Advances in passive treatment of coal mine drainage 1998-2009

Abstract

This report updates the review of passive treatment prepared by the Acid Drainage Technology Initiative (Skousen et al., 1998). Important advances since that report include: 1.Measured and calculated acidities are net acidities that are robust measures of this parameter. 2.Removal rates of Fe at pH>5 can be enhanced by CO2 degassing, by catalysis by solid Fe phases and by specialized aerators; at pH<5, low pH Fe oxidation by bacteria can be helpful in treating high-Fe acidic discharges. 3.For low-Fe-Al AMD, oxic limestone drains can be effective for treatment, but effectiveness declines over years owing to accumulation of precipitate. 4.For high Fe or Al AMD, limestone beds with timed flushing devices can remove large amounts of metals, though eventual cleaning of the limestone may be needed. 5.Addition of limestone sand or lime to streams can be a cost-effective method of restoring watersheds 6.Vertical flow ponds (VFP's, SAPS) can be sized using a loading factor of 25-35 g of acidity/m2/d. 7.Manual flushing of VFP's removes only a few percent of accumulated Al precipitate, but timed flushing can be much more effective. 8.Common problems of VFP's include inadequate size, accumulation of Fe precipitate on compost, deterioration owing to Al coatings, and construction defects. 9.Sulfate reduction in passive systems involves a complex community of microbes, with long-term rates dependent on cellulose degrading microbes. Mixtures of fresh organic matter with high-cellulose material appear to provide good performance in lab tests, but more data on longer-term behavior is needed. 10. Sulfate-reducing bioreactors process Al better than older VFP's. 11. Steel slag and chitin hold promise for effective treatment of AMD. 12. A relation for sizing of limestone beds for Mn removal has been developed. 13. Fe precipitate from sludge is being successfully sold for pigment production, and Mn-rich concentrate has been recovered from limestone beds. 14. A revised flow chart for selection of treatment method has been prepared, and the AMDTreat computer program allows easy costing of passive treatment. Copyright © (2010) by the American Society of Mining & Reclamation.