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

Publication date: December 2018

Source: Journal of Environmental Radioactivity, Volume 192

Author(s): Dien Li, Daniel I. Kaplan, Allison Sams, Brian A. Powell, Anna S. Knox

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.

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