Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures

Kirsten van Zuilen, Thomas Müller, Thomas F. Nägler, Martin Dietzel, Tim Küsters

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Variations in barium (Ba) stable isotope abundances measured in low and high temperature environments have recently received increasing attention. The actual processes controlling Ba isotope fractionation, however, remain mostly elusive. In this study, we present the first experimental approach to quantify the contribution of diffusion and adsorption on mass-dependent Ba isotope fractionation during transport of aqueous Ba2+ ions through a porous medium. Experiments have been carried out in which a BaCl2 solution of known isotopic composition diffused through u-shaped glass tubes filled with silica hydrogel at 10 °C and 25 °C for up to 201 days. The diffused Ba was highly fractionated by up to −2.15‰ in δ137/134Ba, despite the low relative difference in atomic mass. The time-dependent isotope fractionation can be successfully reproduced by a diffusive transport model accounting for mass-dependent differences in the effective diffusivities of the Ba isotope species (D137Ba/D134Ba=(m134/m137)β). Values of β extracted from the transport model were in the range of 0.010–0.011. Independently conducted batch experiments revealed that adsorption of Ba onto the surface of silica hydrogel favoured the heavier Ba isotopes (α = 1.00015 ± 0.00008). The contribution of adsorption on the overall isotope fractionation in the diffusion experiments, however, was found to be small. Our results contribute to the understanding of Ba isotope fractionation processes, which is crucial for interpreting natural isotope variations and the assessment of Ba isotope ratios as geochemical proxies.

Original languageEnglish
Pages (from-to)226-241
Number of pages16
JournalGeochimica et Cosmochimica Acta
Volume186
DOIs
Publication statusPublished - 2016

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barium
Barium
Fractionation
Isotopes
fractionation
isotope
adsorption
Adsorption
Temperature
Hydrogel
Silicon Dioxide
silica
experiment
Experiments
diffusivity
porous medium
stable isotope
isotopic composition
Porous materials
glass

Keywords

  • Adsorption
  • Ba isotopes
  • Barium
  • Diffusion
  • Diffusive transport model
  • Experiment
  • Reactive transport
  • Stable isotope fractionation

ASJC Scopus subject areas

  • Geochemistry and Petrology

Fields of Expertise

  • Advanced Materials Science

Cite this

Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures. / van Zuilen, Kirsten; Müller, Thomas; Nägler, Thomas F.; Dietzel, Martin; Küsters, Tim.

In: Geochimica et Cosmochimica Acta, Vol. 186, 2016, p. 226-241.

Research output: Contribution to journalArticleResearchpeer-review

van Zuilen, Kirsten ; Müller, Thomas ; Nägler, Thomas F. ; Dietzel, Martin ; Küsters, Tim. / Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures. In: Geochimica et Cosmochimica Acta. 2016 ; Vol. 186. pp. 226-241.
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