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

Abstract

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 Fe_0.64Ni_0.36 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 Fe_0.64Ni_0.36 and Fe, (ii) Cr(VI) reduction to Cr(III) by Fe²⁺, (iii) Cr(VI) reduction to Cr(III) by H˙ generated via Fe_0.64Ni_0.36 corrosion, and (iv) Cr(VI) adsorption by BC@FeNi-900-3.