Selective separation and recovery of heavy metal ions using water-soluble N-benzoylthiourea modified PAMAM polymers

Polyamidoamine dendrimers (PAMAM) have been surface modified, using a two-step process with benzoylthiourea groups to provide a new excellent water-soluble chelating ion-exchange material with a distinct selectivity for toxic heavy metal ions. Studies on the complexation of Co(II), Cu(II), Hg(II), Ni(II), Pb(II) and Zn(II) by the dendrimer ligand were performed using the polymer-supported ultrafiltration method. The interactions of the different heavy metal ions with the dendritic ligands were determined by measuring the metal ion retention, which was dependent upon the pH of the solution. The results show that all metal ions can be retained almost quantitatively at pH 9. Cu(II) as well as Hg(II) form the most stable complexes with the benzoylthiourea modified PAMAM derivatives and can be separated selectively from the other heavy metal ions investigated. The bound metal ions can usually be recovered by decreasing the pH of the solution. Successive ultrafiltration yields concentrated solutions of the metal ions and the regenerated dendrimer which can be reused. The separation of the heavy metal ions can even be achieved from aqueous solutions containing competing complexing agents such as ammonia, tartrate, triethanolamine or high concentrations of sodium nitrate.