Method for removing iodate from aqueous solutions

Abstract

Methods and materials for removing iodate from aqueous solutions are described. The methods involve the reduction of iodate to iodide followed by subsequent or simultaneous removal of iodide by adsorption, ion exchange, or precipitation. These methods are effective for removing radioactive iodine from radioactive nuclear waste.

Description

[Technical Field]

[0001] The present invention relates to a method for removing iodate from aqueous solutions by converting the iodate to iodide, followed by subsequent or simultaneous removal of the iodide by adsorption, ion exchange, or precipitation. An important application of the present invention relates to the cleanup of liquid waste streams containing radioactive iodine, some of which may be present as iodate. Such wastes include, inter alia, liquid wastes generated by nuclear reactor operations and the reprocessing of spent nuclear fuel. [Background technology]

[0002] It is a radioactive isotope of iodine 129 I is formed by the fission of uranium and plutonium in nuclear reactors and is therefore present in many types of nuclear waste. 129 I is a beta emitter with a half-life of 15.7 million years. Iodine is highly mobile in the environment because it forms highly soluble anions, such as iodide and iodate. The presence of radioactive iodine in the environment poses risks to the ecosystem in general and to human health, and 129 The extremely long half-life and high environmental mobility of I, combined with the biological activity of iodine, particularly in the thyroid gland, make I a significant environmental risk factor in the performance assessment of nuclear waste repositories. Summary of the Invention [Problem to be solved by the invention]

[0003] The chemical forms of iodine in radioactive liquid waste are typically iodide and iodate, and these forms often dominate. There are several effective options for iodide removal, including ion exchange with strong anion exchangers, precipitation as silver iodide, adsorption on silver-impregnated media such as silver zeolites, and adsorption on cerium-, bismuth-, or iron-based media. In contrast, there are few effective options for iodate removal. As a result, the ability to remove radioactive iodine from a waste stream as a whole can be limited by the amount of iodine present as iodate. The present invention addresses this need by teaching an effective method for removing iodine present in the iodate form. [Means for solving the problem]

[0004] According to a first broad aspect, the present disclosure provides a method for removing iodate from an aqueous liquid, the method comprising adding a water-soluble compound that includes a thiol group and removing iodide, wherein the thiol group is capable of converting iodate to iodide.

[0005] According to a second broad aspect, the disclosure provides a material for converting iodate to iodide in an aqueous solution, the material including a solid substrate to which a thiol group-containing compound is attached.

[0006] According to a second broad aspect, the disclosure provides a method for removing iodate from an aqueous solution using a material for converting iodate in the aqueous solution to iodide, the material including a solid substrate to which a thiol group-containing compound is attached.

[0007] Other applications of the present invention will become apparent to those skilled in the art from the description provided herein. DETAILED DESCRIPTION OF THE INVENTION

[0008] (definition) Where a definition of a term deviates from the commonly used meaning of that term, applicants intend to utilize the definition set forth below unless otherwise indicated.

[0009] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and do not limit any claimed subject matter. In this application, the use of the singular includes the plural unless expressly stated otherwise. It must be noted that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. In this application, the use of "or" means "and / or" unless expressly stated otherwise. Furthermore, the use of the terms "including," as well as other forms such as "include," "includes," and "included," is not limiting.

[0010] In this disclosure, the terms "comprising," "having," "including," and variations of these words are intended to be open-ended and mean that there may be additional elements other than the listed elements.

[0011] In this disclosure, directional terms such as "top," "bottom," "up," "bottom," "above," "down," "left," "right," "horizontal," "vertical," "up," "down," and the like are used merely for convenience in describing various embodiments of the present disclosure. Embodiments of the present disclosure may be oriented in various ways. For example, diagrams, devices, and the like shown in the drawings may be flipped, rotated 90 degrees in any direction, reversed, and the like.

[0012] For purposes of this disclosure, a value or characteristic is "based on" a particular value, characteristic, satisfaction of a condition, or other factor if the value is derived by performing a mathematical calculation or logical decision using the particular value, characteristic, or other factor.

[0013] It should be noted that in the present disclosure, for the sake of a more concise description, some of the quantitative expressions given herein are not qualified by the term "about". Whether the use of the term "about" is expressly stated or not, it is understood that any given amount in this specification refers to an actual given value, and further refers to an approximate value for such a given value that should be reasonably estimated based on ordinary skill in the art. Approximate values ​​include those that are close to experimental and / or measurement conditions for such a given value.

[0014] In this disclosure, the term "organosulfur compound" refers to an organic compound containing sulfur. In this disclosure, this term refers to an organic compound having the general formula R-(SH) n The term "thiol-containing organic compounds" refers to sulfur-containing organic compounds having at least one thiol functional group, which may be represented by the formula:

[0015] In this disclosure, the term "stoichiometry" refers to the relationship between the amounts of reactants and products before, during, and after a chemical reaction.

[0016] In this disclosure, the terms "medium," "substrate," and "resin" are used interchangeably. The term "medium" refers to an organic or inorganic solid ion exchange material consisting of a "substrate" with pendant chemical moieties that can participate in chemical reactions while maintaining the integrity of the substrate. The ion exchange medium may also be an organic polymer "resin." In this context, the terms "medium," "substrate," and "resin" refer to a solid matrix that is a backbone for attaching chemical moieties, such as thiol functional groups, that can participate in ion exchange and other chemical reactions.

[0017] (explanation) While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are described in detail below. It is to be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but rather the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

[0018] The speciation of dissolved iodine in aqueous solutions depends on the concentrations of other dissolved components and other characteristics of the solution, such as pH and redox state. Common forms of dissolved iodine in aqueous solutions include iodide (I - ), iodate (IO3 - ), molecular iodide (I2), and triiodide (I3 - The predominant forms of iodine in radioactive liquid waste from nuclear sources are typically iodide and iodate.

[0019] The removal of iodine present in aqueous solutions as iodide can be effectively achieved by a variety of methods, including ion exchange with strongly basic anion exchangers, other ion exchangers, precipitation as silver iodide, adsorption onto silver-impregnated media such as silver zeolites, or adsorption onto cerium-, bismuth-, or iron-based media. In contrast, there are few effective options for the removal of iodate. For example, many ion exchange media effective for iodide removal are orders of magnitude less effective for iodate removal. Similarly, silver iodide has a water solubility of approximately 3 × 10 at room temperature. -8 g / L, whereas silver iodate has a room temperature water solubility of over 100,000 times that of iodide. As a result, whereas iodide can be removed very effectively by precipitating it as silver iodide, for example by adding silver nitrate, iodate cannot be easily removed by precipitation.

[0020] In one embodiment, the present disclosure describes a novel method for removing iodate from a water stream by first reducing iodine in the form of iodate to iodide. Once converted to iodate, iodate can be readily removed by ion exchange, which has been shown to be effective for iodide removal.

[0021] In one embodiment, the reduction of iodate to iodide is accomplished using a compound having one or more thiol functional groups. Thiol functional groups are abundant in proteins, more particularly in the amino acid cysteine. Thiol functional groups are also found in other low molecular weight organic compounds, such as thioglycolic acid and thioglutathione. These organosulfur compounds have the general formula R-SH, where SH is the thiol functional group and R is the remainder of the organic compound. Compounds having multiple thiol functional groups, which can also be used to reduce iodate to iodide, may be constructed, for example, by polymerization of R-SH compounds. In this case, the polymerized compound has the general formula R'-(SH) n where SH is a thiol functional group, R' is the polymer backbone, and n is the number of thiol groups per polymer molecule, where n is greater than 1 and is limited by the structure of the backbone and its length.

[0022] Oxidation of organosulfur compounds containing thiol functional groups can result in the formation of chemical entities with disulfide bonds.

[0023] In one embodiment, R-(SH) n The stoichiometry of the reduction of iodate by organosulfur compounds represented by the formula (wherein n=1) can be expressed as follows: 6R-SH+IO3 - →3R-SS-R+I - +3H2O

[0024] While this reaction is not intended to limit the invention in any way, it does provide a useful and effective guide to the minimum amount of reducing agent required to achieve reduction of all of the iodate present in solution. Based on the stoichiometry above, at least 6 moles of R-SH are required to reduce 1 mole of iodate.

[0025] In one embodiment, the method described in this disclosure for converting iodate to iodide and removing it as iodide can be carried out as a two-step process or a one-step process.

[0026] In alternative embodiments, other variations of methods for converting iodate to iodide and removing it as iodide will be apparent to those skilled in the art. For example, after converting iodate to iodide, the iodide can be removed by precipitating it as silver iodide or by adsorbing it onto silver-impregnated zeolites or onto cerium-, bismuth-, or iron-containing materials.

[0027] In one embodiment, iodate removal is accomplished in a two-step process. First, at least one reducing agent is added at the required concentration. After the reduction period, the second step of the process involves treatment to remove iodide. In a preferred embodiment, approximately 8 moles of reducing species per mole of iodate in solution is a preferred amount, exceeding the minimum amount required above. In a preferred embodiment, the reducing agent is added as an aqueous solution. In other embodiments, the reducing agent may also be added as a solid dissolved in the liquid to be treated. The reduction of iodate with the reducing agent described in this disclosure proceeds rapidly, generally completing within minutes. Regarding iodide removal after the reduction process, in one embodiment, the solution may be exposed to an anion exchange medium effective for iodide removal. In a preferred embodiment, one such medium is Purolite® A532E, a gel polymer resin having a polystyrene structure crosslinked with divinylbenzene.

[0028] In another embodiment, the reducing agent is bound to a solid medium and then contacted with an iodate-containing solution to effectively reduce iodate to iodide, which is then removed as described above. The solid medium can be organic or inorganic. In a preferred embodiment, the reducing agent can be chemically bound to certain anion exchange resins. The reducing agent-treated resin thus becomes an anion exchange resin with free thiol functional groups attached. The attached free thiol functional groups are effective in reducing iodate to iodide. In one embodiment, the reducing agent-treated resin may be used in combination with a strong basic resin, such as Purolite® A532E, which is effective for removing iodide. In another embodiment, the reducing agent-treated resin can be used alone if it is effective for both reducing iodate and removing iodide. In either of these embodiments, iodate removal can be achieved in a one-step process involving contacting a solution with the reducing agent-treated medium, either alone or in combination with a second medium effective for removing iodide.

[0029] In one embodiment, the ion exchange resin is treated with an aqueous solution of sodium thioglycolate at room temperature for at least 12 hours. In another embodiment, the ion exchange resin is treated with other thiol-containing compounds, such as L-cysteine ​​or sodium glutathione. In one embodiment, any process that binds a reducing agent to a solid medium and leaves thiol functional groups free is effective for producing a reducing agent-treated ion exchange resin that can both reduce iodate and remove iodide. When an aqueous solution containing dissolved iodate ions is allowed to contact the reducing agent-treated resin and allowed to stand, the free thiol groups reduce iodate to iodide, which can then be removed by any of the above processes.

[0030] In one embodiment, the iodate removal method described in this disclosure is effective over a wide range of conditions. In some preferred embodiments, several specific conditions have been tested and verified. These are described in the following examples. The examples are not intended to limit the scope of the present invention in any way.

[0031] Having described several embodiments of the present disclosure in detail, it will be apparent that modifications and variations are possible without departing from the scope of the present invention as defined in the appended claims. Furthermore, it should be recognized that all examples in the present disclosure, while illustrating several embodiments of the present invention, are given as non-limiting examples and therefore should not be used as limitations on the various aspects so illustrated. [Example]

[0032] Example 1 Validation of a two-step iodine removal method The effectiveness of using the two-step process described in this disclosure for the removal of iodate was demonstrated using radioactive iodine ( 129 The chemical composition of a low-level radioactive aqueous waste stream containing iodine (I) was experimentally verified using a solution that simulated the radioactive iodine in the Hanford waste stream, which exists primarily as iodide and iodate. In this example, a chemical analog of this waste stream was prepared using non-radioactive iodine, hereafter referred to as Solution 1.

[0033] In this example, Solution 1 was prepared using the following ingredients and approximate concentrations: Na + , SO4 2- , and HCO3 - , approximately 1,500 ppm each; NH4 + , about 100ppm; Cl - , about 50ppm;NO2 - , about 20ppm; NO3 - , about 0.5 ppm;K + , Ca2 + , Al3 + , F - , and PO4 3- , respectively, about 0.05 ppm; Mg 2+ , about 0.005 ppm. Iodate was added as sodium iodate to give an iodine concentration of 5 ppm, which is about 4 x 10 per liter of solution.-5 The pH of this solution was adjusted to about 10.5. L-cysteine ​​was prepared as an approximately 0.1% aqueous solution of L-cysteine, with a final concentration of cysteine ​​of about 3.3 x 10 per liter of solution. -4 L-cysteine ​​was added to Solution 1 so that iodate was reduced to iodide in a ratio of 1 mole to 1 mole. Using this formulation, the solution contained 8 moles of thiol functional groups for every mole of iodate. The solution was mixed manually for approximately 10 minutes and then sampled to measure the amount of iodate and iodide in the solution. Ion chromatography measurements of the solution before and after the addition of L-cysteine ​​indicated that all of the iodate had been reduced to iodide within the measurement capabilities of the instrument.

[0034] This test was repeated after adjusting the pH of Solution 1 using sulfuric acid to several pH values, including 10.5, 8, 7, 4, and 2. At all pHs, L-cysteine ​​was found to be equally effective in reducing all iodate in solution to iodide.

[0035] The test was also repeated using sodium thioglycolate as the reducing agent. Similar results were obtained when sodium thioglycolate was used instead of L-cysteine ​​to reduce iodate to iodide. When sodium thioglycolate was used as the reducing agent, complete reduction of iodate to iodide was also achieved at an 8:1 molar ratio of reducing agent to iodate.

[0036] The effectiveness of the disclosed method for reducing iodate to iodide was further tested using a variation of Solution 1 in which the concentrations of all components except iodate were increased tenfold. The concentration of iodine as iodate was maintained at 5 ppm in the tests using the variation of Solution 1. L-cysteine ​​was used as the reducing agent at the same concentration as in the previous tests. The pH of the solution was adjusted to several pH values, including 10.5, 8, 7, 4, and 2, using sulfuric acid. Complete reduction of iodate to iodide was achieved using the variation of Solution 1 at all pH values ​​tested.

[0037] After converting iodate to iodide in the test solution as described above, the iodide was removed using a strong base anion exchange resin. The resin selected for this step in this example is a complex amine derivative of styrene-divinylbenzene copolymer in the chloride form, which is commercially available under the name A532E and the Purolite® trademark. This resin is one of several ion exchange resins effective for iodide removal. The effectiveness of iodide removal in solution using A532E was tested by adding 0.5 grams of resin to 10 ml of analog solution. The analog solutions included Solution 1 after the reduction step, which originally contained 5 ppm iodine as iodate and was then reduced to iodide as described above, and a variant of Solution 1. The resin-containing solutions were mixed by continuous end-over-end rotation for approximately 1 hour and then sampled to measure the iodate and iodide concentrations by ion chromatography. Complete removal of iodide was confirmed in all cases, within the measurement capabilities of the instrument, as shown in Table 1 below. Please note that in Table 1 and all tables herein, concentrations of all iodine species (iodate or iodide) are reported as equivalent concentrations of iodine to facilitate direct comparison.

[0038] [Table 1]

[0039] This example demonstrates that complete removal of iodate from solutions of complex ionic compositions over a wide pH range of about 2 to 10.5 can be effectively achieved by the two-step method described in this disclosure, which involves the reduction of iodate to iodide followed by removal of iodide by ion exchange.

[0040] Example 2 Validation of a one-step iodine removal method The effectiveness of using the one-step method described in this invention for iodate removal was experimentally verified, also using Solution 1 described in Example 1. In Example 2, iodate was added as sodium iodate to obtain a concentration of 10 ppm iodine in the solution.

[0041] The goal of this example is to use a mixed bed for iodate removal, consisting of a first resin containing chemical groups that reduce iodate to iodide and a second resin capable of removing iodide. The iodate-reducing resin was prepared by chemical treatment to attach thiol-containing chemical groups to polymer beads of anion exchange resin while maintaining the reducing ability of the thiol functional groups. The resin used for binding the reducing agent was a styrene-divinylbenzene gel resin in hydroxide form, which is commercially available under the name MARATHON A and the trademarks MARATHON® and DOWEX®. MARATHON A is now sold under the name Amberlite HPR4800 OH. The iodide-removing resin was A532E, which was also used in Example 1.

[0042] In this example, thiol groups were attached to MARATHON A resin by immersing 0.5 grams of resin in 10 ml of a 0.5% aqueous solution of sodium thioglycolate at room temperature or 37°C for 24 hours under continuous rotation. The resulting material was then rinsed multiple times with an equal volume of sodium hydroxide solution, preferably at a pH in the range of 10-10.5. This treatment is equally effective for attaching thiol functional groups to MARATHON A resin at either room temperature or 37°C. The resulting thiol-functionalized MARATHON A resin was designated M-A_mod.

[0043] Tests were conducted using 10 ml of Solution 1, with sodium iodate added to achieve a 10 ppm iodine concentration, along with approximately 0.4 grams of the iodate-reducing resin prepared above and 0.5 grams of A532E resin. The solution containing the resin mixture was mixed by continuous end-over-end rotation for approximately 1 hour, then sampled and analyzed for iodine by inductively coupled plasma mass spectrometry (ICPMS). ICPMS measures total iodine regardless of speciation. The iodine concentration before resin addition was also measured. Complete removal of the iodine originally added as iodate was demonstrated, as shown in Table 2 below.

[0044] [Table 2]

[0045] This example demonstrates that complete removal of iodate from a solution of complex ionic composition can be effectively achieved by the one-step method described in this disclosure using a mixed bed resin composed of an anion resin with pendant thiol functional groups that reduce iodate to iodide and an anion resin capable of removing iodide by ion exchange.

[0046] Example 3 Validation of a two-step iodine removal method for removing mixtures of non-radioactive and radioactive iodine The effectiveness of using the two-step method described in this disclosure for the removal of iodate from aqueous solutions was experimentally verified in a manner similar to that described in Example 1, except that a solution containing a mixture of non-radioactive and radioactive iodine was used. The use of radioactive iodine demonstrates that the present invention is applicable to the removal of radioactive iodate, even at very low concentrations of radioactive iodine. These tests included the use of a short-lived radioisotope of iodine with a half-life of 13.2 hours. 123 I was used. This isotope is used in medical applications and is commercially available as an aqueous solution of sodium iodide. For this study, the iodine had to be present in the form of iodate, so the material was treated to convert iodide to iodate. The starting solution for converting iodide to iodate had a stable to radioactive isotope ratio of at least 10. 6The sodium iodide solution was prepared as follows: The iodide in the starting solution was converted to iodate by first buffering the iodide solution with sodium acetate and acetic acid, and then adding sodium chlorite at the appropriate stoichiometric ratio (6 equivalents of sodium chlorite per mole of sodium iodide). This conversion was confirmed by adding the converted iodate solution to Solution 1 and then contacting this solution with Purolite® A532E for 1 hour. The A532E resin removes iodide from solution much more effectively than iodate, therefore, a low degree of iodine removal indicates that the iodine was present as iodate. In these tests, approximately 90% of the starting radioactivity was still present at the end of the test, indicating that most, if not all, of the iodine in the solution was present as iodate, as intended.

[0047] In this example, samples were prepared using 10 ml of Solution 1, a solution containing converted radioactive iodate, with a total iodine concentration of nominal approximately 0.2 ppm and 1 ppm and a radioactivity of nominal approximately 0.3 or 1.5 μCi / ml. As in Example 1, L-cysteine ​​was first added to the iodate-containing solution to reduce the iodate to iodide. This solution was then contacted with Purolite® A532E for 1 hour to remove iodide from the solution. The effectiveness of iodate removal was assessed by comparing the radioactivity in the solution, measured by gamma spectroscopy, before and after treatment with L-cysteine ​​and Purolite® A532E. The iodine concentration in the solution before and after treatment was also measured by ICPMS. Both gamma spectroscopy and ICPMS analysis gave similar results, indicating that under the conditions described in this example, up to 85% of the iodate in solution was removed, as shown in Tables 3 and 4 below.

[0048] This example demonstrates that substantial removal of radioactive iodate from solutions of complex ionic compositions can be effectively achieved by the two-step method described in the present disclosure, which involves reducing iodate to iodide, followed by removal of the iodide by ion exchange.

[0049] [Table 3]

[0050] [Table 4]

[0051] Example 4 Validation of a one-step iodine removal method for removing mixtures of non-radioactive and radioactive iodine The effectiveness of using the one-step method described in this invention for the removal of iodate from aqueous solutions was further verified in a manner similar to that described in Example 2, except that, as in Example 3, a solution containing a mixture of non-radioactive and radioactive iodine was used. A modified version of the hydroxyl form of DOWEX® MARATHON A with a bound reducing agent was prepared as described in Example 2 and used to test the removal of iodate from solution.

[0052] For these tests, samples were prepared using 10 ml of Solution 1, a solution of converted radioiodate salts, with a final iodine concentration of approximately 0.2 ppm, 1 ppm, or 10 ppm nominal, and a radioactivity of approximately 0.3 μCi / ml, 1.5 μCi / ml, or 15 μCi / ml nominal. These tests were performed by first adding approximately 0.15 grams of weighed modified MARATHON A resin (M-A_mod-p) to each sample after partial removal of water and rotating the mixture end-over-end for one hour. A sample of the solution was then taken and analyzed by ICPMS and gamma spectroscopy. Next, 0.1 grams of Purolite® A532E resin was added, and the mixture was rotated end-over-end for an additional hour. After treatment with the A532E resin, a sample of the solution was taken and analyzed by ICPMS and gamma spectroscopy. The effectiveness of these treatments for iodate removal was measured by gamma spectroscopy of the solution before and after treatment. 123The results were evaluated by comparing the iodate activity levels. Evaluation was also performed by comparing the concentrations before and after treatment as measured by ICPMS. Measurements of solutions taken after treatment with M-A_mod-p indicate that when modified MARATHON A resin was used alone, iodate removal was greater than about 85%, as measured by both ICPMS and gamma spectroscopy. Measurements of solutions taken after treatment with A532E demonstrated that the combination of modified MARATHON A resin and Purolite® A532E resin demonstrated greater than 95% iodate removal, as shown by both gamma spectroscopy and ICPMS results in Tables 5 and 6.

[0053] [Table 5]

[0054] [Table 6]

[0055] Another test was performed using 10 ml of Solution 1 spiked with converted radioactive iodate solution to a nominal total iodine concentration of approximately 10 ppb and a nominal activity of approximately 0.5 μCi / ml. Approximately 0.06 grams of modified MARATHON A resin (M-A_mod-d), weighed after being placed on filter paper and allowed to air dry, was added to the iodate-spiked Solution 1 sample, which was then rotated end-over-end for 1 hour. For comparison purposes, two control tests were also performed: one using a Solution 1 sample spiked with 10 ppb / 0.5 μCi / ml iodate and 0.1 gram of unmodified MARATHON A resin, and the other using a Solution 1 sample spiked with 10 ppb / 0.5 μCi / ml iodide and 0.1 gram of unmodified MARATHON A resin. A comparative test was conducted to demonstrate that the iodine in Solution 1, plus the iodate solution used in the tests with the modified resin, was present in the form of iodate. For iodate confirmation, unmodified MARATHON A resin was used in place of Purolite® A532E resin because it has a higher selectivity for iodide, which was particularly useful at the low iodine concentration (10 ppb) of these tests. The tests in this example were performed to determine the iodine content of the solution measured by gamma spectroscopy before and after resin treatment. 123 The radioactivity was assessed by comparing the iodide removal capacity of the unmodified resin with that of the iodate-containing solution. The results showed that approximately 35% of the radioactivity was removed using the unmodified resin when iodine was present as iodate. In comparison, more than 80% of the radioactivity was removed by the unmodified resin when iodine was present as iodide. More than 80% of the radioactivity was removed using the modified resin with the iodate-containing solution, which was comparable to the iodide removal capacity of the unmodified resin, as shown in Table 7.

[0056] [Table 7]

[0057] This example demonstrates that substantial removal of iodate present as a mixture of non-radioactive and radioactive iodate can be effectively achieved by the one-step process described in this invention, which uses either (i) an anion resin having pendant thiol functional groups that reduce iodate to iodide and ion exchange sites that remove iodide by ion exchange, or (ii) a mixed bed composed of an anion resin having pendant thiol functional groups that reduce iodate to iodide and another anion resin capable of removing iodide by ion exchange.

[0058] Example 5 Verification of a method for removing iodine from seawater This example demonstrates the effectiveness of the iodate removal method described in this disclosure when iodate is present in seawater. Carolina® Seawater obtained from Carolina Biological Supply Company was used to conduct the tests. Approximately 4 x 10 iodates per liter of seawater were present. -5 Iodate was added to seawater as sodium iodate to achieve an iodine concentration of 5 ppm, equivalent to 100 moles of iodate. Both iodate removal methods described in this disclosure were tested in this example. In tests using the two-step method, a 10 ml sample of iodate-spiked seawater was first treated with L-cysteine ​​to reduce the iodate to iodide, and then treated with 0.1 grams of Purolite® A532E by end-over-end rotation for 1 hour to remove the iodide from the solution. In tests using the one-step method, approximately 4 x 10 iodate per liter of seawater was removed. -5 A 10 ml sample of seawater spiked with iodate to a concentration of 5 ppm iodine, equivalent to molar iodate, was treated with approximately 0.13 grams of undried, weighed modified MARATHON A resin (M-A_mod) prepared as in Example 2 by end-over-end rotation for 1 hour, followed by the addition of 0.1 grams of Purolite® A532E and an additional hour of end-over-end rotation. The percentage of iodate removed from the seawater was approximately 60% using the two-step method and over 90% using the one-step method. The test results are shown in Table 8.

[0059] [Table 8]

[0060] This example demonstrates that substantial removal of iodate present in seawater can be effectively achieved by both the two-step and one-step methods described in this disclosure, both of which involve reducing iodate to iodide with thiol chemical groups, followed by removal of the iodide by ion exchange.

[0061] Example 6 Verification of iodine removal methods from groundwater This example demonstrates the effectiveness of the iodate removal method described in this disclosure when iodate is present in groundwater. The groundwater selected for these tests is that associated with the Yucca Mountain high-level nuclear waste repository in the United States. The solution used in these tests is an analog of EJ-13, a groundwater preparation made using groundwater from the USGS J-13 well that was treated by equilibration at 90°C with crushed Topopah Spring tuff from the Yucca Mountain site. Iodate was present at approximately 4 x 10 iodate per liter of EJ-13 solution, as sodium iodate. -5The EJ-13 analog was spiked with iodate to achieve a 5 ppm iodine concentration, equivalent to 100 ppm iodate per mole. As in Example 5, this example utilized both the two-step and one-step methods of iodate removal described in this disclosure. In a test using the two-step method, a 10 ml sample of the iodate-spiked EJ-13 analog was first treated with L-cysteine ​​to reduce the iodate to iodide, and then treated with 0.1 grams of Purolite® A532E by end-over-end rotation for 1 hour to remove the iodide from the solution. In a test using the one-step method, a 10 ml sample of the iodate-spiked EJ-13 analog was treated with approximately 0.13 grams of undried, weighed modified MARATHON A resin (M-A_mod) prepared as in Example 2 by end-over-end rotation for 1 hour, followed by the addition of 0.1 grams of Purolite® A532E and further treatment by end-over-end rotation for 1 hour. Iodate removal from the EJ-13 simulant was approximately 80% using the two-step method and greater than 95% using the one-step method, as shown in Table 9.

[0062] [Table 9]

[0063] This example demonstrates that substantial removal of iodate present in groundwater solutions can be effectively achieved by either the two-step or one-step method described in this invention, both of which involve the reduction of iodate to iodide by thiol chemical groups, followed by removal of the iodide by ion exchange.

[0064] It is intended that the invention not be limited to the particular embodiments disclosed herein contemplated for carrying out this invention, but rather that the invention will include all embodiments falling within the scope of the appended claims.

[0065] All documents, patents, journal articles, and other materials cited in this application are hereby incorporated by reference.

[0066] The many features and advantages of the present invention are apparent from the detailed specification, and it is, therefore, intended by the appended claims to cover all such features and advantages of the present invention that fall within the true spirit and scope of the invention. Further, because numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and therefore, all suitable modifications and equivalents are intended to be within the scope of the present invention.

Claims

1. 1. A method for removing iodate from an aqueous liquid, comprising: (i) adding a water-soluble compound containing a thiol group; (ii) removing iodide; Including, The thiol group converts iodate to iodide, The method, wherein the water-soluble compound containing a thiol group is L-cysteine ​​or an enantiomer thereof, or a racemic mixture thereof.

2. 10. The method of claim 1, wherein the iodide is removed by at least one method selected from the group consisting of adsorption, ion exchange, and precipitation.

3. 3. The method of claim 1 or 2, wherein the aqueous liquid comprises a radioactive iodine species.

4. 4. The method of claim 1, wherein the water-soluble compound containing a thiol group is a thioglycolate.

5. 5. The method of claim 4, wherein at least one of the water-soluble compounds containing a thiol group is selected from the group consisting of sodium thioglycolate and thioglycolic acid.

6. 6. The method of claim 1, wherein at least one of the water-soluble compounds containing a thiol group is thioglutathione.

7. 7. The method of any one of claims 1 to 6, wherein the concentration of iodate is in the range of 10 ppb to 10 ppm.

8. 8. The method of any one of claims 1 to 7, wherein the aqueous liquid has a pH in the range of 1 to 11.

9. 9. The method of any one of claims 1 to 8, wherein the aqueous liquid is an aqueous waste stream.

10. 10. The method of claim 1, wherein the aqueous liquid is seawater.

11. 11. The method of any one of claims 1 to 10, wherein the aqueous liquid is groundwater.

12. 12. The method of claim 1, wherein the molar ratio of water-soluble compound to iodate is at least 6.

13. 13. The method of any one of claims 1 to 12, wherein the molar ratio of water-soluble compound to iodate is in the range of 8 to 10.

14. 14. The method of any one of claims 2 to 13, wherein iodide is removed by ion exchange using a strong base anion exchange resin.

15. 15. The method of any one of claims 2 to 14, wherein the iodide is removed by precipitating it as silver iodide.

16. 16. The method of any one of claims 2 to 15, wherein the iodide is removed by adsorption onto a silver-impregnated zeolite or onto a cerium-, bismuth-, or iron-containing material.

17. 17. The method of any one of claims 1 to 16, wherein the aqueous liquid contains sodium at a concentration of up to 12,000 ppm.

18. 18. The method of any one of claims 1 to 17, wherein the aqueous liquid contains chlorine at a concentration of up to 20,000 ppm.

19. 19. The method of any one of claims 1 to 18, wherein the aqueous liquid contains at least one chemical group selected from the group consisting of bicarbonate and sulfate at a concentration of up to 15,000 ppm.

20. 20. The method of any one of claims 1 to 19, wherein the aqueous liquid contains ammonium at a concentration of up to about 1000 ppm.

21. 21. The method of any one of claims 1 to 20, wherein the aqueous liquid contains nitrite at a concentration of up to 200 ppm.

22. 22. The method of any one of claims 1 to 21, wherein the aqueous liquid contains nitrates at a concentration of up to 5 ppm.

23. 23. The method of any one of claims 1 to 22, wherein the aqueous liquid contains at least one chemical selected from the group consisting of potassium, calcium, aluminum, fluoride, phosphate, and magnesium having a concentration of up to 0.5 ppm.

24. 1. A method for removing iodate from an aqueous liquid, the method comprising contacting the aqueous liquid with a material for converting iodate in aqueous solution to iodide, the material comprising a solid substrate to which a thiol group-containing compound is bound.

25. 1. A method for removing iodate from an aqueous liquid, comprising contacting the aqueous liquid with a mixed bed comprising: (i) a material for converting iodate in an aqueous solution to iodide, the material comprising a solid substrate to which a thiol group-containing compound is bound; and (ii) a medium capable of removing iodide by adsorption or ion exchange.

26. 1. A method for removing iodate from an aqueous liquid, comprising contacting the aqueous liquid with a first bed comprising a material for converting iodate in an aqueous solution to iodide, the material comprising a solid substrate to which a thiol group-containing compound is bound, and then contacting the aqueous liquid with a second bed comprising a medium capable of removing iodide by adsorption or ion exchange.

27. ​​The method described in any one of claims 24 to 26, wherein the thiol group-containing compound is at least one selected from the group consisting of L-cysteine; L-cysteine ​​enantiomers; L-cysteine ​​racemic mixture; thioglutathione; or at least one thioglycolate selected from the group consisting of sodium thioglycolate and thioglycolic acid.

28. The method of claim 24, wherein the solid substrate is an ion exchange material.

29. The method of claim 24, wherein the solid substrate is an anion exchange material that absorbs iodide.

30. The method of any one of claims 24 to 26, wherein the solid substrate is a styrene-divinylbenzene ion exchange resin.

31. The method of any one of claims 24 to 26, wherein the solid substrate is aluminum oxide.

32. The method of any one of claims 24 to 26, wherein the solid substrate is silicon oxide.

33. The method of any one of claims 24 to 26, wherein the material is prepared by contacting the solid substrate with an aqueous solution of the thiol group-containing compound and then rinsing.

34. The method of any one of claims 24 to 26, wherein the material is prepared by contacting MARATHON A ion exchange resin or AmberLite HPR4800 OH ion exchange resin with an aqueous solution of at least one thiol-containing compound selected from the group consisting of L-cysteine; L-cysteine ​​enantiomers; L-cysteine ​​racemic mixture; thioglutathione; or at least one thioglycolate selected from the group consisting of sodium thioglycolate and thioglycolic acid, followed by rinsing.

Images