Thermogravimetric Studies for the Incineration of an Anion Exchange Resin Laden with Short- or Long-Chain PFAS Compounds Containing Carboxylic or Sulfonic Acid Functionalities in the Presence or Absence of Calcium Oxide

Anion exchange resins are being used by the drinking water industry to remove per- and polyfluoroalkyl substances (PFAS) including perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) from water, and spent resins are commonly incinerated by the industry. By conducting thermogravimetric analysis (TGA) studies, this investigation is aimed at filling some of the knowledge gaps that currently exists in the incineration of PFAS-laden resins. This work is aimed at understanding the impact of characteristics (i.e., carbon chain length and acid functionality) of nine PFAS compounds, in the presence or absence of a calcium oxide (CaO) additive, on the decomposition and burning characteristics of PFAS-laden resins. The TGA profiles of selected pure PFAS compounds confirmed the near-complete evaporation of these compounds below their boiling points, whereas PFAS-laden resin profiles exhibited the partial holding of PFAS compounds by resin well above their boiling points. Resins laden with PFCAs exhibited TGA profiles similar to those of the blank resins, whereas resins laden with PFSAs showed a drastic weight loss from 400 to 500 degrees C. These results suggested that decomposition and oxidation reactions were accelerated by sulfonic acid functionalities, and the impact of sulfonic acid groups appears to increase with the increase in the chain length of PFSAs. The presence of the CaO additive resulted in similar TGA profiles for all tested PFCA-laden resins, where all exhibited a relatively flat profile in the similar to 470-700 degrees C range as a result of the simultaneous burning of carbon char and the reaction of CO2 with CaO, followed by a rapid weight loss at 700-800 degrees C from the decomposition of the formed CaCO3 to CaO. The TGA profiles of PFSA-laden resins in the presence of CaO exhibited a similar impact of sulfonic acid functionalities accelerating the decomposition and oxidation of the resin without any clear correlation with the PFSA chain length.