Competitive adsorption of heavy-metal ions on monodisperse polystyrene microspheres carrying dithiocarbamate groups

Competitive adsorption of heavy-metal ions, i.e., Cd(II), Cu(II) and Pb(II), from aqueous media onto monodisperse polystyrene (PS) microspheres carrying dithiocarbamate groups were investigated. The crosslinked PS microspheres (2 μm in diameter) were produced by dispersion polymerization, and then dithiocarbamate groups were incorporated by a two-step procedure. The adsorption rate and capacity of these sorbents for selected heavy metal ions from aqueous media containing different amounts of these ions (0.05-600 ppm) and at different pH of 3.0-8.0 were investigated. Very high adsorption rates were observed at the beginning, and adsorption equilibria were then gradually achieved in about 5-90 minutes. The maximum adsorptions of metal ions onto the dithidcarbamate modified PS microsphere were 205.8 mg, 126.0 mg and 129.1 mg per gram of the sorbent microspheres for Pb(II), Cd(II) and Cu(II), respectively. When the metal ions competed (in the case of the adsorption from their mixture) the amounts of adsorption of metal ions were quite close. Desorption of metal ions were studied by using different eluent volume (20-200 ml) with 0.5 M NaCl. High desorption ratios (more than 90%) were achieved in all cases. Adsorption-desorption cycles showed the feasibility of repeated uses of this sorbent system.