Iodate interactions with calcite: implications for natural attenuation

Abstract

Solid-phase interactions and speciation are important to radioiodine transport in groundwater. At the Hanford Site in Southeastern Washington State, iodate (IO 3 − ) is the main aqueous species in dilute radioiodine groundwater plumes. Like other oxyanions, IO 3 − may be incorporated into and/or adsorbed onto calcite, a common mineral at Hanford, decreasing its mobility in the environment. A series of macroscale batch experiments combined with solid-phase characterization were conducted to identify variables impacting time-dependent aqueous IO 3 − removal via calcite precipitation and determine the location of IO 3 − within the calcite crystal structure. Results demonstrated 11.5-97% aqueous IO 3 − removal during initial rapid calcite precipitation. Incorporation was apparently the main removal mechanism, although later slower precipitation and/or adsorption may have also contributed to IO 3 − removal. Using a higher concentration of the calcite-forming solutions (i.e., using 1 M vs. 0.1 M concentrations) resulted in an increase in the amount of precipitated calcite and a greater percentage of IO 3 − removed; however, calcite formed with lower molarity solutions resulted in higher IO 3 − mass (µg/g) removal. Solubility testing of laboratory-produced calcites showed only small differences in solubility for calcite with and without IO 3 − incorporated into the structure. Evidence collected from SEM/FIB and TEM/SAED suggested that the IO 3 − incorporated into calcite was present in regions close to the surface (implying potential easy release upon calcite dissolution).

Conceptual Model of Subsurface Processes for Iodine at the Hanford Site

“…Other evidence collected from NanoSIMS analyses (see Truex et al 2017a andMcElroy et al 2018) and molecular dynamic calculations (Kerisit et al 2018) also strongly suggested that the heavy metal observed in the near-surface regions was indeed iodine (in the form of iodate incorporated into calcite). The SAED measurement included in the bottom image of Figure 7 (small inset in the bottom right corner) confirmed the crystallinity of calcite.…”

Advances in the management of radioactive wastes and radionuclide contamination in environmental compartments: a review

“…Recent advances in the management of radioactive wastes/pollution have involved the development of methodical approaches such as natural attenuation, soil washing, adsorption, and electrochemical processes (Canner et al, 2018;Lingamdinne et al, 2017;McElroy et al, 2020;Song et al, 2015). Tables 5 and 6 provide an overview of the strategies employed in the cleanup of radioactive contaminants.…”