In wastewater treatment, the removal of heavy metals is difficult due to the limited affinity of heavy metal ions to ion exchange resins. Here imprinting polymerization is used to develop resins with high capacity and selectivity for heavy metal ions for water treatment. A random copolymer of methacrylate and methacrylamide was found to be most effective for the removal of hydrophilic metal complexes, like CdCl2, ZnCI2, and the metalloid NaH2AsO4, particularly when the porosity of these resins is increased. For hydrophobic complexes imprinting emulsion polymerization was developed and data for the effective removal of mercury dithizonate will be described. Complete removal for up to 80 ppm of cadmium and mercury with only 200 mg of imprinted resin was obtained; competition and co-imprinting experiments are described as well.

Imprinting polymerization is a flexible method to make resins specific for different compounds. Imprinting polymerization involves the polymerization of the resin in the presence of a template, here cadmium ions or arsenate. The template is then removed by washing, leaving specific binding sites in the resin. In water treatment, the removal of toxic metal ions is difficult due to the limited affinity of these ions to ion exchange resins. Imprinting polymerization of ion-exchange resins is used to develop resins with high capacity and some selectivity for cadmium ions or arsenate for water treatment that still function as general ion-exchange resins. A minimum binding capacity of 325 meq/g was achieved for cadmium ions. Competition experiments elucidate the type of bonds present in the imprinting complex. The capacity and bond types for the cadmium ions and arsenate were contrasted. In the case of cadmium, metal-ligand bonds provide significant specificity of binding, although significant binding also occurs to non-specific surface sites. Arsenate ions are larger than cadmium ions and can only bind via ionic and hydrogen bonds, which are weaker than metal-ligand bonds. This results in lower specificity for arsenate. Additionally, diffusion into the resin is a limiting factor due to the larger size of the arsenate ion. These data elucidate the bonds formed between metal ions and the imprinting sites as well as other parameters that increase the capacity for heavy metals and arsenate.

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