Competitive adsorption of methylene blue and crystal violet to montmorillonite

Methylene blue (MB) and crystal violet (CV) have been found to be adsorbed in amounts greater than the cation exchange capacity (CEC) of clays (Hang & Brindley, 1970; Ghosal & Mukherjee, 1972; Venugopal & Nair, 1974). In previous work (Rytwoet al., 1991), it was shown that CV adsorbs to montmorillonite up to 1·4 mmole dye/g clay. The amount of dye added in those experiments was up to 1·6 mM/g clay. Yet, when the added amount of CV and MB was 3·5 mM/g (Rytwoet al., unpublished), almost 1·6 (200% of the CEC) and 1·2 mM/g clay, respectively, were adsorbed. Margulieset al. (1988), who studied the adsorption of thioflavin T and MB to montmorillonite, showed that these dyes adsorb up to 1·4 and 1·2 mM dye/g clay, which corresponds to 175% and 150% of the CEC, respectively.