Willow residue biochar (BC) and modified biochars (hydrochloric acid washing (HBC), HBC loaded with nanoscale zero-valent iron (nZVI-HBC), and HBC loaded with ferric iron (Fe³⁺-HBC)) after aging were used for aqueous Cr(VI) removal. HBC (> 98.67%), nZVI-HBC (> 98.86%), and Fe³⁺-HBC (> 99.64%) kept high Cr(VI) removal rates under the acidic conditions within a wide pH range (< 7.0), indicating their good adaptability to pH change because of aging. Cr(VI) reduction to Cr(III) was the dominant removal mechanism. The formation of –COOH on BC, HBC, and nZVI-HBC indicates the oxidation of surface functional groups by Cr(VI) and simultaneous Cr(VI) reduction. The disappearance of nZVI peaks indicates the reduction of Cr(VI) to Cr(III) by nZVI. The color reaction result demonstrated that the converted Fe²⁺ in Fe³⁺-HBC contributed to Cr(VI) reduction. Taking into account the removal efficiency, recyclability, cost, preparation process, and stability of adsorbents, Fe³⁺-HBC was recommended for Cr(VI) removal.

老化后使用柳树渣生物炭（BC）和改性生物炭（盐酸洗涤（HBC），装有纳米级零价铁的HBC（nZVI-HBC）和装有三价铁的HBC（Fe ³⁺ -HBC））去除六价铬。HBC（> 98.67％），nZVI-HBC（> 98.86％）和Fe ³⁺-HBC（> 99.64％）在较宽的pH范围（<7.0）的酸性条件下保持较高的Cr（VI）去除率，表明它们对由于老化而引起的pH变化具有良好的适应性。Cr（VI）还原为Cr（III）是主要的去除机理。在BC，HBC和nZVI-HBC上形成–COOH表示表面官能团被Cr（VI）氧化并同时还原了Cr（VI）。nZVI峰的消失表明nZVI将Cr（VI）还原为Cr（III）。显色反应结果表明，Fe ³⁺ -HBC中转化的Fe ²⁺有助于Cr（VI）的还原。考虑到去除效率，可回收性，成本，制备过程和吸附剂的稳定性，建议使用Fe ³⁺ -HBC去除Cr（VI）。