An exhaust gas treatment system for thermally desorbing and repairing contaminated soil

Abstract

This application relates to the technical field of contaminated soil remediation, especially a tail gas treatment system for remediating contaminated soil by thermal desorption. A tail gas treatment system for remediating contaminated soil by thermal desorption includes a dust removal unit, an adsorption unit, a degradation unit, and a detection unit; in the adsorption unit, magnesium chloride-loaded modified zeolite is used as the adsorption material; in the degradation unit, a porous MnO2-RuO2 composite catalyst is used as the catalytic degradation catalyst, and catalytic degradation is carried out under the action of the porous MnO2-RuO2 composite catalyst. The tail gas containing 90 mg / m 3 polycyclic aromatic hydrocarbons, 13.2 mg / m 3 nitrogen oxides, and 15.5 mg / m 3 sulfur dioxide can reach a concentration of 142-215 μg / m³ for polycyclic aromatic hydrocarbons, 125-150 μg / m³ for nitrogen oxides, and 70-83 μg / m³ for sulfur dioxide in the tail gas after being treated by this application, showing excellent removal effects on the pollutants in the tail gas.

Description

Technical Field

[0001] The present application relates to the technical field of contaminated soil remediation, and in particular to an exhaust gas treatment system for thermally desorbing and remediating contaminated soil. Background Art

[0002] Soil is one of the main resources for human survival and an important part of the human ecological environment. With the rapid development of China's economy, the problem of soil pollution has become increasingly prominent.

[0003] In recent years, extensive research has been carried out on various remediation technologies and equipment for organic contaminated sites, and relevant research results have also been applied to the remediation of contaminated sites. The thermal desorption remediation technology has been widely used in treating sites such as soil, sludge, and sediment containing volatile and semi-volatile organic pollutants due to its advantages of high treatment efficiency, short remediation cycle, and wide application range.

[0004] After the organic contaminated soil is heated, the exhaust gas will desorb from the soil. This exhaust gas contains high concentrations of VOCs (especially benzene ring macromolecules that are difficult to degrade such as naphthalene and benzo[a]pyrene), and also contains heavy metals, alkali metals, alkaline earth metals, and particulate matter, with complex components.

[0005] In the prior art, some use the incineration method to dispose of the thermally desorbed exhaust gas. The incineration method is more suitable for the exhaust gas treatment of direct thermal desorption, but this method has high energy consumption and cost, and there is also a risk of generating dioxin pollution. There are also some in the prior art that use the condensation method to transfer most of the organic pollutants in the exhaust gas to the liquid phase. Although some of them also use plasma to remove the remaining extremely small amount of organic pollutants, the wastewater generated by this technology still needs to be further disposed of, increasing the difficulty of wastewater treatment.

[0006] Currently, researchers in this field have tried to use catalysts to catalytically oxidize the desorbed exhaust gas to lower its combustion temperature, but the effect is not good. The secondary pollution control technology is not yet mature, with low professional level and high cost, resulting in a relatively high risk of secondary pollution. Summary of the Invention

[0007] In order to improve the exhaust gas treatment effect of thermally desorbing and remediating contaminated soil, the present application provides an exhaust gas treatment system for thermally desorbing and remediating contaminated soil.

[0008] An exhaust gas treatment system for thermally desorbing and remediating contaminated soil adopts the following technical solutions.

[0009] An exhaust gas treatment system for thermally desorbing and remediating contaminated soil includes a dust removal unit, an adsorption unit, a degradation unit, and a detection unit;

[0010] In the adsorption unit, magnesium chloride-loaded modified zeolite is used as the adsorption material;

[0011] In the degradation unit, a porous MnO2-RuO2 composite catalyst is used as the catalytic degradation catalyst, and catalytic degradation is carried out under the action of the porous MnO2-RuO2 composite catalyst.

[0012] By adopting the above technical solution, after the contaminated soil is heated and desorbed, the tail gas enters the tail gas treatment system. The tail gas entering the tail gas treatment system is first passed through the dust removal unit to remove the particulate soil materials in the tail gas; the dust-removed tail gas enters the degradation unit, and the tail gas in the degradation unit is heated and catalytically degraded of the pollutants in the tail gas under the action of the porous MnO2-RuO2 composite catalyst; the tail gas after being degraded by the degradation unit enters the adsorption unit, and the magnesium chloride-loaded modified zeolite in the adsorption unit effectively removes the gasified tar-containing components and sulfur-containing components in the tail gas. The treated tail gas can be discharged after passing the detection by the detection unit and meeting the emission standard.

[0013] Furthermore, a spray gun for spraying urea solution is provided in the degradation unit, and the spraying speed of the urea solution is 1.6 - 1.8 L / min.

[0014] Furthermore, the mass percentage concentration of the urea solution is 15 - 30%.

[0015] By adopting the above technical solution, the urea solution is sprayed into the tail gas stream, and urea decomposes into ammonia and carbon dioxide at high temperature. Ammonia and nitrogen oxides in the tail gas undergo a selective catalytic reduction reaction under the action of a catalyst to convert NOx into harmless nitrogen and water. The urea solution can also absorb the organic matter in the tail gas and capture it through physical or chemical action, reducing the content of organic matter discharged into the atmosphere.

[0016] Furthermore, the temperature in the degradation unit is 450 - 600 °C, and the residence time of the tail gas is 1 - 5 s.

[0017] Furthermore, the preparation method of the magnesium chloride-loaded modified zeolite is as follows:

[0018] a) Prepare a magnesium chloride solution with a concentration of 0.4 - 0.7 mol / L;

[0019] b) Calcinate the zeolite at 500 - 700 °C for 10 - 12 h, then mix the zeolite with the magnesium chloride solution at a solid-liquid ratio of 1:(5 - 10), and heat and stir for reaction for 40 - 70 min to obtain a reaction solution;

[0020] c) Dry the reaction solution, then wash and dry it to obtain the magnesium chloride-loaded modified zeolite.

[0021] Natural zeolites have a stable structure, with a large number of pores and cavities, but their silicon-aluminum activity is relatively low. By adopting the above technical solution, performance activation is achieved through high-temperature calcination, forming larger cavities, thereby obtaining higher adsorption capacity, enabling pollutant molecules to be adsorbed or stored therein. After calcination, magnesium chloride is loaded, and Mg 2+ There is a strong electrostatic field interaction between it and the zeolite structure, polarizing and dissociating water molecules, so that the zeolite obtains a more stable charge distribution. After loading magnesium chloride, a large number of small particles appear on the zeolite surface, and the lamellar structure becomes more obvious. The pore structure of the zeolite is changed, increasing the adsorption capacity of the zeolite, making the zeolite more completely adsorb pollutants in the tail gas.

[0022] Further, the solid-liquid ratio of the zeolite to the magnesium chloride solution is 1:8.

[0023] Further, the particle size of the zeolite is 5 - 25 μm, and the pore diameter is 0.5 - 1 nm.

[0024] Further, the preparation method of the MnO2-RuO2 composite catalyst is as follows:

[0025] 1) Treat the cordierite honeycomb ceramic substrate with nitric acid solution at 80 °C for 2 - 3 h, then wash it to neutral, dry it at 110 - 120 °C for 3 h, and then calcine it at 550 - 600 °C for 4 h to obtain a pretreated substrate;

[0026] 2) Mix manganese sulfate and ammonium persulfate in a weight ratio of (1 - 1.5):1, and dissolve them in water to obtain a MnO2 precursor solution;

[0027] 3) Immerse the pretreated substrate in the MnO2 precursor solution, then react at 170 - 190 °C for 12 - 14 h. After the reaction, centrifuge, wash, and dry to obtain a substrate loaded with MnO2;

[0028] 4) Dissolve ruthenium trichloride in water to obtain a ruthenium trichloride solution;

[0029] 5) Immerse the substrate loaded with MnO2 in the ruthenium trichloride solution and react at 70 - 80 °C for 8 - 10 h; after the reaction, filter out the precipitate and wash it;

[0030] 6) Dry the washed precipitate at 100 - 120 °C for 3 - 5 h, and then calcine it at 400 - 600 °C for 8 - 10 h to obtain the MnO2-RuO2 composite catalyst.

[0031] By adopting the above technical solution, MnO2 is first grown on a cordierite honeycomb ceramic substrate, and then RuO2 is loaded on the MnO2 to obtain a porous composite catalyst. This catalyst includes a substrate and active components, where the substrate is honeycomb cordierite and the active components are MnO2 and RuO2. This catalyst has high catalytic efficiency in the temperature range of 450 - 650 °C, can completely convert the tail gas of thermal desorption of organic contaminated soil, has good high-temperature stability, strong anti-sintering and anti-carbon deposition capabilities, and also has good resistance to alkali, alkaline earth, heavy metals, chlorine, and sulfur poisoning.

[0032] In summary, the present application has the following beneficial effects:

[0033] The tail gas generated after the thermal desorption of contaminated soil is collected and enters the dust removal unit to remove the particulate matter in the tail gas. The dust-removed tail gas enters the degradation unit, and the pollutants in the tail gas in the degradation unit are catalytically degraded by the porous MnO2-RuO2 composite catalyst at high temperature. The degraded tail gas enters the adsorption unit and is adsorbed by magnesium chloride-loaded modified zeolite to remove the organic matter and nitrogen- and sulfur-containing pollutants in the tail gas, etc. The tail gas containing 90 mg / m 3 polycyclic aromatic hydrocarbons, 13.2 mg / m 3 nitrogen oxides, 15.5 mg / m 3 sulfur dioxide, after being treated by the present application, the concentration of polycyclic aromatic hydrocarbons in the tail gas can reach 142 - 215 μg / m³, the concentration of nitrogen oxides can reach 125 - 150 μg / m³, and the concentration of sulfur dioxide can reach 70 - 83 μg / m³, showing excellent removal effect on the pollutants in the tail gas. Description of the Drawings

[0034] Figure 1 is a schematic diagram of the tail gas treatment system of Example 1 of the present application.

[0035] In the figure, 1, dust removal unit; 2, degradation unit; 3, adsorption unit; 4, detection unit. Detailed Embodiments

[0036] The following further details the present application with reference to the embodiments.

[0037] Preparation Examples of Raw Materials and Intermediates

[0038] Raw Materials

[0039] Magnesium chloride, analytical pure;

[0040] Manganese sulfate, anhydrous manganese sulfate, analytical pure;

[0041] Ammonium persulfate, analytical pure;

[0042] Ruthenium trichloride, analytical pure.

[0043] Preparation Examples

[0044] Preparation Example 1

[0045] A magnesium chloride-loaded modified zeolite, and its preparation method is as follows:

[0046] a) Prepare a magnesium chloride solution with a concentration of 0.6 mol / L;

[0047] b) Calcinate the zeolite at 600 °C for 11 h, then mix the zeolite with the magnesium chloride solution at a solid-liquid ratio of 1:8, and heat and stir to react for 60 min at 350 °C to obtain a reaction solution; wherein the particle size of the zeolite is 15 μm and the pore size is 0.8 nm;

[0048] c) Dry the reaction solution at 120 °C, then wash it with deionized water until neutral and dry it at 120 °C to obtain the magnesium chloride-loaded modified zeolite.

[0049] Preparation Example 2

[0050] The difference from Preparation Example 1 is that in Preparation Example 2, the solid-liquid ratio of the zeolite to the magnesium chloride solution is 1:5.

[0051] Preparation Example 3

[0052] The difference from Preparation Example 1 is that in Preparation Example 3, the solid-liquid ratio of the zeolite to the magnesium chloride solution is 1:10.

[0053] Preparation Example 4

[0054] The difference from Preparation Example 1 is that in Preparation Example 4, the particle size of the zeolite is 5 μm and the pore size is 1 nm.

[0055] Preparation Example 5

[0056] The difference from Preparation Example 1 is that in Preparation Example 5, the particle size of the zeolite is 25 μm and the pore size is 0.5 nm.

[0057] Preparation Example 6

[0058] The difference from Preparation Example 1 is that in Preparation Example 6, the zeolite is calcined at 800 °C for 12 h.

[0059] Preparation Example 7

[0060] A porous MnO2-RuO2 composite catalyst, and its preparation method is as follows:

[0061] 1) Immerse the cordierite honeycomb ceramic substrate in a 15% nitric acid solution, soak and treat it at 80 °C for 2 h, then wash it until neutral, dry it at 120 °C for 3 h, and then calcine it at 600 °C for 4 h to obtain a pretreated substrate;

[0062] 2) After mixing 1.5 kg of manganese sulfate and 1.5 kg of ammonium persulfate, completely dissolve them in water to obtain a MnO2 precursor solution;

[0063] 3) Completely immerse the pretreated substrate in the MnO2 precursor solution, then react at 180 °C for 12 h. After the reaction, centrifuge, wash, and dry at 120 °C to obtain a substrate loaded with MnO2;

[0064] 4) Dissolve 1 kg of ruthenium trichloride in water to obtain a ruthenium trichloride solution;

[0065] 5) Immerse the substrate loaded with MnO2 in the ruthenium trichloride solution and react at 70 - 80 °C for 8 - 10 h; after the reaction, filter out the precipitate and wash it;

[0066] 6) Dry the washed precipitate at 120 °C for 3 h, then calcine it at 500 °C for 9 h to obtain a MnO2-RuO2 composite catalyst.

[0067] Preparation Example 8

[0068] Differing from Preparation Example 7, in step 2) of Preparation Example 8, 2 kg of manganese sulfate and 2 kg of ammonium persulfate are mixed and completely dissolved in water.

[0069] Preparation Example 9

[0070] Differing from Preparation Example 7, in step 2) of Preparation Example 9, 3 kg of manganese sulfate and 3 kg of ammonium persulfate are mixed and completely dissolved in water.

[0071] Preparation Example 10

[0072] Differing from Preparation Example 7, in step 2) of Preparation Example 9, 1.5 kg of manganese sulfate and 1 kg of ammonium persulfate are mixed and completely dissolved in water.

[0073] Preparation Example 11

[0074] A catalyst, the preparation method thereof is:

[0075] 1) Immerse the cordierite honeycomb ceramic substrate in a 15% nitric acid solution, soak it at 80 °C for 2 h, then wash it until neutral, dry it at 120 °C for 3 h, and then calcine it at 600 °C for 4 h to obtain a pretreated substrate;

[0076] 2) After mixing 1.5 kg of manganese sulfate and 1.5 kg of ammonium persulfate, completely dissolve them in water to obtain a MnO2 precursor solution;

[0077] 3) Completely immerse the pretreated substrate in the MnO2 precursor solution, then react at 180 °C for 12 h. After the reaction, centrifuge, wash, and dry at 120 °C to obtain a catalyst loaded with MnO2.

[0078] Preparation Example 12

[0079] A catalyst, and its preparation method is as follows:

[0080] 1) Immerse a cordierite honeycomb ceramic substrate in a 15% nitric acid solution, soak it at 80 °C for 2 h, then wash it until neutral, dry it at 120 °C for 3 h, and then calcine it at 600 °C for 4 h to obtain a pretreated substrate;

[0081] 2) Dissolve 1 kg of ruthenium trichloride in water to obtain a ruthenium trichloride solution;

[0082] 3) Immerse the pretreated substrate in the ruthenium trichloride solution and react at 70 - 80 °C for 8 - 10 h; after the reaction is completed, filter out the precipitate and wash it;

[0083] 4) Dry the washed precipitate at 120 °C for 3 h, and then calcine it at 500 °C for 9 h to obtain a catalyst loaded with RuO2.

[0084] Performance Detection

[0085] Perform anti-poisoning ability tests on the catalysts in Preparation Examples 7 - 12, and the test results are shown in Table 1.

[0086] Anti-lead poisoning detection: Immerse the catalyst in lead liquid (lead nitrate solution, concentration 0.05 mol / L) for 6 h, load the immersed catalyst into a stainless steel fixed bed reactor with an inner diameter of 16 mm, and introduce raw material gas into the reactor for catalytic oxidation. The raw material gas consists of thermally desorbed waste gas from organic contaminated soil, including: 90 mg / m 3 polycyclic aromatic hydrocarbons, 13.2 mg / m 3 nitrogen oxides, 15.5 mg / m 3 sulfur dioxide, set the reaction space velocity to 10000 h -1 ⁻¹, the reaction pressure is atmospheric pressure, the test temperature at the start of the reaction is 250 °C, use T 90 to represent the catalytic activity of the catalyst, T 90 to represent the reaction temperature when the conversion rate of polycyclic aromatic hydrocarbons reaches 90%, test the T 90 of fresh polycyclic aromatic hydrocarbons, and the T 90 after lead poisoning, calculate the activity difference, activity difference = T 90 after poisoning - fresh T 90 .

[0087] Table 1 Catalyst Performance Detection Results

[0088] Example

[0089] Example 1

[0090] Referring to Figure 1 , a tail gas treatment system for thermal desorption to repair contaminated soil, includes a dust removal unit 1, a degradation unit 2, an adsorption unit 3, and a detection unit 4 connected in sequence. The dust removal unit 1 is a cyclone dust collector. The degradation unit 2 includes a degrager, in which the porous MnO2-RuO2 composite catalyst obtained in Preparation Example 7 is provided. The temperature in the degrager is 500 °C, and the residence time of the tail gas is 3 s. The adsorption unit 3 is an adsorber filled with the magnesium chloride loaded modified zeolite obtained in Preparation Example 1. The detection unit 4 is an on-line detector.

[0091] The tail gas generated after the thermal desorption of the contaminated soil is collected and enters the dust removal unit 1. The cyclone dust collector of the dust removal unit 1 removes the particulate matter in the tail gas. The dust-removed tail gas enters the degradation unit 2, and the pollutants in the tail gas in the degradation unit 2 are catalytically degraded by the porous MnO2-RuO2 composite catalyst at high temperature. The degraded tail gas enters the adsorption unit 3 and is adsorbed by the magnesium chloride loaded modified zeolite to remove the organic matter and nitrogen and sulfur-containing pollutants in the tail gas, etc. The tail gas treated by the adsorption unit 3 is detected by the on-line detector of the detection unit 4 and discharged after meeting the standards.

[0092] Examples 2-4

[0093] Different from Example 1, the porous MnO2-RuO2 composite catalysts in Examples 2-4 are respectively from Preparation Examples 8-10.

[0094] Examples 5-9

[0095] Different from Example 1, the magnesium chloride loaded modified zeolites in Examples 5-9 are respectively from Preparation Examples 2-6.

[0096] Different from Example 1, a two-fluid spray gun is further provided in the degrager of the degradation unit 2 in Example 10. The two-fluid spray gun sprays urea solution into the degrager. The mass percentage concentration of the urea solution is 15%, and the spraying speed of the urea solution is 1.8 L / min.

[0097] Example 11

[0098] Different from Example 10, the mass percentage concentration of the urea solution in Example 11 is 30%, and the spraying speed of the urea solution is 1.6 L / min.

[0099] Example 12

[0100] Different from Example 10, the mass percentage concentration of the urea solution in Example 12 is 20%, and the spraying speed of the urea solution is 1.7 L / min.

[0101] Comparative Example

[0102] Comparative Example 1

[0103] Different from Example 1, in Comparative Example 1, magnesium chloride supported modified zeolite was replaced with an equal amount of zeolite.

[0104] Comparative Example 2

[0105] Different from Example 1, in Comparative Example 2, the porous MnO2-RuO2 composite catalyst was replaced with an equal amount of the catalyst obtained in Preparation Example 11.

[0106] Comparative Example 3

[0107] Different from Example 1, in Comparative Example 3, the porous MnO2-RuO2 composite catalyst was replaced with an equal amount of the catalyst obtained in Preparation Example 12.

[0108] Comparative Example 4

[0109] Different from Example 1, in Comparative Example 4, the porous MnO2-RuO2 composite catalyst was replaced with an equal amount of the catalyst obtained by mixing the catalysts obtained in Preparation Example 11 and Preparation Example 12 at a weight ratio of 1:1.

[0110] Performance Detection

[0111] The raw material gas consists of the exhaust gas from the thermal desorption of organic contaminated soil, including: 90 mg / m 3 polycyclic aromatic hydrocarbons, 13.2 mg / m 3 nitrogen oxides, 15.5 mg / m 3 sulfur dioxide. The raw material gas was introduced into the tail gas treatment systems in the examples and comparative examples for treatment, and the pollutant concentrations of the discharged gas were recorded. The results are shown in Table 2.

[0112] Table 2 Detection Results of Discharged Gas

[0113]

[0114] Combining the examples and comparative examples, and referring to Table 2, it can be seen that the tail gas treatment system in the examples has better removal effects on polycyclic aromatic hydrocarbons, nitrogen oxides, and sulfur dioxide than the comparative examples. This shows that the tail gas treatment system of the present application can achieve better treatment effects and the treatment conditions are mild.

[0115] Combining Example 1 and Comparative Example 1, and referring to Table 2, it can be seen that the emission concentrations of polycyclic aromatic hydrocarbons, nitrogen oxides, and sulfur dioxide in Example 1 are all lower than those in Comparative Example 1. This indicates that replacing magnesium chloride with zeolite to load the modified zeolite will affect the treatment effect of the tail gas, and the impact on the treatment effects of nitrogen oxides and sulfur dioxide is greater. This may be because after high-temperature calcination of the zeolite and then loading magnesium chloride, the pore structure of the zeolite is changed, increasing the adsorption capacity of the zeolite, making the zeolite more completely adsorb the pollutants in the tail gas, especially nitrogen oxides and sulfur-containing components.

[0116] Combining Example 1 and Comparative Examples 2-4, and referring to Table 2, it can be seen that the emission concentrations of polycyclic aromatic hydrocarbons, nitrogen oxides, and sulfur dioxide in Example 1 are all lower than those in Comparative Example 1. This indicates that the type of catalyst will affect the treatment effect of the tail gas, and the impact on the treatment effect of polycyclic aromatic hydrocarbons is greater. This may be because the porous MnO2-RuO2 composite catalyst has a high catalytic efficiency, which can completely convert the tail gas from the thermal desorption of organic contaminated soil, greatly improving the treatment effect.

[0117] Combining Examples 1-4, and referring to Table 2, it can be seen that the ratio of Mn to Ru in the porous MnO2-RuO2 composite catalyst will also affect the treatment effect of the tail gas, and the impact on the treatment effect of polycyclic aromatic hydrocarbons is greater. Among them, the porous MnO2-RuO2 composite catalyst applied in Example 1 is superior.

[0118] This specific embodiment is only an explanation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A tail gas treatment system for thermally desorbing and repairing contaminated soil, characterized in that, It includes a dust removal unit (1), a degradation unit (2), an adsorption unit (3), and a detection unit (4); In the adsorption unit (3), magnesium chloride-loaded modified zeolite is used as the adsorption material; In the degradation unit (2), a porous MnO2-RuO2 composite catalyst is used as the catalytic degradation catalyst, and catalytic degradation is carried out under the action of the porous MnO2-RuO2 composite catalyst; A spray gun for spraying urea solution is provided in the degradation unit (2), and the spraying speed of the urea solution is 1.6 - 1.8 L / min; The mass percentage concentration of the urea solution is 15 - 30%; The temperature in the degradation unit (2) is 450 - 600 °C, and the tail gas residence time is 1 - 5 s; The preparation method of the MnO2-RuO2 composite catalyst is as follows: 1) Treat the cordierite honeycomb ceramic substrate with nitric acid solution at 80 °C for 2 - 3 h, then wash it to neutral, dry it at 110 - 120 °C for 3 h, and then calcine it at 550 - 600 °C for 4 h to obtain a pretreated substrate; 2) Mix manganese sulfate and ammonium persulfate in a weight ratio of (1 - 1.5):1, and dissolve them in water to obtain a MnO2 precursor solution; 3) Immerse the pretreated substrate in the MnO2 precursor solution, and then react at 170 - 190 °C for 12 - 14 h. After the reaction, centrifuge, wash, and dry to obtain a substrate loaded with MnO2; 4) Dissolve ruthenium trichloride in water to obtain a ruthenium trichloride solution; 5) Immerse the substrate loaded with MnO2 in the ruthenium trichloride solution and react at 70 - 80 °C for 8 - 10 h; after the reaction, filter out the precipitate and wash it; 6) Dry the washed precipitate at 100 - 120 °C for 3 - 5 h, and then calcine it at 400 - 600 °C for 8 - 10 h to obtain the MnO2-RuO2 composite catalyst; The weight ratio of manganese sulfate to ruthenium trichloride is 1.5:1; The pollutants in the tail gas of the contaminated soil include polycyclic aromatic hydrocarbons, nitrogen oxides, and sulfur dioxide.

2. The tail gas treatment system for repairing contaminated soil by thermal desorption according to claim 1, wherein: The preparation method of the magnesium chloride-loaded modified zeolite is as follows: a) Prepare a magnesium chloride solution with a concentration of 0.4 - 0.7 mol / L; b) Calcinate the zeolite at 500 - 700 °C for 10 - 12 h, then mix the zeolite with the magnesium chloride solution at a solid-liquid ratio of 1:(5 - 10), and heat and stir to react for 40 - 70 min to obtain a reaction solution; c) Dry the reaction solution, then wash and dry it to obtain the magnesium chloride-loaded modified zeolite.

3. The tail gas treatment system for repairing contaminated soil by thermal desorption according to claim 2, characterized in that: The solid-liquid ratio of the zeolite to the magnesium chloride solution is 1:

8.

4. The tail gas treatment system for thermally desorbing and repairing contaminated soil according to claim 2, wherein: The particle size of the zeolite is 5 - 25 μm, and the pore size is 0.5 - 1 nm.

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