Adsorption of silver ions from industrial wastewater using waste coffee grounds

Waste coffee grounds were used as an adsorbent to efficiently adsorb silver ions in actual industrial waste-water. It was found that the functional groups like -COO- and -OH- groups in coffee grounds play an important role in the adsorption of silver ions from the FT-IR spectra, and the SEM images and EDX spectra were used to investigate the surface onto waste coffee grounds and confirm the existence of silver ions onto the waste coffee grounds after adsorption of silver ions. The highest adsorption capacity and removal efficiency was achieved as about 46.2mg/g and 92.4% at the initial pH 6 of wastewater. Two adsorption isotherm models, Langmuir and Freundlich, were used to analyze the equilibrium data. The Langmuir isotherm, which provided the best correlation for silver adsorption onto coffee grounds, showed that the maximum adsorption capacity and affinity constant was calculated as 49.543mg/g and 1.134 L/mg, respectively. The adsorption was an exothermic reaction and the most equilibrium was achieved at less than 60min. From these results, the waste coffee grounds have high possibility to be used as effective and economical adsorbent for silver adsorption.