Repurposing bauxite residue (a waste material) as an adsorbent for removing PFAS from water

Abstract

Per- and polyfluoroalkyl substances (PFAS) are synthetic organic compounds characterized by strong C–F bonds and various functional groups, which contribute to their persistence and mobility in the aquatic environment. Bauxite residue (or red mud) is a highly alkaline waste from the aluminum industry, often stored in large quantities in tailing ponds. Recently, growing interest in sustainable waste management has highlighted the potential of bauxite residue to remove organic pollutants from water. This study investigates the use of activated bauxite residue (ABR) (produced via a reduction roasting process) as an adsorbent for a mixture of 10 PFAS substances in water. Bench-scale testing demonstrated that long-chain PFAS can be effectively removed by ABR (up to 100%) whereas the short-chain ones achieved 20–100% removal. PFAS removal using ABR follows a pseudo-second-order kinetic model, indicating that chemisorption may play a role during adsorption. This is further supported by the XPS analysis that shows the presence of metal–F bond. Isotherm study further indicated that at its current material characteristics (pore volume = 0.14 cm³ g⁻¹, BET surface area = 25 g m⁻², point of zero charge of ∼pH 5), high dosage of ABR (∼10 g L⁻¹) is required to reach >85% removal for ∑PFAS (n = 10). Cytotoxicity results supported the use of <10 g L⁻¹ ABR to minimize ABR toxicity and maximize PFAS removal. Although further material optimization is needed to lower dosage requirements and improve competitiveness with established adsorbents (e.g., powdered activated carbon), our preliminary results highlight the potential of ABR as a promising sorbent for PFAS removal.