Highly reactive iron/nickel bimetallic biochar composites for highly efficient remediation of Cr(VI)

In this study, a type of FeNi alloy embedded in biochar (BC) was prepared by a simple, efficient, and pollution-free method to form core–shell type BC@FeNi magnetic materials (BC@FeNi-T-X). The reduction behavior of Fe3+ and Ni2+ during preparation was analyzed, showing their transformation from ionic states to oxidized states, forming metal monomers and alloys. Increasing the Ni content in the SA–Fe3+/Ni2+ gel led to the formation of Fe0.64Ni0.36 and (Fe,Ni) alloys. Mechanistic insights were obtained through adsorption kinetics and isotherm data fitting and by analyzing composite changes before and after Cr(VI) adsorption. BC@FeNi-900-3 exhibited superior corrosion performance compared to the Fe biochar composite (BC@Fe-900-3), enhancing Cr(VI) reduction. Mechanistic studies revealed that Cr(VI) removal by BC@FeNi-900-3 primarily involved (i) Cr(VI) reduction to Cr(III) by Fe0.64Ni0.36 and Fe, (ii) Cr(VI) reduction to Cr(III) by Fe2+, (iii) Cr(VI) reduction to Cr(III) by H˙ generated via Fe0.64Ni0.36 corrosion, and (iv) Cr(VI) adsorption by BC@FeNi-900-3.