METHYLENE BLUE INTERACTIONS WITH REDUCED …

1 Clays and Clay Minerals, Vol. 49, No. 3, 2 4 4 - 2 5 4 , 2001. M E T H Y L E N E B L U E I N T E R A C T I O N S with . R E D U C E D - C H A R G E SMECTITES. JURAJ BUJDAK, MARI~N JANEK, JANA MADEJOVA, AND PETER KOMADEL. Institute of Inorganic Chemistry, Slovak Academy of Sciences, SK-842 36 Bratislava, Slovakia A b s t r a c t - - T h e objective of this work was to prepare series of REDUCED -charge materials from different parent Li-saturated dioctahedral smectites, to investigate the effects of temperature, chemical composition and charge location in smectites on the charge reduction and to characterize REDUCED -charge smectites (RCSs) using METHYLENE blue (MB) adsorption.

2 The layer charge decrease, induced by Li fixation, is correlated with the trends in the spectra of MB-RCS dispersions in the visible region (VIS) spectra. Distribution of the negative surface charge of the clay minerals controls the distance between the adsorbed MB cations and thus affects the formation of MB dimers and higher agglomerates. Because each form of MB (monomer, dimer, higher agglomerate, J-aggregates) absorbs light at a different wavelength, the VIS spectra of MB depend sensitively on the charge density at the clay surface.

3 Both cation exchange capacity (CEC) values and spectra of MB-clay dispersions clearly detect extensive reduction of the layer- charge density in REDUCED -charge montmorillonites (RCMs) upon Li-thermal treatment. The extent of charge reduction depends on the temperature of the thermal treatment, as well as on the octahedral charge of the montmorillonite. Reduction of the layer charge proceeds to a much lesser extent for smectites with mainly tetrahedral charge and high Fe content (Fe-rich beidellite and ferruginous smectite ).

4 Both CEC. data and MB spectra detect only a slight decrease of the layer charge density, which relates to the low octahedral charge of these minerals. Following heating at higher temperatures (120-160~ slightly higher Li fixation is indicated by CEC values; however, no charge reduction is confirmed by MB spectra. Release of protons accompanying Li + fixation in Fe-rich smectites heated at 180 or 200~ was detected in the spectra of MB-clay dispersions and confirmed by potentiometric titrations. Key W o r d s - - C a t i o n Exchange Capacity, Dye Cation Agglomerates, J-Aggregates, Layer Charge Reduc- tion, METHYLENE blue , Montmorillonite, smectite .)

5 INTRODUCTION octahedral sheets ( B r i n d l e y a n d E r t e m , 1971; E r t e m , 1972; L i m a n d J a c k s o n , 1986; B u j d S k et al., 1991, Layer charge reduction 1992; K o m a d e l et al., 1996). This t r a n s f o r m a t i o n h a s b e e n u s e d to d i s t i n g u i s h m o n t m o r i l l o n i t e f r o m beidel- T h e d e c r e a s e o f the C E C in L i - s a t u r a t e d m o n t m o - lite ( G r e e n e - K e l l y , 1953; Schultz, 1969; L i m a n d Jack- rillonite f o l l o w i n g h e a t i n g at 2 0 0 - 3 0 0 ~ has been son, 1986).

6 In h e a t e d beidellites, Li + ions are not fixed k n o w n for d e c a d e s ( H o f m a n n a n d K l e m e n , 1950;. in the p s e u d o h e x a g o n a l cavities in the tetrahedral G r e e n e - K e l l y , 1953, 1955; G l a e s e r a n d M e t i n g , 1967). a n d is i n d u c e d b y the irreversible m i g r a t i o n o f Li + sheets, as they c a n m i g r a t e b a c k into the interlayer cations into the layers. T h e final position(s) o f fixed space u p o n r e - h y d r a t i o n ( K a w a n o a n d Tomita, 1989).

7 Li(I) h a s b e e n d i s p u t e d in n u m e r o u s works. B e c a u s e I n c r e a s e in c h a r g e r e d u c t i o n w i t h the m a g n i t u d e o f the o f the b o d y o f e v i d e n c e w h i c h s h o w s that layer c h a r g e octahedral c h a r g e was o b s e r v e d (Calvet a n d Prost, r e d u c t i o n does n o t p r o c e e d in beidellites a n d triocta- 1971; J a y n e s and B i g h a m , 1987; W i l l i a m s et al., hedral smectites, m i g r a t i o n o f Li + cations into the va- 1991).

8 E x c h a n g e a b l e Li + cations r e m a i n i n g in diocta- cant o c t a h e d r a was p r o p o s e d ( H o f m a n n a n d K l e m e n , hedral smectites that h a d b e e n h e a t e d at 2 0 0 - 3 0 0 ~. 1950; G r e e n e - K e l l y , 1953; F a r m e r a n d Russell, 1967; c a n therefore b e those c o m p e n s a t i n g for the tetrahedral Sposito et al., 1983; Srasra et al., 1994). H o w e v e r , the c h a r g e a n d / o r the c h a r g e at the sites o f b r o k e n b o n d s fixation o f Li + in the b o t t o m s of p s e u d o h e x a g o n a l cav- at clay particle edges.

9 T h e e x t e n t o f Li fixation, the ities w i t h i n the tetrahedral sheets was s u g g e s t e d b a s e d c h a r g e reduction, and p o s s i b l y the final site o f fixed o n I R a n d N M R spectra (Tettenhorst, 1962; L u c a et Li(I) also d e p e n d o n the h e a t i n g t e m p e r a t u r e (Calvet al., 1989; Trillo et al., 1994). S o m e authors suggest a n d Prost, 1971; K a w a n o and Tomita, 1989; M a d e j o v ~. that Li(I) c o u l d o c c u p y b o t h of these sites (Russell a n d et al.))

10 , 1996). Farmer, 1964; C a l v e t a n d Prost, 1971; Madejov~i et al., In addition to layer c h a r g e reduction, surface acid- 1996, 1999). ification u p o n Li fixation h a s b e e n reported. T h e in- D e c r e a s e in the layer c h a r g e significantly alters the c r e a s e d acidity was attributed to the r e a c t i o n o f Li +. properties o f the treated minerals. Collapsed, p y r o - with the structural h y d r o x y l groups in the o c t a h e d r a l phyllite-like layers are f o r m e d u p o n nearly c o m p l e t e sheets (Russell a n d Farmer, 1964; J a y n e s a n d B i g h a m , c h a r g e r e d u c t i o n ( 8 5 - 9 0 % ) in L i - s a t u r a t e d dioctahed- 1987; W i l l i a m s et al.