The adsorption behavior of anionic dye (Congo Red) from aqueous solutions onto natural clay originated from Agadir region (south Morocco) was examined in this work. Batch mode experiments were performed to describe the Influence of interacting parameters such as contact times (10 - 70 min), adsorbent dose (1 - 6 g·L-1), initial dye concentration (100 - 900 mg·L-1), temperature (22 - 50 °C) and pH values (2 - 12) on dye removal. According to the obtained results, the adsorption of CR onto clay natural was dependent on pH, initial dye concentration and temperature. Experimental data have been modeled according to both Langmuir and Freundlich models. Also, kinetic studies of CR onto clay were evaluated by pseudo-first order and pseudo-second order. It was found that the adsorption of the dye on the clay were well fitted by the Langmuir model with coefficient of correlation R2 = 0.98 and maximum adsorption capacity 74.62 mg·g-1. Adsorption kinetics indicated that the adsorption of CR was found to follow a pseudo second-order model (R2 = 0.999). The thermodynamic parameters were also calculated, which suggested that the adsorption of anionic dye onto clay is physiosorptive process, spontaneous, and endothermic in nature.
