Sorption behavior of impregnated Styrofoam for the removal of Cd(II) ions

A simple and reliable method has been developed using packing waste material (Styrofoam) containing dithizone as a chelating agent, to concentrate ultratrace amounts of cadmium ions in aqueous solutions. After characterization, the static sorption behavior of Cd(II) ions onto modified sorbent has been investigated. The sorption has been optimized with respect to the pH, shaking speed and contact time between the two phases. Maximum sorption has been achieved from solution of pH 6–8 after 8 min of shaking time. Sorbed metal ions are desorbed with 5 ml of 0.2 M EDTA solution with the preconcentration factor of 40. The kinetics and thermodynamics of sorption are studied in detail. The kinetics follows the first order rate equation with the rate constant k, equal to (3.46 ± 0.17 min−1). The variation of equilibrium constant, Kc, with temperature between 15 and 40 °C yields values of ΔH = 80.94 ± 4.95 kJmol−1, ΔS = 290 ± 15.3 JmolK−1 and ΔG is between −3.96 and −10.88 kJmol−1. The sorption data studied in the concentration range of 8.88 × 10−7 mol l−1 to 4.44 × 10−4 mol l−1 Cd(II) ions follows Langmuir, Freundlich, and Dubinin-Radushkevich isotherms at all temperatures investigated. The monitoring of the influence of diverse ions on the sorption of Cd(II) ions has revealed that only Pb(II) ions suppress the sorption to some extent. The possible sorption mechanism of cadmium(II) ions onto impregnated sorbent is also discussed. The sorption procedure is utilized to preconcentrate cadmium ions prior to their determination in human blood and pipe tobacco samples by atomic absorption spectrometry using direct and standard addition methods.