Abstract
Nearly a century of mining activities upstream have contaminated Lake Coeur d’Alene and its tributaries with Pb, Zn, and other heavy metals. Heavy metal concentrations in sediments of the Coeur d’Alene watershed have been shown to be inversely proportional to the sediment size fraction; thus, analysis on a very small scale is essential to determine the mobility and stability of heavy metals in this environment. Micron-scale synchrotron-based methods were used to determine the association of heavy metals with solid phases in sediments of the Coeur d’Alene River. Bulk X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy, and synchrotron-based microfocused XRD combined with microfocused X-ray fluorescence mapping indicate the presence of crystalline Pb- and Zn-bearing mineral phases of dundasite [Pb2Al4(CO3)4(OH)8·3H2O], coronadite [PbMn8O16], stolzite [PbWO4], mattheddleite [Pb10(SiO4)3.5(SO4)2Cl2], bindheimite [Pb2Sb2O7], and smithsonite [ZnCO3]. Likely phases for Zn and Pb adsorption were ferrihydrite, diaspore [AlO(OH)], manganite [Mn(III)O(OH)], muscovite [KAl2(Si3Al)O10(OH,F)2], biotite [K(Fe,Mg)3AlSi3O10(F,OH)2], and montmorillonite [Na0.3(Al,Mg)2Si4O10(OH)2·8H2O]. The large predominance of Fe and Mn (hydr)oxides over other sorbent minerals suggests that the metal sorption behavior is dominated by these (hydr)oxide phases.
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