Physico-chemical characterization and valorization of swelling and non-swelling Moroccan clays in basic dye removal from aqueous solutions

The aim of the present work was to study the application of natural clays to remove a cationic dye (methylene blue (MB) chosen as a pollutant model) from wastewater. Rhassoul-clay and Red clay investigated in this study were extracted from two different sites in Morocco. These clays have different swelling properties. A comparison of their affinity towards cationic dye help to understand the limiting factors controlling the adsorption process. Rhassoul clay and Red clay were characterized using powder X-ray diffraction, Scanning Electron Microscopy, X-ray Fluorescence spectroscopy and surface area measurement (BET). The adsorption capacities of the solids were measured using batch sorption studies as a function of contact time, pH, temperature and initial concentration. Pseudo-second-order model and intraparticle diffusion model were applicables to describe the MB adsorption on both adsorbents. Langmuir and Freundlich isotherms were employed to determine adsorption mechanism. According to the results, the Langmuir model was more suitable to describe MB adsorption on both adsorbents. The maximum monolayer adsorption evaluated with this model is 166.7 mg g−1 and 18.7 mg g−1 for Rhassoul-clay and Red clay, respectively. The temperature exhibited a positive effect on MB adsorption. According to Gibbs energy and enthalpy, the adsorption process was spontaneous and endothermic for both clays, but was more favorable for Rhassoul clay. Hence, Rhassoul clay exhibits much higher adsorption capacity than Red clay. The both clays studied could be potentially used for the removal of cationic dye from wastewater.