The Association of Cobalt with Iron and Manganese (Oxyhydr)oxides in Marine Sediment

Abstract

Formation and dissolution of authigenic Fe and Mn (oxyhydr)oxides influence cycling of trace metals in oxic/suboxic surface sediments. We used the diffusive gradients in thin films technique (DGT) to estimate the association of cobalt with iron and manganese oxides. We compared Co, Fe and Mn maxima measured by DGT in the pore waters of fresh and aged marine sediment cores and estimated the Co/Fe and Co/Mn ratios in the metal oxides. A Mn maximum was not visible in DGT concentration profiles of freshly collected sediment cores, but after ageing the sediment, we observed a distinct Mn peak, presumably due to broadening of the depth range over which the various electron acceptors occur. Estimated Co/Mn ratios from both experiments are within the range of literature values for marine sediments, but the value from the aged experiment is at the lower end of the range. This is attributed to stimulation of sulphate reduction and precipitation of cobalt sulphides. The good correlation between Co and Fe maxima in the fresh sediments is attributed to the similarity of their reactions with sulphide rather than Co being released during authigenic Fe oxide reduction.

High-resolution profiles of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment

“…Compared with the DGT values for Mn, the DGT values for Fe and Co had better correlation (r = 0.854, p \ 0.01, n = 26) in varied trends of the metal concentrations according to depth. This result suggests that a similar mechanism may operate for the two metals' geochemical behavior (Shuttleworth et al 1999;Stockdale et al 2010): (1) the reductive remobilization of the two metals may require very similar conditions and may occur simultaneously but independently; (2) Co may be incorporated into Fe and Mn oxyhydroxides and then released as they are reductively dissolved (but Mn was more readily reducible than Fe); and (3) Co may be released from the organic matter, which is decomposed to supply electrons to the oxyhydroxides. Compared with the DGT values of Zn, the DGT values of Cd and Cu had better correlation (r = 0.747, p \ 0.01, n = 26) in varied trends of the metal concentrations according to depth.…”

“…Due to the complicated interactions between the river and sea and the water chemical condition (such as variations in pH and redox potential) in estuaries, some metals, such as iron (Fe), manganese (Mn), cobalt (Co), cadmium (Cd), copper (Cu) and zinc (Zn), might frequently undergo deposition and resuspension at the interface of sediment and water (Fan et al 2009;Stockdale et al 2010;Sakellari et al 2011). This phenomenon is similar to a ''time bomb'' for estuaries (Gao et al 2006;Feng et al 2011).…”

“…Compared to the dialysis cell technique, DET can determine the pore water concentration in sediment quickly and directly (Davison et al 1991;Harper et al 1997). By vertically inserting a DGT probe into the sediments, the DGT technique directly measures the flux of metals from the sediment to the solution during deployment based on the mass transport of metals Fones et al 2004;Stockdale et al 2010). It uses a layer of Chelex cation exchange resin placed behind a layer of hydrogel that is covered with a 0.45-lm membrane, through which metal ions are allowed to diffuse freely through (Sakellari et al 2011).…”

“…It uses a layer of Chelex cation exchange resin placed behind a layer of hydrogel that is covered with a 0.45-lm membrane, through which metal ions are allowed to diffuse freely through (Sakellari et al 2011). Using a DET or DGT technique, several studies have effectively revealed the behavior and role of diffusional transport and the (re)supply of metals, such as Fe, Mn, Co, Cd, Cu and Zn, from sediments to solution in the sediments of the freshwater and marine depositional environments (Gao et al 2006;Stockdale et al 2010;Sakellari et al 2011).…”

Immobilisation of manganese, cobalt and nickel by deep-sea-sediment microbial communities

“…environment is more oxidising [20] and is known for the slower rate of sediment deposition [21]. The formation and dissolution of authigenic (oxyhydr)oxides of Fe and Mn influence the cycling of trace metals in oxic/sub-oxic surface sediments [23]. In view of that, we performed our experiment under oxic and sub-oxic incubation conditions to test the hypothesis that autochthonous microbial communities from CIB sediments actively participate in metal immobilisation.…”