Iodine elution method, iodine-containing material production method, and reaction apparatus

Abstract

To provide a method for eluting iodine, which can more efficiently elute iodine. [Solution] A method for eluting iodine from iodine-adsorbed activated carbon obtained by adsorbing iodine to activated carbon, the method comprising an iodine elution step of contacting the iodine-adsorbed activated carbon with an eluent having a pH of 13 or higher to elute iodine from the iodine-adsorbed activated carbon, the iodine elution step being carried out at 0 to 40°C.

Description

[Technical Field]

[0001] The present disclosure relates to a method for eluting iodine, a method for producing an iodine-containing material, and a reactor. [Background technology]

[0002] Iodine is a valuable element used in various fields, such as pharmaceuticals, contrast media, materials for electronic devices, and reaction catalysts. Therefore, it is common to recover iodine-adsorbed activated carbon obtained by adsorbing iodine contained in seawater, brine, industrial wastewater, etc. onto activated carbon, and then eluting the iodine adsorbed on the iodine-adsorbed activated carbon from the activated carbon. For example, Patent Document 1 below discloses a method for eluting iodine by boiling the iodine-adsorbed activated carbon with sodium hydroxide or sodium carbonate. Patent Document 2 below also discloses a method for eluting iodine from iodine-adsorbed activated carbon by passing an eluent through the iodine-adsorbed activated carbon and ending the elution when the ORP after elution reaches 180 mV or less, pH 1.7 or higher, and the unreacted rate of the reducing agent reaches 60% or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 01-294502 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-001634 Summary of the Invention [Problem to be solved by the invention]

[0004] However, both of the methods described in Patent Document 1 and Patent Document 2 still have room for improvement in terms of the efficiency of iodine elution.

[0005] The present disclosure has been made in view of the above circumstances, and aims to provide a method for eluting iodine that can more efficiently elute iodine. Another aim of the present disclosure is to provide a method for producing an iodine-containing substance, and a reaction apparatus that can more efficiently obtain an iodine-containing substance. [Means for solving the problem]

[0006] The present disclosure includes the following exemplary embodiments. [1] A method for eluting iodine from iodine-adsorbed activated carbon obtained by adsorbing iodine onto activated carbon, comprising: an iodine elution step of contacting the iodine-adsorbed activated carbon with an eluent having a pH of 13 or more to elute the iodine from the iodine-adsorbed activated carbon; The iodine elution method, wherein the iodine elution step is carried out at 0 to 40°C. [2] The iodine elution method according to [1], wherein a reducing agent is added in the iodine elution step. [3] The method for eluting iodine according to [1] or [2], wherein in the iodine elution step, the iodine-adsorbed activated carbon and the eluent are stirred by blowing in a gas or by circulating the eluent. [4] The method for eluting iodine according to any one of [1] to [3], wherein the pH of the eluent after the iodine elution step is 13 or higher. [5] The method for iodine elution according to any one of [1] to [4], wherein in the iodine elution step, the content of hydroxide ions contained in the eluent is 1 to 6 equivalents relative to the amount of hydroxide ions consumed by the substance adsorbed on the activated carbon. [6] A method for producing a substance containing iodine, comprising: an iodine elution step of contacting the iodine-adsorbed activated carbon obtained by adsorbing iodine onto activated carbon with an eluent having a pH of 13 or more to elute the iodine from the iodine-adsorbed activated carbon; and a step of recovering the iodine-containing substance eluted in the iodine elution step, The production method, wherein the iodine elution step is carried out at 0 to 40°C. [7] a reaction vessel capable of containing a powder and a liquid; A reaction apparatus comprising at least one of a gas introduction means connected to the reaction tank so as to be able to stir the powder and the liquid contained in the reaction tank by blowing a gas into the reaction tank, and a liquid circulation means connected to the reaction tank so as to be able to stir the powder and the liquid contained in the reaction tank by circulating the liquid in the reaction tank. [Effects of the Invention]

[0007] According to the present disclosure, there is provided a method for eluting iodine, which can more efficiently elute iodine. Also, according to the present disclosure, there is provided a method for producing a substance containing iodine, which can more efficiently obtain a substance containing iodine, and a reaction apparatus. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating a reaction apparatus according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] An iodine elution method according to one embodiment of the present disclosure is a method for eluting iodine from iodine-adsorbed activated carbon obtained by adsorbing iodine to activated carbon, and includes an iodine elution step of bringing the iodine-adsorbed activated carbon into contact with an eluent having a pH of 13 or higher to elute iodine, and the iodine elution step is carried out at 0 to 40°C. Examples of iodine-adsorbing activated carbon include iodine-adsorbing activated carbon obtained by oxidizing iodide in brine and adsorbing elemental iodine onto activated carbon; iodine-adsorbing activated carbon obtained by adsorbing iodine in an iodine-containing process solution or wastewater generated in a production process of iodine or an iodine compound onto activated carbon; iodine-adsorbing activated carbon obtained by adsorbing iodine in a polarizing film wastewater or wastewater after an organic iodine reaction onto activated carbon; and iodine-adsorbing activated carbon obtained by adsorbing iodine used as a catalyst onto activated carbon. The activated carbon is not particularly limited as long as it can adhere to iodine, and examples of activated carbon include coconut shells, coal, and charcoal.

[0010] Methods for contacting the iodine-adsorbed activated carbon with an eluent having a pH of 13 or higher include adding the eluent to the iodine-adsorbed activated carbon and immersing the iodine-adsorbed activated carbon in the eluent. In the method of this embodiment, the pH of the eluent may be 13 or higher, and may be 13.5 or higher. When the pH of the eluent is 13 or higher, iodine can be eluted efficiently. The pH of the eluent referred to here refers to the pH of the eluent immediately before contacting it with the iodine-adsorbed activated carbon. The pH of the eluent is, for example, 15 or less, and preferably 14.5 or less. When the pH of the eluent is 14.5 or less, when the alkali is washed off by water until the pH is lowered, the time required for this water washing operation can be shortened. During the iodine elution step, additional eluent may be added. During the iodine elution step, the pH of the eluent may be maintained at 13 or higher. In this case, the effect of efficiently eluting iodine can be sustained. Furthermore, the elution proceeds more quickly and the final elution rate tends to be higher. Furthermore, since the amount of eluent required for elution is smaller than when the pH is lower than 13, it is possible to downsize the equipment required for elution, thereby reducing equipment costs. The pH of the eluent after elution may be 13 or higher. Here, "after elution" refers to the time after immersion in the eluent has stopped eluting iodine.

[0011] The eluent may be any liquid containing hydroxide ions, and may be prepared by adding an alkaline substance such as a hydroxide salt to water. Examples of the alkaline substance include hydroxide salts, such as alkali metal hydroxide salts such as sodium hydroxide and potassium hydroxide. The temperature at which the iodine elution step is carried out is 0 to 40°C. Here, the temperature specifically refers to the temperature of the eluent. When the temperature is 0°C or higher, iodine can be eluted efficiently. When the temperature is 40°C or lower, iodine can also be eluted efficiently. Furthermore, carrying out the iodine elution step at a temperature of 0 to 40°C, which is close to room temperature, is environmentally friendly because it eliminates the need for heating or cooling. The temperature is preferably 5 to 40°C, and more preferably 10 to 40°C.

[0012] In the iodine elution step, the content of hydroxide ions contained in the eluent is preferably 1 to 6 equivalents relative to the amount of hydroxide ions consumed by the substance adsorbed on the activated carbon, which allows iodine to be eluted more efficiently. Here, the hydroxide ion content is the total amount of hydroxide ions contained in the eluent used in the iodine elution step. Substances adsorbed by activated carbon include iodine, organic substances, acid components, and organic iodines. Examples of organic substances include polyvinyl alcohol (PVA). Examples of acid components include sulfuric acid and hydrochloric acid. Examples of organic iodines include iodobenzene and diiodomethane. "Consumed hydroxide ions" refers to the hydroxide ions consumed, and the "amount of consumed hydroxide ions" can be determined by contacting iodine-adsorbed activated carbon with an eluent containing excess alkali (e.g., NaOH) and measuring in advance the amount of hydroxide ions consumed when iodine is eluted from the iodine-adsorbed activated carbon. The content of hydroxide ions in the eluent is more preferably 1.2 to 2.5 equivalents relative to the amount of hydroxide ions consumed by the substance adsorbed on the activated carbon, which allows iodine to be eluted more efficiently. In the iodine elution step, the content of hydroxide ions contained in the eluate may be 1 to 9 equivalents relative to the amount of iodine atoms adsorbed on the activated carbon.

[0013] In the method of this embodiment, a reducing agent may be added in the iodine elution step. When the reducing agent is added, iodate ions (IO3 - ) is reduced by a reducing agent to become iodide ions, and the form of iodine is unified, which facilitates subsequent processing. The reducing agent may be added in a form contained in an aqueous solution separate from the eluent, or in a form contained in the eluent.

[0014] The reducing agent is not particularly limited, but examples thereof include sulfur dioxide, sulfurous acid (H2SO3), sulfites, bisulfites, hydrazine, oxalic acid, formic acid, and hydrogen peroxide. The sulfites and bisulfites may be alkali metal salts, alkaline earth metal salts, etc.

[0015] The amount of reducing agent to be added is not particularly limited, but it is necessary to add the reducing agent in an amount that is sufficient to reduce the iodate ions (IO3 - ) may be determined depending on the amount of IO3 produced. - The amount of iodine may vary depending on the conditions of the iodine elution step. Therefore, the amount of iodine produced by a preliminary run without adding a reducing agent is measured. - The amount of reducing agent to be added may be determined by measuring the amount of IO3 produced. - I - The SO3 required for the reaction in Equation 2 below to convert 2- The amount may be 0.3 to 3 equivalents or 0.5 to 2 equivalents relative to 1 equivalent of the hydroxyl group. IO3 - +3SO3 2- →I - +3SO4 2- (Reaction Scheme 2)

[0016] The method of this embodiment may further include a step of recovering a substance containing iodine (hereinafter also referred to as an "iodine-containing substance") after the iodine elution step. In this case, the method of this embodiment becomes a method for producing an iodine-containing substance. Examples of the iodine-containing substance include molecular iodine (I), hydrogen iodide, and iodide salts such as alkali metal iodides and alkaline earth metal iodides.

[0017] The iodine adsorbed to the activated carbon is eluted in the eluent as, for example, an iodine compound. For example, when the eluent contains a hydroxide salt, iodine is eluted as an iodide salt, which is a salt with a cation of the hydroxide salt. After recovery, the iodine compound may be purified and used as is, or may be converted into another iodine-containing substance.

[0018] The iodine compound may be used to produce molecular iodine. For example, if the iodine compound is a compound containing iodide ions, such as an iodide salt, the iodide ions can be oxidized with an oxidizing agent to produce molecular iodine. Examples of the oxidizing agent include hypochlorous acid, sodium hypochlorite, calcium hypochlorite, and other hypochlorites.

[0019] The iodine compound may be converted into another iodine compound, for example. Examples of the converted iodine compound include hydrogen iodide and iodide salts. These compounds can be obtained by exchanging the cation contained in the iodide salt obtained in the iodine elution step.

[0020] The recovered activated carbon is washed with water or the like and then reused. A drying step may be carried out before reuse.

[0021] In the iodine elution step, the iodine-adsorbed activated carbon and the eluent may be stirred by blowing a gas therethrough or by circulating the eluent.

[0022] In the iodine elution step, if the iodine-adsorbed activated carbon and the eluent are stirred by blowing in a gas or circulating the eluent, the iodine-adsorbed activated carbon can be prevented from being pulverized and finely divided. If the iodine-adsorbed activated carbon is pulverized, it may be difficult to handle. A stirring means for mechanically stirring the eluent, such as a magnetic stirrer or a propeller, may or may not be used, but it is preferable not to use one. In this case, no shear force or pressure is applied to the iodine-adsorbed activated carbon, preventing the iodine-adsorbed activated carbon from being pulverized.

[0023] In the iodine elution step, both of blowing gas into the iodine-adsorbed activated carbon and circulating the eluent may be performed when stirring the iodine-adsorbed activated carbon and eluent.

[0024] The gas to be blown may be a gas containing an inert gas such as nitrogen or argon, or may be air. The gas may be blown by an air pump or the like. The circulation of the eluent may be performed by a circulation pump or the like.

[0025] The iodine elution method of this embodiment may be performed using a reaction apparatus including a reaction vessel capable of accommodating a powder (iodine-adsorbed activated carbon) and a liquid (eluent), and a stirring means for stirring the powder and the liquid. The stirring means may be a gas introduction means connected to the reaction vessel so as to be able to stir the powder and liquid contained in the reaction vessel by blowing a gas into the reaction vessel, or a liquid circulation means connected to the reaction vessel so as to be able to stir the powder and liquid contained in the reaction vessel by circulating the liquid in the reaction vessel. The stirring means may be equipped with both a gas introduction means and a liquid circulation means.

[0026] Fig. 1 is a schematic diagram showing a reaction apparatus according to this embodiment. The reaction apparatus 100 shown in Fig. 1 includes a reaction tank 10 capable of accommodating iodine-adsorbed activated carbon and an eluent 40, a circulation pump 20, and a chemical tank 30. The reaction apparatus 100 is an apparatus that causes iodine in the iodine-adsorbed activated carbon to react with alkali (hydroxide ions) in the eluent 40, thereby eluting iodine from the iodine-adsorbed activated carbon. The reaction apparatus 100 includes the reaction tank 10 capable of accommodating powder (iodine-adsorbed activated carbon) and the eluent 40, the circulation pump 20, and the chemical tank 30. The reaction apparatus 100 includes a first pipe L1 for discharging the eluent 40 and the iodine-adsorbed activated carbon contained in the reaction tank 10, a circulation pump 20 provided in the first pipe L1, and a second pipe L2 branching off from the first pipe L1 downstream of the circulation pump 20 and returning the eluent to the reaction tank 10. In this embodiment, the first pipe L1, the circulation pump 20, and the second pipe L2 constitute a liquid circulation means. According to the reaction apparatus 100, when the circulation pump 20 is operated, the iodine-adsorbed activated carbon is sucked out together with the eluent 40 from the reaction tank 10 and returned to the reaction tank 10 through the first pipe L1 and the second pipe L2. In this way, the iodine-adsorbed activated carbon is agitated by the flow of the eluent 40 formed by the circulation pump (liquid circulation means) 20. As a result, the eluent 40 can easily permeate the iodine-adsorbed activated carbon, and the iodine adsorbed to the activated carbon can be more sufficiently eluted.

[0027] The chemical tank 30 is a tank for preparing the eluent 40. A substance containing hydroxide ions (e.g., NaOH) and a reducing agent (e.g., NaHSO3) are supplied to the chemical tank 30. The chemical tank 30 and the reaction vessel 10 are connected by a third pipe L3, and a pump 50 is provided to the third pipe L3. The pump 50 supplies the eluent 40 in the chemical tank 30 to the reaction vessel 10 through the third pipe L3. The supply of the eluent 40 may be automated. In addition, a fourth pipe L4 that returns the eluent to the chemical tank 30 may be provided to the third pipe L3. The reaction apparatus 100 does not necessarily have to include the chemical tank 30 .

[0028] A liquid transfer pipe (not shown) for recovering the eluent 40 may be connected to the reaction vessel 10. Because there is a risk of the iodine-adsorbed activated carbon clogging the liquid transfer pipe when it is sucked in, the liquid transfer pipe may be equipped with a filter inside. Examples of filters include mesh filters, and the mesh size can be selected depending on the size of the activated carbon used. The liquid transfer pipe may have a suction port located near the bottom of the reaction vessel 10 so that almost the entire amount of liquid can be recovered. The first pipe L1 may also serve as the liquid transfer pipe. In this case, a filter may be attached to the suction port of the first pipe L1 to prevent the iodine-adsorbed activated carbon from being sucked into the first pipe L1, thereby circulating only the eluent 40 through the first pipe L1 and the second pipe L2. This method also allows the eluent 40 and the iodine-adsorbed activated carbon to be stirred. The reaction apparatus 100 may further include a heater provided in the reaction vessel 10 and a temperature regulator that adjusts the temperature of the eluent by the heater. In this case, the temperature of the eluent 40 in the reaction vessel 10 can be controlled to 10 to 40°C by operating the heater and controlling the temperature with the temperature regulator as needed. The reaction apparatus 100 may further include a storage tank for storing pure water (soft water) and a water supply pipe connecting the storage tank to the reaction tank 10. In this case, it is possible to supply pure water from the storage tank through the water supply pipe as needed, and adjust the pH of the eluent 40.

[0029] The reaction apparatus 100 may be provided with a gas introduction means such as an air pump as an agitation means instead of the liquid circulation means described above, or may be provided with both the circulation pump 20 and the gas introduction means. The circulation pump 20 may be configured to suck air together with the eluent 40 from an intake port and discharge both the air and the eluent 40 from an outlet port.

[0030] When an elution tower is used to elute iodine from iodine-adsorbed activated carbon, the pressure inside the tower increases as the amount of iodine-adsorbed activated carbon introduced increases. As a result, a high-power pump and tower pressure resistance are required to feed the eluent, resulting in high equipment costs. On the other hand, if an open system is used, the eluent does not sufficiently contact or penetrate the iodine-adsorbed activated carbon in a single pass under atmospheric pressure, resulting in a deterioration in chemical consumption. Furthermore, if stirring is performed to increase contact, the flowing iodine-adsorbed activated carbon may be transferred to the next process, or the iodine-adsorbed activated carbon may be pulverized by mechanical stirring using a stirrer or the like. In contrast, the reaction apparatus 100 of this embodiment allows efficient elution of iodine from iodine-adsorbed activated carbon without pulverizing the iodine-adsorbed activated carbon. [Example]

[0031] The contents of the present disclosure will be described below with reference to examples, but the present disclosure is not limited to the following examples.

[0032] (Comparative Example 1) In a 2 L glass sealed container, a waste activated carbon sample (0.5 L) was immersed in an eluent (pH 3.19) consisting of diluted sodium bisulfite aqueous solution (1.25 L), and iodine was eluted from the iodine-adsorbed activated carbon by gently stirring the eluent with a stirrer. The eluent was kept at room temperature (20°C). The waste activated carbon sample used was activated carbon that had adsorbed waste iodine generated in the iodine-using process. The eluent was sampled and analyzed at the intervals shown in Table 1. Specifically, the SO2 concentration in the eluent, the density of the eluent, the iodine concentration in the eluent, the iodine concentration in the activated carbon (AC), the pH of the eluent, and the oxidation-reduction potential (ORP, based on a silver-silver chloride electrode) were determined by analysis. The results are shown in Table 1. The SO2 concentration was measured by oxidation-reduction titration (analysis method based on JIS K8059 SO2). The unit of SO2 concentration is "mass%" and was calculated based on the following formula. SO2 concentration (mass%) = 100 x SO2 amount (g) / eluent amount (g) The density of the eluent was calculated based on the mass of a fixed amount (5 mL) taken out of the eluent. The iodine concentration in the eluent was analyzed using ion chromatography (manufactured by Thermo Fisher Scientific Co., Ltd.). Here, the iodine concentration refers to the concentration of iodide ions (I - ) and iodate ion (IO3 - ) concentration. - The concentration is converted to the amount of iodine contained. However, in Comparative Example 1, iodine is eluted as iodide ions according to the following reaction formula, and only I exists in the eluent. - Therefore, the iodine concentration is calculated by the iodide ion concentration (I - ) I2+SO2+2H2O→2HI+H2SO4 The iodine concentration in activated carbon (AC) (the iodine concentration remaining in activated carbon after elution) was analyzed by combustion ion chromatography (manufactured by DKK-TOA Corporation). The iodine concentration in activated carbon (AC) was determined by the iodide ion (I - ) and iodate ion (IO3 - ) concentration. - The concentration is converted into the amount of iodine contained. However, in Comparative Example 1, only iodine remained in the activated carbon. - Therefore, the iodine concentration is calculated by the iodide ion concentration (I - ) The pH and oxidation-reduction potential of the eluent were measured using a pH / ORP meter, model F-73, manufactured by Horiba, Ltd.

[0033] [Table 1]

[0034] After immersing the waste activated carbon sample in the aqueous solution for 4 hours, it was confirmed that the elution of iodine had stopped, and then the activated carbon and the eluent were separated by suction filtration. The filtered activated carbon was washed five times with pure water (0.4 L) and gently stirred, followed by suction filtration. The iodine concentration remaining in the activated carbon before and after elution was analyzed by combustion ion chromatography. The iodine concentration remaining in the activated carbon before elution was 362.8 g I / L-AC, and the iodine concentration remaining in the activated carbon after elution was 54.8 g I / L-AC. Therefore, 15% by mass of iodine remained in the activated carbon, and the iodine elution rate was 85% by mass. In the acidic solution containing only sodium bisulfite, the elution rate was less than 90% by mass.

[0035] Example 1 In a sealed container, a waste activated carbon sample (0.5 L) was immersed as iodine-adsorbed activated carbon in an eluent (1.25 L) prepared in advance at pH 13.7 by mixing 48% by mass NaOH solution and 6% by mass Na bisulfite solution, and a stirrer was placed in the eluent to gently stir the mixture, thereby eluting iodine from the iodine-adsorbed activated carbon. The eluent was kept at room temperature (20°C). The waste activated carbon sample used was activated carbon that had adsorbed waste iodine generated in the iodine-using process. The eluent was sampled and analyzed at the intervals shown in Table 2. Specifically, the SO2 concentration in the eluent, the density of the eluent, the iodine concentration in the eluent, the iodine concentration in the activated carbon (AC), the pH of the eluent, and the oxidation-reduction potential (ORP, based on a silver-silver chloride electrode) were analyzed in the same manner as in Comparative Example 1. The results are shown in Table 2. During the iodine elution treatment, a 48% by mass aqueous solution of NaOH was added as needed to maintain the pH of the eluent at 13. After 20 hours had passed since the waste activated carbon sample was immersed in the eluent, it was confirmed that the elution of iodine had stopped, and then the activated carbon and the eluent were separated by suction filtration. The filtered activated carbon was washed five times with pure water (0.4 L) and gently stirred, followed by suction filtration. Analysis of the iodine concentrations remaining in the activated carbon before and after elution using combustion ion chromatography revealed that the iodine concentration remaining in the activated carbon before elution was 362.8 g I / L-AC, while the iodine concentration remaining in the activated carbon after elution was 1.1 g I / L-AC. Therefore, 0.3 mass% of iodine remained in the activated carbon, and the iodine elution rate was 99.7 mass%.

[0036] [Table 2]

[0037] Example 2 In a sealed container, a waste activated carbon sample (0.5 L) was immersed in an eluent consisting of a sodium hydroxide solution (1.25 L) previously adjusted to pH 13.8, and a stirrer was placed in the eluent to gently stir the mixture, thereby eluting iodine from the iodine-adsorbed activated carbon. The eluent was kept at room temperature (20°C). The waste activated carbon sample used was activated carbon that had adsorbed waste iodine generated in the iodine-using process. The amount of eluent was adjusted so that it was 1.47 equivalents to the amount of iodine in the iodine-adsorbed activated carbon previously analyzed by combustion ion chromatography, and the amount of hydroxide ions (OH) consumed by the substance (OH-consuming component) adsorbed on the activated carbon was 1.47 equivalents. - The amount of OH added was set to 1.27 equivalents relative to the amount of iodine. Here, the OH consuming components are iodine and OH other than iodine. - The amount of hydroxide ions consumed by the OH-consuming components is determined by contacting the iodine-adsorbed activated carbon with an excess amount of eluent in advance. - This was determined by measuring the amount of water consumed. The eluent was sampled and analyzed at the intervals shown in Table 3. Specifically, the pH, hydroxide ion (OH - ) concentration, consumed hydroxide ions (OH - ) concentration, iodine ion (I - ) concentration, iodate ion (IO3 - ) concentration, total iodine concentration (I-total), and iodine elution rate were analyzed. In addition, hydroxide ions (OH - ) concentration and consumed hydroxide ions (OH - ) concentration was measured by neutralization titration. - The concentration was measured using ion chromatography (manufactured by Thermo Fisher Science). When an eluent consisting of a sodium hydroxide solution was allowed to contact iodine-adsorbed activated carbon for 24 hours, the elution rate of iodine reached 100 mass %. In addition, the eluent contained 16% IO3 in terms of elemental iodine. - existed.

[0038] Example 3 In a sealed container, a waste activated carbon sample (0.5 L) was immersed in an eluent consisting of a sodium hydroxide solution (1.25 L) previously adjusted to pH 13.9, and a stirrer was placed in the eluent to gently stir the mixture, thereby eluting iodine from the iodine-adsorbed activated carbon. The eluent was kept at room temperature (20°C). The waste activated carbon sample used was activated carbon that had adsorbed waste iodine generated in the iodine-using process. The amount of eluent was adjusted so that it was 2.21 equivalents to the amount of iodine in the iodine-adsorbed activated carbon previously analyzed by combustion ion chromatography, and the amount of hydroxide ions (OH) consumed by the substance (OH-consuming component) adsorbed on the activated carbon was 2.21 equivalents. - The amount of OH added was set to 1.89 equivalents relative to the amount of iodine. Here, the OH consuming components are iodine and OH other than iodine. - The amount of hydroxide ions consumed by the OH-consuming components is determined by contacting the iodine-adsorbed activated carbon with an excess amount of eluent in advance. - This was determined by measuring the amount of water consumed. The eluent was sampled and analyzed at the intervals shown in Table 3. Specifically, the pH, hydroxide ion (OH - ) concentration, consumed hydroxide ions (OH - ) concentration, iodine ion (I - ) concentration, iodate ion (IO3 -) concentration, total iodine concentration (I-total), and iodine elution rate were analyzed. In addition, hydroxide ions (OH - ) concentration and consumed hydroxide ions (OH - ) concentration was measured by neutralization titration. - The concentration was measured using ion chromatography (manufactured by Thermo Fisher Science). When the eluent consisting of sodium hydroxide solution was contacted with iodine-adsorbed activated carbon for 4 hours, the iodine elution rate was 100 mass %. In addition, the eluent contained 16% IO3 in terms of elemental iodine. - existed.

[0039] Example 4 In a sealed container, a waste activated carbon sample (0.5 L) was immersed in an eluent consisting of a sodium hydroxide solution (1.25 L) previously adjusted to pH 14.4, and a stirrer was placed in the eluent to gently stir the mixture, thereby eluting iodine from the iodine-adsorbed activated carbon. The eluent was kept at room temperature (20°C). The waste activated carbon sample used was activated carbon that had adsorbed waste iodine generated in the iodine-using process. The amount of eluent was adjusted so that it was 6.65 equivalents to the amount of iodine in the iodine-adsorbed activated carbon previously analyzed by combustion ion chromatography, and the amount of hydroxide ions (OH) consumed by the substances (OH-consuming components) adsorbed on the activated carbon was 6.65 equivalents. - The amount of OH added was set to 5.67 equivalents relative to the amount of iodine. Here, the OH consuming components are iodine and OH other than iodine. - The amount of hydroxide ions consumed by the OH-consuming components is determined by contacting the iodine-adsorbed activated carbon with an excess amount of eluent in advance. - This was determined by measuring the amount of water consumed. The eluent was sampled and analyzed at the intervals shown in Table 3. Specifically, the pH, hydroxide ion (OH - ) concentration, consumed hydroxide ions (OH - ) concentration, iodine ion (I - ) concentration, iodate ion (IO3- ) concentration, total iodine concentration (I-total), and iodine elution rate were analyzed. In addition, hydroxide ions (OH - ) concentration and consumed hydroxide ions (OH - ) concentration was measured by neutralization titration. - The concentration was measured using ion chromatography (manufactured by Thermo Fisher Science). When the eluent consisting of sodium hydroxide solution was contacted with iodine-adsorbed activated carbon for 4 hours, the iodine elution rate was 100 mass %. In addition, the eluent contained 16% IO3 in terms of elemental iodine. - existed.

[0040] [Table 3]

[0041] Example 5 The theoretical IO3 generated in reaction 1 below - I - The aqueous bisulfite solution (NaHSO3 solution) at room temperature (20°C) was further added so that 0.73 equivalents of sodium bisulfite were added for 1 equivalent of NaOH required for the reaction of the following reaction formula 2 to convert the compound to - ) concentration, SO2 concentration, iodine ion (I - ) concentration, iodate ion (IO3 - ) concentration, total iodine concentration (I-total), iodate ion (IO3 - ) ratio (IO3 - Iodine elution was carried out in the same manner as in Example 2, except that the iodine elution rate (% of the total iodine) and the iodine elution rate were determined by analysis. 6NaOH + 3I2 → 5NaI + NaIO3 + 3H2O (Reaction 1) IO3 - +3SO3 2- →I - +3SO4 2- (Reaction Scheme 2) When an eluent made by mixing a sodium hydroxide solution and an aqueous bisulfite solution was contacted with iodine-adsorbed activated carbon for 24 hours, the iodine elution rate was 100 mass %.

[0042] Example 6 The theoretical IO3 generated in the above reaction 1 - I - The aqueous bisulfite solution (NaHSO3 solution) at room temperature (20°C) was further added so that 1.47 equivalents of sodium bisulfite were added for each equivalent of NaOH required for the reaction of Reaction Scheme 2 above to convert the bisulfite solution into the above. The pH of the eluent and the hydroxide ions (OH - ) concentration, SO2 concentration, iodine ion (I - ) concentration, iodate ion (IO3 - ) concentration, total iodine concentration (I-total), iodate ion (IO3 - ) ratio (IO3 - Iodine elution was carried out in the same manner as in Example 2, except that the iodine elution rate (% of the total iodine) and the iodine elution rate were determined by analysis. When an eluent made by mixing a sodium hydroxide solution and an aqueous bisulfite solution was contacted with iodine-adsorbed activated carbon for 24 hours, the iodine elution rate was 99 mass %.

[0043] Example 7 The theoretical IO3 generated in the above reaction 1 - I - The aqueous bisulfite solution (NaHSO3 solution) at room temperature (20°C) was further added so that 1.47 equivalents of sodium bisulfite were added for each equivalent of NaOH required for the reaction of Reaction Scheme 2 above to convert the bisulfite solution into the above. The pH of the eluent and the hydroxide ions (OH - ) concentration, SO2 concentration, iodine ion (I - ) concentration, iodate ion (IO3 - ) concentration, total iodine concentration (I-total), iodate ion (IO3 - ) ratio (IO3 -Iodine elution was carried out in the same manner as in Example 3, except that the iodine elution rate (% of the total iodine) and the iodine elution rate were determined by analysis. When an eluent made by mixing a sodium hydroxide solution and an aqueous bisulfite solution was brought into contact with activated carbon to which iodine had been attached for 4 hours, the elution rate of iodine was 100% by mass.

[0044] In addition, from the results of Examples 5 to 7, it was found that the amount of IO3 generated in Examples 5 to 7 was less than that in the systems (Examples 2 to 4) in which only an alkaline substance, sodium hydroxide solution, was added. - It was found that the concentration decreased. In addition, when the amount of sodium bisulfite added was 1 equivalent or more, the IO3 - It was also found that the proportion was less than 1%.

[0045] [Table 4]

[0046] Example 8 First, 500 mL of the iodine-adsorbed activated carbon was taken out and brought into contact with 1250 mL of an aqueous NaOH solution for analysis (NaOH concentration before analysis: 2.04 mol / L) to elute iodine into the aqueous NaOH solution for analysis, and then analysis was performed. Specifically, the NaOH concentration of the aqueous NaOH solution 8 hours or more after the iodine-adsorbed activated carbon was brought into contact with the aqueous NaOH solution for analysis was measured as the post-analysis NaOH concentration, and the consumed NaOH concentration was calculated based on the pre-analysis NaOH concentration and the post-analysis NaOH concentration. Also, elution in aqueous NaOH solution I - Concentration and elution IO3 - The concentration was measured. Furthermore, the amount of iodine adsorbed on the activated carbon was measured. The ratio of the amount of NaOH consumed to the theoretical amount required for the reaction of the adsorbed iodine was calculated. The results are shown in Table 5. Based on the above analysis results, the chemical tank 30 of the reaction apparatus 100 in FIG. 1 was not used, and the NaOH aqueous solution and pure water (soft water) were charged into the reaction tank 10 in the amounts shown in Table 6 to prepare the eluent 40 in the reaction tank 10. At this time, the total amount of the NaOH aqueous solution and pure water (soft water) in the reaction tank 10 was adjusted to 500 L as shown in Table 6. The pH and temperature of the eluent were also set as shown in Table 6. The amount of the NaOH aqueous solution charged was adjusted to 3.7 equivalents relative to the amount of iodine in the iodine-adsorbed activated carbon previously analyzed by combustion ion chromatography, and to 1.4 equivalents relative to the amount of OH consumed by the iodine-adsorbed activated carbon. Next, iodide-adsorbed activated carbon was placed in the reaction vessel 10 and brought into contact with the eluent. Then, the eluent was discharged from the reaction tank 10 by the circulation pump 20 and returned to the reaction tank 10 via the first pipe L1 and the second pipe L2, thereby circulating the eluent and bringing the eluent into contact with the iodine-adsorbed activated carbon, thereby eluting iodine. At this time, the pH of the eluent was kept at 13 or higher even after contacting the eluent with the iodine-adsorbed activated carbon. After 20 hours, the I in the eluate - Concentration and IO3 - The concentration was measured. The iodine elution rate was calculated and was found to be 97.1%, as shown in Table 6. After elution of iodine, the eluent was transferred to a storage tank (not shown in FIG. 1), and in the reaction tank 10, the eluent was extracted, and then pure water was introduced as a cleaning solution and extracted. This operation was repeated until the pH of the cleaning solution reached a constant value (10 or less).

[0047] The iodine form of the eluent in the storage tank and the cleaning solution discharged from the reaction tank were analyzed together, and the proportion of iodide ions was found to be 99% by mass or more in terms of elemental iodine, and the iodine content was 100% by mass or more. - The proportion of this form was 1% by mass or less.

[0048] In Example 8, not only was more NaOH consumed than the amount of iodine eluted, but even though elution was performed with alkali alone, IO3 -This is because substances other than iodine are adsorbed in the activated carbon, and these substances consume NaOH and do not generate IO3 - This is thought to be due to the influence of impurities, such as the reduction effect of [Table 5] [Table 6]

[0049] Example 9 First, 400 mL of activated carbon with adsorbed iodine was taken out and brought into contact with 1000 mL of an aqueous NaOH solution for analysis (NaOH concentration before analysis: 2 mol / L) to elute iodine into the aqueous NaOH solution for analysis, and then analysis was performed. Specifically, the NaOH concentration of the aqueous NaOH solution 8 hours or more after contacting the iodine-adsorbed activated carbon with the aqueous NaOH solution for analysis was measured as the post-analysis NaOH concentration, and the consumed NaOH concentration was calculated based on the pre-analysis NaOH concentration and the post-analysis NaOH concentration. Also, elution in aqueous NaOH solution I - Concentration and elution IO3 - The concentration was measured. Furthermore, the amount of iodine adsorbed on the activated carbon was measured. The ratio of the amount of NaOH consumed to the theoretical amount required for the reaction of the adsorbed iodine was calculated. The results are shown in Table 5. Based on the above analysis results, the chemical tank 30 of the reaction apparatus 100 in FIG. 1 was not used, and the aqueous NaOH solution, the aqueous sodium bisulfite solution, and pure water (soft water) were charged into the reaction tank 10 in the amounts shown in Table 6 to prepare the eluent 40 in the reaction tank 10. At this time, the total amount of the aqueous NaOH solution, the aqueous sodium bisulfite solution, and pure water (soft water) was adjusted to 500 L as shown in Table 6. The pH and temperature of the eluent were also set as shown in Table 6. The amount of the aqueous NaOH solution charged was adjusted to 1.3 equivalents relative to the amount of iodine in the iodine-adsorbed activated carbon previously analyzed by combustion ion chromatography, and to 1.1 equivalents relative to the amount of OH consumed. Next, iodide-adsorbed activated carbon was placed in the reaction vessel 10 and brought into contact with the eluent. Then, the eluent was discharged from the reaction tank 10 by the circulation pump 20 and returned to the reaction tank 10 via the first pipe L1 and the second pipe L2, whereby iodine was eluted while circulating the eluent. At this time, the pH of the eluent was kept at 13 or higher even after contacting the eluent with the iodine-adsorbed activated carbon. After 20 hours, the I in the eluate - Concentration and IO3 - The concentration was measured. The iodine elution rate was calculated and was found to be 97.8%, as shown in Table 6. After iodine was eluted, the eluent was transferred to a storage tank, and in the reaction tank 10, the eluent was extracted, and then pure water was introduced as a cleaning solution and extracted, and this operation was repeated until the pH of the cleaning solution reached a constant value (10 or less).

[0050] The iodine form of the eluent in the storage tank and the cleaning solution discharged from the reaction tank were analyzed together, and the proportion of iodide ions was found to be 99% by mass or more in terms of elemental iodine, and the iodine content was 100% by mass or more. - The proportion of the above form was 1 mass % or less in terms of elemental iodine.

[0051] Example 10 The iodine-adsorbed activated carbon was previously eluted with a large excess of NaOH, and the amount of eluted iodine and the amount of consumed NaOH (corresponding to 1 equivalent) were measured. Next, 100 mL of iodine-adsorbed activated carbon (mass: 75 g, amount of adsorbed iodine: 8.79 g (0.069 mol)) was placed in a 2 L glass light-shielding container. The volume of the iodine-adsorbed activated carbon was measured using a measuring cylinder, and the mass was precisely weighed at that time. Next, 1490 mL of an eluent consisting of a NaOH solution previously adjusted to pH 13 was poured into the light-shielding glass vessel, and the eluent was brought into contact with the iodine-adsorbed activated carbon to elute iodine into the eluent. The eluent was poured in such a way that the amount of hydroxide ions in the eluent was 1.2 equivalents to the amount of NaOH consumed by the iodine-adsorbed activated carbon. A stirrer was then placed in the eluent, and the iodine-adsorbed activated carbon and eluent were gently stirred at a rotation speed of 300 rpm. After the eluent came into contact with the iodine-adsorbed activated carbon, the eluent was sampled at the intervals shown in Table 7, and the pH of the eluent, the OH concentration in the eluent, the concentration of consumed OH, the iodine ion concentration, and the iodine elution rate were analyzed. The results are shown in Table 7. Sampling was performed by transferring approximately 20 mL of the eluent into a 30 mL beaker using a Komagome pipette. Then, 24 hours after the contact of the eluate with the iodine-adsorbed activated carbon, the stirring was stopped. In addition, iodine ions (I - The concentration was determined by filtering the eluent in a 30 mL beaker using a syringe equipped with a disk seal having a filter pore size of 0.45 μm, diluting the resulting filtrate 100 times, and analyzing the resulting diluted solution by ion chromatography. [Table 7]

[0052] (Comparative Example 2) The iodine-adsorbed activated carbon was previously eluted with a large excess of NaOH, and the amount of eluted iodine and the amount of consumed NaOH (corresponding to 1 equivalent) were measured. Next, 43 mL of iodine-adsorbed activated carbon (mass: 32.25 g, amount of adsorbed iodine: 3.78 g (0.030 mol)) was placed in a 2 L glass light-shielding container. The volume of the iodine-adsorbed activated carbon was measured using a measuring cylinder, and the mass was precisely weighed at that time. Then, 2000 mL of eluent consisting of NaOH solution previously adjusted to pH 12.5 was added. Then, as in Example 10, the eluent was gently stirred and, after contact between the eluent and the iodine-adsorbed activated carbon, the eluent was sampled at the intervals shown in Table 7, and the pH of the eluent, the OH concentration in the eluent, the concentration of consumed OH, the iodine ion concentration, and the iodine elution rate were determined by analysis. The results are shown in Table 7. Then, 24 hours after the contact of the eluate with the iodine-adsorbed activated carbon, the stirring was stopped.

[0053] (Comparative Example 3) The iodine-adsorbed activated carbon was previously eluted with a large excess of NaOH, and the amount of eluted iodine and the amount of consumed NaOH (corresponding to 1 equivalent) were measured. Next, 13 mL of iodine-adsorbed activated carbon (mass: 9.75 g, amount of adsorbed iodine: 1.14 g (0.009 mol)) was placed in a 2 L glass light-shielding container. The volume of the iodine-adsorbed activated carbon was measured using a measuring cylinder, and the mass was precisely weighed at that time. Next, 2000 mL of eluent consisting of a NaOH solution previously adjusted to pH 12.0 was added. Then, as in Example 10, the eluent was gently stirred and, after contact between the eluent and the iodine-adsorbed activated carbon, the eluent was sampled at the intervals shown in Table 7, and the pH of the eluent, the OH concentration in the eluent, the concentration of consumed OH, the iodine ion concentration, and the iodine elution rate were determined by analysis. The results are shown in Table 7. Then, 24 hours after the contact of the eluate with the iodine-adsorbed activated carbon, the stirring was stopped.

[0054] Comparative Example 4 The iodine-adsorbed activated carbon was previously eluted with a large excess of NaOH, and the amount of eluted iodine and the amount of consumed NaOH (corresponding to 1 equivalent) were measured. Next, 100 mL of iodine-adsorbed activated carbon (mass: 75.0 g, amount of adsorbed iodine: 8.79 g (0.069 mol)) was placed in a 2 L glass light-shielding container. The volume of the iodine-adsorbed activated carbon was measured using a measuring cylinder, and the mass was precisely weighed at that time. Next, 1490 mL of an eluent consisting of water was poured into the light-shielding glass container. Then, as in Example 10, the eluent was gently stirred and, after contact between the eluent and the iodine-adsorbed activated carbon, the eluent was sampled at the intervals shown in Table 7, and the pH of the eluent, the OH concentration in the eluent, the concentration of consumed OH, the iodine ion concentration, and the iodine elution rate were determined by analysis. The results are shown in Table 7. Then, 24 hours after the contact of the eluate with the iodine-adsorbed activated carbon, the stirring was stopped.

[0055] The results of Example 10 and Comparative Examples 2 to 4 show that the iodine elution rate exceeds 90% and a small amount of liquid can elute a large amount of activated carbon when the eluent pH is 13. On the other hand, when the eluent pH is 12.5 or lower, the iodine elution rate is 90% or lower, and a large amount of eluent is required per mL of activated carbon. [Explanation of symbols]

[0056] 10...reaction tank, 20...circulation pump, 30...chemical tank, 40...eluent, 100...reaction apparatus.

Claims

1. A method for eluting iodine from iodine-adsorbed activated carbon obtained by adsorbing iodine onto activated carbon, comprising: an iodine elution step of contacting the iodine-adsorbed activated carbon with an eluent having a pH of 13 or more to elute the iodine from the iodine-adsorbed activated carbon; A method for eluting iodine, wherein the elution step is carried out at 0 to 40°C.

2. 2. The method for eluting iodine according to claim 1, wherein a reducing agent is added in the iodine elution step.

3. 3. The method for eluting iodine according to claim 1, wherein in the iodine elution step, the iodine-adsorbed activated carbon and the eluent are agitated by blowing a gas thereinto or by circulating the eluent.

4. The iodine elution method according to claim 1 or 2, wherein the pH of the eluent after the iodine elution step is 13 or higher.

5. 3. The iodine elution method according to claim 1, wherein in the iodine elution step, the content of hydroxide ions contained in the eluent is 1 to 6 equivalents with respect to the amount of hydroxide ions consumed by the substance adsorbed on the activated carbon.

6. A method for producing a substance containing iodine, comprising: an iodine elution step of contacting the iodine-adsorbed activated carbon obtained by adsorbing iodine onto activated carbon with an eluent having a pH of 13 or more to elute the iodine from the iodine-adsorbed activated carbon; and a step of recovering the iodine-containing substance eluted in the iodine elution step, A method for producing an iodine-containing substance, wherein the iodine elution step is carried out at 0 to 40°C.

7. a reaction vessel capable of containing a powder and a liquid; A reaction apparatus comprising at least one of a gas introduction means connected to the reaction tank so as to be able to stir the powder and the liquid contained in the reaction tank by blowing a gas into the reaction tank, and a liquid circulation means connected to the reaction tank so as to be able to stir the powder and the liquid contained in the reaction tank by circulating the liquid in the reaction tank.

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