Application of Different Isotherm Models for Humic Acid Adsorption on to Bentonite and Montmorillonite Nanoparticles

Background Adsorption isotherms describe the relationship between the equilibrium concentration of the adsorbed matter in the solution and the amount of adsorbed matter on the surface of the adsorbent. Objectives The main objective of the present research was to investigate different adsorption isotherms for describing adsorption of humic acid by nanoclay. Methods In this study, Langmuir, Freundlich, BET, Temkin and Dubinin Radushkevich isotherms, for describing the behavior of humic acid adsorption by bentonite and montmorillonite nanoparticles, were examined. Results The results showed that due to the regression coefficient (R²), humic acid adsorption on bentonite and montmorillonite nanoparticles has greater compliance with Dubinin Radushkevich isotherms. The value of E or average energy of adsorption for humic acid by bentonite and montmorillonite nanoparticles was 0.17 and 0.15 kJ mol^-1, respectively, which specifies that the type of adsorption of humic acid on both nanoparticles was physisorption. The q_max value obtained from the Dubinin-Radushkevich isotherms, for bentonite and montmorillonite nanoparticles were 27.78 and 28.70 mg/g, respectively. Conclusions According to the results of this study, bentonite and montmorillonite nanoparticles have a great potential for the removal of humic acid from aqueous solutions.