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

A series of La(OH) 3 -modified magnetic pineapple biochar (La x -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 La 3+ and Fe 3+ leakage during adsorption process. Mechanism study revealed that the adsorption mechanism involved precipitation, electrostatic interaction, ligand exchange and inner-sphere complexation.