Method for producing iodine and apparatus for producing iodine

Abstract

To provide a method for producing iodine that can efficiently remove nonvolatile substances using a simple method and efficiently produce high-quality iodine with low levels of nonvolatile substances, and to provide an iodine production apparatus that can efficiently remove nonvolatile substances with a simple configuration and efficiently produce high-quality iodine with low levels of nonvolatile substances. [Solution] The present invention provides a method for producing iodine, comprising: an iodine raw material preparation step of preparing an iodine raw material solution containing iodide ions; a crystallization step of oxidizing the iodide ions in the iodine raw material solution to precipitate iodine and obtain slurry iodine; a separation step of separating the slurry iodine into a liquid portion and a solid portion; a water addition step of adding water so as to come into contact with the solid portion; and a melting step of heating the solid portion to melt the iodine and obtain molten iodine, and separating the molten iodine from the water.

Description

Technical Field

[0001] The present invention relates to a method for producing iodine and an apparatus for producing iodine.

Background Art

[0002] Methods for separating and obtaining iodine from underground brine are industrially established, and examples include the blowing-out method and the ion-exchange resin method. Further, as methods for recovering iodine from industrial waste liquids containing iodine, for example, the combustion recovery method and the electrodialysis method have been put into practical use.

[0003] In any of these methods, a concentrated solution with an iodine concentration of several mass% is obtained. This concentrated solution has different names depending on the method or the manufacturer, and is, for example, referred to as an absorption solution, a desorption solution, a concentrated solution, a crude HI aqueous solution, etc., but all are aqueous solutions with an iodide ion concentration of 1 mass% or more (in this specification, hereinafter also referred to as an "iodine absorption solution"). The iodine absorption solution is refined through a purification process called a crystallization process and is commercialized as iodine (hereinafter also referred to as "product iodine").

[0004] For example, in the blowing-out method, an oxidizing agent such as chlorine water, chlorine gas, or sodium hypochlorite solution is added to an iodine-containing liquid such as underground brine to generate free iodine (I2), and the generated free iodine is volatilized by blowing air and absorbed into an aqueous solution containing a reducing agent to obtain an iodine absorption solution.

[0005] In the ion-exchange resin method, an oxidizing agent such as chlorine water, chlorine gas, or sodium hypochlorite solution is added to an iodine-containing liquid such as underground brine to partially oxidize iodide ions present in the underground brine to generate triiodide ions (I3 - ), the generated triiodide ions are adsorbed onto an anion-exchange resin, and the adsorbed polyiodine ions are eluted to obtain an iodine absorption solution.

[0006] In the combustion recovery method, iodine-containing liquids such as industrial wastewater are sprayed into a combustion furnace, the amount of air is adjusted, and the liquid is burned to produce iodine compounds. The combustion gas is then dissolved and absorbed into an aqueous solution containing a reducing agent to obtain an iodine absorbent solution (see, for example, Patent Document 1).

[0007] In the method described above, a large amount of reducing agent such as sodium bisulfite is added when obtaining the iodine absorption solution, which leads to a problem in that the resulting iodine product contains a large amount of non-volatile matter, or in other words, impurities derived from the reducing agent. Furthermore, according to Patent Document 2, when sodium hypochlorite is used as the oxidizing agent for iodine in the crystallization process, a large amount of non-volatile substances derived from the oxidizing agent are included, making it impossible to obtain high-quality iodine. Therefore, in order to obtain high-quality iodine, the iodine concentration in the crystallization process is kept below 30 g / L before crystallization. The inventors believe that this non-volatile substance originates from salts containing metal elements, such as sodium salts, in the reducing agent used in obtaining the iodine absorption solution and the oxidizing agent used in the crystallization process.

[0008] Therefore, it was difficult to meet the shipping standard value for the concentration of nonvolatile substances contained in the iodine product, specifically the shipping standard of 0.020% by mass or less.

[0009] In particular, iodine absorbent obtained by the combustion recovery method can corrode the combustion recovery equipment if its pH becomes acidic due to the reducing agent. Therefore, the pH is adjusted by adding bases containing metallic elements such as NaOH and Ca(OH)2 to prevent the solution from becoming acidic. As a result, the concentration of non-volatile substances in the resulting iodine product increases further. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Patent No. 2902235 [Patent Document 2] Patent No. 5374050 [Overview of the project] [Problems that the invention aims to solve]

[0011] The object of the present invention is to provide a method for producing iodine that can efficiently remove nonvolatile substances using a simple method and efficiently produce high-quality iodine with low levels of nonvolatile substances, and to provide an iodine production apparatus that can efficiently remove nonvolatile substances with a simple configuration and efficiently produce high-quality iodine with low levels of nonvolatile substances. [Means for solving the problem]

[0012] These objectives are achieved by the following inventions (1) to (8). (1) An iodine raw material preparation step in which an iodine raw material solution containing iodide ions is prepared, A crystallization step to obtain slurry iodine by oxidizing the iodide ions in the iodine raw material solution and precipitating iodine, A separation step for separating the slurry iodine into a liquid portion and a solid portion, A water addition step involves adding water so that it comes into contact with the solid portion, A method for producing iodine, comprising a melting step of heating the solid portion to melt the iodine and obtain molten iodine, and separating the molten iodine from the water.

[0013] (2) The method for producing iodine according to (1) above, wherein a centrifugal separator is used in the separation step.

[0014] (3) The method for producing iodine according to (1) or (2) above, wherein the volume ratio of the water added in the water addition step to the weight of the solid portion is 0.5 L / kg or more and 10 L / kg or less.

[0015] (4) The method for producing iodine according to any one of (1) to (3) above, wherein at least a portion of the liquid portion of the slurry iodine separated in the separation step is recovered and reused as part of the iodine raw material solution.

[0016] (5) The method for producing iodine according to any one of (1) to (3) above, wherein the iodine concentration contained in the iodine raw material solution is more than 30 g / L and 110 g / L or less.

[0017] (6) A crystallization reaction tank for oxidizing iodide ions in an iodine raw material solution to precipitate iodine and obtaining slurry iodine, solid-liquid separation means for separating the slurry iodine into a liquid part and a solid part, water addition means for adding water so as to contact the solid part, and a melting kettle for melting the iodine by heating the solid part to obtain molten iodine. The iodine production apparatus is characterized by comprising these components.

[0018] (7) The iodine production apparatus according to (6) above, wherein the solid-liquid separation means is a centrifugal separation means.

[0019] (8) The iodine production apparatus according to (6) or (7) above, which is configured to recover at least a part of the liquid part of the slurry iodine separated by the solid-liquid separation means and supply it to the crystallization reaction tank as a part of the iodine raw material solution.

Advantages of the Invention

[0020] According to the present invention, there is provided a method for producing iodine capable of efficiently removing impurities by a simple method and efficiently producing high-quality iodine with few impurities. Also, there can be provided an iodine production apparatus capable of efficiently removing impurities with a simple configuration and efficiently producing high-quality iodine with few impurities.

Brief Description of the Drawings

[0021] [Figure 1] It is a diagram schematically showing one configuration example of the iodine production apparatus of the present invention. [Figure 2] It is a diagram schematically showing another configuration example of the iodine production apparatus of the present invention. [Figure 3] It is a diagram schematically showing another configuration example of the iodine production apparatus of the present invention. [Figure 4] This figure schematically shows another configuration example of the iodine production apparatus of the present invention. [Figure 5] This figure schematically shows another configuration example of the iodine production apparatus of the present invention. [Modes for carrying out the invention]

[0022] Preferred embodiments of the present invention will be described in detail below.

[0023] [1] Iodine production apparatus First, the iodine production apparatus of the present invention will be described. Figure 1 is a schematic diagram showing one example configuration of the iodine production apparatus of the present invention. Figures 2 to 5 are schematic diagrams showing other examples configurations of the iodine production apparatus of the present invention.

[0024] The iodine production apparatus 1 comprises a crystallization reaction tank 10 for oxidizing iodide ions in an iodine raw material solution 100 and precipitating iodine to obtain slurry iodine 110; a solid-liquid separation means 20 for separating the slurry iodine 110 into a liquid portion 110b and a solid portion 110a; a water addition means 40 for adding water so as to come into contact with the solid portion 110a; and a melting vessel 30 for heating the solid portion 110a to melt the iodine and produce molten iodine 120.

[0025] With this configuration, non-volatile substances can be efficiently removed with a simple setup, and high-quality iodine with low levels of non-volatile substances can be efficiently produced.

[0026] More specifically, by adding water from the water-adding means 40, and in particular by adding water so that it comes into contact with the solid portion 110a, non-volatile substances contained in the solid portion 110a can be dissolved in the water. As a result, high-quality iodine with low levels of non-volatile substances can be suitably obtained as the product iodine 130.

[0027] The "water" added by the water addition means (water addition step described later) only needs to contain H2O as its main component, and may also contain components other than H2O. However, the content of components other than H2O in the "water" added by the water addition means (water addition step described later) is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less.

[0028] The "water" added by the water addition means (water addition process described later) can be, for example, industrial water, ion-exchanged water, distilled water, ultrapure water, tap water, or a liquid obtained by desalination treatment of the liquid portion obtained by the solid-liquid separation means (separation process described later).

[0029] [1-1] Crystallization reactor The crystallization reaction vessel 10 is a reaction vessel for holding the iodine raw material solution 100 and carrying out the crystallization reaction.

[0030] The crystallization reactor 10 is connected to a raw material supply unit 11 for supplying iodine raw material solution 100 and an oxidizing agent supply unit 12 for supplying an oxidizing agent. In the crystallization reactor 10, the iodine raw material solution 100 supplied from the raw material supply unit 11 and the oxidizing agent supplied from the oxidizing agent supply unit 12 react (crystallization reaction) to produce solid iodine (I2). The reaction product is slurry iodine 110 containing solid iodine (I2) and liquid water.

[0031] The crystallization reaction tank 10 has a cylindrical upper section and a slurry iodine outlet 13 at its bottom for discharging the slurry iodine 110 obtained by the crystallization reaction. The lower part of the crystallization reaction tank 10 may have a uniform diameter throughout its height, but it is preferable that it has a funnel shape with an inner diameter that decreases towards the bottom. This allows for efficient discharge of slurry iodine from the slurry iodine outlet 13.

[0032] A pipe 15 is connected to the slurry iodine outlet 13 of the crystallization reaction tank 10, which communicates with the slurry iodine supply port 22 of the solid-liquid separation means 20. A pump 16 may be provided in the middle of the pipe 15. This allows for efficient transfer of the slurry iodine 110.

[0033] Furthermore, the crystallization reaction tank 10 may be equipped with a stirring means for stirring the composition inside the tank. This allows the crystallization reaction to proceed more favorably.

[0034] [1-2] Solid-liquid separation means The solid-liquid separation means 20 separates the slurry iodine 110 into a solid portion 110a and a liquid portion 110b.

[0035] The solid-liquid separation means 20 is not particularly limited as long as it can separate the slurry iodine 110 into a solid portion 110a and a liquid portion 110b. However, the iodine production apparatus 1 shown in Figure 1 is equipped with a cyclone-type centrifugal separator as the solid-liquid separation means 20.

[0036] This allows for more efficient and favorable separation of the slurry iodine 110 into a solid portion 110a and a liquid portion 110b.

[0037] In the following explanation, a cyclone-type centrifugal separation device will also be simply referred to as a "cyclone."

[0038] The cyclone's main body 21 has a cylindrical outer casing at the top, a funnel shape in its central section where the inner diameter decreases towards the bottom, and a tubular shape at its lower end with an opening.

[0039] A slurry iodine supply port 22 for supplying slurry iodine 110 into the interior of the main body 21 is located on the upper side of the main body 21, and a liquid portion outlet 23 for discharging the liquid portion 110b separated from the solid portion 110a is located in the center of the upper surface of the main body 21. The lower end of the lower part of the main body 21 becomes a solid portion outlet 24 for discharging the solid portion 110a. The solid portion outlet 24 is in communication with the solid portion supply port 31 of the melting vessel 30. The liquid portion 110b discharged from the liquid portion outlet 23 usually contains water supplied from a water addition means. In addition, some of the liquid portion 110b may be discharged from the solid portion outlet 24 together with the solid portion 110a. In such a case, the liquid portion 110b discharged from the solid portion outlet 24 together with the solid portion 110a may contain water supplied from a water addition means.

[0040] [1-3] Melting vessel The melting vessel 30 is equipped with a heating means 32, which heats the solid portion 110a separated from the slurry iodine 110 to melt the iodine contained in the solid portion 110a and obtain molten iodine 120. The molten iodine 120 is obtained with a reduced content of nonvolatile substances.

[0041] The heating means 32 is not particularly limited, but examples include a jacket section for circulating a heated heat transfer medium such as hot air, superheated steam, or oil, an electric heater for heating the melting pot 30 from the outside, and an infrared irradiation device for irradiating infrared rays (including near-infrared and far-infrared rays).

[0042] A molten iodine outlet 33 for extracting molten iodine 120 is provided at the bottom of the melting vessel 30.

[0043] In the iodine production apparatus 1 shown in Figure 1, a solid-liquid separation means 20 and a melting vessel 30 are connected, and the inside of the solid-liquid separation means 20 and the melting vessel 30 are pressurized spaces filled with liquid.

[0044] This allows for the continuous execution of a series of processes, including solid-liquid separation of slurry iodine 110 in the solid-liquid separation means 20, supply of slurry iodine 110 from the solid-liquid separation means 20 to the melting vessel 30, and heating and melting in the melting vessel 30. As a result, productivity can be further improved compared to batch processing.

[0045] Furthermore, the solid-liquid separation means 20 is connected to the melting vessel 30, which will be described in detail later. Because the inside of the solid-liquid separation means 20 and the melting vessel 30 are filled with liquid and under pressure, the liquid portion 110b can be more preferably discharged from the liquid portion outlet 23 (solid-liquid separation means 20). Also, the solid portion 110a can be more preferably discharged from the solid portion outlet 24 (solid-liquid separation means 20). In addition, in the melting vessel 30 (melting process described later), it is possible to suitably prevent the iodine (I2) contained in the solid portion 110a from becoming gaseous, and to suitably molten the iodine (I2) contained in the solid portion 110a.

[0046] [1-4] Water addition means The water-adding means 40 adds water so as to come into contact with the solid portion 110a.

[0047] This allows the non-volatile substances contained in the solid portion 110a to be dissolved in water, and as a result, high-quality iodine with low levels of non-volatile substances can be suitably obtained as product iodine 130.

[0048] Furthermore, "adding water so as to come into contact with the solid portion 110a" is not limited to cases where the water supplied from the water-adding means 40 comes into direct contact with the solid portion 110a, but also includes cases where, for example, water is supplied to the slurry iodine 110 containing the solid portion 110a or to the liquid portion 110b, and as a result the water-diluted liquid portion 110b comes into contact with the solid portion 110a (cases where the liquid portion 110b containing the water supplied from the water-adding means 40 comes into contact with the solid portion 110a).

[0049] The water supplied from the water addition means 40 may come into contact with the solid portion 110a (molten iodine 120) after it has melted in the melting vessel 30, but it is preferable that it comes into contact with the solid portion 110a before it melts in the melting vessel 30.

[0050] This allows the non-volatile substances contained in the solid portion 110a to be suitably dissolved in water, and as a result, the iodine product 130 can be obtained as a higher quality product with particularly low levels of non-volatile substances.

[0051] The water addition means 40 is not particularly limited in its installation location as long as it can add water in contact with the solid portion 110a. For example, it may be installed to add water inside the melting pot 30, or to add water inside the solid-liquid separation means 20, or to add water in the pipeline between the solid-liquid separation means 20 and the melting pot 30, or to add water in the pipeline between the slurry iodine outlet 13 and the slurry iodine supply port 22. Alternatively, water may be added from two or more locations.

[0052] In the configuration shown in Figure 1, the water addition means 40 is provided to add water to the top of the melting pot 30.

[0053] This allows the water supplied from the water-adding means 40 to be suitably brought into contact with the solid portion 110a before it is melted in the melting vessel 30. As a result, the water supplied from the water-adding means 40 can be effectively brought into contact with the solid portion 110a, allowing non-volatile substances contained in the solid portion 110a to be more suitably dissolved in the water, and also to be brought into contact with the solid portion 110a (molten iodine 120) after it has been melted in the melting vessel 30. As a result, the product iodine 130 can be obtained as a higher quality product with particularly low levels of non-volatile substances. Adding water to the top of the melting vessel 30 also provides the following effect: By continuously pouring water into the melting vessel 30, the liquid portion 110b inside the melting vessel 30 is constantly replaced with water, and the salt concentration can be kept low. As a result, re-contamination of the molten iodine 120 can be more suitably prevented.

[0054] The water addition means 40 is not particularly limited, but examples include water injection equipment such as a pump.

[0055] [1-5] Cooling means Furthermore, the iodine production apparatus 1 may also include a cooling means 50 for cooling the molten iodine 120 melted in the melting vessel 30 to convert it into solid iodine. This makes it easier to handle the iodine obtained.

[0056] The cooling means 50 is not particularly limited, but examples include a table flaker, a drum flaker, and the like.

[0057] By using a table flaker as the cooling means 50, flake-shaped solid iodine is obtained as the product iodine 130.

[0058] The iodine product obtained in the manner described above is of high quality with low levels of non-volatile matter.

[0059] Specifically, by applying the present invention, for example, product iodine with a purity of 99.7% by mass or more and a non-volatile matter concentration of 0.020% by mass or less can be obtained.

[0060] The purity of the iodine product obtained by applying the present invention is preferably 99.7% by mass or higher, more preferably 99.9% by mass or higher, and even more preferably 99.98% by mass or higher.

[0061] The concentration of nonvolatiles in the iodine product obtained by applying the present invention is preferably 0.020% by mass or less, more preferably 0.010% by mass or less, and even more preferably 0.008% by mass or less.

[0062] Non-volatile substances are the solid components that remain after the final iodine product is sublimated. Examples of non-volatile substances include NaI, sodium sulfate, and salts containing various metal elements such as NaCl.

[0063] [1-6] Others In the configuration shown in Figure 1, at least a portion of the liquid portion 110b of the slurry iodine 110 separated by the solid-liquid separation means 20 is recovered and supplied to the crystallization reaction tank 10 as part of the iodine raw material solution 100. More specifically, a portion of the liquid portion 110b separated by the solid-liquid separation means 20 is discharged from the liquid portion outlet 23 at the top of the solid-liquid separation means 20 and sent to the crystallization reaction tank 10 as part of the iodine raw material solution 100 via piping 25 to be used in the crystallization reaction described above.

[0064] This allows for effective utilization of the liquid portion 110b (hereinafter also referred to as crystallization wastewater), resulting in a higher iodine yield. Of the liquid portion 110b discharged from the liquid portion outlet 23, the portion not supplied to the crystallization reaction tank 10 is discharged as crystallization wastewater.

[0065] [2] Method for producing iodine Next, the method for producing iodine according to the present invention will be described.

[0066] The present invention provides a method for producing iodine, comprising: an iodine raw material preparation step of preparing an iodine raw material solution 100 containing iodide ions; a crystallization step of oxidizing the iodide ions in the iodine raw material solution 100 to precipitate iodine and obtain slurry iodine 110; a separation step of separating the slurry iodine 110 into a liquid portion 110b and a solid portion 110a; a water addition step of adding water so as to come into contact with the solid portion 110a; and a melting step of heating the solid portion 110a to melt the iodine and obtain molten iodine 120, and then separating the molten iodine 120 from water.

[0067] With this configuration, non-volatile substances can be efficiently removed using a simple method, and high-quality iodine with low levels of non-volatile substances can be produced.

[0068] More specifically, by adding water in a way that brings it into contact with the solid portion 110a during the water addition process, non-volatile substances contained in the solid portion 110a can be dissolved in the water, and as a result, high-quality iodine with low levels of non-volatile substances can be suitably obtained as the product iodine 130. In particular, by adding water in a way that brings it into contact with the solid portion 110a before it melts, non-volatile substances contained in the slurry iodine 110 can be suitably removed.

[0069] The iodine production method of the present invention can be suitably carried out, for example, using the iodine production apparatus 1 of the present invention described above.

[0070] [2-1] Preparation process for iodine raw material solution The iodine raw material liquid 100 is not particularly limited as long as it is a liquid containing iodide ions, but examples include iodine absorption liquid recovered from groundwater, industrial wastewater, etc., by iodine acquisition methods such as the blowing-out method, ion exchange resin method, combustion recovery method, and electrodialysis method.

[0071] This can lead to improved productivity. Furthermore, if the iodine raw material solution 100 is an iodine absorbent obtained from industrial wastewater, it is particularly preferable from the viewpoint of effective resource utilization.

[0072] Iodine absorption solutions are typically aqueous solutions with an iodide ion concentration of 1% by mass or higher. The iodine raw material solution 100 may be an iodine absorption solution obtained by one iodine acquisition method used alone, or a mixture of iodine absorption solutions obtained by multiple iodine acquisition methods may be used. Alternatively, water may be added to the iodine raw material solution 100 to adjust it to a predetermined iodine concentration.

[0073] The iodine concentration contained in the iodine raw material solution 100 is preferably greater than 30 g / L and 110 g / L or less, more preferably between 33 g / L and 80 g / L, and even more preferably between 35 g / L and 60 g / L.

[0074] This allows for more efficient crystallization of iodine, resulting in higher quality iodine.

[0075] Conversely, if the iodine concentration is below the aforementioned lower limit, productivity may decrease. Also, if the iodine concentration exceeds the aforementioned upper limit, the incorporation of non-volatile substances (such as salts containing metallic elements like sodium iodide and sodium sulfate) into the slurry iodine 110 produced by crystallization increases, which may reduce the quality of the resulting iodine.

[0076] Furthermore, the amount of reducing agent (absorbent) used will differ depending on the type of iodine acquisition method and the processing conditions for each method. For example, the blowing-out method uses only sodium bisulfite as a reducing agent, while the combustion recovery method uses both sodium bisulfite and NaOH. Therefore, the Na concentration of iodine absorbent obtained by the combustion recovery method is generally higher than that of iodine absorbent obtained by the blowing-out method. For this reason, when mixing iodine absorbent solutions obtained by multiple iodine acquisition methods to make iodine raw material solution 100, if the mixing ratio of these iodine absorbent solutions changes, the Na / I ratio will also change, even if the iodine concentration in each iodine absorbent solution is the same.

[0077] The Na concentration in the iodine raw material solution 100 is preferably 20 g / L or less, more preferably 18 g / L or less, and even more preferably 15 g / L or less. This allows for obtaining iodine with higher purity.

[0078] The Na / I ratio in iodine raw material solution 100 is preferably 0.50 or less in terms of concentration ratio (mass ratio), more preferably 0.45 or less, and even more preferably 0.40 or less. This allows for the acquisition of iodine with even higher purity.

[0079] Furthermore, the Na / I ratio in the iodine raw material solution 100 is preferably 2.8 or less, more preferably 2.5 or less, and even more preferably 2.1 or less. This allows for the acquisition of iodine with even higher purity.

[0080] Furthermore, the pH of the iodine raw material solution 100 at 25°C is preferably 4.5 or less, more preferably 4.0 or less, and even more preferably 3.0 or less.

[0081] This reduces the amount of non-volatile substances, allowing for more efficient crystallization of iodine.

[0082] The pH of iodine raw material solution 100 can be adjusted to the above value using an acid such as hydrochloric acid, nitric acid, or sulfuric acid.

[0083] When mixing iodine absorption solutions obtained by multiple iodine acquisition methods to form iodine raw material solution 100, it is preferable to mix the iodine absorption solutions obtained by multiple iodine acquisition methods in a manner that satisfies the conditions described above.

[0084] [2-2] Crystallization process In the crystallization process, an oxidizing agent is added to the iodine raw material solution 100 to oxidize the iodide ions in the iodine raw material solution 100, thereby precipitating iodine and obtaining slurry iodine 110.

[0085] Examples of oxidizing agents include chlorine, hypochlorite, hydrogen peroxide, iodate, periodate, and nitrite, and one or more of these can be used in combination. Among these, chlorine and sodium hypochlorite are preferred from the standpoint of cost performance and other factors.

[0086] The amount of oxidizing agent added to the iodine raw material solution 100 is preferably such that the molar ratio of the oxidizing agent to the iodide ions in the iodine raw material solution 100 after the addition of the oxidizing agent is equal.

[0087] Furthermore, while there are no particular limitations on the temperature at which the oxidizing agent is added, it is usually carried out in a range from the freezing point of the iodine absorption solution to room temperature.

[0088] The iodine raw material solution 100 is in a liquid state when supplied to the crystallization reaction tank 10. However, by adding an oxidizing agent to the iodine raw material solution 100, the iodide ions in the iodine raw material solution 100 are oxidized, and solid iodine particles precipitate (crystallization reaction). As the crystallization reaction progresses, the particle size of the solid particles increases. In this way, the crystallization reaction yields a black, slurry-like fluid containing both liquid and solid iodine particles, in other words, slurry iodine 110, from the iodine raw material solution 100.

[0089] The slurry iodine 110 is discharged from the slurry iodine outlet 13 at the bottom of the crystallization reaction tank 10, transported via the piping 15, and supplied to the solid-liquid separation means 20 (cyclone) using the pump 16.

[0090] [2-3] Separation process In the separation step, the slurry iodine 110 obtained in the crystallization step is separated into a liquid portion 110b and a solid portion 110a containing solid iodine particles.

[0091] In the separation process, methods for separating the slurry iodine 110 into a liquid portion 110b and a solid portion 110a include, but are not particularly limited to, centrifugal separation means and sedimentation separation means, although a method using a cyclone-type centrifugal separation means is preferred.

[0092] This allows for more efficient and favorable separation of the slurry iodine 110 into a solid portion 110a and a liquid portion 110b.

[0093] When slurry iodine 110 is supplied to the main body 21 from the slurry iodine supply port 22 of the cyclone while being pressurized using the pump 16, a swirling flow (cyclone) is generated, and due to the difference in mass (specific gravity) between the liquid and solid, the slurry iodine 110 is separated into a solid portion 110a with a relatively high specific gravity and a liquid portion 110b with a relatively low specific gravity. The solid portion 110a with a relatively high specific gravity is then thrown outward by centrifugal force and sinks downward by gravity, and is transferred into the melting pot 30 from the solid portion discharge port 24 at the bottom through the solid portion supply port 31. The liquid portion 110b with a relatively low specific gravity floats above the solid portion 110a, and a portion of the liquid portion 110b is discharged from the liquid portion discharge port 23 at the top.

[0094] The slurry iodine 110, separated into a liquid portion 110b and a solid portion 110a, is sent to the melting vessel 30. At this time, it is sufficient for at least the solid portion 110a to be sent to the melting vessel 30, but usually, at least a portion of the liquid portion 110b is also sent to the melting vessel 30 along with the solid portion 110a.

[0095] [2-4] Water addition process In the water addition step, water is added so as to come into contact with the solid portion 110a.

[0096] This allows the solid portion 110a to be washed and the non-volatile substances contained in the solid portion 110a to be transferred to the liquid portion 110b.

[0097] In the water addition step, water should be added so as to come into contact with at least the solid portion 110a, and the liquid portion 110b may also come into contact with the water. For example, the water supplied from the water addition means 40 may come into contact with the liquid portion 110b (mixed with the liquid portion 110b separated in the separation step) and then come into contact with the solid portion 110a.

[0098] In particular, when the water supplied from the water-adding means 40 comes into contact with the solid portion 110a before it is subjected to the melting process described later, the non-volatile substances contained in the solid portion 110a can be more effectively dissolved in the water. As a result, the iodine product 130 can be obtained as a higher quality product with particularly low levels of non-volatile substances.

[0099] Of the slurry iodine 110 transferred to the molten vessel 30, the solid portion 110a, which has a relatively high specific gravity, settles and accumulates at the bottom of the molten vessel 30, while the liquid portion 110b (including the water added in the water addition step), which has a relatively low specific gravity, separates and accumulates at the top.

[0100] In the solid portion 110a, the water added in the water addition process removes non-volatile substances that were present in the iodine raw material solution 100. Therefore, the settled solid portion 110a (molten iodine 120 formed from the melted solid portion 110a) also has a low content of non-volatile substances.

[0101] Increasing the amount of water added to the melting vessel 30 tends to increase the effect of reducing nonvolatile substances. However, if too much water is added, the solid portion 110a contained in the slurry iodine 110 is pushed back towards the solid-liquid separation means 20, which tends to reduce the efficiency of solid-liquid separation of the slurry iodine 110 by the solid-liquid separation means 20.

[0102] For these reasons, the amount of water added (supplied) in the water addition process preferably satisfies the following conditions. Specifically, the volume ratio of added water to the weight of the solid portion 110a is preferably 0.5 L / kg or more and 10 L / kg or less, more preferably 1.0 L / kg or more and 6.0 L / kg or less, and even more preferably 2.0 L / kg or more and 4.0 L / kg or less.

[0103] Furthermore, the pressure of the water supplied in the water addition process is not particularly limited as long as it is higher than the pressure inside the melting vessel 30, but it is preferably 0.07 MPa or more and 0.90 MPa or less, more preferably 0.10 MPa or more and 0.60 MPa or less, and even more preferably 0.12 MPa or more and 0.40 MPa or less. This suppresses the backflow of the liquid portion 110b inside the melting vessel 30 to the water addition means 40, allowing for the appropriate addition of water, and thus making the above-mentioned effects more pronounced.

[0104] [2-5] Melting process In the melting process, the solid portion 110a is heated to melt the iodine into molten iodine 120, and the molten iodine 120 is separated from water (aqueous phase).

[0105] Specifically, the iodine contained in the solid portion 110a of the slurry iodine 110 introduced into the melting vessel 30 (the solid portion 110a that settles at the bottom of the melting vessel 30) melts when heated by the heating means 32, becoming liquid molten iodine 120. Then, the liquid molten iodine 120 separates from the water (aqueous phase). Here, since the specific gravity (density) of molten iodine 120 is greater than that of water (aqueous phase), the molten iodine 120 is located at the bottom of the melting vessel 30, with the water (aqueous phase) located above it. In particular, iodine has a high specific gravity (specific gravity of approximately 4.93 at room temperature), and the difference in specific gravity (approximately 1) between it and the aqueous phase is sufficiently large, so the liquid molten iodine 120 and the aqueous phase separate appropriately. As a result, highly pure liquid molten iodine 120 can be appropriately separated from the aqueous phase and isolated.

[0106] In the iodine production apparatus 1, the solid-liquid separation means 20 and the melting vessel 30 are connected, so that the slurry iodine 110 supplied to the solid-liquid separation means 20 is separated into a solid portion 110a and a liquid portion 110b, and the solid portion 110a is transferred to the melting vessel 30 while water is supplied (injected) and heated.

[0107] This allows for the continuous execution of a series of processes, including solid-liquid separation of slurry iodine 110 in the separation process (solid-liquid separation means 20), supply of the solid portion 110a from the solid-liquid separation means 20 to the melting vessel 30, and heating and melting in the melting process (melting vessel 30). As a result, productivity can be further improved compared to batch processing.

[0108] Furthermore, since the solid-liquid separation means 20 and the melting vessel 30 are connected, and the insides of the solid-liquid separation means 20 and the melting vessel 30 are filled with liquid and under pressure, the liquid portion 110b can be more preferably discharged from the liquid portion outlet 23 (solid-liquid separation means 20). Also, the solid portion 110a can be more preferably discharged from the solid portion outlet 24 (solid-liquid separation means 20). In addition, in the melting process (melting vessel 30), it is possible to suitably prevent the iodine (I2) contained in the solid portion 110a from becoming gaseous, and to suitably molten the iodine (I2) contained in the solid portion 110a.

[0109] The heating temperature in the melting process is preferably 113°C or higher and less than 185°C, more preferably 130°C or higher and 180°C or lower, and even more preferably 140°C or higher and 175°C or lower. This allows iodine to be dissolved more effectively.

[0110] Furthermore, as mentioned above, the melting process is preferably carried out under pressure. In the melting process, the internal pressure of the melting vessel 30 is preferably 0.05 MPa or more and 0.80 MPa or less, more preferably 0.07 MPa or more and 0.50 MPa or less, and even more preferably 0.10 MPa or more and 0.30 MPa or less. This allows the iodine contained in the solid portion 110a to melt without boiling the liquid portion 110b accumulated at the top of the melting vessel 30, thereby making the above-mentioned effects more pronounced.

[0111] The molten iodine 120 is removed from the molten iodine outlet 33 located at the bottom of the molten vessel 30.

[0112] [2-6] Cooling process The method for producing iodine according to the present invention may further include a cooling step.

[0113] In the cooling process, the molten iodine 120 obtained in the melting process is cooled. This allows for the suitable acquisition of high-purity solid iodine.

[0114] The obtained solid iodine may be molded by granulation or crushing to obtain product iodine 130.

[0115] The method for cooling molten iodine 120 and the method for molding solid iodine are not particularly limited and known methods can be used. For example, when obtaining flake-shaped iodine products, methods using a table flaker or a drum flaker can be employed.

[0116] More specifically, as shown in Figure 1, for example, the molten iodine 120 removed from the molten iodine outlet 33 at the bottom of the melting vessel 30 may be transferred to a table flaker serving as a cooling means 50.

[0117] In a table flaker, molten iodine 120 is applied to the table surface, and while heat exchange is carried out by passing cooling water through the inside of the table, it is cooled to a temperature below the melting point of iodine and solidified. The solidified iodine is scraped off with a blade to obtain flake-shaped iodine product 130.

[0118] On the other hand, it is preferable that at least a portion of the liquid portion 110b of the slurry iodine 110 separated in the separation process (solid-liquid separation means 20) is recovered from the liquid portion discharge port 23 at the top of the main body 21 and reused as part of the iodine raw material liquid 100.

[0119] This allows for effective utilization of the liquid portion 110b, resulting in a higher iodine yield. More specifically, it is as follows:

[0120] The liquid portion 110b (crystallization wastewater) of the slurry iodine 110 separated by the solid-liquid separation means 20 generally contains iodine at a relatively high concentration of 200 mg / L to 2000 mg / L.

[0121] By spraying the crystallization wastewater into an airflow, iodine (I2) present in that form can be extracted and recovered into the airflow, but the majority is lost as iodide ions (I - It remains in the crystallization wastewater in the form of ).

[0122] Therefore, it is preferable to collect the crystallization wastewater separated by the solid-liquid separation means 20 from the liquid portion outlet 23 at the top of the solid-liquid separation means 20, and send it to the crystallization reaction tank 10 as part of the iodine raw material solution 100 via the piping 25, thereby proceeding with the above-described process.

[0123] This allows for the effective recovery of iodine from the crystallization wastewater. In other words, the crystallization wastewater can be utilized effectively, and the yield of iodine can be increased.

[0124] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto.

[0125] For example, the iodine production apparatus of the present invention may have configurations other than those described above.

[0126] More specifically, the iodine production apparatus of the present invention is not limited to the configuration shown in Figure 1, but may also have configurations such as those shown in Figures 2 to 5.

[0127] For example, in the manufacturing apparatus 1 shown in Figure 1, water from the water addition means 40 is supplied into the melting pot 30 from a location different from the solid portion supply port 31. In contrast, in the manufacturing apparatus 1 shown in Figure 2, water is supplied to a pipe between the solid-liquid separation means 20 and the melting pot 30, and is introduced into the melting pot 30 after being mixed with the solid portion 110a discharged from the solid portion discharge port 24 of the solid-liquid separation means 20 within this pipe.

[0128] Furthermore, the manufacturing apparatus 1 shown in Figure 3 differs from both the manufacturing apparatus 1 shown in Figure 1 and the manufacturing apparatus 1 shown in Figure 2 in that the water from the water adding means 40 is supplied into the solid-liquid separation means 20, rather than into the melting pot 30.

[0129] Furthermore, the manufacturing apparatus 1 shown in Figure 3 differs from both the manufacturing apparatus 1 shown in Figure 1 and the manufacturing apparatus 1 shown in Figure 2 in that the liquid portion 110b discharged from the liquid portion outlet 23 is discharged without being sent to the crystallization reaction tank 10 (this also applies to the manufacturing apparatus 1 shown in Figures 4 and 5).

[0130] Furthermore, while the manufacturing apparatus 1 with the configurations shown in Figures 1 to 3 all included a cyclone-type centrifugal separator as the solid-liquid separation means 20, the manufacturing apparatus 1 with the configuration shown in Figure 4 is equipped with a solid-liquid separation means (sedimentation separation means) that separates solids and liquids by sedimentation.

[0131] Furthermore, in the manufacturing apparatus 1 with the configurations shown in Figures 1 to 4, a solid-liquid separation means 20 was provided as a separate component from the crystallization reaction tank 10. In contrast, in the manufacturing apparatus 1 with the configuration shown in Figure 5, the crystallization reaction tank 10 also functions as the solid-liquid separation means 20. More specifically, the crystallization reaction tank 10 is configured to allow solid-liquid separation by sedimentation.

[0132] Even when using an iodine production apparatus 1 with these configurations, the iodine production method of the present invention can be suitably implemented.

[0133] Furthermore, for example, the iodine production method of the present invention may include steps other than those described above (e.g., pre-treatment steps, intermediate treatment steps, post-treatment steps, etc.). [Examples]

[0134] The present invention will be described in detail below based on specific examples, but the present invention is not limited thereto. In the following examples, unless the temperature conditions are specified, the processes and measurements were performed at room temperature (25°C).

[0135] [3] Production of iodine (Example 1) First, as the iodine raw material solution, a mixture of iodine absorbent obtained from groundwater by the blowing-out method and iodine absorbent obtained by the combustion recovery method was prepared in a volume ratio of 4:6, and then diluted with water (iodine raw material solution preparation process).

[0136] The iodine concentration in this iodine raw material solution was 41 g / L, the sodium concentration was 10 g / L, and the Na / I ratio was 0.24 in terms of concentration ratio (mass ratio) and 1.3 in terms of molar ratio.

[0137] Using the iodine production apparatus shown in Figure 1, product iodine was produced from iodine raw material solution. First, in a crystallization reaction tank, chlorine was added to the iodine raw material solution as an oxidizing agent and mixed to oxidize the iodide ions in the iodine raw material solution, causing iodine to precipitate and obtain slurry iodine (crystallization step).

[0138] Next, the slurry iodine was separated into a liquid portion and a solid portion using a cyclone (separation step). Next, the solid portion of the iodine slurry was transferred to a melting vessel. At this time, water was added to the melting vessel at a rate of 3.5 L / kg relative to the weight of the solid portion (water addition step). The pressure of the water supplied during the water addition step was 0.30 MPa.

[0139] Subsequently, the solid portion of the slurry iodine that had settled at the bottom of the melting vessel was heated to melt the iodine, and the molten iodine was separated from the water due to the difference in specific gravity (melting process). The heating temperature in the melting process was 155°C, and the pressure in the cyclone and the internal space (closed space) of the melting vessel during the melting process was 0.16 MPa.

[0140] Next, the molten iodine was cooled and pulverized to obtain flake-shaped iodine product.

[0141] (Examples 2-4) Flake-type iodine was produced in the same manner as in Example 1, except that the iodine raw material solution used was modified by changing the volume ratio of iodine absorbent obtained by the blowing-out method and iodine absorbent obtained by the combustion recovery method, as well as the dilution rate with water, thereby changing the iodine concentration, Na concentration, and Na / I conditions as shown in Table 1, and the amount of water added (amount of water injected) was also changed as shown in Table 1.

[0142] (Example 5) Flake-type iodine was produced in the same manner as in Example 1, except that an iodine absorption solution obtained by the blowing-out method was used as the iodine raw material solution, and the amount of water added was changed as shown in Table 1.

[0143] In each of the above embodiments, the pH of the iodine raw material solution supplied to the crystallization reaction vessel at 25°C was 4.5 or less.

[0144] (Comparative Examples 1-5) Flake-shaped iodine products were manufactured in the same manner as in Examples 1 to 5, except that water was not added to the solid portion of the slurry iodine transferred to the melting vessel.

[0145] [4] Measurement of non-volatile content, etc. The non-volatile content of the iodine product obtained in each of the above examples and comparative examples was measured in accordance with JIS K 8920. Furthermore, the sodium content in the iodine product was measured using ion chromatography. The results, along with the conditions for the iodine raw material solution and the amount of water added to the iodine slurry during the water addition process, are shown in Table 1.

[0146] [Table 1]

[0147] As is clear from Table 1, in each of the above examples in which water was added to the slurry iodine transferred to the melting vessel before heating and melting, it was possible to obtain high-quality product iodine with a reduced non-volatile content.

[0148] In particular, in Examples 1 to 4, where an iodine absorption solution obtained by combustion recovery was used as the iodine raw material solution, the content of non-volatile substances could be sufficiently reduced even when the Na concentration in the iodine raw material solution was high, and high-quality iodine product could be obtained.

[0149] Furthermore, flake-shaped iodine products were manufactured in the same manner as in the above examples, except that the Na / I ratio in the iodine raw material solution supplied to the crystallization reaction tank was varied by a concentration ratio (mass ratio) of 0.50 or less, and by a molar ratio of 2.8 or less, the pH of the iodine raw material solution supplied to the crystallization reaction tank at 25°C was varied by a value of 4.5 or less, the volume ratio of added water to the weight of the solid portion (amount of water added in the water addition step) was varied within the range of 0.5 L / kg to 10 L / kg, the pressure of the water supplied in the water addition step was varied within the range of 0.07 MPa to 0.90 MPa, the heating temperature in the melting step was varied within the range of 113°C to less than 185°C, and the pressure of the internal space of the cyclone and melting vessel in the melting step was varied within the range of 0.05 MPa to 0.80 MPa, and the product was evaluated in the same manner as in the above examples, and excellent results were obtained, similar to the above examples.

[0150] In contrast, satisfactory results were not obtained in each of the comparative examples. [Explanation of Symbols]

[0151] 1: Manufacturing equipment 10: Crystallization reactor 11: Raw material liquid supply section 12: Oxidizing agent supply unit 13: Slurry iodine outlet 15: Piping 16: Pump 20: Solid-liquid separation means 21: Main body 22: Slurry iodine supply port 23:Liquid part outlet 24 :Solid part outlet 25: Piping 30: Melting kettle 31: Solid portion supply port 32: Heating means 33: Molten iodine outlet 40: Water addition means 50: Cooling method (table flaker) 100: Iodine raw material solution 110: Slurry iodine 110a: Solid part 110b:Liquid part 120: Fused iodine 130: Product Iodine

Claims

1. The process involves preparing an iodine raw material solution containing iodide ions, A crystallization step to obtain slurry iodine by oxidizing the iodide ions in the iodine raw material solution and precipitating iodine, A separation step for separating the slurry iodine into a liquid portion and a solid portion, A water addition step involves adding water so that it comes into contact with the solid portion, A method for producing iodine, comprising a melting step of heating the solid portion to melt the iodine and obtain molten iodine, and separating the molten iodine from the water.

2. The method for producing iodine according to claim 1, wherein a centrifugal separator is used in the separation step.

3. The method for producing iodine according to claim 1 or 2, wherein the volume ratio of the water added in the water addition step to the weight of the solid portion is 0.5 L / kg or more and 10 L / kg or less.

4. The method for producing iodine according to claim 1 or 2, wherein at least a portion of the liquid portion of the slurry iodine separated in the separation step is recovered and reused as part of the iodine raw material solution.

5. The method for producing iodine according to claim 1 or 2, wherein the iodine concentration contained in the iodine raw material solution is greater than 30 g / L and less than or equal to 110 g / L.

6. A crystallization reaction tank for oxidizing iodide ions in an iodine raw material solution and precipitating iodine to obtain slurry iodine, A solid-liquid separation means for separating the slurry iodine into a liquid portion and a solid portion, A water-adding means for adding water so as to come into contact with the solid portion, An iodine production apparatus characterized by comprising a melting vessel that melts the iodine by heating the solid portion to produce molten iodine.

7. The iodine production apparatus according to claim 6, wherein the solid-liquid separation means is a centrifugal separator.

8. The iodine production apparatus according to claim 6 or 7, wherein at least a portion of the liquid portion of the slurry iodine separated by the solid-liquid separation means is recovered and supplied to the crystallization reaction tank as part of the iodine raw material solution.

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