Water treatment agent composition and water treatment method

Abstract

To provide a water treatment agent composition containing a high concentration of iodide salt and suppressing liberation of iodine.SOLUTION: A water treatment agent composition containing water, iodide salt and an alkaline agent, in which the content of iodide salt in the water treatment agent composition is 20% or more by mass as iodide ion and the pH of the water treatment agent composition is greater than or equal to the value calculated by the following formula 1. pH=5.24×log (iodide ion content (mass%))-8.27 (1)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water treatment agent composition and a water treatment method using the water treatment agent composition. [Background technology]

[0002] An aqueous iodide solution obtained by dissolving an iodide salt in water is used as an etching solution or cleaning solution in the production of polarizing plates, an analytical reagent for quantifying various substances, a reducing agent for residual chlorine in water to be treated such as tap water, a disinfectant in water treatment, etc.

[0003] It is known that an iodide aqueous solution is oxidized by exposure to air, liberating iodine. Because iodine is sublimable and corrosive, the storage container for the iodide aqueous solution must be made of expensive materials. Furthermore, because iodine has oxidizing power, when an iodide aqueous solution is used to reduce residual chlorine in the water to be treated, the original reducing power may not be obtained. For these reasons, it is necessary to suppress the liberation of iodine in the iodide aqueous solution.

[0004] In the examples of Patent Document 1, it is described that a 1N aqueous sodium hydroxide solution containing 5% by weight of potassium iodide remains colorless at room temperature for one week.

[0005] Furthermore, Patent Document 2 describes that the release of iodine into the air during evaporation and concentration can be suppressed by adjusting the pH by adding an alkaline compound to a liquid containing at least one element selected from the group consisting of elemental iodine, compounds containing iodine element, iodine ions, and ions containing iodine element at a concentration of less than 10 mass %.

[0006] However, the aqueous iodide solutions described in Patent Documents 1 and 2 each have a low iodide salt content, and no method for suppressing iodine release when the aqueous iodide solution is highly concentrated is described. If the aqueous iodide solution has a low iodide salt content, a large amount of the aqueous iodide solution may be required for use in water treatment, for example, which raises concerns about increased transportation costs, storage costs, and production costs associated with increased use of the aqueous iodide solution. Therefore, there is a demand for a water treatment agent composition that is a highly concentrated aqueous iodide solution in which iodine release is suppressed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-271141 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-232662 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a water treatment composition that contains a high concentration of iodide salt and that inhibits the release of iodine, and a water treatment method that uses the water treatment composition. [Means for solving the problem]

[0009] The present invention relates to a water treatment composition containing water and an iodide salt, wherein the content of the iodide salt in the water treatment composition is 20 mass % or more in terms of iodide ions. 42% by mass or less and the pH of the water treatment agent composition is equal to or greater than the value calculated by the following formula (1): pH = 5.24 × log (iodide ion content (mass%)) − 8.27 (1)

[0010] The water treatment agent composition preferably further contains an alkaline agent.

[0011] In the water treatment agent composition, the alkaline agent is preferably a hydroxide.

[0012] In the water treatment agent composition, the TOC of the water treatment agent composition is preferably 10 mg / L or less.

[0013] The water treatment agent composition is preferably a composition used for at least one of reduction and sterilization of water to be treated.

[0014] The water treatment agent composition is preferably a composition used as a sterilization aid in reverse osmosis membrane treatment.

[0015] The present invention is a water treatment method in which the water treatment agent composition is added to water to be treated that contains at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent.

[0016] The present invention is a water treatment method for treating water to be treated, which contains at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent, using a reverse osmosis membrane, and the water treatment agent composition is added to the water to be treated. [Effects of the Invention]

[0017] The present invention can provide a water treatment composition that contains a high concentration of iodide salt and that inhibits the release of iodine, and a water treatment method that uses the water treatment composition. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a graph showing the relationship between the iodide ion content (mass%) in the water treatment agent compositions of the examples and the pH at which free iodine was not detected. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0020] A water treatment agent composition according to an embodiment of the present invention is a composition containing water and an iodide salt. The content of the iodide salt in the water treatment agent composition is 20 mass% or more in terms of iodide ions, and the pH of the water treatment agent composition is equal to or greater than the value calculated by the following formula (1): pH = 5.24 × log (iodide ion content (mass%)) − 8.27 (1)

[0021] The present inventors have found that in a water treatment agent composition that is an aqueous iodide solution containing water and an iodide salt, when the pH is equal to or higher than the value calculated by the above formula (1), iodine liberation is suppressed even when the content of the iodide salt is a high concentration of 20 mass% or more in terms of iodide ions.

[0022] If the pH of the water treatment agent composition is less than the value calculated by the above formula (1), iodine will be liberated during storage, which may lead to permeation through the storage container, a decrease in the original reducing power, etc. The pH of the water treatment agent composition is preferably at least 0.35 above the value calculated by the above formula (1).

[0023] The iodide salt contained in the water treatment agent composition is an inorganic salt of iodine, and examples thereof include sodium iodide, potassium iodide, lithium iodide, copper iodide, zinc iodide, etc., with sodium iodide or potassium iodide being preferred from the viewpoint of cost, etc. The water treatment agent composition may contain one type of iodide salt or two or more types of iodide salts.

[0024] The water is not particularly limited, but examples include tap water and pure water.

[0025] The water treatment agent composition may further contain an alkaline agent. The alkaline agent may be any agent capable of increasing the pH of the solution, and examples thereof include hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, and tetramethylammonium hydroxide; carbonates such as sodium carbonate and potassium carbonate; and bicarbonates such as sodium bicarbonate and potassium bicarbonate. Of these, from the viewpoints of safety, formulation costs, and the like, hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide are preferred, and sodium hydroxide or potassium hydroxide is more preferred.

[0026] From the viewpoint of storage stability, the alkaline agent is preferably contained in the composition in an amount of 0.01% by mass or more, and more preferably 0.1% by mass or more. The upper limit of the alkaline agent content is, for example, 10% by mass or less.

[0027] The content of iodide salt in the water treatment agent composition may be 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more, in terms of iodide ions. If the content of iodide salt is less than 20% by mass in terms of iodide ions, there is a concern that the increased amount used will increase the cost of chemicals. The upper limit of the content of iodide salt is, for example, 42% by mass or less in terms of iodide ions.

[0028] The available iodine in the water treatment composition can be determined by the DPD (N,N-diethyl-p-phenylenediamine) method. DPD is oxidized by an oxidizing agent, and examples of oxidizing agents that can be measured include chlorine, bromine, iodine, hydrogen peroxide, and ozone. The forms of chlorine quantified as total chlorine include all forms with oxidizing power, such as hypochlorous acid, hypochlorite ions, and combined chlorine such as chloramines and dichloramines. Bromine and iodine can also be measured in all forms with oxidizing power. Free chlorine is quantified as a form that can be measured without adding potassium iodide using the "total chlorine" measurement method ("JIS K 0120:2013, 33. Residual chlorine"), such as hypochlorous acid, hypobromous acid, chlorine, bromine, and iodine.

[0029] Additionally, "total chlorine" can be converted to "total iodine." Specifically, this is done based on the "molecular weight of chlorine" and the "molecular weight of iodine." In other words, "total chlorine" x (126.9 / 35.45) ≒ "total chlorine" x 3.58 = "total iodine." "Free chlorine" can also be converted to "free iodine" in the same way.

[0030] The water treatment agent composition according to this embodiment does not contain any organic matter. "Does not contain any organic matter" means that the TOC of the water treatment agent composition is 100 mg / L or less, and preferably 10 mg / L or less.

[0031] The water treatment agent composition according to this embodiment can be suitably used as a water treatment agent for reducing residual chlorine in water to be treated, sterilizing the water to be treated, etc. The iodide ions contained in the water treatment agent composition can effectively reduce residual chlorine and render it harmless. The water treatment agent composition according to this embodiment can be suitably used particularly as a sterilization auxiliary in reverse osmosis membrane treatment.

[0032] In water treatment equipment, oxidizing agents such as hypochlorous acid and hypobromous acid are commonly added for sterilization and slime prevention. However, it is known that these oxidizing agents are not consumed for the intended sterilization or slime prevention purposes, but remain in the water being treated and flow into subsequent water treatment equipment, adversely affecting those equipment. The inflow of residual chlorine and other contaminants is known to cause corrosion in cooling towers, degradation of reverse osmosis membrane performance in reverse osmosis membrane equipment, and significant oxidative degradation in resin towers and electrodeionization (EDI) systems.

[0033] The water treatment agent composition according to the present embodiment can suppress such effects on downstream water treatment devices, and can suppress corrosion in cooling towers, performance deterioration of reverse osmosis membranes in reverse osmosis membrane devices, and oxidative deterioration in resin towers and electrodeionization (EDI) systems.

[0034] <Water treatment method> A water treatment method according to an embodiment of the present invention is a method of treating water using the water treatment agent composition. For example, the water treatment agent composition may be added to water to be treated that contains at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent. Furthermore, in a water treatment method in which water to be treated that contains at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent is treated using a reverse osmosis membrane, the water treatment agent composition may be added to the water to be treated.

[0035] By adding iodide salt to water to be treated using a reverse osmosis membrane, etc., which contains at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent, it is possible to reduce the chlorine-based oxidizing agent, which may cause deterioration of the reverse osmosis membrane, etc. Iodide ions are oxidized by the chlorine-based oxidizing agent to iodine, which has bactericidal properties, and are transformed into a slime inhibitor that suppresses slime formation and hardly causes deterioration of the reverse osmosis membrane, etc. Therefore, by adding iodide ions to water to be treated that contains a chlorine-based oxidizing agent, it is possible to suppress deterioration of the reverse osmosis membrane, etc., and also suppress slime formation. [Example]

[0036] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0037] <Examples 1 to 4, Comparative Examples 1 to 4, Reference Example 1 ~3 > Storage stability tests were conducted by mixing potassium iodide, a pH adjuster (acid or alkali), and water in the compositions shown in Tables 1 to 5. For each composition and pH, the active ingredient was measured after storage at room temperature (25±2°C) in a sealed, light-shielded container for 7, 14, and 30 days. The amount of liberated iodine was measured using a HACH DR3900 spectrophotometer.

[0038] [Table 1]

[0039] [Table 2]

[0040] [Table 3]

[0041] [Table 4]

[0042] [Table 5]

[0043] When water, potassium iodide, 0.35% hydrochloric acid, or 0.48% potassium hydroxide was blended in the ratios shown in Table 1 (Example 1, Comparative Example 1), a substantially homogeneous liquid was obtained. When pH was adjusted to 4.93, the solution turned yellow immediately after formulation, and 0.0004% by mass of free iodine was detected. Under other conditions, the solution immediately after formulation was colorless and transparent, and no free iodine was detected (lower detection limit: <0.10 mg / 100 g). A storage test was conducted on the resulting formulation, and it was found that by maintaining a pH of 11 or higher, iodine generation after 30 days of storage at 25°C could be suppressed. The results are shown in Table 6. In Table 6, "◯" indicates that no free iodine was detected after 30 days of storage at 25°C, and "×" indicates that free iodine was detected after 30 days of storage at 25°C.

[0044] When water, potassium iodide, 0.35% hydrochloric acid, or 0.48% potassium hydroxide was blended in the ratios shown in Table 2 (Example 2, Comparative Example 2), a substantially homogeneous liquid was obtained. Under all conditions, the solution was colorless and transparent immediately after formulation, and no free iodine was detected. A storage test was conducted on the resulting formulation, and it was found that by maintaining a pH of 11 or higher, iodine generation could be suppressed after 30 days of storage at 25°C. The results are shown in Table 6.

[0045] When water, potassium iodide, 0.35% hydrochloric acid, or 0.48% potassium hydroxide was blended in the ratios shown in Table 3 (Example 3, Comparative Example 3), Table 4 (Example 4, Comparative Example 4), and Table 5 (Reference Example 1), a substantially homogeneous liquid was obtained. Under all conditions, the solution was colorless and transparent immediately after formulation, and no free iodine was detected. A storage test was conducted on the resulting formulation, and it was found that iodine generation after 30 days of storage at 25°C could be suppressed by adjusting the pH to 10, 8, or 6 or higher. The results are shown in Table 6.

[0046] [Table 6]

[0047] The relationship between the iodide ion content (% by mass) in the composition and the pH at which free iodine was not detected (the lower limit of the pH at which the evaluation result was "Good" in Table 6) is shown in Figure 1. From these results, the above formula (1) of pH = 5.24 × log (iodide ion content (% by mass)) - 8.27 was derived.

[0048] The appearance of the solution in which free iodine was detected was light yellow, and it became darker yellow as the concentration increased. Since the solution with free iodine causes coloring of the container, it is preferable to store the solution under conditions that do not generate much iodine. If the solution satisfies the iodide salt content and pH values ​​of the examples, it can be stored stably for a long period of time without releasing much iodine.

[0049] Thus, in the examples, a water treatment agent composition containing a high concentration of iodide salt and suppressing the release of iodine was obtained.

Claims

1. A water treatment composition containing water and an iodide salt, the content of the iodide salt in the water treatment agent composition is 20% by mass or more and 42% by mass or less in terms of iodide ions, A water treatment agent composition, characterized in that the pH of the water treatment agent composition is equal to or greater than a value calculated by the following formula (1): pH = 5.24 × log (iodide ion content (mass%)) − 8.27 (1)

2. The water treatment composition according to claim 1, The water treatment composition further comprises an alkaline agent.

3. The water treatment agent composition according to claim 1 or 2, A water treatment agent composition, characterized in that the TOC of the water treatment agent composition is 10 mg / L or less.

4. The water treatment agent composition according to any one of claims 1 to 3, The water treatment agent composition is a composition used for at least one of reduction and sterilization of water to be treated.

5. The water treatment agent composition according to any one of claims 1 to 3, The water treatment composition is a composition used as a sterilization aid in reverse osmosis membrane treatment.

6. A water treatment method comprising adding the water treatment agent composition according to any one of claims 1 to 3 to water to be treated that contains at least one of a chlorine-based oxidizing agent and a bromine-based oxidizing agent.

7. A water treatment method for treating water containing at least one of a chlorine-based oxidant and a bromine-based oxidant using a reverse osmosis membrane, comprising: A water treatment method comprising adding the water treatment agent composition according to any one of claims 1 to 3 to the water to be treated.

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