Precipitation of molybdenum from euxinic waters and the role of organic matter

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Identifying oxygen minimum zone-type biogeochemical cycling in Earth history using inorganic geochemical proxies

Dissimilar behaviors of the geochemical twins W and Mo in hypoxic-euxinic marine basins

Beyond redox: Control of trace-metal enrichment in anoxic marine facies by watermass chemistry and sedimentation rate

Global marine redox evolution from the late Neoproterozoic to the early Paleozoic constrained by the integration of Mo and U isotope records

Relative to continental crust, sediments underlying sulfidic marine waters are molybdenum-rich, a property preserved in the rock record and useful for characterizing paleoenvironments. The enrichment mechanism is not agreed upon but is attributed at least partly to deposition of Fe–Mo–S compounds, which are as yet uncharacterized. Here, we determine the composition and stability of colloidal Fe–Mo–S precipitates formed at mildly basic pH and H2S(aq) > 10–5 M. The first product consists simply of FeMoS4, with Ksp = 10–14.95. Within hours, FeMoS4 irreversibly transforms by internal self-reduction to a Mo(IV) product of similar composition. The reduced product is insoluble in 1 M HCl but soluble in concentrated HNO3, implying that it would be recovered with pyrite in a common assay of sediments. X-ray absorption fine structure data show that Mo(IV) in the colloids is coordinated by a split first shell of about five sulfur atoms at average distances of 2.31 and 2.46 A and in its second shell by an iron atom a...

Wayland Hunter

Papers

Molybdenum Burial Mechanism in Sulfidic Sediments: Iron-Sulfide Pathway