Method for recovering nitrogen resources and calcium fluoride from wastewater containing fluorine and ammonia.

Abstract

To provide a recovery method of nitrogen resource and calcium fluoride from a waste solution containing fluorine and ammonia.SOLUTION: A waste solution containing fluorine and ammonia is reacted with a slurry where calcium carbonate is dispersed in water, then added with an acid to recover a supernatant liquid as a nitrogen resource; a waste solution containing fluorine and ammonia is added to its residual liquid then solid-liquid separated to recover calcium fluoride.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for recovering nitrogen resources and calcium fluoride from waste liquid containing fluorine and ammonia.

Background Art

[0002] Fluorine is regarded as a harmful substance under the Water Pollution Control Law. When discharging wastewater containing fluorine into public water areas or sewers, it is necessary to stably treat it so that its content concentration is below the drainage standard value. Waste liquid containing fluorine is generated from processes using hydrofluoric acid such as semiconductor manufacturing, metal processing, or glass processing. It is treated in the company's in-house wastewater treatment facilities or, if it is highly concentrated, by an external contractor as industrial waste. This waste liquid is often treated by the coagulation sedimentation method using calcium-based chemicals. Fluorine in the waste liquid is immobilized as calcium fluoride and disposed of in landfill as sludge together with other impurities. On the other hand, efforts are also being made to recycle the recovered calcium fluoride. Fluorite containing calcium fluoride as the main component is used as a raw material for hydrofluoric acid production and a flux in the ironmaking field. If conditions such as the unreacted calcium concentration, impurity concentration, moisture concentration, and particle size can be satisfied in addition to the purity, it is possible to recycle the calcium fluoride recovered from the waste liquid as a substitute for fluorite. For this purpose, it is necessary to adjust the recovery conditions according to the properties of the waste liquid, such as removing various components contained in the waste liquid and performing crystal growth to recover calcium fluoride, which is easily atomized, at an appropriate particle size.

[0003] Ammonia, like fluorine, is regulated as a hazardous substance. Wastewater containing ammonia and its salts is generated from various processes, including the production and use of fertilizers such as urea and ammonium salts, the production of raw materials for chemicals such as synthetic resins, refrigerants, and industrial applications such as denitrification. Therefore, the treatment method is selected depending on the nitrogen concentration and type of impurities in the wastewater. Ammonia is difficult to fix with sparingly soluble salts, and is often decomposed using chemical oxidation, biological treatment, or stripping. Chemical oxidation allows for treatment in a short time, but requires a considerable amount of chlorine relative to the ammonia, resulting in high chemical costs, so it is only used for wastewater with low nitrogen concentrations. In the case of biological treatment, aerobic treatment has a limited treatment capacity, and anaerobic treatment requires a digestion and denitrification process, which takes longer than other treatments. Furthermore, due to toxicity to microorganisms, heavy metals and other components must be removed as much as possible through pretreatment. In the case of stripping, even high concentrations can be treated in a short time, but it requires separating the ammonia from the liquid layer and further decomposing it in a catalytic combustion facility, requiring large-scale treatment equipment. As mentioned above, the wastewater is primarily decomposed, but efforts are also being made to recover ammonia from the wastewater. For example, by combining a stripping device with a recovery device, if ammonia can be preferentially separated from heavy metals and other components, it becomes possible to recycle the recovered ammonia water or ammonium salt solution. When recycling ammonia water, its use is limited to internal reuse because it is difficult to store for long periods and requires further purification before being used as a basic raw material for chemical products. On the other hand, ammonium salt solution is stable, easy to store for long periods, and can be recycled as a nitrogen resource for fertilizer or bacterial nutrients.

[0004] In the manufacturing process of semiconductors and printed circuit boards, there is a wet etching process to remove unwanted parts of the metal and insulating film on the silicon substrate in order to pattern them. One of the cleaning chemicals used in this process is buffered hydrofluoric acid (hereinafter referred to as BHF), which is used to remove insulating films mainly composed of silicon dioxide. BHF is a chemical composed of hydrofluoric acid and ammonia, and by mixing hydrofluoric acid, which reacts with silicon dioxide, with ammonia, which has a pH buffering effect, the etching rate can be adjusted and fine processing can be performed. Used BHF is mixed with wastewater from other processes to become a waste liquid containing fluorine and ammonia. If the concentration is low, it is treated in-house, but if the concentration is high, in-house treatment becomes difficult and it is discharged to the outside as industrial waste.

[0005] When attempting to treat and recycle wastewater containing fluorine and ammonia, it is desirable to treat the recovered nitrogen resources at concentrations as close to the original concentration as possible, as higher concentrations are considered more economically viable for recycling. However, calcium fluoride, which is produced when high-concentration fluorine-containing wastewater reacts with calcium, tends to break down into fine particles without growing larger, potentially worsening the efficiency of dewatering and washing after the reaction. Furthermore, if the nitrogen resources are intended for use as fertilizer or nutrients, there is a risk of fluorine leakage into public water bodies, so the fluorine must be removed to the level of wastewater discharge standards. However, adding excessive amounts of calcium-based chemicals to achieve this reduces the purity of the recovered calcium fluoride. For these reasons, it is difficult to stabilize wastewater containing fluorine and ammonia and recycle both the nitrogen resources and calcium fluoride.

[0006] Several processing methods have been investigated to address these problems. Patent Document 1 discloses a method for recovering calcium fluoride, which can be used as a raw material for hydrofluoric acid production, by reacting calcium sulfate and calcium hydroxide with wastewater containing fluorine and ammonia. It is stated that by using calcium sulfate with an average particle size of 25 to 400 μm, calcium fluoride with a similar particle size is produced, making filtration and washing easy and allowing for the acquisition of a high-purity product. However, it is stated that approximately 0.1% of fluoride ions remain in the ammonium sulfate solution obtained after this treatment, so the removal of fluorine is insufficient for use as fertilizer, etc., and further secondary treatment is necessary. Thus, it is difficult to recycle both nitrogen resources and calcium fluoride with this treatment alone.

[0007] Patent Document 2 discloses a method in which BHF is neutralized with caustic potassium to produce potassium fluoride and ammonia, and then hydrogen fluoride and ammonia are individually recovered using an electrodialysis apparatus. The electrodialysis apparatus used here employs a bipolar membrane consisting of a cation and anion exchange membrane, making the apparatus itself large in scale and consuming a large amount of power due to the electrodialysis. In addition, since it is a waste liquid, the presence of impurities such as metals can lead to membrane degradation. Furthermore, the hydrogen fluoride and ammonia water recovered by this method are more volatile and reactive than calcium fluoride and ammonium salts, making them difficult to handle, thus limiting their applications and often resulting in their reuse being restricted to within the company.

[0008] When calcium carbonate is used as the calcium-based agent, it is known to react with hydrofluoric acid while maintaining its particle size, and the calcium fluoride recovered by this method is considered to be of high quality with low water content and excellent washing properties. Patent Document 3 discloses a method for recovering calcium fluoride and ammonia from BHF-containing wastewater using this method, but since fluorine reacts in a column packed with calcium carbonate, it is necessary to avoid the outflow of fine particles due to the rapid reaction, and the fluorine concentration that can be treated is limited to a low concentration of 0.2% or less and low load conditions. Because the multi-stage processing using a packed column and the concentration process of the recovered ammonia water are processed continuously, the sensing and control of each process become complex in order to maintain the specifications of each recovered material.

[0009] Patent Document 4 discloses a batch-type method for producing calcium fluoride with high solid-liquid separation properties from high-concentration hydrofluoric acid-containing water using calcium carbonate with a particle size of 15 μm to 300 μm. However, it does not mention that the hydrofluoric acid-containing water contains ammonia. If we assume that the hydrofluoric acid-containing water contains ammonia, the neutralization step described in this patent document does not assume the use of acid. In this case, a decrease in the purity of calcium fluoride is expected due to an increase in unreacted calcium carbonate. Furthermore, because it is a reaction with excess fluorine, it is not possible to recover low-fluorine nitrogen resources. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2001-137864 Public Relations [Patent Document 2] Japanese Patent Publication No. 07-214068 Public Relations [Patent Document 3] Japanese Patent Publication No. 11-157834 Public Relations [Patent Document 4] Japanese Patent Publication No. 2013-60330 Public Relations [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] In view of the above circumstances, the present invention provides a method for recovering nitrogen resources and calcium fluoride from wastewater containing fluorine and ammonia. [Means for solving the problem]

[0012] The inventors of the present invention have diligently studied to solve the above problems and have found that the above problems can be solved by a stepwise process in which, first, fluorine is coagulated and separated from waste liquid containing fluorine and ammonia by adding calcium carbonate and acid, and the supernatant liquid is recovered as a nitrogen resource. Next, impurities are washed away by adding waste liquid containing fluorine and ammonia to the calcium fluoride slurry remaining after separating the supernatant liquid, and calcium fluoride is recovered by solid-liquid separation of the precipitate. This process has led to the completion of the present invention.

[0013] In other words, the present invention relates to waste liquid containing fluorine and ammonia, (1) The first step involves reacting with a slurry in which calcium carbonate is dispersed in water. (2) The second step involves adding acid to the solution obtained in (1). (3) A third step involves adding a polymer flocculant to the liquid obtained in (2) to perform flocculation and sedimentation, and recovering the supernatant liquid as a nitrogen resource. (4) The fourth step involves adding wastewater containing fluorine and ammonia to the liquid obtained in (3). (5) The fifth step involves separating the liquid obtained in (4) into solid and liquid components, recovering the solid, washing it with water, and then drying it to recover calcium fluoride. A method for recovering nitrogen resources and calcium fluoride from wastewater containing fluorine and ammonia, characterized by performing the following steps. That is the case.

[0014] In the first step, the amount of waste liquid containing fluorine and ammonia added relative to the amount of calcium carbonate is: Fluorine 0.6 molar equivalents or more, less than 1.0 molar equivalent To do soThis is preferable. If the amount is 1.0 molar equivalent or more, fluorine tends to remain in the supernatant recovered in the third step, reducing the quality of the nitrogen resource. Also, if the amount is less than 0.6 molar equivalent, the amount of acid added in the second step increases, raising the calcium concentration in the supernatant, which may inhibit flocculation in the third step. Furthermore, when a supernatant with a high calcium concentration is recovered as a nitrogen resource and used, calcium salt precipitates may form, potentially weakening the effectiveness of nutrients such as phosphoric acid.

[0015] The reaction time after adding the waste liquid containing fluorine and ammonia is preferably 15 minutes or more. While there are no limitations on the concentrations of fluorine and ammonia, higher concentrations are expected to be in greater societal demand.

[0016] It is preferable to use calcium carbonate with a particle size of 2 μm or more and less than 50 μm in the first step. If the particle size is 50 μm or larger, unreacted calcium carbonate tends to remain, reducing the purity of the recovered calcium fluoride. On the other hand, if the particle size is less than 2 μm, the particle size of the generated calcium fluoride becomes small, so the flocs during coagulation and sedimentation in the third step also become small, worsening the efficiency of concentration and separation, and making it difficult to recover the supernatant liquid, which is a nitrogen resource.

[0017] The acid used in the second step is preferably a monoprotic acid. Monoprotic acids include inorganic acids such as hydrochloric acid and nitric acid, and organic acids such as formic acid, acetic acid, or lactic acid. Polyprotic acids such as sulfuric acid, phosphoric acid, or citric acid may also be used, but they may produce sparingly soluble calcium salts as by-products, which could lead to a decrease in the purity of the recovered calcium fluoride. Furthermore, considering that the nitrogen resources recovered in the third step will be used as fertilizer or nutrients for biological treatment, inorganic acids are more preferable than organic acids.

[0018] Next, the amount of acid added in the second step is preferably an amount such that the pH of the liquid is 2 or more and less than 9, and more preferably an amount such that the pH is 4 or more and less than 7. When the pH is less than 2, the calcium fluoride produced is likely to be atomized and the aggregability deteriorates. Further, since the solubility of calcium fluoride increases, the fluorine concentration in the nitrogen resource also increases. On the other hand, when the pH is 9 or more, the reaction between fluorine and calcium carbonate hardly proceeds, so the fluorine concentration of the recovered nitrogen resource increases, and unreacted calcium carbonate remains in the recovered calcium fluoride. Further, since an ammonia odor is likely to be generated from the nitrogen resource, its handling becomes difficult.

[0019] The time required for adding the acid in the second step is preferably 60 minutes or more. In the case of a short time, there is a risk that the above pH adjustment will end the reaction incompletely. Also, when the acid is added rapidly, the calcium fluoride produced is likely to be atomized, which has an adverse effect on the flocculation precipitation in the third step.

[0020] The flocculant used in the third step may be a combination of a plurality of flocculants regardless of whether they are organic, inorganic or ionic. The flocculant is not particularly limited as long as it is generally used. Also, a solid-liquid separation step may be performed after the flocculation precipitation, but in order to smoothly perform the processes after the fourth step, it is preferable to recover the supernatant liquid after the flocculation precipitation.

[0021] The amount of the waste liquid containing fluorine and ammonia added in the fourth step is Fluorine 0.4 molar equivalent or less To do so is preferable. When it exceeds 0.4 molar equivalent, the fluorine concentration in the filtrate increases and the load on the wastewater treatment process is increased. Further, the total amount of the waste liquid containing fluorine and ammonia added in the fourth step and the waste liquid containing fluorine and ammonia used in the first step teeth , with respect to the calcium carbonate used in the first step Fluorine 0.9 molar equivalent or more To do soThis is preferable. If the amount is less than 0.9 molar equivalents, unreacted calcium carbonate and silica will remain in the recovered calcium fluoride. A reaction time of 30 minutes or more is preferable. If the reaction time is too short, these components will remain in the recovered calcium fluoride, similar to when the amount of waste liquid containing fluorine and ammonia is insufficient. Acid may be added as needed. The acid used here is preferably a monoprotic acid. Monoprotic acids include inorganic acids such as hydrochloric acid and nitric acid, and organic acids such as formic acid, acetic acid, or lactic acid. Polyprotic acids such as sulfuric acid, phosphoric acid, or citric acid may also be used, but they may produce sparingly soluble salts of calcium as by-products, and their contamination may lead to a decrease in the purity of the calcium fluoride. Furthermore, considering that the nitrogen resources recovered in the third step will be used as fertilizer or nutrients for biological treatment, inorganic acids are more preferable than organic acids. The fifth step involves washing the recycled material according to the required specifications. It is preferable to adjust the amount of water added after checking the component concentration of the filtrate. [Effects of the Invention]

[0022] The present invention provides a method for recovering nitrogen resources and calcium fluoride from wastewater containing fluorine and ammonia. This method makes it possible to recover nitrogen resources with low fluorine and high nitrogen concentrations, as well as calcium fluoride that can be used as a raw material in hydrofluoric acid production, from wastewater containing fluorine and ammonia, which was previously difficult to treat and recycle simultaneously. Furthermore, the treated water generated in the fifth step is discharged into sewers and public water bodies via general wastewater treatment facilities, but because the nitrogen and fluorine levels are reduced, the load on the treatment facilities is minimized. Additionally, the amount of calcium fluoride generated, which has significant usage restrictions, can be reduced. Therefore, it is possible to stably treat the wastewater and recover both nitrogen resources and calcium fluoride. [Brief explanation of the drawing]

[0023] [Figure 1] This is a processing flow diagram showing an embodiment of the method for recovering nitrogen resources and calcium fluoride from wastewater containing fluorine and ammonia according to the present invention. [Modes for carrying out the invention]

[0024] Embodiments of the present invention will be described below with reference to the drawings. As shown in Figure 1, the present invention relates to wastewater containing fluorine and ammonia, and in the first step, reacts it with calcium carbonate dispersed in water in a reaction tank; in the second step, adds acid to the reaction solution obtained in the first step to react with the fluorine and calcium carbonate remaining in the solution; in the third step, the slurry obtained in the second step is subjected to coagulation and sedimentation treatment to recover the supernatant liquid as a nitrogen resource; further, in the fourth step, wastewater containing fluorine and ammonia is added to the slurry obtained in the third step to react the residual calcium carbonate with fluorine and dissolve and remove the residual silica; and in the fifth step, the slurry obtained in the fourth step is dewatered, washed with water and dried to recover calcium fluoride.

[0025] (first step) In the first step, when preparing the calcium carbonate slurry, water or other liquid is first added to the reaction vessel, and calcium carbonate is added while stirring. Calcium carbonate can be added directly from a flexible container bag or similar, or in small amounts using a hopper and feeder. To recover high-concentration nitrogen resources, a calcium carbonate slurry concentration of 40 wt% or higher is preferable. Furthermore, recovered nitrogen resources may be used in the liquid used to prepare the calcium carbonate slurry. This is effective for concentrating nitrogen resources. The order of adding the calcium carbonate slurry and waste liquid does not matter, but it is preferable to add the waste liquid to the calcium carbonate slurry in the vessel. If the order is reversed, carbon dioxide gas will be generated when adding calcium carbonate, requiring adjustment of the addition rate, which may necessitate a calcium carbonate slurry preparation tank and transfer equipment, potentially increasing the size of the apparatus. Additionally, the waste liquid added in this step may contain the acid used in the second step, but a large amount is undesirable as it will worsen the cohesiveness of the reactants.

[0026] (Second process) In the second step, when adding acid to the slurry obtained in the first step, it is preferable to control the amount added so that the pH of the reaction solution does not change rapidly. It is preferable to use a high concentration of acid to prevent a decrease in the concentration of the recovered nitrogen resources, but this will result in the generation of white fumes of ammonium salts during the reaction, so the concentration should be adjusted as appropriate. If the liquid level of the reaction solution rises due to foaming, an antifoaming agent may be used. To lower the fluorine concentration in the solution, calcium carbonate may be added and the pH adjusted by adding acid as appropriate.

[0027] (Third step) In the third step, a flocculant is added to the slurry obtained in the second step. If the flocculation is poor, it is preferable to use multiple polymer flocculants for treatment. After flocculation and sedimentation, the supernatant liquid is collected using a self-priming pump or the like. The nitrogen resources obtained in this step can be used as fertilizer or nutrients for biological treatment after analysis of fluorine and nitrogen concentrations. If trace amounts of heavy metals are present, it is preferable to remove them by commonly used methods such as treatment with ion exchange resin.

[0028] (Fourth step) In the third step, water is added to the slurry remaining in the reaction vessel as needed to dilute it. This improves the washing efficiency in the fifth step. Next, waste liquid containing fluorine and ammonia is added, and then, if necessary, acid is added.

[0029] (Fifth step) The slurry obtained in the fourth step is subjected to solid-liquid separation using a dewatering machine such as a filter press. After the dewatering step, a certain amount of water is added to wash away impurities. The endpoint of the water washing can be confirmed by the pH of the filtrate, analysis of each component, conductivity, etc.

[0030] The calcium fluoride obtained through the above process can be dried and then mixed directly with fluorite for use in the production of hydrofluoric acid.

[0031] The present invention will be specifically described in the following examples. However, the present invention is not limited to the following examples. [Examples]

[0032] (Reference example 1) By mixing hydrofluoric acid, ammonium fluoride, and silicon dioxide, respectively, and diluting them with water, we prepared simulated waste liquids 1 and 2, which contain fluorine and ammonia, as shown in Table 1. [Table 1]

[0032] The average particle size of calcium carbonate described in the following examples was determined using the median diameter obtained with a laser diffraction scattering particle size distribution analyzer (Beckman Coulter, LS13 320XR). [Examples]

[0033] ·First process 80.0 g of calcium carbonate 1 (average particle size: 12 μm) and 120.0 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 110.0 g of simulated solution 1 (fluorine amount relative to calcium carbonate 1: 0.9 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process 47.0 g of 35% hydrochloric acid was added to the slurry obtained in the first step over a period of 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 5.0. ·Third process A flocculant was added to the slurry obtained in the second step to induce flocculation and sedimentation. The supernatant was then transferred by decantation to obtain 169.0 g of nitrogen resource recovery liquid 1. ·Fourth process In the third step, 50.0 g of water and 16.0 g of simulated solution 1 (fluorine amount per calcium carbonate 1: 0.1 molar equivalent) were added to the concentrated slurry, and the mixture was stirred for 30 minutes. The pH after the reaction was 4.6. ·Fifth process The slurry obtained in the fourth step was separated into solid and liquid components by vacuum filtration, washed with 200 ml of water, and dried to obtain 61.0 g of calcium fluoride recovery material 1. The components of the recovered liquid and recovery material are shown in Table 2. The coagulation properties of the third step and the filtration properties of the fifth step were good.

[0034] This process allowed us to recover nitrogen resources with a sufficiently reduced fluorine content, as well as unreacted calcium carbonate and calcium fluoride with minimal impurities. [Examples]

[0035] ·First process 82.0 g of calcium carbonate 1 (average particle size: 12 μm) and 120.0 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 131.4 g of simulated solution 2 (fluorine amount relative to calcium carbonate 1: 0.8 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process To the slurry obtained in the first step, 131.3 g of 35% hydrochloric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 5.0. ·Third process A flocculant was added to the slurry obtained in the second step to induce flocculation and sedimentation. The supernatant was then transferred by decantation to obtain 251.0 g of nitrogen resource recovery liquid 2. ·Fourth process In the third step, 50.0 g of water and 40.0 g of simulated solution 2 (fluorine amount per 1 liter of calcium carbonate: 0.2 molar equivalents) were added to the concentrated slurry, and the mixture was stirred for 30 minutes. The pH after the reaction was 8.0. ·Fifth process The slurry obtained in the fourth step was separated into solid and liquid components by vacuum filtration, washed with 200 ml of water, and dried to obtain 61.3 g of calcium fluoride recovery material 2. The components of the recovered liquid and material are shown in Table 2. The coagulation properties of the third step and the filtration properties of the fifth step were good.

[0036] This process allowed us to recover nitrogen resources with a sufficiently reduced fluorine content, as well as unreacted calcium carbonate and calcium fluoride with minimal impurities. [Examples]

[0037] ·First process 81.0 g of calcium carbonate 1 (average particle size: 12 μm) and 120.0 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 131.4 g of simulated solution 2 (fluorine amount relative to calcium carbonate 1: 0.8 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process To the slurry obtained in the first step, 128.8 g of 35% hydrochloric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 5.0. ·Third process After adding a flocculant to the slurry obtained in the second step to induce flocculation and sedimentation, the supernatant liquid was transferred by decantation to obtain 277.0 g of nitrogen resource recovery liquid 3. ·Fourth process In the third step, 50.0 g of water and 30.6 g of simulated solution 2 (fluorine amount per 1 liter of calcium carbonate: 0.2 molar equivalents) were added to the concentrated slurry, and then 17.2 g of 35% hydrochloric acid was added and the mixture was stirred for 30 minutes. The pH after the reaction was 5.0. ·Fifth process The slurry obtained in the fourth step was separated into solid and liquid components by vacuum filtration, washed with 200 ml of water, and dried to obtain 60.0 g of calcium fluoride recovered product 3. The components of the recovered liquid and recovered product are shown in Table 2. The coagulation properties of the third step and the filtration properties of the fifth step were good.

[0038] This process allowed us to recover nitrogen resources with a sufficiently reduced fluorine content, as well as unreacted calcium carbonate and calcium fluoride with minimal impurities. [Examples]

[0039] ·First process 90.0 g of calcium carbonate 2 (average particle size: 23 μm) and 120.0 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 131.4 g of simulated solution 2 (fluorine amount per calcium carbonate 1: 0.7 molar equivalents) was added and stirred for 15 minutes. ·Second process To the slurry obtained in the first step, 161.6 g of 50% nitric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 4.0. ·Third process After adding a flocculant to the slurry obtained in the second step to induce flocculation and sedimentation, the supernatant liquid was transferred by decantation to obtain 285.4 g of nitrogen resource recovery liquid 4. ·Fourth process In the third step, 50.0 g of water and 40.0 g of simulated solution 2 (fluorine amount per 1 liter of calcium carbonate: 0.2 molar equivalents) were added to the concentrated slurry, and then 39.1 g of 50% nitric acid was added and the mixture was stirred for 30 minutes. The pH after the reaction was 4.0. ·Fifth process The slurry obtained in the fourth step was separated into solid and liquid components by vacuum filtration, washed with 200 ml of water, and dried to obtain 69.2 g of recovered calcium fluoride 4. The components of the recovered liquid and recovered material are shown in Table 2. The coagulation properties of the third step and the filtration properties of the fifth step were good.

[0040] This process allowed us to recover nitrogen resources with a sufficiently reduced fluorine content, as well as unreacted calcium carbonate and calcium fluoride with minimal impurities. [Examples]

[0041] ·First process 77.5 g of calcium carbonate 3 (average particle size: 3 μm) and 118 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 131.4 g of simulated solution 2 (fluorine amount relative to calcium carbonate 2: 0.9 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process To the slurry obtained in the first step, 121.0 g of 35% hydrochloric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 6.0. ·Third process After adding a flocculant to the slurry obtained in the second step to induce flocculation and sedimentation, the supernatant liquid was transferred by decantation to obtain 203.0 g of nitrogen resource recovery liquid 5. ·Fourth process In the third step, 50.0 g of water and 10.0 g of simulated solution 2 (fluorine amount relative to calcium carbonate 2: 0.1 molar equivalent) were added to the concentrated slurry, and then 7.7 g of 35% hydrochloric acid was added and the mixture was stirred for 30 minutes. The pH after the reaction was 6.0. ·Fifth process The slurry obtained in the fourth step was separated into solid and liquid components by vacuum filtration, washed with 200 ml of water, and dried to obtain 59.0 g of calcium fluoride recovered product 5. The components of the recovered liquid and recovered product are shown in Table 2. The coagulation properties of the third step and the filtration properties of the fifth step were good.

[0042] This process allowed us to recover nitrogen resources with reduced fluorine content, as well as unreacted calcium carbonate and calcium fluoride with fewer impurities. [Examples]

[0043] ·First process 95.2 g of calcium carbonate 1 (average particle size: 12 μm) and 120.0 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 131.4 g of simulated solution 2 (fluorine amount relative to calcium carbonate 1: 0.7 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process To the slurry obtained in the first step, 141.7 g of 50% sulfuric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 4.0. ·Third process After adding a flocculant to the slurry obtained in the second step to induce flocculation and sedimentation, the supernatant was transferred by decantation to obtain 245.3 g of nitrogen resource recovery liquid 6. ·Fourth process In the third step, 50.0 g of water and 46.0 g of simulated solution 2 (fluorine amount per 1 liter of calcium carbonate: 0.3 molar equivalents) were added to the concentrated slurry, and then 19.1 g of 50% sulfuric acid was added and the mixture was stirred for 30 minutes. The pH after the reaction was 4.0. ·Fifth process The slurry obtained in the fourth step was separated into solid and liquid components by vacuum filtration, washed with 200 ml of water, and dried to obtain 78.6 g of recovered calcium fluoride 6. The components of the recovered liquid and recovered material are shown in Table 2. The coagulation properties of the third step and the filtration properties of the fifth step were good.

[0044] This process allowed us to recover nitrogen resources with reduced fluorine content, as well as calcium fluoride with less unreacted calcium carbonate and fewer impurities.

[0045] (Comparative Example 1) • First and second steps 80.0 g of calcium carbonate 1 (average particle size: 12 μm) and 120.0 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. To the resulting slurry, 125.8 g of 35% hydrochloric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 4.0. Next, 131.4 g of simulated solution 2 (fluorine amount relative to calcium carbonate 1: 0.8 molar equivalents) was added, and the mixture was stirred for 15 minutes. ·Third process We attempted to coagulate and precipitate the slurry obtained in the previous step by adding a flocculant, but even after standing for several hours, we were unable to collect the supernatant liquid. Next, we attempted to filtration the slurry under reduced pressure, but the filtration rate was extremely slow, and we had to abandon this method.

[0046] This process failed to recover nitrogen resources and calcium fluoride.

[0047] (Comparative Example 2) ·First process 93.6 g of calcium carbonate 4 (average particle size: 88 μm) and 120.0 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 131.4 g of simulated solution 2 (fluorine amount relative to calcium carbonate 3: 0.7 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process To the slurry obtained in the first step, 134.0 g of 35% hydrochloric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 4.0. ·Third process A flocculant was added to the slurry obtained in the second step to induce flocculation and sedimentation. The supernatant was then transferred by decantation to obtain 279.1 g of comparative nitrogen resource recovery solution 2. ·Fourth process In the third step, 50.0 g of water and 47.0 g of simulated solution 2 (fluorine amount relative to calcium carbonate 3: 0.3 molar equivalents) were added to the concentrated slurry, and then 24.8 g of 35% hydrochloric acid was added and the mixture was stirred for 30 minutes. The pH after the reaction was 4.0. ·Fifth process The slurry obtained in the fourth step was separated into solid and liquid components by vacuum filtration, washed with 200 ml of water, and dried to obtain 73.6 g of comparative calcium fluoride recovery 2. The components of the recovered liquid and recovery material are shown in Table 2. The coagulation properties of the third step and the filtration properties of the fifth step were good.

[0048] This process allowed us to recover nitrogen resources with a sufficient reduction in fluorine, but we were unable to recover calcium fluoride with a small amount of unreacted calcium carbonate.

[0049] (Comparative Example 3) ·First process 63.0g of slaked lime 1 (industrial grade slaked lime) and 157.5g of water were placed in a 500mL beaker and stirred with a magnetic stirrer. Then, 131.4g of simulated solution 2 (fluorine amount per slaked lime 1: 0.8 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process To the slurry obtained in the first step, 123.5 g of 35% hydrochloric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 5.0. ·Third process In the second step, a flocculant was added to the slurry to attempt flocculation and sedimentation, but even after standing for several hours, the supernatant could not be collected. Next, vacuum filtration was attempted on the slurry, but the filtration rate was extremely slow, forcing us to abandon this method.

[0050] This process failed to recover nitrogen resources and calcium fluoride.

[0051] (Comparative Example 4) ·First process 55.0 g of calcium carbonate 1 (average particle size: 12 μm) and 80.0 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 131.4 g of simulated solution 2 (fluorine amount relative to calcium carbonate 1: 1.2 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process 91.0 g of 35% hydrochloric acid was added to the slurry obtained in the first step over a period of 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 5.0. ·Third process In the second step, a flocculant was added to the slurry to induce flocculation and sedimentation. The supernatant was then transferred by decantation to obtain 254.2 g of comparative nitrogen resource recovery solution 4. Analysis of this nitrogen source recovery solution revealed that the F concentration was 20,722 wt ppm, which did not meet the recovery conditions. Therefore, the subsequent steps were not carried out.

[0052] This process failed to recover nitrogen resources with reduced fluorine content.

[0053] (Comparative Example 5) ·First process 133.0 g of calcium carbonate 1 (average particle size: 12 μm) and 120 g of water were placed in a 500 mL beaker and stirred with a magnetic stirrer. Then, 131.4 g of simulated solution 2 (fluorine amount relative to calcium carbonate 1: 0.5 molar equivalents) was added and the mixture was stirred for 15 minutes. ·Second process To the slurry obtained in the first step, 167.0 g of 35% hydrochloric acid was added over 60 minutes, and the mixture was stirred for a further 30 minutes. The pH after the reaction was 5.0. ·Third process A flocculant was added to the slurry obtained in the second step to induce flocculation and sedimentation. The supernatant was then transferred by decantation to obtain 194.0 g of comparative nitrogen resource recovery solution 5. ·Fourth process In the third step, 50.0 g of simulated solution 2 (fluorine amount per calcium carbonate 1: 0.2 molar equivalents) was added to the concentrated slurry, and then 36.2 g of 35% hydrochloric acid was added and the mixture was stirred for 30 minutes. The pH after the reaction was 5.0. ·Fifth process The slurry obtained in the fourth step was separated into solid and liquid components by vacuum filtration, washed with 200 ml of water, and dried to obtain 94.3 g of comparative calcium fluoride recovery material 5. The components of the obtained recovery liquid and recovery material are shown in Table 2. However, there were problems with the coagulation in the third step and the filtration in the fifth step.

[0032] This process allowed us to recover nitrogen resources with a sufficient reduction in fluorine, but we were unable to recover calcium fluoride with a small amount of unreacted calcium carbonate. [Table 2]

Claims

1. Waste liquid containing fluorine and ammonia, (1) The first step involves reacting with a slurry in which calcium carbonate is dispersed in water. (2) The second step involves adding acid to the solution obtained in (1). (3) A third step in which a polymer flocculant is added to the liquid obtained in (2) to perform flocculation and sedimentation, and the supernatant liquid is recovered as a nitrogen resource. (4) The fourth step involves adding waste liquid containing fluorine and ammonia to the liquid obtained in (3). A method for recovering nitrogen resources and calcium fluoride from wastewater containing fluorine and ammonia, characterized by performing a fifth step of recovering calcium fluoride by separating the liquid obtained in (4) from solids and recovering the solid, and then washing and drying it with water.

2. A method for recovering nitrogen resources and calcium fluoride from wastewater containing fluorine and ammonia according to claim 1, characterized in that, in the first step, the wastewater containing fluorine and ammonia is added such that the amount of fluorine relative to calcium carbonate is 0.6 molar equivalents or more and less than 1.0 molar equivalent.

3. A method for recovering nitrogen resources and calcium fluoride from wastewater containing fluorine and ammonia, according to any one of claims 1 to 2, characterized in that the average particle size of the calcium carbonate used in the first step is 2 μm or more and less than 50 μm.

4. A method for recovering nitrogen resources and calcium fluoride from waste liquid containing fluorine and ammonia according to any one of claims 1 to 3, characterized in that the amount of waste liquid containing fluorine and ammonia added in the fourth step is such that the amount of fluorine is 0.4 molar equivalents or less relative to the calcium carbonate used in the first step, and the total amount of waste liquid containing fluorine and ammonia added in the fourth step and the waste liquid containing fluorine and ammonia used in the first step is such that the amount of fluorine is 0.9 molar equivalents or more relative to the calcium carbonate used in the first step.

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