Inexpensive and easily available Moroccan natural clays were
investigated for the removal availability of textile dyes from
aqueous solution. For this purpose, the adsorption of methylene
blue (MB) as reference molecule, malachite green (MG) representative
of cationic dyes and methyl orange (MO) representative of
anionic dyes, was studied in batch mode under various parameters.
The clays were characterized by means of XRD, cationic
exchange capacity and BET surface area analysis. The experimental
results show that, the adsorption was pH dependent with a high
adsorption capacity of MB and MG in basic range and high
adsorption of MO in acidic range. The pseudo-second-order kinetic
model provided the best fit to the experimental data for the
adsorption of MB and MG by the clays. However, the adsorption of
MO was more suitable to be controlled by an intra-particle
diffusion mechanism. The equilibrium adsorption data were
analyzed by Langmuir, Freundlich and Dubinin–Radushkevich
isotherm models. The adsorption process was found to be
exothermic in nature in the case of MB and MO. However, the
adsorption of MG was endothermic