Adsorption of an anionic textile dye from wastewater by bentonitic clay mineral

In this paper, adsorptive performance of natural clay has been investigated as a potential reactive dye adsorbent, on the basis its promising physical-chemical and morphological properties which were compared to several previous works. Sample used in this work, collected from Grombalia (North-East of Tunisia), has been characterized at the first time. Following its physicochemical study, this sample has been employed and tested as an ion exchange medium, for an anionic toxic textile dye removal from textile effluent and watercourse. Physicochemical experiences confirm that the used clay mineral was a clay of bentonite type having the following structure formula Ca0.014Na0.404K0.16(Si7.65Al0.35)(Al2.910Fe0.762Mg0.376)O22. Dye removal from aqueous solution onto raw (GRb) and purified (GRp) bentonite was investigated, using a batch adsorption technique, as a function of various parameters such as initial dye concentration, contact time, temperature and pH medium. Results prove that the amount of dye removed by the raw and the purified bentonite was found to be around 142 and 294 mg/g respectively. According to previous works this quantity of dye removed from aqueous solution (294 mg/g) reach the anionic exchange capacity of bentonitic sample. A contact time (clay/dye solution) of 20 to 30 min was sufficient to reach adsorption equilibrium. Adsorption rate was fast, more than half of the adsorbed dye was removed from the aqueous solution (C = 10–4 M). The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. Experimental data fit well with Freundlich model (the correlation coefficients, R 2, was found to be equal to 0.98).