Oxidation of Dissolved Tetravalent Selenium by Birnessite: Se Isotope Fractionation and the Effects of pH and Birnessite Structure

Pranjal Dwivedi, Kathrin Schilling, Naomi Wasserman, Thomas M. Johnson, Celine Pallud

Research output: Contribution to journalArticlepeer-review

Abstract

Redox reactions control the mobility and bioavailability of selenium (Se) in biogeochemical systems, both modern and ancient. Se isotope ratio measurements (e.g., 82Se/76Se) have been developed to enhance understanding of biogeochemical transformations and transport of Se. Stable isotope ratios of many elements are known to be powerful indicators of redox reactions, and shifts in 82Se/76Se have been observed for Se reduction reactions. However, Se isotope shifts caused by naturally relevant oxidation reactions have not been published. Here, we report Se isotope fractionation factors for oxidation of Se(IV) by birnessite. Experiments were conducted at pH = 4.0 and 5.5, with two types of birnessite of contrasting composition at two concentrations of suspended birnessite. The results are consistent with a single 82Se/76Se fractionation factor, for all times during all experiments, of 0.99767 (±0.0035 2 s.d.). Expressed as ε, the fractionation is 2.33‰ (±0.08‰).

Original languageEnglish (US)
Article number909900
JournalFrontiers in Earth Science
Volume10
DOIs
StatePublished - Jul 6 2022

Keywords

  • Rayleigh fractionation
  • isotope geochemistry
  • manganese oxides
  • paleoredox
  • selenium oxidation

ASJC Scopus subject areas

  • General Earth and Planetary Sciences

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