METAL-BINDING AFFINITY OF IMIDAZOLE LIGANDS IMMOBILIZED ON POLY(GLYCIDYL METHACRYLATE-CO-ETHYLENE DIMETHACRYLATE) AND ON SILICA

Four new chelating ion-exchangers have been obtained by ring-opening reaction of the epoxy groups on poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (GMA-EDMA) and on two types of epoxy-modified silica with the primary amine group of histamine and the primary amine group of 4-(5-methyl-4-imidazolyl)-1-amino-3-thiabutane (memia). The ligand concentration on the resins varied between 0.25 and 1.9 mmol of the ligand per gram of solid carrier, the highest ligand concentration being obtained for histamine-modified GMA-EDMA. For all materials the batch extraction capacities, in the pH range 0.5-5.7, were higher for Cu2+ than for Cd2+, Zn2+, Ni2+, Co2+ and Ca2+. The highest capacity for Cu2+ was found for GMA-EDMA functionalized with histamine, i.e. 1.1 mmol Cu2+ per g resin. No detectable uptake of Ca2+ took place on any of the new materials in the pH range studied. Competitive experiments, which were performed with solutions containing mixtures of metal chloride salts showed that the ion exchange materials described here selectively sorb Cu2+. Kinetic experiments suggest that the rate of metal ion uptake, and also of metal ion stripping with H2SO4, is mainly determined by the particle size of the carrier material and less by the anchored ligand and the type of backbone material (silica or GMA-EDMA). Apparently, diffusion of the metal ions into the pores of the solid supports is rate determining. Good results, viz. loading and de-loading (stripping) within a few seconds, were obtained with ion-exchange material based on the silica Sorbsil C200, which consists of small porous particles.