Sorption studies of Cu(II) on gooseberry fruit ( emblica of fi cinalis ) and its removalfrom electroplating wastewaterRifaqat Ali Khan Rao ⁎ , Shaista IkramEnvironmental Research Laboratory, Department of Applied Chemistry, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh 202002 (U.P.) IndiaArticle infoArticle history:Received 4 December 2010Received in revised form 10 April 2011Accepted 27 April 2011Available online 28 May 2011Keywords:SorptionCu(II)Equilibrium isothermsKineticsThermodynamicsAbstractThe sorption of Cu(II) onto waste residue left after extraction of juice from Indian gooseberry (Amla) fruit(Emblica officinalis ) was studied. Equilibrium isotherms, kinetic data and thermodynamic parameters have beenevaluated. Equilibrium data agreed well with Langmuir, Freundlich, Temkin and Dubinin –Radushkevich (D–R)isotherm models. The kinetic data followed pseudo-second-order model and it was found that intra-particlediffusion was not the sole rate-controlling factor. Gibbs free energy showed spontaneous process for allinteractions. The breakthrough and exhaustive capacities were found to be 4.0 and 24.0 mg/g respectively.Emblica officinalis was shown to be a promising sorbent for Cu(II) removal from aqueous solutions. The practicalutility of the sorbent has been demonstrated by achieving 97.60% removal of Cu(II) from electroplatingwastewater by column process.© 2011 Elsevier B.V. All rights reserved.1.IntroductionOne of the cardinal demerits of rapid industrialization is themanifold increase in industries ranging from metalfinishing, electro-plating, plastics and polymer manufacturing, pigments, textile, pulpand paper, mining etc. giving rise to air, soil and water pollution [1 –3] .The uncontrolled discharge of ef fluent from these industrial unitspollutes different aquatic bodies posing serious health and environ-mental problems [4]. Among the wide variety of toxic compoundsfound in wastewater, heavy metals are of utmost signi ficance becauseof their high toxicity at ultra trace concentrations and persistentnature [5]. Due to their non-biodegradability they tend to accumulatein the vital organs of living organisms causing various diseases andlong term disorders, as well as deleterious ecological effects [6]. Hencethere has been a continuous quest to develop novel process andtechniques over the years to remove these deleterious heavy metalio n s p resen t in in du s tr ia l wa s te wa t er s . A p ra c ti c a l p ro b le m inremoving out these heavy metal ions from wastewater is theirappreciable solubility in aqueous systems and hence their removal byordinary physical and chemical means is very difficult and ineffective[7].There is a variety of conventional treatment techniques employedo remove heavy metals from wastewaters before their final dischargen to the envi ronm ent. Mos t notab le among the se are c hemic alrecipitation, evaporation, electro deposition, ion exchange, adsorp-on, membrane separation, coagulation etc. [8]. However, these techniques suffer from either one drawback or the other. Some ofthese techniques are either too costly or they are ineffective in termsof removal of heavy metal ions present at low concentration. Amongall these enlisted conventional techniques, removal of heavy metalions by adsorption is found to be highly effective, inexpensive andease of operation [9]. The use of sorbent for removing and recoveringheavy metals from contaminated industrial effluents has emerged as apotential alternative method to the conventional ones [10] . In recentyears, the process involving the removal of heavy metal ions bypassive binding with the dead or living biomass, emerges as one of thepotentially cost-effective techniques[11] . Sorption contains manypassive processes of accumulation such as sorption, ion exchange,covalent bonding, complexation, chelation, and micro-precipitationprocesses. Several studies have shown that the method is effective toremove heavy metals from industrial wastewaters and could beemployed most effectively in concentration range below 100 mg/L[12,13].Cu(II) is one of the most common heavy metals which is essentialfor hum an bei ngs, a ni mal s an d m ic ro -or g ani s ms but e xcessi ve ofC u ( I I ) produces many toxic and harmful effects on the living organism[14] . Acute Cu(II) poisoning may lead to hemolysis, liver and kidneydamage, and influenza syndrome while its local effects give rise toirritation of upper respiratory tract, gastrointestinal disturbance withvomiting, and diarrhea and a form of contact dermatitis [15] .Theseriousness of the Cu(II) toxicity and its bioaccumulation propertyhave led the United States Environmental Protection Agency (USEPA)to recommend a t hreshold conce ntrat ion l i mi t, de fi ned a s t hem a x i m um c on ta m i n a n t l ev e l ( MC L ) o f 1. 3 m g /L[16] . C u( I I ) m a in lyor ig in a te s f r om d ye in g , p a p e r, p e tr ol eu m , c op p er / b ra s s - pl a t in g a n d copp er-ammonium r ayon indus tr ial wastewaters. S amples of wastewater co llected from co pper c lean ing, co pper plating an dmetal p ro cessing industries, have s hown Cu(II ) c oncentrations up t o100 –120 mg/L which are a bout 1 00 to 200 times gr e a t er than its MC L[15] . H ence there is a dire need to develop econo mic a ll y feasible andeffective sorbent wh ich c an remo ve Cu(II) thus s aving the life o fpeople engaged i n these abov e mentioned industries. Removal o fheavy metal io ns from the a qu eou s streams b y a gricultural wa stema terials i s a n i nn ovative a nd promising technology . The effi ciencyof the wa ste material depends upon t he capacity, affi nity, andspecifi c it y , i nc l udi n g i t s p h y si co - c hem i ca l n atu re . In r e cen t ye a r s,bio log ica l mat e ria ls i ncludin g ag ri cult ural and i ndust ri a l so li dwastes are b ein g used as sor bents for the removal o f heavy metals[17] . This paper describes the sor ption abil ity o f I ndian go o seberry( A ml a) frui t ( abb re v i a ted a s EO ) f or t he removal o f C u (I I) f romaqueous s olu tio n.2.Materials and methods2.1. SorbentEO belongs to the familyPhyllanthaceae . The tree is medium sizedreaching 8 –18 m in height and found natively in India. Amla fruit isused as valuable ingredient in various Ayurvedic medicines in Indiaand abroad. It contains on an average, moisture 81.8%, protein 0.5%, fat0.1%, minerals 0.5%, fibers 3.4% and carbohydrates 13.7% per 100 g ofedible part. Its minerals and vitamin contents include calcium, iron,phosphorous, carotene, thiamine, riboflavin, niacin and vitamin C. Thefruit juice of EO can be extracted and used in many pharmaceuticalindustries for the formulation of various drugs. The waste material leftafter extraction was used to explore its sorption properties.2.2. Treatment of sorbentThe waste material left after extraction of juice from EO wascollected from local medicine manufacturing unit at Aligarh. Thebiomass was rinsed with water and dried in an oven at 60 °C. Thedried mass was sieved to obtain particle size of 100–300 μm. Thebiomass was washed several times again with double distilled water(DDW), and subsequently dried again in an oven at 60 °C and thenstored in an airtight container in order to avoid moisture and used assuch for the sorption studies.2.3. Sorbate solutionStock solution of Cu(II) was prepared (1000 mg/L) by dissolvingthe desired quantity of copper nitrate trihydrate (AR grade) in DDW.The stock solution was diluted to obtain desired Cu(II) concentration.Solutions of other metal ions were prepared by dissolving theirchlorides or nitrates.2.4. Determination of active sitesActive sites present on the surface of the sorbent were determinedby acid–base titration method [18] at room temperature (30 °C).2.5. Sorption studiesSorption studies were carried out by batch process. 0.5 g sorbentwas placed in a conical flask in which 50 mL solution of metal ion ofdesired concentration was added and the mixture was shaken inshaker. The mixture was then filtered and fi nal concentration of metalion was determined in the filtrate by atomic adsorption spectropho-tometer (AAS) (GBC 902). The amount of metal ions sorbed wascalculated by subtracting final concentration from initial concentra-tion. All the experiments were carried out in triplicate and meanconcentration was calculated by averaging them. The percent sorptionof sorbate and equilibrium sorption capacity (qe), were calculatedusing the following relationships.% Sorption = Co– CeðÞ= Co×100 ð1ÞSorption capacity qeðÞ mg= g ðÞ=Co–CeðÞ×V= W ð2Þwhe re , Cois in it ia l c on c ent ra t ion of so rb at e ( mg/ L ) , Ceis th eequilibrium sorbate concentration (mg/L), V is the volume of thesolution (L) and W is the mass of the sorbent (g).2.6. Effect of pHThe experiment was performed by taking 100 mL of Cu(II) solutionin a beaker and the desired pH of solution was adjusted by addingeither 0.1 N HCl or NaOH solutions. 50 mL of this solution was taken ina conical flask and treated with 0.5 g of sorbent and after equilibrium,the final concentration of Cu(II) was determined.2.7. Effect of contact timeA series of 250 mL conical fl asks, each having 0.5 g sorbent and50 mL solution (of known metal concentration) were shaken intemperature controlled shaker incubator at 120 rpm and at the predetermined intervals (1, 2, 3, 5, 10, 15, 30, 60, 120, 1440 min). Thesolution from the speci fi edflask was taken out and the concentrationof Cu(II) was determined by AAS. The amount of Cu(II) sorbed in eachcase was then determined as described earlier.2.8. Effect of concentration and temperatureThe effect of concentration on sorption of Cu(II) was investigatedwith initial Cu(II) concentrations of 10, 20, 30, 40, 50, 80, 100, and150 mg/L. The experiments were performed by adding 50 mL solution of each concentration to eight different 250 mLflasks each containing0.5 g of sorbent. Theflasks were shaken at 120 rpm and 30 °C for 3 hand the final concentration of Cu(II) was determined by AAS. Thesame experiment was repeated at 40 and 50 °C.Fig. 1. A. Emblica of ficinalis (native). B. Cu (II) adsorbed Emblica of fi cinalis .Fig. 2. IR spectra of Emblica of ficinalis : (a) before sorption; (b) after Cu(II) sorption.2.9. Determination of point of zero chargeThe pH at point of zero charge (pHpzc) of the sorbent wasdetermined by the solid addition method[19] . To a series of 250 mLStoppard conical fl asks, 40 mL of 0.01 N KNO3was transferred. Theinitial pH (pHi) values of the solutions were roughly adjusted between 2 and 10 by adding either 0.1 N HCl or NaOH solution. The total volume of the solution in each flask was made 50 mL by adding KNO3solution of the same strength. The pHiof the solution was thenaccurately noted and 0.5 g of sorbent was added to eachflask, and theflask was securely capped immediately. The suspensions were then manually shaken and allowed to equilibrate for 24 h with intermittentmanual shaking. Thefinal pH (pHf) values of the supernatant liquidwere no t ed. The difference betwe en the init ial and fi nal pH( ΔpH = pHi −pHf) was plotted against pHi. The point of intersectionof the resulting curve with the abscissa, at which ΔpH = 0, gave the pH PZC. The same experiment was repeated with DDW.2.10. Quality assurance and quality controlTo make sure that no metal ions were released to the solution fromthe sorbent, an equilibrium test was performed using sorbent EO inDDW. For assuring quality in the sorption studies DDW blank wasincluded in the experiment. To ensure accuracy after each set of fivesamples, a standard was run to ensure that drift had not occurred.The samples were analyzed in triplicate by AAS. Average of thevalues obtained gives mean concentration of the sample. In order tocompare quantitatively the applicability of different models in fitt in g todata, the percent deviation (P), was calculated. It is generally acceptedthat when P value is less than 5, the fit is considered to be excellent [20] .2.11. Breakthrough capacity0.5 g of sorbent was taken in a glass column (0.6 cm internaldiameter) with glass wool support. 500 m L of Cu(II) solution of 50 m g/Linitial concentration (Co) was then passed through the column with aflow rate of 1 mL/min. The effluent was collected initially in 10 mL andthen 50 mL fractions and the concentration of Cu(II) (Ce) was thendetermined in each fraction with the help of AAS. The breakthroughcurve was obtained by plotting Ce/Coversus volume of the effluent.2.12. Desorption studiesDesorption studies were carried out by batch as well as columnprocess. In batch process desorption of Cu(II) was carried out bytreating 0.5 g of sorbent with 50 mL of Cu(II) solution (50 mg/L) in aconical flask. The solution was fi ltered after 24 h and filtrate wasanalyzed for Cu(II). The sorbent was then washed several times withDDW to remove any excess of Cu(II). It was then treated with 50 mL of0.1 N HCl solutions and then fi ltered after 24 h. The fi ltrate wasanalyzed for Cu(II) desorbed. The same procedure was repeated withdifferent desorbing solutions like sodium chloride, acetic acid, sodiumsulfate, sodium hydroxide and EDTA.Desorption studies by column process were carried out as follows.The exhausted column (from breakthrough capacity) was washedseveral times with DDW to remove excess of Cu(II) ions from thecolumn, then 0.1 N HCl solution was passed through the column with aflow rate of 1 mL/min. The Cu(II) ions eluted were collected in 10 mLfractions and the amount of Cu(II) ions desorbed in each fraction wasdetermined by AAS.2.13. Treatment of electroplating wastewaterElectroplating wastewater was collected from a local electroplatingplant in Aligarh city. The pH of the wastewater was noted. It wasfilt er ed to remove suspended matter and diluted and then analyzed for variousparameters. Heavy metal was determined by AAS. 50 mL of the dilutedwastewater was treated with 0.5 g sorbent by batch as well as columnprocess. In column process wastewater was passed through the columnwith a flow rate of 1 mL/min. The effluent collected was again analyzedand amount of metal ions removed were determined.2.14. Regeneration and recycling studies0.5 g of sorbent was taken in a glass column (0.6 cm diameter)with glass wool support. 50 mL of Cu(II) solution of 50 mg/L initialconcentration (Co) was then passed through the column w ith aflowrate of 1 mL/min.The ef fluent was collected and the amount of Cu(II)was then determined as usual. The sorbent was washed several timeswith DDW to remove any excess of Cu(II) ions and then 50 mL of 0.1 NHCl was passed with the same flow rate. The ef fluent was collected in10 mL fraction and amount of Cu(II) desorbed in each fraction wasthen determined. The sorbent was then washed several times withDDW to remove any excess of HCl and again treated with 50 mL Cu(II)solution. The same procedure was repeated several times.3. Results and discussion3.1. Characterization of sorbent3.1.1. Scanning electron microscope (SEM) analysisThe SEM was used to examine the surface of the sorbent before and after sorption of Cu(II). The surface of the sorbent appeared to beirregular and porous. The pores were prominent on the surface ofsorbent before sorption ( Fig. 1 A). After sorption of Cu(II) the poreswerefilled showing adherence of Cu(II) on the surface ( Fig. 1B).3.1.2. Fourier transform infrared (FTIR) spectroscopyThe FTIR spectra of native and Cu(II) sorbed EO shown in Fig. 2aand b indicated the presence of several functional groups. The peak 3438 cm− 1 in native sorbent indicates the presence of OH groups. Thepeak at 2922 cm− 1may be due to the carboxylic stretching bonds[21] . The peak at 1643 cm− 1may be attributed to C=C and C=Owhere as peaks in the region 1506 and 1452 cm− 1represent OHbonds. The broad peak at 1038 cm− 1may be attributed to the C ―OHstretching vibrations. It has been observed that the peak of ionizablefunctional groups was slightly reduced or distorted in the Cu(II)sorbed sample of EO ( Fig. 2b) showing that Cu(II) was sorbed at thesefunctional groups.3.3. Effect of contact time and initial concentrationSorption of Cu(II) on EO at various initial concentrations was carried out at different intervals of time. The maximum uptake of Cu(II)at equilibrium was found to be 1.7, 3.1 and 5.8 mg/g at 20, 40 and80 mg/L initial Cu(II) concentrations respectively. The extent ofsorption increased rapidly in the initial stages and then became slowat later stages till the equilibrium was attained. Equilibrium time forsorption of Cu(II) at concentrations 20, 40 and 80 mg/L was foundto be 15, 30 and 60 min. showing that equilibrium time dependsupon the initial concentration of Cu(II) (Fig. 3). The increase in initialconcentration of Cu(II) ions resulted an increase in the sorptioncapacity. This is a usual phenomenon observed on various sorbentssince transfer of metal ions from bulk to the surface of the sorbentincreases with increase in concentration of metal ions. This is the basicp rop er ty of th e s or ben t t o be u tiliz ed f or t he re mo va l o f me ta l i on s f ro msolution.3.4. Effect of pHFig. 4 indicates that sorption of Cu(II) on EO was strongly pHdependent. The%sorption was minimum (48%) at pH 2 and reached tomaximum when pH was increased to 3. The sorption of Cu(II) withrespect to pH can be explained by considering the surface charge onthe sorbent and the speciation of Cu(II). The minimum sorption at pH2 (excess of H+ions) was due to the fact that the surface of sorbentbecame positively charged because H+ ions compete with Cu(II) ionsand did not favor the sorption of positively charged Cu2+because ofthe electrostatic repulsion. The sorption of H+ions resulted in theprotonation of various functional groups present on the surface of thesorbent decreasing the negatively charged surface sites. However,when pH was increased to 3, the acidic sites were deprotonated andattractions of positively charged Cu(II) ions increased. Cu(II) exists asCu2+ at pH 3 hence it can be concluded that maximum amount ofcopper was sorbed in the form of Cu2+ions up to pH 3. Above pH 3sorption increased very slowly due to the formation of other Cu(II)species like Cu(OH)+(pH 4 –5) and Cu(OH)2 (pH N 6)[22] . The pH ofthe solution also infl uenced the surface charge of the sorbent. ThepH pzc of EO in DDW was found to be 6 (Fig. 5) showing that surface ispositively charged below pH 6. Therefore, at high pH value (above 6) Cu(II) species mainly present as Cu(OH)+and Cu(OH)2were sorbed (due to micro precipitation). The shifting of pH pzc towards lower pH va lu e (Fi g. 5) in presence of electrolyte (0.01 N KNO3) indicated thatsorption of Cu(II) ions was specific [23] . The effect of electrolyte on thesorption of Cu(II) is also shown in Fig. 4. The sorption of Cu(II) decreasedappreciably in presence of electrolyte (0.1 N KNO3)atpHN 3.3.5. Sorption isothermsThe data obtained from studies were tested for their applicabilityto the isotherm models namely Langmuir, Freundlich, Temkin andDubinin–Radushkevich (D–R) isotherm. The dependence of 1/qe on1/Ce with varying concentration of Cu(II) ions at different tempera-ture was observed to be linear indicating the applicability of theLangmuir isotherm. The values of Langmuir isothermconstants b andqm were calculated from the slope and intercept of the linear plots of1/Ce vs. 1/qe [24]. The values of dimensionless constant separationfactor (RL) were plotted at different initial Cu(II) concentrations andtemperatures (Fig. 6). RL values were found to be in the range 0–1inall experimental systems, which confirmed the favorable uptake ofCu(II). The monolayer sorption capacity (qm) of EO was comparedwith various agricultural byproducts studied earlier [15,25–35].EOrepresented higher Cu(II) sorption capacity than 11 from 14 sorbents,reflecting a promising future for EO utilization in Cu(II) removal fromaqueous solution. The values of Freundlich isotherm constants Kf andn were calculated from the intercept and slope of the freundlich plotsat different temperatures. When ‘n’approached zero, the surface siteheterogeneity increased. The values of nN1(Table 2) at all temperaturesindicated favorable sorption of Cu(II) [36]. The values of Temkinconstants A and B related to sorption potential and heat of sorptionrespectively were calculated from the slope and intercept of the plot ofqe versus lnCe. To distinguish between the physical and chemicalsorption, Dubinin–Radushkevich (D–R) isotherm based on the hetero-geneous nature of the sorbent surface was applied. The values of qm(maximum sorption capacity) and constant βwere calculated from theintercept and slope of the D–R linear plots of lnqm vs. ε 2(Polanyi potential). The constant βgave an idea about the mean free energy (E)(kJ/mol) of sorption molecule of the sorbate when it was transferred tothe surface of the solid from infinity and can be calculated using thefollowing relationship [37].E=1= 2βðÞ1= 2ð3ÞThe fitting procedure was performed using R software version 2.10.1 (2009-12-14). The fitness of the data, correlation coef ficients (R2), error analysis (residual standard error (RSE)) and P-values were calculated. The values of constants obtained from different models werefitted and corresponding q e values were calculated from each model (qecal ). The values of q e found experimentally (q exp) were compared with ecalusing chi-square test (χ2). The chi-square test values were calculated from the following relationχ& =∑q eexp –q ecal hi2 = qe cal ð4ÞThe sum of square error (SSE) values were calculated using the following relationSSE = ∑q eexp –q ecal 2 = N 1 = 2 ð5Þwhere, N is the number of observations. The lower the value ofχ2 andSSE the better is the fit. It was clear fromTable 2that r 2values for all theisotherms were higher (except D –R isotherm at 50 °C), indicating theapplicability of these isotherms. However, Langmuir and Temkinisotherms were better obeyed by the system as indicated by theirle ast χ2 and SSE values. These data also indicated that Freundlichisotherm was obeyed at 40 °C. D–R isotherm was obeyed at 30 and 40 °Cbut at 50 °C the data become insigni ficant because of the higher P-value(P-value N 0.05).3.6. Sorption kineticsIn order to further explore the sorption mechanism of Cu(II) andrate controlling steps, a kinetic investigation was conducted. Pseudo-first-order, Pseudo-second-order and intra-particle diffusion kineticmodels have been used for testing experimental data. The Pseudo-first-order rate equation of Lagergren [38] was widely used for thesorption of liquid/solid system on the basis of solid capacity. The linearform of Lagergren equation is generally expressed aslog q e–qtðÞ=−K1= 2: 303 ðÞ×tðÞ+ logq e ð6Þwh er e , qe ( mg/g) a nd q t (m g/g) ar e th e sorption c apa ci ties at eq uilibriu man d a t tim e t ( min) res pectively. K1(min−1) is the rate constant ofPseudo- first-order sorption process. The values of k1 we re determin edby plotting log(qe–qt)versustandlistedin Table 3. The values of qecalculated from the model (qecal) differed from t he experimen tal values(qeexp) implying that the sorption process did not follow the Pseudo-first-order sorption rate equation.Pseudo-second-order sorption rate equation [39] may be ex- pressed ast =qt=1= K2q2e +1= qeðÞ×t ð7ÞK2(g/mg/min) is the pseudo-second-order sorption rate constant.Plots of t/qtversus t for all experimental concentrations gave straightlines ( Fig. 7), and values of qeand K2 were calculated from the slopeand intercept respectively. The initial sorption rate, h (mg/g/min) isexpressed as [40] .h=K2q2eð8ÞThe values of qe,h,K2and r2 are listed in Table 3. The values ofcorrelation c oef fi ci en ts (r2)werefound tobe verycloseto 1con firming the applicability of the Pseudo-second-order equation. Inaddition, the qe expvalues were very close to qe cal from the modelindicating the better applicability of this model. It can also be seenfrom Table 3 that with an increase in initial metal concentration, therate constant of sorption (K2) decreased. A similar observation was also reported by earlier researchers[41] .The kinetic data were analyzed using intra-particle diffusionmodel to elucidate the diffusion mechanism[42] .qt=Kid×t1= 2+I ð9Þwhere Kid(mg/g/min) is the intra-particle diffusion rate constant and I(mg/g) is another constant that gives an idea about the thickness of aboundary layer, qt is the amount of Cu(II) sorbed (mg/g) at time t (min).Pl ots of qt ve rs us t 1/ 2 are shown in Fig. 8for different concentrations. Thedeviation in the plots from origin for all concentrations indicated thatpore diffusion was not the only sole rate-controlling factor but someother processes likefilm diffusion were also involved in the sorptionProcess.3.7. Sorption thermodynamicsTemperatures used in this study were 30, 40 and 50 °C. Theequilibrium constant at different temperatures can be calculated withthe following relation.Kc=CAc=Ceð10ÞKc is the equilibrium constant. CAc(mg/L) is the amount of Cu(II)sorbed on solid at equilibrium and Ce (mg/L) is the equilibrium concentration of Cu(II) in the solution, respectively. The values of freeenergy change (ΔG°) at different temperatures were calculated fromthe following relationΔG°=−RTlnKcð11Þwhere R is gas constant and T is absolute temperature. van't Hoffequation was applied to calculate the enthalpy change (ΔH°) andentropy change ( ΔS°).lnKc =ΔS°= R –ΔH °=R×1= T ðÞ ð12ÞΔS°and ΔH°can be calculated from the intercept and slope of thelinear plot of lnKcversus 1/T. These values are reported in Table 4. Thenegative value of ΔG°indicated the spontaneous nature of thesorption.ΔG°value was more negative with increase in temperature.The positive value of ΔH°implied that the sorption phenomenon wasendothermic. The positive value of ΔS°suggested increased random-ness at adsorbate –adsorbent interface. The magnitude of Ea indicatedthat the sorption is chemical in nature.3.8. Sorption mechanismIn order to investigate themechanism of Cu(II) sorption by EO, therelease of alkali metals (Na+ and K+) and alkaline earthmetal (Ca2+)present in the sorbent was determined. The released concentrationsof Na+,K+ and Ca2+ during the sorption process were calculated bysubtracting their amount released by washing with DDW (used ascontrol) from the amount released during acidification of EO with0.1 N HCl. The total amount of cations released were 0.07 meq/g(comprise of Ca2+ and Na+ ions) while no K+ was released in eithercase. It has been suggested that the total cationic contents can beconsidered as ameasure of the approximate cation-exchange capacity(CEC) of the sorbent [43].The amount of Na+,K+ and Ca2+ released during the sorption ofCu(II) was also determined in the supernatant liquid (Table 5). Theseresults showed that 0.0634 meq of Cu(II) was sorbed and a sum of0.042 meq Na+ and Ca2+ were released indicating that 0.042 meqremoval of Cu(II) (66.25%) per g of sorbent was by ion-exchangemechanism with Na+ and Ca2+ therefore it may be concluded thatsorption of Cu(II) occurred mainly through ion-exchange mechanisminvolving replacement of Na+ and Ca2+ ions. A similar type ofmechanism has been suggested for mango peel waste [44]. The involvement of ion-exchange process during the sorption of Cu(II)。
