A method for recovering large-particle calcium fluoride from fluoride-containing wastewater

Abstract

The present application relates to the field of wastewater treatment, and in particular to a method for recovering large-particle calcium fluoride from fluoride-containing wastewater, the method comprising: removing impurities from fluoride-containing acidic wastewater to obtain pure fluoride-containing wastewater; activating calcium fluoride-containing seed crystals to obtain activated seed crystals; adding the activated seed crystals to the pure fluoride-containing wastewater, and adding a calcium-containing regulator according to a preset calcium-fluoride ratio, and then adding a crystal growth promoter at a preset mass ratio to obtain a reaction solution; adjusting the pH of the reaction solution at a preset reaction temperature, stirring, and then sedimenting, filtering and drying to obtain large-particle calcium fluoride; wherein the amount of the activated seed crystals added is 5 to 10 times the fluoride ion concentration in the pure fluoride-containing wastewater; the method can ensure that crystals in the activated seed crystals gradually grow and precipitate enough calcium fluoride, and can form large-particle calcium fluoride products, thereby recovering fluorine from fluoride-containing acidic wastewater while recovering high-quality calcium fluoride products.

Description

Technical Field

[0001] The present application relates to the field of wastewater treatment, and in particular to a method for recovering large-particle calcium fluoride from fluoride-containing wastewater. Background Art

[0002] Fluorine is one of the trace elements that are indispensable for the human body to maintain normal physiological activities. An appropriate amount of fluorine can promote the calcification of teeth and bones, help the conduction of nerve excitement and the metabolism of enzymes in the body, but excessive fluorine has serious harm to the human body, soil, animals and plants. The World Health Organization stipulates that the upper limit of fluorine content in drinking water is 1.5 mg / L, the fluoride ion content limit in the "Comprehensive Sewage Drainage" is 10 mg / L, and the fluoride content limit in the "Standards for Drinking Water Quality and Hygiene" is 1 mg / L. The conventional treatment methods for fluoride-containing wastewater, chemical precipitation and flocculation precipitation, will produce a large amount of sludge, and the sludge has a high water content. The purity of calcium fluoride in the sludge is low and cannot be reused as a product. Discharging it into the environment will have serious harm to the human body, soil, animals and plants, and also cause a waste of fluorine resources. If the fluorine in the wastewater is recovered in the form of fluoride, it can not only solve the problem of wastewater defluorination, but also realize fluorine resource recovery, which is of great significance.

[0003] However, the existing technologies for recovering fluorine from fluoride-containing acidic wastewater have problems to varying degrees, such as complex process flow, difficulty in ensuring the quality of calcium fluoride recovery, and the risk of secondary pollution. Therefore, how to provide a method that can treat high-concentration fluoride-containing acidic wastewater and recover high-quality calcium fluoride products is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application provides a method for recovering large-particle calcium fluoride from fluoride-containing wastewater, so as to solve the technical problem in the prior art that it is difficult to recover high-quality calcium fluoride products while recovering fluorine from fluoride-containing acidic wastewater.

[0005] In a first aspect, the present application provides a method for recovering large-particle calcium fluoride from fluoride-containing wastewater, the method comprising:

[0006] The fluorine-containing acidic wastewater is treated to remove impurities to obtain pure fluorine-containing wastewater;

[0007] activating the seed crystal containing calcium fluoride to obtain an activated seed crystal;

[0008] Adding the activated seed crystals to the pure fluorine-containing wastewater, adding a calcium-containing regulator according to a preset calcium-fluorine ratio, and then adding a crystal growth promoter at a preset mass ratio to obtain a reaction solution;

[0009] The pH of the reaction solution is adjusted at a preset reaction temperature, and the reaction solution is stirred, and then the solution is precipitated, filtered and dried to obtain large-particle calcium fluoride;

[0010] Wherein, the added amount of the activated seed crystal is 5 to 10 times the fluoride ion concentration in the pure fluoride-containing wastewater.

[0011] Optionally, the activation of the seed crystal containing calcium fluoride comprises the steps of:

[0012] Screening calcium fluoride until the particle size is less than 30 μm to obtain a screened material;

[0013] A seed crystal activator is added to the sieved material, and ultrasonic treatment is performed, followed by filtration and drying to obtain activated seed crystals.

[0014] Optionally, the liquid-to-solid ratio of the seed activator to the screening material is 2 to 5:1.

[0015] Optionally, the seed activator includes at least one of fatty alcohol polyoxyethylene ether, acetic acid, ammonium bifluoride, ammonium chloride, and sodium fluoride.

[0016] Optionally, the power of the ultrasound is 10w to 100w.

[0017] Optionally, the crystal growth promoter includes at least one of sodium glycocholate, triglyceride, ethanol, lauryl glucoside, gluconic acid, magnesium trichloride, and copper chloride.

[0018] Optionally, the calcium-containing regulator includes calcium chloride and / or clarified lime water.

[0019] Optionally, the preset calcium-fluorine ratio is 1.05-1.15; the preset mass ratio is 0.01‰-0.5‰.

[0020] Optionally, the preset reaction temperature is 10°C to 30°C; and / or,

[0021] The pH value is 6.0 to 9.0.

[0022] Optionally, the stirring includes first stirring and second stirring, the first stirring lasts for 5 min to 10 min, the second stirring lasts for 0.5 h to 1 h, and the rotation speed of the first stirring is greater than that of the second stirring.

[0023] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0024] The embodiment of the present application provides a method for recovering large-particle calcium fluoride from fluoride-containing wastewater. The method comprises the following steps: firstly, the fluoride-containing acidic wastewater is subjected to impurity removal treatment, and then, activated seed crystals are used to react with the impurity-removed fluoride-containing acidic wastewater, and the relationship between the amount of activated seed crystals added and the fluoride ion concentration in the impurity-removed fluoride-containing acidic wastewater is controlled. Meanwhile, a calcium-containing regulator is added to preliminarily adjust the pH value and provide part of the calcium ions. The crystals in the activated seed crystals are used to generate and precipitate part of the calcium fluoride in the fluoride-containing acidic wastewater solution. Then, a crystal growth promoter is added to effectively change the solution micro-electric field distribution and the surface activity of the crystal growth surface, so that it is more conducive to the continued growth and growth of the crystals in the activated seed crystals, thereby ensuring that the crystals in the activated seed crystals gradually grow and precipitate enough calcium fluoride to form large-particle calcium fluoride products, thereby realizing the recovery of fluorine from the fluoride-containing acidic wastewater and the recovery of high-quality calcium fluoride products. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0027] Figure 1 A schematic diagram of a process for a method provided in an embodiment of the present application;

[0028] Figure 2 A detailed flowchart of the method provided in the embodiment of the present application;

[0029] Figure 3 Phase diagram of large-particle calcium fluoride provided in the examples of this application;

[0030] Figure 4 This is a particle size distribution diagram of large-particle calcium fluoride provided in the examples of this application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0032] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0033] The creative thinking of this application is:

[0034] A method for recovering calcium fluoride from fluoride-containing acidic wastewater, comprising:

[0035] (1) A method for treating high-concentration fluorine-containing wastewater and recovering fluorine, wherein two reaction tanks are sequentially set up, chemical gypsum and calcium chloride are added respectively, fluoride ions in the fluorine-containing wastewater are converted into calcium fluoride precipitates, and the effluent is filtered through a fluorite sand filter tank so that the wastewater meets the discharge standards, and calcium fluoride is recovered at the same time. However, the calcium fluoride product obtained by this method cannot be effectively separated from calcium sulfate, and the quality of calcium fluoride is unstable;

[0036] (2) A method for producing calcium fluoride using high-fluorine-containing industrial wastewater, wherein calcium hydroxide and calcium chloride are used to co-precipitate fluoride ions in the fluoride-containing wastewater, and the precipitated product is passed through an inclined plate sedimentation tank, and then concentrated and filtered to obtain a mixed solid product with a calcium fluoride content of 30%-35%. The treated wastewater is passed through a precision filter to ensure that the effluent meets the discharge standards. The calcium fluoride obtained by this method has low purity and low utilization value;

[0037] (3) A multi-stage treatment of high-concentration fluorine-containing wastewater - in-situ preparation of high-purity CaF 2 The principle of this method is to first remove impurities from high-concentration fluoride-containing wastewater, specifically by adding barium chloride to remove SO 4 2- , oxidant to remove organic matter, load Fe 2+ The activated carbon removes heavy metal ions, and then the fluoride-containing wastewater after impurity removal enters the lime bed containing calcium oxide, using part of the calcium sulfate in-situ crystal nucleus and CaF 2 The in-situ two-step generation process forms fluoride-containing sludge with a high calcium fluoride content. Although this method improves the purity of calcium fluoride in the fluoride-containing sludge, it is easy to bring the risk of excessive heavy metals due to the addition of barium salts during the treatment process. In addition, the process flow of the method is cumbersome and the operation is complicated.

[0038] (4) A method and device for treating fluorine-containing wastewater, which introduces a fluidized bed crystallization reactor. By using the principle of induced crystallization, calcium fluoride precipitate with large particles and low water content can be recovered. However, the equipment requirements are high, the process is complicated, and the process conditions are difficult to control;

[0039] (5) A method for graded treatment of fluorine-containing acidic wastewater and recovery of calcium fluoride resources, wherein calcium-containing alkaline substances (one or more of quicklime, carbide slag or lime milk) are added to the fluorine-containing wastewater, followed by additional addition of calcium chloride, inhibitors and collectors, and the removal of impurity foam by inhibitors and collectors combined with aeration flotation, followed by filtration and drying to obtain calcium fluoride particles. The inhibitor is one or two of water glass, acidic water glass, and tannic acid, and the collector is one or a mixture of two or more fatty acid organic substances such as oleic acid, sodium oleate, sodium petroleum sulfonate, and sodium dodecyl sulfate. This method only relies on flotation to remove impurities in the sludge, and the removal effect is poor. The recovered calcium fluoride is of poor quality, with the highest purity being 92.3%;

[0040] (6) A method for recycling and reusing fluorine-containing wastewater based on calcium fluoride induced precipitation, comprising first calculating the total molar number of fluoride ions in the treated fluorine-containing water; and calculating the total molar number of fluoride ions in the treated fluorine-containing water according to the molar ratio n(Ca 2+ / F - )=1.0, calcium chloride is added according to 5.0g / L calcium fluoride is added, and polyacrylamide (PAM) as a coagulant is added according to 30mg / L. After stirring, the mixture is settled to obtain muddy water, and the muddy water is separated. The obtained muddy part can be returned to the fourth step as a calcium fluoride induced precipitation crystal nucleus for reuse, and the remaining muddy can be extracted by calcium fluoride for reuse in preparing fluorine-containing products. The obtained muddy water content is less than 50%, and the content of calcium fluoride as a recyclable component is higher than 80%. The muddy water content of this method is high, and the purity of the recovered calcium fluoride is low.

[0041] Therefore, overall, the existing fluorine recovery technology for fluorine-containing wastewater has problems to varying degrees, such as complex process flow, difficulty in ensuring the quality of calcium fluoride recovery, and the risk of secondary pollution.

[0042] About seed growth promoters, including:

[0043] (1) A method for preparing coarse-grained aluminum hydroxide from ammonium aluminum sulfate solution, wherein the seed growth promoter is sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate or a mixture thereof, and the addition amount is 400 to 600 ppm;

[0044] (2) A method for efficient comprehensive utilization of arsenic alkali slag resources, wherein the crystal growth promoter is citric acid, and the amount of citric acid is measured at a concentration of 30-100 mg / L in a leaching solution containing sodium carbonate and sodium arsenate;

[0045] (3) A potassium sulfate crystal growth promoter and a crystal growth promoter involved in its application, comprising sodium tripolyphosphate, diammonium hydrogen phosphate, magnesium sulfate, urea and sodium sulfate;

[0046] (4) A particle promoter involved in the preparation process of large-particle food-grade calcium hydrogen phosphate is composed of K 2 CO 3, KOH, K 3 C 6 H 5 O 7 or K 2 C 2 O 4 One or two of the above, the added amount accounts for 1.5-3.5% of the total mass of the calcium carbonate suspension and the phosphoric acid solution;

[0047] (5) A method for improving the filtration performance of ferrous sulfate, wherein the promoter is any one of ferrous sulfate heptahydrate or cellulose, and the addition amount is 0.1%-5.0% by weight of the titanium clearing liquid;

[0048] (6) A method for eliminating the periodic refinement of the particle size of the seed product, wherein the aluminum hydroxide trace crystal growth promoter is a mixture of fatty acids and sodium dodecylbenzene sulfonate, wherein the mass fraction of the fatty acid is 20-60%, the mass fraction of the sodium dodecylbenzene sulfonate is 40-80%, and the fatty acid molecular formula is C n H 2n +COOH, n=16 or 18, the added amount is to achieve a volume concentration of 10-300ppm in the solution.

[0049] In general, different types of seed crystal growth have their own specific crystal growth promoters, but no research or reports on calcium fluoride seed crystal growth promoters were found.

[0050] Therefore, how to provide a method that can treat high-concentration fluoride-containing acidic wastewater and recover high-quality calcium fluoride products is a technical problem that urgently needs to be solved.

[0051] like Figure 1 As shown, the embodiment of the present application provides a method for recovering large-particle calcium fluoride from fluoride-containing wastewater, the method comprising:

[0052] S1. removing impurities from the fluorine-containing acidic wastewater to obtain pure fluorine-containing wastewater;

[0053] S2. Activating the seed crystals containing calcium fluoride to obtain activated seed crystals;

[0054] S3. adding the activated seed crystals to the pure fluorine-containing wastewater, adding a calcium-containing regulator according to a preset calcium-fluorine ratio, and then adding a crystal growth promoter at a preset mass ratio to obtain a reaction solution;

[0055] S4. adjusting the pH of the reaction solution at a preset reaction temperature, stirring, and then settling, filtering and drying to obtain large particles of calcium fluoride;

[0056] Wherein, the added amount of the activated seed crystal is 5 to 10 times the fluoride ion concentration in the pure fluoride-containing wastewater.

[0057] In the embodiments of the present application, the positive effect of controlling the amount of activated seed crystals added to be 5 to 10 times the fluoride ion concentration in the pure fluoride-containing wastewater is that within this range, sufficient activated seed crystals are added to effectively control the growth of calcium fluoride crystals during the reaction, so that homogeneous nucleation is subsequently formed to obtain large calcium fluoride particles.

[0058] like Figure 2 As shown, in some optional embodiments, the activation of the seed crystal containing calcium fluoride comprises the steps of:

[0059] S201. Sieving calcium fluoride to a particle size of <30 μm to obtain a sieved material;

[0060] S202. Add a seed crystal activator to the sieved material, perform ultrasound treatment, and then filter and dry to obtain activated seed crystals.

[0061] In the embodiment of the present application, the specific steps of activating the seed crystal containing calcium fluoride are defined, and the calcium fluoride is first sieved to obtain a sieved material with a small particle size, and then a seed crystal activator is added to the sieved material, and ultrasound is performed, so that the seed crystal activator can fully activate the sieved material containing calcium fluoride.

[0062] At the same time, the addition of a seed activator can achieve etching of the seed surface and reset of the surface micro-electric field, making the seed more conducive to continued growth and enlargement of the crystal, thereby subsequently obtaining large particles of calcium fluoride.

[0063] In some optional embodiments, the liquid-to-solid ratio of the seed activator to the sieved material is 2 to 5:1.

[0064] In the embodiment of the present application, the positive effect of controlling the liquid-solid ratio of the seed crystal activator to the screening material to be 2 to 5:1 is that within the liquid-solid ratio range, the activation effect of the seed crystal activator on the calcium fluoride in the screening material can be guaranteed, and the activated seed crystals can be obtained in combination with subsequent ultrasound.

[0065] In some optional embodiments, the seed activator includes at least one of fatty alcohol polyoxyethylene ether, acetic acid, ammonium bifluoride, ammonium chloride, and sodium fluoride.

[0066] In the embodiments of the present application, the specific type of the seed activator is controlled to ensure sufficient activation of the calcium fluoride-containing screening material.

[0067] In some optional embodiments, the power of the ultrasound is 10w to 100w.

[0068] In the embodiments of the present application, controlling the specific power of ultrasound can not only ensure complete mixing of the seed activator and the sieved material, but also ensure that the seed activator can effectively change the distribution of the solution micro-electric field and the surface activity of the crystal growth surface, making it more conducive to the continued growth and expansion of the crystal, thereby obtaining large particles of calcium fluoride.

[0069] In some optional embodiments, the crystal growth promoter includes at least one of sodium glycocholate, triglyceride, ethanol, lauryl glucoside, gluconic acid, magnesium trichloride, and copper chloride.

[0070] In the embodiments of the present application, controlling the specific type of crystal growth promotion can effectively change the solution micro-electric field distribution and the surface activity of the crystal growth surface, making it more conducive to the continued growth and expansion of the crystal, thereby obtaining a large-particle calcium fluoride product.

[0071] In some optional embodiments, the calcium-containing regulator includes calcium chloride and / or clarified lime water.

[0072] In the embodiments of the present application, controlling the specific type of calcium-containing regulator can not only provide a portion of calcium ions, but also preliminarily improve the pH value of pure fluoride-containing wastewater, making it easier for the subsequent crystal growth promoter to promote the formation and growth of crystals.

[0073] In some optional embodiments, the preset calcium-fluorine ratio is 1.05-1.15; the preset mass ratio is 0.01‰-0.5‰.

[0074] In the embodiment of the present application, the preset calcium-fluorine ratio is controlled to be 1.05-1.15 and the preset mass ratio is 0.01‰-0.5‰. Within this range, the growth of the crystal can be effectively controlled and the generation of heterogeneous nucleation can be effectively avoided, thereby ensuring uniform growth of the crystal and obtaining a large-particle calcium fluoride product.

[0075] In some optional embodiments, the preset reaction temperature is 10° C. to 30° C.; and / or,

[0076] The pH value is 6.0 to 9.0.

[0077] In the embodiments of the present application, the specific preset reaction temperature and pH are controlled. On the one hand, the solubility and pH of the reaction solution can be adjusted so that a large amount of calcium fluoride product can be precipitated subsequently. On the other hand, the growth of crystals can be controlled by adjusting the specific conditions of the reaction solution, thereby effectively avoiding the generation of heterogeneous nucleation.

[0078] In some optional embodiments, the stirring includes first stirring and second stirring, the first stirring lasts for 5 min to 10 min, the second stirring lasts for 0.5 h to 1 h, and the rotation speed of the first stirring is greater than the second stirring.

[0079] In the embodiments of the present application, the specific manner and time of controlling the stirring can, on the one hand, utilize a first stirring at a faster speed in combination with a second stirring at a slower speed to ensure uniform dispersion of the solute in the reaction solution, and on the other hand, utilize the first stirring and the second stirring to ensure uniform crystal growth, thereby obtaining a large-particle calcium fluoride product.

[0080] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0081] Example 1

[0082] Fluoride-containing acidic wastewater with a fluoride ion concentration of 1500 mg / L was treated for impurity removal. Chemically pure calcium fluoride with a particle size of less than 30 μm was activated with a mixture of fatty alcohol polyoxyethylene ether and acetic acid at a liquid-to-solid ratio of 2:1 and ultrasonic 100W. Then, 5 times the fluoride ion concentration in the solution was added to the pure fluoride-containing wastewater after impurity removal, and the calcium-fluoride molar ratio n(Ca 2+ / F - )=1.15, and add clarified lime water and calcium fluoride crystal growth promoter to the impurity-removed solution at 0.5‰ of the total mass of the solution to obtain a reaction solution, wherein the crystal growth promoter consists of triglyceride, ethanol and gluconic acid.

[0083] The temperature of the reaction solution was controlled at 30°C and the pH value was adjusted to 9.0. The mixture was stirred rapidly for 5 minutes and then slowly stirred for 1 hour. The mixture was fully settled, filtered, and the filter cake was dried at 105°C. Figure 3 As shown, large-particle calcium fluoride is obtained, and the fluoride ion concentration in the filtrate is less than 10 mg / L, which meets the discharge requirements. The purity of the recovered large-particle calcium fluoride reaches 98.12%. Figure 4 As shown, D90 = 71.223 μm.

[0084] Example 2

[0085] Comparing Example 2 with Example 1, the difference between Example 2 and Example 1 is:

[0086] Fluoride-containing acidic wastewater with a fluoride ion concentration of 2500 mg / L was treated for impurity removal. Chemically pure calcium fluoride with a particle size of less than 30 μm was activated with a mixture of ammonium chloride and sodium fluoride at a liquid-to-solid ratio of 3:1 and ultrasonic 10W. Then, 10 times the fluoride ion concentration in the solution was added to the pure fluoride-containing wastewater after impurity removal, and the calcium-fluoride molar ratio was adjusted to n(Ca 2+ / F- )=1.05, and adding calcium chloride and calcium fluoride crystal growth promoters to the impurity-removed solution at a rate of 0.01‰ of the total mass of the solution to obtain a reaction solution, wherein the crystal growth promoter consists of lauryl glucoside and cupric chloride.

[0087] The temperature of the reaction solution was controlled at 10°C, the pH value was adjusted to 6.0, the mixture was first stirred rapidly for 10 minutes, then stirred slowly for 0.5 hours, and the mixture was fully settled, filtered, and the filter cake was dried at 105°C to obtain large-particle calcium fluoride, and the fluoride ion concentration of the filtrate was less than 10 mg / L, which met the emission standards. The purity of the recovered large-particle calcium fluoride reached 98.03%, and D90=72.681 μm.

[0088] Example 3

[0089] Comparing Example 3 with Example 1, the difference between Example 3 and Example 1 is:

[0090] Fluoride-containing wastewater with a fluoride ion concentration of 800 mg / L was treated for impurity removal. Chemically pure calcium fluoride with a particle size of less than 30 μm was activated with a mixture of fatty alcohol polyoxyethylene ether and ammonium bifluoride at a liquid-to-solid ratio of 5:1 and ultrasonic 60W. Then, 6 times the fluoride ion concentration in the solution was added to the pure fluoride-containing wastewater after impurity removal, and the calcium-fluoride molar ratio was adjusted to n(Ca 2+ / F - )=1.10, and add calcium chloride and calcium fluoride crystal growth promoters to the impurity-removed solution at a total mass of 0.2‰ of the solution to obtain a reaction solution, wherein the crystal growth promoter consists of sodium glycocholate and magnesium trichloride.

[0091] The solution temperature was controlled at 20°C, the pH value was adjusted to 8.0, the solution was first stirred rapidly for 8 minutes, then stirred slowly for 0.8 hours, and the filter cake was fully precipitated, filtered, and dried at 105°C to obtain large-particle calcium fluoride, and the fluoride ion concentration of the filtrate was less than 10 mg / L, which met the emission standards. The purity of the recovered large-particle calcium fluoride reached 98.23%, and D90=73.002 μm.

[0092] Example 4

[0093] Comparing Example 4 with Example 1, the difference between Example 4 and Example 1 is:

[0094] Fluoride-containing wastewater with a fluoride ion concentration of 120 mg / L was treated for impurity removal. Chemically pure calcium fluoride with a particle size of less than 30 μm was activated with a mixture of fatty alcohol polyoxyethylene ether, acetic acid and sodium fluoride under the conditions of liquid-solid ratio of 4:1 and ultrasonic wave of 80W. Then, 7 times the fluoride ion concentration in the solution was added to the pure fluoride-containing wastewater after impurity removal, and the calcium-fluoride molar ratio was adjusted to n(Ca 2+ / F - )=1.12, and add calcium chloride and calcium fluoride crystal growth promoters to the impurity-removed solution at 0.3‰ of the total mass of the solution to obtain a reaction solution, wherein the crystal growth promoter consists of ethanol and cupric chloride.

[0095] The solution temperature was controlled at 15°C, the pH value was adjusted to 7.0, the solution was first stirred rapidly for 7 minutes, then stirred slowly for 0.6 hours, and the filter cake was fully precipitated, filtered, and dried at 105°C to obtain large-particle calcium fluoride, and the fluoride ion concentration of the filtrate was less than 10 mg / L, which met the emission standards. The purity of the recovered large-particle calcium fluoride reached 98.15%, and D90=72.452 μm.

[0096] Example 5

[0097] Comparing Example 5 with Example 1, the difference between Example 5 and Example 1 is:

[0098] Fluoride-containing wastewater with a fluoride ion concentration of 500 mg / L was treated for impurity removal. Chemically pure calcium fluoride with a particle size of less than 30 μm was activated with fatty alcohol polyoxyethylene ether under a liquid-to-solid ratio of 4:1 and ultrasonic 90W. Then, 8 times the fluoride ion concentration in the solution was added to the impurity-removed solution, and the calcium-fluoride molar ratio was adjusted to n(Ca 2+ / F - )=1.13, and add clarified lime water and calcium fluoride crystal growth promoter to the impurity-removed solution at 0.4‰ of the total mass of the solution to obtain a reaction solution, wherein the crystal growth promoter consists of sodium glycocholate, triglyceride, cupric chloride and magnesium trichloride.

[0099] The solution temperature was controlled at 25°C, the pH value was adjusted to 7.0, the solution was first stirred rapidly for 9 minutes, then stirred slowly for 0.7 hours, and the filter cake was fully precipitated, filtered, and dried at 105°C to obtain large-particle calcium fluoride, and the fluoride ion concentration of the filtrate was less than 10 mg / L, which met the emission standards. The purity of the recovered large-particle calcium fluoride reached 98.05%, and D90=72.013 μm.

[0100] One or more technical solutions in the embodiments of the present application also have at least the following technical effects or advantages:

[0101] (1) The embodiment of the present application provides a method for recovering large-particle calcium fluoride from fluoride-containing wastewater, which can recover high-purity, large-particle calcium fluoride while achieving fluoride discharge standards in the wastewater. The overall process is simple, easy to operate, and there is no secondary pollution.

[0102] (2) The embodiment of the present application provides a method for recovering large-particle calcium fluoride from fluoride-containing wastewater. By adding a seed crystal activator, the etching of the seed crystal surface and the resetting of the surface micro-electric field can be achieved, making the seed crystal more conducive to the continued growth and expansion of the crystal.

[0103] (3) The embodiment of the present application provides a method for recovering large-particle calcium fluoride from fluoride-containing wastewater. By adding a regulator with a reasonable calcium-fluoride ratio into the solution and controlling other process conditions, the growth of crystals can be effectively controlled, and the generation of heterogeneous nucleation can be effectively avoided.

[0104] (4) The embodiment of the present application provides a method for recovering large-particle calcium fluoride from fluoride-containing wastewater. By adding a crystal growth promoter, the solution micro-electric field distribution and the surface activity of the crystal growth surface can be effectively changed, making it more conducive to the continued growth and expansion of the crystal.

[0105] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0106] In this application, unless otherwise specified, directional words such as "upper" and "lower" used refer specifically to the directions of the drawings in the accompanying drawings. In addition, in the description of the specification of this application, the terms "include", "comprise", etc. mean "including but not limited to".

[0107] In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "multiple" refers to two or more. "At least one", "the following at least one (individual)" or similar expressions refer to any combination of these items, including any combination of single (individual) or plural (individual). For example, "at least one (individual) of a, b, or c", or "at least one (individual) of a, b, and c", can all represent: a, b, c, ab (i.e. a and b), ac, bc, or abc, wherein a, b, c can be single or multiple respectively.

[0108] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for recovering large-particle calcium fluoride from fluoride-containing wastewater, characterized in that: The method comprises: The fluorine-containing acidic wastewater is treated to remove impurities to obtain pure fluorine-containing wastewater; activating the seed crystal containing calcium fluoride to obtain an activated seed crystal; Adding the activated seed crystals to the pure fluorine-containing wastewater, adding a calcium-containing regulator according to a preset calcium-fluorine ratio, and then adding a crystal growth promoter at a preset mass ratio to obtain a reaction solution; The pH of the reaction solution is adjusted at a preset reaction temperature, and the reaction solution is stirred, and then the solution is precipitated, filtered and dried to obtain large-particle calcium fluoride; Wherein, the amount of the activated seed crystal added is 5 to 10 times the fluoride ion concentration in the pure fluoride-containing wastewater; The method for preparing the activated calcium fluoride-containing seed crystals comprises the steps of: Screening calcium fluoride until the particle size is less than 30 μm to obtain a screened material; Adding a seed crystal activator to the sieved material, performing ultrasound treatment, and then filtering and drying to obtain activated seed crystals; The liquid-to-solid ratio of the seed activator to the sieved material is 2 to 5:1, and the seed activator includes at least one of fatty alcohol polyoxyethylene ether, acetic acid, ammonium bifluoride, ammonium chloride, and sodium fluoride; The crystal growth promoter includes at least one of sodium glycocholate, triglyceride, ethanol, lauryl glucoside, gluconic acid, magnesium trichloride and copper chloride.

2. The method according to claim 1, characterized in that: The power of the ultrasound is 10w-100w.

3. The method according to claim 1, characterized in that The calcium-containing regulator includes calcium chloride and / or clarified lime water.

4. The method according to claim 1, characterized in that The preset calcium-fluorine ratio is 1.05-1.15; the preset mass ratio is 0.01‰-0.5‰.

5. The method according to claim 1, characterized in that The preset reaction temperature is 10°C to 30°C; and / or, The pH value is 6.0 to 9.

0.

6. The method according to claim 1, characterized in that The stirring includes first stirring and second stirring, the first stirring lasts for 5 minutes to 10 minutes, the second stirring lasts for 0.5 hours to 1 hour, and the rotation speed of the first stirring is greater than that of the second stirring.

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