Simultaneous removal of dissolved inorganic and organic phosphorus by magnetic α-Fe2O3/LaOCl composites: Performance, mechanisms and applicability

Growing evidence shows that dissolved organic phosphorus (DOP) triggers eutrophication due to its bioavailability in lakes. However, current removal strategies are focused more on dissolved inorganic phosphorus (DIP) than DOP due to insufficient understanding and analytical challenges. Herein, a facile molten salt-mediated process was used to prepare a series of lanthanum-based adsorbents. In batch experiments, the as-developed LaFeO-U comprising α-Fe2O3/LaOCl displayed higher adsorption capacities for DIP and DOP than the pure La or pure Fe counterparts due to the La/Fe dual-functional sites. Over 79.90% and 95.29% of the dissolved total phosphorus (DTP) in aquaculture tailwater and secondary effluent from WWTP were removed, respectively, of which approximately 23.5% and 44.3% of the DOP were completely captured. Furthermore, the fate of the DOP after the introduction of LaFeO-U was monitored with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), indicating the variations in species and molecular weight, which enabled optimization of the adsorbent for deep-level P removal. The surface precipitation mechanism and inner-sphere complexation caused by the transformation of LaOCl into La(OH)3 facilitated the DIP removal, while inner-sphere complexes formed on the surfaces of the La/Fe composites dominated DOP adsorption. This work provides new insight into the functional materials designed for synchronous removal of DIP and DOP.