Mine water formation, acid

Figure 1. Mechanism of acid mine water formation...

Measures taken to prevent the release of toxic substances from the geosphere can aid in increasing the quality and productivity of the biosphere. An important example is the prevention of acid mine water formation (see Chapter 3, Section 3.5.1). 

Air or biological oxidation of pyrite leads to sulfate formation and dilute sulfuric acid in the mine drainage. This pollutes streams and the water supphes into which the mine water is drained. Means of controlling this problem are under study. 

Ohio State University Research Foundation. 1971. Acid mine drainage formation and abatement. Water Pollution Control Research Series DAST-42-14210 FPR-04/71. USEPA, Washington, DC, 83 pp. 

Anionic detergents and o-phosphates in water 11. Acid mine (or acid rock) drainage 15. Removal of nitric oxide by complex formation... 

As mentioned earlier, large amounts of copiapite have been found accumulating on ore surfaces in areas protected for direct rainfall. The mechanism of its formation is not at all clear but from field observations it appears that acid mine water is being drawn by capillary forces to an exposed surface where it quickly evaporates to melanterite and/or copiapite. Coquimbite is intimately associated with copiapite and these two minerals appear to be very stable as long as they are protected from rainfall or running water. No thermodynamic data... 

Plate III. Schwertmarmite formation in an acid mine water stream in Ohio (Courtesy J.M. Bigham, Ohio State University). 

Pyrite (FeS2> is by far the most abundant sulfide mineral, occurring in most types of geologic formations. Its less common polymorph, marcasite, usually forms in near-surface, low-temperature environments. At 25°C pyrite is more stable than marcasite by about -0.4 kcal/mol. The oxidative breakdown of these minerals as the result of exposure to aerobic conditions due to mining is the chief cause of acid mine waters. 

If a Fe(IlI)-rich acid mine water with minor Fe(II) (pH = 3) flows into a confined formation comprising minerals such as calcite and feldspars, but without reductanls, its Eh will drop as its pH ri.ses. Why ... 

Allen, R.R. and Parry, V.F. 1954. Report of Investigations No. 5034. United States Bureau of Mines, Washington, DC. Ashmead, D. 1955. The influence of bacteria in the formation of acid mine waters. Colliery Guardian, 190 694-698. ASTM. 2011. Standard Test Method for Determining the Relative Degree of Oxidation in Bituminous Coal by Alkali Extraction (ASTM D5263). Annual Book of Standards, American Society for Testing and Materials, West Conshohocken, PA. 

Allen, J. M., S. Lucas, and S. K. Allen, Formation of hydroxyl radical in illuminated surface waters contaminated with acidic mine drainage , Environ. Tox. Chem., 15,107-113 (1996). 

In very acidic solutions (pH < 2.4-3) with ionic strengths below 0.1 M and at 25 °C and 1 bar pressure, scorodite has a pK of about 25.83 0.07. The pK of amorphous Fe(III) arsenate is approximately 23.0 0.3 under the same conditions (Langmuir, Mahoney and Rowson, 2006). At higher pH values, scorodite dissolves incongruently, which means that at least one of its dissolution products precipitates as a solid. The incongruent dissolution of scorodite in water leads to the formation of Fe(III) (oxy)(hydr)oxide precipitates that is, Le(III) (hydrous) oxides, (hydrous) hydroxides and (hydrous) oxyhydroxides (Chapter 3). During the formation and precipitation of the iron(III) (oxy)(hydr)oxides, As(V) probably coprecipitates with them (Chapter 3 also see Section 2.7.6.3). The dissolution rate of scorodite at 22 °C in pH 2-6 water is slow, around 10—9 —10—10 mol m-2 s-1, which explains its presence in many mining wastes (Harvey et al., 2006). 

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