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The role of Fe(III) minerals in controlling acid mine drainage (AMD) chemistry was studied using samples from two AMD sites [Gum Boot (GB) and Fridays-2 (FR)] located in northern Pennsylvania. Chemical extractions, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were used to identify and characterize Fe(III) phases. The mineralogical analysis revealed schwertmannite and goethite as the principal Fe(III) phases in the sediments. Schwertmannite particles occurred as sub-micron sized spheroids. Their transformation into goethite occurred at the GB site where poorly-crystallized goethite rich in surface-bound sulfate was initially formed. In contrast, no schwertmannite transformation occurred at the FR site. The resulting goethite in GB sediments was also of spherical morphology and resulted from an in situ phase transformation involving the conversion of bulkbound schwertmannite sulfate ions into goethite surface complexes. Chemical extractions moreover showed that the poorly-crystallized goethite particles were subject to further crystallization accompanied by sulfate desorption. Changes in sulfate speciation preceded its desorption, with a conversion of bidentate-to monodentate-bound sulfate surface complexes. Laboratory sediment incubation experiments were conducted to evaluate the effect of mineral transformation on water chemistry. Incubation experiments were carried out with schwertmannite-containing sediments and aerobic AMD waters with different pH and chemical composition. The pH decreased to 1.9-2.2 in all suspensions and the concentrations of dissolved Fe and S increased significantly. Regardless of differences in the initial water composition, pH, Fe and S were similar in suspensions of the same sediment. XRD measurements revealed that schwertmannite transformed into goethite in GB and FR sediments during laboratory incubation. The incubation experiments demonstrated that schwertmannite transformation controlled AMD water chemistry under no-flow, batch conditions.

The adsorption and speciation of U(VI) was investigated on contaminated, fine grained sediment materials from the Hanford 300 area (SPP1 GWF) in simulated groundwater using cryogenic laser-induced U(VI) fluorescence spectroscopy combined with chemometric analysis. A series of reference minerals (montmorillonite, illite, Michigan chlorite, North Carolina chlorite, California clinochlore, quartz and synthetic 6-line ferrihydrite) was used for comparison that represents the mineralogical constituents of SPP1 GWF. Surface area-normalized K d values were measured at U(VI) concentrations of 5 Â 10 À7 and 5 Â 10 À6 mol L À1 that displayed the following affinity series: 6-line-ferrihydrite > North Carolina chlorite % California clinochlore > quartz % Michigan chlorite > illite > montmorillonite. Both time-resolved spectra and asynchronous twodimensional (2D) correlation analysis of SPP1 GWF at different delay times indicated that two major adsorbed U(VI) species were present in the sediment that resembled U(VI) adsorbed on quartz and phyllosilicates. Simulations of the normalized fluorescence spectra confirmed that the speciation of SPP1 GWF was best represented by a linear combination of U(VI) adsorbed on quartz (90%) and phyllosilicates (10%). However, the fluorescence quantum yield for U(VI) adsorbed on phyllosilicates was lower than quartz and, consequently, its fractional contribution to speciation may be underestimated. Spectral comparison with literature data suggested that U(VI) exist primarily as inner-sphere complexes with surface silanol groups on quartz and as surface U(VI) tricarbonate complexes on phyllosilicates. Published by Elsevier Ltd.

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SummarySolvent extraction method was used to determine the stability constants of Tc(IV) with oxalate anions in NaCl solutions ranging in concentration from 0.5 M to 2.0 M. All experiments were conducted in an atmosphere-controlled chamber under Ar atmosphere (<1.0 ppm O