development of nano-hydroxyapatite/chitosan composite for cadmium ions removal in wastewater...

Journal of the Taiwan Institute of Chemical Engineers xxx (2013) xxx–xxx

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JTICE-775; No. of Pages 7

Energy and Environmental Science and Technology

Development of nano-hydroxyapatite/chitosan composite forcadmium ions removal in wastewater treatment

Taher A. Salah a,*, Ahmad M. Mohammad b,c, Mohamed A. Hassan a,Bahgat E. El-Anadouli b,*a Nanotechnology Laboratory, Regional Center for Food and Feed, Agriculture Research Center, Giza, Egyptb Chemistry Department, Faculty of Science, Cairo University, PO 12613 Giza, Egyptc Department of Chemical Engineering, Faculty of Engineering, The British University in Egypt, PO 11837 Cairo, Egypt

A R T I C L E I N F O

Article history:

Received 3 June 2013

Received in revised form 8 September 2013

Accepted 20 October 2013

Available online xxx

Keywords:

Hydroxyapatite nanorods

Chitosan

Wastewater

Regeneration

Cadmium

Adsorption isotherms

A B S T R A C T

Hydroxyapatite nanorods (nHAp) and nano-hydroxyapatite chitosan composites (nHApCs) were

proposed for the removal of Cd2+ ions in water treatment. The high resolution transmission electron

microscopy, energy dispersive X-ray analysis, X-ray diffraction spectrophotometer, Fourier transform

infrared spectrophotometer and Zeta potential measurements were all employed to reveal the

morphology, composition, crystal structure, functionality and stability of the prepared sorbents (nHAp

and nHApCs). The potential of these synthesized sorbents to remove Cd2+ ions from aqueous solutions

was investigated in batch experiments, where several parameters such as the sorbate/sorbent’s contact

time, initial Cd2+ ions concentration, pH and sorbent dosage were investigated. The equilibrium

concentration of Cd2+ ions was identified by the atomic absorption spectrophotometry. The Cd2+ uptake

was quantitatively evaluated using the Pseudo second order kinetic equation, Freundlich and Langmuir

models. It is remarkable that with these sorbents (nHAp, nHApCs), up to 92% of Cd2+ could be removed

‘‘100 ppm initial cadmium concentration in 200 mL, 0.4 g nHAp and pH = 5.600. The sorption capacity of

nHAp and nHApCs to Cd2+ was 92 and 122 mg/g respectively, which appears excellent when compared to

other previously reported materials. This capacity could be enhanced by increasing initial Cd2+

concentration and the nHAp/Cd2+ mass ratio. Furthermore, the sorbents’ regeneration was addressed

and found promising.

� 2013 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

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jou r nal h o mep age: w ww.els evier . co m/lo c ate / j t i c e

1. Introduction

There has long been a great deal of effort to eliminate or at leastreduce the concentration of heavy metals such as cadmium,chromium, mercury, lead, copper, manganese, etc. from wastewa-ter coming out of natural and/or industrial streams [1]. Of thesemetals, cadmium (Cd) represents a keystone for recent endemicdiseases in developing countries. It naturally exists in the earth’scrust as a mineral combined with other elements such as oxygen(cadmium oxide), chlorine (cadmium chloride), or sulfur (cadmi-um sulfide) [2]. Like other heavy metals, cadmium can beintroduced into surface waters from industrial effluents, whichultimately makes drinking risky [1]. Not only this, but it can alsoenter the human body through eating, and breathing. When

* Corresponding authors. Tel.: +202 3567 6603/+202 3567 660307/

+201 001030534; fax: +202 3568 5799.

E-mail addresses: [email protected] (T.A. Salah), [email protected]

(A.M. Mohammad), [email protected] (M.A. Hassan),

[email protected] (B.E. El-Anadouli).

Please cite this article in press as: Salah TA, et al. Development of nanin wastewater treatment. J Taiwan Inst Chem Eng (2013), http://dx.

1876-1070/$ – see front matter � 2013 Taiwan Institute of Chemical Engineers. Publis

http://dx.doi.org/10.1016/j.jtice.2013.10.008

entering the human body, most of cadmium goes directly to kidneyand liver and remains there for many years causing serious damageto them [2]. Itai-itai, renal damage, emphysema, hypertension andtesticular atrophy are all harmful diseases of cadmium [3]. Themost common industries releasing cadmium in their effluents arethose of metal plating, cadmium–nickel batteries, phosphatefertilizer, mining, pigments, stabilizers and alloys [4].

Several approaches have been employed to remove heavy metalions from wastewater such as the chemical precipitation,adsorption, cations-exchange, reverse osmosis, electrodialysis,electrochemical reduction, etc. [5]. Generally, the adsorptionprocess has been proved convenient in terms of cost, simplicityand flexibility, and hence has industrially been preferred [6]. In thisregard, several sorbents have been recommended for the removalof Cd2+ ions, such as the activated carbon, and mesoporous andnanoporous materials as clays, zeolites, chitosan and apatite [7].Nevertheless, the apatite family has demonstrated an ideal andefficient sorption’ capability [8].

The general formula of apatite is M10(XO4)6Y2 (M = Ca2+, Sr2+,Pb2+, Cd2+, Ba2+, Zn2+, Mg2+, . . ..; XO4 = PO4

3�, VO43�, AsO4

3�, . . .;Y = F�, OH�, Cl�,. . .) [9]. Hydroxyapatite (Ca10(PO4)6(OH)2, HAp),

o-hydroxyapatite/chitosan composite for cadmium ions removaldoi.org/10.1016/j.jtice.2013.10.008

hed by Elsevier B.V. All rights reserved.


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T.A. Salah et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (2013) xxx–xxx2

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which is a member of the apatite mineral family has shown aremarkable sorption efficiency for long-term containments. This isbasically emerged from its high sorption efficiency for heavymetals, low water solubility, high stability under reducing andoxidizing conditions, availability and low cost.

Recently, biological molecules like chitin, chitosan, lignin havealso been investigated for the removal of toxic metals [10]. Theycould possess amazingly sorption capability, good mechanicalstrength, biocompatibility and biodegradability. Chitosan biopo-lymers (Cs), in particular, which are non-toxic, hydrophilic,biocompatible, and biodegradability exhibited interesting andeffective sorption efficiency for heavy metals [11,12].

With the recent revolution of nanoscience and the advancedsophistication in the tools of characterization, shrinking theparticle size of the sorbents is expected to influence the sorptioncapacity and further assist in developing commercial nano-sorbents for wastewater treatment. In fact, nanotechnology hasa significant impact to deal with legacy environmental pollutionand to predict and prevent future environmental problems [13]. Inthis regard, Nutt et al. [14] have explored a fascinating catalyticactivity for palladium/gold nanoparticles (with diameters less than20 nm) toward the hydro-dechlorination of trichloroethylene inwater, which is a common contaminant in groundwater. Alterna-tively, Mayo et al. [15] have used magnetic properties of iron oxidenano-crystals to efficiently remove arsenic from drinking water. Inaddition, nanomaterials have been proved excellent to improve theeffectiveness and efficiency of water treatment, remediatecontaminated water, and increase the sensitivity of detection ofvarious water toxic contaminants [16–22].

Herein, the efficiency of hydroxyapatite nanorods (nHAp) andhydroxyapatite nanorods/chitosan (nHApCs) composites for Cd2+

ions removal from aqueous solution is investigated. Severalparameters like the Cd2+/sorbent contact time, Cd2+ initialconcentration, pH and adsorbent dosage are examined in orderto evaluate a reasonable optimization for the sorption efficiency.The pseudo second order kinetic equations, Freundlich and theLangmuir models were employed in fitting the experimentalisotherms. Furthermore, the reversibility of Cd2+ sorption/desorp-tion is checked in a way to ensure a sorbent’ regeneration.

2. Material and methods

2.1. Sorbent preparation

All chemicals used in this investigation were of analytical gradeand used without further purification treatment. Calcium nitrate,0.8 mol, (Ca(NO3)2�4H2O, Sigma-Aldrich No. 31218) and phospho-ric acid, 0.479 mol, (H3PO4, Sigma-Aldrich No. 04107) in thestoichiometric molar ratio of 1.67 (Ca/P) were used in thepreparation of nHAp powder by the sol–gel method, and ammoniasolution assisted in the adjustment of solution pH at 10 � 0.05.Typically, H3PO4 was slowly added (3 mL/min) to a solution ofCa(NO3)2�4H2O previously stirred vigorously at constant temperatureof 25 8C.

10Ca2þ þ 6H2PO�4 þ 14OH�! Ca10 PO4ð Þ6 OHð Þ2 #

þ 12H2O pH ¼ 10ð Þ

The suspension was left under vigorous stirring for 16 h, andafter 24 h of aging, the precipitate was rinsed with deionized waterand dried at 100 8C under vacuum.

On the other hand, the nHApCs composite was preparedsimilarly where, phosphoric acid was dropwisely added to amixture of aqueous solution of Ca(NO3)2�4H2O and chitosan(Sigma, No. 48165) (dissolved in acetic acid, HAc).

Please cite this article in press as: Salah TA, et al. Development of nanin wastewater treatment. J Taiwan Inst Chem Eng (2013), http://dx

Cs � NH2 þ HAcðAcidic mediumÞ Ð Cs � NHþ3 þ Ac�

Cs � NHþ3 þ OH�! Cs � NH2 # þ H2OðBasic mediumÞ

The (w/v) ratio of Cs/Ca(NO3)2�4H2O solution was (0.25 g/100 mL) while keeping the stoichiometric ratio of Ca to P at 1.67.The precipitate was rinsed with water and dried at 60 8C.

2.2. Materials characterization

Several characterization tools were employed in the evaluationof the morphology, crystal structure, functionality and stability ofthe sorbents prepared. For the purpose of imaging and crystalstructure revelation, a high resolution transmission electronmicroscope (HR-TEM, Tecnai G20, FEI, Netherland) supportedwith an energy dispersive X-ray (EDX) unit was used. Two differentmodes of imaging were employed; the bright field at 200 kV usingLaB6 electron source gun and the diffraction pattern imaging.Before imaging, the HAp particles were deposited from a diluteaqueous suspension onto Cu grids with the support of a carbonfilm.

The crystal structure was identified by the X-ray diffraction(XRD—X’Pert PRO PANalytical, Netherland) operated at 45 kV and30 mA using Cu Ka radiation (l = 1.5404 A) and high score plussoftware.

Fourier Transform Infrared (FTIR, FT/IR—6100 Jasco, Japan)spectra of the solid residues were measured over a range of 4000–400 cm�1 at room temperature by dispersing the samples in KBr.

Zeta potentials (Zetasizer Nano S, Malvern Instruments, UK) ofnHAp and nHApCs aqueous suspensions of different pH (2–11)were measured to evaluate the point of zero charge (PZC) of thesecolloidal suspensions. Before measurements, nHAp and nHApCswere dispersed in deionized water (Milli-Q Millipore, Billerica, MA,USA) and the pH was adjusted using NaOH and HCl and thesuspension was left under sonication (Ultrasonicator, SB-120DTN,Taiwan) for 10 min.

2.3. Sorption experiment

2.3.1. Determination of the sorption capacity

The batch equilibrium technique was employed at roomtemperature. Cadmium ions solutions with different concentra-tions were prepared by dissolving CdCl2�2H2O (Eastern finechemicals, Italy) in deionized water. Typically, a certain amountof nHAp, nHApCs is added to 200 mL of the Cd2+ solutions afteradjusting the pH. Next, the mixture was shaken (Shaker, Lab-line4625-1CE, USA) at a speed of 300 rpm for different times. After aspecific time, the sorbents (nHAp, nHApCs) were filtered from thesolution by a 0.2 mm syringe filter. The final Cd2+ concentrationwas measured by atomic absorption spectrophotometry (Analytik-jina Zeenit 700p, Germany).

The equilibrium sorption capacity, qe, of nHAp and nHApCs,which is defined by the equilibrium amount (in mg) of Cd2+ ionsadsorbed per gram of sorbent (simply the unit will be noted as mg/g), was calculated using the general equation [23]:

qe ¼C0 � Ceð ÞV

M(1)

Where C0 and Ce represent, respectively, the Cd2+ concentrationsbefore and after adsorption (mg/L), V is the volume of the Cd2+

solution (L) and M is the amount (g) of the sorbent used in thereaction mixture.

2.3.2. Effect of contact time

In order to reveal the influence of contact time, 0.1 g of thesorbent (nHAp, nHApCs) was added to 200 mL of a Cd2+ solution(100 mg/L) and the mixture was shaken at room temperature for

o-hydroxyapatite/chitosan composite for cadmium ions removal.doi.org/10.1016/j.jtice.2013.10.008


T.A. Salah et al. / Journal of the Taiwan Institute of Chemical Engineers xxx (2013) xxx–xxx 3

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different periods (5–90 min). Next the regular procedure offiltration and analysis was employed to calculate the sorptioncapacity.

The pseudo-second-order reaction kinetics is used to determinethe sorption rate constant.

t

qt

¼ 1

kq2e

þ t

qe

(2)

where qt is the sorption capacity (mg/g) at any given time t (min),qe is the equilibrium sorption capacity (mg/g) and k is the secondorder reaction rate constant of adsorption (g/mg min). Thefollowing expression denotes the sorption rate h (mg/g min) [24]:

h ¼ kq2e (3)

2.3.3. Effect of initial Cd2+ concentration

In order to investigate the influence of the initial Cd2+

concentration on the adsorption kinetics, 0.1 g of nHAp was addedto aqueous Cd2+ ions solutions of various concentrations (100, 200,300, 400 and 500 mg/L) and the regular procedure of shaking,filtration and analysis was followed. The data were fitted accordingto the Freundlich and Langmuir adsorption isotherms, which areoften used to describe the adsorption of solutes from aqueoussolutions.

The Freundlich equation proposes an empirical model foradsorption on heterogeneous surfaces with the form:

lnqe ¼ lnk f þ1

n

� �lnCe (4)

where qe is the equilibrium sorption capacity (mg/g), Ce is theequilibrium concentration of metal ion (mg/L), and (kf and n) arethe Freundlich isotherm constants which are temperature depen-dent [25].

On the other hand, the Langmuir isotherm assumes amonolayer adsorption of the adsorbate onto a finite number ofidentical sites of the adsorbent surface [26]. Mathematically, themodel is expressed by the following equation:

Ce

qe

¼ 1

bqmax

þ 1

qmax

� �Ce (5)

where qe is the equilibrium sorption capacity (mg/g), Ce is theequilibrium concentration of metal ion (mg/L), qmax (mg/g) is themaximum sorption capacity, and b (L/mg) is the Langmuir constantwhich correlates to the energy of adsorption [25].

Fig. 1. (A) TEM image of nHAp prepared as described earlier in Section 2.1. The inset of Fi


2.3.4. Effect of pH and sorbent dosage

Finally, the effect of pH in the range of 3–11 and the sorbentdosage from 0.025 to 0.4 g on the sorption capacity wasinvestigated in a regular batch equilibrium adsorption experiment.

2.4. Desorption study

One of the important criteria that should be investigated for agiven sorbent is its potential ability to be regenerated. We haveinspected the desorption process of Cd2+ out of the nHAp’ surface.In this experiment, 0.1 g of nHAp was added to 200 mL Cd2+

solution (100 mg/L, pH = 5.8) and shaking continued for 2 h. Thesorbent residue was washed with deionized water and added to200 mL of Ca(NO3)2�4H2O solution (pH = 3.0) [27] and the mix wasleft for 4 h under magnetic stirring. After filtration, the filtrate wasanalyzed to determine the released Cd2+ concentration.

3. Results and discussion

3.1. Characterization of sorbents

Fig. 1A displays a typical TEM image of the nHAp particlesprepared as described in Section 2.1. As obviously seen, nHApappeared in the form of thin short nanorods �5 nm in diameter and20–50 nm in length. Interestingly, there was a distinct separationbetween these nHAp nanorods with a little aggregation, whichmight result instantly in the preparation procedure before the TEMmeasurements. The inset of Fig. 1A represents the electrondiffraction pattern of nHAp where polycrystalline diffraction ringsappeared corresponding to the crystallographic planes (0 0 2) and(2 1 1) of nHAp crystals. On the other hand, the EDX analysis(Fig. 1B) informed about the relative ratio of calcium tophosphorus (stoichiometric ratio of Ca/P was 1.67) in nHAp,which agreed perfectly with the initial mixing ratio of the startingmaterials.

The XRD was further employed to reveal the crystallography ofthe prepared sorbents (see Fig. 2 for the glancing incident X-raydiffraction pattern of nHAp, Cs and nHApCs). Interestingly, nHApexhibited several signals at 2u = 25.88, 31.88, 32.28, 34.08, 39.78 and49.58, corresponding to the diffraction planes (0 0 2), (2 1 1),(1 1 2), (2 0 2), (1 3 0) and (2 1 3), respectively (JCPDS no.01-073-8417). Two well-defined signals have been appeared for Cs at2u = 20.88 and 10.58. Surprisingly, the nHApCs composite forma-tion did not alter much the crystallographic features of nHAp,nevertheless, the signals appeared shorter and broader. In addition,

g. 1A shows the electron diffraction pattern of nHAp. (B) The EDX analysis of nHAp.



Fig. 2. X-ray diffraction pattern of nHAp, Cs, and nHApCs. The preparation

procedure descried earlier in Section 2.1 was followed to prepare these materials.


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the signals characterizing Cs have almost disappeared from thecomposite, which agrees with previous expectation for certainHAp/Cs ratios [28,29].

Next, FTIR spectra of nHAp, chitosan and nHApCs weremeasured (see Fig. 3) to further confirm the deposition of thesematerials. A typical FTIR for chitosan is depicted in Fig. 3a.Thesignals at 3421 cm�1 corresponding to stretching (–NH), 2900 and1388 cm�1 corresponding to stretching and bending (–CH) grouprespectively, 1643 cm�1 for (C–N) group, and 1039 cm�1 forstretching (C–O–C) group. On the other hand, the nHAp spectrum(Fig. 3b) displays signals at 3450 and 1643 cm�1 were assigned tostretching (s) and bending (b) hydroxyl group, respectively. Theabsorption bands observed at 1036 and 865 cm�1 were assigned toasymmetric stretching (as) while those at 602 and 566 cm�1 forsymmetric stretching of phosphate group. The signals of nHAp/Cscomposite coincided at a great extent with the major absorbancesignals of nHAp. However, the signals at 2900 and 1388 cm�1

corresponding to stretching and bending (–CH) group appeared inthe nHAp/Cs complex verifying its formation (see Fig. 3c).

On the other hand, the zeta-potential measurements for nHApand nHApCs (Fig. 4) revealed a PZC at pH of 7 and 8 for nHAp andnHApCs, respectively. This means that at pH lower than 7, both ofnHAp and nHApCs will carry positive charges and above pH of 8,both will carry a negative charge. However, in between (pH = 7–8),

Fig. 3. FTIR spectra of (a) chitosan, (b) nHAp and (c) nHApCs. The preparation

procedure descried earlier in Section 2.1 was followed to prepare these materials.


of nHAp will be negatively charged but nHApCs will be positivelycharged. This will definitely help in understanding the nature ofbinding Cd2+ to both of nHAp and nHApCs. This, in fact, anticipatesa different adsorption efficiency for Cd2+ ions in solutions ofdifferent pHs, and presumably, at lower pH values (the adsorbentsare positively charged), the cation exchange mechanism willpredominate, while at higher pH values (the adsorbents arenegatively charged), the driving force for Cd2+ removal will mainlybe electrostatic. From another view, the different PZC values fornHAp and nHApCs further confirm the composite formation.

3.2. Sorption study

3.2.1. Effect of contact time

The isotherm of Cd2+ ions (pH = 5.6) adsorption by nHAp andnHApCs is displayed in Fig. 5A. As obviously seen, the Cd2+ ionsremoval was very fast at the beginning (within �20 min), and aslower kinetics continued next until equilibrium. Generally, wenoticed that a contact time of 90 min was sufficient to ensuresaturation in the Cd2+ ions sorption capacity by these sorbents. Inorder to investigate the rate of Cd2+ sorption, the linear form ofpseudo-second-order kinetic model was employed, where t/qt wasplotted versus t (see Fig. 5B). The second-order constants (k, qe, andh) for nHAp and nHApCs were evaluated from Eq. (2) and listed inTable 1. Interestingly, the pseudo-second-order kinetic model wasperfect in fitting the experimental results, where a close matchingwas attained between the experimental and calculated equilibri-um sorption. Interestingly, the uptake capacity we obtained atnHAp in this investigation was much (�4 times) higher than thosereported earlier [30]. The equilibrium sorption capacity of thenHApCs composite was ca. 1.33 times higher than that of nHAp.This is likely because the availability of a large number of –NH2

groups capable of coordinately binding with Cd2+ ions.

3.2.2. Effect of initial Cd2+ concentration

We have so far calculated the Cd2+ ions sorption capacity ofnHAp but at a single initial concentration (100 mg/L) of Cd2+ ions.As we know, the initial concentration of Cd2+ ions may be differentin wastewater treatment and this may influence the sorptionkinetics. To investigate this, a series of several solution containingdifferent concentrations of Cd2+ ions was prepared and thesorption capacity of 0.1 g nHAp for Cd2+ ions was evaluated.Fig. 6 indicated a significant increase in the sorption capacity ofnHAp for Cd2+ ions with the initial Cd2+ ions concentration. Whenthe initial Cd2+ ions concentration increased from 100 to 500 mg/L,the uptake capacity of nHAp increased from (91.94 � 0.16) to(209.6 � 5.58) mg/g. A reasonable explanation for this phenomenonmay originate from the diffusion constrains of the Cd2+ sorptionprocess. At low initial Cd2+ ion concentration, the ratio of Cd2+ to the

Fig. 4. Zeta-potential measurements for nHAp and nHApCs suspensions at different

pHs.



Fig. 5. (A) Effect of contact time on the sorption capacity of Cd2+ ions (pH = 5.6) onto nHAp and nHApCs, (B) the linear fitting of the experimental data using the pseudo-

second-order kinetic equation (Eq. (2)).


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number of available adsorption sites or ions exchange site is small,which leads to mass transfer resistance between the aqueous andsolid phases thus decreased the uptake. A higher initial concentrationprovided an important driving force to overcome the mass transferresistances of the pollutant thus increased the uptake [31].Alternatively, the reversibility of the sorption process of Cd2+ ionson nHAp may explain the dependence of the Cd2+ ions uptake on theinitial concentration of Cd2+ ions. If this happened, the adsorptionprocess will be encountered by desorption process at a certainmoment depending on the initial concentrations of Cd2+ ion.

Kinetically, the Freundlich isotherm (Eq. (4)) was used toaddress this influence of the Cd2+ uptake on the initial Cd2+

concentration. The Freundlich parameters, kf and n, were deter-mined by plotting ln qe versus ln Ce (see Fig. 7A). The values of kf

and 1/n were 26.55 and 0.33, respectively. The small numericalvalue of 1/n (<1) reveals a physical nature for the bonding betweenadsorbent and adsorbate [32].

On the other hand, the Langmuir isotherm, considering the caseof a monolayer adsorption process of molecules on solid surfaces,may offer a better fitting for the experimental data of Cd2+ ionsadsorption on nHAp. The model basically assumes the existence ofa certain number of active sites on the adsorbent to which the samenumber of particles bind (1:1 ratio). In addition, the model ignoresthe dependency of occupying a specific site on the status of theadjacent site. Furthermore, it describes adsorption processeswhere no interaction between the sorbate species occurs on siteshaving the same sorption energies regardless the surface coverage.To investigate the validity of this model, a plot of Ce/qe against Ce isdesigned (see Fig. 7B) and the linear fitting was done. Themaximum sorption capacity, qm, was calculated from Langmuirisotherm as 243.90 mg/g, while Langmuir constant b was 0.010 L/mg. The maximum sorption capacity represented the monolayercoverage of sorbent with sorbate [33].

3.2.3. Effect of pH

The influence of pH on the sorption process of Cd2+ ions onnHAp was studied in the pH range from 3 to 11 (see Fig. 8). The pH

Table 1The parameters obtained from fitting the sorption data of Cd2+ ions onto nHAp and

nHApCs using the pseudo-second-order equation (Eq. (2)). h ¼ kq2e and R is the

regression coefficient for the linear plot.

Sorbents k (g/mg min) qe (mg/g) h (mg/g min) R

nHAp 0.0071 92.6 � 1.18 60.6 0.9992

nHApCs 0.0039 123.5 � 0.39 60.2 0.9988


can influence the adsorption kinetics and the sorption capacity ofmetal ions on solid surfaces by changing the surface charges of theadsorbent and Cd species present at different pH as in its speciationdiagram [34]. It can also affect the number of active sites availablefor this adsorption process [35]. In this investigation, the pH of theaqueous solution of Cd2+ ions could affect its uptake by nHAp, andthe uptake increased at higher pH values. This can likely beattributed to a competition between H+ and Cd2+ ions to beadsorbed on nHAp, and at lower pH values, H+ ions are able toexclude a significant number of adsorption sites at nHAp from theCd2+ adsorption process [36,37]. At high pH values, the H+ ionscompetition disappears and the positively charged Cd2+ andCd(OH)+ ions can easily attach to the free binding sites, increasingthe Cd2+ ions uptake [38]. It is known that precipitation plays amajor role in removing of Cd2+ ions in alkaline media [39]. Thedominant Cd2+ species at pH higher than 8.0 is Cd(OH)2. Therefore,it can assumed that Cd2+ removal by nHAp was dominantlycontrolled by adsorption at pH values between 6.0–8.0, but it couldbe slightly enhanced by cadmium hydroxide precipitation at pHhigher than 8.0 [40].

3.2.4. Effect of adsorbent dosage

In a way of seeking an optimization for the adsorption processof Cd2+ ions by nHAp, the effect of nHAp dosage was investigatedand plotted in Fig. 9. As expected, the Cd2+ sorption increasedrapidly with the nHAp dosage, as a consequence of increasing theadsorption sites available for the Cd2+ ions removal. Interestingly,

Fig. 6. Effect of initial Cd2+ ions concentration on sorption capacity of nHAp sorbent

to Cd2+ ions (pH = 5.8, adsorbent dosage 0.1 g).



Fig. 7. Linear fits of experimental data of the adsorption of Cd2+ onto nHAp using (A) Freundlich, (B) Langmuir sorption isotherms.

Fig. 8. Effect of pH on the adsorption of Cd2+ ions (initial concentration = 100 mg/L)

by 0.1 g of nHAp.Fig. 9. Effect of nHAp dosage on the removal of Cd2+ ions (initial concentration

100 mg/L, pH = 5.8).


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starting with 0.4 g of nHAp could achieve a Cd2+ removal efficiencyof �92%. Although the Cd2+ removal efficiency increases with thenHAp dosage, the sorption capacity, which normalizes the Cd2+

uptake to the nHAp dosage, decreases [25]. Therefore, one shouldcustomize the process to obtain the highest possible removalefficiency for Cd2+ ions with the least amount of the nHAp dosage.

3.3. Desorption study

One of the important parameters featuring the excellentsorbents is its regeneration tendency. We have investigated thedissolution of Cd2+ immobilized on the nHAp in Ca2+ ionscontaining acidic solution (pH � 3) and found it to some extentpossible with regeneration efficiency close to 60%. Research isunderway to improve this efficiency.

4. Conclusions

This investigation highlights the effectiveness of nHAp andnHApCs adsorbents for the removal of Cd2+ ions from aqueoussolutions in wastewater treatments. The adsorption process wasinvestigated as a function of the contact time of Cd2+ ions withthe sorbents, initial Cd2+ ions concentration, pH and sorbentdosage. The kinetics of the sorption process could be fitted to apseudo-second-order reaction model, and the sorption capacityof Cd2+ by nHAp increased with the initial Cd2+ ions concentra-tion. The Freundlich and Langmuir adsorption isotherms havebeen employed to evaluate the adsorption behavior, where amaximum adsorption capacity for nHAp of 243.90 mg/g was


obtained. Interestingly, the Cd2+ ions sorption by nHApincreased with pH and nHAp dosage while the sorption capacitydecreased with the nHAp dosage. Fortunately, a regenerationefficiency of �60% could be achieved for the nHAp after theadsorption process by treating it in Ca2+ containing aqueousslightly acidic solutions.

References

[1] Hammer, Mark J. Water wastewater. Upper Saddle River, NJ: TechnologyPrentice-Hall Inc.; 1996.

[2] ATSDR. Toxicological profile for cadmium. Atlanta, GA: US Department ofHealth and Human Services; 1999 July.

[3] Ramos RL, Mendez JRR, Barron JM, Rubio LF, Coronado RMG. Adsorption ofcadmium(II) from aqueous solutions onto activated carbon. Water Sci Technol1997;35:205.

[4] Removal of Cd(II) from wastewaters. Poon CPC, Mislin H, Raverva O, editors.Cadmium in the environment. Basel, Switzerland: Birkhauser; 1986.

[5] Mohan D, Singh KP. Single- and multi-component adsorption of cadmium andzinc using activated carbon derived from bagasse—an agricultural waste.Water Res 2002;36:18. 2304.

[6] Rengaraj S, Yean KH, Kang SY, Lee JU, Kim KW, Moon SH. Studies on adsorptiveremoval of Co(II) Cr(III) and Ni(II) by IRN77 cation-exchange resin. J HazardMater 2002;185–98. B92.

[7] Ziagova M, Dimitriadis G, Aslanidou D, Papaioannou X, Tzannetaki EL, Liako-poulou-Kyriakides M. Comparative study of Cd(II) and Cr(VI) biosorption onStaphylococcus xylosus and Pseudomonas sp. in single and binary mixtures.Bioresour Technol 2007;98:65. 2859.

[8] Krestou A, Xenidis A, Panias D. Mechanism of aqueous uranium(VI) uptake byhydroxyapatite. Miner Eng 2004;17:373–81.

[9] Smiciklas I, Dimovic S, Plecas I, Mitric M. Removal of Co2+ from aqueoussolutions by hydroxyapatite. Water Res 2006;40:2267–74.

[10] Gonzalez-Davila M, Millero FJ. The adsorption of copper to chitin in seawater.Geochim Cosmochim Acta 1990;54:761–8.


http://refhub.elsevier.com/S1876-1070(13)00269-1/sbref0005




























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[11] Okuyama K, Noguchi K, Hanafusa Y, Osawa K, Ogawa K. Structural study ofanhydrous tendon chitosan obtained via chitosan/acetic acid complex. Int JBiol Macromol 1999;26:285–93.

[12] Muzzarelli RRA. Natural chelating polymers: alginic acid, chitin and chitosan.New York, NY: Pergamon Press; 1973.

[13] Hannah W, Thompson PB. Nanotechnology, risk and the environment: areview. J Environ Monit 2008;10:291–300.

[14] Esterkin CR, Negro AC, Alfano OM, Cassano AE. Air pollution remediation in afixed bed photocatalytic reactor coated with TiO2. AIChE J 2005;51:2298–310.

[15] Mayo JT, Yavuz C, Yean S, Cong L, Shipley H, Yu W, et al. The effect ofnanocrystalline magnetite size on arsenic removal. Science and technologyof advanced materials 2007;8:71–5.

[16] Nangmenyi G, Wei X, Mehrabi S, Mintz E, Economy J. Bactericidal activity of Agnanoparticle-impregnated fibreglass for water disinfection. J Water Health2009;7:657–63.

[17] Choi H, Stathatos E, Dionysiou DD. Photocatalytic TiO2 films and membranesfor the development of efficient wastewater treatment and reuse systems.Desalination 2007;202:199–206.

[18] Vickaryous WJ, Herges R, Johnson DW. Arsenic—(interactions stabilize a self-assembled As2L3 supramolecular complex. Angew Chem Int Ed2004;43:5831–3.

[19] Diallo MS, Christie S, Swaminathan P, Johnson JH, Goddard WA. Dendrimerenhanced ultrafiltration. 1. Recovery of Cu(II) from aqueous solutions usingPAMAM dendrimers with ethylene diamine core and terminal NH2 groups.Environ Sci Technol 2005;39:1366–77.

[20] Lin YH, Cui XL. Novel hybrid materials with high stability for electricallyswitched ion exchange: carbon nanotube-polyaniline-nickel hexacyanoferrate nanocomposites. Chem Commun 2005.

[21] Nair AS, Pradeep T. Halocarbon mineralization and catalytic destruction bymetal nanoparticles. Curr Sci 2003;84:1560–4.

[22] Phenrat T, Liu YQ, Tilton RD. Adsorbed polyelectrolyte coatings decrease Fe–Onanoparticle reactivity with TCE in water: conceptual model and mechanisms.Environ Sci Technol 2009;43:1507–14.

[23] Zheng W, Li XM, Yang Q, Zeng GM, Shen XX, Zhang Y. Adsorption of Cd(II) andCu(II) from aqueous solution by carbonate hydroxyapatite derived fromeggshell waste. J Hazard Mater 2007;147:534–9.

[24] Ho YS, McKay G. Pseudo-second order model for sorption processes. ProcessBiochem 1999;34:451–65.

[25] Bhattacharyya KG, Guptaa SS. Adsorptive accumulation of Cd(II), Co(II), Cu(II),Pb(II), and Ni(II) from water on montmorillonite: influence of acid activation. JColloid Interf Sci 2007;310:411–24.


[26] Langmuir I. The constitution and fundamental properties of solids and liquids.J Am Chem Soc 1916;38:2221–95.

[27] Sugiyama S, Fukuta K, Sotowa K-i. Formation of hydroxyapatite-layer on glassplate and its removal—regeneration properties for aqueous cadmium. J ColloidInterf Sci 2006;299:270–3.

[28] Nikpour MR, Rabiee SM, Jahanshahi M. Synthesis and characterization ofhydroxyapatite/chitosan nanocomposite materials for medical engineeringapplications. Composites Part B 2012;43:1881–6.

[29] Danilchenko SN, Kalinkevich OV, Pogorelov MV, Kalinkevich AN, Sklyar AM,Kalinichenko TG. Chitosan–hydroxyapatite composite biomaterials made by aone step co-precipitation method: preparation, characterization and in vivotests. JBPC 2009;9:119–26.

[30] Corami A, Mignardi S, Ferrini V. Cadmium removal from single- and multi-metal (Cd + Pb + Zn + Cu) solutions by sorption on hydroxyapatite. J ColloidInterface Sci 2007;317:402–8.

[31] Aksu Z, Tezer S. Biosorption of reactive dyes on the green alga Chlorella vulgaris.Process Biochem 2005;40:1347–61.

[32] Lin KL, Pan JY, Chen YW, Cheng RM, Xu XC. Study the adsorption of phenol fromaqueous solution on hydroxyapatite nanopowders. J Hazard Mater2009;161:231–40.

[33] Suzuki T, Hatsushika T, Miyake M. Synthetic hydroxyapatites employed asinorganic cation exchangers. J Chem Soc Faraday Trans 1982;78:3605–11.

[34] Mendoza MSB, Ramos RL, Davila PA, Barron JM, Flores PED. Effect of pH andtemperature on the ion-exchange isotherm of Cd(II) and Pb(II) on clinoptilo-lite. J Chem Technol Biotechnol 2006;81:966–73.

[35] Krivosheeva O, Dedinaite A, Claesson P. Adsorption of Mefp-1: influence of pHon adsorption kinetics and adsorbed amount. J Colloid Interface Sci2012;379:107–13.

[36] Namasivayam C, Ranganathan K. Removal of Pb(II), Cd(II), Ni(II) and mixture ofmetal-ions by adsorption onto waste Fe(III) Cr(III) hydroxide and fixed-bedstudies. Environ Technol 1995;16:851–60.

[37] Doyurum S, Celik A. Pb (II) and Cd (II) removal from aqueous solutions by olivecake. J Hazard Mater 2006;138:22–8.

[38] Snoeyink VL, Jenkins D. Water chemistry. J Chem Educ 1980;58:A382.[39] Srivastava VC, Mall ID, Mishra IM. Equilibrium modelling of single and binary

adsorption of cadmium and nickel onto bagasse fly ash. Chem Eng J2006;117:79–91.

[40] Mobasherpour I, Salahi E, Pazouki M. Removal of divalent cadmium cations bymeans of synthetic nano crystallite hydroxyapatite. Desalination2011;266:142–8.































































































development of nano-hydroxyapatite/chitosan composite for cadmium ions removal in wastewater...

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