Novel metal complexing ligand: thiazolidine carrying poly(hydroxyethylmethacrylate) microbeads for removal of cadmium(II) and lead(II) ions from aqueous solutions

Poly(hydroxyethylmethacrylate) (PHEMA) microbeads carrying thiazolidine (0. 318 mmol/g) were prepared for the removal of Pb(II) and Cd(LI) ions from aq ueous solutions containing different amount of these ions (10-600 mg/l) and at different pH values (3.0-7.0). Adsorption rates were high, and adsorpti on equilibria were reached within 10 min. Adsorption of these metal ions on to the thiazolidine-immobilised microbeads from single solutions were 0.336 and 0.397 mmol/g for Pb(II) and Cd(II), respectively. When the heavy metal ions were in competition, however (in the case of the adsorption from a mi xture) the amounts of adsorption were found to be 0.0356 mmol/g for Cd(II) and 0.326 mmol/g for Pb(II); this novel metal chelating system is selective for Pb(II) ions. Therefore it was great importance to know the stability c onstants of thiazolidine-metal ion complexes. The formation constants of th iazolidine-metal ion complexes were investigated applying the method of Ruz ic. The calculated value of stability constants were 1.24 x 10(4) 1/mol for the Pb(II)-thiazolidine complex and 4.28 x 10(2) 1/mol for the Cd(II)-thia zolidine complex. These values are in good agreement with the competitive a dsorption results. PHEMA microbeads carrying thiazolidine can be regenerate d by washing with a solution of hydrochloric acid (0.05 M). The maximum des orption ratio was as high as 99%. PHEMA microbeads are suitable for repeate d use for more than three adsorption-desorption cycles without considerable loss of adsorption capacity. (C) 2001 Elsevier Science B.V. All rights res erved.