Accessibility-controlled sequestration of mixed PFAS in coal fly ash–cement systems via coupled adsorption and stabilization

Per- and polyfluoroalkyl substances (PFAS) removal via adsorption generates PFAS-laden residuals that require safe long-term management. This study proposes a coupled adsorption–solidification strategy in which thermochemically modified coal fly ash (CFA) serves as both a PFAS adsorbent and a supplementary cementitious material for immobilization in concrete. Both singular and mixed PFAS (PFBA, PFHxA, PFOA, PFDA, and PFDoDA; C4–C12) were adsorbed from deionized water and landfill leachate, followed by incorporation of PFAS-loaded CFA into concrete (10–40% cement replacement). Semi-dynamic leaching tests (EPA Method 1315) were conducted over 63 days to evaluate release kinetics and underlying mechanisms. Adsorption followed Langmuir behavior, with capacities increasing with PFAS chain length. Leaching profiles exhibited a single-peaked release profile with a maximum at approximately Day 7, followed by monotonic decline. Effective diffusion coefficients ranged from 10-13 to 10-13 cm2⸱s-1. All systems exhibited leachability indices (LI) > 8, indicating low PFAS mobility and effective immobilization. Compared to deionized water, landfill leachate significantly suppressed PFAS release, is likely associated with dissolved organic matter and cation-mediated interactions that reduce PFAS availability and transport. This work demonstrates a practical and scalable pathway for managing PFAS-laden residuals while valorizing coal fly ash, providing a sustainable solution for PFAS containment in cementitious systems.