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E L S E V I E R

ioresource Technology

4 8 ( 1 9 9 4 ) 3 1 - 3 5

P r i n t e d i n G r e a t B r i ta i n . A l l r i gh t s r e s e rve d

0 9 6 0 - 8 5 2 4 / 9 4 / 7 . 0 0

P R E P A R A T I O N A N D L I Q U I D P H A S E C H A R A C T E R I Z A T I O N O F

G R A N U L A R A C T I V A T E D C A R B O N F R O M R IC E H U S K

T a n z i l H a i d e r U s m a n i , T a m o o r W a h a b A h m a d & A . H . K . Y o u s u f z a i

Industrial Chemicals Research Centre, PCSIR Laboratories Complex, Karachi -- 75280, Pakistan

(Received 2 Au gus t 1993 ; rev i sed vers ion rece ived 23 Octo ber 1993 ; accep ted 26 Octo ber 1993)

bstract

A method for deashing rice husk by alkaline leaching

was developed and optimum deashing to the extent of

93 was achieved. The preparation of granular acti-

vated-carbon from high- and low-ash rice husk was

carried out with zinc chloride as an activating agent as

well as a binder. It was established that granular

activated-carbon of balanced micro-, meso- and macro-

pores and appropriate hardness may be prepared from

low-ash rice husk with 75 zinc chloride as an activa-

ting agent.

Key words: R i c e h u s k , d e a s h i n g , g r a n u l a r a c t i v a t e d -

c a r b o n , i m p r e g n a t i o n r a ti o , z in c c h l o r i d e , l iq u i d p h a s e .

I N T R OD U C T I O N

T h e m a j o r r i c e - p r o d u c i n g c o u n t r i e s i n t h e w o r l d a r e

I n d ia , C h i n a , P a k i s t a n a n d I n d o n e s i a ( M c G r a w - H i l l,

1 9 6 0 ) . I n P a k i s ta n , 4 . 1 4 3 8 m i l l i o n t o n n e s a r e g r o w n

p e r a n n u m (A k h t a r , 1 9 8 6 - 8 7 ), m a i n l y in t h e p r o v i n c e s

o f P u n j a b a n d S i n d h . R i c e h u s k a n d r i c e b r a n a r e

o b t a i n e d d u r i n g t h e i n i t i a l a n d f i n a l p o l i s h i n g o f r i c e ,

r e s p e c t i v e l y . T h e h u s k o r h u l l a c c o u n t s f o r a b o u t

2 0 - 2 3 % o f t h e w h o l e r i ce ( G ri st , 1 9 7 5 ) . T h u s , a n

a p p r o x i m a t e a m o u n t o f 0 8 2 8 8 m i l l io n to n n e s o f ri c e

h u s k i s a v a i l a b l e i n th e c o u n t r y a n n u a l l y . I t i s r o u g h i n

t e x t u r e , a b r a s i v e i n n a t u r e a n d n o t s u i t a b l e f o r a n i m a l

f e e d d u e i t s l o w n u t r i t i v e v a l u e . B e c a u s e o f h i g h a s h

a n d l i g n i n c o n t e n t s , i t i s c o n s i d e r e d u n s u i t a b l e f o r t h e

p u l p a n d p a p e r i n d u s t ry . T h e h u s k p r e s e n t l y h a s s m a ll

i n d u s t r i a l u s e s i n b r i c k k i l n , c h i c k e n l i t t e r a n d a n i m a l

r o u g h a g e . T h i s s i t u a ti o n d e m a n d s a n e x t e n s iv e i n v e st i-

g a t i o n o f t h e e c o n o m i c u t i l i z a t i o n o f t h i s a g r i c u l t u r a l

w a s t e . It m a y b e n e f i t a c o m i t y o f r i c e - p r o d u c i n g , d e v e -

l o p i n g c o u n t r i e s .

A c t i v a t e d c a r b o n s a r e u n i q u e a n d v e r s a t i l e a d s o r -

b e n t s b e c a u s e o f t h e ir e x t e n s i v e s u rf a c e a r e a , m i c r o -

p o r o u s s t r u c t u r e a n d h i g h a d s o r p t i o n c a p a c i t y . T h e y

a r e a s s u m i n g i n c r e a s i n g i m p o r t a n c e i n t h e c o n t r o l o f

a i r p o l l u t i o n , i n p u r i f y i n g a n d c o n t r o l l i n g t h e g e n e r a l

c h e m i c a l e n v i r o n m e n t , i n c e r t a i n b i o m e d i c a l a p p l i c a -

t i o n s a n d f o r t h e r e m o v a l o f o r g a n ic m a t t e r f r o m w a t e r

a n d w a s t e w a t e r ( M a r t i n , 1 9 8 0 ) . A c c o r d i n g t o a r e c e n t

s u r v e y ( B a n s a l

et al.,

1 9 8 8 ) , t h e a n n u a l p e r c a p i t a c o n -

3 1

s u m p t i o n ( i n k g) o f a c t i v e c a r b o n i s a b o u t 0 5 i n J a p a n ,

0 -4 in t h e U S A , 0 2 in E u r o p e a n d 0 0 3 i n t h e d e v e l o p -

i n g w o r l d , g e n e r a l l y r e f l e c t i n g t h e d e g r e e o f a w a r e n e s s

a m o n g t h e c o m i t y o f n a t io n s f o r a s a f e r a n d c l e a n e r

e n v i r o n m e n t . C a r b o n i s g e n e r a l l y u s e d i n t w o f o r m s ,

p o w d e r e d a n d g r a n u la r . T h e p r i n c i p a l u s e s o f g r a n u l a r

a c t i v a t e d - c a r b o n ( G A C ) a r e i n a i r p u r i f i c a t i o n , s o l v e n t

r e c o v e r y , r e c o v e r y o f g o l d a n d i n c i g a r e t t e f i l t e r s .

A b o u t 8 0 % o f t h e G A C p r o d u c e d w o r l d w i d e is u s e d in

l i q u i d - p h a s e p u r i f i c a t i o n s , a n d t h e r e s t i s u s e d i n g a s -

p h a s e a p p l i c a t i o n s . G A C i s g e n e r a l l y a s s o c i a t e d w i t h

s m a l l p o r e d i a m e t e r a n d l a r g e i n t e r n a l s u r f a c e ,

c o n t r a r y t o t h a t o f t h e p o w d e r e d f o r m w h e r e l a r g e

p o r e s a n d s m a l l e r i n t e r n a l s u r f a c e a r e t h e m a i n

fe a t u re s .

R i c e h u s k ( R H ) , b e i n g h i g h l y s i l i c e o u s i n n a t u r e ,

c o n t a i n i n g 1 7 - 2 3 % a s h , n a t u r a ll y f u r n is h e s a c h a r w i th

l o w f i x e d - c a r b o n c o n t e n t , r e s u l t i n g i n l o w a c ti v it y . B e g

a n d U s m a n i ( 1 9 8 5 ) p r e p a r e d l o w - a s h , p o w d e r e d a c t i -

v a t e d - c a r b o n f r o m r i c e h u s k b y a l k a l i n e l e a c h i n g o f

s il ic a f r o m h i g h - a s h c a r b o n o b t a i n e d b y l o w - t e m p e r a -

t u r e p y r o l y si s in a n i n e r t a t m o s p h e r e . L a t e r , U s m a n i et

al. ( 1 9 9 0 ) d e v e l o p e d a n d p a t e n t e d a p r o c e s s f o r d e a s h -

i n g h i g h - a s h r a w m a t e r i a l s l i k e r i c e h u s k b e f o r e t h e i r

p r o c e s s i n g fo r t h e p r e p a r a t i o n o f a c ti v a t e d c a r b o n . T h e

p r o c e s s o f c h e m i c a l a c t i v a t i o n w a s s t u d i e d i n d e ta i l a n d

z i n c c h l o r i d e w a s f o u n d t o b e t h e b e s t a c t i v a t i n g a g e n t

f o r o b t a i n i n g p o w d e r e d a c t i v a t e d - c a r b o n f r o m i n d i -

g e n o u s a g r o w a s t e s a n d i n f e r i o r w o o d s ( U s m a n i et al.,

1 9 8 8 , 1 9 8 9 ) .

T h i s s t u d y is n o w f u r t h e r e x t e n d e d a n d G A C h a s

b e e n p r e p a r e d f r o m h i g h - a s w e ll as l o w - a s h r ic e h u s k

u s i n g z i n c c h l o r i d e a s a n a c t i v a t in g a g e n t . A p p r o p r i a t e

w o r k i n g c o n d i t i o n s h a v e b e e n e s t a b l is h e d i n th e l i g h t o f

d i f f e r e n t p h y s i c a l a n d c h e m i c a l c h a r a c t e r i s ti c s o f t h e

p r o d u c t s .

ME THO D S

I n t h e p r e s e n t s t u d y , r i c e h u s k w a s u s e d i n it s h i g h - a n d

l o w - a s h f o rm s . T h e f o r m e r w a s a l s o u s e d i n it s g r o u n d

f o r m o f p a r t ic l e s i ze 0 - 5 - 1 0 m m . T h e p r o c e s s s e -

q u e n c e ( F i g . 1 ), f o r t h e p r e p a r a t i o n o f G A C ( h i g h / l o w -

a s h ) , c o n s i s t e d m a i n l y o f t h e f o l l o w i n g fi v e s t e p s : (i )

d e a s h i n g o f r i c e h u s k ; ( i i ) c h e m i c a l t r e a t m e n t o f h i g h /

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32

T a n z il H a i d e r U sm a n i T a m o o r W a h a b A h m a d A . H . K . Y o u s u f z a i

R I C E H U S K

Na O H Z nC l 2 Z nC I 2 (R I~C YC L E D)

LOW H _

~[ DEA SHING RICE HU SK '7

7 ~ TRE XrM EN T ,'~[ [

b .

r

V

GR ANUL AR AC T IVAT ED

C A R B O N

( H I G H / L O W A S H )

DRYING I~ ,

HC I

L E A C H I N G /

WAS HING l - ~

CARBONIZATION

Fig. I. Block diagram of the preparation o f granular activated-carbon (high/low-ash) from rice husk.

l ow- a sh r i c e husk ; ( i i i ) e x t r us ion o f t he c he m ic a l l y -

t r e a t e d g e l a t inous m a ss ; ( iv ) c a r bon iz a t i on o f e x t r u de d

gr a nu le s ; a nd ( v ) l e a c h ing , wa sh ing a nd d r y ing o f t he

f in i she d p r od uc t .

T h e p r o d u c t s o b t a i n e d i n e a c h s e t o f e x p e r i m e n t

w e r e e v a l u a t e d b y s t a n d a r d m e t h o d s . T h e e x p e r i m e n t

w i t h h i g h - a n d l o w - a s h f o r m s o f r i c e h u s k s w a s

r e p e a t e d t w i c e i n c lu d i n g t h r e e r e p l i c a te s o f e a c h t r e a t-

m e n t . R e p l i c a t e s w e r e r e p r o d u c i b l e a n d s t a n d a r d

de v ia t i on wa s c a l c u l a t e d whe r e ve r a pp l i c a b l e .

D e a s h i n g o f r ic e h u s k

Ric e husk f r om a husk ing m i l l wa s c o l l e c t e d , s ie ve d a nd

w a s h e d t o f r e e i t f r o m d i r t a n d f o r e i g n m a t e r i a l a n d

dr i e d t o a c ons t a n t we igh t. It wa s t he n r e f l ux e d w i th

d i f f e re n t c o n c e n t r a t i o n s o f s o d i u m h y d r o x i d e s o l u t io n s

f r om 0 .1 t o 7 5% f or 4 h . T he l e a c he d m a te r i a l wa s

t h e n f i l t e r e d , w a s h e d t o n e u t r a l p H a n d d r i e d t o a

c ons t a n t we igh t . Che m ic a l a na lyse s o f t he o r ig ina l a s

w e l l a s e a c h o f t h e l e a c h e d r i c e h u s k s a m p l e s w e r e

c a r r i e d o u t a n d p e r c e n t y i e ld o f d e a s h e d m a t e r ia l e s ta -

b l i she d . I n t he l igh t o f t he c he m ic a l a na lys i s o f de a she d

s a m p l es , a 1 % c o n c e n t r a t i o n o f s o d i u m h y d r o x i d e w a s

f o u n d t o b e a p p r o p r i a t e a n d u s e d i n f u r t h e r s t ud i es .

h e m i c a l t r e a tm e n t a n d e x t r u s i o n m e t h o d o l o g y

O n e h u n d r e d g r a m s o f h i g h -a s h r i c e h u s k i n i ts o r i g in a l

p a n i c l e s i z e ( G ) a n d i t s g r o u n d f o r m o f 0 - 5 - 1 0 m m

( G 1 ) w e r e w e i g h e d a n d m i x e d w i t h 2 5 , 5 0 , 7 5 a n d 1 0 0

g o f z i n c c h l o r i d e d i s s o l v e d i n 3 0 0 m l o f 5 % H C I i n

s e p a r a t e s e ts o f e x p e r i m e n t s. T h e s e s a m p l e s w e r e t h e n

s lowly he a t e d i n a s t e a m - j a c ke t e d , g l a s s l i ne d ve sse l

w i th c on t inuous s t i r r i ng t o a da r k ge l a t i nous m a ss /

p u tt y . T h i s s e t o f e x p e r im e n t s w a s a l s o c a r d e d o u t w i t h

low-ash r ice husk (L) in i t s or igina l par t ic le s ize . The

pe ne t r a t i on va lue s o f h igh- a s we l l a s l ow- a sh r i c e husk

p u t t i e s w e r e m e a s u r e d b y a S e t a U n i v e r s a l S t a n d a r d

P e n e t r o m e t e r (B S 4 1 6 4 - 1 9 8 7 ; w e ig h t u s e d = 5 0 g ,

t e m pe r a tu r e = 30 C , t im e = 5 s ).

E a c h o f t h e h i g h - a n d l o w - a s h p u t t i e s w a s t h e n

e x t r ude d t h r ough a s t a in l e s s s t e e l d i e ha v ing ho l e s o f

2 .5 m m d i a u n d e r a h y d r a u l ic p re s s u r e o f 2 8 1 0 - 5 6 2 0

k g / c m 2 (Mu r t i , 1976) .

P r o c e s s i n g o f g r a n u l e s

T h e e x t r u d e d g r a n u l e s w e r e f ir s t d r i e d a t 1 0 5 °C a n d

the n c a r bon iz e d i n a s t a in l e s s s t e e l ve s se l i n a n i ne r t

a t m o s p h e r e a t 5 0 0 - 5 5 0 ° C f o r 2 h ( U s m a n i et al.

1 9 9 2 ), a n d t h e n r e f l u x e d w i t h 7 5 0 m l o f 1 0 % H C I f o r 4

h . E a c h s a m p l e w a s t h e n f i l te r e d , w a s h e d f r e e o f a c id

a n d c h l o r i d e io n s a n d d r i e d t o a c o n s t a n t w e i gh t .

P r od u c t c h ar ac t e r i z a t i on

T he por e - spa c e pe r 100 g ( Ja in & Sha r m a , 1971) , ba l l

p a n h a r d n e s s n u m b e r ( A S T M , 1 9 7 9 ) , p e r c e n t y i e l d ,

r e a g e n t r e c o v e r y a n d a s h c o n t e n t s ( B e v ia et al . 1984)

o f t h e s e s a m p l e s w e r e d e t e r m i n e d . T h e a c ti v it y o f t h e s e

sa m ple s wa s e va lua t e d a ga ins t a dsor ba t e o f i od ine ,

m e thy l e n e b lue a n d m o la s se s (Sne l l & Hi l t on , 1969 ;

Da ndy , 1977) .

R E S U L T S A N D D I S C U S S I O N

T a ble 1 shows the c he m ic a l a na lyse s o f t he o r ig ina l a s

w e l l as s a m p l e s d e a s h e d w i t h v a r io u s c o n c e n t r a t i o n s o f

s o d i u m h y d r o x i d e . R e d u c t i o n o f a s h a n d l i g n i n w a s

ne g l ig ib l e i n i ti a ll y a nd t he n i nc r e a se d w i th a n i nc r e a se

i n a l k a l i c o n c e n t r a t i o n . O p t i m u m d e a s h i n g o f R H t o

t h e e x t e n t o f 9 3 % w a s a c h i e v e d a t 1 % a l k al i c o n c e n t r a -

t i o n . T h e p e r c e n t a g e o f a - c e l l u l o s e a l t e r e d w i t h t h e

a lkal i c onc e n t r a t i on , a tt a in ing a va lue o f 71 .75% a t 1%

a lka l i . T a b l e 1 a l so shows a r e gu l a r de c r e a se i n y i e ld

wi th i nc r e a s e i n a lka li c on c e n t r a t i on . I n t he l igh t o f t h i s

c he m ic a l a na lys i s ( h ighe r a - c e l l u lose a nd l ow- a sh

c o n t e n t) , 1 % N a O H c o n c e n t r a t i o n w a s s e l e c t e d f o r u s e

in f u r th e r s t ud i e s .

T a b le 2 shows the e f f e c t o f im pr e gna t ion r a t i o ( I R)

o f a c t i v a t i n g a g e n t ( A A ) o n t h e a v e r a g e p e n e t r a t i o n

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A c t i v a t e d c a r b o n f r o m r ic e h u s k

Tab le 1 . Che mica l analysis and y ield o f orig ina l and a lka l i- leached d ee hus k

3 3

Na OH Yie ld a -Ce l lu lo se L ignin Ash Ext rac t ives Pentosans

(%) (%) (%) (%) (%) (% ) (%)

0 00 100 0 35 88 36 38 18 90 1 16 21 21

0-10 94 0 38 01 35 90 18 04 1 09 22 35

0-25 82 0 43 66 33 14 17 26 0 98 23-02

0-50 80 0 48 81 30 26 13 75 0 73 23 97

0 75 66 0 69 05 22 46 5 57 0 65 24-25

1 0 62 0 71 75 18 69 1-25 0 58 24-67

1 25 61 0 72 51 17 51 1 23 0 52 25 50

2 5 56 0 70 25 17 35 1-22 0'3 3 24 62

5 0 53 4 70 45 17'25 1 22 0 '34 24 00

7 5 47 2 70 07 17'24 1 21 0 '37 24-23

Tab le 2 . Effect o f impregn at ion rat io with zinc chloride IR) on average penetrat ion va lue APV) and true y ield

Sample Impreg na t ion Average Yie ld Ash True y ie ld Reagent

cod e ra t io pene t ra t io n va lue (%) conten t (a f t e r a sh recovery

(%) (mm) (%) deduc t ion) (%)

( )

G H 1 a 25 . . . . .

GH 2 50 4 20 56 80 50 09 26 00 70 93

GH 3 75 4 95 55 00 49 50 27 80 72 88

G H 4 100 5 05 54 73 49 17 27 83 75 55

G IH 1 25 4 60 52 95 50 05 25 45 67 98

G1 H2 50 5 00 52 00 49 22 26 78 71 30

G1 H3 75 5 40 53 30 48 19 27 62 73 25

G 1H 4 100 5-50 54 50 48 15 28 26 74 50

LH 1 25 3 80 35 13 2 95 34-09 68 '39

LH 2 50 5-50 35 67 2 88 34-64 71 '75

LH 3 75 5 80 35 87 2 51 34-96 74 '10

LH 4 100 5 80 34 25 2 42 33 42 75 '33

~H 1-H 4 d enotes d i f fe ren t impregn a t ion ra t ios o f zinc ch lor ide g iven in co lum n 2 ( s ee a lso M ethods ) .

- -

no resul t , see text .

v a l u e ( A P V ) o f t h e p u t t i e s u s e d f o r g r a n u l iz a t io n . I t

s h o w s t h a t w i t h t h e i n c r e a s e in I R , th e A P V o f th e

p u t t y g e n e r a l l y i n c r e a s e d ( A h m a d et al. 1 9 9 2 ) .

Sample Bulk True Pore

F u r t h e r , i t s h o w s t h a t i n g r o u p G t h e r e i s n o p u t t y c o d e d e n si ty d e n si ty s p ac e

f o r m a t i o n a t 2 5 % I R , w h e r e a s f o r m a t i o n o f p u t t y a n d ( g /c m 3) ( g /c m 3) ( p e r 1 0 0 g )

t h e r e a f t e r i t s g r a n u l i z a t i o n w a s a c h i e v e d w i t h 2 5 % I R

i n t h e G 1 a n d L g r o u p s . H e n c e f o r t h , s t u d ie s o n l o w - G H 1 - - - - - -

a s h R H w e r e p e r f o r m e d o n l y w i t h t h e o r i g in a l - si z e G H 2 0 .5 4 4 4 1 .9 6 19 1 33

p a r t i c l e s . G H 3 0 . 5 3 5 9 1 . 9 9 13 1 3 6

G H 4 0 4 6 0 2 2 2 3 0 7 1 7 4

I n e i t h e r c a s e , y i e l d i n c r e a s e d w i t h t h e i n c r e a s e i n I R

o f z i n c c h l o r i d e ( N a c c o & A q u a r o n e , 1 9 7 8 ) . H o w e v e r , G 1 H 1 0 -6 5 93 1 .1 5 93 6 5

G 1 H 2 0 - 6 6 3 5 1 . 87 2 1 9 7

a p h e n o m e n o n o f a s h r e d u c t i o n w a s o b s e r v e d i n t h e s e G 1 H 3 0 .6 4 05 1 .8 19 8 1 01

s a m p l e s w i t h a n i n c r e a s e i n I R o f t h i s p a r t i c u l a r A A G 1 H 4 0 . 5 0 14 2 . 13 5 6 1 5 3

( E 1 - S h o b a k y & Y o u s s e f , 1 9 7 8 ) . R e a g e n t r e c o v e r y L H 1 0 . 5 3 80 1 . 80 2 0 1 2 9

( R R ) i n c r e a s e d g r a d u a l l y w i t h t h e i n c r e a s e o f I R i n L H 2 0 . 5 3 7 7 1 . 83 0 3 1 31

b o t h t h e c a s e s a n d g e n e r a l l y r a n g e d b e t w e e n 6 8 a n d L H 3 0 .5 2 9 9 1 .9 9 73 1 39

7 5 % . T h i s a g r e e s w e ll w i t h t h e s t u d y o f A h m a d et al. L H 4 0 . 5 2 2 2 2 . 1 6 9 6 1 4 5

( 1 9 9 0 ) u s i n g t h e s a m e A A w i t h a n o t h e r r a w m a t e ri a l.

T a b l e 3 s h o w s t h a t i n b o t h h i g h - a n d l o w - a s h s a m -

p l es , b u l k d e n s i t y g e n e r a l l y d e c r e a s e d a n d t r u e d e n s i t y

i n c r e a s e d r e s u l ti n g in a n e n h a n c e d p o r e - s p a c e w i t h t h e

i n c r e a s e o f IR . I n t h e c a s e o f t h e G 1 g r o u p , t h e r e s u lt -

a n t p o r e - s p a c e w a s s o m e w h a t l o w e r i n al l t h e s e

c a r b o n s , a p p a r e n t l y d u e t o t h e i r i n c r e a s e d b u l k a n d

Table 3 . Di f ferent physica l characterist ics o f act ivated

ca rb o n s

Ball-Pan

hardness no .

BPH)

3 05

3 51

53 04

2 '05

25 56

6 1 ' 2 5

6 2 ' 3 2

2 0 ' 0 0

93 00

94 50

95 60

c o m p a r a t i v e l y l o w e r t r u e d e n s it ie s . T h i s h i g h e r b u l k

o b t a i n e d i n g r o u p G 1 s a m p l e s h a d r a t h e r a p o s it i v e

e f f e c t i n i n c r ea s i n g t h e c o m p a c t n e s s o f t h e s e g r a n u l e s

a s m a y c l e a r ly b e s e e n b y th e i r h i gh B P H a s c o m p a r e d

t o G c l as s sa m p l e s . T h e d a t a o n B P H f u r t h e r s h o w s t h a t

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34

T a n z i l H a i d e r U s m a n i , T a m o o r W a h a b A h m a d , A . H . K . Y o u s u f z a i

T a b l e 4 A d s o r p t i v e / s u r f a c e c h a r a c t e r i s t ic s o f a c t iv a t e d c a r b o n s

Sample Iodine no.

code (mg/g)

Methylene Molasses Surface area of Surface area of Surface area of

blue no. value pores > 10 A pores > 15 A pores > 28 A

(mg/g) (m2/g) (m2/g) (m2/g)

GH1

GH2 537

GH3 633

GH4 675

GIH1 397

GIH2 423

G1H3 537

G1H4 744

LH1 941

LH2 1059

LH3 1148

LH4 1232

109 298 486 312 144

169 495 576 484 238

199 663 615 569 319

96 410 355 272 198

101 442 379 289 213

189 657 486 541 317

214 696 679 613 335

172 420 864 492 202

189 466 974 542 225

306 498 1057 876 238

375 550 1136 1073 265

in the high-ash classes (G and G1 ), none of the samples

was able to attain the minimum standard o f hardness of

95 required for GAC (ASTM, 1979), even though at

higher IR, BPH numbers increased in somewhat higher

proportion. However, in the case of samples of group

L, except at an IR of 25 , all the GAC samples

attained a similar BPH value. The prominent increase

in hardness obtained between samples LH1 and LH2

may be correlated well with the sudden increase in

APV (Table 2) of their putties from 3-80 to 5-50

(Usmani

et al . ,

1992). An overview of Tables 2 and 3

shows that GAC samples prepared from high-ash RH

could not gain sufficient strength, probably because

their cellulosic contents were lower than those of low-

ash samples. The binding action of zinc chloride seems

to be the contributing factor as it is effective on the

cellulosic portion of the raw material rather than on the

ash (Ts'ai & Chaung, 1942).

Table 4 depicts activity or adsorptive capability of

the activated carbons against adsorbates of different

molecular dimensions, corresponding to surface areas

of por es> 10, 15 and 28 A respectively (Bonnevie-

Svendsen, 1975). In Table 4 the development of micro-

and mesopores, as indicated by the iodine and MB

numbers, was somewhat low in both the cases of high-

ash RH carbons (G and G1). Contrary to that of high-

ash, quite prominent increases in iodine and MB

numbers were found in low-ash carbons (L). In both

cases, iodine and MB numbers show a pattern of

increase, with a sudden variation in their mesoporos ity

at 75 IR. As far as macroporosity of these carbons

determined by molasses decolorization is concerned, it

was found to be d ependent on IR in both the cases and

increased with it.

This work shows that optimum deashing of rice husk

to the extent of 93 is achieved by refluxing it with 1

sodium hydroxide solution. Granular activated-carbon

of good quality, appropriate hardness, and balanced

micro-, meso- and macropores may be prepared from

low-ash rice husk in its original particle size with 75

zinc chlor ide as an activating agent.

R E F E R E N C E S

Ahmad, T. W., Usmani, T. H. & Ahmad, S. Z. (1990). Acti-

vated carbon from indigenous inferior woods 2. Activa-

tion temperature, time and particle size influence. Pak. J.

Sci. Ind. Res., 33 (4), 177-80.

Ahmad, T. W., Usmani, T. H. & Mumtaz, M. (1992). A

process for the production of granular activated carbon

from indigenous woods. Pakistan patent (filed).

Akhtar, R. (1986-87). Pak i s tan Year Boo k . East and West

Pub. Co., Karachi/Lahore, p. 519.

ASTM (1979).

Standard Tes t Me thods Jbr Bal l -Pan H ardness

of Act iva ted Carbon, Vol . 15.01. ASTM, Philadelphia, PA.

Bansal, R. C., Donnet, J. B. & Stoeckli, F. (1988). Act i ve

Carbon. Marcel Dekker, New York.

Beg, M. A. A. & Usmani, T. H. (1985). Low ash activated

carbon from rice husk. Pak. J. S ci. Ind. Res., 28 (4),

282-7.

Bevia, F. R., Rico, D. P. & Gomis, A. E M. (1984). Activated

carbon from almond shells.

Ind. Eng. Chem., Prod. Res.

Dev.,

23, 266-71.

Bonnevie-Svendsen, M. (1975).

Sorption and Filtration

Methods for Gas and Water Puri f icat ion.

Noordhoft-

Leyden, pp. 275-6.

BS: 4164 (1987). Appendix -- E. Determination and pene-

tration. British Standard Institution, London.

Dandy, A. J. (1977). Production and characterization of acti-

vated carbon from agricultural waste products and wood

charcoals. Ne w Zea land J . Sci. , 20, 291-5.

EI-Shobaky, G. A. & Youssef, A. M. (1978). Chemical acti-

vation of charcoals. Surface Technology, 7, 209-16.

Grist, D. H. (1975). Rice. Longmans, Green & Co., London,

p. 382.

Jain, K. D. & Sharma, M. K. (1971). Preparation of activated

carbon from basmati rice husk. J. Indian Chem. Soc. , 4 8

(12), 1155-60.

Martin, R. J. (1980). Activated carbon product selection for

water and waste water treatment. Ind. Eng. Chem., Prod.

Res. Dev., 19 (3), 435-41.

Mc Graw -Hil l Encycloped ia of Science an d Technology, VoL

i1 1960) .

McGraw-Hill, New York, pp. 562-3.

Murti, H. (1976). Granular activated carbon. Ger. Often.

2,624, 779, 16 Dec. 1976.

Nacco, R. & Aquarone, E. (1978). Preparation of active

carbon from yeast. Carbon, 6, 31-4.

Snell, E D. & Hilton, C. L. (1969). Encyclopedia of Industr ial

Chem ical Analys is, John Wiley, New York, Vol. 1, p. 557;

Vol. 8, pp. 148-9.

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