Removal of lead (II) from waste water by adsorption

Transcription

1 ISSN: Volum 3 Numr 4 (214) pp Original Rsarch Articl Rmoval of lad (II) from wast watr y adsorption Nama H. Yarkandi* Chm. Dpartmnt- Colldg of Applid Scinc, Umm Al-Qura Univrsity, Makkah, Saudi Araia *Corrsponding author A B S T R A C T K y w o r d s Adsorption, Lad; Activatd Caron; Bntonit. Th adsorption proprtis of natural Amrican ntonit and activatd caron, th rmoval of P++ from aquous solution wr studis. Th rsults show that th amount of adsorption of P++ incrass with initial mtal ion concntration, contact tim and solution PH ut dcrass with amount of adsornt and tmpraturs. Th adsorption procss has fit psudo-scond ordr kintic modl. Langmuir and Frundich adsorption isothrm modls wr applis to analyz adsorption data and oth wr found to applical to ths adsorption procss. Thrmodynamic paramtrs.g. G, S and H of th adsorption procss was found to ndothrmic. Finally it can sn that ntonit was found to mor ffctiv for rmoval of P++ than activatd caron. Introduction As a rsult of rapid industrialization, toxic mtals and mtalloid such as cadmium, lad, chromium, mrcury, arsnic and coppr ar rlasd into th nvironmnt rsulting in damag in cosystms and human halth. Unlik organic pollutants, havy mtals ar non-iodgradal in th nvironmnt and can accumulat in living tissus particularly in human odis causing significant physiological disordrs such as damag of cntral nrvous systm and lood composition, production of nrgy and irrvrsil damag of vital organs of ody. Hnc th prsnc of havy mtals in natural or industrial wastwatrs is a sujct of grat intrst in nvironmntal scinc which is on of th most srious worldwid nvironmntal prolm (Axtll t al., 23; Amarasingh t al., 27). Among th diffrnt havy mtals, lad is on of th common and most toxic pollutants into th natural watrs from various industrial activitis such as mtal plating, oil rfining and attry manufacturing (Yurtsvr and Sngil, (28). Lad ions ar takn into ody via inhalation, ingstion or skin adsorption. As a rsult whn th ody is xposd to lad, it can act as a cumulativ poison. Lad accumulats mainly in ons, rain, kidny and muscls and may caus many srious disordrs lik anamia, kidny 27

2 disas, nrvous disordr and sicknss vn dath (Kazi t al., 28; Afridi t al., 26). Lad can rplac calcium, which is an ssntial minral for strong ons and tth, whil play important rol in sympathtic actions of nrv and lood vssl for normal functioning of nrvous systm. Th high lvl of lad damags cognitiv dvlopmnt spcially in childrn. It also acts as an nzym inhiitor in ody,.g. rplacs ssntial lmnt zinc from hm nzyms (Skrfving t al., 1998; Soylac t al., 22). In drinking watr maximum allowal limit of total P of 5 gl -1 is considrd saf y th World Halth Organization, whras lss than 15 gl -1 is adoptd y th Unitd Stats Environmntal Protction Agncy (Raungsomoon t al., 27). Du to toxic ffcts of lad and othr toxic mtal ions, th rmoval of thm from watr and wastwatr is important in trms of protction of pulic halth and nvironmnt (Unlu and Ersoz, 26). Th traditional mthods, for th tratmnt of lad and othr toxic havy mtal contaminatd wastwatrs, includ complxation, chmical oxidation or rduction, solvnt xtraction, chmical prcipitation, rvrs osmosis, ion xchang, filtration, mmran procsss, vaporation and coagulation. Bsids th classical wastwatr tratmnt tchniqus, adsorption of havy mtals is th most promising sparation and purification mthod caus this tchniqu has significant advantags including high fficincy in rmoving vry low lvls of havy mtals from dilut solutions, asy handling, high slctivity, lowr oprating cost, minimum production of chmical or iological sludg and rgnration of adsornt (King t al., 27). Th ojctivs of this study was to invstigat th adsorption potntial of activatd caron and ntonit for th rmoval of P(II) ions from wastwatr. Th ffct of svral paramtrs such as contact tim, initial concntration, ph valu of th solution, adsornt dos, volum and tmpratur wr studid. Th adsorption mchanisms of P(II) ions onto activatd caron and ntonit valuatd in trms of thrmodynamic and kintics. Th adsorption isothrm wr dscrid y using Langmuir and Frundlich modls. Matrials and Mthods Exprimntal All chmicals usd in this prsnt work wr ithr of analytical ragnt or laoratory ragnt grad and wr usd as rcivd. Lad Nitrat supplid y BDH chmicals Ltd. Distilld watr was usd in all prparations. Lad nitrat and dionisd watr wr usd to prpar synthtic chromium containing wastwatr. Powdr activatd caron (PAC) producd from natural origin y ADWIC was usd as adsornt as wll as Amrican Wyoming calcium ntonit usd in Saudi Araia Company for Rfractory's. Powdr activatd caron (PAC) and ntonit (clay) wr supplid from ADWIC and Saudi araia Company for Rfractory's, rspctivly. Elmntal analysis for ntonit was valuatd using X-ray fluorscnc (Philips PW 139) as shown in (Tal-1). Magntic hot plat stirrr was usd to stir th havy mtal ions solutions with adsornts (activatd caron or ntonit). A dfinit volum of havy mtal ions 28

3 Fig.1 Psudo-first ordr kintic plots for th adsorption of diffrnt initial concntrations: 5, 1 and 2 ppm P 2+ ions onto diffrnt adsornts doss of activatd caron: a).1 g/25 ml and ).3 g/25 ml, (ph: 5.5; agitation spd: 2 rpm; tmpratur: 25 C) 6. 5 a p p m 1 p p m 2 p p m ln(q -q) t, m in ln(q -q) t, m in 5 p p m 1 p p m 2 p p m 29

4 Fig.2 Psudo-first ordr kintic plots for th adsorption of diffrnt initial concntrations: 5, 1 and 2 ppm P 2+ ions onto diffrnt adsornts doss of ntonit: a).1 g/25 ml and ).3 g/25 ml, (ph: 5.5; agitation spd: 2 rpm; tmpratur: 25 C) 6.5 a p p m 1 p p m 2 p p m ln(q -q) t, m in ln(q -q) p p m 1 p p m 2 p p m t, m in Fig.3 Psudo-scond ordr kintic plots for th adsorption of diffrnt initial concntrations: 5, 1 and 2 ppm P 2+ ions onto diffrnt adsornts doss of activatd caron: a).1 g/25 ml and ).3 g/25 ml, (ph: 5.5; agitation spd: 2 rpm; tmpratur: 25 C) p p m 1 p p m 2 p p m a 1. t/q t, m i n 21

5 p p m 1 p p m 2 p p m t/q t, m i n Fig.4 Psudo-scond ordr kintic plots for th adsorption of diffrnt initial concntrations: 5, 1 and 2 ppm P 2+ ions onto diffrnt adsornts doss of ntonit: a).1 g/25 ml and ).3 g/25 ml, (ph: 5.5; agitation spd: 2 rpm; tmpratur: 25 C) p p m 1 p p m 2 p p m a 1. t/q t, m in p p m 1 p p m 2 p p m 2.5 t/q t, m in 211

6 Tal.1 Th adsorption kintics modl rat constants for adsorption of P 2+ ions onto activatd caron and ntonit at various concntrations and constant tmpratur 25 C Adsornt (.1 g) Activatd Caron Bntonit C o (mg/l) q, xp. (mg/g) Lagrgrn first ordr Psudo-scond ordr k K 1 q 2 1, tho. (min -1 R 2 (gmg - q 2, tho. R 2 ) (mg/g) 1 min -1 (mg/g) ) x x x x X x x x x x x x Adsornt (.3 g) Activatd Caron Bntonit C o (mg/l) q xp. (mg/g) Lagrgrn first ordr Psudo-scond ordr k K 1 q 2 1, tho. (min -1 R 2 (gmg - q 2, tho. R 2 ) (mg/g) 1 min -1 (mg/g) ) x x x x x x x x x x x x

7 Fig.5 Effct of contact tim (min) on % rmoval of P 2+ ions for: a) 5 ppm and ) 1 ppm, in th prsnc of diffrnt amounts of activatd caron (tmp. = 25 C, ph = 5.5 and quilirium tim = 2 h) 1 a % Rmoval of P T im, m in. 1 g. 3 g. 5 g. 7 g 1. g 1 8 % Rmoval of P T i m, m i n. 1 g. 3 g. 5 g. 7 g 1. g Fig.6 Effct of contact tim (min) on % rmoval of P 2+ ions for: a) 5 ppm and ) 1 ppm, in th prsnc of diffrnt amounts of ntonit (tmp. = 25 C, ph = 5.5 and quilirium tim = 2 h) 1 a % Rmoval of P T i m, m i n. 1 g. 3 g. 5 g. 7 g 1. g 213

8 1 % Rmoval of P T i m, m i n. 1 g. 3 g. 5 g. 7 g 1. g Fig.7 Effct of contact tim on adsord amount of P 2+ for diffrnt concntrations: a) 5 ppm and ) 1 ppm, in th prsnc of diffrnt amounts of activatd caron (tmp. = 25 C, ph = 5.5 and quilirium tim = 2 h) g. 3 g. 5 g. 7 g 1. g a q, mg/g T im, m in g.3 g.5 g.7 g 1. g q, mg/g T im, m in 214

9 Fig.8 Effct of contact tim on adsord amount of P 2+ for diffrnt concntrations: a) 5 ppm, ) 1 ppm, in th prsnc of diffrnt amounts of ntonit (tmp. = 25 C, ph = 5.5 and quilirium tim = 2 h) g. 3 g. 5 g. 7 g 1. g a q, mg/g T im, m in g.3 g.5 g.7 g 1. g q, mg/g T im, m in Fig.9 Th ffct of variant activatd caron adsornt doss (.1,.3,.5,.7 and 1. g/25 ml) on % rmoval for diffrnt P 2+ ions initial concntrations solution at 25 C % Rmoval of P p p m 1 p p m 2 p p m 3 p p m 4 p p m A d s o r n t d o s (g /2 5 m L ) 215

10 Fig.1 Th ffct of variant ntonit adsornt doss (.1,.3,.5,.7 and 1. g/25 ml) on % rmoval for diffrnt P 2+ ions initial concntrations solution at 25 C % Rmoval of P p p m 1 p p m 2 p p m 3 p p m 4 p p m A d s o r n t d o s ( g / 2 5 m L ) Fig.11 Th ffct of variant activatd caron adsornt doss (.1,.3,.5,.7 and 1. g/25 ml) on th quantity adsord for diffrnt P 2+ ions initial concntrations solutions at 25 C Amount adsord (mg/g) p p m 1 p p m 2 p p m 3 p p m 4 p p m A d s o r n t d o s ( g / 2 5 m L ) Fig.12 Th ffct of variant ntonit adsornt doss (.1,.3,.5,.7 and 1. g/25 ml) on th quantity adsord for diffrnt P 2+ ions initial concntrations solutions at 25 C Amount adsord (mg/g) p p m 1 p p m 2 p p m 3 p p m 4 p p m A d s o r n t d o s ( g / 2 5 m L ) 216

11 Fig.13 Th ffct of initial concntrations (namly 5, 1, 2 and 3 mg/l) on % rmoval of P 2+ ions in th prsnc of diffrnt amounts of activatd caron (tmp. = 25 C, ph = 5.5 and quilirium tim = 2 h) p p m 1 p p m 2 p p m 3 p p m 4 p p m % Rmoval of P I n i t i a l c o n c. ( m g / g ) Fig.14 Th ffct of initial concntrations (namly 5, 1, 2 and 3 mg/l) on % rmoval of P 2+ ions in th prsnc of diffrnt amounts of ntonit (tmp. = 25 C, ph = 5.5 and quilirium tim = 2 h) % Rmoval of P I n i t i a l c o n c. ( m g / g ) 5 p p m 1 p p m 2 p p m 3 p p m 4 p p m Fig.15 Th ffct of initial concntrations (namly 5, 1, 2 and 3 mg/l) on quantity adsord of P 2+ ions in th prsnc of diffrnt amounts of activatd caron (tmp. = 25 C, ph = 5.5 and quilirium tim = 2 h). Amount adsord (mg/g) p p m 1 p p m 2 p p m 3 p p m 4 p p m I n i t i a l c o n c. ( m g / g ) 217

12 Fig.16 Th ffct of initial concntrations (namly 5, 1, 2 and 3 mg/l) on quantity adsord of P 2+ ions in th prsnc of diffrnt amounts of ntonit (tmp. = 25 C, ph = 5.5 and quilirium tim = 2 h) Amount adsord (mg/g) p p m 1 p p m 2 p p m 3 p p m 4 p p m I n it ia l c o n c. ( m g / g ) Fig.17 Effct of ph valu for th adsorption of P 2+ ions onto activatd caron (conditions; P 2+ ions initial concntration: 1 mg/l; adsornts dos:.5 g/25 ml; agitation spd: 2 rpm; contact tim: 2 h) at 25 C 1 A c t i v a t d c a r o n 8 % Rmoval of P p H Fig.18 Effct of ph valu for th adsorption of P 2+ ions onto ntonit (conditions; P 2+ ions initial concntration: 1 mg/l; adsornts dos:.5 g/25 ml; agitation spd: 2 rpm; contact tim: 2 h) at 25 C 1 B n t o n i t 8 % Rmoval of P p H 218

13 Fig.19 Langmuir adsorption isothrm for P 2+ ions adsorption onto diffrnt amounts of activatd caron at constant tmpratur 25 C and contact tim 2 h g. 3 g. 5 g. 7 g 1. g C /q C ( m g / L ) Fig.2 Langmuir adsorption isothrm for P 2+ ions adsorption onto diffrnt amounts of ntonit at constant tmpratur 25 C and contact tim 2 h g.3 g.5 g.7 g 1. g C /q C ( m g /L ) Fig.21 Frundlich adsorption isothrm for P 2+ ions adsorption onto diffrnt amounts of activatd caron at constant tmpratur 25 C and contact tim 2 h g.3 g.5 g.7 g 1. g 5. lnq ln C 219

14 Fig.22 Frundlich adsorption isothrm for P 2+ ions adsorption onto diffrnt amounts of ntonit at constant tmpratur 25 C and contact tim 2 h g. 3 g. 5 g. 7 g 1. g 5. ln q l n C Fig.23 Equilirium isothrm of P 2+ ions adsortion using diffrnt amounts of activatd caron at constant tmpratur 25 C and contact tim 2 h g. 3 g. 5 g. 7 g 1. g 5 q (mg/g) C ( p p m ) Fig.24 Equilirium isothrm of P 2+ ions adsorption using diffrnt amounts of ntonit at constant tmpratur 25 C and contact tim 2 h g. 3 g. 5 g. 7 g 1. g q (mg/g) C ( m g / L ) 22

15 Tal.2 Langmuir and Frundlich isothrm for th adsorption of P 2+ ions onto diffrnt doss of activatd caron and ntonit at constant tmpratur (25 C) Adsornt (.1 g/25 ml) Langmuir Isothrm constants q max (mg/g) (L/mol) Frundlich Isothrm constants R 2 K F (mg/g) n R 2 Activatd Caron x Bntonit x Adsornt (.3 g/25 ml) Langmuir Isothrm constants q max (mg/g) (L/mol) Frundlich Isothrm constants R 2 K F (mg/g) n R 2 Activatd Caron x Bntonit x Adsornt (.5 g/25 ml) Langmuir Isothrm constants q max (mg/g) (L/mol) Frundlich Isothrm constants R 2 K F (mg/g) n R 2 Activatd Caron x Bntonit x Adsornt (.7 g/25 ml) Langmuir Isothrm constants q max (mg/g) (L/mol) Frundlich Isothrm constants R 2 K F (mg/g) n R 2 Activatd Caron x Bntonit x Adsornt (1 g/25 ml) Langmuir Isothrm constants q max (mg/g) (L/mol) Frundlich Isothrm constants R 2 K F (mg/g) n R 2 Activatd Caron x Bntonit x

16 Fig.25 A plot of lnk C vrsus 1/T for P 2+ ions adsorption onto activatd caron for diffrnt initial concntrations at constant adsornts dos:.5 g/25 ml ppm 1 ppm 2 ppm 3 ppm 4 ppm ln K C /T (K -1 ) Fig.26 A plot of lnk c vrsus 1/T for P 2+ ions adsorption onto ntonit for diffrnt initial concntrations at constant adsornts dos:.5 g/25 ml ppm 1 ppm 2 ppm 3 ppm 4 ppm 2.2 ln K C /T (K -1 ) 222

17 Tal.3 Thrmodynamic paramtrs for diffrnt concntrations of P 2+ ions onto activatd caron and ntonit C G (kj mol -1 o H S ) Adsornt (mg/l) (kj mol -1 ) (j mol -1 K -1 ) 25 C 3 C 35 C 4 C Activatd caron Bntonit H S G (kj mol -1 ) Adsornt C o (kj mol -1 ) (j mol -1 K -1 ) (mg/l) 25 C 3 C 35 C 4 C Activatd caron Bntonit H S G (kj mol -1 ) Adsornt C o (kj mol -1 ) (j mol -1 K -1 ) (mg/l) 25 C 3 C 35 C 4 C Activatd caron Bntonit H S G (kj mol -1 ) Adsornt C o (kj mol -1 ) (j mol -1 K -1 ) (mg/l) 25 C 3 C 35 C 4 C Activatd caron Bntonit Adsornt C o (mg/l) H (kj mol -1 ) S G (kj mol -1 ) (j mol -1 K -1 ) 25 C 3 C 35 C 4 C Activatd caron Bntonit solution with a known initial ions concntration was stirrd with a dfinit amount of adsornt for crtain tim at fixd tmpratur and agitation rat. Th ph valus of th solutions wr masurd y digital ph mtr (Modl ì ph systm- 361, India). Th mtal ion concntration was masurd using atomic-asorption spctrophotomtr, AAS, (Modl, AA55; Varian Inc., USA). Exprimntal procdurs: Lad Nitrat and rdistilld watr wr usd to prpar a stock solution with a concntration of 1 ppm lad which was dilutd for prparation of tst solutions. Svral solutions with diffrnt initial concntrations of lad nitrat (5, 1, 2, 3 and 4 ppm) wr prpard. Th rquird ph was adjustd y drop wis addition of.1 N NaOH dpnding on th acidity of th sampl. All xprimnts wr carrid out at 25 ºC y adding diffrnt amounts of adsornts (.1,.3,.5,.7 and 1. g) to diffrnt concntrations of 25 ml of havy mtal 223

18 ions solution. Th agitation rat for all xprimnts was 2 rpm and th rsidnc tim was (, 15, 3, 45, 6, 75, 9 and 12 min).. 1 ml of sampl was takn from raction solution and dilutd to 1 ml y rdistilld watr; adsornts wr thn sparatd from th solution y using filtr papr (Whatman No. 4) and th rsidual P +2 ions concntration in th solution was thn dtrmind y atomic-asorption spctrophotomtr. Th ffcts of svral paramtrs, such as contact tim, initial concntration, adsornt dos, ph and tmpratur on th adsorption of Pd(II) ions onto activatd caron and ntonit wr studid. Adsorption kintics Th kintics study for th adsorption of P 2+ was compltd in 2 h for th concntrations (5, 1 and 2 mg/l P 2+ ions onto (.1,.3,.5,.7 and 1. g/25 ml) doss of activatd caron and ntonit at 25 C. Two kintic modls wr considrd to invstigat th mchanism of lad adsorption, as follows: Lagrgrn proposd a psudo-first ordr kintic modl, th intgral form of th modl is: ln(q - q) = lnq k 1 t (1) whr q is th amount of lad sord (mg/g) at tim t (min), q is th amount of lad sord at quilirium (mg/g), K 1 is th quilirium rat constant of psudofirst ordr adsorption (min -1 ). This modl was succssfully applid to dscri th kintics of many adsorption systms. Th adsorption kintics may also dscrid y a psudo-scond ordr raction. Th linarizd-intgral form th modl is: t/q = t/q + 1/k 2 q 2 (2) whr K 2 is th psudo-scond ordr rat constant of adsorption. Th applicaility of th aov two modls can xamind y ach linar plot of ln(q -q) vs. t, and (t/q) vs. t, rspctivly and ar rprsntd in Figs. (1,2) and (3,4), rspctivly. To quantify th applicaility of ach modl, th corrlation cofficint, R 2, was calculatd from ths plots. Th linarity of ths plots indicats th applicaility of th two modls. Howvr, th corrlation, R 2, showd that th psudo-scond ordr modl, fits ttr th xprimntal data (R 2 >.99) than th psudo-first ordr modl (R 2 in th rang of ), th kintic paramtrs calculatd ar shown in Tal 1. Effct of contact tim Th ffct of contact tim on th adsorption of P(II) ions onto activatd caron and ntonit was prformd y contacting of (5, 1, 2, 3 and 4 mg/l) of P(II) concntration at initial ph 5.5 onto (.1,.3,.5,.7 and 1. g/25 ml) of adsornt dos. Th rsults ar dpictd in Figs. (5,6). Th P(II) adsorption rat is high at th ginning of th adsorption caus th adsorption sits ar opn and P(II) intracts asily with ths sits. A largr amount of P(II) was rmovd in th first 1 h of contact tim, and aftr that P(II) incrasd slowly till quilirium tim (2 h). Th rlation twn th amount of adsord P(II) ions pr gram of adsornt and contact tim in prsnc of diffrnt amounts of oth activatd caron and ntonit is 224

19 illustratd in Figs. (1). It can sn that, q incrasd rapidly with incrasing tim till th maximum adsorption. Effct of adsornt dos Th ffct of adsornt dosag (.1,.3,.5,.7 and 1. g/25 ml) for oth activatd caron and ntonit on % rmoval of (5, 1, 2 and 4 mg/l) of P(II) ions concntrations at 25 C is shown in Figs. (9,1). It is apparnt that y incrasing th dosag, % rmoval incrasd till rachd maximum at 1. g dosag of oth activatd caron and ntonit. Th incras in prcntag of rmoval as dosag was incrasd du to th incrasd in th surfac of oth adsornts. A highr adsornt dosag also rflcts a gratr numr of availal adsorption sits, thrfor, mor lad ions wr al to adsord. On th othr hand, th adsorption capacity dcrasd with th incras in adsornt dosag for oth adsornt Figs. (Vijayaraghavan t al., 26; Shukla t al., 22). It is important to not that th concntration of lad was fixd whil th adsornt dosag was incrasd. Thrfor, as th dosag incrasd, th ratio of numr of adsorption sits to th numr of havy mtal ions would incras and thr would plnty of unasord adsorption sits. Anothr possil rason could du to th particl aggrgation, which would lad to a dcras in total surfac ara of th adsornt (Shukla t al., 22). Effct of initial lad(ii) ions concntration Figs. (13,14) show th ffct of varying initial concntration of lad(ii) ions from 5 to 4 mg/l on th adsorption undr th optimizd conditions of ph 5.5 at 25 C and (.1,.3,.5,.7 and 1. g/25 ml) of oth activatd caron and ntonit. It can sn from th figurs that, with incrasd P(II) initial concntration, thr was dcrass in % rmoval of lad(ii) for oth adsornt. Howvr, amount of mtal adsord pr unit wight of adsornt, q, is highr at high concntration as shown in Figs. (15,16) for oth activatd caron and ntonit. According to (Balasuramaniam t al., 29), th adsorption capacity and prcntag of rmoval ar qually important in adsorption xprimnts caus oth factors usually tak part in dciding th adsorption prformanc of givn adsornt. Effct of ph on th uptak of P 2+ Th influnc of ph on th adsorption of P(II) onto activatd caron and ntonit xamind in th ph rang 1-5.5, initial concntration of P(II) 1 mg/l and adsornt dos.5 g/25 ml for oth slctd adsornts at 25 C. Figs.(17,18) shown that for activatd caron, % rmoval of lad(ii) incrasd with an incras in ph of th solution from For ntonit, it can sn that, thr is a dcras for ph 4. This dcras in th adsorption of P(II) proaly rflcts a rduction in th quantity of ngativ surfac chargs on th clay. At low ph, th silica attracts positivly chargd adsorat ions y coulomic forcs. This ngativ charg dnsity on th surfac of th adsornt dcras as th ph incrass and this lads to low adsorption of P(II) from wastwatr at high ph. It is thrfor vidnt, that th prsnc of a ngativ charg on th silica surfac sits of th adsornt ovr th ph rang invstigatd is th main rason for P(II) adsorption. 225

20 Adsorption isothrm Th quilirium adsorption isothrms ar on of th promising data to undrstand th mchanism of th adsorption. Various isothrm quation ar wll known and two diffrnt isothrms ar slctd in this study, which ar th Langmuir and Frundlich isothrms. Th Langmuir adsorption isothrm assums that adsorption taks plac at spcific homognous sits within th adsornt and has found succssful applications in many adsorption procsss of monolayr adsorption. Th linarizd Langmuir isothrm quation is rprsntd y th following (Balasuramaniam t al., 29). C /q = 1/(q max ) + (1/q max ) C (7) Whr q max is th maximum mtal ions uptak pr unit mass of adsornt (mg/g), which is rlatd to th adsorption capacity and is Langmuir constant (L/mol) which is xponntially proportional to th hat of adsorption and rlatd to th adsorption intnsity. Thrfor, a plot of C /q vrsus C for th adsorption of lad(ii) ions onto activatd caron and ntonit givs a straight lin of th slop 1/q max and intrcpt 1/(q max ) as shown in Figs. (19,2). Th Frundlich isothrm is an mpirical quation mployd to dscri htrognous systms. Th linarizd form of th Frundlich isothrm quation is: lnq = lnk F + 1/n lnc (5) whr th Frundlich constants K F and n, which rspctivly indicating th adsorption capacity and th adsorption intnsity, wr calculatd from th intrcpt and slop of th plot of lnq vrsus lnc for th adsorption of lad(ii) ions onto activatd caron and ntonit as shown in Figs. (21,22). Th Langmuir and Frundlich paramtrs for th adsorption of (5, 1 and 2 mg/l) initial concntrations of lad(ii) on (.1,.3,.5,.7 and 1. g/25 ml) for oth activatd caron and ntonit at 25 C ar listd in Tal 11. In othr words, th Frundlich isothrm modl fits vry wll than that of Langmuir isothrm modl whn th R 2 valus ar compard in Tal 11 (R 2 valus of Frundlich plot >.99 was clos to unity, indicating isothrm data fittd wll to Frundlich modl). Th Frundlich constant n is th masur of th dviation from linarity of th adsorption. If a valu for n is lw to unity, this implis that adsorption procss is govrn y a chmical mchanism, ut a valu for n is aov to unity, adsorption is favoural a physical procss. Th valus of n at quilirium ar twn ( ), rprsnting favoural adsorption at studid tmpraturs and thrfor this would sm to suggst that a physical mchanism, which is rfrrd th adsorption ond wak and conductd with Van dr Waals forcs. Plots of (q ) vrsus (C ) ar rprsntd in Figs. ( ), from figurs (q ) incrasd y incrasing (C ) suggsting a vry strong surfac intraction twn th mtal ions P 2+ and oth adsornts (activatd caron and ntonit). Thrmodynamic paramtrs Th dtrmination of thrmodynamic paramtrs has a grat importanc to valuat spontanity and hat chang for th adsorption ractions. Thrmodynamic paramtrs such as fr nrgy ( G ), 226

21 nthalpy ( H ) and ntropy ( S ) changs of adsorption can valuatd from th following quations (21,15): K c = C A /C (21) G = - RT lnk c (15) Whr K c is th quilirium constant and C A and C (oth in mg/l) ar th quilirium concntrations for solut on th sornt and in th solution, rspctivly. Th K c valus ar usd in Eqs. (21) and (15) to dtrmin th G, H and S, th K c may xprssd in trms of th H (kj mol -1 ) and S (kj mol -1 K -1 ) as a function of tmpratur, Eq. (17): lnk c = - H /RT + S /R (17) Thrmodynamic paramtrs such as fr nrgy of sorption ( G ), th hat of sorption ( H ) and standard ntropy ( S ) changs during th sorption procss wr calculatd using Eqs. (21) and (15) on a tmpraturs rang of 25-4 C at initial concntrations (5, 1, 2, 3 and 4 mg/l) of P 2+ ions and dos.5 g/25 ml for activatd caron and ntonit, ( H ) and ( S ) wr otaind from th slop and intrcpt of a plot of lnk c vrsus 1/T Figs. (25,26). Th valus of ths paramtrs wr rcordd in Tal 3. Th ngativ valus of G confirm th fasiility of th procss and th spontanous natur of th adsorption of P 2+ onto activatd caron and ntonit. On th othr hand, th mor ngativ valu with incras of tmpratur indicats that a ttr adsorption is actually otaind at highr tmpraturs. Th positiv valus of H confirmd th ndothrmic natur of adsorption which was also supportd y th incras in valu of P 2+ uptak of th adsornt with th ris in tmpratur. Th positiv valus of S showd th incrasd randomnss at solid/solution intrfacs during th adsorption of mtal ions onto oth adsornts and also rflctd th affinity of activatd caron and ntonit toward P 2+ ions undr considration. Rfrncs Afridi H. I., Kazi T. G., Kazi G. H., Jamali M. K., Shar G. Q., 26. Essntial trac and toxic lmnt distriution in th scalp hair of Pakistani myocardial infarction patints and controls. Biol. Trac Elm. Rs. 113, Amarasingh B. M. W. P. K., Williams R. A., 27. Ta wast as a low cost adsornt for th rmoval of Cu and P from wastwatr. Chm, Eng. J. 32, Axtll N. R., Strnrg S. P. K., Laussn K. C., 23. Lad and nickl rmoval using microspora and lmna minor. Biorsour. Tchnol. 89, Balasuramaniam R., Prumal S. V., Vijayaraghavan K., 29. Equilirium isothrm studis for th multicomponnt adsorption of lad, zinc, and cadmium onto Indonsian pat. Industrial and Enginring Chmistry Rsarch. 48, Kazi T. G., Jalani N., Kazi N., Jamali M. K., Arain M. B., Afridi H. I., Kandhro A., Pirzado Z., 28. Evaluation of toxic mtals in lood and urin sampls of chronic rnal failur patints, for and aftr dialysis. Rnal Failur. 3, King P., Raksh N., Bnalahari S., Prasamna Y. K., Prasad V. S. R. K., 27. Rmoval of lad from aquous 227

22 solution using Syzygium cumini L.: quilirium and kintic studis, J. Hazard. Matr. 142, Raungsomoon S., Chidthaisong A., Bunnag B., Inthron D., Harvy, N.W., 27. Rmoval of lad P +2 y th Cyanoactrium Gloocapsa sp. Biorsour. Tchnol. 99, Shukla A., Zhang Y. H., Duy P., Margrav J. L., Shukla S. S., 22. Th rol of sawdust in th rmoval of unwantd matrials from watr. Journal of Hazardous Matrials. B95, Skrfving S., Ghardsson L., Schütz A., Strömrg U., Lad-iological monitoring of xposur and ffcts. J. Trac Elm. Exp. Md. 11, Soylac M., Elci L., Akkaya Y., Dogan M., 22. On-lin prconcntrayion systm for dtrmination of lad in watr and sdimnt sampls y flow injction-flam atomic asorption spctromtry. Anal. Ltt. 35, Unlu N., Ersoz M., 26. Adsorption charactristic of havy mtal ions onto a low cost iopolymric sornt from aquous solutions. Journal of Hazardous Matrials. 136, Vijayaraghavan K, Palanivlu K, Vlan M., 26. Biosorption of copprii and coaltii from aquous solutions y cra shll particls. Biorsourc Tchnology. 97, Yurtsvr M., Sngil I. A., 28. Biosorption of PII ions y modifid quracho tannin rsin, J. Hazard. Matr., in prss, doi:1.116/j.ihazmat. 6,