Magnetic field-assisted adsorption of phosphate on biochar loading amorphous Zr-Ce (carbonate) oxide composite.

For metal-based phosphate adsorbents, the dispersity and utilization of surface metal active sites are crucial factors in their adsorption performance and synthesis cost. In this study, a biochar material modified with amorphous Zr-Ce (carbonate) oxides (BZCCO-13) was synthesized for the phosphate uptake, and the adsorption process was enhanced by magnetic field. The beside-magnetic field was shown to have a better influence than under-magnetic field on adsorption, with maximum adsorption capacities (123.67 mg P/g) 1.14-fold greater than that without magnetic field. The beside-magnetic field could also accelerate the adsorption rate, and the time to reach 90% maximum adsorption capacity decreased by 83%. BZCCO-13 has a wide range of application pHs from 5.0 to 10.0, with great selectivity and reusability. The results of XPS and ELNES showed that the "magnetophoresis" of Ce under the magnetic field was the main reason for the enhanced adsorption performance. In addition, increased surface roughness, pore size and oxygen vacancies, enhanced mass transfer by Lorentz force under a magnetic field, all beneficially influenced the adsorption process. The mechanism of phosphate adsorption by BZCCO-13 could be attributed to electrostatic attraction and COdominated ligand exchange. This study not only provided an effective strategy for designing highly effective phosphate adsorbents, but also provides a new light on the application of rare earth metal-based adsorbent in magnetic field.