Acid-Assisted Microwave Modification of Bauxite Residue for Organic Adsorption and Removal

High Resolution Image Download MS PowerPoint Slide Activated bauxite residue (ABR) is a waste-derived adsorbent with potential for removing organics from water. This study evaluates an acid-assisted microwave modification as a rapid approach to tune ABR for enhanced adsorption capacity. Five-minute microwave heating (2100 W) with hydrochloric acid pretreatment enhanced the BET surface area by ∼20% and increased the fraction of small mesopores (2−5 nm). (GI)XRD indicated that ABR was dominated by iron oxide phases (Fe 3 O 4 and Fe 2 O 3 ) with only minor changes in their relative fraction after modification, suggesting limited bulk phase transformation. Zeta potential measurements showed a surface charge shift from negative (−8.61 mV) to positive (23.1 mV) after acid-assisted microwave at neutral pH. Proof-of-concept adsorption experiments using model dyes revealed compound-specific responses to modification. While changes in surface area and surface charge influenced adsorption behavior, increased surface area alone did not consistently translate into improved dye removal. These findings suggest that adsorption performance is governed by several interplaying factors, including adsorbent- and contaminant-specific properties. Overall, this work provides preliminary insight into how acid-assisted microwave treatment alters ABR surface characteristics and demonstrates the potential of bauxite residue as a value-added adsorbent supporting waste reuse. Further work is needed to evaluate adsorption mechanisms, kinetics, isotherms, and the applicability of this approach to a wider range of organic pollutants.