Adsorption of

-The adsorption of the cationic oxidized safranine S + by a Na +, Ni 2+ and Fe 3§ montmorillonite has been studied with X-ray powder diffraction, u.v, visible and i.r. spectroscopy. In solution S + may be protonated: S +, SH e+ and SH~ + have characteristic spectra in the 500-600nm region where the clay structure does not absorb. In the Na + as well as in the Ni 2+ and Fe 3+ clays, the adsorption of S § is a cation exchange process accompanied by the protonation of the adsorbed dye such as variable concentrations of M + (Na +, Ni 2 + or Fe 3 +), S + and SH e + are simultaneously present. Protonation activity decreases from Fe 3+ to Ni 2§ and Na +, being the protonation site the amine group as shown by i.r. In the interlamellar space it seems that a SH2+. . S + association exists that could be described as a sandwich structure 6.5 A thick. I N T R O D U C T I O N Smectites such as montmorillonite have been used widely as adsorbents for various kinds of dyes (Grim, 1968). Safranine u has been shown to stain acid treated clays in relation to their mineralogical origin. Methylene blue has been studied by Pham Thi Hang and Brindley (1970) who have shown that both surface area and cation exchange capacity of clay minerals can be measured by adsorption from aqueous solutions. Safranine T. whose oxidized and reduced structure are shown in Figure 1, is a molecule of particular interest because its standard oxidation potential should allow redox reactions within the interlamellar space. The E.,-pH relationship is given by: