(General session) Environment / Mineral processing

[2501-08-01] Geochemical modeling-based evaluation of passive treatment methods for acid mine drainage at a legacy mine

○Sereyroith Tum¹, Taiki Katayama¹, Naoyuki Miyata², Takaya Hamai³, Tetsuo Yasutaka¹ (1. National Institute of Advanced Industrial Science and Technology, 2. Akita Prefectural University, 3. Japan Oil, Gas and Metals National Corporation)

司会：晴山　渉（岩手大学）

Keywords:passive treatment , Life cycle assessment , treatment efficiencies , continuous-flow tank reactors

Since 1979, an active treatment system has been in operation to prevent water contamination at Legacy Mine X in northern Japan. Although effective in removing manganese (Mn) and zinc (Zn), this approach is energy-intensive, resulting in substantial CO₂ emissions and high operational costs. To explore more sustainable alternatives, various pilot-scale experiments have been conducted using passive treatment methods; however, the most suitable approach has yet to be determined.This study aims to evaluate two passive treatment configurations through geochemical modeling and life cycle assessment (LCA). The systems modeled include continuous-flow tank reactors filled with either bio-zeolite or limestone serving as substrates for Mn-oxidizing bacteria. Pilot systems operated for over 1 year and treated acid mine drainage with average influent concentrations of ~20 mg/L Mn and ~9.5 mg/L Zn. Geochemical simulations using Phreeqc predicted that both systems could remove up to 99% of Mn and 80% of Zn under field-relevant conditions. While metal removal efficiencies were comparable, LCA results revealed significant differences in environmental performance. The limestone-based system demonstrated the lower overall environmental burden due to reduced material processing requirements, greater media longevity, and lower maintenance frequency compared to bio-zeolite. Additionally, limestone’s widespread availability contributes to its scalability and economic viability in long-term applications. The comparative analysis highlights the trade-offs between treatment efficiency, environmental sustainability, and operational feasibility. These findings support the use of geochemical modeling and LCA as integrated tools for optimizing passive treatment designs, especially for remote or legacy mine sites where low-maintenance, low-carbon solutions are prioritized.