POLYMER PENDANT LIGAND CHEMISTRY .5. THE SELECTIVE AND COMPETITIVE REMOVAL OF AG-SOLUTION UTILIZING A N-SULFONYLETHYLENEBIS(DITHIOCARBAMATE) LIGAND ANCHORED ON MACROPOROUS POLYSTYRENE-DIVINYLBENZENE BEADS(, HG2+, CU2+, PB2+ AND CD2+ IONS FROM AQUEOUS)

An important new focus for environmental inorganic chemistry is the se lective removal and recovery of metal ions from aqueous solution with organic ligands anchored to modified polymer backbones. Several signif icant criteria for facile metal ion removal from aqueous solution incl udes the hydrophilicity of the pendant organic ligand when it is ancho red to a hydrophobic, pH stable polymer backbone such as modified, mac roporous polystyrene-divinylbenzene beads, as well as the kinetics and thermodynamics of the pendant ligand reaction with the selected metal ion. We report on an example of a polymer pendant ligand that is high ly selective for the removal of metal ions from aqueous solution at pH 3.0 in a competitive environment. Thus, a predisposed polymer pendant N-sulfonyl-ethylenebis(dithiocarbamate) ligand (PS-SED, 1.12 mmol/g), anchored on modified, macroporous 6% polystyrene-divinylbenzene beads , was synthesized and found to be highly selective for the removal of Ag+ ions (2.17 mmol/g, 2:1 Ag+/PS-SED complex, t(1/2) = 7 min) from aq ueous solution at pH 3.0 in the presence of a variety of competing tri - and divalent metal ions such as Fe3(+), Cr3+, Al3+, Cu2+, Ni2+, Zn2, Mg2+, and Pb2+. When Hg2+ ions (1.24 mmol/g, 1:1 Hg2+/PS-SED complex , t(1/2) = 10 min) are added to this mixture of metal ions, including Ag+ ions, there is a pronounced selectivity toward Hg2+ ions for the P S-SED ligand. In the absence of Ag+ and Hg2+, then Pb2+ ions (1.06 mmo l/g, 1:1 Pb2+/PS-SED complex, t(1/2) = 6 min) are moderately selective in the presence of other competing metal ions including Cd2+ ions; Cu 2+ ions are the exception (0.93 mmol/g, similar to 1:1 Cu2+/PS-SED com plex, t(1/2) = 3 min). As well, in the absence of Pb2+ ions, Cd2+ ions (0.65 mmol/g, similar to 1:1 Cd2+/PS-SED complex, t(1/2) greater than or equal to, 10 min) also are moderately selective in the presence of other competing metal ions; but again, Cu2+ is the exception. Whereas Cu2+ has selectivity over Pb2+ and Cd2+ in a competitive reaction, Fe 3+ ion is more selective in competition with Cu2+, while in competitio n with Fe3+ ion, Ag+, Hg2+, Pb2+ and Cd2+ are all more selective. The overall selectivity was found to be: Hg2+ greater than or equal to Ag > Cu2+ > Pb2+ > Cd2+ > Fe3+ similar to Al3+ similar to Cr3+ > Ni2+ > Zn2+ similar to Co2+ > Mn2+ >> Mg2+. Furthermore, a facile recovery of Ag+, Cu2+, and Cd2+ ions from the respective metalion-PS-SED complexe s on the beads were readily accomplished (similar to 99% recovery) usi ng a 10% NaCN solution at pH 11. A full discussion of these results wi ll be presented. Copyright (C) 1996 Elsevier Science Ltd