RAMAN SPECTROSCOPY OF COLLOIDS FROM SITES AFFECTED BY ABANDONED MINE DRAINAGE (AMD)

In Pennsylvania today, over 3000 km of waterways are affected by abandoned mine drainage (AMD) due to the prevalence of coal mining operations. AMD is known for contributing acidity and heavy metals to the surrounding environment, resulting in the degradation of ecosystems and clean waterways. The oxidation of pyrite (FeS₂) is a main contributor to this system, producing high concentrations of dissolved Fe²⁺that oxidizes and forms iron oxyhydroxide precipitates. These precipitates can become a part of either the colloidal or sediment fraction, thereby controlling the mobility of iron and other co-precipitated or adsorbed metals. The specific role colloids play in contaminant transport and the geochemical factors affecting their composition and stability are not well understood in AMD systems. To address this knowledge gap, we characterized and compared the composition of colloids found at several AMD sites. Water samples were collected in Shamokin Creek Basin within the western middle anthracite coalfield of Pennsylvania, and the colloidal fraction was concentrated via ultrafiltration and analyzed using Raman microscopy. Concentrations of dissolved Fe²⁺ and non-purgeable organic carbon (NPOC) in water samples were determined using analytical methods to explore how varying concentrations might affect colloid composition. Additionally, in situ measurements such as pH, dissolved oxygen (DO), and temperature were recorded to correlate these measurements to the composition and formation of colloids. Raman analysis indicated the colloidal fraction is composed of amorphous iron oxides and individual iron-bearing colloidal particles associated with humic material.