Acid mine drainage lakes

Self-Test L.3B Many abandoned mines have exposed nearby communities to the problem of acid mine drainage. Certain minerals, such as pyrite (FeS,), decompose when exposed to air, forming solutions of sulfuric acid. The acidic mine water then drains into lakes and creeks, killing fish and other animals. At a mine in Colorado, a 16.45-mL sample of mine water was completely neutralized with 25.00 mL of 0.255 M KOH(aq). What is the molar concentration of H2S04 in the water ... 

KEYWORDS ground water, tailings, sulfate, pit lake, acid mine drainage... 

A number of methods have been devised to reduce acid mine drainage (AMD) and, therefore, the harmful environmental effects it may cause. One of the simplest approaches (at least in theory) is to divert the flow of water that would normally pass through or over a mine. The principle is that in the absence of water much less sulfuric acid forms and what little is produced is not likely to he carried into lakes, rivers, and other bodies of water. 

Another method of preventing acid mine drainage is to construct barriers around the mine itself. The most important single source of AMD are abandoned coal mines. In some cases, the entrances to those mines can be sealed or barriers can be constructed to prevent the outflow of acidic water from the mines into lakes and streams. Finally, abandoned mines can sometimes simply be filled with sand, gravel, fly ash, or other materials, effectively immobilizing any potential acid-producing substances remaining within them. 

Geller, W., Klapper, H. Salomons, W. (eds) 1998. Acidic Mining Lakes. Acid Mine Drainage, Limnology and Reclamation. Springer, Heidelberg, 435 pp. 

Figure 8.10 Sorption constants for Cu, Zn and Cd on natural oxyhydroxides as a function of pH obtained from field measurements. The points were obtained in the Carnon River, UK (V, Johnson, 1986) in 40 sites in Canadian lakes representing a variety of geological settings, lake pH values, and trace element concentrations in the sediments and in the overlying waters (O, Tessier, 1992) and in streams affected by acid mine drainage (A, Chapman et at., 1983). Log= Fe-M / Fe-ox [Mz+] (adapted from Tessier, 1992).

Hollenberg, J. L. Stephens, E. R. Pitts, J. N., Jr. Demonstrating the Chemistry of Air Pollution, J. Chem. Educ. 1987, 64, 893-894. Horan, J. H. Wildeman, T. R. Ernst, R. Acid Mine Drainage Laboratory Experiments, 214th Am. Chem. Soc. Nat. Meet., Chem. Ed. Division Paper 005. Las Vegas, NV, Sept. 7-11, 1997. Howe, A. C. Cizmas, L. Bereman, R. Eutrophication of Lake Wingra A Chemistry-Based Environmental Science Module, J. Chem. Educ. 1999, 76, 924-926. 

Figure 12.25 (a) Plot of log 1AP versus pH for 64 samples from a drainage basin affected by acid mine waters from the Leviathan mine, Cali-fornia-Nevada. Points shown as open squares have pH <4.6, plus symbols are those with pH >4.9. The solid lines are theoretical solubilities of amorphous AI(0H)3 and microcrystalline gibbsite. (b) Plot similar to (a) for acid mine drainage from Appalachia (solid circles) and Adirondack lake waters affected by acid precipitation (open circles). From Science 232 54-56, D. K. Nordstrom and J. W. Ball, The geochemical behavior of aluminum in acidified surface waters. Copyright 1986 by Science-AAAS. Used by permission. 

According to Davis and Ashenberg (1989), the results of the simulations provide some useful information for the evaluation of the feasibility of using alkaline tailings fluid to neutralize Berkeley Pit water as a remedial action. The authors calculated that it needs three volumes of alkaline fluids to neutralize the pit lake water to pH of 5.0 with the Case 3 scenario. That would result in a water level 20 m above the contact between the alluvial aquifer and the subjacent bedrock, assuming all inflows into the pit except alluvial and bedrock groundwater contributions can be controlled. The authors concluded that this remedial alternative is a tractable solution to the acid mine drainage problems at the Berkeley Pit. 

A study of the chemistry of a small California stream that receives acid mine water (27) showed that above pH 4.9 the dissolved aluminum concentration appeared to be controlled by aluminum hydroxide solubility equilibria, but below pH 4.6 aluminum hydroxy-sulfates apparently predominated. This study also cited data for acid mine drainage in the Appalachian region and lakes affected by acid precipitation that showed a similar pattern of aluminum behavior. 

Clark Fork River, an important tributary of the Columbia River. Acid mine drainage seriously degrades water quality and threatens the existence of animal and plant populations. The average pH is 2.5, an acidity level toxic to most life forms, both macrobial and microbial. Many cations reach levels well above drinking water standards set by the EPA. A sample of Berkeley Pit lake water analyzed by Inductively Coupled Plasma (ICP) has high levels of Fe+2/Fe+3, Al+, Cu+2, and many other cations. It is also very rich in sulfates, the predominant anionic species present (8500 ppm). Some typical cation levels in Pit water (24) and EPA drinking water standards for these same cations are shown below in Table 1 [48],... 

The most common source of pollutant acid in water is acid mine drainage. The sulfuric acid in such drainage arises from the microbial oxidation of pyrite or other sulfide minerals as described in Section 3.5. The values of pH encountered in acid-polluted water may fall below 3, a condition deadly to most forms of aquatic life except the culprit bacteria mediating the pyrite and iron(II) oxidation, which thrive under very low pH conditions. Industrial wastes frequently have the potential to contribute strong acid to water. Sulfuric acid produced by the air oxidation of pollutant sulfur dioxide (see Chapter 7) enters natural waters as acidic rainfall. In cases where the water does not have contact with a basic mineral, such as limestone, the water pH may become dangerously low. This condition occurs in some Canadian and Scandinavian lakes, for example. 

As discussed in Section 2.1.2, all natural waters contain dissolved inorganic chemicals, many present as ions such as sodimn (Na ), potassium (K" "), magnesium (Mgp ), calcium (Ca ), ammonimn (NIL ), sulfate (S04 ), chloride (Cl ), and nitrate (NOs ). Even pure water, containing no dissolved substances, ionizes to a certain extent to form hydrogen ions (H" ") and hydroxide ions (OH ), as discussed in Section 1.6.4. The pH of most natural waters ranges from about 4 to 9 extreme environments, such as streams receiving acid mine drainage, may have a pH below 2, while some alkaline lakes may have a pH above 10. 

Common rock-forming mineral, although most Al-bearing silicates quite insoluble. Potentially soluble Al-hydroxides, hydroxysulfates form in lateric ore deposits, tropical soils, and precipitate in streams affected by acid-rock drainage. Al-rich soluble salts can occur in evaporative lake sediments, and in mine wastes. Potentially reactive forms in cement, concrete, smelter emissions, coal fly ash. 

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