From solubility to efficiency: Per- and polyfluoroalkyl substances (PFAS) regeneration from anion exchange resins

This study investigated the regenerability of anion exchange resins for per- and polyfluoroalkyl substances (PFAS), focusing on the interaction between regenerant composition and resin characteristics. The influence of salt type and concentration on PFAS solubility revealed a general decline in perfluorohexane sulfonate (PFHxS) solubility with increased salt concentrations, most strongly with KCl followed by NaCl and NH₄Cl. Mixed solubility results were observed for perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS). Three resins – A592E and USA291597EPF (strong base resins) and USA21107 (weak base resin) – were evaluated using aqueous and organic solvent regenerants across multiple cycles. Batch regeneration experiments demonstrated that regeneration effectiveness was higher for short chain perfluoroalkyl carboxylates (PFCA) compared to long chain PFCA, followed by n:2 fluorotelomer sulfonates (FtS) and perfluoroalkane sulfonates (PFSA). Chloride-based salts regenerants were more effective, while the type of cation had minimal impact. Organic solvent regenerants outperformed aqueous solutions, with effectiveness increasing at higher percentages. For low organic solvent percentages, acetone demonstrated higher effectiveness compared to ethanol and methanol. Resin regenerability ranked as follows: USA291597EPF > A592E > USA21107. Flow through column studies confirmed the dependency of regeneration effectiveness on PFAS structural characteristics, with shorter chain PFCA demonstrating higher efficiency. The Lin and Huang model's parameters, time to desorb 50% of resin-associated PFAS ($\tau )$ and the column constant ($k_c)$, revealed two distinct desorption phases. The findings highlight the crucial role of regenerant composition in optimizing resin regeneration, offering valuable insights for developing more effective PFAS remediation strategies.