Method for removing trace iodine in ionic membrane caustic soda process brine by using heteroatom modified adsorbent

Abstract

The invention relates to a method for removing trace iodine in brine in an ionic membrane caustic soda process. Based on the selective adsorption capacity of heteroatoms and cyclodextrin to iodine elementary substances, an activated carbon adsorbent is subjected to heteroatom modification and cyclodextrin grafting, so that the removal capacity of activated carbon to trace iodine in ionic membrane caustic soda process brine is improved. Different phosphorus sources are used for modifying the activated carbon, in ionic membrane caustic soda process brine with the iodine initial concentration of 2.5 mg / L, the removal rate of the activated carbon modified by phosphoric acid to iodine is 42.0%, and compared with unmodified activated carbon, the removal rate of iodine is increased by 9.6%. Beta-cyclodextrin is grafted to the surface of phosphoric acid modified activated carbon, the removal rate of iodine by the adsorbent is 76.8%, and compared with unmodified activated carbon, the removal rate of iodine is increased by 44.4%, and the adsorption performance is greatly improved. The invention provides a unique and effective solution for removing trace iodine in the industrial ionic membrane caustic soda method, and has good economic benefit and operability.

Description

Technical Field

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

[0002] Caustic soda is one of the most basic chemical raw materials and is widely used in papermaking, detergents, petrochemical products and other fields. By the end of 2022, my country's annual total production capacity of caustic soda reached 39.8 million tons, making it the world's largest producer and consumer of caustic soda. At present, the main production method of caustic soda is the ion membrane method.

[0003] The ion membrane method is the most advanced caustic soda production method at present, with many advantages such as high concentration of liquid caustic soda, low comprehensive energy consumption and environmental pollution, and is adopted by many chlor-alkali manufacturers at home and abroad. However, iodine is difficult to remove in the circulating brine of the ion membrane caustic soda process, and is continuously enriched in the brine. At the same time, iodine can be oxidized to a high valence state during the electrolysis process and generate extremely insoluble Ba3H4(IO6)2 and other precipitations, which are deposited on the surface of the ion membrane, resulting in a decrease in current efficiency. When the iodine content in the brine is higher than 0.2mg / L, the service life of the ion membrane will be greatly shortened. At present, the ion membrane used in the ion membrane caustic soda device of my country mainly relies on imports and is expensive, so the shortening of the service life of the ion membrane will directly lead to an increase in the production cost of the enterprise. In view of this, it is very important for chlor-alkali enterprises to remove trace iodine in the brine to the maximum extent, and it is also a problem that the current salt and salt chemical industry urgently need to solve. Therefore, the research and development of trace iodine removal technology in the brine of the ion membrane caustic soda process has great practical significance.

[0004] At present, the methods for extracting iodine from brine include air blowing, ion exchange, adsorption (activated carbon method, starch method), solvent extraction, precipitation (copper method, silver method), electrolysis and new technology liquid membrane method. Among them, the adsorption method has become an important method for extracting iodine from brine due to its simple process, low cost, clean and pollution-free. The principle of the adsorption method is to use the advantages of the adsorbent such as porous, large surface area, good water filtration performance and strong adsorption to adsorb iodine through the adsorbent, so as to achieve the effect of removing iodine. Huang Yuying conducted a preliminary study on the iodine removal performance of several domestic coal-based activated carbons. The results showed that most activated carbons have good iodine removal effects. Wu Gang used hydrogen peroxide, sodium hypochlorite, chlorine, ferric chloride, sodium chlorate, etc. as oxidants, activated carbon, molecular sieves, white clay, diatomaceous earth, etc. as adsorbents, and reduced the iodine content from 0.21 mg / L to below 0.05 mg / L under acidic conditions. Gao Shubao used sodium nitrite as an oxidant and activated carbon fiber to remove iodine at pH = 2-3, and the iodine removal rate was greater than 90%. Although the adsorbent can reduce the iodine concentration to below 0.05 mg / L, the initial iodine concentration in the original brine is not high.

[0005] Although the reported use of adsorption methods to remove iodine has achieved good research results in the laboratory stage, our preliminary experimental results show that when saturated salt water is used to prepare iodine elemental solution for commercially available activated carbon to remove iodine, the adsorption capacity of the activated carbon drops sharply at the research 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 saturated salt water seriously inhibits the selective adsorption capacity of activated carbon for iodine.

[0006] In summary, considering production cost, operation difficulty, environmental impact and many other aspects, adsorption method is currently the most suitable method for domestic chlor-alkali enterprises to remove trace iodine in brine of ion membrane caustic soda process. However, the inhibitory effect of chloride ions in brine on the selective removal of iodine limits the specific application of this method in industry. Summary of the invention

[0007] The technical problem solved by the present invention is: to propose a method for removing trace iodine in brine by using a heteroatom-modified and cyclodextrin-grafted activated carbon adsorbent, which is a method for removing trace iodine in brine in an ion membrane caustic soda process. 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 phosphoric acid, and then cyclodextrin is grafted on the modified adsorbent to improve the ability of the activated carbon to remove trace iodine in brine in an ion membrane caustic soda process. In the ion-exchange membrane caustic soda process brine with an initial iodine concentration of 2.5 mg / L, the iodine removal rate of the activated carbon modified with phosphoric acid is 42.0%, which is 9.6% higher than that of the unmodified activated carbon; the iodine removal rate of the activated carbon grafted with β-cyclodextrin is 47.7%, which is 15.3% higher than that of the unmodified activated carbon; and the iodine removal rate of the activated carbon modified with phosphoric acid and grafted with β-cyclodextrin is 76.8%, which is 44.4% higher than that of the unmodified activated carbon. The adsorption performance is greatly improved. The present invention provides a unique and effective solution for the removal of trace iodine in the industrial ion-exchange membrane caustic soda process.

[0008] In order to solve the technical problem of the present invention, the proposed technical solution is: a method for removing trace iodine in brine in an ion membrane caustic soda process using a heteroatom-modified and grafted cyclodextrin activated carbon adsorbent, comprising the following steps:

[0009] (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 phosphoric acid (the mass ratio of the phosphorus content of the modifier to the activated carbon is 4%) and 40mL of hydrogen peroxide (mass concentration 30%), add them to the above beaker in sequence, continue stirring for 24h at room temperature and in the dark, filter, and dry in a 90℃ oven for 12-24h;

[0010] (2) placing the dried sample in a tube furnace, maintaining a nitrogen flow rate of 50 mL / min, heating the sample to 500-900°C at a heating rate of 5°C / min, and calcining the sample for 2 h to obtain a modified adsorbent;

[0011] (3) Take 100g of the modified activated carbon in step (2) and place it in a beaker. Add 500mL of nitric acid and stir continuously at room temperature for 3h at a speed of 150rpm. Filter and separate, wash the solid phase repeatedly in distilled water until the pH is close to 7.0, and then dry the activated carbon in an oven at 80℃ for 4h.

[0012] (4) Take 50g of the modified activated carbon in step (3) and 200mL of DMF, put them into a round-bottom flask, and mix them evenly by ultrasonication. After mixing, add a certain amount of β-cyclodextrin (the amount of cyclodextrin is 5g, 10g, 15g, 20g, 25g, and 30g, respectively) and 1mL of bifunctional linker HMDI. Then, heat the mixture in a 70°C oil bath at 350rpm under a nitrogen atmosphere for 6h, and filter and separate;

[0013] (5) The adsorbent described in step (4) was washed multiple times with ethanol and pure water, and dried in an oven at 80° C. for 4 h.

[0014] (6) The adsorbent prepared in step (5) is used to remove trace iodine in the brine of the ion membrane caustic soda process.

[0015] Preferably, the activated carbon in step (1) is in the shape of a column or a sheet, with a particle size of 4-6 mesh and a specific surface area of ​​1000-1200m 2 / g.

[0016] Preferably, the mass ratio of the phosphorus content of the modifier to the activated carbon is 4%.

[0017] Preferably, the activated carbon is untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g of activated carbon.

[0018] In order to solve the technical problem of the present invention, another technical solution is proposed: the adsorbent in step (6) is used to remove trace iodine in the brine of the ion membrane caustic soda process. The specific steps are:

[0019] (1) Pass the ion membrane caustic soda process brine into 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 (mass concentration 30%), continue stirring for 30 minutes, and set aside;

[0020] (2) The adsorbent is placed in an adsorption tower, and the upper end of the adsorption tower is connected to a pressure pump. While keeping the system airtight, the treated industrial brine is added to the adsorption tower at a flow rate of 100 mL / min.

[0021] (3) Collect 50 mL of brine flowing out of the adsorption column and test the iodine content in the brine.

[0022] The beneficial effects of the present invention are as follows:

[0023] The present invention provides a method for preparing a modified activated carbon adsorbent. Compared with other methods, the method greatly reduces the preparation cost, is simpler to operate and can be expanded. The technical scheme adopted by the present invention is: by using one of phosphoric acid, hypophosphorous acid, triphenylphosphine, diammonium hydrogen phosphate, tetraphenylphosphine bromide, diphenyl hypophosphorous acid and phenylphosphoric acid as an activated carbon surface modifier to modify the activated carbon, and grafting one of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin onto the surface of the above-mentioned heteroatom phosphorus modified activated carbon, an activated carbon adsorbent modified with heteroatom phosphorus and grafted with cyclodextrin is prepared, which has excellent adsorption performance for trace iodine in the brine of ion membrane caustic soda process. At the same time, compared with the prior art: the modifier selected in the present invention is non-toxic and harmless, and the price is low; secondly, the amount of modifier used in the present invention is small, and the utilization rate is high, so the modification cost is lower than other technologies. The present invention will provide an important theoretical basis and practical basis for solving the problem of trace iodine removal that is common in the ion membrane caustic soda industry, and provide a strong technical guarantee for the healthy and sustainable development of the ion membrane caustic soda industry.

[0024] The present invention relates to a method for removing trace iodine in an ion membrane caustic soda process brine. Based on the selective adsorption capacity of heteroatoms and cyclodextrins to elemental iodine, the activated carbon adsorbent is subjected to heteroatom modification and cyclodextrin grafting to improve the removal capacity of the activated carbon to trace iodine in the ion membrane caustic soda process brine. The activated carbon is modified using different phosphorus sources. In the ion membrane caustic soda process brine with an initial iodine concentration of 2.5 mg / L, the iodine removal rate of the activated carbon modified with phosphoric acid is 42.0%, which is 9.6% higher than that of the unmodified activated carbon. β-cyclodextrin is grafted onto the surface of the activated carbon. In the ion membrane caustic soda process brine with an initial iodine concentration of 2.5 mg / L, the iodine removal rate of the activated carbon grafted with cyclodextrin is 47.7%, which is 15.3% higher than that of the unmodified activated carbon. When β-cyclodextrin is grafted onto the surface of activated carbon modified with phosphoric acid, the removal rate of iodine by the adsorbent is 76.8% in the ion membrane caustic soda process brine with an initial iodine concentration of 2.5 mg / L. Compared with the unmodified activated carbon, the iodine removal rate is increased by 44.4%, and the adsorption performance is greatly improved. The present invention provides a unique and effective solution for the removal of trace iodine in the industrial ion membrane caustic soda process, with good economic benefits and operability.

[0025] It can be seen from Table 1 that by comparing different modifiers, the activated carbon modified with phosphoric acid has a better iodine removal effect than the activated carbon modified with other modifiers, with a removal rate of 42.0%. Compared with the unmodified activated carbon adsorbent in Comparative Example 1, the iodine removal rate is increased by 9.6%.

[0026] As shown in Table 2, by comparing the effects of different calcination temperatures (400°C, 500°C, 600°C, 700°C, 800°C and 900°C) on the removal of trace iodine from brine by the adsorbent, when the calcination temperature is 400°C, the iodine removal performance of the adsorbent is the best, and the removal rate reaches 42.0%. The calcination temperature is preferably 400°C.

[0027] As shown in Table 3, by comparing the effects of different phosphorus doping amounts (i.e., the mass ratio of phosphorus to activated carbon is 2%, 4%, and 6%) on the iodine removal performance of the adsorbent, when the phosphorus doping amount is 4%, the iodine removal performance is the best, and the removal rate reaches 42.0%. The phosphorus doping amount is preferably 4%.

[0028] It can be seen from Table 4 that by comparing the effects of different β-cyclodextrin amounts (0g, 5g, 10g, 15g, 20g, 25g, 30g) on ​​the adsorption performance of the adsorbent, when the amount of β-cyclodextrin is 25g, the adsorption performance is best, and the removal rate reaches 76.8%. The optimal amount of β-cyclodextrin is 25g.

[0029] As shown in Table 5, the P1-β-AC adsorbent in Example 1 has a better iodine removal effect than the P1AC grafted with other cyclodextrin adsorbents (P1-α-AC and P1-γ-AC), and the iodine removal rate reaches 76.8%. The iodine removal rates of other phosphorus-modified grafted β-cyclodextrin adsorbents (P6-β-AC and P7-β-AC) in Examples 2 and 3 are 70.5% and 72.3%, respectively, which are slightly lower than the phosphoric acid-modified grafted β-cyclodextrin adsorbent (P1-β-AC). The iodine removal rate of only phosphoric acid-modified P1AC is 40.5%, and the iodine removal rate of only β-AC grafted with cyclodextrin is 47.7%. DETAILED DESCRIPTION

[0030] Example 1 Adsorbent Preparation

[0031] 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 stirring was continued for 30min (speed was 350rpm); 6.2g of phosphoric acid and 40mL of hydrogen peroxide (mass concentration 30%) were weighed, and added to the above beaker in sequence, and stirred for 24h at room temperature and in the dark, filtered, and dried in a 90℃ oven for 12-24h. The dried sample was placed in a tubular furnace, the nitrogen flow rate was maintained at 50mL / min, and the temperature was raised to 400℃ at a heating rate of 5℃ / min and calcined for 2h to obtain the modified adsorbent P1AC.

[0032] Place the modified adsorbent in a beaker, add 500 mL of nitric acid, and stir continuously at room temperature for 3 hours at a speed of 150 rpm. Filter and separate, wash the solid phase repeatedly in distilled water until the pH is close to 7.0, and then dry the activated carbon in an oven at 80°C for 4 hours. Take 50 g of the above adsorbent and 200 mL of DMF, put them into a round-bottom flask, mix them evenly by ultrasonic, add 25 g of β-cyclodextrin and 1 mL of bifunctional linker HMDI after mixing, and then heat the mixture in a 70°C oil bath at a speed of 350 rpm under a nitrogen atmosphere for 6 hours, and filter and separate. Wash the above adsorbent several times in ethanol and pure water, and then dry it in an oven at 80°C for 4 hours to obtain P1-β-AC.

[0033] The iodine removal experiment of the modified adsorbent P1-β-AC includes the following steps:

[0034] (1) Take 500 mL of ion-exchange membrane caustic soda process 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 industrial brine to 2, stir with a magnetic stirrer for 30 min, add 0.05 mL of hydrogen peroxide (mass concentration 30%), stir for 30 min, and set aside.

[0035] (2) Take 70 g of the adsorbent and place it in an adsorption column with a diameter of 3 cm. Fix the adsorption column. Connect the upper end of the adsorption column to a flow pump. While keeping the system closed, add 500 mL of the treated industrial brine into the adsorption column at a flow rate of 100 mL / min.

[0036] (3) 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.

[0037] The P1-β-AC adsorbent of this embodiment has a better adsorption effect than P1AC grafted with other cyclodextrin (α-cyclodextrin, γ-cyclodextrin) adsorbents, and the adsorption rate reaches 76.8%.

[0038] Example 2 Adsorbent Preparation

[0039] 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 stirring was continued for 30min (speed was 350rpm); 29g of diphenylphosphorous acid and 40mL of hydrogen peroxide (mass concentration 30%) were weighed, and added to the above beaker in sequence, and stirred for 24h at room temperature and in the dark, filtered, and dried in a 90℃ oven for 12-24h. The dried sample was placed in a tubular furnace, the nitrogen flow rate was maintained at 50mL / min, and the temperature was raised to 400℃ at a heating rate of 5℃ / min and calcined for 2h to obtain the modified adsorbent P6AC.

[0040] The steps of grafting cyclodextrin onto P6AC adsorbent are the same as those in Example 1 to obtain P6-β-AC.

[0041] The experimental procedure for removing iodine by P6-β-AC adsorbent is the same as that in Example 1.

[0042] Example 3 Adsorbent Preparation

[0043] 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 stirring was continued for 30min (speed was 350rpm); 21g of phenylphosphoric acid and 40mL of hydrogen peroxide (mass concentration 30%) were weighed, and added to the above beaker in sequence, and stirred for 24h at room temperature and in the dark, filtered, and dried in a 90℃ oven for 12-24h. The dried sample was placed in a tubular furnace, the nitrogen flow rate was maintained at 50mL / min, and the temperature was raised to 400℃ at a heating rate of 5℃ / min and calcined for 2h to obtain the modified adsorbent P7AC.

[0044] The steps of grafting cyclodextrin onto P7AC were the same as those in Example 1 to obtain P7-β-AC.

[0045] The experimental procedure for removing iodine by P7-β-AC adsorbent is the same as that in Example 1.

[0046] Comparative Example 1

[0047] The adsorbent selection and modification condition screening experiment includes the following steps:

[0048] (1) Place 100 g of activated carbon in a beaker and add 500 mL of deionized water; add 40 mL of glacial acetic acid while stirring at room temperature, and continue stirring for 30 min at a speed of 350 rpm; weigh the required mass of modifier (the mass ratio of the phosphorus content of the modifier to the activated carbon is 4%) and 40 mL of 30% hydrogen peroxide, add them to the above beaker in turn, continue stirring for 24 h at room temperature and in the dark, filter, and dry in a 90°C oven for 12-24 h.

[0049] The modifier described in step (1) is any one of phosphoric acid, hypophosphorous acid, triphenylphosphine, diammonium hydrogen phosphate, tetraphenylphosphine bromide, diphenyl hypophosphorous acid, and phenylphosphoric acid;

[0050] (2) placing the dried sample in a tube furnace, maintaining a nitrogen flow rate of 50 mL / min, heating the sample to 500-900°C at a heating rate of 5°C / min, and calcining the sample for 2 h to obtain a modified adsorbent;

[0051] (3) Take 70g of the above modified adsorbent (activated carbon, P1AC, P2AC, P3AC, P4AC, P5AC, P6AC, P7AC) and place it in an adsorption column with a diameter of 3cm, and fix the adsorption column; connect the upper end of the adsorption column to a flow pump, and while keeping the system closed, add 500mL of ion-exchange membrane caustic soda process brine containing 2.5mg / L iodine after oxidation treatment into the adsorption column at a flow rate of 100mL / min.

[0052] (4) 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.

[0053] Table 1 Effect of different modifiers on iodine removal rate

[0054] Adsorbent name Modifier Iodine concentration after removal (mg / L) Removal rate (%) Activated carbon (AC) none 1.69 32.4 P1AC P1(Phosphoric acid) 1.45 42.0 P2AC P2 (hypophosphorous acid) 1.61 35.6 P3AC P3(Triphenylphosphine) 1.55 38.0 P4AC P4 (diammonium phosphate) 1.53 38.8 P5AC P5(Tetraphenylphosphine bromide) 1.63 34.8 P6C P6 (diphenylphosphite) 1.49 40.4 P7C P7 (phenylphosphoric acid) 1.53 38.8

[0055] The effects of different modifiers on the iodine removal performance of the adsorbent were investigated. As shown in Table 1, by comparing different modifiers, the activated carbon modified with phosphoric acid in Example 1 has a better iodine removal effect than the activated carbon modified with other modifiers, with a removal rate of 42.0%. Compared with the unmodified activated carbon adsorbent in Comparative Example 1, the iodine removal rate is increased by 9.6%.

[0056] Comparative Example 2

[0057] Take 100g of untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g of 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 stirring was continued for 30min (speed was 350rpm); 6.2g of phosphoric acid and 40mL of hydrogen peroxide (mass concentration 30%) were weighed, and added to the above beaker in turn, and stirred continuously for 24h at room temperature and in the dark, filtered, and dried in a 90℃ oven for 12-24h. The dried samples were placed in a tubular furnace, the nitrogen flow rate was maintained at 50mL / min, and the temperature was increased to 400℃, 500℃, 600℃, 700℃, 800℃ and 900℃ at a heating rate of 5℃ / min for calcination for 2h to obtain modified adsorbents calcined at different temperatures.

[0058] Table 2 Effect of different calcination temperatures on iodine removal rate

[0059] Different calcination temperatures (℃) Concentration after removal (mg / L) Removal rate (%) 400 1.45 42.0 500 1.55 38.0 600 1.52 39.8 700 1.48 40.8 800 1.49 40.4 900 1.5 40.0

[0060] The effect of different calcination temperatures on the iodine removal performance of the adsorbent was investigated. As shown in Table 2, by comparing the effects of different calcination temperatures (400℃, 500℃, 600℃, 700℃, 800℃ and 900℃) on the removal of trace iodine from brine by the adsorbent, when the calcination temperature is 400℃, the iodine removal performance of the adsorbent is the best, and the removal rate reaches 42.0%. The calcination temperature is preferably 400℃. o C.

[0061] Comparative Example 3

[0062] Take 100g of untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g of 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 stirring was continued for 30min (speed was 350rpm); 5.8g, 11.6g, 17.4g of phosphoric acid and 40mL of hydrogen peroxide (mass concentration 30%) were weighed respectively, and added to the above beaker in turn, and stirred continuously for 24h at room temperature and light-proof conditions, filtered, and dried in a 90℃ oven for 12-24h. The dried sample was placed in a tubular furnace, the nitrogen flow rate was maintained at 50mL / min, and the temperature was raised to 400℃ at a heating rate of 5℃ / min and calcined for 2h to obtain a modified adsorbent.

[0063] Table 3 Effect of different phosphorus doping amounts on iodine removal rate

[0064] Different phosphorus doping amount (%) Concentration after removal (mg / L) Removal rate (%) 2 1.51 39.6 4 1.45 42.0 6 1.45 42.0

[0065] The effect of different phosphorus doping amounts on the iodine removal performance of the adsorbent was investigated. As shown in Table 3, by comparing the effect of different phosphorus doping amounts (i.e., the mass ratio of phosphorus element to activated carbon is 2%, 4%, and 6%) on the iodine removal performance of the adsorbent, when the phosphorus doping amount is 4%, the iodine removal performance is the best, and the removal rate reaches 42.0%. The phosphorus doping amount is preferably 4%.

[0066] Comparative Example 4

[0067] The adsorbent P1AC prepared by the method of Example 1 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. After filtration and separation, the solid phase was repeatedly washed in distilled water until the pH was close to 7.0, and then dried in an oven at 80 ° C for 4 h. Take 50 g of the above modified adsorbent and 200 mL of DMF, put them into a round-bottom flask, and mix them evenly by ultrasound. 5 g, 10 g, 15 g, 20 g, 25 g, 30 g of β-cyclodextrin and 1 mL of bifunctional linker HMDI were added respectively, and then the mixture was heated in a 70 ° C oil bath at a speed of 350 rpm under a nitrogen atmosphere for 6 h, and filtered and separated. The above adsorbent was washed several times in ethanol and pure water, and dried in an oven at 80 ° C for 4 h.

[0068] Table 4 Effect of different β-cyclodextrin amounts on iodine removal rate

[0069] Different β-cyclodextrin amounts (g) Concentration after removal (mg / L) Removal rate (%) 0 1.49 40.4 5 1.13 54.8 10 1.01 59.6 15 0.84 66.4 20 0.69 72.4 25 0.58 76.8 30 0.58 76.8

[0070] The effect of grafting different amounts of β-cyclodextrin onto the phosphoric acid-modified adsorbent on the iodine removal performance of the adsorbent was investigated. As shown in Table 4, by comparing the effects of different amounts of β-cyclodextrin (0g, 5g, 10g, 15g, 20g, 25g, 30g) on ​​the iodine removal performance of the adsorbent, when the amount of β-cyclodextrin was 25g, the iodine removal performance was the best, and the removal rate reached 76.8%. The amount of β-cyclodextrin is preferably 25g.

[0071] Comparative Example 5

[0072] The iodine adsorption experiment of the modified adsorbent includes the following steps:

[0073] (1) Take 500 mL of ion-exchange membrane caustic soda process 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%) and stir for 30 min for later use.

[0074] (2) Take 70g of adsorbent (activated carbon, P1AC, β-AC, P1-α-AC, P1-β-AC, P1-γ-AC, P6-β-AC, P7-β-AC) 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, add 500mL of the above-treated industrial brine to the adsorption column at a flow rate of 100mL / min. The activated carbon is untreated 4-6 mesh with a specific surface area of ​​1200m 2 / g of activated carbon, β-AC is activated carbon directly grafted with β-cyclodextrin, P1-α-AC, P1-β-AC, P1-γ-AC are P1 modified activated carbon grafted with α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin adsorbents, respectively, P6-β-AC, P7-β-AC are P6 modified activated carbon and P7 modified activated carbon further grafted with β-cyclodextrin adsorbents, respectively.

[0075] (3) 50 mL of brine was collected from the adsorption column and the iodine content in the brine was tested by the ferric thiocyanate-sodium nitrite catalytic kinetic method. The results are shown in Table 5.

[0076] Table 5 Effect of different adsorbents on iodine removal rate

[0077] Adsorbent name Iodine concentration after removal (mg / L) Removal rate (%) Activated carbon 1.70 32.0% P1AC 1.49 40.4% β-AC 1.31 47.6% P1-α-AC 0.76 69.6% P1-β-AC 0.58 76.8% P1-γ-AC 0.83 66.8% P6-β-AC 0.74 70.4% P7-β-AC 0.69 72.4%

[0078] As shown in Table 5, the P1-β-AC adsorbent in Example 1 has a better iodine removal effect than the P1AC grafted adsorbents of other cyclodextrins (P1-α-AC and P1-γ-AC), and the iodine removal rate reaches 76.8%. The iodine removal rates of other phosphorus-modified grafted β-cyclodextrin adsorbents (P6-β-AC and P7-β-AC) in Examples 2 and 3 are 70.5% and 72.3%, respectively, which are slightly lower than the phosphoric acid-modified grafted β-cyclodextrin adsorbent (P1-β-AC). The iodine removal rate of only phosphoric acid-modified P1AC is 40.4%, and the iodine removal rate of only β-AC grafted with cyclodextrin is 47.6%.

Claims

1. A method for preparing a heteroatom-modified and cyclodextrin-grafted activated carbon adsorbent, 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 phosphoric acid and 40mL of 30% mass concentration hydrogen peroxide, where the mass ratio of phosphorus content of phosphoric acid to activated carbon is 4%; add phosphoric acid and hydrogen peroxide to the above beaker in turn, continue stirring for 24h at room temperature and in the dark, filter, and dry in a 90℃ oven for 12-24h; (2) placing the dried sample in step (1) in a tube furnace, maintaining a nitrogen flow rate of 50 mL / min, heating to 400°C at a heating rate of 5°C / min, and calcining for 2 h to obtain a phosphoric acid-modified activated carbon adsorbent; (3) 100 g of the modified adsorbent prepared 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 separated, and the solid phase was repeatedly washed in distilled water until the pH value 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) and 200 mL of DMF were placed in a round-bottom flask and uniformly mixed by ultrasonication; after mixing, 25 g of β-cyclodextrin and 1 mL of bifunctional linker HMDI were added; the mixture was then heated in a 70°C oil bath at 350 rpm for 6 h under a nitrogen atmosphere and filtered for separation; (5) The adsorbent in step (4) was washed multiple times with ethanol and pure water, and then dried in an oven at 80° C. for 4 h to obtain an activated carbon adsorbent modified with phosphoric acid and grafted with β-cyclodextrin.

2. The method for preparing a heteroatom-modified and cyclodextrin-grafted activated carbon adsorbent according to claim 1, characterized in that: The activated carbon in step (1) is in the shape of a column or a flake, with a particle size of 4-6 mesh and a specific surface area of ​​1000-1200m 2 / g.

3. The method for preparing the heteroatom-modified and cyclodextrin-grafted activated carbon adsorbent according to claim 1, characterized in that: In step (1), the phosphorus content of the modifier is 4% by mass to the activated carbon.

4. An activated carbon adsorbent modified with heteroatoms and grafted with cyclodextrin is prepared according to the method of claims 1-3.

5. The method for removing trace iodine in brine of an ion-exchange membrane caustic soda process using the adsorbent according to claim 4, characterized in that: The specific steps of using the adsorbent to remove trace iodine in brine in an ion-exchange membrane caustic soda process are: (1) Pass the ion membrane caustic soda process brine into the reaction tower, add hydrochloric acid to adjust the pH of the brine to 2, stir with a stirring paddle for 30 minutes, add hydrogen peroxide, continue stirring for 30 minutes, and set aside; (2) The adsorbent is placed in an adsorption tower, and the upper end of the adsorption tower is connected to a pressure pump. While keeping the system airtight, the treated industrial brine is added to the adsorption tower at a flow rate of 100 mL / min; (3) Collect 50 mL of brine flowing out of the adsorption tower and test the iodine content in the brine.

6. The method for removing trace iodine in brine of an ion-exchange membrane caustic soda process using the adsorbent according to claim 5, characterized in that: β-cyclodextrin was grafted onto the surface of activated carbon modified with phosphoric acid. The iodine removal rate of the adsorbent was 76.8%. Compared with the unmodified activated carbon, the iodine removal rate was increased by 44.4%, and the adsorption performance was greatly improved.