Method for producing calcium fluoride and method for producing hydrogen fluoride

Abstract

The present invention provides a novel method for producing calcium fluoride with controlled average particle size from a gas containing hydrogen fluoride, and a method for producing hydrogen fluoride from calcium fluoride produced by the calcium fluoride production method. [Solution] A method for producing calcium fluoride using a gas containing hydrogen fluoride, wherein the gas is brought into contact with a solid sodium-containing compound to obtain a solid containing sodium fluoride, and the aqueous solution of sodium fluoride obtained by dissolving the solid containing sodium fluoride is reacted with a calcium-containing compound to produce calcium fluoride.

Description

Technical Field

[0001] The present invention relates to a method for producing calcium fluoride and a method for producing hydrogen fluoride.

Background Art

[0002] Hydrogen fluoride, which is a raw material for a wide range of fluorine compounds, is industrially produced by reacting fluorite (calcium fluoride ore) with concentrated sulfuric acid. This reaction formula is represented by the following formula 1. CaF2 + H2SO4 → 2HF + CaSO4 Formula 1

[0003] That is, in order to industrially produce hydrogen fluoride, fluorite is required, but fluorite is a natural resource and there is a risk of depletion. Therefore, reduction of the usage amount of fluorite, which is a natural resource, is demanded. For example, a technique for producing calcium fluoride from waste fluorine compounds is demanded.

[0004] In Patent Document 1, a method for recovering calcium fluoride by using a column supporting a chemical such as a hydroxide or carbonate of an alkaline earth metal such as calcium hydroxide or calcium carbonate in a system for burning a perfluorinated compound has been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the method described in Patent Document 1, the reactivity between the agent and the hydrogen fluoride produced by burning the perfluoro compound is insufficient, making it impossible to process large quantities of gas. While it is conceivable to improve reactivity by adjusting the average particle size of the agent, the resulting average particle size of calcium fluoride depends on the average particle size of the agent, posing a challenge in controlling the average particle size of calcium fluoride to one suitable for hydrogen fluoride production.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a novel method for producing calcium fluoride that can process a large amount of gas and produce calcium fluoride with a controlled average particle size from a gas containing hydrogen fluoride, and a method for producing hydrogen fluoride from calcium fluoride produced by the calcium fluoride production method. [Means for solving the problem]

[0008] The present invention is as follows [1] to

[13] . [1] A method for producing calcium fluoride using a gas containing hydrogen fluoride, The aforementioned gas is brought into contact with a solid sodium-containing compound to obtain a solid containing sodium fluoride. A method for producing calcium fluoride, comprising reacting an aqueous solution of sodium fluoride obtained by dissolving a solid containing sodium fluoride with a calcium-containing compound to produce calcium fluoride. [2] The method for producing calcium fluoride according to [1], wherein the gas is exhaust gas. [3] The method for producing calcium fluoride according to [1] or [2], wherein the gas comprises at least one selected from the group consisting of hydrogen chloride and sulfur oxides. [4] The method for producing calcium fluoride according to any one of [1] to [3], wherein the sodium-containing compound comprises sodium bicarbonate. [5] The method for producing calcium fluoride according to any one of [1] to [4], wherein the dissolution of the solid containing sodium fluoride is performed after washing the solid containing sodium fluoride. [6] A method for producing calcium fluoride according to any one of [1] to [5], wherein the liquid used in either washing or dissolving the solid containing sodium fluoride, or both, contains water containing fluoride ions. [7] A method for producing calcium fluoride using a gas containing hydrogen fluoride, The aforementioned gas is supplied to an aqueous solution of a sodium-containing compound to obtain a reaction solution. A method for producing calcium fluoride, comprising reacting an aqueous solution of sodium fluoride obtained from the reaction solution with a calcium-containing compound. [8] The method for producing calcium fluoride according to [7], wherein the gas is exhaust gas. [9] The method for producing calcium fluoride according to [7] or [8], wherein the gas comprises at least one selected from the group consisting of hydrogen chloride and sulfur oxides.

[10] The method for producing calcium fluoride according to any one of [7] to [9], wherein the sodium-containing compound comprises sodium hydroxide.

[11] A method for producing calcium fluoride according to any one of [7] to

[10] , comprising: performing a concentration treatment and / or a recrystallization treatment on the reaction solution to obtain an aqueous slurry containing solid sodium fluoride; performing solid-liquid separation of the aqueous slurry to obtain solid sodium fluoride; and dissolving the solid sodium fluoride to obtain an aqueous solution of sodium fluoride.

[12] The method for producing calcium fluoride according to

[11] , wherein the liquid used in dissolving the solid sodium fluoride comprises water containing fluoride ions.

[13] A method for producing hydrogen fluoride by reacting calcium fluoride produced by any of the methods for producing calcium fluoride described in [1] to

[12] with sulfuric acid. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a novel method for producing calcium fluoride capable of efficiently producing calcium fluoride from a gas containing hydrogen fluoride, and a method for producing hydrogen fluoride for producing hydrogen fluoride from calcium fluoride produced by the method for producing calcium fluoride.

[0010] In the production method of the present invention, hydrogen fluoride in the gas is once converted into sodium fluoride, and then calcium fluoride is produced.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram showing an example of a production system for calcium fluoride used in the dry method of the present embodiment. [Figure 2] It is a schematic diagram showing another example of a production system for calcium fluoride used in the dry method of the present embodiment. [Figure 3] It is a schematic diagram showing an example of a production system for calcium fluoride used in the wet method of the present embodiment. [Figure 4] It is a schematic diagram showing another example of a production system for calcium fluoride used in the wet method of the present embodiment. [Figure 5] It is a diagram showing the temperature dependence of the solubility of 100 g of sodium fluoride, sodium chloride, sodium sulfate, and sodium carbonate in water. [Figure 6] It is a flowchart showing an example of the procedure of a production system for calcium fluoride used in the dry method of the present embodiment. [Figure 7] It is a flowchart showing an example of the procedure of a production system for calcium fluoride used in the wet method of the present embodiment.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, the following description is an example of an embodiment of the present invention, and the present invention is not limited to these contents and can be implemented with modifications within the scope of the gist.

[0013] The definitions used herein are as follows: "Average particle diameter" refers to the volume-based average particle diameter (MV) measured using a laser diffraction scattering particle size distribution analyzer (for example, the Microtrac FRA9220 manufactured by Nikkiso Co., Ltd.). The "dry method" is a method for producing sodium fluoride that does not use water. It involves supplying a solid sodium-containing compound into a gas containing hydrogen fluoride, producing sodium fluoride through a gas-solid reaction, and then producing calcium fluoride from the resulting sodium fluoride. The "wet process" is a method of producing sodium fluoride that uses water, in which a gas containing hydrogen fluoride is supplied to an aqueous solution of a sodium-containing compound, sodium fluoride is produced in the aqueous solution, and calcium fluoride is produced from the obtained sodium fluoride. A "bag filter" is a type of filtration dust collector that collects solid components from gases. "Exhaust gas" is a general term for gases emitted from internal combustion engines used in automobiles and ships, gas turbines used in aircraft, incinerators, thermal power plants, and factories. "Industrial wastewater" is a general term for water discharged from industrial activities carried out at incinerators, thermal power plants, factories, etc.

[0014] ≪Calcium Fluoride Manufacturing Equipment (Dry Method)≫ Figure 1 is a schematic diagram showing an example of a calcium fluoride production apparatus used in the dry method of this embodiment. The calcium fluoride production system 100A comprises a sodium fluoride production facility 10, a dissolution tank 20, a calcium fluoride production apparatus 30, and piping L01, L001, L02, L12, L19, L23, and L03.

[0015] Figure 2 is a schematic diagram showing another example of a calcium fluoride production apparatus used in the dry method of this embodiment. The calcium fluoride production system 100B includes, in addition to the calcium fluoride production system 100A, a cooling tower 50, a filter 60, a pollution control device 70, a washing tank 80, a calcium fluoride separation device 40, and piping L05, L56, L61, L17, L79, L18, L08, L89, L82, L34, L48, and L49. Note that the calcium fluoride production system 100B does not include piping L01 because it includes piping L61. Also, it does not include piping L12 because it includes piping L18 and L82. Furthermore, it does not include piping L19 because it includes piping L17 and L79.

[0016] <Sodium fluoride manufacturing facility> In the sodium fluoride production facility 10 shown in Figure 1, a gas containing hydrogen fluoride (hereinafter also simply referred to as "gas") is brought into contact with a solid sodium-containing compound to produce a solid containing sodium fluoride (hereinafter also referred to as crude product A). The sodium fluoride production facility 10 is equipped with a recovery filter 10A, and piping L01 and L001. As shown in Figure 1, the gas supply source containing hydrogen fluoride and the recovery filter 10A are connected via piping L01. The solid sodium compound supply source and piping L01 are connected via piping L001. The recovery filter 10A and the dissolution tank 20 are connected via piping L12. The recovery filter 10A is connected to piping L19.

[0017] <Dissolution tank> In the dissolution tank 20, crude product A is dissolved in the solvent to produce an aqueous solution of sodium fluoride. As shown in Figure 1, the dissolving solution supply source and the dissolving tank 20 are connected via piping L02. The dissolving tank 20 and the calcium fluoride production apparatus 30 are connected via piping L23. As shown in Figure 2, the washing tank 80 and the dissolution tank 20 are connected via piping L82. As the dissolution tank 20, any dissolution tank known in this field can be used.

[0018] <Calcium Fluoride Production Equipment> In the calcium fluoride production apparatus 30, calcium fluoride is produced by reacting an aqueous solution of sodium fluoride with a calcium-containing compound. As shown in Figure 2, the calcium fluoride production apparatus 30 and the calcium fluoride separation apparatus 40 are connected via piping L34. The calcium fluoride production apparatus 30 and the calcium-containing compound supply source are connected via piping L03. As the calcium fluoride production apparatus 30, any calcium fluoride production apparatus known in this field can be used.

[0019] The calcium fluoride production system 100B shown in Figure 2 is equipped with the following ancillary equipment in addition to the calcium fluoride production system 100A.

[0020] <Defrosting tower> In the cooling tower 50, the gas is cooled by water spraying when the gas temperature is high. As shown in Figure 2, the gas supply source containing hydrogen fluoride and the cooling tower 50 are connected via piping L05. The cooling tower 50 and the filter 60 are connected via piping L56. For the cooling tower 50, any cooling tower known in this field can be used.

[0021] <filter> Filter 60 removes impurities from the gas, thereby purifying it. As shown in Figure 2, the filter 60 and the recovery filter 10A are connected via piping L61. Filter 60 can be any filter known in this field.

[0022] <Abatement device> The pollution control device 70 removes harmful substances such as acidic components contained in the unreacted gas from the sodium fluoride production facility 10. As shown in Figure 2, the recovery filter 10A and the pollution control device 70 are connected via piping L17. The pollution control device 70 and the atmosphere are connected via piping L79. Any pollution control device known in this field can be used as the pollution control device 70.

[0023] <Washing Tank> In the washing tank 80, the crude product A obtained in the sodium fluoride production equipment 10 is washed. As shown in Figure 2, the washing tank 80 is located between the recovery filter 10A and the dissolution tank 20. That is, the recovery filter 10A and the washing tank 80 are connected via piping L18. The washing tank 80 and the dissolution tank 20 are connected via piping L82. The washing water supply source and the washing tank 80 are connected via piping L08. The washing tank 80 is also connected to piping L89. Piping L89 is for discharging washing wastewater. As the washing tank 80, a washing tank known in the art can be used.

[0024] <Calcium Fluoride Separator> The calcium fluoride separation apparatus 40 separates the solid containing calcium fluoride and recovers calcium fluoride with a purity and average particle size suitable for raw materials such as hydrogen fluoride. As shown in Figure 2, the calcium fluoride separator 40 is connected to pipe L49 and pipe L48. Pipe L49 is for discharging wastewater, and pipe L48 is for recovering calcium fluoride.

[0025] <Piping> Various types of piping can be used, including those known in this field, but piping made of materials with chemical resistance, acid resistance, and base resistance is preferred. The shape of the various pipes can be any structure, but a cylindrical shape is preferred.

[0026] ≪Method for producing calcium fluoride (dry method)≫ The calcium fluoride production method of this embodiment includes a sodium fluoride production step of contacting a gas containing hydrogen fluoride with a solid sodium-containing compound to obtain crude product A, a sodium fluoride aqueous solution production step of obtaining an aqueous solution of sodium fluoride from the crude product A, and a calcium fluoride production step of reacting the aqueous solution of sodium fluoride with a calcium-containing compound. A gas cooling and purification step of cooling and purifying the gas containing hydrogen fluoride may be performed before the sodium fluoride production step. Furthermore, a washing step to remove impurities may be performed when producing an aqueous solution of sodium fluoride from crude product A. Furthermore, a calcium fluoride separation step of separating the crude product containing calcium fluoride obtained in the calcium fluoride production step may be performed after the calcium fluoride production step. The gas cooling and purification step, sodium fluoride production step, washing step, sodium fluoride aqueous solution production step, calcium fluoride production step, and calcium fluoride separation step will be described below with reference to Figures 1 and 2.

[0027] <Gas-cooled purification process> In the gas cooling and purification process, the gas is cooled and solid impurities are removed from the gas. This process can be optionally performed before the sodium fluoride production process, and the order of gas cooling and removal of solid impurities from the gas may be reversed, or only one of them may be performed. In the calcium fluoride production system 100B shown in Figure 2, the gas is supplied to the cooling tower 50 through piping L05. Water is injected from the cooling tower 50 to cool the gas. Subsequently, the cooled gas is supplied to the filter 60 through piping L56. The filter 60 removes solid impurities from the gas, purifying it. Alternatively, an adsorbent such as activated carbon may be sprayed onto the gas flowing through piping L56. The activated carbon adsorbs dioxins, which are impurities in the gas, and the filter 60 removes the adsorbent containing the dioxins.

[0028] (Exhaust gas) The gas used in this embodiment may be exhaust gas. The exhaust gas is not particularly limited as long as it contains hydrogen fluoride, and examples include gases produced when waste is burned in an incinerator, or gases produced in semiconductor manufacturing processes or aluminum refining processes. The exhaust gas generated during combustion may contain many solid impurities, such as burnt compounds, dust such as combustion residue, solid foreign matter derived from filter media, and dioxins produced during the cooling process after combustion.

[0029] When the gas is the incineration gas of fluorine compounds, the temperature may exceed 1000°C, which can make the production of sodium fluoride difficult. In such cases, it is preferable to use a cooling tower 50 to inject water into the incineration gas and cool the gas temperature to, for example, 120 to 400°C. The water used in the cooling tower 50 may be the wastewater generated in the cleaning process described later.

[0030] Examples of filters 60 for removing impurities include bag filters, ceramic filters, and electrostatic precipitators. By purifying the gas and removing impurities from solid components in the gas beforehand, the purity of the final calcium fluoride can be increased. The pore size of the filter is preferably 0.5 to 200 μm, more preferably 0.7 to 100 μm, and even more preferably 1 to 30 μm.

[0031] <Sodium Fluoride Manufacturing Process> In the sodium fluoride manufacturing process, crude product A is produced by contacting a gas containing hydrogen fluoride with a solid sodium-containing compound.

[0032] In the calcium fluoride production system 100A shown in Figure 1, a gas containing hydrogen fluoride is supplied to the recovery filter 10A through piping L01. A solid sodium-containing compound is supplied to piping L01 through piping L001. As a result, the gas and the solid sodium-containing compound come into contact, and crude product A is obtained. Crude product A is recovered by the recovery filter 10A. Furthermore, in the calcium fluoride production system 100B shown in Figure 2, a gas containing hydrogen fluoride that has undergone a gas cooling and purification process is supplied to the recovery filter 10A through piping L61. A solid sodium-containing compound is supplied to piping L61 through piping L001. As a result, the gas and the solid sodium-containing compound come into contact, and crude product A is obtained. Crude product A is recovered by the recovery filter 10A.

[0033] The sodium fluoride production equipment 10 can be any equipment that reacts and recovers a gaseous acidic component with a solid alkaline compound, and it is preferable that the equipment has a supply port for adding the solid alkaline compound to the recovery filter 10A described later. Examples of recovery filters 10A include bag filters, ceramic filters, and dry electrostatic precipitators, with bag filters being preferred from the viewpoint of reaction rate and recovery rate of reactants. From the standpoint of ensuring filter performance while preventing clogging and pressure differential increases, a pore size of 1 to 50 μm is preferable for the filter. From a durability standpoint, the filter material preferably contains glass fiber, polytetrafluoroethylene, or ceramic. The filter may be made of woven or non-woven fabric, but it is preferable that the surface of the filter be laminated with a polytetrafluoroethylene film to prevent clogging and pressure differential increase.

[0034] The solid sodium-containing compound is preferably a solid sodium carbonate such as sodium bicarbonate. In this specification, sodium fluoride is not included in the definition of a sodium-containing compound. The average particle size of the solid sodium-containing compound is preferably 5 to 50 μm, more preferably 7 to 25 μm, and even more preferably 8 to 15 μm. If the average particle size is above the lower limit mentioned above, and the solid sodium-containing compound is sodium bicarbonate, the gas diffuses into the porous sodium carbonate particles produced by the thermal decomposition of sodium bicarbonate, allowing the acidic components (hydrogen fluoride) in the gas to react sufficiently with the sodium carbonate, thus improving the reaction efficiency with the acidic components in the gas. In addition, the fluidity of the solid sodium-containing compound (especially solid sodium bicarbonate) improves, particle aggregation is suppressed, and the reaction efficiency with the gas tends to improve. Furthermore, sodium bicarbonate with a small average particle size may be given additives to improve its fluidity. Calcium carbonate is preferred as an additive. If calcium carbonate is used, it can be removed during the calcium fluoride manufacturing process. The supply rate of solid sodium-containing compounds is 0.03 to 200 (g / h) / (m³) relative to the gas supply rate. 3 It may also be 0.1~100(g / h) / (m 3 It may also be 0.3~50(g / h) / (m 3 It may also be / h). The solid sodium-containing compound may be added all at once from pipe L001, or in several portions.

[0035] In the sodium fluoride production facility 10, it is believed that the reaction is proceeding in either the piping L61 or the recovery filter 10A, or both. In particular, when the solid sodium-containing compound is sodium bicarbonate, the following reaction is thought to be occurring. First, sodium bicarbonate undergoes thermal decomposition to form sodium carbonate. This reaction is represented by equation 2 below. 2NaHCO3→Na2CO3+H2O+CO2 formula 2 Next, sodium carbonate reacts with hydrogen fluoride contained in the gas to produce sodium fluoride. This reaction is represented by equation 3 below. Na2CO3+2HF→2NaF+H2O+CO2 formula 3

[0036] The reaction temperature is preferably one suitable for the decomposition of sodium bicarbonate. The reaction temperature is preferably 120 to 400°C, more preferably 150 to 300°C, and even more preferably 170 to 250°C. When the reaction temperature is within the above range, if the solid sodium-containing compound is sodium bicarbonate, the supplied sodium bicarbonate undergoes thermal decomposition to form porous sodium carbonate with a high specific surface area, allowing the reaction to proceed easily into the interior of the sodium carbonate. If the gas temperature is high, it is preferable to dilute it with air or cool it using the above-mentioned de-cooling tower 50.

[0037] Other gases besides hydrogen fluoride that may be present include hydrogen chloride and sulfur oxides (sulfur dioxide, sulfur trioxide, sulfuric acid, etc.). Other gases such as nitrogen, oxygen, water vapor, carbon dioxide, and nitrogen oxides may also be present. The hydrogen fluoride content relative to the total volume of the gas is preferably 10 ppm to 50,000 ppm (volume), more preferably 50 to 10,000 ppm (volume), and even more preferably 100 to 5,000 ppm (volume). The hydrogen chloride content relative to the total volume of the gas is preferably 0 to 10,000 ppm (volume), more preferably 0 to 1,000 ppm (volume), and even more preferably 0 to 100 ppm (volume). The sulfur oxide content relative to the total volume of the gas is preferably 0 to 10,000 ppm (volume), more preferably 0 to 1,000 ppm (volume), and even more preferably 0 to 100 ppm (volume).

[0038] If the gas contains hydrogen chloride and sulfur oxides (sulfur dioxide, sulfur trioxide, sulfuric acid, etc.), they may react with sodium-containing compounds to produce sodium chloride, sodium sulfate, etc. Furthermore, unreacted sodium bicarbonate decomposes at the aforementioned temperature, converting to sodium carbonate. In other words, crude product A may contain sodium chloride, sodium sulfate, and sodium carbonate.

[0039] The sodium fluoride content of crude product A relative to the total mass is preferably 10 to 100% by mass, more preferably 50 to 100% by mass, and even more preferably 80 to 100% by mass. When crude product A has sodium fluoride as its main component, it can also be defined as a solid with sodium fluoride as its main component. The sodium chloride content relative to the total mass of crude product A is preferably 0 to 90% by mass, more preferably 0 to 50% by mass, and even more preferably 0 to 20% by mass. The sodium sulfate content relative to the total mass of crude product A is preferably 0 to 50% by mass, more preferably 0 to 15% by mass, and even more preferably 0 to 5% by mass. The sodium carbonate content relative to the total mass of crude product A is preferably 0 to 20% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass. Since the above product is a solid, it is easy to transport.

[0040] (Gas treatment) After passing through the recovery filter 10A, the gas passes through the piping L19 as shown in Figure 1 and is released into the atmosphere. Furthermore, as shown in Figure 2, it is preferable to decontaminate the material using the decontamination device 70 to comply with environmental standards before releasing it into the atmosphere. The abatement device 70 can be a commonly used dry abatement device or a wet abatement device. A dry abatement device is a device that sprays powdered neutralizing agents, such as those used in the sodium fluoride production equipment mentioned above, into the gas and recovers the reaction products. Sodium bicarbonate or calcium hydroxide can be used as the neutralizing agent. A wet abatement device is a wet scrubber, and the liquid used can be an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, or a calcium hydroxide slurry.

[0041] <Washing process> In the washing step, crude product A obtained in the sodium fluoride production step is washed. The washing step can be optionally performed after the sodium fluoride production step and before the sodium fluoride aqueous solution production step. Performing the washing step tends to increase the purity of the final calcium fluoride obtained.

[0042] As shown in Figure 2, the crude product A recovered by the recovery filter 10A is supplied to the washing tank 80 through piping L18, and washing water is supplied to the washing tank 80 through piping L08 to create water containing the water-soluble components of the recovered crude product A and undissolved components. Next, solid-liquid separation is performed to separate the solid from the separated liquid. The separated liquid is discharged through piping L89, and the solid is supplied to the dissolution tank 20 through piping L82.

[0043] The amount of washing water can be appropriately set depending on the composition of crude product A and the washing temperature. The washing water may be water with dissolved salt, as long as it does not contain solids. The temperature of the washing water is preferably 0°C to 90°C, more preferably 20°C to 80°C, and more preferably 35°C to 65°C. The washing water may be factory wastewater, and factory wastewater with dissolved hydrogen fluoride is preferred.

[0044] Figure 5 shows the temperature dependence of the solubility of sodium fluoride, sodium chloride, sodium sulfate, and sodium carbonate in 100g of water. As shown in Figure 5, the solubility of sodium chloride and sodium fluoride remains almost constant regardless of temperature, while the solubility of sodium carbonate and sodium sulfate increases sharply between 20 and 40°C.

[0045] (Addition of washing water) In the washing process, sodium fluoride is purified by utilizing the difference in solubility mentioned above. The amount of washing water can be appropriately set depending on the composition of crude product A and the washing temperature. Specifically, the amount and temperature of washing water are selected so that sodium fluoride does not dissolve (or hardly dissolves) and sodium chloride, sodium sulfate, and sodium carbonate dissolve. As a result, sodium fluoride tends to remain as a solid, while sodium chloride, sodium carbonate, and sodium sulfate dissolve easily. Therefore, using the recovered crude product A and washing water, an undissolved liquid and a liquid in which some of the undissolved components have been prepared, and by solid-liquid separation into the solid and the separated liquid, a solid with a high sodium fluoride content (hereinafter also referred to as the washing material) is obtained. Furthermore, compared to the case where only sodium fluoride is dissolved in water, the separated liquid contains other sodium salts (sodium chloride, sodium sulfate, and sodium carbonate). Therefore, the sodium concentration in the separated liquid exceeds the sodium concentration at the saturation solubility of sodium fluoride, and the concentration of fluoride ions that can dissolve in the separated liquid decreases significantly. Consequently, the amount of sodium fluoride dissolved and lost in the separated liquid is significantly less compared to other highly soluble salts.

[0046] The washing temperature should be set according to the proportions of sodium fluoride, sodium chloride, sodium sulfate, and sodium carbonate. The temperature is preferably 20 to 90°C, more preferably 30 to 80°C or higher, and even more preferably 35 to 60°C. The sodium fluoride content relative to the total mass of solids after drying the washed items is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The ratio of the sodium fluoride content in the solid content to the sodium fluoride content in crude product A is preferably 1.1 or higher, more preferably 1.5 or higher, and even more preferably 2 or higher. The ratio of sodium sulfate concentration to sodium fluoride concentration after the washing process is preferably 0.2 or less, more preferably 0.05 or less, and even more preferably 0.02 or less. When the ratio of sodium sulfate concentration to sodium fluoride concentration after the washing process is within the above range, the presence of sulfate ions in the calcium fluoride manufacturing process can be suppressed, and the migration of sulfate ions as impurities into calcium fluoride as calcium sulfate can be suppressed.

[0047] The washing tank 80 may simultaneously add washing water and remove the separated liquid, or it may mix with washing water at once and separate the solid and liquid by filtration.

[0048] (Solid-liquid separation method) The solid-liquid separation apparatus is not particularly limited as long as it is capable of separating the separation liquid from the solid, and examples include centrifuges, filter presses, screw decanters, and pressure filters.

[0049] The separated liquid (washing wastewater) obtained from solid-liquid separation may be used in the cooling tower 50 or introduced into the pollution control device 70. By reusing the separated liquid, it is possible to reduce the volume of total wastewater.

[0050] <Sodium fluoride aqueous solution manufacturing process> In the calcium fluoride production system 100A shown in Figure 1, crude product A is supplied to the dissolution tank 20 through piping L12. In the dissolution tank 20, a dissolving solution is supplied from piping L02 to dissolve crude product A. Subsequently, if necessary, acids or other substances may be added to adjust the pH to one suitable for calcium fluoride production. In the calcium fluoride production system 100B shown in Figure 2, the washed material is supplied to the dissolution tank 20 through piping L82. The washed material does not need to be completely dry. In the dissolution tank 20, a dissolving solution is supplied from piping L02 to dissolve the washed material. Afterward, an acid or other substance may be added as needed to adjust the pH to one suitable for calcium fluoride production.

[0051] Water is preferred as the solvent used in the production of an aqueous solution of sodium fluoride. The water may contain fluoride ions, or it may be industrial wastewater. In particular, it is more preferable to use industrial wastewater containing fluoride ions, as this allows for the reuse of the fluorine source. Furthermore, the pH of the aqueous solution of sodium fluoride may be adjusted with hydrogen fluoride and hydrogen chloride contained in the wastewater.

[0052] Examples of acids include hydrochloric acid, but are not particularly limited.

[0053] The temperature of the aqueous solution of sodium fluoride is preferably 0 to 50°C, more preferably 5 to 45°C, and even more preferably 10 to 40°C.

[0054] <Calcium Fluoride Manufacturing Process> The calcium fluoride manufacturing process can be carried out in accordance with Patent No. 6079524, but is not limited to the method described in the above patent.

[0055] In the calcium fluoride manufacturing process, an aqueous solution of sodium fluoride is reacted with a calcium-containing compound to produce an aqueous solution of calcium fluoride. As shown in Figures 1 and 2, the aqueous sodium fluoride solution produced in the sodium fluoride aqueous solution production process is supplied to the calcium fluoride production apparatus 30 through piping L23. A calcium-containing compound is also supplied to the calcium fluoride production apparatus 30 through piping L03. The calcium fluoride production apparatus 30 then reacts the sodium fluoride with the calcium-containing compound to produce an aqueous calcium fluoride solution.

[0056] The reaction temperature is preferably 10 to 50°C, and more preferably 20 to 40°C. The reaction involves adding an aqueous sodium fluoride solution and a calcium compound to a reaction vessel that already contains calcium fluoride particles. Hydrochloric acid may be added to adjust the pH to a predetermined level. The pH is not limited as long as it is the value at which calcium fluoride precipitates, but 1.5 to 7 is preferred, 1.7 to 4 is more preferred, and 2 to 3.5 is even more preferred. Calcium fluoride precipitates easily when the pH is 1.5 or higher. Also, when the pH is 7 or lower, it is possible to suppress the retention of undissolved calcium compounds used as raw materials in the calcium fluoride. Furthermore, when the pH is 4 or lower, silicon dioxide in the reaction solution gels, suppressing its inclusion as an impurity in the calcium fluoride. In addition, impurities other than calcium fluoride are less likely to precipitate, thus suppressing their inclusion. The stirring power is 0.2 kW / m 3 The above is preferable, and 0.3 kW / m 3 The above is even more preferable. It is possible to produce calcium fluoride with a good particle size distribution by suppressing the generation of fine calcium fluoride particles. From the viewpoint of equipment protection, 1 kW / m 3 The following are preferable.

[0057] The fluoride ion content of the aqueous solution is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less, relative to the total mass of the aqueous solution. Within this concentration range, the resulting calcium fluoride tends to form particles with a large average particle size that are easy to handle.

[0058] As for the method of supplying the aqueous sodium fluoride solution and the calcium-containing compound, the calcium-containing compound may be added to the calcium fluoride production apparatus 30 to which the aqueous sodium fluoride solution has been supplied, or the aqueous sodium fluoride solution may be added to the calcium fluoride production apparatus 30 to which the calcium-containing compound has been supplied, or both may be continuously supplied to and withdrawn from the reaction vessel.

[0059] The supplied calcium-containing compound may be a powder, an aqueous slurry of the calcium-containing compound, or an aqueous solution of the calcium-containing compound. In particular, an aqueous slurry of the calcium-containing compound or an aqueous solution of the calcium-containing compound is preferred.

[0060] The calcium-containing compound is not particularly limited and includes calcium carbonate, calcium hydroxide, calcium chloride, etc., and combinations thereof are also acceptable. When using calcium carbonate or calcium hydroxide, the pH of the reaction solution in the calcium fluoride production apparatus 30 can be increased. On the other hand, when using calcium chloride, the calcium ions necessary for the reaction with sodium fluoride can be supplied without affecting the pH of the reaction solution. Therefore, the type and amount of calcium-containing compound should be determined while adjusting the pH of the reaction solution in the calcium fluoride production apparatus 30 to 1.5-7.

[0061] In the case of calcium-containing compounds in powder form, the average particle size is preferably 50 μm or less, and more preferably 20 μm or less.

[0062] <Calcium Fluoride Separation Process> In the calcium fluoride separation process, the calcium fluoride slurry obtained in the calcium fluoride production process is separated into solid and liquid phases, and then washed with water, dehydrated, and dried to recover calcium fluoride with a purity and average particle size suitable for the production of hydrogen fluoride.

[0063] As shown in Figures 1 and 2, the aqueous slurry containing calcium fluoride produced in the calcium fluoride production apparatus 30 is supplied to the calcium fluoride separation apparatus 40 through piping L34. In the calcium fluoride separation apparatus 40, solid-liquid separation of the aqueous slurry containing solid calcium fluoride is performed, and the separated liquid is drained through piping L49. Calcium fluoride is recovered through piping L48.

[0064] In dehydration and drying, filtration or dehydration is performed using a solid-liquid separator (e.g., a filter press or centrifuge), and if necessary, the solid is washed and filtration or dehydration is performed again. After filtration or dehydration, high-purity calcium fluoride is obtained by further drying the resulting cake-like solid. Drying is performed, for example, at 110°C for 6 hours. A commonly used dryer can be used.

[0065] The purity of the calcium fluoride produced by the above manufacturing method is preferably 90% by mass or more on a solid content basis, the average particle size is preferably 15 to 50 μm, and the particle size distribution width (d90 / d10) is preferably 4 or less. Such calcium fluoride is suitable for the production of hydrogen fluoride. Note that d90 (d10) refers to the particle diameter at the point on the cumulative curve where the cumulative volume reaches 90% (10%), calculated by measuring the particle size distribution using a laser diffraction scattering particle size distribution analyzer (for example, Microtrac FRA9220 manufactured by Nikkiso Co., Ltd.), with the total volume of the particle collection set to 100%.

[0066] The discharged separated liquid is neutralized by adding calcium compounds or alkali metal salts, and after removing solid matter by solid-liquid separation, it is confirmed to meet environmental standards before being disposed of.

[0067] As a calcium fluoride production and recovery system, the system described in Japanese Patent No. 6079524 is preferred. By selecting the optimal system, it is possible to obtain calcium fluoride with properties suitable for hydrogen fluoride production.

[0068] ≪Calcium Fluoride Manufacturing Equipment (Wet Method)≫ Figure 3 is a schematic diagram showing an example of a calcium fluoride production system used in the wet method of this embodiment. The calcium fluoride production system 200A comprises a wet sodium fluoride production apparatus 80A, a calcium fluoride production apparatus 30, and piping L08A, L080A, L89A, L83A, and L03.

[0069] Figure 4 is a schematic diagram showing another example of a calcium fluoride production system used in the wet method of this embodiment. The calcium fluoride production system 200B includes, in addition to the calcium fluoride production system 200A, a cooling tower 50, a filter 60, a decontamination device 70, a concentration and separation device 90, a dissolution tank 20, a calcium fluoride separation device 40, and piping L05, L56, L68A, L080A, L17, L79, L89A, L09, L99, L92, L02, L23, L03, L34, L48, and L49. Note that the calcium fluoride production system 200B does not include piping L08A because it includes piping L68A. Also, it does not include piping L83A because it includes piping L89A and L92. Furthermore, it does not include piping L89A because it includes piping L17 and L79.

[0070] <Wet-type sodium fluoride production equipment> In the wet sodium fluoride production apparatus 80A shown in Figure 3, a gas containing hydrogen fluoride is supplied to an aqueous solution of a sodium-containing compound to produce a reaction solution. The reaction solution is an aqueous solution in which sodium fluoride is dissolved or an aqueous slurry containing solid sodium fluoride. As shown in Figure 3, the gas supply source containing hydrogen fluoride and the wet sodium fluoride production apparatus 80A are connected via piping L08A. The wet sodium fluoride production apparatus 80A is connected to piping L89A. The wet sodium fluoride production apparatus 80A and the calcium fluoride production apparatus 30 are connected via piping L83A.

[0071] The calcium fluoride production system 200B shown in Figure 4 is equipped with the following ancillary equipment in addition to the calcium fluoride production system 200A.

[0072] <Defrosting tower> As shown in Figure 4, the gas supply source containing hydrogen fluoride and the cooling tower 50 are connected via piping L05. The cooling tower 50 and the filter 60 are connected via piping L56.

[0073] <filter> The filter 60 and the wet sodium fluoride production apparatus 80A are connected via piping L68A.

[0074] <Abatement device> The pollution control device 70 and the wet sodium fluoride production device 80A are connected via piping L17. The pollution control device 70 is connected to piping 79.

[0075] <Concentration separation equipment> In the concentration and separation apparatus 90, the reaction solution obtained in the wet sodium fluoride production apparatus 80A is subjected to at least one of the group consisting of concentration and recrystallization to obtain an aqueous slurry containing solid sodium fluoride, and the slurry is subjected to solid-liquid separation to obtain solid sodium fluoride. The wet sodium fluoride production apparatus 80A and the concentration and separation apparatus 90 are connected via piping L89A. The concentration and separation apparatus 90 and the dissolution tank 20 are connected via piping L92. The concentration and separation apparatus 90 and the supply source of "sodium salts other than sodium fluoride, or sodium hydroxide" are connected via piping L09. The concentration and separation apparatus 90 and the wash wastewater are connected via piping L99. As the concentration and separation device 90, any concentration and separation device known in this field can be used.

[0076] ≪Method for producing calcium fluoride (wet method)≫ The calcium fluoride production method of this embodiment includes a reaction solution production step of supplying gas to an aqueous solution of a sodium-containing compound to obtain a reaction solution, and a calcium fluoride production step of reacting the reaction solution or an aqueous solution of sodium fluoride obtained from the reaction solution with a calcium-containing compound. A gas cooling and purification step of cooling and purifying a gas containing hydrogen fluoride may be performed before the reaction solution production step. Alternatively, a washing step may be performed to remove impurities from the reaction solution to produce an aqueous solution of sodium fluoride. Alternatively, a calcium fluoride separation step may be performed after the calcium fluoride production step to separate the crude product containing calcium fluoride obtained in the calcium fluoride production step. The gas cooling and purification step, reaction solution production step, washing step, sodium fluoride aqueous solution production step, calcium fluoride production step, and calcium fluoride separation step will be described below with reference to Figures 3 and 4.

[0077] <Gas cooling and purification process> The cooling and purification process for gases using the wet method can be carried out in accordance with the cooling and purification process for gases using the dry method.

[0078] <Reaction solution manufacturing process> In the reaction solution preparation process, a gas containing hydrogen fluoride is supplied to an aqueous solution of a sodium-containing compound to produce the reaction solution. In the calcium fluoride production system 200A shown in Figure 3, gas is supplied to the wet sodium fluoride production apparatus 80A through piping L08A. An aqueous solution of a sodium-containing compound is supplied to the wet sodium fluoride production apparatus 80A through piping L080A. As a result, the gas and the aqueous solution of the sodium-containing compound react to obtain a reaction solution. Furthermore, in the calcium fluoride production system 200B shown in Figure 4, a gas containing hydrogen fluoride that has undergone a gas cooling and purification process is supplied to the wet sodium fluoride production apparatus 80A through piping L68A. An aqueous solution of a sodium-containing compound is supplied to the wet sodium fluoride production apparatus 80A through piping L080A. As a result, the gas and the aqueous solution of the sodium-containing compound react to obtain a reaction solution.

[0079] As the wet sodium fluoride production apparatus 80A, commercially available equipment that reacts an acidic gas with a liquid alkaline agent, such as a droplet spraying device for gas, a wet scrubber, or a wet electrostatic precipitator, can be used. A wet scrubber is particularly preferred.

[0080] Aqueous solutions of sodium-containing compounds are preferred, such as aqueous solutions of sodium compounds including sodium hydroxide, sodium carbonate, sodium bicarbonate, and sodium sesquicarbonate. In particular, inexpensive sodium hydroxide is preferred. Similar recovery is possible with potassium-containing compounds such as potassium hydroxide and potassium carbonate, but they are more expensive than sodium-containing compounds, and the solubility of the reaction product potassium fluoride is greater than that of sodium fluoride. When considering the concentration of fluorine, sodium-containing compounds are preferred, with sodium hydroxide, sodium carbonate, sodium bicarbonate, and sodium sesquicarbonate being more preferred, and sodium hydroxide being even more preferred.

[0081] The gas simply needs to react with an aqueous solution of a sodium-containing compound, and the reaction temperature should be above 0°C. If the temperature is high, a sufficient amount of water should be added to obtain the final liquid in which the reaction product is dissolved. The reaction temperature is preferably, for example, 0 to 100°C, and more preferably 20 to 60°C. If the reaction temperature is above the lower limit, the viscosity of the aqueous sodium compound solution decreases, increasing its contact with the gas and thus increasing the reaction efficiency. If the reaction temperature is high, a sufficient amount of water should be added to obtain the final liquid in which the reaction product is dissolved. If the gas temperature is high, it is preferable to dilute it with air or to provide a cooling tower 50 that uses water spray.

[0082] The reaction may be carried out by spraying an aqueous solution of a sodium-containing compound into the gas, or by contacting the gas in a countercurrent with an aqueous solution of a sodium-containing compound flowing through a packed column.

[0083] Products included in the reaction solution include, but are not limited to, sodium fluoride, sodium chloride, and sodium sulfate, which are obtained when hydrogen fluoride, hydrogen chloride, sulfur oxides, etc., contained in the gas react with an aqueous solution of a sodium-containing compound. If the product is highly concentrated, some of it may precipitate. When precipitation occurs, sodium fluoride precipitates preferentially because its solubility is lower than that of other sodium salts (sodium chloride, sodium sulfate). If the sodium fluoride is completely dissolved, the reaction solution can be used as an aqueous solution of sodium fluoride and the process can proceed to the next calcium fluoride production step. However, if sodium fluoride has precipitated, it is preferable to dissolve the entire amount first before proceeding to the calcium fluoride production step. In that case, it is preferable to precipitate sodium fluoride from the slurry, separate the solid and liquid components to recover it, and then redissolve the recovered sodium fluoride to proceed with the production of calcium fluoride. Furthermore, it is preferable to reduce the concentration of sodium sulfate in an aqueous solution of sodium fluoride, as it produces calcium sulfate that cannot be separated from calcium fluoride. In addition, it is preferable to reduce the concentration of sodium hydroxide, a basic substance in an aqueous solution of sodium fluoride, as it increases the consumption of acid in the calcium fluoride manufacturing process, which is preferably carried out under acidic conditions. The sodium fluoride content relative to the total mass of the reaction solution is preferably 10 to 50,000 ppm by mass, more preferably 100 to 10,000 ppm by mass, and even more preferably 200 to 5,000 ppm by mass. The sodium chloride content relative to the total mass of the reaction solution is preferably 0 to 200,000 ppm by mass, more preferably 5 to 100,000 ppm by mass, and even more preferably 10 to 50,000 ppm by mass. The sodium sulfate content relative to the total mass of the reaction solution is preferably 0 to 10,000 ppm by mass, more preferably 1 to 1,000 ppm by mass, and even more preferably 2 to 100 ppm by mass.

[0084] The gas treatment after passing through the wet sodium fluoride production apparatus 80A can be carried out in accordance with the gas treatment method for the dry method.

[0085] <Washing process> In the washing process, the sodium fluoride component is concentrated and recovered from the reaction solution obtained in the reaction solution production process. The washing process can be optionally performed after the reaction solution production process and before the sodium fluoride aqueous solution production process. Performing the washing process tends to increase the purity of the final calcium fluoride. In addition, if the sodium fluoride production process and the calcium fluoride production process are located far apart, transportation efficiency can be improved. As shown in Figure 4, the reaction solution produced in the wet sodium fluoride production apparatus 80A is supplied to the concentration and separation apparatus 90 through piping L89A. In the concentration and separation apparatus 90, the reaction solution is concentrated or recrystallized to obtain an aqueous slurry containing solid sodium fluoride. Solid-liquid separation is performed on this aqueous slurry to separate it into a solid and a separation liquid. The separation liquid is discharged through piping L99, and the solid is supplied to the dissolution tank 20 through piping L92.

[0086] The precipitation temperature should be set according to the solubility of each sodium compound. For example, a temperature of 20°C or higher is preferred, 30°C or higher is more preferred, and 35°C or higher is even more preferred. Furthermore, when the washing temperature is within the above range, the solubility of sodium fluoride is low, while the solubility of sodium chloride and sodium sulfate is high. In other words, if the precipitation temperature is within the above range, sodium fluoride, which is sparingly soluble in water, precipitates as a solid, while other sodium compounds (sodium chloride and sodium sulfate), which are readily soluble in hot water, remain dissolved in the separation solution. Therefore, by separating the solid from the separation solution using solid-liquid separation, sodium fluoride and other sodium compounds can be efficiently separated.

[0087] The washing time is preferably 0.1 to 10 hours, more preferably 0.3 to 5 hours, and even more preferably 0.5 to 3 hours. The washing tank 80 may be stirred using an agitator.

[0088] The methods of precipitation, namely recrystallization or concentration, are described below.

[0089] (Recrystallization) Recrystallization is a method of obtaining high-purity solid sodium fluoride by adding a sodium salt other than sodium fluoride, or sodium hydroxide, to the reaction solution via piping L09, thereby increasing the sodium ion concentration in the reaction solution to a level lower than the original saturation solubility of sodium fluoride, and thus obtaining high-purity solid sodium fluoride from other easily soluble sodium salts present. The sodium salts used are preferably sodium chloride and sodium carbonate, which have higher solubility than sodium fluoride and are easily removed in the calcium fluoride manufacturing process. The amount of salt used for recrystallization relative to the total mass of the reaction solution is preferably 0.5 to 20% by mass, more preferably 0.5 to 10% by mass, and even more preferably 1 to 5% by mass. If the amount of salt is above the lower limit, solid sodium fluoride precipitates sufficiently, and the loss of sodium fluoride is suppressed. If the amount of salt is below the upper limit, the sodium chloride and sodium sulfate contained in the reaction solution after the addition of the sodium salt tend to have sodium ion concentrations below the saturation solubility. As a result, the precipitation of sodium chloride and sodium sulfate is suppressed, and the purity of sodium fluoride is improved. The amount of sodium salt added may also be changed according to the actual sodium sulfate concentration in the reaction solution. The sodium sulfate content in the recovered sodium fluoride is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. Therefore, the temperature during recrystallization is preferably a temperature at which the difference between the solubility of sodium sulfate and the solubility of sodium fluoride is large, for example, 20°C or higher is preferred, 30°C or higher is more preferred, and 35°C or higher is even more preferred. If sodium fluoride does not precipitate easily, sodium fluoride prepared separately may be added as a seed crystal, or precipitation may be promoted using ultrasound or other means. Sodium fluoride may also be added as a seed crystal to increase the average particle size of the precipitated sodium fluoride and improve handling properties such as solid-liquid separation.

[0090] (concentrated) By removing water from the reaction solution through heating and concentration, and increasing the concentration of the sodium salt dissolved in the water to above the saturation solubility of sodium fluoride, sodium fluoride is preferentially precipitated. This may be combined with the recrystallization process involving the addition of the sodium salt mentioned above.

[0091] There are no particular restrictions on the solid-liquid separation apparatus, as long as it can separate the separation liquid from the solid. Examples include centrifuges, filter presses, and screw decanters.

[0092] The separated liquid may be used in the cooling tower 50 or introduced into the pollution control device 70. By reusing the separated liquid, it is possible to reduce the volume of total wastewater.

[0093] <Sodium fluoride aqueous solution manufacturing process> The wet method for producing sodium fluoride aqueous solution can be carried out in accordance with the dry method for producing sodium fluoride aqueous solution.

[0094] <Calcium fluoride manufacturing process and separation process> The wet method for producing and separating calcium fluoride can be carried out in accordance with the dry method for producing calcium fluoride.

[0095] Figure 6 is a flowchart illustrating an example of the procedure for the manufacturing system used in the dry method of this embodiment. First, it is determined whether the gas containing hydrogen fluoride is suitable for the sodium fluoride manufacturing process (step S1). If it is suitable, the sodium fluoride manufacturing process is carried out using the gas (step S3). If it is not suitable, the gas is purified (step S2) before step S3 is performed. Next, it is determined whether the crude product A obtained in step S3 is suitable for the calcium fluoride manufacturing process (step S4). If it is suitable, the sodium fluoride aqueous solution manufacturing process is carried out using crude product A (step S6). If it is not suitable, the crude product A is washed with sodium fluoride (step S5) before step S6 is performed. The sodium fluoride aqueous solution obtained in step S6 is then subjected to the calcium fluoride manufacturing process (step S7) to produce calcium fluoride.

[0096] Figure 7 is a flowchart illustrating an example of the procedure for the manufacturing system used in the wet process of this embodiment. First, it is determined whether the gas containing hydrogen fluoride is suitable for the reaction solution manufacturing process (step S8). If it is suitable, the reaction solution manufacturing process is carried out using the gas (step S9). If it is not suitable, step S2 is performed on the gas, and then step S9 is carried out. Next, it is determined whether the aqueous solution of sodium fluoride obtained in step S9 is suitable for step S4. If it is suitable, step S6 is carried out using the aqueous solution of sodium fluoride to obtain calcium fluoride. If it is not suitable, a washing process (step S10) is performed on the aqueous solution of sodium fluoride, and then step S6 is carried out. Step S7 is carried out on the aqueous solution of sodium fluoride obtained in step S6 to produce calcium fluoride.

[0097] By reacting the high-quality calcium fluoride obtained by this manufacturing method with sulfuric acid, hydrogen fluoride can be produced.

[0098] <Mechanism of Action> The present invention can process large quantities of gas and enables the production of calcium fluoride with controlled average particle size in the following respects. In Patent Document 1, which assumes a gas containing only hydrogen fluoride as the raw material, the resulting calcium fluoride contains unreacted calcium compounds, such as unreacted calcium hydroxide, as impurities. These unreacted calcium compounds react with sulfuric acid, which is used as a raw material during hydrogen fluoride production, resulting in the waste of sulfuric acid. In particular, calcium hydroxide produces water as a by-product, which causes corrosion. To reduce the proportion of unreacted calcium compounds, it is conceivable to reduce the average particle size of the calcium compounds or extend the reaction time, but this requires increasing the size of the apparatus to prevent pressure rise in the filter section, increase the filtration area, or increase the contact time between the gas and the calcium compounds. Furthermore, since the average particle size of the calcium compounds supplied to the reaction tower becomes the average particle size of the reaction products, it is difficult to adjust the average particle size of the reaction products to a size suitable for hydrogen fluoride production. In addition, even in the case of gases containing acidic gases other than hydrogen fluoride, all of the reaction products remain as impurities in the calcium fluoride. Furthermore, calcium sulfate, which is generated from sulfur oxides in the gas, cannot be removed even by acid washing. On the other hand, in this invention, hydrogen fluoride in a gas is reacted with a water-soluble sodium-containing compound to obtain water-soluble sodium fluoride as an intermediate, and calcium fluoride is produced from an aqueous solution of sodium fluoride. By dissolving all of the sodium fluoride and sodium-containing compound in water once, the target recovered product, calcium fluoride, and the unreacted sodium-containing compound can be separated and recovered. Furthermore, by using the synthesis conditions for calcium fluoride described in Japanese Patent No. 6079524, the average particle size of calcium fluoride can be easily controlled. Moreover, it becomes possible to obtain high-purity calcium fluoride even from gases containing acidic gases other than hydrogen fluoride. In addition, calcium sulfate generated from sulfur oxides in the gas can be easily removed in the washing process of this invention.

[0099] The following operational methods are also conceivable using the manufacturing method of the present invention. Exhaust gas containing hydrogen fluoride is generated in various locations such as incinerators and factories, and the treatment of this exhaust gas must be carried out at the point of generation. On the other hand, the locations where calcium fluoride is used are usually separate from the aforementioned incinerators and factories. By consolidating and processing the exhaust gas treatment by-products from the exhaust gas generation site at the calcium fluoride manufacturing site or calcium fluoride utilization site, the equipment can be scaled up, enabling more efficient operation. [Explanation of symbols]

[0100] 10...Sodium fluoride production equipment, 10A...Recovery filter, 20...Dissolution tank, 30...Calcium fluoride production equipment, 40...Calcium fluoride separation equipment, 50...Temperature reduction tower, 60...Filter, 70...Abatement equipment, 80...Washing tank, 80A...Wet sodium fluoride production equipment, 90...Concentration and separation equipment, L...Piping, L01, L001, L02, L12, L19, L23, L03, L05, L56, L61, L18, L08, L89, L82, L68A, L08A L080A, L17, L79, L89A, L83A, L09, L99, L92, L02, L23, L03, L34, L48, L49, 100A, 100B, 200A, 200B… Calcium fluoride manufacturing system, S1…Step S1, S2…Step S2, S3…Step S3, S4…Step S4, S5…Step S5, S6…Step S6, S7…Step S7, S8…Step S8, S9…Step S9, S10…Step S10

Claims

1. A method for producing calcium fluoride, which involves using a gas containing hydrogen fluoride to produce calcium fluoride, The aforementioned gas is brought into contact with a solid sodium-containing compound to obtain a solid containing sodium fluoride. A method for producing calcium fluoride, comprising reacting an aqueous solution of sodium fluoride obtained by dissolving a solid containing sodium fluoride with a calcium-containing compound to produce calcium fluoride.

2. The method for producing calcium fluoride according to claim 1, wherein the gas is exhaust gas.

3. The method for producing calcium fluoride according to claim 1, wherein the gas comprises at least one selected from the group consisting of hydrogen chloride and sulfur oxides.

4. The method for producing calcium fluoride according to claim 1, wherein the sodium-containing compound includes sodium bicarbonate.

5. The method for producing calcium fluoride according to claim 1, wherein the dissolution of the solid containing sodium fluoride is performed after washing the solid containing sodium fluoride.

6. The method for producing calcium fluoride according to claim 5, wherein the liquid used in either or both washing and dissolving the solid containing sodium fluoride comprises water containing fluoride ions.

7. A method for producing calcium fluoride using a gas containing hydrogen fluoride, The aforementioned gas is supplied to an aqueous solution of a sodium-containing compound to obtain a reaction solution. A method for producing calcium fluoride, comprising reacting an aqueous solution of sodium fluoride obtained from the reaction solution with a calcium-containing compound.

8. The method for producing calcium fluoride according to claim 7, wherein the gas is exhaust gas.

9. The method for producing calcium fluoride according to claim 7, wherein the gas comprises at least one selected from the group consisting of hydrogen chloride and sulfur oxides.

10. The method for producing calcium fluoride according to claim 7, wherein the sodium-containing compound includes sodium hydroxide.

11. A method for producing calcium fluoride according to claim 7, comprising: performing a concentration treatment and / or a recrystallization treatment on the reaction solution to obtain an aqueous slurry containing solid sodium fluoride; performing solid-liquid separation of the aqueous slurry to obtain solid sodium fluoride; and dissolving the solid sodium fluoride to obtain an aqueous solution of sodium fluoride.

12. The method for producing calcium fluoride according to claim 11, wherein the liquid used to dissolve the solid sodium fluoride includes water containing fluoride ions.

13. A method for producing hydrogen fluoride by reacting calcium fluoride produced by the method for producing calcium fluoride according to any one of claims 1 to 12 with sulfuric acid.

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