System and method for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride

Abstract

The invention relates to a system and a method for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride. According to the method, hydrogen fluoride (HF) and silicon tetrafluoride (SiF4) in the tail gas are directionally converted into high-purity magnesium fluoride (MgF2) and sodium fluosilicate (Na2SiF6) through a magnesium hydroxide suspension spraying absorption and multistage separation conversion process, so that the step recovery of fluorine elements is realized. The fluorine recovery rate can reach more than 90%, which is far better than the situation that a large amount of waste is caused by curing fluorine in gypsum in the traditional process, and the resource utilization rate is greatly improved. A magnesium hydroxide regeneration system and sodium sulfate-gypsum synergistic conversion are adopted to construct closed cycle, magnesium hydroxide, sodium hydroxide and sodium sulfate realize internal cycle, and the raw material cost is reduced by more than 50%. Meanwhile, the co-production of magnesium fluoride and sodium fluosilicate directly creates economic benefits, the treatment cost is counteracted, the environmental protection pressure is reduced by a near-zero emission mode, and a pollution control and profit sustainable development path giving consideration to both economic benefits and environmental protection benefits is provided for hydrofluoric acid production enterprises.

Description

Technical Field

[0001] The present invention belongs to the technical field of comprehensive treatment and resource utilization of hydrofluoric acid production tail gas, and more specifically relates to a system and method for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride. Background Art

[0002] The fluorspar process, which uses fluorspar powder (CaF2) and concentrated sulfuric acid (H2SO4) as raw materials, produces anhydrous hydrofluoric acid (also known as anhydrous hydrogen fluoride). The exhaust gas produced during this process contains HF, SiF4, and SO2. According to the "Handbook of Industrial Pollution Generation and Emission Factors" (edited by the Science and Technology Standards Department of the State Environmental Protection Administration), the emission factors calculated based on anhydrous hydrofluoric acid production are: 9.1 kg / t for hydrogen fluoride, 13.6 kg / t for fluorine-silicon dust, and 22.5 kg / t for sulfur dioxide. The traditional method involves neutralization and spray absorption with sodium lye (NaOH), converting HF and SiF4 into sodium fluoride (NaF) and sodium fluorosilicate (Na2SiF6), and SO2 into sodium sulfite (Na2SO3) or sodium sulfate (Na2SO4). This is then precipitated with lime (Ca(OH)2) to produce fluorine-containing gypsum (a mixture of CaSiF6 + CaF2 / CaSO4·2H2O). Fluorine solidifies in gypsum as insoluble calcium fluoride (CaF2), preventing high-value recovery of fluorine resources and leading to waste. Furthermore, the byproduct fluoridated gypsum, due to its fluoride inclusions, is unstable and prone to fluoride ion precipitation, limiting its application in building materials (such as cement retarders), resulting in resource waste and limiting its comprehensive utilization. Furthermore, it also produces a certain amount of high-fluoride and high-salt wastewater, which is costly to treat and places significant pressure on the environment.

[0003] The improved process uses a calcium hydroxide (Ca(OH)2) slurry for direct spray absorption, converting HF and SiF4 into calcium fluoride (CaF2) and calcium fluorosilicate (CaSiF6). Simultaneously, SO2 is absorbed to form calcium sulfite (CaSO3), which is then oxidized by air to calcium sulfate (CaSO4). The resulting calcium sulfate (gypsum) mixture still contains calcium fluoride and calcium fluorosilicate, affecting the gypsum's quality and making it difficult to meet industrial gypsum standards (such as purity requirements). Furthermore, the fluorine resources (such as HF and SiF4) in the exhaust gas remain unutilized.

[0004] Existing methods for preparing magnesium fluoride generally involve directly reacting hydrofluoric acid with magnesium oxide to produce magnesium fluoride. Alternatively, ammonium fluoride is reacted with magnesium hydroxide to produce magnesium fluoride, which is then separated by liquid-solid separation and dried and dehydrated to obtain the magnesium fluoride product. However, these two methods rely on high-purity hydrofluoric acid or ammonium fluoride as raw materials, resulting in high production costs.

[0005] In summary, the current treatment process for exhaust emissions from the fluorite-based production of anhydrous hydrogen fluoride focuses solely on achieving pollutant emission standards, without synergizing with fluorine resource recovery and utilization processes, resulting in an imbalance between environmental investment and economic benefits. Furthermore, existing treatment technologies limit the comprehensive utilization of fluorine-containing byproducts (such as fluorine-containing gypsum and fluorine-containing wastewater), forcing companies to bear the environmental burden of increased solid waste disposal costs. Fluorine-containing resources are wasted, high-value recovery is not achieved, and treatment costs are high, making it difficult to balance environmental protection and economic benefits. Summary of the Invention

[0006] In view of the above technical problems, the present invention provides a system and method for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride, so as to convert the fluorine in the tail gas into high-value-added products such as magnesium fluoride and sodium fluorosilicate through process coupling, thereby achieving the dual goals of hydrofluoric acid production tail gas pollution control and fluorine-containing resource utilization.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride, comprising the following steps:

[0008] S1, adding a magnesium hydroxide suspension to a circulating absorption liquid of hydrofluoric acid production tail gas, spraying and absorbing the hydrofluoric acid production tail gas to obtain a first absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfite;

[0009] S2. aerating the first absorption liquid with air to obtain a second absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfate;

[0010] S3, performing a first solid-liquid separation on the second absorption liquid to obtain a high-purity magnesium fluoride solid and a first filtrate. It can be understood that the first filtrate contains magnesium fluorosilicate and magnesium sulfate;

[0011] S4. Place the first filtrate in a desiliconization tank, add sodium sulfate, filter, and dry to obtain sodium fluorosilicate and a second filtrate, wherein the second filtrate contains magnesium sulfate.

[0012] The magnesium hydroxide suspension in step S1 referred to in the present invention can be directly purchased magnesium hydroxide, or can be made by adding water to light-burned magnesium oxide and slaking, and can be adjusted according to the actual situation and needs of the user. The tail gas circulation absorption liquid mainly contains magnesium hydroxide suspension, and common spray absorption is generally adopted. Magnesium hydroxide and hydrogen fluoride, silicon tetrafluoride, and sulfur dioxide in the tail gas are subjected to a neutralization reaction represented by the following chemical formula (Formula 1 to Formula 3) to generate a first absorption liquid containing magnesium fluoride, magnesium fluorosilicate, and magnesium sulfite.

[0013] 2HF+Mg(OH)2―→MgF2↓+2H2O Formula 1

[0014] SiF4+2HF+Mg(OH)2―→MgSiF6+2H2O (MgSiF6 is easily soluble in water) Formula 2

[0015] SO2+Mg(OH)2―→MgSO3↓+H2O (MgSO3 is slightly soluble in water, with a solubility of about 0.573g / 100gH2O at 20℃)

[0016] Furthermore, the magnesium sulfite produced in the absorption liquid is oxidized by oxygen in the air to become magnesium sulfate which is soluble in water (see the reaction shown in Formula 4).

[0017] 2MgSO3+O2―→2MgSO4 (20℃ solubility: about 33.5g / 100gH2O) Formula 4

[0018] The first filtrate containing magnesium fluorosilicate and magnesium sulfate is placed in a filtrate desiliconization tank, and sodium sulfate is added to react with the magnesium fluorosilicate to form sodium fluorosilicate which is slightly soluble in water (solubility is about 0.7%, see Formula 5).

[0019] MgSiF6 + Na2SO4―→Na2SiF6↓+MgSO4 Formula 5

[0020] In a further preferred method of the above invention, the steps are further included:

[0021] S5. The second filtrate is placed in a conversion tank, sodium hydroxide is added to obtain a magnesium hydroxide precipitate, aged, and subjected to a second solid-liquid separation to obtain a magnesium hydroxide solid and a third filtrate (see Formula 6 for details). The third filtrate contains sodium sulfate. The magnesium hydroxide solid is made into a magnesium hydroxide suspension and reused in S1, and the sodium sulfate is reused in S4.

[0022] MgSO4 + 2NaOH ―→ Mg(OH)2↓+ Na2SO4 Formula 6

[0023] In a further improved method of the present invention, the preparation method of the magnesium hydroxide suspension comprises the following steps:

[0024] Lightly calcined magnesium oxide is added to water for slaking, and then separated by a multi-stage hydrocyclone to remove SiO2, Fe2O3, MgCO3, and MgO to obtain a magnesium hydroxide suspension. The magnesium hydroxide suspension prepared by this method is simple to operate and can greatly reduce costs for S1.

[0025] In a further improved method of the present invention, the method further includes the steps of: precipitating and filtering the magnesium hydroxide suspension to obtain a liquid containing calcium hydroxide, and recycling the liquid containing calcium hydroxide to react with quicklime to obtain slaked lime emulsion.

[0026] Furthermore, the slaked lime emulsion is mixed with the third filtrate and subjected to a third solid-liquid separation to obtain solid gypsum and liquid sodium hydroxide. The liquid sodium hydroxide is reused in S5, and the solid gypsum can be sold to a cement plant as a cement retarder. In this way, the byproducts generated in the method of the present invention can be reused to the greatest extent possible, and the entire system produces almost no waste, thereby minimizing negative environmental impacts.

[0027] In a further improved method of the present invention, the light-burned magnesium oxide contains 80-90 wt% magnesium oxide.

[0028] In a more preferred improvement of the present invention, in S3, the first solid-liquid separation is performed using a plate-and-frame filter press or a centrifugal filter, wherein the plate-and-frame filter press is more conducive to improving the solid-liquid separation effect.

[0029] In a further improved method of the present invention, the pH value of the first absorption liquid is maintained at 5.0-7.0.

[0030] A second aspect of the present invention provides a system for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride, comprising:

[0031] Tail gas absorption unit: includes a spray tower, a magnesium hydroxide suspension storage tank and a circulation pump. The spray tower is provided with a spray device for spraying a tail gas absorption liquid containing magnesium hydroxide suspension into the hydrofluoric acid production tail gas to generate a first absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfite;

[0032] Aeration and oxidation unit: connected to the tail gas absorption unit, including an aeration tank and an air compressor. The aeration tank is used to hold the first absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfite discharged from the spray tower. A gas distributor is provided in the aeration tank for introducing air into the first absorption liquid for aeration and oxidation to generate a second absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfate.

[0033] A first solid-liquid separation unit is connected to the aeration oxidation unit and includes a solid-liquid separation device and a first hydrocyclone. The solid-liquid separation device is a plate-and-frame filter press or a centrifugal filter, which is used to perform solid-liquid separation on the second absorption liquid to obtain high-purity magnesium fluoride solid and a first filtrate containing magnesium fluorosilicate and magnesium sulfate;

[0034] Desiliconization unit: connected to the first solid-liquid separation unit, including a desiliconization tank and a sodium sulfate feeding device. The desiliconization tank is provided with an agitator for mixing the first filtrate with sodium sulfate to react, and after filtering and drying, sodium fluorosilicate and a second filtrate containing magnesium sulfate are obtained.

[0035] A conversion and circulation unit is connected to the desiliconization unit and includes a conversion tank, a sodium hydroxide feeding device, and a second solid-liquid separator. The conversion tank is used to react the second filtrate with sodium hydroxide to generate magnesium hydroxide precipitate. After separation in the second solid-liquid separator, magnesium hydroxide solid and a third filtrate containing sodium sulfate are obtained. The magnesium hydroxide solid is converted into a magnesium hydroxide suspension and then returned to the magnesium hydroxide suspension storage tank through a reflux transmission pipeline for reuse.

[0036] The lime-gypsum conversion unit is connected to the conversion and circulation unit and includes a lime slaking tank, a lime-gypsum conversion tank and a fourth plate and frame filter press connected in sequence. The lime-gypsum conversion tank is used to mix the third filtrate containing sodium sulfate with the slaked lime emulsion obtained from the lime slaking tank to obtain solid gypsum and liquid sodium hydroxide.

[0037] Among them, the magnesium hydroxide suspension storage tank, circulation pump and spray device are connected, the first absorption liquid storage tank is used to store the absorption liquid obtained after spraying and absorbing the hydrofluoric acid production tail gas, and the aeration tank is used to introduce air into the first absorption liquid.

[0038] The further improved system further includes a light-burned magnesium oxide aging unit: connected to the magnesium hydroxide suspension storage tank of the tail gas absorption unit, including a light-burned magnesium oxide aging tank, a second hydrocyclone and a fifth plate and frame filter press. The magnesium hydroxide suspension obtained by pressing the fifth plate and frame filter press is transported to the magnesium hydroxide suspension storage tank via a pipeline.

[0039] Unlike existing technologies, the above-mentioned technical solution introduces magnesium oxide or magnesium hydroxide to simultaneously absorb hydrogen fluoride, silicon tetrafluoride, and sulfur dioxide from hydrofluoric acid tail gas. Taking advantage of the different solubility of the magnesium fluoride generated by absorption, magnesium sulfate, and magnesium fluorosilicate, it is separated and utilized, achieving the dual goals of fluorine resource recovery and tail gas treatment. By utilizing the different solubilities of magnesium fluorosilicate and sodium fluorosilicate, the fluorosilicate produced by the absorption of silicon tetrafluoride is separated to obtain sodium fluorosilicate, fully utilizing fluorine-containing resources. Through a magnesium hydroxide suspension spray absorption and multi-stage separation and conversion process, hydrogen fluoride (HF) and silicon tetrafluoride (SiF4) in the tail gas are directionally converted into high-purity magnesium fluoride (MgF2) and sodium fluorosilicate (Na2SiF6), achieving a cascaded recovery of fluorine. The fluorine recovery rate can reach over 90%, far exceeding the traditional method of solidifying fluorine in gypsum (which results in a significant waste of fluorine resources), significantly improving fluorine resource utilization. Through the coordinated conversion of magnesium hydroxide regeneration system and sodium sulfate-gypsum, a closed loop is constructed, and magnesium hydroxide, sodium hydroxide and sodium sulfate are internally circulated, which reduces the cost of raw materials by more than 50%. The by-product gypsum (cement retarder) can be sold externally, and no fluorine-containing wastewater / waste residue is discharged, which significantly reduces the pressure on environmental protection. The present invention adopts an integrated device design to realize the linkage of absorption-oxidation-separation-desiliconization-conversion units, avoiding the complexity of independent processing of multiple links in traditional processes. The present invention successfully solves the three core problems of fluorine resource waste, secondary pollution and high cost in traditional hydrofluoric acid tail gas treatment through the "resource recovery-recycling-process coupling" three-in-one design. At the same time, the joint production of magnesium fluoride and sodium fluorosilicate directly creates economic benefits, offsets the cost of treatment, and the near-zero emission mode reduces the pressure on environmental protection, providing hydrofluoric acid production enterprises with a "pollution control + profit" sustainable development path that takes into account both economic and environmental benefits.

[0040] The above-mentioned records related to the content of the invention are only an overview of the technical solution of this application. In order to enable ordinary technicians in this field to understand the technical solution of this application more clearly, and then implement it according to the text of the specification and the contents recorded in the drawings, and to make the above-mentioned purposes and other purposes, features and advantages of this application easier to understand, the following is an explanation in combination with the specific implementation methods and drawings of this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings are only used to illustrate the principles, implementation methods, applications, characteristics and effects of the specific embodiments of this application and other related contents, and are not to be considered as limiting this application.

[0042] In the drawings of the specification:

[0043] Figure 1 A schematic diagram of the operation flow of a method for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride using a magnesium hydroxide absorbent provided in a specific embodiment;

[0044] Figure 2 A schematic diagram of the operation flow of another method for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride using light-burned magnesium oxide matured to prepare magnesium hydroxide absorbent, provided in a specific embodiment;

[0045] Figure 3 A schematic diagram of a system for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride using a magnesium hydroxide absorbent provided in a specific embodiment;

[0046] Figure 4 A schematic diagram of another system for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride using light-burned magnesium oxide matured to make magnesium hydroxide absorbent is provided as a specific embodiment.

[0047] The reference numerals in the above drawings are described as follows:

[0048] 100. Tail gas absorption unit; 101. Spray tower; 102. Magnesium hydroxide suspension storage tank; 103. Circulation pump; 104. Spray device;

[0049] 200, aeration and oxidation unit; 201, aeration tank; 202, air compressor; 203, gas distributor;

[0050] 300, first solid-liquid separation unit; 301, first plate-and-frame filter press; 302, first hydrocyclone;

[0051] 400, desiliconization unit; 401, desiliconization tank; 402, sodium sulfate dispensing device; 403, second plate and frame filter press;

[0052] 500, conversion and circulation unit; 501, conversion tank; 502, sodium hydroxide feeding device; 503, third plate and frame filter press; 504, reflux transmission pipeline;

[0053] 600, lime-gypsum conversion unit; 601, lime slaking tank; 602, lime-gypsum conversion tank; 603, fourth plate and frame filter press;

[0054] 700. Light-burned magnesium oxide aging unit; 701. Light-burned magnesium oxide aging tank; 702. Second hydrocyclone; 703. Fifth plate and frame filter press. DETAILED DESCRIPTION

[0055] In order to explain in detail the possible application scenarios, technical principles, specific solutions that can be implemented, and the purpose and effects of this application, the following is a detailed description of the specific embodiments listed in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of this application and are therefore only examples and are not intended to limit the scope of protection of this application.

[0056] References to "embodiments" herein mean that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the word "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the various technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution.

[0057] Unless otherwise defined, the technical terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0058] In the description of this application, the term "and / or" is used to describe a logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and both A and B exist. In addition, the character " / " in this document generally indicates that the objects before and after are in a logical "or" relationship.

[0059] In this application, terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual quantity, priority or sequence relationship between these entities or operations.

[0060] Without further limitations, in this application, the words "include", "comprise", "have" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those defined elements, but also other elements not explicitly listed, or elements inherent to such process, method or product.

[0061] Consistent with the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceed" are understood to exclude the number itself; expressions such as "above," "below," and "within" are understood to include the number itself. Furthermore, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this manner, such as "multiple groups," "multiple times," etc., unless otherwise specifically defined.

[0062] In the description of the embodiments of the present application, the space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present application or facilitating the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, it should not be understood as a limitation on the embodiments of the present application.

[0063] Unless otherwise expressly specified or limited, in the description of the embodiments of the present application, the terms "installed", "connected", "connected", "fixed", "set", etc. used should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integrated setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For those skilled in the art of the present application, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0064] Example 1

[0065] See also Figure 2 The flowchart of the method for comprehensive treatment of hydrofluoric acid production tail gas and magnesium fluoride co-production using light-burned magnesium oxide slaking to make magnesium hydroxide absorbent is shown. Taking a 20,000 tons / year anhydrous hydrogen fluoride production line as an example, the specific steps are as follows:

[0066] 1) About 600 kg (8-hour consumption) of light-burned magnesium oxide (LMGO) meeting the standard "Light-burned Magnesium Oxide YB / T 5206-2023" and containing more than 90% MgO is added to 15 tons of water, stirred, and aged for 3-4 hours. The mixture is then separated and subjected to a multi-stage hydrocyclone to remove high-density slag such as SiO2, MgCO3, MgO, and Fe2O3. The resulting magnesium hydroxide suspension is precipitated and filtered to remove slightly water-soluble calcium hydroxide to obtain a purified magnesium hydroxide filter cake having a magnesium hydroxide content of ≥98%. The calcium hydroxide-containing filtrate is used in step 7).

[0067] 2) adding 1000 kg of water to the purified magnesium hydroxide filter cake obtained in step 1), stirring to obtain a magnesium hydroxide suspension, and adding the suspension to the circulating absorption liquid of the hydrofluoric acid tail gas, maintaining the pH value of the absorption liquid at 6.0±0.2.

[0068] 3) The absorption liquid is sent to the spray absorption tower through the circulation pump to spray and absorb the hydrogen fluoride and sulfur dioxide in the tail gas. By adjusting the circulation pump flow rate (the circulation pump flow rate can be set to 16m 3 / h,) to circulate and absorb the tail gas, and obtain the first absorption liquid (containing MgF2, MgSiF6, MgSO3) after the reaction, which can ensure that the tail gas meets the emission standards.

[0069] 4) The first absorption liquid is pumped into the aeration tank. An air compressor is used to continuously aerate the first absorption liquid in the absorption liquid circulation tank. The aeration pipe pressure is determined based on 120% of the maximum operating liquid level in the slurry tank. The magnesium sulfite is oxidized to magnesium sulfate and gradually dissolved to obtain a second absorption liquid (containing magnesium fluoride, magnesium fluorosilicate, and magnesium sulfate). The second absorption liquid is separated by a hydrocyclone. The overflow liquid is returned to the absorption liquid circulation tank. The underflow liquid is passed through a plate and frame filter press for solid-liquid separation. The solid portion is dried to obtain high-purity magnesium fluoride solid (purity exceeding 98.4%) as industrial magnesium fluoride. After testing, the physical and chemical indicators of the magnesium fluoride of this embodiment are shown in Table 1, which meet the "Magnesium Fluoride YS / T 691-2009" brand MF-1 standard. The filtrate contains magnesium fluorosilicate and magnesium sulfate. The output is approximately 300 kg in 8 hours.

[0070] Table 1 Physical and chemical indicators of magnesium fluoride in Example 1

[0071]

[0072] 5) The filtrate containing magnesium fluorosilicate and magnesium sulfate separated in step 4) is placed in a filtrate desiliconization tank, and the sodium sulfate produced in step 6) is added at a molar ratio of 1:1 between magnesium fluorosilicate (MgSiF6) and Na2SO4. The mixture is stirred thoroughly and reacted until no more precipitate is present. The mixture is filtered through a plate and frame filter press, and the filter cake is dried to obtain the sodium fluorosilicate byproduct. The filtrate is a magnesium sulfate solution.

[0073] 6) The filtrate obtained in step 5) is placed in a filtrate conversion tank, and sodium hydroxide is added to react to form a magnesium hydroxide precipitate. After aging for approximately 2 hours, the precipitate is separated into solid and liquid using a plate and frame filter press or centrifuge to obtain magnesium hydroxide solid and sodium sulfate filtrate. The magnesium hydroxide solid is converted into a magnesium hydroxide suspension, which can be reused in the absorption liquid system, reducing the use of purchased raw materials and reducing costs by approximately 30%. The sodium sulfate filtrate can be used in steps 5) and 7).

[0074] 7) The calcium hydroxide-containing filtrate in step 1) is subjected to a slaking reaction with calcium oxide (quicklime) to obtain slaked lime (calcium hydroxide) emulsion.

[0075] 8) The sodium sulfate-containing filtrate produced in step 6) is placed in a precipitation conversion reaction tank, and the slaked lime emulsion produced in step 7) is added thereto for reaction to produce calcium sulfate dihydrate (gypsum) and sodium hydroxide. Solid-liquid separation is then performed using a plate and frame filter press. After solid-liquid separation, solid gypsum and a filtrate containing sodium hydroxide are obtained. The filtrate containing sodium hydroxide is reused in step 6), and the gypsum is sold to a cement plant as a cement retarder.

[0076] The above-described method in this embodiment achieves a 99.8% HF removal rate and a 99.5% SO₂ removal rate for hydrofluoric acid production tail gas. Furthermore, the market price of the co-produced magnesium fluoride and sodium fluorosilicate during the comprehensive treatment process is approximately RMB 12,000 / ton and RMB 8,000 / ton, respectively.

[0077] Example 2

[0078] See also Figure 1 , different from Example 1, the step 1) of using light-burned magnesium oxide to prepare a magnesium hydroxide suspension as a circulating absorption liquid for the hydrofluoric acid tail gas is cancelled, and commercial magnesium hydroxide is directly used to prepare a magnesium hydroxide suspension as a circulating absorption liquid for the hydrofluoric acid tail gas.

[0079] Steps 4) to 8) are the same as those in Example 1.

[0080] In this embodiment, commercial magnesium hydroxide is used, which simplifies the process and improves the purity of magnesium fluoride.

[0081] Example 3

[0082] Take the 20,000 tons / year anhydrous hydrogen fluoride production line as an example

[0083] 1) About 700 kg (8-hour usage) of light-burned magnesium oxide containing more than 80% magnesium oxide, which meets the standard of "Light-burned Magnesium Oxide YB / T 5206-2023", is added with 15,000 kg of water, stirred, and aged at 80°C for 3-4 hours. The mixture is then separated and removed by a four-stage hydrocyclone (pressure 0.5 MPa) to remove high-density slag such as SiO2, MgCO3, MgO, and Fe2O3. The obtained magnesium hydroxide suspension is precipitated and filtered by plate and frame pressure to remove calcium hydroxide that is slightly soluble in water, thereby obtaining a purified magnesium hydroxide filter cake having a magnesium hydroxide content of ≥90%. After drying, a high-purity magnesium hydroxide solid (purity 99.5%, particle size D 50 =10μm).

[0084] The cost of the magnesium hydroxide produced in this embodiment is approximately 40% of that purchased from outside.

[0085] 2) adding 1000 kg of water to the purified magnesium hydroxide filter cake obtained in step 1), stirring to obtain a magnesium hydroxide suspension, and adding the suspension to the circulating absorption liquid of the hydrofluoric acid tail gas, maintaining the pH value of the absorption liquid at 6.5±0.1.

[0086] 3) The absorption liquid is sent into the absorption tower through a circulation pump to spray and absorb hydrogen fluoride and sulfur dioxide in the tail gas. By adjusting the flow of the circulation pump to circulate and absorb the tail gas, it can be ensured that the tail gas meets the emission standards.

[0087] 4) The absorption liquid in the absorption liquid circulation tank is continuously aerated with air, the absorption liquid is separated by a hydrocyclone, the overflow liquid is returned to the absorption liquid circulation tank, the underflow liquid is passed through a plate and frame filter press for solid-liquid separation, and after drying, the solid is obtained as industrial magnesium fluoride. After testing, the physical and chemical indicators of the magnesium fluoride of this example are shown in Table 2, which meet the standard of "Magnesium Fluoride YS / T 691-2009" grade MF-2, and the output is about 330 kg in 8 hours.

[0088] Table 2 Physical and chemical indicators of magnesium trifluoride in the embodiment

[0089]

[0090] 5) The filtrate containing magnesium fluorosilicate and magnesium sulfate separated in step 4) is placed in a filtrate desiliconization tank, and sodium sulfate produced in step 6) is added until no more precipitate is present. The filtrate is filtered through a plate and frame filter press, and the filter cake is filtered and dried to obtain the sodium fluorosilicate byproduct. The filtrate is a magnesium sulfate solution.

[0091] 6) The magnesium sulfate-containing filtrate obtained in step 5) is placed in a filtrate conversion tank, and sodium hydroxide is added to react to form a magnesium hydroxide precipitate. After aging, the precipitate is separated into solid and liquid using a plate and frame filter press to obtain magnesium hydroxide solid and sodium sulfate filtrate. The magnesium hydroxide is reused in the absorption liquid system. The sodium sulfate-containing filtrate can be used in steps 5) and 7).

[0092] 7) The calcium hydroxide-containing filtrate in step 1) is subjected to a slaking reaction with calcium oxide (quicklime) to obtain slaked lime (calcium hydroxide) emulsion.

[0093] 8) The sodium sulfate-containing filtrate produced in step 6) is placed in a precipitation conversion reaction tank, and the slaked lime emulsion produced in step 7) is added thereto for reaction to produce calcium sulfate dihydrate (gypsum) and sodium hydroxide. Solid-liquid separation is performed using a plate and frame filter press. After solid-liquid separation, solid gypsum and a filtrate containing sodium hydroxide are obtained. The filtrate containing sodium hydroxide is reused in step 6), and the gypsum is sold to a cement plant as a cement retarder.

[0094] Example 4

[0095] Taking a 20,000 ton / year anhydrous hydrofluoric acid production line as an example, high-purity magnesium hydroxide is used as the absorbent.

[0096] 1) 300 kg of magnesium hydroxide powder that meets the Class I standard requirements of "Industrial Magnesium Hydroxide HG / T 3607-2007" is added to 1000 kg of water, stirred to prepare a magnesium hydroxide suspension, and added to the circulating absorption liquid of hydrofluoric acid tail gas, maintaining the pH value of the absorption liquid between 5.0 and 7.0.

[0097] 2) The circulating absorption liquid of the hydrofluoric acid tail gas is sent into the absorption tower through the circulating pump to spray and absorb the hydrogen fluoride and sulfur dioxide in the tail gas. By adjusting the flow of the circulating pump to circulate the tail gas for absorption, it can be ensured that the tail gas meets the emission standards.

[0098] 3) The absorption liquid in the aeration tank is continuously aerated with air, and the magnesium sulfite is oxidized to magnesium sulfate and gradually dissolved to obtain an absorption liquid (containing magnesium fluoride, magnesium fluorosilicate, and magnesium sulfate). The absorption liquid is separated by a hydrocyclone, and the overflow liquid is returned to the absorption liquid circulation tank. The underflow liquid is passed through a plate and frame filter press for solid-liquid separation, and dried to obtain industrial magnesium fluoride as a solid. After testing, the physical and chemical indicators of the magnesium fluoride of this example are shown in Table 3, which meet the standard of "Magnesium Fluoride YS / T 691-2009" grade MF-1, and the output is about 300 kg in 8 hours.

[0099] Table 3 Physical and chemical indicators of magnesium tetrafluoride in the embodiment

[0100]

[0101]

[0102] 4) The filtrate containing magnesium fluorosilicate and magnesium sulfate separated in step 3) is placed in a filtrate desiliconization tank, and the sodium sulfate produced in step 5) is added thereto. The mixture is stirred thoroughly to react until no more precipitation occurs. The mixture is filtered through a plate and frame filter press, and the filter cake is dried to obtain the sodium fluorosilicate byproduct. The filtrate is a magnesium sulfate solution.

[0103] 5) The magnesium sulfate-containing filtrate obtained in step 4) is placed in a filtrate conversion tank, and sodium hydroxide is added to react to form a magnesium hydroxide precipitate. After aging, the precipitate is separated into solid and liquid using a plate and frame filter press or a centrifuge to obtain magnesium hydroxide solid and sodium sulfate filtrate. The magnesium hydroxide is reused in the absorption liquid system, reducing the use of purchased raw materials. The sodium sulfate-containing filtrate can be used in steps 4) and 7).

[0104] 6) Add water to the calcium hydroxide solution and calcium oxide (quicklime) to carry out a slaking reaction to obtain slaked lime (calcium hydroxide) emulsion.

[0105] 7) The sodium sulfate-containing filtrate produced in step 5) is placed in a precipitation conversion reaction tank, and the slaked lime emulsion produced in step 6) is added thereto for reaction to produce calcium sulfate dihydrate (gypsum) and sodium hydroxide. Solid-liquid separation is performed using a plate and frame filter press. After solid-liquid separation, solid gypsum and a filtrate containing sodium hydroxide are obtained. The filtrate containing sodium hydroxide is reused in step 5), and the gypsum is sold to a cement plant as a cement retarder.

[0106] Example 5

[0107] This embodiment provides a system that can achieve comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride and sodium fluorosilicate.

[0108] See also Figure 3 The system includes a connected tail gas absorption unit 100, an aeration oxidation unit 200, a first solid-liquid separation unit 300, a desiliconization unit 400, a conversion and circulation unit 500 and a lime-gypsum conversion unit 600.

[0109] The tail gas absorption unit 100 includes a spray tower 101, a magnesium hydroxide suspension storage tank 102, a spray device 104 provided in the spray tower 101, a circulating pump 103 for conveying the magnesium hydroxide suspension to the spray device 104, and the spray device 104 for spraying the tail gas absorption liquid containing the magnesium hydroxide suspension into the hydrofluoric acid production tail gas. An online pH sensor with an accuracy of ±0.05 is linked to an automatic dosing system to maintain the pH value of the absorption liquid at about 6.0. Magnesium hydroxide undergoes a neutralization reaction represented by Formulas 1 to 3 with hydrogen fluoride, silicon tetrafluoride, and sulfur dioxide in the tail gas to generate a first absorption liquid containing magnesium fluoride, magnesium fluorosilicate, and magnesium sulfite.

[0110] 2HF+Mg(OH)2―→MgF2↓+2H2O Formula 1

[0111] SiF4+2HF+Mg(OH)2―→MgSiF6+2H2O (MgSiF6 is easily soluble in water)

[0112] SO2+Mg(OH)2―→MgSO3↓+H2O (MgSO3 is slightly soluble in water, with a solubility of about 0.573g / 100gH2O at 20℃)

[0113] Aeration and oxidation unit 200 is connected to tail gas absorption unit 100 and includes an aeration tank 201 and an air compressor 202. Aeration tank 201 is connected to spray tower 101 and is used to hold the first absorption liquid containing magnesium fluoride, magnesium fluorosilicate, and magnesium sulfite discharged from spray tower 101. Aeration tank 201 is equipped with a gas distributor 203. Air compressor 202 delivers compressed air to the gas distributor and introduces air into the first absorption liquid for aeration and oxidation, generating a second absorption liquid containing magnesium fluoride, magnesium fluorosilicate, and magnesium sulfate.

[0114] The first solid-liquid separation unit 300 is connected to the aeration and oxidation unit 200 and includes a first hydrocyclone 302 and a first plate-frame filter press 301 connected in sequence. The second absorption liquid that has completed aeration and oxidation in the aeration tank 201 passes through the first hydrocyclone 302 and the first plate-frame filter press 301 to achieve solid-liquid separation, obtaining high-purity magnesium fluoride solid and the first filtrate. In actual use, the filtration area of the plate-frame filter press is 20m 2 , filter cloth material is polypropylene, working pressure is 0.8MPa, filter cake moisture content ≤8%.

[0115] Desiliconization unit 400 includes a desiliconization tank 401 (equipped with an agitator), a sodium sulfate (sodium sulfate purity ≥ 99%) dispensing device 402, and a second plate-frame filter press 403. Desiliconization tank 401 is connected to both the sodium sulfate dispensing device 402 and the second plate-frame filter press 403. Within desiliconization tank 401, sodium sulfate reacts with magnesium fluorosilicate to produce slightly water-soluble sodium fluorosilicate and water-soluble magnesium sulfate. The sodium fluorosilicate and magnesium sulfate are separated into solids and liquids using the second plate-frame filter press 403.

[0116] The conversion and circulation unit 500 includes a conversion tank 501 with a common pH online monitor built in. The conversion tank 501 is connected to the second plate and frame filter press 403, and is respectively connected to the sodium hydroxide feeding device 502 and the third plate and frame filter press 503, and a reflux transmission pipeline 504. The reflux transmission pipeline 504 adopts a DN50 stainless steel pipe and is equipped with a pneumatic valve for returning the magnesium hydroxide suspension to the magnesium hydroxide suspension storage tank 102. In the conversion tank 501, the magnesium sulfate in the second filtrate reacts with the sodium hydroxide to generate magnesium hydroxide and a third filtrate containing sodium sulfate.

[0117] The lime-gypsum conversion unit 600 includes a lime slaking tank 601, a lime-gypsum conversion tank 602, and a fourth plate-and-frame filter press 603, which are connected in sequence. The fourth plate-and-frame filter press 603 is connected to the sodium hydroxide feeding device 502. The lime-gypsum conversion unit 600 mixes the third filtrate with the slaked lime emulsion and performs a third solid-liquid separation using the fourth plate-and-frame filter press 603 to produce solid gypsum and liquid sodium hydroxide. The liquid sodium hydroxide is then recycled to the sodium hydroxide feeding device 502 of the conversion and circulation unit 500.

[0118] Example 6

[0119] This embodiment provides a closed-loop circulation system that can achieve comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride and sodium fluorosilicate.

[0120] See also Figure 4 Based on the system provided in Example 5, this embodiment adds a light-burned magnesium oxide aging unit 700, which is connected to the magnesium hydroxide suspension storage tank 102 of the tail gas absorption unit 100.

[0121] The light-burned magnesium oxide slaking unit 700 includes a light-burned magnesium oxide slaking tank 701, a second hydrocyclone 702, and a fifth plate-and-frame filter press 703. The light-burned magnesium oxide and water are slaking in the light-burned magnesium oxide slaking tank 701, then separated by the multi-stage second hydrocyclone 702 to remove SiO2, Fe2O3, MgCO3, and MgO. The magnesium oxide is then separated by the fifth plate-and-frame filter press 703 into a magnesium hydroxide suspension.

[0122] After the hydrofluoric acid production tail gas is comprehensively treated by the system of this embodiment, only gypsum is produced (for sale), and magnesium hydroxide, sodium sulfate and sodium hydroxide achieve a fully closed-loop circulation without liquid waste discharge.

[0123] The present invention significantly improves resource recycling rates, with magnesium hydroxide utilization reaching 100% and sodium hydroxide reuse rates reaching approximately 95%. Waste is converted into gypsum and sold to cement plants, eliminating wastewater discharge. Therefore, the entire system essentially achieves zero waste discharge.

[0124] During the implementation of the method of the present invention, the capacity, material, specifications, and model of the aforementioned equipment can be selected based on commonly used instruments and equipment in the art. A membrane filter press can also be used as the solid-liquid separation equipment to increase the yield of magnesium fluoride. Furthermore, an online pH meter (accuracy ±0.1) can be installed in the spray absorption tower, allowing precise pH control through adjustment by an automatic dosing system.

[0125] In summary, the present invention uses light-burned magnesium oxide or magnesium hydroxide to prepare a suspension to absorb hydrogen fluoride, silicon tetrafluoride, and sulfur dioxide in hydrogen fluoride production tail gas, ultimately producing industrial magnesium fluoride, sodium fluorosilicate, and calcium sulfate dihydrate (gypsum). The magnesium fluoride produced by the method of the present invention complies with the standard "Magnesium Fluoride YS / T 691-2009" and can be used in fields such as metallurgical flux, solder, ceramics, glass, electrolytic aluminum, fireproof materials, abrasives, and coatings, effectively achieving the dual goals of resource utilization and tail gas treatment.

[0126] Finally, it should be noted that although the above embodiments have been described in the specification and drawings of this application, this does not limit the scope of patent protection of this application. All technical solutions generated by replacing or modifying equivalent structures or equivalent processes based on the essential concepts of this application using the contents recorded in the specification and drawings of this application, as well as directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are included in the scope of patent protection of this application.

Claims

1. A method for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride, characterized in that: The following steps are involved: S1, adding a magnesium hydroxide suspension to a tail gas circulating absorption liquid of a hydrofluoric acid production tail gas, spraying and absorbing the hydrofluoric acid production tail gas to obtain a first absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfite; S2. aerating the first absorption liquid with air to obtain a second absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfate; S3, performing a first solid-liquid separation on the second absorption liquid to obtain a high-purity magnesium fluoride solid and a first filtrate; S4. Place the first filtrate in a desiliconization tank, add sodium sulfate, filter, and dry to obtain sodium fluorosilicate and a second filtrate, wherein the second filtrate contains magnesium sulfate.

2. The method according to claim 1, characterized in that Also includes: S5. The second filtrate is placed in a conversion tank, sodium hydroxide is added to obtain a magnesium hydroxide precipitate, aged, and subjected to a second solid-liquid separation to obtain a magnesium hydroxide solid and a third filtrate. The third filtrate contains sodium sulfate, and the magnesium hydroxide solid is made into a magnesium hydroxide suspension for reuse in S1.

3. The method according to claim 1, characterized in that The S1 magnesium hydroxide suspension can also be prepared by adding water to light-burned magnesium oxide and aging it, and the preparation method comprises the following steps: Light-burned magnesium oxide is added with water for slaking, and then SiO2, Fe2O3, MgCO3 and MgO are separated and removed by a multi-stage hydrocyclone to obtain a magnesium hydroxide suspension.

4. The method according to claim 3, characterized in that The method further comprises the steps of: precipitating and filtering the magnesium hydroxide suspension to obtain a liquid containing calcium hydroxide, and recycling the liquid containing calcium hydroxide to carry out a slaking reaction with quicklime to obtain slaked lime emulsion.

5. The method according to claim 2, characterized in that The slaked lime emulsion is mixed with the third filtrate, and a third solid-liquid separation is performed to obtain solid gypsum and liquid sodium hydroxide, and the liquid sodium hydroxide is reused in S5.

6. The method according to claim 3, characterized in that The light-burned magnesia contains 80-90 wt% of magnesia.

7. The method according to claim 1, characterized in that In S3, the first solid-liquid separation is performed using a plate and frame filter press or a centrifugal filter.

8. The method according to claim 1, characterized in that The pH value of the first absorption liquid is maintained at 5.0-7.

0.

9. A system for comprehensive treatment of hydrofluoric acid production tail gas and co-production of magnesium fluoride, characterized in that: Include: The tail gas absorption unit (100) comprises a spray tower (101), a magnesium hydroxide suspension storage tank (102) and a circulation pump (103). The spray tower (101) is provided with a spray device (104) for spraying a tail gas absorption liquid containing a magnesium hydroxide suspension into the tail gas of hydrofluoric acid production to generate a first absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfite. an aeration oxidation unit (200) connected to the tail gas absorption unit (100), comprising an aeration tank (201) and an air compressor (202); the aeration tank (201) being used to hold a first absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfite discharged from the spray tower (101); and a gas distributor (203) being provided in the aeration tank (201) for introducing air into the first absorption liquid for aeration oxidation to generate a second absorption liquid containing magnesium fluoride, magnesium fluorosilicate and magnesium sulfate; A first solid-liquid separation unit (300) is connected to the aeration oxidation unit (200), comprising a solid-liquid separation device (301) and a first hydrocyclone (302), and is used for performing solid-liquid separation on the second absorption liquid to obtain high-purity magnesium fluoride solid and a first filtrate containing magnesium fluorosilicate and magnesium sulfate; A desiliconization unit (400) is connected to the first solid-liquid separation unit (300), and includes a desiliconization tank (401) and a sodium sulfate feeding device (402). The desiliconization tank (401) is provided with a stirrer for mixing the first filtrate with sodium sulfate for reaction, and obtaining sodium fluorosilicate and a second filtrate containing magnesium sulfate after filtration and drying. The conversion and circulation unit (500) is connected to the desiliconization unit (400) and includes a conversion tank (501), a sodium hydroxide feeding device (502) and a second solid-liquid separator (503). The conversion tank (501) is used to react the second filtrate with sodium hydroxide to generate magnesium hydroxide precipitate. After separation in the second solid-liquid separator (503), magnesium hydroxide solid and a third filtrate containing sodium sulfate are obtained. The magnesium hydroxide solid is converted into a magnesium hydroxide suspension and then returned to the magnesium hydroxide suspension storage tank (102) through a reflux transmission pipeline (504) for reuse. A lime-gypsum conversion unit (600) is connected to the conversion and circulation unit (500), and comprises a lime slaking tank (601), a lime-gypsum conversion tank (602), and a fourth plate and frame filter press (603) connected in sequence. The lime-gypsum conversion tank (602) is used to mix the third filtrate containing sodium sulfate with the slaked lime emulsion obtained from the lime slaking tank (601) to obtain solid gypsum and liquid sodium hydroxide.

10. The system according to claim 9, characterized in that The invention also comprises a light-burned magnesium oxide aging unit (700), which is connected to the magnesium hydroxide suspension storage tank (102) of the tail gas absorption unit (100), and includes a light-burned magnesium oxide aging tank (701), a second hydrocyclone (702) and a fifth plate-frame filter press (703). The magnesium hydroxide suspension obtained by pressing the fifth plate-frame filter press (703) is transported to the magnesium hydroxide suspension storage tank (102) through a pipeline.

Images