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 qmax 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.