Sorption of Cd(II) and Pb(II) from aqueous solutions onto Agave americana fibers

The potential of Agave americana fibers as biosorbent was investigated in batch Pb(II) and Cd(II) removal as a function of pH, initial metal concentration and temperature. Metal sorption followed pseudo-second-order kinetics with excellent correlation. The Langmuir model was successfully applied to describe the sorption isotherms. Under optimum conditions (20 °C, pH 5.0, contact time of 30–60 min and 5 g L−1 biomass concentration), the maximum sorption capacity of A. americana fibers was 40.0 mg g−1 for Pb and 12.5 mg g−1 for Cd, respectively. The results obtained at different temperatures allowed estimating the thermodynamic parameters (ΔG°, ΔH° and ΔS°) from the sorption equilibrium constants. The positive ΔH° value obtained for sorption of both metals indicates the endothermic nature of the process. A. americana fibers were also analyzed by IR-FT spectroscopy and scanning electron and metallographic microscopy, with the aim of investigating the interactions of biomass functional groups with cations and evaluating the mechanisms involved in metal sorption.