Performance comparison of La-loaded D201 resins in the simultaneous removal of nitrate and phosphate

In this study, different forms of lanthanum (La), including La³⁺, La(OH)₃ and La₂(CO₃)₃, were employed to modify D201 resin. The obtained resins were critically examined and compared with each other on the simultaneous removal characteristics of nitrate and phosphate, from the perspective of kinetics, isotherms, influence of coexisting ions, and regeneration. SEM images and component analysis revealed that different species of La were evidently loaded on the D201 surface and the highest La content was obtained on the La₂(CO₃)₃-loaded D201 resin. In addition, the La₂(CO₃)₃-loaded D201 resin maintained favorable dephosphorization performance against coexisting ions. Notably, the original and La-loaded D201 resins could retain the adsorption efficiency after being regenerated by Na₂CO₃ 5 times, an indication of stable denitration and dephosphorization performance. R₄N⁺ groups preferentially captured nitrate so that there was a negligible influence of coexisting ions on nitrate uptake. The phosphate adsorption was attributed to electrostatic interactions with R₄N⁺ groups and chemical precipitation or ligand exchange with the loaded La. Moreover, it was more sensitive to the solution pH change, as supported by the improvement under weak alkaline conditions.