The Potential Use of Geopolymeric Materials to Immobilise Part 2

7/28/2019 The Potential Use of Geopolymeric Materials to Immobilise Part 2

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Pergamon0892-6875(98)00121-6

Minerals Engineering, V o l . 1 2 , N o . I , p p . 7 5 - 9 1 , 1 9 9 9 1 9 9 8 Elsevier Scienc e L t dA l l r i g h ts r e s e r v e d

0 8 9 2 - -6 8 7 5 / 9 9 /5 - - s e e f ro n t m a t t e r

T H E P O T E N T I A L U S E O F G E O P O L Y M E R I C M A T E R I A L S T O I M M O B I L I S ET O X I C M E T A L S : P A R T I I . M A T E R I A L A N D L E A C H I N G

C H A R A C T E R I S T I C S

J .G . S . V A N J A A R S V E L D ~, J .S .J . V A N D E V E N T E R ~ a n d A . S C H W A R T Z M A N * De pa r t me nt o f C he mi c a l Engi ne e r i ng , The Uni ve r s i t y o f Me l bourne ,

Pa rkv i l le , V i c t o r i a 3052 , Aus t ra l ia . E -ma i l : j s j .va n_d e ve n t e r@ c he m e ng .un i m e l b . e du . a ut Sc hool o f Phys i c s , The Uni ve r s i t y o f Me l bou rne , Pa rkv i ll e , V i c t o r i a 3052, A us t ra l ia(Received 21 July 1998; accepted I October 1998)

ABSTRACTThe stabilisation a nd solidification o f was te materials by the technolog y ofgeopolym erisat ion is fair ly unknow n and has not been s tudied in any depth. This pap erpresen ts some exp er imental evidence a s to the phys ical an d chemical characterist ics ofgeop olymers man ufactured fro m f ly a sh or iginating from two di f ferent regions . I t hasbecom e ap paren t that these materials could be used fo r a w ide var iety o f environmentaland other appl icat ions such as the immobil isation of heavy metals an d the fabr ica t ion ofstructu ral prod ucts. In this study compressive strength testing, specific surfac e areadeterminat ions , Transmiss ion Electron M icroscopy (TEM), Nu clear Magnet ic Resonance(NM R) an d leaching tests were u sed in characterising a num ber of geopolym er matr ices.I t i s also show n ho w the inclus ion of heavy me tal ions , alkal i m etal cations an d di f ferentproce ss ing condi t ions af fect the phys ical a nd chem ical characterist ics of the f inal product . 1998 Elsevier Science Ltd. All rights reservedKeywordsLe a c h i ng ; e nv i ronme n t a l ; re c yc l i ng ; wa s t e p roc e s s ing

~ T RODUCT IONANDBACKGROUNDIn a p re v i ou s pa pe r [1] t he poss i b l e a pp l i c at ions o f ge op ol yme rs i n wa s t e p roc e s s ing ha ve be e n d i sc ussed .The se a pp l i c a ti ons c a n be d i v i de d i n t o t w o c a t e gor ie s : (1 ) S t ruc tu ra l p roduc t s suc h a s c o nc re t e r e p l a ce me nt si n va r i ous e nv i ronme nt s a nd (2 ) Immobi l i s a t i on sys t e ms fo r he a vy me t a l c on t a i nme nt . Expe r i me nt a le v i de nc e re ga rd i ng l e a c h i ng da t a a nd p hys i c a l p roper t ie s w a s a l so p re se n te d , a l t hough a l l o f i t c ons i de re dc omme rc i a l l y p roduc e d ge opol yme r c e me nt s t ha t we re mi xe d wi t h wa s t e p roduc t s a nd a l l owe d t o s e t .R e l a t i ve l y h i gh c os t s a nd prob l e ms re l a t i ng t o t r a ns fe r r i ng ne w t e c hnol ogy t o i ndus t ry p re ve n t e d t he sec omme rc i a l l y p roduc e d b i nde rs f rom be c omi ng popul a r a nd t o da t e on l y l i mi t e d suc c e s se s ha ve be e na c h i e ve d [2 ] . The poss i b i l i t y o f p roduc i ng ge opol yme r i c ma t r i c e s by u t i l i s i ng wa s t e ma t e r i a l s ha s be e npropose d [1] a nd t he re fore t h i s pa pe r wi l l p re se n t some e xpe r i me nt a l e v i de nc e on t he phy s i c a l p rope r t ie sa nd l e a c h i ng c ha ra c t e ri s ti c s o f ge o pol ym e rs ma nu fa c t ure d a l mos t e n ti r e ly f rom wa s t e ma t e r i a l s. I t shou l dbe ke p t i n m i nd , how e ve r , t ha t t he p re se n t le ve l o f s c ie n t if i c know l e dge wi t h r e ga rd t o g e opol ym e rs l e a ve sm uc h t o be d e s i re d a nd e ve n t he e v i de nc e p re se n t e d he re c a nnot s erve t o funda m e nt a l l y unde rs t a nd t he seproduc t s a l t hough a numbe r o f qua l i t a t i ve c onc l us i ons c a n be d ra wn.

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76 J.G .S . van Jaarsvelde t a l .Va r iou s f a c to r s a f f e c t t he e ve n tua l m e c ha n ic a l a nd c he m ic a l p r ope r t i e s o f t he f in i she d p r oduc t . T he s einc lude the t he r m a l h i s to r y o f t he c l a y use d , t he t ype a nd a m ount o f a lka l i m e ta l c a t i ons p r e se n t , t he he a vym e ta l be ing im m obi l i se d a s we l l a s c e r t a in phys i c a l c ons ide r a t i ons suc h a s pa r t i c l e s i z e a nd e a se o f m ix ingof t he va r ious r e a ge n t s . T h e l a s t two a spe c t s w i l l no t be a ddr e sse d in t h i s pa pe r , a s t he y w e r e f a i r ly s im i l a rf o r a l l e xa m ple s unde r c ons ide r a t i on . I t wa s no t e d p r e v ious ly [ 1 ,3 ] t ha t t he m e c ha n i sm by whic hg e o p o l y m e r i s a t i o n is t h o u g h t t o o c c u r i n v o l v e s t h e d i ss o l u ti o n , m i g r a t io n a n d p o l y m e r i s a t i o n o f A I a n d S ip r e c u r sor spe c i e s a s w e l l a s a su r f a c e r e a c t ion on the r e m a in ing su r f a c e a re a o f und i s so lv e d wa s t e pa r t i c l e s .A l tho ugh th i s is a ve r y s im pl i s t ic v i e w of t he p r oc e ss i t w i l l ta ke so m e t im e b e f or e su f f i c i e n t e xpe r im e nta le v ide nc e i s a va i l a b l e t o f u l l y qua n t i f y t he r e a c t ion k ine t i c s o f t he syn the s i s r e a c t ion .D e p e n d i n g o n t h e e v e n t u a l a p p l i c a t i o n , t h e p r o d u c t f r o m s u c h a p r o c e s s s h o u l d b e c h e m i c a l l y i n e r t a n dp h y s i c a l l y s t r o n g i n o r d e r t o p r e v e n t a n y f u r t h e r l e a c h in g o f im m o b i l i se d m e t a ls a n d c o m p o u n d s . P h y s i c a ls t r e ng th i s no t on ly a n a dva n ta g e a s f a r a s phys i c a l e nc a psu la t i on o f t ox i c m a te r i a ls i s c onc e r ne d , bu t a l sopr ov ide s f o r t he u t i l is a t i on o f t he se p r oduc t s i n c e r t a in bu i ld ing a pp l i c a ti ons . A l thou gh p hys i c a l p r ope r t i e s ,suc h a s c om pr e ss ive s t r e ng th a nd por os i t y , c a n be u t i l i s e d i n d i s t i ngu i sh ing be twe e n d i f f e r e n t m a t r i c e s ,l e a c h ing t e s t s w i l l usua l ly p r ov ide m or e subs t a n t i a l i n f o r m a t ion r e ga r d ing the im m obi l i s ing e f f i c i e nc y ,c h e m i c a l s t a b il it y a s w e l l a s m e c h a n i s m a n d k i n e t i c s o f to x i c m e t a l i m m o b i l i s a ti o n i n g e o p o l y m e r i cm a t r i c e s . Ap a r t f r om s t a nda r d e nv i r on m e n ta l l e a c h ing t es t s, spe c i f i c a l ly de s igne d t e s t s , suc h a s t hosed i s c u s s e d i n t h i s p a p e r , h a v e n o t y e t b e e n u s e d i n c h a r a c te r is i n g g e o p o l y m e r m a t r i c e s a n d r e m a i n n o v e l t oa l a r ge e x t e n t . As wa s m e nt ione d p r e v ious ly [ 1 ] X- r a y d i f f r a c t i on t e c hn ique s a r e i na de qua te f o r s tudy ingt h e s t r u c t u re o f g e o p o l y m e r s , m a i n l y b e c a u s e o f t h e ir f a ir l y h i g h a m o r p h o u s c o n t e n t . T h i s p r o b l e m c a n b eo v e r c o m e b y u s i n g a c o m b i n a t i o n o f an a l y t ic a l t e c h n iq u e s s u c h a s N u c l e a r M a g n e t i c R e s o n a n c e ( N M R ) a sw e l l a s T r a n s m i s s i o n E l e c t r o n M i c r o s c o p y ( T E M ) .

EXPERIMENTALM a t e r i a l sF l y a s h u s e d i n t h e s y n t h e s is o f m a t ri c e s E l , E 2 , F 1 a n d G 1 w a s o b t a i n e d f ro m S A S O L a t S a so l b u r g , S o u t hA f r i c a a n d t h a t u s e d i n m a t r i c e s H 1 t o H 4 f r o m T a r o n g p o w e r s t a t io n i n Q u e e n s l a n d , A u s t r a li a . B o t h f lya she s a r e o f c oa l o r ig in , w i th pa r t ic l e s i z e s i n t he o r de r o f 50% sm a l l e r t ha n 12 la r n a nd c he m ic a lc o m p o s i t i o n s a s s h o w n i n T a b l e 1 . K a o l i n it e , g r a d e H R 1 , w a s o b t a i n e d f r o m C o m m e r c i a l M i n e r a ls , S y d n e y ,Aus t r a l i a . I n t he p r e pa r a t i on o f m a t r i c e s E 1 a nd E 2 , m e ta ka o l in i t e wa s use d , m a nu f a c tu r e d by c a l c in ing thea b o v e - m e n t i o n e d k a o l in i t e at 6 0 0 C f o r 6 h a s d e s c r i b e d b y M a d a n i [ 4 ]. A l l e x p e r im e n t s w e r e p e r f o r m e dus ing th e sa m e b a t c he s o f r e a ge n t s a nd s t a r t i ng m a te ri a l s . D i s ti l l e d wa te r wa s u se d th r ough out .

TA BLE 1 Composition of f ly ash as determined by fusion and XRF-analysis (mass%)E l e m e n t a s o x i d e S A S O L f l y a s h T a r o n g f l y a s hS iO2 5 0 .1 6 1 .4A1 2 0 3 2 8 . 3 3 3 . 0C a O 8 . 2 0 . 6F e 2 0 3 4.0 1.1M g O 2 .0 0 .3TiO2 1 .5 2 .0N a 2 0 0 . 5 0 .1K 2 0 0 .9 0 .1S O 3 0 .4 0 .0L o s s o n ig n i t io n 4 .1 1 .4


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Use of geopolymericmaterials to imm obilise ox ic metals: part II 77S y n t h e s i sS a m p l e p r e p a r a t i o n w a s p e r f o r m e d a s d e s c r i b e d p r e v i o u s l y [3 ] w i t h a t l e as t a 7 - d a y w a i t in g p e r i o d b e i n go b s e r v e d b e f o r e a n y t e s ts w e r e p e r f o r m e d . In e a c h c a s e t h e s a m p l e s w e r e c a s t i n 5 0 m m c u b e s , v i b r a te d f o r5 m i n u t e s a n d a l l o w e d t o s e t at 3 0 C f o r 2 4 h o u r s b e f o r e b e i n g r e m o v e d f r o m t h e m o u l d s a n d k e p t a t r o o mt e m p e r a t u r e f o r a n o t h e r 6 d a y s . H e a v y m e t a l c a ti o n s w e r e a d d e d t o t h e r e a c ti o n m i x t u r e d u r i n g m i x i n g a sa s o l u t i o n o f C u ( N O 3 ) 2 o r P b ( N O 3 ) 2 in w a t e r. T a b l e s 2 a n d 3 s u m m a r i s e t h e c o m p o s i t i o n s o f t h e r e s p e c t i v em a t r i c es . I t c o u l d w e l l b e n o t e d th a t th e a m o u n t o f N a O H a n d K O H u s e d i n p r o d u c i n g m a t r i c es E l , E 2 ,F 1 , F 2 a n d G 1 w a s c h o s e n s u c h a s t o p r o v i d e fo r e q u a l m o l a r a m o u n t s o f N a a n d K p r e s e n t in t h e s t ru c t u r esof a l l t he m a t r i c e s i n T a b le 2 .

TA BLE 2 Compositions of matrices prepared fro m SASO L fly ash (mass%)Matrix Con taminant Alkali metal Clay W ater/Fly ash A1203/SIO2m ass ratio m ass ratio

E 1 C u 0 .1 K O H 5 . 0 M e t a k a o l i n i t e 1 6 .0 0 . 2 0 . 5 7E 2 P b 0 .1 K O H 5 . 0 M e t a k a o l i n i t e 1 6 .0 0 . 2 0 . 5 7F I C u 0 .1 N a O H 3 . 7 K a o l i n i t e 1 5 . 0 0 . 2 0 . 5 7F 2 P b 0 .1 N a O H 3 . 7 K a o l i n i t e 1 5 .0 0 . 2 0 . 5 7G 1 C u 0 .1 K O H 5 . 0 K a o l i n i t e 1 5 . 0 0 . 2 0 . 5 7

TA BLE 3 Composit ions of matrices prepared from Tarong f ly ash (mass%)M a t r i x C o n t a m i n a n t A l k a l i m e t a l C l a y W a t e r / F l yash r a t i o

A1203/SIO2r a t i o

H 1 C u 0 .1 K O H 5 . 0 K a o l i n i te 1 4 .0 0 . 4 3H 2 P b 0 .1 K O H 5 . 0 K a o l i n i te 1 4 .0 0 . 4 3H 3 P b 0 . 2 N a O H 6 . 0 K a o l i n i te 1 4 .0 0 . 4 5H 4 C u 0 . 2 N a O H 6 . 0 K a o l i n i te 1 4 .0 0 . 4 5

0 . 5 70 . 5 70 . 5 70 . 5 7

A n ~ y s e sCompressive strength test ingC o m p r e s s i v e s t r e n g t h te s t in g w a s p e r f o r m e d a s p e r A S 1 0 1 2 .9 [ 5 ] u s i n g t h r ee 5 0 m m c u b e s o f e a c h s a m p l ea n d a v e r a g i n g t h e e x p e r i m e n t a l v a l u e s o b ta i n e d . A l l s am p l e s w e r e t e s te d a f t e r 1 4 d ay s . A n A m s l e r F M 2 7 5 0c om pr e ss ive s t r e ng th t e s t i ng a ppa r a tus wa s use d .Leaching tes tsSa m ple s subm i t t e d t o l e a c h ing t e s t s we r e c r ushe d a nd s i e ve d in to pa r t i c l e s i z e f r a c t i ons , t he l a t t e r be ingl e a c h e d u n t i l e q u i l i b r iu m c o n d i t i o n s w e r e o b t a in e d . L e a c h i n g o f e a c h p a r t ic l e s i ze f r a c t io n w a s c o n d u c t e dus ing a m odi f i e d T C L P [ 3, 6 ] p r oc e dur e u t i li s i ng a c e t ic a c id buf f e r e d a t pH = 3 .3 by a na ly t i c a l g r a desod iu m a c e t a t e . T h e l i qu id / so l id ra t i o wa s ke p t a t 1 :25 a nd the t e m pe r a tu r e c on t r o l l e d a t 30C. E qu i l i b r iumt e st s o n m a t r ic e s E l , E 2 , F 1 a n d G 1 w e r e c o n d u c t e d b y t w o d i f f er e n t m e t h o d s i . e. b y t h e u s e o f s t ir r edve sse l s w i th ove r h e a d im pe l l e r s a nd a l so by u s ing hor i z on ta l l y ro l l e d bo t t le s . T he l a t t e r t e c hn iq ue a l l ow e df o r e q u i l i b r i u m t o b e o b t a i n e d a f t e r a r o u n d 6 0 h o u r s , w i t h t h e s t i r r e d t e c h n i q u e r e a c h i n g e q u i l i b r i u m i na r o u n d 2 4 h o u r s . I n t h e c a s e o f m a t ri c e s H 1 t o H 4 o n l y t h e s t ir ri n g t e c h n i q u e w a s u s e d w i t h s a m p l i n g b e i n gp e r f o r m e d p e r i o d i c a l l y o v e r a 2 4 - h o u r p e r io d . S a m p l i n g w a s c o n d u c t e d b y s y r i n g e a n d t h e t o t a l s a m p l i n gv o l u m e n e v e r e x c e e d e d 1 0 % o f th e f l ui d v o l u m e , t h u s c re a t in g a n a v e r a g e e r r o r o f 5 % . C o n c e n t r a t i o n s o fC u a n d P b w e r e d e t e r m i n e d u s i n g a P e r k i n E l m e r O p t i m a 3 0 0 0 I C P - O E S , w i t h s c a n d i u m a s i n t e r n a ls t a nda r d .


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78 J .G.S . van Jaa rsve ld e t a l .

Specific surface area, infrared analysis and X-ray diffractionB E T s u r f a c e a r e a s w e r e d e t e r m i n e d f o r a l l s a m p l e s b y u s i n g a M i c r o m e r i t i c s F l o w s o r b A S A P 2 0 2 0 w i t ha 30 /70 r a t i o o f N 2 a nd He , de ga ss ing f o r 18 hour s a t 95C. I n f r a r e d spe c t r a we r e r e c or de d f o r m a t r i c e s E l ,E 2 , F 1 a n d G 1 o n a M a t t s o n G a l a x y 2 0 2 0 s p e c t r o m e t e r u s i n g t h e K B r p e l l et t e c h n i q u e ( 0 .5 m g p o w d e rs a m p l e m i x e d w i t h 2 5 0 m g o f K B r ) . X - r a y p o w d e r d i f f ra c t io n d a t a w e r e o b t a in e d f o r a ll s a m p l e s u s i n g aPh i l l i ps PW 1800 d i f f r a c tom e te r w i th Cu K( x r a d i a t ion .Nuclear magnetic resonance and transmission electron microscopyN u c l e a r m a g n e t i c r e s o n a n c e ( N M R ) s p e c t ra w e r e re c o r d e d u s in g t h e M a g i c A n g l e S p i n n i n g ( M A S )t e c hn ique . 29Si a nd 27A1 spe c t r a w e r e r e c o r de d a t sp inn ing spe e ds o f 15 kH z (27A1) a nd 4 kH z ( 29S i) f o rm a t r i c e s E l , F1 , F2 a nd G1 . Ce r t a in sa m ple s we r e a l so subm i t t e d t o i nve s t i ga t i on by t r a nsm iss ion e l e c t r onm i c r o s c o p y ( T E M ) o n a J E O L C X 1 0 0 T E M f i t t e d w i t h a n X - r a y m i c r o a n a l y s i s s y s t e m . T h e s p e c i m e n sw e r e p r e p a r e d b y m e c h a n i c a l l y g r i n d i n g t h e p o w d e r i n e t h a n o l , f o l l o w e d b y u l t r a s o n i c a g i t a t i o n a n dp r e c i p it a t io n o n a n a m o r p h o u s c a r b o n f i lm .

R E S U L T S A N D D I S C U S S I O NG e n e r a lI t is o f i n t e r e s t t o no t e t ha t in syn the s i s ing t he va r ious ge o po ly m e r sa m ple s , i t be c a m e v e r y obv iou s t ha tm i x i n g w i l l p l a y a n i m p o r t a n t r o le i n a n y p r o p o s e d c o m m e r c i a l v e n t u r e i n v o l v in g t h e l a r g e -s c a l e p r o d u c t i o no f g e o p o l y m e r r e l a te d m a t e ri a ls . A p r o p e r t y s u c h a s t h e r h e o l o g y o f t h e r e a c t in g m i x t u r e w a s q u a n t i t a ti v e l yo b s e r v e d a s b e i n g o f i m p o r t a n c e t o t h e p r o p e r t i e s o f t h e f in a l p ro d u c t a n d a l t h o u g h i t f el l o u ts i d e t h e s c o p eof t h i s s t udy i t w i l l be a n im p or t a n t f a c to r t ha t s ti ll ne e ds t o be i nve s t i ga t e d i n a ny f u tu r e s t udy . T he tw of l y a s h e s u s e d d i f f e r e d a s f a r a s t h e i r c h e m i c a l c o n t e n t s w e r e c o n c e r n e d a n d e s p e c i a l l y t h e a m o u n t s o fc a r bon a nd c a l c ium tha t t he y c on t a ine d . T he m a in c r ys t a l l i ne pha se s i n bo th c a se s we r e m ul l i t e a nd qua r t z ,a l t h o u g h a m o u n t s o f a m o r p h o u s s i li c a a n d a l u m i n a c o m p o u n d s w e r e a l so p r e s e n t. T h e e x a c t n a t u r e a n dq u a n t i t y o f t h e s e a m o r p h o u s p h a s e s c a n n o t b e d e t e r m i n e d e a s il y a l t h o u g h i t is w i d e l y a c c e p t e d t h a t th e y a r er e spons ib l e f o r m os t o f t he r e a c t i v i t y a s soc i a t e d w i th a spe c i f i c f l y a sh [ 7 ] .C o m p r e s s i v e s t r e n g t h a n d s p e c i f i c s u r f a c e a r e aI t is s i gn i f i c a n t t o no t e t ha t t he i nc lus ion o f Pb i ns t e a d o f Cu se r ve s t o s t r e ng the n t he s t r uc tu r e i n t e r m s o fc o m p r e s s i v e s t r e n g th s a c h i e v e d ( T a b l e 4 ). T h i s i s t r u e i n t h e c as e o f E 1 a n d E 2 , H I a n d H 2 a s w e l l a s H 3a n d H 4 . I n e a c h c a s e t h e m a t ri c e s c o n t a in e q u a l m a s s a m o u n t s o f t h e h e a v y m e t a l a lt h o u g h t h e m o l a ra m o u n t s w o u l d d i f f e r a n d t h e r e w o u l d b e l e s s P b i o n s p r e s e n t in e a c h c a s e t h a n i n t h e c o r r e s p o n d i n g m a t r ixc on ta in in g Cu . T a b l e 5 show s tha t Pb r e su l t e d i n h ighe r spe c i fi c su r f a c e a re a s t ha n Cu . Ho we v e r , th i s i s no ta t a ll w h a t w o u l d b e e x p e c t e d f r o m a s tr u c tu r a l p o i n t o f v i e w w h e r e t h e s t ro n g e r s a m p l e c o u l d b e e x p e c t e dto ha ve l e s s por os i t y . I t t he r e f o r e se e m s a r e a sona b le a s sum pt ion t ha t a l t hough the Pb i on i n f lue nc e s t hes t r uc tu r e i n t e r m s o f c a us ing i nc r e a se d por o s i t y t h is e f f e c t is o f f se t by i t s c on t r i bu t ion t o s t r uc tu r a l s t r e ng thin a no the r wa y suc h a s t h r ou gh i t s m uc h l a r ge r i on i c r a d ius t ha n t ha t o f Cu . I t is no t c l e a r whe the r t he seions a r e f i nd ing t he m se lve s bonde d in to t he s t r uc tu r e o r whe the r t he su r r ound ing m a t r i x i s j us t phys i c a l l ye nc a psu l a t i ng t he m . T h i s i s sue w i l l be d i sc usse d i n m or e de t a i l l a t e r .

T A B L E 4 C o m p r e s s i v e s t r e n g t h s a f t e r 1 4 - d a y s ( M P a )Matrix Contaminant Alkali metal Compre ssi vettens~h

El Cu K 28.1E2 P b K 33.7FI Cu Na 43.8GI Cu K 51.4HI Cu K 4.5142 Pb K 7.3H3 Pb Na 18. ![-[4 Cu Na 16.5


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Use of geopolymedcmaterials to im mob ilise ox ic metals: part IIT A B L E 5 B E T s u r f a c e a r e a s f o r d i f f e r e n t m a t r i c e s ( m 2 1 g )

79

Ma tr ix Co nta m ina nt Alka l i m eta l Spec i f i c surfa ce a reaE1 Cu K 12.1E2 Pb K 16.7F1 Cu Na 8.8G1 Cu K 16.4H1 Cu K 9.3H2 Pb K 12.2H3 Pb Na 7.8H4 Cu Na 4.3

R e f e r r i n g t o T a b l e 2 i t c a n b e s e e n t h a t t h e o n l y d i f fe r e n c e b e t w e e n G 1 a n d E 1 i s th e u s e o f c a l ci n e dk a o l i n i t e in t h e c a s e o f E l . T h i s s e e m s t o a d v e r s e ly a f f e c t t h e c o m p r e s s i v e s t re n g t h o f E 1 c o m p a r e d w i t htha t o f G1 . Ac c or d ing to Da v idov i t s [ 8 ] t he c a l c in ing o f ka o l in i t e t r a ns f o r m s the oc t a he dr a l ly c o- or d ina t e dA I l a y e r s i n t o t h e m o r e r e a c t i v e t e t r a h e d r a l f o r m c r e a t i n g m e t a k a o l i n i t e a n d i n c r e a s i n g g e o p o l y m e rr e a c t iv i t y . E 1 w o u l d t h e r e f o r e b e e x p e c t e d t o h a v e a h i g h e r c o m p r e s s i v e s t re n g t h t h a n t h e c o r r e s p o n d i n gm a t r i x m a n u f a c t u r e d w i t h l e s s r e a c t i v e k a o l i n i t e . T h i s r e s u l t i m p l i e s t h a t t h e c o n c e p t o f g e o p o l y m e rs y n t h e s i s d o e s n o t e n t i r e l y d e p e n d o n d i s s o l u ti o n a n d m i g r a ti o n o f io n s d i s s o l v e d f r o m m i n e r a l s u r f a c e sb e c a u s e A 1 i o n s w o u l d f in d i t m u c h e a s i e r to d i s s o l v e f r o m m e t a k a o l in i t e t h an f r o m u n c a l c i n e d k a o l in i t e.I n t he se r e su l t s , ho we ve r , t h i s e f f e c t is no t r e f l e c t e d i n a n i nc r e a se d c o m p r e ss ive s t r e ng th a n d in f a c t r e su l t sin a we a ke r s t r uc tu r e . I f i t i s a s sum e d tha t t he r e i s a re a c t ion t a k ing p l a c e on the su r f a c e s o f i nd iv idua lpa r t i c l e s a nd tha t t he l a ye r s t r uc tu r e o f t he unc a l c ine d ka o l in i t e r e m a ins i n t a c t whi l e p a r t i c l e su r f a c e s b indto t he " b u lk " ge op o ly m e r pha se , t he se r e su l t s c a n be e xp la ine d . S ign i f i c a n t t o no t e i s t he f a c t t ha t t hespe c i f i c su r f a c e a r e a o f t he s t r onge r m a t r ix i s a ga in l a r ge r, im ply in g tha t t he t he r m a l p r oc e ss ing o f theka o l in i t e r e su l t s i n a t o t a l l y d i f f e r e n t f ina l s tr uc tu r e, wh ic h sugge s t s a c om bina t ion o f d i s so lu t ion- m igr a t ion-po lym e r i sa t i on a s we l l a s su r f a c e - so l id s t a t e r e a c t ions t a k ing p l a c e .I n t h e c a se o f F 1 a n d G 1 t h e e x a c t s a m e m o l a r a m o u n t s o f r e s p e c t iv e l y N a O H a n d K O H w e r e u s e d a n dr e su l t e d i n GI ha v ing a h ighe r c om p r e ss ive s t r e ng th a l t hough i t s spe c i f i c su r f a c e a r e a wa s sm a l l e r t ha n tha to f F 1 . T h e p r o p o s e d e x p l a n a t i o n f o r t h e se c o n t r a d i c to r y o b s e r v at i o n s is t h a t N a a n d K f o r m p a r t o f t h e f i n als t r uc tu r e , e f f e c t i ve ly c r e a t ing two d i f f e r e n t ge op o lym e r s . T h i s ob se r va t ion i s a lso i n a c c or da nc e w i th e x i s t i ngk n o w l e d g e o f z e o l i te c h e m i s t r y [ 9 ].C o m p a r i n g t h e c o m p r e s s i v e s t r e n g t h s a c h i e v e d f o r t h o s e s a m p l e s m a n u f a c t u r e d f r o m t h e S A S O L f l y a s h( T a b le 2 ) a nd those f r om the T a r ong f ly a sh ( T a b le 3 ) i t i s e v ide n t t ha t t he f i r s t g r oup e xh ib i t s ge ne r a l l ym u c h h i g h e r c o m p r e s s i v e s t r en g t h s a n d t h i s c a n b e a t tr ib u t e d to a n u m b e r o f f a c to r s : ( a) t h e h i g h e r C a Oc o n t e n t [ 1 0 ] o f t h e S A S O L f ly a s h ( b ) a l o w e r w a t e r t o f ly a s h ra t io u s e d i n t h e s a m p l e s m a d e f r o m t h eSA SO L f ly a sh ( c ) d i f f e r e n t a lka li m e ta l c on te n t o f the two f ly a she s ( d ) d i f f e r e n t A1 a nd S i c on te n t a nd( e ) d i f f e r e n t so lub i l i t ie s o f t he AI a nd S i p r e c ur sors . T he inc r e a se d c a r bon c on te n t o f t he SA SO L f ly a shc ou ld be r e spons ib l e f o r a de c r e a se i n s t r e ng th a s we l l a s i nc r e a se d por os i t y a l t hough i t s e e m s to be m or et h a n c o m p e n s a t e d f o r b y t h e p r e s e n c e o f C a a n d t h e f a c t th a t l es s w a t e r w a s u s e d i n t h e i n it ia l m i x d e s i g n( T a b le s 2 a nd 3 ) .X - r a y d i f f r a c ti o n ( X R D ) a n d e l e ct r o n m i c r o s c o p yAs m e nt io ne d e a r l i e r [1 ] t he s tudy o f ge opo lym e r s us ing X- r a y d i f f r a c t i on is m a de d i f f i c u l t by t he f a c t t ha ta la r ge pa r t o f the s t r uc tu r e i s a m o r pho us t o x - r a ys . Com pa r ing F igu r e s 1 a nd 2 w i th F igur e s 3 a nd 4 showst h e r e l a t i v e l y l a r g e a m o r p h o u s c o n t e n t b e t w e e n 2 0 a n d 4 0 d e g r e e s 2 0 . T h i s i s m u c h m o r e p r o n o u n c e d i nt h e c a s e o f E 1 a n d E 2 t h a n i n F 1 a n d G 1 , m a i n l y b e c a u s e o f a n i n c r ea s e d a m o r p h o u s c o n t r i b u t io n b yu n r e a c t e d m e t a k a o l i n i t e u s e d i n t h e s y n t h e s i s o f E 1 a n d E 2 . T h e a m o u n t o f c r y s ta l l in i t y p re s e n t i s c a u s e dby qua r t z a nd m ul l i t e pha se s p r e se n t i n t he f l y a sh . I t c a n be se e n , howe ve r , t ha t a c e r t a in a m or phousc on te n t i s p r e se n t i n a l l o f t he sa m ple s a nd th i s wa s f u r the r i nve s t i ga t e d by e l e c t r on d i f f ra c t i on . As f a r a s


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8 0 J . G . S . v a n J a a r s v e l d e t a l .

E 1 a n d E 2 a r e c o n c e r n e d t h e d i f f e r en t c o n t a m i n a n t m e t a l i n c lu d e d i n e a c h s t r u c tu r e d i d n o t s e e m t o m a k ea n y d i f f e r e n c e t o t h e c r y s t a l l i n e p a r t o f t h e s p e c t r a a n d i t i s t h e r e f o r e a s s u me d t h a t t h e me t a l f i n d s i t s e l fb o n d e d i n t o t h e a m o r p h o u s p a r t o f t h e ma t r i x . Fu r t h e r p r o o f o f t h i s i s s u p p l ie d b y t h e e l e c t r o n d i f f r a c t i o ns t u d i e s a s w i l l b e d i s c u s s e d b e l o w .

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7/17

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5 0 00

Use of geopolymericmaterials o immobilise oxic metals: part II

I I I I ! ! ! I I0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0

D e g r e e s ( 2 -T h e t a )Fig.4 X-ray diffraction spectrum of matrix G1.

81

Results from the electron diffraction experiments are qualitatively summarised in Tables 6 to 8 for F1, G1and E1 respectively. In each case the structure, relative abundance and constituent elements of each phaseare indicated. In most cases it is possible to quantify most of these phases in terms of d-spacings and semi-quantitative compositional information, although such a discussion will form part of a different study andfalls outside the scope of the present paper. The electron diffraction study concentrated on newly formedphases and with reference to Figure 5 this can be explained by noting the relatively large unreacted fly ashparticles surrounded by newly formed geopolymer phase. Most diffractograms were recorded avoidingobvious unreacted fly ash, kaolinite and metakaolinite particles. In every case the calculated d-spacingsproved whether a phase was new or belonging to unreacted components of the initial mix, all of whose d-spacings are well documented in the literature. Each phase presented in Tables 6 to 8 therefore constitutesa newly formed structure. Matrix F1 (Table 6) consisted of two main phases and a number of less-abundantphases. Although the two main phases were both amorphous and consisted of essentially the same elements,they were in fact different, containing different ratios of Si and A1. It is also significant to note that the mostabundant crystalline phase does not contain any of the added Cu and in fact most of the Cu is containedin the amorphous phases. The presence of Ca in each of the amorphous phases suggests that Ca could befulfilling a charge-balancing role together with K and Na. Although F1 was synthesised with NaOH theamorphous phases almost exclusively contain K as well, suggesting that K is favoured in a charge-balancingenvironment to Na and this could explain why matrices containing primarily K seem to have highercompressive strengths compared with those synthesised with primarily NaOH. In the case of G1 (Table 7)and E1 (Table 8) most new phases seem to be amorphous, especially in the case of El, where no semi-amorphous or micro-crystallinity was detected. In each case the matrices were synthesised using KOH andin each case the added heavy metal appeared in the amorphous phase. The phases described here also differfrom those in the traditional cement field through their fairly high AI content, because traditional cementhydration products usually consist of phases containing either Si or A1. The reason for this can be ascribedto the fact that in most geopolymer mixes an abundance of alkali-metal ions are present which enables theA1 to substitute Si without losing the electronic neutrality of the structure.

TABLE 6 Qualitative electron diffraction results for F1Structure Abundance CompositionAmorphous High A1, Si, K, Ca, CuAmorphous High AI, Si, K, Ca, CuCrystalline Medium Al, Si, Na, K, Ca, FeAmorphous Medium Al, CuAmorphous Low Al, Si, Na, K, CaAmorphous Low Al, Si, Na, K, Ca, Cu, FePolycrystallinv Low Al, Si, Na, K, Ca, CuSemi-Crystalline Low Al, Si, Cu


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82 J. G. S. van Jaarsveld e t a l .T A B L E 7 Qualitative e l e c t r o n d i f f r a c t i o n f o r G1

Structure Abundance Com positionAmorphous HighSem i-amorphous to HighmicrocrystallineAmorphous Medium

A1, Si, K , Ca, CuA1, Si, K , Ca, CuAI, Si, Na, K, Ca, Fe, Ti

T A B L E 8 Q u a l i t a t i v e e l e c t r o n d i f f r a c t i o n f o r E 1

Structure Abu ndance C om positionAm orphous High AI, Si, Na, K, Ca, Cu, TiAm orphous High Al, Si, K, Na, Ca, CuAm orphous M edium A1, Si, K, Ca, C u

Fig.5 TEM micrograph of matrix G1.The micrograph in Figure 6 shows what was typically found for matrices E1 and E2 where the grinding ofthe sample during preparation for electron microscopy resulted in the amorphous phase being dislodged fromthe fly ash particles. This is not the case for matrix G1 in Figure 5 where the amorphous phase seems quitesecurely bonded to the surface of the fly ash particles, even after sample grinding, resulting in a structurewith a much higher compressive strength.I n f r a r e d ( I R ) a n d n u c l e a r m a g n e t i c r e s o n a n c e (NMR)In order to gain a better structural understanding, infrared analyses were conducted on El, E2, F1 and G1and NMR spectroscopy on El, F1, F2 and G1. The main feature of all IR spectra in Figures 7 to 10 is thecentral peak between 1010 and 1040 cm -~ that is attributed to the Si- O- Si or A1-O-Si asymmetric


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Use of geopolymericmaterials to immobilise toxic metals: part II 83

Fig.6 TEM micrograph of matrix El.stretching mode [11]. In the case o f F1 and G1 this peak can be found at exactly 1031 cm -~ and it isreasonable to assume that the presence of K or Na would not affect its locality. On the other hand in thecase of E1 and E2 this peak is found at 1025 and 1012 cm -~ respectively, indicating that the contaminantmetal does affect the structure and suggesting that it might be part of the structure and not just physicallyencapsulated. The peak found at 543 cm -~ in both Figure 9 and 10 has previously been assigned to bendingof S i- O- AI where the AI is in octahedral co-ordination [4] confirming the fact that some kaolinite particlesremain unreacted. E1 and E2 exhibit a peak each at 559 cm -1 that has been assigned to be originating f romdouble-ring structures formed by Si and A1 tetrahedra [11]. In all four spectra a small broad peak can befound between 700 and 800 cm-~ although this is more pronounced in the case of E1 and E2 than for F1and G1. The reason is found in the fact that this region is associated with bonds containing tetrahedrallyco-ordinated A1 and specifically Si--O-AI. Again this agrees with the earlier conclusions that structuresmanufactured from metakaolinite will contain relatively more four co-ordinated A1, not only because ofunreacted metakaolinite but also because of easier dissolution of A1 before and during synthesis. This alsoindicates that in the case of F1 and G1 a degree of dissolution takes place either during or after synthesisas this is the only way that will allow for tetrahedrally co-ordinated A1 to become part of the structure.

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84 J.G .S . van Jaarsvelde t a l .1.5

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1 ! ! I i o500 1000 1500 2000 2500 3000

W a v e l e n g t h ( m - 1 )F i g . 1 0 I n f r a re d s p e c t r u m o f m a t r i x G 1 .

Co m p a r ing F ig ur e s 11 to 14 a nd F igur e s 15 to 18 f o r m a t r i c e s E l , F1 , F2 a nd G1 i t i s e v ide n t tha t bo ththe 29S i a nd the 27A1 M AS NM R spe c t r a a r e v e r y s im i l a r f o r F1 , F2 a nd G1. T he 29Si a nd 27A1 spe c t r a f o rE 1 d i f f e r f ro m t h e s e , m a i n l y b e c a u s e o f t h e r e l a t i v e ly h i g h e r c o n t e n t o f t e tr a h e d r al l y c o - o r d i n a te d A I . F i g u r e15 sugge s t s t ha t E 1 c on ta ins c ons ide r a b ly m o r e t e tr a he dr a i AI, de no te d by the 58 .5 pp m sh i ft , tha n s ix c o-or d ina t e d AI , i nd i c a t e d by the 0 .1 ppm sh i f t [ 12] . T h i s i s i n a c c or da nc e w i th wha t ha s p r e v ious ly be e ns u g g e s t e d . T h e s p e c t ra o f F 1 , F 2 a n d G 1 e x h i b i t t h e s a m e p e a k s h i ft s o f 5 8 .5 a n d 2 . 2 p p m i n d i ca t in g am ix tu r e o f 4 a nd 6 c o- or d in a t e d A1, a ga in c onf i r m ing a nd suppor t i ng the e a r l i e r f i nd ings f r om the T E M a ndI R a n a lyse s . I t is wo r th no t ing tha t d i f f e r e n t a lka li a nd he a vy m e ta l i ons do no t se e m to i n f lue nc e e i the r t he29S i o r 27A1 spe c t r a . T he 29S i spe c t r a f o r E 1 ( F igur e 11) c on ta in tw o m a in sh i f ts i . e . a t - 9 0 a nd - 10 4 .2 ppm .T h e l a t t e r ha s b e e n a t t r i bu t e d to S i a tom s c onn e c t e d in f our d i r e c ti ons v i a oxyg e n l i nka ge s t o 3 S i a nd 1A1 a tom or t o on ly 4 S i a tom s , t he so c a l l e d S i ( 1AI ) o r S i ( 1A1) s i t e s [ 13] . T he sh i f t a t - 90 ppm i s a ga in


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-90 ppm

- .

a ssoc i a t e d w i th S i ( 3A1) s i t e s a nd i t i s a ppa r e n t t ha t no t m a ny S i ( 4A1) s i t e s ( - 80 to - 90 ppm ) a r e p r e se n ti n t h e s p e c t r a o f E l . T h i s i s , h o w e v e r , n o t t h e c a s e w i t h th e 2 9S i s p e c t ra o f F 1 , F 2 a n d G 1 w h e r e t h e t w om a in sh i f t s a r e - 87 .3 a nd - 91 .9 ppm , i nd i c a t ing a n a bun da nc e o f S i ( 4AI ) a nd S i (3A1) s it e s . I n t e rm s o fs t r uc tu r a l p r ope r t i e s t h i s c ou ld e xp la in why the c om pr e ss ive s t r e ng ths a c h i e ve d w i th m a t r i c e s F1 , F2 a ndG 1 w e r e h i g h e r t h a n t h a t o f E 1 a n d E 2 . T h e c l as s i ca l m o d e l o f a g e o p o l y m e r a s p r o p o s e d b y D a v i d o v i t s[ 8 ] t he or e t i c a l l y c on ta ins m a in ly S i (4A1) s i te s a nd a s suc h F1 , F2 a nd G1 c ou ld be r e ga r de d a s r e se m bl ingt h is m o d e l m o r e c l o s e l y t h a n E 1 a n d E 2 . T h e M A S N M R i n v e s ti g a ti o n p re s e n t e d h e r e i s, h o w e v e r , v e r ys i m p l is t ic a n d a m o r e t h o r o u g h i n v e s t ig a t i o n o f g e o p o l y m e r s m a n u f a c t u r e d f r o m w a s t e m a t e ri a ls w i l l b ene c e ssa r y t o f u l l y qua n t i f y a l l t he s t r uc tu r a l c ha r a c t e r i s t i c s .

I I I0 - 100 -200ppmF i g . l l 2 9S i M A S N M R s p e ct ru m o f E l .

-91.9 ppm

-87.3 ppm

Use of geopo lymericmaterials to immo bilise ox ic metals: part II 85

I I I0 -I00 -200

~ m

F i g . 1 2 2 aS i M A S N M R s p e c t ru m o f F 1 .


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-91.9 ppm

-87.3 ppm

I I I0 - 1 0 0 -200

ppmF i g . 1 3 2 9 S i MAS NMR spectrum of F2.

-91.9 ppm

-87.3 ppm

86 J . G .S . van Jaarsveld e t a l .

I I I0 -100 -200

ppmFig.14 29Si MAS NMR spectrum of G1.


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Use of geopolymericmaterials to immobilise toxic metals: part II 87

58.5 ppm

I I I200 0 -200

~ mFig.15 27A1 MAS NMR spectrum of El .

2.2 ppm

58.5 pp m

I I I200 0 -200

ppmFig.16 27A1 MAS NMR spectrum of F1.


14/17

88 J. G. S. van Jaarsveld e t a l .

2.,' ppm

58.5 ppm

I I I200 0 -200

ppmFig .17 27A1MAS NMR spectrum ofF2.

2.2 ppm

58.5 ppm

I I I200 0 -200

ppmFig.18 27A1 MAS NMR spectrum of G1.


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Use of geopol ymeric materials to immobilise toxic metals: part II 89

LeachingIn a previou s s tudy [3] the potent ial of geop olym er binders for the immo bil isat ion of heavy m etals wasdisc usse d and environ m ental leaching results presented. Kinetic leaching tests we re con duc ted with samplingdone pe r iodical ly unt il equ i l ibr ium w as reached. Matr ices El , F1 and G1 contain identical amou nts of Cuand therefore leaching resul ts can be com pared on the sam e basis. Figure 19 shows the leaching curves forf ive par ticle s ize f ract ions o f H2 and for the sake of s implicity al l other leaching tes ts wil l be sum ma risedin terms o f the equ i l ibr ium values obtained. These results are presented in Tables 9 and 10.

Fig. 19

AEQ.Q.vI::ogcQoe,.o0,.Qn

109876543210

0

2 1 2 - 6 0 0 - . m ~ 6 0 0 - 1 0 0 0~ 1 0 0 0 - 1 7 0 01 7 0 0 - 2 3 6 0x 2360 - 28O0

20 0 400 600 800 1000 1200 1400 1800T i m e ( m i n )

Lea chin g curv e of H2. Lea ching in acetic ac id buffered at pH 3.3, solid/liquid ratio 1:25, 30C andmixing speed o f 200 rpm.

TABLE 9 Equilibrium concentrations achieved during leaching (ppm)M a t r i x E l e m e n t 2 1 2 / 6 0 0 ~ tm 1 7 0 0 / 2 3 6 0 ~ tm

S t i r re d R o l l e d b o t t l e S t i r re d R o l l e d b o t t l eE 1 C u 2 2 3 0 1 7 2 8E 2 P b 2 3 3 4 1 7 3 3F 1 C u 1 7 2 4 1 1 2 2G 1 C u 1 2 2 0 9 1 7

T AB L E 1 0 Equilibrium concentrations for differen t particle size fractions using stirred leachingconfiguration (ppm)

M a t r i x 2 1 2 / 6 0 0 6 0 0 1 1 0 0 0 1 0 0 0 1 1 7 0 0 1 7 0 0 1 2 3 6 0 2 3 6 0 / 2 8 0 0C o n t a m i n a n t t I.tm g m g m r tm g mH 1 Cu 26 .1 21 .2 20 .3 19 .2 18 .5H 2 Pb 9 .1 8 .9 8 .6 8 .4 8 .2H 3 Pb 14.8 13.3 11.6 9 .8 9 .2I"t4 C u 17.1 14.1 11.1 7. 5 6.3


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90 J.G .S . van Jaarsveld t a l .I t i s s i g n i f i c a n t t o n o t e t h a t f o r E 1 a n d E 2 t h e Pb i o n s a l w a y s s e e m t o l e a c h s l i g h t l y mo r e t h a n t h e Cu ,r e g a r d l e s s o f t h e p a r t i c l e si z e a n d l e a c h i n g m e t h o d u s e d . T h i s f a c t is p r o b a b l y d u e t o t h e l a r g e r s u r f a c e a r e am e a s u r e d i n E 2 c o m p a r e d w i th E 1 a l t h o u g h c o m p a r i s o n o f F1 a n d G 1 d o e s n o t fo l l o w th e s a m e t re n d w h e r eCu l e a c h i n g f r o m G 1 i s g e n e r a l l y l e s s t h a n f r o m F1 , w i t h t h e l a t t e r h a v i n g h a l f t h e s p e c i f i c s u r f a c e a r e a .O n t h e o t h e r h a n d G 1 h a s a h i g h e r c o m p r e s s i v e s tr e n g t h a n d o n e w o u l d e x p e c t a h i g h e r a b r a s i o n r e s is t a n c et h a n i n th e c a s e o f E l , E 2 o r F 1 . T h e l e a c h i n g o f C u f r o m E l , F 1 a n d G 1 f o l l o w s t he s a m e t re n d a s t h e irr e s p e c t i v e c o m p r e s s i v e s t r e n g t h s a n d t h is s u g g e s t s t h a t a b r a s i o n p l a y s a r o le i n li b e r a t i n g s o m e o f th e me t a ld u r i n g l e a c h i n g . A n i n c r e a s e i n e q u i l i b r i u m l e a c h i n g v a l u e s w i t h d e c r e a s i n g p a r t i c l e s i z e i s a f e a t u r e t h a ti s f o u n d f o r a l l ma t r i c e s a n d t h i s f u r t h e r s u p p o r t s t h e a b o v e s t a t e me n t t h a t s o me l i b e r a t i o n o c c u r s f o r mp a r t i c l e s u r f a c e s , w h e t h e r t h r o u g h m e c h a n i c a l o r c h e m i c a l m e a n s . I t w a s s h o w n p r e v i o u s l y [ 3 ] , h o w e v e r ,t h a t a c e r t a i n a mo u n t o f le a c h i n g a l s o o c c u r s a s a re s u l t o f p o r e d i f f u s i o n a n d t h i s a s p e c t n e e d s t o b ei n v e s t i g a t e d f u r t h e r . T h e d i f f e r e n c e s i n le a c h i n g o f Cu f r o m F1 a n d G 1 a s w e l l a s d i f f e r i n g s u r f a c e a r e a sa n d s t r e n g t h s a g a i n p o i n t t o t h e f a c t t h a t t h e t y p e o f a l k a l i me t a l c a t i o n h a s a n i mp o r t a n t i n f l u e n c e o n a l la s p e c t s o f t h e f i n a l s t r u c t u r e . T h i s i s f u r t h e r s u p p o r t e d b y t h e f a c t t h a t e q u i l i b r i u m v a l u e s f o r t h e r o l l e db o t t l e e x p e r i m e n t s w e r e g e n e r a l l y h i g h e r t h a n t h o s e f o u n d f o r th e s t ir r e d t y p e me t h o d . T h i s is mo s t p r o b a b l yd u e t o t h e l o n g e r l e a c h i n g t i m e ( 6 0 h o u r s ) a s w e l l a s t h e f a c t th a t a b r a s i o n b e t w e e n p a r t i c l e s a n d t h e s i d eo f t h e v e s s e l i s m u c h m o r e s e v e r e t h a n i n t h e c a s e o f t h e l a tt e r m e t h o d l e a d i n g t o h i g h e r d e g r e e o f p h y s i c a lb r e a k d o w n . V i s u a l o b s e r v a t i o n o f t h e s o l id r e s i d u e f r o m t h e l ea c h i n g e x p e r i m e n t a l s o c o n f i r m e d t h is .T a b l e 1 0 s h o w s t h a t i n c r e a s e d l e a c h i n g f r o m s ma l l e r p a r t i c l e s iz e s h o l d s f o r t h e r a n g e o f ma t r i c e s a n dp a r t i c l e s i z e s i n v e s t i g a t e d a l t h o u g h c e r t a i n t r e n d s a p p e a r t o b e d i f f e r e n t f r o m t h o s e o b t a i n e d f o r E l , E 2 , F Ia n d G 1 . A s w a s p r e v i o u s l y r e p o r t e d [ 3 ] t h e i m m o b i l i s a t io n o f P b i n m a t r i c e s n o t c o n ta i n i n g m e t a k a o l i n i t es e e ms t o b e mo r e e f f i c i e n t t h a n f o r Cu a n d t h i s c o u l d b e i n p a r t a t t r i b u t e d t o d i f f e r e n c e s i n i o n i c r a d i u s o rc h e mi c a l i n t e r a c t i o n w i t h t h e o t h e r ma t r i x f o r mi n g c o mp o n e n t s d u r i n g s y n t h e s i s r e s u l t i n g i n s l i g h t l yd i f f e r e n t r o l e s p l a y e d b y Cu a n d Pb i n t h e f i n a l p r o d u c t . I t w a s me n t i o n e d e a r l i e r t h a t Cu i s p r e s e n t i n mo s to f t h e n e w l y f o r m e d a m o r p h o u s p h a s e s . U n f o r t u n a t e l y t hi s c o u ld n o t b e c o n f i r m e d f o r l e a d d u e t oe q u i p m e n t l i m i t a ti o n s. O n e c o u l d s a f e ly a s s u m e , h o w e v e r t h a t a n y m a t r i x w i ll h a v e a l i m i te d c a p a c i t y f o rt h e a m o u n t o f h e a v y me t a l i t s s t r u c t u r e c a n t o l e r a te b e f o r e s t r u c tu r a l f a i l u r e w i ll c a u s e i n c r e a s e d l e a c h i n go f t h a t m e t a l . T h i s p o i n t i s i ll u st r at e d b y c o m p a r i n g t h e d i f f e r e n c e s in l e a c h i n g o f C u a n d P b f r o m m a t r i c e sH I , H 2 , H 3 a n d H 4 . A l t h o u g h H 1 a n d H 2 w e r e s y n t h e s i s e d w i t h K O H , a n d H 3 a n d H 4 w i t h N a O H , t h el a t t e r g r o u p a l s o c o n t a i n s d o u b l e t h e a m o u n t o f h e a v y me t a l i n t r o d u c e d i n t o t h e f ir s t. A t s m a l l e r p a r t ic l es i z e s H 3 r e l e a s e s l e s s Pb t h a n t h e Cu r e l e a s e d b y H 4 a l t h o u g h t h i s t r e n d i s r e v e r s e d w h e n t h e l a r g e r p a r t i c l es i z e f r a c t i o n s a r e c o n s i d e r e d . T h i s t r e n d i s n o t p r e s e n t i n t h e c a s e o f H 1 a n d H 2 w h e r e t h e Cu a l w a y sl e a c h e s m o r e t h a n t h e Pb . Re f e r r i n g t o T a b l e 5 th e s p e c i f i c s u r f a c e a r e a o f Cu c o n t a i n i n g m a t r i c e s H 1 a n dH 4 i s s m a l l e r t h a n t h a t o f t h e i r Pb - c o n t a i n i n g c o u n t e r p a r t s a l t h o u g h t h e l a t te r s e e m t o g e n e r a l l y h a v e ah i g h e r i m m o b i l i s a t io n e f f ic i e n c y .

C O N C L U S I O N ST h e s t u d y a n d s t r u c t u r a l u n d e r s t a n d i n g o f g e o p o l y m e r s d e r i v e d f r o m w a s t e m a t e r i a l s w i l l b e c o m e m o r ee s s e n t i a l a s t h e n u m b e r o f c o m m e r c i a l a p p l i c a t io n s o f t h e s e ma t e r i a l s in c r e a s e s . F r o m t h i s s t u d y i t i s n o to n l y a p p a r e n t t h a t a mu l t i t u d e o f p o s s i b l e a p p l i c a t i o n s e x i s t b u t a l s o th a t t h is t e c h n o l o g y c a n b e a p p l i e d t ow a s t e s o u r c e s f r o m d i f f e r e n t p a r t s o f t h e w o r l d . F r o m a s t ru c t u r a l p o i n t o f v i e w i t is p o s s i b l e t o ma n u f a c t u r em a t e r i a l s w i t h f a i rl y h i g h c o m p r e s s i v e s t r e ng t h s a n d t h e c a p a c i t y t o a l s o i m m o b i l i s e h e a v y m e t a ls . I t w a sa l s o s h o w n t h a t t o ta l d i s s o l u t io n o f th e w a s t e ma t e r i a l s i s n o t n e c e s s a r y a n d t h a t th e s o l i d i f ie d w a s t e ma t e r i a lc o n s i s ts o f a n a m o r p h o u s p h a s e b o n d e d t o th e s u r f a c e s o f u n re a c t e d w a s t e p a r t ic l e s. I n t h e c a s e w h e r e as y s t e m s u c h a s th i s is u t il i se d f o r t h e i mmo b i l i s a t i o n o f h e a v y me t a l s , t h e i mm o b i l i s a t i o n p r o c e e d s t h r o u g ha c o m b i n a t i o n o f p h y s i c a l e n c a p s u l a ti o n a n d c h e m i c a l b o n d i n g i n t o t h e a m o r p h o u s p h a s e o f t h e m a t r ix . I td o e s n o t s e e m a s i f t h e h e a v y me t a l in f l u e n c e s t h e b a s i c t e t r a h e d r a l b u i l d in g b l o c k s o f t h e s tr u c t u r e a l t h o u g hi t i n f l u e n c e s t h e s t r u c t u r e i n a p h y s i c a l ma n n e r s u c h a s to a l t e r t h e c o m p r e s s i v e s t r e n g t h a n d s p e c i f i c s u r f a c ea r e a . F i n a l l y t h e p r e s e n c e o f S i ( 4 A I ) s i t e s is p r e f e r r e d i f a s tr o n g d u r a b l e p r o d u c t i s d e s i r e d a l t h o u g h t h i ss i tu a t io n c a n o n l y b e a c h i e v e d w h e r e s u b s t a n ti a l a m o u n t s o f c h a r g e b a l a n c i n g i o n s a r e a v a i l a bl e . K a n d N au s u a l l y f u l f i l t h i s r o l e a l t h o u g h g e o p o l y m e r s m a n u f a c t u r e d f r o m f l y a s h c o n t a i n i n g s o m e C a c o m p o u n d sh a v e h i g h e r c o mp r e s s i v e s t r e n g t h s t h a n t h o s e w i t h o u t . I t i s f i n a l l y w o r t h n o t i n g t h a t b o t h t h e p h y s i c a l a n d


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Use o f geopolymericmaterials to immobilisc ox ic metals: part I1 91chem ical proper t ies of the f inal product will be interdependent on not only the wa ste mater ials used insynthes is but also the cur ing condi t ions as wel l as ef fects int roduced by the presence of any heavy metalsimm obil ised in the s t ructure.

.

.

3.

.

.

6.7..

.

10 .11 .12.13.

R E F E R E N C E S

Va n Jaarsveld, J .G.S., Va n Deventer, J .S.J. and Lorenzen, L ., The potential use of geo poly m ericmaterials to immobilise toxic metals: Part I . Theory and Applications, Miner a l s Eng ineer ing , 10(7), 1997, pp. 659--669.Da vido vits , J . , Person al Comm unications, 1996.Van Jaarsveld, J .G.S., Van Deventer, J .S.J. and Lorenzen, L., Factors affecting the immobilisationof metals in geop olym erised fly ash, Meta l lu r g ica l and Mater ia l s T r ans ac t ions B , Vol. 29, 1998,pp . 283-291 .M adan i, A ., Aznar, A., Sanz, J . and Serratosa, J .M., 29Si and 27A1 NM R stu dy o f zeolite form ationfrom alkali-leach ed kaolinites. Influence o f thermal preactivation, J . Phys ica l Chem is t r y , Vol. 94,1990, pp. 760-765.Australian Standard, AS 1012.9, M ethods fo r t e s ting concr ete, 1986.Appendix 1 to Pan 268 , U .S . Feder a l R eg i s t e r, Vol. 51, No. 216, November 7, 1986Popo vics , S., Co ncre te materials: Properties , specification a nd testing , 2 nd ed., N oy es Pub lications,We s twood, Ne w Jer sey , 1992 , 661p .Davido vi ts , J. , Geopolym ers : Inorganic polym eric new materials , J . Mater ia l s Educa t ion , Vol. 16,1994, pp. 91-138.Barrer, R.M., H ydr o ther m a l chem is t r y o f z eo l i t e s , Academic Press, 1982, 360p.Wang, S.D. and Scrivener, K.L., Hydration products of alkali activated slag cement, C e m e n t a n dConcr e te Res ear ch , Vol. 25 (3) , 1995, pp. 561-571.Flanigan, E.M., Khatami, H. and Szymanski, H.A., Mo lecula r sieve zeolites, Adva nces in Chem is t r ySer ie s , Vo l. 101, Am erican Chemical So ciety, Washington, D .C., 1971, pp. 20 1-2 29 .Lipm aa, E., S am oson, A . and Magi, M ., High-resolution 27A1 NM R o f aluminosilicates, J .Am er ican Chem ica l Soc ie ty , Vol. 1 08, 1986, pp. 1 730-1735.Lipm aa, E., Sam oson , A., Magi, M ., Tarmak, M . and Engelhardt, G ., Investigation of the structureof ze ol i tes by sol id-state high resolut ion 29Si NM R spectroscopy, J . Am er ican Chem ica l Soc ie ty ,Vol. 103, 1981, pp. 4992--4996.

C o r r e s p o n d e n c e o n p a p er s p u b l is h e d i n M i n e r a l s E n g i n e e r i n g i s i n v i t e d , p r e f e r a b l y b y e -m a i l t o m i n .e n g @ n e t m a t t e r s . c o . u k , o r b y F a x t o + 4 4 - ( 0 ) 1 3 2 6 - 3 1 8 3 5 2

The Potential Use of Geopolymeric Materials to Immobilise Part 2

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