TRACE ELEMENTS IN SLAG BEARING SEDIMENTS FROM LAKE ROOSEVELT, WA: A SEQUENTIAL EXTRACTION AND SEM STUDY
Sediment samples were collected using a box core at three different points in Lake Roosevelt. These samples were analyzed for Fe, Ni, Cr, As, Zn, Mn, Cd, Pb, and Cu following sequential extraction by the European Commission's BCR procedure. (Quevauviller 2002) Within the sediment, this procedure distinguishes three labile fractions: (1) the acid soluble fraction (interpreted as carbonates), (2) the reducible fraction (interpreted as hydrous Fe- and Mn-oxides), and (3) the oxidizable fraction (interpreted as sulfidic and organic material). In addition it distinguishes a "residual" fraction.
A shortcoming of sequential extraction methods is that the fractions are operationally defined. Therefore, to further our understanding of the elements' associations we use the SEM to characterize changes in grain surface chemistry (e.g., disappearance of Fe- and Mn-oxide grain coatings) and grain surface morphology (e.g., etching/dissolution textures) following each step of the process.