Enhancing the Phosphate Adsorption of a Polyallylamine Resin in Alkaline Environments by Lanthanum Oxalate Modification.

Sevelamer hydrochloride (SH), originally developed as an oral pharmaceutical for controlling blood phosphate levels, is a polyallylamine resin that could be used in water treatments. Although it binds phosphates effectively, its adsorption capacity suffers from a significant loss at high pH. Here, we modify SH with lanthanum oxalate to improve its phosphate adsorption in alkaline environments. With less than 6.00 wt% in La content, the composite adsorbent (SH-1C-1La) exhibits an adsorption capacity of 109.3 mg P g at pH 8.0 and 100.2 mg P g at pH 10.0, demonstrating significant enhancement from the original SH (86.3 mg P g at pH 8.0 and 69.4 mg P g at pH 10.0). Besides its high adsorption capacity and rapid adsorption kinetics, SH-1C-1La is capable of maintaining more than 78% of its capacity after four regeneration cycles, showing good durability in long-term applications. Zeta-potential measurements and XPS analysis reveal that the lanthanum oxalate species increase the surface potential to enhance the electrostatic adsorption while introducing chemical binding sites for phosphate ions. Both factors lead to the improved adsorption properties. The modification by lanthanum oxalate species might provide a new alternative for improving the phosphate adsorption properties of anion-exchange resins.