How iodine is produced

Abstract

Iodine is produced without using waste brine. The method for producing iodine of the present invention involves mixing a diluted solution of an oxidizing agent with dilution water (excluding waste brine) with natural brine, thereby oxidizing the iodide ions contained in the natural brine and liberating iodine. Sodium hypochlorite can be used as the oxidizing agent.

Description

[Technical Field]

[0001] The present invention relates to a method for producing iodine by oxidizing natural brine with an oxidizing agent. [Background technology]

[0002] In the method for producing iodine described in Patent Document 1, a mixture of waste brine and chlorine (oxidizing agent) is passed through a packed bed, and then this mixture is mixed with natural brine to liberate iodine, thereby producing iodine.

[0003] In the method for producing iodine described in Patent Document 2, an oxidizing agent is directly added to an iodine-containing liquid containing ions containing iodine element and a metal salt, and the resulting mixed liquid is brought into gas-liquid contact with a gas in a stripper tower to volatilize the iodine. Thereafter, the iodine discharged from the stripper tower is recovered as an absorption liquid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2-184504 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-184837 Summary of the Invention [Problem to be solved by the invention]

[0005] When waste brine is used as in Patent Document 1, the oxidizing agent must be added in excess because impurities contained in the waste brine decompose the oxidizing agent. In Patent Document 2, the iodine-containing solution contains less components that consume the oxidizing agent, allowing the oxidizing agent to be added directly.

[0006] The present invention provides a technique for producing iodine without using waste brine, by a means different from that described in Patent Documents 1 and 2. [Means for solving the problem]

[0007] The method for producing iodine of the present invention involves mixing a diluted solution of an oxidizing agent diluted with dilution water (excluding waste brine) with natural brine, thereby oxidizing iodide ions contained in the natural brine and liberating iodine.

[0008] As the oxidizing agent, hypochlorite can be used.

[0009] The dilution water can be soft water with a hardness of 5 mg / L or less, or water that has an effective chlorine concentration of 0.11% or more when an oxidizing agent with an effective chlorine concentration of 12% is diluted 50 times.

[0010] The diluted solution may have a ratio of chlorine equivalents per iodine equivalent of 3.0 or less. [Effects of the Invention]

[0011] According to the present invention, iodine can be produced without using waste brine. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the method for producing iodine according to the present embodiment, an oxidizing agent is diluted with dilution water, the diluted solution containing the oxidizing agent is mixed with natural brine to liberate iodine, and the liberated iodine is then recovered. This will be described in detail below.

[0013] (Diluted water) Dilution water is water used to dilute the concentration of an oxidant, and examples thereof include ion-exchanged water, groundwater, and natural brine. Ion-exchanged water is water in which the amount of impurities contained in tap water has been reduced by contacting tap water with an ion exchange resin. Groundwater is water that exists below the earth's surface. Natural brine is water that contains salt, and examples thereof include seawater and brackish water.

[0014] Since the dilution water may contain impurities, a process for removing the impurities can be carried out. For example, this process may involve a process using an RO membrane (reverse osmosis membrane). Alternatively, a water softening process may be carried out to reduce the content of hardness components (divalent or higher ions such as calcium ions, magnesium ions, and aluminum ions) in the dilution water. For example, the water softening process may involve a process using an ion exchange resin, a process using an RO membrane, or an electrolytic process. The above-mentioned processes may be carried out alone or in combination.

[0015] The dilution water that has been softened preferably has a hardness of 5 mg / L or less. By using dilution water with a hardness of 5 mg / L or less, it is possible to suppress the formation of scale caused by hardness components.

[0016] The dilution water can be one that will result in an effective chlorine concentration of 0.11% or more when an oxidizing agent with an effective chlorine concentration of 12% is diluted 50 times. Here, it is preferable to use dilution water that will result in an effective chlorine concentration of 0.20% or more when an oxidizing agent with an effective chlorine concentration of 12% is diluted 50 times. Examples of such dilution water include ion-exchanged water, groundwater, and natural brine that has been treated with a reverse osmosis (RO) membrane.

[0017] (oxidizing agent) The oxidizing agent oxidizes iodide ions contained in natural brine, and can liberate iodine by oxidizing the iodide ions. Examples of the oxidizing agent that can be used include hypochlorite, nitrite, hydrogen peroxide, iodate, periodate, and chlorine. Here, from the viewpoint of safety, it is preferable to use hypochlorite, particularly sodium hypochlorite.

[0018] (Iodine production method) First, dilution water and an oxidizing agent are mixed to produce a diluted solution containing the oxidizing agent. Next, the diluted solution and natural brine are mixed (e.g., stirred) to oxidize the iodide ions contained in the natural brine, liberating iodine. Iodine is obtained by extracting the liberated iodine.

[0019] As a method for extracting iodine, any known method can be appropriately adopted, such as an ion exchange resin method in which iodine is extracted by adsorbing it onto an ion exchange resin, or a blow-out method in which vaporized iodine is taken into an absorption liquid and extracted.

[0020] In the mixture of the diluted solution and natural brine, the ratio of chlorine equivalents per iodine equivalent (equivalent ratio) is preferably 3.0 or less. When the blowout method described above is used, the equivalent ratio can be 1.0 or more. Here, the equivalent ratio is preferably 1.5 or more. [Example]

[0021] (Type of dilution water) The decomposition effect of sodium hypochlorite depending on the type of dilution water was examined. The dilution water used was ion-exchanged water, groundwater, wastewater treated with an RO membrane (waste brine), and wastewater not treated with an RO membrane (waste brine), and the sodium hypochlorite used was sodium hypochlorite with an effective chlorine concentration of 12%. The dilution ratio was kept constant (50 times) for all dilution waters.

[0022] The iodide ions in 1 g of potassium iodide were oxidized using sodium hypochlorite diluted with dilution water, and the available chlorine concentration of the sodium hypochlorite solution was measured (iodine method). The measurement results are shown in Table 1 below.

[0023] [Table 1]

[0024] In Table 1 above, the concentration of sodium hypochlorite diluted with ion-exchanged water is set to 100% (standard), and the concentrations of sodium hypochlorite diluted with groundwater, waste brine (with RO membrane treatment), and waste brine (without RO membrane treatment) are shown.

[0025] When waste brine (without RO membrane treatment) was used, the effective chlorine concentration was lower than when other dilution waters were used. When wastewater (without RO membrane treatment) and sodium hypochlorite were mixed, bubbles were observed to form, so it is assumed that impurities in the waste brine caused the sodium hypochlorite to decompose, resulting in a decrease in the effective chlorine concentration.

[0026] According to the measurement results shown in Table 1, it is preferable to use ion-exchanged water, groundwater, or waste brine (treated with an RO membrane) as dilution water. In other words, it is preferable to use dilution water that has an effective chlorine concentration of 0.11% or more when an oxidizing agent (sodium hypochlorite) with an effective chlorine concentration of 12% is diluted 50 times.

[0027] Next, the ratio of chlorine equivalents to 1 iodine equivalent (hereinafter referred to as "equivalent ratio") was measured when sodium hypochlorite (effective chlorine concentration: 12%) was diluted using waste brine and soft water. The measurement results are shown in Table 2 below. In Table 2 below, the waste brine used was waste brine that had not been treated to remove impurities. The soft water used was groundwater with a pH of 8 that had been treated in a water softener to reduce the hardness to 5 mg / L or less.

[0028] [Table 2]

[0029] According to Table 2 above, regardless of the dilution ratio between soft water and waste brine, when soft water was used, the equivalence ratio (chlorine / iodine) could be reduced compared to when waste brine was used. Here, for soft water, the equivalence ratio was 3.0 or less.

[0030] Next, the influence of the dilution ratio of sodium hypochlorite (effective chlorine concentration: 12%) with dilution water was evaluated. The soft water described in Table 2 above was used as dilution water, and the equivalence ratio (chlorine / iodine) was measured for diluted solutions in which sodium hypochlorite was diluted at multiple dilution ratios. The measurement results are shown in Table 3 below.

[0031] [Table 3]

[0032] According to Table 3 above, the equivalence ratio (chlorine / iodine) decreased as the dilution ratio increased. On the other hand, when the dilution ratio was 104 or 112, there was no difference in the equivalence ratio. Furthermore, for soft water, the equivalence ratio was 3.0 or less regardless of the dilution ratio.

[0033] Tables 2 and 3 show the results of measurements taken over different periods using the same equipment using the blowout method. The equivalence ratio measurement results vary depending on the operating conditions of the equipment. However, it was confirmed that the equivalence ratio for soft water never exceeded 3.0.

[0034] Next, sodium hypochlorite (available chlorine concentration: 12%) was diluted using the waste brine and soft water described in Table 2 above, and the diluted solution was mixed with natural brine to liberate iodine. Iodine was then extracted using the blow-out method, and the iodine recovery rate was measured. The iodine recovery rate is the ratio of the amount of extracted iodine to the amount of iodine contained in the natural brine. The measurement results are shown in Table 4 below. In Table 4 below, the equivalence ratio indicates the equivalence ratio of the diluted solution before mixing with the natural brine.

[0035] [Table 4]

[0036] According to Table 4 above, the use of soft water resulted in a higher iodine recovery rate than the use of waste brine. Even when the dilution ratio of the soft water (38, 55, or 64 times) was equal to or greater than that of the waste brine (37 times), or even when the dilution ratio of the soft water (29 times) was lower than that of the waste brine (37 times), the use of soft water resulted in a higher iodine recovery rate than the use of waste brine. It is presumed that the use of waste brine resulted in a lower iodine recovery rate because sodium hypochlorite was decomposed by impurities contained in the waste brine. On the other hand, it is presumed that the use of soft water suppressed the decomposition of sodium hypochlorite, thereby improving the iodine recovery rate.

[0037] According to Table 4 above, when the equivalent ratio was 3.0 or less, the iodine recovery rate was improved compared to when the equivalent ratio was higher than 3.0. Here, within the range of an equivalent ratio of 3.0 or less, the iodine recovery rate increased as the equivalent ratio became lower, but when the equivalent ratio was 2.2 or 1.9, there was no difference in the iodine recovery rate.

[0038] Next, sodium hypochlorite (available chlorine concentration: 12%) was diluted using the waste brine and soft water described in Table 2 above, and the diluted solution was mixed with natural brine to liberate iodine. The iodine recovery rate was then measured by extracting iodine using the blowout method. The iodate ion concentration was also measured in the mixture of the diluted solution and natural brine. The measurement results are shown in Table 5 below. In Table 5 below, the equivalent ratio indicates the equivalent ratio of the diluted solution before mixing with natural brine.

[0039] [Table 5]

[0040] According to Table 5, when the equivalence ratio was 3.0 or less, the iodine recovery rate was higher than when the equivalence ratio was higher than 3.0. When the equivalence ratio was higher than 3.0, the iodate ion concentration in the mixture of the diluted solution and natural brine was 1 mg / L or higher. This is thought to have led to the decomposition of sodium hypochlorite by the natural brine or poor mixing, which likely led to the generation of iodate ions due to the peroxidation of iodide ions in the natural brine. On the other hand, when the equivalence ratio was 3.0 or less, the iodate ion concentration in the mixture of the diluted solution and natural brine was less than 1 mg / L. This is thought to have prevented the decomposition of sodium hypochlorite by the natural brine or poor mixing, thereby suppressing the generation of iodate ions.

[0041] Tables 4 and 5 above show measurement results for different periods using the same equipment using the blowout method. The measurement results for the iodine recovery rate vary depending on the operating conditions of the equipment during different periods. However, within the same period (Tables 4 and 5 above), it is possible to understand the trend in the iodine recovery rate versus equivalence ratio.

[0042] Within the range of an equivalent ratio of 3.0 or less, the lower the equivalent ratio, the higher the iodine recovery rate. However, when the equivalent ratio was reduced to 1.7, there was no difference in the improvement effect of the iodine recovery rate.

Claims

1. The oxidizing agent is diluted with dilution water (excluding waste brine) and the diluted solution is mixed with natural brine to oxidize the iodide ions contained in the natural brine, liberating iodine. A method for producing iodine, characterized in that soft water having a hardness of 5 mg / L or less is used as the dilution water.

2. 2. The method for producing iodine according to claim 1, wherein the oxidizing agent is hypochlorite.

3. 2. The method for producing iodine according to claim 1, wherein the dilution water is dilution water in which the effective chlorine concentration becomes 0.11% or more when the oxidizing agent having an effective chlorine concentration of 12% is diluted 50 times.

4. 2. The method for producing iodine according to claim 1, wherein the ratio of chlorine equivalents per iodine equivalent in the diluted solution is 1.7 or more and 3.0 or less.

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