Adsorption of radioactive metals by strongly magnetic iron sulfide nanoparticles produced by sulfate-reducing bacteria

The adsorption of a number of radioactive ions from solution by a strongly magnetic iron sulfide material was studied. The material was produced by su lfate-reducing bacteria in a novel bioreactor. The uptake was rapid and loa ding on the adsorbent was high due to the high surface area of the adsorben t and because many of the ions were chemisorbed. The structural properties were examined with high-resolution imaging and electron diffraction by tran smission electron microscopy. The adsorbent surface area was determined to be 400-5OOm(2)/g by adsorption of heavy metals, the magnetic properties, ne utron scattering, and transmission electron microscopy. The adsorption of a number of radionuclides was examined at considerably lower concentration t han in previous work with these adsorbent materials. A number of ions studi ed are of interest to the nuclear industry, particularly the pertechnetate ion (TcO4-). Tc-99 is a radionuclide thought to determine the long-term env ironmental impact of the nuclear fuel cycle because of its long half-life a nd because it occurs normally in the form of the highly soluble pertechneta te ion, which can enter the food chain. This bacteria-generated iron sulfid e may provide a suitable matrix for the long-term safe storage of the perte chnetate ion. Also, because of the prevalence of the anaerobic sulfate-redu cing bacteria worldwide and, in particular, in sediments, the release of ra dioactive 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.