Adsorption of a basic dye, Methylene Blue, in aqueous solution on bentonite

The dyes are used in many industrial sectors such as textiles, paper and leather dyeing, as well as in the food and cosmetics industry. Dyes are known to be toxic and persistent in the environment and require physico-chemical techniques to degrade them.  This work deals with the study of the adsorption of the cationic dye methylene blue on raw bentonite from the region of Nador (Morocco). The physico-chemical properties show that our bentonite indicates a very high alkalinity.  The amplitude of swelling shows that this bentonite is very high is sensitive to water. The SEM shows petaloid-shaped aggregates of the grains in spherical form with heterogeneous dimensions. Various experimental parameters were analyzed; initial concentration of the dye, pH, mass of the adsorbent and temperature. Adsorption tests showed that the maximum duration of this cationic dye on bentonite is established after 80 minutes. Experimental results showed that the adsorption of the methylene blue dye on raw bentonite depends on the pH of the solution and the initial concentration of the dye. Although the amount of methylene blue adsorbed decreases with increasing temperature, this indicates that adsorption is an exothermic process. The adsorption capacity was determined using the Langmuir, Freundlich, Elovich and Temkin isotherms. The binding of methylene blue follows Freundlich's law.