PNNL

Abstract

Radioactive iodine-129 (129I) poses a risk to groundwater due to its long half-life (~16M years), toxicity, and mobility in the environment. To reduce iodine-129 mobility in the environment, the natural and engineered materials are tested for their potential use as a deployed technology to treat iodine in situ and ex situ. Materials were evaluated with respect to several metrics that included their capacity for iodine uptake, iodine selectivity and the long-term ability for iodine immobilization. Materials were also evaluated for the technology deployability, as well as any potential adverse environmental impacts. Batch testing was used to determine iodate sorption under aerobic conditions for each material in synthetic groundwater (pH~8) and at different solution to solid ratios. The effect of the groundwater constituents on sorption capacity of materials for iodate was investigated. Association of iodine with the different materials was spatially resolved using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and the potential for redox reactions was assessed using I K-edge X-ray absorption near edge structure (XANES) spectroscopy. Of the materials tested (iron oxides, sulfide phases, bismuth-based materials, resin, activated carbon, organoclays, aerogels and metal organic frameworks), bismuth oxy(hydroxide) performed the best for iodine immobilization with a batch-test removal efficiency of >1000-fold, followed by bismuth-cobalt-aluminum and ferrihydrite materials. All three of these materials showed evidence that both iodate and iodide were associated with the solid phase, showing promise as potential remedial approaches since both species may be present in the subsurface.