Lead and selenite adsorption at water-goethite interfaces from first principles

Area of Science:

• Geochemistry
• Environmental Science
• Materials Science

Background:

• Complexation of toxic ions on mineral surfaces is crucial for geochemistry.
• Understanding lead (Pb(II)) and selenite (SeO3(2-)) interactions with iron oxides like goethite is vital for environmental remediation.

Purpose of the Study:

• To investigate the coordination and adsorption mechanisms of Pb(II) and Pb(II)/selenite ion pairs on goethite surfaces using computational methods.
• To compare simulation results with experimental data, specifically EXAFS measurements, for validation.

Main Methods:

• Applying periodic-boundary-conditions density functional theory (DFT) molecular dynamics simulations.
• Examining Pb(II) coordination to goethite (101) and (210) surfaces, including FeOH deprotonation effects.
• Analyzing Pb(II)/selenite contact ion pair interactions and stability.

Main Results:

• DFT simulations accurately predict Fe-Pb distances when Pb(II) coordinates to three FeO/FeOH groups, aligning with EXAFS data.
• Pb(II) coordination to fewer surface groups shows greater Pb-O distance fluctuations.
• Pb(II)/selenite ion pairs are metastable on goethite (210) surfaces with monodentate Se-O-Fe bonds.

Conclusions:

• DFT molecular dynamics provide a foundation for calculating Pb(II) and Pb(II)/selenite binding constants.
• The study clarifies adsorption sites and mechanisms for lead and selenite on goethite.
• Accurate simulation of ion-surface interactions is essential for predicting contaminant behavior in geological systems.