Polymer pendant ligand chemistry-5. The selective and competitive removal of Ag⁺, Hg²⁺, Cu²⁺, Pb²⁺ and Cd²⁺ ions from aqueous solution utilizing a N-sulfonylethylenebis(dithiocarbamate) ligand anchored on macroporous polystyrene-divinylbenzene beads

An important new focus for environmental inorganic chemistry is the selective removal and recovery of metal ions from aqueous solution with organic ligands anchored to modified polymer backbones. Several significant criteria for facile metal ion removal from aqueous solution includes the hydrophilicity of the pendant organic ligand when it is anchored to a hydrophobic, pH stable polymer backbone such as modified, macroporous 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 highly 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, t1/2 = 7 min) from aqueous 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, t1/2 = 10 min) are added to this mixture of metal ions, including Ag+ ions, there is a pronounced selectivity toward Hg2+ ions for the PS-SED ligand. In the absence of Ag+ and Hg2+, then Pb2+ ions (1.06 mmol/g, 1:1 Pb2+/PS-SED complex, t1/2 = 6 min) are moderately selective in the presence of other competing metal ions including Cd2+ ions; Cu2+ ions are the exception (0.93 mmol/g, ∼ 1:1 Cu2+/PS-SED complex, t1/2 = 3 min). As well, in the absence of Pb2+ ions, Cd2+ ions (0.65 mmol/g, ∼ 1:1 Cd2+/PS-SED complex, t1/2 ≥ 10 min) also are moderately selective in the presence of other competing metal ions; but again, Cu2+ is the exception. Whereas Cu2+ has a selectivity over Pb2+ and Cd2+ in a competitive reaction, Fe3+ ion is more selective in competition with Cu2+, while in competition with Fe3+ ion, Ag+, Hg2+, Pb2+ and Cd2+ are all more selective. The overall selectivity was found to be : Hg2+ ≥ Ag+ > Cu2+ > Pb2+ > Cd2+ > Fe3+ ∼ Al3+ ∼ Cr3+ > Ni2+ > Zn2+ ∼ Co2+ > Mn2+ ≫ Mg2+. Furthermore, a facile recovery of Ag+, Cu2+, and Cd2+ ions from the respective metal-ion-PS-SED complexes on the beads were readily accomplished (∼99% recovery) using a 10% NaCN solution at pH 11. A full discussion of these results will be presented. Copyright © 1996 Elsevier Science Ltd.

Duke Scholars

Author Katherine J. Franz Chemistry