Simultaneous Adsorption of Rare Earth Metal Ions on Chitosan-coated Fumed Silica: Characterization, Kinetics, and Isotherm Studies

Abstract

The present study manufactured and utilized the chitosan-modified fumed silica composite (CS@silica) for simultaneous adsorption of rare earth elements (REEs) of Ce(III), La(III), and Nd(III) cations in an aqueous solution. The CS@silica composite underwent characterization using a CHNOS analyzer, BET surface area analyzer, ATR-FTIR spectrophotometer, SEM-EDX spectrophotometer, and XRD analyzer. The findings indicated that the CS@silica composite exhibited a lack of pores and possessed a specific surface area of 1.27 m2/g. Additionally, it was observed that the composite contained a significant amount of oxygen and nitrogen atoms, which serve as the active sites for the adsorption of REEs. The maximum adsorption capacities of Ce(III), La(III), and Nd(III) cations were determined under optimal experimental conditions. These parameters included a pH of 4, an adsorbent dose of 0.01 g, and an equilibrium duration of 20 min. The maximum adsorption capacities for Ce(III), La(III), and Nd(III) cations were found to be 341, 241, and 299 mg/g, respectively. The adsorption kinetics followed the pseudo-second-order kinetic model. The desorption percentage of REEs-loaded CS@silica composite was significantly low when exposed to deionized water and hydrochloric acid (0.01 and 0.02 M). This suggests that there is a chemical interaction between the REEs and the active site on the surface of the composite. The predominant adsorption process proposed was complexation, with ion exchange and electrostatic contact playing a minor role. The CS@silica composite is highly promising for the recovery of REEs because of its rapid adsorption and high adsorption capacities.

Keywords

• adsorption
• chitosan
• fumed silica
• isotherm
• kinetics
• rare-earth elements