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Acid Mine Drainage Problem - Part 2

Western Pennsylvania was once a great coal mining region. The remnants of this industry are still with us in the form of abandoned mines that underlay a great portion of the land on which we live, and in the drainage of acidic waters from the mines into our streams and rivers. Studies have shown a drastic reduction in fish counts when the pH of a stream goes below 5.5.

The main culprit in the formation of acidic mine runoff is pyrite, FeS2. When exposed to air and water, FeS2 forms iron(III) hydroxide, Fe(OH)3, which precipitates out of solution, and sulfuric acid, H2SO4. The solubility of Fe(OH)3 is both temperature and pH dependent.

Problem 2 considers the effect of temperature changes. We'll consider the same mine that puts out 10 liters of effluent every hour, with the river flowing at a rate of 10,000 liters/hour. The stockroom contains a sample of mine effluent - a solution of H2SO4 that is saturated with Fe(OH)3 with a pH of 1.00.

Assume that the river is still pure water, but consider the changes in solubility of Fe(OH)3 due to temperature changes throughout the year:

  • Perform experiments to determine if the amount of Fe(OH)3 that precipitates outside the mine is greater in the winter or in the summer.
  • Based on your measurements from part (a), what can you say about the thermodynamic properties of the following reaction: Fe(OH)3(s) ⇌ Fe+3(aq) + 3 OH-(aq)

Previous: Part 1 - Dilution Effects | Next: Part 3 - Buffer Effects