Tungsten Adsorption on Goethite: Insights from First-Principles Molecular Dynamics Simulations

The environmental fate of tungsten (W) has received particular attention due to its increasing utilization and potential health hazards. Adsorption on minerals is considered as a major factor in governing tungsten's mobility and bioavailability. Goethite, a highly stable iron oxide in soils and sediments, is pivotal in determining tungsten's environmental behavior. In this study, the sorption mechanisms of tungsten on the primary (110) surface of goethite were investigated by using systematic first-principles molecular dynamics (FPMD) simulations. First, we computed the bidentate corner-sharing complexation structures of tungsten in all protonation states (i.e., WO₄^2-, HWO₄^-, and H₂WO₄⁰) on the goethite surface. Tungsten exhibits a fivefold coordination in the WO₄^2- and HWO₄^- systems, whereas it transforms into a sixfold coordination in the H₂WO₄⁰ system. By using the vertical energy gap method for pK_a calculations, it is revealed that the adsorbed WO₄(H₂O)^2- species is predominant at pH > 2.0, which is different from WO₄^2- in aqueous solutions (pH > 4.9). The desorption free energy of WO₄(H₂O)^2- species suggest that the bidentate corner-sharing form of WO₄(H₂O)^2- is highly stable with a binding energy of 19.8 kcal/mol. This study fills a critical gap in the atomic-scale knowledge of tungsten behavior and stability in natural environments, providing a theoretical foundation for managing tungsten mobilization in both natural and industrial settings.