Removal of Heavy Metals by Sawdust Adsorption: Equilibrium and Kinetic Studies

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1 Environ. Eng. Rs. Vol. 3, No., pp. 79~84, 008 Koran Socity of Environmntal Enginrs Rmoval of Havy Mtals by Sawdust Adsorption: Equilibrium and Kintic Studis Jihyun Lim, H-Man Kang, L-Hyung Kim, and Sok-Oh Ko Dpartmnt of Civil Enginring, Kyungh Univrsity, Kora Kora Highway & Transportation Tchnology Institut, Hwasung, Kora Dpartmnt of Civil and Environmntal Eng., Kongju National Univrsity, Kongju, Kora Rcivd Novmbr 007, accptd March 008 Abstract Adsorption of havy mtals by sawdust was invstigatd to valuat th ffctivnss of using sawdust to rmov havy mtals from aquous solutions. Kintic and isothrm studis wr carrid out by considring th ffcts of initial concntration and ph. Th adsorption isothrms of havy mtals fittd th Langmuir or Frundlich modl rasonably wll. Th adsorption capacity of mtal was in th ordr Pb + > Cu + > Zn +. A high concntration of co-xisting ions such as Ca + and Mg + dprssd th adsorption of havy mtal. Adsorption data showd that mtal adsorption on sawdust follows a psudo-scond-ordr raction. Kintic studis also indicatd that both surfac adsorption and intraparticl diffusion wr involvd in mtal adsorption on sawdust. Column studis prov that sawdust could b ffctiv biosorbnt for th rmoval of havy mtals from aquous phas. Kywords: Adsorption, Brakthrough, Havy mtal, Isothrm, Kintics, Sawdust. Introduction Havy mtals ar toxic pollutants rlasd into aquous systm as a rsult of various activitis such as industry, mining, and agricultur. Thr ar many mthods for th rmoval of mtal ions from solutions including, chmical prcipitation, complxation, solvnt xtraction, and mmbran procsss. Howvr, most of ths mthods ar ithr conomically prohibitiv or too complicatd for th tratmnt of mtals. ) Manwhil, adsorption procsss hav shown many advantags ovr ths physicochmical mthods. Thy ar quit slctiv, ffctiv, and ar abl to rmov various lvls of solubl havy mtals in solution. In rcnt yars, considrabl attntion has bn focusd on th rmoval of havy mtals using biosorbnts drivd from low-cost matrials. Svral biosorbnts such as pat, sawdust, swag sludg, and crop wast hav bn usd for th tratmnt of mtals in aquous solution. -7) In this study, sawdust, which has nvironmntal bnfits in trms of th rus of solid wast, was tstd to valuat its potntial for th tratmnt of havy mtals. Th adsorption rat and capacity pr unit mass of sawdust may b Corrsponding author soko@khu.ac.kr Tl: , Fax: important paramtrs in th tratmnt procss. It dtrmins th sorbnt rplacmnt frquncy and th conomics of opration. Thrfor, th paramtrs and mchanisms affcting th mtal adsorption of sawdust must b idntifid prior to th application of adsorption systm. Th objctiv of this study is to invstigat th fasibility of utilizing sawdust for th adsorption of havy mtals in aquous solution. Kintics and isothrms of mtal adsorption on sawdust wr studid and dscribd by svral modls. Th ffcts of various paramtrs such as initial concntration and ph ar valuatd. Column tsts wr also prformd to invstigat th applicability of th sawdust adsorption systm for th tratmnt of havy mtals in aquous systm.. Matrials and Mthods.. Sorbnt and Sorbats Th sawdust of Pinus korainsis usd as an adsorbnt was purchasd from Jada, Inc., Kora, and was washd with dionizd watr thr tims to nsur that all fin particls wr rmovd. Th cland matrials wr drid at an ovn tmpratur of 60 C for 4 hr. Th drid matrials wr thn sivd with a #30 msh (0.6 mm) to b usd for adsorption tsts. Th

2 80 Jihyun Lim, H-Man Kang, L-Hyung Kim, and Sok-Oh Ko cation xchang capacity (CEC) of sawdust masurd by an NH4Ac xchang mthod 9) was 7.9±3.8 mq/00 g. Th analytical grads of Pb(NO 3 ), Cu(NO 3 ).5H O, and Zn(NO 3 ) 6H O wr purchasd from Aldrich Chmicals. All havy mtal solutions wr prpard in stock solutions of up to 000 mg/l of mtal. Concntratd stock solution was usd to mak various rquird dilutions for th adsorption xprimnts... Adsorption Tsts Kintic studis wr carrid out in batch ractors. Solutions (000 ml) of diffrnt Pb + concntrations (i.., 3-0 mg/l) wr prpard from th stock solution and thn transfrrd into th ractor containing sawdust (.0 g). Th initial ph of th mtal solution was adjustd to th dsird valu (ph 3.0, 4.5, or 7.0) with HCl or NaOH. Th ph valu was masurd using a digital ph mtr (90A, Orion Inc.). Blank solutions containing no sawdust wr also includd. All ractors wr mixd using a shakr bath at ± C. Fiv millilitrs of th sampl was withdrawn at prdtrmind tim intrvals, and was filtrd using a 0.45 μm syring filtr (PVDF, Millx HV). Th mtals in filtrats wr analyzd by an inductivly coupld plasma atomic mission spctroscopy analyzr (ICP-AES, Lman Abs., Inc.). No corrction for volum chang was mad bcaus th prcntag of total volum rmovd was sufficintly small (~ 0.5%). For adsorption isothrm tsts, solutions with diffrnt mtal concntrations ranging from 0 to 500 mg/l wr prpard in ractors containing sawdust. Aftr quilibrium, th sampl was withdrawn and filtrd for analysis. Th quantity of adsorbd havy mtal on sawdust was calculatd by a mass balanc rlationship. Duplicat tsts wr carrid out for all xprimnts, and th man valus ar prsntd. Th ffcts of othr cations on th adsorption of ach singl mtal wr valuatd considring th ral conditions. First, adsorption isothrm tsts wr carrid out for trnary combinations of havy mtals, maintaining qual concntrations of ach mtal ion. Nxt, th ffct of a co-ion such as Na +, K +, Mg +, and Ca + on th adsorption of mtal was valuatd. Th concntration of Na +, K +, Mg +, and Ca + was varid from 0 M to 0.5 M. Dissolvd organic mattr (DOM) was obtaind by purification of humic acid (Aldrich) according to th mthod of a prvious study. 0) Th DOM concntration usd in this study was 0, 0, 50, or 00 mg/l basd on total organic carbon contnt. Column xprimnts wr carrid out using a glass column (0.5 m long, 0.05 m i.d., Ac glass, Inc.) with an adjustabl plungr. Th column was packd with 4.8 g of sawdust, and th bd lngth was maintaind at 0.03 m. Aftr packing th column, hlium gas was usd to rmov th air trappd in th sorbnt pors. Dionizd watr was thn passd through mor than 00 por volums to condition th column. Th bulk dnsity and porosity wr dtrmind gravimtrically as 50 g/l and 0.64, rspctivly. An HPLC pump (Alltch Inc.) was connctd to th column, with a thr-way valv placd in-lin to facilitat switching btwn solutions with and without havy mtals. Consrvativ tracr tsts wr carrid out using a sodium bromid solution. Th tracr solution was rgularly takn from th outflow, and its concntration was masurd using ion chromatography (ACME, Younglin Inc.). Th solution of havy mtal mixtur (i.., Pb +, Cu +, and Zn + ) with th sam concntration (0 mg/l) was pumpd through th column at a flow rat of 30.0 ml/min. Th sampls wr collctd at th nd of th column at diffrnt tim intrvals, and thy wr analyzd for mtal concntration using ICP-AES. Aftr th adsorption tst, flushing of th column with 0. M CaCl solution was followd, and th sampls wr collctd for analysis. 3. Rsults and Discussion 3.. Adsorption Isothrms Th quilibrium adsorption of havy mtals, q (mg/g), can b rlatd to th quilibrium concntration of ths mtals, C (mg/l), ithr by th linarizd form of th Langmuir isothrm modl: C = q K S or th Frundlich isothrm modl: L m C + S log q = log K F + logc n whr S m and K L ar th Langmuir constants, rprsnting th maximum adsorption capacity of th solid phas loading and th nrgy constant rlatd to th hat of adsorption, rspctivly. K F is th Frundlich constant rlatd to th adsorption capacity, whr /n is rlatd to th adsorption intnsity. A linar plot of th Langmuir quation was drawn, and th valus of Sm and K L wr dtrmind using th last squars mthod (Fig. ). Also, th slop and intrcpt of th linar plot of log q against log C corrsponds to /n and log K F, rspctivly (Fig. ). Th quilibrium adsorption of ach mtal and mixtur of mtals (i.., Pb +, Cu +, and Zn + ) ar wll rprsntd by th Langmuir or th Frundlich modl with high R valus, as dscribd in Tabl. Th suitability of both isothrm modls in rprsnting th quilibrium data of thr havy mtals indicats that a monolayr of mtal ions formd on th sawdust surfac. ) Th ordr of adsorption affinity on sawdust is Pb + > Cu + > Zn, which is rlatd to th diffrncs in lctrongativity of th atoms. Considring that th adsorption of havy mtals on sawdust is mainly du to ion xchangs at th surfac lvl, it is xpctd that mor lctrongativ mtals will show a highr adsorption tndncy. Th lctrongativity of ach mtal is.33,.9, and.65 for Pb +, Cu +, Zn +, rspctivly. ) Th adsorption affinity of havy mtal obsrvd hr is in agrmnt with th ordr of lctrongativity. It is also known that th adsorption of havy mtal with a largr ionic radius is gratr than thos with a smallr ionic radius. 3) Th ionic radius of ach mtal, namly, Pb +, Cu +, and Zn + is.33, 0.87, and 0.88, rspctivly. Howvr, th adsorption of Cu + onto th sawdust was gratr than that of Zn +, implying that othr factors might play important rols in th adsorption m () ()

3 Rmoval of Havy Mtals by Sawdust Adsorption: Equilibrium and Kintic Studis 8 Tabl. Langmuir and Frundlich adsorption isothrm paramtrs of havy mtal on sawdust Langmuir constant q,xp Systm Mtal typ (mg/g) S m (L/mg) K L (mg/g) R L Frundlich constant K F (mg -n L n /g) /n R F Mtal ion in singl Mtal ion in mixtur Pb(II) Cu(II) Zn(II) Pb(II) Cu(II) Zn(II) Fig.. Langmuir isothrm plot for th adsorption of havy mtals on sawdust. Fig.. Frundlich isothrm plot for th adsorption of havy mtals on sawdust. procss. It could b concludd that lctrongativity and othr factors including th ionic radius of th mtal might b wll corrlatd with its slctivity on sawdust. 3.. Effcts of Co-xisting Cations In th mixd systm of mtals, th ordr of mtal adsorption was Pb + > Cu + > Zn +, which is consistnt with th ordr of th singl mtal systm (Tabl ). Th adsorption of a particular mtal ion on sawdust in mixd mtal solutions was lss than that in singl mtal systm rsulting in a dcras in rmoval fficincy. Also, our rsults showd that th prsnc of Na +, K +, Mg +, and Ca + partially dprssd th adsorption of Pb + on sawdust. In Fig. 3, th control rprsnts th Pb + adsorption in a singl systm without any othr cations. Divalnt ions such as Ca + and Mg + xhibit a strongr inhibition of Pb + adsorption than monovalnt Na + and K + ions. This is in agrmnt with othr studis that showd strongr inhibition with highr valnt ions than that with lowr ons. ) As th concntrations of ths ions incrasd from 0. M to 0.5 M, th ffcts of Ca + and Mg + wr much mor pronouncd than thos of K + and Na +. Additionally, it was obsrvd that DOM significantly affcts Pb + adsorption on sawdust. It was known that DOM forms complxs with mtals, bcaus its structur contains a larg proportion of functional groups such as carboxyl, hydroxyl, sulfat, phosphat, and amino groups. 4) At a low concntration of DOM, an nhancd adsorption of Pb + was obsrvd. Addd DOM was prfr- Fig. 3. Effct of inorganic ions and dissolvd organic mattr on th Pb + adsorption by sawdust. ably adsorbd on th availabl surfac sits of th sawdust, and sorbd DOM ractd with Pb + via complxation, rsulting in th incrasd adsorption of Pb +. As DOM dosag incrasd, a rlativ amount of DOM in aquous phas also bgan to incras as th surfac sits of th sawdust bcam saturatd. DOM in th aquous phas thn comptd with sorbd DOM and surfac sits for Pb + partitioning. Corrspondingly, th incrasd intraction of Pb + with DOM in aquous phas at a high dos of DOM rsultd in dcrasd nhancmnt of Pb + adsorption on sawdust Effct of Contact Tim and Initial Sorbat Concntration Th amount of Pb + adsorbd incrasd with th incras in-

4 8 Jihyun Lim, H-Man Kang, L-Hyung Kim, and Sok-Oh Ko th adsorption rat, givs important information for dsigning th procsss. Th kintics of th adsorption data ar analyzd using diffrnt kintic modls such as psudo-first-ordr and psudo-scond-ordr kintic modls. 7) Th kintic rat xprssion of th first-ordr modl is givn as: k log( q qt ) = log q - t.303 (3) Fig. 4. Adsorption rat of Pb(II) on sawdust. initial concntration and rmaind narly constant aftr quilibrium (Fig. 4). Equilibrium was attaind within 360 min and th quilibration tims wr found to b indpndnt of all concntrations studid. Th adsorption rat was rlativly fast in th initial stag, showing approximatly 90% quilibrium attaind within 30 min. This rsult indicats that adsorption of Pb + is mainly occurring at th surfac of th sawdust. Aftr this stag, th adsorption rat bcam slowr, which was probably du to th diffusion of th mtal ion into th sawdust Effct of ph Th ffct of ph on th adsorption of Pb + on sawdust was dscribd in Tabl. It indicats that th adsorption of Pb + on sawdust is strongly ph dpndnt, as has bn commonly obsrvd for havy mtal adsorption on biosorbnts.,5,6) It is obsrvd that Pb + rmoval dcrass as ph dcrass. Th adsorption of havy mtal on sawdust is mainly attributd to ion xchang with hydrogn ions. Additionally, a numbr of anionic ligands such as carboxyl and hydroxyl groups may tak part in th complxation with mtal ions at th sawdust surfacs. At a low ph, th xistnc of a rlativly larg numbr of hydrogn ions rsultd in a dprssion of th xchang btwn mtal and hydrogn ions. Also, th complxs formd via intraction btwn th mtal ions and acidic functional groups wr dstabilizd at a low ph. 6) 3.5. Kintic Studis Th kintic paramtr, which is hlpful for th prdiction of whr q t and q ar th amounts of adsorbat (mg/g) at tim t (min) and at quilibrium, rspctivly. Th constant k can b obtaind from th slop of th plot of log(q -q t ) vs. tim. Th valus of k at diffrnt sorbat concntrations and ph wr calculatd and ar rprsntd in Tabl. Th R valus in Tabl indicat that th first-ordr modl is not appropriat to dscrib th adsorption procss. Th psudo-scond-ordr modl 7) for adsorption kintics is xprssd as: t q t = k q + t q whr k (g/mg hr) is th scond-ordr rat constant dtrmind from th plot of t/q t vs. t, as shown in Fig. 5. Th scondordr rat constants ar usd to calculat th initial sorption rat, givn by (4) h = kq. (5) Th scond-ordr rat constants and th calculatd initial sorption rats ar shown in Tabl. From Tabl, it was obsrvd that th psudo-scond-ordr rat constant (k ) dcrasd with incrasing initial concntration and th initial sorption rat (h) dcrasd with highr initial Pb + concntration. As ph incrasd, th rat constant and initial sorption rat incrasd. Th calculatd q valus agr wll with th xprimntal valus, and high R valus indicat that th psudo-scond-ordr modl can b applid for th ntir adsorption procss. Prdiction of th rat-limiting stp is an important factor to b considrd in th dsign of an adsorption procss. For a solidliquid sorption procss, th solut transfr is usually charactrizd by xtrnal mass transfr (boundary layr diffusion), or intraparticl diffusion, or both. 8) To idntify th mchanism involvd in th adsorption procss, an intraparticl diffusion plot has bn utilizd. Th rat constant of intraparticl diffu- Tabl. Kintic paramtrs undr diffrnt conditions Paramtrs First-ordr kintics Psudo-Scond-ordr kintics Intraparticl diffusion paramtr Conc. (mg/l) ph q,xp (mg/g) k (/hr) R q,cal (mg/g) k (g/mg hr) h (mg/g hr) R k id (mg/g hr / )

5 Rmoval of Havy Mtals by Sawdust Adsorption: Equilibrium and Kintic Studis 83 Fig. 5. Th scond-ordr rat constant plot for Pb(II) adsorption on sawdust at diffrnt adsorbat concntrations. sion (kid) is givn by th following quation. 8,9) 0.5 qt = kidt (6) Th plot of q t vs. t 0.5 as shown in Fig. 6 rprsnts th diffrnt adsorption stags. Th initial curvd portion is rlatd to boundary layr diffusion and th lattr linar curv rprsnts intraparticl diffusion. Th two rgions in th plot indicat that both surfac adsorption and intraparticl diffusion ar involvd in mtal adsorption on sawdust. Th slop of th scond linar portion of th plot (k id) rprsnts th intraparticl diffusion cofficint. Th calculatd cofficint valus ar listd in Tabl. Manwhil, th intrcpt of th plot indicats th boundary layr ffct. Th largr th intrcpt, th gratr th contribution of surfac adsorption was obsrvd. It indicats that high initial concntration has rlativly strong tndncy for surfac adsorption. Fig. 6. Intraparticl diffusion plots for Pb(II) adsorption on sawdust at diffrnt adsorbat concntrations Column Studis Th rsults of mtal adsorption on sawdust in th column ar dscribd using brakthrough curvs (BTCs) whr th concn- Fig. 7. Brakthrough curvs of havy mtals from a sawdust-packd column (Mtal concntration of fd solution = 0 mg/l). tration ratio (C t/c o) is plottd vrsus por volums (tim). Fig. 7 shows an obsrvd BTC of a consrvativ tracr (Br - ). A concntration ratio of C t/c o = 0.5 was rachd at.0 por volum, implying that th sawdust layr in th column was rlativly homognous. Th BTCs of mtals show a larg xtnt of rtardation (Fig. 7). Th brakthrough occurrd at about 800, 500, and 50 por volums for Pb +, Cu +, and Zn +, rspctivly. As provn from batch tsts, th most favorably sorbd mtal, Pb +, occupid most of th adsorption sits on th sawdust in th column. Thrfor, lss favorably sorbd mtals such as Cu + and Zn + showd mor rapid brakthrough. Also, th slops of th Zn + and Cu + curvs wr stpr than that of th Pb + curv. Th quantity of Pb + adsorbd in th column was obtaind by numrical intgration of th ara abov th BTC. Th adsorption capacity pr sorbnt mass (q ) was dtrmind to b.34 for Zn +, 3.6 for Cu +, and 7.73 mg/g for Pb +, rspctivly. Ths valus ar lowr than thos obtaind from batch quilibrium tsts. This diffrnc might b du to th diffusion-limitd adsorption rat. 8,5) A flow condition mostly rsults in an insufficint rsidnc tim and diffusion is limitd insid th sorbnt pors. A solution of 0.M CaCl was usd to lut th havy mtals adsorbd insid th column. Th lution curvs of th thr havy mtals ar shown in Fig. 8. Th curvs show a sharp incras in th bginning followd by a gradual dcras. Also, highly concntratd mtal solutions wr lutd within shortnd por volums (tim). Opposit th ordr of th adsorption procss, th ordr of th lution of havy mtals was Zn > Cu > Pb, rspctivly. Th mass of lutd mtal was calculatd using th lution curv, and it masurd 37.8, 0.6, and 6.8 mg for Pb +, Cu +, and Zn +, rspctivly. Most of th havy mtals adsorbd onto th sawdust wr lutd. 4. Conclusions Sawdust was found to b an ffctiv biosorbnt for th rmoval of havy mtals in aquous systm. Th adsorption on sawdust incrasd with incrass in sorbat concntration and ph. Th quilibrium adsorption of havy mtals on sawdust fit th Langmuir or Frundlich modl rasonably wll. Th adsorption

6 84 Jihyun Lim, H-Man Kang, L-Hyung Kim, and Sok-Oh Ko Fig. 8. Brakthrough curvs of havy mtals from a sawdust-packd column flushd with 0.M CaCl solution. capacity of mtal varid from on mtal systm to anothr, and dpndd upon th prsnc of othr mtals in th solution. Divalnt ions (i.., Ca +, Mg + ) wr mor fficint in dprssing th mtal adsorption on sawdust than monovalnt ions (i.., Na +, K + ). DOM showd a significant ffct on th mtal adsorption on sawdust via th complxation raction. Th rmoval of Pb + was rapid at th initial stags, but it bcam slowr aftrward. Kintic studis indicat that adsorption follows a psudoscond-ordr modl. Also, intraparticl diffusion plots indicat that both surfac adsorption and por diffusion ar involvd in mtal adsorption on sawdust. Th rsults of th column xprimnts showd rtardd brakthrough of mtals du to th high adsorption capacity of sawdust. Th rsults of this study suggst that an adsorption systm utilizing sawdust can b an conomically fasibl tchniqu for th tratmnt of havy mtals in aquous solution. Rfrncs. Jang, A., So, Y., and Bishop, P. L., Th rmoval of havy mtals in urban runoff by sorption on mulch, Env. Poll., 33, 7-7 (005).. Garda-Torrsdy, J. L., Tang, L., and Salvador, J. M., Coppr adsorption by strifid and unstrifid fractions of Sphagnum pat moss and its diffrnt humic substancs, J. Hazard. Matr., 48, 9-06 (996). 3. Al-Ashh, S., and Duvnjak, Z., Sorption of havy mtals by canola mal, Watr, Air, Soil Poll., 4, 5-76 (999). 4. Kim, M.-S., Hong, S. C., and Chung, J. G., Adsorption of Pb(II) on mtal oxid particls containing aluminum and titanium in aquous solutions, Environ. Eng. Rs., 0, (005) 5. Brown, P. A., Gill, S. A., and Alln, S. J., Mtal rmoval from wastwatr using pat, Wat. Rs., 6, (000). 6. Taty-Costods, V. C., Faudut, H., Port, C., and Dlacroix, A., Rmoval of Cd(II) and Pb(II) ions, from aquous solutions, by adsorption onto sawdust of Pinus sylvstris, J. Hazard. Matr., B05, -4 (003). 7. Vijayaraghavan, K., Jgan, J., Palanivlu, K., and Vlan, M., Biosorption of coppr, cobalt and nickl by mirin grn alga Ulva rticulat in a packd column, Chmosphr, 60, (005). 8. Al-Qunaibit, M., Khalil, M., and Al-Wassil, A., Th ffct of solvnts on mtal ion adsorption by th alga Chlorlla vulgaris, Chmosphr, 60, 4-48 (005). 9. Sumnr, M. E., and Millr, W. P., Cation xchang capacity and xchang cofficints. In : Sparks t al. (Eds) Mthod of Soil analysis, Part 3, Chmical analysis, Amrican Socity of Agronomy, Madison, WI, pp. -30 (996). 0. Hur, J., and Schlautman, M. A., Using slctd oprational dscriptors to xamin th htrognity within a bulk humic substanc, Environ. Sci. Tchnol., 37, (003).. Al-Ashh, S., and Duvnjak, Z., Sorption of cadmium and othr havy mtals by pin bark, J. Hazard. Matr., 56, 35-5 (997).. Wikipdia, Elctrongativity, Elctrongativity (007). 3. Stumm, W., and Morgan, J. J., Aquatic Chmistry: Chmical quilibria and rats in natural watrs, Third d., John Wily & Sons, Nw York, pp (996). 4. Rangsivk, R., and Jkl, M. R., Rmoval of dissolvd mtals by zro-valnt iron (ZVI): Kintics, quilibria, procsss and implications for stormwatr runoff tratmnt, Wat. Rs., 39, (005). 5. Taty-Costods, V.C., Faudut, H., Port, C., and Ho, Y.-S., Rmoval of lad(ii) ions from synthtic and ral fflunt using immobilizd Pinus sylvstris sawdust: Adsorption on a fixd-bd column, J. Hazard. Matr., B3, (005). 6. Yu, B., Zhang, Y., Shukla, A., Shukla, S. S., and Dorris, K. L., Th rmoval of havy mtals from aquous solutions by sawdust adsorption - rmoval of lad and comparison of its adsorption with coppr, J. Hazard. Matr., B84, (00). 7. Al-Dgs, Y. S., El-Barghouthi, M. I., Issa, A. A., Khraishh, M. A., and Walkr, G. M., Sorption of Zn(II), Pb(II), and Co(II) using natural sorbnts: Equilibrium and kintic studis, Wat. Rs., 40, (006). 8. Kalavathy, M. H., Karthikyan, T., Rajgopal, S., and Miranda, L. R., Kintic and isothrm studis of Cu(II) adsorption onto H 3PO 4-activatd rubbr wood sawdust, J. Coll. Intrf. Sci., 9, (005). 9. Singh, K. K., Singh, A. K., and Hasan, S. H., Low cost bio-sorbnt what bran for th rmoval of cadmium from wastwatr: Kintic and quilibrium studis, Biorsour. Tchnol., 97, (006).