Iodine K-Edge Exafs Spectroscopy of Iodine-Bearing AFm-(Cl2, CO3, SO4)

Abstract

Extended X-ray absorption fine structure (EXAFS) spectroscopy at the iodine K-edge was performed to investigate the immobilization of iodide by AFm-Cl2/CO3/SO4 phases. AFm-I2 and various compositions of AFm-(I2, Cl2), AFm-(I2, CO3), and AFm-(I2, SO4) were synthesized by coprecipitation and exchange reaction. X-ray diffraction (XRD) showed that AFm-(I2, Cl2) sample crystallize in two separate crystalline phases AFm-I2 and AFm-Cl2. This finding was supported by EXAFS measurements, which showed that the coordination environment of iodine is similar for AFm-(I2, Cl2) and pure AFm-I2. AFm-(I2, CO3) interlayers alternately filled with I− and with (OH−–CO3 2−) were observed by XRD, whereas a more limited short-range ordering of iodide was found by EXAFS spectroscopy. XRD indicated that AFm-(I2, SO4) forms a solid solution between AFm-I2 and AFm-SO4. In addition, the EXAFS spectra revealed that I− and SO4 2− occupy neighbouring positions. The formation of an AFm-I2–AFm-SO4 solid solution together with the complete mixing of I− and SO4 2− confirms the capability of AFm-SO4 to trap 129I.