Geochemistry of rare earth elements in the mainstream of the Yangtze River,China |
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| Institution: | 1. Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100101, China;2. State Key Laboratory of Cryospheric Sciences, Cold and Arid Regions Environmental and Engineering of Research Institute, CAS, Lanzhou 730000, China;3. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing, 100101, China;4. Laboratory of Green Chemistry, Lappeenranta University of Technology, Mikkeli 50130, Finland;5. University of Chinese Academy of Sciences, Beijing 100049, China;1. Department of Earth Sciences, Faculty of Experimental Sciences, University of Huelva, Campus ‘El Carmen’ s/n, 21071 Huelva, Spain;2. Research Center on Natural Resources, Health and the Environment (RENSMA), University of Huelva, 8, 21071 Huelva, Spain;3. Institute of Environmental Assessment and Water Research, CSIC, Jordi Girona 18, 08034 Barcelona, Spain |
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| Abstract: | Water, suspended matter, and sediment samples were taken from 8 locations along the Yangtze River in 1992. The concentration and speciation (exchangeable, bound to carbonates, bound to Fe–Mn oxides, bound to organic matter, and residual forms) of rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu) were determined by instrumental neutron activation analysis (INAA).The contents of the soluble fraction of REEs in the river are low, and REEs mainly reside in particulate form. In the particles, the chondrite-normalized distribution patterns show significant LREE enrichment and Eu-depletion. While normalized to shales, both sediments and suspended matter samples show relative LREE enrichment and HREE depletion. REEs are relatively enriched in fine-grained fractions of the sediments.The speciation characteristics of REEs in the sediments and suspended matter are very similar. The amount of the five forms follows the order: residual>>bound to organic matter～bound to Fe–Mn oxides>bound to carbonates>>exchangeable. About 65 to 85% of REEs in the particles exist in the residual form, and the exchangeable form is very low. High proportions of residual REEs reveal that REEs in sediments and suspended matter are controlled by their abundances in the earth's crust. Carbonate, Fe–Mn oxide and organic fractions of REEs in sediments account for 2.4–6.9%, 5.2–11.1%, and 7.3–14.0% of the total contents respectively. They are similar to those in the suspended matter. This shows that carbonates, Fe–Mn oxides and organic matter play important roles during the particle-water interaction processes. By normalization to shales, the 3 forms of REEs follow convex shapes according to atomic number with middle REE (Sm, Eu, and Tb) enrichment, while light REE and heavy REE are depleted. |
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