Formation of Ni- and Zn-Sulfides in Cultures of Sulfate-Reducing Bacteria

Abstract

The purpose of this study was to characterize Ni- and Zn-sulfides precipitated in sulfate-reducing bacterial cultures. Fe-free media containing 58 mM SO ₄ ²⁻ were amended with Ni and Zn chloride followed by inoculation. Precipitates were sampled from cultures after two weeks of incubation at 22, 45, and 60 ^° C. Abiotic controls were prepared by reacting bacteria-free liquid media with Na ₂ S solutions under otherwise identical conditions. Precipitates were collected anaerobically, freeze-dried and analyzed by x-ray diffraction (XRD), scanning electron microscopy, and for total Ni, Zn, and S. In Ni-containing media, biogenic sulfide precipitates were mostly heazelwoodite (Ni ₃ S ₂ ), whereas abiotic precipitates were mixed heazelwoodite and vaesite (NiS ₂ ). The biogenic Ni-precipitates were better crystalline than the corresponding abiotic samples. Sphalerite (ZnS) was identified by XRD in precipitates sampled from Zn-containing media. Scanning electron microscopy revealed disordered morphological features for the sulfides, which occurred mostly as aggregates of fine particles in biogenic samples, whereas abiotic precipitates contained more plate- and needle-like structures.

Keywords:

• biogenic sulfides
• nickel sulfide
• sulfate-reducing bacteria
• X-ray diffraction
• zinc sulfide

Acknowledgments

We are grateful to F.S. Jones for assistance in sample preparation and analysis of total S and magnetic susceptibility and D.E. Fulton, Molecular and Cellular Imaging Center of the Ohio Agricultural Research and Development Center, for advice on scanning electron microscopy. Partial salary and research support were provided to and to J.M. Bigham by state and federal funds appropriated to the Ohio Agricultural Research and Development Center. Research support from the Finnish Funding Agency for Technology and Innovation (Finland Distinguished Professor Program, 402/06) to O.H. Tuovinen is also gratefully acknowledged. We thank two anonymous reviewers whose insightful comments were helpful in revising the manuscript.

Notes

^aInsufficient sample material for elemental analysis.