Biosorption of Nickel Ion by Chitosan-immobilized Brown Algae Laminaria japonica

Transcription

1 W. FAN and Z. XU, Biosorption of Nickl Ion by Chitosan-immobilizd Brown, Chm. Biochm. Eng. Q. 25 (2) (2011) 247 Biosorption of Nickl Ion by Chitosan-immobilizd Brown Alga Laminaria japonica W. Fan a,* and Z. Xu a,b a Dpartmnt of Environmntal Scinc and Enginring, School of Chmistry and Environmnt, Bihang Univrsity, Bijing, , China b Stat Ky Laboratory of Environmntal Auatic Chmistry, Rsarch Cntr for Eco-Environmntal Scincs, Chins Acadmy of Scincs, Bijing , China Original scintific papr Rcivd: July 21, 2010 Accptd: April 27, 2011 Highly toxic nickl is rlasd into th nvironmnt from a numbr of industrial procsss, but currnt tchnius for its rmoval ar xpnsiv and may caus scondary pollution. W dvlopd a biosorbnt of chitosan-immobilizd brown alga (Laminaria japonica). Th ffcts of diffrnt paramtrs on th adsorption capacity and biosorption-dsorption of Ni 2+ from auous solution wr valuatd. Kintic studis showd that th adsorption of Ni 2+ by th immobilizd algal bads followd scond-ordr kintics. Whn th adsorbnt dos was incrasd, th biosorption capacity dcrasd and th rmoval fficincy incrasd. Ni 2+ biosorption by th immobilizd alga cll bads was a good fit for th Langmuir and Frundlich isothrm modls. In addition, th rgnratd biosorbnt by 1 mol L 1 HCl or 1 mol L 1 HNO 3 could b rusd, and maintaind 90 % rmoval fficincy for at last thr cycls. Ky words: Biosorption, chitosan, immobilization, nickl, Laminaria japonica Introduction * To whom corrspondnc should b addrssd: -mail: fanwh@buaa.du.cn; Phon: ; Fax: Nickl is rlasd into th nvironmnt by a larg numbr of procsss, such as lctroplating, lathr tanning, wood prsrvation, pulp procssing, and stl manufacturing. High concntrations of Ni 2+ may b toxic and harmful to organisms in watr, and also to consumrs of auatic organisms. 1 Many procsss ar usd to rmov havy mtals from industrial fflunts, including chmical prcipitation, coagulation, solvnt xtraction, mmbran sparation, ion xchang, and adsorption. Howvr, compard with biosorption procsss, ths mthods ar xpnsiv and may caus scondary pollution. 2 3 Biosorption involvs using biological matrial to rmov mtal or mtalloid spcis, compounds, and particulats from solution. 4 Many biosorbnts such as fungi, bactria, and yast hav rcntly bn valuatd for thir ability to sustr havy mtals. Among ths, brown algal biomass has provn highly ffctiv, rliabl and prdictabl in th rmoval of mtal ions such as Pb 2+,Cu 2+,Cd 2+, and Zn 2+ from auous solutions. 5 9 Th biosorption capability of brown alga has bn attributd mainly to th cll wall, which has a fibr-lik structur and an amorphous mbdding matrix of various polysaccharids. On typ of ths polysaccharids, alginat, has bn rportd to hav high affinity for divalnt cations. 10 Laminaria japonica is a spcis of brown alga abundant and ubiuitous in th littoral zons of th world. To dat, som applications in nvironmntal scinc hav utilizd this spcis. Du to th high uptak capacity ( mmol g 1 for Pb 2+,Cd 2+, F 2+,Cu 2+,Ni 2+,Zn 2+ and Cr 6+ )ofl. japonica and its low cost, it is a promising adsorbnt. 9,11 14 Howvr, alga as biosorbnts ar usually usd in powdr form. Du to th low dnsity and strngth of powdrd alga, this introducs practical problms in continuous procsss, such as softning upon contact with watr, and difficult sparation from th watr. Thrfor, cll immobilization or chmical modification is ruird for th practical application of alga. 1 Th objctiv of this work was to prpar a nw biosorbnt with th brown alga L. japonica as th biomatrial and chitosan as a carrir. Th Ni 2+ adsorption and dsorption charactristics of th immobilizd L. japonica sorbnt wr invstigatd. This includd valuating th ffct of diffrnt paramtrs, such as contact tim, initial ph, adsorbnt dos, and initial Ni 2+ concntration, on th sorption capacity. Euilibrium modling was carrid out using th Langmuir and Frundlich isothrm uations.

2 248 W. FAN and Z. XU, Biosorption of Nickl Ion by Chitosan-immobilizd Brown, Chm. Biochm. Eng. Q. 25 (2) (2011) Matrials and mthods Prparation of th biosorbnt L. japonica was sourcd in Qingdao (China). It washd svral tims with dionizd watr to liminat impuritis and frz drid for 24 h. Th drid biomass was crushd and ground to granuls of m and stord in a dsiccator. Immobilizd bads of powdrd L. japonica in a chitosan matrix wr prpard by ionic polymrization in sodium pyrophosphat and potassium oxalat solution. First, th powdrd L. japonica clls wr suspndd in a chitosan solution (1 % in actic acid) and agitatd. Th mixtur was smashd in an ultrasonic cll pulvrizr for a st tim, and thn droppd into a mixd solution of 2 % sodium pyrophosphat and 4 % potassium oxalat using a pristaltic pump. Th drops of chitosan solution glld into 2 ± 0.1 mm diamtr bads upon contact with th mixd solution. Th immobilizd algal cll bads wr stord in th mixd solution for at last 1 h to complt glation. Th bads wr rinsd and thn frozn dry for 12 h bfor us. Blank chitosan bads wr also prpard in a chitosan solution by th abov mthod without alga. Biosorption xprimnts All sorption xprimnts wr prformd by agitating 100 ml of th appropriat concntration mtal solution and with a st amount of adsorbnt in 300 ml bottls at 200 rpm. Th nickl solutions, which wr prpard using NiSO 4 6H 2 O, wr placd in a watr bath shakr at room tmpratur for a prdtrmind tim. Th initial ph was adjustd using dilut hydrochloric acid and sodium hydroxid solutions. All xprimnts in this work wr conductd in duplicat and th avrag rsults wr prsntd. Analysis Th concntration of mtal ions was dtrmind using an inductivly coupld plasma atomic mission spctromtr (ICP-AES IRIS AP; Thrmo Jarrll Ash Co., USA). Biosorption-dsorption cycl xprimnts For adsorption-dsorption studis, 2 g L 1 immobilizd algal bads wr placd in a Ni 2+ solution and agitatd for 5 h. Th Ni 2+ loadd bads wr collctd and gntly washd with dionizd watr to rmov any unadsorbd Ni 2+. Th bads wr agitatd with a st volum of various lunts, including mol L 1 thylndiamin ttraactic acid (EDTA), 1 mol L 1 HCl, and 1 mol L 1 HNO 3, in a watr bath shakr at room tmpratur (25 C). 15 Aftr dsorption, th bads wr immrsd in 1 mol L 1 sodium hydroxid solution for 10 min to nutraliz any surplus hydrogn ions on th bads. To tst th rusability of th bads, th adsorption-dsorption cycls wr rpatd fiv tims with th sam bads and nw lunts. Evaluation of adsorption Th biosorption proprtis of th immobilizd algal bads and th dsorption fficincy of th dsorbnts wr valuatd. This involvd calculating uptak capacity, rmoval fficincy and dsorption fficincy using th following uations: C C ( C0 C ) V m 0 0 C C 0 C i C (1) 100 % (2) 100 % (3) whr is th uilibrium uptak capacity (mg g 1 ), C 0 is th initial Ni 2+ concntration (mg L 1 ), C is th uilibrium Ni 2+ concntration (mg L 1 ), V is th volum of th solution (L), m is th mass of th sorbnt (g), is th rmoval fficincy, C i is th dsorbd Ni 2+ concntration (mg L 1 ), and is th dsorption fficincy. Rsults and discussion Optimization of th adsorbnt bads prparation Th ffct of th chitosan concntration usd in prparation of immobilizd algal bads on Ni 2+ rmoval was invstigatd. Of th concntrations ( %) tstd, 2.5 % chitosan solution providd th highst rmoval fficincy of Ni 2+ and th most simpl and convnint prparation of th adsorbnt bads. Consuntly, this concntration of chitosan was usd in subsunt prparation of th adsorbnt bads. Th biomass concntration in th chitosan solution was dtrmind to b 13 g L 1 basd on th rmoval of Ni 2+. Biosorption kintics Th biosorption kintics of Ni 2+ on th sorbnts wr studid. Th amount of Ni 2+ adsorbd by th immobilizd algal bads incrasd until 300 min, aftr which it rmaind constant (Fig. 1). This is consistnt with prvious studis on th kintics of mtal ion rmoval by alga, which hav shown that sorption is initially rapid and thn slows down. 1,16

3 W. FAN and Z. XU, Biosorption of Nickl Ion by Chitosan-immobilizd Brown, Chm. Biochm. Eng. Q. 25 (2) (2011) 249 whr k 2 is th uilibrium constant of th scond-ordr modl, and h = 2 k 2 rprsnts th initial rat constant. Th intra-particl diffusion modl is givn as: t k t id 12 / (8) whr t is th uptak capacity at tim t, and k id is th rat constant of intraparticl diffusion. 17 Figs. 2(a), (b), and (c) illustrat th linar plots of log ( t ) against t, t/ t against t, and t against t 1/2, rspctivly. Fig.1 Effct of contact tim on adsorption of Ni 2+ : powdrd L. japonica, immobilizd algal bads, and blank bads. Exprimntal conditions: initial Ni 2+ concntration, 80 mg L 1 ; biosorbnt dos, 2.0 g L 1 ; ph, 5.5; tmpratur, 25 C. In contrast, th sorption of Ni 2+ on powdrd L. japonica rachd uilibrium in fiv minuts. Th sorption procsss of Ni 2+ by th immobilizd algal bads and th blank bads wr similar in th first 60 minuts and thn diffrd drastically aftr that point. It indicatd that th powdrd L. japonica in th immobilizd sorbnt playd a dominant rol in th adsorption of Ni 2+ and immobilization of th alga affcts th adsorption procss of Ni 2+ on th alga clls. Psudo-first ordr and psudo-scond ordr kintics and intraparticl diffusion wr utilizd to modl th xprimntal adsorption data. Th psudo-first ordr kintic modl is givn by: dt dt k1( t)( t 0, t 0) (4) Th linar form of. (4) is: k1 log ( t) log t (5) whr k 1 is th uilibrium constant of th first-ordr modl, t is th uptak capacity at tim t, and is th uilibrium uptak capacity. Th psudo-scond ordr kintic modl is givn by: dt dt 2 t t k ( ) ( t 0, 0) (6) 2 Th linar form of. (6) is: t t 1 t k 1 2 h t 2 (7) Fig. 2 Kintics of Ni 2+ adsorption for (a) psudo first-ordr, (b) psudo scond-ordr, and (c) intraparticl diffusion modls: powdrd L. japonica, immobilizd algal bads, and blank bads. Exprimntal conditions: initial Ni 2+ concntration, 80 mg L 1 ; ph, 5.5; biosorbnt dos, 2.0 g L 1.

4 250 W. FAN and Z. XU, Biosorption of Nickl Ion by Chitosan-immobilizd Brown, Chm. Biochm. Eng. Q. 25 (2) (2011) Th sorption kintic paramtrs and corrlation cofficints for th thr kintic modls ar prsntd in Tabl 1. Although th corrlation cofficints of th thr kintic modls for th immobilizd algal bads wr all high (R 2 > 0.96), th uilibrium biosorption capacity (32.25 mg g 1 ) dtrmind by th psudo-scond ordr modl approachd th xprimntal valu (29.94 mg g 1 ). Th intraparticl diffusion modl did not hav an intrcpt ual to zro (Fig. 2(c)), which indicatd that intraparticl diffusion is not th only rat-controlling stp of th kintic procss. Th psudo-scond ordr modl can dscrib th sorption kintics of th Ni 2+ on th immobilizd sorbnt (R 2 = 0.992). According to th mchanism of th scond-ordr modl, th sorption of Ni 2+ on th immobilizd sorbnt involvd chmical sorption procss. Th chmical adsorption procss is th main rat-limiting stp, which may b connctd with th covalnt intraction of lctron xchang and sharing btwn biosorbnt and mtal ions. Th adsorption of Ni 2+ on powdrd L. japonica was also a good fit to th psudo-scond ordr modl (R 2 = 0.999). This suggstd that th powdrd L. japonica in th immobilizd sorbnt plays a dominant rol in th adsorption of Ni 2+. Sn from Fig. 2(c), th boundary layr diffusion ffct was gratr on th adsorption of Ni 2+ by powdrd L. japonica than that of immobilizd algal bads and blank bads according to th largr intrcpt. 17 In addition, th k 2 valu of g mg min 1 for adsorption of Ni 2+ on powdrd L. japonica was highr than that of immobilizd algal bads (0.001 g mg min 1 ). It could b infrrd that immobilization could impact th adsorption procss but not th biosorption capacity of powdrd L. japonica. Effct of th biosorbnt dos on Ni 2+ rmoval Th ffct of adsorbnt dos ( g L 1, th concntration of immobilizd algal bads in solution) on th adsorption proprtis was studid at ph 5.5 at a fixd initial mtal concntration of 80 mg L 1. As th adsorbnt dos incrasd, th Ni 2+ rmoval fficincy incrasd and th biosorption capacity of th adsorbnt bads dcrasd (Fig. 3). Th incras in rmoval fficincy is du to an incras in th numbr of th binding sits as th adsorbnt dos incrass. 18,19 High concntrations of adsorbnt can act lik a scrn to prvnt th conjunction of mtal ions and adsorption sits. Th lowr utilization of th adsorbnts adsorptiv capacity rsults in lss commnsurat incras in biosorption capacity. 15,20 Tabl 1 Kintic modl paramtrs for th adsorption of Ni 2+ by algal bads Immobilizd Powdry Blank chitosan algal cll alga bads bads Euilibrium biosorption capacity/mg g First-ordr kintic modl Scond-ordr kintic modl Intra-particl diffusion modl (mg g 1 ) k 1 (min 1 ) R (mg g 1 ) k 2 (g mg min 1 ) R k id (mg g 1 min 1/2 ) R Fig. 3 Effct of th biosorbnt dos on Ni 2+ adsorption: biosorption capacity, and rmoval fficincy. Exprimntal conditions: initial Ni 2+ concntration, 80 mg L 1 ; ph, 5.5; tmpratur, 25 C. Effct of initial Ni 2+ concntration Adsorption of Ni 2+ by th bads was carrid out at diffrnt initial mtal ion concntrations ( mg L 1 ). Th rmoval fficincy of Ni 2+ dcrasd and th uptak capacity of th adsorbnt incrasd with incrasing initial Ni 2+ concntrations (Fig. 4). Som studis hav rportd that th initial concntration provids an important driving forc to ovrcom th mass transfr rsistanc of Ni 2+ btwn th auous and solid phass. 21,22 Othrwis, incrasing initial mtal ion concntrations incras th chanc of collisions btwn mtal ions and

5 W. FAN and Z. XU, Biosorption of Nickl Ion by Chitosan-immobilizd Brown, Chm. Biochm. Eng. Q. 25 (2) (2011) 251 Fig. 4 Effct of th initial Ni 2+ concntration on Ni 2+ adsorption powdry L. japonica, immobilizd algal bads and blank bads. Exprimntal conditions: ph, 5.5; biosorbnt dos, 2.0 g L 1 ; tmpratur, 25 C. sorbnts. This nhancs th adsorption procss and incrass th uptak capacity. Howvr, as th initial concntration of Ni 2+ incrass, th adsorption sits rach saturation at th point of adsorption uilibrium. Consuntly, th Ni 2+ rmoval fficincy dcrass with incrasing Ni 2+ concntration. In addition, th adsorption of Ni 2+ by th immobilizd algal bads, powdrd L. japonica, and blank bads showd th sam pattrns, and wr ffctiv in th rmoval of low concntration nickl ions from auous solution. So th initial Ni 2+ concntration 80 mg L 1 was chos in furthr studis. Effct of ph Th ffct of initial ph (2 8) on Ni 2+ rmoval was studid at an initial Ni 2+ concntration of 80 mg L 1. Th Ni 2+ rmoval fficincy was vry low at ph 2, and thn incrasd until ph 3. From ph 3 8 th biosorption of Ni 2+ was constant (Fig. 5). Fig. 5 Effct of ph on Ni 2+ adsorption: powdrd L. japonica, immobilizd algal bads, and blank bads. Exprimntal conditions: initial Ni 2+ concntration, 80 mg L 1 ; biosorbnt dos, 2.0 g L 1 ; tmpratur, 25 C. Similar pattrns wr obsrvd for th powdrd alga, blank bads, and immobilizd algal bads. Th ph is xpctd to influnc both mtal binding sits on th cll surfac and mtal chmistry in watr. At low ph, protons can compt ffctivly with Ni 2+ for th binding sits, and th protonatd binding sits ar no longr abl to bind Ni 2+ from solution. As th initial ph incrass, th ligands of th alga cll, such as carboxyl, phosphat, imidazol and amino groups, bcom ngativly chargd and attract th mtal ions, which incrass biosorption onto th cll surfac. 23,24 Highr ph valus wr not xamind, bcaus at ph valus >8.0 prcipitation of th mtal can occur du to mtal hydroxid formation. Th biosorption of Ni 2+ by th immobilizd algal bads could b adaptd to solutions with wid rang ph valus (3 8). Biosorption isothrms Biosorption isothrm curvs, drivd from th uilibrium batch sorption xprimnts, wr usd to charactriz th intraction of Ni 2+ with th immobilizd algal bads. Th Langmuir modl is basd on th assumptions that maximum adsorption occurs whn a saturatd monolayr of solut molculs is prsnt on th adsorbnt surfac, th nrgy of adsorption is constant, and thr is no migration of absorbat molculs in th surfac plan. 4 Th Langmuir adsorption isothrm has traditionally bn usd to uantify and contrast th prformanc of diffrnt biosorbnts. 25 Maximum biosorption capacity (Q max ) is dtrmind by non-linar rgrssion from isothrm studis. In comparison, th Frundlich isothrm is an mpirical modl that is basd on sorption on a htrognous surfac. It is assumd that th adsorption nrgy of a mtal binding to a sit on an adsorbnt dpnds on whthr th adjacnt sits ar alrady occupid. 26 Analysis of th uilibrium data is important to dvlop an uation which accuratly rprsnts th rsults, and which could b usd for dsign purposs. For ach isothrm, th initial Ni 2+ concntrations wr varid whil th adsorbnt dos in ach sampl was kpt constant (2 g L 1 ). In this cas, th Langmuir uation (. (9)) is traditionally applid: Q 1 max bc bc (9) Th following form is th linarization of. (9): C 1 C Q b Q max max whr b is th sorption uilibrium constant. (10)

6 252 W. FAN and Z. XU, Biosorption of Nickl Ion by Chitosan-immobilizd Brown, Chm. Biochm. Eng. Q. 25 (2) (2011) Th Frundlich isothrm is dfind as follows: KC 1/ n (11) Th linar form of. (11) is givn by: ln ln K ln C 1 n (12) whr K and n ar mpirically dtrmind constants, with K bing rlatd to th maximum binding capacity, and n rlatd to th affinity or binding strngth. Th linarizd Langmuir and Frundlich adsorption isothrms of Ni 2+ obtaind at 25 C ar givn in Fig. 6. Th adsorption paramtrs and thir corrlation cofficints ar prsntd in Tabl 2. Th corrlation cofficints of th two modls for th immobilizd bads and powdrd L. japonica wr high (R 2 > 0.94), which indicats that th two modls can b usd to dscrib th adsorption of nickl on th immobilizd bads and powdrd L. japonica. Th adsorption of Ni 2+ on th sorbnt is both a physical and chmical procss, and is to htrognous surfac or surfacs supporting sits of varid affinitis. 27 Th corrlation cofficint for th Frundlich modl of th blank bads is vry low. According to th maximum uptak capacity and corrlation cofficints, th immobilizd algal bads and powdrd L. japonica hav th sam adsorption proprtis for Ni 2+. This suggsts L. japonica plays an important rol in th adsorption of Ni 2+ by th bads. Using th Langmuir isothrm, th Q max of Ni 2+ by th immobilizd algal bads, powdrd L. japonica and blank bads was 38.3, 39.5 and 25 mg g 1 (Tabl 3), rspctivly. Ths valus indicat that th immobilization dos not impact th adsorption of Ni 2+ on powdrd L. japonica. Th Q max valus rportd for Ni 2+ adsorption on various clls can b compard: Sargassum natans (Q max mg g 1 ), 7 Chlorlla vulgaris (31.3mgg 1 ), 1 Ascophyllum nodosum (40.5mgg 1 ), Scndsmus (26.7 mg g 1 ), 28 Scndsmus uadricauda immobilizd by Ca-alginat (30.4 mg g 1 ), 8 and L. japonica immobilizd in Ca-alginat gl Fig. 6 Th Langmuir (a) and Frundlich (b) isothrms for Ni 2+ biosorption: powdrd L. japonica, immobilizd algal bads, and blank bads. Exprimntal conditions: biosorbnt dos, 2.0 g L 1 ; ph, 5.5; tmpratur, 25 C. Tabl 3 Prcntag of Ni 2+ dsorbd from th algal bads with diffrnt solvnts ovr fiv suntial cycls Cycl numbr Rmoval fficincy (%) HCl HNO (39.43 mg g 1 ). 22 Ths rsults illustrat that immobilization of powdrd L. japonica in chitosan gl provids a vry good biosorbnt for Ni 2+ rmoval. Dirct comparison of th rportd biosorbnts is Tabl 2 Biosorption isothrms paramtrs for th adsorption of Ni 2+ by algal bads Langmuir modl Frundlich modl Q max (mg g 1 ) (L mg 1 ) b R 2 K n R 2 (mg (1 1/n) L 1/n g 1 ) Immobilizd algal cll bads Powdry alga Blank chitosan bads

7 W. FAN and Z. XU, Biosorption of Nickl Ion by Chitosan-immobilizd Brown, Chm. Biochm. Eng. Q. 25 (2) (2011) 253 difficult du to variations in xprimntal conditions. Howvr, it appars that th biosorption capacity of th biosorbnt in th currnt study is high. Biosorption-dsorption cycls Dsorption of mtal ions from th loadd sorbnt is ruird to rcovr th mtal and rus th sorbnt. Elution is an ffctiv mthod for this bcaus it dos not significantly rduc th binding capacity of th biomass and svral cycls can b mployd. Th Ni 2+ dsorption fficincy with 1 mol L 1 HCl or 1 mol L 1 HNO 3 approachd >90 %, whil with EDTA it was about 65 %. Consuntly, 1 mol L 1 HCl or 1 mol L 1 HNO 3 could b usd as an ffctiv dsorbnt of Ni 2+. To dtrmin th rusability of th immobilizd algal bads, adsorption-dsorption cycls wr rpatd suntially fiv tims with th sam bads. Th rmoval fficincis of th rcycld bads wr highr for th scond and third cycls than th first (Tabl 3). This can b xplaind by th chmical modification of th sorbnt bads by immrsion in sodium hydroxid solutions, and an incras in nw binding sits. Th rmoval fficincis dcrasd aftr thr to fiv cycls. This was du to gradual dstruction of th binding sits in th bads with ach cycl. In addition th < 100 % dsorption of adsorbd Ni 2+ in ach cycl, which rsultd in carrid ovr occupid adsorption sits from cycl to cycl. Th rlativ fficincis of adsorption and dsorption indicat that rcycling of th algal bads is fasibl. Th concntration ratio (th ratio of th concntration of th rcovrd mtal to th concntration of mtal in th original solution) valu of Ni 2+ was about 0.7 as S/L ratio (th ratio of adding amount of adsorbnt to volum of dsorbing agnt) was 2 g L 1. Th mtal ions in dsorbnt could b rusd as mtal chlorid/nitrat. Scanning lctron microscopy Th blank and immobilizd algal bads wr charactrizd by scanning lctron microscopy (Figs. 7(a) and (b), rspctivly). Th intrnal structur of th immobilizd algal bads is opn, and diffrnt from that of th blank bads. Th powdrd L. japonica in th immobilizd bads was mbddd prsnting fibrous structur aftr smashd in an ultrasonic cll pulvrizr in th prparation of th immobilizd bads, which is also bnficial for adsorption of Ni 2+. Figs. 7(c) and (d) ar SEM imags of th immobilizd algal bads bfor and aftr ad- Fig. 7 SEM imags of blank bads (a) and immobilizd algal bads (b) ( 2000), and SEM imags of th immobilizd bads bfor (c) and aftr (d) adsorption ( 600)

8 254 W. FAN and Z. XU, Biosorption of Nickl Ion by Chitosan-immobilizd Brown, Chm. Biochm. Eng. Q. 25 (2) (2011) sorption of Ni 2+. W can s that th opn structur of th immobilizd algal bads bcoms closd aftr adsorption. Conclusions Immobilizd L. japonica was prpard and usd for th rmoval of Ni 2+ from auous solution. Th prparation of th sorbnt bads was optimizd basd on th strngth, adsorption proprtis, and modling of th bads. Adsorption of Ni 2+ onto th immobilizd L. japonica followd psudo-scond ordr kintics. Th immobilization affctd th adsorption procss but not th adsorption capacity of powdrd L. japonica. As th adsorbnt dos incrasd, th Ni 2+ uptak capacity dcrasd and th rmoval fficincy incrasd. Th biosorption of Ni 2+ by th sorbnt occurrd ovr a larg ph rang (3 8). Th xprimntal rsults fit th Langmuir and Frundlich isothrm modls. Th powdrd L. japonica in th immobilizd bads playd an important rol in th adsorption of Ni 2+. Th bttr dsorbnts wr 1 mol L 1 HCl and 1molL 1 HNO 3. Th immobilizd L. japonica sorbnt could b usd at last thr sorption/dsorption cycls to rmov Ni 2+ from auous solutions. ACKNOWLEDGMENTS This work was supportd by grants from China s National Basic Rsarch Program Watr nvironmntal uality volution and watr uality critria in laks (grant numbr 2008CB418201), th Natural Scinc Foundation of China (grant numbr ), and th Natural Scinc Foundation of Bijing (grant numbr ). Symbols uilibrium uptak capacity, mg g 1 C 0 initial Ni 2+ concntration, mg L 1 C uilibrium Ni 2+ concntration, mg L 1 V volum of th solution, L m mass of th sorbnt, g rmoval fficincy, C i dsorbd Ni 2+ concntration, mg L 1 dsorption fficincy, k 1 uilibrium constant of th first-ordr modl, min 1 t uptak capacity at tim t, mgg 1 t biosorption tim, min k 2 uilibrium constant of th scond-ordr modl, g mg min 1 h initial rat constant of th scond-ordr modl, mg g 1 min 1 k id rat constant of intraparticl diffusion modl, mg g 1 min 1/2 t/ t min g mg 1 t 1/2 min 1/2 Q max maximum biosorption capacity, mg g 1 b uilibrium constant of Langmuir modl, L mg 1 K mpirically dtrmind constant of Frundlich modl, mg (1 1/ n) L 1/ n g 1 n mpirically dtrmind constant of Frundlich modl, C / gl 1 Rfrncs 1. Abu Al-Rub, F. A., El-Naas, M. H., Bnyahia, F., Procss Biochm. 39 (2004) Wang, J. L., Chn, C., Biotchnol. Adv. 24 (2006) Rangsayatorn, N., Pokthitiyook, P., Upatham, E. S., Environ. Int. 30 (2004) Wang, J. L., Chn, C., Biotchnol. Adv. 27 (2009) Saygidgr, S., Gulnaz, O., Istifli, E. S., Yucl, N., J. Hazard. Matr. B126 (2005) Robrto, H., Pablo, L., Carlos, R. C., Watr Rs. 39 (2005) Davis, T. A., Volsky, B., Alfonso, M., Watr Rs. 37 (2003) BayramoNlu, G., Yakup Arrca, M., Biorsour. Tchnol. 100 (2009) Liu, Y. H., Cao, Q. L., Luo, F., Chn, J., J. Hazard. Matr. 163 (2009) Chojnacka, K., Chojnacki, A., Górcka, H., Chmosphr 59 (2005) Ghimir, K. N., Inou, K., Ohto, K., Hayashida, T., Biorsour. Tchnol. 99 (2008) Luo, F., Liu, Y. H., Li, X. M., Xuan, Z. X., Ma, J. T., Chmosphr. 64 (2006) Wang, X. S., Li, Z. Z., Clan. 37 (2009) Wang, X. S., Li, Z. Z., Sun, C., J Hazard. Matr. 153 (2008) Jon, C., Park, K. H., Watr Rs. 39 (2005) Singh, R. S., Singh, V. K., Tiwari, P. N., Singh, J. K., Sharma, Y. C., Environ. Tchnol. 30 (2009) Laohaprapanon, S., Marus, M., Hogland, W., Clan. 38 (2010) Tüzüna,., BayramoNlub, G., Yalçin, E., J Environ. Manag. 77 (2005) Gok, C., Aytas, S., J. Hazard. Matr. 168 (2009) Lodiro, P., Ry-Castro, C., Barriad, J. L., J Colloid and Intrfac Sci. 289 (2005) Hashima, M. A., Chub, K. H., Chm. Eng. J. 97 (2004) Xu, Z. Z., Fan, W. H., Fng, L. J., Prog. Environ. Sci. Tchnol. 1 (2007) Yang, L., Chn, J. P., Biors. Tchnol. 99 (2008) Romra, E., Gonzálz, F., Ballstr, A., Biorsour. Tchnol. 98 (2007) Lin, C., Lai, Y., J. Hazard. Matr. 137 (2006) Vijayaraghavan, K., Padmsh, T. V. N., Palanivlu, K., Vlan, M., J. Hazard. Matr. B133 (2006) Tuzna, M., Sarl, A., Mndila, D., J. Hazard. Matr. 165 (2009) 566, 28. Hu, Z. L., Wong, Y., Tam, F. Y., Acta Botanica Sinica. 44 (2002) 97.