Radon exhalation and migration mechanisms across stratigraphic units: a case study from Inner Mongolia

Area of Science:

• Geochemistry
• Environmental Science
• Subsurface characterization

Background:

• Radon (²²²Rn) serves as a valuable tracer for identifying concealed fractures and subsurface heterogeneity.
• Understanding radon's behavior in coal-bearing strata is crucial for resource exploration and environmental assessment.

Purpose of the Study:

• To investigate the relationship between radon exhalation and pore characteristics in coal-mining drill cores.
• To assess the influence of pore volume, pore size distribution, and moisture content on radon exhalation.

Main Methods:

• Utilized Laser Threshold Nephelometry Analysis (LTNA) for pore characterization of drill cores.
• Conducted sealed-chamber exhalation tests to measure radon release rates.
• Performed moisture-conditioning tests to evaluate water content effects on radon exhalation.

Main Results:

• Observed a distinct vertical zonation in pore volume, with peak values in the middle transition zone.
• Radon exhalation showed an increase-then-decrease trend with depth, peaking at approximately 7.6 Bq·kg^-1·h^-1.
• Radon exhalation strongly correlated with total pore volume (R² ≈ 0.95) and mesopore volume (R² ≈ 0.98).
• Moisture content significantly modulated radon release, exhibiting an inverted-U response.

Conclusions:

• Mesopores are key to matrix-accessible pore space and diffusion supply of radon at the core scale.
• Radon anomalies can effectively delineate high-permeability pathways and potential concealed fractures in coal-bearing strata.
• Radon exhalation patterns provide insights into subsurface heterogeneity and fracture networks.