Abstract
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.
Highlights
Organic dyes constitute one of the larger groups of pollutants in wastewater released from textile and other industries
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
Summary
Organic dyes constitute one of the larger groups of pollutants in wastewater released from textile and other industries. Among 7 Â 105 t and approximately 10,000 different types of dyes and pigments produced world wide annually, it is estimated that 1–15% of the dye is lost in the effluents during the dyeing process [1] This massive influx of untreated organic chemicals into the waterways introduces aesthetic concerns, but far more importantly it promotes eutrophication and adversely affects the environmental health of the region. In addition to activated carbon, some adsorbents including agricultural wastes [4,5], lignite [6], natural phosphate [7], chitosan [8], silica [9], kaolinite [10], hydroxyapatite [11,12], perlite [13], sepiolite [14], montmorillonite [15] and some natural biosorbents have been reported [16,17] Studies in this field have not produced materials which meet all demands of adsorption activity.
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