JOURNAL OF ENVIRONMENTAL SCIENCES 56 (2017) Available online at ScienceDirect.

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1 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) Aville online t ScienceDirect Removl of Cs + from wter nd soil y mmonium-pillred montmorillonite/fe 3 composite Xinming Zheng, Junfeng Dou, Jing Yun, Wei Qin, Xioxi Hong, Aizhong Ding College of Wter Sciences, Beijing Norml University, Beijing 187, Chin. Emil: zhengxinming1@163.com ARTICLE INFO Article history: Received 3 My 16 Revised 1 August 16 Accepted 16 August 16 Aville online 3 Septemer 16 Keywords: Ammonium-pillred montmorillonite Iron oxide Mgnetic composite Adsorption Cesium ABSTRACT To remove cesium ions from wter nd soil, novel dsorent ws synthesized y following one-step co-precipittion method nd using non-toxic rw mterils. By comining mmonium-pillred montmorillonite () nd mgnetic nnoprticles (Fe 3 ), n / Fe 3 composite ws prepred nd chrcterized. The dsorent exhiited high selectivity of Cs + nd could e rpidly seprted from the mixed solution under n externl mgnetic field. Aove ll, the dsorent hd high removl efficiency in cesium-contminted smples (wter nd soil) nd lso showed good recycling performnce, indicting tht the composite could e widely pplied to the remedition of cesium-contminted environments. It ws oserved tht the ph, solid/liquid rtio nd initil concentrtion ffected dsorption cpcity. In the presence of coexisting ions, the dsorption cpcity decresed in the order of C 2+ >Mg 2+ >K + >N +, which is consistent with our theoreticl prediction. The dsorption ehvior of this new dsorent could e expressed y the pseudo-second-order model nd Freundlich isotherm. In ddition, the dsorption mechnism of Cs + ws NH + 4 ion exchnge nd surfce hydroxyl group coordintion, with the former eing more predominnt. 16 The Reserch Center for Eco-Environmentl Sciences, Chinese Acdemy of Sciences. Pulished y Elsevier B.V. Introduction In order to solve the prolems of energy demnd nd environmentl pollution, mny countries re seeking new clen energy lterntives to fossil fuels. Nucler power, which hs provided pproximtely 18.93% of the world's electricity (Interntionl Atomic Energy Agency, ), is one of the most promising methods. However, nucler power plnts emit pproximtely to 3 tons of rdioctive wste glolly ech yer (Yng et l., 14). In ddition, when nucler power ccidents occur, rdioctive pollutnts lek into the environment. For exmple, in Jpn's 11 Fukushim nucler ccident, pproximtely 63, 77, TBq rdionuclides were relesed into the environment, including thousnds of tons of rdioctive wste (Yng et l., 14c; Ysunri et l., 11), which thretened humn helth nd the ecosystems. Menwhile, the Chinese government decided to uild 6 to 8 nucler power plnts ech yer strting in 16, which drew more ttention to rdioctive wstewter (Zhng et l., ). Rdioctive isotopes of cesium ( 134 Cs nd 137 Cs) re the primry concerns mong rdioctive wstes, ecuse of their undnt content nd long hlf-life (with 2.6 nd 3 yers, respectively) (Zhng et l., ). At present, there re mny wys to decontminte rdionuclide from wstewter. Precipittion, solvent extrction, memrne dilysis, nd dsorption re the most commonly used methods (Long et l., 13; Wu Corresponding uthor. E-mil: doujf@nu.edu.cn (Junfeng Dou) / 16 The Reserch Center for Eco-Environmentl Sciences, Chinese Acdemy of Sciences. Pulished y Elsevier B.V.

2 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) et l., 9; Yng et l., 16). Among these methods, dsorption is simple opertion, economicl nd fesile. Cly minerls such s entonite, illite, kolinite, montmorillonites, sepiolite, nd zeolite which re nturl nd low cost dsorption mterils hve een widely used for the removl of cesium ions from the solution (Byülken et l., 11; Nkno et l., 3; Poinssot et l., 1999). Montmorillonite () elongs to the 2:1 cly fmily nd its lyered structure consists of two silic tetrhedrl sheets fused to one lumin octhedrl sheet. The isomorphous sustitution of Al 3+ for Si 4+ in the tetrhedrl lyer nd Mg 2+ or Fe 2+ for Al 3+ in the octhedrl lyer results in negtive surfce chrge on the cly, nd these negtive sites cn dsor ctions such s C 2+,K + nd N + etween the lyers through electrosttic ttrction (Wu et l., 9; Yng et l., 16). Compred with other cly minerls, hs higher dsorption cpcity of cesium ecuse of its high ction exchnge cpcity (CEC), lrge surfce re, stle chemicl properties nd lrge reserves in Chin (Wng et l., 1; Westrich et l., 199). Nturl primrily occurs in the form of C- or N-, which hs low selective dsorption to Cs +. pillred with ethylmine (Krmnis nd Assimkopoulos, 7; Long et l., 13) nd luminum (Krmnis nd Assimkopoulos, 7) hs een investigted, ut the performnce of selective dsorption of Cs + ws not high. The hydrtion rdius of NH 4 + is similr to tht of Cs +. C- pillred y NH 4 + would preferentilly exchnge Cs + under other coexisting ions. In ddition, is usully powder-suspended in the solution, which is difficult to e seprted nd reused fter Cs + sorption. Mgnetic seprtion, which hs een used to remove cesium ions from the solution, is convenient to seprte the dsorent from wstewter (Co et l., 8; Fn et l., 11; Hshemin et l., ; Oliveir et l., 4; Pn et l., 11; Sheh, 12; Yntsee et l., 7). hs een used to remove hevy metls (Cu 2+, P 2+, nd Ni 2+ ) from queous solutions (Klntri et l., ). However, the cpture of Cs + in wter nd soil systems with the use of mmonium-pillred mgnetic composites, nd its dsorption mechnism hve not een investigted. In this study, mmonium-pillred ws synthesized y the in situ co-precipittion technique. The sorption of Cs + on, Fe 3 nd composite ws mesured, nd the dsorption equilirium, kinetics, thermodynmics nd their pplicility in rel smples were lso discussed. In ddition, the dsorption mechnism ws investigted y mens of tch experiments, dsorption model nd chrcteriztion techniques. 1. Experimentl section 1.1. Mterils The chemicls FeCl 2 4H 2 O, FeCl 3 6H 2 O, NCl, KCl, MgCl 2, nd CCl 2 of nlyticlly pure (A.R.) grde were otined from Sinophrm Chemicl Regent Co., Ltd., Chin. Ethnol, NH 3 H 2 O (2 wt.%) nd hydrochloric cid of A.R. grde were purchsed from Beijing Beihu Fine Chemicls Co., Ltd., Chin. Nonrdioctive cesium chloride (CsCl) of extr-pure grde ws purchsed from Amresco, USA. Pure wter generted y Synergy Ultrviolet (UV) ultr-pure wter system (Millipore, USA) ws used to prepre the solution nd synthesize the novel dsorent Preprtion of composite Fe 3 ws synthesized y the co-precipittion method s reported previously (Jolivet et l., 4) with slight modifiction. The synthetic process of the mgnetic prticles ws similr to tht of Fe 3. The composite mechnism is in situ ggregtion (Zho et l., 11). First, g of FeCl 2 4H 2 O (.16 mol) ws dissolved in 3 ml of deionized wter; 3. g of ws dded into the mixture to ultrsonic th for min, nd the mixture ws stirred for 3 min. Next, g of FeCl 3 6H 2 O (.28 mol) ws dissolved in the suspension y stirring the mixture solution for 3 min t 8 C under nitrogen tmosphere. Then, 4 ml of NH 3 H 2 O ws injected into the mixture rpidly, stirred under nitrogen for nother hour, nd cooled t room temperture. The otined lck precipittes were mgneticlly seprted nd wshed repetedly with distilled wter nd ethnol. Finlly, the mgnetic fluid underwent vcuum freeze-drying for 12 hr Chrcteriztion Fourier trnsform infrred (FT-IR) spectrum ws recorded with KBr over the spectrl rnge from 4 to 4 cm 1 t resolution of 4 cm 1 (Affinity-1, Shimdzu, Jpn). Therml grvimetric nlysis (TGA) curves were mesured using TG-DSC instrument from 2 to 8 C under N 2 t heting rte of C/min (TGA/DSC1, Mettler-Toledo, Switzerlnd). Powder X-ry diffrction (XRD) ptterns were recorded on powder XRD (X Pert Pro MPD, Pnlyticl, Hollnd) with Cu Kα rdition over the 2θ rnge of 8 t scnning rte of.33 /sec. X-ry photoelectron spectrometry (XPS) ws performed on Scnning X-ry Microproe (ESCSLAB 2Xi, ThermoFisher, USA), nd the inding energy (BE) ws clirted using the C (1s) pek t ev. The surfce micromorphology ws nlyzed y scnning electron microscopy (SEM) equipped with energy dispersive spectroscopy (S-48/EX-3, Hitchi, Jpn) Adsorption experiments The dsorption ehviors of inctive cesium (cesium-133) were determined y using tch mode of opertions. A certin mount of sorents were ground into the powdered mteril nd then dispersed in the queous cesium chloride solution. After the predetermined time of shking t r/min on rottory shker, the dsorent suspended in queous solution ws seprted with.22 μm cellulose cette filter memrne. The residul concentrtions of metl ions remining in the solution were mesured using n tomic sorption spectrophotometer (ICE3, ThermoFisher, USA), nd the concentrtion of mmonium ion ws determined y UV spectrophotometer (UV-26, Shimdzu, USA).

3 14 J O U RN A L OF E N V I RO N ME N TA L SC IE N CE S 6 (2 1 7) structure. The onds ner 3433 nd 1643 cm 1 re due to the OH stretching nd deformtion of wter. The new ond ner 144 cm 1 of /Fe3O4 composite is ttriuted to virtion of N\H. Compred with, most onds of /Fe3O4 composite re in the sme position, mening tht the sic crystl structure of the /Fe3O4 composite remins unchnged fter loding Fe3O4. However, the reltive intensity of onds from 1 to 6 cm 1, especilly t 623 cm 1 compred with the, imply tht Fe3O4 nd my form new chemicl ond to comine together. The crystl structures of the Fe3O4, nd /Fe3O4 composites were investigted using XRD nd the ptterns re shown in Fig. 2. A series of chrcteristic peks of Fe3O4 MNPs t 2θ = 3.2, 3., 43.2, 7.2, 62.7 were ssigned to the (2), (311), (4), (422), (11), (44), nd (33) plnes of cuic structure, respectively, with cell constnt =.8397 nm (JCPDS crd NO ). The min chrcteristic peks of (Montmorillonite-A) cn e indexed to.8 (1), 17.7 (3), 19.8 (1), 29. (), 34.9 (11), 36. (6), 4. (21), nd 61.9 (1) plnes of the hexgonl structure with cell constnt = =.169 nm, nd c = 1.2 nm (JCPDS crd NO ). Qurtz is lso present in ccording to this XRD pttern t 2θ =.8 nd The chrcteristic peks of Fe3O4 nd re shown in the pttern of /Fe3O4 composites, suggesting tht the crystl structure of Fe3O4 nd do not chnge noticely. The (1) reflection nd the sic spcing of nd /Fe3O4 composite is.81 (d1 = 1.2 nm) nd 6.93 (d1 = 1.27 nm), indicting tht the structure of interlyer hs chnged fter loding Fe3O4 MNPs. In ddition, the (1) reflection reltive intensity of /Fe3O4 is significntly lower thn tht of, implying tht (1) plnes of /Fe3O4 ecome more disordered thn 2. Results nd discussion 2.1. Mterils chrcteristics The microstructures nd morphologies of the smples were chrcterized y SEM. The Fe3O4 (Fig. 1) ws gglomerted together nd hd rough surfce. Fig. 1 revels tht the hs lyered structure with irregulr edges nd reltively smooth surfce. Fig. 1c shows tht the Fe3O4 is closely comined with the surfce of, the structure of which hs not chnged significntly. The ove results show tht /Fe3O4 composite ws successfully synthesized. Prticle size distriution of /Fe3O4 composite (Fig. 1d) ws mesured using lser prticle size nlyzer (Mlvern, Mlvern Instruments Ltd., UK). Two different sizes of peks re oserved t different loctions (ner 1 nd 1 μm), which my e ssigned to Fe3O4 nd. The verge prticle size of /Fe3O4 composite is μm. The FT-IR spectrums of Fe3O4,, nd /Fe3O4 composite re presented in Fig. 2. The 66 cm 1 nd of Fe3O4 is ssigned to the virtion of Fe\O, which is lso oserved in the /Fe3O4 composite (Wng et l., 1). The onds t 3626 nd 79 cm 1 of the nd /Fe3O4 composite correspond to stretching virtions of the structure for the Al\OH nd Si\O groups (Wu et l., 12). The strong onds t 186 nd 134 cm 1 of the nd /Fe3O4 composite re relted to the Si\O virtions of morphous silic nd the tetrhedrl sheet (Mdejová, 3). The ond positions t 914, 844,, nd 463 cm 1 for the nd / Fe3O4 composite re ttriuted to the deformtion virtions of the Al\Al\OH, Al\Mg\OH, Si\O\Al nd Si\O\Fe 7 c d 6 Fe3O4 Volume (%) Prticle size (µm Fig. 1 SEM imges of () Fe3O4, (), (c) /Fe3O4 composite, nd prticle size distriution of (d) /Fe3O4 composite. SEM: scnning electron microscopy; : montmorillonite.

4 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) (1) d=1.2 nm Trnsmittnce (.u.) Fe Intensity (.u.) d=1.27 nm (3) (1) qurtz (6) () (11) (311) (2) (4) (1) (1) (44) (11) Fe Wvenumer (cm -1 ) (degree) Fig. 2 () FT-IR spectrums of Fe 3, nd composites, () XRD ptterns of, Fe 3 nd composite. FT-IR: Fourier trnsform infrred; XRD: X-ry diffrction.. The reltive intensity of chrcteristic peks of Fe 3 is higher thn tht of in composite pttern, mening tht Fe 3 hs higher proportion in composites, nd more ccurte ssessment of composite component rtio y TGA. As shown in Fig. 3, the weight loss from Fe 3 (2%) nd composite (3.%) elow C is scried to the evportion of dsored wter, which is reflected y strong endothermic pek t 82 C (Joshi et l., 9; Tn et l., 14). The weight loss from Fe 3 (2%) nd composite (1.%) from to 4 C is ssigned to the desorption of crystl wter. The weight of Fe 3 incresed y pproximtely.4% from 4 to 8 C nd my e oxidized to Fe 2 O 3, resulting in strong exothermic pek t 4 nd 44 C. The first weight loss of corresponds to the dehydrtion of wter molecules sored in pores nd etween the silicte lyers, which pper the endothermic vlleys t 96 nd 4 C (Zhung et l., ). However, the endothermic vlley of composite t 4 C did not pper, suggesting tht wter molecules dsored the lyers were replced y new ions. The lst weight loss of the nd composite seen from to 7 C is cused y the loss of structurl hydroxyl groups (Bjj nd Jsr, 7). According to the weight loss of ech smple, the contents of Fe 3 nd in composites re clculted to e pproximtely wt.% nd wt.%, respectively Effect of solid/liquid rtio nd initil concentrtion The effect of solid/liquid (S/L) rtio on Cs + dsorption y Fe 3, nd composite is shown in Fig. 4. The dsorption cpcity of nd composite is significntly higher thn tht of Fe 3. The dsorption cpcity of Fe 3 nd composite do not chnge significntly with incresing solid/liquid rtio, wheres tht of which decreses noticely. Fig. 4 shows the effect of initil concentrtion on Cs + dsorption y Fe 3,, nd composite. The dsorption cpcity of Fe 3, nd composite increses with the increse of the initil concentrtion. The dsorption cpcity of Fe 3 nd is nerly liner in reltion to initil concentrtion. However, when the initil concentrtion of Cs + is higher thn mg/l, incresing rte of composite decreses oviously, which implies tht it my rech sturtion dsorption cpcity. There re two resons tht cn explin the effect of solid/ liquid rtio nd initil concentrtion. Firstly, the collision proility of Cs + on the mteril surfce increses with the Weight (%) Temperture ( o C) Fe 3 Het flow (mw/mg) Exo. 82 o C 2 o C 96 o C Fe 3 4 o C 4 o C 684 o C Temperture ( o C) Fig. 3 TGA () nd DSC () curves of Fe 3, nd composite. TGA: therml grvimetric nlysis; DSC: Differentil Scnning Clorimetry.

5 16 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) Fe (mg/g) 2 1 (mg/g) 1 Fe S/L (g/l) C (mg/l) Fig. 4 Effect of () solid/liquid rtio (ph 6.7, [Cs + ] initil : mg/l, temperture: 2 C, contct time: 2 hr) nd () initil concentrtion study of Cs + dsorption y Fe 3, nd composite (ph 6.7, temperture: 2 C, contct time: 2 hr, S/L:. g/l). increse of the solution volume nd initil concentrtion. Secondly, dsorption of cesium on the surfce of the dsorent hs different ehviors t different stges. At reltively low concentrtion, most of the Cs + cn e dsored nd increse proportiontely with the rising concentrtion. However, when the dsorent is out to rech sturtion dsorption cpcity, the dsorption ehvior cn e seen s reversile rection, resulting in only prt of the cesium eing dsored y the dsorent. Furthermore, the dsorption ecomes more difficult with the increse of concentrtion. (mg/g) T= T=2 T=3 (mg/g) T= T=2 T= ph ph (mg/g) c T= T=2 T=3 Ions concentrtion (mol/l) d H + N + H + +N + OH ph ph Fig. Effect of ph nd temperture (T) study of Cs + dsorption y () Fe 3, () nd (c) composite ([Cs + ] initil : mg/l, temperture: 2 C, contct time: 2 hr, S/L:. g/l), (d) ions concentrtion in the initil solution.

6 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) Blnk (Milli-Q wter) 2 Blnk (Milli-Q wter) 1.2 (mg/g) (mg/g) (mg/g). 2 1 c Concentrtion of ction ions (mmol/l) Concentrtion of ction ions (mmol/l) Blnk (Milli-Q wter) N + K + Mg 2+ C Concentrtion of ction ions (mmol/l) Fig. 6 Effect of coexisting ions study of Cs + dsorption y () Fe 3, () nd (c) composite (ph 6.7, [Cs + ] initil : mg/l, temperture: 2 C, contct time: 2 hr, S/L:. g/l) Effect of ph nd temperture Usully, ph plys n importnt role in the dsorption process. To investigte the effect of ph on the dsorption cpcity of Fe 3, nd composite, experiments were conducted t ph levels from 2 (HCl) to 12 (NOH). Fig. c shows tht the dsorption cpcity for Cs + onto Fe 3,, nd composite grdully increses s ph increses from 2 to 4. The incresing rte slows down in the ph rnge from 4 to 1, reches its mximum t ph 11, nd then decreses rpidly. This phenomenon could e explined y the chnge of different ion concentrtions in the initil solution in Fig. d. H 3 O + is preferentilly dsored y Fe 3,, nd composites, leding to fewer surfce dsorption sites ville for Cs + t low ph (Yng et l., 16). As shown in Fig. d, with the increse of ph (2 4), the H 3 O + of the solution is neutrlized y the OH, nd thus reducing competition with Cs +, which leds to rpid increse in the dsorption cpcity of the dsorent. As the ph (4) increses further, H 3 O + in the solution decresed slightly nd more dsorption sites re relesed slowly. However, when the ph exceeds 11, the concentrtion of N + increses rpidly, resulting in competition with Cs + gin, which tkes over the rective surfce dsorption sites nd lso restrins the onding of Cs +. The effect of different tempertures (, 2, nd 3 C) on the dsorption cpcity of Fe 3,, nd composite is shown in Fig. c. The dsorption cpcity for Cs + onto Fe 3 increses with n increse in temperture, indicting tht the dsorption process is endothermic, contrry to. However, the dsorption cpcity of Cs + onto the composite is nerly constnt with the chnge of temperture, indicting tht Fe 3 nd re oth involved in the dsorption process. Tle 1 The re nd hydrted rdii of ctions (Volkov et l., 1997). Ion Ionic rdius (nm) Hydrted rdius (nm) H 3 O N K Mg C NH Cs

7 18 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) q (mg/g) Time (hr) Fe 3 (mg/g) Ce (mg/l) Fe 3 Fig. 7 Effect of () contct time (ph 6.7, [Cs + ] initil : mg/l, temperture: 2 C, S/L:. g/l) nd () the kinetic study of Cs + dsorption y Fe 3, nd composite (ph 6.7, temperture: 2 C, contct time: 2 hr, S/L:. g/l) Effect of coexisting ions The phenomenon of competitive dsorption of H +,N +, nd Cs + hs een oserved. To further investigte the effects of coexisting ction ions on the dsorption of Cs +, monovlent Group I nd divlent Group II ctions (N +,K +,Mg 2+,C 2+ ) were selected owing to their undnce in nturl environment. In Fig. 6 c, the dsorption cpcity of Fe 3,, nd composite with dded ctions is lower thn tht of the lnk. plys mjor role in the dsorption process of cesium in composite y compring the dsorption cpcity. The dsorption cpcity decreses with incresing coexisting ction ion concentrtion. When N + or K + coexist, the dsorption cpcity of nd composite is lmost 2 times tht of Mg 2+ nd C 2+, nd it decreses in the order of C 2+ >Mg 2+ >K + >N +. The results indicte tht dsorption of Cs + is significnt inhiition in the presence of coexisting ction ions. The effect of coexisting ions cn e explined y ction exchnge (Krmnis nd Assimkopoulos, 7), ut the internl mechnism remins uncler. Recently, some studies hve explined the influence of different ions on competitive dsorption y compring the ionic rdii (Yng et l., 14, 16). The ction ion is hydrted nd it represents the effective form in the wter solution, with greter size thn the ionic rdius. As shown in Tle 1, the hydrted rdii of ctions decrese in the order of Mg 2+ >- C 2+ >N + >K + >NH 4 + >Cs + >H 3 O +. The dsorption cpcity nd the hydrted rdiuses of the ctions re in the reverse sequence under the sme chrge numer condition. However, ccording to previous studies, the different effects of N +,K + etween C 2+,ndMg 2+ on the dsorption cpcity could not e explined only y compring the ion hydrtion rdius. Therefore, it could e speculted tht ction inding on the dsorent surfce involves multiple fctors not only relted to the ionic rdius, ut lso to the chrge numer of the ions. Tht is to sy, we could compre the dsorption ffinity (F, N)ofthe coexisting ction ions on dsorent ( or composite) y the following eqution, which is similr to Coulom electrosttic lw: F ¼ k q 1 q 2 r 2 where, k ((N m 2 )/C 2 )isconstnt,q 1 (C) nd q 2 (C) re the chrge of the ion nd the dsorent, the sclr r (m) is the distnce etween the chrges. The higher the F vlue of the coexisting ions, the stronger the inding ffinity, nd the more ovious the inhiitory effect on the dsorption of Cs +. The hypothesis is tht dsorption ffinity decreses in the order of F C 2þ > F Mg 2þ > F H3O þ > F Cs þ > F NH4 þ > F K þ > F þ N, in ccordnce with the experimentl dsorption cpcity increse. The results my provide guidnce in the process of finding nd modifying n dsorent for selective dsorption of cesium. 2.. Adsorption kinetics nd isotherms Fig. 7 shows the kinetics for the dsorption of Cs + y Fe 3,, nd composite t different time intervls. For Fe 3,, nd composite, the dsorption cpcity reched pproximtely 1.82, 18.8 nd mg/g, respectively. It ws oserved tht Fe 3 hs little sornce for Cs +, nd the dsorption of composite should e minly ttriuted to the composition of. The reson for the higher dsorption cpcity of composite thn ð1þ Tle 2 Adsorption kinetic constnts nd their correltion coefficients. Smple Pseudo-first-order model Pseudo-second-order model (mg/g) k 1 /hr R 2 (mg/g) k 2 (g/(mg hr)) R 2 Fe

8 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) Tle 3 Adsorption isotherm constnts nd their correltion coefficients. Smple Lngmuir Freundlich q mx (mg/g) K L (L/mg) R 2 K F (L n /(g mg n 1 )) n R 2 Fe tht of is tht the ctions (C 2+ ) etween the lyers of my e exchnged y other ions (NH 4 + ) in the process of synthesizing the composite mteril. It is lso shown tht the dsorption process is very rpid within min nd then grdully reches dsorption equilirium in 1 hr. Therefore, the connect time of dsorent ws determined s 2 hr in the following experiments. In order to explore the mechnism of the dsorption process, the pseudo-first-order (2) nd pseudo-second-order (3) were used to nlyze which model ws more consistent -Cs Fe 2p 1/2 Fe 2p Intensity (.u.) Fe 3p Si 2p O 1s Fe 2p Fe(LMM) O(KLL) Mg 1s Intensity (.u.) Fe 2p 3/2 O 2s Al 2p Al 2s Si 2s C 1s C 2p N 1s c Si 2p Si 2p d Al 2p Intensity (.u.) -Cs Intensity (.u.) -Cs Cs 4d /2 Intensity(.u.) Al 2p Al 2p Cs 4d 3/ e -Cs Fe 3 -O Fe 3 -OH -O -OH O 1s f -Cs Cs 3d H 2 O Cs 3d /2 Intensity (.u.) Intensity (.u.) Fe 2p 1/2 Cs 3d 3/ Fig. 8 XPS spectr of wide scn (), Fe 2p spectr (), Si 2p spectr (c), Al 2p spectr (d), O 1s spectr (e) nd Cs 3d spectr of composite. XPS: X-ry photoelectron spectrometry;

9 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) Tle 4 The inding energy vlues of the Fe 2p, Si 2p, Al 2p nd O 1s spectr of composite efore nd fter Cs + sorption. Smple Fe 2p 3/2 Si 2p Al 2p O 1s Fe 3 O 2 OH O 2 OH H 2 O \Cs with the experimentl dt. These two models cn e expressed y the following equtions (Vipin et l., 13): ¼ K F C 1=n e ðþ ln q t ¼ lnqe k 1 t ð2þ t q ¼ 1 k 2 q 2 þ 1 t e where, (mg/g) nd q t (mg/g) re the sorption cpcity t equilirium nd t time t (hr); k 1 /hr nd k 2 (g/(mg hr)) re the pseudo-first-order nd pseudo-second-order dsorption rte constnts, respectively. The fitted pseudo-first-order nd the pseudo-second-order model prmeters re summrized in Tle 2. For Fe 3, nd composite, the correltion coefficient (R 2 ) of the pseudo-second-order ll tter tht of the pseudo-first-order, suggesting tht electron trnsfer or shring occurred nd chemicl dsorption my e rte limiting step in the process of dsorption. The reltionship etween the dsorption cpcity of the dsorent nd the concentrtion of the dsorte under equilirium conditions t given temperture could e descried y the dsorption isotherm, which could provide the informtion of the dsorption process (Hmdoui nd Nffrechoux, 7). Fig. 7 shows the dsorption of Cs + y Fe 3,,nd composite t different equilirium concentrtions, with n dsorption time of 2 hr, temperture of 2 C, S/L of. g/l, nd ph of 6.7. In order to determine the dsorption mechnism, the Lngmuir (4) nd Freundlich () isotherm models were used to fit the experimentl dt, expressed s: ¼ q mx K LC e 1 þ K L C e ð4þ ð3þ where, (mg/g) nd q mx (mg/g) re the equilirium nd mximum sorption cpcity; K L (L/mg) is the Lngmuir dsorption constnt; C e (mg/l) is the equilirium concentrtion of the dsorte; K F (L n /(g mg n 1 )) nd n re the Freundlich dsorption constnts. The Lngmuir nd Freundlich prmeters re listed in Tle 3. The q mx vlue of is mg/g, which is pproximtely 14.2 nd 2.6 times higher, respectively, thn tht of Fe 3 nd the composite. A possile reson is tht prtil surfce of is covered y Fe 3, which eventully leds to decrese of the mximum dsorption cpcity of the composite. For Fe 3 nd, the correltion coefficient (R 2 ) of Lngmuir is etter thn tht of Freundlich, which elongs to monolyer dsorption. However, Freundlich is found to e etter fit for the composite, suggesting tht it elongs to multilyer dsorption. The n vlue is lrger thn unity, indicting tht the interction force etween Cs + nd composite is strong (Ngh et l., 1) Adsorption mechnism The ph nd coexisting ctions hve gret influence on the dsorption cpcity of Cs + onto composite. This indictes tht H + nd other ctions ply very importnt role in the dsorption process, which ffect the surfce functionl groups (hydroxyl groups) nd the interlyer ctions, respectively. The former is the coordintion rection etween Cs + nd the surfce hydroxyl group (chemicl inding process), nd the ltter is the ion exchnge rection etween Cs + nd the interlyer ction (electrosttic inding process). The Tle Reltionship etween the cesium dsored, ph nd ions relesed on composite. Dosge (g/l) Initil Cs + concentrtion (mmol/l) ph Cs + dsored (μmol) N + relesed (μmol) K + relesed (μmol) Mg 2+ relesed (μmol) C 2+ relesed (μmol) NH 4 + relesed (μmol) Fig. 9 () Reusing of composite with HCl, NCl nd NOH solution (C HCl = C NCl = C NOH =.1 mol/l, [Cs + ] initil : mg/l, temperture: 2 C, contct time: 2 hr, S/L:. g/l), () remove efficiency of composite in different wter ([Cs + ] initil : mg/l, temperture: 2 C, contct time: 2 hr, S/L:. g/l), (c) mgnetiztion curves of Fe 3 (c1)nd composite (c2), (d) mgnetic of composite (wter), (e) mgnetic of composite (soil).

10 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) Removl of Cs ions (%) HCl NCl NOH Sewter Hungpu River wter Zhunhe River wter Drinking wter Deionized wter Numer of reuse Removl of Cs + ions (%) 6 c1 4 c2 4 3 Moment/Mss(emu/g) - -4 Moment/Mss(emu/g) Mngetic Field (Guss) Mngetic Field (Guss) d Fe 3 Fe 3 After 3 sec Mgnet e

11 22 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) Tle 6 Concentrtion of some selected mjor ction ions nd ph vlue of the wter type. Wter type N + (mmol/l) K + (mmol/l) Mg 2+ (mmol/l) C 2+ (mmol/l) ph Se wter Hungpu River wter Zhunhe River wter Drinking wter Deionized wter experimentl results from ph nd coexisting ions cn predict the existence of chemicl inding nd electrosttic inding. However, direct evidence is lcking, nd the importnce of the two rections is not cler. To verify the presence of the chemicl onding rection, the element chrcteristics of the smples efore nd fter dsorption were nlyzed y XPS. Fig. 8 shows tht Al, Si, C, O, C, Mg, nd Fe exist in the surfce of nd composite. The spectrum of the composite ppers new chrcteristic pek of N 1s nd the pek re of C 2p reduces significntly, indicting tht C 2+ in is replced y NH 4 + in the process synthesizing the composite. In ddition, the chrcteristic pek of Cs 3d of composite fter Cs + sorption ( \Cs) is lso oserved (Fig. 8f). As shown in Fig. 8, the BE of Fe 2p pek demonstrtes tht iron oxides in the composite re Fe 3 rther thn Fe 2 O 3 (Lu et l., 9), which is consistent with the nlysis of XRD. The BE vlues of the Fe 2p, Si 2p, Al 2p, nd O 1s spectr of the composite efore nd fter Cs + sorption re presented in Tle 4. The chnges of the BE vlues of Al 2p nd Si 2p re not significnt, which mens tht Al nd Si toms my not prticipte in Cs + chemicl onding dsorption process. However, fter Cs + sorption, the BE vlue of Fe 2p is significntly reduced y.2 ev, indicting strong interction etween Cs nd Fe toms. The O 1s spectr cn e deconvoluted into three peks with metl oxide (M\O), hydroxyl onded to metl (M\OH), nd dsored H 2 O (Bhowmick et l., 14; Tng et l., 13). The O 1s pek of composite is oth composed of O 1s peks of Fe 3 nd ccording to pek shpe nd BE position. After Cs + sorption, the BE vlues of M\OH decrese y.2 (Fe 3 ) nd.1 ev (), respectively, implying tht oxygen constituents on the surfce of composite hve chnged nd portion of the surfce hydroxyl groups re exchnged y Cs +. Tht is to sy, the chemicl onding rection etween Cs + nd the surfce of composite exists. Similrly, in order to verify the presence of n electrosttic inding rection, experiments studied the concentrtion of ctions in the solution efore nd fter Cs + dsorption (Tle ). With the increse of initil Cs + concentrtion, N +,K +,Mg 2+, nd C 2+ hd insignificnt chnges, ut oth Cs + dsorption nd NH 4 + relese incresed synchronously, indicting tht ion exchnge occurred etween Cs + nd NH 4 +. Additionlly, the mount of Cs + dsorption ws slightly higher thn NH 4 + relesed, considering the effect of the lnk, nd ph decresed grdully, possily due to the H + relesed. This demonstrtes tht the electrosttic inding rection (ion exchnge) is more dominnt thn the chemicl onding rection (surfce hydroxyl group) in the process of Cs + dsorption y the / Fe 3 composite. Adsorption rections cn e expressed y the following equtions, where X nd S stnd for the surfce of nd Fe 3, respectively. XNH 4 þ Cs þ XCs þ NH 4 þ SOH þ Cs þ SOCs þ H þ 2.7. Regenertion, reuse nd ppliction of composite The mgnetic field of Fe 3 nd composite ws mesured t room temperture (Fig. 9c). The extrpolted sturtion mgnetiztion (M s ) nd remnnt mgnetiztion (M r )offe 3 re 47.2 nd emu/g. The M s nd M r of composite re nd emu/g, which showed tht it is lower thn tht of Fe 3. The result demonstrted tht the composite could e esily seprted from the solution under n externl mgnetic field (Fig. 9d). Adsorent recycled from mgnetic seprtion should e regenerted nd reused in order to lower the usge cost. In this study, HCl, NCl nd NOH solutions were used to test the regenertion of the composite. The used / Fe 3 composite ws dded to. mol/l different solutions (HCl, NCl nd NOH), ultrsonic clening for min, nd then mgnetic seprtion. The min regenertive chemicl rection is expressed y the following eqution, where Y nd Z stnd for the surfce of the composite nd the ddition of ctions (H + nd N + ). YCs þ Z þ YZ þ Cs þ Fig. 9 shows tht the removl of Cs + y the composite grdully decreses with the increse of cycling times. The HCl solution hd the est regenertion effect, nd the removl efficiency of Cs + ws still over 6% fter reuse in four cycles. Some resons cn explin these results. Firstly, prt of the qulity ws lost in the process of regenertion. Secondly, compred with N +, hydrted rdii of H + is smller thn tht of cesium ion, nd it is esier to regenerte. Furthermore, the crystl structureofmyedestroyedynoh,whichledstothe lowest regenertion efficiency. In order to evlute the ppliction of the composite, nturl wter smples without ny further tretment, including sewter (the Pcific Ocen ner Qingdo, Chin), river wter (the Hungpu River ner Shnghi nd Zhunhe River ner Beijing, Chin), drinking wter (Beijing, ð6þ ð7þ ð8þ

12 JOURNAL OF ENVIRONMENTAL SCIENCES 6 (17) Chin), nd deionized wter, ll with the sme dded concentrtion of cesium ions, were treted. The removl efficiency of Cs + y the composite ws ll over 8% in ll cses except sewter, ecuse the coexisting ctions in sewter were significntly higher thn in other wter smples (Tle 6). The removl rte of Cs + y the composite decresed with the increse of coexisting ctions, which hs gret influence on the prcticl ppliction of the dsorent in rel wter environments. Simulted cesium-contminted soil ws lso prepred nd then studied to reserch the elimintion efficiency (Fig. 9e). For this prt of the study, 1. g of cesium-contminted soils ws dded to ml plstic centrifuge tue, long with 4 ml solution (deionized wter, HCl nd NCl). A certin mss of dsorent ws dded to the plstic centrifuge tue while stirring. The tues were shken for 2 hr t r/min t room temperture. Then the composite ws seprted from the soil suspension under mgnetic field. Next, the rest of the suspension of soils ws dried for 24 hr in freeze dryer to test the concentrtion of cesium with HNO 3 \HCl \H 2 S- HF. Tle 7 shows tht the removl efficiency of Cs + y the composite increses with incresing dosge. The removl efficiencies were ll over 6%, nd the NCl solution showed the est effect compred with other solutions, suggesting tht the composite could e widely used to tret cesium-contminted soils in the future. 3. Conclusions In this pper, novel dsorent ws synthesized for removing cesium ions from wter nd soil. The process of synthesis ws simple nd environmentlly friendly y using one-step co-precipittion method nd non-toxic rw mterils. By comining mmonium-pillred nd mgnetic nnoprticles, the composite showed high dsorption cpcity for cesium ions nd cn e rpidly seprted from the mixed solution under n externl mgnetic field. It still hd high selectivity for cesium in the presence of coexisting ions nd ws not influenced y temperture. It ws oserved tht the ph, solid/liquid rtio nd initil concentrtion ll ffected the dsorption cpcity. The dsorption cpcity decresed in the order of C 2+ >Mg 2+ >K + >N +, which greed with our theoreticl prediction. The dsorption ehvior could e expressed y the pseudo-second-order model nd the Freundlich isotherm. NH 4 + ion exchnge ws more dominnt thn hydroxyl groups in the cesium dsorption process. The dsorent hd high removl efficiency with regrd to cesium-contminted smples (wter nd soil) nd lso showed good recycling performnce. It is sfe Tle 7 The elimintion efficiency of composite for cesium-contminted soils. Dosge (g)..1.2 E% (H 2 O) E% (HCl) E% (NCl) E: elimintion efficiency. to conclude tht the composite cn e widely pplied for the remedition of cesium-contminted environments. Acknowledgments This work ws supported y the Specil Scientific Reserch Fund of Pulic Welfre Profession (Environmentl Protection) of Chin (no. 974). REFERENCES Bjj, H.C., Jsr, R.V., 7. 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