This study describes the removal of Cr3+ ions from aqueous solutions by magnesium oxide (MgO) and montmorillonite nanoparticles (NPs). Optimum values of contact time, adsorbent dosage, temperature, and pH as well as adsorption isotherms, were obtained using concentrations of the metal ions. A scanning electron microscopy-energy dispersive X-ray (SEM–EDX) technique was used to determine adsorbents characteristics. The results showed the maximum uptake values of solutions, by the final point of isotherm experiments were 1033.8 and 3.6 mg/g for MgO nanoparticles (MgO-NPs) and montmorillonite, respectively. The adsorption process followed pseudo-second order kinetic model. Langmuir adsorption isotherm model fitted better to montmorillonite data (R2 = 0.9769), and Freundlich isotherm was in a good agreement with MgO experimental data (R2 = 0.9948). Also, thermodynamic studies were carried out to determine the nature of the process. Thermodynamic results revealed the nature of sorption in MgO-NPs was spontaneous, and in montmorillonite NPs was unspontaneous. Based on the results and by considering the economic aspects of examinations, the MgO-NPs can potentially be used as efficient sorbents for Cr3+ ion removal from aqueous solutions in different conditions.
