Highly Efficient Recovery of Ruthenium from Aqueous Solutions by Adsorption Using Dibenzo-30-Crown-10 Doped Chitosan

Ruthenium, as an industrial by-product or from natural sources, represents an important economical resource due to its specific applications. A complex problem is represented by ruthenium separation during reprocessing operations, therefore, different materials and methods have been proposed. The present study aims to develop a new material with good adsorbent properties able to be used for ruthenium recovery by adsorption from aqueous solutions. Absorbent material was obtained using chitosan (Ch) surface modification with dibenzo-30-crown-10 ether (DB30C10). Chitosan represents a well-known biopolymer with applicability in different adsorptive processes due to the presence of hydroxyl-, carboxyl-, and nitrogen-containing groups in the structure. Additionally, crown ethers are macromolecules with a good complexation capacity for metallic ions. It is expected that the adsorptive efficiency of newly prepared material will be superior to that of the individual components. New synthesized material was characterized using scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller surface area analysis (BET), and determination of point of zero charge (pZc). Results obtained from the performed kinetic, thermodynamic, and equilibrium studies confirmed the good adsorptive capacity of the prepared material, Ch-DB30C10, obtaining a maximum adsorption capacity of 52 mg Ru(III) per gram. This adsorption capacity was obtained using a solution with an initial concentration of 275 mg L^-1, at pH 2, and 298 K. Ru(III) adsorption kinetics were studied by modeling the obtained experimental data with pseudo-first order and pseudo-second order models. Desorption studies established that the optimum eluent was represented by the 5M HNO₃ solution. Based on the performed studies, a mechanism for recovery of ruthenium by adsorption was proposed.