Microbially
mediated sulfate reduction is a promising cost-effective
and sustainable process utilized in permeable reactive barriers (PRB)
and constructed wetlands to treat mine wastewater. Laboratory batch
experiments were performed to evaluate nickel (Ni) isotope fractionation
associated with precipitation of Ni-sulfides in the presence of the
sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans
T (DSM-642). Precipitates were collected anaerobically
and characterized by synchrotron powder X-ray diffraction (PXRD),
scanning electron microscopy combined with energy-dispersive X-ray
spectroscopy (SEM-EDS), and transmission electron microscopy (TEM).
Solid-phase analyses showed that the precipitates associated with
bacteria attached to the serum bottle walls were characterized by
enhanced size and crystallinity. Lighter Ni isotopes were preferentially
concentrated in the solid phase, whereas the solution was enriched
in heavier Ni isotopes compared to the input solution. This fractionation
pattern was consistent with closed-system equilibrium isotope fractionation,
yielding a fractionation factor of Δ60Nisolid‑aq = −1.99‰.
The Ni isotope fractionation measured in this study indicates multiple
Ni reaction mechanisms occurring in the complex SRB-Ni system. The
results from this study offer insights into Ni isotope fractionation
during interaction with SRB and provide a foundation for the characterization
and development of Ni stable isotopes as tracers in environmental
applications.
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