Thermodynamics of Cu 2+ Adsorption on soil Humin

Transcription

1 Int. J. Environ. Rs., 9(1):43-52,Wintr 2015 ISSN: Thrmodynamics of Cu 2+ Adsorption on soil Li, C.L. 1, Wang, S. 2, Ji, F. 1, Zhang, J.J. 1* and Wang, L.C. 3 1 Collg of Rsourc and Environmntal Scinc, Jilin Agricultural Univrsity, Changchun, ,P.R. China 2 Collg of Plant Scinc, Jilin Agricultural Scinc and Tchnology Collg, Jilin, , P.R. China 3 Institut of Agricultural Rsourcs and Environmnts, Jilin Acadmy of Agricultural Scincs, Changchun, , P.R. China Rcivd 15 Jun 2014; Rvisd 30 Aug. 2014; Accptd 4 Nov ABSTRACT: Th adsorption thrmodynamic charactristic of Cu 2+ from aquous solution onto humin and also humic acid from a typical black soil in northast China wr xamind at thr diffrnt tmpraturs (298, 318 and 338 K) by batch isothrm xprimnts. Rsults showd that humin was structurally diffrnt from humic acid. Th incras of tmpratur had a positiv ffct on th adsorption procss. Frundlich quation dscribd th quilibrium data bttr with rspct to Langmuir quation. Thrmodynamic paramtrs, i.. standard fr nrgy changs (ΔGº), standard nthalpy chang (ΔHº) and standard ntropy chang (ΔSº), rvald that Cu 2+ adsorption by humin and humic acid wr a fasibl, spontanous and ndothrmic procss with an incras in disordr. Th valus of isostric hat of adsorption (ΔH x ) incrasd with incrasing surfac Cu 2+ loading, and th incras in ΔH x valus was smallr for humin than for humic acid. Th rsults indicatd that humin and humic acid possssd nrgtically htrognous surfacs. had gratr surfac htrognity than humin Ky words:,, Cu 2+, Adsorption isothrm, Thrmodynamic paramtrs INTRODUCTION Soil organic mattr is on of th most important soil componnts. It has a profound ffct on th physical, chmical and biological functions of soil, including aggrgat stability, watr-holding capacity, cation xchang capacity, nutrint rtntion and rlas, tc. (Krull t al., 2004). Humic substancs rprsnt th largst constitunt (60-80%) of soil organic mattr, rsponsibl for many complx chmical ractions in soil such as adsorption, ion xchang, complxation, rdox, dissolution, and prcipitat (Stvnson, 1994; Schnitzr, 1999). Gnrally, humic substancs can b dividd into thr main fractions basd on th basis of thir solubility in aquous solution at diffrnt ph valus: humic acid, which is not solubl in watr at ph<2 but is solubl at lss acidic ph valus; fulvic acid, which is solubl in watr at all ph valus; and humin, which is not solubl in watr at any ph valu (Aikn t al., 1985; Stvnson, 1994). On of th most striking faturs of humic substancs is thir strong intraction with inorganic and organic pollutants (Prminova t al., 2005). Th adsorption of mtal ions on humic substancs has long *Corrsponding author zhangjinjing@126.com bn known to play an important rol in controlling th bhavior and fat of trac mtals in th nvironmnt. Th majority of studis publishd to dat hav focusd on th adsorption charactristics of mtal ions on bas-solubl fractions of humic substancs, namly humic and fulvic acids. Howvr, vry littl information is availabl on humin. Only a fw hav rportd on th adsorption proprtis of mtal ions on humin from pat (Contrras t al., 2006; D la Rosa t al., 2003; Garda-Torrsdy t al., 1996), lignit (Havlcová t al., 2009), and brown coal (Alvarz-Publa t al., 2005; Alvarz-Publa t al., 2006). In addition, Hlal t al. (1998, 2006a, 2006b) and Rigol t al. (1998) rportd th adsorption faturs of som radionuclids ( 134 Cs, 137 Cs, 90 Sr, 153 Gd, 110m Ag, 60 Co and 65 Zn) on humin from pat soil or agricultural soil. Coppr (Cu) is an ssntial trac lmnt for plant nutrition, whil it could bcom toxic whn its concntration is high in th soil. In our prvious study, w dtrmind, for th first tim, th adsorption isothrm of Cu 2+ on humin isolatd from a forst soil 43

2 Li, C.L. t al. using batch quilibration mthod (Zhang t al., 2012). Howvr, th thrmodynamic proprtis of th adsorption of Cu 2+ on soil humin, which can provid usful information for valuating th mchanisms of adsorption procss, ar still lacking. On th othr hand, th intraction of humin with mtal ions is closly rlatd to thir chmical structurs. Elmntal analysis and solid-stat 13 C crosspolarization magic angl spinning nuclar magntic rsonanc ( 13 C CPMAS NMR) spctroscopy ar powrful tools for lucidating th structural charactristics of humin (Ric and MacCarthy, 1991; Simpson t al., 2011). Th black soil is important for its high lvl of frtility and productivity. Black soil rgion in northast China is on of th thr major black lands in th world. Th main objctiv of th prsnt study ar to valuat th thrmodynamics of Cu 2+ adsorption on humin from a typical black soil in northast China at diffrnt tmpraturs (298, 318 and 338 K) by conducting batch isothrm xprimnts. Morovr, th isolatd humin ar charactrizd using lmntal analysis and solid-stat 13 C CPMAS NMR spctroscopy. Th diffrncs of structural and Cu 2+ adsorption charactristics btwn humin and humic acid ar also compard. MATERIALS & METHODS Th soil usd in th study is black soil (Haplic haozm according to th FAO Soil Classification, and Typic Hapludoll according to th USDA Soil Taxonomy). Th surfac soil (0-20 cm) sampls wr collctd from a cultivatd maiz fild locatd at Changchun City (43º N, 125º E, m abov sa lvl), Jilin Provinc, Northast China. Th collctd soil sampls wr air-drid, milld and sivd through a 2 mm siv. Slctd physical and chmical proprtis of th soil wr analyzd using th procdur rcommndd (Lao, 1988), and th rsults ar prsntd in Tabl 1. Th xtraction, fractionation and purification of humic acid and humin wr prformd following th procdur dscribd by Zhang t al. (2009b, 2011a). Brifly, 100 g of ach soil sampl was first suspndd in distilld watr and dilut HCl to rmov poorly dcomposd light fractions and carbonats, rspctivly. Th soil rsidu was thn xtractd with a solution of 0.1 mol L -1 NaOH and 0.1 mol L -1 Na 4 P 2 O 7 using a 1:10 sampl:xtractant ratio at room tmpratur. Th xtraction procdur was rpatd 25 tims until th suprnatant was almost colorlss. Th combind alkalin suprnatant was acidifid to ph 1.0 with 6 mol L -1 HCl to sparat th humic acid fraction. Th insolubl solid rsidu rmaining aftr alkalin xtraction was rfrrd to as humin fraction. Th humic acid fraction was purifid by d-ashing with 0.5% HCl- HF solution aftr thr cycls of dissolution in 0.1 mol L -1 NaOH and rprcipitation with 6 mol L -1 HCl. Th humin fraction was purifid by d-ashing with 20% HCl-HF solution. Th humic acid and humin sampls wr thn furthr purifid by dialyzing against distilld watr until thy wr Cl - -fr. Finally, th purifid humic acid and humin wr frz-drid, ground to <0.1 mm and stord in a dsiccator for furthr us. Th C, H, N, and S contnts wr dtrmind using an Elmntar Vario MICRO lmntal analyzr (Grmany), and th O contnt was calculatd by mass diffrnc. Th ash contnts wr masurd by thrmogravimtric analysis prformd with a Shimadzu DTG-60 thrmal analyzr (Japan) from room tmpratur to 750 ºC at a hating rat of 10 ºC min -1. Solid-stat 13 C cross-polarization magic angl spinning nuclar magntic rsonanc ( 13 C CPMAS NMR) spctra wr obtaind using a Brukr AVANCE III 400 WB spctromtr (Switzrland) oprating at MHz. Th oprating conditions wr as follows: spinning rat 12 khz, contact tim 2 ms, and rcycl tim 6 s. Th spctra wr dividd into four main chmical shift rgions: alkyl C (0-50 ppm), O-alkyl C ( ppm), aromatic C ( ppm), and carbonyl C ( ppm). Th total rang of O-alkyl C was furthr dividd into rgions of mthoxyl C (50-60 ppm) and carbohydrat C ( ppm), and th total rang of aromatic C into rgions of aryl C ( ppm) and phnolic C ( ppm) (Zhang t al., 2011a). Th rlativ intnsity of ach chmical shift rgion was dtrmind using th intgration routin of th spctromtr. Th corrction of spinning sid band (SSB) was mad according to Cont t al. (1997). Th adsorption xprimnts wr carrid out undr ambint conditions by using batch tchniqu. Th solid adsorbnts (humic acid and humin), NaNO 3 background lctrolyt solution and Cu(NO 3 ) 2 stock solution wr addd into 50 ml polythyln cntrifug tubs to achiv th dsird concntrations of diffrnt componnts (i.. adsorbnt dosag 0.2 g L -1, ion strngth 0.01 mol L -1 NaNO 3, initial Cu 2+ concntration 0-80 mg L - 1 ). Th initial ph of th solution was adjustd to 5.5 with 0.1 mol L -1 HNO 3 and 0.1 mol L -1 NaOH, but no furthr Tabl 1. Slctd proprtis of th soil usd in th xprimnt Organic C Total N Total P ph Sand ( μm) Silt (2-20 μm) Clay (<2 μm) (g kg -1 ) (g kg -1 ) (g kg -1 ) (g kg -1 ) (g kg -1 ) (g kg -1 )

3 Int. J. Environ. Rs., 9(1):43-52,Wintr 2015 ph adjustmnt was conductd during th adsorption procss. Th suspnsions wr shakn at a constant spd of 140 rpm in a shaking watr bath with tmpratur 298, 318 and 338 K, rspctivly. Aftr shaking th tubs for 24 h, th solid and liquid phass wr sparatd by cntrifugation at rpm for 15 min. Th solution was thn filtrd, and th filtrat was analyzd for Cu 2+ concntration using TAS-990 atomic absorption spctromtry (China). All xprimntal data wr th avrag of duplicat or triplicat dtrmination. Th amounts of adsorbd Cu 2+ wr calculatd by th mass balanc quation [Eq. (1)]: q V ( C 0 C (1) m ) whr q is th amount of Cu 2+ adsorbd at quilibrium (mg g -1 ), C 0 is th initial Cu 2+ concntration (mg L -1 ), C is th quilibrium Cu 2+ concntration in solution (mg L -1 ), V is th volum of th solution (L), m is th mass of th adsorbnts (g). Th adsorption isothrm data wr fittd using th Langmuir modl [Eqs. (2) and (3)] and th Frundlich modl [Eqs. (4) and (5)]: q k q C 1 m (non-linar form) (2) 1 k1c C q q C 1 (linar form) (3) q q k m 1/ n 2C ln q m 1 k (non-linar form) (4) 1 ln C ln k 2 (linar form) (5) n whr q m and k 1 ar th Langmuir constants rlatd to th maximum adsorption capacity (mg g -1 ) and adsorption nrgy (L mg -1 ), rspctivly; k 2 and n ar th Frundlich constants rprsnt th adsorption capacity (mg g -1 (mg L -1 ) -1/n ) and adsorption intnsity, rspctivly. Th thrmodynamic paramtrs of adsorption, i.., th standard fr nrgy changs (ΔGº, kj mol -1 ), th standard nthalpy chang (ΔHº, kj mol -1 ) and th standard ntropy chang (ΔSº, J mol -1 K -1 ), wr calculatd from th tmpratur dpndnt adsorption isothrms using classical thrmodynamic quations [Eqs. (6)-(8)] (Mahmoodi t al., 2011; Shng t al., 2009): K d ln K d C C V 0 (6) C m S H R RT (7) G H TS (8) whr K d is th thrmodynamic quilibrium constant (ml g -1 ), R is th idal gas constant (8.314 J mol -1 K -1 ), T is th raction tmpratur (K). Th valus of ΔHº and ΔSº ar obtaind from th slop and y- intrcpt of th plot of ln K d vrsus 1/T. Th isostric hat of adsorption (ÄH x, kj mol -1 ) at constant surfac loading (q =2, 4, 6, 8, 10, 12, 14, 16 mg g -1 ) was calculatd using th Clausius-Clapyron quation [Eq. (9)] (Anirudhan and Radhakrishnan, 2011): d(lnc ) H x 2 (9) dt RT whr C (mg L -1 ) is th quilibrium Cu 2+ concntration at constant q (mg g -1 ), which was obtaind from th adsorption isothrm data at various tmpraturs T (K). Th ΔH x valus wr calculatd from th slop rsulting from plotting of ln C vrsus 1/T. RESULTS & DISCUSSION Th lmntal composition and atomic ratios of humic acid and humin ar prsntd in Tabl 2. Compard with humic acid, humin containd mor C, H and S and lss N and O. Th H/C ratio was lowr whras th O/C ratio was highr for humic acid than for humin, indicating that humin was mor aliphatic and lss polar (Xing t al., 2005). Manwhil, th C/N ratio of humic acid was lowr than that of humin, suggsting that rsistant forms of N wr dpltd in humin during th humification procss (Zhang t al., 2011b). Th 13 C CPMAS NMR spctra of humic acid and humin ar shown in Fig. 1. Th spctra xhibitd major Tabl 2. Elmntal composition and atomic ratios of humic acid and humin from black soil Sampls C a (g kg -1 ) H a (g kg -1 ) N a (g kg -1 ) S a (g kg -1 ) O a (g kg -1 ) H/C (atomic ratio) O/C (atomic ratio) C/N (atomic ratio) a On a ash-fr basis. 45

4 Cu 2+ adsorption on humin Tabl 3. Rlativ carbon distribution (%) in diffrnt rgions of chmical shift in 13 C CPMAS NMR spctra of humic acid and humin from black soil Sampls Chmical shift rgions (ppm) A/ Alip/ HB/ O-A a Arom b HI c a alkyl C/O-alkyl C = (0-50)/(50-110). b aliphatic C/aromatic C = [(0-50)+(50-110)]/( ). c hydrophobic C/hydrophilic C = [(0-50)+( )]/[(50-110)+( )]. Fig C CPMAS NMR spctra of humic acid and humin from black soil signal paks at 21, 25, 30, 32, 43, 54, 73, 105, 128, 151 and 173 ppm. Basd on Zhang t al. (2009b; 2011a), th paks at 21, 25, 30, 32 and 43 ppm in th alkyl C rgion wr assignd as -CH 3, -CH 2 -, amorphous -(CH 2 ) n -, crystallin -(CH 2 ) n -, and branchd aliphatic C, rspctivly. Th signals at 54, 73 and 105 ppm in th O-alkyl C rgion wr ascribd to mthoxyl C in lignin, and -CHOH-, and anomric C in carbohydrat, rspctivly. Th signals at 128 and 151 ppm in th aromatic C rgion rprsntd C- and H-substitutd, and O-substitutd aromatic C from lignin, rspctivly. Th signal at 173 ppm in th carbonyl C rgion was indicativ of carboxylic acid, amid and str. Morovr, a distinct pak appard in th rang of ppm was assignd as spinning sid band (SSB). Th rlativ intnsitis of C functional groups of humic acid and humin ar prsntd in Tabl 3. Across th two humic substanc fractions, th intnsity of aliphatic C (th sum of alkyl C and O-alkyl C, 46.9%- 54.8%) was highr than that of aromatic C (22.2%-26.5%) and carbonyl C (23.1%-26. 9%). Morovr, carbohydrat C showd th highst intnsity (17.5%- 18.5%) in th O-alkyl C rgion, and th intnsity of aryl C (19.8%-23.2%) was th highst in th aromatic C rgion. Compard with humic acid, humin containd largr proportions of alkyl C, but smallr proportions of mthoxyl C, carbohydrat C, aryl C, phnolic C and carbonyl C. Th ratios of alkyl C/O-alkyl C, aliphatic C/aromatic C and hydrophobic C/ hydrophilic C of humin wr highr than thos of humic acid. Th ratios of alkyl C/O-alkyl C, aliphatic C/aromatic C and hydrophobic C/hydrophilic C hav bn usd as indics of th dgrs of humification, aliphaticity and hydrophobicity of humic substancs, rspctivly. Largr valus of th ratios indicat that humic substancs ar mor humifid, aliphatic and hydrophobic (Zhang t al., 2011a). Furthrmor, alkyl C/O-alkyl C ratio is gnrally considrd a mor suitabl indx for dscribing th humification dgr of humic substanc fractions with rspct to othr indics such as aromaticity (Chn and Chiu, 2003; Mathrs and Xu, 2003). Thus, our rsults implid that humin was th mor humifid, aliphatic and hydrophobic compard 46

5 Int. J. Environ. Rs., 9(1):43-52,Wintr 2015 Fig. 2. Cu 2+ adsorption isothrms of humic acid and humin from black soil at diffrnt tmpraturs. Symbols dnot xprimntal data, and lins rprsnt th modl fitting of Frundlich quation mg/l 20 mg/l 40 mg/l 60 mg/l 80 mg/l Linar (10 mg/l) mg/l 20 mg/l 40 mg/l lnk d (ml g -1 ) 9.0 lnk d (ml g -1 ) /T (K -1 ) /T (K -1 ) Fig. 3. Linar plot of ln K d vs. 1/T for Cu 2+ adsorption on humic acid and humin from black soil with corrsponding humic acid. Th rsult of aliphatic C/aromatic C ratio was in accordanc with that of H/ C ratio. Th adsorption isothrms of Cu 2+ on humic acid and humin at thr diffrnt tmpraturs ar shown in Fig. 2. It could b sn that th amounts of adsorbd Cu 2+ on th two humic substanc fractions incrasd with incrasing Cu 2+ concntration. On th othr hand, th amounts of Cu 2+ adsorbd on th two adsorbnts also incrasd with rising tmpratur, indicating that th adsorption of Cu 2+ was promotd at highr tmpratur. Th possibl intrprtation for th promotion of Cu 2+ adsorption at highr tmpratur is that th adsorption of wll hydratd Cu 2+ on humic acid and humin is an ndothrmic procss in ssnc (Li t al., 2011; Shng t al., 2009). Compard with humic acid, th adsorption amounts of humin for Cu 2+ wr lowr. Th adsorption prcntags of Cu 2+ rangd from 47.7% to 79.2% for humic acid and from 40.1% to 62.5% for humin. Th paramtrs of linarizd Langmuir and Frundlich quations obtaind by fitting th isothrms ar givn in Tabl 4. Th adsorption data could b wll dscribd by both Langmuir and Frundlich quations with cofficint of dtrmination (R 2 ) gratr than Howvr, th Frundlich quation gav a bttr fit with R 2 valus ranging from to Basd on th Langmuir quation, th maximum adsorption capacitis of Cu 2+ (q m ) on humic acid and humin wr and mg g -1 at 298 K, rspctivly. Th highr adsorption capacitis of humic acid to Cu 2+ was confirmd by th largr valus of th Langmuir constant k 1 and th Frundlich constant k 2 for humic acid than for humin. Th n valus in th Frundlich quation wr largr than 1, indicating a favorabl and 47

6 Li, C.L. t al. Tabl 4. Adsorption isothrm paramtrs drivd from linar Langmuir and Frundlich quations for Cu 2+ adsorption on humic acid and humin from black soil at thr diffrnt tmpraturs Sampls T (K) Langmuir Frundlich a q m b k 1 R 2 n c d k 2 R a q m : Maximum adsorption quantity (mg g -1 ). - b k 1 : Langmuir constants (L mg -1 ). - c n: Frundlich constants (dimnsionlss). d k 2 : Frundlich constants (mg g -1 (mg L -1 ) -1/n ). - R 2 : Cofficint of dtrmination. Tabl 5. Valus of thrmodynamic paramtrs for th adsorption of Cu 2+ on humic acid and humin from black soil. Sampls C 0 (mg L -1 ) ΔHº(kJ mol -1 ) ΔSº(J mol -1 K -1 ) ΔGº(kJ mol -1 ) 298 K 318 K 338 K htrognous adsorption of Cu 2+ on th two fractions of humic substancs (Zhang t al., 2009a). Th dgr of adsorption favorability and htrognity was highr for humic acid than for humin, which was also consistnt with th largr Cu 2+ adsorption of th formr. Th gratr amounts of Cu 2+ adsorption on humic acid than on humin could b attributd to th highr carboxyl and phnolic hydroxyl groups of th formr (Tabl 3). On th othr hand, th Langmuir and Frundlich isothrm paramtrs all incrasd with th incras in tmpratur, which agrd with th promotion of Cu 2+ adsorption at highr tmpratur. Th thrmodynamic paramtrs calculatd from Eqs. (6) to (8) ar listd in Tabl 6, and th rlvant plot of ln K d vs. 1/T is givn in Fig. 3. Th magnitud of ΔGº, ΔHº, and ΔSº valus rangd from kj mol -1, 3.81 kj mol -1, 81.3 J mol -1 K -1 to kj mol -1, 5.80 kj mol -1, 97.4 J mol -1 K -1 for humic acid, and from kj mol -1, 4.43 kj mol -1, 80.1 J mol -1 K -1 to kj mol -1, 7.50 kj mol -1, 96.4 J mol -1 K -1 for humin, rspctivly. Th ngativ ΔGº valus at all tmpraturs indicatd th fasibility and spontanous natur of th adsorption of Cu 2+ on humic acid and humin, which mans that th adsorptiv forc is strong nough to brak th potntial and lad th raction to bind Cu 2+ onto th surfac functional groups of humic substanc fractions (Li t al., 2008). Th dcras in ΔGº valus with incras in tmpratur implid that th adsorption procss was mor favorabl at highr tmpratur. Th positiv ΔHº valus indicatd that th adsorption raction was an ndothrmic procss, which is supportd by th rsults that th adsorption of Cu 2+ on humic acid and humin incrasd with incrasing tmpratur. Th positiv ΔSº valus rflctd th affinity of th humic substanc fractions towards Cu 2+ and th incras of th dgr of frdom at th solid/liquid intrfac during th adsorption procss. In th study of Prado and Airoldi (2003), thy showd that th adsorption of Cu 2+ on 48

7 Int. J. Environ. Rs., 9(1):43-52,Wintr 2015 ln C 1/T ln C 1/T Fig. 4. Linar plot of ln C vs. 1/T for diffrnt amounts of Cu 2+ adsorption on humic acid and humin, q =2 ( ), 4 ( ), 6 ( ), 8 ( ), 10 (*), 12 ( ), 14 (+), 16 (-) mg g -1, from black soil H x(kg mol -1 ) Surfac loading (mg g -1 ) Fig. 5. Plot of isostric hat of adsorption (Hx) against surfac loading for th adsorption of Cu 2+ on humic acid and humin from black soil humic acids from pat soil and commrcial Aldrich was spontanous, ndothrmic and incrasingly disordrd procss, in accordanc with our rsults. Compard with humic acid, th ΔGº valus of Cu 2+ adsorption on humin wr always mor positiv at ach Cu 2+ concntrations studid. It indicatd that th adsorption of Cu 2+ was mor favorabl on humic acid, in agrmnt with th largr valus of th Frundlich constant n of humic acid. Howvr, thr was no consistnt diffrnc of th valus of ΔHº and ΔSº btwn humic acid and humin. Th plots of ln C vrsus 1/T ar plottd in Fig. 4, and th corrsponding ΔH x valus ar listd in Tabl 6. Th plots of ln C vrsus 1/T wr found to b linar with R 2 valus gratr than Th ΔH x valus rangd from to kj mol -1 for humic acid and from to kj mol -1. Th valus of ΔH x for physical and chmical adsorption ar blow 80 kj mol -1 and btwn 80 and 400 kj mol -1, rspctivly (Chowdhurg t al., 2011). Thus, our prsnt rsults implid that th chmical adsorption involving ion xchang was th dominating mchanism. On th othr hand, th variation of ΔH x with surfac loading (Fig. 5) showd that th ΔH x valus incrasd with th incras of q valus, indicating that th adsorbnts had nrgtically htrognous surfacs. Th abov variation in ΔH x 49

8 Cu 2+ adsorption on humin Tabl 6. Isostric hat of adsorption (H x ) of Cu 2+ on humic acid and humin from black soil Sampls q (mg g -1 ) ΔH x (kj mol -1 ) R valus was usually du to th adsorbat-adsorbat intraction followd by th adsorbat-adsorbnt intraction, and th possibility of having latral intractions btwn adsorbd Cu 2+ ions (Chowdhurg t al., 2011; Srivastava t al., 2007). Th xtnt of th incras in ΔH x valus was largr for humic acid (49.8%) than for humin (37.8%), implying that humic acid had gratr surfac nrgy htrognity than humin. It agrd with th largr n valus of humic acid with rspct to humin in th Frundlich constant. In th study of Li t al. (2004), thy indicatd that th humic substanc fractions with lowr molcular wights, gratr O/C atomic ratios, and highr contnts of oxygn and lignin-drivd aromatic structural units wr mor htrognous. Basd on our prsnt study, th O/C atomic ratio and th contnts of oxygn and lignin-drivd aromatic structural units of humic acid wr all highr than that of humin. Manwhil, th molcular wight of humic acid was gnrally considrd lowr than that of humin (Stvnson, 1994). It confirmd that th htrognity of humic acid was largr than that of humin. Thus, th diffrnc in htrognity of adsorption surfac of humic acid and humin could b du on thir diffrnt chmical composition. CONCLUSIONS Th chmical compositions of humin diffrd from thos of corrsponding humic acid. Th formr was mor humifid, aliphatic, hydrophobic, and lss polar compard with th lattr. Th adsorption amounts of humin for Cu 2+ wr lowr than that of humic acid. Th maximum adsorption capacitis of Cu 2+ on humin and humic acid wr and mg g -1 at 298 K, rspctivly. Th adsorption data could b bttr dscribd Frundlich quation with rspct to quation. Th incras in tmpratur had a positiv ffct on th sorption procss. Th adsorption of Cu 2+ on humin and humic acid was a spontanous, ndothrmic, and incrasingly disordrd procss. Both humin and humic acid had nrgtically htrognous surfacs for th adsorption of Cu 2+, and th surfac nrgy htrognity of humic acid was gratr than that of humin. ACKNOWLEDGEMENTS This work was financially supportd by th National Ky Tchnology R&D Program (2013 BAD07B02 and 2013BAC09B01), th National Agricultural Dpartmnt Public Bnfit Rsarch Foundation ( ), and th Postdoctoral Projct of Jilin Provinc (01912). Th authors ar gratful to Dr. Zijiang Jiang of th Changchun Institut of Applid Chmistry, Chins Acadmy of Scincs, for his tchnical assistanc in obtaining th solid-stat 13 C NMR spctra. REFERENCES Aikn, G. R., McKnight, D. M., Wrshaw, R. L. and MacCarthy, P. (1985). Humic substancs in soil, sdimnt, and watr: Gochmistry, isolation, and charactrization. Nw York: Wily. Alvarz-Publa, R. A., Aroca, R. F., Valnzula-Calahorro, C. and Garrido, J. J. (2006). Rtntion of cobalt on a humin 50

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