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<p>Acid mine drainage (AMD) generated by pyrite oxidation in mine overburden dumps poses a persistent threat to groundwater quality, with contaminant generation and migration governed by soil texture, moisture conditions, and oxygen availability. Despite extensive studies on pyrite oxidation chemistry, the integrated influence of unsaturated flow, soil texture, and water content on the temporal evolution and spatial dispersion of oxidation products remains inadequately understood. This study examines the role of surface soil texture and moisture conditions in controlling coupled unsaturated flow and multicomponent reactive transport of pyrite oxidation products in mine waste deposits. A two-dimensional numerical framework is developed by integrating Richards’ equation for variably saturated flow with multispecies reactive transport equations, incorporating Monod-type pyrite oxidation kinetics and a shrinking-core formulation. The model simulates the generation and migration of ferrous (Fe<sup>2</sup>⁺), sulfate (SO₄<sup>2</sup>⁻) and ferric (Fe<sup>3</sup>⁺) ions, under varying hydrogeological conditions. Simulations are conducted over a 10-year period for three representative soil textures (clay, loam, and sand), porosity values (θ = 0.2, 0.4, and 0.6), and water content scenarios (w<sub>c</sub> = 0.1, 0.5, and 0.9). Model predictions are validated against published benchmarks and field-scale observations. The results demonstrate strong texture-dependent behavior. Clay restricts oxygen ingress, resulting in reduced oxidation rates and enhanced retention of dissolved species, whereas loam exhibits relatively uniform transport, and sand facilitates rapid advective migration of oxidation products. Ion concentrations decrease from approximately 200 to 40 mol m⁻<sup>3</sup> in clay, 300 to 95 mol m⁻<sup>3</sup> in loam, and 1 to 0.2 mol m⁻<sup>3</sup> in sand. Elevated moisture conditions (w<sub>c</sub> = 0.9) significantly enhance the ion mobility, increasing the contamination potential. Sensitivity analysis indicates that sulfate exhibits the highest sensitivity in clay under low moisture conditions (w<sub>c</sub> = 0.2), with SI values up to ~ 4.3 × 10<sup>4</sup>, while ferrous ions show maximum sensitivity in loam under similar conditions (10<sup>2</sup>–10<sup>3</sup>). Overall, clay-rich layers provide effective attenuation of pyrite oxidation products, highlighting their suitability for AMD mitigation.</p>

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Impact of Surface Soil Texture on the Temporal Dynamics and Spatial Dispersion of Pyrite Oxidation Products in Unsaturated Mine Overburden Dumps

  • 期刊论文

  • 发表日期：

    2026年7月3日

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  • Gautam Roy,
  • Bellie Sivakumar

摘要

Acid mine drainage (AMD) generated by pyrite oxidation in mine overburden dumps poses a persistent threat to groundwater quality, with contaminant generation and migration governed by soil texture, moisture conditions, and oxygen availability. Despite extensive studies on pyrite oxidation chemistry, the integrated influence of unsaturated flow, soil texture, and water content on the temporal evolution and spatial dispersion of oxidation products remains inadequately understood. This study examines the role of surface soil texture and moisture conditions in controlling coupled unsaturated flow and multicomponent reactive transport of pyrite oxidation products in mine waste deposits. A two-dimensional numerical framework is developed by integrating Richards’ equation for variably saturated flow with multispecies reactive transport equations, incorporating Monod-type pyrite oxidation kinetics and a shrinking-core formulation. The model simulates the generation and migration of ferrous (Fe2⁺), sulfate (SO₄2⁻) and ferric (Fe3⁺) ions, under varying hydrogeological conditions. Simulations are conducted over a 10-year period for three representative soil textures (clay, loam, and sand), porosity values (θ = 0.2, 0.4, and 0.6), and water content scenarios (wc = 0.1, 0.5, and 0.9). Model predictions are validated against published benchmarks and field-scale observations. The results demonstrate strong texture-dependent behavior. Clay restricts oxygen ingress, resulting in reduced oxidation rates and enhanced retention of dissolved species, whereas loam exhibits relatively uniform transport, and sand facilitates rapid advective migration of oxidation products. Ion concentrations decrease from approximately 200 to 40 mol m⁻3 in clay, 300 to 95 mol m⁻3 in loam, and 1 to 0.2 mol m⁻3 in sand. Elevated moisture conditions (wc = 0.9) significantly enhance the ion mobility, increasing the contamination potential. Sensitivity analysis indicates that sulfate exhibits the highest sensitivity in clay under low moisture conditions (wc = 0.2), with SI values up to ~ 4.3 × 104, while ferrous ions show maximum sensitivity in loam under similar conditions (102–103). Overall, clay-rich layers provide effective attenuation of pyrite oxidation products, highlighting their suitability for AMD mitigation.