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Abstract: Uranium (U) mobility in the environment strongly depends on its oxidation state and the presence of complexing agents such as inorganic carbon, phosphates, and dissolved organic matter (DOM). Despite the importance of DOM in U mobility, the exact mechanism is still poorly understood. Therefore, the aim of our investigation was to characterise sediment porewater DOM in two lakes in Ontario, Canada (Bow and Bentley Lakes) that were historically contaminated with U and propose possible composition of UO2-bearing DOM. Depth profiles of U concentrations in porewaters and total sediment digests reveal U levels of up to 1.3 mg L−1 in porewater and up to 0.8 mg−1 g in sediment. Depth profiles of U did not correlate with Fe, Mn, SO4 2−, or Eh profiles. Therefore, porewater DOM was analysed and taken into consideration as the primary source of U mobility. Porewater DOM in each sediment section (1 cm sections, 20 cm core length) was analysed by high-resolution electrospray ionisation mass spectrometry. PCA analyses of porewater DOM mass spectra showed grouping and clear separation of DOM in sediment sections with elevated U concentrations in comparison to sections with background U concentrations. Several criteria were set to characterise UO2-bearing DOM and more than 70 different molecules were found. The vast majority of these UO2-DOM compounds fell in the category of carboxyl-containing aliphatic molecules (H/C between 0.85 and 1.2 and O/C≤0.4) and had a mean value of m/z about 720.
Keywords: Uranium Lake sediments Porewater Disolved organic matter High resolution mass spectrometry
Published in RUNG: 09.10.2019; Views: 3874; Downloads: 0
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Abstract: The majority of the world’s goods are transported over water and dredging is essential for the development of harbors and ports. Therefore, the management of dredged material is a worldwide issue. Due to its chemical and petrographic, mineralogical and homogeneity composition, marine sediments are an appropriate raw material to use in the brick industry. Marine sediments can serve as raw material for the production of clay blocks, roofing and ceramic tiles. Different analyses were carried out in order to determine if the dredged material from the Port of Koper is environmentally friendly and suitable to use in the brick industry. These analyses included: a chemical analysis, a mineralogical analysis, a particle size analysis and a chloride content (Cl-) analysis, and tests of firing in a gradient furnace. Furthermore, tests of mechanical properties, as well as tests of frost-resistance of the samples were carried out. On the basis of primary analyses and samples prepared in a lab, it was established that marine sediments from the Port of Koper without any additives are only conditionally suitable as a source material for producing brick products. In collaboration with Gorica brickworks (Goriške opekarne), a pilot production from a mixture of 60% component B from Gorica brickworks and 40% component A (marine sediments) from the Port of Koper was prepared. Different tests showed the mixture could be appropriate for brick production.
Keywords: marine sediments, recycling, clay bricks, chemical analysis, mechanical properties, brick production.
Published in RUNG: 05.09.2016; Views: 6339; Downloads: 278
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