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2 Uranium(VI), which is often elevated in granitoidic groundwaters, is known to adsorb 3 strongly to iron (hydr)oxides under certain conditions. This process can be used in 4 water treatment to remove uranium(VI). To develop a consistent geochemical model 5 for uranium(VI) adsorption to ferrihydrite, batch experiments were performed and 6 previous data sets reviewed to optimize a set of surface complexation constants using 7 the three-plane CD-MUSIC model. To consider the effect of dissolved organic matter 8 (DOM) on uranium(VI) speciation, new parameters for the Stockholm Humic Model 9 (SHM) were optimized using previously published data. 10The model, which was constrained from available X-ray absorption fine structure 11 (EXAFS) spectroscopy evidence, fitted the data well when the surface sites were 12 divided into low-and high-affinity binding sites. Application of the model concept to 13 other published data sets revealed differences in the reactivity of different 14 ferrihydrites towards uranium(VI). Use of the optimized SHM parameters for 15 uranium(VI)-DOM complexation showed that this process is important for 16 uranium(VI) speciation at low pH. However in neutral to alkaline waters with 17 substantial carbonate present, Ca-U-CO 3 complexes predominate. 18The calibrated geochemical model was used to simulate uranium(VI) adsorption to 19 ferrihydrite for a hypothetical groundwater in the presence of several competitive 20 ions. The results showed that uranium(VI) adsorption was strong between pH 5 and 8. 21Also near the calcite saturation limit, where uranium(VI) adsorption was weakest 22 according to the model, the adsorption percentage was predicted to be > 80 %. Hence 23 uranium(VI) adsorption to ferrihydrite-containing sorbents may be used as a method 24 to bring down uranium(VI) concentrations to acceptable levels in groundwater. 25 3 1 Keywords: uranium, surface complexation, speciation, dissolved organic matter, 2 ferrihydrite, groundwater 3 4 Introduction 5In recent years it has been revealed that many groundwaters in granitoidic 6 environments contain excessive amounts of dissolved uranium. The recommended 7 guideline value for uranium in groundwater is 15 µg/L (WHO, 2004). In Sweden it 8 has been estimated that about 17 % of all private bedrock wells contain higher 9 concentrations of dissolved uranium (Ek et al., 2007). Also many larger waterworks 10 contain excessive uranium concentrations (Falk et al., 2004) and research into 11 technologies for uranium removal is ongoing. One possible technique could be 12 uranium removal by iron-oxide-coated sand, for which the chemical mechanism is 13 surface complexation of uranium(VI) onto the Fe (hydr)oxides ferrihydrite and 14 goethite (Logue et al., 2004). Of these, ferrihydrite may often be more important 15 because of its much larger surface area and content of reactive surface groups. 16 17To evaluate the possible use of iron-oxide-based sorption media for uranium 18 removal, we need to understand the various mechanisms that affect it. Uranium occ...

Several roadside soil samples were collected at two field sites in Sweden. They were analysed for total elemental content (using both ICP-MS and XRF) and stable lead isotopes. Extraction with deicing salt solution and sequential extraction were performed in order to elucidate the potential mobility due to the use of deicing agents. The total concentrations of elements, especially lead, have decreased and lead is presently almost at background concentrations (15-51 ppm for surface samples). However, the isotopic signature indicates that old gasoline lead still is left at the site constructed prior to 1975. The field site constructed in 1992 showed, however, no 206Pb/207Pb ratio below 1.14. Only minor amounts were leached using deicing salt solutions; for lead only 0.29%, on average, was extracted indicating that the mobile fraction already was released. Sequential extraction indicated that lead mainly was associated with reducible (34.4%) and oxidisable (35.4%) fractions. Exchangable and acid soluble fractions contained 20.3% while 10.0% was found in the residual fraction. The salt extraction released, however, very low concentrations indicating that most in fraction 1 is acid soluble (e.g. carbonates). Tungsten was also found at high concentrations indicating a possible impact from studded tires. For tungsten the following composition was obtained: residual (48.0%) > oxidisable (47.6%) > reducible (3.3%) > exchangeable/acid soluble (1.1%). From the isotopic studies it was also suggested that the order for incorporating anthropogenic lead into soils is exchangeable/carbonates > (hydr)oxides > organic matter > residual. The multivariate technique principal component analysis (PCA) seems promising for evaluating large sequential extraction datasets.

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