2, Brookhaven National Laboratory, Brookhaven, New York, United States
Nuclear activities (nuclear power plants, reprocessing plants, dismantling activities…) produce important volume of radioactive effluents which must be treated to minimize their impact on environment. Also, large volumes of contaminated groundwater and seawater have been generated during the Fukushima-Daiichi nuclear power plant disaster. Among the fission products present in these effluents, 90Sr is one of the most abundant and hazardous radionuclides for human health. Processes commonly used for 90Sr sorption generally involve an ion exchange mechanism on specific sorbents such as sodium titanates and zeolites 1. However, 90Sr removal efficiency by these ion exchange minerals is significantly reduced by the presence of competitive cations (Ca, Mg). On the other hand, in the radioactive liquid effluent treatment stations, barium sulfate is used to extract selectively radioactive strontium from effluents by a coprecipitation process 2. This process is selective towards Ca but leads to large volumes of radioactive sludge that have to be managed. To address these concerns, our approach consists in coupling ion exchange and coprecipitation processes. A barium zeolite material has proved to be an effective and selective sorbent for the extraction of strontium from effluents of high salinity like seawater 3. This material demonstrates considerably high capacity and selectivity for strontium with distribution coefficient Kd of 18200 mL.g-1, obtained from batch sorption tests with seawater spiked with 90Sr (59355 Bq.L-1, m/V = 5 g.L-1). As evidenced by the SEM image in Figure 1, and XRD analysis, the precipitation of BaSO4 occurs at the surface of the zeolite grains. The evidenced mechanisms of Sr extraction with this material are quite complex, involving both ion exchange with the Ba ions from the zeolite and the coprecipitation in insoluble barium sulfate formed at the surface of the zeolite grains upon contact with the effluent containing sulfate ions. We propose to expose in more details this material’s characteristics and related extraction mechanisms at the conference.
1) TEPCO Decommissioning plan of Fukushima Daiichi nuclear power - Contaminated water treatment. http://www.tepco.co.jp/en/decommision/planaction/alps/index-e.html (accessed 20/08/2015).
(2) IAEA Radioactive Waste Management Profiles: A compilation of data from the waste management database; Vienna, 2000.
(3) Kim, K. W.; Lee, K.Y.; Lee, E. H.; Baek, Y.; Chung, D. Y.; Moon, J.K. Nuclear Technology, 2016, 193, 318-329.