Magnetic phosphazene porous organic polymer for efficient and selective recovery of rare earth elements from acidic wastewater

Efficient recovery of rare earth elements (REEs) from secondary resources is highly recommended to meet industrial production demand and maximize resource utilization. Herein, a magnetic porous organic polymer, termed MTAP, was developed by choosing natural polyphenol tannic acid as a monomer and hexachlorocyclotriphosphazene as a crosslinker. The integration of magnetic nanoparticles further enhanced its advantages since it can be rapidly isolated using an external magnetic field, simplifying the overall operation. Batch adsorption experimental results showed that MTAP can quickly capture REEs including Ce, Nd, Eu, and Gd, achieving the adsorption equilibrium just in 2 min. Furthermore, the adsorption isotherms exhibited an excellent fit with the Langmuir model with the maximum adsorption capacities ranging from 145.5 to 164.2 mg/g at 25 °C. What's more, MTAP was successfully applied to recycle REEs in industrial wastewater with high recovery efficiencies. These characteristics including low cost, easy preparation, rapid adsorption kinetics, and high adsorption capacities highlight the outstanding application prospects of MTAP for the recovery of REEs.