A method for preparing a magnesium-based flue gas desulfurizer by using molten salt chlorination slag

Abstract

This invention discloses a method for preparing a magnesium-based flue gas desulfurizer using molten salt chlorination slag, belonging to the field of chemical environmental protection. The method includes the following steps: molten salt chlorination slag is leached with water, and after sufficient leaching, solid-liquid separation is performed to obtain leachate A and solid slag B; leachate A undergoes multi-stage pH adjustment, and after sufficient reaction, solid-liquid separation is performed to obtain filtrate C and solid slag D; NaOH is added to filtrate C, and after sufficient reaction, solid-liquid separation is performed to obtain filtrate E and solid slag F; solid slag F undergoes three-stage countercurrent slurry washing, and after settling and removing the supernatant, an emulsion Mg(OH)2 slurry is obtained; after adjusting the solid content of the emulsion Mg(OH)2 slurry, a magnesium-based flue gas desulfurizer is obtained, which can be directly used for flue gas desulfurization. This invention recovers Mg element in the form of magnesium hydroxide slurry, and the obtained emulsion Mg(OH)2 slurry can be directly applied to flue gas desulfurization, with a simple process.

Description

Technical Field

[0001] This invention belongs to the field of chemical environmental protection and relates to a method for preparing magnesium-based flue gas desulfurizing agent using molten salt chlorination slag. Background Technology

[0002] Currently, industrial desulfurization primarily employs wet desulfurization methods, mainly divided into calcium and magnesium methods. Magnesium methods offer higher flue gas desulfurization efficiency, and the byproducts have higher solubility, making them less prone to deposition and equipment corrosion. Magnesium desulfurization equipment is also less expensive than calcium desulfurization equipment. Furthermore, the byproducts of magnesium desulfurization, magnesium sulfate and magnesium sulfate, have a wider range of applications and more disposal pathways. Traditional magnesium-based desulfurizing agents are MgO and Mg(OH)2, which require a slurry preparation process before use in flue gas desulfurization. For example, CN113813758A discloses a magnesium oxide-based desulfurizing agent and its preparation method, which first uses magnesite to prepare magnesium oxide, then slurries it to prepare magnesium hydroxide, and finally prepares the magnesium-based desulfurizing agent. However, this method is cumbersome, has high production costs, and fails to effectively utilize industrial solid waste resources.

[0003] The molten salt chlorination process for producing TiCl4 is characterized by low production cost and high product quality. However, it also suffers from the problems of large quantities of waste salt and waste brine (hazardous waste), resulting in severe pollution. This significantly hinders the promotion of molten salt chlorination technology and the high-value utilization of primary titanium ore. Existing technologies have proposed various methods for utilizing molten salt chlorination slag. For example, CN101343070A discloses a method for treating waste molten salt, mainly recovering NaCl solution; CN105883911A discloses a method for resource-based treatment of molten salt chlorination slag. Although this method can separate multiple components, the application pathways for iron and manganese slag are unclear. Molten salt chlorination slag contains more than 20% MgCl2 resources, which can be used to prepare magnesium-based desulfurizing agents. CN103566719A discloses a method for preparing desulfurizing agent raw materials using chlorinated waste molten salt generated during TiCl4 production. However, this method prepares Mg(OH)2 into magnesium hydroxide flame retardant, failing to directly recover and utilize Mg from the molten salt chlorination slag as a raw material for desulfurizing agents.

[0004] Therefore, there is an urgent need to develop a method that can directly and efficiently utilize MgCl2 resources in molten salt chlorination slag to prepare magnesium-based desulfurizers. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the preparation process of existing traditional magnesium-based desulfurizers is cumbersome and costly.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a magnesium-based flue gas desulfurizer using molten salt chlorination slag, comprising the following steps:

[0008] S1. The molten salt chlorination slag is leached with water, and after full leaching, solid-liquid separation is performed to obtain leachate A and solid slag B;

[0009] S2. The leachate A undergoes multi-stage pH adjustment, and after sufficient reaction, solid-liquid separation is performed to obtain filtrate C and solid residue D.

[0010] S3. Add NaOH to filtrate C, and after the reaction is complete, separate the solid and liquid to obtain filtrate E and solid residue F;

[0011] S4. Solid slag F is subjected to three-stage countercurrent pulping and washing, and then allowed to settle to remove the supernatant, resulting in an emulsion Mg(OH)2 slurry;

[0012] S5. Add distilled water or Cl to the Mg(OH)2 emulsion slurry. - Magnesium-based flue gas desulfurizer is obtained by adjusting the solid content of the Mg(OH)2 slurry emulsion to 30-35% with water with a concentration of <200 mg / L.

[0013] In step S1 above, the mass ratio of molten salt chlorination residue to water is 1:1.8~2.1, and the water soaking time is 18~24h.

[0014] In step S2 above, the multi-stage pH adjustment specifically involves: adding NaOH to leachate A to adjust the pH to 4.0~6.0, then adding sodium carbonate to adjust the pH to 6.9~7.5, and finally adding sodium hypochlorite or hydrogen peroxide to adjust the pH to 7.8~8.2.

[0015] In step S3 above, filtrate C and NaOH are mixed and reacted using a two-way feeding method, and the NaOH contains OH... - With Mg in filtrate C 2 + The molar ratio is (1.95~2.05):1; the mixing reaction time is not less than 1 hour.

[0016] In step S4 above, the three-stage countercurrent pulping and washing specifically involves: using an appropriate amount of secondary filtrate to perform primary pulping and washing on the solid slag F, separating the solid and liquid to obtain primary filtrate and filter cake a; using an appropriate amount of tertiary filtrate to perform secondary pulping and washing on filter cake a, separating the solid and liquid to obtain secondary filtrate and filter cake b; and using an appropriate amount of distilled water or Cl... - The filter cake b was subjected to three-stage pulping and washing with water with a concentration of <200 mg / L, followed by static sedimentation and separation to obtain a three-stage filtrate and an emulsion Mg(OH)2 slurry.

[0017] Furthermore, during the first-stage pulping and washing, the liquid-to-solid ratio of the second-stage filtrate to the solid residue F is ≥5; during the second-stage pulping and washing, the liquid-to-solid ratio of the third-stage filtrate to the filter cake a is ≥5; during the third-stage pulping and washing, distilled water or Cl... -The liquid-to-solid ratio of water with a concentration of <200 mg / L and filter cake b is ≥5.

[0018] In step S4 above, the obtained emulsion Mg(OH)2 slurry is separated into solid and liquid phases and then dried to obtain a finished Mg(OH)2 product that meets the Class III qualified product standard of HG / T 3607-2007.

[0019] Furthermore, the Mg(OH)2 product and Cl... - A mixture of water with a concentration of <200 mg / L and a pore-forming agent, after maturation and pulping, can be used directly as a desulfurizing agent.

[0020] Furthermore, the pore-forming agent is at least one of starch, wood flour, rice husk, and polystyrene / corn starch mixture; the amount of the pore-forming agent added is 0.1-1% of the total mass of the desulfurizer.

[0021] In step S5 above, sodium dodecylbenzenesulfonate is added during the process of adjusting the solid content of the Mg(OH)2 emulsion slurry. The amount added is 2 to 4% of the solid content in the Mg(OH)2 emulsion slurry.

[0022] The beneficial effects of this invention are as follows: This invention proposes a method for preparing magnesium-based flue gas desulfurizing agents using molten salt chlorination slag. Using molten salt chlorination slag directly as raw material, through efficient separation and conversion, the MgCl2 resources rich in the slag are converted into magnesium hydroxide slurry that can be directly used for flue gas desulfurization. The emulsion Mg(OH)2 slurry obtained by this method can be applied to flue gas desulfurization processes after adjusting its solids content, achieving a desulfurization efficiency greater than 95%. Simultaneously, this invention also achieves the recovery of other valuable components from the molten salt chlorination slag during the process. Solid slag containing C, TiO2, and SiO2 can be used as building materials and metallurgical auxiliary materials. Solid slag containing Fe, Mn, Al, Ca, and Mg can be used as metallurgical auxiliary materials for steelmaking and vanadium extraction. NaCl brine is used for NaCl purification and recovery. Compared with traditional methods for preparing magnesium-based desulfurizers, the method of this invention simplifies the complex curing and pulping steps, not only realizing the resource utilization of molten salt chlorination slag, but also providing a stable and low-cost magnesium-based desulfurizer for flue gas desulfurization, which has significant environmental and economic benefits and broad application prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process flow of the method of the present invention. Detailed Implementation

[0024] To make the technical problems, solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with the embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as understood by one of ordinary skill in the art.

[0025] The process flow for preparing magnesium-based flue gas desulfurizers using molten salt chlorination slag is as follows: Figure 1 As shown, it includes the following steps:

[0026] S1. The molten salt chlorination slag is leached with water, and after full leaching, solid-liquid separation is performed to obtain leachate A and solid slag B;

[0027] S2. The leachate A undergoes multi-stage pH adjustment, and after sufficient reaction, solid-liquid separation is performed to obtain filtrate C and solid residue D.

[0028] S3. Add NaOH solution to filtrate C, and after the reaction is complete, separate the solid and liquid to obtain filtrate E and solid residue F;

[0029] S4. Solid slag F is subjected to three-stage countercurrent pulping and washing, and then allowed to settle to remove the supernatant, resulting in an emulsion Mg(OH)2 slurry;

[0030] S5. Add distilled water or Cl to the Mg(OH)2 emulsion slurry. - Magnesium-based flue gas desulfurizer is obtained by adjusting the solid content of the Mg(OH)2 slurry emulsion to 30-35% with water with a concentration of <200 mg / L.

[0031] In one embodiment of the present invention, during the water leaching of molten salt chlorination slag, the slag-to-water ratio is 1:1.8 to 2.1, and the leaching time is 18 to 24 hours. The resulting solid slag B mainly contains C, TiO2, and SiO2, and can be used in building materials and metallurgical auxiliaries. As a non-limiting example, the slag-to-water ratio can be 1:1.8, 1:1.9, 1:2.0, 1:2.1, or any ratio within this range; the water leaching time can be 18 hours, 20 hours, 22 hours, 24 hours, or within any two of the above values.

[0032] In one embodiment of the present invention, selective precipitation of impurity metals is achieved through multi-stage pH adjustment. First, NaOH solution is added to leachate A to adjust the pH to 4.0-6.0, then sodium carbonate solution is added to adjust the pH to 6.9-7.5, and finally sodium hypochlorite solution or hydrogen peroxide is added to adjust the pH to 7.8-8.2. The mixture is stirred for 8-15 hours to achieve solid-liquid separation. The NaOH solution, sodium carbonate solution, sodium hypochlorite solution, or hydrogen peroxide used for pH adjustment can be of any concentration. The resulting solid slag D mainly contains Fe, Mn, Al, Ca, and Mg, and can be used as a metallurgical auxiliary material for steelmaking and vanadium extraction. As a non-limiting example, the stirring reaction time can be 8 hours, 10 hours, 12 hours, 15 hours, or any combination of two of these values.

[0033] In one embodiment of the present invention, based on the Mg in filtrate C 2+ Concentration, according to n(OH) -): n(Mg 2+ The ratio is (1.95~2.05): 1. Calculate the amount of NaOH solution and filtrate C to be added. The NaOH solution and filtrate C are mixed and reacted using a two-way feeding method, and the mixing reaction time is not less than 1 hour. The resulting filtrate E is the initial NaCl brine, used for NaCl recovery. The solid residue F is the initial Mg(OH)2 filter cake, which contains soluble Na, K, and Cl, etc. The NaOH solution used can be of any concentration. As a non-limiting example, n(OH) - ): n(Mg 2+ The ratio can be 1.95:1, 2.00:1, 2.05:1 or any ratio in between.

[0034] In one embodiment of the present invention, solid slag F is subjected to three-stage countercurrent pulping and washing (to remove soluble ions Na, K, and Cl). A certain amount (liquid-to-solid ratio ≥ 5) of secondary filtrate is used for primary pulping and washing, resulting in solid-liquid separation. The filtrate is the primary filtrate, and filter cake a is obtained for secondary pulping and washing. The liquid-to-solid ratio is the mass ratio of the secondary filtrate to solid slag F. Secondary pulping and washing is performed using a certain amount (liquid-to-solid ratio ≥ 5) of tertiary filtrate, resulting in solid-liquid separation. The filtrate is the secondary filtrate, and filter cake b is obtained for tertiary pulping and washing. The liquid-to-solid ratio is the mass ratio of the tertiary filtrate to filter cake a. Tertiary pulping and washing is performed using a certain amount (liquid-to-solid ratio ≥ 5) of distilled water or purified water (Cl concentration < 200 mg / L), and allowed to settle for at least 4 hours. The supernatant is the tertiary filtrate for later use, and the lower emulsion is the Mg(OH)2 slurry. The liquid-to-solid ratio is the mass ratio of distilled water or purified water to filter cake b. The resulting primary filtrate has a pH > 10 and can be used for the treatment of acidic wastewater.

[0035] In one embodiment of the present invention, the solid-liquid separation method may be vacuum filtration, pressure filtration, or centrifugation.

[0036] In one embodiment of the present invention, a magnesium-based flue gas desulfurizer is obtained by adjusting the solid content in the Mg(OH)2 emulsion slurry to 30-35% for flue gas desulfurization. The water content in the adjusted Mg(OH)2 emulsion slurry is 65-70% by mass. As a non-limiting example, the solid content in the adjusted Mg(OH)2 emulsion slurry can be 30%, 31%, 32%, 33%, 34%, 35%, or within any two of the above values.

[0037] In one embodiment of the present invention, to improve the desulfurization efficiency of the magnesium-based flue gas desulfurizer, sodium dodecylbenzenesulfonate, a surfactant, can be added during the adjustment of the solids content of the emulsion Mg(OH)2 slurry; the amount of sodium dodecylbenzenesulfonate added is 2-4% of the solids content in the emulsion Mg(OH)2 slurry. As a non-limiting example, the amount of sodium dodecylbenzenesulfonate added can be 2%, 3%, or 4% of the solids content in the emulsion Mg(OH)2 slurry, or within any two of the above values.

[0038] In one embodiment of the present invention, to address the inconvenience of slurry transportation, Mg(OH)2 finished product can also be directly produced in step S4. This involves separating the solid and liquid components of the obtained emulsion Mg(OH)2 slurry and drying it to prepare the Mg(OH)2 finished product, which meets the HG / T 3607-2007 Class III qualified product standard (environmental protection applications, flue gas desulfurization and wastewater treatment). The Mg(OH)2 finished product and Cl... - A mixture of water with a concentration of <200 mg / L and a pore-forming agent, after maturation and pulping, can be used directly as a desulfurizing agent. The pore-forming agent can be a natural organic material (starch, wood flour, rice husk, etc.) or a composite pore-forming agent (polystyrene / corn starch mixture), and the addition amount is 0.1% to 1% of the total amount of desulfurizing agent.

[0039] The following specific embodiments will be provided to explain the solution of the present invention. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0040] The molten salt chlorination slag used in this embodiment of the invention comprises, by mass percentage: TiO2 4.65%, C 4.96%, FeCl3 5.42%, FeCl2 17.46%, CaCl2 4.01%, SiO2 5.66%, AlCl3 1.06%, MgCl2 26.21%, MnCl2 0.78%, NaCl 29.06%, and others 0.73%.

[0041] The specific evaluation method for the desulfurization efficiency of the desulfurizing agent in this embodiment of the invention is as follows: A micro-reactor is used to simulate flue gas components at a space velocity of 36000 h⁻¹. -1 A balance gas consisting of 600ppm SO2, 3% O2, 600ppm NH3, and N2 is introduced, and its concentration changes are monitored in real time by a Bruker flue gas analyzer.

[0042] According to the formula Calculate the desulfurization efficiency of the catalyst; where:

[0043] SO2 (%): SO2 removal efficiency;

[0044] [ SO 2 ] in SO2 input concentration, ppm; the experimental input SO2 concentration is 600ppm.

[0045] [ SO 2 ] out SO2 output concentration, ppm.

[0046] Example 1 describes a method for preparing a magnesium-based flue gas desulfurizer using molten salt chlorination slag, which specifically includes the following steps:

[0047] (1) Molten salt chlorination residue and water were leached in a mass ratio of 1:2. After leaching for 24 hours, solid and liquid were separated to obtain leachate A.

[0048] (2) Add NaOH solution (30% by mass) to leachate A to adjust the pH to 6.0, then add sodium carbonate (18% by mass) to adjust the pH to 7.5, and finally add sodium hypochlorite (6% by mass) to adjust the pH to 8.0. After stirring and reacting for 15 hours, perform solid-liquid separation to obtain filtrate C.

[0049] (3) Based on the Mg in filtrate C 2+ Concentration, according to n(OH) - ): n(Mg 2+ The ratio of NaOH solution (30% by mass) to filtrate C was calculated to be 2.0:1. The NaOH solution and filtrate C were mixed and reacted by a two-way feeding method. After 1 hour of mixing and reaction, solid-liquid separation was performed to obtain solid residue F (Mg(OH)2 filter cake initial product).

[0050] (4) Solid slag F is subjected to three-stage countercurrent pulping and washing: Solid slag F is pulped and washed in the first stage with secondary filtrate at a liquid-to-solid ratio of 5:1, and solid-liquid separation is obtained to obtain primary filtrate and filter cake a; Filter cake a is pulped and washed in the second stage with tertiary filtrate at a liquid-to-solid ratio of 5:1, and solid-liquid separation is obtained to obtain secondary filtrate and filter cake b; Filter cake b is pulped and washed in the third stage with distilled water at a liquid-to-solid ratio of 5:1, and allowed to settle for 4 hours. The supernatant is the tertiary filtrate, and the lower emulsion is the Mg(OH)2 slurry; The tertiary filtrate (pH 11.0) and the emulsion Mg(OH)2 slurry are separated.

[0051] (5) According to the solid content of the emulsion Mg(OH)2, a certain amount of distilled water and sodium dodecylbenzenesulfonate (accounting for 2% of the solid content in the emulsion Mg(OH)2 slurry) are added to adjust the solid content and control the solid-liquid ratio to 30:70 (solid content is 30%). The magnesium-based flue gas desulfurizer is prepared for flue gas desulfurization and the desulfurization efficiency is 95.8%.

[0052] In this process, the Mg(OH)2 slurry obtained in step (4) is separated into solid and liquid phases and then dried to prepare the Mg(OH)2 finished product. Its main components, by mass percentage, are: CaO 0.80%, Mg(OH)2 94.54%, and Cl 0.12%; which meets the Class III qualified product standard of HG / T 3607-2007 (CaO≤1%, Mg(OH)2≥92%, Cl≤0.5%).

[0053] Example 2 describes a method for preparing a magnesium-based flue gas desulfurizer using molten salt chlorination slag, which specifically includes the following steps:

[0054] (1) Molten salt chlorination residue and water were leached in a mass ratio of 1:2. After leaching for 18 hours, solid and liquid were separated to obtain leachate A.

[0055] (2) Add NaOH solution (20% by mass) to leachate A to adjust the pH to 5.5, then add sodium carbonate (20% by mass) to adjust the pH to 7.3, and finally add sodium hypochlorite (5% by mass) to adjust the pH to 7.8. After stirring for 8 hours, perform solid-liquid separation to obtain filtrate C.

[0056] (3) Based on the Mg in filtrate C 2+ Concentration, according to n(OH) - ): n(Mg 2+ The ratio of NaOH solution (20% by mass) to filtrate C was calculated to be 1.95:1. NaOH solution and filtrate C were mixed and reacted by a two-way feeding method. After 1 hour of mixing and reaction, solid-liquid separation was performed to obtain solid residue F (Mg(OH)2 filter cake initial product).

[0057] (4) Solid slag F is subjected to three-stage countercurrent pulping and washing: Solid slag F is pulped and washed in the first stage with the secondary filtrate at a liquid-to-solid ratio of 6:1, and the solid and liquid are separated to obtain the first-stage filtrate and filter cake a; Filter cake a is pulped and washed in the second stage with the tertiary filtrate at a liquid-to-solid ratio of 6:1, and the solid and liquid are separated to obtain the second-stage filtrate and filter cake b; Filter cake b is pulped and washed in the third stage with distilled water at a liquid-to-solid ratio of 6:1, and allowed to settle for 4 hours. The supernatant is the third-stage filtrate, and the lower emulsion is the Mg(OH)2 slurry; The third-stage filtrate (pH 10.5) and Mg(OH)2 filter cake are separated; The filter cake is dried at 105℃ for 8 hours to obtain the Mg(OH)2 finished product. Its main components by mass percentage are: CaO 0.76%, Mg(OH)2 92.63%, Cl 0.10%; It meets the Class III qualified product standard of HG / T3607-2007.

[0058] (5) The Mg(OH)2 product is crushed and sieved, with a particle size D90≤5μm. A certain amount of Mg(OH)2 product is mixed with a certain amount of distilled water and pore-forming agent to make a slurry. The mass ratio of Mg(OH)2 product, distilled water and pore-forming agent is controlled to be 35:64:1. The mixture is stirred and mixed evenly to obtain a magnesium-based flue gas desulfurizing agent for flue gas desulfurization. The desulfurization efficiency is 97.5%.

[0059] Example 3 describes a method for preparing a magnesium-based flue gas desulfurizer using molten salt chlorination slag, which specifically includes the following steps:

[0060] (1) Molten salt chlorination residue and water were leached in a mass ratio of 1:1.8. After leaching for 20 hours, solid and liquid were separated to obtain leachate A.

[0061] (2) Add NaOH solution (30% by mass) to leachate A to adjust the pH to 4.0, then add sodium carbonate (20% by mass) to adjust the pH to 6.9, and finally add sodium hypochlorite (8% by mass) to adjust the pH to 7.9. After stirring and reacting for 15 hours, perform solid-liquid separation to obtain filtrate C.

[0062] (3) Based on the Mg in filtrate C 2+ Concentration, according to n(OH) - ): n(Mg 2+ The ratio of NaOH solution (30% by mass) to filtrate C was calculated to be 2.05:1. The NaOH solution and filtrate C were mixed and reacted by a two-way feeding method. After 1 hour of mixing and reaction, solid-liquid separation was performed to obtain solid residue F (Mg(OH)2 filter cake initial product).

[0063] (4) Solid slag F is subjected to three-stage countercurrent pulping and washing: Solid slag F is pulped and washed in the first stage with the secondary filtrate at a liquid-to-solid ratio of 5:1, and the solid and liquid are separated to obtain the first-stage filtrate and filter cake a; Filter cake a is pulped and washed in the second stage with the tertiary filtrate at a liquid-to-solid ratio of 5:1, and the solid and liquid are separated to obtain the second-stage filtrate and filter cake b; Filter cake b is pulped and washed in the third stage with water (Cl concentration of 186 mg / L) at a liquid-to-solid ratio of 5:1, and allowed to settle for 4 hours. The supernatant is the third-stage filtrate, and the lower emulsion is the Mg(OH)2 slurry; The third-stage filtrate (pH 11.0) and the emulsion Mg(OH)2 slurry are separated.

[0064] (5) According to the solid content of the emulsion Mg(OH)2, a certain amount of water (Cl concentration of 179 mg / L) and sodium dodecylbenzenesulfonate (accounting for 4% of the solid content in the emulsion Mg(OH)2 slurry) are added to adjust the solid content and control the solid-liquid ratio to 33:67 (solid content of 33%). The magnesium-based flue gas desulfurizer is prepared for flue gas desulfurization and the desulfurization efficiency is 96.01%.

[0065] In this process, the Mg(OH)2 slurry obtained in step (4) is separated into solid and liquid phases and then dried to prepare the Mg(OH)2 finished product. Its main components, by mass percentage, are: CaO 0.68%, Mg(OH)2 93.14%, and Cl 0.32%; which meets the Class III qualified product standard of HG / T 3607-2007.

Claims

1. A method for preparing magnesium-based flue gas desulfurizing agent using molten salt chlorination slag, characterized in that, Includes the following steps: S1. The molten salt chlorination slag is leached with water, and after full leaching, solid-liquid separation is performed to obtain leachate A and solid slag B; S2. The leachate A undergoes multi-stage pH adjustment, and after sufficient reaction, solid-liquid separation is performed to obtain filtrate C and solid residue D. S3. Add NaOH to filtrate C, and after the reaction is complete, separate the solid and liquid to obtain filtrate E and solid residue F; S4. Solid slag F is subjected to three-stage countercurrent pulping and washing, and then allowed to settle to remove the supernatant, resulting in an emulsion Mg(OH)2 slurry; S5. Distilled water or Cl is added to the emulsion Mg(OH)2 slurry - Clean water with concentration <200 mg / L is added to adjust the solid content of the emulsion Mg(OH)2 slurry to 30-35%, and a magnesium-based flue gas desulfurization agent is obtained.

2. The method according to claim 1, characterized in that: In step S1, the mass ratio of molten salt chlorination residue to water is 1:1.8~2.1, and the water soaking time is 18~24h.

3. The method according to claim 1, characterized in that: In step S2, the multi-stage pH adjustment specifically involves: adding NaOH to leachate A to adjust the pH to 4.0-6.0, then adding sodium carbonate to adjust the pH to 6.9-7.5, and finally adding sodium hypochlorite to adjust the pH to 7.8-8.

2.

4. The method according to claim 1, characterized in that: In step S3, filtrate C and NaOH are mixed and reacted using a two-way feeding method, and the OH in NaOH... - With Mg in filtrate C 2+ The molar ratio is (1.95~2.05):1; the mixing reaction time is not less than 1 hour.

5. The method according to claim 1, characterized in that: In step S4, the three-stage countercurrent pulping and washing specifically involves: using an appropriate amount of secondary filtrate to perform primary pulping and washing on the solid slag F, separating the solid and liquid to obtain primary filtrate and filter cake a; using an appropriate amount of tertiary filtrate to perform secondary pulping and washing on filter cake a, separating the solid and liquid to obtain secondary filtrate and filter cake b; and using an appropriate amount of distilled water or Cl... - The filter cake b was subjected to three-stage pulping and washing with water with a concentration of <200 mg / L, followed by static sedimentation and separation to obtain a three-stage filtrate and an emulsion Mg(OH)2 slurry.

6. The method according to claim 5, characterized in that: During primary pulping and washing, the liquid-to-solid ratio of the secondary filtrate to the solid residue F is ≥5; during secondary pulping and washing, the liquid-to-solid ratio of the tertiary filtrate to the filter cake a is ≥5; during tertiary pulping and washing, the liquid-to-solid ratio of distilled water or clean water to the filter cake b is ≥5.

7. The method according to claim 1, characterized in that: In step S4, the obtained emulsion Mg(OH)2 slurry is separated into solid and liquid phases and then dried to obtain a finished Mg(OH)2 product that meets the Class III qualified product standard of HG / T 3607-2007.

8. The method according to claim 1, characterized in that: In step S5, sodium dodecylbenzenesulfonate is added during the process of adjusting the solid content of the Mg(OH)2 emulsion slurry. The amount added is 2-4% of the solid content in the Mg(OH)2 emulsion slurry.

9. The method according to claim 7, characterized in that: Mg(OH)2 product, Cl - A mixture of water with a concentration of <200 mg / L and a pore-forming agent, after maturation and pulping, can be used directly as a desulfurizing agent.

10. The method according to claim 9, characterized in that: The pore-forming agent is at least one of starch, wood flour, rice husk, and polystyrene / corn starch mixture; the amount of the pore-forming agent added is 0.1-1% of the total mass of the desulfurizer.

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