Abstract
The application of lignin-based adsorbents in the efficient removal of phosphate from wastewater has attracted much attention and been intensively studied in recent years. However, most currently reported lignin-based adsorbents are difficult to recover and recycle. Herein, we have developed a recyclable, nanostructured bio-adsorbent, poly(ethyleneimine) (PEI)-modified lignin (LG) integrated with Fe3O4 and Zr-La dual-metal hydroxide (LG-NH2@Fe3O4@Zr-La), by the Mannich reaction followed by the chemical coprecipitation method. Multilayer adsorption existed on the surface of LG-NH2@Fe3O4@Zr-La based on the isotherm fitting curve, and its adsorption capacity reached 57.8 mg P g-1, exhibiting a higher phosphate uptake than most reported metallic oxide-based composites. The adsorption process was dominated by inner-sphere complexation of ligand-exchange and electrostatic interactions. Moreover, LG-NH2@Fe3O4@Zr-La exhibited excellent selectivity against coexisting anions, and the adsorption was more efficient under acidic conditions. When the phosphate concentration was 2.0 mg P L-1, the removal efficiency of phosphate reached 99.5% and the residual concentration was only 10 μg P L-1, which meets the United States Environmental Protection Agency (USEPA) standard for eutrophication prevention. In addition, the LG-NH2@Fe3O4@Zr-La displayed excellent reusability, maintaining 91.8% of removal efficiency after five cycles. Importantly, owing to the magnetic properties of the loaded Fe3O4, the resulting composite could be separated within 30 s under an external magnetic field. Thus, the separable and recyclable biobased magnetic adsorbent developed in this work exhibited promising application in phosphate capture from real sewage. This research study provides a new perspective for lignin valorization in lignocellulose biorefineries and establishes an approach for developing an economical and efficient bio-adsorbent for phosphate removal from wastewater.
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