Bioreduction of Red Mud with Two Stages (Bacteriology-Phytoreduction) to Synthesize "Bio-Derived Iron-Based Nanoparticle (BDINP)"

Purpose: Red mud, a solid by-product of bauxite ore processing, has significant management challenges due to the high alkalinity, large volume, and complex polymetallic composition. Therefore, this study aims to evaluate a two-stage, low-temperature process that couples bacteria iron reduction with plant-mediated phytoreduction can valorized red mud into functional iron-based nanomaterials. Methods : In the first stage, indigenous iron-reducing bacteria (IRB) were used to transform iron while conditioning the system by increasing Fe(II) and lowering red mud alkalinity. In the second stage, green tea extract was used as a natural reducing and stabilizing agent to synthesize bio-derived iron-based nanoparticle (BDINP) from the bacterial reduction filtrate. Subsequently, BDINP was evaluated for the antibacterial activity and co-catalytic performance in photo Fenton system for methyl orange (MO) degradation. Result : Halalkalibacterium halodurans showed the most effective performance to enhance Fe(II) formation (1.39 mM) and pH reduction from 10 to 4.78. The results showed that the co-catalytic system consisting of BDINP-H/Fe(NH₄)₂(SO₄)_2.6H₂O/TiO₂ demonstrated a maximum MO degradation efficiency of 93.63. In addition, BDINP-H showed inhibitory effects against Escherichia coli and Staphylococcus aureus with inhibition zone 5.5 ± 0.06 mm and 6.5 ± 0.06 mm respectively. Conclusion : This approach demonstrate a laboratory-scale route to couple biological conditioning of red mud with phytochemical nanoparticle synthesis yielding BDINP with catalytic and antibacterial functionality, and supporting integrated environmental remediation with waste valorization concepts. © The Author(s), under exclusive licence to Springer Nature B.V. 2026.