MgFe2O4-biochar based lanthanum alginate beads for advanced phosphate removal

Abstract

MgFe2O4-biochar based lanthanum alginate beads (MgFe2O4-BM-La(b)) were prepared and used for phosphate removal from aqueous solution. MgFe2O4-BM-La(b) was synthesized via co-precipitation of Fe and Mg ions onto the reed precursor, followed by gelation-calcination method, in which gelation was achieved by in-situ crosslinking of lanthanum alginate. Based on pre-screen adsorption experiments, MgFe2O4-BM-La(b) fabricated under optimal conditions showed the adsorption capacity over 20 times higher than pristine biochar(BC), and about 2.5 times higher than that of beads without the addition of BC or MgFe2O4. MgFe2O4-BM-La(b) exhibited favorable mass transfer performance through kinetic adsorption comparison between powder and bead type adsorbents. Results from characterization of MgFe2O4-BM-La(b) showed the rough morphologies with numerous MgFe2O4 nanoparticles adhered on the BC substrate, endowed the bead with excellent magnetic performance for easy separation. In fixed-bed column runs of synthetic secondary treated wastewater (STWW), MgFe2O4-BM-La(b) showed the treatment volume of ~1205 BV when effluent phosphate concentration was below 0.5 mg/L, with the capacity loss of about 30% in three continuous adsorption-regeneration cycles. These results illustrated the synergistic effect of MgFe2O4, La2O3 and BC during phosphate adsorption in practical application. The comparison of FTIR and XPS analyses revealed that through protonation between surface hydroxyl groups and H+, the phosphate adsorption of MgFe2O4-BM-La(b) was dominated by specific forces ligand exchange and inner-sphere complexation, followed by electrostatic attraction. The superiorities of magnetic bead adsorbent with preferable adsorption capacity and mass transfer performance suggested that MgFe2O4-BM-La(b) can serve as a promising filling adsorbent for phosphate removal in industrial application.