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<p>Mineral replacement reactions influence the long-term fate of arsenic in natural and contaminated environments. This study explores the transformation of anglesite (PbSO₄) in contact with arsenate-bearing solutions, focusing on how pH, ion concentrations, and temperature affect replacement mechanisms, products and arsenate sequestration. Synthetic or natural anglesite crystals were reacted with arsenate solutions (5 or 50&#xa0;mg As/L) in the presence of chloride ions (Cl⁻), across a pH range of 2–8 for up to 3 months. Cl⁻ promoted the formation of mimetite (Pb₅(AsO₄)₃Cl), particularly at circumneutral pH. The reaction pathway was pH-dependent: schultenite (PbHAsO₄) formed at pH 2, while mimetite precipitated at pH 4–8. At low arsenate concentrations, mimetite nucleated locally and gradually formed patchy crusts; at higher concentrations, arsenate phases crystallized both heterogeneously and homogeneously, producing extensive encrustations. SEM imaging showed etch pits from anglesite dissolution and mimetite crusts (2–100&#xa0;μm) whose thickness varied with crystal morphology. A reaction front gap suggested diffusion-limited growth. Under acidic conditions, schultenite grew inward with a sharp boundary, indicating partial replacement. Temperature and pressure did not alter the replacement mechanism but influenced growth rates, with larger crystals observed under hydrothermal conditions. Arsenic sequestration efficiencies ranged from 23.0% to 84.4%, depending on the experimental conditions. These findings reveal how fluid composition and environmental parameters govern arsenate immobilization by secondary lead minerals, providing mechanistic insight into mineral-fluid interactions relevant for the stability of arsenate in natural systems.</p>

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Coupled dissolution and precipitation at the anglesite - arsenate solution interface

  • 期刊论文

  • 发表日期：

    2026年1月19日

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  • Ewa Stępień,
  • Maciej Manecki

摘要

Mineral replacement reactions influence the long-term fate of arsenic in natural and contaminated environments. This study explores the transformation of anglesite (PbSO₄) in contact with arsenate-bearing solutions, focusing on how pH, ion concentrations, and temperature affect replacement mechanisms, products and arsenate sequestration. Synthetic or natural anglesite crystals were reacted with arsenate solutions (5 or 50 mg As/L) in the presence of chloride ions (Cl⁻), across a pH range of 2–8 for up to 3 months. Cl⁻ promoted the formation of mimetite (Pb₅(AsO₄)₃Cl), particularly at circumneutral pH. The reaction pathway was pH-dependent: schultenite (PbHAsO₄) formed at pH 2, while mimetite precipitated at pH 4–8. At low arsenate concentrations, mimetite nucleated locally and gradually formed patchy crusts; at higher concentrations, arsenate phases crystallized both heterogeneously and homogeneously, producing extensive encrustations. SEM imaging showed etch pits from anglesite dissolution and mimetite crusts (2–100 μm) whose thickness varied with crystal morphology. A reaction front gap suggested diffusion-limited growth. Under acidic conditions, schultenite grew inward with a sharp boundary, indicating partial replacement. Temperature and pressure did not alter the replacement mechanism but influenced growth rates, with larger crystals observed under hydrothermal conditions. Arsenic sequestration efficiencies ranged from 23.0% to 84.4%, depending on the experimental conditions. These findings reveal how fluid composition and environmental parameters govern arsenate immobilization by secondary lead minerals, providing mechanistic insight into mineral-fluid interactions relevant for the stability of arsenate in natural systems.