Lychee peels-derived biochar-supported CaFe2O4 magnetic nanocomposite as an excellent adsorbent for effective removal of nitrate and phosphate from wastewater

In this work, the lychee peels-derived biochar-supported calcium ferrite magnetic nanocomposite (LP-BC@CaFe2O4) was successfully developed and used as an excellent adsorbent for simultaneous removal of nitrate and phosphate from water medium. The adsorption behaviors and mechanisms were studied using property analysis, batch experiments and mathematical model data fitting. The results showed that the LP-BC@CaFe2O4 exhibited the higher removal performance of NO3- and PO43- compared with pristine biochar (LP-BC) by about twice thanks to enrichment of M-OH groups on the LP-BC@CaFe2O4’s surface. The removal of NO3- and PO43- maximized at pH of 6.0 and 5.0, respectively. The adsorption behaviors of NO3- and PO43- were the best described by Sips model with the highest adsorption capacities of NO3- and PO43-, respectively, were 60.3 mg N/g and 57.4 mg P/g. The adsorption kinetic data of NO3- and PO43- were fitted well by Elovich model, suggesting that the adsorption process was chemisorption onto heterogeneous surface. The adsorption mechanisms of NO3- and PO43- on the LP-BC@CaFe2O4 were through electrostatic attraction, surface complexion and ligand exchange. Besides, the surface precipitate participated in removal of PO43-. In addition, the LP-BC@CaFe2O4 had high regeneration and reusability, indicating the LP-BC@CaFe2O4 was a fully promising nanocomposite biochar for effective removal of NO3- and PO43- from water environment.