Novel chitosan derivative for the removal of cadmium in the presence of cyanide from electroplating wastewater

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<ul><li><p>Journal of Hazardous Materials 148 (2007) 353359</p><p>Novel chitosan derivative for the remctrr Sian Iruary</p><p>y 200</p><p>Abstract</p><p>Chitosan ckbochemically m ovallaboratory c allycadmium by of 8.0electroplatin ce osignificant. T , howat higher do adsoNi(II) and Z cesswere calculated. Desorption of the bound cadmium from CMC was accomplished with 0.01N H2SO4. The data from regeneration efficiencies for10 cycles evidenced the reusability of CMC in the treatment of cadmium-laden wastewater. 2007 Elsevier B.V. All rights reserved.</p><p>Keywords: Cadmium; Electroplating wastewater; Biosorption; Chitosan</p><p>1. Introdu</p><p>The incrresents a secologicalfrom wastesistent, bioand economderived froindustrial welectrochemwastewatertoxic in naof metals sThe use oftry generatdue to high</p><p> CorresponE-mail ad</p><p>0304-3894/$doi:10.1016/jction</p><p>easing level of heavy metals in the environment rep-erious threat to human health, living resources andsystems [1]. These contaminants must be removedwaters before discharge, as they are considered per-accumulative and toxic [2]. Of special technicalic importance is the selective removal of metals</p><p>m the discharge from electrochemical activities intoastewater. In comparison with other industries, theical industries uses less water, hence, the volume ofproduced is smaller, and the wastewater is highly</p><p>ture because of the presence of high concentrationsuch as copper, nickel, zinc, cadmium and cyanides.cadmium cyanide baths in the electroplating indus-</p><p>es a strong concern related to environmental impactscadmium and cyanide toxicity [3]. Adverse health</p><p>ding author. Tel.: +91 512 2597844; fax: +91 512 2597844.dress: nalini@iitk.ac.in (N. Sankararamakrishnan).</p><p>effects due to cadmium are well documented and it has beenreported to cause renal disturbances, lung insufficiency, bonelesions, cancer and hypertension in humans [3]. To minimizethese environmental impacts, wastewater treatment processesusing biosorbents have attracted wide attention in recent years[46].</p><p>The use of chitosan as biosorbent for heavy metals offersa potential alternative to conventional methods such as chemi-cal precipitation, ion exchange, electrochemical treatments, etc.Chitosan is a hydrophilic, natural cationic polymer and an effec-tive ion-exchanger, with a large number of amino groups whichare responsible for the high adsorption property of chitosan.The oxygen atom in the hydroxyl group of the chitosan can beclassified as a hard ligand group having less affinity for heavymetals according to the HSAB (hard and soft acids and bases)classification system [7]. If soft ligand groups such as sulfurcan be introduced on to the chitosan backbone, it will increasethe uptake capacity for many heavy metals because cadmiumcan be classified as soft acids, which have a strong affinity tosoft ligands. Since sulfur has a very strong affinity for mostheavy metals, the metalsulfur complex is very stable in basic</p><p> see front matter 2007 Elsevier B.V. All rights reserved..jhazmat.2007.02.043the presence of cyanide from eleNalini Sankararamakrishnan , Ajit Kuma</p><p>Facility for Ecological and Analytical Testing, 302 Southern Laboratories, IndReceived 21 December 2006; received in revised form 15 Feb</p><p>Available online 23 Februar</p><p>was chemically modified by introducing xanthate group onto its baodified chitosan flakes (CMC) was used as an adsorbent for the rem</p><p>onditions. CMC was found to be far more efficient than the conventionCMC in batch studies was found to be 357.14 mg/g at an optimum pHg wastewater contains cyanide in appreciable concentrations, interferenhis problem could be easily overcome by using higher doses of CMC</p><p>ses. Due to the high formation constant of cadmium with xanthate andn(II) did not interfere in the adsorption. Dynamics of the sorption prooval of cadmium inoplating wastewaterharma, Rashmi Sanghinstitute of Technology, Kanpur, U.P. 208016, India2007; accepted 17 February 2007</p><p>7</p><p>ne using carbondisulfide under alkaline conditions. Theof cadmium ions from electroplating waste effluent underused adsorbent activated carbon. The maximum uptake ofwhereas for plain chitosan flakes it was 85.47 mg/g. Since</p><p>f cyanide ions in cadmium adsorption was found to be veryever, activated carbon was not found to be effective even</p><p>rption was carried out at pH 8, cations like Pb(II), Cu(II),were studied and the values of rate constant of adsorption</p></li><li><p>354 N. Sankararamakrishnan et al. / Journal of Hazardous Materials 148 (2007) 353359</p><p>conditions [8]. The use of materials with surface functionalgroups, such as xanthate group, shows improved selectivity forthe removal of heavy metals in wastewater [9].</p><p>For this purpose, we have developed [10] an effective, sim-ple and low cost alternative employing chelating agent withxanthate groups incorporated on chemically modified chitosanflakes (CMC). This modified chitosan can further enhance themetal binding capacities of chitosan. Comparative evaluationof CMC with plain flakes (PF) and activated carbon (AC) wasinvestigated. Influence of the presence of different ions such as:sulfate, chloride, carbonate, cyanide and other cations at variousinitial concentrations on cadmium sorption by CMC, in batchconditions were studied. The present study also explores thepossibilities of recycling the electroplating wastewaters free ofcadmium ions. The economic and environmental advantages ofrecycling and reusing waste make CMC adsorbent an attractivetreatment option.</p><p>2. Materials and methods</p><p>2.1. Materials</p><p>Chitosan flakes was purchased from Sigma Chemicals andused in the present study without any further purification. Thedegree of deacetylation was reported to be 85% by the manufac-turer. Glutaraldehyde and carbondisulfide were purchased fromSigmaAldrich and used without further purification. Stock</p><p>solution of Cd(II) was prepared using Cd(NO3)24H2O (BDHchemicals). All the inorganic chemicals used were analar gradeand all reagents were prepared in Millipore milli-Q deionisedwater.</p><p>2.2. Chemical modication of the chitosan akes (CMC)</p><p>Chitosan flakes were cross-linked with glutaraldehyde andchemically modified (Scheme 1) and characterized as describedearlier [10]. To obtain 20% cross-linking [11], chitosan flakes(ca. 0.5 g) were suspended in methanol (100 ml), and a 25%aqueous glutaraldehyde solution (0.046 ml, 0.12 mmol) wasadded. After stirring at room temperature for 6 h, the product wasfiltered. Cross-linked chitosan flakes (0.5 g) were treated with25 ml of 14% NaOH and 1 ml of CS2. The mixture was stirredat room temperature for 24 h. The obtained orange product,cross-linked chemically modified chitosan flakes were washedthoroughly with water, air-dried and used for further experi-ments.</p><p>2.3. Metal concentration analysis</p><p>Dissolved cadmium was determined by Analyst 400Perkin-Elmer Atomic Absorption Spectrophotometer using anairacetylene burner. The measurements were done at wave-length 228.8 nm using a slit width of 0.7 nm. Experimentalsamples were filtered using Whatman 0.45 mm filter paper and</p><p>in chScheme 1. Chemical modification of pla itosan flakes.</p></li><li><p>N. Sankararamakrishnan et al. / Journal of Hazardous Materials 148 (2007) 353359 355</p><p>the filtrates after suitable dilutions, were analyzed. Controlexperiments showed that no sorption occurred on either glass-ware or filtration systems. All assays were carried out in triplicateand only m</p><p>2.4. Waste</p><p>The samtry locatedThe wastewusing standelectroplati55,292 mg/3322 mg/l;</p><p>2.5. Cadm</p><p>Batch exof cadmiumstirring in acontact timWhatman NUnless othwere: sampion concenpH studiesconditionsthe doses wthe samplesample wasadsorbent dconcentratisieved thro</p><p>2.6. Studie</p><p>The effewere carriethe sorbentconditionsplating waswas diluted</p><p>Sorptionwhereby thwastewateries were dH2SO4 wit</p><p>2.7. Effect</p><p>The effebonate andkeeping othter. The effof Cu2+ (Cuand Ni2+ (Nin Table 6.</p><p>Effect of initial pH on cadmium adsorption: sample volume, 20 ml;dose, 5 g/l; initial pH 210; Cd2+ conc., 100 mg/l; equilibration time,</p><p>ults and discussion</p><p>ffect</p><p>H efwhiwa</p><p>hydough1.5 tsligg. 1)akemax</p><p>ment. Upted te toratioriumlainin fl80%wer</p><p>miumted tavailand s</p><p>hange in pH with time: sample volume, 20 ml; sorbent dose, 5 g/l; initialCd2+ conc., 100 mg/l; equilibration time, 16 h.ean values are presented.</p><p>water samples</p><p>ples were acquired from a local electroplating indus-in Kanpur City, U.P., India, during September 2005.ater samples were analyzed promptly after collectionard analytical methods [12]. The characteristics ofng wastewater were: color, colorless; pH 11.1; TDS,l; TSS, 5397 mg/l; cadmium, 1570 mg/l; cyanide,sulfate, 1784 mg/l; carbonate, 50,312 mg/l.</p><p>ium adsorption batch experiments</p><p>periments were carried out with synthetic solutionsin 100 ml flasks with stopper at 100 rpm of orbital</p><p>n incubator shaker, at room temperature and 16 h ofe with the adsorbent. Samples were then filtered with</p><p>o. 42 filter paper, diluted and analyzed for Cd(II).erwise stated, the parameters with synthetic waterle volume, 20 ml; sorbent dose, 5 g/l; initial metal</p><p>tration, 100 mg/l; pH 8; equilibration time, 16 h. For, the pH was varied from 2 to 10 keeping the otherthe same. For the effect of initial adsorbent dose,ere varied from 0.25 to 9 g/l. For kinetic studies,volume was maintained at 50 ml and at every 1 hwithdrawn for analysis. For equilibrium studies, theose was minimized to 0.5 g/l varying the initial Cdon from 10 to 100 ppm. The adsorbents used were allugh a sieve of 0.40.6 mm particle size range.</p><p>s with real electroplating wastewater</p><p>ct of sorbent dose and sorptiondesorption studiesd out with real electroplating wastewater wherebydose was varied from 1 to 50 g/l keeping the other</p><p>same as with synthetic wastewater. Since the electro-tewater had very high concentrations of cadmium, itbefore use to the working range.desorption studies were carried out for 10 cyclese adsorption conditions were same as for syntheticand the stripping solutions used for desorption stud-</p><p>istilled water, 0.01N HCl, 0.01N EDTA and 0.01Nh shaking time 2 h.</p><p>of other ions</p><p>ct of anions were studied using sulfate, chloride, car-cyanide with varying concentrations from 0.1 to 5 g/ler conditions same as that with synthetic wastewa-ect of cations were studied using 100 mg/l solutionSO45H2O), Pb2+ (Pb(NO3)2), Zn2+ (ZnSO47H2O)iSO47H2O) either alone or in combination as given</p><p>Fig. 1.sorbent16 h.</p><p>3. Res</p><p>3.1. E</p><p>A ption at2 to 10sodiumpH thrfrom 8after apH (Fitosan flof AC,experifor ACattribuues, duequilibequilibwith pthe plaaroundimentsof cadattributhe unmium</p><p>Fig. 2. CpH 48;of pH</p><p>fect test is performed to determine the pH of adsorp-ch maximum uptake of metal occurs. The pH froms adjusted initially with either hydrochloric acid orroxide (0.1 M). No efforts were made to maintain theout the adsorption procedure. The removal increasedo 99.9% with increase of pH from 6.0 to 8.0 and there-ht decline in removal was observed with increase in. The optimum pH for the removal of Cd(II) by chi-s as well as by CMC was found to be 8.0. In the caseimum removal was found to be pH 9. Hence, furthers were conducted at pH 8 for CMC and PF and pH 9take of cadmium even at lower pH values could beo the change in initial pH (Fig. 2). At lower pH val-inherent alkalinity present in CMC, within 10 min ofn time the initial pH increased sharply and attainedafter 30 min (Fig. 2). A similar trend was observed</p><p>flakes (results not shown). The results obtained forakes was in agreement with an earlier report where</p><p>removal was observed at pH 4 [13]. When the exper-e conducted at pH 3 using citrate buffer, adsorption</p><p>by CMC reduced from 80 to 50%. This could beo two factors. First, protonation of amine groups andability of amine groups for complexation with cad-econd, H+ ions compete with cadmium ions to same</p></li><li><p>356 N. Sankararamakrishnan et al. / Journal of Hazardous Materials 148 (2007) 353359</p><p>Table 1Cadmium speciation with pH</p><p>pH Cadmium species</p><p>8.6 Cd(OH)2</p><p>binding sites on the adsorbent. From Table 1, it is evident thatat pH 8 cadmium predominantly exists as Cd(OH)+ species.Hydroxy metal complexes are known to adsorb with a higheraffinity than the completely hydrated metals because the for-mation of an OH group on the metal reduced the free energyrequirement for adsorption [14]. Therefore, it seems that theadsorption of cadmium ions can be related to the change in theavailability of Cd(OH)+. The pKa of xanthatexanthic acid dis-sociation constant is reported to be 1.70. Thus, in the pH rangeused in thethe adsorbe</p><p>3.2. Effect</p><p>It is evidis adsorbenaround 4 g/could achie</p><p>3.3. Sorpti</p><p>The kinrapid bindiminutes folis reached.and furtherchange in tmaintainedwere in agrmetal ion</p><p>Kineticspseudo sec</p><p>t</p><p>qt= 1</p><p>kq2e</p><p>Fig. 3. Effectsorbent dose,16 h.</p><p>Fig. 4. Pseudo second-order plot of CMC with cadmium(II): sample volume,50 ml; sorbent dose, 0.5 g/l; initial pH 8; Cd2+ conc., 100, 500 and 1000 mg/l;equilibration time, 124 h.</p><p>Table 2Pseudo second-order sorption kinetics of Cd(II) by CMC</p><p>g/l)</p><p>k ismin)at e</p><p>rsus</p><p>wn</p><p>ed iadsotrati</p><p>orpti</p><p>ptiond by</p><p>qmaxbCeq</p><p>1 + bCeq (2)</p><p>qeq is the equilibrium adsorbate loading on the adsor-eq the equilibrium concentration of the adsorbate, qmax</p><p>imate capacity and b is the relative energy (intensity)present study, the characteristics of surface group ofnt are unlikely to change.</p><p>of initial adsorbent dose</p><p>ent from Fig. 3 that for lower adsorbent doses, CMCt of choice and shows complete removal of Cd(II) atl. The efficiency of PF and AC were comparable andve complete removal at a higher dose of around 7 g/l.</p><p>on kinetics</p><p>etics of cadmium removal by PF and CMC indicatedng of cadmium by the sorbent during the first fewlowed by a slow increase until a state of equilibriumThe necessary time to reach this equilibrium was 16 hincrease in equilibration time up to 24 h showed no</p><p>he uptake capacity. Hence, the equilibrium time wasat 16 h in subsequent analysis. These observations</p><p>eement with the work reported earlier with the otherbiomaterial systems [15].</p><p>of heavy metals adsorption was modeled by theond-order equation [16]:</p><p>+ tqe</p><p>(1)</p><p>Conc. (m100500</p><p>1000</p><p>where(g/mg/(mg/g)t/qt veare shofurnishparedconcen</p><p>3.4. S</p><p>Sorresente</p><p>qeq =</p><p>wherebent, Cthe ultof adsorption dose on cadmium adsorption: sample volume, 20 ml,0.259 g/l; initial pH 8; Cd2+ conc., 100 mg/l; equilibration time,</p><p>Fig. 5. Sorptisample volumequilibrationR2 k (g/mg/min)0.9991 0.6220.9996 0.4420.9974 0.280</p><p>the pseudo second-order rate constant of adsorptionand qe and qt are the amounts of metal ion sorbed</p><p>quilibrium and at time t, respectively. Linear plots oft for CMCF for 100, 500 and 1000 mg/l of cadmiumin Fig. 4. The results obtained for the model are alson Table 2. It is evident from the table that the pre-rbent followed pseudo second-order kinetics for theon range studied.</p><p>on equilibrium</p><p>isotherms are modeled using Langmuir model rep-Eq. (2) and shown in Fig. 5.( )on isotherms of plain and chemically modified chitosan flakes:e, 20 ml; sorbent dose, 0.5 g/l; initial pH 8; Cd2+ conc., 0100 mg/l;time, 16 h.</p></li><li><p>N. Sankararamakrishnan et al. / Journal of Hazardous Materials 148 (2007) 353359 3...</p></li></ul>

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