Adsorption mechanism of Ca, Mg, Fe, and Al ions in phosphoric acid-nitric acid solution on 001 × 7 and S957 resins.

Selective removal of Ca and Mg ions using the 001 × 7 resin and Fe and Al ions using the S957 resin is able to achieve the deep purification of the phosphoric acid-nitric acid solution, but the adsorption behaviors of Fe and Al ions are seriously suppressed by phosphoric acid. In order to understand the interaction mechanism of separation processes and the influence of phosphoric acid, we first studied the bonding form of Ca, Mg, Fe, and Al ions on 001 × 7 and S957 resins using FT-IR and XPS techniques; subsequently, quantum chemistry computation was carried out to further explore the bonding mechanism between the functional groups on resins and metal ions. FT-IR and XPS results reveal that for the adsorption process on the 001 × 7 resin, hydroxyls from sulfonic acid groups combine with Ca and Mg ions. Whereas Fe and Al ions are adsorbed on the S957 resin through an exchange reaction with hydroxyls on the phosphonic acid group but not on the sulfonic acid group. Quantum chemistry computation results reveal that the phosphonic acid group has a larger binding energy with Fe and Al ions. Thus, the S957 resin still presents great adsorption performance for Fe and Al ions despite the influence of dihydrogen phosphate ions in the phosphoric acid-nitric acid solution.