Tail gas treatment device in praseodymium-neodymium metal production

Abstract

The utility model provides a tail gas treatment device in praseodymium-neodymium metal production. The tail gas treatment device comprises an electrolysis workshop, an induced draft fan, a first absorption tower, a second absorption tower and a third absorption tower which are sequentially connected in series, the first absorption tower and the second absorption tower are respectively connected with the acid water treatment device to form a loop, the first absorption tower and the second absorption tower are also respectively connected with the clear water storage tank, and the acid water treatment device is also connected with the cerous carbonate solution storage tank; the third absorption tower is also connected with an alkali absorption liquid treatment device to form a loop. According to the scheme, the equipment is used in cooperation, fluorine in the electrolytic tail gas is converted into cerium fluoride with high recovery value to achieve recovery of fluorine resources, residual fluorine is treated through the alkaline calcium solution to achieve defluorination of the electrolytic tail gas, and the defect that the fluorine resources in the electrolytic tail gas in existing praseodymium-neodymium metal treatment production cannot be fully utilized is overcome.

Description

Technical Field

[0001] This application relates to the field of rare earth metal production technology, and in particular to a tail gas treatment device in praseodymium-neodymium metal production. Background Technology

[0002] Rare earth elements (RE) are a collective term for the lanthanides in the periodic table, along with their congeners scandium (Sc) and yttrium (Y). Rare earth elements readily react with elements such as oxygen and hydrogen to form corresponding stable compounds. Due to their excellent optical, electrical, magnetic, and reactive physicochemical properties, rare earth elements are widely used in light industry, metallurgy, military industry, and glass and ceramics.

[0003] Praseodymium (Pr) is a rare earth metal element with a unique hexagonal crystal structure. Praseodymium is more resistant to corrosion in air than neodymium, but it readily forms a brittle green oxide layer. Praseodymium is used in petroleum catalytic cracking, where it can improve the activity, selectivity, and stability of the catalyst. Neodymium (Nd) is found alongside praseodymium and is also one of the most reactive rare earth metal elements.

[0004] Praseodymium-neodymium (Pr-Nd) metal production typically uses praseodymium-neodymium fluoride-lithium fluoride as the electrolyte and praseodymium oxide as the raw material, employing a molten salt electrolysis method. The resulting exhaust gas contains raw material and electrolyte dust, as well as fluorine-containing gases. For every ton of praseodymium-neodymium metal produced, approximately 20 kilograms of directly recoverable fluorine resources are generated from the exhaust gas.

[0005] Existing methods for treating praseodymium-neodymium electrolysis tail gas typically involve using bag filters to recover dust from the raw material, followed by neutralization of the fluorine-containing gases with calcium oxide spray to produce calcium fluoride. This method not only fails to fully utilize the fluorine resources in the tail gas, but also results in the limited uses of the generated calcium fluoride, most of which is disposed of as general solid waste in landfills. Therefore, this leads to a waste of fluorine resources in the tail gas. Utility Model Content

[0006] This application provides a tail gas treatment device for praseodymium-neodymium metal production, which solves the problem of insufficient utilization of fluorine resources in the electrolytic tail gas of praseodymium-neodymium metal production.

[0007] This application provides a tail gas treatment device for praseodymium-neodymium metal production, comprising an electrolysis workshop, an induced draft fan, a first absorption tower, a second absorption tower, and a third absorption tower connected in series.

[0008] The first and second absorption towers are respectively connected to the acid water treatment device to form a loop. The first and second absorption towers are also respectively connected to the clean water storage tank. The acid water treatment device is also connected to the cerium carbonate solution storage tank.

[0009] The third absorption tower is also connected to the alkali absorption liquid treatment device to form a loop.

[0010] Optionally, the acid water treatment device includes a filter, an acid water storage tank, a fluorination reactor, a first filter press, and a first filtrate storage tank connected in series.

[0011] The input end of the filter is connected to the material output end of the first absorption tower and the second absorption tower, respectively;

[0012] The first filtrate storage tank is connected to the absorbent inlet of the first absorption tower and the second absorption tower, respectively.

[0013] The first filter press is also connected to a cerium fluoride storage silo;

[0014] The cerium carbonate solution storage tank is connected to the fluorination reactor.

[0015] Optionally, the alkaline absorption liquid treatment device includes a neutralization reaction vessel, a second filter press, and a second filtrate storage tank connected in series.

[0016] The neutralization reactor is connected to the material output end of the third absorption tower, and the second filtrate storage tank is also connected to the material input end of the third absorption tower.

[0017] The neutralization reactor is also connected to the alkali storage tank;

[0018] The second filter press is also connected to the calcium fluoride storage silo.

[0019] Optionally, a solenoid valve is installed between the third absorption tower and the second filtrate storage tank;

[0020] A pH meter is installed inside the third absorption tower;

[0021] The pH meter is interlocked with the solenoid valve.

[0022] Optionally, a re-filter is also provided below the first filter press;

[0023] The re-filter includes a filter box, inside which a support perforated plate is horizontally installed;

[0024] The support plate is equipped with a filter inner liner;

[0025] A drain outlet is provided on one side of the lower part of the filter box.

[0026] Optionally, a dust collection hood is installed on the top of the electrolysis workshop, and the dust collection hood is connected to the induced draft fan.

[0027] Optionally, the first absorption tower is one of a packed tower, a plate tower, or a bubble tower.

[0028] The exhaust gas treatment device provided in this application absorbs most of the fluorine-containing compounds in the exhaust gas through a first absorption tower and a second absorption tower, forming a fluorinated acidic water. This acidic water reacts with a cerium carbonate solution supplied from a cerium carbonate solution storage tank in the acidic water treatment device, causing the fluorine in the acidic water to react with the cerium carbonate to form cerium fluoride precipitate, thereby achieving fluorine resource recovery. Residual fluorine in the exhaust gas is absorbed by lime water in a third absorption tower, fixing the fluorine in the form of calcium fluoride, thus achieving defluorination treatment of the exhaust gas and ensuring that the fluorine content in the emitted exhaust gas meets standards. This application's solution, through the combined use of the above-mentioned equipment, converts the fluorine in the electrolytic exhaust gas into cerium fluoride with high recovery value, achieving fluorine resource recovery. Residual fluorine is then treated with an alkaline calcium solution to achieve defluorination of the electrolytic exhaust gas, overcoming the drawback of insufficient utilization of fluorine resources in existing praseodymium-neodymium metal production electrolytic exhaust gas treatment methods. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A schematic diagram of a tail gas treatment device in praseodymium-neodymium metal production is provided for one embodiment of this application;

[0031] Figure 2 A schematic diagram of a tail gas treatment device in praseodymium-neodymium metal production provided in another embodiment of this application;

[0032] Figure 3 A schematic diagram of a tail gas treatment device in praseodymium-neodymium metal production provided in another embodiment of this application;

[0033] Figure 4 A schematic diagram of a re-filter is provided for one embodiment of this application.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Electrolysis workshop; 2. First absorption tower; 3. Second absorption tower; 4. Third absorption tower; 5. Acid water treatment device; 6. Alkali absorption liquid treatment device; 10. Exhaust fan; 11. Dust collection hood; 20. Clean water storage tank; 30. Cerium carbonate solution storage tank; 40. Alkali solution storage tank; 41. pH meter; 51. Filter; 52. Acid water storage tank; 53. Fluorination reactor; 54. First filter press; 55. First filtrate storage tank; 56. Re-filter; 61. Neutralization reactor; 62. Second filter press; 63. Second filtrate storage tank; 100. Solenoid valve; 541. Cerium fluoride storage silo; 551. Filter box; 552. Support perforated plate; 553. Filter inner liner; 621. Calcium fluoride storage silo; 5501. Drain outlet. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0037] Current methods for treating exhaust gas from praseodymium-neodymium metal production enterprises: Typically, baghouse dust collectors are used to recover dust from the raw materials, followed by calcium oxide spraying to neutralize fluorine-containing gases and generate calcium fluoride. This not only fails to fully utilize fluorine resources, but also results in the generated calcium fluoride being disposed of as general solid waste in landfills. The process involves: praseodymium-neodymium metal production enterprises first collecting flue gas through a gas collection hood, then passing it through a baghouse dust collector to meet the rare earth industry pollutant emission standards (dust concentration less than 10 mg / m³). 3 The requirements are as follows: the fluorine in the waste gas is absorbed by a three-stage spray tower, the fluorine-containing wastewater is neutralized with calcium oxide to obtain a calcium-containing solution and calcium fluoride precipitate, calcium fluoride is obtained by plate and frame separator, the calcium-containing solution is returned to the spray tower for recycling, and the calcium fluoride filter cake is packaged and transported for landfill disposal as general solid waste.

[0038] This operating method has two drawbacks: First, the return of calcium-containing solution to the spray tower system easily causes scaling and clogging of the filter plates, leading to a rapid decrease in ventilation, a deterioration of the electrolysis working environment, and the problem of unorganized emissions failing to meet standards. Second, the transportation and landfilling of calcium fluoride also incurs costs, resulting in a complete waste of fluorine resources.

[0039] like Figure 1 As shown, this application provides a tail gas treatment device for praseodymium-neodymium metal production, including an electrolysis workshop 1, an induced draft fan 10, a first absorption tower 2, a second absorption tower 3 and a third absorption tower 4 connected in series.

[0040] The first absorption tower 2 and the second absorption tower 3 are respectively connected to the acid water treatment device 5 to form a loop. The first absorption tower 2 and the second absorption tower 3 are also respectively connected to the clean water storage tank 20. The acid water treatment device 5 is also connected to the cerium carbonate solution storage tank 30.

[0041] The third absorption tower 4 is also connected to the alkali absorption liquid treatment device 6 to form a loop.

[0042] In this application, during the electrolysis production process in the electrolysis workshop 1, the electrolytic tail gas (containing fluorides) is drawn in by the induced draft fan 10 and input into the first absorption tower 2. The filtrate supplied by the acid water treatment device 5 is used as the absorbent (with clean water from the clean water storage tank 20 as a supplement and supplied during the initial startup of the device) for washing and absorption. During absorption in the tower, the electrolytic tail gas enters the tower from the gas inlet at the bottom of the first absorption tower 2 and travels upwards. Simultaneously, the absorbent is sprayed downwards from the top of the tower (a circulating pump can be used to pump the absorbent from the bottom storage tank into the spray layer above the tower for circulating absorption and washing). The sprayed absorbent comes into countercurrent contact with the tail gas, washing and absorbing the fluoride-containing compounds and other water-soluble substances in the tail gas. It also washes away the dust in the tail gas. The absorbed liquid, after washing and absorbing the tail gas, falls into the storage tank at the bottom of the tower, while the washed tail gas is discharged from the top of the tower into the second absorption tower 3. The absorbent in the storage tank at the bottom of the tower is pumped back into the spray layer at the top of the tower for further circulation and washing. The absorbed exhaust gas then enters the second absorption tower 3 for re-absorption. The absorption process in the second absorption tower 3 is the same as that in the first absorption tower 2, and will not be described again here. After two stages of washing in the first absorption tower 2 and the second absorption tower 3, most of the fluorides in the exhaust gas can be removed (in practice, approximately 93% of the fluorides in the exhaust gas can be removed after two stages of washing and absorption), and the washed-out fluorides dissolve in the absorbent.

[0043] The tail gas, after two stages of scrubbing and absorption, is then fed into the third absorption tower 4, where it is absorbed using filtrate (an aqueous solution containing calcium hydroxide or lime slurry with a pH of 12-13) supplied by the alkaline absorption liquid treatment unit (the absorption process is the same as that in the first absorption tower 2). After absorption in the third absorption tower 4, the fluoride content in the tail gas has been reduced to 5 mg / m³. 3 The following can be concentrated in the exhaust chimney for emission.

[0044] When the acidity of the absorbent in the first absorption tower 2 and the second absorption tower 3 reaches a certain value (the acidity of the absorbent in the first absorption tower 2 is 0.8-1.0 mol / L, and the acidity of the absorbent in the second absorption tower 3 is 0.4-0.6 mol / L), the absorbent in the first absorption tower 2 and the second absorption tower 3 is discharged (and at the same time, the absorbent is replenished into the tower through the acid water treatment device 5). The discharged absorbent is treated by the acid water treatment device 5 and then reused in the first absorption tower 2 and the second absorption tower 3 for repeated use.

[0045] In the third absorption tower 4, when the pH of the absorbent in the tower is detected to be lower than 9, the low-alkalinity absorbent in the third absorption tower 4 is transferred to the alkaline absorbent treatment device 6 for treatment; at the same time, the alkaline absorbent (pH 12~13) treated in the alkaline absorbent treatment device 6 is added to the third absorption tower 4.

[0046] The exhaust gas treatment device provided in this application absorbs most of the fluorine-containing compounds in the exhaust gas through a first absorption tower 2 and a second absorption tower 3, forming a fluorinated acid. This fluorinated acid reacts with a cerium carbonate solution supplied from a cerium carbonate solution storage tank 30 in an acid water treatment device 5, causing the fluorine in the acid water to react with the cerium carbonate to form cerium fluoride precipitate, thus achieving fluorine resource recovery. Residual fluorine in the exhaust gas is absorbed by lime water in a third absorption tower 4, fixing the fluorine in the form of calcium fluoride, thereby achieving defluorination treatment of the exhaust gas and ensuring that the fluorine content in the emitted exhaust gas meets standards. This application's solution, through the combined use of the above-mentioned equipment, converts the fluorine in the electrolytic exhaust gas into cerium fluoride with high recovery value, achieving fluorine resource recovery. Residual fluorine is then treated with an alkaline calcium solution to achieve defluorination of the electrolytic exhaust gas. This treatment device overcomes the drawback of existing methods for treating praseodymium-neodymium metal production, which fail to fully utilize fluorine resources in electrolytic exhaust gas.

[0047] like Figure 2 As shown, optionally, the acid water treatment device 5 includes a filter 51, an acid water storage tank 52, a fluorination reactor 53, a first filter press 54 and a first filtrate storage tank 55 connected in series.

[0048] The input end of filter 51 is connected to the material output end of the first absorption tower 2 and the second absorption tower 3, respectively;

[0049] The first filtrate storage tank 55 is connected to the absorbent inlet of the first absorption tower 2 and the second absorption tower 3 respectively;

[0050] The first filter press 54 is also connected to the cerium fluoride storage 541;

[0051] The cerium carbonate solution storage tank 30 is connected to the fluorination reactor 53.

[0052] When the acidity of the absorbent in the first absorption tower 2 and the second absorption tower 3 reaches a certain value (the acidity of the absorbent in the first absorption tower 2 is 0.8-1.0 mol / L, and the acidity of the absorbent in the second absorption tower 3 is 0.4-0.6 mol / L), the absorbent in the first absorption tower 2 and the second absorption tower 3 is discharged (and absorbent is simultaneously replenished into the tower through the first filtrate storage tank 55). The discharged absorbent is filtered by the filter 51 and then discharged into the acid water storage tank 52 for temporary storage. The acid water (which is hydrofluoric acid with a low concentration) in the acid water storage tank 52 is then transferred to the fluorination reactor 53 to neutralize the cerium carbonate solution supplied by the cerium carbonate solution storage tank 30. In this reaction, the cerium carbonate solution and the acid water react to form cerium fluoride precipitate. After the fluorination reaction is completed, the reaction precipitate is discharged from the bottom of the fluorination reactor 53 and transferred to the first filter press 54 for filtration to obtain cerium fluoride filter cake, which is then temporarily stored in the cerium fluoride storage silo 541 for subsequent centralized processing. The filtrate after being filtered by the first filter press 54 is transferred to the first filtrate storage tank 55 for recycling and reuse.

[0053] like Figure 2 As shown, optionally, the alkali absorption liquid treatment device 6 includes a neutralization reaction vessel 61, a second filter press 62, and a second filtrate storage tank connected in series.

[0054] The neutralization reactor 61 is connected to the material output end of the third absorption tower 4, and the second filtrate storage tank 63 is also connected to the material input end of the third absorption tower 4.

[0055] The neutralization reactor 61 is also connected to the alkali storage tank 40;

[0056] The second filter press 62 is also connected to the calcium fluoride storage silo 621.

[0057] In the third absorption tower 4, when the pH of the absorbent in the tower is below 9, the alkaline filtrate in the second filtrate storage tank 63 is transferred to the third absorption tower 4. At the same time, the absorbent in the third absorption tower 4 is pumped or overflowed into the neutralization reactor 61 by a water pump to react with the aqueous solution containing calcium hydroxide or lime milk supplied by the alkaline storage tank 40. After the reaction, calcium fluoride precipitate is obtained. After the reaction is completed, the calcium fluoride precipitate is discharged from the bottom of the neutralization reactor 61 and transferred to the second filter press 62 for filtration. The filtrate obtained by filtration is transferred to the second filtrate storage tank 63 and supplied to the third absorption tower 4 for reuse. The filter cake is transferred to the calcium fluoride storage silo 621 for centralized treatment.

[0058] like Figure 3 As shown, optionally, a solenoid valve 100 is provided between the third absorption tower 4 and the second filtrate storage tank 63;

[0059] A pH meter 41 is installed inside the third absorption tower 4;

[0060] pH meter 41 is interlocked with solenoid valve 100.

[0061] In this application, the pH meter 41 in the third absorption tower 4 monitors the pH change of the absorbent in the tower in real time and feeds back the data in real time. When the pH meter 41 detects that the pH of the absorbent in the tower is lower than 9, the solenoid valve 100 is opened because the pH meter 41 is interlocked with the solenoid valve 100, and the alkaline filtrate in the second filtrate storage tank 63 is transferred into the third absorption tower 4 to achieve real-time and automatic replenishment.

[0062] like Figure 2 and Figure 4 As shown, optionally, a re-filter 56 is also provided below the first filter press 54;

[0063] The re-filter 56 includes a filter box 551, and a support perforated plate 552 is horizontally arranged inside the filter box 551.

[0064] A filter liner 553 is provided on the support perforated plate 552;

[0065] A drain port 5501 is provided on one side of the lower part of the filter box 551.

[0066] In this application, the filtrate after being filtered by the first filter press 54 needs to undergo secondary filtration through the filter inner tank 553 of the re-filter 56 to prevent a small amount of cerium fluoride from leaking into the filtrate due to filter breakage during the filtration process. The filtrate after filtration through the filter inner tank 553 falls into the filter box 551 through the holes on the support perforated plate 552, and is then discharged through the drain port 5501 and transferred to the first filtrate storage tank 55 for recycling and reuse.

[0067] In this application, the filter liner 553 can be a container structure made of filter bag or filter mesh that matches the shape of the filter box 551, and the filtration accuracy of the filter liner 553 should be higher than that of the first filter press 54 to prevent secondary leakage of cerium fluoride.

[0068] like Figure 2 As shown, optionally, a dust collection hood 11 is installed on the top of the electrolysis workshop 1, and the dust collection hood 11 is connected to the induced draft fan 10.

[0069] In this application, the dust collection hood 11 and the induced draft fan 10 are used together to collect the exhaust gas emitted from the electrolysis workshop, preventing the electrolysis exhaust gas from escaping and causing environmental pollution. In actual operation, the induced draft fan 10 draws the electrolysis workshop 1 into a slightly negative pressure state through the dust collection hood 11 to prevent exhaust gas leakage.

[0070] Optionally, the first absorption tower 2 is one of a packed tower, a plate tower, or a bubble tower.

[0071] A tail gas treatment device for praseodymium-neodymium metal production, the working process of which is as follows:

[0072] During operation, the electrolytic tail gas (containing fluorides) generated during the electrolysis process in electrolysis workshop 1 is collected by dust collection hood 11 and drawn into the first absorption tower 2 by induced draft fan 10. The filtrate supplied by the first filtrate storage tank 55 is used as the absorbent (clean water from the clean water storage tank 20 is used for supplementation and supply during initial startup) for washing and absorption. During absorption within the tower, the electrolytic tail gas enters the tower from the gas inlet at the bottom and travels upwards. Simultaneously, the absorbent is sprayed downwards from the top of the tower (a circulating pump can be used to pump the absorbent from the bottom storage tank into the spray layer above the tower for circulating absorption and washing). The sprayed absorbent comes into countercurrent contact with the tail gas, washing and absorbing the fluoride-containing compounds and other water-soluble substances in the tail gas. It also washes away dust from the tail gas. The washed and absorbed absorbent falls into the storage tank at the bottom of the tower, while the washed tail gas is discharged from the top of the tower into the second absorption tower. The absorbent in the storage tank at the bottom of the tower is pumped back into the spray layer at the top of the tower for circulating washing. The absorbed tail gas then enters the second absorption tower 3 for further absorption (the absorbent comes from the filtrate supplied by the first filtrate storage tank 55, or from the clean water storage tank 20 during initial startup). The absorption process in the second absorption tower 3 is the same as that in the first absorption tower 2, and will not be described again here. After two stages of washing in the first absorption tower 2 and the second absorption tower 3, most of the fluoride in the tail gas can be removed (in practice, about 93% of the fluoride in the tail gas can be removed after two stages of washing and absorption), and the washed fluoride dissolves in the absorbent.

[0073] The tail gas, after two stages of scrubbing and absorption, is then fed into the third absorption tower 4. It is absorbed using filtrate supplied by the second filtrate storage tank 63 (an aqueous solution or lime slurry containing calcium hydroxide with a pH of 12-13; initially, an aqueous solution or lime slurry containing calcium hydroxide supplied by the alkaline solution storage tank 40 can be used as the absorbent). The absorption process is the same as in the first absorption tower 2. Simultaneously, the pH meter 41 inside the third absorption tower 4 monitors the pH changes of the absorbent in real time and provides real-time data feedback. After absorption in the third absorption tower 4, the fluoride content in the tail gas has been reduced to 5 mg / m³. 3 The following can be concentrated in the exhaust chimney for emission.

[0074] When the acidity of the absorbent in the first absorption tower 2 and the second absorption tower 3 reaches a certain value (the acidity of the absorbent in the first absorption tower 2 is 0.8-1.0 mol / L, and the acidity of the absorbent in the second absorption tower 3 is 0.4-0.6 mol / L), the absorbent in the first absorption tower 2 and the second absorption tower 3 is discharged (and absorbent is simultaneously replenished into the tower through the first filtrate storage tank 55). The discharged absorbent is filtered by the filter 51 and then discharged into the acid water storage tank 52 for temporary storage. The acid water (which is hydrofluoric acid with a low concentration) in the acid water storage tank 52 is then transferred to the fluorination reactor 53 to neutralize the cerium carbonate solution supplied by the cerium carbonate solution storage tank 30. In this reaction, the cerium carbonate solution and the acid water react to form cerium fluoride precipitate. After the fluorination reaction is completed, the reaction precipitate is discharged from the bottom of the fluorination reactor 53 and transferred to the first filter press 54 for filtration to obtain cerium fluoride filter cake, which is then temporarily stored in the cerium fluoride storage silo 541 for subsequent centralized processing. The filtrate after filtration by the first filter press 54 needs to undergo secondary filtration in the inner filter chamber 553 of the re-filter 56 to prevent a small amount of cerium fluoride from leaking into the filtrate due to filter breakage during the filtration process. After filtration in the inner filter chamber 553, the filtrate falls into the filter box 551 through the holes on the support perforated plate 552, and is then discharged through the drain port 5501 and transferred to the first filtrate storage tank 55 for recycling and reuse.

[0075] In the third absorption tower 4, when the pH meter 41 detects that the pH of the absorbent in the tower is below 9, the solenoid valve 100 is opened because the pH meter 41 is interlocked with the solenoid valve 100. The alkaline filtrate in the second filtrate storage tank 63 is transferred to the third absorption tower 4. At the same time, the absorbent in the third absorption tower 4 is pumped or overflowed into the neutralization reactor 61 by a water pump to react with the aqueous solution containing calcium hydroxide or lime milk supplied by the alkaline storage tank 40. After the reaction, calcium fluoride precipitate is obtained. After the reaction is completed, the calcium fluoride precipitate is discharged from the bottom of the neutralization reactor 61 and transferred to the second filter press 62 for filtration. The filtrate obtained by filtration is transferred to the second filtrate storage tank 63 for reuse in the third absorption tower 4, and the filter cake is transferred to the calcium fluoride storage silo 621 for centralized treatment.

[0076] The proposed solution uses water spraying in the first and second stages of the spray towers to absorb the majority of fluoride (based on the principle that hydrogen fluoride gas and water are infinitely miscible). Specifically, the first absorption tower (2) and the second absorption tower (3) absorb fluoride with water to generate hydrofluoric acid. This hydrofluoric acid is then introduced into a fluorination tank, where it undergoes an absorption reaction with cerium carbonate to produce cerium fluoride. After drying, this product is supplied to cerium metal production enterprises as an electrolyte. The filtrate separated by the plate and frame separator is recycled back to the first and second absorption towers (2 and 3) for continued use in the spray towers. The third absorption tower (4) uses a calcium solution for absorption. A pH meter automatically replenishes the calcium-containing solution, maintaining the pH value at the third-stage discharge outlet above 9.0 to achieve compliance with emission standards (rare earth industry pollutant emission standard F < 5 mg / m³).

[0077] Through this operation, over 93% of the fluorine in the tail gas of the first absorption tower 2 and the second absorption tower 3 is absorbed to form hydrofluoric acid. Cerium fluoride is then precipitated from cerium carbonate, achieving 93% fluorine resource recovery. Calcium fluoride production is reduced by 14 times, significantly decreasing the amount of calcium fluoride landfilled and its environmental impact, thus achieving energy conservation and emission reduction. Simultaneously, the blockage problem in the first absorption tower 2 and the second absorption tower 3 is completely resolved, ensuring a safe environment in the electrolysis workshop production area.

[0078] Using electrolytic spray water and cerium carbonate as raw materials, the process involves fluorination in a fluorination tank and solid-liquid separation in a plate and frame. The solid is wet cerium fluoride, which is dried to obtain dry cerium fluoride for use in the electrolysis workshop of cerium metal production enterprises. The cerium-containing wastewater is returned to the first and second stages for circulating spraying, and there is no wastewater discharge during the process.

[0079] The device of this application also has the following advantages:

[0080] 1) Different methods are used for the three-stage spray system: the first two stages use cerium-containing water to absorb fluoride (i.e., cerium carbonate is used to recover fluoride), and the third stage uses calcium-containing water to absorb fluoride (i.e., calcium oxide is used to recover fluoride). This ensures that the pH value is greater than 9, thereby guaranteeing that fluoride emissions meet standards. Each spray tower is relatively independent and does not cross-contaminate, preventing pollution. Fluorine resources are recycled and reused, greatly reducing the generation of solid waste and environmental pollution.

[0081] 2) Cerium carbonate replaces calcium oxide, and the product is recycled.

[0082] 3) The spray water from the third-stage spray tower is automatically adjusted to ensure continuous compliance with discharge standards.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A tail gas treatment device for praseodymium-neodymium metal production, characterized in that, It includes an electrolysis workshop (1), an induced draft fan (10), a first absorption tower (2), a second absorption tower (3) and a third absorption tower (4) connected in series. The first absorption tower (2) and the second absorption tower (3) are respectively connected to the acid water treatment device (5) to form a loop. The first absorption tower (2) and the second absorption tower (3) are also respectively connected to the clean water storage tank (20). The acid water treatment device (5) is also connected to the cerium carbonate solution storage tank (30). The third absorption tower (4) is also connected to the alkali absorption liquid treatment device (6) to form a loop.

2. The tail gas treatment device in praseodymium-neodymium metal production according to claim 1, characterized in that, The acid water treatment device (5) includes a filter (51), an acid water storage tank (52), a fluorination reactor (53), a first filter press (54), and a first filtrate storage tank (55) connected in series. The input end of the filter (51) is connected to the material output end of the first absorption tower (2) and the second absorption tower (3), respectively; The first filtrate storage tank (55) is connected to the absorbent inlet of the first absorption tower (2) and the second absorption tower (3); The first filter press (54) is also connected to a cerium fluoride storage tank (541); The cerium carbonate solution storage tank (30) is connected to the fluorination reactor (53).

3. The tail gas treatment device in praseodymium-neodymium metal production according to claim 1, characterized in that, The alkaline absorption liquid treatment device (6) includes a neutralization reaction vessel (61), a second filter press (62), and a second filtrate storage tank (63) connected in series. The neutralization reactor (61) is connected to the material output end of the third absorption tower (4), and the second filtrate storage tank (63) is also connected to the material input end of the third absorption tower (4). The neutralization reactor (61) is also connected to the alkali storage tank (40); The second filter press (62) is also connected to the calcium fluoride storage silo (621).

4. The tail gas treatment device for praseodymium-neodymium metal production according to claim 3, characterized in that, A solenoid valve (100) is provided between the third absorption tower (4) and the second filtrate storage tank (63). A pH meter (41) is installed inside the third absorption tower (4). The pH meter (41) is interlocked with the solenoid valve (100).

5. The tail gas treatment device for praseodymium-neodymium metal production according to claim 2, characterized in that, A re-filter (56) is also provided below the first filter press (54); The re-filter (56) includes a filter box (551), and a support perforated plate (552) is horizontally arranged inside the filter box (551). The support perforated plate (552) is provided with a filter inner liner (553); A drain port (5501) is provided on one side of the lower part of the filter box (551).

6. The tail gas treatment device for praseodymium-neodymium metal production according to claim 1, characterized in that, The top of the electrolysis workshop (1) is equipped with a dust collection hood (11), which is connected to the induced draft fan (10).

7. The tail gas treatment device for praseodymium-neodymium metal production according to claim 1, characterized in that, The first absorption tower (2) is one of a packed tower, a plate tower or a bubble tower.

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