Hexavalent chromium (Cr(VI)) removal by ball-milled iron-sulfur @biochar based on P-recovery: Enhancement effect and synergy mechanism.

After the biochar recovery of phosphorus (P), its role in eliminating Cr(VI) is uncertain. In this study, the iron-sulfur biochar (Fe/S@BC) was made by grinding Fe, S, and biochar with a ball mill. P-loaded iron-sulfur biochar (P-Fe/S@BC) was produced after recovering P from simulated wastewater and then used to remove Cr(VI) contamination in waterbodies. P-Fe/S@BC got a rich pore structure and more reactive sites through P-recovery. The experiments revealed that P-Fe/S@BC had an enhancement effect on Cr(VI) pollution with removal efficiencies of 76.9 % ∼ 99.4 %, all greater than Fe/S@BC (58.2 %). In particular, 25P-Fe/S@BC (with 6.55 mg P/g) had the most significant advantage. The combination of physical adsorption, electrostatic attraction, and precipitation contributed to Cr(VI) removal. This is an efficient strategy for reusing Fe/S@BC followed by P-recovery, intending to improve the Cr(VI) removal effect and achieve the sustainable use of P resources and wastes.