A modified montmorillonite adsorbent for the combined removal of lead, chromium and cadmium in flue gas, and its preparation method and application

Abstract

The present invention discloses a modified montmorillonite adsorbent for the combined removal of lead, chromium, and cadmium in flue gas, and its preparation method and application. The preparation method comprises: dissolving montmorillonite in water, adding a sodiumizing agent, heating and stirring, and obtaining sodium-based montmorillonite; mixing the sodium-based montmorillonite with tetramethylammonium bromide and then mechanically grinding it to obtain tetramethylammonium bromide intercalation-stripping sodium-based montmorillonite; fully swelling the tetramethylammonium bromide intercalation-stripping sodium-based montmorillonite in water, adding an aged iron pillaring agent, vigorously stirring under ultrasonication, drying, and calcining to obtain the modified montmorillonite adsorbent. The modified montmorillonite adsorbent obtained by the present invention can effectively adsorb lead, chromium, and cadmium in industrial flue gas, has the advantages of high combined removal efficiency, large adsorption capacity, good resistance to SO2, HCl, and water vapor poisoning, good anti-sintering performance, and is easy to separate and recycle. The preparation method is simple and reliable, low cost, and easy to industrialize.

Description

Technical Field

[0001] The present invention belongs to the technical field related to flue gas pollutant control, and in particular relates to a modified montmorillonite adsorbent for the combined removal of lead, chromium and cadmium in flue gas, and a preparation method and application thereof. Background Art

[0002] Lead, chromium, and cadmium are three typical toxic heavy metals, and their harmful effects on humans and the environment are of particular concern. Coal-fired power plants are one of the major anthropogenic sources of lead, chromium, and cadmium into the atmosphere. Coal combustion emits thousands of tons of lead, chromium, and cadmium into the atmosphere annually. Given my country's large base of thermal power plants and the high levels of lead, chromium, and cadmium in coal, lead, chromium, and cadmium pollution requires particular attention. Furthermore, lead, chromium, and cadmium are also present at high levels in waste, and emissions from waste incineration in my country have increased dramatically in recent years. Furthermore, lead, chromium, and cadmium pollution can also occur during processes such as sludge incineration and metal smelting. In summary, lead, chromium, and cadmium emissions from industrial flue gases have become an urgent environmental issue, and the development of efficient, economical, and environmentally friendly technologies to control lead, chromium, and cadmium is imperative.

[0003] During coal combustion, waste incineration, sludge treatment, and metal smelting processes, high-temperature flue gases contain large amounts of lead, chromium, and cadmium vapor. These vapors primarily exist in oxidized or chlorinated forms, making them difficult to effectively remove. Emissions of these gases into the atmosphere pose significant risks to humans and the environment. Therefore, their removal is one of the greatest challenges in controlling emissions from industrial flue gases.

[0004] Adsorbent injection technology is considered a promising technology for controlling lead, chromium, and cadmium emissions. Its core lies in the development of highly efficient and inexpensive adsorbents. Three common adsorbent types are: ① Activated carbon adsorbents: Activated carbon's poor applicability and high cost significantly limit its use, hindering fly ash utilization. ② Metal oxide adsorbents: Metal oxides have low adsorption capacity, high consumption, and are expensive. ③ Mineral adsorbents: Mineral adsorbents are gaining increasing attention due to their low price and good stability. However, the adsorption capacity per unit mass of mineral adsorbents and their adsorption capacity under complex flue gas conditions need to be further improved.

[0005] Furthermore, most adsorbents are only capable of removing one heavy metal (lead, chromium, or cadmium), but their combined removal of lead, chromium, and cadmium is poor. Therefore, there is an urgent need to develop new, highly efficient adsorbents for the combined removal of lead, chromium, and cadmium to better meet the diverse and complex requirements of lead, chromium, and cadmium emission control in modern industry. Summary of the Invention

[0006] Purpose of the invention: In order to solve the technical problems of low adsorption efficiency of existing adsorbents, low adsorption capacity under complex flue gas conditions, and difficulty in combined removal, the present invention provides a modified montmorillonite adsorbent for the combined removal of lead, chromium and cadmium in flue gas, as well as its preparation method and application. The obtained modified montmorillonite adsorbent can effectively adsorb lead, chromium and cadmium in industrial flue gas, and has the advantages of high combined removal efficiency, large adsorption capacity, good resistance to SO2, HCl and water vapor poisoning, good anti-sintering performance, and easy separation and recovery. Therefore, it is particularly suitable for applications such as the combined removal of lead, chromium and cadmium in industrial flue gases such as coal-fired power plant flue gas, waste incineration power plant flue gas, sludge incineration flue gas, and metal smelting flue gas.

[0007] Summary of the invention: To achieve the above objectives, the present invention provides a method for preparing a modified montmorillonite adsorbent for the combined removal of lead, chromium and cadmium in flue gas, comprising the following steps:

[0008] (a) dissolving montmorillonite in deionized water, heating and stirring once to form a montmorillonite suspension, adding a sodiumizing agent and stirring twice, filtering, washing, drying and grinding the obtained solid phase to obtain sodium montmorillonite;

[0009] (b) mixing sodium montmorillonite with tetramethylammonium bromide, and mechanically grinding the mixture in a ball mill, and washing, drying, and grinding the mixture after standing to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite;

[0010] (c) dissolving Fe(NO3)3 in deionized water to form an Fe(NO3)3 solution, adding NaOH or Na2CO3 solution, stirring, and then standing in air for aging to obtain an iron pillaring agent;

[0011] (d) dissolving the tetramethylammonium bromide intercalated-stripped sodium montmorillonite obtained in step (b) in deionized water, adding the iron pillaring agent obtained in step (c) after heating and stirring, stirring under ultrasonic action, filtering, washing and drying after standing, and finally calcining and grinding to obtain an iron oxide pillared tetramethylammonium bromide intercalated-stripped montmorillonite material.

[0012] Furthermore, in step (a), the sodium-forming agent is NaCl, and the mass ratio of montmorillonite to the sodium-forming agent is 20:(1-4).

[0013] Furthermore, in step (a), the heating temperature is 60-100° C., the first stirring time is 0.5-3 h, and the second stirring time is 2-5 h.

[0014] Furthermore, in step (b), the mass ratio of sodium montmorillonite to tetramethylammonium bromide is 1:(0.5-2), and the mixture is ground in a ball mill at a speed of 100-400 r / min for 2-6 hours, and the ground compound is allowed to stand for 12-48 hours.

[0015] Furthermore, in step (c), the concentration of the Fe(NO3)3 solution is 0.1-1.5 mol / L, and the molar ratio of sodium to iron after mixing is (1-5):1, the stirring speed is 600-800 r / min, the stirring time is 10-24 h, and the static aging time is 48-72 h.

[0016] Furthermore, in step (d), the ratio of tetramethylammonium bromide intercalation-stripping sodium montmorillonite to iron pillaring agent is 1g: (5-30)mL, the ultrasonic frequency is 40-80KHz, the stirring speed under ultrasonic action is 600-800r / min, the stirring time is 10-24h, and the static aging time is 10-24h.

[0017] Furthermore, in step (d), the calcination conditions include: using an air atmosphere, heating from room temperature to 300-600° C. at a rate of 3-10° C. / min, and calcining at 300-600° C. for 2-7 hours.

[0018] Furthermore, in step (d), after the iron oxide pillared tetramethylammonium bromide intercalation-exfoliation montmorillonite material is ground and pulverized, a screening operation is also included to obtain an iron oxide pillared tetramethylammonium bromide intercalation-exfoliation montmorillonite product with a particle size of less than 150 μm.

[0019] In addition, the present invention also includes a modified montmorillonite adsorbent prepared by the above method and its application. The modified montmorillonite adsorbent is used to jointly remove lead, chromium and cadmium from industrial flue gases such as coal-fired power plant flue gas, waste incineration power plant flue gas, and metal smelting flue gas.

[0020] Beneficial effects:

[0021] 1. The modified montmorillonite adsorbent prepared by the present invention fully considers factors affecting the performance of the adsorbent, such as specific surface area and active components, and studies and designs montmorillonite. It uses montmorillonite as a raw material, which is low in cost and widely available. The preparation method is simple and reliable, easy to control, energy-saving and environmentally friendly. At the same time, the prepared modified montmorillonite adsorbent is non-toxic and harmless and can be stored for a long time.

[0022] 2. The modified montmorillonite adsorbent prepared by the present invention solves the problem that the current adsorbents are relatively single in removing heavy metals, realizes the combined removal of lead, chromium and cadmium, and has a high removal capacity. The optimal adsorption efficiency of lead, chromium and cadmium reaches 92.59%, 94.57% and 92.74% respectively, and the maximum adsorption capacity can reach 295.66 mg / g, 305.24 mg / g and 296.35 mg / g, which provides more reference basis and selection direction for laboratory research and practical industrial application.

[0023] 3. The present invention uses tetramethylammonium bromide to perform intercalation-stripping modification on montmorillonite, which expands the interlayer spacing of montmorillonite without destroying the original layered structure of montmorillonite, improves the physical and chemical properties of montmorillonite, and is beneficial to the adsorption of lead, chromium and cadmium.

[0024] 4. The modified montmorillonite adsorbent prepared by the present invention introduces metal active components on the surface of montmorillonite, combines the adsorption capacity of minerals and metal oxides for lead, chromium and cadmium, further promotes the adsorption of lead, chromium and cadmium, and improves the adsorbent's combined removal capacity for lead, chromium and cadmium.

[0025] 5. The modified montmorillonite adsorbent prepared by the present invention can effectively improve the activity of the adsorbent after calcination, reduce the particle size of the adsorbent, and increase its specific surface area. At the same time, due to the presence of iron oxide, the modified montmorillonite adsorbent has a certain magnetic property, which facilitates the rapid separation and recovery of the adsorbent and fly ash after use.

[0026] 6. The modified montmorillonite adsorbent prepared by the present invention has a large specific surface area, a developed pore structure and abundant surface active sites, which are conducive to the efficient combined removal of lead, chromium and cadmium. Therefore, it is a material with great industrial application prospects for the combined removal of lead, chromium and cadmium.

[0027] 7. The modified montmorillonite adsorbent prepared by the present invention and suitable for the combined removal of lead, chromium and cadmium in flue gas can, while removing lead, chromium and cadmium, also utilize the unique surface structure of montmorillonite to adsorb H2O in the flue gas and form hydroxyl functional groups on the surface, further promoting the adsorption of lead, chromium and cadmium on the adsorbent surface. This not only solves the problem of low combined removal ability of traditional adsorbents for lead, chromium and cadmium, but also plays a role in controlling other pollutants in flue gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Flow chart of the preparation of modified montmorillonite adsorbent in an embodiment of the present invention;

[0029] Figure 2 : is a hysteresis loop diagram of the modified montmorillonite adsorbent in an embodiment of the present invention;

[0030] Figure 3(a) to (c) are graphs showing the adsorption efficiency test results of the modified montmorillonite adsorbent for lead, chromium and cadmium according to the embodiments of the present invention;

[0031] Figure 4 Graph showing the adsorption capacity test results of the modified montmorillonite adsorbent for lead, chromium and cadmium in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] To make the technical solutions of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0033] Reference Figure 1 The present invention provides a method for preparing a modified montmorillonite adsorbent for the combined removal of lead, chromium and cadmium from flue gas as follows:

[0034] (a) dissolving montmorillonite in deionized water and heating and stirring once, adding a sodium agent after sufficient swelling and stirring twice, filtering after sufficient reaction, washing, drying and grinding the obtained solid phase to obtain sodium montmorillonite;

[0035] (b) mixing sodium montmorillonite with tetramethylammonium bromide, and mechanically grinding the mixture in a ball mill. After standing for a period of time, washing and drying are performed to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite;

[0036] (c) dissolving Fe(NO3)3 in deionized water, adding NaOH or Na2CO3 solution to the Fe(NO3)3 solution, stirring vigorously, and then allowing to stand in air for aging to obtain an iron pillaring agent;

[0037] (d) dissolving the tetramethylammonium bromide intercalated-stripped sodium montmorillonite obtained in step (b) in deionized water, heating and stirring to form a suspension, adding the iron pillaring agent obtained in step (c), vigorously stirring under ultrasonic action, filtering, washing, and drying after standing, and finally placing in a muffle furnace for calcination, grinding, and sieving to obtain an iron oxide pillared tetramethylammonium bromide intercalated-stripped montmorillonite material.

[0038] In some embodiments, in step (a), the sodium-forming agent is NaCl, and the mass ratio of montmorillonite to the sodium-forming agent is 20:(1-4). Preferably, the mass ratio of montmorillonite to the sodium-forming agent is 20:(1-3).

[0039] In some embodiments, in step (a), the heating temperature is 60-100° C., the first stirring time is 0.5-3 h, and the second stirring time is 2-5 h. Preferably, the heating temperature is 80-95° C., the first stirring time is 1-2 h, and the second stirring time is 3-4 h.

[0040] In some embodiments, in step (b), the mass ratio of sodium montmorillonite to tetramethylammonium bromide is 1:(0.5-2), the mixture is ground in a ball mill at a speed of 100-400 r / min for 2-6 hours, and the ground compound is allowed to stand for 12-48 hours. Preferably, the mass ratio of sodium montmorillonite to tetramethylammonium bromide is 1:(1-2), the mixture is ground in a ball mill at a speed of 200-400 r / min for 2-6 hours, and the ground compound is allowed to stand for 20-40 hours.

[0041] In some embodiments, in step (c), the concentration of the Fe(NO3)3 solution is 0.1-1.5 mol / L, the molar ratio of sodium to iron is (1-5):1, the stirring speed is 600-800 r / min, the stirring time is 10-24 h, and the static aging time is 48-72 h. Preferably, the concentration of the Fe(NO3)3 solution is 0.2-1 mol / L, the molar ratio of sodium to iron is (2-4):1, the stirring speed is 600-800 r / min, the stirring time is 12-20 h, and the static aging time is 48-72 h.

[0042] In some embodiments, in step (d), the ratio of tetramethylammonium bromide intercalated-stripped sodium montmorillonite to the iron pillaring agent is 1 g: (5-30) mL, the ultrasonic frequency is 40-80 kHz, the stirring speed under ultrasonic action is 600-800 r / min, the stirring time is 10-24 hours, and the static aging time is 10-24 hours. Preferably, the ratio of tetramethylammonium bromide intercalated-stripped sodium montmorillonite to the iron pillaring agent is 1 g: (10-20) mL, the ultrasonic frequency is 50-60 kHz, the stirring speed under ultrasonic action is 600-800 r / min, the stirring time is 12-20 hours, and the static aging time is 12-20 hours.

[0043] In some embodiments, in step (d), the dried sample is calcined by heating the sample from room temperature to 300-600° C. at a rate of 3-10° C. / min in an air atmosphere, and calcining the sample at 300-600° C. for 2-7 hours. Preferably, the sample is heated from room temperature to 300-500° C. at a rate of 5-10° C. / min in an air atmosphere, and calcining the sample at 300-500° C. for 3-6 hours.

[0044] In some embodiments, in step (d), after the iron oxide pillared tetramethylammonium bromide intercalated-exfoliated montmorillonite is ground and pulverized, a screening operation is preferably included to obtain an iron oxide pillared tetramethylammonium bromide intercalated-exfoliated montmorillonite product with a particle size of less than 150 μm.

[0045] Example 1:

[0046] (a) 10 g of montmorillonite was dissolved in 300 mL of deionized water and stirred at 80°C for 2 h. After sufficient swelling, 1 g of NaCl was added and stirred for 4 h. After sufficient reaction, the mixture was filtered and the solid phase was washed, dried overnight, and ground to obtain sodium montmorillonite.

[0047] (b) 10 g of sodium montmorillonite was mixed with 10 g of tetramethylammonium bromide, and the mixture was placed in a ball mill and ground at 400 r / min for 4 h. The ground compound was allowed to stand for 24 h, then washed and dried overnight to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite;

[0048] (c) Fe(NO3)3 was dissolved in deionized water to prepare a 0.2 mol / L Fe(NO3)3 solution, 0.4 mol / L NaOH solution was slowly added to the Fe(NO3)3 solution, the mixture was stirred at 600 r / min for 12 h, and the mixture was allowed to stand in air for 48 h to obtain an iron pillaring agent;

[0049] (d) Take 10g of tetramethylammonium bromide intercalated-stripped sodium montmorillonite and dissolve it in 100mL of deionized water. Stir it at 80℃ for 2h. After it is fully swollen, add 100mL of aged iron pillaring solution, ultrasonicate it at 50KHz, stir it at 600r / min for 12h, let it stand for 20h, filter, wash it, and dry it overnight. The dried sample is placed in a muffle furnace and heated from room temperature to 300℃ at a heating rate of 5℃ / min in an air atmosphere. It is calcined at 300℃ for 4h, ground and sieved to obtain iron oxide pillared tetramethylammonium bromide intercalated-stripped montmorillonite material with a particle size of less than 150μm.

[0050] Example 2:

[0051] (a) 10 g of montmorillonite was dissolved in 300 mL of deionized water and stirred at 80°C for 2 h. After sufficient swelling, 1 g of NaCl was added and stirred for 4 h. After sufficient reaction, the mixture was filtered and the solid phase was washed, dried overnight, and ground to obtain sodium montmorillonite.

[0052] (b) 10 g of sodium montmorillonite was mixed with 12 g of tetramethylammonium bromide, and the mixture was placed in a ball mill and ground at 400 r / min for 5 h. The ground compound was allowed to stand for 24 h, then washed and dried overnight to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite;

[0053] (c) Fe(NO3)3 was dissolved in deionized water to prepare a 0.2 mol / L Fe(NO3)3 solution, 0.6 mol / L NaOH solution was slowly added to the Fe(NO3)3 solution, the mixture was stirred at 600 r / min for 12 h, and the mixture was aged in air for 48 h to obtain an iron pillaring agent;

[0054] (d) Take 10g of tetramethylammonium bromide intercalated-stripped sodium montmorillonite and dissolve it in 100mL of deionized water. Stir it at 80℃ for 2h. After it is fully swollen, add 100mL of aged iron pillaring solution, ultrasonicate it at 50KHz, stir it at 600r / min for 12h, let it stand for 20h, filter, wash it, and dry it overnight. The dried sample is placed in a muffle furnace and heated from room temperature to 300℃ at a heating rate of 5℃ / min in an air atmosphere. It is calcined at 300℃ for 4h, ground and sieved to obtain iron oxide pillared tetramethylammonium bromide intercalated-stripped montmorillonite material with a particle size of less than 150μm.

[0055] Example 3:

[0056] (a) 10 g of montmorillonite was dissolved in 300 mL of deionized water and stirred at 80°C for 2 h. After sufficient swelling, 1 g of NaCl was added and stirred for 4 h. After sufficient reaction, the mixture was filtered and the solid phase was washed, dried overnight, and ground to obtain sodium montmorillonite.

[0057] (b) 10 g of sodium montmorillonite was mixed with 20 g of tetramethylammonium bromide, and the mixture was placed in a ball mill and ground at 400 r / min for 4 h. The ground compound was allowed to stand for 24 h, then washed and dried overnight to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite;

[0058] (c) Fe(NO3)3 was dissolved in deionized water to prepare a 0.2 mol / L Fe(NO3)3 solution, 0.6 mol / L NaOH solution was slowly added to the Fe(NO3)3 solution, the mixture was stirred at 600 r / min for 12 h, and the mixture was aged in air for 48 h to obtain an iron pillaring agent;

[0059] (d) Take 10g of tetramethylammonium bromide intercalated-stripped sodium montmorillonite and dissolve it in 100mL of deionized water. Stir it at 80℃ for 2h. After it is fully swollen, add 200mL of aged iron pillaring solution, ultrasonicate it at 50KHz, stir it at 600r / min for 12h, let it stand for 20h, filter it, wash it, and dry it overnight. The dried sample is placed in a muffle furnace and heated from room temperature to 400℃ at a heating rate of 5℃ / min in an air atmosphere. It is calcined at 400℃ for 4h, ground and sieved to obtain iron oxide pillared tetramethylammonium bromide intercalated-stripped montmorillonite material with a particle size of less than 150μm.

[0060] Example 4:

[0061] (a) 10 g of montmorillonite was dissolved in 300 mL of deionized water and stirred at 80°C for 2 h. After sufficient swelling, 1.5 g of NaCl was added and stirred for 4 h. After sufficient reaction, the mixture was filtered and the solid phase was washed, dried overnight, and ground to obtain sodium montmorillonite.

[0062] (b) 10 g of sodium montmorillonite was mixed with 10 g of tetramethylammonium bromide, and the mixture was placed in a ball mill and ground at 400 r / min for 4 h. The ground compound was allowed to stand for 24 h, then washed and dried overnight to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite;

[0063] (c) Fe(NO3)3 was dissolved in deionized water to prepare a 0.2 mol / L Fe(NO3)3 solution, 0.4 mol / L NaOH solution was slowly added to the Fe(NO3)3 solution, the mixture was stirred at 600 r / min for 12 h, and aged in air for 72 h to obtain an iron pillaring agent;

[0064] (d) Take 10g of tetramethylammonium bromide intercalated-stripped sodium montmorillonite and dissolve it in 100mL of deionized water. Stir it at 80℃ for 2h. After it is fully swollen, add 100mL of aged iron pillaring solution, ultrasonicate it at 50KHz, stir it at 600r / min for 12h, let it stand for 20h, filter, wash it, and dry it overnight. The dried sample is placed in a muffle furnace and heated from room temperature to 300℃ at a heating rate of 5℃ / min in an air atmosphere. It is calcined at 300℃ for 4h, ground and sieved to obtain iron oxide pillared tetramethylammonium bromide intercalated-stripped montmorillonite material with a particle size of less than 150μm.

[0065] Example 5:

[0066] (a) 10 g of montmorillonite was dissolved in 300 mL of deionized water and stirred at 80°C for 2 h. After sufficient swelling, 1.5 g of NaCl was added and stirred for 4 h. After sufficient reaction, the mixture was filtered and the solid phase was washed, dried overnight, and ground to obtain sodium montmorillonite.

[0067] (b) 10 g of sodium montmorillonite was mixed with 10 g of tetramethylammonium bromide, and the mixture was placed in a ball mill and ground at 400 r / min for 4 h. The ground compound was allowed to stand for 24 h, then washed and dried overnight to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite;

[0068] (c) Fe(NO3)3 was dissolved in deionized water to prepare a 0.8 mol / L Fe(NO3)3 solution, 2 mol / L NaOH solution was slowly added to the Fe(NO3)3 solution, the mixture was stirred at 600 r / min for 12 h, and the mixture was allowed to stand in air for 60 h to obtain an iron pillaring agent;

[0069] (d) Take 10 g of tetramethylammonium bromide intercalated-stripped sodium montmorillonite and dissolve it in 100 mL of deionized water. Stir it at 80 ° C for 2 h. After sufficient swelling, add 100 mL of aged iron pillaring solution, ultrasonicate it at 50 kHz, stir it at 600 r / min for 12 h, let it stand for 20 h, filter, wash it, and dry it overnight. The dried sample is placed in a muffle furnace and heated from room temperature to 400 ° C at a heating rate of 5 ° C / min in an air atmosphere. It is calcined at 400 ° C for 3 h, ground and sieved to obtain iron oxide pillared tetramethylammonium bromide intercalated-stripped montmorillonite material with a particle size of less than 150 μm.

[0070] Example 6:

[0071] (a) 10 g of montmorillonite was dissolved in 300 mL of deionized water and stirred at 80°C for 2 h. After sufficient swelling, 1.5 g of NaCl was added and stirred for 4 h. After sufficient reaction, the mixture was filtered and the solid phase was washed, dried overnight, and ground to obtain sodium montmorillonite.

[0072] (b) 10 g of sodium montmorillonite was mixed with 15 g of tetramethylammonium bromide, and the mixture was placed in a ball mill and ground at 300 r / min for 3 h. The ground compound was allowed to stand for 24 h, then washed and dried overnight to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite;

[0073] (c) Fe(NO3)3 was dissolved in deionized water to prepare a 0.5 mol / L Fe(NO3)3 solution, 1.5 mol / L NaOH solution was slowly added to the Fe(NO3)3 solution, the mixture was stirred at 600 r / min for 12 h, and aged in air for 72 h to obtain an iron pillaring agent;

[0074] (d) Take 10g of tetramethylammonium bromide intercalated-stripped sodium montmorillonite and dissolve it in 100mL of deionized water. Stir it at 80℃ for 2h. After sufficient swelling, add 150mL of aged iron pillaring solution, ultrasonicate it at 50KHz, stir it at 600r / min for 20h, let it stand for 20h, filter, wash it, and dry it overnight. The dried sample is placed in a muffle furnace and heated from room temperature to 300℃ at a heating rate of 5℃ / min in an air atmosphere. It is calcined at 300℃ for 4h, ground and sieved to obtain iron oxide pillared tetramethylammonium bromide intercalated-stripped montmorillonite material with a particle size of less than 150μm.

[0075] Result analysis:

[0076] The hysteresis loops of Examples 1-6 are as follows: Figure 2 As shown, the modified montmorillonite adsorbents prepared in Examples 1-6 all exhibit a certain degree of superparamagnetism, with low residual magnetization and coercivity, and good magnetic response. The magnetic properties of the modified montmorillonite adsorbent facilitate post-use separation and recovery of the adsorbent. The low coercivity facilitates good dispersion of the material after magnetic separation, reducing magnetic agglomeration.

[0077] The combined removal performance of lead, chromium and cadmium of the modified montmorillonite adsorbent prepared in Examples 1-6 was tested by experiments. The experimental method is as follows:

[0078] The experiment was carried out in a fixed-bed reactor with an inner diameter of 10 mm at atmospheric pressure, and the amount of adsorbent used was 0.5 g.

[0079] The experimental simulated atmosphere composition is: the concentration of gaseous lead is 50ppm, the concentration of gaseous chromium is 50ppm, the concentration of gaseous cadmium is 50ppm, N2 is the carrier gas, the O2 content is 8%, the H2O content is 10%, the SO2 concentration is 800ppm, the NO concentration is 200ppm, the HCl concentration is 1000ppm, the flue gas flow rate is 120mL / min, the adsorption temperature is 800-1100℃, and the adsorption time is 40min.

[0080] Before the experiment begins, 0.5 g of modified montmorillonite adsorbent is placed in a quartz reactor, simulated flue gas is introduced, and the tubular furnace heating program is started. When the temperature reaches the preset temperature, the lead, chromium and cadmium steam generators are started to feed gaseous lead, chromium and cadmium, and the lead, chromium and cadmium combined removal performance test experiment begins.

[0081] After the experiment, the adsorbed samples were taken out and digested in a graphite digester, and the content of lead, chromium and cadmium in the samples was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The adsorption efficiency and adsorption capacity of the modified montmorillonite adsorbents prepared in Examples 1-6 were as follows: Figure 3 (a) to 3(c) and Figure 4 shown.

[0082] from Figure 3 (a) to 3(c) and Figure 4 As can be seen, the modified montmorillonite adsorbents prepared in Examples 1-6 of the present invention have excellent combined removal capabilities for lead, chromium, and cadmium, with optimal adsorption efficiencies reaching 92.59%, 94.57%, and 92.74% for lead, chromium, and cadmium, respectively, and maximum adsorption capacities reaching 295.66 mg / g, 305.24 mg / g, and 296.35 mg / g. Furthermore, the modified montmorillonite adsorbents prepared in the present invention maintain high lead, chromium, and cadmium removal capabilities in the presence of flue gas components such as SO₂, NO, HCl, and H₂O, exhibit strong anti-poisoning properties, and have promising application prospects.

[0083] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is intended to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a modified montmorillonite adsorbent for the combined removal of lead, chromium and cadmium from flue gas, characterized in that: The following steps are involved: (a) dissolving montmorillonite in deionized water, heating and stirring once to form a montmorillonite suspension, adding a sodiumizing agent and stirring twice, filtering, washing, drying, and grinding the resulting solid phase to obtain sodium-based montmorillonite; the sodiumizing agent is NaCl, and the mass ratio of montmorillonite to the sodiumizing agent is 20:(1-3); the heating temperature is 80-95°C, the first stirring time is 1-2 hours, and the second stirring time is 3-4 hours; (b) mixing sodium montmorillonite with tetramethylammonium bromide, and mechanically grinding the mixture in a ball mill. After standing, the mixture is washed, dried, and ground to obtain tetramethylammonium bromide intercalated-exfoliated sodium montmorillonite; the mass ratio of sodium montmorillonite to tetramethylammonium bromide is 1:(1-2). The mixture is ground in a ball mill at a speed of 200-400 r / min for 2-6 hours, and the ground compound is allowed to stand for 20-40 hours. (c) dissolving Fe(NO3)3 in deionized water to form a Fe(NO3)3 solution, adding NaOH or Na2CO3 solution, stirring, and then standing in air for aging to obtain an iron pillaring agent; (d) dissolving the tetramethylammonium bromide intercalated-stripped sodium montmorillonite obtained in step (b) in deionized water, heating and stirring, then adding the iron pillaring agent obtained in step (c), stirring under ultrasonication, standing, filtering, washing and drying, and finally calcining and grinding to obtain an iron oxide pillared tetramethylammonium bromide intercalated-stripped sodium montmorillonite material; the ratio of the tetramethylammonium bromide intercalated-stripped sodium montmorillonite to the iron pillaring agent is 1 g: (10-20) mL, the ultrasonic frequency is 50-60 kHz, the stirring speed under ultrasonication is 600-800 r / min, the stirring time is 12-20 h, and the standing aging time is 12-20 h; the calcination conditions include: using an air atmosphere, heating from room temperature to 300-500°C at a rate of 5-10°C / min, and calcining at 300-500°C for 3-6 h.

2. The preparation method according to claim 1, characterized in that In the step (c), the concentration of the Fe(NO3)3 solution is 0.1-1.5 mol / L, the molar ratio of sodium to iron after mixing is (1-5):1, the stirring speed is 600-800 r / min, the stirring time is 10-24 h, and the static aging time is 48-72 h.

3. The preparation method according to claim 1, characterized in that In the step (d), after the iron oxide pillared tetramethylammonium bromide intercalated-exfoliated montmorillonite material is ground and pulverized, a screening process is further included to obtain an iron oxide pillared tetramethylammonium bromide intercalated-exfoliated montmorillonite product with a particle size of less than 150 μm.

4. Use of the modified montmorillonite adsorbent prepared by the preparation method according to claim 1 for the combined removal of lead, chromium and cadmium from industrial flue gas.

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