Response surface methodology for the optimization of lanthanum removal from an aqueous solution using a Fe₃O₄/chitosan nanocomposite

In the present work, magnetite nanoparticles/chitosan composites (Fe₃O₄/CS) were prepared by a chemical precipitation method. We demonstrated the efficient removal of a rare earth metal, lanthanum (La³⁺), from an aqueous solution using the composite. The removal of La³⁺ was optimized by using response surface methodology. Analysis of variance and Fisher's F-test were used to determine the reaction parameters which affect the removal of La³⁺. Optimal conditions, including adsorbent dosage, pH, temperature, and contact time for the removal of La³⁺, were found to be 6.5 mg, pH 11, 40 °C, and 50 min, respectively. The adsorption capacity was 99.88%. The rate of La³⁺ adsorption was significantly affected by the solution pH and adsorbent amount. An adsorption isotherm was fitted well by the Freundlich model with a linear regression correlation value of 0.9975. The adsorption of La³⁺ using the composite followed pseudo second-order kinetics. Thermodynamic studies have revealed that the negative values of Gibbs free energy confirmed the spontaneous and feasible nature of adsorption.