Well after a coal mine has stopped production, it can strongly impact the environment around it through a process called acid mine drainage (AMD). Water discharging from local coal mines and flowing through the tailings becomes contaminated with heavy metals due to the dissolution of minerals such as pyrite and acidified by the subsequent oxidation of the reduced iron. After being oxidized, the iron precipitates out of the water leaving behind a distinctive orange sediment along the banks of local waterways. The poorly crystalline mineral ferrihydrite, Fe(OH)3, makes up most of the orange sediment lining waterways impacted by AMD. If this AMD sediment is dredged from a stream or a settling pond, it can be used as a coloring agent of varying pigments formed from a series of mineralogical transformations. By analyzing these mineralogical and geochemical transformations of the ferrihydrite extracted from the sediment through X-ray powder diffraction and scanning electron microscopy, we can better understand the development of crystalline mineral phases in the sediment and how they pertain to the development of varying pigments. This should also help us to understand the similar transformations of iron oxides occurring in the sediments impacted by AMD.
Dr. David Singer
Abandoned coal mines around America are still impacting the environment as they discharge contaminated waters into local environments. This is referred to as acid mine drainage (AMD), and it results in highly acidified and heavy metal contaminated waters. Along the beds of the streams running through these areas impacted by coal mining a bright orange sediment composed of poorly crystalline iron oxides. These sediments can be filtered, dried, and baked to form a color agent with varying shades of pigments. Through the analysis of the mineral transformations of these AMD sediments with X-ray powder diffraction and scanning electron microscopy, we can better understand the mineralogical and geochemical transformation of the iron oxides in AMD sediments.