these *Corresponding author.

type of applications. Some chemical modifications can improve the adsorbent behavior of these materials. Modification reactions include crosslinking and/or functionalization to enhance the adsorbent stability and/or adsorption capacity. In this way, the low cost and simplicity of the modification methods are also desirable for applications, for example, in treatment of great volumes of industrial and mining wastewater prior to discharge. Recently, we reported the use of lignin from sugar cane bagasse as copper adsorbent

0.7 • 0.6-

• •

Pb- in binary C d - in binary

• •

Pb-single Cd-single

q 1 j •

o.~ ~. o.40 ~ 0.3-

-at

IY 0.20.1 0.0

0.o

lo

20

3.0

40

slo

Ce ( mmol.dm -3 ) Fig. 1. Adsorption isotherms of Pb(lI) and Cd(lI) onto CLSCB at 30°C, pH 6.0 and 0.1 mol dm -3 of ionic strength. Symbols are experimental data and solid lines are Langmuir fits.

0960-8524/99/$ - - see front matter © 1998 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 0 - 8 5 2 4 ( 9 8 ) 0 0 0 8 3 - 2

W.S. Peternele et aL/Bioresource Technology 68 (1999) 95-100

96

(Consolin Filho et al., 1996). The objective of this study was to contribute in the search for less expensive adsorbents and utilization possibilities for some agricultural byproducts, which are in many cases also pollution sources.

acid and precipitated with cold water, washed with hot water and dried overnight at 50°C, 2.2. Lignin reticulation Formic lignin (0.4 g) was dissolved in 10 c m 3 formaldehyde (38%) and 5.0cm 3 HCI, then refluxed for 30min. After reflux, lignin was precipitated with diluted NaOH solution, filtered, washed with water until neutral pH, and dried at 50°C.

2. Methods

2.1. Lignin extraction

2.3. Reaction with chloroacetic acid

Sugar cane bagasse was extracted sequentially with n-hexane, ethanol and water in a soxhlet system. The sample obtained was then air dried. Formic acid (115 c m 3, 88%) was added to pre-extracted sugar cane bagasse (10 g) and heated until reflux, when HCI was added to obtain a 1% solution. After 3 h in reflux, the sample was filtered and washed with concentrated formic acid. The solution was concentrated at reduced pressure until a viscous liquid was formed. This liquid was poured on cooled water and precipitated lignin was obtained. This lignin was dissolved in hot formic

To a dispersion of reticulated lignin (2.5g lignin+20cm 3 of a 10% NaOH aqueous solution), 5 cm 3 of a 36% aqueous chloroacetic acid solution was added under cooling with tap water. The resulting solution was kept at 45°C and maintained under stirring during 4h. After acidification to p H 2 by diluted sulfuric acid addition, the solid precipitated was filtered, and washed with water until neutral pH.

2.4. Methodology of adsorption experiments Adsorption experiments were realized analogously as described previously (Hawthorne-Costa et al., 1995; Consolin Filho et al., 1996). Approx 0.050 g adsorbent were placed in a 50 c m 3 erlenmeyer and 25.0 c m 3 of cadmium and/or lead chloride solutions (Ci = 1.00 x 10 -3 to 6.00 x 10 -3 m o l d m -3) w e r e a d d e d . The dispersions were shaked in a Dubnoff thermostatic bath for 8 h. The dispersions were then filtered and metals concentration in solution (Co) were determined through atomic absorption spectrometry using a Varian Spectra AA 10 Plus atomic absorption spectrophotometer, at wavelengths 228.8 nm (for Cd) and 217 nm (for Pb) using an acetylene-air flame. The band pass was 0.5 nm for Cd and 1 nm for Pb. The adsorbed metal concentration (q) was calculated from the difference of the metal remaining in solution and the known

0.4-

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~

0.2-

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0.1 -

0.0-

• • • ~

Cd in Binar/ Pb in Binary I:~

~ 1

2

3

4

5

6

7

Ce (mmol / dm 3)

Fig. 2. Adsorption isotherms of Pb(II) and Cd(II) onto CLSCB at 30°C, pH 5.0, 0.1 mol dm -3 of ionic strength. Symbols are experimental data and solid lines are Langmuir fits.

Table 1 Langmuir parameters on Pb(II) and Cd(II) adsorptions onto CLSCB in different conditions (ionic strength: 0.1 mol dm -3) Metal ion, system, pH

Pb(II), single, 6.0 Pb(II), binary, 6.0 Cd(II), single, 6.0 Cd(II), binary, 6.0 Pb(II), single, 5.0 Pb(II), binary, 5.0 Cd(II), single, 5.0 Cd(II), binary, 5.0 Cd(II), binary, 6.0

30°C

40°C

50°C

qm (mmol/g)

KL (dm3/mol)

qm (mmol/g)

KL (dm3/mol)

q~, (mmol/g)

KL (dm3/mol)

0.519 0.594 0.338 0.083 0.388 0.447 0.602 0.309 0.032

1.749 2.146 2.297 1.671 1.340 0.708 0.543 0.366 -

0.641 0.630 0.386 0.138 0.486 0.458 0.213 0.101 0.022

2.058 2.141 2.030 2.256 1.197 0.843 0.075

0.653 0.635 0.401 0.187 0.645 0.552 0.213 0.096 0.814

1.770 2.036 2.529 1.627 0.632 0.510 0.062

W.S. Peternele et al./Bioresource Technology 68 (1999) 95-100

initial concentration. A digital Micronal B 375 pH meter was used for pH measurements and buffer solutions of acetic acid/sodium acetate 0.1 mol dm -3 was used in pH controlled adsorption experiments. 3. Results and discussion

Adsorption of Cd(II) and Pb(II) from chloride salts in aqueous solutions, onto carboxymethylated lignin from sugar cane bagasse (CLSCB) was studied in single component and binary systems. Three experimental parameters were varied: temperature; pH; and ionic strength. The results obtained at 30°C and at pH 5.0 and 6.0 are presented as adsorption isotherms in Figs 1 and 2. Saturation of Pb(II) and Cd(II) in both systems and pH isotherms are shown, and could be fitted to a Langmuir isotherm (Adamson, 1990). The Langmuir equation, q/qm=KLCJ(I+KLCe) (where q is the amount of metal ion adsorbed, qm is the maximum adsorption capacity, KL is the Langmuir

97

equilibrium constant and Ce is metal ion concentration dissolved at the equilibrium) was utilized for estimating qm and KL. Single saturation was not observed in some isotherms. In these cases, the first saturation step was considered for qm determination. In general, Pb(II) adsorption was higher than Cd(II) adsorption. For Cd(II), adsorption was always higher in the single system compared with the binary system. This behavior is expected, considering that in the last case both metal ions will compete for the disposable binding sites at the adsorbent surface. However, Pb(II) is more adsorbed in the binary than in the single system, which support a synergistic effect. These way, adsorption of Pb(II) is selective in relation to a binary system (with Cd(II)). Adsorption capacity (qm) is enhanced with increasing temperature in all the systems studied here (Table 1). The KL constant shows variable tendencies with temperature variation. On the other hand, a tendency is observed for Pb(II) adsorption: KL at pH 6.0 is higher for the binary system and KL at pH 5.0 is higher for the single system at the three temperatures. In general, adsorption increases when pH is increased.

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Ce( mmol.dm-3)

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Ce(mrnol.dm "3) Fig. 3. Adsorption isotherms for Pb(II) in single system on CLSCB at 30oc. Ionic strength is indicated: (A) pH 5.0; (B) pH 6.0.

O.O

1.0

2.0

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Ce(mmol.drn-3) Fig. 4. Adsorption isotherms for Pb(II) in binary system on CLSCB at 30°C. Ionic strength is indicated: (A) pH 5.0; (B) pH 6.0.

98

W.S. Petemele et aL/Bioresource Technology 68 (1999) 95-100

This behavior must be related to the increase in the ionization degree of the carboxylate groups present in the modified lignin (Hawthorne-Costa et al., 1995, Consolin Filho et al., 1996). NaC1 was added to give ionic strength of 0.5 and 1.0 mol dm -3 to evaluate the ionic strength influence on the Pb(II) and Cd(II) adsorption experiments at 30°C and at 50°C. Some of these isotherms obtained are in Figs 3-6. The general tendency was adsorption decreasing with increasing ionic strength. In many cases, the addition of the neutral salt resulted in a change of the shape of the isotherm. These changes have been interpreted as being due to the presence of more than one binding site present at the surface lignin particles (Wieber et al., 1988). As observed with ionic strength 0.1 mol dm -3, Cd(II) adsorption was always higher in the single than in the binary system (Figs 5 and 6). On the other hand, there is not a definite tendency with respect to pH in Cd(II) adsorption. Pb(II) adsorption showed better defined isotherms (Figs 3 and 4). To qm data, a full 23 factorial design

Iorac Slam~h • 0.1

e .

(three factors, each at two levels) was applied. The standard experimental matrix for the factorial design and the results of q , are shown in Table 2. A statistical analysis was performed on these qm results, and the main effects and interaction effects for the different variable combinations were calculated. The results (Table 2) show that temperature is the most important factor in the single system (Pb(II)), while ionic strength is the most important variable for the binary system.

4. Conclusions Cheap materials such as lignin can be easily modified in order to obtain new materials able to adsorb heavy metals ions. Carboxymethylated lignin from sugar cane bagasse can adsorb Pb(II) and Cd(II) from aqueous solutions. In general, the Pb(II) adsorption process obeys Langmuir's model and Cd(II) presents adsorption in multilayer, especially when the temperature is higher than 30°C. When ionic strength increases, the maximum adsorption capacity diminishes.

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Fig. 5. Adsorption isotherms for Cd(II) in single system on CLSCB at 30°C. Ionic strength is indicated: (A) pH 5.0; (B) pH 6.0.

1.bo

zbo

abo

Ce (mmol.dm -3)

4.bo

5.00

Fig. 6. Adsorption isotherms for Cd(II) in binary system on CLSCB at 30°C. Ionic strength is indicated: (A) pH 5.0; (B) pH 6.0.

W.S. Peternele et al./Bioresource Technology 68 (1999) 95-100

99

Table 2 Adsorption capacity (qm) of CLSCB toward Pb(ll) in different conditions and factorial analysis Symbol, variable

Data (level)

A, ionic strength (mol dm -3) B, temperature (°C) C, pH

1.0 ( + ) 0.1 ( - ) 50.0 ( + ) 30.0 ( - ) 6.0 ( + ) 5.0 ( - ) Variable

qm (rnmol/g)

Experiment

A

B

C

In single system

In binary system

1 2 3 4 5 6 7 8

+ + + +

+ + + +

+ + + +

0.388 0.141 0.645 0.786 0.519 0.398 0.653 0.505

0.447 0.317 0.552 0.352 0.594 0.425 0.635 0.481

Effect in qm

For Pb(II) in single system

For Pb(II) in binary system

I A B AB C AC BC ABC

0.504 -0.0936 0.286 0.090 0.029 - 0.04 1 - 0.165 0.104

0.476 -0.164 0.059 0.014 0.117 0.002 - 0.011 0.021

CMLSCB can adsorb Pb(II) selectively rather than Cd(II) under special conditions (pH 6.0, 30°C and ionic strength of 0.1 mol dm-3), when both ions are present in mixture. Factorial analysis of Pb(II) adsorption suggests that temperature is the most important factor in the single system, adsorption increases with increasing temperature. When Pb(II) and Cd(II) are present in a binary system, ionic strength is the most important factor. In this case adsorption diminishes with increasing ionic strength. Acknowledgements AAWH, EAGP, WSP acknowledge grants from CNPq Proc. 500.527/95-0 and 300.694/90-3 and DQI-UEM. References Adamson, A.W., 1990. Physical Chemistry of Surfaces, 5th edn. New York: Wiley-Interseience, Chap. XI. Allen, S.J., Brown, P.A., 1995. Isotherm analyses for single component and multicomponent metal sorption onto lignite. J Chem Tech Biotechnol 62, 7-24.

Asai, S., Konishi, Y., Tomisaki, H., 1986. Separation of mercury from aqueous mercury chloride Solutions by onion skins. Sep Sci and Technol 21(8), 809-821. Consolin Filho, N., Winlder-Hechenleitner, A., G-6mez-Pineda, E. A., 1996. Copper(II) adsorption onto sugar cane bagasse. Intern J Polymeric Mater 34, 211-218. Freer, J., Baeza, J., Maturana, H., Palma, G., 1989. Removal and recovery of uranium by modified Pinus radiata D don bark J Chem Technol Biotechno146, 41-48. Gabald6n, C., Marzal, P., Seco, A., 1996. Cadmium and zinc adsorption onto activated carbon: influence of temperature, pH and metal/carbon ratio. J Chem Tech Biotechnol 66, 279-285. Hawthorne-Costa, E.T., Winkler Hechenleitner, A.A., G6mezPineda, E.A., 1995. Removal of cupric ions from aqueous solutions by contact with corn cobs. Sep Sci Technol 30(12), 2593-2602. Huang, C.P., Ostovic, F.B., 1978. Removal of cadmium(II) by activated carbon adsorption. J Envir Div ASCE 104, 863-878. Kumar, P., Dara, S.S., 1981. Binding heavy metal ions with polymerized onion skin. J Polym Sci, Polym Chem Ed 19, 397-402. L6pez, F.A., Perez, C., Sainz, E., Alonso, M., 1995. Adsorption of Pb(II) on blast furnace sludge. J Chem Tech Biotechnol 62, 200-206. Okeimen, F.E., Ogbeifun, D.E., Nwala, G.N., Kumsah, C.A., 1985. Binding of cadmium, copper and lead ions by modified cellulosic materials. Bull Environ Contam Toxicol 34, 866-870. Omgbu, J.A., Iweanya, V.I., 1990. Dynamic sorption of Pb 2÷ and Zn 2+ with Palm (Elaesis guineensis) kernel husk. J Chem Ed 67(19), 800-801. Randall, J.M., Reuter, F.W., Waiss, A.C. Jr., 1975.. Removal of cupric ions from solution with peanut skins. J Appl Polym Sci 19, 1563-1571.

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Shukla, S.R., Sakhardande, V.D, 1990. Cupric ion removal by dyed cellulosics materials. J Appl Polym Sci 41, 2655-2663. Wieber, J., Kulick, F., Pethica, B.A., Zuman, P., 1988. Sorptions on

lignin, wood and celluloses. III. Copper (II) and zinc (II) ions. Colloids and Surfaces 33, 141-152.