Chemical species of iodine during sorption by activated carbon -Effects of original chemical species and fulvic acids

Radioactive iodine is one of the mobile radionuclides contained in the contaminated water generated by cooling of the fuel debris at Fukushima Daiichi nuclear power plant (FDNPP). It is reported that chemical species of iodine transform between iodate, iodide, and organo-I in the environments. In FDNPP, the contaminated water is merged with ground water containing fulvic acids and then passed through a series of treatment columns to remove radionuclides. The objective of this study was to determine if iodide or iodate speciation changed after it was sorbed by activated carbon (AC), a potential adsorbent at the FDNPP for waste water treatment. Chemical species of the sorbed iodine was determined by X-ray absorption near edge spectroscopy (XANES) at the SPring-8 Synchrotron Radiation Facility. Sorption experiments of iodate and iodide showed systematic decreases of the distribution coefficients with increasing pH of the solution. Additionally, greater sorption of iodate than iodide was measured. The novelty of these results includes that the chemical species of iodate and iodide on the AC did not change during sorption; however, the presence of fulvic acids promoted the transformation of iodate to the less strongly bound species, iodide, during sorption to AC. The results from this study have important implications on the long-term effectiveness and eventual disposal of used AC from the FDNPP facility.