Selective and reversible extraction of heavy metal-ions by mixed-donor crown ether-modified oxirane and thiirane resins

Three mixed-donor crown ethers, [15]aneNO(2)S(2), [12]aneNOS(2) and [15]aneN(2)O(2)S have been coupled to the oxirane- and thiirane-containing copolymers of glycidyl methacrylate and ethylene glycol dimethacrylate p(GMA-O) and p(GMA-S) by nucleophilic ring-opening reactions of the epoxy and thiirane groups. The ligand concentrations on the modified p(GMA-O) resins varied from 0.77 to 1.13 mmol g(-1), the ligand concentrations on the modified p(GMA-S) resins were found to be much lower, ranging from 0.22 to 0.37 mmol g(-1) resin. The resulting oxa-azathiacrown ether containing polymers showed interesting metal-ion affinities. In competitive experiments in the presence of a range of divalent (post) transition metal-ions p(GMA-O)-[15]aneNO(2)S(2) and p(GMA-O)-[12]aneNOS(2) exhibit a very high capacity and selectivity towards Ag+ over a wide range of pH (from 1 to 6), Indeed, Ag+ is the only extracted ion. In contrast, the Ag+ affinity of p(GMA-O)[15]aneN(2)O(2)S is much lower, due to the presence of only one rather than two thioether moieties. In this case the Ag+ uptake is relatively low (0.17 mmol g(-1)) at pH 1.5 and relatively high (0.58 mmol g(-1)) at pH 5. The relative stabilities of the resin-metal-ion complexes have been determined by measuring log D (D = distribution coefficient), which showed that the Ag+ complexes are up to 100 times more stable than the corresponding complexes with other metal-ion species. Regeneration of metal-loaded polymers appeared to be possible with 2.0 M solutions of HNO3 or H2SO4 (in the case of Cu2+, Cd2- and Pb2+), or with a 1.0 M (NH2)(2)CS solution (in the case of Ag+), respectively. (C) 2002 Elsevier Science B.V. All rights reserved.