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Biosorptive behaviour of rice hulls for Cs134 from aqueous solutions: A radiotracer study

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Biosorptive behaviour of rice hulls for Cs134 from aqueous solutions: A radiotracer study
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  This article was srcinally published in a journal published byElsevier, and the attached copy is provided by Elsevier for theauthor’s benefit and for the benefit of the author’s institution, fornon-commercial research and educational use including withoutlimitation use in instruction at your institution, sending it to specificcolleagues that you know, and providing a copy to your institution’sadministrator.All other uses, reproduction and distribution, including withoutlimitation commercial reprints, selling or licensing copies or access,or posting on open internet sites, your personal or institution’swebsite or repository, are prohibited. For exceptions, permissionmay be sought for such use through Elsevier’s permissions site at:http://www.elsevier.com/locate/permissionusematerial     A   u    t    h   o   r    '   s    p   e   r   s   o   n  a    l    c   o   p   y Applied Radiation and Isotopes 65 (2007) 280–286 Biosorptive behaviour of rice hulls for Cs-134 from aqueous solutions:A radiotracer study Shuddhodan P. Mishra a , Shailesh K. Prasad b , Ram S. Dubey c , Manisha Mishra c,1 ,Diwakar Tiwari d , Seung-Mok Lee d,  a Nuclear & Radiation Chemistry Laboratory, Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India b Department of Chemistry, National Institute of Technology, Jamshedpur 831 014, India c Department of Biochemistry, Banaras Hindu University, Varanasi 221 005, India d Department of Environment & Disaster Prevention, Kwandong University, Yangyang 215 802, Korea Received 9 August 2006; received in revised form 26 September 2006; accepted 27 September 2006 Abstract Removal behaviour of rice hulls was assessed for the removal of Cs-134 from aqueous solutions. Results obtained from batch-typeexperiments revealed that relatively low uptake of Cs(I) was favoured with increasing the sorptive concentration (from 1  10  8 to1  10  2 molL  1 ), temperature (298–328), and pH (2.40–10.20). The concentration dependence data fitted well for Freundlich adsorptionisotherm. Thermodynamic parameters revealed that the uptake process was endothermic and proceeded via ‘ion exchange’ along with‘surface complexation’. Moreover, the adsorbed species were not to be desorbed into the bulk concentration even at elevatedtemperatures, i.e., up to 328K hence forming a stable adsorption phase. Further, the radiation stability of the rice hulls samples was alsoassessed by exposing it towards 300mCi neutron source having the neutron flux of ca. 3.85  10 6 ncm  2 s  1 associated with nominal  g -dose of ca. 1.72Gyh  1 and indeed it was observed that the rice hulls samples were found to be stable at least for the removal of Cs-134. r 2006 Elsevier Ltd. All rights reserved. Keywords:  Cs-134; Rice hulls; Sorption; Freundlich isotherm; Radiation stability; ion exchange 1. Introduction The role of dead biomasses in the removal of heavymetal toxic ions received an increased attention duringrecent past as due to its fairly good exchange capacity, large abundance, and also cost effectiveness (Daifullah etal., 2003; Mishra et al., 1998; Tiwari et al., 1999; Volesky, 1994). However, scanty reports appeared for the possibleapplication of dead biomasses in the removal of radiotoxicions particularly the radiocesium and radiostrontium. Thefeasibility of cesium removal was assessed by using variousderived biosorbents to ferrocyanide type1 (FAS1) andtype2 (FAS2) and these modified biosorbents were moreefficient than the srcinal one as they can remove almost allcesium from aqueous solutions (370mgL  1 cesium solu-tion) just within 30min of contact and the uptake processwell suited at a wide pH range (1–10) and unaffected withthe sodium and/or potassium ion concentrations 0.5 and1mM (Jalali-Rad et al., 2004). Moss ( Funaria hygrome-trica ), a phyto-sorbent was used for the removal of   137 Csand  90 Sr in batch laboratory experiments. It was reportedthat very rapid uptake of these radionuclides furtherincreased with increasing the solution pH and also withpre-NaOH-treated moss. They proposed that if the largequantities of this moss could be grown under artificialconditions, phyto-sorption using moss might emerge as aviable technology for the routine cleanup of low level wastesolutions and the recovery of carrier-free  137 Cs/ 90 Sr alsoappears to be possible (Balarama et al., 2004).Further, the abundance of rice hulls has been welldocumented (Grist, 1975) and the statistical data of theFAO, there is an estimated annual rice production of 500 ARTICLE IN PRESS www.elsevier.com/locate/apradiso0969-8043/$-see front matter r 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.apradiso.2006.09.007  Corresponding author. Tel.: +82336703355; fax: +82336703369. E-mail addresses:  s_mishra99@yahoo.co.in (S.P. Mishra),leesm@kd.ac.kr (S.-M. Lee). 1 Present address: Department of Biochemistry, VBS PurvanchalUniversity, Jaunpur 222 001, India.     A   u    t    h   o   r    '   s    p   e   r   s   o   n  a    l    c   o   p   y million tons in developing nations; approximately 100million tons of rice hulls are available annually forutilization in these countries. However, the amount of ricehusk available is far in excess of any local uses and, thus,has posed disposal problems (Guo et al., 2000). Theliterature revealed that rice husk has a low calorific value of 3585kcalkg  1 and high ash content (Olmez, 1988). Due toits high ash content, a proper method of disposal andutilization of rice hulls has yet to be developed (Mansaralyand Ghaly, 1998). However, studies have also shown that rice hulls are suitable for the production of activatedcarbon (Guo et al., 2000; Usmani et al., 1993). It is to be noted that rice hulls widely been applied for the removal of several heavy metal, toxic ions along with the dyes fromaqueous solutions are well reviewed earlier (Chuah et al.,2005). However, its role in the removal of radionuclides isyet to be studied. We already tried to employ such deadbiomasses viz., rice hulls, Mango ( Mangifera indica ), andNeem ( Azadirachta indica ) bark samples in the removal of one of the important fission fragment viz.,  (85+89) Sr andindeed these are found to be quite promising for suchstudies. In addition to their good uptake behaviour, thesesolids are also found to be stable towards ionizingradiations (Mishra and Tiwari, 2002). Hence, in a line,with an increased interest we also tried to assess theremoval behaviour of rice hulls for one of the importantradionuclide  134 Cs. 2. Experimental  2.1. Materials Stock solution of Cs(I) (1.0molL  1 ) was prepared bydissolving the appropriate amount of cesium sulphate (GRGrade) in double distilled water. Radioisotope Cs-134 (t 1/2 ¼ 2.06yr; specific activity ¼ 8.44Ciml  1 ) was procuredfrom the Board of Radiation and Isotope Technology(BRIT), Mumbai (India). All other chemicals used wereAR/GR grade and were used without any further purifica-tion.Rice hulls were taken out mechanically from the seeds of  cv  Jaya in the laboratory in a usual way, crushed andwashed repeatedly by doubly distilled water; dried at roomtemperature, and then employed as an adsorbent during allthe batch experiments.  2.2. Constituents of rice hulls Tables 1 and 2 showed the typical composition andchemical compositions of  rice hulls and already reported values of its physicochemical characteristics (Malik, 2003;Rahman and Ismail, 1993; Rahman et al., 1997).  2.3. Instrumentation The  b - and  g -activities were measured respectivelyby using end-window GM counter (ECIL, ElectronicsCorporation of India Ltd., Hyderabad, Type 1600 counter)and  g -ray single channel spectrophotometer (ECIL SC-604)coupled with NaI(Tl) scintillation detector obtained fromECIL. Multichannel analyzer, Canberra Series 35 Plus(model 3501), was also used for measuring the  g -activity.The radiation stability of rice hulls samples was assessed byexposing the sample towards 11.1GBq (Ra–Be) neutronsource having an integral neutron flux of 3.85  10 6 ncm  2 s  1 and associated with a nominal  g -doseof ca. 1.72Gyh  1 (obtained from BRIT, Mumbai). ThepH metre (ECIL, S-290, pH 5651) was used with glass andcalomel electrode assembly.  2.4. Sorption experiments The sorption procedure consists of keeping a weighedquantity of rice hulls sample (0.1000g) in 10.0mL of thelabelled sorptive solution (i.e., Cs(I) of the requiredconcentration and acidity in a conical glass centrifuge tube(Vensil)). The whole system was thermostated at therequired temperature. Unless otherwise specified, allexperiments were carried out at 298K except in thetemperature dependence studies, where temperature wasvaried from 298 to 328K. During the total period of adsorption, the solution was constantly stirred withuniform speed so that the sphere of the concentration ARTICLE IN PRESS Table 1Typical composition of rice husk (Rahman and Ismail, 1993; Rahman et al., 1997)Composition PercentCellulose 32.24Hemicellulose 21.34Lignin 21.44Extractives 1.82Water 8.11Mineral ash 15.05 Chemical composition in mineral ash SiO 2  96.34K 2 O 2.31MgO 0.45Fe 2 O 3  0.2Al 2 O 3  0.41CaO 0.41K 2 O 0.08Table 2Reported physicochemical characteristics of rice hulls (Malik, 2003)Bulk density (gmL  1 ) 0.73Solid density (gmL  1 ) 1.5Moisture content (%) 6.62Ash content (%) 45.97Particle size (mesh) 200–16Surface area (m 2 g  1 ) 272.5Surface acidity (meqg  1 ) 0.1Surface basicity (meqg  1 ) 0.45 S.P. Mishra et al. / Applied Radiation and Isotopes 65 (2007) 280–286   281     A   u    t    h   o   r    '   s    p   e   r   s   o   n  a    l    c   o   p   y gradient around one particle does not interface with theother. Before adding the adsorbent, an aliquot of the bulksolution was withdrawn using a 50 m L SIGMA micropip-ette for the measurement of the initial radioactivity. Theprogress of adsorption of Cs(I) ions with time was thenfollowed by measuring the radioactivity of such with-drawals of the contact solution at definite time intervals.Special care was taken to avoid any particle coming withthe solution. For this, the tubes were placed in a centrifugemachine, centrifuged at 3000rpm and the solution wasallowed to stand for ca. 30s before each withdrawal. Toachieve a constant adsorption value and to be able toobserve various steps of the adsorption, the experimentswere carried out for 24h of contact time. Each aliquot wastransferred to an aluminium planchette and dried slowlyunder an infrared lamp. The radioactivities of all thesamples were measured for its  b -activities; also somesamples were chosen for their  g -activities by usingrespectively, the  b - and  g -counters. The parallel controlexperiments were performed and the activities wererecorded after 24h of contact and it was observed thatthe change in activity was found to be insignificant as lessthan 1%. Hence, no necessary correction was done for theadsorption studies.The relative amount of adsorption was evaluatedadopting the differential method, i.e., the differencebetween the activity (and hence, concentration) beforeand after the addition of adsorbents: a t  ¼ R 0  R t R 0  C   V m , (1)where  a t  is the amount adsorbed (molg  1 ) at time ‘ t ’,  R 0 and  R t  are the radioactivities of bulk at zero time andtime ‘ t ’, respectively.  C   is the initial concentrationof the adsorptive solution (molL  1 ),  V   is the volumeof the adsorptive solution ( L ) and  m  is the mass of adsorbent ( g ). 3. Results and discussion 3.1. Effect of concentration The sorption of Cs(I) on the surface of rice hulls wascarried out as a function of time and the results obtainedfor different initial sorptive concentrations are showngraphically in Fig. 1. The figure clearly showed a sharpinitial rise of uptake slowed down with lapse of time andattained a constant value within 6h of contact. No furtherchange in sorption was observed even after a contact timeof 24h. Quantitatively, it is evident that with increasingsorptive concentration (from 1.0  10  8 to 1.0  10  2 molL  1 ), the amount adsorbed increased from0.1774  10  9 to 0.0852  10  3 molg  1 . However, thepercent removal decreased from 17.74 to 8.52% for asimilar increase in sorptive concentration. This suggeststhat, at low sorptive concentrations, more and more activesites are available for relatively lesser number of sorbingspecies. Hence, an enhanced percentage of adsorption wasobserved at low sorptive concentration. 3.2. Equilibrium modelling The concentration dependence data obtained at equili-brium stage between the solid/solution interfacewere further utilized for adsorption isotherm studiesand it was found that these data were fitted well forFreundlich adsorption isotherm (Eq. (2)) as a goodlinear regression was obtained (Fig. 2) while plotting ARTICLE IN PRESS Time (hrs)024681012    A  m  o  u  n   t  a   d  s  o  r   b  e   d   (  m  o   l  g   -   1    ) 0.000.040.080.120.160.20 ×  10 -3 ×  10 -4 ×  10 -5 ×  10 -6 ×  10 -7 ×  10 -8 ×  10 -9 Multiplication factor for Y-axis10 -8  mol L -1 10 -7  mol L -1 10 -6  mol L -1 10 -5  mol L -1 10 -4  mol L -1 10 -3  mol L -1 10 -2  mol L -1 Fig. 1. Variation of sorption of Cs(I) on rice hulls at various concentrations of Cs(I) solutions (temperature ¼ 298K; pH  6.40). S.P. Mishra et al. / Applied Radiation and Isotopes 65 (2007) 280–286  282     A   u    t    h   o   r    '   s    p   e   r   s   o   n  a    l    c   o   p   y Log a e  vs. Log C  e .Log a e  ¼ 1 n Log C  e þ Log K  , (2)where  a e  and  C  e  are the amount adsorbed (molg  1 ) andbulk concentration (molL  1 ) at equilibrium, respectivelyand  K   and 1 /n  are the Freundlich constants referring toadsorption capacity and adsorption intensity, respectively.These constants, i.e.,  K   and 1 /n  were estimated respectivelyby intercept and slope of the straight line and the valuesobtained were respectively, 7.87 7 0.03  10  3 and0.949 7 0.004molg  1 . The fractional value of 1/ n  (0 o 1/ n o 1) points towards a heterogeneous surface structure of rice hulls (Benes and Majer, 1980). 3.3. Effect of temperature In order to find out the thermodynamic data, weperformed the sorption studies by varying the solutiontemperature from 298 to 328K in the step of 10K whilekeeping the initial sorptive concentration1.0  10  5 molL  1 and pH  6.40 as constant and theresults were returned in Table 3. Results clearly showedthat with the increase in temperature, an apparent increasein uptake of Cs(I) occurred on the surface of rice hulls.Moreover, it was interesting to note that the time requiredto attain saturation was almost unaffected by the variationof temperature. This increase in sorption could be due tocreation of some new active sites or even due to thetransport against a concentration gradient and/or diffusion-controlled transport across the energy barrier (Ting andTeo, 1994). Al-Asheh and Duvnjak (1995) assumed that the increase of biosorption with temperature is due, likelyto the acceleration of the movement of metal ions from thebulk solution to the surface of biosorbent or due to theenhanced temperature-dependent hydrolysis of some com-ponents available at the surface of sorbent, which respondto metal sorption.Kinetic analysis for the sorption of Cs(I) on rice hullswas worked out at different temperatures followed the first-order rate kinetics [Lagergren’s Eq. (3)] since a goodlinearity was obtained while plotting Log( a e  a t ) vs. time:Log ð a e  a t Þ¼ Log a e   k  1 2 : 303 t , (3)where  a e  and  a t  are the amount of Cs(I) adsorbed atequilibrium and at time ‘ t ’.  k  1  denotes the adsorption rateconstant. The numerical values of the rate constants atdifferent temperatures were estimated and are given inTable 3. The values of the adsorption rate constantsincreased with increasing temperature. These kinetic datawere further utilized in deducing the activation energy ( E  a )of adsorption process as obtained by the slope of theArrhenius plot (i.e., Log k  1  vs. 1/ T  ) (Fig. 3). The activationenergy involved was found to be 14.45 7 0.09kJmol  1 .Numerically low value of activation energy indicates thatthe forces of attraction operating during the adsorption of Cs(I) on rice hulls were relatively strong and the elementary ARTICLE IN PRESS -Log C e  (mol dm -3 )02468   -   L  o  g  a   e    (  m  o   l  g   -   1    ) 0246810R 2  = 0.9996 Fig. 2. Freundlich adsorption isotherm of Cs(I) on rice hulls at 298K.Table 3Temperature dependence of equilibrium sorption/desorption of Cs(I) on rice hulls (initial sorptive concentration ¼ 1.0  10  5 molL  1 ; pH  6.40)Temperature ( K  ) Amount of Cs(I) sorbed, 7 3 s  10  6 (molg  1 )Rate constant  k  1 7 3 s  10  3 (min  1 )Desorption in equilibrium bulkconcentration (%)298 0.152 7 0.001 4.28 7 0.02 2.2308 0.177 7 0.004 5.28 7 0.05 3.2318 0.202 7 0.002 6.25 7 0.03 2.8328 0.226 7 0.002 7.30 7 0.04 3.8 1/T (K -1 ) x 10 -3 3.003.053.103.153.203.253.303.353.40    L  o  g   k    1    (  m   i  n   -   1    ) -2.05-2.00-1.95-1.90-1.85-1.80-1.75R 2  = 0.9980 Fig. 3. Arrhenius plot for the sorption of Cs(I) on rice hulls (initialconcentration of Cs(I) ¼ 1.0  10  5 molL  1 ; pH  6.40]). S.P. Mishra et al. / Applied Radiation and Isotopes 65 (2007) 280–286   283

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