Mass transfer process in the removal of Congo Red (CR) onto Natural Clay (NC): Kinetic, isotherm modeling, and thermodynamic study

Abstract

Abstract Industrial growth and technological advancement have led to the worldwide introduction of pollutants of diverse nature into water bodies including pollutants such as dyes and organic contaminants. Their presence in industrial effluents or drinking water is a public health problem. The aim of this study was to evaluate the adsorption of Congo Red (CR) onto Natural Clay (NC) realized in a batch system. The effects of contact time, initial pH, stirring speed, temperature, adsorbent dose, and initial CR concentration on the adsorption capacity were investigated. The NC was characterized by the FTIR, DRX, BET, and point of zero charge. The experimental isotherm data follow well the Langmuir equation, providing a better fit of the equilibrium adsorption data. Under optimized conditions, up to 212.766 mg/g at 25 °C is removed from the solution. The adsorptions kinetics were found to follow rather a pseudo second-order kinetic model with a determination coefficient (R2) of 0.999. The adsorption isotherms at different temperatures have been used for the determination of thermodynamic parameters, i.e., the negative free energy ΔG0 (10.081 to 1.087 kJ/mol), positive enthalpy change ΔH0 Q5 (64 = 175 kJ/mol) values indicate that the overall CR adsorption is spontaneous and endothermic in nature.