How iodine is produced

Abstract

To provide a method for producing iodine that can reduce the concentration of iodine components in wastewater generated during the production of iodine. [Solution] The method for producing iodine of the present invention includes the steps of mixing a first solution with a first oxidant solution to obtain a second solution, reducing the iodine separated from the second solution to obtain a third solution, mixing a solution containing residues of the second solution with the second oxidant solution to obtain a fourth solution, reducing the iodine separated from the fourth solution to obtain a fifth solution, and mixing the third solution, the fifth solution, and an oxidant to obtain a solution containing iodine, and crystallizing and separating iodine from the iodine-containing solution to obtain iodine, wherein the concentration of the oxidant contained in the first oxidant solution relative to the total amount of the first solution and the first oxidant solution is 3.00 mmol / L or less, and the concentration of iodine ions contained in the first solution relative to the total amount of the first solution and the first oxidant solution is 4.80 mmol / L or less.

Description

[Technical Field]

[0001] The present invention relates to a method for producing iodine. [Background technology]

[0002] Various methods are known for producing iodine, and for example, Patent Document 1 discloses a method for producing iodine by the blowing-out method. Here, an example of a method for producing iodine by the blowing-out method is as follows. First, iodine ions in a solution containing iodine ions (e.g., brine) are oxidized to obtain a solution containing iodine. Next, the iodine-containing solution is supplied to a stripping tower, and the iodine-containing solution is blown into air to separate the iodine. The separated iodine is then reduced to obtain a solution containing iodine ions at a high concentration (concentrated solution). Next, the iodine ions in the concentrated solution are oxidized to obtain a solution containing iodine, and the iodine is then crystallized and separated from the iodine-containing solution. In this manner, iodine is obtained. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 02-208201 Summary of the Invention [Problem to be solved by the invention]

[0004] In the iodine production process, in order to improve the yield, it is necessary to extract iodine components (e.g., iodine (I2), iodine ions (I - ), iodate ion (IO3 - )) content may need to be reduced. The present inventors attempted to produce iodine by referring to the method described in Patent Document 1, and found that there were cases where the concentration of iodine components in wastewater generated during the production of iodine could not be sufficiently reduced, and that there was room for improvement.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing iodine that can reduce the concentration of iodine components in wastewater generated during the production of iodine. [Means for solving the problem]

[0006] As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by the following configuration. [1] A step 1a of mixing a first solution containing iodine ions with a first oxidant solution containing an oxidant to obtain a second solution containing iodine; a step 2a of separating iodine from the second solution and reducing the separated iodine to obtain a third solution containing iodine ions; a step 1b of mixing a solution containing a residue of the second solution obtained by separating iodine from the second solution in the step 2a with a second oxidant solution containing an oxidant to obtain a fourth solution containing iodine; a step 2b of separating iodine from the fourth solution and reducing the separated iodine to obtain a fifth solution containing iodine ions; a step 3 of mixing the third solution, the fifth solution, and an oxidizing agent to oxidize iodine ions to obtain a solution containing iodine, and crystallizing and separating iodine from the obtained solution containing iodine, a concentration of the oxidant contained in the first oxidant solution relative to the total amount of the first solution and the first oxidant solution is 3.00 mmol / L or less; a concentration of the iodine ions contained in the first solution relative to the total amount of the first solution and the first oxidant solution of 4.80 mmol / L or less. [2] The concentration of the oxidant contained in the first oxidant solution relative to the total amount of the first solution and the first oxidant solution is defined as M A1 [mmol / L], The concentration of the iodine ions contained in the first solution relative to the total amount of the first solution and the first oxidizer solution is defined as M A2 When expressed as [mmol / L], M A1 / M A2 The method for producing iodine according to [1], wherein the iodine content is 0.80 or less. [3] The concentration of the oxidant contained in the first oxidant solution relative to the total amount of the first solution and the first oxidant solution is defined as M A1 [mmol / L], The concentration of the oxidant contained in the second oxidant solution relative to the total amount of the solution containing the residue of the second solution and the second oxidant solution is defined as M B1 When expressed as [mmol / L], M A1 / M B1 The method for producing iodine according to [1] or [2], wherein the iodine content is 4.20 or less. [4] The method for producing iodine according to any one of [1] to [3], wherein a concentration of the oxidant contained in the second oxidant solution relative to a total amount of the solution containing residues of the second solution and the second oxidant solution is 0.81 mmol / L or less. [5] The method for producing iodine according to any one of [1] to [4], wherein a solution containing a residue of the fourth solution obtained by separating iodine from the fourth solution in step 2b is used as a component of the second solution in step 1a. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a method for producing iodine that can reduce the concentration of iodine components in wastewater generated during the production of iodine. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a partial schematic diagram showing an example of the configuration of an iodine production apparatus used in the iodine production method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, modes for carrying out the present invention will be described in detail. However, the embodiments of the present invention are not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and they do not limit the embodiments of the present invention.

[0010] In the present invention, the numerical range indicated using "to" includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present invention, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages.Furthermore, in the numerical ranges described in the present invention, the upper or lower limit value of the numerical range may be replaced with the value shown in the examples. In the present invention, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the solution, the content of each component means the total content of the multiple substances present in the solution, unless otherwise specified.

[0011] In the present invention, the iodine component means a substance having an iodine element, specifically, iodine (I2); iodine ion (I - ); iodate ion (IO3 - ), hypoiodite ion (IO - ) and other iodine oxoacid ions; I2Cl - , I3 - , ICl2 - and the like. The inorganic anion having an iodine element may be, for example, one produced by reducing iodine molecules in a concentrate solution with a reducing agent.

[0012] [Iodine production method] The method for producing iodine of the present invention (hereinafter also referred to as "the present production method") comprises the steps of: A step 1a of mixing a first solution containing iodine ions with a first oxidant solution containing an oxidant to obtain a second solution containing iodine; a step 2a of separating iodine from the second solution and reducing the separated iodine to obtain a third solution containing iodine ions; a step 1b of mixing a solution containing a residue of the second solution obtained by separating iodine from the second solution in the step 2a with a second oxidant solution containing an oxidant to obtain a fourth solution containing iodine; a step 2b of separating iodine from the fourth solution and reducing the separated iodine to obtain a fifth solution containing iodine ions; and step 3 of mixing the third solution, the fifth solution, and an oxidizing agent to oxidize iodine ions to obtain a solution containing iodine, and crystallizing and separating iodine from the obtained solution containing iodine to obtain iodine. In the present production method, the concentration of the oxidant contained in the first oxidant solution relative to the total amount of the first solution and the first oxidant solution is 3.00 mmol / L or less. In the present production method, the concentration of the iodine ions contained in the first solution relative to the total amount of the first solution and the first oxidant solution is 4.80 mmol / L or less.

[0013] According to this production method, the content of iodine components in the wastewater generated during the production of iodine can be reduced. Although the details of the reason for this are still unknown, it is presumed to be due to the following reasons. The method for producing iodine by the blowing-out method includes a step of oxidizing iodine ions in a solution containing iodine ions (e.g., brine) to obtain a solution containing iodine, and then blowing the solution containing iodine into air to separate the iodine. In this case, in order to recover more iodine (I2), it is possible to use a solution containing iodine ions with a high concentration before mixing with the oxidizing agent, or to increase the concentration of the oxidizing agent added to the solution containing iodine ions. However, when such a method is adopted, iodate ions (IO3) are generated by excessive oxidation of iodine ions. - ) may be contained in the solution in large amounts, which may result in a decrease in yield. To solve this problem, the present inventors carried out a step (first stage) of obtaining a third solution by carrying out steps 1a and 2a, and a step (second stage) of obtaining a fifth solution by carrying out steps 1b and 2b, and discovered that when the concentrations of the oxidizing agent and iodine ions in step 1a of the first stage were set to predetermined values ​​or less, the concentration of iodine components in the effluent generated in the second stage was reduced. This is presumably because excessive oxidation of iodine ions was suppressed in the first stage.

[0014] An example of an iodine production apparatus that can be used in this production method will be described below, and then each step in this production method will be described in detail.

[0015] <Iodine manufacturing equipment> 1 is a partial schematic diagram showing an example of the configuration of an iodine production apparatus used in this production method. The iodine production apparatus 100 is an apparatus that produces iodine using the blowing-out method (also called the blow-out method or the iodine vaporization absorption method), and includes a first stripper tower 10, a first absorption tower 20, a second stripper tower 30, and a second absorption tower 40. Unless otherwise specified, the components constituting the iodine production apparatus 100 may be the same as those constituting known iodine production apparatuses. Each pipe described later may be connected to a pump (not shown) for pressure-feeding the solution, etc. Furthermore, each pipe described later may be provided with a valve (not shown) for adjusting the flow rate of the solution.

[0016] The first stripper 10 and the first absorber 20 are also referred to as pre-stage towers in this specification, and are used to carry out step 2a, which will be described later.

[0017] The first stripping tower 10 is provided with a nozzle 11 for spraying a second solution (described later) containing iodine supplied from a pipe 50 into the first stripping tower 10, and a blower 12 for volatilizing the iodine in the second solution.

[0018] A pipe 60 is connected to the upper part of the first stripper tower 10. The pipe 60 is a pipe for supplying the iodine evaporated in the first stripper tower 10 to the first absorption tower 20, and is connected to the upper part of the first stripper tower 10. A pipe 55 is connected to the lower part of the first stripper tower 10. The pipe 55 is a pipe for supplying a fourth solution (described later) containing iodine to a nozzle 31 for spraying the fourth solution into the second stripper tower 30.

[0019] The pipe 50 is a pipe for supplying a second solution (described later) containing iodine to the nozzle 11. The pipe 52a is a pipe for supplying a first oxidizer solution (described later) containing an oxidizer to the pipe 50. The pipe 50 and the pipe 52a are connected at a junction C1 so that the solution flowing through the flow path in the pipe 50 and the solution flowing through the flow path in the pipe 52a can merge. At the junction C1, a first solution (described later) containing iodine ions supplied from the upstream side of the junction C1 in the pipe 50 and a first oxidizer solution (described later) containing an oxidizer supplied from the pipe 52a are mixed (corresponding to step 1a described later). That is, the second solution supplied to the nozzle 11 is obtained by mixing the first solution and the first oxidizer solution at the junction C1. The pipe 50 may be connected to a reservoir (not shown) that stores the first solution. 1, the pipe 50 and the pipe 52a are directly connected to each other, but the present invention is not limited to this. For example, a mixer may be installed at the confluence C1, and the solutions may be mixed in the mixer.

[0020] Pipe 51 is a pipe for supplying a solution containing an oxidizing agent to pipe 52a. Pipe 51 and pipe 52a are connected at a junction C2 so that the solution flowing through the flow path in pipe 51 and the solution flowing through the flow path in pipe 52a can merge. At the junction C2, the solution containing the oxidant supplied from the pipe 51 is mixed with a solution containing residues of the fourth solution (described later) supplied from the pipe 52a upstream of the junction C2. That is, the first oxidant solution (described later) containing the oxidant supplied to the junction C1 is obtained by mixing the solution containing the oxidant with the solution containing residues of the fourth solution at the junction C2. 1, the pipe 51 and the pipe 52a are directly connected to each other, but the present invention is not limited to this. For example, a mixer may be installed at the confluence C2, and the solutions may be mixed in the mixer. 1, an example in which a solution containing residues of the fourth solution is used to obtain the first oxidant solution is shown, but the present invention is not limited to this, and a solution containing residues of the fourth solution does not have to be used. In this case, a solution containing an oxidant supplied from the pipe 51 is used as the first oxidant solution.

[0021] A pipe 60 is connected to the upper part of the first absorption tower 20. The iodine separated from the second solution in the first stripper tower 10 is supplied to the first absorption tower 20 via the pipe 60. Here, a solution (not shown) containing a reducing agent is supplied into the first absorption tower 20. As a result, iodine supplied into the first absorption tower 20 via the piping 60 is reduced by the reducing agent, and a third solution (described later) containing iodine ions is obtained. A pipe 70 is connected to the lower part of the first absorption tower 20. The pipe 70 is a pipe for supplying the third solution that accumulates in the lower part of the first absorption tower 20 to a crystallization separation section (not shown). The crystallization separation section is not particularly limited as long as it is equipped with a mechanism for carrying out step 3 described below.

[0022] The second stripper 30 and the second absorber 40 are also referred to as subsequent towers in this specification, and are used to carry out step 2b, which will be described later.

[0023] The second stripper tower 30 is provided with a nozzle 31 for spraying a fourth solution (described later) containing iodine supplied from a pipe 55 into the second stripper tower 30, and a blower 32 for volatilizing the iodine in the fourth solution.

[0024] A pipe 61 is connected to the upper part of the second stripper tower 30. The pipe 61 is a pipe for supplying the iodine evaporated in the second stripper tower 30 to the second absorption tower 40, and is connected to the upper part of the second stripper tower 30. A pipe 52 is connected to the lower part of the second stripper tower 30. The pipe 52 is a pipe for supplying a solution (described later) containing residues of the fourth solution that accumulates in the lower part of the second stripper tower 30 to the confluence C2 and the confluence C4. The pipe 52 branches into a pipe 52a and a pipe 52b at a branch point B1.

[0025] Pipe 55 is a pipe for supplying a fourth solution (described later) to nozzle 31. Pipe 52b is a pipe for supplying a second oxidant solution (described later) containing an oxidant to pipe 55. Pipe 55 and pipe 52b are connected at a junction C3 so that the solution flowing through the flow path in pipe 55 and the solution flowing through the flow path in pipe 52b can merge. At the confluence C3, a solution containing residues of the second solution (described later) supplied from the upstream side of the confluence C3 in the pipe 55 and a second oxidizer solution containing an oxidizer (described later) supplied from the pipe 52b are mixed (corresponding to step 1b described later). That is, the fourth solution supplied to the nozzle 31 is obtained by mixing the solution containing residues of the second solution and the second oxidizer solution at the confluence C3. 1, the pipe 55 and the pipe 52b are directly connected to each other, but the present invention is not limited to this. For example, a mixer may be provided at the confluence C3, and the solutions may be mixed in the mixer.

[0026] The pipe 56 is a pipe for supplying a solution containing an oxidizing agent to the pipe 52b. The pipe 56 and the pipe 52b are connected at a junction C4 so that the solution flowing through the flow path in the pipe 56 and the solution flowing through the flow path in the pipe 52b can merge. At the junction C4, the solution containing the oxidant supplied from the pipe 56 is mixed with a solution containing residues of the fourth solution (described later) supplied from the pipe 52b upstream of the junction C4. That is, the second oxidant solution containing the oxidant (described later) supplied to the junction C3 is obtained by mixing the solution containing the oxidant with the solution containing residues of the fourth solution at the junction C4. 1, the pipe 56 and the pipe 52b are directly connected to each other, but the present invention is not limited to this. For example, a mixer may be provided at the confluence C4, and the solutions may be mixed in the mixer. 1, a solution containing residues of the fourth solution is used to obtain the second oxidizer solution, but the present invention is not limited to this, and a solution containing residues of the fourth solution may not be used. In this case, a solution containing an oxidizer supplied from the pipe 56 is used as the second oxidizer solution.

[0027] A pipe 61 is connected to the upper part of the second absorption tower 40. The iodine separated from the fourth solution in the second stripper tower 30 is supplied to the second absorption tower 40 via the pipe 61. Here, a solution (not shown) containing a reducing agent is supplied into the second absorption tower 40. As a result, iodine supplied into the second absorption tower 40 via the pipe 61 is reduced by the reducing agent, and a fifth solution (described later) containing iodine ions is obtained. A pipe 71 is connected to the lower part of the second absorption tower 40. The pipe 71 is a pipe for supplying the fifth solution that accumulates in the lower part of the second absorption tower 40 to the above-mentioned crystallization separation part (not shown).

[0028] <Process 1a> Step 1a is a step of mixing a first solution containing iodine ions with a first oxidant solution containing an oxidant to obtain a second solution containing iodine.

[0029] Step 1a will be described using an example in which the iodine production apparatus 100 shown in FIG. 1 is used. The first solution flowing through the flow path in the pipe 50 and the first oxidizer solution flowing through the flow path in the pipe 52a join at the joining point C1, whereby the two solutions are mixed. As a result, the iodine ions (I - ) is oxidized by an oxidizing agent to obtain a second solution containing iodine (I2).

[0030] (First solution) The first solution contains iodine ions (I - ) is an aqueous solution containing Examples of the first solution include brine (underground seawater), or a mixed solution of brine and at least one selected from the group consisting of waste liquid generated in the method for producing iodine (for example, a solution containing residues of the fourth solution described below, or crystallization waste liquid), a concentrated solution of brine, a solution obtained by mixing brine and iodide, a concentrated solution of waste liquid generated in the method for producing iodine, a concentrated solution of crystallization waste liquid, a recycled liquid containing iodine, and a concentrated solution of a recycled liquid containing iodine. In addition to iodine components such as iodine ions, the brine may also contain salt components similar to those found in seawater, such as sodium chloride, potassium chloride, calcium chloride, and magnesium sulfate. Here, the recycled liquid containing iodine refers to a solution containing iodine obtained by removing impurities in a separate process from waste liquid discharged from a manufacturing process in which iodine is used, and includes, for example, waste liquid discharged in the manufacturing process of polarizing films.

[0031] The concentration of iodine ions in the first solution is preferably 3.50 mmol / L or more, more preferably 4.50 mmol / L or more, and even more preferably 5.00 mmol / L or more, in order to further reduce the concentration of iodine components in the effluent. The concentration of iodide ions in the first solution is preferably 8.00 mmol / L or less, more preferably 7.50 mmol / L or less, and even more preferably 7.30 mmol / L or less, in terms of further improving the yield. The concentration of iodide ions in the first solution can be determined by using ion chromatography.

[0032] In step 1a, the concentration of iodine ions contained in the first solution relative to the total amount of the first solution and the first oxidizing agent solution (hereinafter referred to as "M A2 ") is 4.80 mmol / L or less, and from the viewpoint of further reducing the concentration of iodine components in the effluent, it is preferably 4.75 mmol / L or less, more preferably 4.60 mmol / L or less, and even more preferably 4.40 mmol / L or less. M A2 In terms of further improving the yield, the concentration is preferably 2.50 mmol / L or more, more preferably 3.00 mmol / L or more, and even more preferably 3.50 mmol / L or more.

[0033] (First oxidant solution) The first oxidant solution is an aqueous solution containing an oxidant.

[0034] The first oxidant solution may contain water (preferably soft water) and an oxidant, but may further contain a solution containing residues of the fourth solution (described below). 1, the first oxidant solution is obtained by joining at a joining point C2 a solution containing an oxidant (specifically, a solution containing an oxidant and water (preferably soft water)) flowing through the flow path in pipe 51 and a solution containing residues of the fourth solution (described below) flowing through the flow path in pipe 52a. In this case, the solution containing residues of the fourth solution is used as a component of the second solution in step 1a. In preparing the first oxidant solution, the solution containing the residue of the fourth solution may be used, but need not be used. In this case, the solution containing the oxidant flowing through the flow path in the pipe 51 is used as the first oxidant solution.

[0035] Specific examples of the oxidizing agent include nitrite, hydrogen peroxide, sodium hypochlorite (sodium hypochlorite), iodate, periodate, and chlorine. Among them, sodium hypochlorite is preferred because of its ease of handling.

[0036] The concentration of the oxidizing agent in the first oxidizing agent solution is preferably 1.0 mmol / L or more, more preferably 2.0 mmol / L or more, even more preferably 4.0 mmol / L or more, and still more preferably 10 mmol / L or more, in order to further improve the yield. The concentration of the oxidizing agent in the first oxidizing agent solution is preferably 50 mmol / L or less, more preferably 30 mmol / L or less, more preferably 20 mmol / L or less, and even more preferably 15 mmol / L or less, in order to further reduce the concentration of iodine components in the effluent.

[0037] In step 1a, the concentration of the oxidizing agent contained in the first oxidizing agent solution relative to the total amount of the first solution and the first oxidizing agent solution (hereinafter referred to as "M A1 ") is 3.00 mmol / L or less, preferably 2.99 mmol / L or less, and more preferably 2.98 mmol / L or less, in order to further reduce the concentration of iodine components in the effluent. M A1 In terms of further improving the yield, the concentration is preferably 1.20 mmol / L or more, more preferably 1.40 mmol / L or more, and even more preferably 1.80 mmol / L or more.

[0038] In step 1a, the above M A2 The above M A1 The ratio (M A1 / M A2 ) is preferably 0.80 or less, more preferably 0.75 or less, and even more preferably 0.74 or less, in order to further reduce the concentration of iodine components in the effluent. M A1 / M A2 is preferably 0.40 or more, more preferably 0.45 or more, and even more preferably 0.48 or more, in terms of further improving the yield.

[0039] (Second solution) The second solution is an aqueous solution containing iodine (I2) and is used in step 2a described below. The concentration of iodine in the second solution is preferably 1.50 mmol / L or more, more preferably 2.00 mmol / L or more, and even more preferably 3.00 mmol / L or more. The concentration of iodine in the second solution is preferably 4.00 mmol / L or less, more preferably 3.50 mmol / L or less. The concentration of iodine in the second solution is, for example, the concentration of iodine ions in the first solution (M A2 ) minus the iodine concentration in the solution containing the residue of the second solution.

[0040] <Process 2a> Step 2a is a step of separating iodine from the second solution and reducing the separated iodine to obtain a third solution containing iodine ions.

[0041] Step 2a will be described using the iodine production apparatus 100 of FIG. 1 as an example. The second solution obtained in step 1a flows through a flow path in the pipe 50 downstream of the junction C1 and is supplied to the nozzle 11 of the first stripper tower 10. Next, in the first stripper tower 10, the second solution discharged from the nozzle 11 and the gas supplied from the blower 12 undergo gas-liquid contact (countercurrent contact) to volatilize iodine. In this way, iodine is separated from the second solution. Furthermore, the solution containing the residue of the second solution obtained by separating iodine from the second solution flows through the flow path of the pipe 55 provided in the lower part of the first stripper tower 10, and is supplied to the junction C3. Details of the solution containing the residue of the second solution will be described later in step 1b.

[0042] Next, the iodine vaporized in the first stripper tower 10 flows through the flow path in the pipe 60 and is supplied to the first absorption tower 20. The iodine supplied to the first absorption tower 20 comes into contact with a solution containing a reducing agent discharged from a nozzle (not shown) provided in the first absorption tower 20. As a result, the iodine separated from the second solution is reduced by the reducing agent to produce iodine ions (I - ) is obtained.

[0043] (solution containing a reducing agent) In step 2a, in order to reduce the iodine separated from the second solution, a solution containing a reducing agent is preferably used in the first absorption tower 20. The solution containing a reducing agent is an aqueous solution containing a reducing agent.

[0044] Specific examples of the reducing agent include sodium sulfite and sodium bisulfite. The concentration of the reducing agent in the solution containing the reducing agent is not particularly limited and may be set within a known range.

[0045] (third solution) The third solution contains iodine ions (I - ) and is used in step 3 described below. The concentration of iodide ions in the third solution is preferably 0.60 mol / L or more, more preferably 0.70 mol / L or more, and even more preferably 0.75 mol / L or more. The concentration of iodide ions in the third solution is preferably 2.60 mol / L or less, more preferably 2.40 mol / L or less, and even more preferably 1.20 mol / L or less. The concentration of iodide ions in the third solution can be determined in the same manner as the concentration of iodide ions in the first solution.

[0046] <Process 1b> Step 1b is a step of mixing a solution containing the residue of the second solution with a second oxidant solution containing an oxidant to obtain a fourth solution containing iodine.

[0047] Step 1b will be described using an example in which the iodine production apparatus 100 shown in FIG. 1 is used. The solution containing the residue of the second solution flowing through the flow path in the pipe 55 and the second oxidizing agent solution flowing through the flow path in the pipe 52b join at the joining point C3, whereby the two solutions are mixed. As a result, the iodine ions (I - ) is oxidized by an oxidizing agent to give a fourth solution containing iodine (I2).

[0048] (Solution containing residues of the second solution) The solution containing the residue of the second solution is the waste liquid resulting from carrying out step 2a, and is used as a raw material for the fourth solution in step 1b. The solution containing the residue of the second solution contains iodine ions (I - The solution containing the residue of the second solution preferably contains iodine components other than iodine ions (for example, iodate ions (IO3 - )) may be included.

[0049] The concentration of iodine ions in the solution containing the residue of the second solution is preferably 0.75 mmol / L or more, more preferably 0.95 mmol / L or more, and even more preferably 1.10 mmol / L or more, in order to further reduce the concentration of iodine components in the effluent. The concentration of iodide ions in the solution containing the residue of the second solution is preferably 1.60 mmol / L or less, more preferably 1.40 mmol / L or less, and even more preferably 1.30 mmol / L or less, in order to further improve the yield. The concentration of iodine ions in the solution containing the residue of the second solution can be determined in the same manner as the concentration of iodine ions in the first solution.

[0050] In step 1b, the concentration of iodine ions contained in the solution containing the residue of the second solution relative to the total amount of the solution containing the residue of the second solution and the second oxidizing agent solution (hereinafter referred to as "M B2 " is preferably 1.20 mmol / L or less, more preferably 1.10 mmol / L or less, and even more preferably 1.00 mmol / L or less, in order to further reduce the concentration of iodine components in the effluent. M B2 In terms of further improving the yield, the concentration is preferably 0.60 mmol / L or more, more preferably 0.70 mmol / L or more, and even more preferably 0.90 mmol / L or more.

[0051] (Second oxidizer solution) The second oxidant solution is an aqueous solution containing an oxidant.

[0052] The second oxidant solution may contain water (preferably soft water) and an oxidant, but may further contain a solution containing residues of the fourth solution (described below). 1, the second oxidant solution is obtained by joining at a joining point C4 a solution containing an oxidant (specifically, a solution containing an oxidant and water (preferably soft water)) flowing through the flow path in pipe 56 and a solution containing residues of the fourth solution (described below) flowing through the flow path in pipe 52b. In this case, the solution containing residues of the fourth solution is used as a raw material for the fourth solution in step 1b. In preparing the second oxidant solution, the solution containing the residue of the fourth solution may be used, but need not be used. In this case, the solution containing the oxidant flowing through the flow path in the pipe 56 is used as the second oxidant solution.

[0053] Specific examples of the oxidizing agent contained in the second oxidizing agent solution are the same as those of the oxidizing agent contained in the first oxidizing agent solution.

[0054] The concentration of the oxidizing agent in the second oxidizing agent solution is preferably 1.0 mmol / L or more, more preferably 2.0 mmol / L or more, and further preferably 4.0 mmol / L or more. The concentration of the oxidizing agent in the second oxidizing agent solution is preferably 10 mmol / L or less, more preferably 8.0 mmol / L or less, and even more preferably 5.0 mmol / L or less.

[0055] In step 1b, the concentration of the oxidizing agent contained in the second oxidizing agent solution relative to the total amount of the solution containing the residue of the second solution and the second oxidizing agent solution (hereinafter referred to as "M B1 " is preferably 1.00 mmol / L or less, more preferably 0.90 mmol / L or less, and even more preferably 0.81 mmol / L or less, in order to further reduce the concentration of iodine components in the effluent. M B1 In terms of further improving the yield, the concentration is preferably 0.40 mmol / L or more, more preferably 0.50 mmol / L or more, and even more preferably 0.60 mmol / L or more.

[0056] The above M B1The above M A1 The ratio (M A1 / M B1 ) is preferably 4.20 or less, more preferably 4.00 or less, and even more preferably 3.90 or less, in order to further reduce the concentration of iodine components in the effluent. M A1 / M B1 is preferably 3.00 or more, more preferably 3.30 or more, and even more preferably 3.50 or more, in terms of further improving the yield.

[0057] (4th solution) The fourth solution is an aqueous solution containing iodine (I2) and is used in step 2b described below. The concentration of iodine in the fourth solution is preferably 0.60 mmol / L or more, more preferably 0.70 mmol / L or more, and even more preferably 0.90 mmol / L or more. The concentration of iodine in the fourth solution is preferably 1.20 mmol / L or less, more preferably 1.10 mmol / L or less, and even more preferably 1.00 mmol / L or less. The concentration of iodine in the fourth solution can be determined in the same manner as the concentration of iodine in the second solution.

[0058] <Process 2b> Step 2b is a step of separating iodine from the fourth solution and reducing the separated iodine to obtain a fifth solution containing iodine ions.

[0059] Step 2b will be described using the iodine production apparatus 100 of FIG. 1 as an example. The fourth solution obtained in step 1b flows through a flow path in pipe 55 downstream of junction C3 and is supplied to nozzle 31 of second stripper tower 30. Next, in second stripper tower 30, the fourth solution discharged from nozzle 31 and the gas supplied from blower 32 undergo gas-liquid contact (countercurrent contact) to volatilize iodine. In this way, iodine is separated from the fourth solution. In addition, a solution containing residue of the fourth solution obtained by separating iodine from the fourth solution flows through the flow path of piping 52 provided at the bottom of the second stripper tower 30 and is supplied to junction C2 and junction C4.

[0060] Next, the iodine vaporized in the second stripper tower 30 flows through the flow path in the pipe 61 and is supplied to the second absorption tower 40. The iodine supplied to the second absorption tower 40 comes into contact with a solution containing a reducing agent discharged from a nozzle (not shown) provided in the second absorption tower 40. As a result, the iodine separated from the fourth solution is reduced by the reducing agent to produce iodine ions (I - ) is obtained.

[0061] (solution containing a reducing agent) In step 2b, in order to reduce the iodine separated from the second solution, a solution containing a reducing agent is preferably used in the first absorption tower 20. The solution containing a reducing agent is an aqueous solution containing a reducing agent. Specific examples of the reducing agent that can be used in step 2b are the same as those of the reducing agent that can be used in step 2a. In step 2b, the concentration of the reducing agent in the solution containing the reducing agent is not particularly limited and may be set in accordance with a known range.

[0062] (Solution containing residues of the fourth solution) The residue-containing solution of the fourth solution is the wastewater resulting from carrying out step 2b. The solution containing the residue of the fourth solution is obtained by the present production method, and therefore has a low concentration of components that inhibit the oxidation reaction of iodine ions (specifically, iodine, etc.). Therefore, even when the solution containing the residue of the fourth solution is used as a component of the second solution in step 1a, the oxidation reaction of iodine ions in step 1a is not easily inhibited, and the oxidation reaction of iodine ions is promoted.

[0063] The solution containing the residue of the fourth solution contains iodine ions (I - The solution containing the residue of the fourth solution preferably contains iodine ions (I -) other iodine components (e.g., iodate ion (IO3 - )) may be included.

[0064] The concentration of iodide ions in the residue-containing fourth solution is preferably 100 μmol / L or less, more preferably 50.0 μmol / L or less, even more preferably 30.0 μmol / L or less, and particularly preferably 20.0 μmol / L or less. The lower the concentration of iodide ions in the residue-containing solution of the fourth solution, the better, but the lower limit thereof is usually 0.01 μmol / L. The concentration of iodine ions in the residue-containing solution of the fourth solution can be determined in the same manner as the concentration of iodine ions in the first solution.

[0065] The concentration of the iodine component in the residue-containing solution of the fourth solution is preferably 150 μmol / L or less, more preferably 80.0 μmol / L or less, more preferably 40.0 μmol / L or less, still more preferably 40.0 μmol / L or less, and even more preferably 30.0 μmol / L or less. The lower the concentration of iodide ions in the residue-containing solution of the fourth solution, the better, but the lower limit thereof is usually 0.01 μmol / L. The concentration of the iodine component in the fourth solution containing the residue can be determined by using ion chromatography.

[0066] (Fifth solution) The fifth solution contains iodine ions (I - ) and is used in step 3 described below. The concentration of iodide ions in the fifth solution is preferably 0.60 mol / L or more, more preferably 0.70 mol / L or more, and even more preferably 0.75 mol / L. The concentration of iodide ions in the third solution is preferably 2.60 mol / L or less, more preferably 2.40 mol / L or less, and even more preferably 1.20 mol / L or less. The concentration of iodide ions in the fifth solution can be determined in the same manner as the concentration of iodide ions in the first solution.

[0067] <Process 3> Step 3 is a step of mixing the third solution, the fifth solution, and an oxidizing agent to oxidize iodine ions to obtain a solution containing iodine, and then crystallizing and separating iodine from the obtained solution containing iodine to obtain iodine. The crystallization and separation of iodine in step 3 can be carried out by a known method.

[0068] Step 3 will be described using the iodine production apparatus 100 of FIG. 1 as an example. The third solution obtained in step 2a flows through the flow path in pipe 70 and is supplied to a crystallization separation section (not shown). The fifth solution obtained in step 2b flows through the flow path in pipe 71 and is supplied to a crystallization separation section (not shown). In the crystallization separation section, an oxidizing agent is added to the third solution and the fifth solution, thereby crystallizing iodine and recovering the iodine as sludgy iodine.

[0069] Specific examples of oxidizing agents that can be used in step 3 include nitrites, hydrogen peroxide, iodates, periodates, and chlorine. Specific examples of acids that can be used to acidify the solution in step 3 include hydrochloric acid, nitric acid, and sulfuric acid, with sulfuric acid being preferred.

[0070] <Other processes> The present production method may include steps other than those described above (hereinafter also referred to as "other steps"). The other steps are not particularly limited as long as they are steps that are usually carried out in a method for producing iodine, and examples thereof include a melting step of melting and purifying the iodine obtained in step 3, and a manufacturing step of cooling the molten iodine and then molding the cooled iodine to produce an iodine product. The melting method in the melting step may be a method in which iodine is heated at 120 to 160°C to melt it. The molding method in the manufacturing process includes granulation, crushing, and the like. [Example]

[0071] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment details, and treatment procedures shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0072] [Example 1] Using the apparatus shown in Figure 1, iodine was produced according to the following procedure.

[0073] <Process 1a> The first solution (brine containing iodine) and the first oxidant solution (a solution obtained by mixing a solution containing the residue of the fourth solution, soft water, and sodium hypochlorite) were supplied to the confluence C1 to obtain a second solution containing iodine (I2). In step 1a, the above-mentioned M A1 and M A2 The amounts of each solution mixed were adjusted so that the values ​​shown in Table 1 were obtained.

[0074] <Process 2a> The second solution was supplied to the nozzle 11, and the second solution discharged from the nozzle 11 was brought into contact with a gas supplied from the blower 12, thereby volatilizing iodine in the first stripper tower 10. In this way, iodine was separated from the second solution. Next, the iodine vaporized in the first stripper 10 was supplied to the first absorber 20, and the iodine supplied to the first absorber 20 was brought into contact with a solution containing a reducing agent discharged from a nozzle (not shown) provided in the first absorber 20. In this way, iodine ions (I - ) to obtain a third solution.

[0075] <Process 1b> A solution containing the residue of the second solution obtained by separating iodine from the second solution and a second oxidant solution (a solution obtained by mixing a solution containing the residue of the fourth solution, soft water, and sodium hypochlorite) were supplied to a confluence C3 to obtain a fourth solution containing iodine. B1 and M B2 The amounts of each solution mixed were adjusted so that the values ​​shown in Table 1 were obtained.

[0076] <Process 2b> The fourth solution was supplied to the nozzle 31, and the fourth solution discharged from the nozzle 31 was brought into contact with a gas supplied from the blower 32, thereby volatilizing iodine in the second stripper tower 30. In this way, iodine was separated from the fourth solution. Next, the iodine vaporized in the second stripper tower 30 was supplied to the second absorption tower 40, and the iodine supplied to the second absorption tower 40 was brought into contact with a solution containing a reducing agent discharged from a nozzle (not shown) provided in the second absorption tower 40. In this way, iodine ions (I - ) was obtained.

[0077] <Process 3> The third and fifth solutions obtained as described above were supplied to a crystallization separation section (not shown), and an oxidizing agent (a solution containing sodium hypochlorite) was added to the third and fifth solutions. In this way, iodine was separated by crystallization from the third and fifth solutions to obtain iodine.

[0078] [Examples 2 to 4] In step 1a, M A1 and M A2 The mixing amounts of each solution are adjusted so that the value of M B1 and M B2 The amounts of the solutions mixed were adjusted so that the values ​​of were as shown in Table 1. Other than this, iodine was produced in the same manner as in Example 1.

[0079] [Comparative Examples 1 to 3] In step 1a, M A1 and M A2 Iodine was produced in the same manner as in Example 1, except that the amounts of the solutions mixed were adjusted so that the values ​​of were the values ​​in Table 1, and steps 1b and 2b were not performed. That is, in Comparative Examples 1 to 3, iodine was produced only using the front-stage tower, without using the rear-stage tower.

[0080] [Comparative Examples 4 to 5] In step 1a, M A1 and M A2The mixing amounts of each solution are adjusted so that the value of M B1 and M B2 The amounts of the solutions mixed were adjusted so that the values ​​of were as shown in Table 1. Other than this, iodine was produced in the same manner as in Example 1.

[0081] [Evaluation results] Table 1 shows the yields and other information for the methods for producing iodine in the examples and comparative examples.

[0082] In Table 1, the "pre-column yield" was calculated as follows. Pre-column yield (%) = 100 × {(mass of iodine ions contained in the total amount of the first solution used in the pre-column) - (mass of iodine components contained in the total amount of the solution including the residue of the second solution discharged from the pre-column)} / (mass of iodine ions contained in the total amount of the first solution used in the pre-column)

[0083] In Table 1, the "second-stage column yield" was calculated as follows. Second-stage column yield (%) = 100 × {(mass of iodine ions contained in the total amount of solution including residues of the second solution used in the second-stage column) - (mass of iodine components contained in the total amount of solution including residues of the fourth solution discharged from the second-stage column)} / (mass of iodine ions contained in the total amount of solution including residues of the second solution used in the first-stage column)

[0084] In Table 1, the "total yield" is the same as the "pre-column yield" for Comparative Examples 1 to 3, which used only the pre-column, and was calculated as follows for Examples 1 to 4 and Comparative Examples 4 to 5, which used both the pre-column and the post-column. Overall yield (%) = 100 × {(mass of iodine ions contained in the total amount of the first solution used in the pre-column) - (mass of iodine components contained in the total amount of the solution including the residue of the fourth solution discharged from the post-column)} / (mass of iodine ions contained in the total amount of the first solution used in the pre-column)

[0085] In Table 1, “M A1 " means the concentration of the oxidant contained in the first oxidant solution relative to the total amount of the first solution and the first oxidant solution. Also, "M A2 " means the concentration of iodide ions contained in the first solution relative to the total amount of the first solution and the first oxidizer solution. Also, "M B1 " means the concentration of the oxidant contained in the second oxidant solution relative to the total amount of the solution containing the residue of the second solution and the second oxidant solution. Also, "M B2 " means the concentration of iodide ions contained in the solution containing the residue of the second solution relative to the total amount of the solution containing the residue of the second solution and the second oxidizer solution.

[0086] In Table 1, the iodine concentration, I2 concentration, and I - Concentration and IO3 - The concentration was measured as follows. The I2 concentration was measured using an Agilent Technologies Cary 60 UV-vis spectrophotometer. - Concentration and IO3 - The concentration was measured using a "Dionex Integrion HPIC system" (ion chromatograph) manufactured by Thermo Scientific. Each solution contains iodine components, such as I2 and I - , and IO3 - Therefore, the I2 concentration, I - Concentration and IO3 - The total concentration was taken as the iodine component concentration.

[0087] [Table 1]

[0088] The iodine component concentration in the waste liquid finally obtained by the iodine production methods of Examples 1 to 4 corresponds to the "iodine component concentration in the solution containing the residue of the fourth solution" in Table 1. The iodine component concentration in the wastewater finally obtained by the iodine production methods of Comparative Examples 1 to 3 corresponds to the "iodine component concentration in the solution containing the residue of the second solution" in Table 1. The iodine component concentration in the wastewater finally obtained by the iodine production methods of Comparative Examples 4 and 5 corresponds to the "iodine component concentration in the solution containing the residue of the fourth solution" in Table 1. From the results in Table 1, it was confirmed that the use of this production method makes it possible to reduce the concentration of iodine components in the wastewater generated during the production of iodine (Examples 1 to 4). [Explanation of symbols]

[0089] 10. First Dissipation Tower 11,31 Nozzle 12,32 Blower 20. First Absorption Tower 30 Second Dissipation Tower 40 Second Absorption Tower 50, 51, 52, 52a, 52b, 55, 56 Piping 60,61 Piping 70,71 Piping 100 Iodine manufacturing equipment C1,C2,C3,C4 confluence B1 Junction

Claims

1. A step 1a of mixing a first solution containing iodine ions with a first oxidizer solution containing an oxidizer to obtain a second solution containing iodine; Step 2a: separating iodine from the second solution and reducing the separated iodine to obtain a third solution containing iodine ions; a step 1b of mixing a solution containing a residue of the second solution obtained by separating iodine from the second solution in the step 2a with a second oxidant solution containing an oxidant to obtain a fourth solution containing iodine; Step 2b: separating iodine from the fourth solution and reducing the separated iodine to obtain a fifth solution containing iodine ions; a step 3 of mixing the third solution, the fifth solution, and an oxidizing agent to oxidize iodine ions to obtain a solution containing iodine, and crystallizing and separating iodine from the obtained solution containing iodine, a concentration of the oxidant contained in the first oxidant solution relative to a total amount of the first solution and the first oxidant solution is 3.00 mmol / L or less; a concentration of the iodine ions contained in the first solution relative to a total amount of the first solution and the first oxidant solution is 4.80 mmol / L or less.

2. The concentration of the oxidant contained in the first oxidant solution relative to the total amount of the first solution and the first oxidant solution is M Ａ１ [mmol / L], The concentration of the iodine ions contained in the first solution relative to the total amount of the first solution and the first oxidizer solution is defined as M Ａ２ When expressed as [mmol / L], M Ａ１ / M Ａ２ The method for producing iodine according to claim 1, wherein the iodine content is 0.80 or less.

3. The concentration of the oxidant contained in the first oxidant solution relative to the total amount of the first solution and the first oxidant solution is M Ａ１ [mmol / L], The concentration of the oxidant contained in the second oxidant solution relative to the total amount of the solution containing the residue of the second solution and the second oxidant solution is M Ｂ１ When expressed as [mmol / L], M Ａ１ / M Ｂ１ The method for producing iodine according to claim 1 or 2, wherein the iodine content is 4.20 or less.

4. 3. The method for producing iodine according to claim 1, wherein a concentration of the oxidant contained in the second oxidant solution with respect to a total amount of the solution containing the residue of the second solution and the second oxidant solution is 0.81 mmol / L or less.

5. 3. The method for producing iodine according to claim 1, wherein a solution containing a residue of the fourth solution obtained by separating iodine from the fourth solution in step 2b is used as a component of the second solution in step 1a.

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