Method for removing trace iodine in ion membrane alkali-making light salt brine

Abstract

The invention provides a method for removing trace iodine in light salt brine produced by using an ionic membrane, which comprises the following steps: adding a pH regulator and a ferrous reducing agent into the light salt brine, regulating the pH value of the light salt brine to 1-4.5, adding an excessive amount of the ferrous reducing agent, and stirring until the reaction is completed; and adsorbing and removing iodine in the light salt brine after the reaction is completed by adopting a composite adsorbent to obtain the light salt brine after the iodine removal. According to the removal method, iodide, iodate and periodate in the light salt brine are converted into elemental iodine to be removed by utilizing the reducibility of Fe < 2 + > and the oxidizability of the product Fe < 3 + >, the problem of over-reduction or over-oxidation does not exist, the process is simple, the cost is low, the removal rate is high, and the removal effect is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of removing iodine from light brine, and in particular relates to a method for removing trace iodine from light brine in ion-exchange membrane caustic soda production. Specifically, it is a method for removing iodine and iodides in various valence states present in light brine, which are formed by oxidation after electrolysis of iodine in the salt water entering the ion-exchange membrane electrolyzer. Background Art

[0002] Ion-exchange membrane caustic soda production is the mainstream caustic soda production technology in the world's chlor-alkali industry. It is a process that uses a cation-exchange membrane electrolyzer to electrolyze brine solution to produce chlorine, hydrogen, and high-purity caustic soda (sodium hydroxide). The process steps mainly include: brine purification: after the saturated crude brine is purified, refined brine that meets the operating requirements of the ion-exchange membrane electrolyzer is obtained; electrolysis: the refined brine enters the anode chamber of the electrolyzer, and pure water (added with a certain amount of NaOH solution) enters the cathode chamber. Under the action of direct current, ions migrate through the ion-exchange membrane, and finally caustic soda is formed in the cathode liquid phase, light brine is produced in the anode liquid phase, H2 is generated in the cathode gas phase, and Cl2 is generated in the anode gas phase; light brine dechlorination: after the electrolyzed light brine is mixed with the chlorine water from chlorine and hydrogen treatment, the pH value is adjusted with high-purity hydrochloric acid, and then sent to a dechlorination tower for dechlorination treatment. The dechlorinated light brine is recycled.

[0003] The ion-exchange membrane used in ion-exchange membrane caustic soda production is a polymer membrane with high selective permeability, and its performance is greatly affected by metal ions such as Ca 2+ , Mg 2+ , Ni 2+ , A1 3+ , Sr 2+ , Ba 2+ and anions such as SO4 2- , I - . Among them, iodide ions will be oxidized to iodine in higher valence states during electrolysis, such as IO 3- , IO6 5- , etc. These iodine in higher valence states will combine with metal cations such as Na + , Ba 2+ to form insoluble precipitates such as Na3H2IO6 and Ba3H4(IO6)2 and accumulate on the ion-exchange membrane, thus shortening the service life of the ion-exchange membrane and increasing production costs. Research shows that when the iodine content in the brine is higher than 0.4 mg / L, this deposition phenomenon is obvious, resulting in a rapid decrease in the conductivity of the ion-exchange membrane, an increase in the cell voltage, a decrease in the current efficiency, and a shortening of the ion-exchange membrane life. Therefore, ion-exchange membrane manufacturers generally require that the iodine content in the salt water entering the electrolyzer does not exceed 0.2 mg / L.

[0004] During the ion-exchange membrane caustic soda production process, the iodine in the dilute brine generated after electrolysis will be enriched to a relatively high concentration due to multiple cycles of reuse. The iodine in the dilute brine will be oxidized to a high-valence state in the electrolytic cell, which will have a great impact on the ion-exchange membrane. Therefore, it is necessary to remove the iodine. Since the form of iodine in the dilute brine is complex, including both low-valence iodine and high-valence iodine, there are problems of over-reduction or over-oxidation in the conversion of iodine during the removal process. Therefore, it is urgent to develop an iodine removal method for dilute brine with complex iodine forms. Summary of the Invention

[0005] In view of this, to solve the above technical problems, the present invention proposes a method for removing trace iodine in dilute brine for ion-exchange membrane caustic soda production, which has a simple process and low cost. The method can convert iodide, iodate, and periodate in the dilute brine into elemental iodine and then remove it, without problems of over-reduction or over-oxidation, and has a high removal rate and good removal effect.

[0006] To achieve the above object, the technical solution of the present invention is realized as follows:

[0007] A method for removing trace iodine in dilute brine for ion-exchange membrane caustic soda production, characterized by comprising the following steps:

[0008] S1. Add a pH regulator and a ferrous reducing agent to the dilute brine, adjust the pH value of the dilute brine to 1-4.5, and overdose the ferrous reducing agent, and stir until the reaction is completed; wherein, the addition order of the pH regulator and the ferrous reducing agent is not sequential.

[0009] S2. Use a composite adsorbent to adsorb and remove the iodine in the dilute brine after the reaction is completed to obtain deiodized dilute brine.

[0010] Since the form of iodine in the dilute brine is complex, including both low-valence iodine and high-valence iodine, the key technology for removing iodine in this dilute brine is to use a suitable iodine conversion method to convert iodide, iodate, and periodate into elemental iodine. The present invention uses a ferrous reducing agent to reduce the high-valence iodine in the dilute brine to elemental iodine. Fe 2+ There is no problem of over-reduction when reducing high-valence iodine, that is, elemental iodine cannot react further with Fe 2+ Furthermore, the generated Fe 3+ can further oxidize the original iodide ions (I - ) in the dilute brine into elemental iodine, and then adsorb and remove it with a composite adsorbent.

[0011] Furthermore, in the step S1, the ferrous reducing agent is FeCl2 and / or FeSO4.

[0012] Furthermore, in S1, the concentration of the divalent iron reducing agent added to the light salt water is 0.10 g / L to 0.50 g / L; and the iodine content in the treated light salt water is 5 mg / L to 10 mg / L.

[0013] Furthermore, in S1, the pH regulator is hydrochloric acid.

[0014] Furthermore, in S1, the reaction time is 60 min to 120 min.

[0015] Furthermore, in S2, an adsorption column loaded with a composite adsorbent is used to perform on-column adsorption on the brine after the reaction is completed, and the composite adsorbent is modified activated carbon.

[0016] Furthermore, the deionized water is deionized water produced by electrolysis of brine in an ion membrane alkali production process and / or dechlorinated deionized water produced by electrolysis of brine in an ion membrane alkali production process and then subjected to a dechlorination treatment.

[0017] Compared with the prior art, the method for removing trace iodine from ion-exchange membrane alkali-making brine of the present invention has the following advantages:

[0018] The method for removing trace iodine from ion-exchange membrane alkali-making brine of the present invention utilizes Fe 2+ The reducibility of Fe 3+ The oxidizing property of high-valent iodine (such as IO 3- IO6 5- etc.) to iodine element, and the low-valent iodine ion (I - ) is oxidized to iodine. This avoids the over-reduction or over-oxidation problem in the prior art when converting iodine. 2+ or Fe 3+ It is also easy to remove in the primary brine refining process, with simple process and low cost. By controlling appropriate process conditions, the removal rate of iodine in the brine can be as high as over 97%. DETAILED DESCRIPTION

[0019] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0020] The present invention will be described in detail below with reference to the embodiments.

[0021] Example 1

[0022] S1. Take 200 mL of light brine with an iodine content of 7.75 mg / L, add 36% HCl solution, and adjust the pH to 1.0; drip FeCl2 solution to make its concentration reach 0.10 g / L, and stir and react for 75 min;

[0023] S2. Use an adsorption column filled with a modified activated carbon composite adsorbent to conduct on-column adsorption of the light brine after the reaction to obtain deiodized light brine.

[0024] After testing, the iodine content in the treated light brine decreased from 7.75 mg / L to 0.18 mg / L, and the deiodization rate reached 97.68%.

[0025] Example 2

[0026] S1. Take 200 mL of light brine with an iodine content of 7.75 mg / L, add 36% HCl solution, and adjust the pH to 1.5; drip FeCl2 solution to make its concentration reach 0.10 g / L, and stir and react for 90 min;

[0027] S2. Use an adsorption column filled with a modified activated carbon composite adsorbent to conduct on-column adsorption of the light brine after the reaction to obtain deiodized light brine.

[0028] After testing, the iodine content in the treated light brine decreased from 7.75 mg / L to 0.16 mg / L, and the deiodization rate reached 97.93%.

[0029] Example 3

[0030] S1. Take 200 mL of light brine with an iodine content of 7.75 mg / L, add 36% HCl solution, and adjust the pH to 2; drip FeCl2 solution to make its concentration reach 0.15 g / L, and stir and react for 100 min;

[0031] S2. Use an adsorption column filled with a modified activated carbon composite adsorbent to conduct on-column adsorption of the light brine after the reaction to obtain deiodized light brine.

[0032] After testing, the iodine content in the treated light brine decreased from 7.75 mg / L to 0.15 mg / L, and the deiodization rate reached 97.54%.

[0033] Example 4

[0034] S1. Take 200 mL of light brine with an iodine content of 7.75 mg / L, add 36% HCl solution, and adjust the pH to 2.5; drip FeCl2 solution to make its concentration reach 0.24 g / L, and stir and react for 120 min;

[0035] S2. Use an adsorption column filled with a modified activated carbon composite adsorbent to perform on-column adsorption on the light brine after the reaction to obtain deiodized light brine.

[0036] After testing, the iodine content in the treated light brine decreased from 7.75 mg / L to 0.19 mg / L, and the deiodization rate reached 97.54%.

[0037] Example 5

[0038] S1. Take 200 mL of light brine with an iodine content of 7.75 mg / L, add 36% HCl solution to adjust the pH = 4; dropwise add FeCl2 solution to make its concentration reach 0.5 g / L, and stir and react for 100 min.

[0039] S2. Use an adsorption column filled with a modified activated carbon composite adsorbent to perform on-column adsorption on the light brine after the reaction to obtain deiodized light brine.

[0040] After testing, the iodine content in the treated light brine decreased from 7.75 mg / L to 0.20 mg / L, and the deiodization rate reached 97.41%.

[0041] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for removing trace iodine from dilute brine in ion-exchange membrane caustic soda production, characterized in that, It includes the following steps: S1. Add a pH regulator and a divalent iron reducing agent to the light brine, adjust the pH value of the light brine to 1 - 4.5, overdose the divalent iron reducing agent, and stir until the reaction is completed; among them, the addition order of the pH regulator and the divalent iron reducing agent is not sequential; S2. Use a composite adsorbent to adsorb and remove iodine in the light brine after the reaction is completed to obtain deiodized light brine.

2. The method for removing trace iodine in the dilute brine for ion-exchange membrane caustic soda production according to claim 1, characterized in that: In S1, the divalent iron reducing agent is FeCl2 and / or FeSO4.

3. The method for removing trace iodine in the dilute brine for ion-exchange membrane caustic soda production according to claim 1, characterized in that: In S1, the concentration of the divalent iron reducing agent added to the light brine is 0.10 g / L - 0.50 g / L; the iodine content in the treated light brine is 5 mg / L - 10 mg / L.

4. The method for removing trace iodine in the dilute brine for ion-exchange membrane caustic soda production according to claim 1, characterized in that: In S1, the pH regulator is hydrochloric acid.

5. The method for removing trace iodine from the dilute brine in ion-exchange membrane caustic soda production according to claim 1, characterized in that: In S1, the reaction time is 60 min - 120 min.

6. The method for removing trace iodine in the dilute brine for ion-exchange membrane caustic soda production according to claim 1, characterized in that: In S2, use an adsorption column filled with a composite adsorbent to perform on-column adsorption on the light brine after the reaction is completed, and the composite adsorbent is modified activated carbon.

7. The method for removing trace iodine in the dilute brine for ion-exchange membrane caustic soda production according to claim 1, characterized in that: The light brine is the light brine generated after electrolysis of the brine in the ion-exchange membrane caustic soda process and / or the dechlorinated light brine obtained after the light brine generated after electrolysis of the brine in the ion-exchange membrane caustic soda process is further subjected to dechlorination treatment.