Water, acid drainage

These acidic waters are toxic to plant and animal life, including fish and aquatic insects. Streams affected by acid drainage may be rendered nearly lifeless, their stream beds coated with unsightly yellow and red precipitates of oxy-hydroxide minerals. In some cases, the heavy metals in acid drainage threaten water supplies and irrigation projects. 

In this chapter we construct geochemical models to consider how the availability of oxygen and the buffering of host rocks affect the pH and composition of acid drainage. We then look at processes that can attenuate the dissolved metal content of drainage waters. 

Acid drainage results from the reaction of sulfide minerals with oxygen in the presence of water. As we show in this section, water in the absence of a supply of oxygen gas becomes saturated with respect to a sulfide mineral after only a small amount of the mineral has dissolved. The dissolution reaction in this case (when oxygen gas is not available) causes little change in the water s pH or composition. In a separate effect, it is likely that atmospheric oxygen further promotes acid drainage because of its role in the metabolism of bacteria that catalyze both the dissolution of sulfide minerals and the oxidation of dissolved iron (Nordstrom, 1982). 

Fig. 31.5. Minerals formed during reaction at 25 °C of a hypothetical acid drainage water with calcite (top), and fractions of the amounts of arsenite, arsenate, copper, lead, and zinc present initially in solution that sorb onto ferric hydroxide over the course of the reaction path (bottom). Bottom figure is plotted against pH, which increases as the water reacts with calcite.

Contaminated media at these sites result primarily from sedimentation in surface waters, acid mine drainage, and household chemical waste. As with other contaminated sites throughout the United States, the predominant contaminated media are soil and groundwater. 

Dave, N. K. and A. J. Vivyurka. 1994. Water cover on acid generating uranium tailings—laboratory and field studies. In Proceedings of International Land Reclamation and Mine Drainage Conference and Third International Conference on the Abatement of Acidic Drainage. Pittsburgh, PA, April 24-29, 1994, pp. 1,297. 

Ritcey, G. M. 1991. Deep water disposal of pyritic tailings. In Proceedings of the Second International Conference on the Batement of Acidic Drainage. Sept. 16-18. Montreal, Quebec, pp. 421-442. 

The storage and release of acidity by these mechanisms can cause considerable temporal variability in water quality and can cause acid drainage to continue even after pyrite oxidation has ceased. 

Kleinmann R. P. L., Edenbom H. M., and Hedin R. S. (1991) Biological treatment of mine water—an overview. In 2nd Int. Conf. Abatement of Acidic Drainage. MEND Secretariat, Tome, vol. 1, pp. 27-42. 

Ten alternatives for correcting or preventing water pollution from acid drainage produced by piles of coal-cleaning wastes are compared. Options 1, 2 and 10 involve pretreatments of the waste before it is disposed to the pile. Options 3 to 6 refer to treatments undertaken as the pile is being formed. Options 7 to 9 refer to chemical treatment of the pile effluent. All costs are based on 1985 dollars. 

In 1996, the open pit was decommissioned by flooding it with seawater from the adjacent Inlet. This created a 528-acre (214-hectare) lake, which stabilized the pit walls and provided an effective receptacle for the moderate amount of acid drainage from the waste rock. The acid drainage is diluted by the large volume of the lake, and heavy metals are precipitated to the bottom by the action of sulfate-reducing bacteria. Precipitation and surface drainage have formed a cap of fresh to brackish water on the surface of the lake. 

Acid areas which collect corrosive process wastes are usually provided with an acid-resistant, curbed paving to confine and collect any acid drainage or spillage within these curbed areas. Curbed and paved areas should be provided in locations where pump groups, storage and handling areas are subject to spillage and wash-down water. 

Wash water collected in these surface-drainage areas should be collected in the acid sewer. Where possible, however, storm-water surface drainage should not be run into the acid sewers, if avoidable. 

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