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Treatment of acid mine water by wetlands.
Control of acid mine drainage: proceedings of a technology transfer seminar. Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, IC 9027, 1985 Jan; :48-52
Wetlands are a potential natural treatment system for small flows of acid mine water. Previous studies of mine water flowing through bogs dominated by Sphagnum moss indicate that such a wetland removes the iron and reduces acidity, without harm to the moss. A group from Wright State University studied a site in the Powelson Wildlife area in Ohio where Sphagnum recurvum was found growing in pH 2.5 water. Iron, magnesium, sulfate, calcium, and manganese all decreased, while pH increased from 2.5 to 4.6 as the water flowed through the bog. A natural outcrop of limestone located at the downstream end provided sufficient neutralization to raise the effluent pH to between 6 and 7. A similar study was conducted by a West Virginia University group at Tub Run Bog in northern West Virginia. They f ound that acid drainage flowing into the wetland area rapidly improved in quality. In 20 to 50 m, pH rose from 3.05-3.55 to 5. 45-6.05, while only 10 to 20 m of flow through the bog was needed to reduce sulfate concentrations from 210-275 mg/L t o 5-15 mg/Land iron from 26-73 mg/L to l ess than 2 mg/L. Overall, they found t hat the water quality of the bog eff luent was equal or superior to that of nearby streams unaffected by mine drainage. In laboratory experiments it has been shown that 1 kg (wet weight) of S. recurvum can remove up to 92 pct of the influent 50 mg/L of iron in 16.S L of pH 3.8 synthetic mine water solution by cation exchange. In a natural wetland, bacterial oxidation and sulfate reduction in the organic-rich bottom waters add to the iron removal capability. It has also been demonstrated in the laboratory that S. recurvum can tolerate acid mine drainage with iron concentrations as high as 500 mg/L for 4 weeks. Although the moss was stressed, iron removal by cation exchange continued. In the field, higher evapotranspiration rates and less ideal conditions result in a long-term threshold of less than 150 mg/L. Such field observations and laboratory studies suggest that a Sphagnum-dominated biological treatment system is feasible. Since discharge from such a biological treatment system will not meet Federal and State pH limitations (pH 6-9) for mine water discharges, it was decided to incorporate a passive limestone neutralization step down-gradient of the moss to raise the pH to at least 6.0. Normally, limestone in mine water would be rendered useless by Fe(OH)3 precipitation, but efficient iron removal by the wetland would eliminate this problem.
Acid mine drainage; Mining; Mining industry; Waste treatment; Waste abatement
IH; Conference/Symposia Proceedings
Control of acid mine drainage: proceedings of a technology transfer seminar
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division