Comparative study of laterite clay and activated smectite in the adsorption of indigo carmine in aqueous solution

The aim of this work was to compare the adsorption efficiency of two clay materials, namely activated smectite (SMT) and laterite clay (ALT). The comparison was focused on the removal of indigo carmine (IC) dye from aqueous solution. The characterizations showed that the initial materials were mainly mesoporous for effective adsorption. Batch adsorption studies were investigated to optimize the operating parameters such as adsorbent dose, contact time, solution pH, and initial concentration. The pH of point of zero charge (pH pzc ) was found to be 2.5, and the optimal adsorption pH obtained was 2 for laterite clay (ALT) and activated smectite (SMT) adsorbents with adsorption capacities of 1.64 mg/g and 1.37 mg/g, respectively, and 10 min as contact time. Surface heterogeneity of both adsorbents was proportional to the amount of IC adsorbed. Freundlich, Langmuir, Dubinin–Kaganer–Radushkevich (D–K–R), and Temkin isotherm models clearly described the retention of the IC on these mesoporous materials. The values of adsorption energies located between 2.23 and 2.54 kJ/mol demonstrated the physisorption of the process. The adsorption capacities obtained by Langmuir model were 4.08 and 4.38 mg/g for ALT and SMT, respectively. The pseudo-second-order kinetic model has been approvingly fitted with complete curves derived from experimental data of both adsorbents. ALT was found to be more effective in the removal of IC compared to SMT. Activated smectite and laterite clay appear to be tenable and profit-making materials for the clean-up of indigo carmine from wastewater. Graphical abstract