Analysis of colloids and flume simulations of abandoned mine drainage

Abandoned mine drainage (AMD) is a result of coal mining operations and is known for contributing acidity and heavy metals to the surrounding environment. The oxidation of pyrite (FeS2) is the main contributor to this system, producing Fe2+ which oxidizes to form 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, water samples were collected in Shamokin Creek Basin in Pennsylvania and the colloidal fraction was concentrated via ultrafiltration and analyzed using Raman microscopy. Analysis revealed that colloids are composed of sheet silicates, ferrihydrite, ferric carbonates, and natural organic matter. Colloids analyzed from a passive remediation system’s outflow indicated the presence of hematite, which is not typically found in AMD bulk sediments. An acid digestion procedure paired with the ferrozine assay was developed and used to quantify total iron in AMD waters and flume simulations. Suspended iron was quantified near the mouth of Shamokin Creek, indicating that it contributes iron to the Susquehanna River even though Fe2+ concentrations are below detection limits. Flume simulations revealed that both the presence of bed material and increased ionic strength enhance the rate of sediment deposition in AMD systems without affecting the rate of loss of Fe2+. When present in significant quantities, goethite catalyzes Fe2+ oxidation