Method for recovering Ti and W elements in waste SCR (Selective Catalytic Reduction) denitration catalyst

Abstract

The invention discloses a method for recovering Ti and W elements in a waste SCR (Selective Catalytic Reduction) denitration catalyst, which comprises the following steps of: firstly, sequentially carrying out cleaning, ball milling, sieving and drying treatment on the waste SCR denitration catalyst, then fully mixing the treated waste SCR denitration catalyst with carbon powder, paving the mixture in a crucible, and putting the mixture in a reaction furnace; the method comprises the following steps: introducing argon into a reaction furnace to remove air in the reaction furnace, raising the temperature in the reaction furnace to 850-1200 DEG C, introducing ammonia gas to carry out a reduction nitridation reaction, introducing argon after the reaction is finished, cooling a sample to room temperature along with the furnace, and taking out the sample to obtain a mixture of TiNxOy and W. According to the method, NH3 is used as a green reduction nitriding agent, selective reduction nitriding of titanium and tungsten elements in the waste SCR denitration catalyst is successfully achieved, a mixture of TiNxOy and W is obtained, the mixture can be further separated and purified through a low-temperature chlorination technology, and the purity of the mixture is improved. And a brand new technical route is provided for high-value recycling of valuable metals in the waste SCR denitration catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and in particular relates to a method for recovering Ti and W elements from a waste SCR denitration catalyst. Background Art

[0002] With the rapid development of global industrialization, environmental problems such as acid rain and photochemical smog caused by nitrogen oxide (NOx) emissions are becoming increasingly severe, posing a serious threat to the ecological environment and human health. Against this backdrop, the Selective Catalytic Reduction (SCR) denitrification process, with its high denitrification efficiency and excellent selectivity, has been widely used in flue gas denitrification treatment in numerous industrial sectors, including power, steel, and cement.

[0003] In recent years, to further improve environmental quality, countries have continuously increased their nitrogen oxide emission limits. In response, the use of SCR denitrification catalysts has continued to expand. However, during their actual use, SCR denitrification catalysts are affected by various physical and chemical factors, such as high-temperature sintering, alkali metal poisoning, heavy metal poisoning, and physical wear. These factors can gradually reduce the catalyst's activity and eventually lead to deactivation, ultimately resulting in a large amount of waste SCR denitrification catalysts. These waste SCR denitrification catalysts contain a large amount of valuable metal elements, including TiO2 at a content of up to 800-900 kg / t, V2O5 at 5-15 kg / t, and WO3 at 7-10 kg / t. Directly discarding these catalysts would result in a significant waste of resources, making it necessary to recover the valuable metals for resource utilization.

[0004] Currently, the mainstream recovery process for spent SCR denitrification catalysts relies on acid-base leaching to selectively extract, precipitate, and purify elements such as V, W, and Ti. However, this method faces several technical bottlenecks. First, the chemical properties of the metal elements in spent SCR denitrification catalysts vary. Complex chemical reactions easily occur during the acid-base leaching process, forming difficult-to-separate co-precipitates or complexes. This makes element separation difficult and inefficient, and some target metal elements are lost along with impurities, resulting in resource waste. Second, the acid-base leaching process is complex, involving multiple steps such as pretreatment, leaching, filtration, washing, precipitation, and calcination. Each step requires precise control of reaction conditions, and each step is interconnected. Failures in any one step can affect the final recovery, increasing equipment investment and operating costs while also reducing production efficiency. Furthermore, the acid-base leaching process generates large amounts of waste acid containing heavy metal ions and hazardous substances. This waste acid is difficult to handle, is costly, and difficult to recycle, further increasing environmental pressures and production costs. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for recovering Ti and W elements in discarded SCR denitration catalysts, so as to solve the problems of the existing acid-base leaching method, such as the difficulty in element separation, complex process flow, low efficiency, high recovery cost and difficulty in waste acid treatment.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for recovering Ti and W elements from a waste SCR denitration catalyst comprises the following steps:

[0008] (1) The waste SCR denitration catalyst is sequentially cleaned, ball-milled, sieved, and dried to obtain dry waste SCR denitration catalyst powder;

[0009] (2) mixing the dried waste SCR denitration catalyst powder with carbon powder to obtain a mixed raw material;

[0010] (3) The mixed raw materials are evenly spread in a crucible, and then the crucible containing the mixed raw materials is placed in a reactor. Argon gas is first introduced into the reactor to remove the air in the reactor, and then the temperature in the reactor is raised to 850-1200°C. Ammonia gas is introduced into the reactor and kept warm until the ammonia gas and the mixed raw materials fully react. The heating is stopped and argon gas is introduced into the reactor until the sample is cooled to room temperature with the furnace. The sample is then taken out to obtain the reduction nitridation product of Ti and W;

[0011] (4) Separate and purify the reduction nitridation products of Ti and W, that is, realize the recovery of Ti and W elements.

[0012] Furthermore, in step (1), the sieving is through a 100-200 mesh sieve.

[0013] Furthermore, in step (1), the drying temperature is 380-450°C.

[0014] Furthermore, in step (2), the mass ratio of the dried waste SCR denitration catalyst powder to the carbon powder is 1:0.8-2.

[0015] Furthermore, in step (2), the mass ratio of the dried waste SCR denitration catalyst powder to the carbon powder is 1:0.8-1.4. With this carbon content, the reduction and nitridation effect of Ti in the waste SCR denitration catalyst is optimal, and the carbon impurities in the low-temperature chlorination raw material are relatively low.

[0016] Furthermore, in step (3), the temperature after heating is 1000-1100°C.

[0017] Furthermore, in step (3), the gas flow rate of ammonia is 500 to 1000 mL / min.

[0018] Furthermore, in step (3), the gas flow rate of ammonia is 900-1000 mL / min.

[0019] Furthermore, in step (3), the gas flow rate of argon is 500 to 600 mL / min.

[0020] Furthermore, in step (4), the separation and purification is as follows: placing the reduction nitridation product in a crucible, then placing the crucible containing the reduction nitridation product in a working furnace, first introducing nitrogen, and exhausting the air in the working furnace; then heating to 450°C at a heating rate of 10°C / min under the protection of argon, disconnecting the argon, and introducing Cl2 instead, and keeping warm until the reduction nitridation product and Cl2 fully react, switching Cl2 to N2, and taking out the sample after the temperature in the furnace drops to room temperature; distilling the obtained sample to obtain TiCl4 and WCl6, respectively, thereby realizing the recovery of Ti and W elements.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The method for recovering Ti and W elements in waste SCR denitration catalyst provided by the present invention uses ammonia as a reducing agent and a nitriding agent to selectively reduce and nitride the Ti and W elements in the waste SCR denitration catalyst, and obtains TiN x O y Mixing with W reduces nitrides with excellent reduction and nitriding efficiency, reaching up to 95.4% and achieving a high recovery rate, effectively avoiding resource waste. Ammonia is a carbon-free, clean energy source. Using ammonia as a reduction and nitriding agent to recover spent SCR denitrification catalysts avoids the environmental pollution caused by the large amounts of acid and alkali used in traditional recovery processes, as well as the difficulty of element separation. The entire recovery process is simple, highly efficient, and low-cost, offering promising application prospects.

[0023] 2. The present invention further adds high-purity carbon powder to the waste SCR denitration catalyst powder before performing reduction nitridation, which can effectively promote the reduction nitridation reaction of TiO2 in an ammonia atmosphere, thereby improving the reduction nitridation rate of TiO2.

[0024] 3. The reduced nitridation product produced by the present invention can be used to chlorinate the Ti and W elements through a low-temperature chlorination process, and further separated and purified by utilizing the difference in boiling points of the chlorinated products (TiCl4 boiling point is 136°C, and WCl6 boiling point is 347°C). This technical approach not only achieves high-value recovery of Ti and W from spent SCR denitration catalysts, but also minimizes energy consumption and pollutant emissions through a full-process clean production design. This provides an innovative green technology solution for the sustainable recovery of valuable metals from spent SCR denitration catalysts, and is of great significance for promoting the development of my country's environmental protection industry and circular economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a process flow chart for recovering Ti and W elements from waste SCR denitration catalysts according to the present invention.

[0026] Figure 2 The XRD patterns of representative products recovered from the present invention include Example 1, Example 5 and Comparative Example 1. DETAILED DESCRIPTION

[0027] The specific implementation methods of the present invention are further described in detail below with reference to specific examples.

[0028] The numerical ranges herein are understood to specifically disclose every intervening value between the upper and lower limits of the range. Each smaller range between any stated value or intervening value in a stated range and any other stated value or intervening value in that stated range is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0029] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art. Although the present invention has only described preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail. As used herein, "comprising", "including", "having", "containing", etc. are all open-ended terms, meaning including but not limited to.

[0030] Unless otherwise specified, the experimental methods used in the present invention are all conventional methods.

[0031] Unless otherwise specified, the materials, reagents, etc. used in the present invention can be purchased or synthesized by known methods.

[0032] The quantitative tests in the present invention were repeated three times and the results were averaged.

[0033] Example 1

[0034] This embodiment provides a method for recovering Ti and W elements from a waste SCR denitration catalyst. The waste SCR denitration catalyst is a batch of waste SCR denitration catalysts eliminated from a thermal power plant, and its chemical composition is shown in Table 1.

[0035] Table 1 Chemical composition of spent SCR denitrification catalyst

[0036]

[0037] The specific steps include:

[0038] (1) The waste SCR denitration catalyst is sequentially cleaned, ball-milled, and sieved to obtain a waste SCR denitration catalyst raw material powder having a particle size of less than 200 mesh, and the obtained powder is then dried at 400° C. to remove free water and crystal water in the powder, thereby obtaining a dry waste SCR denitration catalyst powder;

[0039] (2) mixing the dried waste SCR denitration catalyst powder and carbon powder in a mass ratio of 1:1 to obtain a mixed raw material;

[0040] (3) Spread the mixed raw materials evenly in the corundum crucible to ensure that the raw material powder can fully react with NH3;

[0041] (4) The crucible containing the mixed raw materials is placed in the constant temperature zone of a horizontal tube furnace, and high-purity argon gas is introduced into the tube furnace at a gas flow rate of 1000 mL / min for 0.5 h to achieve the purpose of clearing the air in the furnace; then, in an atmosphere of high-purity argon gas, the tube furnace is heated to 850°C at a heating rate of 10°C / min, and the introduction of high-purity argon gas is stopped at this temperature, and high-purity ammonia gas (gas flow rate of 1000 mL / min) is introduced instead, and the temperature is kept in this temperature range for 6 h, and then the gas is switched back to high-purity argon gas, and the furnace is cooled at a gas flow rate of 500 mL / min;

[0042] (5) After the furnace is cooled to room temperature, the sample after the reaction is taken out and the reduction nitridation product obtained is TiN x O y (Due to the low reaction temperature, W is not reduced), where x = 0.524, y = 0.476; x is the reduction nitridation rate of TiO2, that is, the reduction nitridation rate of TiO2 is 52.4%.

[0043] Example 2

[0044] This embodiment provides a method for recovering Ti and W elements from a waste SCR denitration catalyst, which is similar to that of Example 1, except that the temperature is raised to 950° C. before ammonia is introduced and the temperature is maintained at this temperature for 6 hours.

[0045] After the reaction in this embodiment is completed, the reduction and nitridation products obtained are simple W and TiN x O y , where x = 0.628, y = 0.372; the reduction nitridation rate of TiO2 is 62.8%.

[0046] Example 3

[0047] This embodiment provides a method for recovering Ti and W elements from a waste SCR denitration catalyst, which is similar to that of Example 1, except that the temperature is raised to 1100° C. before ammonia is introduced and the temperature is maintained for 6 hours.

[0048] After the reaction in this embodiment is completed, the reduction and nitridation products obtained are simple W and TiN x O y , where x=0.916, y=0.094; the reduction nitridation rate of TiO2 is 91.6%.

[0049] Example 4

[0050] This embodiment provides a method for recovering Ti and W elements from waste SCR denitration catalysts, which is similar to that of Example 3, except that the dried waste SCR denitration catalyst powder is mixed with carbon powder in a mass ratio of 1:1.2.

[0051] After the reaction in this embodiment is completed, the reduction and nitridation products obtained are simple W and TiN x O y , where x = 0.932, y = 0.068; the reduction nitridation rate of TiO2 is 93.2%.

[0052] Example 5

[0053] This embodiment provides a method for recovering Ti and W elements from waste SCR denitration catalysts, which is similar to that of Example 3, except that the dried waste SCR denitration catalyst powder is mixed with carbon powder in a mass ratio of 1:1.4.

[0054] After the reaction in this embodiment is completed, the reduction and nitridation products obtained are simple W and TiN x O y , where x = 0.954, y = 0.046; the reduction nitridation rate of TiO2 is 95.4%.

[0055] Example 6

[0056] This embodiment provides a method for recovering Ti and W elements from a waste SCR denitration catalyst, which is similar to that of Example 3, except that the dried waste SCR denitration catalyst powder is mixed with carbon powder in a mass ratio of 1:1.6.

[0057] After the reaction in this embodiment is completed, the reduction and nitridation products obtained are simple W and TiN x O y , where x=0.856, y=0.144; the reduction nitridation rate of TiO2 is 85.6%.

[0058] Example 7

[0059] This embodiment provides a method for recovering Ti and W elements from waste SCR denitration catalysts, which is similar to that of Example 3, except that the mass ratio of the dried waste SCR denitration catalyst powder to the carbon powder is 1:2.

[0060] After the reaction in this embodiment is completed, the reduction and nitridation products obtained are simple W and TiN x O y , where x = 0.824, y = 0.176; the reduction nitridation rate of TiO2 is 82.4%.

[0061] Example 8

[0062] This embodiment provides a method for recovering Ti and W elements from a discarded SCR denitration catalyst, which is similar to that of Example 3, except that the gas flow rate of high-purity ammonia is 500 mL / min.

[0063] After the reaction in this embodiment is completed, the reduction nitridation product obtained is TiN x O y , where x = 0.426, y = 0.574; the reduction nitridation rate of TiO2 is 42.6%.

[0064] Example 9

[0065] This embodiment provides a method for recovering Ti and W elements from a discarded SCR denitration catalyst, which is similar to that of Example 3, except that the gas flow rate of high-purity ammonia is 700 mL / min.

[0066] After the reaction in this embodiment is completed, the reduction and nitridation products obtained are simple W and TiN x O y , where x = 0.687, y = 0.313; the reduction nitridation rate of TiO2 is 68.7%.

[0067] In a specific implementation, after obtaining the reduction nitridation product, the chlorination of Ti and W elements can be achieved through a low-temperature chlorination process, and further separation and purification can be achieved. The specific steps are as follows: the product obtained in step (5) of the embodiment is spread flat in a quartz crucible, placed in a low-temperature chlorination furnace, and high-purity nitrogen is introduced to exhaust the air in the furnace; then, under the protection of high-purity argon, the temperature is raised to 450°C at a heating rate of 10°C / min, the argon is disconnected, 100mL / min of Cl2 is introduced (controlling a low flow rate to ensure that the material and Cl2 fully react) and the temperature is kept for 6 hours, and then Cl2 is switched to N2. After the temperature in the furnace is reduced to room temperature, the sample is taken out to obtain chlorinated slag containing titanium chloride (TiCl4) and tungsten chloride (WCl6). Since the boiling point of TiCl4 is 136°C and the boiling point of WCl6 is 347°C, the separation and recovery of TiCl4 and WCl6 can be achieved by distilling the chlorinated slag.

[0068] Comparative Example 1

[0069] This embodiment provides a method for recovering Ti and W elements from a discarded SCR denitration catalyst, which is similar to that of Example 3, except that no carbon powder is added.

[0070] After the reaction of this comparative example is completed, the reduction nitridation product obtained is TiN x O y , where x = 0.617, y = 0.383; the reduction nitridation rate of TiO2 is 61.7%. Compared with Example 3, the reduction degree is greatly reduced and no elemental W is generated. It can be seen that carbon powder has a significant enhancing effect on the reduction nitridation of TiO2.

[0071] Figure 2 The XRD patterns of the representative products of the present invention include: Example 1, Example 5 and Comparative Example 1. Figure 2 It can be seen that the present invention successfully achieves the reduction of Ti and W.

[0072] In summary, the use of ammonia reduction and nitridation of the waste SCR denitrification catalyst of the present invention can obtain a nitrided product with a high degree of reduction, and the product reduction degree is closely related to process systems such as reduction temperature, carbon content, and ammonia flow rate. The higher the reduction temperature, the higher the reduction degree. The carbon content increases with the increase of the carbon content before 1:1.4, and then continuing to increase will inhibit the reduction. The greater the ammonia flow rate, the higher the reduction degree and the nitridation degree (that is, the larger the x value and the smaller the y value). The higher the degree of reduction and nitridation is, the more beneficial it is to the chlorination process, and the chlorination rate also increases accordingly, and the recovery rate of Ti and W is also higher.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the technical solutions. Those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present invention that do not depart from the purpose and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for recovering Ti and W elements from waste SCR denitration catalysts, characterized in that: The following steps are involved: (1) The waste SCR denitration catalyst is sequentially cleaned, ball-milled, sieved, and dried to obtain dry waste SCR denitration catalyst powder; (2) mixing the dried waste SCR denitration catalyst powder with carbon powder to obtain a mixed raw material; (3) The mixed raw materials are evenly spread in a crucible, and then the crucible containing the mixed raw materials is placed in a reactor. Argon gas is first introduced into the reactor to remove the air in the reactor, and then the temperature in the reactor is raised to 850-1200°C. Ammonia gas is introduced into the reactor and kept warm until the ammonia gas and the mixed raw materials fully react. The heating is stopped and argon gas is introduced into the reactor until the sample is cooled to room temperature with the furnace. The sample is then taken out to obtain the reduction nitridation product of Ti and W; (4) Separate and purify the reduction nitridation products of Ti and W, that is, realize the recovery of Ti and W elements.

2. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 1, characterized in that: In step (1), the sieving is through a 100-200 mesh sieve.

3. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 1, characterized in that: In step (1), the drying temperature is 380-450°C.

4. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 1, characterized in that: In step (2), the mass ratio of the dried waste SCR denitration catalyst powder to the carbon powder is 1:0.8-2.

5. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 4, characterized in that: In step (2), the mass ratio of the dried waste SCR denitration catalyst powder to the carbon powder is 1:0.8-1.

4.

6. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 1, characterized in that: In step (3), the temperature after heating is 1000-1100°C.

7. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 1, characterized in that: In step (3), the gas flow rate of ammonia is 500 to 1000 mL / min.

8. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 7, characterized in that: In step (3), the gas flow rate of ammonia is 900-1000 mL / min.

9. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 1, characterized in that: In step (3), the gas flow rate of argon is 500-600 mL / min.

10. The method for recovering Ti and W elements from waste SCR denitration catalyst according to claim 1, characterized in that: In step (4), the separation and purification is: The reduction nitridation product is placed in a crucible, and then the crucible containing the reduction nitridation product is placed in a working furnace. Nitrogen is first introduced to exhaust the air in the working furnace; then, under the protection of argon, the temperature is raised to 450°C at a heating rate of 10°C / min, the argon is disconnected, Cl2 is introduced instead, and the temperature is kept until the reduction nitridation product and Cl2 fully react, Cl2 is switched to N2, and the sample is taken out after the temperature in the furnace drops to room temperature; the obtained sample is distilled to obtain TiCl4 and WCl6, respectively, thereby realizing the recovery of Ti and W elements.

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