Exploiting Differences in Molecular Interactions for Selective PFAS Separation from Natural Organic Matter during Ion-Exchange Regeneration

Ion-exchange resins effectively remove per- and polyfluoroalkyl substances (PFAS) from water but generate concentrated brines co-loaded with natural organic matter, complicating downstream PFAS destruction. Here, we present a sequential selective regeneration strategy exploiting differences in adsorption mechanism and desorption kinetics between PFAS and humic substances to recover them in separate streams. Molecular dynamics simulations reveal that perfluoroalkyl carboxylic acids bind to the resin through dual hydrophobic and electrostatic interactions disrupted by organic solvents, while humic substances bind predominantly electrostatically and are selectively displaced by Cl⁻ ions, desorbing 3–5 times faster than PFOA in sodium chloride solutions. A sequential protocol combining propanol regeneration with a rapid low-contact-time NaCl step recovers over 60% of loaded PFAS in an organic fraction essentially free of humic substances, while humic substances are quantitatively eluted in a separate brine. The PFAS-enriched organic fraction is directly compatible with incineration and emerging destruction technologies, where co-concentrated organic matter would otherwise increase energy demand and reduce treatment efficiency. This work demonstrates that solvent composition, ionic strength, and contact time can be systematically tuned during regeneration to engineer selectivity, a powerful but underexplored dimension of sorption-based water treatment.