Acid Mine Drainage Remediation
Acid mine drainage (AMD) is pollution that occurs when water trapped in abandoned coal mines leaks out into the local environment. One of the most abundant metals found in AMD is iron. Iron precipitates out of the system naturally in the form of iron(III) hydroxide, leading to a decrease in fluid pH. Iron oxidizing bacteria can promote this reaction process, assisting in the removal of Fe(II) ions from the AMD. This paper develops a model of an AMD system that includes thin film sheet flow and reactive transport of ions. In addition the model analyzes the precipitation of an iron(III) hydroxide crust as a function of space and time. Several parameters are varied to compare model predictions with field observations. Forcing low concentrations of oxygen in the system slows the rate of iron(III) hydroxide crust growth. Increasing the angle of inclination of the sheet flow while holding the flow rate fixed causes a very small decrease in iron(III) hydroxide crust growth due to faster flow through a thinner fluid film. Decreasing the flow rate of the system while maintaining a fixed angle of inclination to simulate a thinning of the liquid layer produces a slower iron(III) hydroxide crust growth rate. When the angle of inclination is increased with fixed fluid film thickness, iron(III) hydroxide crust growth decreases due to downstream transport of the ions. Oxidation and precipitation reaction rates had the greatest influence on crust growth. An increase in iron oxidizing bacteria can increase the oxidation of Fe(II). Therefore, an increase in the abundance of iron oxidizing bacteria can increase the rate of iron(III) hydroxide crust growth.