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Iron sulfide oxidation as influenced by calcium carbonate application
1Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX 77843, USA. l-hossner@tamu.edu
Journal of Environmental Quality
|June 18, 2003
Summary
Liming overburden materials with calcium carbonate (CaCO3) controls pyrite (FeS2) oxidation by managing pH. However, CaCO3 dissolves faster than FeS2 oxidizes, potentially leading to acid minesoil formation even with high lime rates.
Area of Science:
- Environmental Science
- Geochemistry
- Soil Science
Background:
- Overburden materials from mining often contain pyrite (FeS2), a precursor to acid mine drainage.
- Low acid neutralization potential in overburden necessitates effective management strategies to prevent environmental contamination.
- Understanding the kinetics of FeS2 oxidation and the efficacy of liming is crucial for mine site remediation.
Purpose of the Study:
- To investigate the effect of calcium carbonate (CaCO3) application rates on the oxidation of pyrite (FeS2) in overburden materials.
- To determine the kinetics of FeS2 oxidation under varying pH conditions influenced by liming.
- To assess the long-term stability of CaCO3 and its potential to prevent acid mine drainage.
Main Methods:
- Two overburden materials with differing FeS2 content were treated with CaCO3 at rates from 0% to 125% of the acid-base account deficit.
- Limed materials were inoculated with Thiobacillus ferrooxidans and subjected to weekly leaching with deionized water over 378 days.
- Residual FeS2 and CaCO3 were quantified, and oxidation kinetics were analyzed based on pH-dependent reaction orders.
Main Results:
- FeS2 oxidation followed zero-order kinetics at pH > 4 and first-order kinetics at pH < 4.
- Zero-order oxidation rates varied from 0.01 to 0.46 µmol g⁻¹ d⁻¹ for 1.9% FeS2 and 0.01 to 0.22 µmol g⁻¹ d⁻¹ for 4.1% FeS2 overburden.
- CaCO3 dissolution was faster than FeS2 oxidation at pH > 4, and liming beyond 50% of the acid-base account deficit did not significantly alter the zero-order oxidation rate.
Conclusions:
- CaCO3 application effectively controls FeS2 oxidation by maintaining a higher system pH.
- The rapid dissolution of CaCO3 suggests it may be leached from the system before complete FeS2 oxidation, posing a risk of future acid mine soil formation.
- Optimized liming strategies are necessary to ensure long-term prevention of acid mine drainage from overburden materials.