Method for removing hypervalent iodine in ionic membrane caustic soda light salt brine

Abstract

The invention belongs to the technical field of iodine removal of light salt brine, and particularly relates to a method for removing high-valence iodine in ionic membrane caustic soda light salt brine. Comprising the following steps: (1) adding a pH regulator and sodium sulfite into light salt brine, regulating the pH to 1-3, stirring until the reaction is completed, and carrying out primary adsorption deiodination by adopting a composite adsorbent to obtain light salt brine 1; and (2) adding a pH regulator and hydrogen peroxide into the light salt brine 1, regulating the pH value to 1-2, stirring until the reaction is completed, and carrying out secondary adsorption by adopting a composite adsorbent to remove iodine, thereby obtaining the deiodinated light salt brine. According to the removal method disclosed by the invention, high-valence iodine such as periodate and iodate in the light salt brine is converted into low-valence iodine such as iodate and iodide ions by utilizing the reducibility of sodium sulfite and the oxidation-reduction property of hydrogen peroxide in the coexistence of iodide ions and iodate, and then is further converted into simple substance iodine, and the simple substance iodine is efficiently removed by utilizing a composite adsorbent; the process is simple, the cost is low, the removal rate is high, and the removal effect is good.

Description

Technical Field

[0001] This invention belongs to the field of iodine removal technology in saline solution, specifically relating to a method for removing high-valent iodine from caustic soda saline solution using an ion-exchange membrane. Background Technology

[0002] Caustic soda is an important basic chemical raw material. The ion-exchange membrane process for caustic soda production has become the mainstream technology due to its advantages such as low overall energy consumption, high liquid caustic soda concentration, high chlorine and hydrogen purity, and minimal pollution. Electrolytic cells and ion-exchange membranes account for a large proportion of the cost of caustic soda production, with the ion-exchange membrane being the core of the membrane-based caustic soda production process. Extending the membrane's lifespan is crucial for the operation and management of chlor-alkali enterprises.

[0003] The ion-exchange membrane method for alkali production places extremely high demands on the quality of the brine used in electrolysis. The quality of the brine is also a key factor affecting the lifespan of the ion-exchange membrane. Impurities in the brine all affect the electrolytic performance of the ion-exchange membrane, such as Ca2+. 2+ Mg 2+ Ni 2+ A1 3+ 、Sr 2+ Ba 2+ Metal ions and SO4 2- I - The influence of anions is significant. Specifically, iodide ions will be oxidized to higher valence states of iodine during electrolysis, such as IO3-. - IO6 5- These high-valence iodine states will react with Na. + Ba 2+ When metal cations combine, they form insoluble precipitates such as Na3H2IO6 and Ba3H4(IO6)2, which accumulate on the ion-exchange membrane. Over long-term operation, this leads to iodine accumulation, resulting in decreased current efficiency and shortened membrane lifespan. Studies have shown that when the iodine content in the brine exceeds 0.4 mg / L, the deposition rate accelerates, causing a very rapid decline in membrane performance. Therefore, ion-exchange membrane manufacturers generally require that the iodine content in the incoming brine not exceed 0.2 mg / L.

[0004] However, since domestic ion-exchange membrane caustic soda manufacturers currently lack iodine removal devices in their brine refining systems, iodide ions introduced from industrial salt are electrolytically oxidized into high-valence iodine during the ion-exchange membrane caustic soda production process. This iodine then enters the dilute brine and participates in the system's brine circulation. After multiple cycles, the iodine accumulates to a high concentration, exacerbating the impact on the ion-exchange membrane. Therefore, timely removal of iodine from the dilute brine to prevent its excessive accumulation and irreversible damage to the ion-exchange membrane is crucial.

[0005] Because iodine exists in salt water in complex forms, and is mainly in the high valence state, it is difficult to remove. Furthermore, the iodine conversion during the removal process can lead to problems such as over-reduction or over-oxidation. Therefore, it is urgent to develop a method for removing iodine from salt water in various forms. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a simple, low-cost, and highly effective method for removing high-valence iodine from ion-exchange membrane caustic soda brine. This method converts iodate and periodate in the brine into lower-valence iodine, which is then further converted into elemental iodine for removal. The iodine concentration in the brine after removal can be reduced to below 0.1 mg / L.

[0007] To achieve the above-mentioned objectives of this invention, the specific technical solution adopted by this invention is as follows: A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane includes the following steps: (1) Add pH adjuster and sodium sulfite to the brine, adjust the pH to 1-3, stir until the reaction is complete, and use composite adsorbent for primary adsorption and deiodination to obtain brine 1; (2) Add pH adjuster and hydrogen peroxide to dilute brine 1, adjust pH to 1-2, stir until the reaction is complete, and use composite adsorbent for secondary adsorption to remove iodine to obtain deiodized dilute brine.

[0008] Preferably, the iodine content in the brine treated in step (1) is 0.2 mg / L-5 mg / L, and the amount of sodium sulfite added is adjusted according to the iodine content to control n(SO3) 2- ) / n(I)=3-7.

[0009] Preferably, the amount of hydrogen peroxide added in step (2) is based on the initial iodine content of the brine, and n(H2O2) / n(I) = 10-20.

[0010] Preferably, the pH adjuster mentioned in steps (1) and (2) is hydrochloric acid.

[0011] Preferably, the reaction time in step (1) is 60-120 min, more preferably 60-90 min, and the reaction time in step (2) is 30-120 min, more preferably 60-90 min.

[0012] Preferably, the composite adsorbents in steps (1) and (2) are both modified activated carbon.

[0013] Preferably, the brine is dechlorinated brine produced by electrolysis of brine in the ion-exchange membrane alkali production process, which is then further dechlorinated.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The reagents used have no additional pollution impact on the system. The sulfate ions generated after the reaction of sodium sulfite can be treated by the membrane denitrification process of the system. The hydrogen peroxide reagent has no impact on the system. Compared with other redox agents, it is cleaner and more environmentally friendly, avoiding the impact on the system.

[0015] (2) This technology can achieve efficient removal of high-valence iodine. It utilizes the reducing properties of sodium sulfite to reduce periodic acid in dilute brine to low-valence states such as iodate and iodide ions. Then, it utilizes the redox properties of hydrogen peroxide in the coexistence of iodide ions and iodate to oxidize iodide ions to elemental iodine and reduce iodate ions to elemental iodine. Finally, it uses a composite adsorbent to achieve efficient adsorption of elemental iodine. The process is simple and low-cost. Furthermore, by controlling appropriate process conditions, the iodine content can be reduced to below 0.1 ppm. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of iodine removal from dechlorinated brine in this invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are not intended to limit the present invention, but only to illustrate the present invention. Unless otherwise specified, the experimental methods used in the following embodiments are generally performed under conventional conditions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0018] Modified activated carbon, purchased from Fushun Yuqi Technology Co., Ltd., model C-03.

[0019] Example 1 A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane, the flowchart of which is shown below. Figure 1 As shown, the steps are as follows: (1) Take 500 mL of dilute saline with an iodine content of 5 mg / L and add it to reaction tank 1. Add HCl solution with a mass concentration of 36% and adjust the pH to 1.0. Add sodium sulfite solution dropwise to make its concentration reach 15 mg / L. Stir the reaction at 200 rpm for 60 min. Use the composite adsorbent (modified activated carbon) in adsorption tower 1 to remove the iodine in the dilute saline after the reaction is completed by primary adsorption to obtain dilute saline 1.

[0020] (2) The brine 1 is introduced into the reaction tank 2, and HCl solution with a mass concentration of 36% is added to adjust the pH to 1.5. Hydrogen peroxide solution with a mass concentration of 30% is added dropwise to make its concentration reach 14 mg / L. The reaction is stirred at 200 rpm for 60 min. The iodine in the brine after the reaction is completed is removed by secondary adsorption using the composite adsorbent (modified activated carbon) in the adsorption tower 2 to obtain deiodized brine.

[0021] According to the high concentration iodide colorimetric method in GB / T5750.5-2023 Standard Examination Methods for Drinking Water, the iodine content in the treated deiodized saline solution decreased from 5 mg / L to 0.08 mg / L, and the deiodination rate reached 98.4%.

[0022] Example 2 A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane, comprising the following steps: (1) Take 500 mL of dilute saline with an iodine content of 5 mg / L and add it to reaction tank 1. Add HCl solution with a mass concentration of 36% and adjust the pH to 2. Add sodium sulfite solution dropwise to make its concentration reach 15 mg / L. Stir the reaction at 150 rpm for 90 min. Use the composite adsorbent (modified activated carbon) in adsorption tower 1 to remove the iodine in the dilute saline after the reaction is completed by primary adsorption to obtain dilute saline 1.

[0023] (2) The brine enters the reaction tank 2, and HCl solution with a mass concentration of 36% is added to adjust the pH to 2. Hydrogen peroxide solution with a mass concentration of 30% is added dropwise to make its concentration reach 14 mg / L. The reaction is stirred for 90 min. The iodine in the brine after the reaction is completed is removed by secondary adsorption using the composite adsorbent (modified activated carbon) in the adsorption tower 2 to obtain deiodized brine.

[0024] According to the high concentration iodide colorimetric method in GB / T5750.5-2023 Standard Examination Methods for Drinking Water, the iodine content in the treated salt water decreased from 5 mg / L to 0.09 mg / L, and the deiodination rate reached 98.2%.

[0025] Example 3 A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane, comprising the following steps: (1) Take 500 mL of dilute saline with an iodine content of 5 mg / L and add it to reaction tank 1. Add HCl solution with a mass concentration of 36% and adjust the pH to 1.5. Add sodium sulfite solution dropwise to make its concentration reach 25 mg / L. Stir the reaction at 200 rpm for 60 min. Use the composite adsorbent (modified activated carbon) in adsorption tower 1 to remove the iodine in the dilute saline after the reaction is completed by primary adsorption to obtain dilute saline 1.

[0026] (2) The brine enters the reaction tank 2, and HCl solution with a mass concentration of 36% is added to adjust the pH to 1.5. Hydrogen peroxide solution with a mass concentration of 30% is added dropwise to make its concentration reach 20 mg / L. The reaction is stirred for 60 min. The iodine in the brine after the reaction is completed is removed by secondary adsorption using the composite adsorbent (modified activated carbon) in the adsorption tower 2 to obtain deiodized brine.

[0027] According to the high concentration iodide colorimetric method in GB / T5750.5-2023 Standard Examination Methods for Drinking Water, the iodine content in the treated salt water was reduced from 5 mg / L to 0.05 mg / L, and the iodine removal rate reached 99%.

[0028] Example 4 A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane, comprising the following steps: (1) Take 500 mL of dilute saline with an iodine content of 5 mg / L and add it to reaction tank 1. Add HCl solution with a mass concentration of 36% and adjust the pH to 1.5. Add sodium sulfite solution dropwise to make its concentration reach 30 mg / L. Stir the reaction at 250 rpm for 60 min. Use the composite adsorbent (modified activated carbon) in adsorption tower 1 to remove the iodine in the dilute saline after the reaction is completed by primary adsorption to obtain dilute saline 1.

[0029] (2) The brine enters the reaction tank 2, and HCl solution with a mass concentration of 36% is added to adjust the pH to 1.5. Hydrogen peroxide solution with a mass concentration of 30% is added dropwise to make its concentration reach 25 mg / L. The reaction is stirred for 60 min. The iodine in the brine after the reaction is completed is removed by secondary adsorption using the composite adsorbent (modified activated carbon) in the adsorption tower 2 to obtain deiodized brine.

[0030] According to the high concentration iodide colorimetric method in GB / T5750.5-2023 Standard Examination Methods for Drinking Water, the iodine content in the treated salt water decreased from 5 mg / L to 0.03 mg / L, and the iodine removal rate reached 99.4%.

[0031] Example 5 A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane, comprising the following steps: (1) Take 500 mL of dilute saline with an iodine content of 5 mg / L and add it to reaction tank 1. Add HCl solution with a mass concentration of 36% and adjust the pH to 3. Add sodium sulfite solution dropwise to make its concentration reach 30 mg / L. Stir the reaction at 200 rpm for 90 min. Use the composite adsorbent (modified activated carbon) in adsorption tower 1 to remove the iodine in the dilute saline after the reaction is completed by primary adsorption to obtain dilute saline 1.

[0032] (2) The brine enters the reaction tank 2, and HCl solution with a mass concentration of 36% is added to adjust the pH to 2. Hydrogen peroxide solution with a mass concentration of 30% is added dropwise to make its concentration reach 25 mg / L. The reaction is stirred for 90 min. The iodine in the brine after the reaction is completed is removed by secondary adsorption using the composite adsorbent (modified activated carbon) in the adsorption tower 2 to obtain deiodized brine.

[0033] According to the high concentration iodide colorimetric method in GB / T5750.5-2023 Standard Examination Methods for Drinking Water, the iodine content in the treated salt water decreased from 5 mg / L to 0.06 mg / L, and the iodine removal rate reached 98.8%.

[0034] Comparative Example 1 A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane, comprising the following steps: (1) Take 500 mL of dilute saline with an iodine content of 5 mg / L and add it to reaction tank 1. Add HCl solution with a mass concentration of 36% and adjust the pH to 3. Add ferrous chloride solution dropwise to make its concentration reach 30 mg / L. Stir the reaction at 200 rpm for 90 min. Use the composite adsorbent (modified activated carbon) in adsorption tower 1 to remove the iodine in the dilute saline after the reaction is completed by primary adsorption to obtain dilute saline 1.

[0035] (2) The brine enters the reaction tank 2, and HCl solution with a mass concentration of 36% is added to adjust the pH to 2. Sodium hypochlorite solution is added dropwise to make its concentration reach 25 mg / L. The reaction is stirred at 200 rpm for 90 min. The iodine in the brine after the reaction is completed is removed by secondary adsorption using the composite adsorbent (modified activated carbon) in the adsorption tower 2 to obtain deiodized brine.

[0036] According to the high concentration iodide colorimetric method in GB / T5750.5-2023 Standard Examination Methods for Drinking Water, the iodine content in the treated salt water decreased from 5 mg / L to 2.5 mg / L, with a deiodization rate of 50%.

[0037] Comparative Example 2 A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane, comprising the following steps: Add 500 mL of dilute saline solution with an iodine content of 5 mg / L to reaction tank 1, add 36% HCl solution to adjust the pH to 3, and add sodium sulfite solution dropwise to make its concentration reach 30 mg / L. Stir the reaction at 200 rpm for 90 min. Use the composite adsorbent (modified activated carbon) in adsorption tower 1 to adsorb and remove the iodine from the dilute saline solution after the reaction is completed to obtain deiodized dilute saline solution.

[0038] According to the high concentration iodide colorimetric method in GB / T5750.5-2023 Standard Examination Methods for Drinking Water, the iodine content in the treated salt water decreased from 5 mg / L to 4.6 mg / L, with a deiodization rate of 8%.

[0039] Comparative Example 3 A method for removing high-valent iodine from caustic soda brine using an ion-exchange membrane, comprising the following steps: The brine was introduced into reaction tank 2, and a 36% HCl solution was added to adjust the pH to 2. A 30% hydrogen peroxide solution was then added dropwise to bring the concentration to 25 mg / L. The mixture was stirred at 200 rpm for 90 minutes. The iodine in the brine after the reaction was completed was adsorbed and removed using the composite adsorbent (modified activated carbon) in adsorption tower 2, resulting in deiodized brine.

[0040] According to the high concentration iodide colorimetric method in GB / T5750.5-2023 Standard Examination Methods for Drinking Water, the iodine content in the treated salt water decreased from 5 mg / L to 3.3 mg / L, with a deiodization rate of 34%.

[0041] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for removing high-valent iodine from dilute brine of ion-exchange membrane caustic soda, characterized by, Includes the following steps: (1) Add pH adjuster and sodium sulfite to the brine, adjust the pH to 1-3, stir until the reaction is complete, and use composite adsorbent for primary adsorption and deiodination to obtain brine 1; (2) Add pH adjuster and hydrogen peroxide to dilute brine 1, adjust pH to 1-2, stir until the reaction is complete, and use composite adsorbent for secondary adsorption to remove iodine to obtain deiodized dilute brine.

2. The removal method according to claim 1, characterized in that, The iodine content in the treated brine in step (1) is 0.2 mg / L-5 mg / L, and the dosage of sodium sulfite is added according to the iodine content, and n(SO3 2- ) / n(I)=3-7 is controlled.

3. The removal method according to claim 2, characterized in that, The amount of hydrogen peroxide added in step (2) is based on the initial iodine content of the brine, and n(H2O2) / n(I) = 10-20 is controlled.

4. The removal method of claim 1, wherein, The pH adjuster mentioned in steps (1) and (2) is a hydrochloric acid solution.

5. The removal method according to claim 1, characterized in that, The stirring speed in step (1) is 150-250 rpm and the reaction time is 60-120 min. The reaction time in step (2) is 30-120 min.

6. The removal method according to claim 1, characterized in that, The composite adsorbents mentioned in steps (1) and (2) are both modified activated carbon.

7. The removal method according to any one of claims 1-6, characterized in that, The brine is dechlorinated brine produced by electrolysis of brine in the ion-exchange membrane alkali production process, which is then further dechlorinated.

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