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; (3) carrying out primary lime water spraying treatment on the waste gas subjected to water spraying by adopting lime water to obtain waste gas subjected to primary lime water spraying and primary lime water spraying absorption liquid; the pH value of the primary lime water spraying absorption liquid is 4-6; (4) carrying out secondary lime water spraying treatment on the waste gas subjected to primary lime water spraying by adopting lime water to obtain tail gas and secondary lime water spraying absorption liquid; the pH value of the secondary lime water spraying absorption liquid is greater than or equal to 10.

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, comprising 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;

[0010] Step 3) using lime water to treat the waste gas after water spraying, to obtain the waste gas after lime water spraying and the lime water spraying absorption liquid; the pH value of the lime water spraying absorption liquid is 4 to 6;

[0011] Step 4) using lime water to treat the waste gas after the first lime water spraying with a second lime water spraying to obtain tail gas and a second lime water spraying absorption liquid; the pH of the second lime water spraying absorption liquid is ≥10.

[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 a small amount of dissolved hydrogen fluoride and carbon dioxide; the water spray slag contains the separated fluorine-containing rare earth compounds.

[0013] In step 3), a small amount of lime water is used to react with the waste gas after water spraying. Since the pH of the absorption liquid sprayed with lime water after the reaction is only 4-6, the formation of calcium carbonate can be prevented. High-purity calcium fluoride is formed in the absorption liquid sprayed with lime water. After solid-liquid separation, calcium fluoride with a purity of more than 99% can be obtained.

[0014] In step 4), the remaining fluorine-containing waste gas is further absorbed with lime water, and the pH of the absorption liquid sprayed with secondary lime water is ≥ 10 to ensure that the fluorine in the tail gas is completely absorbed.

[0015] Optionally, the water spray absorption liquid is subjected to solid-liquid separation to obtain water spray residue and water spray separation liquid;

[0016] The primary lime water spray absorption liquid is subjected to solid-liquid separation to obtain a calcium fluoride product and a primary lime water spray separation liquid.

[0017] The secondary lime water spray absorption liquid is subjected to solid-liquid separation to obtain waste residue and secondary lime water spray separation liquid.

[0018] Optionally, the water-sprayed slag is dried at a temperature of 200-400°C.

[0019] 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.

[0020] Optionally, the volume flow ratio of water to the exhaust gas after dust removal in step 2) is 1:100-500;

[0021] In the step 3), the volume flow ratio of the waste gas after the lime water is sprayed with water is 1:90-400.

[0022] In the step 4), the volume flow ratio of the lime water to the waste gas after the first lime water spraying is 1:80-350.

[0023] Optionally, the water spray separation liquid, the primary lime water spray separation liquid and the secondary lime water spray separation liquid are used to prepare the lime water.

[0024] A treatment system for waste gas from electrolysis of rare earth metals, comprising:

[0025] 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;

[0026] 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;

[0027] a second spraying device, the second spraying device being connected to the first spraying device, and being used for spraying the waste gas after water spraying with lime water once to obtain the waste gas after lime water spraying and a lime water spraying absorption liquid; the pH value of the lime water spraying absorption liquid is 4 to 6;

[0028] The third spray device is connected to the second spray device, and the second spray device is used to spray the waste gas after the first lime water spray with two lime water to obtain tail gas and secondary lime water spray absorption liquid; the pH of the secondary lime water spray absorption liquid is ≥10.

[0029] Optionally, a first solid-liquid separation device is connected to the first spraying device and is used to perform solid-liquid separation on the water spray absorption liquid to obtain water spray residue and water spray separation liquid;

[0030] A second solid-liquid separation device, which is connected to the second spraying device and is used to perform solid-liquid separation on the primary limewater spray absorption liquid to obtain a calcium fluoride product and a primary limewater spray separation liquid;

[0031] The third solid-liquid separation device is connected to the third spraying device and is used for performing solid-liquid separation on the secondary lime water spray absorption liquid to obtain waste residue and secondary lime water spray separation liquid.

[0032] Optionally, the dust separation and recovery device adopts a bag dust removal device.

[0033] Optionally, a fan is provided between the dust separation and recovery device and the first spraying device.

[0034] Optionally, the system further includes:

[0035] A recovery tank, wherein the recovery tank is connected to the first solid-liquid separation device, the second solid-liquid separation device and the third solid-liquid separation device respectively; the water spray separation liquid, the primary lime water spray separation liquid and the secondary lime water spray separation liquid are sent to the recovery tank;

[0036] A limewater preparation tank, which is connected to a recovery tank and is used to mix the solution in the recovery tank with lime to form limewater; the limewater preparation tank is connected to an automatic weighing device, which is connected to a lime storage tank;

[0037] Lime water clarification tank; the lime water clarification tank is connected to the lime water preparation tank.

[0038] Preferably, the first spray device is provided with a primary water supply and drainage device, the second spray device is provided with a secondary water supply and drainage device, and the third spray device is provided with a tertiary water supply and drainage device. The water outlets of the second spray device and the third spray device are both provided with pH detectors.

[0039] Preferably, the pH detector is connected to a controller, and the controller is connected to an automatic weighing device.

[0040] The present invention has the following beneficial effects:

[0041] This process is simple and convenient to operate, with a short process and high fluorine collection efficiency. The particulate matter collected in the first and second steps can be directly returned to the electrolysis workshop for use after drying, thereby increasing the yield of electrolytic rare earth metal products. Inexpensive lime is used as a treatment agent to obtain calcium fluoride with a purity greater than 99%, fully realizing the green recycling and reuse of fluorine-containing waste gas treatment from electrolytic rare earth metals, laying the foundation for clean production and energy conservation and carbon reduction in the electrolytic rare earth metal industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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.

[0043] Figure 1 Schematic diagram of the device of the present invention.

[0044] Reference numerals:

[0045] 1. Fan 2. First spray device 3. Second spray device 4. Primary water supply and drainage device 5. Secondary water supply and drainage device 6. pH meter 1 7. Lime tank 8. Automatic lime weighing device 9. Lime water preparation pool 10. Clarifying lime water pool 11. Recovery pool 12. Bag filter 13. First filter press 14. Primary water spray liquid phase 15. Second filter press 16. Secondary alkali spray liquid phase 17. Third spray device 18. Third tower water pool 19. pH meter 20. Third filter press 21. Third alkali spray liquid phase. DETAILED DESCRIPTION

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0050] Example 1

[0051] For the production line with monthly production capacity of 80.5 tons of rare earth metals.

[0052] Step 1) Separating dust from the waste gas of electrolytic rare earth metals 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 obtained particles weigh 362.5 kg. The main components of the particles are rare earth compounds (REO: 68.5%), 3.6% iron oxide, and 6.8% carbon powder, which are directly returned to the workshop for use;

[0053] 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 1:250. The water spray slag is dried to obtain 82.5 kg of dry fluorine-containing rare earth compounds, 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 98.8%. The water spray separation liquid after filter pressing is returned to prepare lime water for use;

[0054] Step 3) lime water is used to treat the waste gas after water spraying, the volume flow ratio of lime water to waste gas after water spraying is 1:200, the pH is 5, and tail gas and lime water spray absorption liquid are obtained; the lime water spray absorption liquid is subjected to solid-liquid separation to obtain lime water spray residue (calcium fluoride purity is greater than 99.2%) and lime water spray separation liquid. The lime water spray residue is dried to obtain 1809 kg of calcium fluoride with a purity of 99.2%, and the lime water spray separation liquid is returned to prepare lime water for use.

[0055] Step 4) The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in the process of step 3 are sprayed with excess lime water, and the volume flow ratio of the waste gas after lime water spraying is 1:150, and the pH is maintained at 10 to obtain the three-stage spray tower lime water spray slag (general solid waste, the main components are calcium fluoride, calcium carbonate and calcium hydroxide, dried 50kg) and lime water spray separation liquid, and the lime water spray separation liquid is returned to the recovery pool for the preparation of lime water, and the F content in the tail gas is 0.8mg / m 3 .

[0056] The system used in the present invention is as follows Figure 1 As shown:

[0057] A treatment system for waste gas from electrolysis of rare earth metals, comprising:

[0058] The dust separation and recovery device 12 is used to separate and recover dust in the waste gas from the electrolysis of rare earth metals to obtain the waste gas after dust removal; specifically, a bag dust collector is used; a fan 1 is provided between the dust separation and recovery device 12 and the first spray device 2.

[0059] A first spray device 2, the first spray device 2 is connected to the dust separation and recovery device 12, and the first spray device 2 is used to perform water spraying treatment on the waste gas after dust removal to obtain the waste gas after water spraying and the water spraying absorption liquid;

[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 perform a lime water spray treatment on the waste gas after water spraying, so as to obtain the waste gas after the lime water spraying and the lime water spraying absorption liquid; the pH value of the lime water spraying absorption liquid is 4-6;

[0061] The third spray device 17 is connected to the second spray device 3, and the second spray device is used to spray the waste gas after the first lime water spray with two lime water to obtain tail gas and secondary lime water spray absorption liquid; the pH of the secondary lime water spray absorption liquid is ≥10.

[0062] A first solid-liquid separation device 13, which is connected to the first spraying device 2 and is used to perform solid-liquid separation on the water spraying absorption liquid to obtain water spraying residue and water spraying separation liquid;

[0063] A second solid-liquid separation device 15, which is connected to the second spraying device 3 and is used to perform solid-liquid separation on the primary lime water spray absorption liquid to obtain a calcium fluoride product and a primary lime water spray separation liquid;

[0064] The third solid-liquid separation device 20 is connected to the third spraying device 17 and is used for performing solid-liquid separation on the secondary lime water spray absorption liquid to obtain waste residue and secondary lime water spray separation liquid.

[0065] Optionally, the system further includes:

[0066] A recovery tank 11, wherein the recovery tank 11 is connected to the first solid-liquid separation device, the second solid-liquid separation device and the third solid-liquid separation device respectively; the water spray separation liquid, the primary lime water spray separation liquid and the secondary lime water spray separation liquid are sent to the recovery tank;

[0067] A limewater preparation tank 9, which is connected to a recovery tank and is used to mix the solution in the recovery tank with lime to form limewater; the limewater preparation tank is connected to an automatic weighing device, which is connected to a lime storage tank;

[0068] Lime water clarification tank 10; the lime water clarification tank is connected to the lime water preparation tank.

[0069] The first spray device is provided with a primary water supply and drainage device, the second spray device is provided with a secondary water supply and drainage device, and the third spray device is provided with a tertiary water supply and drainage device. The water outlets of the second spray device and the third spray device are both provided with a pH detector. The pH detector is convenient for detecting the pH of the spray water. The pH detector is connected to a controller, and the controller is connected to an automatic weighing device 8.

[0070] The controller can monitor the pH of lime water in real time. If the pH is too low during the continuous reaction, the automatic weigher can be controlled to automatically add lime to achieve automatic lime addition.

[0071] It should be noted that the recovery tank 11 simultaneously recovers three solutions, namely, the water spray separation liquid, the primary lime water spray separation liquid and the secondary lime water spray. The water spray separation liquid contains hydrofluoric acid and carbon dioxide, while the secondary lime water spray contains unreacted calcium hydroxide, etc. The three solutions react in the recovery tank 11 to generate precipitates such as calcium fluoride and calcium carbonate; the recovery tank 11 can function as a sedimentation tank. A cleaning port is provided on the recovery tank 11 for regularly cleaning the precipitates in the recovery tank 11.

[0072] Example 2

[0073] For the production line with monthly production capacity of 89.5 tons of rare earth metals.

[0074] Step 1) Separate dust from the waste gas of electrolytic rare earth metals 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 420.6 kg. The main components of the particles are rare earth compounds (REO: 70.5%), iron oxide 2.8%, and carbon powder 5.4%, which are directly returned to the workshop for use;

[0075] 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 1:500. The water spray slag is dried to obtain 94.3 kg of dry fluorine-containing rare earth compounds, 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 98.7%. The water spray separation liquid after filter pressing is returned to prepare lime water for use;

[0076] Step 3) lime water is used to treat the waste gas after water spraying, the volume flow ratio of lime water to waste gas after water spraying is 1:350, the pH is 4, and tail gas and lime water spray absorption liquid are obtained; the lime water spray absorption liquid is subjected to solid-liquid separation to obtain lime water spray residue (calcium fluoride purity greater than 99.3%) and lime water spray separation liquid. The lime water spray residue is dried to obtain 1993 kg of calcium fluoride with a purity of 99.2%, and the lime water spray separation liquid is returned to prepare lime water for use.

[0077] Step 4) The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in the process of step 3 are sprayed with excess lime water, and the volume flow ratio of lime water to waste gas after water spraying is 1:200, and the pH is maintained at 11 to obtain three-stage spray tower lime water spray slag (general solid waste, the main components are calcium fluoride, calcium carbonate and calcium hydroxide, drying 75.2kg) and lime water spray separation liquid, and the lime water spray separation liquid is returned to the recovery pool for the preparation of lime water, and the F content in the tail gas is 1.1mg / m 3 .

[0078] Example 3

[0079] For the production line with monthly production of 172.8 tons of rare earth metals.

[0080] Step 1) Separate dust from the waste gas of electrolytic rare earth metals 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 933.1 kg. The main components of the particles are rare earth compounds (REO: 69.2%), 3.1% iron oxide, and 5.9% carbon powder, which are directly returned to the workshop for use;

[0081] Step 2) Use water to spray the dust-removed waste gas, 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; the water-sprayed absorption liquid is subjected to solid-liquid separation by filter pressing to obtain water-sprayed slag and water-sprayed separation liquid. The volume flow ratio of water to dust-removed waste gas is 1:100. The water-sprayed slag is dried to obtain 151.2 kg of dry fluorine-containing rare earth compounds, 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 98.5%. The water-sprayed separation liquid after filter pressing is returned to prepare lime water for use;

[0082] Step 3) lime water is used to treat the waste gas after water spraying, the volume flow ratio of lime water to waste gas after water spraying is 1:90, the pH is 6, and tail gas and lime water spray absorption liquid are obtained; the lime water spray absorption liquid is subjected to solid-liquid separation to obtain lime water spray residue (calcium fluoride purity is greater than 99%) and lime water spray separation liquid. The lime water spray residue is dried to obtain 4652 kg of calcium fluoride with a purity of 99.2%, and the lime water spray separation liquid is returned to prepare lime water for use.

[0083] Step 4) The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in the process of step 3 are sprayed with excess lime water, and the volume flow ratio of lime water to waste gas after water spraying is 1:80, and the pH is maintained at 12 to obtain three-stage spray tower lime water spray slag (general solid waste, the main components are calcium fluoride, calcium carbonate and calcium hydroxide, drying 163.8kg) and lime water spray separation liquid, and the lime water spray separation liquid is returned to the recovery pool for the preparation of lime water, and the F content in the tail gas is 0.7mg / m 3 .

[0084] Comparative Example 1

[0085] For the production line with monthly production capacity of 82.5 tons of rare earth metals.

[0086] 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 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 372.5 kg. The main components of the particles are rare earth compounds (REO: 69.3%), iron oxide 3.1%, and carbon powder 6.5%, which are directly returned to the workshop for use;

[0087] 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 1:450. The water spray slag is dried to obtain 90.6 kg of dry fluorine-containing rare earth compounds, 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 98.9%. The water spray separation liquid after filter pressing is returned to prepare lime water for use;

[0088] Step 3) lime water is used to treat the waste gas after water spraying, the volume flow ratio of lime water to waste gas after water spraying is 1:400, the pH is 7, and tail gas and lime water spray absorption liquid are obtained; the lime water spray absorption liquid is subjected to solid-liquid separation to obtain lime water spray residue (calcium fluoride purity is 93.6%) and lime water spray separation liquid. The lime water spray residue is dried to obtain 1925 kg of calcium fluoride with a purity of 93.6%, and the lime water spray separation liquid is returned to prepare lime water for use.

[0089] Step 4) The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in the process of step 3 are sprayed with excess lime water. The volume flow ratio of lime water to waste gas after water spraying is 1:350. The pH is maintained at 11 to obtain three-stage spray tower lime water spray slag (general solid waste, the main components are calcium fluoride, calcium carbonate and calcium hydroxide, dried 43kg) and lime water spray separation liquid. The lime water spray separation liquid is returned to the recovery pool for the preparation of lime water. The F content in the tail gas is 1.1mg / m 3 .

[0090] Comparative Example 2

[0091] For the production line with monthly production of 84.2 tons of rare earth metals.

[0092] 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 are subjected to bag dust removal in step 1 to settle the particles generated during the electrolysis process, and the obtained particles weigh 386.5 kg. The main components of the particles are rare earth compounds (REO: 67.9%), iron oxide 2.9%, and carbon powder 6.8%, which are directly returned to the workshop for use;

[0093] 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 1:300. The water spray slag is dried to obtain 75.8 kg of dry fluorine-containing rare earth compounds, 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 98.7%. The water spray separation liquid after filter pressing is returned to prepare lime water for use;

[0094] Step 3) lime water is used to treat the waste gas after water spraying, the volume flow ratio of lime water to waste gas after water spraying is 1:250, the pH is 4, and tail gas and lime water spray absorption liquid are obtained; the lime water spray absorption liquid is subjected to solid-liquid separation to obtain lime water spray residue (calcium fluoride purity is 99.3%) and lime water spray separation liquid. The lime water spray residue is dried to obtain 1452.6 kg of calcium fluoride with a purity of 99.3%, and the lime water spray separation liquid is returned to prepare lime water for use.

[0095] Step 4) The fluorine-containing waste gas and carbon dioxide that are not completely absorbed in the process of step 3 are sprayed with excess lime water. The volume flow ratio of lime water to waste gas after water spraying is 1:100, and the pH is maintained at 11 to obtain the three-stage spray tower lime water spray slag (general solid waste, the main components are calcium fluoride, calcium carbonate and calcium hydroxide, dried 254kg) and lime water spray separation liquid. The lime water spray separation liquid is returned to the recovery pool for the preparation of lime water. The F content in the tail gas is 1.3mg / m 3 .

[0096] Comparative Example 3

[0097] A production line for rare earth metals with a monthly production capacity of 43.5 tons.

[0098] 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 194.6 kg. The main components of the particles are rare earth compounds (REO: 65.7%), 3.5% iron oxide, and 6.3% carbon powder, which are directly returned to the workshop for use;

[0099] 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 1:300. The water spray slag is dried to obtain 41.2 kg of dry fluorine-containing rare earth compounds, 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 98.6%. The water spray separation liquid after filter pressing is returned to prepare lime water for use;

[0100] Step 3) Use lime water to treat the waste gas after water spraying. The volume flow ratio of lime water to waste gas after water spraying is 1:250, and the pH is 5 to obtain tail gas and lime water spray absorption liquid; the lime water spray absorption liquid is subjected to solid-liquid separation to obtain lime water spray residue (calcium fluoride purity is 99.15%) and lime water spray separation liquid. The lime water spray residue is dried to obtain 711.2 kg of calcium fluoride with a purity of 99.15%, and the lime water spray separation liquid is returned to prepare lime water. The F content in the tail gas is 4.9 mg / m 3 .

[0101] 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 following steps are included 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 dust-removed waste gas to obtain water-sprayed waste gas and water-sprayed absorption liquid; Step 3) using lime water to treat the waste gas after water spraying, to obtain the waste gas after lime water spraying and the lime water spraying absorption liquid; the pH value of the lime water spraying absorption liquid is 4 to 6; Step 4) using lime water to treat the waste gas after the first lime water spraying with a second lime water spraying to obtain tail gas and a second lime water spraying absorption liquid; the pH of the second lime water spraying absorption liquid is ≥10.

2. The method for treating waste gas from electrolysis of rare earth metals according to claim 1, characterized in that: The water spray absorption liquid is subjected to solid-liquid separation to obtain water spray residue and water spray separation liquid; Performing solid-liquid separation on the primary limewater spray absorption liquid to obtain a calcium fluoride product and a primary limewater spray separation liquid; The secondary lime water spray absorption liquid is subjected to solid-liquid separation to obtain waste residue and secondary lime water spray separation liquid.

3. The method for treating waste gas from electrolysis of rare earth metals according to claim 1, characterized in that: Drying the water-sprayed slag at a temperature of 200 to 400° C.; Preferably, 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 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 1:90-400; In the step 4), the volume flow ratio of the lime water to the waste gas after the first lime water spraying is 1:80-350.

5. The method for treating waste gas from electrolysis of rare earth metals according to claim 2, characterized in that: The water spray separated liquid, the primary lime water spray separated liquid and the secondary lime water spray separated liquid are used to prepare the lime water.

6. 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 second spraying device, the second spraying device being connected to the first spraying device, and being used for spraying the waste gas after water spraying with lime water once to obtain the waste gas after lime water spraying and a lime water spraying absorption liquid; the pH value of the lime water spraying absorption liquid is 4 to 6; The third spray device is connected to the second spray device, and the second spray device is used to spray the waste gas after the first lime water spray with two lime water to obtain tail gas and secondary lime water spray absorption liquid; the pH of the secondary lime water spray absorption liquid is ≥10.

7. The treatment system for waste gas from electrolysis of rare earth metals according to claim 6, characterized in that: 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 solid-liquid separation device, which is connected to the second spraying device and is used to perform solid-liquid separation on the primary limewater spray absorption liquid to obtain a calcium fluoride product and a primary limewater spray separation liquid; The third solid-liquid separation device is connected to the third spraying device and is used for performing solid-liquid separation on the secondary lime water spray absorption liquid to obtain waste residue and secondary lime water spray separation liquid.

8. The treatment system for waste gas from electrolysis of rare earth metals according to claim 6, characterized in that: The dust separation and recovery device adopts a bag dust removal device.

9. The treatment system for waste gas from electrolysis of rare earth metals according to claim 6, characterized in that: A fan is provided between the dust separation and recovery device and the first spraying device.

10. The treatment system for waste gas from electrolysis of rare earth metals according to claim 7, characterized in that: Also includes: A recovery tank, wherein the recovery tank is connected to the first solid-liquid separation device, the second solid-liquid separation device and the third solid-liquid separation device respectively; the water spray separation liquid, the primary lime water spray separation liquid and the secondary lime water spray separation liquid are sent to the recovery tank; A limewater preparation tank, which is connected to a recovery tank and is used to mix the solution in the recovery tank with lime to form limewater; the limewater preparation tank is connected to an automatic weighing device, which is connected to a lime storage tank; A lime water clarification tank; the lime water clarification tank is connected to the lime water preparation tank; Preferably, the first spray device is provided with a primary water supply and drainage device, the second spray device is provided with a secondary water supply and drainage device, and the third spray device is provided with a tertiary water supply and drainage device; the water outlets of the second spray device and the third spray device are both provided with pH detectors; Preferably, the pH detector is connected to a controller, and the controller is connected to an automatic weighing device; Preferably, the recovery tank is provided with a cleaning port for cleaning the sediment generated in the recovery tank.

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