.. ..

- -

Journal 01' Scicntlric & Inuu,trial Rc,ca rch

Vol. 61, J)cccmhcr ~OO~, pp 10:19-1 ( 4)

Fluoride Uptake Characteristics of Acti vated Carbon From Agricul tural- waste

R Si\'abalan". S Rcngaraj "!,. l3a nu mathi Arabindoo and V Murugcsa n';'

J)eparimClll orChcmi,tr:, ,\nna L'niler,ity, Chcnnai 60002:;

';' Dl'parill1L'lll or J:illironlllcntal SL'ICIll'C anu I: nginening, KllangJu In,titute orScicnce anu Tcchnulog), KllangJu, South Korea

Recel\ eU: l :'i NllI enohcr ::'00 I: acccptcu 09 October 200~

RcnlOI al ur l'\CC', llumiuL' rrom ground \\'atcl' to \1 ithin thc pcrmi ,si hle lim it , or 1,0- 1,) mg/ L is the only \\'ay to

con trol Iluormi" Batch and column t)Pl' l'\perimClll, \\'ere carrieu out Ill r the ad,orption or Iluoriuc u,ing actil'ateu carbon pl'c pared rmm palm ,ccu L'oat IPS( 'r J h) uoloillitc procc", In the hatch study. inllucnce or pH , ausorhent uo,e. con tact time and initi~d Iluoriuc L'OIKClllrall (),l II:" in\ L',tigatcd, Au,orptlon or Ilumidc lI'as pll uepcnucnt and higher relllol'al e lTici encies \ITre oh'l' ncu In the pll r:lIlgl' "l 4-8 , Fluoriuc ITmo\:d Incrca,eu with dosagc or carhon, A loll' co ncentration aluminiulll \lliphatc \o luti on (2 pCI' CCllll clkcti\'l'l) rcgcneratcu the C\hausteu ca l'ilon heu , The adsorption proce" oheyeu FreunuliL'h ad,orptlon "othl'rlll, Thc ~Inetic stuui c, rcn:aku that the Illrwaru rate constan t \I'as comparati\TI) Illuch higher than the h:ld,lIard ratL' con,tant. C{)IlJiIlUOU' Ilow e\perilllent s in ri\ed hed columns I\ere ca rri eu out with groulld water ill order to ~1"C,' th l' rca' th ilit) Il l' tim l'arhon ror rielu applicat ion , The pnrurillance or the carbon in Iluoride remova l was stlluicd a, a rlilKtioll or Ilow ratl', I'lilial Iluoridc Incl and pariicle ,ill' or the adsorben t. Filloriuc I'c lllo l' al incrca,cu wit h uccreasing pari lcle >lIe or the carhon, The interesting rcaturc or the ,tud: was that the delluoridation capacit y increa,cu with increase in thl' 1Illiiai Iluonde 1011 COncentr~lllon , Thc pi!. toted alkalinity, to tal h:lI'dn cs,. tota l ui ~so l l'ed so lius or the treated water did Iwt dl:1I1f:e appreCiahl) indlGlling SlILTe" or this tLT hlliquc ror liclu application ,

Introdudion

Fluo rid e is a hcalth allccting substancc, T he chronic and toxic e llccts o f excess iw intaKc of riuoriuc ,trc us ual ly obscrvcd as ~Ke l eta l abnormali­tics m damage t that ran gc from stillne ss anu rheumati sm to a permancnt crippling sKcletal ri gid it) , It is a reco mmcnded csscntial subs tance in water for buildi ng healthy teeth when prese nt \\'ithin I mg/L. It is bcnefic ial. particular ly to infal1l s and you ng chil dren « cight yca rs) for calc ifi cat ion of dcntal enamcl when prcsc nt \\ ithin the permi ss ible range of 1,0- 1,5 mg/ L as the ma xillluill acceptable leve l in drinKing watc rC is 1,5 mg/L. Man y natural dr inKing water so urccs contain morc flu oride requiring de fi uoridati on ( 0 prevent thc occurrence o f flu oros is, Fluoride ge ts leached into ground water from the igneous or scdimenuHY rocKs in the earth' s crust. Thc efflu ent from chemica l process ing industric s liKe aluminium proceSS tng. e lec tropl ating. phosphat c

* Corrc,ponuing author. TL'IcI'a;..: +CJ 1 -44 - ~200660

e- mail auurc,s: \'_lllurugu 0 l llOtlllail ,co lll # PrL',elli auul'c,s: Il igh EnC'lgy Material;, Rc,cell 'ch Lahoreltory,

SutharlVaui, Pune 4 11 02 1

rertilize r. g lass etc constitute another source of fluorid e in wate r.

A large amount of so lid wastes such as palm secd. rubber seed, cashewnut shea th are produced in the agricultural sec tor in Indi a, In Tami l Nad u. which is ha ving a large number or palm trce s. a maj or part or thi s palill seed is usuall y used as a domestic Cud For bctter utili sati on of thi s cheap and abundant material. it ca n be a prospective sta rting material for the preparation o f acti\ 'ated carbon owi ng to thcir rclatively hi gh fixcd ca rbon content (98,93 pCI' ccnt ). low ash content ( 1,07 pCI' cem) and presc nce of porous structure, Dc flu oridati on has long been practiced in wa ter suppl y. and a vari ety of method~

for fluor idc reillova l are Kn ow n" -I . such as the chemica l prec tpttatt olr'. ad sorpti on on acti vatcd a lum in} . ion exc hange 7

• e lec trodia lys is and re\'erse osmos ts,

A rew report s have appea red on the usc of acti va ted carbon for the removal of flu oride from waterX

, 9, Recentl y, considerabl e attenti on ha s bee n devoted to identify low cost material s such as coconut she ll to , o il palm she ll s tt, o li ve srones t2 ,

I04() J SC II N D IU::S VO L 6 1 D EC EMI3ER 200:2

almond shell s" . fi sh bone c harcoal l~ . tree bark ' 5 and other waste mat erial s for the preparation o f acti vated ca rbon. Ma ny reports have appeared on the de ve lopment o r ~I c ti vat ed ca rbon from cheaper and

1'1 '1 I I . I I" 1( ,. 17 reae. I y aval a) e materia s rom \'a rl ous sources . No report s on use o r pa lm seed coat ac ti vat ed ha ve appeared ror ddluoridati on. llence. the producti on o r acti\ 'at ed ca rbon rrom palm seed coat arc be ing reported in thi s paper ror fluorid e re moval.

i\ laterials and i\1ethods

f1repOUltioll o(" / IClim{cd Co r/)()II

,\ ct i vat ed ca rbon rrom p~ilm seed CO~lt

(flOWS.I/{1 .flu/Jc lly/ i' r L) was prepared by the pmcec\ure reported by Rengaraj et ~ iI . ' x . T he ra w ma teri al \vas washed wi th water to rem()I'e soil and other e ~lrth y mailer and dri ed at II () "c. T he c leaned material was ca rboni zed with do lomite at 55{) "c ror ] h and washed with 10 per ce nt hydroc hl ori c ac id. and excess wa ter. to remove dolomite. and dri ed at II(J°C. The mater ial was the rmall y acti vat ed in ca rbon d iox ide atmosphere at 8 5 {) - ()()() "C for ] 0 min . Arte r act ivati on. the ca rbon was washed with I () per cen t hydroc hloric ac id to remove residua l in orga ni c impuriti es and \va shed with wate r repeatedl y and rinall y dri ed at II () "c. ground and sieved to 3()()-80() micron ror rurther c h a ra c t c ri s~lti o n .

C//(/wu{'/"i.w{ioll of /l uii'll/I'd CO,./)()II

The important characte ri sti cs of acti vated carDo n we re determin ed by the standard procedures ' lJ-

.'1 and prese nted in Table I. The moi sture was determined hy hea ting a kn ow n quaill it y of the sample in an air ove n at liD "c ror ahout.+ h. The ash was dete rmined by igni ting the residue at IO()( ) "(' in a mulTIe fu mace for about :1 h. I ron in ash W~I S

determ ined by at omic absorp ti on spec trophotometer (Perkin Elmer 238() ). A know n quantit y o r carbon wa s diges ted v.,' ith fresh boiled water and the pH was measured with Ori on pH e lectrode. Deco louri s in g powe r o f the ca rbon was dete rmined with ll1ethylene blue. T he amo un t of ca rbon required for 90 per cent re lllo \'al 0 1" phenol was taken as the pheno l number. Surl"ace area measure illent was ca rri ed out usin g Micromerit ic s Pul se Chemi sorb 27()() equipment.

/5({/ ciI T r {J e' Crperilll cllt

Batc h type ad sorp ti on expe ril11ent s we re conducted with 100 mL aqueous soluti on containing

Tahl e 1- Charac((: I-isl ics o r aCl ivaled l'arhun

SI. No. CO ll trol test PSCC Cr-\C

Bulk densi ty. g/cc 0.3 '+ 0.6

:2 M oist ure. pl' r ce lli IS OI 12.)7

"\ A sh. pL' r lT lll 1.07 2.0 I

.+ Fi xed l'~lrh"n, pL' 1 L'Clli 0S.Il.' '>7.()0

.~ 1\I\all cr ,>oluhlc in \\ · ~ll c r. per (Til l OJ)'i I.'> :i

() ;'v1al tn so luhlc' i ll ac id . pCI' ("L' nt 1.:2 1 .+ .:i 0

7 pll ~.6S 0.2

S DL'Ullourisillg power. Illg/g 00 73.:i

0 Phellul nll ll1hl' r. IIlg :'):\ 'i. I '>

10 lUll exchange cl p ~lci t y . Illeq/g O.U'+() \Ji I

II Surrace area. Ill '/g 'i77 296

1:2 l roll. pL'r ce lli -"il ;\ i I

PS(,C - 1\11111 SL'cd CO~ II Cllhlll C:\ C - ('oll1 llll'l"c ial ' \l' li v ~l t e d Clrholl

I () mg/ L nu oride adju sted to dille rent pH values in Ieak -proor reac ti on bolli es. The ~o l u ti o n s we l"e equi librated for 24 h in a mec hani ca l shaker at 27 "C'. the carbon was ri lte red and flu or ide in the ril tratc \\'as estimated using pHIiS E Illete r (lvlodel 7 10A. Ori on Research Inc .. USA). From the prelimina ry hatch studi es it was apparent that the nuol"ide removal errieiency was poor in both PSCC and CAC'. To improve the e lTic iency. the carbon was impregna ted with diffe rent concentrati ons of aluill inium sulphate. Aluminiull1 sulph ate soluti on at :2 per ce nt and pH 3A . showed belle r n uoride re illova I e ffi c iency. Ex perimcnt s were perrormed to understa nd the e llec t o r contact time and ca rbon dosage on nuorid e removal. Desorpti on studi es we re al so cond ucted using a lu miniulll sulphate sol uti on. The :-e l11oval cflic ienc ), o f PSCC was co mpa red with aluminium sulphat e impregnated co mmercial acti vated ca rbon (CAC).

COlltillllOIlS Firm' CO/II III II CI"{Jcrill l e' lIt

Con tinu ous now ad sorpti on process has ad vantages ove r the batch operati on. Unless the se lecti vit y o f an ion to be removed is ve ry large. batch operati ons arc ind fi c ient in util is ing ad sorpti on capac it y o f the sorbe nt ow in g to the dec rease in so lut e concentrati on as with increasing ad sorpti on. In the continu ous operat ion, the adsorbent is permanentl y in contact with a so lut ion o r same concentrati on. Gla ss co lumn . 25 mm J iam x 600 mm length , connec ted to a 5 L capa it)' reservoir contain ing flu oride soluti on. and a pe ri sta lti c pump at the bottom o r the co lumn to contro l the fl ow rat e. was

SIVA B;\ L/\ N 1' 1 al .: ACTI VATED C;\R BON - CII A RACTERI STICS 1041

operated con tinuously and with a constant water height to maintain til l: fl ow acc urate ly. A know n quantit y of carbon was we ighed. sieved , was hed with di still ed wa ter to remove ca rbon fin es and then packed close ly in the co lumn by tapp ing to minimi se air vo ids in the ca rbon bed. To optimi se field condit ions. simulated flu oride solutions of different initial concentrati ons \ve re prepared by adding sodium flu oride to ground water. The charact eri stics of the simul ated water we re: pH = 7.45. flu oride iOll s = :'i . I±O.1 Il1g/L. total hardness = 1]7 mg/L. total alkalinity = 110 mg/ L. conducti vit y = 6-Hl ~l mho/c m. a:ld total di ssolved so li ds = l 7Cl mg/L alld visibl y no co lour was obse rved. The test solution was passed through the bed at 60(J mLlh and every time I(J(J() mL volume was co ll ected separately. For eac h I (J(J() mL volume collected. the parameters like riu ori de ions. pH . total alkalillity. tota l hardness . total di ssolved soli ds. and conducti vit y we re measured according to the standard procedure (A PH A. 1989). Fluoride ion concentrati on (mg/L) and pH ill the aqueous so lut ion we re measured using Ori on Ion Meter 7 10A with a flu orid e and pH elec trode respec ti ve ly. The co lu mns we re rec harged more than eight -t imes be fore reject ing the bed material. The regenerant was passed through the colu mn at 10 mLlmin for a few cyc les and kept it over ni ght. During the rege nerat ion cyc le the efflu ent was tested for flu oride. Fin a ll y. the carbon bed was rinsed thoroughl y with ground water and reused for flu oride adsorption.

Results and Discussion

A close exa mination o r the characte ri sti cs of ca rbon reveal s that the PSCC possessed less bul k density th an the comme rcial acti vated ca rbon (CAC). The high moisture content was due to the porous nature o r the ca rbon. though the poros it y was not determined. Surface area of PSCC was S77 nY~I£ . much more than that for to CAC (296 me/g). ~\ prel i rni nary screen i ng study was performed to assess the suitability of PSCC and CAC for removal of flu oride from aq ueous so lut ions. The crfec t of pH. dosage of ad sorbent. and cont act time was studi ed in the batch ex periments.

Effect oj'pll

Figure I shows the effect of pH on flu oride removal. Batch ex periment s we re conducted with 100 IllL of 10 mg/L of fluor ide containing know n qua ntit y

of PSCC alld CAC ill the pH range 2- 1]. It is evidcnt that flu ori de removcd was hi ghcr and rcmained so in a wide pH range of 4-8. and at pH leve ls >8. it graduall y dec reased. The r1uoride removal reached a ma ximum of 82 per cent at pH 7 and showed poor e ffi ciency above pH 8. Thcrfo re. so luti on pH was main tai ned at 6.9 1'01' further studi es. In the casc of C AC'. the flu oride removal effic iency of maximum 60 per cc nt was observed in a narrow pH ran ge or 5-8 . Thu s PSCC was more e ffi c icnt ove r a wide ran ge of pH for thc remova l or l'iuoride.

1:)/('0 of C(frhol/ Dose

The variati on in l'iuori de rcmoval at dirfercnt doses of (J.05 to :? g of PSCC and CAe at a contact peri od of 2-1. h is show n in Fig ure 2. The riuor ide removal increascd as thc dose o r the adsorbcnt increased. The maximum removal effici cncy corresponded to around 0.5 g. beyond whi ch furt her addi ti on of ca rbon d id not show an y signifi cant e frcct on the re l110val cl'fi c iency. It is due to ove rlapp ing of the acti ve sitcs at hi gher concentrati ons. thus reducin g the net surface area 22

. The res ult s clearly indi ca te that the optimum ca rbon dosage of 0.] and 1. 4 gl I 00 mL were required for 89 and S6 per cent flu oride remova l for the PSCC and CAe. res pect ively. The res ult s also revealed that PSCC with onl y one-third the concen trati on ga\/e belter flu oride removal crri c iency than the CAe.

E//ecl oj' COI/ /(fel Till/ e

Figure ] ex hi bits the var iati on o r flu oride remova l 1'1'0111 aq ueo us soluti on by PSCC and CAC with res pect to contact time. The flu oride removal

100 90 -+- PSCC

0:: SO --- CAe 0 70 E ~ 60 ()

-0 SO 0 -1.0 =>

G: ]0 -----t:" :W

10 0

0 2 6 8 10 12 I ~

pll

FigurL: 1-· Fl uoriue remo val V ~ pll

IO-t2 J 5C II;\1) RI·:S \ 0 1, (,l DI£ I:[\113I-:R ::'00::'

ICX) I

(X) .-.- SO 70

2 (I) 'J

50 -::;

~ -to .:.. .,0 -- ('r\( '

20 , ~ - to --I>SC '('

0

0 O.-t O.S 1. 2 J.() 2

Carhol1 d()~ag~ I g)

l' l~url'::' - FlullJ'IJc I l'11l1l\al \ ' , Carholl dmagc

100

()O

.- ::iO ;::

70 -2 (,() '..)

-:J 50 ::l -+0

!..L :10

-+- PSCC ' ,~

~

20 -- t' :\(,

10

(J

0 -+ I ::' 20

C(lll laCI lime (h)

1:lunrilk ICI1101;ri I, (\'IlI,IL'1 II I Ill'

il1cr~ase I \\ 'ith contact tillie until the elJ uilibriulll fluoride Ie\'e l in the d fluent \\ ~ I ~ reac hed . It can be ohse l'\'ed that -t() per cent fluorid e reillma l tOOK place \\ ithin I h 01' cllntact \\ ith :\ giL or PS( 'C', which increased to 82 per ce nt in -t h. Th~ increase in the l'iuoride rem()\'al \\as nOI signi l'i callt ~11'[er () h, Whereas with CAe. oill y 5() pCI' ccnt flu oride rem(wal lOOK place within -t h 01' COil tact. Clearl ) PSCC is Illore crfcctive than CAC I'or the reilloval 01' fluoride , The result s or batch stud y C\perimen ls ror the relll()\ 'al or l'iuoride arc give n in Table 2,

f) e.I'O!'/i1 iOIl o( FI{{()rir/e

ACJuellus so lution 01' alumin iu ll1 sulphate was suitahle I'or the desorpti on 0 1' J'iuoride. T he desorpli on sllIdi cs we re cond ucted with (J .I - IO perce nt rege nera nt. Frolll the res ult s (Figure -t ), it can be

Tahk::' - OplilllUllll'Olldilillll " I'm Im\illlUIII ;Ilbmpllllil Ill' lluOrllk lIll PS CC alld C,\C

SI :\0 ( 'll lldllll lll, ('seC' ('.\( ,

:\d,"rill'Il[. gil . , 1-+

-, p ll (1 ,9 6,9 -

i Clllll ;ll' l lJ 1I1L', h 6 -+

-+ 1:lumldl' J'l'1I101 al. Pl'1 Cl'1l1 SS :'i l l

[0 -, II 2J

S

7 £. (,

-; 5 ~ 4 '",

~ 2 -

"

0

0 .l 4

Fi gurl' -+ - I)l',mpl lllll or 11 1I0f'lJc

obse rved that nearl y 2 pCI' cent alulllinium sulphate is relJuired I'm quantitati\'l; desorption o r Ilu()('ide I'mlll PSCC as \\ e ll as rrolll CAC'. AbO'.'e 2 pCI' ceiH k\els, the re \\'as no signi ricant change in the de sorption capacit y. llence , 2 per ce nt solu ti on \\~ I S seleL'led i"or regenerat ion.

11r/.IO!Pli(1/I 1.lol/w/'II{

Ex perimcn tal data on the adsorpti un oi" flunrid c on act i vated carbon at room temp 'rat me under opt imulll conditi ons ur Cl)ntact time and dl) ~age or adsorbent \\ere round to obey Freundlich ad . orption isotherm (Eq, I), and the model \va~ appli l'd to ll lL' ad sorpti on equilibl'i~1 for both PSCC and C ,\(' .

IOg(~) = log(k ) + ~ . log( C, ) III 1/

The re sult s revealed that the adsorption or l'iuoridc on PSCC and C AC' under opl imulll conditi ons at room temperature (27 ± I (lC) al so oheyed the Freu ndli ch ad . orption isotherm. Freundli ch ad sorpti on iso therm re lates f'iuorid e ad sorbed by pCI' unit ma ss o r the ads(Jl'bent X/ III with flu oride at equilibrium (C). T he con , tant s f.:. and /I

..

,

SIV/\l3 r\L;\ i\' ('/ (//.: /\ CTI VATED CA RBOi\' - CI-I ,\R ACT[RI STI CS IO·B

represent the adsorpti on capacity and intensity of the adsorpti on. res pective ly. The data ohtained in thi s study gave good rit s to the rreundlich ad so rption isotherm (Figure 5 ). The plot or log (rill! ) against log (C) was linear at vari ous initial concentration s justirying the application o r Freund li ch adsorpti on isotherm. The values or f.:.. 3.07 and (J.n ror PSCC and CAe. ind icated great er aflinity for r1uoride and the n value s. 2.5.+ and 1.89 fo r PSCC and CAC. re pec ti ve ly. showed the good adsorpti on character or the ca rbonsc-, .

Ad.I'O'p tioll Ki ll etics

The kineti cs of flu or ide adsorpti on on PSCC fo ll owed the first-order rate reac li onc-l (Eq. 2).

.. . (2)

(c C) where U = () I .

I (Co -C..)

CII , C, and C are flu oride levels initiall y, at time t. and at equi li brium respect ive ly, The straight line plot of In ( I - UI ) against t indi cated that the

1.(,

1.2

O.S

'" 0.-1 .< e..l,

0 S'

·0.-1 • PS('e ·o.x • CAe

· 1.2

0 0.) 1.5 2.5

Jog Cc

Figure .'i - Freunuli ch ausorption isotherm 1'0 1' PSCC ~HlU CAC systems

u ................ - _ ... _-._.. .. ... .... ..-........ --

.. 0 .5

::; I ·1

.. 1. 5 4 .II) mgll

x -II) mgll

• 50 1llgli

.. 2.5 I-----~--~-_,_------,----

o 0.5 1.5 Tilllellil

:1.:1

Figure 6 - Kinelics Ill s luI' Ihe ausorpliolll)r Ilunriue :lIlU PSCC

adsorpti on process foll owed the rirst order kinetic s (Fi gure 6), The st rai ght line porti ons o r these CUl'W S

were used I'm cal culatin g the s lope which ga\ e the overa ll rate constant k o r the process . The 1'0 1'\\ ~Ird

(k l ) and back\\'ard (kc) rat e constant s \\ 'ere calculated usin g the roll owing eq uation (Eq. 3).

... (3)

f.:. , = f.:. ,H 2• where f.:. " is the equi libriulll constant. The comp uted va lues of these constants are gi\'en in Tab le 3. The forwa rd rat e consta nt was much higher than the backward rate consta nt sugges ting that the ra te o r adsorpti on was clearly dominant.

CO/l/lIIII Adsorptioll Experilll ellt

The res ult s of the co lumn ex periment s in the determina tion of fl ow rate of water th rough acti vated ca rbon bed are given in Tab le 4, The de fiuorid ati on capac ity decreased with increase in the fl ow rate of water. T hi s is due to the minimum contact time between the fluoride ion and carbon surface. In the case of low flow rate. the flu oride ion may stay for longer time in the bed and hence there is more chance for adsorpti on,

There is a signifi ca nt change in the fl ow rate of wa ter with change in particle size of the adsorbent. The rate of fl ow is increased with increase in panicle size because the pore vo lume of the act iva ted ca rbon bed increases with increas ing particle size, The defluoridat ion capac ity of grade II carbon (297-74 p) is hi gher (3577 mg/kg) than grade I carbon (7 10-297 ~t ) 2960 mg/kg, Thi s is due to the larger surface area (578 m2/g) associated with grade 1I carbon compared to grade 1 (406 m2/g). But the rate of flow with grade II is low , Hence, grade I carbon is suitab le for flu oride removal as the fl ow rale is hi gh with reasonable adsorpti on capac ity. CAC fl uoride remova l capacity was poor (638 mg/kg) and hence furth er study with CAC was not undertaken. The co lumn operation was stopped when the res idual flu oride in \-va ter reached 1.5 mg/L. Alu minium sulphate as 0.2 - 5 per cent solution was tri ed fo r regenerati on. Regenerati on study of ex hausted bed showed that the 2 per cent soluti on was most suitable. Eac h co lumn was rec harged e ight-times before rejec ti on of the bed material.

10.+.+ J SC II ND RES VO L 6 1 DECEM I3 ER 2002

T he flu or ide leve l in wat er was brought we ll be low the permi ss ible limit o f 1. 5 mg/L with PSCC The effl ue nt flu or ide ion conce ntrati on and it s pH un iform ly incn.:ased In the e il lueill a rt er the treatment. The alkalinit y in the treat ed water was I,em

in the beginning of tlie run and it reac hed SO per cent o f the influent a lka linity at the 11 11i litre. The total hardness "vas reduced to a ve ry lilli e ex ten t. Initiall y the total di ssolved so lids we re more in the treated samples due to leac hi ng or in organ ics from the hed. As the run s progressed the total di sso lved so lids decrea sed and total hardness was red uced to litt le ex tent. An interesting rea ture o r the co lumn operati on is that the total flu oride remova l capac ity o r the bed appea red to be higher for wat er with hi gher flu or ide concentrati on. Fluoride conce ntrati on or 2.5 ± 0.2 mg/L showed the minimum uptake ca pac it y o r 1870 mg/kg and at IO.() ± 0.2 mg f1u oride/L hi gher ad sorpti ve capacit y of .+73.+ mg/kg was observed. The da ta of the e ffec t of initial concentrati on o r flu oride on deflu or id ati on ca pac it y arc prese nted in Tabl e 5. Beyond thi s conce ntrati on. the ca paci ty decreased considera bl y.

Conclusion

Ac ti vated ca rbon prepared from pa lm seed coa t impregnated witli aluminium sulph ate is ca pab le o r remov ing flu ori de e llcc ti ve ly in the ground wat er. The stud y indica tes that remova l o r flu oride from aqueous so lution depend s on pH . contact time. parti c le size and dose of the ad sorbe nt. The removal of flu oride is more for the fin er · variety of carbon. The adsorpti on of flu or ide from aqueous so luti on wit h PSCC and CAC ro ll owed Freundli ch absorpti on equati on based on the formati on o r mono la ye r. The values of adsorpti on capac it y (/.:.) and intensit y o r adsorpti on (1/ ) indi ca te greater aiTinit y for flu oride. T he kineti cs o f ad sorpti on of flu oride with PSCC foll owed first order kineti cs. The low rat e constant o f the desorpti on process reveal s that the adsorpti on of flu or ide remain s almost stable on the carbon. It can be recovered onl y on regenerati on with aluminium sul phate. De flu orid ati on ca pacity is ma ximum at a fl ow ra ie o r 30() mLih. Moderate fl ow rate or 600 mLih Can he conve ni entl y maintained 'vv ith grade I ca rbon. as thi s carbon is suitable fo r de riuoridati on. Each co lumn IS rec harged eight -times before

rejec ting the carbon bed. An in te resting rcalure or the stud y is th at flu or ide upt ake capac it y illc redsed with hi ghcr initial flu oride conce ntrati on.

Acknowledgement

The authors grate rull y ack nowledgc the Raji v Candhi Nati onal Drinki ,lg Water Miss ion. Mini stry of Rural Areas and Empl oYl11e nt. Nc\\' Delhi I'm fin anci;ti support to ca rry out thi s resea rch pru jcc l.

Re fe re n l'CS

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