Adsorption of methylene blue dye from aqueous solutions onto natural clay: Equilibrium and kinetic studies

Abstract

The objective of this work was the removal of the cationic dye (methylene blue (MB) chosen as a pollutant model) from an aqueous solution using a Moroccan clay sample from the region of raw Wazanne as a low-cost adsorbent. The effects of various parameters, such as adsorbent dose (0.05 to 5 g/L), dye concentration (100 to 1000 mg/L), contact time (10 to 120 min), temperature (20–60 °C), and solution pH (3–12), were investigated. The results showed that MB's adsorption on clay strongly depends on the solution's initial dye concentration, temperature, and pH. The kinetic adsorption results fitted well with a pseudo-second-order model with a correlation coefficient of R2 = 0.99. Langmuir and Freundlich isotherms were used to determine the adsorption mechanism. According to the results, the Langmuir model better describes the adsorption of MB with a maximum adsorption capacity of 456.62 mg/g. According to the thermodynamic parameters, Gibbs free energy ΔG°, enthalpy ΔH°, and entropy ΔS°, the adsorption process was feasible, spontaneous, and exothermic. Reusing the adsorbent is considered an important economic and environmental aspect of a sustainable development approach, given the regenerative capacity of the material. Various techniques for characterization of the adsorbent have been applied, including zero-point charge measurement (pH zpc), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses with an X-ray diffractometer.