Adsorption of La (III) on Chitosan-Imprinted Nano Zero-Valent Iron Nanocomposite (CS@nZVI): Process Optimization, Isotherm, Kinetic, and Thermodynamic Studies

Abstract

Background: The recovery of rare-earth elements (REEs) like toxic lanthanides from contaminated waters is vital because of their irreversible effects on humans and the environment. Objectives: In the present research, a chitosan-imprinted nano zero-valent iron (CS@nZVI) nanocomposite was fabricated and utilized to the successful separation of Lanthanum as a model lanthanides. Methods: The morphological and structural properties of the composites were studied through BET, FTIR, SEM, TEM, and XRD techniques. The adsorption process was modeled and optimized by methodology of response surface (RSM). Then, its four important models were validated by data fitting. Afterward, they were affirmed using ANOVA test. Results: According to the outputs of the models, the reduced model was obtained as an appropriate model. Based on RSM plots, the adsorption rate at preliminary pH is low and gets better with increasing the pH value. At lower pH, there is a high concentration of H+ ion with smaller ionic radii and higher adsorption possibility, which makes it difficult to adsorb lanthanum ions by creating a competition between the excess of protons in the solution and cationic metal ions. This competitive adsorption and saturation of adsorptive sites on the surface of CS@nZVI sorbent with hydrogen ions together with repulsion forces are responsible for the La (III) less sorption. The optimum CS@nZVI removal efficiency of La (III) was 88% under the following conditions: pH = 8, 1.2 g/L CS@nZVI dosage, 5 mg/L initial La (III) concentration, and 180 min shaking time. Based on uptake kinetic models, the pseudo-second-order model is optimum in describing the rate equation of the adsorption process. Conclusions: Successfully regeneration of CS@nZVI along with its good performance for Lanthanum separation provide a promising and feasible method in order to contaminated streams purification.