Iodine species uptake by cement and CSH studied by IK-edge X-ray absorption spectroscopy

Abstract

SummaryThe uptake of iodine species (I−/IO3−) by HCP (hardened cement paste) and a CSH (calcium silicate hydrate) phase under highly alkaline conditions has been investigated using X-ray absorption spectroscopy (XAS). The study was performed at the I K-edge (33.169 keV) instead of the I L3-edge (4.557 keV) to avoid interference with Ca (K-edge=4.038 keV), a major element in HCP and CSH phases. The XANES (X-rays absorption near-edge structure) spectra revealed no changes in the formal oxidation state of iodide (I(-I)−) and iodate (I(V)O3−) upon uptake by HCP and CSH. The EXAFS (extended X-ray absorption fine structure) oscillations from I−treated HCP and CSH samples were found to be extremely weak, limiting interpretation of the EXAFS data. The IO3−EXAFS spectra showed that the IO3−entity consisting of three oxygen atoms with a characteristic I-O distance (∼1.78 Å) is maintained upon uptake by HCP and CSH. XANES further indicated that CSH is not the uptake-controlling phase in HCP.