Molybdenum and nickel partitioning during the oxidative precipitation of iron: implications for paleo-environmental proxies during BIF formation; Mo K-edge XANES data

The deposition of banded iron formations (BIFs) from Precambrian oceans likely affected the abundance and bioavailability of trace metal nutrients. Utilizing BIFs as proxies for paleo-ocean composition requires careful constraints on the mechanisms and partition coefficients of trace element incorporation into BIF precursor phases. These precursors likely varied in their structure and Fe oxidation state over time and with local and global fluctuations in ocean chemistry. We studied the partitioning of two bio-relevant trace metals, nickel(II) and molybdenum(VI), during the oxidative precipitation of iron oxyhydroxides from solution under a range of oxygen fluxes and fluid chemistries. We characterized the mechanisms of Ni and Mo incorporation by measuring elemental yields after sequential phase dissolution and by Mo K-edge X-ray absorption near-edge structure (XANES) spectral analysis. This dataset accompanies the publication of the same name and comprises Mo K-edge XANES spectra for products from the above experiments and for a series of standards and synthesized iron phases with sorbed Mo. The pre-edge peak varies in intensity with Mo oxidation state and coordination. Using the prominence of this pre-edge peak as a proxy, we show that Mo is reduced over the course of Fe(II) oxidation, and the extent of Mo oxidation depends on solution chemistry and the mineralogy of newly formed precipitates. Mo undergoes late re-oxidation in some experiments as the last of Fe(II) is oxidized.