Process for the recovery of alkaline oxide-containing fine powder off-gas and process for the preparation of heavy metal and desulfurization resistant catalysts containing alkaline oxides

Abstract

This invention relates to the field of powder raw material recycling, and discloses a method for recycling tail gas containing alkaline oxide fine powder and a method for preparing an anti-heavy metal and desulfurization catalyst containing alkaline oxide. The method for recycling tail gas containing alkaline oxide fine powder includes the following steps: (1) passing the spray tail gas containing alkaline oxide fine powder into fine powder collecting water for tail gas absorption to obtain a first composite slurry; (2) passing the calcination tail gas containing alkaline oxide fine powder into the first composite slurry for tail gas absorption to obtain a second composite slurry; (3) transporting the second composite slurry to the preparation section of the anti-heavy metal and desulfurization catalyst containing alkaline oxide as raw material for recycling. The recycling method provided by this invention can effectively improve the catalyst product yield and reduce production costs.

Description

Technical Field

[0001] This invention relates to the field of powder raw material recycling, and discloses a method for recycling tail gas containing alkaline oxide fine powder and a method for preparing a catalyst containing alkaline oxide for resisting heavy metals and desulfurization. Background Technology

[0002] Generally, in the preparation of heavy metal and desulfurization catalysts containing alkaline oxides, the slurry containing alkaline oxides needs to be uniformly mixed with other raw material slurries before spray drying and high-temperature calcination to obtain the finished catalyst. Due to the limitations of the cyclone separator itself during the spray drying and calcination processes, some fine catalyst particles, carrying acidic gases, are separated out with the hot air of the drying medium, accounting for about 5-10% of the total, resulting in significant losses. This portion of the alkaline oxide catalyst fine powder contains a large amount of sodium oxide impurities and has a large particle size, far exceeding the particle size requirements of the raw materials needed for preparation. Directly reusing it in the catalyst preparation process would affect the activity and stability of the catalyst product. Currently, there is no effective way to directly recycle the fine powder containing alkaline oxides. To avoid environmental pollution from solid particulate matter, most methods involve directly absorbing it through a wet dust removal system using alkaline wastewater. However, this wastewater can only enter the external drainage system, resulting in resource waste. Summary of the Invention

[0003] The purpose of this invention is to overcome the problem that there is currently no effective direct recycling method for alkaline oxide fine powder in the prior art, and to provide a method for recycling tail gas from alkaline oxide fine powder and a method for preparing anti-heavy metal and desulfurization catalysts containing alkaline oxides. The method for recycling tail gas from alkaline oxide fine powder provided by this invention utilizes the heat and acidic medium in the spray drying tail gas and calcination tail gas in a cascade manner to modify the alkaline oxide fine powder slurry. The resulting stable composite slurry can be directly recycled into the production process of anti-heavy metal and desulfurization catalysts. Without affecting the activity and stability of the catalyst product, the product yield can be improved. In summary, this invention effectively realizes the recycling of alkaline oxide fine powder, not only avoiding resource waste and reducing production costs, but also improving the yield of anti-heavy metal and desulfurization catalyst products.

[0004] To achieve the above objectives, the present invention provides a method for recovering and utilizing tail gas containing alkaline oxide fine powder, the method comprising the following steps: (1) The spray exhaust gas containing alkaline oxide fine powder is passed into the fine powder collection water for exhaust gas absorption to obtain the first complex slurry; (2) The calcination tail gas containing alkaline oxide fine powder is passed into the first composite slurry for tail gas absorption to obtain the second composite slurry; (3) The second composite slurry is transported to the preparation section of the anti-heavy metal and desulfurization catalyst containing alkaline oxides for recycling as raw material; The spray exhaust gas containing alkaline oxide fine powder and the calcination exhaust gas containing alkaline oxide fine powder come from the spray drying stage and calcination stage in the preparation section of the anti-heavy metal and desulfurization catalyst containing alkaline oxide.

[0005] A second aspect of the present invention provides a method for preparing a heavy metal-resistant and desulfurization catalyst containing alkaline oxides, the method comprising: I: Preparation of anti-heavy metal and desulfurization catalyst containing alkaline oxides: The active components, binder and carrier required for the anti-heavy metal and desulfurization catalyst are added to the reaction vessel in proportion and order. After being thoroughly stirred, the catalyst product is obtained by spray drying and high-temperature calcination. Spray drying produces spray exhaust gas and high-temperature calcination produces calcination exhaust gas. II: The spray exhaust gas and roasting exhaust gas are treated according to the recycling method described in this invention; III: Return the second composite slurry obtained in step II to step I as a raw material.

[0006] The present invention provides a method for recovering and utilizing tail gas containing alkaline oxide fine powder. This method modifies and adjusts the alkaline oxide fine powder slurry by utilizing the heat and acidic medium in the spray drying and roasting tail gas in a cascade manner. The resulting stable composite slurry can be directly reused in the production process of heavy metal-resistant and desulfurization catalysts. This improves product yield without affecting the activity and stability of the catalyst product. In summary, the present invention effectively realizes the recycling of alkaline oxide fine powder, not only avoiding resource waste and reducing production costs, but also improving the yield of heavy metal-resistant and desulfurization catalyst products. Attached Figure Description

[0007] Figure 1 This is a flowchart of the recovery and utilization process for tail gas containing alkaline oxide fine powder. Detailed Implementation

[0008] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0009] This invention provides a method for recovering and utilizing tail gas containing alkaline oxide fine powder, the method comprising the following steps: (1) The spray exhaust gas containing alkaline oxide fine powder is passed into the fine powder collection water for exhaust gas absorption to obtain the first complex slurry; (2) The calcination tail gas containing alkaline oxide fine powder is passed into the first composite slurry for tail gas absorption to obtain the second composite slurry; (3) The second composite slurry is transported to the preparation section of the anti-heavy metal and desulfurization catalyst containing alkaline oxides for recycling as raw material; The spray exhaust gas containing alkaline oxide fine powder and the calcination exhaust gas containing alkaline oxide fine powder come from the spray drying stage and calcination stage in the preparation section of the anti-heavy metal and desulfurization catalyst containing alkaline oxide.

[0010] In this invention, the range of alkaline oxides that can be selected is relatively wide, and the specific selection depends on the raw materials used in the catalyst preparation process. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the alkaline oxide includes one or more of sodium oxide, potassium oxide, calcium oxide, and magnesium oxide.

[0011] In this invention, there are no special requirements for the type of water used for collecting fine powder. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the water used for collecting fine powder is neutral water and / or acidic water with a pH of 3 to 5.

[0012] In fact, in this invention, the fine powder composition in the spray exhaust gas and roasting exhaust gas mainly includes alkaline oxides, aluminum oxide and chloride ions.

[0013] In this invention, the content of alkaline oxides in the fine powder of the spray exhaust gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the fine powder in the spray exhaust gas contains 30 to 70 wt% alkaline oxides.

[0014] In this invention, the alumina content in the fine powder of the spray exhaust gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the alumina content in the fine powder of the spray exhaust gas is 20 to 60 wt%.

[0015] In this invention, the chloride ion content in the fine powder of the spray exhaust gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the chloride ion content in the fine powder of the spray exhaust gas is 5 to 15 wt%.

[0016] In this invention, the temperature range of the spray exhaust gas is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature of the spray exhaust gas is 100-200°C.

[0017] In this invention, the fine powder content in the spray exhaust gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the fine powder content in the spray exhaust gas is 300–3500 mg / m³. 3 .

[0018] In this invention, the chloride ion concentration in the spray exhaust gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the chloride ion concentration in the spray exhaust gas is 500–2000 mg / m³. 3 .

[0019] In this invention, the range of alkaline oxide content in the fine powder of the roasting tail gas is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the alkaline oxide content in the fine powder of the roasting tail gas is 35 to 75 wt%.

[0020] In this invention, the alumina content in the fine powder in the roasting tail gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the alumina content in the fine powder in the roasting tail gas is 25 to 65 wt%.

[0021] In this invention, the chloride ion content in the fine powder in the roasting tail gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the chloride ion content in the fine powder in the roasting tail gas is 3 to 10 wt%.

[0022] In this invention, the temperature range of the roasting exhaust gas is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature of the roasting exhaust gas is 450 to 650°C.

[0023] In this invention, the fine powder content in the roasting exhaust gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the fine powder content in the roasting exhaust gas is 100–2000 mg / m³. 3 .

[0024] In this invention, the chloride ion concentration in the roasting tail gas can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the chloride ion concentration in the roasting tail gas is 5000–10000 mg / m³. 3 .

[0025] The method for recovering and utilizing tail gas containing alkaline oxide fine powder provided by the present invention modifies and transforms the alkaline oxide fine powder slurry by utilizing the heat and acidic medium in the tail gas of spray drying and roasting in stages. The resulting stable composite slurry can be directly reused in the production process of anti-heavy metal and desulfurization catalysts.

[0026] In this invention, the pH value and temperature of the first composite slurry are controlled by controlling the amount of spray exhaust gas introduced.

[0027] In this invention, the fine powder content in the first composite slurry can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the fine powder content in the first composite slurry is 5 to 25 wt%.

[0028] In this invention, the pH value of the first composite slurry can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the pH value of the first composite slurry is 8 to 10.

[0029] In this invention, the temperature range of the first composite slurry is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature of the first composite slurry is 50 to 70°C.

[0030] In this invention, the absorption time in step (1) can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the absorption time in step (1) is 0.2 to 0.8 hours.

[0031] In this invention, the pH value and temperature of the second composite slurry are controlled by controlling the amount of roasting tail gas introduced.

[0032] In this invention, the fine powder content in the second composite slurry can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the fine powder content in the second composite slurry is 8 to 30 wt%.

[0033] In this invention, the pH value of the second composite slurry can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the pH value of the second composite slurry is 2 to 5.

[0034] In this invention, the temperature range of the second composite slurry is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature of the second composite slurry is 60-90°C.

[0035] In this invention, the absorption time in step (2) can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the absorption time in step (2) is 0.5 to 1.5 hours.

[0036] In this invention, there are no special requirements for the ratio of the dry basis of the second complex slurry added in step (3) to the amount of catalyst product. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the dry basis of the second complex slurry added in step (3) accounts for 5 to 30 wt% of the weight of the catalyst product.

[0037] The aforementioned method for recovering and utilizing alkaline oxide fine powder tail gas of the present invention modifies and transforms the alkaline oxide fine powder slurry by utilizing the heat and acidic medium in the spray drying tail gas and roasting tail gas in stages. The resulting stable composite slurry can be directly reused in the production process of anti-heavy metal and desulfurization catalysts.

[0038] This invention provides a method for preparing a heavy metal-resistant and desulfurization catalyst containing alkaline oxides, the method comprising: I: Preparation of anti-heavy metal and desulfurization catalyst containing alkaline oxides: The active components, binder and carrier required for the anti-heavy metal and desulfurization catalyst are added to the reaction vessel in proportion and order. After being thoroughly stirred, the catalyst product is obtained by spray drying and high-temperature calcination. Spray drying produces spray exhaust gas and high-temperature calcination produces calcination exhaust gas. II: The spray exhaust gas and roasting exhaust gas are processed according to the recycling method described in this invention; III: Return the second composite slurry obtained in step II to step I as a raw material.

[0039] According to a preferred embodiment of the present invention, the amount of the second composite slurry dry basis added in step III accounts for 5 to 30 wt% of the catalyst product weight.

[0040] The method for preparing a heavy metal-resistant and desulfurization catalyst containing alkaline oxides provided by this invention can improve product yield without affecting the catalyst's activity and stability. In summary, this invention effectively realizes the recycling of fine alkaline oxide powder, not only avoiding resource waste and reducing production costs, but also improving the yield of the catalyst product.

[0041] In this invention, the weight ratio of the dry base of the second composite slurry to the total weight of the catalyst product is equal to the concentration of the fine powder slurry × the volume of the fine powder slurry / the total weight of the dry base of the catalyst.

[0042] Example 1 I: Catalyst Preparation Section: The active components, binder, and support required for the heavy metal resistance and desulfurization catalyst are added to the reactor in a specific ratio and order. After thorough mixing, the catalyst product is obtained through spray drying and high-temperature calcination. Specifically, this can be carried out according to Example 1 of patent CN100425339C.

[0043] The generated spray exhaust gas has a temperature of 150℃ and a fine powder content of 2500 mg / m³. 3 The chloride ion concentration is 1000 mg / m³. 3 The fine powder in the spray exhaust gas includes 60 wt% alkaline oxides, 32 wt% aluminum oxide, and 5 wt% chloride ions. The generated roasting exhaust gas has a temperature of 550℃ and a fine powder content of 1000 mg / m³. 3 The chloride ion concentration is 8000 mg / m³. 3 The fine powder in the roasting exhaust gas includes 50% alkaline oxides, 42 wt% alumina, and 8 wt% chloride ions.

[0044] II: Exhaust Gas Treatment Section: The exhaust gas treatment process is as follows... Figure 1 As shown, the specific steps include: (1) The spray tail gas containing alkaline oxide fine powder was passed into neutral water for absorption for 0.2 h. The first composite slurry obtained had a fine powder content of 5 wt%, a pH of 8, and a temperature of 50 °C. (2) The roasting tail gas was passed into the first composite slurry for absorption for 0.5 h. The resulting second composite slurry had a fine powder content of 8 wt%, a pH of 5, and a temperature of 60 °C. (3) The second composite slurry is transported to catalyst preparation section I, and the dry basis of the second composite slurry is 5 wt% of the total catalyst product weight.

[0045] Example 2 I: Catalyst preparation section: As described in Example 1.

[0046] II: Exhaust Gas Treatment Section (1) The spray tail gas containing alkaline oxide fine powder was passed into neutral water for absorption for 0.8h. The fine powder content in the first composite slurry was 25wt%, the pH was 10, and the temperature was 70℃. (2) The roasting tail gas was passed into the first composite slurry for absorption for 1.5 h. The resulting second composite slurry had a fine powder content of 30 wt%, a pH of 2, and a temperature of 90 °C. (3) The second composite slurry is transported to catalyst preparation section I, and the dry basis of the second composite slurry is 30 wt% of the total catalyst product weight.

[0047] Example 3 I: Catalyst preparation section: As described in Example 1.

[0048] II: Exhaust Gas Treatment Section (1) The spray tail gas containing alkaline oxide fine powder was passed into neutral water for absorption for 0.5 h. The first composite slurry obtained had a fine powder content of 8 wt%, a pH of 9, and a temperature of 65 °C. (2) The roasting tail gas was passed into the first composite slurry for absorption for 0.8 h. The resulting second composite slurry had a fine powder content of 12 wt%, a pH of 5, and a temperature of 85 °C. (3) The second composite slurry is transported to catalyst preparation section I, and the dry basis of the second composite slurry is 18 wt% of the total catalyst product weight.

[0049] Example 4 I: Catalyst preparation section: As described in Example 1.

[0050] II: Exhaust Gas Treatment Section (1) The spray tail gas containing alkaline oxide fine powder was passed into neutral water for absorption for 0.1 h. The first composite slurry obtained had a fine powder content of 5wt%, a pH of 8, and a temperature of 60℃. (2) The roasting tail gas was passed into the first composite slurry for absorption for 0.8 h. The resulting second composite slurry had a fine powder content of 12 wt%, a pH of 4, and a temperature of 80 °C. (3) The second composite slurry is transported to catalyst preparation section I, and the dry basis of the second composite slurry accounts for 18% of the total catalyst product weight.

[0051] Example 5 I: Catalyst preparation section: As described in Example 1.

[0052] II: Exhaust Gas Treatment Section (1) The spray tail gas containing alkaline oxide fine powder was passed into neutral water for absorption for 0.5 h. The first composite slurry obtained had a fine powder content of 8 wt%, a pH of 9, and a temperature of 65℃. (2) The roasting tail gas was passed into the first composite slurry for absorption for 0.3 h. The resulting second composite slurry had a fine powder content of 10 wt%, a pH of 5, and a temperature of 75 °C. (3) The second composite slurry is transported to catalyst preparation section I, and the dry basis of the second composite slurry accounts for 18% of the total catalyst product weight.

[0053] Example 6 I: Catalyst preparation section: As described in Example 1.

[0054] II: Exhaust Gas Treatment Section (1) The spray tail gas containing alkaline oxide fine powder was passed into water with pH 9 and absorbed for 0.5 h. The first composite slurry obtained had a fine powder content of 8 wt%, pH 10, and temperature of 65℃. (2) The roasting tail gas was passed into the first composite slurry for absorption for 0.8 h, and the resulting second composite slurry had a fine powder content of 12wt%, a pH of 5, and a temperature of 85℃. (3) The second composite slurry is transported to catalyst preparation section I, and the dry basis of the second composite slurry accounts for 18% of the total catalyst product weight.

[0055] Example 7 I: Catalyst preparation section: As described in Example 1.

[0056] II: Exhaust Gas Treatment Section (1) The spray tail gas containing alkaline oxide fine powder was passed into neutral water for absorption for 0.5 h. The first composite slurry obtained had a fine powder content of 8 wt%, a pH of 9, and a temperature of 65℃. (2) The roasting tail gas was passed into the first composite slurry for absorption for 0.8 h. The resulting second composite slurry had a fine powder content of 12 wt%, a pH of 4, and a temperature of 85 °C. (3) The second composite slurry is transported to catalyst preparation section I, and the dry basis of the second composite slurry accounts for 35% of the total catalyst product weight.

[0057] Comparative Example 1 I: Catalyst preparation section: As described in Example 1.

[0058] II: Exhaust Gas Treatment Section (1) Spray tail gas containing alkaline oxide fine powder and calcination tail gas are simultaneously introduced into water with pH 4. Spray tail gas is absorbed for 0.5 h and calcination tail gas is absorbed for 0.8 h to obtain a slurry with fine powder content of 12wt%, pH 4 and temperature of 85℃. (2) The above-mentioned composite slurry is transported to catalyst preparation section I, and the dry basis of the composite slurry is added at 18% of the total catalyst product weight.

[0059] Test example: The catalysts obtained using the above examples and comparative examples were subjected to desulfurization tests. The specific test methods can be carried out according to Example 12 of patent CN100425339C. The results are shown in Table 1.

[0060] Table 1 project Product yield, % Compared to not recycling, the product yield increases by % SOx removal rate, % Example 1 a-1 3 93 Example 2 a+1 5 92 Example 3 a 4 95 Example 4 a-2 2 85 Example 5 a-3 1 85 Example 6 a-3 1 80 Example 7 a+2 6 80 Comparative Example 1 a-3 1 70 The preferred embodiments of the present invention have been described above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for recycling a fine powder tail gas containing alkaline oxides, characterized by, The method includes the following steps: (1) The spray exhaust gas containing alkaline oxide fine powder is passed into the fine powder collection water for exhaust gas absorption to obtain the first complex slurry; (2) The calcination tail gas containing alkaline oxide fine powder is passed into the first composite slurry for tail gas absorption to obtain the second composite slurry; (3) The second composite slurry is transported to the preparation section of the anti-heavy metal and desulfurization catalyst containing alkaline oxides for recycling as raw material; The spray exhaust gas containing alkaline oxide fine powder and the calcination exhaust gas containing alkaline oxide fine powder come from the spray drying stage and calcination stage in the preparation section of the anti-heavy metal and desulfurization catalyst containing alkaline oxide.

2. The recycling method according to claim 1, characterized in that, The alkaline oxide includes one or more of sodium oxide, potassium oxide, calcium oxide, and magnesium oxide; and / or The water used for collecting fine powder is neutral water and / or acidic water with a pH of 3 to 5.

3. The recycling method according to claim 1 or 2, characterized in that, The fine powder composition in the spray exhaust gas includes: 30-70 wt% alkaline oxides, 20-60 wt% aluminum oxide, and 5-15 wt% chloride ions.

4. The recycling method according to any one of claims 1 to 3, characterized in that, The spray tail gas: temperature is 100-200℃, fine powder content is 300-3500mg / m 3 , chloride ion concentration is 500-2000mg / m 3 .

5. The recycling method according to any one of claims 1 to 4, characterized in that, The fine powder in the roasting exhaust gas includes: 35-75 wt% basic oxides, 25-65 wt% alumina, and 3-10 wt% chloride ions.

6. The recycling method according to any one of claims 1 to 5, characterized in that, The roasting tail gas: temperature is 450-650℃, fine powder content is 100-2000mg / m 3 , chloride ion concentration is 5000-10000mg / m 3 .

7. The recycling method according to any one of claims 1 to 6, characterized in that, In step (1), The fine powder content in the first composite slurry is 5–25 wt%; and / or The pH of the first composite slurry is 8–10; and / or The temperature of the first composite slurry is 50–70°C; and / or The absorption time is 0.2 to 0.8 hours.

8. The recycling method according to any one of claims 1 to 7, characterized in that, In step (2), The fine powder content in the second composite slurry is 8–30 wt%; and / or The pH of the second complex slurry is 2–5; and / or The temperature of the second composite slurry is 60–90°C; and / or The absorption time is 0.5 to 1.5 hours.

9. The recycling method according to any one of claims 1 to 8, wherein, In step (3), The amount of the second composite slurry dry basis added accounts for 5 to 30 wt% of the catalyst product weight.

10. A process for the preparation of an anti-heavy metal and desulfurization catalyst containing basic oxides, characterized in that, The method includes: I: Preparation of anti-heavy metal and desulfurization catalyst containing alkaline oxides: The active components, binder and carrier required for the anti-heavy metal and desulfurization catalyst are added to the reaction vessel in proportion and order. After being thoroughly stirred, the catalyst product is obtained by spray drying and high-temperature calcination. Spray drying produces spray exhaust gas and high-temperature calcination produces calcination exhaust gas. II: The spray exhaust gas and roasting exhaust gas are treated by the recycling method according to any one of claims 1-9; III: Return the second composite slurry obtained in step II to step I as a raw material; Preferably, the dry basis of the second composite slurry is added at a rate of 5 to 30 wt% of the catalyst product.

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