Polymer-Supported Aminomethylphosphinate as a Ligand with a High Affinity for U(VI) from Phosphoric Acid Solutions: Combining Variables to Optimize Ligand–Ion Communication

Aminomethylphosphinic acid (AMPA) is immobilized onto cross-linked polystyrene beads and found to have a high affinity for the uranyl ion, especially from solutions as acidic as 6 M H3PO4. The trend in uranyl affinity by different ligands is AMPA > phosphinic > phosphonic > sulfonic. For example, the percent sorbed from 6 M H3PO4 is 89.5% (AMPA), 44.8% (phosphinic), 5.38% (phosphonic), and 2.60% (sulfonic). The high affinity shown by AMPA is due to the decreased hydrogen bonding in the phosphinic acid ligand as well as synergistic coordination of the uranyl ion by a proximate P=O of a second phosphinate ligand. AMPA contacted with synthetic wet process phosphoric acid solution sorbed 72.2% uranium compared to 0.14% for a commercially available sulfonic acid.