Oxidative scavenging of cerium on hydrous Fe oxide: Evidence from the distribution of rare earth elements and yttrium between Fe oxides and Mn oxides in hydrogenetic ferromanganese crusts

Abstract

The distribution of the rare earths and yttrium (REY) in co-existing hydrous Mn oxides and Fe oxides that form marine hydrogenetic ferromanganese crusts is used to better describe the partitioning and fractionation of the REY between these (hydr)oxides and seawater in the natural marine system. Four fractions (easily exchangeable, Mn-oxide-bound, Fe-oxidebound, and insoluble-residue-bound REY) were separated by an adjusted sequential leaching procedure from two ferromanganese crusts from the Central Pacific. The distribution of the REY differs significantly between these leaching fractions and gives evidence for decoupling of La, Ce, Gd, Y, and Lu from their respective neighbours in the REY series during partitioning between hydrous Fe oxides, Mn oxides and seawater. Both the Mn oxides and the Fe oxides display pronounced positive Ce anomalies of almost similar size. This suggests that in the natural marine system oxidative scavenging of Ce from seawater is not restricted to Mn oxides but also occurs on hydrous Fe oxides. The distribution of Ce between the Mn oxides and the hydrous Fe oxides follows that of the trivalent REY and contrasts sharply with that of tetravalent Zr, Hf and Th. This suggests that preferential Ce removal from seawater does not result from the oxidation of dissolved Ce(III) within the marine water column, but that Ce(III) is oxidized after its sorption at the metal (hydr)oxide surface. Patterns of apparent hydrous Fe oxide/Mn oxide distribution coefficients show a sigmoidal shape and display negative anomalies for La, Gd, Y, and Lu (and the M-type lanthanide tetrad effect), indicating preferential scavenging of these elements by the Mn oxides as compared to the Fe oxides. The pronounced differences between the REY distribution in the Mn oxides and that in the Fe oxides cannot solely be explained by the REY speciation in seawater, but require additional and mineral-specific REY fractionation during surface-complexation.

Geochemistry of REE, Zr and Hf in a wide range of pH and water composition: The Nevado del Ruiz volcano-hydrothermal system (Colombia)

“…The different charge of metal complexes determines the adsorption behaviour onto the solid surfaces (Koschinsky and Hein, 2003). Bau and Koschinsky (2009) show that the Y/Ho ratio in marine Fe-Mn hydroxydes is significantly lower than seawater, suggesting an enhanced scavenging of Ho with respect to Y in the Fe-Mn crusts. Recently, Schmidt et al (2014) investigating the fractionation of Zr-Hf between seawater and Fe-Mn crusts, showed that Zr/Hf ratio is lower in the Fe-Mn oxyhydroxides compared to seawater.…”

“…9) shows the simultaneous variation of these elements, with the involvement of Fe and Al controlling the abundance of REE dissolved in water. Strong processes of scavenging occur during the co-precipitation and/or adsorption onto the surface of oxide and oxyhydroxide of Fe, Al, and Mn (Censi et al, 2007;Bau and Koschinsky, 2009). …”

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

“…These studies have drawn from a sound understanding of REE+Y cycling in modern anoxic basins. In general, oxygenated marine settings display a strong negative Ce anomaly when normalised to a shale composite (Ce (SN) ), because oxidation of Ce(III) to Ce(IV) greatly reduces Ce solubility, resulting in its preferential removal onto Mn(IV)-Fe(III)-oxyhydroxides, organic matter, and clay particles (Byrne and Sholkovitz, 1996;Bau and Koschinsky, 2009). This process leaves the residual water column depleted in Ce, thus creating the characteristic negative Ce 50 anomaly.…”

Zirconium–hafnium and rare earth element signatures discriminating the effect of atmospheric fallout from hydrothermal input in volcanic lake water

“…Cerium is sensitive to redox changes and easily removed from solution as CeO 2 and/or by adsorption onto Mn-and Fe-oxyhydroxide under oxidizing conditions (Bau, 1999;Seto and Tsaku, 2008;Bau and Koschinsky, 2009 and references therein). A strong positive Ce anomaly was found in the lake water, quite different from the hydrothermal waters.…”