La(OH)3-modified magnetic pineapple biochar as novel adsorbents for efficient phosphate removal

A series of La(OH)(3)-modified magnetic pineapple biochar (Lax-MC) with different contents of La(OH)(3) were prepared and used as phosphate adsorbents for the first time. With the increase of La(OH)(3) content, the adsorption capacity for phosphate increased while the magnetic property decreased. La10-MC exhibited excellent magnetic property for easy recovery and high adsorption capacity up to 101.16 mg P/g, which was 27 times that of pineapple biochar and much higher than most phosphate adsorbents. Adsorption isotherm and adsorption kinetics were better fitted by Langmuir model and pseudo second-order model, respectively. The removal efficiency > 96.04% in coexisting ions indicated its high selectivity to phosphate. Little decrease in removal efficiency after three adsorption-desorption cycles suggested its excellent stability and cyclic utilization. Leaching study demonstrated the negligible risk of La3+ and Fe3+ leakage during adsorption process. Mechanism study revealed that the adsorption mechanism involved precipitation, electrostatic interaction, ligand exchange and inner-sphere complexation.