Geochemical Processes in Iron-Rich Mine Drainages: Enhancing Passive Treatment Systems through Colloid Stability and CO2 Reduction

This study presents a potential advancement for passive mine water treatment, transforming it from a purely remedial activity into a proactive carbon capture technology, by addressing the limitations of a conventional system in acid mine drainage (AMD) system. By introducing crushed basalt into an AMD system at the Shojin River, Japan, we utilize the acidic nature of the system to accelerate enhanced rock weathering (ERW). ERW is a carbon reduction process that utilizes crushed ultramafic rock powder to capture atmospheric carbon dioxide (CO2). This approach slightly raised the pH, thereby increasing the Fe colloid precipitation and stability for improved As sequestration, while the same weathering process simultaneously mineralizes atmospheric CO2 into stable bicarbonate alkalinity. In contrast, stable ferrihydrite colloids were observed at our circumneutral control site (Ainai Mine drainage), thereby emphasizing the pH-dependency of remediation in passive treatment systems. While most ERW research has focused on agricultural soils, this study explores a new frontier — evaluating ERW efficacy in mine-impacted environments. These settings provide naturally acidic and metal-rich conditions that can substantially accelerate silicate dissolution and CO2 drawdown. The insights gained here establish a foundation for expanding ERW applications to diverse geochemical fields such as mine tailings, industrial effluents, and water treatment systems.