Selective extraction of metal ions by azathiacrown ether-modified polar polymers

The metal-ion uptake behaviour of two chelating ion exchange resins has been investigated. A 16-membered azathiacrown ether, 7-aza-1,4,10,13-tetrathiacyclohexadecane ([16]aneS4N), has been immobilised on poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), p(GMA-O) and on its corresponding sulfur analogue, p(GMA-S). A lariat ether moiety on the polymer is formed after ring-opening of the oxirane or thiirane ring, respectively. The hydrophilic resin p(GMA-O)-[16]aneS4N shows a very high capacity and selectivity towards Ag+ ions in the presence of Cu2+, Zn2+ and Cd2+ ions. The Ag+ ion uptake of the ring-opened thiirane backbone appeared to be equal to the Ag+ ion uptake of the ligand-functionalised polymer and therefore the thiirane-based resin p(GMA-S)-[16]aneS4N has been tested for metal-ion mixtures without silver. With this thiirane-based resin Cu2+ ions have been extracted selectively from mixtures of divalent metal ions. The regeneration characteristics of the loaded polymers have been tested by utilising a range of potential stripping agents. The p(GMA-O)-[16]aneS4N resin, loaded with Ag+ or Cu2+ ions, was successfully regenerated with an aqueous thiourea solution, while the p(GMA-S)-[16]aneS4N resin, loaded with Cu2+, could be regenerated best with an aqueous solution of ethylenediamine in combination with ammonium nitrate.