Iodine adsorption on ion-exchange resins and activated carbons: batch testing

Abstract

Among radioactive contaminants, iodine-129 (129 I) is commonly either the top or among the top risk drivers, along with technetium-99 (99 Tc), at radiological waste disposal sites and contaminated groundwater sites where nuclear material fabrication or reprocessing has occurred. Radioactive iodine (129 I) is of environmental concern due to its long half-life (1.6 × 10 7 years), toxicity, and mobility in the environment (Councell et al. 1997). However, there are currently very few approaches that effectively manage risks to human health and the environment. At the Hanford Site in Washington State, radioactive iodine (129 I), a fission product of plutonium, was discharged in 200 West Area disposal cribs. This discharge is responsible for the majority of 129 I contamination found in the groundwater (Zhang et al. 2013). The 200 West Area contains two separate plumes covering 1,500 acres where 129 I concentrations are ~3.5 pCi/L. The objective of this study was to evaluate the efficacy of commercial ion exchange resins and granular activated carbon (GAC) materials which will enable direct removal of all iodine species present in Hanford groundwater through treatment at the 200W pump and treat. Iodine sorption onto seven resins and six carbon materials was evaluated using water from well 299-W19-36 on the Hanford Site. These materials were tested using a range of solution-to-solid ratios. The test results are as follows:  The efficacy of the resin and granular activated carbon materials was less than predicted based on manufacturers' performance data. It is hypothesized that this is due to the differences in speciation previously determined for Hanford groundwater.  The sorption of iodine is affected by the iodine species in the source water. Iodine loading on resins using source water ranged from 1.47 to 1.70 µg/g with the corresponding K d values from 189.9 to 227.0 mL/g. The sorption values when the iodine is converted to iodide ranged from 2.75 to 5.90 µg/g with the corresponding K d values from 536.3 to 2979.6 mL/g. It is recommended that methods to convert iodine to iodide be investigated in fiscal year (FY) 2015.  The chemicals used to convert iodine to iodate adversely affected the sorption of iodine onto the carbon materials. Using as-received source water, loading and K d values ranged from 1.47 to 1.70 µg/g and 189.8 to 226.3 mL/g respectively. After treatment, loading and K d values could not be calculated because there was little change between the initial and final iodine concentration. It is recommended the cause of the decrease in iodine sorption be investigated in FY15.  In direct support of CH2M HILL Plateau Remediation Company, Pacific Northwest National Laboratory has evaluated samples from within the 200W pump and treat bioreactors. As part of this analysis, pictures taken within the bioreactor reveal a precipitate that, based on physical properties and known aqueous chemistry, is hypothesized to be iron pyrite or chalcopyrite, which could affect iodine adsorption. It is recommended these mater...

A simple method for quantifying iodate and iodide fractions in solution using Ag+-impregnated activated carbon

“…refs. [8] and [9]), this approach only removes iodide and not iodate, offering a tool for the separation between the two iodine species.…”

“…It is crucial to notice that iodine can exist in several forms even at the same time. Further, the speciation of iodine affects essentially its geochemical behaviour and interactions with natural materials [5][6][7] or synthetic solid sorbents developed for iodine removal [8,9]. To reliably assess the interaction of different remediation materials, it is essential to precisely control and survey the speciation of iodine.…”

“…While iodine separation from aqueous solution has been extensively studied in many studies (i.e. references [8] and [9]), usually studies are considering either total iodine removal or removal efficiency for different iodine species from contaminated water. Instead, Ag-GAC is selective only to one species of iodine (I − ) and not to another (IO 3 − ).…”

Identification of Promising Remediation Technologies for Iodine in the UP-1 Operable Unit

“…There are a plethora of potential adsorbents, both natural and synthetic, including activated carbon (e.g., Hoskins et al 2002;Parker et al 2014;Kosaka et al 2012;Ikari et al 2015), zeolites (e.g., Li et al 2014), layered double hydroxides (e.g., Kentjono et al 2010;Theiss et al 2014), organoclays (e.g., Li et al 2014), argentite (e.g., Li et al 2014;Kaplan et al 2000;Mattigod et al 2007), aerogels (e.g., Sánchez-Polo et al 2006, self-assembled monolayers on mesoporous silica (SAMMS) (e.g., Mattigod et al 2007;Kaplan et al 2000), carbon nanotubes (e.g., Pishko et al 2013), and a number of other materials. Some of these adsorbents include silver impregnation (doping) to promote iodine capture and formation of immobile silver iodide when adsorbed.…”

“…ABEC resin development for large-scale chromatographic equipment has been undertaken (Bond et al 1999;Alexandratos 2009). Batch testing (Parker et al 2014) of ion exchange on synthetic resin media for iodine treatment has shown adsorption rates similar to those for certain activated carbon media, on the order of 1.7 µg iodine per gram of resin. Reduction of iodine to iodide in the testing by Parker et al (2014) was found to more than double the loading capacity of most resins (except Dowex 21K and SIR-700).…”