Acid mine water

A second important factor is the particle size of the FeS2. Caruccio et al. (1976) concluded that AMD production was a serious problem when exposed pyrite grains were about 0.25 fxm in diameter in framboidal pyrite. This corresponds to a surface area of 4.8 m /g. For crystal sizes in excess of 5 to 10 m (5 fxm s 0.24 m /g), AMD production was greatly diminished, and became unlikely when crystal sizes exceeded 400 fiva. Particle sizes were smallest in marine coals and became larger in lacustrine coals (Caruccio and Perm 1974). A third factor determining the risk of AMD is the proximity of carbonate rocks that can neutralize AMD acidity. 

Usually base and precious metal sulfide deposits also have important amounts of pyrite. The pyrite in hydrothermal ore deposits is most often coarse grained and relatively unreactive. Mining and milling the rock to fine particle sizes for the purpose of metal extraction, vastly increases pyrite surface area and exposes the pyrite in waste-tailings piles to oxidation and weathering. Serious AMD releases can result. 

Of basic importance when determining risk is the absolute and relative amounts of the exposed pyrite that occur above or below the water table. Above the water table, oxidation rates are usually catalyzed by bacteria and can be very fast in fine-grained waste-rock piles. Rates in water-saturated spoil materials or below the water table are generally much slower because of the unavailability of free oxygen. 

Overall FeSg and Fe(ll) oxidation reactions. Oxidation of pyrite first occurs at its exposed surface, where pyritic sulfur with a formal charge of (-1) is oxidized to sulfate (+6) and the 

if O2 is the oxidizing agent, 2 moles of H+ are produced by 1 mole of pyrite. In contrast, oxidation by Fe releases 16 moles of protons for each mole of pyrite. Obviously, it is essential to know which reaction dominates in any attempt to predict the acid-generating capacity of a system. 

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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 ... 

Nordstrom, D. K., E. A. Jenne and J. W. Ball, 1979, Redox equilibria of iron in acid mine waters. In E. A. Jenne (ed.), Chemical Modeling in Aqueous Systems, American Chemical Society, Washington DC, pp. 51-79. 

Acidic mine waters emerging naturally from underground mines... 

Espana, J.S., Pamo, E.L., Pastor, E.S., Andres, J.R., Rubi, J.A.M. 2006. The removal of dissolved metals by hydroxysulfate precipitation during oxidation and neutralization of acid mine waters, Iberian Pyrite Belt. Aquatic Geochemistry, 12,269-298. 

In addition to sulphate, selenate (J. M. Bigham, unpubl.) and chromate (S. Regen-spurg unpubl.) can also be incorporated in the tunnels of synthetic schwertmannite. Whether or not two different Se-O distances (based on EXAFS) attributable to surface and tunnel selenate, respectively, exist in the Se-form is still under discussion (Waychunas et al., 1995, 1995 a). The Cr form has the bulk composition Fei6Oi6(OH)i0.23(CrO4)2.gg. In fact, synthetic schwertmannite formed in the sul-phate/arsenate system tolerates arsenate only up to a As/(As-rS) mole ratio of ca. 0.5, and it is likely that most of this arsenate is surface-bound. Above this ratio, a new, very poorly ordered Fe-hydroxy arsenate with two broad XRD peaks at ca. 0.31 and 0.16 nm and BhfS at 4.2K and ca. 1.5 K of 41.6 and 47.3T, respectively, forms (Carlson et al. 2002). From this one may conclude that, whereas the tetrahedral oxyanions with hexavalent central cations (S Se Cr) can be accomodated in the tunnel positions, the pentavalent cations can not, or not as easily. Schwertmannite from acid mine water contained between 6 and 70 g kg As (Carlson et al. 2002). 

Schwertmannite Acid pyrite-weathering waters, acid mine waters Ferrihydrite... 

Bands in unconsolidated Quaternary rocks, ferriferous springs, acid mine water deposits, bog ores, lake waters... 

Noll, W. (1980) Chemie vor unserer Zeit. Antike Pigmente. Chemie in unserer Zeit 2 37—43 Nordstrom, D.K. Alpers, C.N. (1999) Geochemistry of acid mine waters, pp. 133—160. In Plumlee, G.S. Logsdon, M.J. (eds.) The Environmental Geochemistry of Mineral Deposits. Rev. Econ. Geol. V. 6A, Littleton, CO, Soc. Econ. Geol. Inc. 

Plate 13.1 The colour changes of the ochreous precipitates formed from ferrifer- water-pH of 3.7 on the right to 2-line ferrihydrite after neutralization by a ous acid mine water from a lignite mine near Sokolov, Czech Republic, and their pH 8.2-water on the left side (arrows) (Courtesy E. Murad Murad Rojik, X-ray patterns clearly indicate the abrupt transition from schwertmannite at a 2003, with permission). 

Plate 15.VII Acid mine water precipitate, Ohio (courtesy J.M. Bigham). 

Younger, P. L., Jayaweera, A. et al. 2003. Passive treatment of acidic mine waters in subsurface-flow systems exploring RAPS and permeable reactive barriers. Land Contamination and Reclamation, 11, 127-135. 

Ml It means that the activity of H (discussed in Chapter 8) is I036. D. ft Nordstrom. C. N. Alpers, C. J. Ptacek, and D. W. Blowes. Negative pH and Extremely Acidic Mine Waters from Iron Mountain, California, Environ. Sci. Technoi. 2000, 34.254.]... 

Acidic mine water. Iron Mountain, Calif. 

D. W. Blowes, Negative pH and Extremely Acidic Mine Waters from Iron Mountain. California. Environ. Sci. Technol. 2000, 34, 254. 

Figure 1. The effect of temperature on the separation factor (ff) for n-heptane extraction of acid mine water (pH = 2.35)...

Bednar, A.J., Garbarino, J.R., Ranville, J.F. and Wildeman, T.R. (2005) Effects of iron on arsenic speciation and redox chemistry in acid mine water. Journal of Geochemical Exploration, 85(2), 55-62. 

Nordstrom DK, Alpers CN, Placek CJ, Blowes DW (2000) Negative pH and extremely acidic mine waters from Iron Mountain, California. Environ Sci Technol 34 254-258... 

Acid mine waters The addition of EDTA 3 months 28... 

Weathering may also involve oxidation reactions, such as occurs when pyrite, FeS2, is oxidized, a process that can produce sulfuric acid (acid mine water) ... 

Colmer and Hinkle (14) identified T. ferrooxidans in acidic mine waters. Subsequent studies by Silverman et al. (15,16) confirmed that T. ferrooxidans could be utilized to oxidize FeSo in coal in 3 to 4 days, and the rate of oxidative dissolution was a function of the particle size and rank of the coal. Dugan and Apel (4,5) showed that a mixed culture of T. ferrooxidans and T. thiooxidans was most effective at a pH of 2 to 2.5 when the nutrient was enriched with NH " -. They reported 97% removal of pyritic sulfur from a coal sample with 3.1 weight percent sulfur. Norris and Kelly (17) reported that other acidophilic bacteria, Leptospirillum ferrooxidans in mixed cultures with T. thiooxidans, was effective for FeS2 removal. ... 

Factors involved in corrosion are low-pH acid mine water due to oxidation of iron sulfides or bacterial oxidation such as SRB carbon dioxide chloride and sulfate (lOppm CP, 25ppm sulfate 1080ppm CP 300ppm sulfate). Mine air contains SO2 and NO2. 

An acid mine water mixes downstream of a mine with groundwater of the following chemical composition (Table 33). 

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