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Bodennec is an old exploratory Pb-Zn mine in Britany which produces a low-flow, near-neutral mine drainage containing 8 mg/l of dissolved ferric iron. The current water treatment installations consist of three settling ponds, with the treated water being discharged to the Rudalveget River. However, the average concentration of total iron in the outlet is about 4-5 mg/l compared with the 3 mg/l required by the French authorities. A pilot plant has been constructed on site consisting of a small pump controlled by a flow meter which injects a small volume of concentrated sodium hydroxide solution into the drainage. Electricity is supplied to the system using a solar panel connected to a battery for night-time operation. Sodium hydroxide consumption is very low as, due to the neutral pH, there is no requirement to reduce the solubility of iron by significantly increasing the pH. At pH 6, a small increase in pH is sufficient to greatly increase kinetic ferrous iron oxidation. Chemically induced iron (oxy)hydroxide precipitates have a far better settling velocity than biogenic precipitates, and precipitation and settling are therefore far more efficient. Injecting a small amount of concentrated sodium hydroxide solution allows the use of a small 10 m3 sodium hydroxide tank which is refilled only once a year. The low maintenance and low chemical consumption make the system an economical solution for near-neutral mine drainage at sites with limited area available for a passive treatment plant. The final plant is expected to be constructed in 2016., Bodennec is an old exploratory Pb-Zn mine in Britany which produces a low-flow, near-neutral mine drainage containing 8 mg/l of dissolved ferric iron. The current water treatment installations consist of three settling ponds, with the treated water being discharged to the Rudalveget River. However, the average concentration of total iron in the outlet is about 4-5 mg/l compared with the 3 mg/l required by the French authorities. A pilot plant has been constructed on site consisting of a small pump controlled by a flow meter which injects a small volume of concentrated sodium hydroxide solution into the drainage. Electricity is supplied to the system using a solar panel connected to a battery for night-time operation. Sodium hydroxide consumption is very low as, due to the neutral pH, there is no requirement to reduce the solubility of iron by significantly increasing the pH. At pH 6, a small increase in pH is sufficient to greatly increase kinetic ferrous iron oxidation. Chemically induced iron (oxy)hydroxide precipitates have a far better settling velocity than biogenic precipitates, and precipitation and settling are therefore far more efficient. Injecting a small amount of concentrated sodium hydroxide solution allows the use of a small 10 m3 sodium hydroxide tank which is refilled only once a year. The low maintenance and low chemical consumption make the system an economical solution for near-neutral mine drainage at sites with limited area available for a passive treatment plant. The final plant is expected to be constructed in 2016.

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 was stable. A final water treatment plant based on this system was built in 2017. (Authors.), 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 was stable. A final water treatment plant based on this system was built in 2017. (Authors.)