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

Area of Science:

• Environmental Science
• Geochemistry
• Computational Chemistry

Background:

• Increasing tungsten (W) utilization raises concerns about its environmental fate and health hazards.
• Tungsten's mobility and bioavailability in the environment are significantly influenced by its adsorption onto minerals.
• Goethite, a common iron oxide in soils and sediments, plays a crucial role in controlling tungsten's environmental behavior.

Purpose of the Study:

• To investigate the sorption mechanisms of tungsten on the primary (110) surface of goethite.
• To elucidate the atomic-scale interactions and stability of tungsten species adsorbed on goethite.
• To provide a theoretical basis for understanding and managing tungsten mobilization.

Main Methods:

• Systematic first-principles molecular dynamics (FPMD) simulations were employed.
• Calculated bidentate corner-sharing complexation structures for different tungsten protonation states (WO₄²⁻, HWO₄⁻, H₂WO₄⁰).
• Utilized the vertical energy gap method for pKa calculations and determined desorption free energy.

Main Results:

• Tungsten coordination changes from fivefold (WO₄²⁻, HWO₄⁻) to sixfold (H₂WO₄⁰) upon adsorption.
• The adsorbed WO₄(H₂O)²⁻ species is predominant at pH > 2.0, differing from aqueous solutions.
• The bidentate corner-sharing WO₄(H₂O)²⁻ complex exhibits high stability with a binding energy of 19.8 kcal/mol.

Conclusions:

• The study provides atomic-scale insights into tungsten's behavior and stability on goethite surfaces.
• Adsorbed tungsten species, particularly the bidentate WO₄(H₂O)²⁻ complex, are highly stable.
• Findings offer a theoretical foundation for managing tungsten mobilization in natural and industrial contexts.