Selective extraction and transport of copper(II) with new alkylated pyridinecarboxylic acid derivatives.

Two kinds of N-(6-alkylamido)-2-pyridine carboxylic acid with a pyridine moiety and a carboxylic acid as chelating ligands were newly synthesized for the selective extraction and the transport of copper(II) from aqueous solution. Liquid-liquid extraction was carried out to examine the extraction ability of extractants with metal ions. The selectivity for the metal ions with N-6-(2-ethylhexylamido)-2-pyridine carboxylic acid (EHPA) was in the following order: Cu(II)>>Zn(II) approximately Pb(II) approximately Ni(II) approximately Co(II)>Cd(II)>Mn(II). All metals tested in this study were selectively extracted at a lower pH by 2-3 units compared with commercial available alkyl carboxylic acids such as naphthenic acid and Versatic 10. The extraction equilibria of copper(II) were measured by a batchwise method at 303K with EHPA and N-6-(t-dodecylamido)-2-pyridinecarboxylic acid (t-DAPA). Copper(II) was extracted as a 1:2 complex according to the following reaction: Cu(2+)+2(HR )(2)=CuR(2)2HR +2H(+). The extraction equilibrium constant, K(ex) was evaluated and the values were found to be 1.13 and 0.31 for EHPA and t-DAPA, respectively. It was demonstrated that t-DAPA was very stable to be incorporated into a polymer inclusion membrane (PIM) consisting of cellulose triacetate (CTA) as a base polymer and 2-nitrophenyl octylether (NPOE) as a plasticizer. This novel PIM containing t-DAPA as a carrier exhibited an excellent copper(II) transport characteristic and a high selectivity for copper(II) over cadmium(II) from aqueous solution.