A pH-activated molecular switch: Multiscale control of ODA-H desorption via charge-driven wettability transition at solid-liquid interfaces

Octadecylamine hydrochloride (ODA H) as an efficient flotation collector is extensively employed in KCl manufacturing. However, the residual of ODA-H not only directly influences KCl application fields, but also poses environmental risks owing to its low biodegradability. Meanwhile, the removal cost is comparatively high because of KCl solubility. In this study, a simple yet effective strategy was proposed to achieve efficient in-situ desorption of ODA-H from the solid KCl surface. The desorption behavior and underlying mechanism were systematically investigated, focusing on charge state conversion, interfacial wettability change, and ODA-H aggregation. The results demonstrated that OH − significantly enhanced the removal efficiency of ODA H, with a removal rate of 86 % achieved when the pH of the saturated KCl solution was raised to 14. In-situ Raman spectroscopy and Molecular Dynamics simulation elucidated the mechanism of OH − , which could accelerate ODA-H desorption kinetics by disrupting the electrostatic interaction between ODA-H and KCl surface, thereby altering its aggregation behavior. Furthermore, the disruption mechanism of interfacial hydrogen-bonding networks during the OH − -promoted desorption process was confirmed. The synergistic effects resulting from these enhancements facilitated the highly efficient desorption of ODA-H from the solid KCl surface. Importantly, industrial-grade KCl was refined with the ODA-H desorption efficiency of 73.95 %. This study will provide a new idea and mechanism explanation for the removal of pollutants on the soluble solid surface in high-salt solution.