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Sebastiaan van de Velde (2013)

Simultaneous release of sulphides and trace metals in sediments

Master thesis, Vrije Universiteit Brussel.

Combined microchelex-AgI di usive gradients in thin lms (DGT) probes were used to obtain 2D pore water pro les of trace metals and sulphides in di erent aquatic sediments. Sediments were taken from the Zenne River (mixed fresh and marine sediments, Belgium), the Deule River (industrial polluted channel sediments, France) and station 130 in the North Sea (marine sediment, Belgian coastal zone). In Zenne sediments the sulphate reduction zone appears at the SWI where no trace metals are presenting. The fresh organic matter depositions result in the remobilisation of sulphide but the release of metals was immediately oxidised at this area. In marine sediments, the formation process of sulphide hotspots has been illustrated with AgI-gels that were deployed for different times. At the sediment-water interface (SWI) increase of Fe, Co and Mn are linked to decrease in sulphide, while deeper in the sediment, an elevation of sulphide is linked to an obvious decline of metal concentration. The simultaneous remobilisation of sulphide and Ni was found at a depth of 11.2 cm to 11.3 cm in this marine sediment. The size of the Ni hotspot is around 2.36 mm2, but the sulphide hotspot, which is corresponding to the Ni one is much bigger with a size of 240 mm2. The formation of the Ni hotspot happens at the edge of the sulphide hotspot. No simultaneous release was found for the Deule sediments. Discrepancy between the results of chelex-100 and microchelex led to a few new experiments. The spiking experiment and the saturation test gave the explanation for this problem. The microchelex resin becomes much faster saturated than the chelex-100 resin when the metal concentration levels are high in the sediments. This is also different from what has been reported in previous literature. The general trend observed during the held experiments is that with sulphide and especially high sulphide concentrations, no metals appear. Sometimes however, coincident metal/S2- signals are observed, but this does not appear to be a general feature.
Master thesis
sediments, Belgian Continental Shelf
Filed under: Master thesis

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