Modelling of leachates from dolomitic mine tailings

Area of Science:

• Environmental Chemistry
• Geochemistry
• Computational Modeling

Background:

• Dolomitic lead mine tailings can release toxic metals into the environment.
• Understanding metal speciation in leachates is crucial for assessing environmental risk.
• Computer modeling provides a powerful tool to simulate complex geochemical processes.

Purpose of the Study:

• To investigate the speciation of Pb, Cd, Zn, and Ca in leachates from lead mine tailings using the REDEQL.EPAK model.
• To evaluate the impact of atmospheric CO2 equilibration, solid precipitation, phosphate treatment, and humic acid complexation on metal speciation.
• To compare model predictions with experimental findings.

Main Methods:

• Utilized the REDEQL.EPAK computer model to simulate leachate chemistry.
• Manipulated model parameters to represent fresh vs. aged leachates, atmospheric CO2 interaction, and phosphate addition.
• Incorporated equilibrium constants for metal ion-humic acid complexation into the thermodynamic database.

Main Results:

• Initial leachates were supersaturated with Cd and Zn; free Cd(2+) and Zn(2+) were predicted as dominant species.
• Pb was predicted to exist primarily as PbCO3 ion pairs.
• Leachate equilibration with atmospheric CO2 led to CdCO3 and ZnSiO3 precipitation.
• Phosphate addition at low pH favored Pb5(PO4)3Cl precipitation.
• Humic acid complexation effectively competed with other ligands for metal ions.

Conclusions:

• The REDEQL.EPAK model successfully simulated metal speciation in lead mine tailings leachates under various conditions.
• Environmental factors like CO2, phosphate, and organic matter significantly influence the mobility and fate of metals.
• Model predictions align with experimental observations, validating its utility for risk assessment.