Systematically varying properties and reactivities have led to focused research of the environmental forensic capabilities of rare earth elements (REE). Increasing anthropogenic inputs to natural systems may permanently alter the natural signatures of REE, motivating characterization of natural REE variability. We compiled and analyzed reported dissolved REE concentration data over a wide range of natural water types (ground-, ocean, river, and lake water) and groundwater chemistries (e.g., fresh, brine, and acidic) with the goal of quantifying the extent of natural REE variability, especially for groundwater systems. Quantitative challenges presented by censored data were addressed with nonparametric distributions and regressions. Reported measurements of REE in natural waters range over nearly 10 orders of magnitude, though the majority of measurements are within 2-4 orders of magnitude, and are highly correlated with one another. Few global correlations exist among dissolved abundance and bulk solution properties in groundwater, indicating the complex nature of source-sink terms and the need for care when comparing results between studies. This collection, homogenization, and analysis of a disparate literature facilitates interstudy comparison and provides insight into the wide range of variables that influence REE geochemistry.
International audienceMany nanoparticles (NPs) are transformed in the environment, and the properties of the transformed materials must be determined to accurately assess their environmental risk. Sulfidation is expected to alter the speciation and properties of CuO NPs significantly. Here, commercially available 40 nm CuO NPs were characterized and sulfidized in water by inorganic sulfide, and the properties of the resulting products were determined. X-ray absorption spectroscopy, X-ray diffraction, and transmission electron microscopy indicate that CuO (tenorite) is sulfidized by inorganic sulfide to several copper sulfide (CuxSy) species including crystalline CuS (covellite), and amorphous (CuxSy) species at ambient temperature. Some Cu(II) was reduced to Cu(I) during sulfidation, coupled with sulfide oxidation to sulfate, resulting in the formation of small amounts of several copper sulfate hydroxide species as well. The extent of sulfidation depends on the sulfide to CuO molar concentration ratio used. At the highest S/Cu molar ratio of 2.16, 100% sulfidation was not reached in 7 days, as evidenced by the persistence of small amounts of CuO in the NPs. Sulfidation increased the fraction of copper passing a 3 kDa MWCO filter representing soluble forms of Cu and any small CuxSy clusters compared to the pristine CuO NPs at environmentally relevant neutral pH. This high solubility is a result of oxidative dissolution of CuxSy, formation of relatively more soluble copper sulfate hydroxides, and the formation of small CuS nanoclusters that pass the 3 kDa MWCO filter. These findings suggest that sulfidation of CuO may increase its apparent solubility and resulting bioavailability and eco-toxicity attributed to toxic Cu2+
Silica adsorbents were grafted with REE-selective ligands and their lanthanide binding ability was evaluated in the presence of multiple competing ions.
In this work, the geochemistry of the rare earth elements (REE) was studied in eleven outcrop samples and six, depth-interval samples of a core from the Marcellus Shale. The REE are classically applied analytes for investigating depositional environments and inferring geochemical processes, making them of interest as potential, naturally occurring indicators of fluid sources as well as indicators of geochemical processes in solid waste disposal. However, little is known of the REE occurrence in the Marcellus Shale or its produced waters, and this study represents one of the first, thorough characterizations of the REE in the Marcellus Shale. In these samples, the abundance of REE and the fractionation of REE profiles were correlated with different mineral components of the shale. Namely, samples with a larger clay component were inferred to have higher absolute concentrations of REE but have less distinctive patterns. Conversely, samples with larger carbonate fractions exhibited a greater degree of fractionation, albeit with lower total abundance. Further study is necessary to determine release mechanisms, as well as REE fate-and-transport, however these results have implications for future brine and solid waste management applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12932-015-0022-4) contains supplementary material, which is available to authorized users.
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