Redox Properties of Structural Fe in Clay Minerals: 4. Reinterpreting Redox Curves by Accounting for Electron...

Area of Science:

• Environmental Science
• Geochemistry
• Clay Science

Background:

• Iron-bearing smectite clays are crucial environmental electron shuttles.
• Previous studies noted redox hysteresis in smectite electrochemical analyses, varying with redox history.
• This hysteresis was linked to incomplete equilibration during experiments.

Purpose of the Study:

• To investigate the cause of redox hysteresis in smectite clays.
• To develop a model simulating interfacial electron transfer and charge redistribution.
• To validate the model and determine thermodynamic/kinetic parameters for smectites.

Main Methods:

• Developed a computational model for interfacial electron transfer and charge redistribution.
• Simulated mediated electrochemical experiments on smectite SWa-1.
• Experimentally validated model findings with extended equilibration times (≥12 h).
• Extended simulations to smectites NAu-1, NAu-2, and SWy-2.

Main Results:

• Simulated redox curves accurately matched experimental data for SWa-1.
• Model demonstrated that longer equilibration periods significantly decrease redox hysteresis.
• Experimental validation confirmed the reduction of hysteresis with extended equilibration.
• Extracted thermodynamic and kinetic parameters for four smectite types.

Conclusions:

• Redox hysteresis in smectites is primarily due to slow particle equilibration kinetics.
• The developed model provides a framework for interpreting and predicting clay redox behavior.
• This research offers crucial parameters for understanding redox reactions on common clay surfaces.