SEDIMENTARY SPECIATION OF METALS IN FERRICRETES RECOVERED FROM A STREAM IMPACTED BY ACID MINE DRAINAGE

The goal of this research is to evaluate the sedimentary speciation of metals in ferricrete samples collected from West Little Sugar Creek, Vigo County, Indiana, a stream significantly impacted by acid mine drainage (AMD). Ferricrete is composed of sediments cemented by Fe and Al oxyhydroxide precipitates. The ferricrete deposits sampled in this study formed as a result of AMD originating from the abandoned Green Valley coal mine site mixing with uncontaminated stream water. Streams impacted by AMD are commonly polluted with heavy metals, and previous results from surface ferricrete samples indicate that concentrations of Fe, Al, Cd, Ni, and Zn are indeed elevated. To evaluate the sedimentary speciation, a sequential extraction technique (after Tessier et al., 1979) was used. This extraction isolates five sedimentary phases based on reaction order and reagent strength, thus providing an estimation of metal bioavailability and susceptibility to remobilization. Following the extraction, elemental concentrations were determined by ICP-OES. Results from surface samples indicate that in general, the highest concentrations of Fe and Al, as well as highly variable amounts of Zn and Ni are found in association with oxides. Zn is also commonly found in association with organic matter while the unreactive residual component contains the highest concentrations of Cd, Zn, and Ni. The extraction of core samples and X-ray Diffraction (XRD) analysis is ongoing to evaluate potential diagenetic alterations that might further mitigate AMD contaminants. The results of this study provide an estimation of potential metal bioavailability and geochemical remobilization and, thus, ferricretes viability as a long term sink for heavy metals.