MECHANISM OF POLYMER-BASED SEPARATIONS .2. TARGETED METAL-ION COMPLEXATION BY REACTIVE POLYMERS

The metal ion affinities of polystyrene-supported phosphinic and phosphonic acid ligands have been examined under a wide variety of solution conditions in order to elucidate the interaction mechanisms displayed by the two polymeric reagents for different metals. Nitrate solutions of Fe(III), Hg(II), Ag(I), and Mn(II) were contacted with the resins. Three variables studied were the pH, ionic strength, and initial metal concentration (viz., 10-1 to 10-5 N). It was concluded that: the phosphinic resin is more sensitive to loading effects and its phosphoryl oxygen has a lower H+ affinity than the phosphonic resin under highly acidic conditions; the phosphinic resin's recognition mechanism, reduction, intervenes at Hg(II) concentrations ≥ 10-4 N; and Ag(I) is reduced to Ag metal by the phosphinic resin only from relatively high metal ion concentrations coupled with low acid solutions. The log D / pH correlations were found to fall into one of four categories from which the relative affinities displayed by the resin for Mn+ / H+ / Na+ could be deduced. The inherent ligand / Mn+ affinity is best defined in dilute solutions (10-5 N) and acid concentrations wherein the ratio of solution H+ to polymer ligand is 1:1 or less; the relative coordinative affinity for Mn+ / H+ displayed by the ligand is best defined in dilute solutions and high acid concentrations (≥ 2 N HNO3). The sensitivity of the polymer to loading effects may then be defined by increasing the initial metal concentration from 10-5 N to 10-1 N. © 1990.