Method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid

Abstract

The invention relates to a method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid. The method comprises the following steps: step 1, treating waste liquid; step 2, primary filtration; step 3, precisely filtering; step 4, concentrating and thickening; step 5, centrifugal separation; and step 6, drying and packaging. According to the method, the waste liquid for producing the precipitated active hydrated white carbon black is fully utilized, waste is turned into wealth by physical and chemical methods through the processes of flocculation modification, filtration and impurity removal, concentration, crystallization, centrifugal filtration, flash drying, packaging and the like, a sodium fluoride product with relatively high purity is produced, and meanwhile, silicon dioxide filter residues obtained by filtration can also be used as a defluorination agent.

Description

Technical Field

[0001] The invention relates to the field of inorganic compounds, and in particular to a method for preparing sodium fluoride based on precipitation of hydrated white carbon black waste liquid. Background Art

[0002] Sodium fluoride is a white crystalline powder, soluble in water and hydrogen fluoride, slightly soluble in ethanol, with a melting point of 993°C and a boiling point of 1700°C. Its aqueous solution is weakly alkaline and has conductivity in the molten state or in aqueous solution. The aqueous solution of sodium fluoride reacts with calcium chloride or calcium carbonate to form a colloidal calcium fluoride precipitate that is difficult to filter; it reacts with ferric chloride to form a white crystalline complex salt; it directly transforms into fluorosilicate with silicon dioxide under acidic conditions. Therefore, sodium fluoride is an important chemical raw material and is widely used in various fields.

[0003] In traditional industries, sodium fluoride is widely used, but the purity requirements are not high. As a raw material for the production of sodium ion batteries, there are high requirements for the purity of sodium fluoride. As the most likely ion energy storage battery to replace lithium ion batteries in the future, sodium ion batteries will have huge demand in the future. Battery-grade sodium fluoride, as one of the most important raw materials for sodium ion battery electrolytes, has broad application prospects. Therefore, it is necessary to prepare high-purity sodium fluoride to meet its application in batteries.

[0004] The production methods of sodium fluoride include melt leaching, hydrofluoric acid neutralization, ammonium fluoride soda method, and sodium fluosilicate soda method. Each production enterprise adopts different production processes according to its own resource allocation and local conditions. In the production process of preparing precipitated hydrated white carbon black from silicon slag produced by anhydrous hydrogen fluoride in patent CN118183631A, a large amount of sodium fluoride waste liquid is generated. This not only causes a waste of resources, but also causes relatively serious environmental pollution to downstream water and land, bringing a series of environmental problems. Therefore, the present invention attempts to prepare sodium fluoride using the production waste liquid of hydrated precipitated white carbon black, which solves environmental problems on the one hand and can also recycle waste on the other hand. However, due to the excessive impurities in the hydrated precipitated white carbon black waste liquid, the purity of the sodium fluoride obtained by direct production is not high, and the impurity content is relatively high, which limits the application of the obtained sodium fluoride. Therefore, it is necessary to develop a novel method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid so that relatively pure sodium fluoride can be obtained. Summary of the invention

[0005] In view of the problems existing in the prior art, the object of the present invention is to provide a method for preparing sodium fluoride based on precipitating hydrated silica waste liquid.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] A method for preparing sodium fluoride based on precipitation of hydrated white carbon black waste liquid comprises the following steps:

[0008] Step 1, treating the waste liquid: adding a flocculant to the waste liquid from the production of hydrated silica, and placing the waste liquid in a filtrate storage tank for aging treatment;

[0009] Step 2, primary filtration: the filtrate slurry in the filtrate storage tank is filtered through a diaphragm plate and frame to remove large particles of impurities;

[0010] Step 3, precision filtration: the filtrate after the plate and frame filter press treatment is filtered through a precision filter with a back-flushing function to remove small particles of impurities, and the obtained filtrate is stored;

[0011] Step 4, concentration and thickening: The filtrate from the previous process enters the MVR concentration system, and the concentrated slurry is taken out with a solid content requirement of 10%-25%. It enters the thickener for cooling and thickening until the solid content is greater than 25%;

[0012] Step 5, centrifugal separation: the slurry from the thickener is passed through a horizontal screw centrifuge for further centrifugal separation and enters the next process of drying. The mother liquor flows into the mother liquor tank, is diluted with fresh filtrate and then returned to the system;

[0013] Step 6, drying and packaging: the material enters the drying system through the scattering device, collects dust, and is transported to the packaging silo by positive pressure airflow, and then negative pressure packaging and palletizing are carried out in sequence to obtain the product.

[0014] Preferably, in step 1, the amount of flocculant added is 0.1-0.5% of the mass of the hydrated silica production waste liquid, and the aging time is 3-4 hours.

[0015] Preferably, in step 1, in the waste liquid of hydrated white carbon black production, F - The concentration is 3587-7209 mg / L, CO3 2- The concentration is 256-478mg / L, SO4 2- The concentration is 142-328 mg / L, the silica concentration is 342-428 mg / L, and the Na + The concentration is 2678-3534mg / L, Al 3+ The concentration is 12-35mg / L, Mg 2+ The concentration is 27-43 mg / L, Ca 2+ The concentration is 174-325 mg / L, Fe 2+ The concentration is 11-24mg / L.

[0016] Preferably, in step 1, the method for preparing the flocculant comprises:

[0017] S1. Weigh hydroxyethylidene diphosphonic acid (HEDPA) and add it to dimethyl sulfoxide (DMSO), introduce nitrogen as protective gas, stir thoroughly, heat to 150-170° C., keep warm and stir for 1-2 hours, and then remove dimethyl sulfoxide under reduced pressure to obtain vinyl diphosphonic acid;

[0018] S2. Add DL-mercaptosuccinic acid and vinyl diphosphonic acid to tetrahydrofuran (THF), introduce nitrogen as protective gas, stir thoroughly, add a photosensitizer dropwise, place under ultraviolet lamp and stir to react for 20-40 min. After the reaction is completed, remove the solvent under reduced pressure to obtain a flocculant.

[0019] Preferably, in S1, the mass volume ratio of hydroxyethylidene diphosphonic acid and dimethyl sulfoxide is 1 g:(5-10) mL.

[0020] Preferably, in S2, the mass volume ratio of DL-mercaptosuccinic acid, vinyl diphosphonic acid and tetrahydrofuran is (0.7-1.4) g: (1-2) g: (20-30) mL.

[0021] Preferably, in S2, the photosensitizer is benzoin dimethyl ether, and the added amount is 2%-8% of the mass of DL-mercaptosuccinic acid.

[0022] Preferably, in S2, the power of the ultraviolet lamp is 15-45W, and the wavelength is 200-400nm.

[0023] Preferably, in step 2, the mesh size of the filter cloth is greater than 300 meshes.

[0024] Preferably, in step 3, the pore size of the precision filtration is 25-50 μm.

[0025] Preferably, in step 4, in order to reduce energy consumption and save electricity, two shell-and-tube evaporators are connected in series to force circulation, concentration and evaporation.

[0026] Preferably, in step 4, the concentration temperature is controlled at 75-80°C and the pressure is controlled at 30-40Pa.

[0027] Preferably, in step 4, the concentrated filtered water can be used as washing water in the primary filtration and precision filtration process, and can also be used as dissolving water for flocculants or circulating water replenishment.

[0028] Preferably, in step 5, centrifugal separation is performed to obtain a filter cake having a water content of 15%-30%.

[0029] Preferably, in step 5, due to long-term concentration, impurities will be gradually enriched. In order to solve this problem and ensure product quality, it is necessary to gradually remove part of the mother liquor to a sewage treatment plant.

[0030] Preferably, in step 6, the drying method is to use one of a flash dryer, a horizontal drum dryer, and a vibrating fluidized bed.

[0031] Preferably, in step 6, the dust collection is one of cyclone dust collection, bag dust collection, and electrostatic dust collection.

[0032] The beneficial effects of the present invention are:

[0033] 1. The present invention makes full use of the waste liquid produced by the precipitation of active hydrated white carbon black, and transforms waste into treasure by physical and chemical methods through flocculation modification, filtration and impurity removal, concentration, crystallization, centrifugal filtration, flash drying, packaging and other processes, so as to produce a sodium fluoride product with a higher purity. At the same time, the silica residue obtained by filtration can also be used as a defluorinating agent.

[0034] 2. The process of the present invention not only reduces the cost of precipitated white carbon black and improves the utilization rate of raw materials, but also reduces the environmentally unfriendly waste discharge mode of wastewater pollution and air pollution.

[0035] 3. In addition to a large amount of sodium sulfate, the precipitated hydrated white carbon black waste liquid also contains a variety of metal ions, such as Fe 2+ 、Al 3+ Mg 2+ , Ca 2+ In order to improve the purity of the obtained sodium fluoride, it is necessary to remove these impurity elements in a targeted manner. The present invention uses a homemade flocculant to treat the waste liquid. After a certain period of aging, the interference of the impurity elements can be removed to the greatest extent. The purity of the sodium fluoride finally prepared reaches 91.2%, which is much higher than the application effect of the traditional flocculant and can meet the third-level requirements of the sodium fluoride quality standard (non-ferrous metal industry YS / T517-2009).

[0036] 4. The flocculant used in the present invention is modified on the basis of the traditional organic phosphorus flocculant hydroxyethylidene diphosphonic acid (HEDPA). The specific process includes: firstly olefinizing hydroxyethylidene diphosphonic acid (HEDPA) in dimethyl sulfoxide (DMSO), and then combining it with DL-mercaptosuccinic acid containing two carboxyl groups by utilizing the sulfhydryl-double bond click chemistry reaction to obtain a flocculant containing a diphosphate group, a dicarboxyl group and a thioether group, thereby improving the flocculation effect and greatly improving the purity of the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention is further described using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the present invention. A person skilled in the art can obtain other drawings based on the following drawings without creative work.

[0038] Figure 1 It is a schematic flow chart of the method for preparing sodium fluoride based on precipitation of hydrated silica waste liquid in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. The change or adjustment of the relative relationship thereof shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0040] In order to better understand the above technical scheme, the exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0041] The hydrated silica production waste liquid used in the embodiment of the present invention comes from the waste liquid produced by the production of anhydrous hydrogen fluoride in silicon slag to prepare hydrated silica. The production method is detailed in patent CN118183631A. The concentration of the waste liquid components is: F - The concentration is 3587-7209 mg / L, CO3 2- The concentration is 256-478mg / L, SO4 2- The concentration is 142-328 mg / L, the silica concentration is 342-428 mg / L, and the Na + The concentration is 2678-3534mg / L, Al 3+ The concentration is 12-35mg / L, Mg 2+ The concentration is 27-43 mg / L, Ca 2+ The concentration is 174-325 mg / L, Fe 2+ The concentration is 11-24mg / L.

[0042] The present invention will be further described below in conjunction with the following examples.

[0043] Example 1

[0044] A method for preparing sodium fluoride based on precipitation of hydrated white carbon black waste liquid, such as Figure 1 As shown, the following steps are included:

[0045] Step 1, treating the waste liquid: adding a flocculant to the hydrated silica production waste liquid, the amount of which is 0.3% of the mass of the hydrated silica production waste liquid, and entering the filtrate storage tank for aging treatment;

[0046] Step 2, primary filtration: the filtrate slurry in the filtrate storage tank is filtered through a diaphragm plate and frame, and the filter cloth mesh number is greater than 300 meshes to remove large particles of impurities;

[0047] Step 3, precision filtration: the filtrate after the plate and frame filter press treatment is filtered through a precision filter with a back-flushing function, the filter pore size is 35 μm, small particles of impurities are removed, and the obtained filtrate is stored;

[0048] Step 4, concentration and thickening: The filtrate from the previous process enters the MVR concentration system. In order to reduce energy consumption and save electricity, two shell-and-tube evaporators are connected in series to force circulation and concentration evaporation to produce concentrated slurry. The concentration temperature is controlled at 80°C, the pressure is controlled at 35Pa, and the solid content is required to be 15%. The slurry enters the thickener for cooling and thickening until the solid content is greater than 25%. The water filtered out by the concentration can be used as washing water in the primary filtration and precision filtration process, and can also be used as flocculant dissolving water or circulating water replenishment;

[0049] Step 5, centrifugal separation: the slurry from the thickener is passed through a horizontal screw centrifuge for further centrifugal separation to obtain a filter cake with a water content of 15%-20%, which enters the next process for drying. The mother liquor flows into the mother liquor tank, is diluted with fresh filtrate and returned to the system. Due to long-term concentration, impurities will gradually accumulate. In order to solve this problem and ensure product quality, it is necessary to gradually remove part of the mother liquor to the sewage treatment plant;

[0050] Step 6, drying and packaging: the material enters the horizontal drum drying system through the scattering device, the cyclone dust is collected, and the positive pressure airflow is transported to the packaging silo, and then negative pressure packaging and palletizing are carried out in sequence to obtain the product.

[0051] In step 1, the preparation method of the flocculant comprises:

[0052] S1. Weigh hydroxyethylidene diphosphonic acid (HEDPA) and add it to dimethyl sulfoxide (DMSO). The mass volume ratio of hydroxyethylidene diphosphonic acid to dimethyl sulfoxide is 1 g:8 mL. Nitrogen is introduced as a protective gas. After sufficient stirring, the temperature is raised to 160° C., and after stirring for 1.5 hours, the dimethyl sulfoxide is removed under reduced pressure to obtain vinyl diphosphonic acid.

[0053] S2. Add DL-mercaptosuccinic acid and vinyl diphosphonic acid to tetrahydrofuran (THF), the mass volume ratio of DL-mercaptosuccinic acid, vinyl diphosphonic acid and tetrahydrofuran is 1.1g:1.5g:25mL, introduce nitrogen as protective gas, after sufficient stirring, add photosensitizer benzoin dimethyl ether dropwise, the addition amount is 5% of the mass of DL-mercaptosuccinic acid, place it under a 30W power, wavelength 365nm ultraviolet lamp, stir and react, the reaction time is 30min, after the reaction is completed, remove the solvent under reduced pressure to obtain a flocculant.

[0054] Example 2

[0055] A method for preparing sodium fluoride based on precipitation of hydrated white carbon black waste liquid comprises the following steps:

[0056] Step 1, treating waste liquid: adding a flocculant to the hydrated silica production waste liquid, the preparation of the flocculant is the same as in Example 1, the amount of the flocculant added is 0.1% of the mass of the hydrated silica production waste liquid, and the waste liquid enters the filtrate storage tank for aging treatment;

[0057] Step 2, primary filtration: the filtrate slurry in the filtrate storage tank is filtered through a diaphragm plate and frame, and the filter cloth mesh number is greater than 300 meshes to remove large particles of impurities;

[0058] Step 3, precision filtration: the filtrate after the plate and frame filter press treatment is filtered through a precision filter with a back-flushing function, the filter pore size is 25 μm, small particles of impurities are removed, and the obtained filtrate is stored;

[0059] Step 4, concentration and thickening: The filtrate from the previous process enters the MVR concentration system. In order to reduce energy consumption and save electricity, two shell-and-tube evaporators are connected in series to force circulation and concentration evaporation to produce concentrated slurry. The concentration temperature is controlled at 75°C, the pressure is controlled at 30Pa, and the solid content is required to be 10%. The slurry enters the thickener for cooling and thickening until the solid content is greater than 25%. The water filtered out by the concentration can be used as washing water in the primary filtration and precision filtration process, and can also be used as dissolving water for flocculants or circulating water replenishment.

[0060] Step 5, centrifugal separation: the slurry from the thickener is passed through a horizontal screw centrifuge for further centrifugal separation to obtain a filter cake with a water content of 20%-30%, which enters the next process for drying, and the mother liquor flows into the mother liquor tank, is diluted with fresh filtrate and returned to the system. Due to long-term concentration, impurities will gradually accumulate. In order to solve this problem and ensure product quality, it is necessary to gradually remove part of the mother liquor to the sewage treatment plant;

[0061] Step 6, drying and packaging: the material enters the horizontal drum drying system through the scattering device, the dust is collected by the bag, and the positive pressure airflow is transported to the packaging silo, and then negative pressure packaging and palletizing are carried out in sequence to obtain the product.

[0062] Example 3

[0063] A method for preparing sodium fluoride based on precipitation of hydrated white carbon black waste liquid comprises the following steps:

[0064] Step 1, treating the waste liquid: adding a flocculant to the hydrated silica production waste liquid. The flocculant preparation is the same as in Example 1, and the added amount is 0.5% of the mass of the hydrated silica production waste liquid. The waste liquid enters the filtrate storage tank for aging treatment;

[0065] Step 2, primary filtration: the filtrate slurry in the filtrate storage tank is filtered through a diaphragm plate and frame, and the filter cloth mesh number is greater than 300 meshes to remove large particles of impurities;

[0066] Step 3, precision filtration: the filtrate after the plate and frame filter press treatment is filtered through a precision filter with a back-flushing function, the filter pore size is 50 μm, small particles of impurities are removed, and the obtained filtrate is stored;

[0067] Step 4, concentration and thickening: The filtrate from the previous process enters the MVR concentration system. In order to reduce energy consumption and save electricity, two shell-and-tube evaporators are connected in series to force circulation and concentration evaporation to produce concentrated slurry. The concentration temperature is controlled at 80°C, the pressure is controlled at 40Pa, and the solid content is required to be 20%. The slurry enters the thickener for cooling and thickening until the solid content is greater than 25%. The concentrated filtered water can be used as washing water in the primary filtration and precision filtration process, and can also be used as flocculant dissolving water or circulating water replenishment.

[0068] Step 5, centrifugal separation: the slurry from the thickener is passed through a horizontal screw centrifuge for further centrifugal separation to obtain a filter cake with a water content of 30%, which enters the next process for drying, and the mother liquor flows into the mother liquor tank, is diluted with fresh filtrate and returned to the system. Due to long-term concentration, impurities will gradually accumulate. In order to solve this problem and ensure product quality, it is necessary to gradually remove part of the mother liquor to the sewage treatment plant;

[0069] Step 6, drying and packaging: the material is sent into the vibrating fluidized bed drying system through a scattering device, electrostatic precipitator, and transported to the packaging silo by positive pressure airflow, and then negative pressure packaging and palletizing are carried out in sequence to obtain the product.

[0070] Example 4

[0071] A method for preparing sodium fluoride based on precipitation of hydrated silica waste liquid, which is different from Example 1 only in that the preparation method of the flocculant in step 1 is different.

[0072] The preparation method of the flocculant comprises:

[0073] S1. Weigh hydroxyethylidene diphosphonic acid (HEDPA) and add it to dimethyl sulfoxide (DMSO). The mass volume ratio of hydroxyethylidene diphosphonic acid to dimethyl sulfoxide is 1 g:5 mL. Nitrogen is introduced as a protective gas. After sufficient stirring, the temperature is raised to 150° C., and after stirring for 1 hour, the dimethyl sulfoxide is removed under reduced pressure to obtain vinyl diphosphonic acid.

[0074] S2. Add DL-mercaptosuccinic acid and vinyl diphosphonic acid to tetrahydrofuran (THF), the mass volume ratio of DL-mercaptosuccinic acid, vinyl diphosphonic acid and tetrahydrofuran is 0.7g:1g:20mL, introduce nitrogen as protective gas, and after sufficient stirring, add photosensitizer benzoin dimethyl ether dropwise, the addition amount is 2% of the mass of DL-mercaptosuccinic acid, place it under a 15W power, wavelength 365nm ultraviolet lamp, stir and react, the reaction time is 20min, after the reaction is completed, remove the solvent under reduced pressure to obtain a flocculant.

[0075] Example 5

[0076] A method for preparing sodium fluoride based on precipitation of hydrated silica waste liquid, which is different from Example 1 only in that the preparation method of the flocculant in step 1 is different.

[0077] The preparation method of the flocculant comprises:

[0078] S1. Weigh hydroxyethylidene diphosphonic acid (HEDPA) and add it to dimethyl sulfoxide (DMSO). The mass volume ratio of hydroxyethylidene diphosphonic acid to dimethyl sulfoxide is 1 g:10 mL. Nitrogen is introduced as a protective gas. After sufficient stirring, the temperature is raised to 170° C., and after keeping the temperature and stirring for 2 hours, the dimethyl sulfoxide is removed under reduced pressure to obtain vinyl diphosphonic acid.

[0079] S2. Add DL-mercaptosuccinic acid and vinyl diphosphonic acid to tetrahydrofuran (THF), the mass volume ratio of DL-mercaptosuccinic acid, vinyl diphosphonic acid and tetrahydrofuran is 1.4g:2g:30mL, introduce nitrogen as protective gas, and after sufficient stirring, add photosensitizer benzoin dimethyl ether dropwise, the addition amount is 8% of the mass of DL-mercaptosuccinic acid, place it under a 45W power, wavelength 365nm ultraviolet lamp, stir and react, the reaction time is 40min, after the reaction is completed, remove the solvent under reduced pressure to obtain a flocculant.

[0080] Comparative Example 1

[0081] A method for preparing sodium fluoride based on precipitation of hydrated silica waste liquid, which is different from Example 1 only in that the preparation method of the flocculant in step 1 is different.

[0082] The flocculant used in this comparative example is hydroxyethylidene diphosphonic acid (HEDPA), and the amount used is the same as that in Example 1.

[0083] Comparative Example 2

[0084] A method for preparing sodium fluoride based on precipitation of hydrated silica waste liquid, which is different from Example 1 only in that the preparation method of the flocculant in step 1 is different.

[0085] The flocculant used in this comparative example is DL-mercaptosuccinic acid, and the amount used is the same as that in Example 1.

[0086] Comparative Example 3

[0087] A method for preparing sodium fluoride based on precipitation of hydrated silica waste liquid, which is different from Example 1 only in that the preparation method of the flocculant in step 1 is different.

[0088] The flocculant used in this comparative example is a mixture of hydroxyethylidene diphosphonic acid and DL-mercaptosuccinic acid, the mass ratio of hydroxyethylidene diphosphonic acid to DL-mercaptosuccinic acid is 1.5:1.1, and the amount used is the same as that in Example 1.

[0089] Experimental testing

[0090] The NaF content, SiO2 content, carbonate (CO3 2- ) content, sulfate (SO4 2- ) content, Al content, Mg content, Ca content, Fe content, acidity (HF), and water (H2O) content were tested. The test results are shown in Table 1. The test standard is non-ferrous metal industry YS / T517-2009.

[0091] Table 1 Performance of different sodium fluorides

[0092] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 NaF content (%) 91.27 86.84 85.13 85.32 <![CDATA[SiO2 content (%)]]> - - - - Al content (%) 0.16 0.64 0.89 0.75 Mg content (%) 0.21 0.71 0.93 0.88 Ca content (%) 0.78 1.35 1.57 1.40 Fe content (%) 0.09 0.34 0.26 0.28 <![CDATA[Carbonate (CO3 2- , %)]]> 1.07 1.55 1.92 1.83 <![CDATA[Sulfate radical (SO4 2- , %)]]> 1.21 1.71 1.65 1.68 Acidity (HF,%) 0.07 0.09 0.08 0.08 water(%) 1.8 1.9 2.0 1.9

[0093] It can be seen from Table 1 that the sodium fluoride prepared in Example 1 of the present invention meets the third-level level of the YS / T517-2009 standard of the non-ferrous metal industry, and the NaF content is much higher than the requirement of the third level (NaF ≥ 84%). In addition, the content of impurity components of the sodium fluoride obtained in Example 1 is much lower than that of Comparative Examples 1-3, indicating that compared with the traditional method, the purity of the sodium fluoride product prepared by Example 1 of the present invention is greatly improved.

[0094] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0095] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing sodium fluoride based on precipitation hydrated white carbon black waste liquid, characterized in that: The following steps are involved: Step 1, treating the waste liquid: adding a flocculant to the waste liquid from the production of hydrated silica, and placing the waste liquid in a filtrate storage tank for aging treatment; Step 2, primary filtration: the filtrate slurry in the filtrate storage tank is filtered through a diaphragm plate and frame to remove large particles of impurities; Step 3, precision filtration: the filtrate after the plate and frame filter press treatment is filtered through a precision filter with a back-flushing function to remove small particles of impurities, and the obtained filtrate is stored; Step 4, concentration and thickening: The filtrate from the previous process enters the MVR concentration system, and the concentrated slurry is taken out with a solid content requirement of 10%-25%. It enters the thickener for cooling and thickening until the solid content is greater than 25%; Step 5, centrifugal separation: the slurry from the thickener is passed through a horizontal screw centrifuge for further centrifugal separation and enters the next process of drying. The mother liquor flows into the mother liquor tank, is diluted with fresh filtrate and then returned to the system; Step 6, drying and packaging: the material enters the drying system through the scattering device, collects dust, and is transported to the packaging silo by positive pressure airflow, and then negative pressure packaging and palletizing are carried out in sequence to obtain the product.

2. A method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid according to claim 1, characterized in that: In the step 1, the amount of flocculant added is 0.1-0.5% of the mass of the hydrated silica production waste liquid, and the aging time is 3-4 hours.

3. The method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid according to claim 1, characterized in that: In step 1, the preparation method of the flocculant comprises: S1. Weigh hydroxyethylidene diphosphonic acid (HEDPA) and add it to dimethyl sulfoxide (DMSO), introduce nitrogen as protective gas, stir thoroughly, heat to 150-170° C., keep warm and stir for 1-2 hours, and then remove dimethyl sulfoxide under reduced pressure to obtain vinyl diphosphonic acid; S2. Add DL-mercaptosuccinic acid and vinyl diphosphonic acid to tetrahydrofuran (THF), introduce nitrogen as protective gas, stir thoroughly, add a photosensitizer dropwise, place under ultraviolet lamp and stir to react for 20-40 min. After the reaction is completed, remove the solvent under reduced pressure to obtain a flocculant.

4. A method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid according to claim 3, characterized in that: In the S1, the mass volume ratio of hydroxyethylidene diphosphonic acid and dimethyl sulfoxide is 1 g: (5-10) mL.

5. The method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid according to claim 3, characterized in that: In S2, the mass volume ratio of DL-mercaptosuccinic acid, vinyl diphosphonic acid and tetrahydrofuran is (0.7-1.4) g: (1-2) g: (20-30) mL.

6. The method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid according to claim 3, characterized in that: In the S2, the photosensitizer is benzoin dimethyl ether, and the added amount is 2%-8% of the mass of DL-mercaptosuccinic acid; in the S2, the power of the ultraviolet lamp is 15-45W, and the wavelength is 200-400nm.

7. The method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid according to claim 1, characterized in that: In the step 2, the mesh number of the filter cloth is greater than 300 meshes; in the step 3, the filter pore size of the precision filtration is 25-50 μm.

8. The method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid according to claim 1, characterized in that: In step 4, the concentration temperature is controlled at 75-80° C. and the pressure is controlled at 30-40 Pa.

9. The method for preparing sodium fluoride based on precipitated hydrated white carbon waste liquid according to claim 1, characterized in that: In the step 5, centrifugal separation is performed to obtain a filter cake having a water content of 15% to 30%.

10. The method for preparing sodium fluoride based on precipitated hydrated white carbon black waste liquid according to claim 1, characterized in that: In step 6, the drying method is one of a flash dryer, a horizontal drum dryer, and a vibrating fluidized bed; and the dust collection is one of a cyclone dust collection, a bag dust collection, and an electrostatic precipitator.

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