Thermodynamic Two-Site Surface Reaction Model for Predicting Munition Constituent Reduction Kinetics with Iron...

Area of Science:

• Environmental Science
• Geochemistry
• Soil Science

Background:

• Iron (oxyhydr)oxides are key redox-active soil components.
• They act as reductants for remediating munition constituents (MCs).
• Previous research focused on sorbed Fe(II) concentration for MC reduction kinetics.

Purpose of the Study:

• To develop a thermodynamic framework for predicting sorbed Fe(II) concentrations.
• To build a reaction kinetic model for MC degradation.
• To establish a predictive model for MC degradation timescales.

Main Methods:

• Formulated a thermodynamic framework with a generalized double-layer model.
• Utilized surface acidity and complexation reactions to predict sorbed Fe(II).
• Employed monodentate and bidentate Fe(II)-binding sites and data fitting for oxide sorption characteristics.

Main Results:

• Good agreement between observed and predicted surface area-normalized rate constants for four oxides and four nitro compounds.
• Both monodentate and bidentate sites are necessary for redox titration accuracy.
• Monodentate site concentration was identified as the primary control on MC reaction kinetics.

Conclusions:

• The developed model accurately predicts sorbed Fe(II) concentrations.
• This model is a significant advancement for predicting MC degradation timescales in subsurface environments.
• The findings enhance understanding of iron oxide reactivity in environmental remediation.