Preparation of red mud-based iron-carbon adsorption-reaction materials through biomass pyrolytic reduction for application of dyes removal

Red mud, a byproduct of aluminium production, poses serious environmental risks due to its high alkalinity and large volume. This study explores the synthesis of two iron-carbon adsorption-reaction materials (Fe-C ARMs), Fe₃O₄-BC and ZVI-BC, using corn straw (CS) and red mud (RM) through biomass pyrolytic reduction. CS serves as a pore-forming and reducing agent, while RM acts as the iron precursor. We explored the impact of various preparation conditions, including the raw CS to RM ratio (2:1–1:4), pyrolysis time (45–120 min), and temperature (400°C to 600°C for Fe₃O₄-BC, and 700°C to 1000°C for ZVI-BC), on the characteristics of the Fe-C ARMs. Response Surface Methodology (RSM) identified optimal conditions: for Fe₃O₄-BC, a CS to RM ratio of 1:1, 600°C pyrolysis temperature, and 75 minutes; for ZVI-BC, a CS to RM ratio of 1:3, 912°C pyrolysis temperature, and 75 minutes. Maximum dye removal capacities were 342.4 mg/g for GV and 145.4 mg/g for MO with Fe₃O₄-BC, and 480.5 mg/g for GV and 215.1 mg/g for MO with ZVI-BC. The synthesis mechanisms and physiochemical characteristics of the Fe-C ARMs synthesized under optimal conditions were analyzed using TGA/DTA, FE-SEM coupled with EDS, FTIR, XRD, XPS and BET surface area analysis. The removal of dyes by Fe-C ARMs occurs via a combination of adsorption and reduction on carbon and iron oxides, with efficiency varying according to experimental conditions. Additionally, the materials exhibited reusability over five operational cycles, suggesting their potential for sustainable wastewater treatment applications.