Die Methylenblauadsorption an Montmorillonit

Abstract

From a solution of Methylene blue chloride the dye cation is exchanged for the exchangeable cations of kaolinite or clay. The methylene blue cations are adsorbed quantitatively. Adsorbed methylene blue cannot be exchanged again. By sodium salts, which give an alkaline reaction, the sorption of methylene blue is increased considerably, because additional adsorption of methylene blue hydroxide occurs. In the case of bentonite (montmorillonite) most of the methylene blue is taken up between the silicate layers, increasing the layer distance considerably.
Although potassium salts too give an alkaline reaction, they do not increase the methylene blue adsorption above that of the cation exchange capacity.
Sodium and potassium ions are migrating faster between the silicate layers of montmorillonite than methylene blue. Na⁺- ions are not so tightly bound to the silicate layers; therefore in alkaline medium an additional take-up of methylene blue hydroxide is possible. K⁺-ions are stronger bound and therefore retard the sorption of methylene blue. The behavior of Li⁺ is similar to that of Na⁺, the one of Cs⁺ similar to that of K⁺.