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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Iodine sorption study on the proposed use of Viton A in a shuttle galley water accumulator

The installation of a Viton A accumulator in the Shuttle galley has been proposed to prevent overpressurization of the hot water supply system. A laboratory study has been conducted to determine if there would be any interaction between the Viton A material and the iodine used to disinfect the water. Coupons of Viton A were exposed for 24 hours to aqueous iodine solutions similar in quality to the Shuttle's potable water. Changes in the iodine residual were monitored to determine the rate of iodine sorption by the coupon. Total organic carbon (TOC) was monitored to determine the rate of desorption of organic materials from the Viton A. The same coupons were then soaked in reagent-grade water for 24 hours, and iodine was monitored to determine the rate of iodine desorption. The coupons were again exposed to iodine solutions for 24 hours and iodine and TOC were monitored. No significant change in the iodine sorption rate was detected between the first and second exposures. A triangle taste test indicated at a 1 percent confidence level that the water exposed to Viton A had a different taste which was less acceptable to the panelists.

Gibbons, Randall E.↗
DOE OSTI2021

Iodine Sorption on AgZ-PAN

The Department of Energy (DOE) Nuclear Fuel Cycle and Supply Chain Program Material Recovery and Waste Form Development (MRWFD) Campaign Off-gas Sigma Team has performed research and development on iodine control and iodine waste forms for the past several years. This research and development has included iodine adsorption tests using a laboratory-scale test system containing multiple-segmented fixed beds of iodine adsorbents. Iodine capture performance has been tested using (a) non-radioactive synthetic gas mixtures blended from air, nitrogen, NO, NO 2 , water, to simulate dissolver off-gas (DOG) and vessel off-gas (VOG) streams from used nuclear fuel aqueous reprocessing, (b) inorganic and organic iodine species, and (c) different sorbents. An initial test of silver-functionalized mordenite in polyacrylonitrile matrix (AgZ-PAN) was conducted to assess if this sorbent, initially designed for selective sorption of Xe that evolves into used fuel reprocessing off-gas streams, could also be a candidate for iodine sorption. This test was conducted using the same deep-bed test system and methodologies used in many prior iodine sorption tests using other sorbents. Diatomic iodine (I2) was used as the target iodide in a gas stream containing air, NO, NO 2 , and moisture designed to simulate an aqueous reprocessing dissolver off-gas (DOG) stream.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

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

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 materials be tested at different solution-to-solid ratios in FY15 to determine their effect on iodine sorption.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Evaluating the Physisorption and Chemisorption of Iodine on Bismuth-Functionalized Carbon Foams

Bismuth-containing carbon materials have been shown to be highly promising sorbents for the capture of radioiodine. However, there is still a need to understand the effects of carbon and bismuth on the iodine sorption mechanism. In this study, we show the relationship between the physical and chemical sorption of iodine under different bismuth loading conditions. Here, highly porous and non-friable conductive carbon foams were prepared and bismuth was electrodeposited to provide strong iodine binding sites. For pure carbon foams, equal ratios of physisorbed and chemisorbed iodine-carbon phases were detected before desorption. As the concentration of bismuth increased, the chemisorption between bismuth and iodine dominated the total capture mechanism and physisorption was almost completely eliminated. Additionally, chemisorption of iodine depended upon the size and specific surface area of the bismuth particles present within the framework of the foam.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Evaluation of Iodine and Water Co-adsorption on Silver-Functionalized Aerogel

The co-adsorption of iodine and water on silver-functionalized silica aerogel was evaluated using research quantities of the aerogel prepared at Pacific Northwest National Laboratory. A macro thermogravimetric analyzer was used to measure weight changes in a thin bed of the aerogel as air streams containing moisture and/or iodine flowed through the bed. The total gas flow in all tests was adjusted to achieve a velocity of 10 m/min through the bed. Initial heating of the aerogel sample to 150°C in dry air (dew point < -60°C) resulted in weight loss on the order of 1 wt %. Because subsequent phases of the tests indicated that the aerogel did not sorb water, the weight loss was speculated to be caused by volatilization of material that may have been used in the manufacture of the aerogel. Follow-on tests are recommended to ascertain if the aerogel sorbs water at low temperatures, such as 25°C—this would help to determine if a manufacturing reagent is volatilized when raising the sample to iodine sorption temperatures (i.e., 150°C). Alternatively, the off-gas released upon heating could be condensed and analyzed. In tests using humidified air streams with dew points between -60°C and +10°C, the aerogel did not adsorb water at test temperatures of either 75°C or 150°C. Because water alone was not adsorbed, tests were performed to ascertain if iodine sorption varied between cases when nearly no water was present in the gas stream and when water was present. In one experiment, the gas stream consisted of dry air (dew point < -60°C) with an iodine concentration of 50 ppmv. In the other experiment, the gas stream consisted of air with a water dew point of 0°C and an iodine concentration of 50 ppmv. The ultimate weight gain was nearly the same in both experiments and was presumed to be due entirely to adsorption of iodine. However, a reduced rate of iodine uptake is indicated when water vapor is present. The reason for this is unclear. In both cases, purging the sample with dry, iodine-free air resulted in some weight loss (~2 wt %). It is recommended that the gas phase chemistry of the iodine–water system be reviewed to ascertain if iodine species that are less reactive with silver than molecular iodine are present; this could explain the reduced sorption rates when water is present. Further evaluation of the desorption is recommended, especially to determine how raising the temperature would affect desorption.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

RedOx-controlled sorption of iodine anions by hydrotalcite composites

The radioactive contaminant iodine-129 (I-129) is one of the top risk drivers at radiological waste disposal and contaminated groundwater sites where nuclear material fabrication or reprocessing has occurred. Currently there are very few options available to treat I-129 in the groundwater, which is partially related to its complex biogeochemical behavior in the subsurface and occurrence in the multiple chemical forms. We hypothesize that layered hydrotalcite materials containing redox active transition metal ions offer a potential solution, benefiting from the simultaneous adsorption of iodate (IO3-) and iodide (I-) anions, which exhibit different electronic and structural properties and therefore may require dissimilar hosts. To test this hypothesis, Cr3+- based materials were selected based on the rationale that Cr3+ readily reduces IO3- in solution. It was combined with either redox-active Co2+ or redox-inactive Ni2+ so that two model materials were prepared by hydrothermal synthesis including Co2+-Cr3+ and Ni2+-Cr3+(M-Cr). Obtained M-Cr materials comprised of Co2+-Cr3+ or Ni2+-Cr3+ layered hydrotalcite and small fractions of Co3O4 spinel or Ni(OH)2 theophrastite phases were structurally characterized before and after uptake of periodate (IO4-), IO3-, and I- anions. It was found that the IO3- uptake is driven by its chemical reduction to I2 and I-. Interestingly, in the Co2+-Cr3+ hydrotalcite, Co2+ and not Cr3+ serves as a reductant while in the Ni2+-Cr3+ hydrotalcite Cr3+ is responsible for the reduction of IO3-. A different uptake mechanism was identified for the IO4- anion. The Co2+-Cr3+ hydrotalcite phase efficiently uptakes IO4- by a diffusion-limited ion exchange mechanism and is not accompanied by the redox process, while Cr3+ in the Ni2+-Cr3+ hydrotalcite reduces IO4- to IO3-, I2 and I-. Iodide exhibited high affinity only to the Co-Cr material. The Co-Cr material performed remarkably well for the removal of IO3-, I- and total iodine from the groundwater collected from the US DOE Hanford site, WA, USA outperforming non-redox active hydrotalcites (e.g., Mg2+-Al3+) reported previously. This work demonstrates that redox-controlled sorption can be a highly effective method for the treatment of anions based on elements with mobile oxidation states. Further, multiple anions of interest could be simultaneously removed through combination of approaches.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2012

Impact of Pretreatment and Aging on the Iodine Capture Performance of Silver-Exchanged Mordenite - 12314

Volatile gas emissions from a nuclear fuel recycle facility in the United States are governed by several key regulations, including 10 CFR 20, 40 CFR 61, and 40 CFR 190. Under 40 CFR 190, the total quantity of iodine that may be released to the environment from the entire fuel cycle is limited to 5 millicuries of I-129 per gigawatt-year of electrical energy produced by the fuel cycle. With a reasonable engineering margin, an iodine decontamination factor (DF) of approximately 1000 will be required for the complete fuel cycle. Off-gas treatment in a fuel reprocessing plant must address several gas streams containing iodine, among a number of volatile radionuclides. Past research and developmental activities identified silver-exchanged mordenite (AgZ) as a very promising sorbent based on its acid resistance, relatively high iodine and methyl iodide capacity, and high achievable DF. Recent studies at ORNL have focused on the impacts of long-term exposure to simulated off-gas streams (aging) and pretreatment on the iodine adsorption performance of hydrogen-reduced silver-exchanged mordenite (Ag{sup 0}Z). Experiments were conducted to determine the effects of long-term exposure to both dry and moist air on the iodine sorption capacity of Ag{sup 0}Z. The data indicates that aging reduces the capacity of Ag{sup 0}Z, which must be accounted for to prevent degradation of DF. Because of its high acid resistance, a AgZ sorbent has been selected specifically for application in treating off-gas streams containing iodine. While extensive tests have been conducted in the United States on a form of this sorbent, the specific material previously tested is no longer commercially available and similar materials are currently being evaluated. As part of this evaluation, tests were conducted to determine the iodine sorption properties of this replacement media and the effects of long-term (up to 6 months) exposure to simulated off-gas streams. The ultimate goal is to develop an understanding of the fundamental phenomena that controls aging for this material and other zeolites that could be considered for use in off-gas treatment in the future. The trends in the study results indicate that the amount of elemental silver observed by XRD increases from 0.3 wt% in vendor-supplied AgZ to approximately 5 wt% by reducing the material with hydrogen. The study also concluded that aging decreases the quantity of elemental silver in the material. After 2 months of aging, the Ag{sup 0} content of an experimental sample was reduced from 5 wt% to about 1.3 wt%. The form into which the elemental silver is converted during aging was not determined. Experimental tests have been initiated to study how aging of Ag{sup 0}Z impacts iodine loading on the zeolite. Loading tests with un-aged Ag{sup 0}Z resulted in an 81% silver utilization. The loading capacity of iodine on Ag{sup 0}Z was reduced with aging in dry air. Material aged for 6 months in dry air had a 40% reduction in iodine loading capacity. Under moist-air aging conditions, a significant decrease in the rate and total loading (∼45% of theoretical) of iodine uptake can be observed beginning with the shortest aging period (i.e., after 1 month) when compared with the loading curve using Ag{sup 0}Z with no aging. Increasing exposure time to the humid air used to age the Ag{sup 0}Z beyond 1 month resulted in a slight additional reduction in capacity to about 35% of theoretical at 2 months. Virtually identical capacity was observed with 4 months of aging. Compared to the non-aged material, the 1 month dry-air aged Ag{sup 0}Z shows about a 35% reduction (approximate) in iodine loading capacity and the 6 month dry-air aged Ag{sup 0}Z shows about a 50% reduction. These studies generated several questions that will be addressed in future tests. They include the following: Is there indeed degradation over time (in storage) in the iodine adsorption performance of Ag{sup 0}Z? Once reduced, how should the Ag{sup 0}Z be stored- under a hydrogen atmosphere, an inert atmosphere, a desiccant, or some other method or combination of methods? Does Ag{sup 0}Z have a 'shelf life' that must be considered after receipt from a vendor and before use in a plant? Also, how should a column of Ag{sup 0}Z be stored offline in a processing plant (parallel column) arrangement? Future tests will also include increasingly challenging aging environments such as acid vapor conditions. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Sorption of Iodine Species on SRS Wetland Soils

This research work has been supported by the DOE-FIU Science & Technology Workforce Development Initiative, an innovative program developed by the U.S. Department of Energy’s Office of Environmental Management (DOE-EM) and Florida International University’s Applied Research Center (FIU-ARC). During the summer of 2021, a DOE Fellow intern, Phuong Pham, spent 10 weeks doing a summer internship at Savannah River National Laboratory under the supervision and guidance of Hansell Gonzalez-Raymat. The intern’s project was initiated on May 24, 2021, and continued through July 30, 2021, with the objective of gaining a better understanding of the dominant attenuation mechanisms for 129 I in the wetlands, the strength of the attenuation, and what conditions would influence it.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

Initial Assessment of Alternate Metals in Chalcogels

This report provides an up-to-date account of the non-Pt based chemistries available in the literature for making non-oxide, chalcogen-based aerogels, called chalcogels. In each case, a combination of multiple precursors is required to make the chalcogels and, in most cases, the precursors are not commercially available and must be prepared in the laboratory. References for the preparation details of these precursors have been provided for each. An account of the chalcogels made at PNNL is also given in this report along with iodine sorption efficiencies for three very diverse chalcogel chemistries. A brief account of consolidation options is provided.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Multicomponent adsorption of radioactive iodine and krypton using ETS-10 supported carbon nano-polyhedrons

Over 13% of the world's energy demand is supplied by nuclear power plants in 31 countries. This demand is growing; by 2030 the IAEA predicts a 100% increase in the demand for nuclear energy. The increase in nuclear energy production imposes a growing strain on the uranium fuel supply. At current consumption rates the world's supply of uranium is projected to last ∼100 years. Following the IAEA's prediction for increased nuclear energy, uranium supplies will dwindle even more quickly. However, this consequence can be limited as ∼95% of uranium is left in used nuclear fuel (UNF). Reprocessing of UNF will utilize this remaining uranium and extend the lifetime of the world's uranium supply. One of the concerns with nuclear reprocessing is that it frees radionuclides created by the fission of uranium to be released into the atmosphere through off-gas. The major constituents of off-gas include: {sup 85}Kr, {sup 129}I, {sup 14}C, {sup 3}H, and various Xe isotopes. {sup 85}Kr and {sup 129}I present the largest threat due to their harmful environmental effects and abundance. They are the most practical contaminants to be removed to meet requirements for radionuclide release. Removal of these contaminants has been a challenge since the 1950's, and several methods including cryogenic distillation, fluorocarbon absorption, wet scrubbing, and adsorption have been employed. Currently, adsorption on porous solid sorbents shows the most promising results. Until now, several sorbents such as silver impregnated mordenite, silver Engelhard titanosilicate 10, chalcogen based aerogels, and metal organic framework, MOFs have been investigated for this purpose. Despite these advances, development of economical and highly active sorbents for complete removal and immobilization of volatile radioactive gases remains a key challenge in realizing advanced fuel cycles. This work is focused on the multicomponent of {sup 85}Kr and {sup 129}I from a simulated off-gas with an Engelhard titanosilicate 10 (ETS-10) supported carbon nano-polyhedron sorbent. Adsorption studies were performed to determine iodine sorption capacity as a function of temperature and iodine inlet concentration. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Preparation of NO 2 -Aged Silver-Functionalized Silica-Aerogel and Silver Mordenite Samples

Reprocessing used nuclear fuel can result in the volatilization of radioactive gaseous species, including 129 I, into the various process off-gas streams. In order to comply with US regulatory requirements, plant off-gas streams must be treated to remove the iodine prior to discharging the off-gas into the environment. The performance of available gas removal methods depends not only on the concentration of the volatile radioisotope of interest, but also on other constituents that could be present in the reprocessing off-gas streams. Some of the constituents, such as NOx produced during fuel dissolution, are known to have deleterious effects on the capture performance of silver-based sorbents used for iodine removal. Commercially available reduced silver mordenite (AgZ) has an iodine saturation concentration of 7.0-9.0 wt%, and its iodine sorption capacity is reduced by 20-50% as a result of NO2 aging. Silverfunctionalized silica aerogel (AgAerogel), an alternative for iodine capture, has an initial iodine saturation of 29.0 wt% and its iodine capacity is only reduced by 15% from NO2 aging. Understanding the differences in aging behavior between AgZ and AgAerogel is critical to determining the behavior of these sorbents under realistic off-gas conditions. To assist in future technical studies on this topic, samples of both AgZ and AgAerogel were aged with NO2. In the experiment, 10.2190 g of AgZ and 10.1771 g of AgAerogel were exposed to a static 0.75% NO 2 /dry air blend for a period of 28 days. The samples were then removed and stored under argon until needed for future experiments.=

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

IODINE ADSORPTION IN FIXED BED ADSORBER TESTS

I-129 emissions control is needed for used fuel aqueous reprocessing. I-129 capture has been studied for 40 years; Two sorbents tested in recent years – Silver Zeolite (AgZ) and silver-functionalized Aerogel (AGAero). Results show needed iodine adsorption efficiencies are possible, DFs up to10,000. Mass transfer zone (MTZ) depths ~2 in. for I2 and 8 in. for CH3I, but increase over time; deeper sorbent beds needed for efficient CH3I capture. Ag utilization between 10-70% for most test durations; lower for higher NOx. Iodine sorption capacities: ~10 g/100 AgZ and ~20 g/100 g AgAero; lower for high NOx. Nearly all adsorbed I was physisorbed iodine for I2 and CH3I.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Iodine in Metal–Organic Frameworks at High Pressure

Capture of highly volatile radioactive iodine is a promising application of metal–organic frameworks (MOFs), thanks to their high porosity with flexible chemical architecture. Specifically, strong charge-transfer binding of iodine to the framework enables efficient and selective iodine uptake as well as its long-term storage. As such, precise knowledge of the electronic structure of iodine is essential for a detailed modeling of the iodine sorption process, which will allow for rational design of iodophilic MOFs in the future. Here we probe the electronic structure of iodine in MOFs at variable iodine···framework interaction by Raman and optical absorption spectroscopy at high pressure (P). The electronic structure of iodine in the straight channels of SBMOF-1 (Ca- sdb , sdb = 4,4'-sulfonyldibenzoate) is modified irreversibly at P > 3.4 GPa by charge transfer, marking a polymerization of iodine molecules into a 1D polyiodide chain. In contrast, iodine in the sinusoidal channels of SBMOF-3 (Cd- sdb ) retains its molecular (I 2 ) character up to at least 8.4 GPa. Such divergent high-pressure behavior of iodine in the MOFs with similar port size and chemistry illustrates adaptations of the electronic structure of iodine to channel topology and strength of the iodine···framework interaction, which can be used to tailor iodine-immobilizing MOFs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Preliminary Study on Sorption Behavior of Iodine on Ca-Al-Si Hydrate - 19310

Sorption behavior of Ca-Al-Si hydrate with iodine sign ion and iodide ion was investigated using ion chromatography and Raman spectroscopy. In the experiment I-127 which is a stable isotope was used instead of I-129 which is a radionuclide. Ca-Al-Si hydrate was synthesized by mixing fumed silica (SiO{sub 2}) calcium oxide (CaO) and aluminum nitrate nonahydrate (Al(NO{sub 3}){sub 3}.9H{sub 2}O) with the solution containing iodine in a polypropylene tube. Two chemical forms of iodine, i.e., iodide ion and iodate ion, were considered in this study. In the samples of Ca-Al-Si hydrate, the Ca/Si molar ratios were adjusted in the range from 0.8 to 1.6, and the Al / Si ratios were in the range from 0.0 to 0.5. The samples liquid / solid (L/S) ratio was 20. In order to adjust the concentration to 0.5 mM for each samples, NaIO{sub 3} solution or NaI solution were added to the sample. NaClO solution was added as an oxidizing agent to maintain the form of iodate ion. The synthesis procedure for all the samples was carried out in a glove bag filled with nitrogen gas. The curing time was 1, 7, 30 days at room temperature (298 K) with shaking at 120 strokes / minute. In the results, although the iodide ion concentration in the liquid phase hardly changed, the liquid phase amount had been reduced to less than the liquid phase amount initially added. This means that iodide ions are incorporated in the solid phase together with the water of hydration. Besides, the concentration of iodate ion remarkably decreased for all samples under experimental conditions. In the Raman analysis, some differences in structure due to incorporation of Al were observed, but the structure of the Ca-Al-Si hydrate hardly changed due to other factors. Based on the sorption distribution coefficients obtained in this study, the Ca-Al-Si hydrate can be expected to have a barrier performance against iodine. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗