Effects of Acid Mine Drainage

Topics: PH, Water, Iron Pages: 7 (1170 words) Published: March 23, 2014
Abandoned Acid Mine Drainage at Shoup’s Run
Introduction
Acid mine drainage (AMD) is an industrial waste which is the result of the extraction process of the mineral coal from the ground. It causes widespread pollution in the streams above and below the coals fields. AMD is caused when water flows through sulfur-bearing materials forming acidic solutions. It is formed when pyrite (FeS2), an iron sulfide, is exposed and then reacts with air (O2) and water (H2O) to form sulfuric acid.

2FeS2 (s) + 7O2 (g) + 2H2O (l)  2Fe2+ (aq) + 4SO4-2 (aq) + 4H+ (aq) Ferrous Iron also reacts with air causing the creation of Ferric Iron which then reacts with water forming Ferric Hydroxide and more acidity.

4Fe2+ (aq) + O2 (g) + 4H+ (aq)  4Fe3+ (aq) + 2H2O (l)
4Fe3+ (aq) + 12H2O (l)  4Fe(OH)3 (s) + 12H+ (aq)
The low pH levels are due to the mass amounts of heavy metals polluting the water. The heavy metals found in AMD sites are iron, aluminum, and manganese. The excess amounts of heavy meals harm the streams’ ecosystems such as killing off species of plants, fish, and other organisms living within the water.

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To treat AMD there are two categories that the treatments can fall into. The treatments can either be passive or active. Passive treatment sites require little upkeep or power source. Passive treatments treat the AMD runoff by running the water through beds of limestone. The acid latches onto the rocks and does not continue down through the ecosystem. Active systems use dangerous chemicals to try to breakdown the AMD runoff. Both treatment styles work to neutralize the acids and remove the heavy metals.

Method
On November 13, 2013 we travelled to Saxton, PA where we observed Shoup’s Run along with Miller’s Run stream which have been noted for having poor pH due to AMD (Figure 1). Miller’s Run had a passive treatment system working so it is on better shape than Shoup’s Run. The passive treatment for the water in Miller’s run is working to drop the acid and heavy metal levels (Figure 2). First, it neutralizes the pH and alkalinity, which is the ability to buffer changes in pH and withstand the changes. When the water flows over the limestone and reacts with it, the rock is dissolved by the acid in the water and neutralizes it. The next part of the passive treatment is draining the water into settling ponds. The metals settle onto the bottom of the pond and do not continue down the stream because the flow of the water is slowed down. The metals settle and turn the rocks a rusted red from the iron and a blue from the aluminum.

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Figure 1: Map of streams of where water was observed and tested.

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Figure 2: Diagram of Shoup’s Run passive water treatment plan

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Field Work
Measurements were taken at Shoup’s Run to calculate the pH of the inlet and outlet, along with the alkalinity of each pond and the output flow of the wetland. The pH was taken with a handheld Oakton pH meter. The pH was taken at the inlet of the limestone bed, the wetland, the settling pond, and the outlet of the settling pond. The alkalinity was then taken using a HACH field titration kit. The alkalinity was taken at the same locations as the pH tests except for the wetland outlet. Along with the alkalinity, the flow in the wetland was measured, how many gallons per minute. This was done but timing how quickly a three gallon bucket was filled. After three trials the average was taken. All data was recorded in tables and then observed (Tables 1, 2, and 3). Results

Table 1: (see below) Data collected on pH, alkalinity, and flow.

Minersville Passive Treatment System

Flow

Aerobic wetland

pH

3.2

6.7

0 ppm

89 ppm

Fe: 2 mg/L Al: 19.1 mg/L Mn: 2.7 mg/L

Fe: 1 mg/L Al: 0.2 mg/L

pH

6.5

6.4

Alkalinity
Metals

Outlet Water quality

Modified limestone bed

Alkalinity
Metals

System Type
Inlet water quality

Minersville Wetland

107 ppm

---

Fe: 0.3 mg/L Al: 0.9 mg/L...

References: Hoffert, Raymund J. (1947) Acid Mine Drainage. Industrial & Engineering Chemistry, 39(5),
642-646.
Seftas, Celina, ed. AMD-Abandoned Mine Drainage. Saxton, PA. 11/13/13
Senko, J.M., Gengxin, Z., McDonough, J. T., Bruns, M., & Burgos, W. D. (2009). Metal
Reduction at Low pH by a Desulfosporosinus Species: Implications for the Biological
Treatment of Acidic Mine Drainage. Geomicrobiology Journal, 26(2), 71-82.
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