Lanthanum Carbonate Hydroxide/Magnetite Nanoparticles Modified Porous Biochar for Advanced Phosphate Removal

Herein, lanthanum carbonate hydroxide (La(CO3)OH)/Magnetite (Fe3O4) nanoparticles modified porous biochar (La/Fe-NBC) were prepared through molten salt pyrolysis-coprecipitation-hydrothermal method for further removal of phosphate in aqueous solution with various pH. La(CO3)OH functioned as active sites for phosphate adsorption and Fe3O4 conferred the complex magnetic properties, also porous biochar acted as the carrier to prevent the agglomeration of La(CO3)OH and Fe3O4 nanoparticles. Specifically, the adsorption process of La/Fe-NBC for phosphate was fit to the Pseudo-second order and Langmuir model, with the theoretical maximum adsorption capacity up to 99.4637 mg P/g. La/Fe-NBC possessed high selective adsorption ability for phosphate adsorption with representative coexisting anions, and the adsorption process was rarely affected upon the solution ionic strength. The excellent magnetic field (14.50 emu/g) and stability enabled the multiple solid-liquid separation of La/Fe-NBC. Mechanistic investigation revealed that ligand exchange (inner-sphere complexation) between phosphate and carbonate/surface hydroxyls of La(CO3)OH and electrostatic attraction are the dominant contribution involved in the adsorption process, while co-precipitation is the minor contribution with various pH conditions