posted on 2023-12-06, 18:33authored byHannah J. Veldhuizen, Joel S. MacKinney, Thomas M. Johnson
Stable isotope ratios of antimony
(Sb) in the environment can provide
valuable information about sources and processes such as redox transformations.
To investigate the fractionation when Sb(V) is chemically reduced
by sulfide to Sb(III), experiments with 0.008 to 0.01 mM Sb(V) and
0.009 to 6 mM sulfide at a pH of 1 to 8 were performed. Experiments
at pH 1 to 6 precipitated Sb-sulfide, whereas at pH 7 to 8, Sb(III)
remained in the solution. The Sb(III) product was enriched with the
lighter isotope. The isotopic fractionation (ε ≈ δinstantaneous product – δreactant) for the pH 1 experiment was −1.42 ± 0.04‰, whereas
those at the pH 5 to 8 experiments ranged from −0.46 ±
0.04 to −0.62 ± 0.04‰. The small magnitude of fractionation
observed in experiments at circumneutral pH may decrease the utility
of Sb isotope measurement as reduction indicators in natural systems,
as adsorption of Sb has been shown to fractionate isotopes in the
same direction and similar magnitude (up to 1.14‰) (Wasserman,
2020; Zhou et al., 2023).