Matrix effects on fluorine mass balance during simulated incineration of per- and polyfluoroalkyl substance laden solids

The widespread persistence and global distribution of per- and polyfluoroalkyl substances (PFAS) have intensified interest in thermal treatment technologies for permanent destruction, particularly during incineration of contaminated soils and spent PFAS adsorbents. However, evaluating destruction efficiency remains challenging due to difficulties in closing fluorine mass balance. Hydrogen fluoride (HF) is commonly used as an indicator of fluorine mineralization, yet its quantitative recovery can be strongly influenced by matrix-dependent processes. Here, we investigate analytical barriers to fluorine mass balance during simulated incineration using combustion ion chromatography across 21 PFAS-laden materials, including ion exchange resins, granular activated carbons, soils, and soil components. Samples spiked with perfluorooctanesulfonic acid or sodium fluoride were combusted at 800, 900, and 1050 °C, and fluorine recovery was quantified via HF. Fluorine recovery showed strong matrix dependence. Soils and some clays exhibited elevated recoveries (>100%) due to background fluorine release, whereas calcium- and clay-rich materials showed suppressed or highly variable recoveries due to fluorine retention in mineral-associated forms. Ion-exchange resins exhibited recoveries near 100% but with variability linked to analytical interferences, including a non-monotonic response to moisture, where intermediate moisture levels decreased apparent recovery while higher moisture improved it. These findings demonstrate that fluorine recovery is governed by matrix composition, fluorine speciation, moisture effects, and analytical limitations, rather than PFAS mineralization alone, and should be interpreted with caution when assessing thermal treatment performance.