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

Abstract

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.