Insight into simultaneous selective removal of nitrogen and phosphorus species by lanthanum-modified porous polymer: Performance, mechanism and application

In this study, the ion-exchange resin (D201) was modified with hydrous lanthanum oxide (HLO) to prepare the sorption material HLO-modified resin (LMR), which was used to simultaneous removal of various nutrients containing nitrogen (N) and phosphorus (P) from eutrophic water (e.g., nitrate (NO3--N), nitrite (NO2--N), orthophosphate (OP), pyrophosphate (PP) and myo-inositol hexakisphosphate (IP)). Characterization analysis demonstrated that HLO was successfully immobilized in a porous structure with abundant quaternary ammonium groups in the form of crystalline hydrated oxide. The batch experiments systematically studied the effectiveness of LMR on the adsorption of N and P multicomponent pollutants, and the maximum adsorption capacities of LMR for NO3--N, NO2--N, OP, PP and IP were 35.0 mg N/g, 38.3 mg N/g, 50.5 mg P/g, 53.3 mg P/g, and 14.7 mg P/g, respectively. Moreover, LMR can complete the effective separation of N and P species from aqueous solution within a wide pH range (3-11) and can still maintain good removal performance and selectivity for objective pollutants in a complex environment. Results of density functional theory (DFT) calculations indicated that the highest occupied molecular orbital energy and dipole moment of different species were highly correlated with their adsorption process. Notably, after 10 adsorption/desorption cycles, LMR retained >75% of the adsorption capacity for N and P species. The application of LMR in a fixed-bed column proved to be an effective application-oriented environmental functional material for the simultaneous adsorption of N and P species. Overall, this work provided the possibility to effectively solve the eutrophic problem of water bodies.