Cadmium removal using waste residue generated after recovery of base metals from manganese nodules

Transcription

1 Indian Journal of Chmical Tchnology Vol. 0, Novmbr 013, pp Cadmium rmoval using wast rsidu gnratd aftr rcovry of bas mtals from mangans noduls N S Randhawa 1, N N Das & R K Jana 1, * 1 Mtal Extraction & Forming Division, CSIR-National Mtallurgical Laboratory, Jamshdpur , India PG Dpartmnt of Chmistry, North Orissa Univrsity, Baripada , India Rcivd 9 May 01; accptd May 013 Th laboratory scal invstigations on Cd + rmoval charactristics of wast mangans lach rsidu (wmnr), gnratd by rduction roasting ammonia laching of mangans noduls hav bn studid. Adsorption studis show rapid kintics of Cd + adsorption. About 90% of total Cd + adsorption occurs within 15 min contact tim and quilibrium is attaind within 30 min. Th quantity of Cd + adsorption incrass with incras in lachd rsidu dos but dcrass with incras in initial Cd + concntrations. Th adsorption is found to b dpndnt on initial ph of Cd + solution, which incrass with incras in initial ph of th solution. Adsorption data ar satisfactory fittd to th Langmuir isothrms. Th loading capacity of Cd + on lachd rsidu calculatd from Langmuir data is 3.6 mg g -1 at ph 5.5 and 303 K, which improvs to mg g -1 at 33 K. Psudo scond-ordr kintics is applicabl for th Cd + adsorption. Thrmodynamic studis indicat spontanous ( G 0 = -3.88, and -6.0 kj mol -1 at 303, 313 and 33 K rspctivly) and ndothrmic ( H 0 = 8.3 kj mol 1 ) natur of adsorption. Th activation nrgy for Cd + adsorption onto wmnr is calculatd to b kj mol -1, suggsting chmisorption typ adsorbat-adsorbnt intraction. Kywords: Adsorption, Cadmium, Chmisorption, Mangans noduls, Mangans noduls lach rsidu Th surfac watr bodis on th arth ar oftn pollutd by th fflunts from various typs of industris. Havy mtals prsnt in ths fflunts, whn dischargd untratd, ar thrat to cosystm. Ths mtals ar non-biodgradabl and tnd to accumulat in living organisms, causing various lif thratning disordrs. Among th toxic havy mtals, mrcury, lad and cadmium ar known as th highly toxic ons, du to thir major impact on th nvironmnt 1. Th toxic and harmful ffcts of cadmium to human body systm ar vry wll known,3. Cadmium as a pollutant is found in dischargs from lctroplating, alkalin battris, paints, plastics and papr manufacturing industris 4. Among th important tchnologis availabl for rmdiation of cadmium contaminatd fflunts, adsorption tchniqu has bn viwd as most attractiv du to factors lik simpl opration, ffctivnss, tc 5. In addition, many adsorption tchniqus rgnrat th adsorbnt and rduc th oprational cost. Th ky factor for th slction of an adsorbnt lis with its ffctivnss and most importantly its cost. Apart from much studid adsorbnts lik activatd carbon, bio-sorbnts basd on agricultur (stms, pals, husks, shlls, lavs, tc.), *Corrsponding author. rkjana@nmlindia.org agro-industris wast matrials hav also bn trid for th rmoval of cadmium from wast watr 5. Mtallic oxids (F, Mn and Al), spcially of wast catgory, ar of much intrst du to thir ffctivnss towards rmdiation of havy mtals from contaminatd aquous bodis 5. Rsidus gnratd aftr hydromtallurgical tratmnt of mangans noduls or polymtallic sa noduls contain oxids/oxy-hydroxids of F, Mn, Al and Si with a rasonabl porosity and surfac ara. Ths rsidus hav bn utilizd as an ffctiv adsorbnt for a varity of spcis 6-8. Th prsnt study is aimd at invstigating th sorption charactristics of rsidu, gnratd in th rduction roast ammoniacal laching of mangans noduls, for th rmoval of Cd + from its aquous solution. Emphasis has bn givn on charactrization of lachd rsidu of cadmium, its rgnration aftr adsorption and th undrlying mchanism of adsorption. Exprimntal Procdur Matrials Th adsorbnt matrial, i.. lachd mangans nodul rsidu (MNR), was obtaind from larg scal trial of rduction roasting - ammoniacal laching of mangans noduls at CSIR-National Mtallurgical

2 37 INDIAN J. CHEM. TECHNOL., NOVEMBER 013 Laboratory, Jamshdpur, India. Th MNR was air-drid for svral days, mixd thoroughly and stord in air-tight bottls for charactrization and furthr us. To rmov th ntrappd lach liquors, MNR was washd with dionisd watr with 1:10 solid-to-liquid ratio and stirrd for h. Th washd mangans nodul rsidu (wmnr) was sparatd by filtration, washd with dionisd watr, air-drid for svral days and thn usd for subsqunt charactrization and adsorption studis. Th synthtic stock solution (1000 mg L -1 ) was prpard by dissolving Cd(NO 3 ) in dionisd watr and th solution was mad slightly acidic by adding a fw drops of HNO 3 to prvnt hydrolysis of th solution. Solutions of 0.01 M HNO 3 and 0.01 M NaOH wr usd for ph adjustmnt. 0.1N KNO 3 was usd to maintain th ionic strngth in th adsorption xprimnts. All th chmicals wr Mrck - AR grad. Th watr procssd by Milli-Q systm was usd for all th xprimntal and analytical purposs. Mthods Sampl charactrization Th chmical composition of lachd mangans noduls rsidu of wmnr was dtrmind by standard convntional wt and instrumntal mthods. Surfac ara masurmnt was conductd using Quantachrom (Modl: 4000E) surfac ara analysr (Nova Instrumnts, USA). Siz analysis was carrid out in Malvrn Mastrsizr aftr ultrasonic libration of particls. Morphology of wmnr particls was xamind in a Hitachi-S3400N scanning lctron microscopy (SEM, Japan) oprating at 15 kv. Th wmnr particls for SEM studis wr mountd on mtal stubs with doubl-sid adhsiv, and coatd in vacuum using an Emitch K575X sputtr coatr. X-ray diffraction pattrns wr rcordd on a Simns D500 X-ray diffractomtr using Cu Kα radiation. FTIR spctra mploying th KBr disc tchniqu wr collctd using a ThrmoNicolt 870 FTIR spctrophotomtr in th absorption mod, avraging 3 scans at a rsolution of 4 cm 1. Adsorption kintics xprimnts For kintic studis typically 50 ml of Cd + solution at dsird concntration with appropriat amount of adsorbnt in 100 ml stopprd conical flask was takn. Th rquird ph was adjustd and it was thn mchanically shakn (10 stroks min -1 ) using a watr bath shakr, maintaind at tmpraturs 303, 313 and 33 K as pr rquirmnt. Sampls wr withdrawn at crtain tim intrval and th solid adsorbnt was sparatd by filtration. Th rmaining cadmium in th filtrat was analyzd by atomic absorption spctromtr (Prkin Elmr, modl: A Analyst 400). Th amount of cadmium pr gram of th wmnr [Q t (mg g -1 )] was calculatd using th following quation: ( C C ) o t V Qt = w 1000 (1) whr C o and C ar th initial and final cadmium ion concntration (mg L -1 ) in solution rspctivly; V, th volum of solution in ml; and w, th mass of sorbnt in gram. Equilibrium xprimnts Th quilibrium adsorption xprimnts wr carrid out to invstigat th ffct of various paramtrs, such as ph of th adsorbat solution (3-8), initial cadmium concntration (5-100 mg L -1 ), adsorbnt dos ( g L -1 ) and tmpratur ( K) undr fixd quilibration tim obtaind by kintic xprimnts. For all th quilibrium xprimnts, 50 ml of solution in100 ml stopprd conical flask was mchanically shakn (10 stroks min -1 ) using a watr bath shakr. Each xprimnt was duplicatd undr idntical conditions. Rsults and Discussion Adsorbnt charactrization Dtaild chmical analysis of mangans nodul rsidu (MNR) and washd rsidu (wmnr) is givn in Tabl 1. Th ph pzc and spcific gravity ar 6.5 and 3.1 rspctivly. Th bulk surfac ara of wmnr Tabl 1 Chmical analysis of mangans nodul rsidu (MNR) and washd rsidu (wmnr). Elmnt/radical Mn(T) a Mn + Mn 3+ Mn 4+ Chmical composition, % by mass MNR wmnr F SiO Al O S Not found Co Ni Cu Moistur LOI b NH 4 + a Th valus for Mn +, Mn 3+ and Mn 4+ rprsnt th rspctiv wt% of th total mangans contnt in th sampls. b Loss in wight on ignition.

3 RANDHAWA t al.: CADMIUM REMOVAL USING WASTE RESIDUE 373 obtaind by BET isothrm of N adsorption is 66.7 m g -1. Particl siz analyss of wmnr rvals vry fin granulomtry with man particl diamtrs (d 50 ) of 17.8 µm. Th morphology of wmnr particls undr scanning lctron microscop is shown in Fig. 1(a), which rvals irrgular shaps of wmnr particls, congrgatd modratly. Th point analysis by EDX also rvals th Mn and F as major constitunt. Th wight % of Si is found to b vry lss prsumably du to th rason that Si phass containing particl ar finr and partially covrd by Mn and F containing phass. Th X-ray diffraction pattrns of air-drid MNR and wmnr ar dpictd in Fig. 1(b). Th prominnt paks ar assignd to mainly thr phass, namly MnCO 3, Mn SiO 4 and Mn SiO 3 (OH).H O. On washing with distilld watr, no changs in th position of th charactristic paks in wmnr ar obsrvd from thos of MNR. Th FTIR spctra of air-drid MNR and wmnr ar prsntd in Fig. 1(c). Th broad absorption band at 3445 cm 1 and th band of modrat intnsity at 1650 cm 1 in th spctra of both th sampls may b attributd to O H strtching and vibration bnding mods 9. Th absorption bands in MNR at 1470, 1070 and 870 cm 1 ar mainly attributd to th ν(c O) and δ(oco) vibrations of th carbonat ion rspctivly 9,10. This dnots th formation of MnCO 3 in MNR during th rduction roasting laching cycl for th procssing of mangans noduls. Positions of th majority of th bands in MNR rmain unchangd aftr washing, xcpt for th disapparanc of th absorption band at 107 cm 1, prsumably du to th loss of a small amount of loosly bound NH 3 or sulphat on washing 6. Th sulphat is most likly gnratd from th impuritis in th ful oil mployd during th rduction roasting of mangans noduls. Effct of ph on adsorption of Cd + onto wmnr Th solution ph is an important paramtr which affcts adsorption of havy mtal ions. Th adsorption of cadmium was studid ovr th ph rang ~ 3 8 and th rsults ar shown in Fig.. It is obsrvd that th adsorption of Cd(II) incrass with th incras in ph. Fig. 1 Charactrisation of MNR and wmnr (a) SEM imag and EDX point analysis of wmnr, (b) powdr X-ray diffraction pattrns. [Abbrviations associatd with th pattrns MC - MnCO 3, MS Mn SiO 4, MS1 Mn SiO 3 (OH).H O], and (c) FTIR spctra Fig. Effct of ph on Cd + adsorption on wmnr [[Cd(II)] 50 mg L -1, tmpratur 303 K, wmnr 1000 mg L -1 and tim 1 h]

4 374 INDIAN J. CHEM. TECHNOL., NOVEMBER 013 This may b attributd to comptitiv binding btwn H 3 O + ions and Cd(II) ions at th wmnr surfac. As ph valu incrass, th compting ffct of H 3 O + ions dcrass and th positivly chargd Cd + ions gt adhr to fr binding sits. Th othr important factor, which might contribut to th highr adsorption of mtal ions with incrasd ph, is th ph pzc of wmnr. Whn th solution ph xcdd ph pzc, th mtal spcis ar mor asily attractd by th ngativly chargd surfac of adsorbnt, favoring accumulation of mtal spcis on th surfac and thus promoting adsorption. In addition to that, Cd + uptak is almost unchangd in th ph rang of 4-6, indpndnt of surfac charg. Howvr, whn solution ph incrass abov th ph pzc of wmnr, i.. 6.5, thr is suddn ris in adsorption of Cd +. In addition to this, incras in Cd + adsorption may b partly attributd to th formation of diffrnt hydroxo spcis with ris in solution ph. Basd on th hydrolysis constants of diffrnt mtal ions 11,1 as dfind in th following quation, th ionic spcis of Cd will dpnd upon th ph of th solution, as shown blow: M + +nh O M(OH) n n + nh + whr M stands for mtal. () Th Cd(II) spciation diagram 6 shows that th dominant Cd(II) spcis up to ph 7.5 is Cd +. Th Cd(OH) xists at ph > 9.5 and Cd(OH) + xists in th ph rang Sinc maximum adsorption for Cd + is achivd at ph 7, it may safly b statd that th rmoval of cadmium is mostly du to adsorption and not prcipitation. incras in th wight of wmnr, which is 40 mg L -1 for 0.5 g L -1 wmnr and lowrd to 17 mg L -1 for 5.0 g L -1 of wmnr addition. Incras in wmnr dos provids highr surfac ara and activ sits for adsorption of Cd + and ultimatly is rsponsibl for mor uptak of Cd +. Effct of tim and initial concntration on adsorption Th tim cours of Cd + adsorption onto wmnr at varying initial concntration is givn in Fig. 4(a). Th Cd + rmoval at quilibrium is 64, 46, 30 and 34% for 5, 50, 75 and 100 mg L -1 initial Cd + rspctivly. For a fixd dos of adsorbnt th dcras in adsorption with incrasing Cd + concntration is primarily du to availability of limitd numbr of sit for adsorption. Although th prcntag of Cd + adsorption dcrass with incras in its initial concntration, th ovrall uptak incrass progrssivly. It is apparnt from Fig. 4(a) that cadmium adsorption is rlativly fast during initial priod, mor than 85-90% of th total adsorption Effct of wmnr dos on Cd + adsorption Adsorption of Cd + with varying adsorbnt dos, carrid out to assss th ffct of adsorbnt on Cd + rmoval, is prsntd in Fig. 3. Th rsults show that th quilibrium concntration (C ) of Cd + dcrass with Fig. 3 Effct of wight of wmnr on Cd + adsorption [[Cd(II)] 50 mg L -1, tmpratur 303 K, tim 1 h, ph 5.5] Fig. 4 (a) Effct of tim and initial concntration on Cd + adsorption onto wmnr and (b) Intraparticl diffusion plots for Cd + adsorption wmnr at diffrnt tmpraturs

5 RANDHAWA t al.: CADMIUM REMOVAL USING WASTE RESIDUE 375 taks plac within 15 min and thraftr it slows down to attain th quilibrium at ~ 30 min. Th quilibrium tim obtaind from prsnt studis is applicabl for C o 100 mg L -1. This rlativly high adsorption rat with lowr quilibrium tim has grat practical importanc, which is favorabl in column or continuous opration, whr th contact tim btwn th mtal solution and th sorbnt is gnrally short. Som of th othr systms ar rportd to hav quilibrium achivd btwn h and 7 h Th short quilibrium adsorption tim btwn 15 min and 30 min is rportd for PEI-coatd silica gl and ligand-modifid gl bads 16,17. Evn shortr quilibrium tim -10 min is obtaind whn sawdust is mployd in th rmoval of Cd + ions 18,19. Adsorption kintics modls Kintics and th quilibrium of adsorption ar th two important factors for th valuation of adsorption fficincy of an adsorbnt. Th adsorption kintic mchanism is valuatd using two convntional modls, namly th psudo first-ordr 0 and th psudo scond-ordr 1 quations, as shown blow: ( q q ) = ln q k t ln 1 (3) t q t t. 1 1 = + (4) k q q t whr q and q t (mg g 1 ) ar th adsorption capacitis at quilibrium and at tim t (min) rspctivly. Th valu of k 1 is drivd xprimntally from th slop of th linar plots of log (q q t ) vrsus t. Th k is th rat constant for psudo scond-ordr adsorption (g mg 1 min 1 ) and k q or h (mg g 1 min 1 ) is th initial adsorption rat. Th valus of 1/k q and 1/q ar drivd xprimntally from th intrcpt and slop of th linar plots of t/q t vrsus t, which vntually lads to valus of k and q (cal.). Th rat constants and othr paramtrs of psudo first-ordr and psudo scond-ordr ar givn in Tabl. Th good agrmnt btwn modl fit and xprimntally obsrvd quilibrium adsorption capacity in addition to th larg corrlation cofficints suggsts that cadmium adsorption follows psudo scond-ordr kintics. It is intrsting to not that valu of rat constant (k ) at particular tmpratur incrass by factor of whn C o is doubld. Howvr, this is valid for C o 50 mg L -1. It is also notabl that for ach 10 o C incrmnt of solution tmpratur, at fixd C o, th rat constant (k ) is incrasd by factor of 1½-3. Th kintic data is also fittd in to th intraparticl diffusion modl, xprssd with th following Eq. (5), givn by Wbr and Morris. According to this modl, th uptak varis almost proportionatly with t ½ rathr than with th contact tim t. q = k id. t 1 (5) t whr q t is th amount of mtal ions adsorbd at tim t (mg g 1 ); and k id, th intraparticl diffusion rat constant (mg g 1 min -½ ). Plots of q t vrsus t ½ ar shown in Fig. 4(b). Each plot in Fig. 4(b) compriss thr distinct sctions, namly initial plot or stp-slopd portion rprsnts th bulk diffusion or xtrior adsorption rat which is vry high, th subsqunt linar portion is attributd to th intraparticl diffusion and platau portion rprsnts Tabl Adsorption kintic modl rat constants for Cd + adsorption on wmnr at diffrnt tmpraturs Tmp. K C o mg L -1 r r q xp. Psudo first-ordr Psudo scond-ordr mg g -1 k 1 q cal 1 k q cal h min -1 mg g -1 g mg -1 min -1 mg g -1 mg g -1 min

6 376 INDIAN J. CHEM. TECHNOL., NOVEMBER 013 th quilibrium 3. Th intraparticl diffusion constants ar calculatd from th slops of th linar portion of th plots and givn in Tabl 3. Th high corrlation cofficints >0.99 suggst involvmnt of intrnal diffusion in th Cd + uptak on wmnr. Adsorption activation nrgy Th ffct of tmpratur on kintics of Cd + adsorption onto wmnr was furthr valuatd using Arrhnius quation. Arrhnius quation paramtrs ar calculatd using psudo scond-ordr rat constants to dtrmin tmpratur indpndnt rat paramtrs and adsorption typ. Th Arrhnius quation for calculating adsorption activation nrgy is xprssd as: E a RT k = k. (6) whr k is th rat constant for psudo scond-ordr adsorption (g mg 1 min 1 ); k, th tmpraturindpndnt factor (g mg 1 min 1 ); E a, th activation nrgy of sorption (kj mol 1 ); R, th univrsal gas constant (8.314 J mol 1 K); and T, th solution tmpratur (K). A plot of ln k vrsus 1/T yilds a straight lin, with slop E a /R. Th valus of slop (m) and intrcpt (c) for initial Cd + concntrations 5 mg L -1, 50 mg L -1, 75 mg L -1 and 100 mg L -1 ar m=-6.906, , , and c=17.4, 14.19, 17.17, 0.1 rspctivly. Th magnitud of th activation nrgy is commonly usd as th basis for diffrntiating btwn physical and chmical adsorption. Th activation nrgy for Cd + adsorption onto wmnr is rangd btwn kj mol 1 for diffrnt initial concntrations, suggsting that th Cd + ions ar chmically adsorbd onto th wmnr surfac 4,5. Adsorption isothrms Th quilibrium adsorption data ar fittd into th linarizd form of isothrm modls proposd by following Langmuir (Eq. 7) and Frundlich (Eq. 8) modls 6,7 : Tabl 3 Intraparticl diffusion cofficints and intrcpt valus for Cd + adsorption on wmnr at diffrnt tmpraturs Tmp., K K id Intrcpt r C q C = 1 + (7) o o bq Q ln q = ln K f + nlnc... (8) whr C is th quilibrium concntration (mg L -1 ); q, th amount adsorbd at quilibrium (mg g -1 ); K f, b, n, th isothrm constants; and Q o, th adsorption maxima or adsorption capacity (mg g -1 ). Th calculatd paramtr from Langmuir plot of C vrsus C /q and Frundlich plot of ln q vrsus ln C ar givn in Tabl 4. Langmuir modl is mor likly applicabl du to highr corrlation cofficints, suggsting possibl monolayr covrag of Cd + on th surfac of wmnr. Furthr, th valu of Q o, which is a masur of adsorption capacity, incrass with th ris in tmpratur and, thrfor, th incras in uptak with tmpratur is xpctd, which is supportd by th prsnt findings (Tabl 4). Th monolayr adsorption capacity (Q o ) calculatd from slop of Langmuir plot at th tmpratur of 303 K is 3.6 mg g 1 (Tabl 4), which improvs to mg g -1 at 33 K. Analogous trnd is obsrvd with th Langmuir constant b. Dimnsionlss sparation factor (R L ), masur of favorability of adsorption, is calculatd using th following quation: R L 1 = 1 + bc o (9) whr C o is th initial mtal concntration (mg L -1 ); and b, th Langmuir paramtr i.. nrgy of intraction at th surfac. Th conditions, R L > 1: unfavorabl; R L = 1: linar; 0 < R L < 1: favourabl; and R L = 0: irrvrsibl ar rportd in litratur 8. Th calculatd valus of R L ar obtaind in th rang , suggsting that th adsorption of Cd + on wmnr is favorabl and rvrsibl. Effct of tmpratur and thrmodynamic valuation Th ffct of tmpratur on Cd + uptak by wmnr is also invstigatd via thrmodynamic valuation of quilibrium data. Th thrmodynamic paramtrs of fr nrgy chang ( G 0, kj mol -1 ), nthalpy chang ( H 0, kj mol -1 ) and ntropy chang ( S 0, J mol -1 K) ar Tabl 4 Langmuir and Frundlich isothrm modl paramtrs and cofficints for adsorption of Cd + on wmnr Tmp. K Langmuir isothrm Frundlich isothrm Adsorption maxima (Q o ), mg g -1 Binding nrgy constant (b), L mg -1 Rgrssion cofficint r Adsorption capacity (K f ), mg g -1 Adsorption intnsity1/n Rgrssion cofficint r

7 RANDHAWA t al.: CADMIUM REMOVAL USING WASTE RESIDUE 377 calculatd to dscrib th associatd thrmodynamic bhavior. Ths paramtrs ar calculatd using th following quations 3 : o G = RT ln K d (10) o o S ln H K d = (11) R RT K d can b dfind as as γ scs K d = = (1) a γ C whr R is th univrsal gas constant (8.314 J mol -1 K); T, th solution tmpratur (K); and K d, th distribution cofficint (cm 3 g 1 ). Also, a s = activity of adsorbd Cd +, a = activity of Cd + in solution at quilibrium, γ s = activity cofficint of adsorbd Cd +, γ = activity cofficint of Cd + in quilibrium solution, C s = Cd + adsorbd on wmnr (mg g 1 ), and C = Cd + concntration in quilibrium solution (mg L -1 ). K d at diffrnt tmpraturs is dtrmind by plotting ln(c s /C ) vrsus C s (Fig. 5a) and xtrapolating C s to zro. Th plot of ln K d vrsus 1/T is a straight lin (Fig. 5b) and from th slop and intrcpt th valus of Fig. 5 (a) Dtrmination of distribution cofficint (K d ) and (b) Vant Hoff plot, for Cd + adsorption onto wmnr S 0 and H 0 rspctivly ar calculatd. Th positiv valu of H 0 (8.3 kj mol 1 ) confirms th ndothrmic natur of th ovrall adsorption procss, which is supportd by th incrasing adsorption of Cd + with incras in tmpratur. Th positiv standard ntropy chang (106.5 J mol 1 K 1 ) rflcts th affinity of th wmnr particls towards Cd + ions 9. Ngativ valus of G 0 (-3.88, and -6.0 kj mol -1 at 303, 313 and 33 K rspctivly) indicat spontanous adsorption. Th dgr of spontanity is found to b asd with incrasing tmpratur. Mchanism of Cd + sorption onto wmnr It is widly accptd that th adsorption of havy mtals onto adsorbnt surfacs involvs various mchanisms such as lctrostatic attraction/rpulsion, chmical intraction and ligand-xchang. Th adsorption mchanisms ar oftn dducd from sorption kintics and quilibrium data. Fastr kintics, lik in prsnt cas, is attributd to chmical intraction/ion xchang mchanism of sorption. As apparnt from Tabl, sorption of Cd + onto wmnr follows psudo scond-ordr kintics, indicating chmical intraction btwn adsorbnt and adsorbat during sorption. Howvr, it may not b rat controlling stp for th sorption of Cd + onto wmnr du to rapid rat of uptak. H 0 btwn 5.0 and 100 kcal mol 1 ( kj mol 1 ) is rportd as nrgy of chmical raction comparabl to adsorption taking plac by chmical raction i.. chmisorption 30. Th H 0 valu obtaind in prsnt work (8.3 kj mol 1 ) suggsts chmisorption typ uptak of Cd + on wmnr. Morovr, valus of nrgy of activation ( kj mol 1 ) for tmpratur rang K also support th chmical intraction btwn Cd + and wmnr surfac. In addition to that chmical intraction may tak plac in association with diffusion occurring through th pors of th sorbnt. Th quilibrium sorption capacity also incrass with tmpratur indicating involvmnt of chmical ractions as wll as diffusion basd intraction btwn adsorbat and adsorbnt during adsorption 4,31. Th adsorption procss on porous sorbnts is gnrally dscribd with four stags, and on or mor of which may dtrmin th rat of adsorption and amount of adsorption on th solid surfac. Thos stags ar dscribd as bulk diffusion, film diffusion, intraparticl diffusion and finally adsorption of th solut on th surfac 3. Gnrally, bulk diffusion and adsorption stps ar assumd to b rapid and thrfor not rat dtrmining. Th

8 378 INDIAN J. CHEM. TECHNOL., NOVEMBER 013 adsorbnt usd in prsnt studis (wmnr) has xtnsiv rang of por sizs ( nm), including micro-, mso- and macropors. Morovr, in aquous systm, macropors ar hydratd and may act as mso- or micro-pors. This typ of matrial givs ris to thr-stag plot of q t vrsus t ½, as shown in Fig. 4(b). Th scond stag in Fig. 4(a) can b attributd to th intraparticl diffusion 33. Th valu of th intrcpt C in this stag of Fig. 4(b) also provids information rlatd to th thicknss of th boundary layr 34. Th incrasing valus of intrcpt with th ris in tmpratur suggst importanc of surfac diffusion at lvatd tmpraturs (Tabl 4), which is prsumably, du to th gratr random motion associatd with th incrasd thrmal nrgy. Although, linar sction supports involvmnt of intraparticl diffusion in Cd + adsorption onto wmnr, dviation of curv from origin indicats rol of anothr rat-limiting stps. Th multilinarity (lik in prsnt cas) in curvs drawn btwn q t and t ar oftn attributd to involvmnt of two or mor stps in adsorption kintics 4,35. Thus, it may b concludd that th sorption of Cd + on to wmnr taks plac via chmical intraction at intrfac occurring undr diffusion gradint throughout th porous surfac of lachd mangans nodul rsidu. Rgnration/dsorption studis Rgnration of an adsorbnt by mans of dsorption is of crucial importanc as it hlps assssing th potntial of sorbnt for commrcial application. Dsorption study also hlps to clarify th natur of th adsorption procss. In prsnt studis, dsorption studis wr carrid out by in-situ dsorption xprimnts 36. Th dsorption of Cd + at ph, 3, 4, and 5 ar 79.80, 9., and 3.09% rspctivly. Th quilibrium Cd + aftr dsorption xprimnt is found to dcras aftr ph 5. Th rgnration of wmnr shows that adsorption of Cd + on to th wmnr is a rvrsibl procss and rgnration via dsorption can b achivd to rus it. Conclusion Th lachd mangans nodul rsidu (wmnr) gnratd by rduction roast-ammonia laching is found to b a potntially usful matrial for rmoval of aquous cadmium. Th uptak of Cd + incrass with incrasing its initial concntrations and quilibrium is attaind aftr 30 min tim irrspctiv of initial concntration. Th rgrssion cofficint valu shows that th adsorption of Cd + on lachd mangans nodul rsidu follows psudo scondordr kintics. Th adsorption data ar fittd wll into th Langmuir isothrm. Th valus of sparation factor (R L ) calculatd from isothrm data dpicts favorabl adsorption of cadmium. Th Q o i.. maximum loading capacity valu obtaind from Langmuir data is found to b 3.3 mg g -1 at 303 K, which improvs to mg g -1 at 33 K. Activation nrgy and thrmodynamic data suggst ndothrmic, spontanous and chmisorption typ uptak of Cd + onto wmnr. Th Cd + loadd wmnr could b rgnratd by dsorption in acidic ph (-4) for furthr us in adsorption. Rfrncs 1 Hanaa M, Ewida S, Ewida A & Farag A, Procdings ICEHM000 (Cairo Univrsity, Egypt), 000, 54. Koji N, Etsuko K, Yasushi O & Yasushi S, J BioMtals, 17 (004) Swaddiwudhipong W, Mahasakpan P, Funkhiw T & Limpatanachot P, J Md Assoc Thailand, 93 (010) Holan Z R, Volsky B & Prastyo I, J Biotchnol Biong, 41 (1993) Rao K S, Mohapatra M, Anand S & Vnkatswarlu P, Int J Eng Sci Tchnol, (010) Jana R K, Pandy B D & Prmchand, Hydromt, 53 (1999) Jana R K, Srikanth S, Pandy B D, Kumar V & Prmchand, Mt Matr Proc, 11 (1999) Das N N & Jana R K, J Colloid Intrfac Sci, 93 (006) Nakamato K, Infrard Spctra of Inorganic and Coordination Compounds, Part B, 5th dn (John Wily & Sons, Nw York), Nour E M, Tlb S M, AL-Khsosy N A & Rfat M S, Synth Ract Inorg Mt-Org Chm, 7 (1997) Prin D D & Dmpsy B, Buffrs for ph and Mtal ion Control (Chapman & Hall, London), Martll A E & Smith R M, Critical Stability Constants (Inorganic Chmistry), Vol, IV (Plnum, NwYork), Rd N E & Matsumoto M R, Sp Sci Tchnol, 8 (1993) Bahrami S, Bassi A S & Yanful E, Can J Chm Eng, 77 (1999) Wang C C, Chang C Y & Chn C Y, Macromol Chm Phys, 0 (001) Dnizil A, Snl S, Alsancak G, Uzman N T & Say R, Ract Funct Polym, 55 (003) Dlacour M L, Gailliz E, Bacqut M & Morcllt M, J Appl Polym Sci, 73 (1999) Taty-Costods V C, Faudut H, Port C & Dlacroix A, J Hazard Matr, 105 (003) Mmon S Q, Mmon N, Shah S W, Khuhawar M Y & Bhangr M I, J Hazard Matr, 139 (007) Ho Y S, Scintomtrics, 59 (004) Ho Y S, J Hazard Matr, 136 (006) 681. Wbr W J (Jr) & Moris J C, Procdings 1st Intrnational Confrnc on Watr Pollution Rsarch (Prgamon Prss, Oxford), 196, Boparai H K, Josph M & O Carroll D M, J Hazard Matr, 186 (011) 458.

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