ADSORPTION OF RADIOACTIVE METALS BY STRONGLY MAGNETIC IRON SULFIDE NANOPARTICLES PRODUCED BY SULFATE-REDUCING BACTERIA

Abstract

The adsorption of a number of radioactive ions from solution by a strongly magnetic iron sulfide material was studied. The material was produced by sulfate-reducing bacteria in a novel bioreactor. The uptake was rapid and loading on the adsorbent was high due to the high surface area of the adsorbent and because many of the ions were chemisorbed. The structural properties were examined with high-resolution imaging and electron diffraction by transmission electron microscopy. The adsorbent surface area was determined to be 400–500m²/g by adsorption of heavy metals, the magnetic properties, neutron scattering, and transmission electron microscopy. The adsorption of a number of radionuclides was examined at considerably lower concentration than in previous work with these adsorbent materials. A number of ions studied are of interest to the nuclear industry, particularly the pertechnetate ion (TcO₄ ⁻). ⁹⁹Tc is a radionuclide thought to determine the long-term environmental impact of the nuclear fuel cycle because of its long half-life and because it occurs normally in the form of the highly soluble pertechnetate ion, which can enter the food chain. This bacteria-generated iron sulfide may provide a suitable matrix for the long-term safe storage of the pertechnetate ion. Also, because of the prevalence of the anaerobic sulfate-reducing bacteria worldwide and, in particular, in sediments, the release of radioactive heavy metals or toxic heavy metals into the environment could be engineered so that they are immobilized by sulfate-reducing bacteria or the adsorbents that they produce and removed from the food chain.

ACKNOWLEDGMENTS

The authors wish to acknowledge the provision of time on DARTS, the UK national synchrotron radiation service at the CLRC Daresbury Laboratory, and ISIS, the pulsed neutron facility at the Rutherford-Appleton Laboratory. We are grateful to Prof D. J. Vaughan and Dr. R. A. D. Pattrick of the Department of Earth Sciences, Manchester University, for making available the XANES spectra of the iron sulfide model compounds; to Dr Bill Bostick, MCL Inc; and to Dr Gilbert Brown, ORNL, for much appreciated private communication. We also wish to thank colleagues at the University of Southampton, namely, Profs Brian Rainford, Peter de Groot and George Attard, and Drs. Alan Howard, and Andrew P. Roberts, for useful discussion. We also gratefully acknowledge financial support from Biopraxis Developments Ltd, the Office of Innovation and Research Support at the University of Southampton, Southampton Innovation Ltd, and NSG Environmental Ltd.