Preparation of activated carbon modified adsorbent and application thereof in removal of iodine from ion-exchange membrane caustic soda raw material brine

Abstract

The application relates to application of an activated carbon modified adsorbent to removal of iodine in ion-exchange membrane caustic soda raw material brine. Heteroatom modification and cyclodextrin grafting are carried out on the activated carbon adsorbent to improve the removal capacity of the activated carbon to trace iodine in ion-exchange membrane caustic soda raw material brine. Different nitrogen sources are used to modify the activated carbon, and in ion-exchange membrane caustic soda raw material brine with an initial iodine concentration of 2.5 mg / L, the removal rate of iodine by the activated carbon modified by pyridine is 43.6%, which is 11.2% higher than that of the unmodified activated carbon. The surface of the activated carbon modified by pyridine is grafted with beta-cyclodextrin, and the removal rate of iodine by the adsorbent is 73.2%, which is 41.2% higher than that of the unmodified activated carbon, and the adsorption performance is greatly improved. The application provides an effective removal method for trace iodine in ion-exchange membrane caustic soda raw material brine in industry, and has good economic benefits and operability.

Description

Technical Field

[0001] The invention relates to a method for removing trace iodine in brine. Background Art

[0002] Caustic soda is one of the most basic chemical raw materials, widely used in papermaking, detergents, petrochemicals, and other fields. By the end of 2022, my country's annual caustic soda production capacity reached 39.8 million tons, making it the world's largest producer and consumer. Currently, caustic soda is produced primarily through the diaphragm process and the ion-exchange membrane process. The diaphragm process is being phased out by the ion-exchange membrane process due to its high energy consumption and severe environmental pollution.

[0003] The ion-exchange membrane process is currently the most advanced caustic soda production method, with many advantages such as high liquid caustic soda concentration, low comprehensive energy consumption and environmental pollution, and is adopted by many chlor-alkali manufacturers at home and abroad. However, the ion-exchange membrane caustic soda process has strict requirements on the content of iodine in the electrolytic brine. When the iodine content in the brine is higher than 0.2 mg / L, it can be oxidized to a high valence state and generate extremely insoluble Ba3H4(IO6)2 and other precipitates once it enters the alkaline environment of the ion-exchange membrane, which deposits on the surface of the ion-exchange membrane, resulting in a decrease in current efficiency and shortening the service life of the ion-exchange membrane. At present, the ion-exchange membranes used in my country's ion-exchange membrane caustic soda plants mainly rely on imports and are expensive. Therefore, the shortening of the service life of the ion-exchange membrane will directly lead to an increase in the company's production costs. In view of this, removing the trace iodine in the brine to the greatest extent is of vital importance to chlor-alkali companies and is also a problem that urgently needs to be solved in the current salt and salt chemical industries. Therefore, the research and development of trace iodine removal technology in the raw brine of ion-exchange membrane caustic soda has great practical significance.

[0004] Currently, the main methods for extracting iodine from brine include air extraction, ion exchange, adsorption (activated carbon, starch), solvent extraction, precipitation (copper, silver), electrolysis, and the new liquid membrane method. With the exception of precipitation and electrolysis, most of these methods extract iodine in the form of molecules, sharing the same principles for pre-treatment of iodine in the raw material solution. From a process perspective, ion exchange is more advanced. However, the choice of method depends on a variety of factors, and therefore all of these methods are used to varying degrees.

[0005] The adsorption method utilizes the advantages of an adsorbent—its porous structure, large surface area, excellent water filtration performance, and strong adsorption properties—to absorb iodine, thereby achieving iodine removal. Due to its simplicity, low cost, and clean, pollution-free nature, the adsorption method has attracted considerable attention from domestic researchers. Huang Yuying conducted preliminary research on the iodine removal performance of several domestically produced coal-based activated carbons. The results showed that most activated carbons had good iodine removal performance. Wu Gang used hydrogen peroxide, sodium hypochlorite, chlorine, ferric chloride, and sodium chlorate as oxidants, and activated carbon, molecular sieves, clay, and diatomaceous earth as adsorbents. Under acidic conditions, he reduced the iodine content from 0.21 mg / L to below 0.05 mg / L. Gao Shubao used activated carbon fibers with sodium nitrite as an oxidant to remove iodine at a pH of 2-3, achieving an iodine removal rate exceeding 90%. Although this adsorbent was able to reduce the iodine concentration to below 0.05 mg / L, the initial iodine concentration in the raw brine was not high.

[0006] Although the reported use of adsorption methods for iodine removal has achieved good research results in the laboratory stage, our preliminary experimental results show that when iodine elemental solution is prepared in saturated salt water and commercially available activated carbon is used to remove iodine, the adsorption capacity of the activated carbon drops sharply at the studied flow rate, and the iodine removal rate is only about 30%. It is speculated that this may be because chlorine and iodine belong to the same main group, and the presence of a large amount of chloride ions in the salt water seriously inhibits the selective adsorption capacity of activated carbon for iodine.

[0007] In summary, considering a variety of factors, including production cost, operational difficulty, and environmental impact, adsorption is currently the most suitable method for removing trace iodine from ion-exchange membrane caustic soda raw material brine for domestic chlor-alkali companies. However, the inhibitory effect of chloride ions in brine on the selective removal of iodine limits the specific industrial application of this method. Summary of the Invention

[0008] The technical problem solved by the present invention is: to propose a method for removing trace iodine in ion-exchange membrane caustic soda raw material brine using a heteroatom-modified and grafted cyclodextrin adsorbent. The present invention performs heteroatom modification on commercially available activated carbon and grafts cyclodextrin to improve its iodine removal rate. The innovation of this method is that the activated carbon is modified by using pyrridine, pyrrole, vitamin B1, EDTA, imidazole, quinoline, trichloroisocyanuric acid, etc., and cyclodextrin is grafted on the modified adsorbent to improve the activated carbon's ability to remove trace iodine in brine. In ion-exchange membrane caustic soda raw material brine with an initial iodine concentration of 2.5 mg / L, the iodine removal rate of the pyridine-modified activated carbon is 43.6%, which is 11.2% higher than that of the unmodified activated carbon. β-cyclodextrin was grafted onto the surface of activated carbon. In ion-exchange membrane caustic soda raw material brine with an initial iodine concentration of 2.5 mg / L, the β-cyclodextrin-grafted activated carbon achieved an iodine removal rate of 46.7%, a 14.3% improvement compared to unmodified activated carbon. Furthermore, when β-cyclodextrin was grafted onto the surface of pyridine-modified activated carbon, the adsorbent achieved an iodine removal rate of 73.2%, a 41.2% improvement compared to unmodified activated carbon, representing a significant improvement in adsorption performance. This invention provides a unique and effective method for removing trace iodine from ion-exchange membrane caustic soda raw material brine in industrial applications.

[0009] In order to solve the technical problem of the present invention, a technical solution is proposed: a method for removing trace iodine from ion-exchange membrane caustic soda raw material brine using a heteroatom-modified and grafted cyclodextrin adsorbent, comprising the following steps:

[0010] (1) Place 100g of activated carbon in a beaker and add 500mL of deionized water; add 40mL of glacial acetic acid while stirring at room temperature, and continue stirring for 30min at a speed of 350rpm; weigh the required mass of modifier, the nitrogen content of the modifier and the mass ratio of activated carbon is 2%-6%, and 40mL of 30% hydrogen peroxide, and add them to the above beaker in sequence, continue stirring for 24h at room temperature in the dark, filter, and dry in a 90℃ oven for 12-24h;

[0011] The modifier described in step (1) is any one of pyridine, pyrrole, vitamin B1, EDTA, imidazole, quinoline, and trichloroisocyanuric acid;

[0012] (2) The dried sample was placed in a tube furnace, the nitrogen flow rate was maintained at 50 mL / min, and the temperature was increased to 400-900 °C at a heating rate of 5 °C / min and calcined for 2 h to obtain a modified adsorbent;

[0013] (3) 100 g of the adsorbent described in step (2) was placed in a beaker, 500 mL of nitric acid was added, and stirring was continued at room temperature for 3 h at a speed of 150 rpm; the solid phase was filtered and repeatedly washed in distilled water until the pH was 7.0, and the adsorbent was dried in an oven at 80 ° C for 4 h;

[0014] (4) 50 g of the adsorbent described in step (3) was mixed with 200 mL of DMF by ultrasonication. After mixing, 25 g of cyclodextrin and 1 mL of bifunctional linker HMDI were added. The mixture was placed in a round-bottom flask and heated in an oil bath at 70 °C under a nitrogen atmosphere and a rotation speed of 350 rpm for 6 h, and then filtered and separated.

[0015] (5) The adsorbent described in step (4) was washed with ethanol and pure water for several times, and dried in an oven at 80°C for 4 h;

[0016] (6) The grafted adsorbent prepared in step (5) is used to remove trace iodine from the raw material brine of ion-exchange membrane caustic soda.

[0017] Preferably, the modifier in step (1) is pyridine.

[0018] Preferably, the calcination temperature in step (2) is 600°C.

[0019] Preferably, the mass ratio of the nitrogen content of the modifier to the activated carbon is 4%.

[0020] Preferably, the cyclodextrin in step (4) is β-cyclodextrin.

[0021] The activated carbon in step (1) is preferably in the shape of a column or a sheet, with a particle size of 4-6 mesh and a specific surface area of ​​1000-1200 m 2 / g.

[0022] Preferably, the method comprises the following steps:

[0023] (1) Place 100g of activated carbon in a beaker and add 500mL of deionized water; add 40mL of glacial acetic acid while stirring at room temperature, and continue stirring for 30min at a speed of 350rpm; weigh the required mass of modifier, the mass ratio of nitrogen content of modifier to activated carbon is 4%, and 40mL of 30% hydrogen peroxide, and add them to the above beaker in sequence, continue stirring for 24h at room temperature in the dark, filter, and dry in a 90℃ oven for 12-24h;

[0024] The modifier described in step (1) is pyridine;

[0025] (2) The dried sample was placed in a tube furnace, the nitrogen flow rate was maintained at 50 mL / min, and the temperature was increased to 600 °C at a heating rate of 5 °C / min and calcined for 2 h to obtain the modified adsorbent;

[0026] (3) 100 g of the adsorbent described in step (2) was placed in a beaker, 500 mL of nitric acid was added, and stirring was continued at room temperature for 3 h at a speed of 150 rpm; the solid phase was filtered and repeatedly washed in distilled water until the pH was 7.0, and the adsorbent was dried in an oven at 80 ° C for 4 h;

[0027] (4) 50 g of the adsorbent described in step (3) was mixed with 200 mL of DMF by ultrasonication. After mixing, 25 g of β-cyclodextrin and 1 mL of bifunctional linker HMDI were added. The mixture was placed in a round-bottom flask and heated in an oil bath at 70 °C under a nitrogen atmosphere and a rotation speed of 350 rpm for 6 h, and then filtered and separated.

[0028] (5) The adsorbent was washed several times with ethanol and pure water, and dried in an oven at 80 °C for 4 h;

[0029] (6) The adsorbent prepared in step (5) is used to remove trace iodine from the raw material brine of ion-exchange membrane caustic soda.

[0030] Preferably, the specific steps of using the adsorbent in step (6) to remove trace iodine in the raw material brine of ion-exchange membrane caustic soda are:

[0031] (1) The raw material brine of ion membrane caustic soda is introduced into the reaction tower, hydrochloric acid is added to adjust the pH of the brine to 2, and the mixture is stirred for 30 minutes using a stirring paddle. Hydrogen peroxide is added and stirred for 30 minutes, and the mixture is set aside.

[0032] (2) Place the adsorbent in the adsorption tower, connect the upper end of the adsorption tower to the pressure pump, and keep the system closed at 0.5m 3 The treated brine is added to the adsorption tower at a flow rate of / h.

[0033] (3) Collect 50 mL of brine flowing out of the adsorption column and test the iodine content in the brine using the bromine water method.

[0034] The invention discloses a preparation method of an activated carbon modified adsorbent and its application in removing iodine from ion-exchange membrane caustic soda raw material brine, comprising the following steps:

[0035] (1) Place 100g of activated carbon in a beaker and add 500mL of deionized water; add 40mL of glacial acetic acid while stirring at room temperature, and continue stirring for 30min at a speed of 350rpm; weigh the required mass of modifier, the nitrogen content of the modifier and the mass ratio of activated carbon is 2%-6%, and 40mL of 30% hydrogen peroxide, and add them to the above beaker in sequence, continue stirring for 24h at room temperature in the dark, filter, and dry in a 90℃ oven for 12-24h;

[0036] The modifier described in step (1) is any one of pyridine, pyrrole, vitamin B1, EDTA, imidazole, quinoline, and trichloroisocyanuric acid;

[0037] (2) The dried sample was placed in a tube furnace, the nitrogen flow rate was maintained at 50 mL / min, and the temperature was increased to 400-900 °C at a heating rate of 5 °C / min and calcined for 2 h to obtain the modified adsorbent;

[0038] (3) Place 100g of activated carbon in a beaker, add 500mL of nitric acid, and stir continuously at room temperature for 3h at 150rpm. Filter and separate, and wash the solid phase repeatedly in distilled water until the pH is close to 7.0. Dry the activated carbon in an oven at 80℃ for 4h.

[0039] (4) Take 50 g of activated carbon and 200 mL of DMF, mix them evenly by ultrasonication, add a certain amount of cyclodextrin (the amount of cyclodextrin is 5 g, 10 g, 15 g, 20 g, 25 g, and 30 g, respectively) and 1 mL of bifunctional linker HMDI, and put them into a round-bottom flask. Heat the mixture in an oil bath at 70 °C under a nitrogen atmosphere and a rotation speed of 350 rpm for 6 h, and filter and separate.

[0040] (5) The above adsorbent was washed several times with ethanol and pure water and then dried in an oven at 80 °C for 4 h.

[0041] (6) The adsorbent prepared in step (5) is used to remove trace iodine from the raw material brine of ion-exchange membrane caustic soda.

[0042] The mass ratio of the nitrogen content of the modifier to the activated carbon is 4%; the mass ratio of the cyclodextrin to the activated carbon is 50%.

[0043] The beneficial effects of the present invention are as follows:

[0044] The present invention provides a method for preparing an activated carbon-modified adsorbent. Compared to other methods, this method significantly reduces preparation costs, is simpler to operate, and is scalable. The technical solution employed in this invention involves modifying activated carbon using one of pyridine, pyrrole, vitamin B1, EDTA, imidazole, quinoline, and trichloroisocyanuric acid as a surface modifier, and then grafting one of α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin onto the activated carbon surface. This results in a heteroatom nitrogen-modified activated carbon adsorbent grafted with cyclodextrin, which exhibits excellent adsorption properties for iodine in brine. Furthermore, compared to existing technologies, the modifier used in this invention is non-toxic and inexpensive. Furthermore, the modifier used in this invention is low in quantity and has a high utilization rate, resulting in lower modification costs compared to other technologies. This invention will provide an important theoretical and practical basis for solving the common problem of trace iodine removal in the ion-exchange membrane caustic soda industry, providing strong technical support for the healthy and sustainable development of the industry.

[0045] Based on the selective adsorption capacity of heteroatoms and cyclodextrin for elemental iodine, activated carbon adsorbents were modified with heteroatoms and grafted with cyclodextrin to enhance their ability to remove trace iodine from ion-exchange membrane caustic soda raw brine. Using different nitrogen sources to modify the activated carbon, the pyridine-modified activated carbon achieved an iodine removal rate of 43.6% in ion-exchange membrane caustic soda raw brine with an initial iodine concentration of 2.5 mg / L, an 11.2% improvement compared to unmodified activated carbon. β-cyclodextrin was grafted onto the activated carbon surface. In ion-exchange membrane caustic soda raw brine with an initial iodine concentration of 2.5 mg / L, the β-cyclodextrin-grafted activated carbon achieved an iodine removal rate of 47.7%, a 15.3% improvement compared to unmodified activated carbon. By grafting β-cyclodextrin onto the surface of pyridine-modified activated carbon, the adsorbent achieved an iodine removal rate of 73.2%, a 41.2% increase compared to unmodified activated carbon, significantly improving adsorption performance. This invention provides a unique and effective method for removing trace iodine from brine, the raw material for industrial ion-exchange caustic soda production, with excellent economic benefits and operability.

[0046] As shown in Table 1, activated carbon has a better performance in removing iodine from saturated salt water than other adsorbents, with a removal rate of 42.4%. Activated carbon is the preferred adsorbent.

[0047] As shown in Table 2, the adsorbent modified with N1=pyridine (N1AC) in Example 1 has a better removal effect on iodine from brine than other modifiers, with a removal rate of 43.6%. Compared with the unmodified activated carbon adsorbent, the iodine removal rate is increased by 11.2%.

[0048] As shown in Table 3, when the nitrogen doping amount is 4%, the iodine removal performance of the adsorbent is the best, and the removal rate reaches 43.6%. The optimal nitrogen doping amount is 4%.

[0049] As shown in Table 4, when the calcination temperature is 600°C, the iodine removal performance of the adsorbent is the best, and the removal rate reaches 55.6%. The calcination temperature is preferably 600°C.

[0050] As shown in Table 5, the adsorption effect of the N1AC grafted β-cyclodextrin adsorbent (N1AC-2) in Example 2 is better than that of other cyclodextrin grafted adsorbents (N1AC-1 and N1AC-3), with an iodine removal rate of 73.2%. The iodine removal rate of N1AC is 41.4%, and the iodine removal rate of the activated carbon grafted with cyclodextrin only (AC-2) is 47.7%.

[0051] It can be seen from Table 6 that when the amount of cyclodextrin is 25 g, the iodine removal performance of the adsorbent is the best, and the removal rate reaches 73.2%. The optimal amount of cyclodextrin is 25 g. DETAILED DESCRIPTION

[0052] Example 1 Adsorbent Preparation

[0053] Take 100g of untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g activated carbon was placed in a beaker and 500mL of deionized water was added. 40mL of glacial acetic acid was added while stirring at room temperature for 30 minutes (at 350rpm). 22.6g of pyridine and 40mL of hydrogen peroxide (30% mass concentration) were weighed and added to the beaker in sequence. Stirring was continued at room temperature in the dark for 24 hours, filtered, and dried in a 90°C oven for 12-24 hours. The dried sample was placed in a tube furnace with a nitrogen flow rate of 50mL / min and heated to 600°C at a heating rate of 5°C / min for 2 hours to obtain the modified adsorbent N1AC.

[0054] The modified adsorbent was placed in a beaker, 500 mL of nitric acid was added, and stirring was continued at room temperature at 150 rpm for 3 hours. The solid phase was separated by filtration, and the solid phase was repeatedly washed in distilled water until the pH was close to 7.0. The adsorbent was then dried in an 80°C oven for 4 hours. 50 g of the above adsorbent and 200 mL of DMF were placed in a round-bottom flask and ultrasonically mixed. After mixing, 25 g of α-cyclodextrin and 1 mL of the bifunctional linker HMDI were added. The mixture was heated in a 70°C oil bath at 350 rpm under a nitrogen atmosphere for 6 hours and separated by filtration. The adsorbent was washed repeatedly with ethanol and purified water and dried in an 80°C oven for 4 hours. This yielded N1AC-1.

[0055] The iodine adsorption experiment of the modified adsorbent N1AC-1 includes the following steps:

[0056] (1) Take 500 mL of ion-exchange membrane caustic soda raw material brine with an iodine concentration of 2.5 mg / L (the main components are 300 g / L sodium chloride, 2-3 g / L sodium chlorate and trace amounts of other impurity ions), add hydrochloric acid to adjust the pH of the brine to 2, use a magnetic stirrer to stir for 30 minutes, add 0.05 mL of hydrogen peroxide (mass concentration 30%) and stir for 30 minutes, and set aside.

[0057] (2) Take 70g of adsorbent and place it in an adsorption column with a diameter of 3cm. Fix the adsorption column. Connect the upper end of the adsorption column to a flow pump. While keeping the system closed, pump the adsorption column at a speed of 0.5m 3 500 mL of the treated brine was added to the adsorption column at a flow rate of 1 / h.

[0058] (3) Collect 50 mL of brine flowing out of the adsorption column and test the iodine content in the brine using the bromine water method.

[0059] Example 2 Adsorbent Preparation

[0060] Take 100g of untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g activated carbon was placed in a beaker and 500mL of deionized water was added. 40mL of glacial acetic acid was added while stirring at room temperature for 30 minutes (at 350rpm). 22.6g of pyridine and 40mL of hydrogen peroxide (30% mass concentration) were weighed and added to the beaker in sequence. Stirring was continued at room temperature in the dark for 24 hours, filtered, and dried in a 90°C oven for 12-24 hours. The dried sample was placed in a tube furnace with a nitrogen flow rate of 50mL / min and heated to 600°C at a heating rate of 5°C / min for 2 hours to obtain the modified adsorbent N1AC.

[0061] The modified adsorbent was placed in a beaker, 500 mL of nitric acid was added, and stirring was continued at room temperature at 150 rpm for 3 hours. The solid phase was separated by filtration, and the solid phase was repeatedly washed in distilled water until the pH was close to 7.0. The adsorbent was then dried in an oven at 80°C for 4 hours. 50 g of the above adsorbent and 200 mL of DMF were placed in a round-bottom flask and mixed ultrasonically. After mixing, 25 g of β-cyclodextrin and 1 mL of the bifunctional linker HMDI were added. The mixture was heated in a 70°C oil bath at 350 rpm under a nitrogen atmosphere for 6 hours and separated by filtration. The adsorbent was washed repeatedly with ethanol and purified water and dried in an oven at 80°C for 4 hours. This yielded N1AC-2.

[0062] The experimental steps for adsorbing iodine by the adsorbent are the same as those in Example 1.

[0063] In this embodiment, the modified adsorbent grafted with β-cyclodextrin has a better adsorption effect than the adsorbent grafted with other cyclodextrins, and the adsorption rate reaches 73.2%.

[0064] Example 3 Adsorbent Preparation

[0065] Take 100g of untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g activated carbon was placed in a beaker and 500mL of deionized water was added. 40mL of glacial acetic acid was added while stirring at room temperature for 30 minutes (at 350rpm). 22.6g of pyridine and 40mL of hydrogen peroxide (30% mass concentration) were weighed and added to the beaker in sequence. Stirring was continued at room temperature in the dark for 24 hours, filtered, and dried in a 90°C oven for 12-24 hours. The dried sample was placed in a tube furnace with a nitrogen flow rate of 50mL / min and heated to 600°C at a heating rate of 5°C / min for 2 hours to obtain the modified adsorbent N1AC.

[0066] The modified adsorbent was placed in a beaker, 500 mL of nitric acid was added, and stirring was continued at room temperature at 150 rpm for 3 hours. The solid phase was separated by filtration, and the solid phase was repeatedly washed in distilled water until the pH was close to 7.0. The adsorbent was then dried in an 80°C oven for 4 hours. 50 g of the above adsorbent and 200 mL of DMF were placed in a round-bottom flask and ultrasonically mixed. After mixing, 25 g of γ-cyclodextrin and 1 mL of the bifunctional linker HMDI were added. The mixture was heated in a 70°C oil bath at 350 rpm under a nitrogen atmosphere for 6 hours and separated by filtration. The adsorbent was washed repeatedly with ethanol and purified water and dried in an 80°C oven for 4 hours. This yielded N1AC-3.

[0067] The experimental steps for adsorbing iodine by the adsorbent are the same as those in Example 1.

[0068] Comparative Example 1

[0069] The adsorbent selection and modification condition screening experiment includes the following steps:

[0070] (1) Take 70g of untreated adsorbent (activated carbon, diatomaceous earth, molecular sieve, kaolin) and place it in an adsorption column with a diameter of 3cm. Fix the adsorption column. Connect the upper end of the adsorption column to a flow pump. While keeping the system closed, pump the adsorption column at a speed of 0.5m 3 500 mL of saturated saline solution containing 2.5 mg / L iodine was added to the adsorption column at a flow rate of / h.

[0071] (2) Collect 50 mL of brine flowing out of the adsorption column and test the iodine content in the brine using the ferric thiocyanate-sodium nitrite catalytic kinetic method.

[0072] The comparison of iodine removal efficiency of various adsorbents in saturated salt water is shown in Table 1.

[0073] Table 1 Effect of different adsorbents on iodine removal rate

[0074] adsorbent Concentration after removal (mg / L) Removal rate (%) activated carbon 1.70 32.0 diatomite 1.82 27.2 molecular sieves 1.74 30.3 Kaolin 1.83 26.7

[0075] As shown in Table 1, activated carbon has a better performance in removing trace iodine from brine than other adsorbents, with a removal rate of 32.0%. Activated carbon is the preferred adsorbent.

[0076] Comparative Example 2

[0077] The adsorbent selection and modification condition screening experiment includes the following steps:

[0078] (1) Place 100g of activated carbon in a beaker and add 500mL of deionized water; add 40mL of glacial acetic acid while stirring at room temperature, continue stirring for 30min, and the speed is 350rpm; weigh the required mass of modifier, the mass ratio of nitrogen content of modifier to activated carbon is 4%, and 40mL of 30% hydrogen peroxide, add them to the above beaker in sequence, continue stirring for 24h at room temperature in the dark, filter, and dry in a 90℃ oven for 12-24h.

[0079] The modifier described in step (1) is any one of pyridine, pyrrole, vitamin B1, EDTA, imidazole, quinoline, and trichloroisocyanuric acid;

[0080] (2) The dried sample was placed in a tube furnace, the nitrogen flow rate was maintained at 50 mL / min, and the temperature was increased to 500-900 °C at a heating rate of 5 °C / min and calcined for 2 h to obtain the modified adsorbent;

[0081] (3) Take 500 mL of ion-exchange membrane caustic soda raw material brine with an iodine concentration of 2.5 mg / L, add hydrochloric acid to adjust the pH to 2, stir with a magnetic stirrer for 30 min, add 0.05 mL of hydrogen peroxide (30%), stir for 30 min, and set aside.

[0082] (4) Take 70g of the above modified adsorbents (activated carbon, N1AC, N2AC, N3AC, N4AC, N5AC, N6AC, N7AC) and place them in an adsorption column with a diameter of 3cm. Fix the adsorption column. Connect the upper end of the adsorption column to a flow pump. While keeping the system closed, pump the adsorption column at a speed of 0.5m 3 The above-mentioned ion membrane caustic soda raw material brine is added to the adsorption column at a flow rate of / h.

[0083] (5) Collect 50 mL of brine flowing out of the adsorption column and test the iodine content in the brine using the bromine water method.

[0084] Table 2 Effect of different modifiers on iodine removal rate

[0085]

[0086] The effects of different modifiers on the iodine removal performance of the adsorbent were investigated. Table 2 shows that the adsorbent (N1AC) modified with pyridine (N1) in Example 1 showed better iodine removal from brine than the other modifiers, achieving a removal rate of 43.6%. This iodine removal rate was also improved by 11.2% compared to the unmodified activated carbon adsorbent.

[0087] Comparative Example 3

[0088] Take 100g of untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g activated carbon was placed in a beaker and 500mL of deionized water was added. 40mL of glacial acetic acid was added while stirring at room temperature and continued stirring for 30 minutes (at 350rpm). 11.3g, 22.6g, and 34g of pyridine and 40mL of hydrogen peroxide (mass concentration 30%) were weighed and added to the beaker in sequence. Stirring was continued for 24 hours at room temperature in the dark, filtered, and dried in a 90°C oven for 12-24 hours. The dried sample was placed in a tube furnace with a nitrogen flow rate of 50mL / min and heated to 600°C at a heating rate of 5°C / min for 2 hours to obtain the modified adjuvant.

[0089] The effect of nitrogen doping on the iodine removal efficiency of ion-exchange membrane caustic soda raw material brine containing 2.5 mg / L iodine was investigated.

[0090] Table 3 Effect of different nitrogen doping amounts on iodine removal rate

[0091] Nitrogen doping amount Concentration after removal (mg / L) Removal rate (%) 2% 1.56 37.6 4% 1.41 43.6 6% 1.49 40.4

[0092] The effects of different nitrogen doping levels on the iodine removal performance of the adsorbent were investigated. Table 3 shows that the adsorbent exhibits the best iodine removal performance when nitrogen doping levels (nitrogen to activated carbon mass ratios of 2%, 4%, and 6%) are used to remove trace iodine from brine. A nitrogen doping level of 4% achieves optimal iodine removal, reaching a removal rate of 43.6%. A nitrogen doping level of 4% is optimal.

[0093] Comparative Example 4

[0094] Take 100g of untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g activated carbon was placed in a beaker and 500mL of deionized water was added. 40mL of glacial acetic acid was added while stirring at room temperature and continued stirring for 30 minutes (at 350rpm). 22.6g of pyridine and 40mL of hydrogen peroxide (mass concentration 30%) were weighed and added to the beaker in sequence. Stirring was continued for 24 hours at room temperature in the dark, filtered, and dried in a 90°C oven for 12-24 hours. The dried sample was placed in a tube furnace with a nitrogen flow rate of 50mL / min. The temperature was increased to 400°C, 500°C, 600°C, 700°C, 800°C, and 900°C at a heating rate of 5°C / min and calcined for 2 hours to obtain the modified adsorbent.

[0095] Table 4 Effect of different calcination temperatures on iodine removal rate

[0096] Calcination temperature (℃) Concentration after removal (mg / L) Removal rate (%) 400 1.52 39.2 500 1.47 41.2 600 1.41 43.6 700 1.55 38.0 800 1.61 35.6 900 1.56 37.6

[0097] The effects of different calcination temperatures on the adsorbent's iodine removal performance were investigated. Table 4 shows that, when calcined at 400°C, 500°C, 600°C, 700°C, 800°C, and 900°C, the adsorbent exhibited the best iodine removal performance from the raw brine of ion-exchange membrane caustic soda, achieving a removal rate of 43.6%. A calcination temperature of 600°C is the optimal temperature.

[0098] Comparative Example 5

[0099] The iodine adsorption experiment of the modified adsorbent includes the following steps:

[0100] (1) Take 500 mL of ion-exchange membrane caustic soda raw material brine with an iodine concentration of 2.5 mg / L, add hydrochloric acid to adjust the pH to 2, stir with a magnetic stirrer for 30 min, add 0.05 mL of hydrogen peroxide (30%), stir for 30 min, and set aside.

[0101] (2) Take 70g of adsorbent (activated carbon, N1AC, AC-2, N1AC-1, N1AC-2, N1AC-3) and place it in an adsorption column with a diameter of 3cm. Fix the adsorption column. Connect the upper end of the adsorption column to a flow pump. While keeping the system closed, pump the adsorption column at a speed of 0.5m 3 500 mL of the treated industrial brine was added to the adsorption column at a flow rate of 1 hour. The activated carbon was untreated 4-6 mesh with a specific surface area of ​​1200 m 2 / g of activated carbon, AC-2 is activated carbon directly grafted with β-cyclodextrin.

[0102] (3) 50 mL of brine flowing out of the adsorption column was collected and the iodine content in the brine was tested by the bromine water method. The results are shown in Table 5.

[0103] Table 5 Effect of different adsorbents on iodine removal rate

[0104] adsorbent Iodine concentration after removal (mg / L) Removal rate (%) activated carbon 1.70 32.0% N1AC 1.47 41.2% AC-2 1.31 47.6% N1AC-1 1.10 56.0% N1AC-2 0.67 73.2% N1AC-3 0.86 65.6%

[0105] The iodine removal performance of different adsorbents was investigated. As shown in Table 5 above, the N1AC grafted β-cyclodextrin adsorbent (N1AC-2) in Example 2 had a better adsorption effect than other grafted cyclodextrin adsorbents (N1AC-1 and N1AC-3), with an iodine removal rate of 73.2%. The iodine removal rate of N1AC was 41.2%, and the iodine removal rate of activated carbon grafted with cyclodextrin alone (AC-2) was 47.6%.

[0106] Comparative Example 6

[0107] Place 100g of N1AC in a beaker, add 500mL of nitric acid, and stir continuously at room temperature for 3 hours at 150rpm. Filter and separate, then wash the solid phase repeatedly in distilled water until the pH is close to 7.0 and dry in an 80°C oven for 4 hours. Add 50g of the above adsorbent to 200mL of DMF and mix thoroughly using ultrasonic technology. After mixing, add 5g, 10g, 15g, 20g, 25g, and 30g of β-cyclodextrin and 1mL of the bifunctional linker HMDI, respectively. Place the mixture in a round-bottom flask and heat the mixture in a 70°C oil bath under nitrogen at 350rpm for 6 hours. Filter and separate. Wash the adsorbent multiple times with ethanol and pure water, then dry in an 80°C oven for 4 hours.

[0108] Table 6 Effect of different β-cyclodextrin amounts on iodine removal rate

[0109] β-cyclodextrin amount Concentration after removal (mg / L) Removal rate (%) 0g 1.47 41.2 5g 1.19 52.4 10g 1.05 58.0 15g 0.93 62.8 20g 0.77 69.2 25g 0.67 73.2 30g 0.69 72.4

[0110] The effects of different amounts of cyclodextrin grafted onto the modified adsorbent on its iodine removal performance were investigated. Table 6 shows that the effects of different cyclodextrin amounts (0g, 5g, 10g, 15g, 20g, 25g, and 30g) on ​​the adsorbent's ability to remove trace iodine from the caustic soda raw material brine were compared. The adsorbent exhibited optimal iodine removal performance when 25g of cyclodextrin was added, achieving a removal rate of 73.2%. Therefore, a 25g cyclodextrin amount was the optimal amount.

Claims

1. An application of an activated carbon modified adsorbent in removing iodine from ion-exchange membrane caustic soda raw material brine, characterized in that: The following steps are involved: (1) Place 100g of activated carbon in a beaker and add 500mL of deionized water; add 40mL of glacial acetic acid while stirring at room temperature, and continue stirring for 30min at a speed of 350rpm; weigh the required mass of modifier and 40mL of 30% hydrogen peroxide, the nitrogen content of the modifier and the mass ratio of activated carbon are 2%-6%, add the modifier and hydrogen peroxide to the above beaker in turn, continue stirring for 24h at room temperature in the dark, filter, and dry in a 90℃ oven for 12-24h; The modifier described in step (1) is any one of pyridine, pyrrole, vitamin B1, EDTA, imidazole, quinoline, and trichloroisocyanuric acid; (2) The dried sample was placed in a tube furnace, the nitrogen flow rate was maintained at 50 mL / min, and the temperature was increased to 400-900 °C at a heating rate of 5 °C / min and calcined for 2 h to obtain the modified adsorbent; (3) 100 g of the adsorbent described in step (2) was placed in a beaker, 500 mL of nitric acid was added, and stirring was continued at room temperature for 3 h at a speed of 150 rpm; the solid phase was filtered and repeatedly washed in distilled water until the pH was 7.0, and the adsorbent was dried in an oven at 80 ° C for 4 h; (4) 50 g of the adsorbent described in step (3) was mixed with 200 mL of DMF by ultrasonication. After mixing, a certain amount of cyclodextrin and 1 mL of bifunctional linker HMDI were added. The mixture was placed in a round-bottom flask and heated in an oil bath at 70 °C for 6 h under a nitrogen atmosphere and a rotation speed of 350 rpm, and then filtered and separated. (5) The adsorbent was washed several times with ethanol and pure water, and dried in an oven at 80 °C for 4 h; (6) The adsorbent prepared in step (5) is used to remove trace iodine from the raw material brine of ion-exchange membrane caustic soda.

2. The use of the activated carbon modified adsorbent according to claim 1 in removing iodine from ion-exchange membrane caustic soda raw material brine, characterized in that: The modifier in step (1) is pyridine.

3. The use of the activated carbon modified adsorbent according to claim 1 in removing iodine from ion-exchange membrane caustic soda raw material brine, characterized in that: The calcination temperature in step (2) is 600°C.

4. The use of the activated carbon modified adsorbent according to claim 1 in removing iodine from ion-exchange membrane caustic soda raw material brine, characterized in that: The mass ratio of the nitrogen content of the modifier to the activated carbon is 4%.

5. The use of the activated carbon modified adsorbent according to claim 1 in removing iodine from ion-exchange membrane caustic soda raw material brine, characterized in that; The grafted cyclodextrin in step (4) is β-cyclodextrin.

6. The use of the activated carbon modified adsorbent according to claim 1 in removing iodine from ion-exchange membrane caustic soda raw material brine, characterized in that: The activated carbon in step (1) is in the shape of columnar or flake, with a particle size of 4-6 mesh and a specific surface area of ​​1000-1200m 2 / g.

7. The use of the activated carbon modified adsorbent according to claim 1 in removing iodine from ion-exchange membrane caustic soda raw material brine, characterized in that: The following steps are involved: (1) Place 100g of activated carbon in a beaker and add 500mL of deionized water; add 40mL of glacial acetic acid while stirring at room temperature, and continue stirring for 30min at a speed of 350rpm; weigh the required mass of modifier, the mass ratio of nitrogen content of modifier to activated carbon is 4%, and 40mL of 30% hydrogen peroxide, and add them to the above beaker in sequence, continue stirring for 24h at room temperature in the dark, filter, and dry in a 90℃ oven for 12-24h; The modifier described in step (1) is pyridine; (2) The dried sample was placed in a tube furnace, the nitrogen flow rate was maintained at 50 mL / min, and the temperature was increased to 600 °C at a heating rate of 5 °C / min and calcined for 2 h to obtain the modified adsorbent; (3) 100 g of the adsorbent described in step (2) was placed in a beaker, 500 mL of nitric acid was added, and stirring was continued at room temperature for 3 h at a speed of 150 rpm; the solid phase was filtered and repeatedly washed in distilled water until the pH was 7.0, and the adsorbent was dried in an oven at 80 ° C for 4 h; (4) 50 g of the adsorbent described in step (3) was mixed with 200 mL of DMF by ultrasonication. After mixing, 25 g of β-cyclodextrin and 1 mL of bifunctional linker HMDI were added. The mixture was placed in a round-bottom flask and heated in an oil bath at 70 °C under a nitrogen atmosphere and a rotation speed of 350 rpm for 6 h, and then filtered and separated. (5) The adsorbent described in step (4) was washed with ethanol and pure water for several times, and dried in an oven at 80°C for 4 h; (6) The adsorbent prepared in step (5) is used to remove trace iodine from the raw material brine of ion-exchange membrane caustic soda.

8. The use of the activated carbon modified adsorbent according to claim 1 in removing iodine from ion-exchange membrane caustic soda raw material brine, characterized in that: The specific steps of using the adsorbent in step (6) to remove trace iodine from the raw material brine of ion-exchange membrane caustic soda are: (1) Add industrial brine to the reaction tower, add hydrochloric acid to adjust the pH of the industrial brine to 2, stir with a stirring paddle for 30 minutes, add hydrogen peroxide and stir for 30 minutes, and set aside; (2) Place the adsorbent in the adsorption tower, connect the upper end of the adsorption tower to the pressure pump, and keep the system closed at 0.5m 3 The treated industrial brine is added to the adsorption tower at a flow rate of / h; (3) Collect 50 mL of brine flowing out of the adsorption column and test the iodine content in the brine using the bromine water method.

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