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Removal capacity and chemical speciation of groundwater iodide (I−) and iodate (IO3−) sequestered by organoclays and granular activated carbon

Li, Dien, Kaplan, Daniel I., Sams, Allison, Powell, Brian A., Knox, Anna S.
Journal of environmental radioactivity 2018 v.192 pp. 505-512
X-radiation, activated carbon, adsorption, aerobic conditions, chemical speciation, groundwater, groundwater contamination, iodates, iodides, iodine, ligands, liquids, minerals, radioactive waste, radioactivity, sorbents, spectroscopy, sulfur, synthetic products
Radioiodine (present mostly as ¹²⁹I) is difficult to remove from waste streams or contaminated groundwater because it tends to exist as multiple anionic species (i.e., iodide (I⁻), iodate (IO3⁻) and organo-iodide) that do not bind to minerals or synthetic materials. In this work, the efficacy of organoclay OCB and OCM, and granular activated carbon (GAC) as sorbents to bind I⁻ and IO3⁻ from artificial groundwater (AGW) was examined. These sorbents were highly effective at removing I⁻ and IO3⁻ from AGW under oxic condition, with the adsorption capacity up to 30 mg I/g sorbent. Based on X-ray spectroscopy measurements, I⁻ was bound to organic ligands in organoclays OCB and OCM, but when GAC was exposed to I⁻ in groundwater, the sequestered I species was molecular I2. For IO3⁻ interacting with organoclay OCB and GAC, the adsorbed I species remained being IO3⁻, but when organoclay OCM that contains both quaternary amine and sulfur was exposed to IO3⁻, the sulfur compound would reduce IO3⁻ to I⁻ that was then bound to organic ligands. Thus, the inexpensive and high-capacity organoclays and GAC may provide a practical solution for removing ¹²⁹I contaminant from environmental systems and liquid nuclear wastes.