Modeling uranium transport in acidic contaminated groundwater with base addition

Area of Science:

• Environmental Science
• Geochemistry
• Hydrogeology

Background:

• Uranium(VI) contamination in sediments under oxic, low pH conditions poses environmental challenges.
• Groundwater and sediments analyzed contain high levels of nitrate, sulfate, uranium, and various metal cations.

Purpose of the Study:

• To investigate reactive transport modeling for uranium(VI) sequestration in contaminated sediments.
• To assess the effectiveness of controlled base addition for uranium immobilization.

Main Methods:

• Column experiments with base (NaOH) addition to influent groundwater to gradually increase pH.
• Development and modification of an equilibrium and kinetic reaction model to simulate geochemical processes.
• Monitoring of pH, aqueous metal cation concentrations (Al, Ca, Mg, Sr, Mn, Ni, Co), sulfate, and U(VI).

Main Results:

• An initial equilibrium model underestimated aluminum (Al) reduction; kinetic modeling for Al precipitation/dissolution was necessary.
• The combined kinetic and equilibrium model accurately described observed variations in pH, metal cations, sulfate, and U(VI).
• Uranium(VI) sequestration was achieved through sorption onto slowly precipitated aluminum with pH-dependent surface charge.

Conclusions:

• Controlled base addition is an effective method for sequestering uranium(VI) in contaminated sediments.
• Kinetic processes, particularly aluminum precipitation, are crucial for accurate modeling of uranium immobilization.
• The developed model shows potential for predicting field-scale uranium remediation effectiveness.