Preferred uptake of Cu(II) and Cd(II) by novel pyrazole-functionalized chelating polymers

The synthesis and characterization of two novel pyrazole-functionalized chelating polymers are reported. Functionalization of p-aminomethyl substituted poly(styrene-co-divinylbenzene) was effected by treatment with 3,5-dimethyl-1-hydroxymethylpyrazole (product: LDp) and 1-hydroxymethylpyrazole (product: LPz), respectively. For LDp a chelating group with one dimethylpyrazole per amine nitrogen resulted; in the case of LPz both amine hydrogen atoms were substituted by pyrazole groups. The capacities for Cu²⁺ and for Cd²⁺ and their distribution coefficients appeared to be substantially larger than those for Ca²⁺, Co²⁺, Ni²⁺ and Zn²⁺ for both chelating polymers in the pH range 3.5-5.5. These results were confirmed by competitive experiments between pairs of metal ions. Regeneration (stripping) of Cu²⁺-loaded LPz with strong mineral acids resulted in the decomposition of the chelating ligand. In contrast, the capacity of LDp was unchanged after several cycles of consecutive loading (with Cu²⁺) and stripping. Sulphuric acid (0.5 M) was the most suitable stripping reagent.