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

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.