Regeneration method of waste denitration catalyst
By treating spent denitrification catalysts with acid and reducing agents, arsenic is dissolved while active components are retained. This solves the problem of active component loss caused by arsenic removal in existing technologies, and achieves efficient and low-cost regeneration of spent denitrification catalysts.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-25
- Publication Date
- 2026-04-03
AI Technical Summary
In the regeneration process of waste denitrification catalysts, the existing technology for removing arsenic leads to the leaching of the active component VW, which increases regeneration costs and the difficulty of wastewater treatment. In addition, it generates a large amount of waste residue and has high costs for the disposal of hazardous solid waste.
The waste denitrification catalyst is reacted with a first treatment liquid containing acid and reducing agent to dissolve arsenic. After the arsenic is dissolved, it is converted into a precipitate by alkaline substances and decomposed by heating to obtain arsenic trioxide, thus achieving selective arsenic dissolution and retention of active components.
This method achieves efficient arsenic leaching and low leaching of active components, simplifies wastewater treatment, reduces regeneration costs, and improves catalyst regeneration efficiency and the purity of white arsenic products.
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Figure CN121775918A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to denitrification catalysts, and more particularly to a method for regenerating arsenic-containing waste denitrification catalysts. Background Technology
[0002] The spent denitrification catalyst (or deactivated denitrification catalyst) contains arsenic oxides (As2O3 or As2O5). In order to regenerate the spent denitrification catalyst, the arsenic element needs to be removed.
[0003] Some existing technologies employ alkaline dissolution for arsenic removal, which involves leaching spent arsenic-containing catalysts with a sodium hydroxide solution to transfer arsenic into the solution. However, alkaline dissolution not only efficiently dissolves harmful arsenic oxides but also dissolves the active components VW (V₂O₅ and WO₃) from the catalyst, reducing its activity. This necessitates replenishing the active components VW during catalyst regeneration, increasing regeneration costs.
[0004] Furthermore, the alkaline leaching process yields a complex solution containing impurities such as V, W, and As. V and As are both toxic metals, increasing the difficulty and cost of treating catalyst regeneration wastewater. For waste liquid treatment, precipitation can be obtained through oxidation and calcification to ultimately produce calcium arsenate. However, this also contains calcium tungstate and calcium vanadate, increasing the amount of waste residue and the presence of harmful elements, thus raising the disposal cost of hazardous solid waste. Summary of the Invention
[0005] To overcome at least one of the defects of the prior art, in a first aspect, one embodiment of the present invention provides a method for regenerating waste denitrification catalyst, comprising the following steps: The waste denitrification catalyst is mixed with the first treatment liquid to dissolve the arsenic element in the waste denitrification catalyst, thereby obtaining an arsenic-containing treatment liquid and an arsenic-removing catalyst. The arsenic-containing treatment solution is reacted with a first alkaline substance to convert the arsenic and iron elements therein into precipitates. The precipitate is reacted with a second alkaline substance to dissolve the arsenic-containing precipitate, yielding a solution containing ammonium metaarsenite; and The solution containing ammonium metaarsenite was heated and decomposed to obtain arsenic trioxide; The first treatment solution contains an acid and a reducing agent, wherein the reducing agent includes a ferrous salt.
[0006] The regeneration method for waste denitrification catalyst according to one embodiment of the present invention can achieve efficient leaching of oxides of harmful arsenic and low leaching of active components, and selective dissolution of arsenic, thereby achieving efficient regeneration of arsenic-containing waste denitrification catalyst. Attached Figure Description
[0007] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention. Wherein: Figure 1 This is a flowchart illustrating a method for regenerating a waste denitrification catalyst according to one embodiment of the present invention. Detailed Implementation
[0008] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the description herein is for illustrative purposes only and not intended to limit the present invention.
[0009] One embodiment of the present invention provides a method for regenerating waste denitrification catalyst, comprising the following steps: S1: The spent denitrification catalyst (SCR catalyst) is mixed and reacted with the first treatment liquid (reduction-acid leaching) to dissolve the arsenic element in the spent denitrification catalyst, resulting in an arsenic-containing treatment liquid and an arsenic-removing catalyst; S2: The arsenic-containing treatment solution is reacted with the first alkaline substance to convert the arsenic and iron elements into precipitates. S3: The precipitate is reacted with a second alkaline substance to dissolve the arsenic-containing precipitate (arsenic trioxide or metaarsenic acid), yielding a solution containing ammonium metaarsenite; and S4: The solution containing ammonium metaarsenite is heated and decomposed to obtain arsenic trioxide; The first treatment solution contains acid and a reducing agent, the reducing agent including ferrous salt.
[0010] In one embodiment, the first alkaline substance includes one or more of ammonia, alkaline ammonium salt, sodium carbonate, monoethanolamine, and urea; the second alkaline substance includes ammonia and / or alkaline ammonium salt.
[0011] In one embodiment, the basic ammonium salt of the first basic substance and / or the second basic substance includes ammonium carbonate and / or ammonium bicarbonate.
[0012] In one embodiment, the waste denitrification catalyst comprises arsenic oxide (As₂O₃ and / or As₂O₅), the active component vanadium pentoxide (V₂O₅), and a support. Further, the support may include titanium dioxide and silicon dioxide.
[0013] In one embodiment, the waste denitrification catalyst may be treated to remove ash before being mixed with a first treatment liquid; the ash removal treatment includes soot blowing and washing.
[0014] In one embodiment, the waste denitrification catalyst can be blown away with a dust collection device, and then cleaned with a high-pressure water gun.
[0015] In one embodiment, the acid in the first treatment solution includes sulfuric acid and / or hydrochloric acid, and the reducing agent includes ferrous sulfate and / or ferrous chloride.
[0016] In one embodiment, the solvent of the first treatment liquid includes water.
[0017] In one embodiment, the following reaction may occur in step S1: As₂O₃ + H₂SO₄ = (AsO)₂SO₄ + H₂O As2O5+ H2SO4+ 2FeSO4=(AsO)2SO4+Fe2(SO4)3+H2O.
[0018] In one embodiment, based on the mass (100%) of the solvent contained in the first treatment solution, the mass content of acid in the first treatment solution can be 5-10%, for example 5.5%, 6%, 6.2%, 6.5%, 6.7%, 6.8%, 6.9%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.5%, 8.7%, 9%, 9.2% or 9.5%.
[0019] In one embodiment, based on the mass (100%) of the solvent contained in the first treatment liquid, the mass content of the reducing agent in the first treatment liquid can be 1-5%, more specifically 1-4%, for example 1.5%, 1.8%, 2%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.8%, 3.0%, 3.2%, 3.5%, 3.6%, 3.7%, 4.0%, or 4.5%.
[0020] In this article, the mass content of acid and reducing agent in the first treatment solution is based on the mass of solvent.
[0021] In one embodiment, in step S1, the temperature at which the waste denitrification catalyst is mixed with the first treatment liquid can be 20–50°C, for example 22°C, 24°C, 25°C, 26°C, 28°C, 30°C, 32°C, 35°C, 37°C, 40°C, or 45°C; and the time can be 15–50 min, for example 18 min, 20 min, 25 min, 30 min, 35 min, 40 min, or 45 min.
[0022] In one embodiment, an acid, a ferrous salt, and a solvent are mixed to prepare a first treatment solution. Further, the solvent may be water (e.g., deionized water). The acid may be sulfuric acid and / or hydrochloric acid. The ferrous salt is a soluble ferrous salt, such as one or more of ferrous sulfate and its hydrate, ferrous chloride and its hydrate.
[0023] In one embodiment, a permeabilizer is included in the reaction system of the waste denitrification catalyst and the first treatment liquid to further improve the arsenic removal effect.
[0024] In one embodiment, the penetrant may be contained in the first treatment liquid, or it may be added to the mixed system after the waste denitrification catalyst is mixed with the first treatment liquid.
[0025] In one embodiment, the mass content of the penetrant can be 0.05 to 0.2%, for example, 0.06%, 0.08%, 0.1%, 0.12%, 0.15% or 0.18%, based on the mass of the first treatment liquid.
[0026] In one embodiment, the penetrant may include one or more of penetrant OEP, penetrant JFC, and penetrant OE.
[0027] In one embodiment, the mass ratio of the waste denitrification catalyst to the first treatment liquid can be 1:(0.5-5), for example 1:0.6, 1:0.8, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4 or 1:4.5.
[0028] In one embodiment, during the mixing and reaction of the waste denitrification catalyst and the first treatment liquid in step S1, the reaction system is subjected to ultrasonic bubbling to further improve the arsenic removal effect.
[0029] In one embodiment, the ultrasonic frequency in step S1 can be 28–40 kHz, for example 30 kHz, 32 kHz, 35 kHz or 38 kHz; the ultrasonic power can be 30–50 W / L, for example 32 W / L, 35 W / L, 38 W / L, 40 W / L, 42 W / L, 45 W / L or 48 W / L; and the ultrasonic time can be 5–30 min, for example 10 min, 15 min, 20 min, 23 min, 24 min, 25 min, 26 min, 27 min or 28 min.
[0030] In one embodiment, the pressure of the bubbling (compressing) gas in step S1 can be 0.2 to 0.4 MPa, for example 0.3 MPa; the bubbling time can be 10 to 20 minutes, for example 12 minutes, 15 minutes or 18 minutes.
[0031] In one embodiment, after the reaction in step S1 is completed, the system is subjected to solid-liquid separation to obtain an arsenic-containing treatment liquid and an arsenic removal catalyst. Further, the arsenic removal catalyst can be cleaned and dried.
[0032] In one embodiment, in step S2, a first alkaline substance is added to the arsenic-containing treatment solution obtained in step S1 to react, so that the arsenic and iron elements in the treatment solution are converted into precipitates. The first alkaline substance can adjust the pH of the reaction system in step S2 to 1–10, more specifically 2–9, and even more specifically 4–6, for example, 2, 2.5, 2.6, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, or 9.5.
[0033] In one embodiment, the following reaction may occur in step S2: 2AsO + +2OH - = As2O3 H2O (2HAsO2) ↓ Fe 3+ +3OH - =Fe(OH) 3(絮凝剂） In the reaction system of step S2, arsenic ions will be converted into As2O3 (or its hydrate HAsO2), while Fe in the solution... 3+ At this pH, ions also generate Fe(OH)3, which has a flocculating effect, and achieve As2O3 flocculation and precipitation, thereby improving the precipitation efficiency of arsenic and providing raw materials for the preparation of high-purity white arsenic.
[0034] In one embodiment, in step S2, a first alkaline substance may be added to the arsenic-containing treatment solution under stirring to maintain a uniform concentration of hydroxide ions in the solution. Further, the first alkaline substance may be added in the form of an aqueous solution.
[0035] In one embodiment, in step S2, after the first alkaline substance is added, the reaction system is allowed to stand for 30 to 150 minutes, for example, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, 115 minutes, 118 minutes, 120 minutes, 122 minutes, 125 minutes, 130 minutes, or 140 minutes.
[0036] In one embodiment, the reaction time of step S2 (i.e. the reaction time of the arsenic-containing treatment solution with the first alkaline substance) can be 30 to 120 min, for example 40 min, 50 min, 55 min, 58 min, 59 min, 60 min, 61 min, 62 min, 65 min, 70 min, 80 min, 90 min, 100 min or 110 min.
[0037] In one embodiment, the temperature of the reaction system in step S2 (i.e., the reaction temperature of the arsenic-containing treatment solution with the first alkaline substance) can be 60 to 90°C, for example 65°C, 70°C, 75°C, 78°C, 79°C, 80°C, 81°C, 82°C or 85°C.
[0038] In one embodiment, the reaction of the precipitate with the second alkaline substance in step S3 can be carried out at a temperature of 40 to 60°C, for example, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C or 58°C.
[0039] In one embodiment, the reaction time between the precipitate and the second alkaline substance in step S3 can be 60 to 120 minutes, for example, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 90 minutes, 100 minutes, or 110 minutes.
[0040] In one embodiment, the pH value of the reaction system in step S3 (i.e., the precipitation and dissolution reaction system) can be 9 to 14, for example 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13 or 13.5; the addition of the second alkaline substance can bring the pH value of the system to the above range.
[0041] In one embodiment, the metaarsenic acid or arsenic trioxide formed in step S2 is both acidic and alkaline, while ferric hydroxide does not react with alkali. Therefore, the use of a second alkaline substance, an ammonia-based alkaline solution, can cause the metaarsenic acid precipitate to react, allowing arsenic to re-enter the solution and form ammonium metaarsenite, while ferric hydroxide remains in the form of a precipitate.
[0042] In one embodiment, in step S3, the solid precipitate obtained in step S2 is mixed with a solution of the second alkaline substance and heated under stirring to completely dissolve the arsenic-containing precipitate in the solid phase.
[0043] In one implementation, the reaction in step S3 can be: HAsO2+NH3 H2O = NH4AsO2 + H2O.
[0044] In one embodiment, the material after the reaction in step S3 is subjected to solid-liquid separation to obtain ferric hydroxide solid and ammonium metaarsenite solution.
[0045] In one embodiment, in step S4, the ammonium metaarsenite solution obtained in step S3 is heated and decomposed to obtain ammonia and arsenic trioxide (white arsenic). The ammonia can be absorbed by water and recycled, for example, as a first or second alkaline substance. The corresponding reaction is as follows: 2NH4AsO2 = As2O3↓ + H2O + 2NH3↑ H₂O + NH₃ = NH₃ H2O.
[0046] In one embodiment, in step S4, the solution containing ammonium meta-arsenite can be heated to decompose and evaporate to crystallize. That is, the solution containing ammonium meta-arsenite is heated to obtain arsenic trioxide. During the heating process, the solvent continuously evaporates and arsenic trioxide crystals precipitate.
[0047] In one embodiment, the temperature for heating and decomposition in step S4 can be 90–100°C, for example 92°C, 95°C, 96°C, 98°C, 99°C, or 100°C; the heating time can be 60–240 min, for example 70 min, 80 min, 90 min, 120 min, 150 min, 170 min, 180 min, 190 min, 200 min, 210 min, or 220 min.
[0048] In one embodiment, the arsenic trioxide obtained in step S4 is washed. To avoid dissolution of the solid during the washing process, a 10-30 wt% ethanol aqueous solution can be used for washing. Further, the washed solid can be dried. To avoid high-temperature volatilization, the drying temperature should not exceed 350°C, for example, 250°C.
[0049] In one embodiment, step S4 is performed in a device capable of condensing and recovering gas.
[0050] In one embodiment, the method for regenerating spent denitrification catalyst includes the following steps: Soot blowing and cleaning: The ash inside the waste denitrification catalyst module and channels is thoroughly removed by negative pressure dust collection equipment and blower dust collection chamber, and then the catalyst channels are further washed with high pressure water gun to remove ash. Preparation of the first treatment solution: Mix acid and water to prepare an acid solution of a certain concentration, add reducing agent to the acid solution to obtain the first treatment solution; Arsenic removal: The cleaned waste denitrification catalyst is mixed with the first treatment liquid and subjected to reduction-acid leaching to remove arsenic oxide from the catalyst, resulting in an arsenic-containing treatment liquid and an arsenic-removed catalyst. Arsenic-iron co-precipitation: Under stirring, a first alkaline substance is added to the arsenic-containing treatment solution, and the pH is adjusted to 1-10. After standing, precipitates containing arsenic and iron are obtained. Arsenic-iron separation: The precipitate containing arsenic and iron elements is mixed with a second alkaline substance and reacted under stirring to completely dissolve the arsenic compound in the solid phase, resulting in a solution containing ammonium metaarsenite and ferric hydroxide precipitate. The solution containing ammonium metaarsenite is obtained through solid-liquid separation. White arsenic precipitation: The solution containing ammonium metaarsenite is evaporated and crystallized. During the process, the ammonium metaarsenite decomposes, and the resulting solid is white arsenic, while the resulting liquid is ammonia.
[0051] One embodiment of the present invention discloses a method for regenerating a spent denitrification catalyst. By limiting the concentration of acid and the type of reducing agent contained in the first treatment liquid, As2O5, which is poorly soluble in acid, can be dissolved through reaction, while V2O5, which has oxidizing properties, is retained in the catalyst. This achieves efficient dissolution of arsenic and retention of vanadium, thereby improving the catalyst regeneration efficiency. At the same time, the efficient recovery of arsenic can yield high-purity white arsenic products, reducing the cost of wastewater and solid waste treatment and increasing the recovery value of arsenic.
[0052] One embodiment of the present invention discloses a method for regenerating waste denitrification catalysts. The method uses a reduction-acid leaching reaction to dissolve arsenic compounds in the catalyst, and then obtains white arsenic through hydrolysis-precipitation. This simplifies the wastewater treatment process, recovers valuable element arsenic, and yields arsenic trioxide as a byproduct during catalyst regeneration. It has excellent economic and environmental benefits.
[0053] The following describes a method for regenerating spent denitrification catalyst according to one embodiment of the present invention, with reference to specific examples. At least some of the raw materials and testing methods involved in each embodiment and comparative example are as follows.
[0054] raw material The waste denitrification catalyst to be treated was a honeycomb-shaped deactivated SCR catalyst module (a power plant under Shenhua Group) as an example and a comparative example; wherein, the arsenic content in the waste denitrification catalyst was 1.89%, and the arsenic content was calculated as arsenic pentoxide content; the vanadium pentoxide content was 0.81%.
[0055] Test methods 1. Measurement of arsenic content in solid materials The arsenic content in solid materials was measured by X-ray fluorescence spectroscopy (XRF).
[0056] 2. Measurement of vanadium concentration in solution The concentration of vanadium in a solution was measured using inductively coupled plasma (ICP).
[0057] Example 1 S0: Select a honeycomb-shaped degraded SCR catalyst module and clean it using a negative pressure dust collection device and a blower dust collection chamber for 5 minutes. Then, rinse the catalyst with a high-pressure water gun for 5 minutes. After that, place the rinsed catalyst module into a blower drying oven and dry it at 120℃ for 4 hours. Then, disassemble the dried catalyst module and extract one intact catalyst to cut into a 3×3 hole (number of holes) catalyst sample with a height of 200mm. The sample size is approximately 23.4×23.4×200mm.
[0058] S1: Weigh 30g of concentrated sulfuric acid (98%) into a beaker, add water to 400g, and stir until well mixed to obtain a sulfuric acid solution; then, weigh 10g of ferrous sulfate and add it to the prepared sulfuric acid solution, stirring until completely dissolved to obtain the first treatment solution; wherein, in the first treatment solution, the mass content of sulfuric acid is 7.5% and the mass content of ferrous sulfate is 2.5%; A 3×3-well catalyst sample and 250g of the first treatment solution were placed in a 1000ml volumetric flask, and 0.25g of JFC permeating agent was added to the flask. The flask was then sonicated in an ultrasonic machine at a frequency of 40kHz, a power of 50W / L, and a time of 25min. After sonication, the sample was bubbled at 0.3MPa for 15min, followed by solid-liquid separation to obtain an arsenic-containing treatment solution and an arsenic-removed catalyst solid. The catalyst solid was then washed and dried. The concentration of vanadium in the arsenic-containing treatment solution was measured by ICP, and the concentration of arsenic in the washed and dried catalyst solid was measured by XRF.
[0059] S2: Transfer the arsenic-containing treatment solution into a 500ml beaker, place it under an electromagnetic stirrer, and add 10ml of 5wt% ammonia water to the beaker while stirring to adjust the pH of the treatment solution system to 2.5; then, stir the treatment solution system at 80℃ for 60min, and then let it stand for 120min to allow natural precipitation; then, centrifuge the above precipitation system (slurry) to obtain solid and solution; measure the concentration of arsenic in the solution, and wash the solid with water.
[0060] S3: Take 5g of the solid obtained in step S2 and 7.5g of 10wt% ammonia water and place them in a 50ml beaker. Adjust the pH of the system to 11.5. After adding the magnetic rotor, seal it with a sealing film. Place the beaker on an electromagnetic stirrer and react at 60℃ for 1h. Then separate the solid and liquid to obtain solid iron hydroxide and a solution containing ammonium metasaturite.
[0061] S4: The solution containing ammonium metaarsenite was heated and decomposed at 100℃ and evaporated to crystallize. After 3 hours, solid-liquid separation was performed. The separated solid was washed with 10wt% ethanol solution and then dried at 250℃ to obtain white arsenic.
[0062] Example 2 This embodiment uses the same raw materials and processes as in Example 1 to regenerate the waste denitrification catalyst. The difference is that in step S1, the amount of ferrous sulfate used is 15g, and the mass content of ferrous sulfate in the first treatment liquid is 3.75%.
[0063] Example 3 This embodiment uses the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst. The difference is that in step S2, ammonium carbonate (to replace ammonia) is added to adjust the pH of the treatment liquid system to 9.5.
[0064] Example 4 This embodiment uses the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst. The difference is that 5g of ammonia water is used in step S3, and the pH value of the system is adjusted to 10.
[0065] Example 5 This embodiment uses the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst, the difference being that the reaction time in step S4 is 3.5 hours.
[0066] Example 6 This example uses the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst. The difference is that in step S1, the amount of ferrous sulfate used is 20g, and the mass content of ferrous sulfate in the first treatment liquid is 5%.
[0067] Example 7 This embodiment uses the same raw materials and processes as in Example 1 to regenerate the waste denitrification catalyst. The difference is that the amount of concentrated sulfuric acid added in step S1 is 40g, and the mass content of sulfuric acid in the first treatment liquid is 10%.
[0068] Comparative Example 1 This example uses essentially the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst. The difference is that ferrous sulfate is not used in step S1, that is, the first treatment liquid does not contain ferrous sulfate.
[0069] Comparative Example 2 This example uses essentially the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst, the difference being that 10g of sodium sulfite is used instead of ferrous sulfate in step S1.
[0070] Comparative Example 3 This example uses essentially the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst, the difference being that the sulfuric acid content in the first treatment liquid obtained in step S1 is 15 wt%.
[0071] Comparative Example 4 This example uses essentially the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst. The difference is that in step S1, 2.5 grams of metallic Zn are used to replace ferrous sulfate.
[0072] Comparative Example 5 This example uses essentially the same raw materials and processes as Example 1 to regenerate the waste denitrification catalyst, the difference being that the sulfuric acid content in the first treatment liquid obtained in step S1 is 1.5 wt%.
[0073] The materials of each embodiment and comparative example were tested according to the aforementioned method, and the results are shown in Table 1. The white arsenic content of each embodiment and comparative example was analyzed by XRF, and the results are shown in Table 2.
[0074] Table 1
[0075] In Table 1, the As2O5 content of each embodiment and comparative example is the arsenic content in the catalyst solid after cleaning and drying in step S1; the arsenic removal rate is calculated according to the following formula: (arsenic content of raw material waste catalyst - arsenic content of catalyst solid in step S1) / arsenic content of raw material waste catalyst × 100%.
[0076] Table 2 Purity of White Arsenic Products
[0077] The difference between Example 1 and Comparative Examples 1, 2, and 4 is that the first treatment solution of Comparative Example 1 does not contain the reducing agent ferrous sulfate, while the reducing agents used in Comparative Examples 2 and 4 are different from those in Example 1. According to the results in Tables 1 and 2, the arsenic removal rate of Example 1 (83.60%) is significantly higher than that of Comparative Example 1 (47.62%). Although Comparative Examples 2 and 4 also have high arsenic removal rates, the vanadium leaching amount from their spent catalysts is much higher than that of Example 1, and the purity of the byproduct white arsenic is significantly lower than that of Example 1. This indicates that during the treatment process in step S1, more vanadium from the spent catalysts of Comparative Examples 2 and 4 dissolves in the first treatment solution, reducing the activity of the regenerated catalyst. Simultaneously, vanadium is impurities mixed in with the white arsenic product, further reducing the purity of the white arsenic.
[0078] Therefore, by adding a ferrous salt reducing agent to the first treatment liquid, the present invention can improve the arsenic removal rate of the waste denitrification catalyst, reduce the leaching of vanadium, and improve the purity of the white arsenic product.
[0079] The difference between Example 1 and Comparative Examples 3 and 5 lies in the concentration of sulfuric acid in the first treatment solution; the concentration of sulfuric acid in Comparative Examples 3 and 5 is either too high or too low. According to the results in Tables 1 and 2, although Comparative Example 3 also has a high arsenic removal rate, its vanadium leaching amount is also significantly higher; the arsenic removal rate of Comparative Example 5 is much lower than that of Example 1, indicating a poor arsenic removal effect.
[0080] Furthermore, the difference between Example 1 and Example 6 of the present invention lies in the concentration of ferrous sulfate in the first treatment solution; the concentration in Example 6 is greater than that in Example 1. According to the results in Table 1, although the arsenic removal rate of Example 6 is slightly higher than that of Example 1, its vanadium dissolution is also higher. Meanwhile, based on the results of Example 2, the preferred mass content of the reducing agent ferrous salt in the first treatment solution is 1–4%.
[0081] Based on the above description, the embodiments of the present invention can achieve comprehensive optimization of arsenic removal and vanadium leaching inhibition during the regeneration process of waste denitrification catalysts by using specific concentrations of acid and specific types of reducing agents (ferrous salts), and obtain high-purity white arsenic byproducts.
[0082] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.
[0083] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.
Claims
1. A method for regenerating spent denitrification catalyst, comprising the following steps: The waste denitrification catalyst is mixed with the first treatment liquid to dissolve the arsenic element in the waste denitrification catalyst, thereby obtaining an arsenic-containing treatment liquid and an arsenic-removing catalyst. The arsenic-containing treatment solution is reacted with a first alkaline substance to convert the arsenic and iron elements therein into precipitates. The precipitate is reacted with a second alkaline substance to dissolve the arsenic-containing precipitate, yielding a solution containing ammonium metaarsenite; and The solution containing ammonium metaarsenite was heated and decomposed to obtain arsenic trioxide; in, The first treatment solution contains an acid and a reducing agent, the reducing agent including a ferrous salt.
2. The regeneration method according to claim 1, wherein, The acid includes sulfuric acid and / or hydrochloric acid; the reducing agent includes ferrous sulfate and / or ferrous chloride; and / or, The temperature at which the waste denitrification catalyst is mixed and reacted with the first treatment liquid is 20–50°C; and / or, The time for mixing and reacting the waste denitrification catalyst with the first treatment liquid is 15 to 50 minutes.
3. The regeneration method according to claim 1, wherein, Based on the mass of the solvent contained in the first treatment solution, the mass content of the acid in the first treatment solution is 5-10%, and the mass content of the reducing agent is 1-5%; and / or, The pH of the arsenic-containing treatment solution is adjusted to 1-10 using the first alkaline substance to carry out the reaction.
4. The regeneration method according to claim 1, wherein, The reaction temperature between the arsenic-containing treatment solution and the first alkaline substance is 60–90°C; and / or, The reaction time between the arsenic-containing treatment solution and the first alkaline substance is 30–120 min; and / or, The pH of the arsenic-containing treatment solution is adjusted to 2-9 using the first alkaline substance to carry out the reaction.
5. The regeneration method according to claim 1, wherein, The mass content of the reducing agent in the first treatment solution is 1-4%; and / or, A permeabilizer is included in the reaction system of the waste denitrification catalyst and the first treatment liquid.
6. The regeneration method according to claim 1, wherein, During the mixing and reaction of the waste denitrification catalyst and the first treatment liquid, the reaction system is subjected to ultrasonic bubbling; and / or, The first alkaline substance includes one or more of ammonia, alkaline ammonium salt, sodium carbonate, monoethanolammonium, and urea; the second alkaline substance includes ammonia and / or alkaline ammonium salt.
7. The regeneration method according to claim 6, wherein, The ultrasonic frequency is 28–40 kHz, and the power is 30–50 W / L; and / or, The pressure of the bubbling gas is 0.2–0.4 MPa; and / or, The basic ammonium salts include ammonium carbonate and / or ammonium bicarbonate.
8. The regeneration method according to claim 1, wherein, The reaction of the precipitate with the second alkaline substance is carried out at a temperature of 40–60°C; and / or, The reaction time between the precipitate and the second alkaline substance is 60–120 min; and / or, The pH value of the reaction system for dissolving the precipitate is 9 to 14.
9. The regeneration method according to claim 1, wherein, The solution containing ammonium metasalicylate is heated to decompose and evaporate to crystallize, wherein the temperature of the heating decomposition is 90-100°C.
10. The regeneration method according to claim 1, wherein, The waste denitrification catalyst is treated to remove ash, and then mixed with the first treatment liquid; the ash removal treatment includes soot blowing and washing.