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Contents lists available at SciVerse ScienceDirect

Journal of Environmenta

.eIntroduction

Toxic metal compounds are frequently used in industrialprocesses and are widely distributed in the environment. Thepresence of toxic metals in the environment can be harmful tohumans and living species even in low concentration. Since toxicmetals do not degrade into harmless end-products, they canaccumulate in living bodies and getting concentrated through thefood chain [1]. Numerous metals such as cadmium, mercury, lead,chromium, copper, manganese, etc., are known to be signicantlytoxic. The removal and recovery of heavy metals from wastewater issignicant in the protection of the environment and human health.

Many physicochemical methods are available for heavy metalremoval from aqueous solution, including sorption [2], chemicalprecipitation [3], solvent extraction [4], reverse osmosis [5], ionexchange [6], ltration [7], and electrochemical treatment [8].Among the various water-treatment techniques described, sorp-tion is generally preferred for the removal of heavy metal ions dueto its high efciency, easy handling and availability of differentsorbents. At present, there is a growing interest in using low-costand non-conventional alternative materials instead of traditionalsorbents.

The use of natural biomaterials is a promising alternative due totheir relative abundance and their low commercial value. Recently,many industrial, agricultural and forestry sources are used asbiosorbents such as, red mud [9], sunower stalks [10], spent grain[11], wheat bran [12], Aspergillus niger [13], Scolymus hispanicus L.[14], eggshell and coral [15], maize bran [16], saw dust and neembark [17], citrus peels [18], Rosa gruss an teplitz [19], Echorniaspeciosa [20], Cupressus sempervirens, Eucalyptus longifoliaand andPinus halepensis [21] and Pleurotus cornucopiae [22].

The prickly pear cactus (Opuntia cus indica; Opuntia spp.,Cactaceae) is a cheap and easily available plant. The cactuscladodes are mainly constituted by a heteropolysaccharide with amolecular weight from 2.3 104 to 3 106 g/mol [23,24]. The O.cus indica mucilage is a mixture of acidic and neutral poly-saccharides consisting primarily of arabinose; galactose; galac-turonic acid; rhamnose and xylose [25]. Multiples uses have beenfound for this component, for instance as a food thickener, foodemulsier, as a water purier (polyelectrolyte molecule), as anadhesive for lime [Ca(OH)2], as a natural super plasticizer inmortars and as a food product [23,24,26,27].

The focus of the present study was to assess the potentiality ofdried prickly pear cactus cladodes biomass as a low-cost, naturaland eco-friendly biosorbent for the biosorption of cadmium (II)and lead (II) ions from aqueous solution as an ideal alternative tothe current expensive methods of removing metals from waste-water. The effects of average biosorbent particle size, pH,

Low-cost biosorbent

Heavy metals

Biosorption

biosorption occurred at pH of 5.8 and 3.5, respectively for cadmium (II) and lead (II) ions. Biosorption

kinetic data were properly tted with the pseudo-second-order kinetic model. The equilibrium data

tted very well to the Langmuir model with a maximum monolayer biosorption capacity of 30.42 and

98.62 mg/g, respectively for cadmium (II) and lead (II) ions. The biosorption yield decreases with an

increase in solution temperature. The FTIR analysis of unloaded and metal loaded biosorbent indicated

the involvement of C55O, OC and COC groups in metal binding.

2013 Elsevier Ltd All rights reserved.

* Corresponding author. Tel.: +212 661 66 66 22; fax: +212 523 49 03 54.

E-mail address: barkanoureddine@yahoo.fr (N. Barka).

2213-3437/$ see front matter 2013 Elsevier Ltd All rights reserved.http://dx.doi.org/10.1016/j.jece.2013.04.008Biosorption characteristics of cadmium (Opuntia cus indica) cladodes

Noureddine Barka a,*, Mohamed Abdennouri a, Moha Equipe de Recherche Gestion de lEau et Developpement Durable (GEDD), Faculte Polydiscib Equipe de Recherche Analyse Controle et Environnement (ERACE), Ecole Superieure de c Equipe de Materiaux, Photocatalyse et Environnement, Departement de Chimie, Faculte

A R T I C L E I N F O

Article history:

Received 1 February 2013

Accepted 15 April 2013

Keywords:

Prickly pear cactus

A B S T R A C T

The biosorption of cadmiu

developed from cactus clad

function of average bioso

concentration and tempera

increases with an increase

uptake was increased with

jou r n al h o mep ag e: w wwnd lead onto eco-friendly dried cactus

mmed El Makhfouk b, Samir Qourzal c

inaire de Khouribga, Universite Hassan 1er, Hay Ezzaitouna, B.P. 145 Khouribga, Morocco

chnologie de Sa, B.P. 89, Route Dar Si Aissa, Sa, Morocco

es Sciences, Universite Ibn Zohr, B.P. 8106 Cite Dakhla, Agadir, Morocco

(II) and lead (II) ions onto a natural, plentiful and low-cost biosorbent

des was investigated in batch mode. Experiments were carried out as a

ent particle size, pH, biosorbent mass, contact time, initial metal

re. The experimental results indicate that, the percentage of biosorption

the biosorbent dosage and the decrease of particle size. The equilibrium

n increase in the initial metal concentration in solution. The maximum

l Chemical Engineering

l sev ier . co m / loc ate / jec e

where q (mg/g) is the quantity of metal ions biosorbed per unitmass of biosorbent, % biosorption is the biosorption yield, C0 (mg/L)is the initial metal ions concentration, C (mg/L) is the metal ionsconcentration after biosorption and R (g/L) is the mass ofbiosorbent per litre of aqueous solution.

Results and discussion

Effect of pH

The pH of the aqueous solution is one of the major parameterscontrolling the biosorption process [2830]. Fig. 1 shows the effectof pH on the biosorption capacity of dried cactus. The gureindicates that the removal of both Cd(II) and Pb(II) ions fromaqueous solution was strongly affected by medium pH. Thebiosorption was week in acidic medium and increases with pHsolution increase. The biosorption capacity of dried cactusincreased from 2.97 to 12.34 mg/g and from 19.76 to 29.18 mg/g when the solution pH was increased from 2.3 to 5.8 and from 2.3

N. Barka et al. / Journal of Environmental Chemical Engineering 1 (2013) 144149 145biosorbent dosage, contact time, initial metal concentration andtemperature were investigated.

Experimental

Preparation of the biosorbent

The prickly pear cactus cladodes were naturally collected in July2011 near Sa in Morocco. They were repeatedly washed withdistilled water to remove dirt particles and were sun dried for 3weeks, cutting into small pieces and then were dried at 60 8C for24 h. The dried plant was then powdered using domestic mixer.The biosorbent was stored in a glass bottle for further use withoutany pre-treatment.

Preparation of metal ions solutions

A stock solutions of 1 g/L of Cd(II) and Pb(II) ions was preparedby dissolving appropriate amount of Cd(NO3)2.4H2O and Pb(NO3)2in distilled water. The used concentrations were obtained bydilution of the stock solution. The pH was adjusted to a given valueby addition of HCl (1 N) and was measured using a JENWAY pH-Meter 3305. All the necessary chemicals used in the study were ofanalytical grade.

Biosorption experiments

Biosorption experiments were conducted in 250 mL conicalasks at a constant agitation speed. The effect of biosorbentparticle size was carried out by varying the biosorbent particlesizes from particles less than 100 mm to particles bigger than500 mm, the initial metal concentration was 100 mg/L, thetemperature was 25 8C, the biosorbent dosage was 2 g/L and thepH was 5.8 for Cd(II) and 3.5 for Pb(II). For all other experiments,the fraction of particles less than 100 mm was used. Theseexperiments were carried out by varying the pH from 2.3 to 6.5 andfrom 2.3 to 5; respectively for Cd(II) and Pb(II), the biosorbentdosage was varied from 0.5 to 10 g/L, contact time from 5 to120 min, the initial metal concentrations from 30 to 300 mg/L andthe temperature from 25 to 60 8C. The temperature was controlledusing an isothermal shaker. After each biosorption experimentcompleted, the sample were centrifuged at 3000 rpm for 10 min toseparate the solid phase from the liquid phase.

Analyses

Specic surface area was determined by using N2 as the sorbateat 77 K in a Micromeritics TriStar II 3020 sorptometer. Sampleswere outgassed prior to use at 473 K a night under vacuum.Specic total surface areas were calculated using the B.E.T.equation. FTIR was also used to identify functional groupsresponsible for metal binding. Original dried cactus, Cd- and Pb-loaded dried cactus (ltered and dried after contact with Cd(II) andPb(II) solution) were mixed with KBr at a ratio of 1:100 andcompressed into lms for FTIR analysis using a SCO-Tech SP-FTIR-1spectrometer (Germany). Metal ions concentrations were deter-mined using an atomic absorption spectrophotometer type GBC904 (Australia).

The biosorbed quantity and the biosorption yield werecalculated using the following equations:

q C0 CR

(1)

% Biosorption C0 CC0

100 (2)to 3.5, respectively for Cd(II) and Pb(II). At lower pH values, thebiosorption of Cd(II) and Pb(II) are low because large quantities ofproton compete with metal cations for biomass surface. As the pHincreased, the number of positively charged available sitesdecreased and the number of negatively charged sites increased.The surface of the biosorbent becomes negatively charged, and thisincreases the biosorption of the positively charged metal ionsthrough electrostatic forces of attraction. Similar results werefound by Wang et al. for the biosorption of Cd(II) and Pb(II) ontodried activated sludge [31]. The decrease of the xation of lead forpH upper than 3.5 is due to the complexation of lead ions by OH

groups which would prevent the metal biosorption [32].The difference in biosorption trend of cadmium and lead may be

attributed to the differences in behaviour among these metals ortheir ions in solution. Whereas, Pb(II) is adsorbed as hydrolysedspecies, Cd(II) is not. This behaviour is attributed to a number offactors which include (i) the smaller hydrated radius of lead (II)(0.401 nm) compared to cadmium (II) (0.426 nm); (ii) the higherelectronegativity of Pb than Cd (2.10 and 1.69 respectively); (iii)the pKOH (negative log. of hydrolysis constant) of 7.78 and 11.70 forPb(OH)2 and Cd(OH)2 respectively; and (iv) the strength of acidityof these metals (Pb is a border line hard Lewis acid while Cd is softLewis acid). These factors make Pb(II) to be more preferentiallyadsorbed through inner-sphere surface complexation reactionsthan Cd(II).

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7

pH

qe

(m

g/g

)

Cd

Pb

Fig. 1. Effect of pH on the biosorption of Cd(II) and Pb(II) by dried cactus cladodes:C0 = 100 mg/L, particle size

05

10

15

20

25

30

10 20 30 40 50 60 70

Temperature (C)

qe

(m

g/g

)

Cd

Pb

Fig. 2. Effect of temperature on the biosorption of Cd(II) and Pb(II) by dried cactus:C0 = 100 mg/L, R = 0.5 g/L, particle size 500 mm 0.533

to the experimental ones. This suggests that the biosorption ofCd(II) and Pb(II) onto dried cactus is presumably a chemisorptionprocess involving exchange or sharing of electrons mainly betweenmetal ions and functional groups (mainly hydroxyl and carboxylgroups) of the biosorbent.

Biosorption isotherm

The equilibrium sorption capacity of dried cactus for cadmiumand lead ions increased with a rise in initial concentration, asshown in Fig. 6. Metal ions removal is highly concentrationdependent. The increase in biosorption capacity with concentra-tion is probably due to a high driving force for mass transfer. In fact,high concentration in solution implicates high metal ions xed atthe surface of the biosorbent. The isotherms form was type L inGiles classication [37]. These types of isotherms are usuallyassociated with ionic solute adsorption (e.g., metal cations andionic dyes) with weak competition with the solvent molecules[38]. The Langmuir and Freundlich models were applied for theanalysis of equilibrium sorption data obtained. The Langmuir

40

60

80

Bio

so

rptio

n

Cd

Pb

N. Barka et al. / Journal of Environmental Chemical Engineering 1 (2013) 144149 147model. The rst-order rate expression of Lagergren based on solidcapacity is generally expressed as follows [35]:

dq

dt k1qe q (3)

After integrating and applying the boundary conditions, for q = 0 att = 0 and q = q at t = t, the integrated form of Eq. (3) becomes:

q qe1 ek1t (4)where qe and q (both in mg/g) are respectively the amounts of dyeadsorbed at equilibrium and at any time t, and k1 (min

1) is therate constant of biosorption

The pseudo-second-order model proposed by Ho and McKay[36] was used to explain the sorption kinetics. This model is basedon the assumption that the adsorption follows second orderchemisorption. The pseudo-second-order model can be expressedas:

dq

dt k2qe q2 (5)

After integrating for the similar boundary conditions, the followingequation can be obtained:

q k2q2et

1 k2qet(6)

0

20

0 3 6 9 12 15

R(g/L)

%

Fig. 5. Effect of biosorbent dosage on the biosorption of Cd(II) and Pb(II) by driedcactus: C0 = 100 mg/L, particle size

This result suggests that the Langmuir isotherm may be a suitablemodel for our data. It was concluded that the removal process ofCd(II) and Pb(II) by dried cactus was monolayer biosorption, andthe maximum monolayer biosorption capacity was found to be30.42 and 98.62 mg/g, respectively for Cd(II) and Pb(II).

The obtained biosorption capacities of dried cactus cladodeswas compared to previously reported works on the biosorptioncapacities of various low-cost biosorbent. Table 4 shows thatexperimental data of the present study was found to be higher thanthose of many corresponding biosorbents in the literature.

FTIR characterization and contribution of functional groups to metal

binding

Table 3Langmuir and Freundlich isotherms constants for the biosorption of Cd(II) and Pb(II)

onto dried cactus.

Freundlich constants Langmuir constants

KF(mg11/ng1 L1/n)

n r2 qm(mg/g)

KL(L/mg)

r2

Cd(II) 1.55 2.05 0.972 30.42 0.011 0.991

Pb(II) 2.21 1.59 0.976 98.62 0.008 0.995

Table 4Comparison of maximum biosorption capacity of dried cactus cladodes for

cadmium(II) and lead(II) with other low-cost biosorbents.

Biosorbent material qm (mg/g) qm (mg/g) References

Cd(II) Pb(II)

Spent grain 17.30 35.50 [11]

Wheat bran 62.00 21.00 [12]

Scolymus hispanicus L. 54.05 [14]

Neem bark 25.57 [17]

Citrus peels 480.70 [18]

Dried activated sludge 84.3 131.6 [31]

Alginate 30.91 58.02 [41]

Anaerobic granular biomass 59.67 254.85 [42]

Penicillium simplicissimum 61.35 87.72 [43]

Wheat straw 14.61 [44]

Maize bran 142.86 [45]

Carpobrotus edulis 27.9 175.6 [46]

Euphorbia echinus 23.5 165.1 [46]

Senecio anthophorbium 18.9 149.6 [46]

Launea arborescens 11.50 129.90 [46]

Cephalosporium aphidicola 92.41 [47]

Flammulina velutipes 8.43 18.34 [48]

Trichoderma ressie 82.645 [49]

Dried cactus cladodes 30.42 98.62 This study

N. Barka et al. / Journal of Environmental Chemical Engineering 1 (2013) 144149148The FTIR spectra of dried cactus biosorbent and metals ionsloaded biosorbent were compared to determine which functionalgroups are responsible for the Cd(II) and Pb(II) biosorption. Theobtained results are presented in Fig. 7. The spectra of dried cactushas a broad absorption peaks at around 32003500 cm1, indicatesthe presence of carboxylic acid and amino groups. The absorptionband at 2921 cm1 could be assigned to asymmetric vibration of CH. The stretching vibration band at 2850 cm1 is due to methoxygroup (CH3O). The stretching vibration band 1620 cm

1 is due toasymmetric stretching of the carboxylic C55O double bond. A1432 cm1 is of phenolic OH and C55O stretching of carbox-ylates. A 1384 cm1 band could be stretching vibration of COO.The band at 1072 cm1 band could be due to the vibration of COC and OH of polysaccharides. Peaks in the region of lower wavenumbers (under 800 cm1) appeared as a broad peak and thiscould be attributed to N containing bioligands [30,47]. Spectraanalysis after Cd(II) and Pb(II) biosorption showed that there was asubstantial decrease in the wave number of asymmetric stretchingFig. 7. FT-IR spectra of unloaded (1), Cd-loaof the carboxylic C55O double bond from 1620 for unloaded driedcactus to 1616 and 1604 cm1, respectively for Cd- and Pb-loadeddried cactus. The band at 1432 cm1 was shifted to 1427 cm1 forCd-loaded biosorbent and was not observed for Pb-loadedbiosorbent. The band at 1072 cm1 shifted to 1060 and1043 cm1, respectively for Cd- and Pb-loaded dried cactus. Thisresults indicates that carboxylic acid groups were likely responsi-ble for binding Cd(II) and Pb(II) by dried cactus biosorbent. Thegroups of COH, and COC also involved in Cd(II) and Pb(II)binding to some extent.

Conclusions

In this study, biosorption experiments for the removal ofcadmium and lead ions from aqueous solutions have been carriedout using dried cactus as low-cost and natural available biosorbent.It was found that the biosorption was rapid and increased by thedecrease in biosorbent average particle size. The optimumbiosorption was achieved at pH 5.8 and 3.5 for Cd(II) and Pb(II)ded (2) and Pb-loaded (3) dried cactus.

ions, respectively. The increase in mass biosorbent leads toincrease in metals ions biosorption due to increase in number ofbiosorption sites. The equilibrium metals uptake was increasedwith increasing the initial metal concentration. The biosorptionkinetics was well described by the pseudo-second order kinetic

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N. Barka et al. / Journal of Environmental Chemical Engineering 1 (2013) 144149 149model equation. The biosorption isotherms could be well tted bythe Langmuir equation. The biosorption capacity decreases with anincrease in solution temperature. The carboxylic acid groups werelikely responsible for metal binding. Finally, dried cactus can beused as an alternative effective natural biosorbent in the removalof metals from wastewaters.

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Biosorption characteristics of cadmium and lead onto eco-friendly dried cactus (Opuntia ficus indica) cladodesIntroductionExperimentalPreparation of the biosorbentPreparation of metal ions solutionsBiosorption experimentsAnalyses

Results and discussionEffect of pHEffect of temperature on biosorptionEffect of biosorbent particle sizeEffect of biosorbent dosageBiosorption kinetics modellingBiosorption isothermFTIR characterization and contribution of functional groups to metal binding

ConclusionsReferences