Iodate in calcite and vaterite: Insights from synchrotron X-ray absorption spectroscopy and first-principles calculations

Abstract

Calcium carbonates such as calcite are the dominant hosts of inorganic iodine in nature and are potentially important for the retention and removal of radioactive iodine isotopes (129 I and 131 I) in contaminated water. However, little is known about the structural environment of iodine in carbonates. In this study, iodate (IO 3 −) doped calcite and vaterite have been synthesized using the gel-diffusion method at three NaIO 3 concentrations (0.002; 0.004; 0.008 M) and a pH value of 9.0, under ambient temperature and pressure. Inductively coupled plasma mass spectrometry (ICP-MS) analyses show that iodine is preferentially incorporated into calcite over vaterite. Synchrotron iodine K-edge X-ray absorption near-edge structure (XANES) spectra confirm that IO 3 − is the dominant iodine species in synthetic calcite and vaterite. Analyses of iodine K-edge extended X-ray absorption fine structure (EXAFS) data, complemented by periodic first-principles calculations at the density functional theory (DFT) levels, demonstrate that the I 5+ ion of

Contaminant Attenuation and Transport Characterization of 200-DV-1 Operable Unit Sediment Samples from Boreholes C9497, C9498, C9603, C9488, and C9513

“…The mechanism for the relatively large portion of iodine found in the extractions not associated with equilibrium partitioning may be association of iodate with carbonate precipitates. This type of co-precipitation has been observed in the scientific literature (Zhang et al 2013;Podder et al 2016) and is consistent with release of iodine in the third and fourth extractions that are targeted at dissolving carbonate precipitates.…”

“…Speciation was not possible in the carbonate precipitate extractions for the sequential extraction procedure, but it is likely that the iodine present in these extractions was iodate. Scientific literature has shown coprecipitation of iodate and carbonates (Zhang et al 2013;Podder et al 2016) The leaching experiments showed some slow-release behavior of iodine that may be associated with these carbonate precipitates.…”

Intensified Ocean Deoxygenation During the end Devonian Mass Extinction

“…). Experimental and computational work has demonstrated that IO 3 − is the dominant ion incorporated into calcite through replacing carbonate ion (e.g.,Feng & Redfern, 2018 ;Lu et al, 2010;Podder et al, 2017). Therefore, stratigraphic I/Ca trends are mostly controlled by changes in IO 3 − concentrations in the local water column (e.g.,Hardisty et al, 2017;Lu et al, 2010).…”

Evaluation of Central Plateau Remediation Alternatives: Interim Status Report

“…Based on previous co-precipitation studies (Zhang et al 2013;Szecsody et al 2017;Truex et al 2017a,b;Qafoku and Icenhower 2008;Qafoku et al 2017;Podder et al 2017;Montes-Hernandez et al 2007;Zachara et al 2007a,b;Catalano et al 2008), it is hypothesized that dissolved contaminants can be sequestered into calcium carbonates via co-precipitation mechanisms. Iodine incorporation into calcite under saturated conditions has been demonstrated (Szecsody et al 2018;Zhang et al 2013); however, fewer data are available for other Central Plateau COCs and for use of a gaseous source of CO 2 .…”