Metal-ion extraction using bifunctional ion exchangers

Metal-ion extraction studies were performed using two different (monoarylphosphinic acid)-(diarylphosphine oxide) resins, one containing 2.0% crosslinking agent, the other containing 15.0%. The metal ions selected were Na(I), Cu(II), Mn(II), Cr(III), and Sr(II). The distribution of these ions between aqueous and resin phases as a function of pH was measured. Distribution studies yielded information concerning the extraction capabilities of the resins, resin selectivities, and the effects of crosslinking.

Batch equilibrations were carried out using less than 0.20 meq of metal ion in contact with a known amount of resin containing 1.00 meq of H⁺. Samples were equilibrated overnight, phases were separated, and aliquots of the supernatants were analyzed for metal ion concentrations using a Varian atomic absorption spectrophotometer.

Plots of log D against log [HR]_r/[H⁺]_a were constructed where D represents the distribution coefficient, [HR]_a denotes the concentration of H⁺ on the resin and [H⁺]_r represents the aqueous H⁺ concentration. Slope and intercept measurements yielded the number of H⁺ ions liberated per metal ion extracted and empirical equilibrium constant values. From these plots, it was found that the extraction behaviors of the 2.0% and 15.0% resins were similar with the 2.0% resin extracting more metal ion at a given pH in most instances. Resin selectivity on the 2.0% resins was determined from the equilibrium constant values and is as follows: Mn(II) > Cr(III) > Cu(II) > Sr(II) >> Na(I). The affinity sequence on the 15.0% resin is; Mn(II) > Cu(II) > Cr(III) > Sr(II) » Na(I). Results Indicate a high degree of extraction by both resins for all metal ions investigated, with the high extraction of Na(I) being noteworthy.