Chemical Engineering Journal 242 (2014) 109–116

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Chemical Engineering Journal

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Preparation of natural cation exchanger from persimmon waste and itsapplication for the removal of cesium from water

1385-8947/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.cej.2013.12.042

⇑ Corresponding author. Tel.: +81 952 28 8671; fax: +81 952 28 8669.E-mail address: inoue@elechem.chem.saga-u.ac.jp (K. Inoue).

Bimala Pangeni a, Hari Paudyal a, Katsutoshi Inoue a,⇑, Keisuke Ohto a, Hidetaka Kawakita a, Shafiq Alam b

a Department of Applied Chemistry, Saga University, Honjo 1, Saga 840-8502, Japanb Faculty of Engineering and Applied Science, Memorial University, St. John’s, NL A1B 3X5, Canada

h i g h l i g h t s

� Novel bio-sorbent for cesium (Cs+) ion removal was fabricated from persimmon waste.� The Cs+ was completely adsorbed onto cross-linked persimmon waste in fixed bed system.� Maximum uptake capacity of persimmon waste was drastically improved after cross-linking.� Mechanism of Cs+ adsorption is inferred to be ion exchange rexn between proton and Cs+.� 92% Toxic volume of Cs+ loaded cross-linked persimmon waste was reduced by simple incineration process.

a r t i c l e i n f o

Article history:Received 5 November 2013Received in revised form 12 December 2013Accepted 17 December 2013Available online 28 December 2013

Keywords:AdsorptionAquatic environmentPersimmon wasteRemoval of radioactive elementsCesium

a b s t r a c t

A novel bioadsorbent prepared from persimmon waste via cross-linking with concentrated sulphuric acidwas investigated for its adsorption behavior towards Cs+. The adsorbent characterization included func-tional group analysis, elemental analysis, total organic carbon measurements and thermo-gravimetricanalysis. The maximum adsorption capacity of PW (0.11 mmol/g) for Cs+ was drastically improved aftercross-linking (0.76 mmol/g), furthermore the uptake capacity of the resulting cross-linked adsorbentappeared to increase with increasing temperature. The observed positive value of enthalpy change andnegative value of Gibbs free energy change suggest that adsorption of Cs+ by this adsorbent is endother-mic and spontaneous in nature. The mutual separation of Cs+ from Na+ can be successfully achieved withquantitative removal of Cs+ within 105 h using a packed column of the adsorbent. Thus, it can beexpected that the CPW investigated in this study will contribute to the remediation of water pollutedby radioactive cesium.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

The existence of radioactive elements in water is of growing con-cern because of their toxic and carcinogenic effects on living organ-isms. The release of large amounts of radioactive elements intoaquatic environment has occurred and the results have been con-firmed as a direct threat to human health [1]. 137Cs is one of suchtoxic radionuclides which had been generated during the nuclearfission reaction of 235U in nuclear weapons testing and some disas-ters that have occurred at atomic power stations such as the Fuku-shima incident on March 11, 2011, in particular [2–4]. Due to theemission of highly penetrating hazardous radiation (c rays and brays), high fission yield, long half life (30 year) and high water sol-ubility, 137Cs can easily enter into human body and persist for longperiod of time where it can potentially irradiate the living tissue,

thus possibly leading to serious diseases such as cancer and leuke-mia [5–7]. Thus, decontamination of aquatic environments pollutedwith Cs+ is a subject which should be urgently resolved [8].

Several physiochemical methods such as evaporation, liquid–liquid extraction, chemical treatment, micro-filtration and mem-brane processes have proven to be effective for the removal ofradionuclide including 137Cs from water and nuclear effluents[9–13]. However, disadvantages such as incomplete removal, highreagent cost and considerable energy requirements, in addition toissues related to the disposal of a considerable quantity of toxicwaste resulting from such processes have all significantly hinderedfurther adoption of such methods. Ion exchangers such as Prussianblue, zeolite, metal hexacyanoferrate and polyphenol rich ion ex-change resins are all effective in removing radioactive cesium fromwater [14,15]. However, due to their high cost, the development ofmore cost-effective remediation system is strongly desired [16].

In recent years, research interest has been focused on theuses of biomass waste for the treatment of water polluted with

110 B. Pangeni et al. / Chemical Engineering Journal 242 (2014) 109–116

radionuclides like 137Cs. Several bio-sorbents such as those derivedfrom coir pith, Azolla filiculoides, marine algae, pine cone powder,Ocimum basilicum, walnut shells and rice hulls were identified aseffective biomaterials for the removal Cs+ from water [16–22].Other studies reported that polyphenol rich ion exchange resinsare also effective for the treatment of Cs+ polluted water [15,23,24].

Persimmon tannin extract is produced by juicing astringentpersimmon rich in persimmon tannin and has been extensivelyuses for various purposes including; natural dyes, paints as wellas historically in leather tanning in Eastern Asia. In the previousstudy, an adsorption gel was prepared from commercially availablepersimmon tannin (PT) extract, produced and marketed by Persim-mon–Kaki Technology Development Co. Ltd., Jincheng, China, foreffective removal of Cs+ from aqueous medium [25]. The commer-cially available powdered persimmon extract are produced fromastringent persimmon in a sequence of juicing by mechanicalcrushing, fermentation and lastly spray drying, taking some costs.During this process, a large amount juice residue is generated aswaste. Thus, the development of adsorbents from such biomasswaste containing high concentration of retained of persimmon tan-nin for the removal and recovery of hazardous radionuclide such as137Cs appears highly promising from the view point of materialcosts and environmental concerns.

In the present work, an attempt has been made to prepare amore economical and environmentally benign adsorbent derivedfrom persimmon waste (PW) generated after the extraction of tan-nin as a potential adsorbent for the adsorption of Cs+ from water.

2. Materials and methods

2.1. Chemicals and analysis

The reagent grade cesium chloride (CsCl) and sodium chloride(NaCl) used in this study were purchased from Wako ChemicalCo. Ltd., Japan. The stock solution (1000 mg/l) of Cs+ was preparedby dissolving 1.26 g of CsCl in 1000 ml of deionized water, whereasthat of Na+ was prepared by dissolving 2.52 g of NaCl in 1000 ml ofdeionized water. The glassware and sample bottles were firstwashed with distilled water then rinsed with deionized water.The pH of the solution was adjusted using a small volume of0.1 M HCl or 0.1 M NaOH (M = mol/l) solution. The concentrationof metal ions in the sample solution before and after adsorptionwas measured using an atomic absorption spectrophotometer(AAS, Shimadzu model AA6800). The total organic carbon leakedfrom feed material, PW, before and after the cross linking was mea-sured using a Shimadzu model TOC–VHS total organic carbon ana-lyzer, whereas the incineration behavior of the adsorbent beforeand after Cs+ adsorption was carried out by means of thermogravi-metrical analysis using a Shimadzu model DTG-60H DTA–TGapparatus.

2.2. Preparation of cross-linked persimmon waste gel

The sample of persimmon waste employed in this study waskindly provided from TOMIYAMA Co. Ltd., Kyoto, Japan. To avoidthe partial dissolution of the adsorbent in aqueous solutions, itwas cross-linked using concentrated sulphuric acid in similar man-ner to the persimmon tannin extract, CPT gel [25]. The sample wasfirst dried and crushed into fine powder, yielding about 15 g ofwhich was mixed together with 30 ml of concentrated sulphuricacid (96%) in a 250 ml eggplant flask, followed by refluxing themixture for 24 h at 373 K in oil bath to achieve cross-linking viacondensation reaction between hydroxyl groups of the polyphenolcompounds contained in the persimmon waste. After completionof the reaction, the black product thus obtained was washed with

deionized water several times until a pH of approx. 7 was obtainedfor the washing water, after which the mixture was then dried in aconvection oven at 343 K for 24 h. The final product thus obtainedwas designated as cross-linked persimmon waste and abbreviatedas CPW gel, hereafter, while the crushed and dried sample of per-simmon waste, the feed material, is abbreviated as PW, hereafter.

2.3. Batch wise adsorption tests

Batch wise adsorption tests were carried out in order to inves-tigate the effect of pH, contact time, concentration and tempera-ture on the adsorption of Cs+ by the CPW gel. Fifteen mg of theCPW gel was combined and mixed with 10 ml of the sample solu-tion containing 0.1 mmol/l of Cs+ ions in a 50 ml glass bottle at var-ious pH ranging from 1 to 8. The mixture was shaken for 24 h at303 K to attain equilibrium, after which the gel was separated fromthe solution by filtration. The concentrations of Cs+ before and afterthe adsorption were measured using the atomic absorption spec-trophotometer. Kinetic measurements were performed by varyingcontact times for a solid liquid ratio of 1 g/l. Isotherm studies werecarried out at a solid/liquid ratio of 1.5 g/l, a pH of 5.7 and usingvarying concentrations (1–10 mmol/l) of Cs+ solutions at differenttemperatures. The % adsorption and the adsorption capacity werecalculated according to the following mass balance equations.

% adsorption ð% AÞ ¼ ðCi � CeÞCi

� 100 ð1Þ

Adsorption capacity ðqÞ ¼ ðCi � CeÞW

� V ð2Þ

where Ci and Ce (mmol/l) are the initial and final concentration ofCs+, respectively. W (g) is dry weight of the CPW gel and V (l) is vol-ume of the metal solution.

2.4. Continuous adsorption test of Cs+ using a fixed bed column

Dynamic adsorption tests for Cs+ and Na+ ions onto the CPW gelwas carried out in fixed bed system using a binary solution con-taining 0.015 mmol/l of Cs+ and 0.30 mmol/l of Na+ ions, within aglass column of 20 cm length and 0.8 cm internal diameter. Beforecolumn packing, 0.15 g of the CPW gel was soaked in deionisedwater for 6 h to allow for complete swelling and to avoid airentrapment in the bed. Conditioning of the gel was then achievedby flowing a metal free solution at the same pH as the metal solu-tion (pH = 5.7) through the column overnight. Afterwards, theabove-mentioned metal solution was percolated through the col-umn at a constant flow rate of 5.1 ml/h in an upward flow modeusing an IWAKI model 100 N peristaltic pump. The effluent sam-ples were collected at various time intervals using a Bio-Rad mod-el-2100 automatic fraction collector. The concentrations of Cs+ andNa+ in the effluent samples were measured using an atomicabsorption spectrophotometer similar to that used during batchwise tests.

2.5. Incineration tests of CPW before and after Cs+ loading

In order to evaluate the incineration behavior, thermogravimet-ric analysis of the dried sample of CPW gel was carried out in a TGAanalyzer, before and after the adsorption of Cs+. For this experi-ment, 10 mg of Cs+ loaded CPW and non loaded CPW were heatedfrom 30 to 900 �C at a heating rate of 10 �C/min to record the per-centage of the remaining weight at varying temperatures for bothsamples.

(a)

(b)

C

ONa

Si

S

S

Ca

Ca

Mn

Mn

Fe

FeCu

C

S

Na

S

Fe

Fe Cu

CsCs

Cs

Cs

Cs

Si

O

Fig. 2. Elemental analysis of CPW gel (a) before and (b) after Cs+ adsorption byenergy dispersive X-ray spectroscopy.

B. Pangeni et al. / Chemical Engineering Journal 242 (2014) 109–116 111

3. Results and discussion

3.1. Characterizations of the adsorbent

Persimmon waste is one of the cellulosic materials which con-tain polyphenolic compounds. Fig. 1 shows the FTIR spectra ofthe feed material for the persimmon waste gel (PW), before andafter cross-linking. The spectrum of the PW shows a broad bandat around 3200–3410 cm�1 which is attributed to the stretchingvibration of phenolic OH groups. The bands observed at around2900 cm�1 and 1687 cm�1 correspond to the CAH and C@Ostretching vibration, respectively. The peak identified at approx.1472 cm�1, 1365 cm�1 and 1240 cm�1 are due to bending vibra-tions of OH groups. In the case of the cross-linked product i.e.CPW gel, the OH stretching peak at 3200–3410 cm�1 becomes lessapparent which is the indication of the OH group of polyphenoliccompounds in PW are mainly involved in the cross-linking reactionby the aid of concentrated sulphuric acid. Most importantly, a newpeak corresponding to CAOAC stretching vibration appeared ataround 1073 cm�1 for the CPW gel, the cross-linked product. Theseresults are likely attributed to the formation of a new structure(CAOAC linkage) via cross-linking reaction between the OH groupsof different polyphenolic compounds.

The adsorption of Cs+ by the CPW gel was further evidencedfrom elemental analysis by EDX spectroscopy. That is, in order toconfirm the direct evidence of Cs+ adsorption by the CPW gel, ele-mental analysis of the CPW gel before and after Cs+ adsorptionwas carried out using an energy dispersive X-ray (EDX) spectros-copy as shown in Fig. 2. It is clear from this figure that the EDXspectra before adsorption (Fig. 2a) showed intense peaks corre-sponding to C(0.24 keV), O(0.36 keV), Na(1.02 keV), Si(1.72 keV),S(2.30, 2.51 keV), Ca(3.69, 3.98 keV), Mn(5.93, 6.49 keV), Fe(6.40,7.06 keV) and Cu(8.06 keV). Comparatively, after the Cs+ adsorption(Fig. 2b), new peaks corresponding to cesium appeared at energyvalues of 4.28, 4.63, 4.95, 5.28, and 5.57 keV, thus providing strongevidence that Cs+ was effectively adsorbed onto the CPW gel.

Furthermore, in order to confirm that cross-linking was effec-tively achieved, the leakage of organics from the persimmon wastebefore and after the cross-linking was examined by measuring the

4000 3100 2200 4001300

Wave number [cm-1]

% T

PW

CPW

Fig. 1. Fourier transform infra red (FT-IR) spectra of persimmon waste (PW) andcross-linked persimmon waste (CPW).

total organic carbon (TOC) concentration as follows. After shakingthe sample before and after cross-linking together with an aqueoussolution at pH = 1 and solid/liquid ratio of 1 g/l for 24 h, the samplewas measured using a total organic carbon analyzer. The total or-ganic carbon concentration was measured as 138.8 and 4.0 mg/lbefore and after the cross-linking, respectively, therefore suggest-ing that the polymer matrix of persimmon waste can be madenearly insoluble in water by the cross-linking reaction with con-centrated sulphuric acid. Thus, the CPW can be expected to beeffectively employed as solid adsorbent for Cs+ ion removal fromwater.

3.2. Batch wise adsorption test

3.2.1. Kinetic studiesThe effect of contact time on the adsorption of Cs+ ions onto the

PW and CPW gel is presented in Fig. 3a. In both cases, a rapid up-take of Cs+ ions was observed at the beginning, possibly a result ofthe high availability of adsorption sites compared to the density ofCs+ ions. It was found that equilibrium was attained within 1 h forboth the adsorbents, suggesting fast kinetics; but in subsequentexperiments, solid liquid mixtures were shaken for 24 h to ensurecomplete equilibrium. The fast adsorption rate of Cs+ onto PW andCPW can be reasonably attributed to the ionization of hydroxylgroups of polyphenol compounds in the adsorbents at around neu-tral pH to form polyphenolate anion, which enhances the effectivecapture of cesium ion, and also to the location of the adsorption

(a)

(b)

Fig. 3. Adsorption kinetics of Cs+ onto CPW and PW gels (a) time dependencystudies and (b) pseudo-second-order plot. Condition: volume of solution = 250 ml,weight of gel = 250 mg, concentration of Cs+ = 0.5 mmol/l, pH = 5.7 andtemperature = 303 K.

Fig. 4. Effect of pH on the adsorption of Cs+ from aqueous solutions onto the CPWgel and PW. Condition: weight of dry gel = 15 mg, volume of the solution = 10 ml,concentration of Cs+ ion = 0.1 mM, temperature = 30 �C, shaking time = 24 h, pHadjusted by 0.1 M HCl and 0.1 M NaOH, shaking speed = 150 rpm.

112 B. Pangeni et al. / Chemical Engineering Journal 242 (2014) 109–116

sites. That is, different from usual adsorbents such as ion exchangeresins and activated carbon, because they are not porous materials,the adsorption does not take place in micropores of the adsorbentbut on their outer surface, which results in the fast kinetics freefrom the diffusion resistance in micropores. Modeling of experi-mental kinetic data was carried out in terms of the pseudo-first-order and pseudo-second-order kinetic models for the evaluationof the best fit model. The pseudo-first-order and pseudo-second-order rate equations are expressed by Eqs. (3 and 4), respectively.

logðqe � qtÞ ¼ log qe �k1

2:303� t ð3Þ

tqt¼ 1

k2 q2eþ t

qeð4Þ

where qt and qe are the amount of adsorbed Cs+ (mmol/g) at time tand at equilibrium time, respectively. k1 and k2 are first-order andsecond-order rate constants for adsorption. The kinetic parameterswere estimated by plotting log(qe–qt) vs t for the pseudo-first orderreaction and t/qt vs t for the pseudo-second order reaction, respec-tively. It was found that the values of correlation coefficientobtained for the pseudo-second-order equation for both the adsor-bents (Fig. 3b) were higher than that for the pseudo-first-order

equation (<0.85 for both, not shown); thus, the pseudo-second-order model was concluded to be best fit equation. Moreover, theevaluated values of qe (0.24 and 0.10 mmol/g for CPW and PW,respectively) according to the pseudo-second-order kineticequation were found to be very close to those evaluated in the equi-librium adsorption test (0.23 and 0.09 mmol/g for CPW and PW,respectively); thus, it can be concluded that the Cs+ adsorption ontoCPW and PW takes place in accordance with the pseudo-second-orderkinetics. The values of adsorption rate constant k2 for CPW and PWwere evaluated to be 5.02 and 2.24 g mmol�1 h�1

, respectively.

3.2.2. Influence of pH on Cs+ adsorptionFig. 4 shows the % adsorption of Cs+ ions onto the PW and CPW

gel at varying pH. Sharp increase in the adsorption from 3.7% to75.8% onto CPW gel is observed with increasing pH from 1.5 to3.8, followed by a gradual increase up to a pH of around 5, eventu-ally reaching a constant value at pH 5. However, in the case of PW,the % adsorption increased from 0.34 to only 24% with the increasein solution pH from 1.5 to 5, from which it may be inferred that themajority of polyphenolic compounds which function as activeadsorption sites in the PW leaked out into the water during theadsorption tests, resulting in the possible reduction in adsorptionefficiency. As mentioned earlier, the leakage of total organic carbonincluding polyphenolic compounds from the PW was drasticallysuppressed by cross-linking using concentrated sulphuric acid(from 133 down to less than 4 mg/l), which is hypothesized to beresponsible to the potential improvement in Cs+ ion adsorption.The increase in the adsorption with increasing pH suggests thatCs+ ion is adsorbed according to the cation exchange mechanismwith proton as follows. That is, with increasing pH, polyphenolcompounds contained in PW and CPW are dissociated into poly-phenolate anion as depicted by Scheme 1(a). Such polyphenolateanions are easy to interact with cationic species including Cs+

ion. It was found that equilibrium pH of the solution after Cs+

adsorption onto PW and CPW decreased which is one of the strongevidence of releasing protons during adsorption process. At lowerpH, there is strong competition between hydrogen and cesiumion for the active sites resulting the decrease of adsorption effi-ciency for cesium ion. This effect is insignificant or low at pH high-er than 5 showing negligible interference in the Cs+ adsorption.

Since, as well known, polyphenolate anions are apt to form sta-ble five-membered chelating complexes with cationic metal ions, it

OH

OH+ H+

O-

OH

Higher

pH

Polyphenol Polyphenolate anion

Cs

O

OH

O-

OH

Cs+

solution

Polyphenolate anion Cs chelated polyphenol

(b)

(a)

Scheme 1.

B. Pangeni et al. / Chemical Engineering Journal 242 (2014) 109–116 113

can be reasonably inferred that the interacted Cs+ ions furtherforms chelating complex as shown in Scheme 1(b). That is, it is in-ferred that adsorption of Cs+ onto the PW and CPW gel takes placeby cation exchange and chelation mechanism similar to that ob-served in cross-linked tea leaves (CTL) and cross-linked persimmontannin (CPT) investigated earlier [25]. In such studies, the equilib-rium pH of the solution in both cases was found to decrease afterCs+ adsorption, which is likely attributable to the release of protonsas demonstrated by reaction (a).

3.2.3. Adsorption isotherm of Cs+ on the CPW gelFig. 5 shows the adsorption isotherms of Cs+ on the CPW gel at

varying temperatures from 298 up to 313 K, as well as for the PWat 303 K, for comparison. The results clearly demonstrate that theextent of adsorption in all cases was found to increase withincreasing equilibrium concentration and temperature. Theamount of Cs+ adsorbed increased abruptly with the increase inconcentration of Cs+ in the low concentration range whereas it at-tains a plateau value at higher concentrations. The experimentaldata were modeled on the basis of the Freundlich and Langmuirisotherm models. The Freundlich isotherm equation is expressedas:

log qe ¼ log Kf þ ð1=nÞ log Ce ð5Þ

where Ce (mmol/l) and qe (mmol/g) are equilibrium concentrationand amount of adsorption, respectively. The values of the

Fig. 5. Adsorption of Cs+ on the CPW gel at different temperature and onto PW at303 K for comparison. Condition: weight of dry gel = 15 mg, volume of thesolution = 10 ml, pH = 5.7, shaking time = 24 h, shaking speed = 150 rpm.

Freundlich adsorption isotherm constants, n and Kf, were calculatedfrom the slope and the intercept of the straight line for the plot oflog qe vs log Ce according to Eq. (5), respectively, and the valuesare listed in Table 1.

On the other hand, the Langmuir isotherm equation can be ex-press as:

Ce

qe¼ 1

qmaxbþ Ce

qmaxð6Þ

where qmax (mmol/g) is the maximum loading capacity and theconstant, b (l/mmol), is the Langmuir’s adsorption equilibriumconstant, which is related to binding energy associated with theadsorption process.

The maximum adsorption capacities (qmax) and bindingconstant (b) for the PW at 303 K and for the CPW gel at varyingtemperatures were evaluated from the slopes and intercepts ofthe straight lines for the plot of Ce/qe vs Ce calculate using Eq. (4)and the evaluated values are also listed in Table 1. The experimen-tal data were best fitted to the Langmuir model than the Freundlichmodel as evident from the high correlation regression coefficient(Table 1), suggesting that adsorption of Cs+ by the CPW gel takesplace according to the Langmuir’s monolayer adsorption model.

From the comparison of the maximum adsorption capacity ofthe PW and the CPW gel at 303 K, it is clear that the adsorptioncapacity of PW (0.11 mmol/g) was drastically enhanced aftercross-linking into the CPW gel (0.76 mmol/g), as mentioned earlier.It is also clear from Fig. 5 that Cs+ adsorption onto the CPW gelincreased with increasing temperature, suggesting that the adsorp-tion of Cs+ onto the CPW gel is endothermic in nature, which wasfurther proven by the calculation of thermodynamic parameters.From the Langmuir’s adsorption equilibrium constants, b, at differ-ent temperatures, thermodynamic parameters such as enthalpychange (DH), entropy change (DS) and Gibbs free energy change(DG) for the adsorption reaction of Cs+ by the CPW gel, were calcu-lated based on the following equations:

DG ¼ DH � TDS ð7Þ

DG ¼ �RT lnb ð8Þ

Combination of Eqs. (7 and 8) gives

lnb ¼ �DH=RT þ DS=R ð9Þ

where DG (kJ/mol), DH (kJ/mol) and DS (kJ/mol K) are the change inGibbs free energy, enthalpy and entropy, respectively. R (8.314 J/mol K) is the universal gas constant and T is the absolute temper-ature in Kelvin.

The Gibbs free energy change (DG) were calculated for all thetemperatures according to Eq. (7) and the values of enthalpychange (DH) and entropy change (DS) were calculated from theslope and intercept of the straight line of the lnb vs 1/T plot(Fig. 6), respectively. These values are also listed in Table 2, whichshows that the values of Gibbs free energy change (DG) for alltemperatures examined is negative, thus confirming the sponta-neous nature of adsorption. The evaluated value of enthalpychange (DH, 40.69 kJ/mol) was positive, indicating that theadsorption of Cs+ onto the CPW gel is endothermic in nature.The positive value of the entropy change observed (DS, 0.14kJ/mol K), suggests that the adsorption reaction taking place onthe adsorbent surface with increasing entropy is accompaniedby the release of protons as well as water molecules during theadsorption process.

3.2.4. Comparisons with other adsorbentsAlthough the maximum uptake capacity of the adsorbent is

dependent on pH, temperature and the nature of the competingspecies, the comparison of the maximum adsorption capacity of

Table 1The Langmuir and Freundlich adsorption isotherm parameters for the adsorption of Cs+ onto PW and CPW gel.

Adsorbents and temperature pH Langmuir isotherm parameters Freundlich isotherm parameters

qmax (mmol/g) b (l/mmol) r2 Kf 1/n r2

CPW at 293 K 5.7 0.38 2.79 0.99 0.48 0.38 0.98CPW at 398 K 5.7 0.54 4.75 0.98 0.54 0.39 0.99CPW at 303 K 5.7 0.76 4.96 0.99 0.62 0.35 0.97CPW at 308 K 5.7 0.92 1.31 0.99 0.69 0.33 0.98PW at 303 K 5.7 0.11 0.64 0.99 0.35 0.09 0.87

Fig. 6. Vent Hoff’s plot for the adsorption of Cs+ onto the CPW gel.

Table 2Thermodynamic parameters calculated from the Langmuir equilibrium constants forthe adsorption of Cs+ onto the CPW gel.

Temp. (K) qmax

(mmol/g)b(l/mmol)

DG(kJ/mol)

DH(kJ/mol)

DS(kJ/mol K)

293 0.38 2.79 �2.50 40.7 0.14298 0.54 4.75 �3.80303 0.76 4.96 �4.03308 0.92 6.79 �4.90

Table 3Comparison of the maximum adsorption capacities of the persimmon wasteadsorbent investigated in this study with that of various adsorbent for Cs+.

Adsorbents pH Temp.(K)

qmax (mmol/g)

Ref.

CPW gel 5.7 308 0.92 Thiswork

CPW gel 5.7 303 0.76 Thiswork

CPW gel 5.7 298 0.54 Thiswork

CPW gel 5.7 293 0.38 Thiswork

PW 5.7 303 0.11 Thiswork

Zeolite A 8 298 1.67 [14]Dry Azolla filiculoides adsorbent 8 - 0.53 [16]Unmodified Coir pith (CP) 5 300 0.41 [17]NiHCF modified coir pith

(NIHCF-CP)5 300 0.70 [17]

Dictyota indica biomass 5.5 303 0.23 [18]FAS1 derived Scinaia carnosa 5.5 303 0.67 [18]Chemically modified walnut

shell– 298 0.03 [21]

CPT gel 6.1 303 1.31 [25]Prussian blue (PB) 7.5 310 5.38 [26]

114 B. Pangeni et al. / Chemical Engineering Journal 242 (2014) 109–116

the reported adsorbents provides some indication as to thepotential for real application. Table 3 shows the comparison ofthe maximum adsorption capacity of the PW and CPW gel for Cs+

with other various adsorbents reported in literature. This tablesuggests that the CPW gel exhibits a higher adsorption capacityfor Cs+ than the majority of the adsorbents reported in the litera-tures although Prussian blue, Zeolite A, and CPT gel appear toexhibit a higher adsorption capacity than the CPW gel. However,the porous structure of Prussian blue and Zeolite A generally sufferfrom clogging of their micropores by very fine solid particlesusually existing in waste water during the treatment, potentiallyreducing adsorption capacity in addition to their high cost.Comparatively, the preparation of the CPW gel investigated in thisstudy is very simple. It is environmentally friendly and economicalbecause the feed material is persimmons waste itself and usesfewer chemicals. The Cs+-loaded CPW is easily incinerated andmore than 92.6% of its volume can be reduced by the simple incin-eration process as will be described in detail in the later section.Therefore, the utilization of persimmon waste for the preparationof a more sophisticated adsorbent for Cs+ appears more promisingfor environmental remediation.

3.3. Mutual separation of Cs+ from Na+ using a packed column of theCPW gel

Fig. 7 shows the breakthrough profile of Cs+ in the presence ofNa+ which is usually present in Cs+ polluted water, from a fixedbed column of the CPW gel. It is clear from this figure that the con-centration of Cs+ in the outlet stream is negligible up to 90 h, afterwhich trace concentrations of Cs+ appears and gradually increases;reaching nearly the same concentration as that observed in thefeed solution after 200 h. However, in the case of Na+, the break-through appeared after only 1 h, suggesting that the adsorptionof Cs+ was hardly affected by co-existing Na+, which is attributedto the high affinity of the polyphenolic functional groups of theCPW gel for Cs+ in compared to Na+. Thus, mutual separation ofCs+ from Na+ can be successfully achieved using a packed columnof the CPW gel. The column capacity for Cs+ and Na+ onto thebed of the CPW gel was evaluated as 0.067 and 0.039 mmol/g,respectively, from the area of breakthrough curve. The value forthe Cs+ is much lower than the maximum adsorption capacity eval-uated from batch wise studies (0.76 mmol/g), which may be rea-sonably attributed to the reduced velocity of the feed solution inattaining equilibrium.

3.4. Thermogravimetric analysis of CPW gel before and after Cs+

adsorption

One of the most important and advantageous characteristic ofadsorbents prepared from waste biomass is their ease of incinera-tion, which makes post-treatment much easier compared withorganic and inorganic ion-exchangers produced from plastics and

Fig. 7. Breakthrough profile of Na+ and Cs+ from a fixed bed column packed withthe CPW gel. Condition: weight of dry gel = 0.15 g, flow rate = 5.1 ml/h, pH = 5.7,metal ion concentrations = 0.015 mmol/l Cs+ and 0.30 mmol/l Na+, tempera-ture = room temp.

Fig. 8. Thermo gravimetric analysis of the CPW gel before and after Cs+ loading (therelationship between weight loss percentage and incineration temperature).

B. Pangeni et al. / Chemical Engineering Journal 242 (2014) 109–116 115

refractory materials. Because the natural polymeric materialsincluding PW and the CPW gel are partly deteriorated by irradia-tion, PW and the CPW are unsuitable for prolonged use by repeatedadsorption and elution during the treatment of radioactive wastes.For such a cases, the best scenario is one time adsorption withoutelution, but followed by incineration of the adsorbents loaded withradioactive elements, which results in dramatically reducing theirvolume as the smaller the volume of such hazardous materials, thegreater the ease for their extended safe storage. An incinerationbehavior of CPW before and after Cs+ loading was carried out inorder to evaluate the ease of incineration as shown in Fig. 8. Theresult shows the percentage of weight loss for both CPW andCs–CPW as a function of incineration temperature. The organic partof the gel is decomposed into CO2 and H2O whereas the inorganicpart of the gel including the loaded cesium is converted into itsoxide and left in the ash. It is clear from this figure that 92.6%weight of the cesium loaded gel (Cs–CPW) was reduced afterincineration, whereas it was 97.4% in the case of the non-loadedgel (CPW), which suggests the presence of 4.8% of cesium in

Cs–CPW. From this result, easy incineration of Cs–CPW with a dra-matic reduction of its toxic volume indicating that, the incinerationof Cs–CPW can be a more advantageous and promising alternativefrom the view point of effective management of CPW loaded withradioactive cesium for environmental remediation.

4. Conclusions

In this study, a novel and highly efficient adsorbent for Cs+ havebeen developed from persimmon waste, which were characterizedby IR and EDX spectroscopy. The uptake capacity of Cs+ was eval-uated to be 0.76 mmol/g at 303 K, which increased with increasingtemperature. The calculation of the thermodynamic parametersshowed that the adsorption of Cs+ onto the CPW gel is an endother-mic and spontaneous process. The removal of Cs+ using a packedcolumn of the CPW gel exhibited 100% removal up to 105 h, thusthe CPW gel could be a promising adsorbent for the remediationof Cs+ polluted water.

Acknowledgement

This study was financially supported by Grant-in-Aid forExploratory Research by the Japan Society for the Promotion ofScience (JSPS) (KAKENHI No. 24656551).

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