A method for treating a silicic acid-containing acid gas

Abstract

The present application belongs to the technical field of industrial waste gas treatment, and discloses a method for treating silicon-containing acidic gas, which aims at the problem of treating the acidic waste gas containing hydrogen fluoride and submicron silicon particles generated in the wet smelting of tantalum and niobium, and solves the problems of low purification efficiency, easy crystallization blockage, agglomeration of active components of the absorption material, and high operation cost in the traditional process. In the method, the silicon-containing acidic gas is converted into an acid-containing liquid by being absorbed by deionized water in a prewashing tower, and then the acid-containing liquid is added with a mesoporous aluminum-zinc-based composite absorption material synthesized by using PAA micelles as a soft template, and after the pH is adjusted, the purification is completed by stirring and reaction, and then filtration and separation are performed. The present application utilizes the space blocking effect of PAA micelles to inhibit particle agglomeration and improve the exposure rate of active sites, and the composite absorption material realizes the synergistic effect of silicon capture and fluorine removal, so that high purification efficiency is achieved without the need for high-dose medicaments, and the system has strong stability, can effectively avoid equipment blockage and corrosion, and is suitable for efficient and environmentally-friendly treatment of silicon-containing acidic waste gas generated in the wet smelting of tantalum and niobium.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste gas treatment technology, specifically relating to a method for treating silica-containing acid gases. Background Technology

[0002] In the hydrometallurgical process of tantalum and niobium, the acidolysis of the ore generates a large amount of silica-containing acidic waste gas. This waste gas is mainly composed of hydrogen fluoride, accompanied by a large number of submicron-sized silicon particles. Both readily dissolve or disperse in the process liquid, forming a highly stable liquid-phase mass transfer system, making it significantly more difficult to treat than conventional acidic waste gas. In practical engineering applications, traditional processes combining alkaline scrubbing, physical adsorption, and chemical absorption generally suffer from low liquid-phase purification efficiency, high operating costs, and poor system stability, making it difficult to meet increasingly stringent environmental emission requirements.

[0003] In current engineering practice, traditional combined processes of alkaline spraying, physical adsorption, and chemical absorption generally suffer from high operating costs and poor system stability, making it difficult to meet increasingly stringent environmental emission requirements. The current technical bottleneck mainly lies in the absorbent material itself: First, conventional absorbent materials lack effective means to disperse and regulate the active components. Most mainstream materials are prepared by physically mixing inorganic carriers and metal active components, which leads to severe agglomeration of the active components, extremely low exposure of active sites, and insufficient contact and reaction with silicon particles and HF in the liquid phase, thus limiting the purification efficiency.

[0004] Secondly, the absorbent materials exhibit extremely poor structural stability and interfacial compatibility under complex operating conditions. In environments with strong acid erosion and high concentrations of silicon ions, physically composite materials are prone to component shedding, pore blockage, and silicate crystal precipitation, resulting in frequent system shutdowns for cleaning, short service life, and high operating costs. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for treating silica-containing gases. The core of this invention lies in constructing a PAA micellar soft template-mediated mesoporous alumina-zinc-based composite adsorbent material. By controlling the microstructure, the problem of zinc-based particle aggregation and poor interfacial stability is solved, achieving highly efficient purification.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for treating silica-containing gases includes the following steps: S11. Waste gas absorption and pretreatment The silica-containing acidic gas is passed into a pre-washing tower filled with deionized water absorbent. The gas-liquid ratio is controlled at 1:3-1:5 and the absorption temperature is 25-35℃, so that HF ​​in the gas is fully absorbed by silicon particles and converted into process liquid. After pretreatment to remove large particulate impurities, pretreated acidic liquid is obtained.

[0007] S12, Liquid-phase purification reaction Take the pretreated acidic liquid, add mesoporous alumina-zinc-based composite absorbent, adjust the pH of the system to 6-7 with dilute sodium hydroxide solution, first stir at high speed to ensure full contact between liquid and solid, then stir at low speed for adsorption, and obtain purified liquid.

[0008] S13. After-treatment and emissions After the reaction is complete, the material is filtered and separated, the purified liquid is discharged in compliance with standards, and the waste absorbent material is disposed of in accordance with hazardous waste regulations.

[0009] The preparation method of the mesoporous alumina-zinc-based composite absorbent material includes the following steps: Preparation of S21 and PAA micelle soft template solutions: Dissolve 0.5-2g of polyacrylic acid (PAA) with a molecular weight of 5000 in 4-6mL of deionized water and stir for 10-15min until completely dissolved to form a homogeneous aqueous solution. Under continuous stirring, slowly add 20-30mL of anhydrous ethanol to induce PAA chain aggregation by utilizing the difference in polarity between alcohol and water, forming a stable PAA micelle dispersion system as a soft template solution.

[0010] S22, Mesoporous alumina precursor combined with PAA micelles: Measure 30-40 mL of aluminum isopropoxide, 10-12 mL of N,N-dimethylformamide, 50-60 mL of anhydrous ethanol, and 2-3 mL of 5% hydrochloric acid, mix them, stir evenly at 45-55℃, and then slowly add them dropwise to the PAA micelle soft template solution in step S21. Control the dropping rate and stirring intensity to avoid instantaneous and violent hydrolysis and aggregation of the precursor. Continue stirring for 1-1.5 h to obtain PAA micelle-mesoporous alumina precursor composite sol.

[0011] S23, Dispersion and Hydrothermal Synthesis: Mix 1.36-2.72g of zinc chloride and 3.84-7.68g of citric acid evenly, and add them to the composite sol described in step S22. After all the sol has been added, continue ultrasonic dispersion for 5-8 minutes to ensure that the zinc-based active component is uniformly dispersed within the PAA micelle confinement space, forming a mixed system. Transfer the mixed system to a hydrothermal reactor and perform a hydrothermal reaction at 120-140℃ for 8-10 hours. Allow it to cool naturally to room temperature, and collect the precipitate by centrifugation. Wash the precipitate three times with anhydrous ethanol and dry it in a vacuum drying oven at 60℃ for 12 hours to obtain the mesoporous alumina-zinc-based composite absorbent material.

[0012] The beneficial effects of this invention are as follows: (1) This invention utilizes PAA micelles as a soft template to create a steric hindrance effect. During the hydrothermal process, the PAA micelles strictly restrict the aggregation of the precursor, ultimately constructing a well-developed mesoporous alumina-zinc-based framework. This structure significantly increases the exposure of active sites.

[0013] (2) The mesoporous alumina-zinc-based framework prepared by this invention has a high specific surface area, and the material exhibits a loose, well-connected mesoporous structure with no obvious particle agglomeration. The zinc-based active components are highly uniformly dispersed in the mesoporous alumina support. This structure can provide sufficient adsorption sites and reaction channels for the liquid phase system, which is beneficial for the capture of silicon particles in the liquid phase and the efficient mass transfer and reaction of HF.

[0014] (3) The composite absorbent material prepared by the present invention can simultaneously remove silicon particles and hydrogen fluoride from the system. Compared with traditional mixed adsorption materials, the removal efficiency of silicon and HF is significantly improved. Attached Figure Description

[0015] Figure 1 The images shown are transmission electron microscope (TEM) and scanning electron microscope (SEM) images of the material prepared in Example 1. Figure 1 (a) is a TEM photograph. Figure 1 (b) is a SEM image; Figure 2 Laser-irradiated images of PAA micelles; Figure 3 XRD curves of the material prepared in Example 1; Figure 4 TEM image of the material in Comparative Example 1; Figure 5 The N2 adsorption-desorption isotherm of the material is shown below. Figure 5 (a) is the material prepared in Example 1. Figure 5 (b) is the material prepared in Comparative Example 1; Figure 6 The figures show the silicon and HF removal rate curves in the liquid phase for Example 1 and Comparative Example 1, where... Figure 6 (a) represents the silicon removal rate. Figure 6 (b) represents the HF removal rate. Detailed Implementation

[0016] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the concept of the invention, they should all fall within the protection scope of the present invention.

[0017] The preparation method of the present invention will be described below through specific embodiments and comparative examples.

[0018] Example 1 S1. Preparation of PAA micelles: Dissolve 0.5g of PAA with a molecular weight of 5000 in 4mL of ammonia water and stir for 10min until completely dissolved; slowly add 20mL of anhydrous ethanol at 1mL / min and continue stirring until homogeneous to form a stable PAA micelle soft template solution.

[0019] S2. Measure 30 mL of aluminum isopropoxide, 10 mL of N,N-dimethylformamide, 50 mL of anhydrous ethanol and 2 mL of 5% hydrochloric acid, mix them, and slowly add them dropwise to the micelle solution. Stir at 45°C for 1 h to obtain the composite sol.

[0020] S3. Mix 1.36g of zinc chloride and 3.84g of citric acid evenly, add to the composite sol, and ultrasonically disperse for 5 minutes to form a mixed system.

[0021] S4. Transfer the mixture to a hydrothermal reactor, heat at 120℃ for 8 hours, cool, centrifuge, wash three times with anhydrous ethanol, and vacuum dry at 60℃ for 12 hours to obtain mesoporous alumina-zinc-based composite absorbent material.

[0022] S5. Pass the silica-containing gas into the pre-washing tower filled with deionized water absorbent, control the gas-liquid ratio to 1:3 and the absorption temperature to 25℃ to complete the absorption and conversion, and then pre-treat to obtain the process liquid; take 200mL of this liquid, add 40mg of composite absorbent material, adjust the system to a weakly acidic environment with 1% sodium hydroxide solution, stir at 400r / min for liquid-solid contact for 8min, and stabilize the reaction at 120r / min for 160min. The purified liquid meets the discharge standards, and the waste absorbent material is disposed of in accordance with the hazardous waste regulations.

[0023] Example 2 S1. Preparation of PAA micelles: Dissolve 1g of PAA with a molecular weight of 5000 in 5mL of ammonia water and stir for 12min until completely dissolved; slowly add 25mL of anhydrous ethanol at 1mL / min and continue stirring until homogeneous to form a stable PAA micelle soft template solution.

[0024] S2. Measure 35 mL of aluminum isopropoxide, 11 mL of N,N-dimethylformamide, 55 mL of anhydrous ethanol and 2.5 mL of 5% hydrochloric acid, mix them, and slowly add them dropwise to the micelle solution. Stir at 50°C for 1.2 h to obtain a composite sol.

[0025] S3. Mix 2.04g of zinc chloride and 5.76g of citric acid evenly, add to the composite sol, and ultrasonically disperse for 6 minutes to form a mixed system.

[0026] S4. Transfer the mixture to a hydrothermal reactor, heat at 130℃ for 9 hours, cool, centrifuge, wash three times with anhydrous ethanol, and vacuum dry at 60℃ for 12 hours to obtain mesoporous alumina-zinc-based composite absorbent material.

[0027] S5. Pass the silica-containing gas into the pre-washing tower filled with deionized water absorbent, control the gas-liquid ratio to 1:4 and the absorption temperature to 30℃ to complete the absorption and conversion, and then pre-treat to obtain the process liquid; take 200mL of this liquid, add 70mg of composite absorbent material, adjust the system to a weakly acidic environment with 3% sodium hydroxide solution, stir at 400r / min for 9min of liquid-solid contact, and stabilize the reaction at 120r / min for 240min. The purified liquid meets the discharge standards, and the waste absorbent material is disposed of in accordance with the hazardous waste regulations.

[0028] Example 3 S1. Preparation of PAA micelles: Dissolve 2g of PAA with a molecular weight of 5000 in 6mL of ammonia water and stir for 15min until completely dissolved; slowly add 30mL of anhydrous ethanol at 1mL / min and continue stirring until homogeneous to form a stable PAA micelle soft template solution.

[0029] S2. Measure 40 mL of aluminum isopropoxide, 12 mL of N,N-dimethylformamide, 60 mL of anhydrous ethanol and 3 mL of 5% hydrochloric acid, mix them, and slowly add them dropwise to the micelle solution. Stir at 55°C for 1.5 h to obtain a composite sol.

[0030] S3. Mix 2.72g of zinc chloride and 7.68g of citric acid evenly, add to the composite sol, and ultrasonically disperse for 8 minutes to form a mixed system.

[0031] S4. Transfer the mixture to a hydrothermal reactor, heat at 140℃ for 10 hours, cool, centrifuge, wash three times with anhydrous ethanol, and vacuum dry at 60℃ for 12 hours to obtain mesoporous alumina-zinc-based composite absorbent material.

[0032] S5. Pass the silica-containing gas into the pre-washing tower filled with deionized water absorbent, control the gas-liquid ratio to 1:5 and the absorption temperature to 35℃ to complete the absorption and conversion, and then pre-treat to obtain the process liquid; take 200mL of this liquid, add 100mg of composite absorbent material, adjust the system to a weakly acidic environment with 5% sodium hydroxide solution, stir at 400r / min for liquid-solid contact for 10min, and stabilize the reaction at 120r / min for 300min. The purified liquid meets the discharge standards, and the waste absorbent material is disposed of in accordance with the hazardous waste regulations.

[0033] Comparative Example 1 The S1 micelle preparation step was omitted, and aluminum isopropoxide, N,N-dimethylformamide, ethanol and hydrochloric acid were directly mixed to prepare a sol. The remaining raw materials, ratios and operating parameters were completely consistent with those in Example 1, and mesoporous alumina and zinc-based materials were directly synthesized.

[0034] Figure 1 These are TEM and SEM images of the material prepared in Example 1, wherein... Figure 1 (a) is a TEM photograph. Figure 1 (b) is a SEM image; as can be seen from the image, the material exhibits a loose, well-connected mesoporous structure with no obvious particle agglomeration, and the zinc-based active components are highly uniformly dispersed in the mesoporous alumina carrier.

[0035] This structure can provide sufficient adsorption sites and reaction channels for the liquid phase system, which is beneficial for the capture of silicon particles in the liquid phase and the efficient mass transfer and reaction of HF.

[0036] Figure 2 The image shows a laser irradiation pattern of the PAA micelle solution, revealing a clear Tyndall effect. This demonstrates that under the formulation conditions of this invention, PAA can form a stable and uniform micelle dispersion system, which can serve as an effective soft template to achieve precise control of the mesoporous structure and spatially confined dispersion of active components.

[0037] Figure 3 The XRD pattern of the material in Example 1 is shown. Characteristic diffraction peaks of alumina and zinc oxide appear in the pattern. The peaks are regular in shape and free of impurities, indicating that the product phase is pure and has good crystallinity. The weak diffraction peak intensities indicate that the grain size is small and the zinc-based component is well dispersed, which is conducive to the full exposure of active sites in the liquid phase.

[0038] Figure 4 The image shows a TEM image of the material in Comparative Example 1 without the use of a PAA micelle soft template. It is evident that the material exhibits agglomeration, a dense structure, few pores, poor connectivity, and a significant reduction in specific surface area and the number of active sites.

[0039] Figure 5 The N2 adsorption-desorption isotherm of the material is shown below. Figure 5 (a) is the material prepared in Example 1. Figure 5 (b) The material prepared in Comparative Example 1. Example 1 exhibits a typical type IV isotherm and H1 hysteresis loop, demonstrating a mesoporous structure, high specific surface area, and abundant pores. Comparative Example 1 shows no obvious mesoporous characteristics, low adsorption capacity, and small specific surface area. This indicates that PAA micellar soft templates are key to constructing high specific surface area mesoporous structures and adapting to liquid-phase purification.

[0040] Figure 6 The figures show the silicon and HF removal rate curves in the liquid phase for Example 1 and Comparative Example 1, where... Figure 6 (a) represents the silicon removal rate. Figure 6(b) represents the HF removal rate. Example 1 showed significantly higher removal rates of both silicon particles and HF in the liquid phase compared to Comparative Example 1, with a faster reaction rate and a higher equilibrium removal rate. This invention utilizes PAA micellar soft templates for in-situ synthesis, significantly improving the material's pore structure, active component dispersibility, and liquid-phase stability, achieving silicon capture and defluorination. It can efficiently purify silicic acid gaseous components transferred from the gas phase to the liquid phase.

Claims

1. A method for treating silica-containing acidic gases, characterized in that, Includes the following steps: S1. Waste gas absorption and pretreatment: The silica-containing acidic gas is passed into a pre-washing tower filled with deionized water absorbent, so that the hydrogen fluoride and silicon particles in the gas are fully absorbed and converted into process liquid. After pretreatment to remove large particulate impurities, the pretreated acidic liquid is obtained. S12. Liquid-phase purification reaction: Take the pretreated acidic liquid, add mesoporous alumina-zinc-based composite absorbent, adjust the pH of the system to 6-7 with dilute sodium hydroxide solution, first stir at high speed to make the liquid and solid fully contact, then stir at low speed to carry out adsorption, and obtain purified liquid. S13. Post-treatment and discharge: After the reaction is completed, the liquid is filtered and separated, the purified liquid is discharged in compliance with standards, and the waste absorbent material is disposed of in accordance with the hazardous waste regulations. The preparation method of the mesoporous alumina-zinc-based composite absorbent material includes the following steps: S21. Preparation of polyacrylic acid micelle soft template solution: Polyacrylic acid is dissolved in ammonia water, and anhydrous ethanol is slowly added under continuous stirring to induce the aggregation of polyacrylic acid segments to form a stable micelle dispersion system, i.e., soft template solution. S22. Composite of mesoporous alumina precursor and polyacrylic acid micelles: Aluminum isopropoxide, N,N-dimethylformamide, anhydrous ethanol and hydrochloric acid are mixed and stirred evenly. The mixture is then slowly added dropwise to the soft template solution in step S21 and stirred continuously to obtain a composite sol of polyacrylic acid micelles and mesoporous alumina precursor. S23. Dispersion and hydrothermal synthesis: Zinc chloride and citric acid are mixed evenly and added to the composite sol in step S22. The mixture is then ultrasonically dispersed and transferred to a reaction vessel for hydrothermal reaction. After naturally cooling to room temperature, the precipitate is collected by centrifugation, washed with anhydrous ethanol, and vacuum dried to obtain the mesoporous alumina-zinc-based composite absorbent material.

2. The method for treating silica-containing acidic gases according to claim 1, characterized in that, In step S11, the gas-liquid ratio in the pre-washing tower is controlled at 1:3-1:5, and the absorption temperature is 25-35℃.

3. The method for treating silica-containing acidic gases according to claim 1, characterized in that, In step S12, the high-speed stirring speed is 400 r / min and the stirring time is 8-10 min; the low-speed stirring speed is 120 r / min and the stabilization reaction time is 160-300 min.

4. The method for treating silica-containing acidic gases according to claim 1, characterized in that, In step S21, the molecular weight of polyacrylic acid is 5000, the amount used is 0.5-2g, the amount of deionized water is 4-6mL, the amount of anhydrous ethanol is 20-30mL, and the stirring and dissolving time is 10-15min.

5. The method for treating silica-containing acidic gases according to claim 1, characterized in that, The amounts of each raw material used in step S22 are as follows: 30-40 mL of aluminum isopropoxide, 10-12 mL of N,N-dimethylformamide, 50-60 mL of anhydrous ethanol, and 2-3 mL of 5% hydrochloric acid; the stirring temperature is 45-55℃, and the stirring time is 1-1.5 h.

6. The method for treating silica-containing acidic gases according to claim 1, characterized in that, In step S23, the amount of zinc chloride used is 1.36-2.72g, the amount of citric acid used is 3.84-7.68g, and the ultrasonic dispersion time is 5-8min.

7. The method for treating silica-containing acidic gases according to claim 1, characterized in that, In step S23, the hydrothermal reaction temperature is 120-140℃ and the reaction time is 8-10h; the vacuum drying temperature is 60℃ and the drying time is 12h; the precipitate is washed three times with anhydrous ethanol.

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