SUBSTRATE EFFECTS ON SEDIMENT DEPOSITION IN ABANDONED MINE DRAINAGE

Although the mineralogy of bulk abandoned mine drainage (AMD) sediment has been previously characterized as a mixture of various iron oxyhydroxides, the mechanism of sediment deposition is unclear as competing homogeneous and heterogeneous processes may be involved. Dissolved ferrous iron in AMD is oxidized upon mixing with surface water and can form suspended colloidal iron oxyhydroxide precipitates that may aggregate and deposit to the stream bed. Additionally, heterogenous nucleation of iron oxyhydroxide precipitation may occur directly on the stream bed. To investigate the role of bed materials on sediment deposition, we placed pre-characterized substrates in an AMD impacted stream and allowed them to collect sediment for a period of days. Substrates with varying mineral composition were selected to explore whether common minerals – or specific anomalies on their surfaces – affect nucleation sites for the heterogenous precipitation of iron oxyhydroxide sediment. Using 2-dimensional Raman mapping, the composition of each substrate was characterized. Substrates were then installed at an AMD site to collect sediment. After collection, the surfaces were re-mapped using Raman spectroscopy to assess the influence of common minerals found at AMD sites on the nucleation of iron oxyhydroxides.