Study on the Removal of Cr(VI) from Aqueous Solutions Using Iron–Aluminum Bimetallic Modified Biochar

While adsorption is a mainstream technique for Cr(VI) remediation, conventional iron-based powder materials suffer from agglomeration, passivation, and separation difficulties. The introduction of aluminum (Al) to construct Fe–Al bimetallic systems can effectively overcome the surface passivation barrier of single metals and induce interfacial synergistic effects. In this study, waste bamboo powder was employed as the carbon source, and Fe–Al bimetallic modified biochar beads (FeAlBCSA) with a three-dimensional porous cage-like structure were successfully fabricated via sodium alginate cross-linking encapsulation coupled with high-temperature pyrolysis. The results demonstrate that, at an initial concentration of 100 mg L –1, FeAlBCSA achieves nearly complete removal (∼100%) of Cr(VI) from aqueous solutions, with the effluent concentration below the limits specified in the Integrated Wastewater Discharge Standard. The maximum theoretical adsorption capacity of FeAlBCSA for Cr(VI) reaches 136.15 mg g –1, and exhibits strong resistance to oxidative deactivation of zerovalent iron (Fe 0 ), maintaining stable Cr(VI) removal activity even after 30 days of air exposure. Characterization techniques, including XRD and XPS, reveal that the efficient removal of Cr(VI) by FeAlBCSA is governed by the synergistic interplay of interfacial reduction and adsorption processes. Specifically, the macroscopic bead structure facilitates direct physical solid–liquid separation, while the removal process is driven by electrostatic attraction, inner-sphere complexation, and the chemical reduction of Cr(VI) to Cr(III) by zerovalent iron (Fe 0 ). This study effectively addresses the key limitations of conventional adsorbents, including rapid deactivation, limited adsorption capacity, and challenges in recovery.