Adsorption and immobilization of phosphorus from water and sediments using a lanthanum-modified natural zeolite: Performance, mechanism and effect

The challenge of effectively controlling endogenous pollution and achieving phosphate recovery remains a hotspot worldwide. The development of a passivator with high adsorption capacity and superior passivating effect is crucial for effective implementation in controlling endogenous pollution. In this study, a lanthanum-modified natural zeolite (LZ) and a lanthanum-modified magnetic zeolite (LMZ) were synthesized using precipitation and hydrothermal methods. Additionally, characterization and incubation experiments were conducted to assess the adsorption and passivation effects of the material. The results showed that the LZ and LMZ had excellent phosphorus (P) adsorption and passivation capabilities. LZ and LMZ exhibited remarkable adsorption capacities of 122.7 and 109.17 mg/g, respectively, surpassing those of most lanthanum-modified materials. The characterization showed that inner sphere complexation and electrostatic attraction served as the primary mechanisms facilitating phosphate adsorption. Moreover, LZ and LMZ were also used as sediment passivators to immobilize P within sediments. The addition of LZ and LMZ could not only control the release of P in overlying water but also transform unstable iron-bound phosphorus (BD-P) and organoclastic phosphorus (Org-P) into stable aluminum-bound phosphorus (OH-P) and calcium-bound phosphorus (H-P). The application of both LZ and LMZ could effectively reduce various forms of Bio-P in the sediment, including algal-available phosphorus (Al-P), sodium bicarbonate extractable phosphorus (Olsen-P), water-soluble phosphorus (WA-P), and iron oxide extractable phosphorus (Fe-P). The amount of LZ and LMZ needed for fixed Fe-P in sediments could be quantitatively calculated within a certain range. Since LMZ could be recovered from water under the action of an applied magnetic field and had better effects on the potential active phosphorus (Mob-P) and Bio-P in the sediments, LMZ could have high potential for use as a passivator for internal pollution control.