Unlocking the sorption mechanism of perfluoroalkyl acids (PFAAs) on geosynthetics: Case of the geotextile components of geosynthetic clay liners

We present here an experimental investigation on the sorption of four perfluoroalkyl acids (PFAAs): namely, two perfluorocarbonic acids (PFCAs) - perfluorooctanoic acid (PFOA) and perfluorohexanoic acid (PFHxA); and two perfluorosulfonic acids - perfluorooctane sulfonate (PFOS) and, perfluorobutane sulfonic acid (PFBS) to polypropylene cover and carrier geotextiles commonly used in geosynthetic clay liners. The impacts of various operational parameters, such as sorbent mass, contact time, and initial PFAA concentration, were investigated. A bi-exponential adsorption model was observed to describe the adsorption kinetics for all PFAAs sufficiently. The model indicates two (probably physically) different types of adsorption sites involved in the PFAAs adsorption. The Freundlich and Langmuir equations well represented the adsorption isotherms. Furthermore, it was observed that PFAA sorption was strongly dependent on the end functional groups and perfluorinated carbon chain length of PFAAs. The maximum adsorption capacities for all PFAAs on geotextiles were consistent with results obtained for clay minerals, indicating that, in the absence of sufficient organic matter, sorption of PFAAs onto solids is mainly analyte and solution dependent. The results obtained and reported for the first time herein are imperative for understanding the fate and migration of PFAAs in modern geosynthetic composite liner systems.