applied clay mineralogy today and tommorow

7/28/2019 Applied Clay Mineralogy Today and Tommorow

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Clay Minerals (1999) 34, 39M.9

A p p l i e d c l a y m i n e r a l o g y t o d a y a n dt o m o r r o wH . H . M U R R A Y

Departme nt o f Geological Sciences, Indiana U niversity, Bloomington, IN 474 05, USA(Received 11 Ap r i l 1997," rev i sed 27 October 1997)

A B S T R A C T: The c lay m inera l s kao l in , smect i t e and pa lygorsk i t e -sep io li t e a re am ong the w or ld ' smo s t impor tan t and usefu l indus t r i a l minera l s . Clay m inera l s a re im por tan t in a num ber o f geo log ica lappl icat ions such as s tratigraphic correlations, indicators of enviro nm ents of deposi t ion andtempera tu re fo r genera t ion o f hydrocarbons . In agr i cu l tu re , the c lay m inera l s a re a ma jor com ponen tof so i ls and d e termina n t o f so i l p ropert ies . The c lay m inera l s a re impo r tan t in cons t ruc t ion wherethey are a ma jor cons t i tuen t in b r i ck and t i le . The phy s ica l and chem ical p roper ti es o f the c laym inera l s de termine the i r u t i l i za t ion in the p rocess indus t r ies .W h a t ab o u t t o mo r r o w ? P r o ces s in g t e ch n i q u es w i ll b e i mp r o v ed an d n ew eq u i p men t w i l l b eavai l ab le so tha t im proved c lay m inera l p roduct s wi l l be a vai l ab le . P i ll a red c lays and nanoco mp os i t eswi l l becom e impo r tan t . Fur ther developm ents in o rganoclay techno logy an d sur face t rea tments wi l lp rov ide ne w usages fo r these spec ia l c lays. Tom orrow w i l l see fu r ther g rowth and u t i l i za t ion o f thec lay minera l s .

C l a y m i n e r a l s a re s o m e o f t h e m o s t i m p o r t a n t , i fn o t t h e m o s t i m p o r t a n t , o f o u r i n d u s t r i a l m i n e r a l s .M i l l io n s o f t o n s a r e u t i l iz e d a n n u a l l y i n a l a rg ev a r i e t y o f a p p l i c a t i o n s . T h e s e a p p l i c a t i o n s i n c l u d eu s es i n g eo l o g y , t h e p r o ces s i n d u s t r i e s , ag r i cu l t u r e ,e n v i r o n m e n t a l r e m e d i a t i o n a n d c o n s t r u c t i o n . T h i sp a p e r f o c u s e s o n t h e m a j o r a p p l i c a t i o n s o f th e c l a ym i n e r a l s to d a y a n d l o o k s i n t o th e f u t u r e g r o w t h a n dap p l i ca t i o n s o f c e r t a i n s p ec i f i c c l ay mi n e r a l s .

W h y a r e c e r t a i n c l a y m i n e r a l s u s e d i n s p e c i f i ca p p l i c a t i o n s ? T h e r e a s o n i s t h a t t h e p h y s i c a l a n dc h e m i c a l p r o p e r t ie s o f a p a r t i c u l a r c l a y m i n e r a l a r ed e p e n d e n t o n i t s s t r u c t u r e a n d c o m p o s i t i o n . T h es t ru c t u r e a n d c o m p o s i t i o n o f k a o l i n s , s m e c t it e s, a n dp a l y g o r s k i t e an d s ep i o l i t e a r e v e r y d i f f e r en t ev ent h o u g h t h ey each h av e o c t ah ed r a l an d t e t r ah ed r a ls h ee t s a s t h e i r b a s i c b u i l d i n g b l o ck s . H o w e v e r , t h ea r r a n g e m e n t a n d c o m p o s i t i o n o f th e s e o c t a h e d r a la n d t e t r a h e d r a l s h e e t s a c c o u n t f o r m a j o r a n d m i n o rd i f f e r e n c e s i n t h e p h y s i c a l a n d c h e m i c a l p r o p e r t i e so f k ao l i n , s mec t i t e s an d p a l y g o r s k i t e .T a b l e 1 s h o w s s o m e o f t h e p r o p e r ti e s o f k a o l in s ,s m e c t i t e s a n d p a l y g o r s k i t e s t h a t a c c o u n t f o r m a n yo f t h e i r a p p l i c a t io n s

T h e i m p o r t a n t c h a r a c t e r i s t i c s r e l a t i n g t o t h eap p l i ca t i o n s o f c l ay mi n e r a l s a r e p a r t i c l e s i z e an ds h ap e , s u r f ace ch emi s t r y , s u r f ace a r ea , s u r f acech a r g e , an d o t h e r p r o p e r t i e s s p ec i f i c t o p a r t i cu l a rap p l i ca t i o n s , i n c l u d i n g v i s co s i t y , co l o u r , p l a s t i c it y ,g r e e n , d r y a n d f i r e d s t r e n g t h , a b s o r p t i o n a n dad s o r p t i o n , ab r a s i o n an d p H . I n a l l ap p l i ca t i o n s ,t h e c l a y m i n e r a l s p e r f o r m a f u n c t i o n a n d a r e n o tj u s t i n e r t c o m p o n e n t s o f th e s y s t e m . T h e r e a r es e v e r a l a r t i c l e s a n d b o o k s t h a t d i s c u s s c l a y m i n e r a lap p l i ca t i o n s an d , a l t h o u g h s o me a r e h i s t o r i ca l , t h eya r e e s s e n t i a l t o o u r p r e s e n t u n d e r s t a n d i n g o f h o wa n d w h y t h e c l a y m i n e r a l s h a v e s u c h a n e x t e n s i v ei n d u s t r ia l u t i li z a t io n . S o m e o f t h e se a r e A n o n y m o u s( 1 9 5 5 ) , P a s k & T u r n e r ( 1 9 5 5 ) , M u r r a y & L y o n s( 1 9 5 6 ) , G r i m ( 1 9 6 2 ) , C l e m & D o e h l e r ( 1 9 6 3 ) ,H a d e n ( 1 9 6 3 ) , J o r d a n ( 1 9 6 3 ) , K o n t a ( 1 9 9 5 ) , M u r r a y( 1 9 6 3 , 1 9 8 4 , 1 9 9 1 , 1 9 8 6 ) , N a h i n ( 1 9 6 3 ) , Sm o o t( 1 9 6 3 ) , O v c h a r e n k o et a l . ( 1 9 6 4 ) , B u n d y et a l .( 1 9 6 5 ) , S i d d i q u i ( 1 9 6 8 ) , G r i m s h a w ( 1 9 7 1 ) , G r i m &G u v e n ( 1 9 7 8 ), R o b e r t s o n ( 1 9 8 6 ), G a l f i n ( 1 9 8 7 ,1 9 9 6) , E l z e a & M u r r a y ( 1 9 9 4 ) , H e i v i l i n &M u r r a y ( 1 9 9 4 ) , P i c k e r i n g & M u r r a y ( 1 9 9 4 ) , a n dK e i t h & M u r r a y ( 1 9 9 4 ) .

9 199 9 The M ineralogical Society


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4 0 H . H . M u r r a yTABLE 1 . Som e p roper t ies o f c lay m inera l s tha t ca n be re la ted to the i r ap p l ica t ions .

K ao l i n S m ec t i t e P a l y g o r s k i te1:1 layerW h i t e o r n ea r w h i t eLit t le subst i tut ionM i n i m a l l ay e r ch a rg eL o w b as e ex ch an g e cap ac i t yP s eu d o -h ex ag o n a l f l ak esL o w s u r f ace a r eaV ery l o w ab s o rp t i o n cap ac i t yL o w v i s co s i t y

2:1 layerTan , o l ive g reen , whi teOctahedral and tetrahedralsubst i tut ionH i g h l ay e r ch a rg eH i g h B E CThin f lakes and la thsV ery h i g h s u r f ace a r eaHigh absorp t ion capaci tyV ery h i g h v i s co s i t y

2 :1 layer inver tedL i g h t t anOctahedral subst i tut ionM o d e ra t e l ay e r ch a rg eM o d e r a t e B E CE l o n g a t eH i g h s u r f ace a r eaHigh absorp t ion capaci tyH i g h v i s co s i t y

S p e c i f i c a p p l i c a t i o n s a r e d i s c u s s e d u n d e r t h eh e a d i n g s k a o l i n s , s m e c t i t e s , a n d p a l y g o r s k i t e a n ds e p i o l i t e . T h e l a s t s e c t i o n c o v e r s g r o w t h o fa p p l i c a t io n s f o r t o m o r r o w .

K A O L I N SK a o l i n s a r e r o c k s t h a t a r e c o m p r i s e d l a r g e l y o f o n eo f th e k a o l i n g r o u p o f m i n e r a l s w h i c h a r e k a o l i n i te ,h a l l o y s i t e , d i c k i t e a n d n a c r i t e . T h e m o s t c o m m o nk a o l i n m i n e r a l i s k a o l i n i t e ; t h i s m i n e r a l ' s p h y s i c a la n d c h e m i c a l p r o p e r t i e s , a n d i t s a p p l i c a t i o n s a r ed i s c u s s e d i n th i s s e c t io n . T h e o t h e r m e m b e r s o f th ek a o l i n g r o u p a r e r e l a ti v e l y ra r e , a l t h o u g h s o m eo c c u r r e n c e s o f h a l l o y s it e ( M u r r a y e t a l . , 1977) ,d i c k i t e ( S u d o & S h i m o d a , 1 9 7 8 ) , a n d n a c r i t e( H a n s o n e t a l . , 1 9 8 1 ) a r e b e i n g , o r h a v e b e e n ,m i n e d . T h e t e r m ' C h i n a C l a y ' i s , a n d h a s b e e n ,u s e d a s a s y n o n y m f o r k a o l i n .

F o r m o s t i n d u s t r i a l a p p l i c a t io n s k a o l i n m u s t b er e f i n e d a n d p r o c e s s e d f r o m t h e c r u d e s t a t e t oe n h a n c e i t s w h i t e n e s s , p u r i t y a n d o t h e r i m p o r t a n tc o m m e r c i a l c h a r a c t e r i s t i c s . C o m m o n i m p u r i t i e s i nk ao l i n s a r e q u a r t z , m i ca s , i l l i t e , m o n t m o r i l l o n i t e ,g o e t h i t e , h em a t i t e , p y r i t e , an a t a s e , r u t i l e , i l m en i t ea n d t r a c e a m o u n t s o f t o u r m a l i n e , z i r c o n a n d o t h e rh e a v y m i n e r a l s, m o s t o f w h i c h c a n b e r e m o v e d b yw e t p r o c e s s i n g .

K a o l i n s a r e m o s t o f t e n f o r m e d b y t h e a l t e r a t i o no f A 1 s i l i c a t e m i n e r a l s i n a w a r m , h u m i de n v i r o n m e n t . F e l d s p a r i s t h e m o s t c o m m o n s o u r c em i n e r a l . K a o l i n s w h i c h h a v e a l t e r e d i n s i t u , e i t h e rb y w e a t h e r i n g o r b y h y d r o t h e r m a l a l t e r a t io n ,g e n e r a l l y r e t a i n t h e t e x t u re a n d f o r m o f t h e p a r e n tr o c k a n d t h e s e a r e r e f e r r e d t o a s p r i m a r y k a o l i n s .T h o s e k a o l i n s w h i c h h a v e b e e n d e p o s i t e d b y

s e d i m e n t a t i o n i n f r e s h o r b r a c k i s h w a t e r e n v i r o n -m e n t s a r e c a l l e d s e c o n d a r y . B o t h t y p e s o f k a o l i na r e m i n e d a n d u s e d c o m m e r c i a l l y .

K a o l i n o c c u r r e n c e s a r e c o m m o n a n d k n o w n o na l l t h e c o n t i n e n t s o f t h e w o r l d e x c e p t A n t a r c t i c a ,b u t c o m m e r c i a l l y v i a b l e d e p o s i ts a r e r e l a t i v e l y f e wi n n u m b e r . T h e b e s t k n o w n a n d m o s t h i g h l y u t il i z e dd e p o s i t s a r e p r i m a r y k a o l i n s i n t h e C o r n w a l l a r e a o fs o u t h w es t e rn E n g l an d (B r i s t o w , 1 9 7 7 ) , t h e s ed i -m e n t a r y k a o l i n s i n G e o r g i a a n d S o u t h C a r o l i n a i nt h e U n i t e d S t a t es ( P i c k e r i n g & M u r r a y , 1 9 9 4) a n dt h e s e d i m e n t a r y k a o l i n s f r o m t h e A m a z o n r e g i o n o fB raz i l (M u r ray , 1 9 8 1 ) .

A s m en t i o n e d i n T ab l e 1 , k ao l i n i t e i s c l a s s i f i ed a sa t w o - l ay e r c l ay , i . e . a s h ee t o f s i l i c a t e t r ah ed rac o m b i n e d t h ro u g h o c t a g o n a l h y d r o x y ls w h i c h a r es h a red w i t h an a l u m i n a o c t ah ed ra l s h ee t (F ig . 1 ).T h i s s t ru c t u re h a s l i t tl e s u b s t it u t io n o f o t h e r e l em e n t s ,b u t t h e re m ay b e s o m e F e s u b s t i t u ti n g fo r A l an ds o m e A 1 p o s s i b l y s u b s t i t u t in g fo r S i . B ec au s e o f th i sl i m i t ed s u b s t i t u t i o n i n t h e k ao l i n i t e l ay e r , t h e ch a rg eo n t h e k ao l i n i t e l ay e r i s m i n i m a l t h u s acco u n t i n g fo rt h e l o w ca t i o n ex ch an g e cap ac i t y . S o m e ch a rg eso ccu r o n t h e ed g e o f t h e k ao l i n i t e c ry s ta l d u e t ob ro k en b o n d s (G r i m , 1 9 6 2 ) . A b s o rp t i o n , w h i ch i sr e l a t ed t o s u r f ace a r ea , i s an o t h e r p ro p e r t y t h a t i si m p o r t an t i n m an y i n d u s t r i a l ap p l i ca t i o n s . K ao l i n i t eh as a r e l a t i v e l y l o w s u r f ace a r ea an d a l o w s u r f acech a rg e co m p ared t o s m ec t i t e s an d p a l y g o r s k i t e an ds ep i o l i t e , s o i t ex h i b i t s l o w ab s o rp t i o n an d ad s o rp -t i o n . E l ec t ro n m i c ro g rap h s o f k ao l i n i t e s h o w t h a t i ng en e ra l i t h a s r e l a t i v e l y s h a rp c ry s t a l l i n e m o rp h o l o g yw h i ch ex h i b i t s a p s eu d o -h ex a g o n a l s h ap e (F i g . 2 ) .K a o l i n i t e i s w h i t e o r n e a r - w h i t e i n c o l o u r w h i c hi s an o t h e r i m p o r t an t a t t r i b u t e t h a t r e l a t e s t o i t sc h e m i c a l c o m p o s i t io n . O n e o f t h e m o r e i m p o r t a n t


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Applied clay mineralogy today and tomorrow 41

O Oxygenatoms @Hydroxyl ions= Silicon atom s tetrahedrally OAlu mini um atoms octahedrallycoordinated coordinated

FIG. 2. S EM of kaolinite (Capim River).

FIa. 1. Kaolinite stmcture.

propert ies that many kaolins exhibit is that theyhave good f low propert ies when present in la rgeamounts in water. This is part icularly important inone of the major uses of kaol in the coat ing ofpaper. The reasons that kaolin has good rheologyare that i t has l i t t le or no charge deficiencies in thestructure, has a low surface area, exhibits a goodcrystal l ine morphology and i ts part icle size is finewith a broad part icle size distribution.

Kaolini te is soft with a hardness of ~1.5 on theMohs sca le which means tha t re la t ive ly purekaolins are not abrasive. This property is veryimportant in many industrial applicat ions. Becausekaolin is softer than almost al l materials with whichi t comes in to contac t , the wear and tear onequipment i s min imal .

Rela t ive ly pure kaol ins are refrac tory and m el t o rf u s e a t a t e m p e r a t u r e o f - 1 8 5 0 ~ I n m o s tins tances , kao l ins and part icu lar ly ba l l c lays ,which primari ly comprise kaolini te, are plast ic andfi re to a whi te or near-whi te co lour . Thesepropert ies, in addit ion to low shrinkage, makekaol ins very importan t ceramic raw mater ia l s . Bal lclays general ly are natural ly much finer in part iclesize than kaolins and thus have higher plast ici ty andhigher modulus of rup ture than kaol ins . O ne o f themajor reasons why a ball clay is added to a ceramicbody is to confer green and dry strength.

Kaolini te is hydrophil ic and, with the addit ion ofa smal l amount of chemical d ispersan t to negate theedge charges due to broken bonds, wil l dispersereadi ly in water . Therefore , kao l ins are used

extensive ly in water-based pa in t and paper-coat ingformulations. T he dispersion o f kaolin part icles in awater-based system is essential in order for thekaol in to im part the propert ies of p r in tabi l i ty ,smoothness and opacity to a coated sheet of paper(Murray, 1984).

The part icle shape of kaolini te is an importan tfactor in i ts industrial ut i l izat ion. Kaolini te part iclesthat are ~2 lam thick are thin plates that orient on acoated surface because of the ir f la t two-d imensionalnature. This orientat ion gives a gloss or sheen to thecoated surface and, in the case of coat ed paper,makes for excellent print quali ty.

Although there are other specific propert ies thatcould be enumerated, i t can be seen that kaolin isone o f the most versa t i le o f the industr ia l minera lsin i ts diverse applicat ion because i t is chemicallyinert over a pH range of 4 to 9; is white or nearwhi te in co lour; has good covering or h id ing power(opacity) when used as a pigment or extender incoating and fi l l ing applicat ions; is soft and non-abras ive ; i s f ine in par t ic le s ize ; i s p las t ic ,refractory, and fires to a white or near whitecolour; has low cond uctivi ty of both heat andelectrici ty; is hydrophil ic and disperses readily inwater; is relat ively low in cost .

Some of the many uses of kaol in are shown inTable 2. The large st user o f kaolin is the paperindustry where i t is used both as a fi l ler in the sheetand as a coating on the surface o f the sheet . Som epropert ies that are important to the paper maker aredispersion, rheology (both low and high shear),brightness and whiteness, gloss and smoothness,adhesive demand, fi lm strength, ink receptivi ty, andprint quality.


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42 H. H. MurrayTABLE 2. industrial uses of kaolin.

Paper coating Cemen t Food additivesPaper filling Pencil leads BleachingExtender in paint Adhesives FertilizersCeram ic raw material Tanning leather PlasterFiller in rubber Pharmaceuticals Filter aidsFiller in plastics Enamels Cosm eticsExtender in ink Pastes and glues CrayonsCracking catalysts Insecticide carriers DetergentsFibreglass Medicines Roofing granulesFoundries Sizing LinoleumDesiccants Textiles Polishing compounds

Another very large user of kaolins is the ceramicsindustry, part icularly in whiteware, sanitaryware,insulators, pottery and refractories. Both primaryand secondary kaol ins can have excel len t ceramicpropert ies (Murray, 1986). A kaolin which does nothave the physical and chemical propert ies for use ina paper-coat ing appl ica t ion can have excel len tceram ic propert ies. Halloysi te, one of the kaolinminerals, is used as an addit ive in high quali tydinnerware to provide translucency and strength.The major source of halloysi te is on the NorthIs land of New Zealand (Murray et al. , 1977).

A treatment that is used to produce special value-added products from kaolin is calcining. Calcininginvolves heating to high temperatures to drive offthe structural water and to reorganize the A1 andsil ica into new high-temperature crystal l ine phases.One product is heated to a temperature range of650 -70 0~ which i s above the normal dehydrox-y l a t io n t e m p e r a t u r e o f ~ 5 5 0 - 5 7 0 ~ A t t hi stemperature, the structural hydroxyl groups havebeen driven o ff as water vapour. The kaolini te(which is cal led meta-kaolin at this point) is bulkyand has propert ies tha t make i t an excel len tdielectric which is used as a fi l ler in electricalwire coatings. A second type of calcined product isheated to -1050


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Applied clay mineralogy today and tomorrowA nothe r spe c i a l a pp l i c a t i on f o r ka o l in i t e i s i n t he

p r o d u c t i o n o f s y n t h e t ic z e o l i t e s . K a o l i n i t e c a n b et r e a te d w i t h N a , C a , M g a n d K h y d r o x i d e s w h i c hw h e n h e a t e d t o - 1 0 0 ~ w i l l c o n v e r t t h e k a o l i n i t e t oz e o l i t e s t r uc tu r e s w i th d i f f e r e n t po r e s i z e s . T he sesyn the t i c z e o l i t e s a r e u se d p r im a r i l y a s c r a c k ingc a t a l y s t s i n p e t r o l e u m r e f i n i n g a n d t o r e m o v e w a t e rf r om ga s s t r e a m s .

F r om the a bove , i t c a n be s e e n tha t ka o l in s a r einde e d a va lua b le a nd ve r sa t i l e i ndus t r i a l m ine r a l .O n l y a f e w k a o l i n s i n t h e w o r l d c a n b e u s e d f o rp a p e r c o a t i n g b e c a u s e o f t h e s t r i n g e n t r e q u i r e m e n t sf o r l o w v i s c o s i t y a n d g o o d c o l o u r . M a n y m o r ede pos i t s , how e ve r , c a n be u t i l i z e d f o r c e r a m ic s a ndf i l l e r a pp l i c a t i ons , so a c a r e f u l e va lu a t ion o f ak a o l i n d e p o s i t m u s t b e m a d e i n o r d e r t o d e t e r m i n ew h e t h e r o r n o t t h e m a t e r i a l c a n b e p r o c e s s e d f o rsom e indus t r i a l u se o r u se s .

S M E C T I T E SS m e c t i t e i s t h e m i n e r a l n a m e g i v e n t o a g ro u p o fN a , C a , M g , F e , a nd L i - A 1 s i l i c a t e s . T he m ine r a ln a m e s i n t h e s m e c t i te g r o u p w h i c h a r e m o s tc o m m o n l y u s e d a r e N a - m o n t m o r i l l o n i t e , C a - m o n t -m or i l l on i t e , s a pon i t e ( M g) , non t r on i t e ( F e ) , a ndh e c t o r i t e ( L i ) . T h e r o c k i n w h i c h t h e s e s m e c t i t em i n e r a l s a r e d o m i n a n t i s b e n t o n i t e . T h e t e r mb e n t o n i t e w a s d e f i n e d b y R o s s & S h a n n o n ( 1 9 2 6)a s a c l a y a l t e r e d f r om g l a s sy i gne ous m a te r i a l ,u s u a l l y a t u f f o r v o l c a n i c a sh . G r i m & G u v e n( 1 9 7 8 ) r e d e f i n e d t h e t e r m b e n t o n i t e t o b e a n y c l a yp r e d o m i n a n t l y c o m p o s e d o f a s m e c t i t e m i n e r a l ,r e ga r d l e s s o f i t s o r ig in .

B e n t o n i t e s w h i c h a r e u s e d i n d u s t r i a l l y p r e d o m i -n a n t l y c o m p r i s e e i th e r N a - m o n t m o r i l l o n i t e o r C a -m o n t m o r i l l o n i t e a n d t o a m u c h l e s s e r e x t e n tsa pon i t e a nd he c to r i t e . T he se sm e c t i t e m ine r a l st h a t c o m p r i s e b e n t o n i t e s h a v e s i g n i f i c a n t ly d i f f e re n tphys i c a l a nd c he m ic a l p r ope r t i e s w h ic h d i c t a t e t he i ru t i l i t y t o a m a jo r de g r e e .

S m e c t i t e i s a 2 :1 l a ye r s i l i c a t e ( F ig . 4 ) i n c on t r a s tt o ka o l in i t e w h ic h i s a 1 :1 l a ye r s i l i c a t e . S m e c t i t eha s tw o s i l i c a t e t r a he d r a l sh e e t s j o i ne d to a c e n t r a lo c t a h e d r a l s h e e t. T h e r e c a n b e c o n s i d e r a b l esubs t i t u t i on i n t he oc t a he d r a l she e t , u sua l ly by F ea nd M g f o r A 1 , w h ic h c r e a t e s a c ha r ge de f i c i e nc y inthe l a ye r ( B r ind l e y & B r ow n , 1980 ) . A l so , t he r e c a nbe subs t i t u t i on i n t he t e t r a he d r a l she e t s o f A 1 f o r S iw h i c h a g a i n c r e a t e s a c h a r g e i m b a l a n c e . G r i m( 1 9 6 2 ) p o i n t e d o u t t h a t m a n y a n a l y s e s h a v e s h o w nt h a t t h i s c h a r g e i m b a l a n c e i s ~ - 0 . 6 6 p e r u n i t - c e l l .

43

E x c h a n g e a b l e C a t i o n snH20

O Oxygens @ Hydroxyls 9 A l u m i n iu m , i ro n , m a g n e s i u mo , S i l i c o n , o c c a s i o n a ll y a l u m i n u m

FIG. 4. S m ect ite structure.

T h i s n e t p o s i t i v e c h a r g e d e f i c i e n c y i s b a l a n c e d b ye x c h a n g e a b l e c a t i o n s a b s o r b e d b e t w e e n t h e u n i tl a y e rs a n d a r o u n d t h e e d g e s . T h u s , i f t h e e x c h a n g e -a b l e c a t i o n i s p r e d o m i n a n t l y N a , t h e s p e c i f i cm i n e r a l i s N a - m o n t m o r i l l o n i t e a n d i f i t i sp r e d o m i n a n t l y C a , i t i s a C a - m o n t m o r i l l o n i t e .B o th t he N a a nd C a ions a r e hyd r a t e d i n t h i si n t e r l a y e r p o s i t i o n . S o d i u m - m o n t m o r i l l o n i t e s g e n e r -a l l y h a v e o n e w a t e r l a y e r i n t h e i n t e r l a y e r p o s i t i o na n d C a - m o n t m o r i l l o n i t e s g e n e r a l l y h a v e t w o w a t e rl a y e r s w h i c h a c c o u n t f o r t h e b a s a l s p a c i n g o n t h eX - r a y d i f f r a c t io n p a t t e rn o f 1 5 .4 A f o r a C a -m o n t m o r i l l o n i t e a n d 1 2 .6 A . f o r a N a - m o n t m o r i l l o n -ite .T he h igh c ha r ge on the sm e c t i t e l a ye r i s s a t i s f i e db y c a t i o n s s u c h a s N a , C a , M g , F e a n d L i .S m e c t i t e s h a v e a h i g h C E C w h i c h i s g e n e r a l l y o ft h e o r d e r o f 6 0 1 00 m E q / 1 0 0 g o f c l ay . T h e s ein t e r l a ye r c a t i ons a nd w a te r l a ye r s c a n be r e p l a c e db y p o l a r o r g a n i c m o l e c u l e s s u c h a s e t h y l e n e g l y c o l ,q u a t e r n a r y a m i n e s a n d p o l y a l c o h o l s . T h i s i s a ni m p o r t a n t p r o p e r t y w h i c h c a n b e t r a n s l a t e d i n t os o m e v e r y u s e f u l o r g a n o - c l a y p r o d u c t s. S m e c t i t e so c c u r n o r m a l l y a s v e r y t h in f l a k e s o f e x t r e m e l ysm a l l pa r t i c l e s i z e ( F ig . 5 ) w h ic h g ive t he c l a y ah i g h s u r f a c e a r e a w h e n w e l l d i s p e r s e d . T h e h i g hc ha r ge , C E C , a nd su r f a c e a r e a g ive sm e c t i t e s a h ighd e g r e e o f a b s o r b e n c y f o r m a n y m a t e r i a l s ( o i l,


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44 H. H. Murray

FIG. 5. SEM of Na-montmorillonite (Wyoming).

water, chemicals, etc.); when mixed with water, thehigh charge and fine part icle size give the fluid avery h igh v iscosi ty . These basic propert ies ofsmecti te relate to many industrial uses which aredescribed in the fol lowing paragraphs.

The co lour of smect i tes can vary from whi te totan to brown or brownish green to blue-green.Colour, es pecial ly if the colour is white, controlsthe use in many instances. The many uses ofsmecti tes are shown in Table 3.

The primary uses are in dri l l ing muds, as foundrybond clays, for pel let izing iron ores, and as sealantsin irrigat ion ditches, farm ponds, earthen dams,landfi l l l iners, etc. The major Na-montmoril lonitedeposits are the Western Bentonites which aremined in South Dakota , Wyoming and Montana inthe USA (Elzea & Murray, 1990). These are high-swell ing clays which wil l expand up to ten or moret imes the i r c lay volume when p laced in water . Thisunique swel l ing property makes them necessary

ingredients in most freshwater dri l l ing muds. TheseWes tern (Na) B entonites yield 100 barrels of mu dper ton. Only 5% of this high-swe ll ing bentonite isrequired to produce the high viscosi ty, thixotropicfluid with low fi l ter cake permeabil i ty that isn e c e s s a r y t o m e e t t h e A m e r i c a n P e t r o l e u mI n s t i t u t e ( A P I ) d r i l l i n g f l u i d s p e c i f i c a t i o n s .Hectori te is also a very high-swell ing clay butbecause the deposits are relat ively much smaller, i tis used primari ly for special applicat ions wherehigh viscosi ty suspensions are required. Some Ca-montmori l lon i te can be t rea ted wi th a Na compoundsuch as soda ash or Na polyacrylate to exchange Nafor Ca to make a dri l l ing mud, but nei ther theviscosi ty nor the water loss propert ies are as goodas with the natural Na Western Bentonites.The major Ca-bentonite deposits in the world arein Texas and Mississippi in the USA, in England,Germany, Greece, Italy, Spain and India. The termfuller 's earth is used for any fine-grained earthymaterial sui table for bleaching oils and absorbentuses. It has no composit ional or mineralogicalmeaning . However , most fu l le r ' s ear th mater ia l sare composed of Ca-montmori l lon i te and/or pa ly-gorskite.

The moulding sands used in foundries consist ofquartz sand and bentonite. The bentonite providesbonding strength and plast ici ty. A small amount oftempering water is added to the mixture to make i tplast ic. This mixture of sand, clay and water is thenmoulded around a pattern and is cohesive enough tomaintain the shape after the pattern is removed.Then, molten metal is poured into i t . The importantfoundry propert ies of bentoni te a re green compres-s io n s t ren g th , d ry co mp ress io n s t ren g th , h o tstrength, flowabil i ty, permeabil i ty and durabil i ty.These propert ies vary grea t ly wi th the amount oftempering water added (Grim & Guven, 1978).

TABLE 3. Industrial uses of smectites.

Drilling mudFoundry bond clayPelletizing iron oresSealantsAnimal feed bondsBleaching clayIndustrial oil absorbentsAgricultural carriersCat box absorbentsBeer and wine clarification

Medical formulationsPolishing & cleaning agentsDetergentsAerosolsAdhesivesPharmaceuticalsFood additivesDe-inking of paperTape-joining compoundsEmulsion stabilizer

CrayonsCementDesiccantsCosmeticsPaintPaperFillersCeramicsCatalystsPencil leads


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Applied clay mineralogy today and tomorrow 45B o t h N a - a n d C a - b e n t o n i t e s a r e u s e d a s f o u n d r yb o n d i n g c la y s. C a l c i u m - m o n t m o r i l l o n i t e h a s ah i g h e r g r een s t r en g t h , l o w er d r y s t r en g t h , l o w erh o t s t r e n g th a n d b e t t e r f l o w a b i l it y t h a n N a - m o n t -m o r i l l o n i t e . B l e n d s o f N a - a n d C a - b e n t o n i t e s ar ec o m m o n l y u s e d to g a i n t h e o p t i m u m p r o p e r t i e s f o rt h e m o u l d i n g s a n d w h i c h i s n e e d e d f o r a p a r t i c u l a rm e t a l .

B e n t o n i t e s a r e u s e d e x t e n s i v e l y to p e l l e ti z e i r o no r e s ( D e V a n e y , 1 9 5 6) . F i n e l y p u l v e r i z e d o r ec o n c e n t r a t e s a r e p e l l e t i z e d t o b a l l s o f - 2 . 5 c m i nd i a m e t e r f o r e a s e o f t ra n s p o r t a n d t o p r o d u c e as u p e r i o r f u r n a c e f e e d . B e n t o n i t e c o n s t i t u t e s~0 . 5 w t % o f t h e p e l l e ts . Bec au s e o f i ts s u p e r i o rd r y s t r en g t h , N a - b en t o n i t e i s p r e f e r r ed f o r p e l l e -t i z i n g o r e s .B e c a u s e o f t h e i r h i g h s w e l l i n g c a p a c it y , N a -b e n t o n i t e s a r e u s e d a s w a t e r b a r r ie r s . T h e b e n t o n i t ei s u s e d t o p r e v e n t t h e f l o w o f w a t e r t h r o u g h e a r t h e ns t r u c t u r e s s u ch a s d ams , t o p r ev en t seep ag e o f w a t e rf r o m p o n d s a n d i r r i g a t i o n d i tc h e s , to c o n t a i nc h e m i c a l s i n l a n d f i l l s a n d t o x i c w a s t e i m p o u n d -m e n t s , a n d t o p r e v e n t w a t e r f r o m e n t e r i n g b a s e -m e n t s o f h o m e s .

A n o t h e r u s e o f h i g h - s w e l l i n g N a - b e n t o n i t e is i nt h e s l u r r y - t r e n c h o r d i a p h r a g m - w a l l m e t h o d o fe x c a v a t i o n i n c o n s t r u c t i o n w h e r e u n c o n s o l i d a t e dr o ck s o r s o i l s a r e en co u n t e r ed ( L an g , 1 9 7 1 ) . I n t h i sm e t h o d , t h e t r e n c h b e i n g e x c a v a t e d i s f i l l e d w i t hb e n t o n i t e s l u r r y a n d t h e e a r t h m a t e r i a l b e i n gex cav a t ed i s mo v ed t h r o u g h i t . A t h i n f i l t e r c ak eo n t h e w a l l s o f t h e e x c a v a t i o n p r e v e n ts l o s s o f f l u i da n d t h e h y d r o s ta t i c h e a d o f t h e s l u r r y p r e v e n t sc a v i n g a n d r u n n i n g o f lo o s e s o i l w h i c h m a k e c o s t lys h o r i n g u n n e c e s s a r y .

C a l c i u m - s m e c t i t e s a re u s e d a s a n i m a l f e ed b o n d s .I n a d d i t i o n to t h e i r b i n d i n g a b i l i ty , th e y a c t a sa b s o r b e n t s f o r b a c t e r i a a n d c e r t a i n e n z y m e s w h i c hp r o m o t e t h e g r o w t h a n d h e a l t h o f th e a n i m a l .A n o t h e r v e r y l a r g e a n d g r o w i n g u s e f o r t h e C a -s mec t i t e s i s a s a p e t w as t e ab s o r b en t . T h i s mar k e tu s e s g r a n u l e s o f C a - s m e c t i t e w h i c h a r e t re a t e d w i t hd e o d o r a n t s a n d m o r e r e c e n t l y a p e r c e n t a g e o fp o w d e r e d h i g h - s w e l l i n g N a - s m e c t i t e t o p r o d u c ec l u m p i n g c a t l it te r . S o m e C a - m o n t m o r i l l o n i te s a r ea c i d a c t i v a t e d t o r e m o v e i o n s f r o m t h e s u r f a c e a n dt h e ed g es o f th e o c t ah ed r a l s h ee t s . T h i s i n c r ea s e st h e c h a r g e o n t h e c l a y p a rt i c le a n d m a k e s t h e m v e r ye f f e c t i v e i n d e c o l o u r i z i n g m i n e r a l , v e g e t a b l e a n da n i m a l o il s. T h e C a - m o n t m o r i l l o n i te i s g e n e r a l l ya c t i v a t e d b y u s i n g e i t h e r h y d r o c h l o r i c o r s u l p h u r i cac id .

A p r o c e s s b a s e d o n t h e e x c h a n g e c a p a c i t y i s u s e dt o m a k e s p e c i a l p r o d u c t s f r o m N a - m o n t m o r i l l o n i t ew h i ch a r e t e r med o r g an o - c l ay s . I n t h i s p r o ces s , t h ee x c h a n g e a b l e i o n s o n t h e m o n t m o r i l l o n i t e s u r f a c ea r e r e p la c e d w i th a l k y l a m i n e c a t io n s w h i c h p r o d u c ea h y d r o p h o b i c s u r f a c e ( J o r d a n , 1 9 5 0) . T h e s eo r g a n i c - c la d N a - m o n t m o r i l l o n i te s a re u s e d a st h i ck en e r s i n p a i n t s , g r ea s e s , o i l - b a s e d d r i l l i n gf l u i d s , an d t o g e l v a r i o u s o r g an i c l i q u i d s .

A n o t h e r r e c e n t l y d e v e l o p e d c o n c e p t i s to u s e N a -m o n t m o r i l l o n i t e s in p l a s t ic c o m p o s i t i o n s c a l l e dn a n o c o m p o s i t e s . T h e N a - m o n t m o r i l l o n i t e i s d e la -m i n a t e d t o p r o d u c e e x t r e m e l y t h i n , s m a l l p a r t i c l e sw h i c h c a n t h e n b e t r e a t e d w i t h o r g a n i c m o l e c u l e s t oc a u s e t h e m t o i n t e r a c t w i t h t h e p l a s t i c p o l y m e r s t op r o d u c e e x c e e d i n g l y s tr o n g a n d h e a t - r e s i s t a n tp r o d u c t s . T h e s e p r o d u c t s a r e n o w b e i n g u s e d i nc e r t a i n a u t o m o t i v e p l a s t i c c o m p o n e n t s .

P i l l a r e d c l a y s a r e a n o t h e r r e c e n t d e v e l o p m e n t i nw h i c h t h e i o n s o n t h e N a - m o n t m o r i l l o n i t e a r ee x c h a n g e d w i t h s p e c i f i c c h e m i c a l s s u c h a s A 1h y d r o x i d e w h i ch g o es i n t o th e i n t e r l ay e r p o s i t i o n .B y c o n t r o l l i n g t h e a m o u n t o f c h e m i c a l a d d e d , p o r es i ze s can b e r eg u l a t ed . T h es e p i l l a r ed c l ay s can b et a i l o r ed f o r s p ec i f i c c a t a l y s t an d ab s o r b en t u s e s .

P A L Y G O R S K I T E ( A T T A P U L G I T E )A N D S E P I O L I T E

P a l y g o r s k i t e a n d a tt a p u l g i te a r e s y n o n y m o u st e r m s f o r t h e s a m e h y d r a t e d M g - A 1 s i l i c a t em a t e r i a l . T h e n a m e s p e c i f i e d b y t h eI n t e r n a ti o n a l N o m e n c l a t u r e C o m m i t te e i s p a ly -g o r s k i t e . H o w e v e r , t h e n a m e a t t a p u l g i t e i s s o w e l le s t a b l i s h e d i n tr a d e c i r c l e s t h a t i t c o n t i n u e s t o b eu s e d b y m a n y p r o d u c e r s a n d u s e r s. S e p i o l it e i ss t r u c t u r a l l y s i m i l a r to p a l y g o r s k i t e e x c e p t t h a t i th a s a s l i g h t l y l a r g e r u n i t - c e l l . B o t h m i n e r a l sc o n s i s t o f d o u b l e s i l ic a t e t ra h e d r a l c h a i n s l i n k e dt o g e t h e r b y o c t a h e d r a l o x y g e n a n d h y d r o x y lg r o u p s c o n t a i n i n g A I a n d M g i o n s i n a c h a i n -l i k e i n v e r t e d s t r u c t u r e . T h e s e i n v e r t e d t e t r a h e d r ao c c u r r e g u l a r l y a n d c a u s e c h a n n e l s t h r o u g h t h es t r u c t u r e ( F i g . 6 ) . B o t h p a l y g o r s k i t e a n d s e p i o l i t ea r e e l o n g a t e i n h a b i t a s s h o w n o n t h e e l e c t r o nm i c r o g r a p h o f p a l y g o r s k i t e ( F i g . 7) .

A s m e n t i o n e d p r e v i o u s l y , t h e t e r m f u l l e r ' s e a r thi s u s ed t o d e s c r i b e p a l y g o r s k i t e ( a t t ap u l g i t e ) , an ds m e c t i t e c l a y s w h i c h h a v e s o r p t i v e a n d b l e a c h i n gq u a l it ie s . T h u s , t h e re i s s o m e c o n f u s i o n i n m i n e r a ls t a t i s t i c s , b ecau s e t h e t e r m f u l l e r ' s e a r t h can b ee i t h e r o f th e s e m i n e r a l t y p es .


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46

II

H. H. Murray

O' C OC ,,.-,w.o" '," f " " 0 O " "

.O

r ~

O C O C1~1 b= 18 .0A ~[

O H 2 O ,",Hydrox yl O Mg or AI(~)2OH O Oxygen 9 Silicon

Attapulgite OH2)4 OH)2MgsSi8O204H20FIG. 6. Palygorskite structure.

Sepioli te is normally l ight tan or cream in colour,whereas pa lygorsk i te genera l ly has a b lu ish-greytint. They are classed as a 2:1 layer invertedstructure (Fig. 6). Ferrous iron com mo nly substi-tutes for A1 in the octahedral sheet thus producing amoderate charge on the layer. This charge causesthese minerals to have a CEC that is intermediatebetween kaol in i te and Na-montmori l lon i te , usual lyin the range o f 30 to 40 mE q/100 g. Because o f theinvers ions in the s i l ica te t rahedra l sheet , thestructure has paral lel channels or holes throughout,which along with the elongate habit and the finepart icle size, give a high surface area. The chargeon the part icles, the channels through the structure,and the high surface area give palygorskite andsepioli te a high capacity to absorb and adsorbvarious mater ia l s which makes them benefic ia l formany industrial applicat ions. Also, the elongate

Fro. 7. SEM of palygorsk ite (Florida).

part icles cause higher viscosi ty when i t is added toany l iquid. It is a physical and not a chemicalviscosi ty, so i t is very stable as a suspendingmedium in many applicat ions such as sal t waterdrilling fluids.

A major occurrence of palygorskite is in thesoutheastern USA in southern Georgia and northernFlorida , where major deposi t s o f pa lygorsk i te(a t t ap u lg i t e ) o ccu r . Th e ma jo r o ccu r ren ce o fsepioli te is near Madrid in Spain. Two other largeoccurrences of palygors kite are in Senegal nearTheis , -100 km east o f Dakar and in China inAnhui Province , - 120 km northwest o f Nanjing .There are also occurrences of sepioli te in Turkey.

The appl ica t ions o f pa lygo rsk i te and sep io l i teare many (Table 4) . One o f the grea ter uses i s asv iscosi ty bu i lders in sa l twater or h igh-e lec t ro ly teconten t d r i l l ing muds. The v iscosi ty and gels t rength of the mud are no t a ff ec ted by varia t ionsin e lec t ro ly te concent ra t ion and thus i t can beused wi th sa l t water o r when format ion br inesbecome a ser ious problem, and wi th o i l -baseddri l l ing f lu ids .

TABLE 4. Industrial uses o f palygors kite (attapulgite) and sepiolite.

Drilling fluids AdhesivesPaint PharmaceuticalsPaper Catalyst supportsCeramics Animal feedAsphalt emulsions Petroleum refiningCosmetics Anti-caking agentSealants Reinforcing fillers

Cat box absorbentsSuspension fertilizerAgricultural carrierIndustrial floor absorbentsMineral and vegetable oil refiningTape-joint compoundsEnvironmental absorbent


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Applied clay mineralogy today and tomorrow 47B e c a u s e p a l y g o r s k i t e a n d s e p i o l i t e a r e n o t e a s i l y

f loc c u la t e d , t he y a r e u se d a s su spe nd ing a ge n t s i npa in t s , su spe ns ion f e r t i l i z e r s , m e d ic ine s , pha r m a -c e u t i c a l s a nd c osm e t i c s . I n pa in t , t he se m ine r a l si m p r o v e t h e t h i c k e n i n g a n d t h i x o t r o p i c p r o p e r t i e s .A n o t h e r m a j o r u s e o f t h e s e m i n e r a l s i s as f l o o r -s w e e p c o m p o u n d s f o r a b s o r b i n g o i l a n d g r e a s esp i l l s on f a c to r y a nd se r v i c e s t a t i on f l oo r s . G r a nu la rp a r t i c le s o f th e s e m i n e r a l s a r e t h e m o s t e f f e c ti v e .P a l y g o r s k i t e a n d s e p i o l i t e a r e u s e d e x t e n s i v e l y i na g r i c u l t u r e a s a b s o r b e n t s a n d a d s o r b e n t s f o rc he m ic a l s . T he f e r t i l i z e r , c he m ic a l , pe s t i c ide o rh e r b i c i d e i s a d s o r b e d o n t o t h e g r a n u l a r c l a yp a r t i c l e s w h i c h a r e t h e n p l a c e d i n t h e g r o u n d w i t hthe s e e d o r f o r l a t e r t r e a tm e n t s u s ing sp r e a de r s . T hec h e m i c a l i s r e l e a s e d s l o w l y to p r o v i d e t h e n e c e s s a r yp l a n t f o o d o r p r o t e c t i o n f o r t h e g r o w i n g p l a n t .F i n e l y p u l v e r i z e d p a l y g o r s k i t e a n d s e p i o l i t e c l a y sa r e a l s o u s e d t o a b s o r b c h e m i c a l s w h i c h c a n b ed u s t e d o r s p r a y e d o n t h e p l a n t o r o n t h e s u r f a c e o fthe g r ound .

A n o t h e r u s e f o r f u l l e r ' s e a r t h m a t e r i a l s , w h i c hinc lude pa lygo r sk i t e a nd se p io l i t e , i s a s so r be n t s f o rpe t w a s t e . G r a nu la r c l a y pa r t i c l e s a r e a n e f f e c t i vem e d i u m f o r a b s o r b i n g a n i m a l w a s t e , p a r t i c u l a r l y f o rdom e s t i c c a t s . T he c l a y m a te r i a l s c a n be t r e a t e dw i t h c h e m i c a l s w h i c h w i l l p r e v e n t o d o u r s a n dba c t e r i a l de g r a da t ion f o r s e ve r a l da ys .

A no the r s i z e a b le u se f o r pa lygo r sk i t e i s f o r t a pe -j o i n t c o m p o u n d s w h i c h a r e u s e d t o s m o o t h t h ej o i n t s i n a w a l l b o a r d s u r f a c e . T h e s e c o m p o u n d sp r o v i d e a s m o o t h , s t r o n g , u n i f o r m a n d p a i n t a b l esu r f a c e w he n d r i e d .

O t h e r u s e s f o r th e s e m i n e r a l s a r e s h o w n i nT a b le 4 . G a l f in de sc r ibe d o the r u se s f o r pa lygo r sk i t ea nd se p io l i t e i n a r e c e n t pa pe r ( 1996 ) .

G R O W T H A N D A P P L I C A T I O N S F O RT H E F U T U R E

q u a l i t y a n d m o r e u n i f o r m c l a y p r o d u c t s . T h i s w i l lc o n t i n u e a n d w i l l b e e v e n m o r e a c c e l e r a t e d i n th ef u tu r e . I n T a b le 5 i s a l i s t o f p r oc e s se s t ha t a r ec o n t i n u a l l y b e i n g i m p r o v e d a n d m o d i f i e d t op r o d u c e h i g h e r q u a l i t y a n d n e w p r o d u c t s .R a the r t ha n d i s c us s e a c h o f t he p r oc e s se s l i s t e din T a b le 5 , m a g ne t i c s e pa r a t i on a nd f l o t a t i on w i l lb e u s e d a s e x a m p l e s a s t o h o w t h e p r o c e s s e s h a v eb e e n c o n t i n u a l l y i m p r o v e d f o r a p p l i c a t i o n s t o c l a y sa nd pa r t i c u l a r ly t o ka o l in s .

H i g h - i n t e n s i t y w e t m a g n e t i c s e p a r a t i o n( I a nn ic e l l i , 1976 ) be c a m e a s t a nda r d p r oc e s s i nt h e k a o l i n i n d u s t r y i n G e o r g i a a n d i n E n g l a n d i n t h ee a r ly 1970s . T he se m a gne t s w e r e de s igne d so t ha tt h e r e t e n t i o n t i m e i n t h e m a g n e t i c f i e l d c o u l d b ec on t r o l l e d a nd the f i e ld s t r e ng th s e t be tw e e n 0 . 5a nd 2 T e s l a . T he u se o f a m a t r ix suc h a s s t e e l w o o lin a c a n i s t e r i n t he m a g ne t i c f i e ld p r ov id e d au n i f o r m m a g n e t i c f i e l d th r o u g h o u t t h e c a n is t er .T he se m a g ne t s w e r e 2 .1 m in d i a m e te r a nd 0 . 5 mde e p . T he th r oughpu t c ou ld be a s h igh a s 100 tons /hi n s o m e a p p l i c a ti o n s . T h e p u r p o s e o f t h e m a g n e tw a s t o r e m o v e c o l o u r e d i m p u r i t i e s , p a r t i c u l a r l y F ea nd T i m ine r a l s . S in c e t he f ir s t ge ne r a t i on o f t he sem a g n e t s , t h e r e h a v e b e e n v e r y s i g n i f i c a n t i m p r o v e -m e n t s i n th e c o m p o s i t i o n a n d s i z e o f t h e m a t r i xm a t e r i a ls , a n d s u p e r c o n d u c t i n g m a g n e t s a r e n o wa v a i l a b l e w h i c h g r e a t l y r e d u c e t h e p o w e r c o n s u m p -t ion a nd p r ov ide i nc r e a se d f i e ld s t r e ng th s a s h igh a s6 T e s l a. P r o d u c ts o f v e r y h i g h p u r i t y a n d w h i t e n e s sa r e n o w r o u t i n e l y p r o d u c e d a t l o w e r c o s t a n d , i na dd i t i on , m a r g ina l c r ude c l a ys c a n be u t i l i z e d t om a k e s t a n d a r d p r o d u c t s . T h e s e m a r g i n a l c l a y s w e r en o t b e i n g m i n e d p r e v i o u s l y , s o t h e m a g n e t h a sp r o v i d e d a w a y t o e x t e n d t h e u s e a b l e r e s e r v e s o fka o l in .

F l o t a t i o n i s a n o t h e r p r o c e s s w h i c h h a s p r o v i d e d am e t h o d t o p r o d u c e p r o d u c t s w i t h g r e a t e r p u r i t y a n dh ighe r b r igh tne s s a nd w h i t e ne s s . T he f i r s t f l o t a t i on

T he f u tu r e w i l l s e e f u r the r g r ow th in t he u se o fc l a y s i n t h e a p p l i c a t i o n s t h e y n o w s e r v e a n d w i l ls e e ne w u t i l i z a t i on , pa r t i c u l a r ly i n i ndus t r i a l a nde n v i r o n m e n t a l a p p l i c a t i o n s . T h e g r o w t h o f t h ec u r r e n t i ndus t r i e s w i l l c r e a t e e xpa nde d m a r ke t s f o rpa pe r , c e r a m ic s , p l a s t i c s , e t c . T h i s w i l l c a use ad e m a n d f o r e x p l o r a t i o n f o r n e w d e p o s i t s a n di m p r o v e d p r o c e s s i n g t o u p g r a d e m a r g i n a l q u a l i t yde pos i t s so t ha t m a r ke t a b l e p r oduc t s c a n be m a de .A s w e h a v e s e e n h i s t o r i c a l l y , i m p r o v e d m i n i n gt e c h n o l o g y a n d p a r t i c u l a r l y n e w a n d i m p r o v e db e n e f i c i a t i o n m e t h o d s h a v e r e s u l t e d i n h i g h e r

TABLE 5. Sp ecial proce sses applica ble to c lays.

Ac id ac t iva t ion F ine pulve r iza t ionAir c lass i f ica t ion F lo ta t ionCalc ina t ion Granula r s iz ingCentr i fuging High-hea t dry ingChem ica l leaching Mag ne t ic separa t ionD e la m ina t ion O r ga noc la dd ingD e w a te r ing O x ida t ionDispers ion Se lec t ive f loccula t ionExtrus ion Sur face t r ea tments


10/11

4 8 H. H. Murrayp r o c e s s u s e d i n t h e k a o l i n i n d u s t r y i n v o l v e d th e u s eo f ca l c i t e p a r t i c l e s a s c a r r i e r s i n o r d e r t o f l o a t t h ev e r y f i n e k a o l i n c l a y s ( G r e e n e & D u k e , 1 9 6 2 ) .C o n t i n u a l i m p r o v e m e n t s i n t h e f l o t a t i o n p r o c e s s ,b o t h i n e q u i p m e n t ( s u c h a s c o l u m n f l o t a t i o n ) a n df l o t a t i o n c h e m i c a l s , h a v e i m p r o v e d t h e r e c o v e r yan d t h e p r o d u c t q u a l i t y . T o d ay , p r o d u c t s c an b em a d e r o u t i n e l y w i t h v e r y l o w T i c o n t e n t s , a h ig hb r i g h t n es s an d w h i t en es s , an d a t r ed u ced co s t .

P r o c e s s i m p r o v e m e n t s , m o r e p r e c i s e i d e n t i f i c a -t i o n a n d q u a n t i f i c a t io n o f m i n e r a l s p r e s e n t i n m i n o rq u an t i t i e s i n a c l ay w h i ch a r e d e l e t e r i o u s t o i t s u s e ,b e t t e r d i s p e r s i o n t e c h n i q u e s u t i l i z i n g i m p r o v e dp r o c e s s e q u i p m e n t a n d n e w c h e m i c a l s , a n d o t h e rp r o c e s s e s w i l l p e r m i t t h e p r o d u c t i o n o f h i g h e rq u a l i t y p r o d u c t s an d t h e ab i l i t y t o u t i l i z e d ep o s i t st h a t a r e n o t n o w e c o n o m i c . A l s o , c o n t i n u e dr e s e a r c h a n d d e v e l o p m e n t w i ll d e v e lo p n e wp r o d u c t s t h a t c an s e r v e mar k e t s n o t n o w acces s i b l e .

O r g a n o - c l a y s a n d s u r f a c e - m o d i f i e d c l a y s w i l lc o n t i n u e t o b e a s i g n i f i c a n t g r o w t h a r e a - -o r g a n o - c l a y s f o r t h e b e n t o n i t e i n d u s t r y a n ds u r f a c e - m o d i f i e d c l a y s f o r k a o l i n a n d p a l y g o r s k i t e -s e p io l it e . T h e d e v e l o p m e n t o f n e w c h e m i c a l s t oc l a d t h e m o n t m o r i l l o n i t e w i l l a l l o w m a r k e t p e n e t r a -t i o n i n t o n ew a r ea s w h i ch n eed f u n c t i o n a l f i l l e r s .S u r f a ce m o d i f i c a t i o n o f h y d r o p h i l i c c l a y s c a n m a k et h e s e c l a y s o r g a n o p h y l l i c a n d / o r h y d r o p h o b i c s ot h a t t h ey can b e d i s p e r s ed i n s y s t ems o t h e r t h anw a t e r an d i n s o me i n s t an ces s o t h a t t h ey w i l l r e ac tw i t h t h e m e d i u m i n to w h i c h t h e y a r e d i s p e r se d t ob e c o m e a n i n t e g r a l p a r t o f th e s y s t e m , t h u sp r o v i d i n g a n e e d e d f u n c t i o n s u c h a s s t r e n g t h , h e a tres i s t ance , e t c .

A n o t h e r g r o w t h a r ea f o r t h e f u t u r e i s p i l l a r edc l ay s ( L u s s i e r et al . , 1980; Occel l i , 1986 ; Vaughan ,1 9 8 8 a , b ) . T h e p i l l a r s t h a t a r e b u i l t i n t h e i n t e r l ay e rp o s i t i o n can b e t a i l o r ed t o p r o d u ce s e l ec t i v e p o r es i ze s , s p ec i f i c ab s o r b en t an d ad s o r b en t ch a r ac t e r -i s t i c s , an d u n i q u e ca t a l y t i c p r o p e r t i e s . T h e b e s t c l ayb a s e f o r p i l l a r i n g is a h i g h - s w e l l i n g N a - m o n t -m o r i l l o n i t e .

T h e f i e ld o f n a n o c o m p o s i t e s is a v e r y p r o m i s i n gg r o w t h a r e a ( B a n d o s z et a l . , 1 9 9 4 a , 1 9 9 4 b ) .U l t r a fi n e m o n t m o r i l l o n i te p l a te l e ts h a v e b e e ns h o w n t o b e e x c e l l e n t f u n c t i o n a l c o m p o n e n t s , i nce r t a i n p l a s t i c co mp o s i t e s , t o i mp r o v e t h e i r s t r en g t ha n d h e a t r e s i s ta n c e . T h i s i s a v e r y p r o m i s i n g g r o w t ha r e a n o t o n l y f o r N a - m o n t m o r i l l o n i t e , b u t f o r o t h e rc l a y m i n e r a l s .

W e t p r o c e s s i n g o f b a l l c l a y s , s m e c t i te s a n dp a l y g o r s k i t e a n d s e p i o l i t e w i l l b e u s e d i n t h e

f u t u r e t o p r o d u c e i m p r o v e d v a l u e - a d d e d q u a l i t yp r o d u c t s f o r s p ec i f i c ap p l i ca t i o n s .

S U M M A R YT h e n u m b e r o f a p p l i c a t i o n s f o r t h e c l a y m i n e r a l sk a o l i n i te , N a - a n d C a - m o n t m o r i l lo n i t e , p a l y g o r sk i te ,a n d s e p i o l i te c o n t i n u e s t o e x p a n d . B e c a u s e o f t h e i rv e r y f i n e p a r t i c l e s i z e a n d p h y s i c a l a n d c h e m i c a lp r o p e r t i e s t h a t a r e d i r ec t l y r e l a t ed t o t h e i r s t r u c t u r ea n d c o m p o s i t i o n , c l a y m i n e r a l s h a v e t h e m o s td i v e r s e u t i l i z a t i o n o f t h e i n d u s t r i a l mi n e r a l s . T h e i ra v a i l a b i l i ty a s a n a b u n d a n t ra w m a t e r i a l t h a t c a n b eb e n e f i c i a t e d to p r o d u c e a l a rg e n u m b e r o f r e l a t iv e l yi n e x p e n s i v e p r o d u c ts e n s u r e s t h a t m a r k e t g r o w t hw i l l co n t i n u e f o r th e f o r e s ee ab l e f u t u r e .N e w a n d i m p r o v e d p r o c e s s in g , c o n t i n u e dr e s e a r c h a n d d e v e l o p m e n t a n d n e w m a r k e t o p p o r -t u n i t ie s w i l l l e a d t o e x p a n s i o n i n t o n e w m a r k e t s .T h i s w i l l r e q u i r e c o n t i n u e d e x p l o r a t i o n a n dd e v e l o p m e n t o f n e w d e p o s i t s i n a l l a r e a s o f t h ew o r l d . T h e f u tu r e f o r th e g r o w t h o f c l a y m i n e r a lap p l i ca t i o n s i s i n d eed o p t i mi s t i c .

REFERENCESA n o n y mo u s ( 1 95 5 ) Kaolin Clays' and their MdustrialUses, J .M. Huber Corp. , New York.Bandosz TJ . , Gomez-Salazar S . Pu tyera K. & Schwarz

J .A. (1994a) P ore s t ructures of carb on-sm ect i tenanocompos i t es . Microporous Mat., 3, 177 184 .

Bandosz T.J . , Putyera K. , Jagiel lo J . & Schwarz J .A.(1994b) Study of carbon-sm ect i te composi tes andcarbons ob ta ined by in s i tu carbon iza t ion o f po ly -furfuryl alcohol . Carbon, 32, 659 664.Br ind ley G.W. & B rown G. (1980) Crystal S tructures' o fC l a y M i n er a l s a n d t h e i r X - r a y I d en t i f i ca t i o n .M ineralogica l Society, M onograph No. 5 , Lon don.

Bris tow C.M. (1977) A review o f the eviden ce for theorigin of the kaol in deposi ts in SW England. In:Proc. 8th int. Kaolin Symposium, Madrid-Rome.Bu n d y W . M. , J o h ns W . D . & Mu r r ay H . H . ( 19 6 5)Phy sico-che m ical propert ies of kaol ini te and rela-t i o n s h i p t o p ap e r co a t i n g q u a l i t y . Tappi, 4 8 ,6 8 8 - 6 9 6 .Clem A .G. & D oeh ler R.W. (1963) Indu str ial appl ica-t ions o f ben ton i t e . In : Proc. lOth C onf. Clays' an dClay Minerals, 2 7 2 - 2 8 3DeVaney F.D. (1956) U.S. Patent 2743172.Elzea J .M. & Murray H.H. (1990) Var ia t ion in theminera log ica l , chemical and phys ica l p roper t i es o fthe Cretaceous Clay Spur Ben ton i t e in Wyom ing andM o n t an a ( U SA ). Appl. Clay Sci., 5, 229 248.Elzea J .M. & M urray t t .H . (1994) B en ton i t e . Pp .


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