Modeling EDTA-facilitated cadmium migration in high- and low-permeability systems using MODFLOW and RT3D

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Cadmium (Cd) contamination poses significant risks to groundwater quality, human health, and ecosystems.
• Predicting cadmium's fate in groundwater is complex due to factors like adsorption, ligand complexation, and hydraulic conductivity variations.

Purpose of the Study:

• To simulate and analyze cadmium migration in groundwater, with and without EDTA, using a reactive transport model.
• To investigate the effectiveness of EDTA in removing cadmium from heterogeneous subsurface environments.

Main Methods:

• A 2D reactive transport model (MODFLOW/RT3D) was employed to simulate experimental data.
• The model was extended to conceptual flow cells with varying low-permeability zone (LPZ) configurations.
• Cadmium effluent concentrations were analyzed under different conditions (with/without EDTA, varying heterogeneity).

Main Results:

• Model simulations closely matched experimental results.
• EDTA significantly enhanced cadmium removal from LPZs compared to water alone.
• EDTA facilitated cadmium removal by complexing with adsorbed Cd, promoting solubilization and back-diffusion.
• Increased LPZ heterogeneity led to greater Cd retention and enhanced EDTA effectiveness due to increased interface areas.

Conclusions:

• EDTA shows promise for removing cadmium from heterogeneous contaminated sites.
• Model limitations include simplified conditions (pH, redox, competing cations) requiring cautious interpretation.