The removal of the pertechnetate ion and actinides from radioactive waste streams at Hanford, Washington, USA and Sellafield, Cumbria, UK: the role of iron-sulfide-containing adsorbent materials

Abstract

In previous work the adsorption of a number of radioactive ions from solution by a strongly-magnetic iron sulfide material has been studied. The material was produced by sulfate-reducing bacteria in a novel bioreactor. The uptake is rapid and the loading on the adsorbent is high due to the high surface area of the adsorbent and because many of the ions are chemisorbed. The structural properties have been examined using high-resolution imaging and electron diffraction, by transmission electron microscopy (TEM). The magnetisation versus field and temperature, extended X-ray absorption fine-structure (EXAFS) spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy and neutron diffraction have been reported previously. The surface area is of the order of 400–500 m 2 g −1, as determined by the adsorption of heavy metals, the magnetic properties, neutron scattering and transmission electron microscopy. Following the success of the biologically-generated material, Lidzey at Bio Separation Ltd. was able to produce an iron sulfide material with the tochilinite structure which has similar adsorption properties for cations, but not anions, as the biologically-generated material but the Lidzey material is considerably cheaper to produce. One of the radionuclides of particular interest is the pertechnetate ion TcO 4 −. 99 Tc is a radionuclide determining 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 paper examines methods by which adsorbent materials containing iron sulfide can play a part in the extraction and the safe long-term storage of many radionuclides and in particular the pertechnetate ion occuring at the Hanford Plant, Washington, USA and the Sellafield Plant, Cumbria, UK.