Passive Treatment of Arsenic-Contaminated Dewatering Water Using a Natural Laterite Permeable Reactive Barrier (PRB): Performance Evaluation and Implications for Sustainable Mine Water Management
Arsenic contamination of dewatering water is a major environmental challenge associated with gold mining. Permeable Reactive Barriers (PRBs) offer a sustainable and low-cost passive treatment alternative to conventional technologies. This study evaluated the performance of a natural laterite-based PRB installed at the Sabodala-Massawa gold mine (Senegal) for treating arsenic-contaminated dewatering water. Monitoring was conducted from September 2023 to June 2026 using 49 paired measurements of arsenic concentrations upstream and downstream of the PRB. Influent arsenic concentrations ranged from 46 to 935 μg？L？1, while effluent concentrations varied between 0 and 386.5 μg？L？1. The PRB achieved a mean arsenic removal efficiency of 82.2 ± 22.2%, with a median of 88.9%, demonstrating consistently high treatment performance despite moderate temporal variability. Most treated water samples complied with the Senegalese discharge standard (300 μg？L？1) and frequently met the International Finance Corporation guideline value (100 μg？L？1). A moderate positive correlation was observed between influent and effluent arsenic concentrations (r = 0.457), while treatment efficiency improved during the initial months before showing a slight decline after September 2025, suggesting gradual ageing of the reactive material. Sediment analyses further revealed substantial reductions in arsenic (56.6%) and antimony (78.2%) concentrations between the upstream and downstream sections of the PRB, confirming efficient metalloid retention. The treatment performance is mainly attributed to physical filtration, adsorption onto iron oxyhydroxides contained in the lateritic material, and co-precipitation processes. Overall, the results demonstrate that natural laterite is an effective, sustainable, and cost-efficient reactive medium for passive treatment of arsenic-contaminated mine water under tropical conditions. Long-term monitoring is recommended to optimize PRB performance and support the wider application of this technology in mining environments affected by arsenic contamination.
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