1979 - The Hydrothermal Transformation of Sepiolite to Stevensite and the Effect of Added Chlorides and Hydroxides

7/28/2019 1979 - The Hydrothermal Transformation of Sepiolite to Stevensite and the Effect of Added Chlorides and Hydroxi

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Clays and Clay Minerals , Vol. 27, No. 4, pp. 253-260, 1979.

THE H Y D R O T H E R M A L T R A N S F O R M A T I O N O F S E P IO L IT ET O S T E V E N S I T E A N D T H E E F F E C T O F A D D E D

C H L O R I D E S A N D H Y D R O X I D E S

NECIP GOVENDepartment of Geosciences, Texas Tech University, Lubbock, Texas 79409

LEROY L. CARNEYImco Services, Division of Halliburton Company, Houston, Texas 77027

Abstraet---Hydrothermal reactions in the system sepiolite/HzO have been examined between 149~ and316~ Approximately 10-20% of the starting sepiolite was converted to a smectite (stevensite) at 204~within 24 hr. Similar results were obtained when CaClz, NaOH, Ca(OH)z, or Mg(OH)2 was added to thesystem. In the presence of NaCI, about 60% of the sepiolite was converted to stevensite, whereas, only5% stevensite formed in the presence of MgCIz. Greater amounts of stevensite formed at 260~ in thesesystems. Above 316~ 60-80% of the sepiolite was converted to stevensite in 24 hr, regardless of thepresence or absence of salts. Within the experimental conditions used, temperature is the most importantfactor in the sepiolite-to-stevensite conversion.At or below 216~ sepiolite appears to transform into stevensite by dislocations involving c/2 glides thatare triggered by the stresses of the hydrothermal conditions. Above this temperature, stevensite seems toform by direct precipitation after dissolution of sepiolite.Key Words---Drilling Fluids, Hydrothermal Stability, Sepiolite, Smectite, Stevensite.

INTRODUCTIONSepiolite-based drilling fluids have been suggested

for use at the extreme temperatures and pressuresencoun tered in deep-well drilling (Carney and Meyer,1976). The conversion of sepiolite to smectite underthese conditions may favorably alter the rheolog-ical properti es of the drilling fluid. Using both a natu ralsepiolite and a synthetic gel of sepiolite composition,Mum pto n and Roy (1958) obtai ned a magnes ium smec-tite between 200~ and 350~ and und er 1379 bars w aterpressure in 8 hours to 3 weeks time. Fran k-Kam enets kye t a l . (1970, 1972) and Ots uka e t a l . (1974), however,found sepiolite to be hydrothermally stable to 325~and that a "hydrotalc" or "hydrated talc" phase witha basal spacing of 9.6 ,~ was produced above this tem-perature. Furthermore, Frank-Kamenetsky e t a l .(1970, 1972) fou nd that sepiol ite was stable up to 400~in the prese nce of NaCI, up to 350~ in the prese nce ofCaCIz, and up to 300~ in the pre sen ce of MgCIz.

The magnes ium smectite obtained by Mu mpton andRoy (1958) was obviously not a saponite per se, butstevensite, the Al-free member of the trioctahedralsmectite group, since by definition, significant amountsof AI are prese nt in saponite. Stevensite was proposedas a distinc t species by Fa ust a nd Mura ta (1953). Type-locality material from Springfield, New Jersey (U.S.National Museum #R4719) was later examined byBrindley (1955) who pointed out the existence of su-perlattice reflections at 25/~ that had been missed bythe previous investigators. Faust e t a l . (1959) thenreexamined the Springfield sample and confirmed theCopyright 9 1979, The Clay Minerals Society

presence of supeflattice reflections, attributing them tothe coexistence of talc domains (without octahedralvacancies) and t a l c - l i k e domains (with octahedral va-cancies). Thus, the concept of stevensite as a defecttrioctahedral magnesium smectite with octahedral va-cancies was developed. The close chemical relation-ship between stevensite and sepiolite was pointed outby Randall (1959) and Imai e t a l . (1970).

To clarify the hydrot herma l stability of sepiolite andto provide information on the mechanism of conversi onof sepiolite to stevensite, a series of experiments wascarried out under deep-well drilling conditions. Be-cause fluids are com monly contaminat ed with salts ofalkali and alkaline earth metals from the penetratedsedimentary formation, similar experiments were con-ducted in which known amounts of NaCI, CaCIz,MgCIz, NaOH , Ca(OH)2, and Mg(OH)z were added tothe system.

MATERIALS AND METHODSS e p i o l i t e s t a r t i n g m a t e r i a l

The sepiolite sample used in the experiments wasobtained from the Asche nbre nner deposit, Nye Coun-ty, Nevada, courtesy of Industrial Mineral VenturesCompany , Golden, Colorado. The deposit is located 9miles northeast of Death Valley Junction, California,and 3 miles due south of Devils Hole as indicated onthe U.S.G.S. map NJ 11-11: Death Valley, California-Nevada. The sample was obtained from a depth of 12.5-13.0 m at the co mp an y' s grid location of 12S/8E by Jack

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254 Gfiven and Carne y Clays and C lay Minerals

Table 1. Chemical composition of the Aschenbrenn er se-piolite after the ignition to 1000~Wt. %

SiO2 67.1AlzO3 2.70Fe203 (total iron) 0.66MgO 26.50CaO 1.48Na~20 0.32K20 0.55LizO 0.11TOTAL 99.42

(Loss on ignition: 21.91%)

May h ew , r e s i d en t g eo lo g i s t. T h e o n l y i mp u r i t y d e t ec t -ab l e b y X - r ay p o w d e r d i f f r ac t i o n w as ab o u t 2 -3 % d o -l o mi t e . T h e ch emi ca l co m p o s i t i o n o f t h e s amp l e i s l is t -ed i n T ab l e 1 an d w as d e t e r mi n ed b y a t o mi c ab s o rp t i o ns p ec t ro s co p y a s d e s c r i b ed b y L ee an d G / i v en (1 9 7 5 ) .T h e X - r ay p o w d e r d i f f r ac t i o n p a t t e rn s o f o r i en t eds l ides gave s t rong 001 ref l ec t ions charac ter i s t i c o f se-p io l i t e in the a i r -d r i ed s t a t e a t 12 .14 /~ , unde r 40% re la-t i v e h u mi d i t y an d a t r o o m t emp e ra t u r e . T h i s r e fl e c t io nshow ed a s l igh t bu t reproduc ib le expans ion to 12 .28 /~w h en t h e s amp l e w as s a t u r a t ed w i t h e t h y l en e g l y co l .A 0 .1 to 0 .7 ,~ expa ns ion o f sep io l i t e wi th e thy le ne g ly -co l was cons i s t en t ly observed by Powe (1977) . Trans -m i s s i o n e l e c tr o n m i c r o s c o p i c ( T E M ) e x a m i n a t i o ns h o w s t h a t t h e A s c h en b re n n e r s ep i o l i te o ccu r s a s i n -d iv idual f ibers up to 2 /z m in l eng th and f rom 200 to 300

in wid th and as b i rd nes t - l ike aggregates o f f ibers( s ee F i g u re s l a an d l b ) .Methods o f analysis

H y d ro t h e rm a l ex p e r i men t s w e re ca r r i ed o u t i n a s p e -c i a l l y d e s i g n ed h i g h - t emp e ra t u r e / h i g h -p re s s u re au t o -c l av e a t th e Ch em i ca l Res ea r ch L ab o r a t o ry o f H a f li -b u r t o n Se rv i ce s i n D u n can , O k l ah o ma . O n e h u n d redmi l l i l i t e rs o f a 4% sep io l i t e suspen s ion in d i s t i ll ed anddeion iz ed wa ter was h ea ted fo r 24 h r be twee n 149 ~ and316~ unde r p ressur e f rom 14 to 1379 bars . In o therru n s , 1 g o f t h e ch l o r i d e s an d h y d ro x i d e s o f N a , Ca , an dMg per 4 g o f sep io l i t e was a dded to the suspen s ion . Al lp ro d u c t s w e re cen t r i f u g ed w i th w a t e r an d d i a l y zed tor emo v e ex ces s s a l t s .

T h e p ro d u c t s w e re t h en ex ami n ed b y X - r ay p o w d e rd i f f r ac ti o n u s in g a Ph i l i ps N o re l co X - r ay d i f f r ac t o m e t e rw i t h N i - fi l te r ed Cu K a r ad i a t i o n , 1~ d i v e rg en ce an dsca t t e r s l i t s , a 0 .005" rece iv ing s l i t , and a scann ings p eed o f 1~ 20 /ra in . Or ien te d c lay f i lms were a i r -d r i eda t r o o m t em p e ra t u r e u n d e r 4 0 % r e l a t i v e h u mi d i t y . T h emeas u red d -v a l u e s w e re n o t co r r ec t ed fo r L o ren t z -p o -l a r i z a t i o n f ac t o r s . F o r s emi q u an t i t a t i v e e s t i ma t i o n o ft h e r e l a t i v e amo u n t o f s ep i o l i te an d s t ev en s i t e i n p ro d -uc t s , mix tu res o f the s t a r t ing sep io l i t e and a Ch eto ,

Figure 1. Transm ission electro n images of the original se-piolite: (a) individua l sepiolite fibers, and (b) a typica l birdnest-like aggregate of fibers.

A r i zo n a , m o n t mo r i l l o n i t e w e re p r ep a red a t 10 % i n t e r -v a l s . T h e C h e t o m a t e r i a l w a s c h o s e n b e c a u s e o f i ts

mo rp h o l o g i ca l s i mi l a r i ty to t h e s t ev en s i t e f o rmed i n t h eex p e r i men t s . G l y c o l - s a t u r a t ed s amp l e s w e re p r ep a redfor the sem iquan t i t a t ive es t imate s , and the 011 and 001re f l e c ti o n s o f s ep i o l i te an d s t ev en s i t e , r e s p ec t i v e l y ,w e r e c o m p a r e d .

E l ec t ro n mi c ro s co p i c s t u d i e s w e re mad e w i t h aJ E M-7 t r an s mi s s i o n e l ec t ro n mi c ro s co p e w i t h acce l -era t ing vo l t ages o f 80 and 100 kV. Smal l d rops o f veryd i l ut e s u s p en s i o n s w e re a i r - d r i ed o n 2 0 0 -mes h co p p e rg r i d s t h a t h ad b een p r ev i o u s l y co a t ed w i t h Fo rmv a rf i lms fro m a 0 . 3% Fo rm v a r s o l u t io n i n ch l o ro fo rm. T h egr ids were then coa ted wi th go ld and carbon .

E X P E R I M E N T A L R E S U L T ST h e r e s u l t s o f a l l r u n s i n t h e s y s t em s ep i o l i t e / w a t e r

an d t h e s y s t ems co n t a i n i n g ch l o r i d e s an d h y d ro x i d e sof Na, Ca , an d Mg are l i s t ed in Tab le 2 . The s ign i f ican tp o r t i o n s o f t h e X - r ay p o w d e r d i f f r ac ti o n p a t t e rn s o f k ey


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2 5 6 G f iv e n a n d C a rn e y Clays and Clay Minerals

T a b le 2 . H y d ro th e rma l t r e a tm e n t s o f s e p io l i t e f lu id s .T e m p e r a t u r e / P r e s s u r e

~ ~Sepiol i te d(011) (A)b e f o r e a n d a f t e rg lycola t ion % s mec t i t e i nproduct

300/475 149/33300/10,000 149/690400/500 204/35500/1000 260/69600/20,000 316/1379300/475 149/33300/10,000 149/690400/1000 204/69500/1000 260/69600/20,000 316/1379300/200 149/14400/500 204/35500/1000 260/69300/475 149/33300/10,000 149/690400/1000 204/69500/1000 260/69600/20,000 316/1379300/200 149/14400/500 204/35500/1000 260/69300/475 149/33300/10,000 149/690400/1000 204/69500/1000 260/69600/20,000 316/1379300/200 149/14400/500 204/35500/1000 260/69

S e p i o l i t e/ H 2 0 S y s t e m12.24 12.35 212.16 12.28 51 12.28 201 12.85 4012.24 80

S e p io l i te /N a C 1 S y s te m12.11 12.38 212.11 12.28 a1 12.28 601 12.70 7012.34 80

S e p i o l i t e / N a O H S y s t e m1 1 . 9 0 1 2 . 1 4 2i 12.38 20

12.84 70S e p io l it e /C a C l2 S y s te m

12.01 12.28 211.98 12.28 a1 12.24 201 12.28 501 12.81 80

S e p io l i t e /C a (O H )z S y s te m12.01 12.28 212.28 1012.27 30

S e p io l it e /Mg C l2 S y s te m12.14 12.28 211.98 12.28 212.28 512.28 4012.27 60

S e p io l i t e /Mg (O H )z S y s te m12.14 12.281 12.28 101 12.55 70

1 S e p io l i t e a n d s me c t i t e r e f l e c t io n s o v e r l a p .2 N o t d e t e c t a b le w i th X - ra y p o w d e r d i f f r a c t io n .3 P re s e n t b u t a t a l e v e l b e lo w 5 %.

p r o d u c t s a r e s h o w n i n F i g u r e 2 . S t e v e n s i t e w a s n o t d e -t e c t e d i n r u n s m a d e a t 1 49 ~ a n d 3 3 b a r s i n t h e s e p i o l i t e /H 2 0 s y s t e m w i t h o r w i t h o u t t h e a d d i t io n o f c h l o ri d e s .S i m i l a r r e s u l t s w e r e o b t a i n e d i n t h e s e p i o l i t e / h y d r o x i d es y s t e m s a t 1 49 ~ a n d 1 4 b a r s . W h e n t h e p r e s s u r e w a si n c r e a s e d t o 6 9 0 b a r s a t 1 4 9~ v e r y s m a l l q u a n t i t i e s( 5 % o r l es s ) o f s m e c t i t e f o r m e d i n t h e s e p i o l i t e / H 2 0s y s t e m a n d i n th e s e p i o l i t e / N a C 1 a n d s e p i o l i t e / C a C l 2s y s t e m s . A s i n d i c a t e d i n F i g u r e 2 , t h e s e s m e c t i t e p r o d -u c t s g a v e b r o a d , w e a k r e f l e c t i o n s a t 1 7 - 1 8 / ~ . N o s m e c -t i t e, h o w e v e r , f o r m e d a t 1 4 9~ a n d 6 90 b a r s i n t h e s e -p i o l i t e / M g C l z s y s t e m . T h u s , i n c r e a s i n g p r e s s u r e a t1 4 9~ h a d l i t tl e o r n o e f f e c t o n t h e s e p i o l i t e - t o - s t e v e n s -i t e c o n v e r s i o n .

A t 2 0 4~ a p p r e c i a b l e a m o u n t s o f s m e c t i t e f o r m e d int h e s e p i o l i t e / N a C l s y s t e m . A t 2 6 0 ~ a n d 6 9 b a r s , 4 0 -7 0 % o f t h e s a m p l e w a s c o n v e r t e d t o s t e v e n s i t e . W h e nt h e p r e s s u r e w a s r a i s e d t o 1 37 9 b a r s i n t h e s e p i o l i t e /C aC 12 s y s t e m , s i m i l a r r e s u l t s w e r e o b t a i n e d . T h e s e d a t aa g a i n s h o w t h a t p r e s s u r e h a d o n l y m i n o r i n f lu e n c e o nt h e c o n v e r s i o n o f s e p i o l it e to s t e v e n s i t e i n t h e s e h y -d r o t h e r m a l s y s t e m s . A t 2 6 0 ~ a s t r o n g r e f l e c t i o n w a sn o t e d a t 1 2 .7 0 A i n t h e X - r a y p a t t e r n o f th e s e p i o l i t e /N a C I p r o d u c t a n d a t 1 2 . 8 5 / ~ i n t h e p a t t e r n o f th e s e -p i o l i t e / H 2 0 p r o d u c t . A s i m i l a r r e f l e c t i o n w a s n o t e d a t1 2 .8 1 /~ f o r t h e se p i o l i t e / C a C 1 2 p r o d u c t a t 3 1 6 ~ a n d1 37 9 b a r s , b u t n o t f o r t h e c o r r e s p o n d i n g s e p i o l i t e /M g C I 2 p r o d u c t ( F i g u r e 2 ). H i g h e r o r d e r r e f l e c t i o n s w e r e


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Vol. 27, No. 4, 1979 Sepio tite-to-steve nsite transform ation 257

Figure 3. Typical smectite particles formed during the hy-drothe rmal treatme nt at 260~ and 69 bars (a) in the systemsepiolite/CaC12 and (b) in the system sepiolite/NaC1.Figure 4. Typica l smectite aggregates formed during the hy-drother mal treatments at 316~ and 1379 bars (a) in the systemsepiolite/CaC12, and (b) in the system sepiolite/NaC1.

no t obse rved , and the 12 .7 -12 .8 A ref l ec t ion does no ts eem t o h av e b een cau s ed b y p a r t i c l e - s iz e e f f ec ts . I nf ac t , e l e c t ro n mi c ro s co p i c ex am i n a t i o n o f t h e s e p ro d -u c t s s h o w ed n o o b s e rv ab l e d ec r ea s e i n t h e s i z e o f th esep io l i t e f ibers . No e xp lana t ion can be o f fere d fo r th i sref l ec t ion , a l though i t may be the re su l t o f a sep io l i t e !s t even s i t e mixed - layer ing . At 316~ and 1379 bars ,mo s t o f t h e s ep i o l i t e w as co n v e r t ed t o s t ev en s i t e i n -d ep en d en t o f w h e t h e r o r n o t ch l o r i d e s o r h y d ro x i d e sw ere p r e s en t i n t h e s y s t em.

H y d ro t h e rm a l t r e a t men t o f 14 9~ cau s ed n o d e t ec t -ab l e ch an g e i n t h e mo rp h o l o g y o r s t r u c t u r e o f t h e s e -p i o l i t e s t a r t i n g ma t e r i a l a s i n d i ca t ed b y t r an s mi s s i o ne l ec t ro n mi c ro s co p y . D i s c r e t e p a r t i c l e s o f s mec t i t ew e re n o t o b s e rv e d ev en w h en t h e p r e s s u r e w as r a i s edto 690 ba rs . At 260~ and 69 bars , how eve r , typ ica ls mec t i t e p a r t i c l e s co u l d b e s een i n t h e h y d ro t h e rma lprod uct s in the sep io l i t e /CaClz and sep io l i t e /NaC1 sys -t ems a s s h o w n i n F i g u re s 3 a an d 3 b , r e s p ec t i v e l y . H e ret h e t r an s i ti o n f ro m t h e o r i g i n a l f i b rou s mo rp h o l o g y o f

sep io l i t e to the f l aky ( lamel la r ) morph ology o f smect i t ecan be see n . T he o r ig ina l f iber ou t l ines a re s t il l v i s ib le ,an d t h e f i b e r s d o n o t s eem t o h av e b een d i s s o l v ed . S i m-i l a r s mec t i t e s w e re fo rmed d u r i n g t h e t r e a t men t s a t204~

T h e s mec t i t e s f o rmed b y h y d ro t h e rma l t r e a t men t o fsep io l i t e a t 316~ and 1379 b a r s a r e mo rp h o l o g i ca l l yd i f f e ren t f r o m t h o s e d e s c r i b e d ab o v e . T h es e s mec t i t e soccu r as i r regu lar , f l aky aggregates (Figures 4a and 4b)in which the o r ig ina l f iber fo rms are no t d i sc ern ib le .T h es e i r r eg u l a r f l ake s w e re p ro b a b l y fo rmed b y d i r ec tp r ec i p i t a t i o n a f t e r d i s s o lu t i o n o f t h e p a r en t s ep i o l i te . Alarge number o f spher i ca l par t i c l es o f s i l i ca(?) assoc i -a t ed w i t h t h e s t ev en s i t e p ro d u c t s c an a l s o b e s een i nF i g u re s 4 a an d 4 b .

M E C H A N I S M S O F TH ES E P I O L I T E - T O - S T E V E N S I T E C O N V E R S I O NT h e ex p e r i men t a l ev i d en ce p r e s en t ed h e r e o n t h eh y d ro t h e rm a l s t ab i li t y o f s ep i o l it e an d s u b s eq u en t f o r -


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258 G i iven and Car ney Clays and Clay Minerals

,C/2 ~C/2 *C/2

C Zr ~

)b

S E P I OLI TE

c/~' GLIDE)

INTERLAYERCATION

S TE V E N S I TEFigur e 5. Schemat ic r epr esen ta t ion of sep io l i t e s t r uc tur e aspr o jec ted a long the a - ax is ( pa r a l le l to f ibe r d i rec t ion) and i t st r ans f or mat ion to s tevens i te by the c g l ide mechanism.

m a t i o n o f s t e v e n s i t e a l l o w s a m o d e l t o b e p r o p o s e d f o rt h e t r a n s f o r m a t i o n o f a c h a i n s i l i c a t e t o a l a y e r s i l i c a t ea n d a l s o p r o v i d e s i n f o rm a t i o n o n t h e n a t u r e o f t h e d e -f e c t s i n t h e s t r u c t u r e o f s t e v e n s i t e .

T h e c r y s t a l s t r u c tu r e o f s e p i o li t e i s s h o w n s c h e m a t -i c a l l y i n F i g u r e 5 a s p r o j e c t e d a l o n g t h e f i b er d i r e c ti o n .I n a c c o r d a n c e w i th Z v y a g i n et al. ( 1 9 6 3 ) , t h e c r y s t a l -l o g r a p h i c a - a x i s o f s e p i o l i t e i s s e t p a r a l le l t o t h e f i b e rd i r e c t i o n . T h e r e c t a n g u l a r e n v e l o p e - l i k e b l o c k s i n F i g -u r e 5 r e p r e s e n t t h e p r o j e c t i o n s o f ta l c - li k e r i b b o n s i nt h e s e p i o l i t e s t r u c t u re . T h e h a t c h e d a n d d a r k t r i a n g l e si n d i c a t e t h e d i r e c t i o n s i n w h i c h t h e s i l i c a t e t r a h e d r ap o i n t i n t h e s e r i b b o n s . T h e s e p i o l i t e s t r u c t u r e m a y t h u sb e d e s c r i b e d a s t a l c - l i k e r i b b o n s t h a t a r e d i s p l a c e d w i t hr e s p e c t t o e a c h o t h e r b y a c/2 g l id e . A s t h e s e r i b b o n sa r e a t ta c h e d t o e a c h o t h e r o n ly b y S i - O - S i b o n d s a tt h e i r f o u r c o r n e r s , t h e s e p i o l i t e s t r u c t u r e i s a r a t h e rd e l i c a t e o n e . A t h i g h e r t e m p e r a t u r e a n d p r e s s u r e t h er i b b o n s m a y c h a n g e t o a m o r e s t a b l e c o n f ig u r a t i o n b yu n d e r g o i n g a c/2 g l i d e , e . g . , i n a s e r i e s o f d i s l o c a t i o n s ,a n d b y e s t a b l i s h i n g a d d i t i o n a l b o n d s b e t w e e n t h e i r o c t a -h e d r a l n e t w o r k s . A l t e r n a t i v e l y , se p i o l i t e m a y b r e a kd o w n i n t o t a l c -l i k e r i b b o n s , e . g . , b y p a r t i a l d is s o l u t i o n ,w h i c h i n t u r n m a y r e a s s e m b l e i n t h e s a m e m a n n e r a sa c h i e v e d b y c/2 g l i d e s . A s i n d i c a t e d i n F i g u r e 6 ,~ th e n e wp h a s e , f o r m e d b y e i t h e r m e c h a n i s m , c a n n o t b e t al ~: T h em a g n e s i u m o c t a h e d r a i n t h e t a l c -l i k e r i b b o n s a r e l o c a t e da t z = 8 8 i n o n e r i b b o n a n d a t z = 3A a t t h e n e x t r i b b o ni n t h e s e p i o l i t e s t r u c t u re . M a g n e s i u m p o s i t i o n s a l o n gt h e e d g e s o f t h e ri b b o n s a t z = 8 8 a r e d e s i g n a t e d b y M 1a n d M 2 , a n d t h o s e a l o n g t h e e d g e s o f t h e r i b b o n a t z = 3 ~a r e s i m i l a rl y d e s i g n a t e d b y M I ' a n d M 2 ' . E a c h o f t h eM 1 a n d M 1 ' m e t a ls h a v e t w o w a t e r l i g a n d s , w h o s e p o -s i t io n s a r e m a r k e d b y X i n t h e c - p r o j e c t i o n o f t h e s t r u c -t u r e ( F i g u r e 6 ). A f t e r t h e c / 2 g l i d e s (o r w h e n t h e r i b b o n sa r e r e a s s e m b l e d ) , t h e H 2 0 l i g a n d s s u p e r i m p o s e , a n d ar e a c t i o n s u c h a s t h a t f o r m u l a t e d i n F i g u r e 7 sh o u l d o c -c u r , t h e r e b y g e n e r a t i n g l a y e r c h a r g e i n th e s m e c t i t es t r u c t u r e . D e p e n d i n g o n t h e n u m b e r o f w a t e r m o l e c u l e st h a t u n d e r g o t h i s r e a c t i o n , t h e s e p i o l i t e - t o - s t e v e n s i t ec o n v e r s i o n c a n b e f o r m u l a t e d a s :

0 9 b

12 M2' M MI

MI MI' M2' M2

a2 M2* M MIa

Z = 3/4

X : HaGZ =114

Figur e 6. D is t r ibu tion of the oc tahedr a l ca t ions in sep io l i t es t r uc tur e and f or mat ion of va canc ies , E l, f o l low ing the c g l idesin s tevensi te s tructure.

[ Mgs( H 2 0) 4( O H ) 4 S i12O30]~ --~sepiol i t e

3 [Mg2.67(H20)0.67- -~s t e v e n s i t e

+ 2 H 2 0 + 3 ( x ) [ H + ]w h e r e t h e z e o l i t ic w a t e r o f s e p i o l i te is d i s r e g a r d e d . I fa l l o f t h e c r y s t a l li n e w a t e r l ig a n d s b e c o m e h y d r o x y l s ,t h e l a y e r c h a r g e o f s t e v e n s i t e w i ll r e a c h a m a x i m u mv a l u e o f + 0 . 6 7 p e r f o r m u l a u n i t . I n a d d i t i o n , c e r t a i no c t a h e d r a l p o s i t i o n s ( F i g u r e 6 ) w il l b e v a c a n t . T h e s eo c t a h e d r a l d e f e c t s a r e l o c a t e d o n t h e c g l i d e p l a n e a n dm a k e u p ~/9 o f t h e t o t a l o c t a h e d r a l p o s i t i o n s . A d d i t i o n a lm a g n e s i u m t o f il l t h e s e p o s i t i o n s c a n b e s u p p l i e d o n l yb y a d e c o m p o s i t i o n o f s o m e o f th e s e p i o l i t e i n t h e s y s -t e m . S u c h a d e c o m p o s i t i o n w o u l d a l s o g e n e r a t e fr e es i li c a . A d d i t i o n a l m a g n e s i u m i n s t e v e n s i t e ( i . e ., w h e nM g i s g r e a t e r t h a n 2 .6 7 i n t h e f o r m u l a ) d e c r e a s e s i t s l a y -e r c h a r g e . F o r e x a m p l e , a b o u t h a l f o f t h e v a c a n t p o s i -t i o n s a r e f i l l e d i n t h e s t r u c t u r e o f s t e v e n s i t e f r o mS p r i n g fi e ld , N e w J e r s e y , i n w h i c h t h e t o t a l o c t a h e d r a lo c c u p a n c y i s 2. 92 p e r f o r m u l a u n it ( F a u s t a n d M u r a t a ,1 95 3). A s t h e s e v a c a n t o c t a h e d r a l p o s i t i o n s f i l l w i t hm a g n e s i u m , , t a lc d o m a i n s f o r m w i t h i n t h e s t e v e n s i t es t r u c t u r e , a n d m a y b e r a n d o m l y m i x e d w i t h s m e c t i t ed o m a i n s w i t h i n a l a y e r . A l s o , th e t a l c d o m a i n s m a y b er a n d o m l y s t a c k e d i n s u c c e s s i v e l a y e r s in t h e f o rm o fm i x e d - l a y e r i n g . T h i s s i t u a t i o n c o n t i n u e s u n t i l a l l o f t h ev a c a n t o c t a h e d r a l s i t e s a r e f il l e d a n d t a l c is f o r m e d .

T h e s m e c t i t e s s h o w n i n F i g u r e s 3 a a n d 3 b w e r e p r o b -a b l y fo r m e d b y t h e p r o p o s e d c/2 g l i d in g m e c h a n i s m .H e r e , t h e t r a n s i t i o n f r o m f i b r o u s m o r p h o l o g y t o a l a -m e l l a r o n e i s w e l l d i s p l a y e d . T h e f o r m a t i o n o f i r r e gu -l a r l y f o l d e d s m e c t i t e f l a k e s, h o w e v e r , s u c h a s t h o s e i nF i g u r e s 4 a a n d 4 b , i s p r o b a b l y r e l a t e d t o a d i r e c t p r e -c i p i t a t io n o f s m e c t i t e a f t e r t o t a l d i s s o l u t i o n o f t h e s e -p i o l i te . I n f a c t , w h e n t h e t e m p e r a t u r e o f r u n s w a s r a i s e dt o 3 1 6~ m o s t o f t h e s m e c t i t e s e e m e d to f o r m b y t h ed i s s o l u t i o n - r e p r e c i p i t a t i o n m e c h a n i s m , i n d e p e n d e n t o fa d d i t i v e s .


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Vol. 27, No. 4, 1979 Sepiolite-to-stevensite transformation 259

0O ~ / H z OEg0 ~ H 2 0

0

0H 2 0 ~ I ~ 0

+ H,O0

0 0

o / - t - + ~0 b

CREATES LAY ERCHARGEFigure 7. Reaction mechanism between the magnesium oc-tahedra along the edges of talc-like ribbons after c glides (mag-nesium at the edge ofone ribbon is designated by Mg and mag-nesium at the edge of the other r ibbon is designated by Mg').

CONCLUSIONS(1) The effect of pressure within the range applied in

this stud y is negligible for the c onve rsio n of se-piolite to stevensite.

(2) Temp erat ure is the major factor in sepiolite-to-ste-vensite conversi on within the period of 24 hr. Ap-preciable am ount s (> 10%) of smectite first developat 204~ with in this period . At 316~ most of thesepiolite converts to smectite regardless of thepresence or absence of salts or hydl"oxides, dem-onstratin g the param0~nt importance of tempera-ture in this conver~on.

(3) Chlorides of Na and Ca are more effective than theirhydroxides in converting sepiolite to smectite intemper atures up to and includ ing 260~ howev er,Mg(OH)2 p romote s the co nver sion more than doesMgC12. NaCl is by far the most effective agent inthis conv ersi on up to 260~

(4) In fresh water, sepiolite converts to smectite as eas-ily as it does in the presence of calcium.

The present work found that sepiolite converts hy-drother mally to smectite at 204~ in agre emen t withthe results by Mu mpt on and Roy (1958). Discre panciesexist between the results of this study and those byFrank-Kamenetsky e t a l . (1970, 1972) and by Ot suk a

e t a l . (1974) ( v i de s u p r a ) . At the present time no expla-nation can be offered for these discrepancies.

ACKNOWLEDGMENTSSincere thanks are due to G. W. Brindley and F. A.

Mumpto n for their most stimulating interest and sug-gestions in this work. We thank also Mr. Mark Shuranof IMCO Services, Division of Halliburton Companyfor this careful analysis of the sepiolite sample withatomic absorption spectroscopy. D. D. Eberl is ac-knowledged for his critical review of the manuscriptand for pointing out the possible dissolution mechanismin the sepiolite-to-stevensite conversion.

REFERENCESBrindley, G. W. (1955) Stevensite, a montmorillonite-typemineral showing mixed-layer characteristics: A m e r . M i n -eral. 40, 239-247.Carney, L. L. and Meyer, R L. (1976) A'new approach tohigh temperature drilling fields: S o c . P e t r o l . E n g . , P a p e rN o . S P E 6 02 5, 8 pp.Faust, G. T. and Murata, K. J. (1953) Stevensite, redefinedas a member of the montmorillonite group: A m e r . Min e r a l .38, 973-987.Faust , G. T., Hathaway, J. C., and Millot, G. (1959) A re-study of stevensite and allied minerals: A m e r . Min e r a l . 4 4 ,342-370.Frank-Kamenetsky, V. A., Kotov, N. V., and Klochkova, G.N. (1970) Phase transformations of sepiolite and palygor-skite under hydrothermal conditions at elevated pressure inthe presence of KCI and NaCI: G e o c h e m . I n t . 7, 934-942.Frank-Kamenetsky, V. A., Kotov, N. V., and Klochkova, G.N. (1972) Phase and structural changes in sepiolite and pal-

ygorskite under hydrothermal conditions in the presence ofCa and Mg chlorides: G e o c h e m . I n t . 9, 818-826.Imai, N., Otsuka, R., Nakamura, T., and Tsunashima, A.(1970) Stevensite from the Akatani mine, Niigata Prefec-ture, northeastern Japan: Clay Sc i . 4, 11-29.Lee, R. W. and Gfiven, N. (1975) Chemical interferences inatomic absorption spectrometric analysis of silicates in thefluoboric-boric acids matrix: C h e m . G e o l . 16, 53-58.Mumpton, F. A. and Roy, R. (1958) New data on sepioliteand attapulgite: P r o c . 5 th N a t . C o n f . C la y s a n d C la y Min -erals, Urbana, II1., 1956, 136-143.Otsuka, R., Sakamoto, T., and Hara, Y. (1974) Phase trans-formations of sepiolite under hydrothermal conditions:N e n d o K a g a k u 14, 8-19.Powe, W. H., II I (1977) Mineralogical studies on coexistingsaponite and sepiolite: M.S. Thesis, Texas Tech University,Lubbock, Texas, 84 pp.Randall, B. A. O. (1959) Stevensite from the Whin Sill in theregion of the North Tyne: Min e r a l . Ma g . 32, 218-225.Zvyagin, B. B., Mishchenko, K. S., and Shitov, V. A.(1963) Electron diffraction data on the structures of sepio-lite and palygorskite: Sov. Phys.---4?rystallogr. 8, 148-153.(R e c e iv e d 4 O c to b e r 1 9 7 8 ; a c c e p te d 2 6 Ma r c h 1 9 7 9 )


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2 6 0 G f i v e n a n d C a r n e y Clays and Clay Minerals

Pe31oMe- -- -- I/ I3yqa. ll ltC b rKllpoTepMa~qbHble pe aK lm n B C ltC TeMe cen H o~ nT /H zO npH Te Mn epa Ty pe OT 149 ~ ~Io3 1 6 ~ H p n 2 0 4 ~ a T eq eH 1 4e 2 4 q a c o B n p n M e p H o 1 0 - 2 0 % H a q a _ a b H or o c e n n o ~ n T a 6 bIY lO n p e B p a m e r t oB cMerTr tT (C TeB eHC B T). An ano r i~q Hb m pe3y .l IbTaTbI 6b lJ IH no J lyqeH bl npH j io6aa. rl eHla t, 1 C aC 12 , N a O H ,C a ( O H ) z , r i.n n M g ( O H ) 2 B C H C Te M y . B I lp rl Cy T CT B H H N a C I o K o .r lO 6 0 % c e n n o Y m T a 6 b l ~ O n p e o 6 p a 3 0 a a H oB C TeB eHC nT, B TO B peM~l KaK B HpncyTCTB HI, 1 MgC 12 06p a30 B aJ Iocb TOJ IbKO 5% C TeB eHC l tTa . B oJ ~hmeeKOJIHHeC TBO C TeB eHC HTa B :gTHX C r lC TeMax 6b lJ IO no J Iyqe Ho np n 260 ~ FIpI~ TeM r lepaT ypa x , n pe ab i -m a t o t t t n x 3 1 6 ~ B T e q e H i t e 2 4 q aC O B 6 0 - - 8 0 % c e n n o J m T a n p e o 6 p a 3 o B b m a z i o c b B C T eB eH C M T H e 3a B Il Cl IM OOT HpHCyTCTBH~I H.rn40TCyTCTBH~I co JIe~ . BbldlO yCTaHOBJIeHO, qTO np H co6 a~o ~aB mn XC ~i yCJIOBM~IX3KC I IepHMeHTOB , Te M ne paT yp a ~IB JLqeTC ~I Ha n6o J lee B a~KHbIM qbaKTOpOM B npe o6 pa3 oB as r I H cen r tonr lT aB CTeBeHCHT.

I J pr t T em ne pa Ty pe 21 6~ r tn rt Hnm e cenHoJ I~IT , HOB It JIHMOMy, nep exo J l~T B C TeBeHC HT B pe3 y~ bT aT enep em elU eH rlf i , BK.r lloqaioII IHX CKOJIb>KeHIDIel2, KOT Opble BO3H ItKaiOT FIOJ1 B.IIIt~IHIteM rltJlpo Te pz aJIb rll, lXyCJIOBMI~. I 'l pn 6o Jie e BbICOKI,X T e M n e p a T y p a x C T eB eH C I, T , n O B rI ~H M O M y , q b o p M n p y e T c n n y T e m o e n o c p e J l -C TB eHHOrO ocax

Documents

1979 - The Hydrothermal Transformation of Sepiolite to Stevensite and the Effect of Added Chlorides and Hydroxides