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<p>Coal gangue subgrade filler (CGSF) is extensively utilized in road embankments; nevertheless, its utilization is constrained by the possible leaching of heavy metals into groundwater due to compaction and acid rain. This study assesses the combined impacts of compaction and pH on metal release and forecasts long-term migration in the foundation soil beneath a CGSF subgrade. We conducted dynamic column leaching tests at pH levels ranging from 3 to 9, quantified metal speciation through sequential extraction, characterized microstructural alterations using SEM and XRD, and developed a COMSOL model that integrates unsaturated flow and advection–dispersion transport with a time-varying kinetic leaching source term calibrated from the column data. Compaction resulted in 15.8% particle fragmentation and elevated the peak leachate concentrations of Mn, Pb, and Cu at pH 3 by approximately 2.00, 2.62, and 1.43 times, respectively, compared to neutral conditions. Simulations suggest three phases of migration: vertical infiltration, lateral dispersion, and quasi-equilibrium. Over a span of 50&#xa0;years, heavy metals predominantly collect in the foundational soil 5 to 8&#xa0;m beneath the slope toe and extend laterally around 6&#xa0;m. Mn exhibits the maximum mobility due to its predominance in exchangeable and carbonate-bound fractions. SEM and XRD indicate acid driven dissolution of carbonates and silicates and increased porosity, which explains the enhanced release after compaction. This coupled experimental and modeling framework provides quantitative risk zoning to support environmentally safe reuse of CGSF in road engineering.</p>

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Compaction-Acid Rain Synergy Drives Dynamic Release and Long-Term Accumulation of Heavy Metals from Coal Gangue Subgrade Fillers

  • 期刊论文

  • 发表日期：

    2026年2月27日

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  • Xiaotong Li,
  • Junmeng Li,
  • Pucheng Rui,
  • Haoxin Li,
  • Bowen Li,
  • Xiangru Wu,
  • Yanli Huang

摘要

Coal gangue subgrade filler (CGSF) is extensively utilized in road embankments; nevertheless, its utilization is constrained by the possible leaching of heavy metals into groundwater due to compaction and acid rain. This study assesses the combined impacts of compaction and pH on metal release and forecasts long-term migration in the foundation soil beneath a CGSF subgrade. We conducted dynamic column leaching tests at pH levels ranging from 3 to 9, quantified metal speciation through sequential extraction, characterized microstructural alterations using SEM and XRD, and developed a COMSOL model that integrates unsaturated flow and advection–dispersion transport with a time-varying kinetic leaching source term calibrated from the column data. Compaction resulted in 15.8% particle fragmentation and elevated the peak leachate concentrations of Mn, Pb, and Cu at pH 3 by approximately 2.00, 2.62, and 1.43 times, respectively, compared to neutral conditions. Simulations suggest three phases of migration: vertical infiltration, lateral dispersion, and quasi-equilibrium. Over a span of 50 years, heavy metals predominantly collect in the foundational soil 5 to 8 m beneath the slope toe and extend laterally around 6 m. Mn exhibits the maximum mobility due to its predominance in exchangeable and carbonate-bound fractions. SEM and XRD indicate acid driven dissolution of carbonates and silicates and increased porosity, which explains the enhanced release after compaction. This coupled experimental and modeling framework provides quantitative risk zoning to support environmentally safe reuse of CGSF in road engineering.