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Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

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Treatment of industrial wastewater containing copper and cobalt ionsusing modified chitosan

Nabel A. Negm a,*, Ragaa El Sheikh b, Ahmed F. El-Farargy b, Hassan H.H. Hefni a,Mahmoud Bekhit a

a Petrochemicals Department, Egyptian Petroleum Research Institute, Cairo, Egyptb Chemistry Department, Faculty of Science, Zagazig University, Zagazig, Egypt

A R T I C L E I N F O

Article history:

Received 5 December 2013

Accepted 5 March 2014

Available online xxx

Keywords:

Chitosan

Industrial waste water

Adsorption efficiency

Langmuir

Thermodynamics

A B S T R A C T

Chitosan was extracted and characterized using several analyses. The produced chitosan was reacted by

glycine and chloroacetic acid. Chemical structures of biosorbents were confirmed. Adsorption efficiencies

of the two biosorbents in neutral and alkaline medium at 25 8C were determined using atomic absorption

spectroscopic analysis. Adsorption capacity of modified biosorbents toward Cu(II) and Co(II) ions was

determined and compared to virgin chitosan. The biosorbents showed lower adsorption efficiency toward

copper and cobalt ions compared to virgin biosorbent. Furthermore, adsorption capacity of glycine–

chitosan was higher than chloroacetic acid–chitosan biosorbents, which attributed to chelating of amino

groups than chloro-substituted polymer. Thermodynamicstudies showed the spontaneous behavior of the

adsorption process of metal ions under the studied conditions. Entropy changes indicatethat the adsorption

of the metal ions are endothermic process, and lower values of DS8 indicate the affinity towardmetal ions by

the biosorbents at different degrees depending on their chemical structures.

� 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights

reserved.

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry

jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / j iec

27282930313233343536373839404142

43

1. Introduction

Heavy metal water pollution is the contamination of water innatural resources by heavy metals [1,2]. Traditional treatmentmethods including: chemical precipitation [2], electrochemicaldeposition [3], ion exchange, and membrane separation [4] havebeen applied. Adsorption method using natural biosorbents isalternative to these methods. Numerous studies have demonstratedthe effectiveness of chitosan and derived products in the uptake ofmetal cations such as lead, cadmium, copper, and nickel and theuptake of oxyanions as well as complexed metal ions [5–9,1].Chitosan is undoubtedly one of the most popular adsorbents formetal ions removal from aqueous solution and is widely used inwaste treatment applications[10]. The binding ability of chitosan formetal cations is mainly due to the amine groups (–NH2) on thechitosan chain which can serve as coordination sites for manymetals. The extent of metal adsorption depends on the source ofchitosan [11], the degree of deacetylation [12], the nature of themetal ion[13], and solution conditions such as pH[14]. In spite of its

44

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* Corresponding author. Tel.: +20 1275704384.

E-mail address: nabelnegm@hotmail.com (N.A. Negm).

Please cite this article in press as: N.A. Negm, et al., J. Ind. Eng. Che

http://dx.doi.org/10.1016/j.jiec.2014.03.015

1226-086X/� 2014 The Korean Society of Industrial and Engineering Chemistry. Publis

prolific use, the adsorption ability of chitosan has not been realizedto a satisfying level. In recent years, attention focused on severaladsorbents which have metal-binding capacities and high selectivityto remove heavy metals from contaminated water [15]. In order toimprove the sorption selectivity and adsorption ability of chitosanfor metal ions, a great number of chitosan derivatives have beenprepared by grafting new functional groups such as histidine [16],heparin [17], succinic anhydride [18], N,O-carboxymethyl [19]through a crosslinked chitosan back bone. Further, chemicalmodifications of chitosan were made to improve the selectivityand the capacities toward heavy metal ions [20]. Substitutedchitosan was prepared and regarded as a simple and effectiveprocess to facilitate the adsorption ability of chitosan with heavymetals [21,22]. In the present study, two chitosan derivatives wereprepared and characterized. Their adsorption efficiency andmechanism of adsorption were determined and discussed.

2. Experimental techniques

2.1. Materials

CuSO4, CoSO4, and NH4OH were purchased from Chimia MisrCompany and were used without purification. The transition

m. (2014), http://dx.doi.org/10.1016/j.jiec.2014.03.015

hed by Elsevier B.V. All rights reserved.

47 m48 Cu

49 2.

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110111

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Fig. 1. Chitosan extraction from shrimp shell.

N.A. Negm et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx2

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etals solutions were prepared by dissolving known weight ofSO4 and CoSO4 salts in deionized water.

2. Preparation of chitosan

Shrimp shells were collected and washed with warm water tomove soluble organics, adherent proteins and other impurities,d dried at 70 8C for 24 h.

2.1. Deproteinization

Shrimp shells were treated with 3.5% (w/w) sodium hydroxidelution for 2 h at 65 8C under stirring, considering the ratiotween shells to sodium hydroxide at 1:10 (w/v). After 2 h, theaction was filtered, and the solid mass washed several times withstilled water for 30 min.

2.2. Demineralization

Demineralization was performed by soaking the deprotenizedells in 1 N HCl for 1 day at room temperature and maintainingell–HCl ratio at 1:15 (w/v). The reaction medium then filteredder vacuum, the solid obtained washed with distilled water, anden-dried.

2.3. Decolouration

Deproteinized and demineralized shells were soaked in acetone decolorize the shells. The shells were left in acetone for 2 h at

8C under stirring, and then filtered and dried in vacuum oven at 8C for 2 h.

2.4. Deacetylation

Treated shrimp shells (500 g) were washed with water andsed in 50% solution of sodium hydroxide at 115 8C for 2 h. Thetained deacetylated chitin was washed thoroughly with distilled

ater till neutralization, filtered, and dried at 60 8C for 24 h. Theoduced chitosan was about 20% by weight of shrimp shell beforeeatment [22]. The obtained chitosan was analyzed and charac-rized using different analytical methods. Fig. 1 represents theethodology of chitosan extraction from shrimp shell.

3. Preparation of biosorbents

Equivalent molar amounts of chitosan (relative to the amino-ucose units) and glycine/chloroacetic acid were reacted in xylene

solvent at 130 8C for 3 h to eliminate the water of reaction byan-stark connection. The reaction was stopped when theuivalent amount of water was obtained. The products werestilled off and dried in vacuum oven at 80 8C, washed withdistilled water, and dried in vacuum oven at 50 8C. IR spectraere used to confirm the structure of glycine–chitosan, andloroacetic acid–glycine polymers, Fig. 2.

4. Adsorption study

Copper (II) and cobalt (II) solutions were prepared by dissolving25 gL�1 of CuSO4�2H2O and CoSO4�H2O in deionized water. Forch experiment, 0.5 g of each biosorbent was added in 100 mL ofetal solution (250 ppm) in 250 mL Erlenmeyer flask. The flasksere stirred (150 rpm) at 25, 35, 45 8C for different time intervals: 20, 40, 60, 80, and 100 min. After the treatment, biosorbentsere separated by vacuum filtration. Several experiments werenducted to evaluate the effect of pH on biosorption at neutrald alkaline medium (7 and 9) at 250 ppm solution of the differentetals. Values of pH were adjusted by adding few drops of NH4OH

HCl solutions. The residual metal concentrations remained inlutions after treatments were determined by atomic absorptionectroscopy (AAS).

Please cite this article in press as: N.A. Negm, et al., J. Ind. Eng. Ch

2.5. Data processing

The obtained data from adsorption experiments were analyzedusing different adsorption isotherms.

The percent removal (h%) and the equilibrium adsorptioncapacity qe (mg g�1) of M(II) in solutions were calculated using thefollowing equations:

h% ¼ C0 � Ce

C0� 100

qe ¼ ðC0 � CeÞV

M

where Ce: concentration of adsorbed metal ions at equilibrium(mg L�1), C0: initial concentration of metal ions in the solution(mg L�1), V: volume of solution (L), M: weight of used biosorbent(g), h%: efficiency of biosorbent in metal adsorption process, andqe: amount of metals adsorbed by 1 g of biosorbent at equilibrium(mg g�1).

3. Results and discussion

3.1. Structure of biosorbents

Chemical structures of modified biopolymers were confirmedusing IR spectroscopy, Fig. 2A and B. IR spectra of the biosorbents

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141142143144145146147148149150151152153154155156157158159

Fig. 2. IR spectra of glycine–chitosan biopolymer.

N.A. Negm et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx 3

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represent the following absorption bands: 540, 785 cm�1 corre-sponding to CH2Cl group from the chloroacetic acid, 1032 cm�1

corresponds to C–N stretching of CH2NH2 group of glycine. Thecarbonyl group of chloroacetic acid derivative appeared at1716 cm�1, and 1732 cm�1 for glycine derivative.

3.2. Adsorption capacity of biosorbents

The amounts of adsorbed metals on different biosorbents weredetermined by determining the remaining amounts of dissolvedmetal ions in the solutions after adsorption processes. The values ofremaining metal ions in solutions after treatment with differentbiosorbents are listed in Table 1.

Data in Table 1 represent the concentrations of metal ionsremained in the solutions and adsorption efficiency (h%) ofbiosorbents. It is clear that the concentration of metal ions decreasedgradually by the gradual increase of immersion time. The highestadsorption efficiency was obtained in presence of unmodifiedchitosan. The maximum efficiency is reached 99.4% and 99.8% in case

Table 1Equilibrium concentration (Ce) and removal efficiency (h%) of Co(II) and Cu(II) in prese

Biosorbent t (min) Co (pH 7) Co (pH

Ce (mg L�1) h% Ce (m

Chitosan 20 123.6 50.6 0.27

40 128.3 48.7 0.86

60 129.5 48.2 1.52

80 132.2 47.2 1.63

100 132.2 47.13 1.63

Chitosan–chloroacetic acid 20 116.3 53.48 46.3

40 171.3 31.48 50.4

60 181.8 27.28 54.3

80 182.5 27.00 54.5

100 183.5 26.60 54.6

Chitosan–glycine 20 154.4 38.24 4.3

40 155.1 37.96 4.7

60 157.6 36.96 5.8

80 163.7 34.52 12.0

100 163.9 34.44 12.2

Please cite this article in press as: N.A. Negm, et al., J. Ind. Eng. Che

of unmodified chitosan in presence of both Co(II) and Cu(II) metalions in alkaline medium (pH 9). In neutral medium (pH 7), theadsorption efficiency is reached 47.2% and 73.9%, respectively.

The adsorption efficiency of glycine–chitosan modified biosor-bents depressed to 94.1% and 95.4% in presence of Co(II) and Cu(II)in alkaline medium (pH 9). In neutral medium (pH 7), thedepression in adsorption efficiency reached to 34.4% and 65.8% incase of Co(II) and Cu(II) metal ions, respectively.

The adsorption efficiency of chloroacetic acid–chitosan modi-fied biopolymer had similar trend for Co(II) and Cu(II) metal ions.In case of alkaline medium, the adsorption efficiency of Co(II) andCu(II) reached to 65.3% and 78.2%, respectively. While, changing pHof the medium to alkaline (pH 7) decreased the adsorptionefficiency to 26.6% and 34.4%, respectively.

It is clear from the data obtained in Table 1 that, the adsorptionprocess of metal ions in alkaline medium is more efficient than thatoccurred in neutral medium. Also, the adsorption of copper ions ismore pronounced than cobalt ions. The pronouncement of adsorp-tion in alkaline medium can be attributed to the precipitation of

nce of chitosan and chitosan modified biosorbents.

9) Cu (pH 7) Cu (pH 9)

g L�1) h% Ce (mg L�1) h% Ce (mg L�1) h%

99.9 90.8 63.9 2 99.2

99.7 86.7 65.3 1.8 99.3

99.4 77.8 68.9 0.7 99.7

99.3 65.3 73.9 0.6 99.8

99.35 65.3 73.91 0.8 99.76

81.48 84.8 66.10 92.5 62.99

79.86 89.5 64.21 92.7 63.12

78.26 91.5 63.39 90.9 63.62

78.20 102.1 59.16 87.3 65.20

78.15 108.8 56.48 86.8 65.28

98.28 102.5 59.00 88.0 64.80

98.21 101.5 59.40 81.6 67.42

97.69 90.2 63.92 51.6 79.46

95.20 86.0 65.61 17.7 92.90

95.12 85.4 65.84 14.9 94.03

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160 m161 fo162

M

163164165

166 al167 Cu168 co169 an170 m171 io172 co173 fo174 ac175 m176 fo177

178 ef179 re180 su

181 3.

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183 M184 so185 ro186 m187 ch188 m189 (M190

191 m192 pr193 ch194 ce195 us196 at197 fo198 ta199 th200 ef201

202 ef203

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221 ad222 Co223 ex

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270

271272273274275276277278279280281282283284285

N.A. Negm et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx4

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etal ions in the form of insoluble hydroxides, as represented in thellowing equation:

2þ þ OH�! MðOHÞ2 #

Copper and cobalt ions are highly sensitive toward thekalinity of the medium [23]. Depending on pH of the medium,(II) and Co(II) ions start to precipitate at pH 8–10, and reached tomplete precipitation at pH 12. In pH 9, the ionic species of Cu(II)d Co(II) start to change to hydroxide form, as a result, theedium contains both hydroxide form and ionic form of the metalns. That decreases the metal ion amounts in the solution, andnsequently the efficiency of metal removal increased [24]. Thermed hydroxides precipitate in the network of the biopolymerscording to intraparticle model. The ions in the In neutraledium, the ionic species of Cu(II) and Co(II) remains in their ionicrms.

The data listed in Table 1 showed acceptable adsorptionficiency for chitosan and its modified forms in Cu(II) and Co(II)moval from wastewater by adjusting the pH of the medium to aitable values.

3. Effect of pH

The dominant species of M(II) ions in solution such as M2+,(OH)2, M(OH)3

� and M(OH)42� depend on pH value of the

lution [25]. At pH >7, precipitation of M(OH)2 plays the mainle in removing of M(II) [26]. Metal ions in acidic medium areainly present in positively charged forms with two or threearges (M2+ and M3+). In alkaline medium, the active species ofetal ions changed to oxides MO, hydroxides M(OH)2, peroxidesO2)2�, perhydroxide M(OH)3

�, and M(OH)42�.

The removing protocol of the ionic species depends on pH of theedium. In acidic medium, the process of metal removing isedominantly the adsorption of metal ions in their positivelyarged form. That requires a presence of negatively chargednters or coordination site in the chemical structure of sorbentsed. While, in alkaline medium, the removing of the metal ions istained by the adsorption of metal ions in negatively chargedrms, and also the precipitation of the metal oxides or hydroxideskes place. Precipitation of metal hydroxides takes place betweene networks of adsorbents, which increases considerably theficiency of metal removal.

Data in Table 1 showed the effect of pH on the metal removalficiency of Cu(II) and Co(II).

In neutral medium, the adsorption capacity (h%) of Co(II) usinge different adsorbents are ranged between 26.6% and 53.48%.ese values are relatively low compared to Cu(II), which are in thenge of 56.48–73.91%. This can be attributed to the ionic species of(II) in the solution. Co(II) ions in the neutral medium turned toide form, which has no charge and consequently its interaction adsorbents decreases markedly. In alkaline medium, thesorption capacity (h%) of Co(II) are ranged between 78.15%d 99.9%, while for Cu(II) were 62.99–99.8%. the increase insorption capacity obtained by increasing pH of the medium istributed to increase in solubility of the two metal ions. Thecrease in solubility is attributed to formation of soluble metalmplexes of Co(NH3)6

2+ and Cu(NH3)42+ [27], and the increase of

gative charged sites on adsorbents surface. Comparing thetained results of metal removal efficiency in neutral and alkalineedia showed their increasing trend by increasing pH of theedium from 7 (neutral) to 9 (alkaline).

The results in Table 1 showed that chitosan has the highestsorption efficiency in the alkaline medium reached to 99.4% for(II) and 99.8% for Cu(II) ions. While in neutral medium, chitosanhibited the lowest metal removal efficiency. Glycine modified

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chitosan showed moderate to high metal removal efficiency inboth media. The metal removal efficiency by glycine modifiedchitosan for Co(II) at pH 9 was 94.1% and 95.4% for Cu(II) ions,respectively. That was attributed to the high availability of NH2

groups in the alkaline medium. Furthermore, the precipitationprocess takes place in the alkaline medium, which increased theefficiency markedly. While, chloroacetic acid modified chitosanshowed low adsorption efficiency toward Cu(II) and Co(II) ions.That was attributed to the unavailability of the biosorbent foradsorption of metal ions, due to the linkage formed betweenClCH2– and H2N– groups in the chemical structure of thechloroacetic acid modified chitosan. This linkage decreases theavailable amino groups which responsible for metals ionsadsorption. On the other hand, the metal removal efficiencyincreased by chloroacetic acid modified chitosan in alkalinemedium than performed in neutral medium. That can be attributedto the breakdown of the –CH2Cl and –NH2 linkage.

3.4. Effect of contact time

The contact time defined as the time of immersing thebiosorbents in the metal ion solution. The influence of biosorbentstoward the immersion time is determined by the stability of themetal complex formed during the adsorption process between themetal ions and the biosorbents. Highly stable metal/biosorbentcomplexes associated by high metal adsorption efficiency, whilelow stable metal/biosorbent complexes dissociated in the medium,and consequently decreases the adsorption efficiency by time.

For cobalt complexes in neutral and alkaline medium, theremoval percent was decreased by increasing the immersion timeof the biosorbents. That can be attributed to the weak complexa-tion tendency of cobalt ions and the different biosorbents. Table 1showed that the concentration of cobalt ions decreased consider-ably in the initial time of adsorption process (t = 20 min). While,the gradual increase in immersion time increase the remainingconcentrations (Ce) of the metal ions after adsorption process. Thatcan be attributed to the weak Co(II)/biosorbents bonds, whichdissociate after short time of metal complex formation.

In case of copper ions, the formed complexes between copperions and chitosan and chitosan–glycine biosorbents are stablecomplexes. That is due to the decrease of Ce by increasing theimmersion time. While, in case of chitosan–chloroacetic acidmodified polymer, the stability of the metal complex decreasedconsiderably. That is due to the shielding of NH2 groups in thebiosorbent. In addition, the high electronegativity of chloridesubstituent decreases the participation of the lone-pair ofelectrons of NH2 groups, which decreases the stability of theformed complex, Fig. 3a–d.

3.5. Adsorption kinetics

The kinetic parameters were studied using 250 ppm of Cu(II)and Co(II) in pH 7 and 9, in presence of 0.5 gL�1 adsorbent, at 25 8C.The remained concentrations of Cu(II) and Co(II) were analyzedduring time intervals of: 20, 40, 60, 80, and 100 min during theadsorption process. The obtained data were processed usingseveral adsorption models including: pseudo first order kinetic,pseudo second order kinetic, first order reversible reaction modeland intraparticle diffusion model [28]. These models describe theadsorption of transition metal ions onto the different biosorbents.The data were fitted according to the pseudo second order kineticsand the intraparticle diffusion model as potential models for thebehavior of Cu(II) and Co(II) adsorption.

Table 2 represents the obtained adsorption kinetic parametersof pseudo second order kinetic model. The correlation coefficients(R2) were around unity as shown in Fig. 4, which indicates that the

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(a) (b)

(d)(c)

Fig. 3. Effect of immersion time on the adsorption efficiency (h%) of the different biosorbents in presence of (a) Cu(II) at pH = 7; (b) Cu(II) at pH = 9; (c) Co(II) at pH = 7; (d)

Co(II) at pH = 9.

N.A. Negm et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx 5

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adsorption of Cu(II) and Co(II) metal ions on the differentbiosorbents follow the pseudo second order rate expression. Thatindicates the adsorption of the tested metal ions on the differentbiosorbents depends on both the concentration of the metal ionand also the amount of the added biosorbents [29].

The intraparticle diffusion model commonly divides theadsorption process into three stages: the rapid surface adsorptionstage, the gradual inward diffusion stage and the final equilibriumstage. Plotting the adsorption capacity (qt) verses square root ofadsorption time (t1/2) gave characteristic curves with threeperiods. These periods are attributed to the adsorption stages ofthe exterior surface, interior surface, and equilibrium, respectively,as shown in Fig. 5.

Intraparticle diffusion model describes three stages of metaladsorption process by adsorbents. In the first stage, adsorption takesplace on exterior surface of adsorbent until the exterior surface issaturated by metal ions. The second stage takes place by entering theadsorbed metal ions into pores of adsorbents within the particle.When the metal ions diffused into adsorbent pores, the diffusionresistance increased due to crowding, and consequently the

Table 2Kinetic parameters for pseudo-second-order equation.

Biosorbent Co (pH 7) Co (pH 9)

qe (mg g�1) k2 (g mg�1 min�1) qe (mg g�1) k2 (g m

Chitosan 115.4 0.0044 247.3 0.0247

Chitosan–chloroacetic acid 59.1 0.0017 193.1 0.0048

Chitosan–glycine 82.9 0.0029 234.9 0.0030

Please cite this article in press as: N.A. Negm, et al., J. Ind. Eng. Che

diffusion rate decrease. The third stage is the equilibrium betweenthe metal ions in the solution and the adsorbed ions. This stage isvery slow due to the decrease of metal ions concentration in thesolution. Inspection of Fig. 5a–d showed two different characteristicsfor Co(II) and Cu(II) metal ions adsorption. In case of Co(II) metalions, it is clear that the adsorption in the first stage occurred in faststep. That leads to saturation of the adsorbent surface, and then therate of adsorption decreases considerably. The third step occurred atlonger time with very small rate. The gradual decrease in theadsorption capacity of the adsorbent at the third stage indicates thedesorption of Co(II) ions to the medium. Desorption of Co(II) ionsindicates the weak bond between the adsorbent and the metal ions.That behavior is inverted in case of Cu(II) ions adsorption. Theadsorption capacity increased gradually by time, indicating thesuccessive adsorption of Cu(II) ions on the adsorbent surface. Thatindicates the strong bond formed between the adsorbent and metalions [30]. The intercepts (C) in Fig. 5a–d are not equal to zero(Table 3), which indicates that the intraparticle diffusion model isthe controlling model to determine the kinetics of the adsorptionprocess [2].

Cu (pH 7) Cu (pH 9)

g�1 min�1) qe (mg g�1) k2 (g mg�1 min�1) qe (mg g�1) k2 (g mg�1 min�1)

196.08 0.0008 249.91 0.0220

175.12 0.0010 165.48 0.0038

165.91 0.0014 281.28 0.0002

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326 3.

327

328 ad329 ar330 Ha331 La332 m333 tio334 us335 m

336337338339340341342343344345346

Fig. 4. The pseudo-second-order kinetic model of: (a) Co–chitosan alkaline medium, (b) Co–chitosan neutral medium, (c) Cu–chitosan alkaline medium (d) Cu–chitosan

neutral medium. The different metals in alkaline and neutral medium; compound (I): chitosan–chloroacetic acid biosorbent, compound (II): chitosan–glycine biosorbent.

Figalk

N.A. Negm et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx6

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6. Adsorption isotherms

There are several adsorption isotherms and models describe thesorption of metal ions on the different adsorbent systems. Thesee: Freundlich isotherm, Brunauer–Emmer–Teller (BET) model,lsey isotherm, Flory–Huggins isotherm, Temkin isotherm, andngmuir isotherm. Calculation of adsorption data using severalodels and isotherms revealed that the system under investiga-n obeys Langmuir adsorption isotherm. Langmuir isotherm wased to analyze the adsorption equilibrium data of Co(II) and Cu(II)etal ions on the targeted adsorbents. Langmuir adsorption

. 5. The intraparticle diffusion kinetic model of: (a) Co–chitosan alkaline medium,

aline medium; compound (I): chitosan–chloroacetic acid biosorbent, compound (I

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isotherm describes the adsorption of metal ions on the adsorbentsas monolayer, and that adsorption takes place at specifichomogeneous sites [31]. Linear plots of Langmuir adsorptionisotherm are shown in Fig. 6a–d. Adsorption isotherm constants forLangmuir model determined in this work are given in Table 4.

It can be seen that the equilibrium data for M(II) adsorption onchitosan and its derivatives fit the Langmuir model [30], whichindicated that M(II) adsorption on the these adsorbents was amonolayer adsorption process occurring at specific homogeneoussites [32]. The Langmuir monolayer adsorption capacities (qmax)and the Langmuir equilibrium constant kL values for chitosan were

(b) Co–chitosan neutral medium, (c) Cu–chitosan neutral medium, (d) Cu–chitosan

I): chitosan–glycine biosorbent.

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364 365

366367

368

369370371

372

373374375376377378379380381382

Table 3Intraparticle diffusion model constants for the adsorption of Co(II) and Cu(II) onto chitosan and its derivatives.

Biosorbent Co (pH 7) Co (pH 9) Cu (pH 7) Cu (pH 9)

Ki (mg g�1 min�1/2) C Ki (mg g�1 min�1/2) C Ki (mg g�1 min�1/2) C Ki (mg g�1 min�1/2) C

Chitosan 0.60 79.88 2.66 688.65 0.18 23.36 2.98 734.34

Chitosan–chloroacetic acid 0.07 12.89 0.56 117.71 0.20 23.61 0.70 104.79

Chitosan–glycine 0.44 47.63 0.48 124.52 0.24 28.65 0.06 4.62

Table 4Parameters of Langmuir adsorption isotherm.

Biosorbent pH Metal ions R2

Chitosan 7 Co(II)

Cu(II)

0.999

0.999

9 Co(II)

Cu(II)

1

1

Chitosan–glycine 7 Co(II)

Cu(II)

0.999

0.999

9 Co(II)

Cu(II)

0.999

1

Chitosan–chloroacetic acid 7 Co(II)

Cu(II)

0.999

0.999

9 Co(II)

Cu(II)

0.999

0.999

N.A. Negm et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx 7

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higher than the values of compounds I and II, indicated that themodification process reveres influenced M(II) adsorption equilib-rium.

3.7. Thermodynamic parameters

In adsorption studies, the energetic values of entropy andenthalpy in addition to adsorption free energy must be taken inconsiderations to determine the adsorption process. Values ofthermodynamic parameters are the actual indicators for practicalapplicability of metal ions adsorption process. The amounts ofCu(II) and Co(II) ions adsorbed by the different biosorbents underconsideration at different temperatures 25, 35 and 45 8C, atequilibrium have been used to obtain thermodynamic parametersfor the adsorption process. The dependence of Langmuir constant(kL) with temperature was used to predict the thermodynamicparameters associated with the adsorption process [33]. Thestandard Gibbs free energy change (DG8), standard enthalpychange (DH8) and standard entropy change (DS8) were determinedby using the following equations:

DG� ¼ �RTln kL

ln kL ¼ �DG�

RT¼ �DH�

RTþDS�

R

The plot of ln kL as a function of 1/T shown in Fig. 7 yields astraight line from which DH8 and DS8 are calculated from the slope

Fig. 6. Langmuir adsorption isotherm of: (c) Cu–glycine chitosan derivative in alkaline me

derivative in alkaline medium, (b) Co–glycine chitosan derivative in neutral medium.

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and intercept, respectively. The values of standard Gibbs freeenergy change (DG8), standard enthalpy change (DH8) andstandard entropy change (DS8) are presented in Table 5. Theoverall free energy changes during the adsorption process at 25, 35and 45 8C are negative, corresponding to a spontaneous andthermodynamically favorable process of adsorption of Cu(II) andCo(II) ions by the synthesized biosorbents. The positive values ofthe enthalpy changes indicate that the adsorption is endothermicin nature. Endothermic adsorption of Cu(II) and Co(II) ionsbiosorbents has been reported [34]. The negative and infinite

dium, (d) Cu–glycine chitosan derivative in neutral medium, (a) Co–glycine chitosan

m. (2014), http://dx.doi.org/10.1016/j.jiec.2014.03.015

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

401

402

403

404

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407

408

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411

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418

419

420

421

422

423

424

Table 5Thermodynamic parameters for the adsorption of Cu(II) and Co(II) ions on the modified biosorbents.

Biosorbent pH Metal ions Temperature KL DG8 DH8 DS8

Chitosan–glycine 7 Co 25 0.121 �5.23 14.08 �0.0296

35 0.144 �4.96

45 0.173 �4.64

9 Co 25 0.100 �5.71 23.89 �0.0606

35 0.117 �5.50

45 0.184 �4.48

7 Cu 25 0.271 �3.24 24.78 �0.0719

35 0.325 �2.88

45 0.510 �1.78

9 Cu 25 0.310 �2.90 24.83 �0.0732

35 0.372 �2.53

45 0.584 �1.42

Chitosan–chloroacetic acid 7 Co 25 0.091 �5.94 24.26 �0.0611

35 0.108 �5.70

45 0.169 �4.70

9 Co 25 0.044 �7.74 24.88 �0.0571

35 0.053 �7.52

45 0.083 �6.58

7 Cu 25 0.028 �8.86 25.02 �0.0539

35 0.034 �8.66

45 0.053 �7.77

9 Cu 25 0.150 �4.70 25.03 �0.0678

35 0.181 �4.38

45 0.284 �3.33

Fig. 7. Plot of ln kL against 1/T for the adsorption of Cu(II) and Co(II) on: (A) chitosan–

glycine biosorbent (^: Co(II), pH = 7; &: Co(II), pH = 9; ~: Cu(II), pH = 7; � Cu(II),

pH = 9); (B) chitosan–chloroacetic acid biosorbent (^: Co(II), pH = 7; &: Co(II),

pH = 9; ~: Cu(II), pH = 7; � Cu(II), pH = 9).

N.A. Negm et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx8

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JIEC 1961 1–9

Please cite this article in press as: N.A. Negm, et al., J. Ind. Eng. Ch

small entropy change (DS8) values of the adsorption process on thesynthesized biosorbents reflect the affinity of the differentbiosorbents for Cu(II) and Co(II) ions by different degreesdepending on their chemical structures.

3.8. Mechanism of adsorption

The percent removal (h%) of metal ions on the active groupssuch as OH and NH2 depends on the molecular structure of thesorbent compounds, which bind to the metal ions by coordinationbonds. The proposed adsorption of the transition metals by thechitosan and its derivatives were represented in Q2Fig. 8. In ourresults, we found that the percent removal of the different metalions on the surfaces of compounds (I) and (II) are lower thanchitosan itself. That can be attributed to the formation of the intra-molecular hydrogen bonding between the substitution groups andunit monomer of chitosan, which leads to the decrease in the freeactive groups such as OH and NH2 on the chitosan. That causes alower in the percent removal of metal ions. While in chitosan freewhich reaching by free active groups, ceasing a higher adsorptioncapacity than its derivatives.

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