Using UCODE_2005 and PHREEQC to determine thermodynamic constants from experimental data.

Area of Science:

• Environmental Chemistry
• Geochemistry
• Computational Chemistry

Background:

• Accurate estimation of chemical thermodynamic constants is crucial for understanding and predicting chemical processes in environmental and geological systems.
• Traditional methods often lack robust uncertainty quantification and model validation capabilities.

Purpose of the Study:

• To present a computational method for estimating chemical thermodynamic constants from experimental data.
• To demonstrate the application of this method for determining conditional stability constants, sorption constants, and degradation rate constants.
• To highlight the advantages of the method, including uncertainty estimation and model evaluation.

Main Methods:

• Utilized two computer programs: UCODE_2005 for parameter estimation and PHREEQC for geochemical modeling.
• Applied the method to estimate the conditional stability constant for lead (Pb) complexation with carboxymethyl-beta-cyclodextrin.
• Employed statistical techniques for model assessment and comparison.

Main Results:

• Successfully estimated the conditional stability constant for Pb complexation.
• The method provides a framework for estimating various thermodynamic parameters, including sorption and degradation constants.
• Demonstrated the capability to quantify uncertainties associated with estimated parameters.

Conclusions:

• The presented method offers a powerful tool for refining thermodynamic databases using experimental data.
• It enhances the reliability of geochemical models by incorporating uncertainty analysis and model validation.
• This approach facilitates a statistically sound comparison of different conceptual models.