Optimization by Response Surface Methodology of the adsorption of Coomassie Blue dye on natural and acid-treated clays.

The effect of acid treatment on natural agalmatolite (AN) and natural kaolinite (KN) was investigated, together with the influence of those modifications on the removal of Coomassie Blue (CB) dye. The process was optimized using the Response Surface Methodology (RSM) developed by the application of the quadratic model associated with the Central Composite Design. Adsorption was promoted by initial CB concentration of 25 mg L(-1), pH 2 and adsorbent mass of 0.1 g. The adsorption kinetics study carried out in optimized conditions established that the equilibrium times were 1 h for AN and AA (treated agalmatolite), 4 h for KN and 2 h for KA (treated kaolinite). The kinetics data for AN, KN and KA were best fitted to the pseudo second order model, whilst for AA, the result pointed to the pseudo first order model. In the isotherm of adsorption the maximum quantities were obtained with reference to 11.29 mg g(-1), 9.84 mg g(-1), 22.89 mg g(-1) and 30.08 mg g(-1) for the samples AN, AA, KN and KA respectively. The data fitting showed that the Sips model was the most satisfactory for all the adsorbents. The calculated thermodynamic parameters showed that the process was spontaneous in all the adsorbents, endothermic for the KN and KA samples, exothermic for AN and AA, involved the disorganization of the adsorption system for the KN and KA and its organization for the AN and AA samples. The results showed that the KN and KA samples were more appropriate for use as adsorbents.