Although ball milling is effective for biochar modification with metal oxides for efficient phosphate removal, the recyclability of the adsorbent as well as the precursors for modification, still need to be optimized. Herein, a magnesium-modified biochar was first prepared with the precursor of MgCl2·6H2O through the solvent-free ball milling method. After that, recyclable biochar beads were fabricated with the introduction of sodium alginate and Fe3O4. The beads were proved to have excellent adsorption performance for phosphate with a saturated capacity of 53.2 mg g-1, which is over 12 times higher than that of pristine biochar beads. Although the particle size reduction, surface area, and O-containing group increments after milling are beneficial for adsorption, the remarkable promotion in performance should mainly result from the appropriate formation of magniferous crystals on biochar, which greatly accelerates the electrostatic interactions as well as precipitation for adsorption. The beads also exhibited excellent magnetism-driven recyclability, which greatly avoids secondary contamination and broadens the application field of the adsorbent.
Keywords: adsorption; biochar; modification; phosphate; recyclable; sodium alginate.