Adsorption of Cu2+, Cd2+ and Pb2+ ions by layered double hydroxides intercalated with the chelating agents diethylenetriaminepentaacetate and meso-2,3-dimercaptosuccinate

The hydrotalcite-like compound Zn₂Al(OH)₆]NO₃·nH₂O (ZnAl-NO₃) was intercalated with the chelating agents diethylenetriaminepentaacetic acid (dtpa) and meso-2,3-dimercaptosuccinic acid (dmsa) by anion-exchange to uptake Cu²⁺, Cd²⁺ and Pb²⁺ from aqueous solutions. The amounts of heavy metals adsorbed at variable contact times and metal concentration were determined by atomic absorption spectrometry. The amounts removed of the three metal cations by both adsorbents were high. The shape of the adsorption isotherms obtained indicated specific interactions and a high host–guest affinity. However, the metal ions were removed from solution not only by chelation, but also by precipitation or even by isomorphic substitution of Zn²⁺ by another metal ions in the brucite-like layer.