Mechanisms of PFOA immobilization in typical clay minerals during wet-dry cycling in reservoir drawdown zones

Reservoir drawdown zones experience repeated wetting and drying that can mobilize persistent contaminants such as PFOA, yet the mineral controls on long-term retention under such dynamics remain poorly constrained. Here we quantify and compare PFOA uptake and persistence on three representative minerals, kaolinite, illite, and mordenite, using (i) static batch tests and (ii) two consecutive wet-dry cycles (20 days wet + 20 days dry each) that emulate drawdown hydrology. Under static conditions (pH 4, 25 °C), maximum capacities were 10.03, 9.68, and 8.59 mg/g for kaolinite, illite, and mordenite, respectively. Under dynamic cycling, the performance ranking reversed: mordenite showed the strongest long-term retention, ending with the lowest aqueous concentration (8.1 mg/L) and the highest solid-phase loading (0.213 mg/g; p < 0.05) after 80 days, whereas kaolinite and illite exhibited greater desorption. Spectroscopy and surface analysis indicate complementary mechanisms: FTIR detection of -COO⁻ and C-F features (kaolinite, mordenite), XPS evidence for carboxylate binding and metal-F coordination (including Ca 2 + association in mordenite), and charge conditions favorable to electrostatic attraction at pH ≈ 5 for mordenite and kaolinite. These results show that structurally robust, microporous frameworks promote pore-scale confinement and hysteresis that persist through wet-dry cycling, while layered clays are more susceptible to interlayer fluctuations and remobilization. The findings highlight that static capacities alone may misrepresent field persistence; dynamic retention provides a more realistic indicator for drawdown-zone remediation. Mordenite emerges as a promising, low-cost mineral candidate for passive stabilization of PFOA under fluctuating hydrological conditions. • Studied PFOA immobilization on clays under static and dynamic wet–dry cycles. • Dynamic wet–dry cycles significantly alter PFOA adsorption by clay minerals. • Mordenite retains higher long-term PFOA loadings than kaolinite under cycling. • Static sorption results cannot predict PFOA fixation under wet–dry conditions. • Electrostatic, hydrophobic, and surface complexation synergize in PFOA fixation.