Sorption and desorption studies on silver ions from aqueous solution by coconut fiber

This paper presents a method for removing silver ions from aqueous solutions using sorption on biological material (coconut fiber). Sorption was carried out in a bath-type bed. The effect of several parameters, such as initial concentration, pH, temperature, etc. on the degree of removal of Ag+ from the solution was examined. The results obtained at the equilibrium state allowed us to fit an isotherm sorption model and to calculate the maximum sorption capacity. The models that best fit the results for the sorption of silver ions on coconut fiber at different temperatures are the Langmuir and Freundlich isotherm models, but at various pH-values the highest fit ratio is characterized by the Langmuir isotherm model. The results of the sorption kinetics revealed that the pseudo second-order model is best suited for the sorption process of Ag+ on coconut fiber, and on that basis it can be concluded that the limiting step of the sorption process is chemisorption. The thermodynamic calculations indicate that adsorption of silver on coconut fiber occurs in two different ways (sorption and biosorption), depending on the concentration of silver. Desorption of silver from coconut fiber showed that the best eluents for this process are organic acids (citric and acetic acids). The use of NaOH as eluent allows silver particles of nanometric size to be obtained on the surface of the sorbent.