Formation of X-Ray Aluminium Hydroxides

8/13/2019 Formation of X-Ray Aluminium Hydroxides

1/20

7 4 9

F o rm a t i o n o f X r a y amo r p h o u s a n d c r y st al l i n ea l u m i n i u m h y dr o x i d es 1B y P A H o H s u , P h . D . , a n d T ~O M AS F . B A TE S, P h . D .

D e p a r t m e n t o f G e o c h e m i s t r y a n d M i n e ra l o g y , T h e P e n n s y l v a n i aS t a t e U n i v e r s i t y , U n i v e r s i t y P a r k , P e n n s y l v a n i a , U . S . A .

[ T a k e n a s r e a d 3 0 J a n u a r y 1 9 6 4 ]

S u m m a r y V a r i o u s c r y st a ll i n e a n d X - r a y a m o r p h o u s f o r m s o f a l u m i n i u m h y d r -o x i d e p r e p a r e d f r o m s u l p h a t e a n d c h l o r id e so l u t i o n s b y v a r y i n g t h e m o l e r a t i o o fN a O H t o A1a+ h a v e b e e n c h a r a c t e r i z e d b y c h e m i c a l a n a l y s i s a n d X - r a y d i f f ra c t io n .W h e n t h e N a O H / A 1 r a t i o i s 3 o r 3.3 , c r y s t a l l i n e A l O H ) a i n t h e f o r m o f b a y e r i t e ,n o r d s t r a n d i t e , g i b b s i t e , o r m i x t u r e s is o b t a i n e d i n s e v e r a l h o u r s . W h e n t h e r a t i oi s 2.7 5 o r b el o w , n o A I O H )a i s e v i d e n t a n d t h e p r o d u c t s a r e X - r a y a m o r p h o u s a n dr e m a i n so e v e n a f t e r a g e i n g f o r s i x m o n t h s . C h e m i c a l a n a l y s i s i n d i c a t e s t h a t t h ea m o r p h o u s p r e c i p i t a t e s a r e b a s ic a l u m i n i u m s u l p h a t e s o r c h lo r i de s . I n t h e 0 t o 2 .1r a n g e o f N a O H / A 1 , t h e c o m p o s i t i o n o f t h e p r o d u c t s i s c o n s t a n t , b e i n g a p p r o x i m a t e l yAI OH)~.~X0.s . In th e 2 .1 to 2 .7 5 r a n g e , a c o n t in u o u s s e ri e s o f b a s i c s a l t s , o f c o m-pos i t ion ra ng ing f rom AI OH)~ .2X0. to Al OIt )~ .TsX0.25 , i s ob ta in ed .T h e f o l l o w i n g h y p o t h e s i s i s p r o p o s e d t o a c c o u n t f o r t h e o c c u r r e n c e o f X - r a ya m o r p h o u s v e r s u s c r y s t a l l i n e f o r m s : W h e n N a O H i s a d d e d t o a n a l u m i n i u m s a l ts o l u ti o n , t h e i n i t i a l r e a c t i o n y i e ld s A I O H ) + i o ns , w h i c h p o l y m e r i z e i n t o s t a b l e6 - m e m b e r e d r i n g u n i t s o f c o m p o s i t i o n A ls O H )~ + o r m u l t i p l e s t h e r e o f d o u b l e a n dtr ip le r ings o f co m pos i t ion Al~0 OI-I ) + an d AI~s OH)~+ ) , a l l w i t h H 2 0 m o l e c u le s o nth e s u r fa c e . A t N a O H /A 1 ~ 2 o r n e a r ly so , t h e in c lu s io n o f A 1a+ i n t h e b a s i c r i n gu n i t s i s c o m p l e t e ; s ti l l f u r t h e r O H - t h e n t r a n s f o r m s t h e s e r i n g u n i t s t o l a r g e rp o ly m e rs , g iv in g r i s e to a c o n t in u o u s s e r i es o f s p e cie s. A t N a O H /A 1 ~ 2 .7 5 a n db e l o w , t h e p o s i t i v e l y c h a r g e d h y d r o x y - a h m i n i u m p o l y m e r s r e p e l o n e a n o t h e ru n l e s s j o i n e d t o g e t h e r b y t h e c o u n t e r - a n i o n s t o f o r m b a s i c a l u m i n i u m s a l t s , w h i c h a r eu s u a ll y X - r a y a m o r p h o u s b ec a u se o f t h e i r h i g h l y h y d r a t e d s t a te . A t N a O H / A 1 ~ 3 ,t h e n e t p o s i t i v e c h a r g e p e r a l u m i n i u m d i s a p p e a r s a n d c o n s e q u e n t l y t h e r e p u l s i o na m o n g p o l y m e r s a s w e l l a s t h e i r w a t e r o f h y d r a t i o n b e c o m e s n e g l ig i b l e ; t h e r e f o r e ,a l l t h e p o l y m e r s c l u s t e r t o g e t h e r a n d f o r m c r y s t a l l i n e A I O H )a i n a m a t t e r o f h o u r so r d a y s , d e p e n d i n g o n t h e c o n d i t i o n s o f c r y s t a l g r o w t h .R E C I P I T A T I O N o c c u rs w h e n a n a h m i n i u m s a l t s o lu t i o n i s m i x e dw i t h a b a s e i f b o t h r e a g e n t s a r e o f t h e p r o p e r c o n c e n t r a t i o n . T h e

p r e c i p i t a t e is s o m e t i m e s X - r a y a m o r p h o u s , s o m e t i m e s c r y s t a l l i n e . A ss h o w n i n t h e l i t e r a tu r e a n d r e v i e w e d b y N e w s o m e e t a l 1 9 6 0 ) , m a n yw o r k e r s h a v e a t t e m p t e d t o d e s c r ib e a n d c h a r a c t e r i z e t h e s e p r e c i p i t a t e s .

1 C o n t r i b u t i o n N o . 6 2 - 5 0 f r o m t h e C olle ge o f M i n e r a l I n d u s t r i e s , T h e P e n n -s y l v a n i a S t a t e U n i v e r s i t y .


2/20

750 PA HO HSU AND T F BATES ONH o w e v e r , l it tl e a t t e n t i o n h a s b e e n p a i d t o t h e m e c h a n i s m o f th e i r f o r m a -t io n a n d t h e r e as o n s f o r th e a m o r p h o u s c h a r a c t e r o f s o m e a n d t h ec ry s t a l l i n i t y o f o t h e rs . M a rb o e a n d B e n t u r (19 61 ) r e c e n t l y d e sc r ib e dt h e m e c h a n i s m o f a l u m i n i u m h y d r o x i d e f o r m a t i o n a s a c o n s eq u e nc e o f t h ere m o v a l o f p ro t o n s f ro m t h e h y d ra t i o n sh e l l o f a l u m i n i u m io ns . A c c o rd -i n g t o t h e i r c o n c e p t s , f o r e i g n i o n s h a s t e n o r r e t a rd t h e fo rm a t i o n o fa l u m i n i u m h y d ro x i d e b y t h e i r p o s i t i v e o r n e g a t i v e e f f e ct o n t h e r e m o v a lo f th e p ro t o n s .

Th e m a i n o b j e c t iv e o f t h e p re se n t s t u d y i s t o p ro v i d e a d d i t i o n a l e x p e r i -m e n t a l d a t a a n d t o fu r t h e r c o n s i d e r p o s s i b l e m e c h a n i sm s o f a l u m i n i u mh y d ro x i d e fo rm a t i o n i n t h e l i g h t o f t h e a v a i l a b l e e v i de n c e .In m o s t e a r l i e r w o rk , v a r i o u s p ro d u c t s w e re fo rm e d b y c o n t ro l l i n gt h e p H o f so l ut io n s d u r i n g p re p a ra t i o n o r a g e in g (W e i se r e t a l . 1940 and1941 ; H arr i s a nd Sing, 1955 an d 1957 ; Pap 6e, Te rt ian , an d Bia is , 1958 ;B a l e a n d S e h m i d t , 1 9 5 8 a n d 1 95 9 ; M a rb o e a n d B e n t u r , 1 96 1 ; M a c K e n z i ee t a l . 1 96 2) . H o w e v e r , a c c o rd i n g t o t h e p re l i m i n a ry w o rk in th i s s t u d y ,p H i s c lo se ly r e l a t e d t o t h e p ro d u c t o n l y u n d e r r e s t r i c t e d e x p e r i m e n t a lc o n d i ti o n s. B y v a ry i n g t h e c o n d i ti o n s o f p r e p a ra t i o n , q u i t e d i f f er e n tp ro d u c t s c a n b e p ro d u c e d a t t h e s a m e p H ( e .g . H e rb i l l o n a n d G a s t u e h e ,1962). Th e reaso n fo r t h i s va r i a t ion i s no t c l ea r ly know n, bu t t hek i n e ti c s o f r e a c t i o n a n d t h e p re se n c e o f a n i o n s m a y p l a y i m p o r t a n t ro le s .P re l i m i n a ry e x p e r i m e n t s i n d i c a t e t h a t so m e p re c i p i t a t e s fo rm e d a sa resu l t o f l oca l ly h igh a lka l in i ty a re no t read i ly , o r a re never , red i sso lvedi n a w e a k l y a c id i c m e d i u m . I t h a s lo n g b e e n k n o w n t h a t t h e k i n d a n da m o u n t o f an i on s p r e se n t a r e i m p o r t a n t t o t h e p r o d u c t ; t h e m e c h a n i s mi n v o l v e d , h o w e v e r , is f a r f ro m t h o ro u g h l y u n d e r s t o o d .

In th i s s tudy , i n o rde r to min imize loca l i zed h igh a lka l in i ty , a l l t hesa m p l e s w e re p re p a re d b y a d d i n g d i l u t e N a O H t o a r e l a t i v e l y c o n c e n -t r a t e d a l u m i n i u m c h lo r id e o r su l p h a t e so lu t io n . Th e a m o u n t s o f N a O Hand a lumin ium sa l t s were c r i t i ca l ly con t ro l l ed to p rov ide a se r i e s o fp re p a ra t i o n s w i t h v a r io u s r a t io s o f N a O H / A 1 i n o rd e r t o u n d e r s t a n dm o re e a s i l y b o t h t h e n a t u r e o f th e r e a c t i o n b e t w e e n O H - a n d A 13+ i o nsa n d t h e c o m p o s i ti o n o f t h e p ro d u c t s .

T h e e q u i l i b r i u m p H o f t h e se sp e c im e n s w a s r e a c h e d i m m e d i a t e l ya f t e r m ix i ng . U p o n a g e in g , s o m e s a m p l e s m a i n t a i n e d t h e i r e q u i l i b r iu mp H fo r o n e y e a r , t h e l i m i t o f o b se rv a t io n , w h il e o t h e r s m a i n t a i n e d t h e i rp H fo r s e v e ra l m o n t h s , a f t e r w h i c h t i m e i t d ro p p e d a p p re c i a b l y , a c c o m -p a n i e d b y a c h a n g e i n t h e n a t u r e o f t h e p ro d u c t . Em p h a s i s i n t h ep re se n t s t u d y i s o n th e i n i ti a l r e a c t io n . I n v e s t i g a t i o n o f t h e su b se q u e n tchan ges i s s t i l l in progress .


3/20

LUMINIUM HYDROXIDES 75Preparat ion of a luminium hydroxides

M o s t o f t h e a l u m i n i u m h y d r o x i d e s u s e d i n t h i s s t u d y w e r e p r e p a r e db y a d d i n g v a r i o u s a m o u n t s o f 0 .1 N N a O H t o 5 0 0 m l o f 0 2 N A l e( S 04 ) ss o l u t i o n o r t o 2 0 0 m l o f 0 5 N A 1C1 s o l u t i o n d r o p w i s e w i t h v i g o r o u s s t i r -r i n g , t h e n d i l u t i n g t o 2 0 0 0 m l . T h e a m o u n t s o f N a O H w e r e a d j u s t e d t o g i v ea N a O H / A 1 r a t i o o f 0 - 0 t o 3 3 i n t h e f i n a l s u s p e n s i o n . T h e r a t e o f a d d i t i o no f N a O H w a s k e p t a t 5 0 m l i n 3 0 m i n u t e s . T h e c o n c e n t r a t i o n s o f a l u m i -n i u m , c h l o r id e , o r s u l p h a t e i n t h e f i n a l s u s p e n s i o n w e r e a l l 0 . 0 5 e q / l i t r e .

E i g h t a d d i t i o n a l s a m p l e s w e r e p r e p a r e d a s f o l l o w s : F o u r s a m p l e s i nt h e A 1 C 1 3 s y s t e m ( N a O H / A 1 = 2 .4 0 , 2 .5 5 , 2 .7 0 , a n d 2 .7 5 ) w e r ep r e p a r e d b y a d d i n g 0 - 4 N N a O H t o 12 5 m l o f N A 1C 1 d r o p w i s e w i t hv i g o r o u s s t i r r in g , t h e n d i l u t i n g t o 5 0 0 m l ; t h e c o n c e n t r a t i o n o f c h l o r id ei n t w o o f t h e s e s a m p l e s ( N a O H / A 1 = 2 . 7 0 a n d 2 - 7 5) w a s 0 .2 5 e q / l i t r e ,b u t N aC 1 w a s a d d e d t o t h e o t h e r t w o s a m p l e s ( N a O H / A I = 2 .5 0 a n d 2 5 5 )t o g i v e a f i n a l c o n c e n t r a t i o n o f 1 ,0 e q / l i t r e o f c h l o r i d e . F o u r s a m p l e sw i t h N a 0 H / A 1 = 1 8 i n t h e A 1 2 ( S 0 4 ) a + N a O H s y s t e m w e re p r e p a r e d b ya d d i n g d r o p w i s e w i t h v i g o r o u s s t i r r i n g 6 0 0 m l o f 0 ,1 N N a 0 H t o 2 0 0 m lo f 0 , 5 N A 1C 13 s o l u t i o n c o n t a i n i n g v a r i o u s a m o u n t s o f N a 2 S 0 a , t h e n d i -l u t i n g t o 2 0 0 0 m l ; t h e s u l p h a t e c o n t e n t s i n t h e f i n a l s u s p e n s i o n s w e r e0 , 0 2 , 0 , 0 5, 0 ,2 , a n d 1 , 0 e q / l i t r e , r e s p e c t i v e l y .

Methods of characterizationChemical ana lysis of the precipitate product A 5 0 - m l s u s p e n s io n a l iq u o t w a s t a k e nf r o m e a c h s a m p l e a n d c e n t r i f u g e d ( t h e l e n g t h o f c e n t r i f u g e t i m e a n d t h e s p e e dw e r e n o t f o u n d t o b e c r i t ic a l ). T h e p I { o f t h e c e n t r i f u g a t e w a s m e a s u r e d w i t h aB e c k m a n pI -I m e t e r , M o d e l G . T h e p r e c i p i t a t e w a s w a s h e d o n c e w i t h w a t e r a n do n c e w i t h 7 0 % a l co h o l , t h e n 1 0 m l o f N H C 1 w e r e a d d e d , a n d t h e p r e c i p i t a t e w a s

d i sp e r se d a n d m a i n t a i n e d f o r e x a c t l y 2 0 m i n u t e s w i t h f r e q u e n t s t i r r i n g ; t h e s u sp e n -s i o n w a s c e n t r i f u g e d a g a in . T h e p r e c i p i t a t e r e m a i n i n g u n d i s s o lv e d , i f a n y , w a sb r o u g h t i n t o s o l u t i o n w i t h 1 0 m l 6 N H C 1 w h i l e i m m e r s e d i n a b o i li n g w a t e r b a t h .I n s o m e ca se s, w h e n t h e a l u m i n i u m c o n t e n t i n t h e p r e c i p i t a t e w a s o f i n t e r e s t , t h ep r e c i p i t a t e w a s d r i e d a t 1 00 ~ C a n d w e i g h e d . T h e a l u m i n i u m c o n t e n t i n b o t h H C Ie x t r a c t s w a s d e t e r m i n e d w i t h a l u m i n o n ( H s u , 1 9 63 ). I n t h o s e sa m p l e s c o n t a i n i n gs u l p h a te , t h e s u l p h a t e c o n t e n t i n t h e H C I e x t r a c ts w a s d e t e r m i n e d . T h e s u l p h a t ew a s p r e c i p i t a t e d a s b a r i u m s u l p h a t e a n d w e i g h e d a c c o rd i n g t o t h e p r o c e d u r e o f t h eU . S . S a l i n i t y L a b o r a t o r i e s ( 1 95 4) . A c o n t r o l o f k n o w n s u l p h a t e c o n t e n t w a s r u n a l o n gw i t h t h e u n k n o w n s ; t h e a c i d i ty , s u l p h a t e c o n t e n t , v o l u m e o f s a m p l e , a n d a m o u n t o fr e a g e n t u s e d fo r t h e c o n t r o l w e r e k e p t a s clo se t o t h a t o f t h e u n k n o w n s a s p o s si b le .T h e O H - i n t h e p r e c i p i t a t e w a s d e t e r m i n e d a s f ol lo w s : a s e p a r a t e 5 0 - m l a l i q u o tw a s t a k e n f r o m e a c h s a m p l e , c e n t r i f u g e d , a n d w a s h e d w i t h w a t e r a n d a l c o h o l a sb e f o re . T h e n t h e p r e c i p i t a t e w a s d i ss o l v e d i n 50 m l o f 0 . 5 N N a F s o l u ti o n . T h eO H - r e l ea s e d w a s t i t r a t e d w i t h 0 .1 N H C 1, u s i n g p h e n o l p h t h a l e i n a s t h e i n d i c a t o r .T h e n t h e s a m p l e w a s h e a t e d a t 9 0 ~ C f o r t w o h o u r s a n d t i t r a t e d w i t h H C 1 a g a i n .T h i s h e a t - a n d - t i t r a t i o n p r o c e d u re w a s r e p e a t e d s e v e r a l t i m e s u n t i l t h e p i n k c o lo u rd e v e l o p e d a f t e r h e a t i n g w a s v e r y f a i n t ; a t t h i s p o i n t o n e o r t w o d r o p s o f 0.1 N H C 1


4/20

75 PA HO HSU AND T. F. BATES ONsufficed to turn the solution colourless. The total OH - titrat ed is referred to as theOH - bound in the precipitate. If the number of heat-and-titrations is moretha n three, it is desirable to repeat t he dete rmination by adding the approxim atetitre in the first titrati on in order to reduce the error due to blank and titrations.This procedure works satisfactorily for the amorp hous products, b ut is not suitablefor crysta lline AI(OH)3, as the rate of react ion is too slow in this case.Chem ical analysis of the hydroxy aluminium solution. The nature of the hydroxy-aluminium species in the solution was studied by treating the latter with sodiumsaturated Dowex-50 (XS, 20-50 mesh) in the following two ways:A one-tenth gram portion of sodium-saturated Dowex-50 was allowed to equili-brate with 100 ml of hydroxy-aluminium solution by letting the mixture stand inan Erle nmeyer flask for several hours (with occasional shaking), replacing the spe ntsolution with fresh, and repeating the process--the complete experiment involvingl0 changes of solution over a period of 48 hours. The resin was then washed thr eetimes with alcohol, and shaken five times with N KC1 solution (using 20 ml and15 minutes for each extraction) to replace any exchangeable A13+. The resin wasthen washed with alcohol and shaken five times with N CaCl~ solution in the sameman ner as for the N KC1 extract ion. The an munt of pota ssium in the CaC12 ext rac tindicated the cation exchange capacity after the treatment with the hydroxy-aluminium solution. The aluminium not exchangeable with neutral salt wasextracte d with 3 N HC1 on a steam hot plate for 2 hours a nd determined. Thedifference between the original cation exchange capacity of the resin and t hat afterthe hydro xy-a lumin ium trea tment s represent s the exchange charge on the resininactivated by the non-exchangeable aluminium.

Secondly, a one-gram portio n of the Na-resin was equilibrated with 50 ml of thehydroxy-aluminium solution for 24 hours with frequent shaking; the solution wasthen decanted and the pH and concentration of aluminium were determined. Theresin was washed three times with alcohol, then extracted five times with N KC1as before. The aluminium tha t was not exchangeable with KC1 was extracted with3 N HC1 on a steam hot plate for about 2 hours, and determined.The pH and aluminium were determined in the same manner as for the precipi-tate product. The potassium was determined wit h a Beckman DU flame photomet er.X ray diffraction. A suitable aliquot of produc t suspension (10 ml for mostsamples) was transfer red to a 15 ml test- tube a nd centrifuged. The precipitate waswashed once with water, dispersed in 1 ml of water, pcm ed on to a glass slide, anddried at room temperat ure. In those samples containing sulphate, an additionall0 ml aliquot of suspension was transferr ed to a 15 ml test-tube and centrifuged.Ten ml of N HCI was added and th e sample dispersed. This acid treatme nt w asmaintained for exactly 20 minutes, then the sample was centrifuged, washed, andmounte d on a glass slide as before. In some cases, a rando mly moun ted specimenwas desirable in order to obta in a more complete diffraction patte rn. Then a 200 mlaliquot was taken and treated as before, but an additional acetone washing wasmade and the precipitate was dried under vacuum. The dried specimen was lightlyground to a fine powder and mount ed in a special aluminium holder with a hole inthe centre to obtain as rand om an orientation of particles as possible. The X-r aydiffraction patterns were take n with a Norelco unit, using copper radiation.

R e s u l t s a n d d i s c u s s i o nThe p roduc t s can be separa t ed in to two ca t egor i es accord ing to the

Na0H/ A1 ra t io invo lved in the i r p repa ra t io n . When Na0H/ A1 = 3 and3-3 , c rys t a l l i ne AI(0H)8 in the fo rm o f bayer i t e , no rds t r and i t e , o r g ibbs i t e


5/20

L U M I N I U M H Y D R O X I D E S 7 5 3o r m i x t u r e s w a s t h e m a i n c o n s t i t u e n t o f t h e p r e c ip i t a t e . W h e n t h e r a t i ow a s 2 75 o r b e l o w , t h e p r o d u c t s w e r e b a s i c a l u m i n i u m s u l p h a t e s o r c h l o r id e s ,a n d w e r e a m o r p h o u s t o X - r a y d i f f r a c t io n e v e n a f t e r 6 m o n t h s o f a g e in g .

Products in the A 1 2 ( S O ~ ) a + N a O H systemX ray crystalline material. C r y s t a l l i n e A I (O H ) a f o r m e d r a p i d l y i n t h e

t w o p r e c i p i t a t e s p r e p a r e d a t N a O H / A 1 = 3 0 ( P r o d u c t 1 3 ) a n d 3 3 ( P r o -d u c t 1 4). T h e p h y s i c a l a p p e a r a n c e , r a t e o f s o l u t io n in a c id , a n d X - r a yd i f f ra c t i o n p a t t e r n s o f t h e se t w o p r o d u c t s c h a n g e d r a p i d l y i n t h e f i r s tTABLE I . Pe rcen tage o f a lumin ium ex t rac ted b y N HC1 in 20 minu te s a t roomtempera tu re f rom rep re sen ta t ive c rys ta l l ine p rec ip i t a t e s

A1C13+ N a 0 H A ld S O 4) a+ N a O H^Tim e o f Prod . 1 Pred . 2 Prod . 13 Prod . 14agein g (R = 3.0)* (R = 2.93)* (R : 3-0)* (R -- 3.3)*

2 hr. 88.6 100.0 85.0 - -4 hr. 69-5 86.3 46.2 16.78 h r . 50 .0 77-8 - - - -1 d ay 32.1 39.2 11.9 5.32 da ys 23.3 31.8 6.6 4.81 week 14.6 17.8 - - - -2 weeks - - 14 .8 2 .8 1 .93 weeks - - - - 2 -8 1 -71 m on th 13-7 - - 2 .2 1 .12 m on ths 11.4 11.8 2.1 1.04 m onth s - - 12 .0 2 .2 0-8* R = N a 0 H / A 1 m o l e r a t io .

t w o d a y s , t h e n c o n t i n u e d c h a n g i n g a t a s lo w e r r a t e . I t i s b e l i e v e d t h a tt h e r a p i d - c h a n g i n g s t a g e is f a r f r o m e q u i l i b r i u m a n d t h e r e f o r e n o t s ig n i-f i c a n t i n t h i s s t u d y ; h e n c e m o s t o f t h e r e s u l t s a n d d i s c u s s io n p r e s e n t e dh e r e c o n c e rn c h a ra c t e r iz a t io n s m a d e t w o o r m o r e d a y s a f t e r p r e p a ra t i o n ,

T h e p H v a l u e s o f P r o d u c t s 1 3 a n d 1 4 w e r e 9 .6 a n d 1 1 .0 , r e s p e c t iv e l y ,m e a s u r e d t w o d a y s a f t e r p r e p a r a t i o n , a n d t h e r e w a s n o n o t i c e a b l e c h a n g ei n p H d u r i n g t h e e n t i r e a g e i n g p e r i o d o f o n e y ea r .

T h e p r e c i p i t a t e s b e c a m e h i g h l y re s i s t a n t t o t h e N H C 1 t r e a t m e n ts h o r t l y a f t e r p r e p a r a t io n , a s s h o w n b y t h e d a t a i n t a b l e I . T h e r e s is t a n c eo f t h e c r y s t a l l i n e f r a c t i o n t o t h e a c i d t r e a t m e n t e m p l o y e d h e r e i n i s u s e f u li n f r a c t i o n a t i n g a n d i d e n t i f y i n g t h e p r o d u c t . I n 6 N H C 1 i n a b o i l in g w a t e r -b a t h , i t r e q u i r e d a b o u t t w o h o u r s t o d i s s o lv e t h e r e s i d u a l p r e c i p i t a t ec o m p l e t e l y a f te r t h e p r e v i o u s N H C 1 t r e a t m e n t .

I n P r o d u c t 1 3 ( N a O H / A 1 = 3 .0 ), a l u m i n i u m w a s c o m p l e t e l y r e m o v e df r o m t h e s o l u ti o n . T h e f r e e O H - r e m a i n i n g i n s o l u t io n w a s n e g l ig i b l e


6/20

754 PA HO HS U AND T :F BA TES ON(0"04 meq/1 , pH 9"6) a s com pared w i th the to t a l O H - add ed (50 meq/1) ,i n d i c a t in g th a t t h i s O H - w a s p r a c ti c a l l y c o m p le t e ly p r e c ip i t a t e d w i tha lu min iu m, t h e r e b y p re su m a b ly r e su lt i n g in a p ro d u c t o f c o mp o s i t i o nAI(OH)a. Chem ica l ana lys i s showed th a t th i s p roduc t , wh en d r ied a t1 00 ~ C , c o n ta in e d t r a c e su lp h a t e a n d th a t i t s a lu m in iu m c o n te n t w a s34-6 2 .0 % , which cor responds to the co m pos i t ion o f AI(OH)3 . A N HC1wa sh (2 0 min u te s ) r e m o v e d th e t r a c e su lp h a t e t o g e th e r w i th a sma ll p o t -t i o n o f a lu min iu m ( t a b le I ) , a n d r e d u c e d th e p r e c ip i t a t e t o a b o u t ~ t o 8 9 fi t s fo rm er vo lum e. Th is sugges ts th a t t he o r ig ina l p rec ip i ta te was a mix-tu r e o f AI(OH)s a n d a h ig h ly h y d ra t e d c o m p o n e n t c o n ta in in g a lu min iu ma n d su lp h a te . P ro d u c t 1 4 c o n ta in e d t r a c e su lp h a t e in t h e f r e sh pr e c ip i -t a t e , b u t t h i s d i s a p p e a re d a fe w d a y s a f t e r p r e p a ra t io n . T h e p r e c ip i ta t e ,d r ied a t 100 ~ C, con ta ined 34"64-2"0 % a lumin ium , charac te r i s t ic o fAI (OH)s. I n t h i s p ro d u c t , t h e c o n c e n t r a t i o n o f a lu min iu m in so lu t io na m o u n t e d t o a b o u t 1 00 p p m , p r e s u m a b l y i n t h e f o r m o f a l u m i n a te .

X -ra y d i f f rac t ion pa t te rn s showed th a t bay er i te (4.36 ~_ ; 4 -72 A), w i thno rds tra nd i te (4 .15 ; 4"37 A ; 4-79 A) or g ibbsi te (4-34 A ; 4 .82 A) orb o th , s t a r t e d to d e v e lo p in b o th p ro d u c t s sh o r t l y a f t e r p r e p a ra t io n , t h eX - ra y p e a k s b e c o min g sh a rp e r a n d l a rg e r a s t h e p e r io d o f a g e in g in -c r e a se d u p to o n e mo n th w i th n o fu r th e r n o t i c e a b le c h a n g e a f t e r t h i sp e r io d ( fi g . 1 ). A b ro a d p e a k wi th i t s d i f f ra c t io n m a x im u m re p re se n t in ga sp a c in g o f a p p ro x im a te ly 6 "5 A wa s a l so o b se rv e d , a n d in a r a n d o m lyp a c k e d , f r e e z e-d r ie d , s a mp le o f P ro d u c t 1 3, a d d i t i o n a l b ro a d p e a k s w i thdiffra c t ion m ax im a a t 3"20 X, 2 .33 _&, an d 1 "86 ] t we re a lso presen f . InP ro d u c t 1 3, t h i s b ro a d 6 "5 X p e a k p e r s is t e d w i th o u t c h a n g e in h e ig h t o rb re a d th d u r in g th e e n t i r e a g e in g p ro c e s s o f o n e y e a r , wh e re as i n P ro d u c t1 4 i t d e c re a se d in i n t e n s i ty w i th i n c re a se d a g e a n d d i s a p p e a re d in t h r e ewe ek s. T h e se b ro a d p e a k s c o r r e sp o n d to t h o se o f t h e m a te r i a l r e fe r r e dto b y Ca lv e t e t a l (1953) as pseudoboehmi te because the X-ray d i f f rac -t i o n p a t t e r n is c lo se t o b u t d i s t i n c t ly d i f f e r e n t f ro m th a t o f b o e h m i t e .Pap~e , Ter t ian , and Bia is (1958 , p . 1304 ) pos tu la ted t ha t th e b ro add i f fr a c t io n p e a k s re su l t f r o m a p o o r ly o rd e re d a r r a n g e m e n t o f e l e m e n ta rysh e e t- l ik e u n it s . A 2 0 -m in u te N HC1 wa sh c o m p le t e ly r e m o v e d th i s6 ,5 A peak , whi le the AI(OH)3 peaks rem ained unch ange d ( f ig . 2 ). S incethe N HC1 wash a lso caused a la rge redu c t ion in the vo lu m e o f p rec ip i ta teto g e th e r w i th t h e r e m o v a l o f t r a c e su lp h a t e a n d a sma l l p o r t i o n o fa lu min iu m ( t ab l e I ) , i t is b e l ie v e d th a t t h i s b ro a d p e a k is in so me wa yr e l a te d t o t h e a f o r e m e n t i o n ed h ig h l y h y d r a t e d c o m p o n e n t c o n t a in i n ga lu min iu m a n d su lp h a t e .

The charac te r i s t ic s o f p roduc ts l ike No . 13 , fo rmed a t an NaOH/A1


7/20

ALUMINIUM HYDROXIDES 755r a t i o o f 3 0 , v a r i e d c o n s i d e r a b l y w i t h a s l i gh t d e v i a t i o n o f t h e r a t i o f r o mt h i s v a l u e . I n t h e c ase o f P r o d u c t 1 4 ( N a O H / A 1 = 3 .3 ) a n d t h e X - r a ya m o r p h o u s p r o d u c t s d i s c u s se d i n t h e n e x t s e c t i o n f o r m e d a t r a t i o s o f

o4.35A o472A oi i 7 8 A

l P rodu c t No . 14

2 0 1 5 I bN a O H = 2 . b , I Y e a r 2 {)

Product No. 12

o4.72A o:4.78A

N a O H _ 3 .0A IP r o d u c t N o . 1 3

i l

20 15 10 5 20 15 10 520 20:FIG. 1. X-ra y diffraction patterns of representati ve crystalline and a morpho usaluminiu m hydrox ides prepared from A12 SO4)aq-NaOH.

2 .7 o r l e ss , a s l igh t dev ia t ion f rom the g iven r a t io does no t have a s imi -l a r l y d r a s t i c e f fe c t o n t h e n a t u r e o f t h e p r o d u c t .X ray amorphous material. T h e p ro d u c t s p r e p a r e d a t N a O H / A 1 = 2 7a n d b e lo w w e re a m o r p h o u s to X - r a y d i ff ra c ti on . E l e c t r o n m i c r o g r a p h st a k e n o f m a t e r i a l p r e p a r e d b y f r e e z e -d r y in g r e v e a le d la c y a g g re -g a t e s o f r o u g h l y e q u i d i m e n s i o n a l p a r ti c l e s 5 0 to 2 50 A i n d i a m e t e r a n dh a v i n g r o u n d e d t o i r r e g u l a r o u t li n es . E l e c t r o n d i ff r a ct io n d id n o t r e v e a lt h e p r e se n c e o f a n y c r y s t a l li n e c o m p o n e n t s .


8/20

756 t A H O H S U A N D T . F . B A T E S O NT h e p H v a l u e s o f t h e s e p ro d u c t s , p l o t t e d a g a i n s t t h e N a O H / A I m o l e

r a t i o i n t h e i r p r e p a r a t i o n , s h o w e d a b r e a k a t t h e r a t i o o f 2 (fig . 3 ).B e l o w th i s i n fl e ct io n p o in t , t h e p H v a l u e c h a n g e d s m o o t h l y a n d o n l ys l ig h t l y w i t h t h e i n c r e a s e d N a O H / A 1 r a t i o ; t h is s u g g e s t s t h a t t h e O H -a d d e d i s s t r o n g l y h e l d i n a p r o d u c t w i t h l it tl e d i s so c i a ti o n . T h e O H -

N a O H 3.3A I14, I Week

4.35.~

4.73.~ 6.,s~~. W ithoutlLjWithHCI Washing

2b ~b2O

N a O H : 3 0A I13, 3 Weekso 7 9 ~ ,4.72A,

4 3 5 ~

6.42.~

; , h a n g

2b2O

WithHCI Washing

lbFla. 2 . Removal of the pseudoboehmite X -ray peak w ith N HC1 washing.

i n t h e p r o d u c t s a b o v e t h i s p o i n t w a s r e l a t i v e l y m o r e d i s s o c i a b l e ; h o we v e r , t h e O H - a d d e d w a s s t i l l n e a r l y c o m p l e t e l y c o m b i n e d w i t h a l u m i -n i u m , a s s h o w n b y t h e fr e e O H - i n s o lu t io n a n d t h e t o t a l O H a d d e d i nt h e p r e p a r a t i o n .

T h e t i m e r e q u i r e d f o r s o l u t i o n i n N H C 1 g r a d u a l l y i n c r e a s e d w i t h a ni n c re a s e in N a O H / A 1 r a t io , b u t c o m p l e t e s o lu t i o n t o o k p l ac e i n 2 0m i n u t e s e v e n a t N a O H / A I - - 2 -7 . T h i s b e h a v i o u r is s i g n if ic a n t w h e nc o m p a r e d w i t h t h e h i g h r e s is ta n c e t o a c i d o f t h o s e p r o d u c t s p r e p a r e d a tN a O H / A 1 = 3 a n d 3 3 .

C h e m i c a l a n a l y s i s o f t h e s e p r o d u c t s i n d i c a t e d t h a t t h e y w e r e b a si ca l u m i n i u m s u l p h a t e (fig . 4 ). I n t h e r a n g e o f N a O H / A 1 - - 0 3 t o 2 1, t h e


9/20

ALUM INIUM HYDROX IDES 757a m o u n t o f p r e c i p i t a t e i n c r e a s e d w i t h i n c r e a s e d r a t io , b u t t h e c o m p o s i t i o no f th e p r e c i p it a te s w a s a p p r o x i m a t e l y c o n s t a n t , a v e r a g i n g a t A I O H ) 2 .,S 04)0. 4. F o u r s p e c i m e n s p r e p a r e d a t N a O H / A 1 = 1 ,8 d e se r v e p a r t i c u l a r2 ]

1 1 I

9 -

o A I C I 3 S y s t e m A I 2 S O 4 ) 3 S y s t e m

8

7~ X

6

5

o

3

0 1 2 3N a O H / A I , M o l a r R a t io

FI~. 3. iT he pH values of alum inium hydroxide suspensions or solutions preparedat various N aOII/A1 mole ratios.

m e n t i o n f or , a l t h o u g h t h e s u l p h a te c o n t e n t i n t h e o r i g in a l p r e p a r a t i o n w a sa d j u s t e d w i t h N a 2 S O 4 t o c o v e r t h e r a n g e f r o m 0 .0 2 t o 1 N , t h e c o m p o s i t i o no f t h e p r e c i p i t a te s d i d n o t c h a n g e . I t i s b e l ie v e d , th e r e f o r e , t h a t t h ep r e c i p i t a t e i s a c h e m i c a l c o m p o u n d o f d e f i n it e c o m p o s i t i o n , A I O H )~ .~

S 0 4) o 4, w h i c h s h o u l d b e u n u s u a l l y s t a b le . T h e f o r m a t i o n o f b as i c3 D


10/20

758 PA t tO HSU AND T F BATE S ONa l u m i n i u m su l p h a t e o f d e f in i te c o m p o s i t i o n u n d e r s i m i la r c o n d it io n s h a sa l so b e e n r e p o r t e d b y W e i se r e t a l (1941) and Wi l l i amson (1923) ; t hec o m p o s i t io n s t h e y f o u n d w e r e A le Oa . S0 a . 1 .5H 20 and (Al~03)5 (SOa)3 .1 5 H 2 0 , r e sp e c t i v e l y .

A l u m i n i u m w a s c o m p l e t e l y r e m o v e d f r o m so l u ti o n a t N a O H / A 1 = 2 ,1 .Chem ica l ana lys i s o f p rec ip i t a t es a t h igh er r a t ios (2 ,1 to 2 ,7) ind ica ted

=

a 3 . 5. - -Q .~ I,

3 . 0c. -

Formation of X-Ray Aluminium Hydroxides

Documents

Transcript of Formation of X-Ray Aluminium Hydroxides