Ag(I) adsorption on different grape residues: Effect of the residue type on the physicochemical and thermodynamic adsorption behavior

Abstract

The present study compared the effectiveness of using waste (grape peel, seeds, and stems) from wineries as biosorbents for removing silver (Ag) in liquid media. Adsorption isotherms were analyzed from the perspective of statistical physics modeling; for this purpose, five models were tested to determine which model was the most representative of the system. The experimental results reveal significant differences in the adsorption capacity between the biosorbents, with the grape stem presenting the highest maximum experimental adsorption capacity (39.15 mg g−1) at 298 K. The analysis of the models revealed that the most suitable model to describe the process is the monolayer with adsorption energy. The number of ions adsorbed per site for all biosorbents increased with increasing temperature and presented values greater than 1, which indicates that the process interaction between Ag ions and the surface of the adsorbents occurs in a multiionic way. The adsorption energy and the thermodynamics indicate that the process, through physical interactions (<40 kJ mol−1), is spontaneous and exothermic (negative internal energy and Gibbs free energy). The grape seed biosorbent's adsorption capacity at saturation (61.90 mg g−1) shows the highest affinity with Ag at 298 K. The biosorbents studied effectively removed Ag from aqueous solutions, showing potential for environmental and industrial applications. The mechanism and understanding of the process were made possible through statistical physics models, which show that the Ag removal in the biosorbents analyzed occurs predominantly through electrostatic interactions.