This study shows that Moroccan natural clays can efficiently remove dyes from aqueous solutions.
The adsorption was dependent on the pH of the aqueous solution, with a high uptake of cationic dyes
at high pH, and high uptake of anionic dye at low pH. The adsorption was rapid and could be
considered to fit pseudo-second order kinetics model in the case of methylene blue and malachite
green. The equilibrium uptake was increased with increasing the initial concentration of dye in
solution. The adsorption isotherm could be well fitted by Langmuir equation in the case of cationic
dyes and Dubinin–Radushkevich equation in the case of anionic dye. The adsorption capacity of
cationic dyes was found to be higher than anionic dye. The rise in temperature increases the adsorbed
amount of malachite green and decreases the adsorbed amount of methyl orange and methylene blue
dyes. The adsorption of cationic dyes is more correlated to cationic exchange capacity and BET surface
area then that of anionic dye. The adsorption of anionic dye was more influenced by the change in
solution temperature. These results suggest that the adsorption of cationic dyes by the clays could be
chemisorption. However, a physisorption is proposed for the adsorption of anionic. Finally, the use of
Moroccan natural clays shows a greater potential for the removal of textile dyes, as no costly
equipment is required.