Treatment of Mine Drainage with Significant Topographical Constraints: Case Study of the Bodennec Site (France)

The Bodennec lead and zinc mine site produces circumneutral mine drainage that contains 8 mg/L of dissolved iron, while the water quality objective is 3 mg/L at the outlet. The water treatment installation in use, based on three settling ponds, could not reach this objective, but there was insufficient surface area to build additional ponds or a passive treatment plant. A pilot-scale NaOH system, made of a pump controlled by a flow meter, was built on site to assess the feasibility of a low maintenance, low chemical consumption system to inject a small volume of concentrated NaOH solution into the water. The system was supplied with electricity by a solar panel connected to a battery for night-time functioning. No pH probe was needed since the pH in the drainage is stable. A final water treatment plant based on this system was built in 2017.