A heat-induced self-activating exhaust gas volatile heavy metal control material and its preparation method and application

Abstract

The present application relates to the technical field of waste gas purification treatment, in particular to a kind of thermal induction self-activation volatile heavy metal control material of waste gas and its preparation method and application, the control material is composed of the microcapsule of inner core, intermediate layer and shell;Wherein the inner core is the sodium alginate-polyvinyl alcohol microcapsule containing ferrous sulfide, graphene and sodium bicarbonate, the intermediate layer is calcium sulfate isolation layer, and the shell is manganese dioxide, cerium nitrate oxide layer.The material prepared in the application can realize thermal induction self-activation reaction at high temperature, by generating elemental sulfur, iron oxide, manganese oxide and cerium oxide and other active components, simultaneously and efficiently remove volatile heavy metals such as mercury, arsenic, thallium and other volatile heavy metals in waste gas, with the advantages of multifunctional synergy, high heavy metal removal rate, good selectivity, fast response rate and the like.

Description

Technical Field

[0001] This invention belongs to the field of waste gas purification and treatment technology, and particularly relates to a thermally induced self-activated waste gas volatile heavy metal control material, its preparation method and application. Background Technology

[0002] Volatile heavy metal pollution in waste gases has become a major environmental problem that urgently needs to be addressed. Common volatile heavy metals include mercury, arsenic, and thallium. These heavy metals not only have significant biotoxicity but also readily transform into gaseous forms under high-temperature conditions (above 100°C), exhibiting strong mobility and posing a serious threat to regional and even global ecological and environmental security. These volatile heavy metals are prevalent in high-temperature waste gases such as exhaust gases from thermal desorption treatment of heavy metal-contaminated soil, waste incineration exhaust gases, and coal-fired flue gas, and are difficult to remove using conventional waste gas treatment technologies such as dust removal, desulfurization, and denitrification. Therefore, developing efficient control technologies for volatile heavy metals in high-temperature waste gases is of significant practical importance for maintaining ecological and environmental security and protecting public health.

[0003] Currently, the main methods for treating volatile heavy metals in high-temperature waste gas include adsorption, catalytic oxidation, wet scrubbing, and membrane separation technology.

[0004] (1) Adsorption method. Activated carbon is a common adsorbent, which has a certain adsorption capacity for mercury and arsenic in waste gas. However, activated carbon has poor selectivity. When volatile organic compounds are present in the waste gas, these organic compounds will preferentially occupy adsorption sites due to their stronger affinity with activated carbon, thus significantly reducing the removal efficiency of heavy metals. Although sulfidation modification can enhance the adsorption capacity and selectivity of activated carbon for mercury in waste gas, sulfidation-modified activated carbon is unstable and easily oxidized in air, requiring high transportation and storage conditions.

[0005] (2) Catalytic oxidation method. Although catalysts containing precious metals such as cobalt, silver, and platinum can effectively catalyze the oxidation of low-valence volatile heavy metals (such as zero-valent mercury and monovalent thallium) in waste gas, converting them into high-valence products, these materials have obvious limitations in practical applications. For example, the raw materials for preparing these catalysts are expensive, and the preparation process often requires high-temperature calcination, resulting in high costs. Furthermore, this method has poor arsenic removal efficiency and is difficult to meet the needs of synergistic purification of multiple heavy metals in complex waste gases.

[0006] (3) Wet scrubbing. The absorbent can be adjusted according to the type of volatile heavy metals in the waste gas, and it has a good removal effect on volatile heavy metals with good water solubility, such as trivalent arsenic and monovalent thallium. However, zero-valent mercury is difficult to dissolve in water, requiring the addition of a large amount of strong oxidant for absorption. Moreover, the oxidant is prone to decomposition and failure at high temperatures, which leads to complex operation and high requirements for the transportation and storage conditions of the raw materials.

[0007] (4) Membrane separation technology. Membrane separation technology can selectively retain heavy metal vapors by adjusting the membrane pore size and surface modification, especially mercury. However, due to the differences in partial pressure, molecular polarity and particle size of different heavy metal vapors, the adsorption effect of membrane separation technology on mixed heavy metals is poor. In addition, the manufacturing cost of membrane materials is high, and they are easily contaminated during actual operation and need to be replaced frequently, which increases maintenance costs.

[0008] Existing technologies for treating volatile heavy metals in high-temperature waste gas still have significant shortcomings. For example, adsorption methods suffer from poor selectivity and are easily interfered with by organic matter; catalytic oxidation methods have high operating costs and limited effectiveness in removing arsenic; wet scrubbing processes are complex and ineffective in treating mercury; while membrane separation technology is highly effective in treating mercury, its comprehensive treatment capacity for multiple heavy metals is insufficient, and its maintenance costs are high. These technological limitations severely restrict the effective control of heavy metal pollution in high-temperature waste gas. Therefore, developing new treatment materials that combine high efficiency, stability, and economy has become an urgent need to solve the problem of heavy metal pollution in high-temperature waste gas. Summary of the Invention

[0009] In view of the problems existing in the prior art, the present invention provides a thermally induced self-activated material for controlling volatile heavy metals in waste gas, its preparation method and application.

[0010] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0011] A method for preparing a thermally induced self-activated material for controlling volatile heavy metals in waste gas includes the following steps:

[0012] (1) Ferrous sulfide powder and graphene powder were added to sodium alginate-polyvinyl alcohol solution under anaerobic conditions. After mixing evenly, the mixture was dropped into a saturated boric acid solution containing 5-8% w / v calcium chloride. The mixture was allowed to stand and solidify, and then freeze-dried to obtain microcapsules containing a reducing core.

[0013] (2) Immerse the microcapsules containing the reducing core prepared in step (1) in an 8-10% w / v sodium bicarbonate solution for 1-2 hours, and freeze-dry to obtain microcapsules containing sodium bicarbonate.

[0014] (3) The microcapsules containing sodium bicarbonate prepared in step (2) are coated with a calcium sulfate isolation layer by spray deposition method to encapsulate the microcapsules;

[0015] (4) A manganese dioxide oxide layer is formed on the surface of the calcium sulfate isolation layer prepared in step (3) by spray deposition;

[0016] (5) A cerium nitrate-loaded absorption layer is formed on the surface of the manganese dioxide oxide layer prepared in step (4) by spray deposition method, and a material for controlling volatile heavy metals in waste gas is obtained.

[0017] W / V is the mass-to-volume ratio concentration, which represents the mass of solute contained in a unit volume of solution. It is usually expressed as a percentage (such as % w / v), that is, the number of grams of solute in 100 ml of solution. For example, 0.9% w / v physiological saline means that 100 ml of solution contains 0.9 grams of sodium chloride.

[0018] In chemistry, w% means mass fraction, which is equal to the mass of the substance in question divided by the total mass of the substance multiplied by 100%.

[0019] Furthermore, the contents of sodium alginate and polyvinyl alcohol are 3 w% and 1.5 w% of the total mass of the sodium alginate-polyvinyl alcohol solution, respectively, and the dosages of ferrous sulfide powder and graphene are (0.8-1) w% and (0.15-0.30) w% of the total mass of the sodium alginate-polyvinyl alcohol solution, respectively.

[0020] Furthermore, in step (1), the solidification is allowed to stand for 24 hours, and the freeze-drying conditions are freeze-drying at -20℃ for 24 hours.

[0021] Furthermore, in step (3), saturated calcium chloride and 2-3% w / v sodium sulfate water mist are sprayed onto the surface of the microcapsules at gas flow rates of 10 mL / min and 5 mL / min, respectively, to form a calcium sulfate isolation layer with a thickness of 0.5-1.0 mm.

[0022] Furthermore, in step (4), a spray deposition method is used to spray saturated sodium hydroxide and 2-3% w / v manganese nitrate water mist at gas flow rates of 10 mL / min and 5 mL / min respectively to form a manganese dioxide oxide layer on the surface of the calcium sulfate isolation layer, with an oxide layer thickness of 0.1-0.2 mm.

[0023] Furthermore, in step (5), a spray deposition method is used to spray 4-6% w / v cerium nitrate water mist at a gas flow rate of 10 mL / min to form a cerium nitrate absorption layer on the surface of the manganese dioxide oxide layer, with a thickness of 0.1-0.2 mm.

[0024] This invention provides a waste gas volatile heavy metal control material prepared by a method for preparing a thermally induced self-activated waste gas volatile heavy metal control material. The material consists of a core, an intermediate layer and an outer shell. The core is a sodium alginate-polyvinyl alcohol microcapsule containing ferrous sulfide, graphene and sodium bicarbonate. The intermediate layer is a calcium sulfate isolation layer and the outer shell is a manganese dioxide oxide layer.

[0025] Furthermore, the outer layer of the manganese dioxide oxide layer is also coated with a cerium nitrate absorption layer.

[0026] This invention provides the application of the above-mentioned thermally induced self-activated waste gas volatile heavy metal control material in high-temperature waste gas purification treatment.

[0027] The beneficial effects of the present invention include: (1) The present invention provides a thermally induced self-activated volatile heavy metal control material for waste gas, which uses sodium alginate-polyvinyl alcohol as a skeleton material to embed ferrous sulfide and graphene, loads sodium bicarbonate inside the material using an immersion method, and constructs a calcium sulfate isolation layer and a manganese dioxide oxide layer on the surface using a spray deposition method. Among them, the dense calcium sulfate isolation layer can effectively isolate ferrous sulfide from contact with oxidants at room temperature, and at the same time significantly improve the mechanical strength of the material. The material is stable under room temperature conditions, can be stored stably for a long time under normal conditions, and is convenient for storage and transportation.

[0028] (2) The present invention provides a thermally induced self-activated waste gas volatile heavy metal control material, which undergoes a thermally induced self-activation reaction at high temperature to produce a variety of active components such as elemental sulfur, iron oxide and manganese oxide, and simultaneously and efficiently removes volatile heavy metals such as mercury, arsenic and thallium in the waste gas. Compared with adsorption materials such as activated carbon with single function and poor selectivity, it has the advantages of multifunctionality and good selectivity.

[0029] (3) The present invention provides a thermally induced self-activated material for controlling volatile heavy metals in waste gas, which uses readily available raw materials and has a low cost. The preparation process uses mild conditions and does not require harsh processes commonly found in traditional technologies, such as high-temperature calcination, which significantly reduces process complexity and energy consumption. Compared with existing precious metal catalytic oxidation materials, the present invention effectively reduces raw material costs.

[0030] In summary, the thermally induced self-activated volatile heavy metal control material for waste gas, its preparation method, and its application provided by this invention have advantages such as convenient transportation and storage, multifunctionality, good selectivity, and low cost compared with conventional materials and methods. It has good application prospects in the field of purifying volatile heavy metals in soil thermal desorption tail gas, incinerator tail gas, and coal-fired flue gas. Attached Figure Description

[0031] Figure 1 This is a process flow diagram for preparing the waste gas volatile heavy metal control material of the present invention;

[0032] Figure 2 The nitrogen adsorption-desorption curve and pore size distribution diagram of the waste gas volatile heavy metal control material prepared in Example 1 of the present invention;

[0033] Figure 3 The images shown are SEM images of the waste gas volatile heavy metal control material prepared in Example 1 of the present invention before the experiment, where a and b are images at the 50 μm and 10 μm scales, respectively.

[0034] Figure 4 The images shown are SEM images of the waste gas volatile heavy metal control material prepared in Example 1 of the present invention after the experiment, where a and b are images at the 50 μm and 10 μm scales, respectively.

[0035] Figure 5 This is an X-ray photoelectron spectrum of Fe element in the microcapsule stage without sodium bicarbonate during the synthesis of the volatile heavy metal control material for waste gas in Example 1.

[0036] Figure 6 This is an X-ray photoelectron spectrum of sulfur in the microcapsule stage of the material for controlling volatile heavy metals in waste gas, which does not contain sodium bicarbonate, during the synthesis of the material in Example 1.

[0037] Figure 7 This is an X-ray photoelectron spectrum of carbon element in the microcapsule stage of the material for controlling volatile heavy metals in waste gas during the synthesis of waste gas in Example 1, which does not contain sodium bicarbonate.

[0038] Figure 8 This is an X-ray photoelectron spectrum of Ca element in the microcapsule stage with calcium sulfate isolation layer during the synthesis of volatile heavy metal control material in waste gas in Example 1.

[0039] Figure 9 X-ray photoelectron spectroscopy of sulfur element in the microcapsule stage with calcium sulfate isolation layer during the synthesis of volatile heavy metal control material in waste gas in Example 1.

[0040] Figure 10 This is an X-ray photoelectron spectrum of Fe element in the microcapsule stage with calcium sulfate isolation layer during the synthesis of volatile heavy metal control material in waste gas in Example 1.

[0041] Figure 11 This is an X-ray photoelectron spectrum of carbon element in the microcapsule stage with calcium sulfate isolation layer during the synthesis of volatile heavy metal control material in waste gas in Example 1.

[0042] Figure 12 The X-ray photoelectron spectroscopy of Mn element in the composite microcapsule stage during the synthesis of the volatile heavy metal control material for waste gas in Example 1 is shown.

[0043] Figure 13 The X-ray photoelectron spectrum of Ce element in the composite microcapsule stage during the synthesis of the waste gas volatile heavy metal control material in Example 1 is shown. Detailed Implementation

[0044] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, the reagents used in this invention are all conventional reagents in the art and can be obtained commercially. Unless otherwise specified, the experimental methods used in this invention are all conventional experimental methods in the art.

[0045] See attached document Figure 1 - Appendix Figure 13 The present invention provides:

[0046] Example 1

[0047] 1. Preparation method of ferrous sulfide

[0048] Under anaerobic conditions, 40 g of ferrous chloride was weighed and dissolved in 200 mL of deoxygenated deionized water to prepare a saturated ferrous chloride solution. Nitrogen gas was passed through the solution while stirring at 80 rpm. Separately, 30 g of sodium sulfide was weighed and dissolved in 50 mL of deoxygenated deionized water to prepare a supersaturated sodium sulfide solution. Nitrogen gas was passed through the solution while stirring at 80 rpm. Then, excess saturated sodium sulfide solution was added to the saturated ferrous chloride solution. The solution was filtered, washed, and freeze-dried at -20°C for 24 h to obtain ferrous sulfide crystalline powder.

[0049] 2. Preparation of materials for controlling volatile heavy metal emissions from waste gas

[0050] (1) 100 mL of deionized water was added to a 250 mL three-necked flask equipped with a magnetic stirrer. The flask was placed under nitrogen protection and aerated for 15 min to remove oxygen. 1.571 g of polyvinyl alcohol powder was weighed and added to the flask in three portions. The mixture was stirred slowly at 300 rpm for 30 min at 80 °C until the polyvinyl alcohol dissolved. The solution was then cooled to room temperature and 3.141 g of sodium alginate was added under a nitrogen atmosphere. The mixture was stirred at 300 rpm until homogeneous to obtain a sodium alginate-polyvinyl alcohol solution. The sodium alginate-polyvinyl alcohol solution was kept under an inert atmosphere and 10 mL was transferred to a 50 mL beaker. 0.314 g of graphene powder was added under ice bath conditions and sonicated in pulse mode for 5 min to obtain a uniform graphene dispersion without obvious agglomeration. This graphene dispersion was added to the sodium alginate-polyvinyl alcohol solution and stirred at 300 rpm for 10 min. 1.047 g of polyvinyl alcohol powder was weighed under anaerobic conditions. g of ferrous sulfide powder was quickly transferred to the feeding port and added to the sodium alginate-polyvinyl alcohol solution in three portions. The mixture was stirred at 300 rpm for 10 minutes to ensure uniform mixing and obtain a mixed solution. Then, the mixed solution was slowly dripped into a saturated boric acid solution containing 5% calcium chloride using a syringe, while controlling the drip height to 8 cm and the drip rate to 1 drop / second. After standing and solidifying for 24 hours, cross-linking was formed to form microcapsules. The microcapsules were then freeze-dried at -20°C for 24 hours to obtain microcapsules containing a reducing core.

[0051] (2) Using the immersion method, the microcapsules containing the reducing core prepared in step (1) were immersed in an 8% w / v sodium bicarbonate solution. After immersion for 2 h, the microcapsules were taken out with a sieve, drained of surface residue, and spread evenly in a glass petri dish. The dish was immediately placed in a freezer. The freezing rate was controlled to first cool down to 4°C at 1°C / min, maintain for 30 min, and then cool down to -20°C at 2°C / min. The microcapsules were freeze-dried at -20°C for 3 h to obtain the microcapsules containing sodium bicarbonate.

[0052] (3) Using the spray deposition method, saturated calcium chloride and sodium sulfate solution with a mass fraction of 2.5% w / v were prepared and loaded into the A / B storage tanks of the atomizer respectively. The carrier gas was nitrogen. The solution was sprayed synchronously through a dual-channel spray system. Saturated calcium chloride and sodium sulfate water mist were sprayed at rates of 10 mL / min and 5 mL / min respectively. The carrier gas flow rate was 5 mL / min. The solution was sprayed onto the surface of the sodium bicarbonate-containing microcapsules prepared in step (2) to form a calcium sulfate isolation layer with a thickness of 1.0 mm. After standing at room temperature for 5 min, the microcapsules were freeze-dried at -20℃ for 24 h to obtain the encapsulated microcapsules.

[0053] (4) Using the spray deposition method, saturated sodium hydroxide and 2.5% w / v manganese nitrate solution were prepared and loaded into the A / B storage tanks of the atomizer respectively. The carrier gas was nitrogen. The solution was sprayed synchronously through a dual-channel spray system. The saturated sodium hydroxide and 2.5% w / v manganese nitrate water mist were sprayed at gas flow rates of 10 mL / min and 5 mL / min respectively. The carrier gas flow rate was 8 mL / min. The solution was sprayed onto the surface of the encapsulated microcapsules prepared in step (3) to form a manganese dioxide oxide layer with a thickness of 0.2 mm. After standing at room temperature for 10 min, the composite microcapsules were obtained by freeze-drying at -20℃ for 3 h.

[0054] (5) Using the spray deposition method, 5% w / v cerium nitrate was prepared and sprayed with 5% w / v cerium nitrate water mist at a gas flow rate of 10 mL / min and a carrier gas flow rate of 5 mL / min to form a cerium nitrate absorption layer on the surface of the composite microcapsule prepared in step (4). The thickness of the absorption layer was 0.2 mm. After freeze-drying at -20℃ for 3 hours, the final composite microcapsule, namely the waste gas volatile heavy metal control material, was obtained.

[0055] Example 2

[0056] The preparation method for ferrous sulfide is the same as in Example 1. The specific preparation method for the material used to control volatile heavy metals in waste gas is as follows:

[0057] (1) 100 mL of deionized water was added to a 250 mL three-necked flask equipped with a magnetic stirrer. The flask was placed under nitrogen protection and aerated for 15 min to remove oxygen. 1.571 g of polyvinyl alcohol powder was weighed and added to the flask in three portions. The mixture was stirred at 300 rpm for 30 min at 80 °C until the polyvinyl alcohol dissolved. The solution was then cooled to room temperature and 3.141 g of sodium alginate was added under a nitrogen atmosphere. The mixture was stirred at 300 rpm until homogeneous to obtain a sodium alginate-polyvinyl alcohol solution. The sodium alginate-polyvinyl alcohol solution was kept under an inert atmosphere and 10 mL was transferred to a 50 mL beaker. 0.157 g of graphene powder was added under ice bath conditions and sonicated in pulse mode for 5 min to obtain a homogeneous graphene dispersion without obvious agglomeration. This graphene dispersion was added to the sodium alginate-polyvinyl alcohol solution and stirred at 300 rpm for 10 min. 0.838 g of graphene powder was weighed under anaerobic conditions. g of ferrous sulfide powder was quickly transferred to the feeding port and added to the sodium alginate-polyvinyl alcohol solution in three portions. The mixture was stirred at 300 rpm for 10 minutes to ensure uniform mixing and obtain a mixed solution. Then, the mixed solution was slowly dripped into a saturated boric acid solution containing 6% calcium chloride using a syringe, while controlling the drip height to 8 cm and the drip rate to 1 drop / second. After standing and solidifying for 24 hours, crosslinking was formed to form microcapsules. The microcapsules were then freeze-dried at -20°C for 24 hours to obtain microcapsules containing a reducing core.

[0058] (2) Using the immersion method, the microcapsules containing the reducing core prepared in step (1) were immersed in a 9% w / v sodium bicarbonate solution. After immersion for 1.5 h, the microcapsules were taken out with a sieve, drained of surface residue, and spread evenly in a glass petri dish. The dish was immediately placed in a freezer. The freezing rate was controlled to first cool down to 4°C at 1°C / min, maintain for 30 min, and then cool down to -20°C at 2°C / min. The microcapsules were freeze-dried at -20°C for 3 h to obtain the microcapsules containing sodium bicarbonate.

[0059] (3) Using the spray deposition method, saturated calcium chloride and 2% w / v sodium sulfate solutions were prepared and loaded into the A / B storage tanks of the atomizer. The carrier gas was nitrogen. The solutions were sprayed synchronously through a dual-channel spray system at rates of 10 mL / min and 5 mL / min, respectively. The carrier gas flow rate was 5 mL / min. The calcium chloride and 2% w / v sodium sulfate water mists were sprayed onto the surface of the sodium bicarbonate-containing microcapsules prepared in step (2) to form a calcium sulfate isolation layer with a thickness of 0.5 mm. After standing at room temperature for 5 min, the microcapsules were freeze-dried at -20℃ for 24 h to obtain the encapsulated microcapsules.

[0060] (4) Using the spray deposition method, saturated sodium hydroxide and 2% w / v manganese nitrate solution were prepared and loaded into the A / B storage tanks of the atomizer respectively. The carrier gas was nitrogen. The solution was sprayed synchronously through a dual-channel spray system. The saturated sodium hydroxide and 2% w / v manganese nitrate water mist were sprayed at gas flow rates of 10 mL / min and 5 mL / min respectively. The carrier gas flow rate was 8 mL / min. The solution was sprayed onto the surface of the encapsulated microcapsules prepared in step (3) to form a manganese dioxide oxide layer with a thickness of 0.1 mm. After standing at room temperature for 10 min, the composite microcapsules were obtained by freeze-drying at -20℃ for 3 h.

[0061] (5) Using the spray deposition method, 4% w / v cerium nitrate was prepared and sprayed with 4% w / v cerium nitrate water mist at a gas flow rate of 10 mL / min and a carrier gas flow rate of 5 mL / min to form a cerium nitrate absorption layer on the surface of the composite microcapsule prepared in step (4). The thickness of the absorption layer was 0.1 mm. After freeze-drying at -20℃ for 3 hours, the final composite microcapsule, namely the waste gas volatile heavy metal control material, was obtained.

[0062] Example 3

[0063] The preparation method for ferrous sulfide is the same as in Example 1. The specific preparation method for the material used to control volatile heavy metals in waste gas is as follows:

[0064] (1) 100 mL of deionized water was added to a 250 mL three-necked flask equipped with a magnetic stirrer. The flask was placed under nitrogen protection and aerated for 15 min to remove oxygen. 1.571 g of polyvinyl alcohol powder was weighed and added to the flask in three portions. The mixture was stirred slowly at 300 rpm for 30 min at 80 °C until the polyvinyl alcohol dissolved. The solution was then cooled to room temperature, and 3.141 g of sodium alginate was added under a nitrogen atmosphere. The mixture was stirred at 300 rpm until homogeneous to obtain a sodium alginate-polyvinyl alcohol solution. The sodium alginate-polyvinyl alcohol solution was kept under an inert atmosphere, and 10 mL was transferred to a 50 mL beaker. 0.209 g of graphene powder was added under ice bath conditions. The mixture was sonicated with a probe in pulse mode for 5 min to obtain a homogeneous graphene dispersion without significant agglomeration. This dispersion was then added to the sodium alginate-polyvinyl alcohol solution and stirred at 300 rpm for 10 min. 0.942 g of graphene powder was weighed under anaerobic conditions. g of ferrous sulfide powder was quickly transferred to the feeding port and added to the sodium alginate-polyvinyl alcohol solution in three portions. The mixture was stirred at 300 rpm for 10 minutes to ensure uniform mixing and obtain a mixed solution. Then, the mixed solution was slowly dripped into a saturated boric acid solution containing 8% calcium chloride using a syringe, while controlling the drip height to 8 cm and the drip rate to 1 drop / second. After standing and solidifying for 24 hours, cross-linking was formed to form microcapsules. The microcapsules were then freeze-dried at -20°C for 24 hours to obtain microcapsules containing a reducing core.

[0065] (2) Using the immersion method, the microcapsules containing the reducing core prepared in step (1) were immersed in a 10% w / v sodium bicarbonate solution. After immersion for 1 h, the microcapsules were taken out with a sieve, drained of surface residue, and spread evenly in a glass petri dish. The dish was immediately placed in a freezer. The freezing rate was controlled to first cool down to 4°C at 1°C / min, maintain for 30 min, and then cool down to -20°C at 2°C / min. The microcapsules were freeze-dried at -20°C for 3 h to obtain the microcapsules containing sodium bicarbonate.

[0066] (3) Using the spray deposition method, saturated calcium chloride and 3% w / v sodium sulfate solutions were prepared and loaded into the A / B storage tanks of the atomizer. The carrier gas was nitrogen. The solutions were sprayed synchronously through a dual-channel spray system at rates of 10 mL / min and 5 mL / min, respectively. The carrier gas flow rate was 5 mL / min. The calcium chloride and 3% w / v sodium sulfate water mists were sprayed onto the surface of the microcapsules containing sodium bicarbonate prepared in step (2) to form a calcium sulfate isolation layer with a thickness of 0.8 mm. After standing at room temperature for 5 min, the microcapsules were freeze-dried at -20℃ for 24 h to obtain the encapsulated microcapsules.

[0067] (4) Using the spray deposition method, saturated sodium hydroxide and 3% w / v manganese nitrate solution were prepared and loaded into the A / B storage tanks of the atomizer respectively. The carrier gas was nitrogen. The solution was sprayed synchronously through a dual-channel spray system. The saturated sodium hydroxide and 3% w / v manganese nitrate water mist were sprayed at gas flow rates of 10 mL / min and 5 mL / min respectively. The carrier gas flow rate was 8 mL / min. The solution was sprayed onto the surface of the encapsulated microcapsules prepared in step (3) to form a manganese dioxide oxide layer with a thickness of 0.2 mm. After standing at room temperature for 10 min, the composite microcapsules were obtained by freeze-drying at -20℃ for 3 h.

[0068] (5) Using the spray deposition method, 6% w / v cerium nitrate was prepared and sprayed with 6% w / v cerium nitrate water mist at a gas flow rate of 10 mL / min and a carrier gas flow rate of 5 mL / min to form a cerium nitrate absorption layer on the surface of the composite microcapsule prepared in step (4). The thickness of the absorption layer was 0.2 mm. After freeze-drying at -20℃ for 3 hours, the final composite microcapsule, namely the waste gas volatile heavy metal control material, was obtained.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that sodium bicarbonate is not added in step (2) of the preparation of the controlled material, while the other steps are the same.

[0071] Comparative Example 2

[0072] The difference from Example 1 is that the manganese dioxide oxide layer is not prepared in step (4) of the preparation of the control material, while the other steps are the same.

[0073] Comparative Example 3

[0074] The difference from Example 1 is that the cerium nitrate absorber layer is not prepared in step (5) of the preparation of the control material, while the other steps are the same.

[0075] The waste gas volatile heavy metal control material prepared in Example 1 was characterized, and the results are as follows.

[0076] (1) Specific surface area and pore size

[0077] The specific surface area and pore size of the waste gas volatile heavy metal control material prepared in Example 1 were tested, and the results are shown in Table 1 and Appendix. Figure 2 As shown, the BET specific surface area of ​​the material for controlling volatile heavy metals in exhaust gas is 4.5665 m² / g, the t-Plot micropore area is 0.5612 m² / g, the micropore volume (t-Plot) is 0.000169 cm³ / g, and the average adsorption pore size (BET method) is 33.8066 nm.

[0078] Table 1. Specific surface area and pore size test results

[0079]

[0080] (2) Scanning electron microscope (SEM)

[0081] As attached Figure 3 and 4 As shown, the morphology of the waste gas volatile heavy metal control material prepared in Example 1 before and after the adsorption temperature experiment at 150℃ was characterized. Before and after the experiment, obvious cracking phenomenon appeared on the surface of the waste gas volatile heavy metal control material, proving that it can spontaneously generate large gaps at high temperature so that the core can fully contact the waste gas.

[0082] (3) X-ray photoelectron spectroscopy (XPS)

[0083] The elemental valence states of the three stages synthesized in Example 1 (microcapsules without sodium bicarbonate, encapsulated microcapsules with a calcium sulfate isolation layer, and composite microcapsules) were characterized by XPS, and the results are shown in the attached figure. Figure 5-13 As shown.

[0084] 1) Microcapsules that do not contain sodium bicarbonate: made from... Figure 5-7 It can be seen that the main form of Fe is Fe2+. 2+ The S element mainly exists in the form of S. 2- The C element mainly exists in the form of C. 60 It can be inferred that the main substances in the microcapsules are FeS and C. 60 .

[0085] 2) Encapsulated microcapsules with a calcium sulfate barrier: (The text abruptly ends here, so the translation stops as well.) Figure 8-11 It can be seen that the main form of Ca is Ca2+. 2+ The S element mainly exists in the form of S. 2- S (VI), Fe mainly exists in the form of Fe. 2+ The C element mainly exists in the form of C. 60 This suggests that the calcium sulfate isolation layer successfully encapsulated the microcapsules, while the main components FeS and C60 in the microcapsules were not lost.

[0086] 3) Composite microcapsules: composed of... Figure 12 and attached Figure 13 It can be seen that Mn mainly exists in the form of MnO2 and Ce mainly exists in the form of CeO2. It can be inferred that manganese dioxide and cerium dioxide absorption layers are formed on the surface of the composite capsule.

[0087] In summary, through three material characterization methods, it is demonstrated that the waste gas volatile heavy metal control material prepared in Example 1 has a multi-layer structure. At room temperature, it has a smooth and dense surface that can prevent core activation, and at high temperature, it can self-activate to allow the core to fully contact and absorb the volatile heavy metals.

[0088] High-temperature exhaust gas purification function test

[0089] First, a three-necked flask was used as a reactor to simulate a high-temperature waste gas source. 500 mg of sodium chloride, 50 mg of sodium arsenate, and 50 mg of thallium nitrate were added to the three-necked flask and dissolved thoroughly in 10 mL of deionized water to form a heavy metal mixed solution. The three-necked flask was placed in a constant-temperature heating mantle and slowly heated to allow the moisture to gradually evaporate to a near-dry state. Then, a programmed temperature increase was used to continue heating the three-necked flask to 300°C at a rate of 5°C / min, gradually releasing the volatile vapors of arsenic and thallium in the solution to simulate a high-temperature waste gas environment. A high-temperature resistant silicone tube was connected to the waste gas outlet as a gas guide to direct the evaporated gas to a condensation and collection system. A filtration zone for volatile heavy metal control materials was set up along the gas guide path. 1 g of composite microcapsules were evenly placed in a quartz funnel as the experimental treatment group, ensuring that the high-temperature waste gas flow fully contacted the volatile heavy metal control materials. The blank control group did not have any materials for controlling volatile heavy metals in the exhaust gas. The exhaust gas directly entered the absorption bottle, which was pre-filled with 100 mL of 2% nitric acid to condense and capture the residual heavy metal vapors in the exhaust gas.

[0090] After the reaction, the absorbent solutions from the experimental group and the blank control group were collected separately, and the heavy metal content was detected by ICP-MS to calculate the corresponding removal rate. ICP-MS detection was performed using an Agilent 7900 inductively coupled plasma mass spectrometer with an injection rate of 1 mL / min. The radio frequency power was 1550 W, the plasma gas flow rate was 15 L / min, the auxiliary gas flow rate was 1 L / min, and the carrier gas flow rate was 0.9 L / min.

[0091] Removal rate (%) = ( C 对照 - C 实验 ) / C 对照 ×100%.

[0092] In the formula C 对照 This represents the heavy metal concentration in the absorbent solution of the blank control group; C 实验 This represents the concentration of heavy metals in the absorbent solution of the experimental group.

[0093] Table 2 Results of the purification capacity (mg / L) of heavy metals in high-temperature exhaust gas from the examples and comparative examples

[0094]

[0095] Table 3. Results of heavy metal removal rates in purified high-temperature exhaust gas from the examples and comparative examples.

[0096]

[0097] The experimental results are shown in Tables 2 and 3. The composite microcapsules prepared in this invention have a significant purification effect on volatile heavy metals in high-temperature waste gas. Among them, the composite microcapsules prepared in Example 1 showed the best removal rates for mercury, arsenic, and thallium, at 93.00%, 88.11%, and 82.16%, respectively, indicating that the component ratios of the composite microcapsules prepared in Example 1 were optimal. The differences in removal rates among the comparative examples further demonstrate that there is a significant synergistic effect among the functional components of the composite microcapsules in the purification process of high-temperature waste gas.

[0098] To further verify the purification effect of the composite microcapsules prepared in Example 1 on mercury-containing exhaust gas, a mercury permeation tube was used to simulate mercury-containing exhaust gas, and a treatment experiment was conducted at an adsorption temperature of 150℃ for 60 min. The experimental subjects included a blank control group, composite microcapsules, activated carbon, and materials ball-milled with elemental sulfur (9:1). The results are shown in Tables 4 and 5.

[0099] Table 4. Experimental results of mercury-containing exhaust gas purification in the examples and comparative examples.

[0100]

[0101] Table 5. Results of mercury-containing exhaust gas removal rates in the examples and comparative examples.

[0102]

[0103] The results showed that the composite microcapsules removed 92.060% of mercury-containing exhaust gas, which was comparable to that of activated carbon and elemental sulfur ball milling material. This indicates that the single component of the composite microcapsules can achieve a removal efficiency similar to that of the mixed material, and has the ability to remove mercury efficiently, showing good application prospects.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a thermally induced self-activated material for controlling volatile heavy metals in waste gas, characterized in that, Includes the following steps: (1) Ferrous sulfide powder and graphene powder were added to sodium alginate-polyvinyl alcohol solution under anaerobic conditions. After mixing evenly, the mixture was dropped into a saturated boric acid solution containing 5-8% w / v calcium chloride. The mixture was allowed to stand and solidify, and then freeze-dried to obtain microcapsules containing a reducing core. (2) The microcapsules containing a reducing core prepared in step (1) are immersed in an 8-10% w / v sodium bicarbonate solution for 1-2 hours and then freeze-dried to obtain microcapsules containing sodium bicarbonate. (3) The microcapsules containing sodium bicarbonate prepared in step (2) are coated with a calcium sulfate isolation layer by spray deposition method to encapsulate the microcapsules; (4) A manganese dioxide oxide layer is formed on the surface of the calcium sulfate isolation layer prepared in step (3) by spray deposition. (5) A cerium nitrate-loaded absorption layer is formed on the surface of the manganese dioxide oxide layer prepared in step (4) by spray deposition method to obtain the volatile heavy metal control material of the exhaust gas.

2. The preparation method of a thermally induced self-activated waste gas volatile heavy metal control material according to claim 1, characterized in that, In step (1), the contents of sodium alginate and polyvinyl alcohol are 3w% and 1.5w% of the total mass of the sodium alginate-polyvinyl alcohol solution, respectively. The dosages of ferrous sulfide powder and graphene powder were (0.8-1)w% and (0.15-0.30)w% of the total mass of the sodium alginate-polyvinyl alcohol solution, respectively.

3. The preparation method of a thermally induced self-activated waste gas volatile heavy metal control material according to claim 1, characterized in that, In step (1), the solidification is allowed to stand for 24 hours, and the freeze-drying conditions are freeze-drying at -20°C for 24 hours.

4. The preparation method of a thermally induced self-activated waste gas volatile heavy metal control material according to claim 1, characterized in that, In step (3), saturated calcium chloride and 2-3% w / v sodium sulfate water mist are sprayed onto the surface of the microcapsules at gas flow rates of 10 mL / min and 5 mL / min, respectively, to form a calcium sulfate isolation layer. The thickness of the isolation layer is 0.5-1.0 mm.

5. The preparation method of a thermally induced self-activated waste gas volatile heavy metal control material according to claim 1, characterized in that, In step (4), a spray deposition method is used to spray saturated sodium hydroxide and manganese nitrate water mist with a concentration of 2-3% w / v onto the surface of the calcium sulfate isolation layer at gas flow rates of 10 mL / min and 5 mL / min, respectively, to form a manganese dioxide oxide layer with a thickness of 0.1-0.2 mm.

6. The preparation method of a thermally induced self-activated waste gas volatile heavy metal control material according to claim 1, characterized in that, In step (5), a spray deposition method is used to spray a cerium nitrate water mist with a concentration of 4-6% w / v onto the surface of the manganese dioxide oxide layer at a gas flow rate of 10 mL / min to form a cerium nitrate absorption layer with a thickness of 0.1-0.2 mm.

7. A thermally induced self-activated material for controlling volatile heavy metals in waste gas, characterized in that, The thermally induced self-activated waste gas volatile heavy metal control material is prepared according to the preparation method described in any one of claims 1-6. The material for controlling volatile heavy metals in exhaust gas consists of a core, an intermediate layer, and an outer shell. The core is a sodium alginate-polyvinyl alcohol microcapsule containing ferrous sulfide, graphene, and sodium bicarbonate. The intermediate layer is a calcium sulfate isolation layer, and the outer shell is a manganese dioxide oxide layer.

8. The thermally induced self-activated waste gas volatile heavy metal control material according to claim 7, characterized in that, The outer layer of the manganese dioxide oxide layer is also covered with a cerium nitrate absorption layer.

9. The application of the thermally induced self-activated waste gas volatile heavy metal control material according to claim 7 in high-temperature waste gas purification treatment.

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