In recent decades, mining-related activities in the Lusatian lignite mining area have led to an extensive pyrite weathering, contributing thereby to the elevation of sulfate and iron concentrations in the groundwater and surface water.
Due to the complicated pathways of pyrite oxidation and the complex spatial distribution of the pyrite-bearing layers, it is difficult to develop a comprehensive restoration plan. Therefore, developing a quick and non-intrusive geophysical measuring technique for estimating pyrite oxidation in various depths and areas is highly desirable. Previous laboratory studies have shown the effect of iron bearing minerals on the nuclear magnetic resonance (NMR) response signal. However, further research is required to link these findings to the subsurface pyrite oxidation state or the accompanied sulfate concentrations in the groundwater.
To this end, column experiments containing different pyrite mass-percentages are performed under various redox conditions. The pyrite oxidation in the columns is measured via the mass balance between the inlet, the initial content, and the outlet. In addition, laboratory NMR is used to constantly monitor the column for the entire experiment duration. For modeling purposes, we developed a PHREEQC-based reactive transport model to simulate pyrite oxidation inside the columns. A comparison between the model results, laboratory NMR data, and the experimental measurements provides a basis for the future surface-based NMR applications in the field.
The outcome ultimately enables us to estimate the groundwater contamination due to pyrite oxidation with a NMR-based technique that is less time-consuming, more reliable, and less labor-intensive.