Congo red dye removal from aqueous solution using Algerian clay: adsorption isotherms, thermodynamics, and kinetics

The development of natural adsorbents that are abundant, cost-effective, and efficient for the treatment of ecosystems is a significant challenge. In this study, the sorption of Congo red, as a toxic dye, from aqueous media was investigated using an Algerian clay sample from the western town of Maghnia as a low-cost adsorbent that has undergone simple purification. Different parameters such as contact time (5–120 min), initial dye concentration (5–20 mg/L), solution pH (4–12), adsorbent weight (10–100 mg), and temperature (15–50 °C) have been investigated. The equilibrium (9.8 mg g⁻¹) was obtained for a contact time of 60 min, and the maximum sorption occurred at pH 8.5. The adsorption kinetic followed the pseudo-second-order kinetic model with a high degree of correlation coefficient (R² = 0.99). The adsorption isotherm showed an appropriate fit to the Freundlich model. Thermodynamic investigations revealed that the adsorption process is feasible, spontaneous, and endothermic. These results demonstrate that Algerian clay can be employed as a low-cost alternative for the removal of recalcitrant dyes from industrial wastewater.