Acid mine drainage (AMD) is a common issue in areas of historic coal mining, resulting in acid and toxic metal-rich runoff which can severely impact local ecosystems. Huff Run watershed, near Mineral City, Ohio, is currently affected by mining operations abandoned decades ago. Chemical breakdown of pyrite through oxidative dissolution is the primary source of AMD, releasing Fe3+ and sulfuric acid and subsequent precipitation of Fe-oxides. Weathering of coal mine spoil transports colloidal pyrite suspended in runoff into nearby streams. A crucial area of colloid-facilitated transport study is the isolation of the colloidal fraction (1-1000 nm) of the soil. The current study used centrifugation to separate the colloidal fraction from the bulk sample of two sites to examine particle composition and morphology during transport. Dynamic light scattering analyses from two field sites showed a bimodal distribution of particle sizes after centrifugation, with average particle sizes of 299 ± 42 nm and 2,293 ± 269 nm (site 1) and 290 ± 75 and 3,338 ± 2,040 nm (site 2). The smaller values are the most important, as they indicated a clear separation between particles in the colloidal size range and residual soil particles. Scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS)analyses indicated the presence of pyrite attached to grains of aluminosilicates and the presence of sulfur-rich colloids. This is an important discovery as it shows the colloidal fraction of soils (containing the pollutant transport) has the potential to be consistently isolated in a soil sample.
Acid mine drainage (AMD) is a common result of historic coal mining. Mine spoils, left over waste from decades ago, can serve as a transport medium for AMD, causing severe ecosystem impacts. Pollutants are transported in the colloidal fraction (1-1000nm) making them hard to mitigate. In order to be studied, the colloidal fraction must first be separated from the sample. This study attempted to use centrifugation to separate hydrated soil samples into their colloidal fraction. The size of the separated colloids was measured, along with the composition and morphology of the soil. Significant separation was determined, but future research will be needed to further confirm the composition of the colloids.