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Dissolved Solute Sampling Across an Oxic-Anoxic Soil-Water Interface Using Microdialysis Profilers
Published on: March 24, 2023
Process-based interpretation of groundwater arsenic mobility via oxidative and reductive dissolution in a complex
Maria Prieto-Espinoza1, David M Hilger2, David Wilson2
1Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON, Canada; Département des génies civil, géologique et des mines, Polytechnique Montréal, Montréal, QC, Canada.
Journal of Hazardous Materials
|July 4, 2026
Summary
Iron oxides in Giant Mine tailings are a long-term source of arsenic (As), driven by microbial activity. Understanding reductive dissolution and adsorption mechanisms is key to optimizing remediation of these As-bearing mine wastes.
Area of Science:
- Environmental Science
- Geochemistry
- Hydrogeology
Background:
- Giant Mine, a former gold producer, is undergoing major remediation due to arsenic-contaminated mine waste.
- Mine waste, including flotation tailings and iron (Fe) oxide residues, was deposited in the Northwest Tailings Containment Area (NW-TCA).
- Arsenic (As) mobility in mine waste is a significant environmental concern requiring detailed study.
Purpose of the Study:
- To investigate the hydrogeological and geochemical controls on arsenic mobility within the NW-TCA.
- To develop a comprehensive conceptual model of arsenic behavior in the tailings.
- To inform and optimize remediation strategies for arsenic-bearing mine residues.
Main Methods:
- Longitudinal field study from 2017-2024 at the NW-TCA, including an 18-m depth profile (GM7).
- Integration of field measurements: hydrogeology, isotope geochemistry, mineralogy, and microbiology.
- Application of multicomponent reactive transport modeling.
Main Results:
- Elevated dissolved As concentrations (>25 mg/L) were found in saturated tailings with circumneutral pH and excess neutralization capacity.
- Reductive dissolution of As-bearing Fe oxides controls As mobility; As from arsenopyrite oxidation is attenuated by Fe-arsenate phases.
- Adsorption of arsenite onto existing Fe oxides is a likely attenuation mechanism in saturated tailings.
Conclusions:
- Fe oxides are the primary As-bearing phase and a long-term As source in Giant Mine tailings, influenced by microbial activity and carbon availability.
- Understanding these geochemical processes is crucial for effective remediation of As-contaminated mine waste.
- Findings guide the optimization of remediation efforts for roaster residues and flotation tailings.
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