Deep potential molecular dynamics study on the hydrogen bonding interactions and diffusion behavior of fluorine in...

The mechanisms underlying the decline in defluorination efficiency during late-stage wet-process phosphoric acid (WPA) production remain elusive, as the critical role of the fluorine (F^-) hydrogen bonding is often overlooked. This study employs multiscale simulations, combining first-principles molecular dynamics (FPMD) and deep potential molecular dynamics (DPMD), to investigate the evolution of the hydrogen bond network (HBN) and its impact on fluorine migration across varying P₂O₅ concentrations and temperatures. Our results identify fluorine as the most potent H-bond acceptor in the system. The results reveal a concentration-driven coordination transition: in dilute acid, F preferentially binds to phosphoric acid hydrogen (H_p), whereas in concentrated acid, it forms stronger, shorter H-bonds with hydronium ions (H₃O⁺). DPMD simulations further demonstrate that the evaporation-concentration process densifies the global HBN, increasing its connectivity and structural compactness. Collectively, it can be concluded that residual fluorine is immobilized by a dual constraint: strong localized H-bond interactions and global HBN confinement. This study provides a novel perspective for enhancing industrial defluorination efficiency through H-bond modulation.