Treatment method and system for electrolytic rare earth metal waste gas

Abstract

The invention discloses an electrolytic rare earth metal waste gas treatment method which comprises the following steps: 1) separating dust in electrolytic rare earth metal waste gas to obtain dust particles and dust-removed waste gas; (2) carrying out water spraying treatment on the dust-removed waste gas by adopting water to obtain water-sprayed waste gas and water spraying absorption liquid; carrying out solid-liquid separation on the water spraying absorption liquid to obtain water spraying slag and a water spraying separation liquid; (3) carrying out lime water spraying treatment on the waste gas subjected to water spraying by adopting lime water to obtain tail gas and lime water spraying absorption liquid; carrying out solid-liquid separation on the lime water spraying absorption liquid to obtain lime water spraying slag and lime water spraying separation liquid; and 4) mixing the water spraying separation liquid and the lime water spraying slag for reaction to obtain calcium fluoride. Cheap lime is adopted as a treatment agent, calcium fluoride with the purity larger than 99.5% can be obtained, and environment-friendly recycling of electrolytic rare earth metal fluorine-containing waste gas treatment is completely achieved.

Description

Technical Field

[0001] The invention relates to the field of waste gas treatment, and in particular to a method and system for treating waste gas from electrolysis of rare earth metals. Background Art

[0002] At present, rare earth metal production adopts the fluoride-oxide system electrolysis method. During the electrolysis process, part of the fluoride will volatilize with the electrolytic flue gas, generating fluorine-containing waste gas. The existing technology mainly treats the fluorine-containing waste gas in the following ways:

[0003] 1. After the waste gas is captured and the rare earth dust in the waste gas is removed, it is passed into lime water. The process can recover most of the rare earth dust. The treatment process is relatively simple and does not require secondary treatment, but it will cause a waste of fluorine resources.

[0004] Second, the waste gas is treated by spraying with alkali solution. For example, the tail gas generated by electrolysis is treated by dust removal equipment and then introduced into a spray absorption tower with lithium bicarbonate as absorbent for chemical absorption. After chemical absorption, the waste gas with carbon dioxide as the main component is directly introduced into the lithium carbonate liquid pool to convert lithium carbonate into lithium bicarbonate with high solubility, thereby reducing carbon dioxide emissions. However, this process is complicated due to multiple spray treatments, and lithium carbonate is expensive, making it difficult to implement.

[0005] Therefore, the existing process has problems such as waste of fluorine resources, high process costs, and generation of difficult-to-treat waste residues, and cannot meet the development of green ecology and circular economy. Summary of the invention

[0006] The purpose of the present invention is to provide a method and system for treating waste gas from electrolysis of rare earth metals to solve the problem of treating waste gas from electrolysis of rare earth metals. The above purpose is achieved through the implementation of the following technical solutions:

[0007] A method for treating waste gas from electrolysis of rare earth metals comprises the following steps:

[0008] Step 1) separating dust from the waste gas of electrolytic rare earth metals to obtain dust particles and waste gas after dust removal;

[0009] Step 2) using water to spray the dust-removed waste gas to obtain water-sprayed waste gas and water-sprayed absorption liquid; performing solid-liquid separation on the water-sprayed absorption liquid to obtain water-sprayed residue and water-sprayed separation liquid;

[0010] Step 3) using lime water to treat the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid; performing solid-liquid separation on the lime water spray absorption liquid to obtain lime water spray residue and lime water spray separation liquid;

[0011] Step 4) mixing the water spray separation liquid and the lime water spray residue to react and obtain calcium fluoride.

[0012] Among them, the waste gas after water spraying in step 2) is mainly fluorine-containing waste gas and carbon dioxide, the water spray absorption liquid mainly contains dry fluorine-containing rare earth compounds and partially dissolved hydrogen fluoride and carbon dioxide; the water spray slag is the separated fluorine-containing rare earth compounds; the water spray separation liquid mainly contains hydrogen fluoride and carbon dioxide.

[0013] In step 3), lime water is used to absorb the fluorine-containing waste gas and carbon dioxide that are not completely absorbed in step 2), and the lime water spray absorption liquid mainly contains calcium fluoride, calcium carbonate and unreacted calcium hydroxide. The lime water spray residue obtained after solid-liquid separation mainly contains calcium fluoride and calcium carbonate.

[0014] After the water spray separation liquid and the lime water spray residue are mixed and reacted, the hydrogen fluoride in the water spray separation liquid and the calcium carbonate in the lime water spray residue are completely reacted to generate calcium fluoride, that is, high-purity calcium fluoride is obtained. The purity of calcium fluoride is greater than 99%.

[0015] Optionally, in the step 2), the water-sprayed slag is dried at a temperature of 200 to 400°C.

[0016] Optionally, the dust particles obtained in step 1) and the water-sprayed slag obtained in step 2) are sent to the electrolysis of rare earth metals for recycling.

[0017] Optionally, the pH of the lime water in step 3) is ≥ 10;

[0018] Optionally, in the step 3), the lime water spray separation liquid is used to prepare the lime water;

[0019] Optionally, in the step 3), the pH of the lime water is monitored in real time, and when the pH is less than 10, lime is added to the lime water.

[0020] Optionally, in the step 4), the water spray separation liquid and the lime water spray residue are stirred and reacted for 8 to 16 hours, filtered after the reaction is completed, and the solid phase product obtained by filtration is dried at 300 to 500° C. to obtain calcium fluoride.

[0021] Optionally, the volume flow ratio of water to the exhaust gas after dust removal in step 2) is 1:100-500;

[0022] In the step 3), the volume flow ratio of the waste gas after the lime water is sprayed with water is 1:50-300.

[0023] A treatment system for waste gas from electrolysis of rare earth metals, comprising:

[0024] A dust separation and recovery device is used to separate and recover dust from the waste gas of electrolytic rare earth metals to obtain the waste gas after dust removal;

[0025] a first spraying device, the first spraying device being connected to the dust separation and recovery device, and being used for performing water spraying treatment on the waste gas after dust removal to obtain the waste gas after water spraying and the water spraying absorption liquid;

[0026] A first solid-liquid separation device, which is connected to the first spraying device and is used to perform solid-liquid separation on the water spraying absorption liquid to obtain water spraying residue and water spraying separation liquid;

[0027] A second spraying device, the second spraying device is connected to the first spraying device, and the second spraying device is used to spray the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid;

[0028] a second solid-liquid separation device, the second solid-liquid separation device being connected to the second spraying device and used for performing solid-liquid separation on the limewater spraying absorption liquid to obtain limewater spraying residue and limewater spraying separation liquid;

[0029] The reaction device is connected to the first solid-liquid separation device and the second solid-liquid separation device and is used for mixing and reacting the water spray separation liquid and the lime water spray residue to obtain calcium fluoride.

[0030] Optionally, the dust separation and recovery device adopts a bag dust removal device.

[0031] Optionally, a fan is provided between the dust separation and recovery device and the first spraying device.

[0032] Optionally, a stirrer is provided in the reaction device.

[0033] Optionally, the second spraying device is connected to a lime water storage tank;

[0034] Optionally, the first spraying device is connected to a water tank.

[0035] Optionally, the second solid-liquid separation device is sequentially connected to a lime water preparation tank and a lime water clarification tank, the lime water clarification tank is connected to the lime water storage tank; the lime water preparation tank is connected to an automatic weighing device, and the automatic weighing device is connected to a lime storage tank;

[0036] Optionally, a pH detector is provided on the limewater storage tank;

[0037] Optionally, the pH detector is connected to a controller, and the controller is connected to an automatic weighing device.

[0038] The present invention has the following beneficial effects:

[0039] The process of the present invention is simple and convenient to operate, has a short process flow, and has a high fluorine collection efficiency. The particles collected in step 1) and step 2) can be directly returned to the electrolysis workshop for use after drying, thereby improving the yield of electrolytic rare earth metal products. By using cheap lime as a treatment agent, calcium fluoride with a purity greater than 99.5% can be obtained, and the green recycling and reuse of fluorine-containing waste gas treatment from electrolytic rare earth metals is fully realized, laying a foundation for clean production and energy conservation and carbon reduction in the electrolytic rare earth metal industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 It is a schematic diagram of the device of the present invention.

[0042] Figure 2 Schematic diagram of the reaction apparatus.

[0043] Reference numerals:

[0044] 1. Fan 2. First spray device 3. Second spray device 4. Water storage tank 5. Lime water tank 6. Real-time pH meter 7. Lime storage tank 8. Automatic weigher 9. Lime water preparation tank 10. Lime water clarification tank 11. Recovery tank 12. Dust separation and recovery device 13. First solid-liquid separation device 14. Water spray separation liquid tank 15. Second solid-liquid separation device 16. Lime water spray separation liquid tank 17. Reaction device 18. Agitator 19. Feed inlet. DETAILED DESCRIPTION

[0045] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0046] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0047] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0048] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0049] Embodiment 1:

[0050] This embodiment is directed to a production line that produces 89.5 tons of rare earth metals per month.

[0051] Step 1) Separate dust from the waste gas of rare earth metal electrolysis to obtain dust particles and waste gas after dust removal: The fluorine-containing waste gas and dust particles generated by the electrolysis of rare earth metals are subjected to bag dust removal in step 1 to settle the particles generated during the electrolysis process, and the weight of the obtained particles is 402.7 kg. The main components of the particles are rare earth compounds (REO: 73.5%), 3.1% iron oxide, and 4.8% carbon powder, which are directly returned to the workshop for use;

[0052] Step 2) Use water to spray the waste gas after dust removal, further settle the fluorine-containing particles, and dissolve part of the fluorine-containing waste gas and carbon dioxide in water to obtain water-sprayed waste gas and water-sprayed absorption liquid; use filter press to separate the solid and liquid of the water-sprayed absorption liquid to obtain water-sprayed slag and water-sprayed separation liquid. The volume flow ratio of water to waste gas after dust removal is 1:250, and the drying temperature of the water-sprayed slag is 312°C. 85kg of dry fluorine-containing rare earth compounds are obtained, which are returned to the electrolytic rare earth metal workshop together with the rare earth compounds recovered in step 1. The yield of rare earth metal products is 98.8%. The hydrogen fluoride content of the water-sprayed separation liquid after filter press is 20%, which is retained for use;

[0053] Step 3) Use lime water to treat the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid; separate the lime water spray absorption liquid into solid and liquid to obtain lime water spray residue and lime water spray separation liquid. The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in step 2) are absorbed by lime water, and the lime water spray separation liquid is reused to prepare the above-mentioned lime water to ensure that the PH value of the lime water is 11. The volume flow ratio of lime water to waste gas after water spraying is 1:200, and the F content in the tail gas is 1.2mg / m 3 .

[0054] Step 4) reacting the lime water spray residue with the water spray separation liquid containing hydrogen fluoride retained in step 2), stirring at room temperature for 8 hours, filtering by pressure and drying at 300° C. to obtain 2188 kg of calcium fluoride with a purity of 99.57%.

[0055] The above scheme can be implemented by the following device:

[0056] like Figure 1 , Figure 2 A treatment system for waste gas from electrolysis of rare earth metals is shown, comprising:

[0057] The dust separation and recovery device 12 adopts a bag dust removal device to separate and recover dust in the waste gas of the electrolytic rare earth metal to obtain the waste gas after dust removal;

[0058] The first spray device 2 is connected to the dust separation and recovery device 12, and a fan 1 is provided between the dust separation and recovery device 12 and the first spray device 2. The first spray device is used to perform water spray treatment on the waste gas after dust removal to obtain the waste gas after water spray and the water spray absorption liquid;

[0059] The first solid-liquid separation device 13 is connected to the first spraying device 2 and is used to separate the water spray absorption liquid into solid and liquid to obtain water spray residue and water spray separation liquid. The water spray separation liquid is sent to the water spray separation liquid tank for storage.

[0060] A second spray device 3, the second spray device 3 is connected to the first spray device 2, and the second spray device is used to spray the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid;

[0061] The second solid-liquid separation device 15 is connected to the second spraying device 3 and is used to perform solid-liquid separation on the lime water spray absorption liquid to obtain lime water spray residue and lime water spray separation liquid; the lime water spray separation liquid enters the lime water spray separation liquid tank 16 for circulating preparation of lime water.

[0062] The reaction device 17 is connected to the first solid-liquid separation device 13 and the second solid-liquid separation device 15, and is used to mix and react the water spray separation liquid and the lime water spray residue to obtain calcium fluoride. A stirrer 18 is provided in the reaction device. A feed port 19 is provided at the top of the reaction device 17. The water spray separation liquid and the lime water spray residue are put into the reaction device 17 through the feed port 19.

[0063] The first spray device 2 is connected to a water tank 4 for water supply; the second spray device is connected to a lime water tank 5 for providing lime water. A real-time pH meter 6 is provided on the lime water tank 5. The lime water tank 5 is connected to a lime water preparation device. As shown in the figure, the lime water preparation device includes: a lime water spray separation liquid tank 16, a recovery tank 11, a lime water preparation tank 9, and a lime water clarification tank 10 connected in sequence to the second solid-liquid separation device 15, and the lime water clarification tank 10 is connected to the lime water tank 5; the lime water preparation tank 9 is connected to an automatic weighing device 8, and the automatic weighing device 8 is connected to a lime storage tank 7. The pH detector is connected to a controller, and the controller is connected to the automatic weighing device. In this way, the controller can monitor the pH of the lime water in real time. If the pH is too low during the continuous reaction process, the automatic weighing device can be controlled to automatically add lime to realize automatic lime feeding.

[0064] Embodiment 2:

[0065] This embodiment is directed to a production line that produces 172.8 tons of rare earth metals per month.

[0066] Step 1) Separating dust from the waste gas of rare earth metal electrolysis to obtain dust particles and waste gas after dust removal: The fluorine-containing waste gas and dust particles generated by the electrolysis of rare earth metals, step 1 passes through a gravity sedimentation chamber to settle the particles generated during the electrolysis process, the weight of the particles is 864kg, the main components of the particles are rare earth compounds (REO: 75.2%), iron oxide 2.7%, and carbon powder 3.2%, which are directly returned to the workshop for use;

[0067] Step 2) Use water to spray the waste gas after dust removal, further settle the fluorine-containing particles, and dissolve part of the fluorine-containing waste gas and carbon dioxide in water to obtain water-sprayed waste gas and water-sprayed absorption liquid; use filter press to separate the solid and liquid of the water-sprayed absorption liquid to obtain water-sprayed slag and water-sprayed separation liquid. The volume flow ratio of water to waste gas after dust removal is 1:300, and the drying temperature of the water-sprayed slag is 200°C. 185.6 kg of dry fluorine-containing rare earth compounds are obtained, which are returned to the electrolytic rare earth metal workshop together with the rare earth compounds recovered in step 1. The yield of rare earth metal products is 98.91%. The hydrogen fluoride content of the water-sprayed separation liquid after filter press is 16.2%, which is retained for use;

[0068] Step 3) Use lime water to treat the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid; separate the lime water spray absorption liquid into solid and liquid to obtain lime water spray residue and lime water spray separation liquid. The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in step 2) are absorbed by lime water, and the lime water spray separation liquid is reused to prepare the above-mentioned lime water to ensure that the PH value of lime water is 11. The volume flow ratio of lime water to waste gas after water spraying is 1:250, and the F content in the tail gas is 0.8mg / m 3 .

[0069] Step 4) reacting the lime water spray residue with the water spray separation liquid containing hydrogen fluoride retained in step 2), stirring at room temperature for 12 hours, filtering by pressure and drying at 400° C. to obtain 5680 kg of calcium fluoride with a purity of 99.57%.

[0070] Embodiment 3:

[0071] This embodiment is directed to a production line that produces 100.6 tons of rare earth metals per month.

[0072] Step 1) Separating dust from the waste gas of rare earth metal electrolysis to obtain dust particles and waste gas after dust removal: The fluorine-containing waste gas and dust particles generated by the electrolysis of rare earth metals, step 1 passes through a gravity sedimentation chamber to settle the particles generated during the electrolysis process, the weight of the particles is 450.3kg, the main components of the particles are rare earth compounds (REO: 74.1%), 3.4% iron oxide, and 2.8% carbon powder, which are directly returned to the workshop for use;

[0073] Step 2) Use water to spray the waste gas after dust removal, further settle the fluorine-containing particles, and dissolve part of the fluorine-containing waste gas and carbon dioxide in water to obtain water-sprayed waste gas and water-sprayed absorption liquid; use filter press to separate the solid and liquid of the water-sprayed absorption liquid to obtain water-sprayed slag and water-sprayed separation liquid. The volume flow ratio of water to the waste gas after dust removal is 1:500, and the drying temperature of the water-sprayed slag is 400°C. 98.5 kg of dry fluorine-containing rare earth compounds are obtained, which are returned to the electrolytic rare earth metal workshop together with the rare earth compounds recovered in step 1, and the yield of rare earth metal products is 98.63%. The hydrogen fluoride content of the water-sprayed separation liquid after filter press is 1.0%, which is retained for use;

[0074] Step 3) Use lime water to treat the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid; separate the lime water spray absorption liquid into solid and liquid to obtain lime water spray residue and lime water spray separation liquid. The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in step 2) are absorbed by lime water, and the lime water spray separation liquid is reused to prepare the above-mentioned lime water to ensure that the PH value of lime water is 11. The volume flow ratio of lime water to waste gas after water spraying is 1:300, and the F content in the tail gas is 1.5mg / m 3 .

[0075] Step 4) reacting the lime water spray residue with the water spray separation liquid containing hydrogen fluoride retained in step 2), stirring at room temperature for 12 hours, filtering by pressure and drying at 500° C. to obtain 2972 ​​kg of calcium fluoride with a purity of 99.50%.

[0076] Embodiment 4:

[0077] For the production line with monthly production of 152 tons of rare earth metals.

[0078] Step 1) Separating dust from the waste gas of rare earth metal electrolysis to obtain dust particles and waste gas after dust removal: The fluorine-containing waste gas and dust particles generated by the electrolysis of rare earth metals, step 1 passes through a gravity sedimentation chamber to settle the particles generated during the electrolysis process, the weight of the particles is 729.6kg, the main components of the particles are rare earth compounds (REO: 69.45%), iron oxide 2.7%, and carbon powder 3.8%, which are directly returned to the workshop for use;

[0079] Step 2) Use water to spray the waste gas after dust removal, further settle the fluorine-containing particles, and dissolve part of the fluorine-containing waste gas and carbon dioxide in water to obtain water-sprayed waste gas and water-sprayed absorption liquid; use filter press to separate the solid and liquid of the water-sprayed absorption liquid to obtain water-sprayed slag and water-sprayed separation liquid. The volume flow ratio of water to the waste gas after dust removal is 1:300, and the drying temperature of the water-sprayed slag is 400°C. 156.2 kg of dry fluorine-containing rare earth compounds are obtained, which are returned to the electrolytic rare earth metal workshop together with the rare earth compounds recovered in step 1, and the yield of rare earth metal products is 98.63%. The hydrogen fluoride content of the water-sprayed separation liquid after filter press is 15%, which is retained for use;

[0080] Step 3) Use lime water to treat the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid; separate the lime water spray absorption liquid into solid and liquid to obtain lime water spray residue and lime water spray separation liquid. The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in step 2) are absorbed by lime water, and the lime water spray separation liquid is reused to prepare the above-mentioned lime water to ensure that the PH value of lime water is 11. The volume flow ratio of lime water to waste gas after water spraying is 1:150, and the F content in the tail gas is 1.0mg / m 3 .

[0081] Step 4) reacting the lime water spray residue with the water spray separation liquid containing hydrogen fluoride retained in step 2), stirring at room temperature for 16 hours, filtering by pressure and drying at 500° C. to obtain 4878 kg of calcium fluoride with a purity of 99.62%.

[0082] Embodiment 5:

[0083] For the production line with monthly production of 148.56 tons of rare earth metals.

[0084] Step 1) Separating dust from the waste gas of rare earth metal electrolysis to obtain dust particles and waste gas after dust removal: The fluorine-containing waste gas and dust particles generated by the electrolysis of rare earth metals, step 1 passes through a gravity sedimentation chamber to settle the particles generated during the electrolysis process, the weight of the particles is 738.6kg, the main components of the particles are rare earth compounds (REO: 75.48%), iron oxide 2.3%, and carbon powder 2.6%, which are directly returned to the workshop for use;

[0085] Step 2) Use water to spray the waste gas after dust removal, further settle the fluorine-containing particles, and dissolve part of the fluorine-containing waste gas and carbon dioxide in water to obtain waste gas after water spraying and water spray absorption liquid; the water spray absorption liquid is subjected to solid-liquid separation by filter pressing to obtain water spray slag and water spray separation liquid. The volume flow ratio of water to waste gas after dust removal is 1:200, and the drying temperature of the water spray slag is 300°C. 150.3kg of dry fluorine-containing rare earth compounds are obtained, which are returned to the electrolytic rare earth metal workshop together with the rare earth compounds recovered in step 1, and the yield of rare earth metal products is 98.88%. The hydrogen fluoride content of the water spray separation liquid after filter pressing is 14.8%, which is retained for use;

[0086] Step 3) Use lime water to treat the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid; separate the lime water spray absorption liquid into solid and liquid to obtain lime water spray residue and lime water spray separation liquid. The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in step 2) are absorbed by lime water, and the lime water spray separation liquid is reused to prepare the above-mentioned lime water to ensure that the PH value of lime water is 11. The volume flow ratio of lime water to waste gas after water spraying is 1:200, and the F content in the tail gas is 0.9mg / m 3 .

[0087] Step 4) reacting the lime water spray residue with the water spray separation liquid containing hydrogen fluoride retained in step 2), stirring at room temperature for 12 hours, filtering by pressure and drying at 400° C. to obtain 4938 kg of calcium fluoride with a purity of 99.62%.

[0088] Comparative Example 1

[0089] Compared with Example 1, this comparative example does not perform water spraying, but directly sprays the exhaust gas after dust removal in step 1) with lime water with pH = 11, and the F content in the exhaust gas is 4.5 mg / m 3 After the lime water spray absorption liquid is separated into solid and liquid, the solid phase product obtained contains a small amount of calcium carbonate about 1-3%, calcium hydroxide 0.5-2%, rare earth fluoride 0.1-1%, and the rest is calcium fluoride.

[0090] Comparative Example 2

[0091] Compared with Example 1, this comparative example adopts lime water with pH=9.5 for spraying treatment, and the remaining steps are the same as those in Example 1. As a result, the F content in the tail gas is 3.6 mg / m 3 .

[0092] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for treating waste gas from electrolysis of rare earth metals, characterized in that: The steps include: Step 1) separating dust from the waste gas of electrolytic rare earth metals to obtain dust particles and waste gas after dust removal; Step 2) using water to spray the waste gas after dust removal to obtain waste gas after water spraying and water spraying absorption liquid; performing solid-liquid separation on the water spraying absorption liquid to obtain water spraying residue and water spraying separation liquid; Step 3) using lime water to treat the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid; performing solid-liquid separation on the lime water spray absorption liquid to obtain lime water spray residue and lime water spray separation liquid; Step 4) mixing the water spray separation liquid and the lime water spray residue to react and obtain calcium fluoride.

2. The method for treating waste gas from electrolysis of rare earth metals according to claim 1, characterized in that: In the step 2), the water-sprayed slag is dried at a temperature of 200-400°C.

3. The method for treating waste gas from electrolysis of rare earth metals according to claim 1, characterized in that: The dust particles obtained in step 1) and the water-sprayed slag obtained in step 2) are sent to the rare earth metal electrolysis process for recycling.

4. The method for treating waste gas from electrolysis of rare earth metals according to claim 1, characterized in that: The pH of the lime water in the step 3) is ≥ 10; Preferably, in the step 3), the lime water spray separation liquid is used to prepare the lime water; Preferably, in the step 3), the pH of the lime water is monitored in real time, and when the pH is less than 10, lime is added to the lime water.

5. The method for treating waste gas from electrolysis of rare earth metals according to claim 1, characterized in that: In the step 4), the water spray separation liquid and the lime water spray residue are stirred and reacted for 8 to 16 hours, and filtered after the reaction is completed. The solid phase product obtained by filtration is dried at 300 to 500° C. to obtain calcium fluoride.

6. The method for treating waste gas from electrolysis of rare earth metals according to claim 1, characterized in that: The volume flow ratio of the water in step 2) to the exhaust gas after dust removal is 1:100-500; In the step 3), the volume flow ratio of the waste gas after the lime water is sprayed with water is 1:50-300.

7. A treatment system for waste gas from electrolysis of rare earth metals, characterized in that: include: A dust separation and recovery device is used to separate and recover dust from the waste gas of electrolytic rare earth metals to obtain the waste gas after dust removal; a first spraying device, the first spraying device being connected to the dust separation and recovery device, and being used for performing water spraying treatment on the waste gas after dust removal to obtain the waste gas after water spraying and the water spraying absorption liquid; A first solid-liquid separation device, which is connected to the first spraying device and is used to perform solid-liquid separation on the water spraying absorption liquid to obtain water spraying residue and water spraying separation liquid; A second spraying device, the second spraying device is connected to the first spraying device, and the second spraying device is used to spray the waste gas after water spraying with lime water to obtain tail gas and lime water spray absorption liquid; a second solid-liquid separation device, the second solid-liquid separation device being connected to the second spraying device and used for performing solid-liquid separation on the limewater spraying absorption liquid to obtain limewater spraying residue and limewater spraying separation liquid; The reaction device is connected to the first solid-liquid separation device and the second solid-liquid separation device and is used for mixing and reacting the water spray separation liquid and the lime water spray residue to obtain calcium fluoride.

8. The treatment system for waste gas from electrolysis of rare earth metals according to claim 7, characterized in that: The dust separation and recovery device adopts a bag dust removal device; Preferably, a fan is provided between the dust separation and recovery device and the first spraying device; Preferably, a stirrer is provided in the reaction device.

9. The treatment system for waste gas from electrolysis of rare earth metals according to claim 7, characterized in that: The second spraying device is connected to a lime water storage tank; Preferably, the first spraying device is connected to a water tank.

10. The treatment system for waste gas from electrolysis of rare earth metals according to claim 9, characterized in that: The second solid-liquid separation device is sequentially connected to a lime water preparation tank and a lime water clarification tank, the lime water clarification tank is connected to the lime water storage tank; the lime water preparation tank is connected to an automatic weighing device, and the automatic weighing device is connected to a lime storage tank; Preferably, a pH detector is provided on the limewater storage tank; Preferably, the pH detector is connected to a controller, and the controller is connected to an automatic weighing device.

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