Method for preparing sodium fluoride from calcium fluoride sludge

Abstract

The invention provides a method for preparing sodium fluoride from calcium fluoride sludge, and belongs to the technical field of recycling of fluorine resources in fluorine-containing solid waste. Comprising the following steps: S1, mixing pretreated calcium fluoride sludge with concentrated sulfuric acid in a corrosion-resistant reactor, and carrying out a thermochemical conversion reaction to generate hydrogen fluoride and carbon dioxide mixed gas and solid residues; s2, hydrogen fluoride gas generated in the reaction in the step S1 is captured and absorbed, a sodium fluoride product is obtained, and tail gas containing carbon dioxide is generated in the absorption process; s3, collecting and treating carbon dioxide-containing tail gas generated in the reaction process to obtain a sodium carbonate solution, and further separating out a sodium carbonate solid by cooling; and S4, carrying out post-treatment on solid residues after the reaction in the step S1 to obtain a solid by-product. According to the method, the fluorine element in the fluorine-containing sludge is efficiently recycled, meanwhile, residues are converted into building materials with utilization value, and harmlessness and recycling of the fluorine-containing sludge are achieved.

Description

Technical Field

[0001] This invention provides a method for preparing sodium fluoride using calcium fluoride sludge, belonging to the technical field of fluorine resource recovery and reuse in fluorine-containing solid waste. Background Technology

[0002] With the rapid development of my country's new energy industry, photovoltaic, optoelectronic, and semiconductor companies generate large amounts of fluoride-containing wastewater during etching and other processes. This wastewater contains fluorides, which are toxic and highly corrosive to plants and animals, and cannot be directly discharged. Currently, neutralization is often achieved by adding defluorinating agents, but this results in the generation of large amounts of fluoride-containing sludge (mainly composed of calcium fluoride).

[0003] Based on the above, the inventors discovered that: Existing methods for disposing of calcium fluoride sludge mainly include solidification and landfill, hydrometallurgy, and high-temperature incineration. These methods generally suffer from high disposal costs, risks of secondary pollution, and loss of fluorine resources.

[0004] Meanwhile, as my country's fluorochemical industry continues to develop, fluorite resources, which are the main source of fluorine, are becoming increasingly scarce. Seeking alternative fluorine resources to replace fluorite has become an urgent need for the industry.

[0005] Therefore, in view of this, we studied and improved the existing structure and proposed a method for preparing sodium fluoride using calcium fluoride sludge to solve the above-mentioned problems. Summary of the Invention

[0006] To address the problems of resource waste, secondary pollution, and high costs in existing calcium fluoride sludge treatment technologies, this invention provides a method for preparing sodium fluoride from calcium fluoride sludge, achieving efficient recovery of fluorine from fluoride-containing sludge, and simultaneously converting the residue into valuable building materials, thus achieving the harmlessness and resource utilization of fluoride-containing sludge.

[0007] To address the aforementioned problems, the present invention proposes the following technical solution: a method for preparing sodium fluoride using calcium fluoride sludge, comprising the following steps: S1. The pretreated calcium fluoride sludge is mixed with concentrated sulfuric acid in a corrosion-resistant reactor to carry out a thermochemical conversion reaction, generating a mixed gas of hydrogen fluoride and carbon dioxide and solid residue. S2. Capture and absorb the hydrogen fluoride gas produced in step S1 to obtain sodium fluoride product. This absorption process also produces tail gas containing carbon dioxide. S3. Collect and process the carbon dioxide-containing tail gas generated during the reaction to obtain a sodium carbonate solution, and further precipitate sodium carbonate solid by cooling. S4. Post-process the solid residue after the reaction in step S1 to obtain solid byproducts.

[0008] Furthermore, in step S1, the pretreated calcium fluoride sludge needs to be mixed with concentrated sulfuric acid at a mass ratio of 1:(2-5) and stirred and reacted under sealed conditions at 160-240℃ for 2-3 hours. The pretreatment of the calcium fluoride sludge needs to be dried until the moisture content is less than 10% and crushed to a particle size of 50-160μm.

[0009] Furthermore, in step S2, sodium carbonate solution is used to absorb hydrogen fluoride gas, and sodium carbonate is cooled to 5-10°C to crystallize sodium fluoride from the absorption liquid. The sodium carbonate solution is a saturated solution.

[0010] Furthermore, in step S3, a sodium hydroxide solution is used to absorb the carbon dioxide-containing tail gas, and the mass fraction of the sodium hydroxide solution is 10%-30%.

[0011] Furthermore, the post-processing in step S4 includes washing and drying the solid residue, wherein washing is done by washing with water until neutral, and drying is done by drying at 105°C.

[0012] Due to the adoption of the above technical solution, the beneficial effects of the method for preparing sodium fluoride from calcium fluoride sludge according to the present invention are as follows: 1. It achieves the harmless treatment of calcium fluoride sludge, converting harmful fluoride-containing sludge into high-purity sodium fluoride and gypsum, thus realizing the resource utilization of fluoride-containing waste; 2. After effective treatment, the exhaust gas is recovered to obtain sodium carbonate solid, which can be reused in the hydrogen fluoride absorption process, reducing production costs while avoiding secondary pollution. 3. The process is simple, resource utilization is high, and it is environmentally friendly. The recovered sodium fluoride can be used as a raw material for fluorochemicals, effectively alleviating the shortage of fluorite resources and providing a new solution for the treatment of calcium fluoride sludge, with broad application prospects. Attached Figure Description

[0013] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 The image shows the XRD pattern of the sodium fluoride product obtained in an example of a method for preparing sodium fluoride from calcium fluoride sludge according to the present invention.

[0014] Figure 2 This is an EDS spectrum of the sodium fluoride product obtained in an example of a method for preparing sodium fluoride from calcium fluoride sludge according to the present invention. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] This invention provides a method for preparing sodium fluoride from calcium fluoride sludge. Specifically, the fluoride-containing sludge is dried in an oven, crushed, and sieved to obtain pretreated raw material A. A certain amount of A is taken and mixed with a certain amount of concentrated sulfuric acid in a certain proportion to obtain a mixed slurry B. A certain amount of B is placed in a corrosion-resistant reaction device for thermochemical conversion to obtain a mixed gaseous product C and a solid product D. The gaseous product C is discharged and absorbed and converted through a gas phase capture system to obtain sodium fluoride product and residual tail gas E. Gas E is introduced into a tail gas absorption device, cooled, and crystallized to obtain solid sodium carbonate. The residual solid product D is taken out from the reaction vessel, thoroughly washed, and dried to obtain gypsum solid by-product, which can be used in the building cement industry.

[0017] Includes the following steps: Step 1: Dry the fluoride-containing sludge at 105℃ to constant weight or with a moisture content of less than 10%, then crush and sieve to control the particle size to 50-160μm, to obtain uniformly sized dried powder A.

[0018] Step 2: Mix the powder A obtained in Step 1 with concentrated sulfuric acid with a mass fraction of ≥96% at a mass ratio of 1:(2~5), stir evenly, and obtain mixed slurry B.

[0019] Step 3: Add the mixed slurry B to the corrosion-resistant reaction apparatus, heat it in an oil bath, and seal it for 2-3 hours at 160-240℃. During the reaction, a mixed gaseous product C and a solid residue D are obtained. The main reaction equation is: CaF₂ + H₂SO₄ → 2HF + CaSO₄ CaCO3 + H2SO4 → CaSO4 + H2O + CO2 Step 4: The mixed gas product C (mainly HF and CO2) generated in Step 3 is introduced into a gas phase trapping device and absorbed by a saturated sodium carbonate solution to obtain sodium fluoride product and tail gas E. The main reaction equation is as follows: HF + Na₂CO₃ → NaF + H₂O + CO₂ Step 5: The exhaust gas E generated in Step 4 is introduced into an exhaust gas collection device and absorbed by a 10%~30% sodium hydroxide solution. The mixture is then cooled to 5~10℃ to crystallize and obtain solid sodium carbonate. The main reaction equation is: 2NaOH + CO2 → Na2CO3 + H2O Step 6: Remove the solid residue D from the reaction apparatus after the reaction in Step 3, wash it with water until neutral, and dry it at 105°C to obtain a byproduct whose main component is calcium sulfate (gypsum), which can be used in building materials and other fields.

[0020] Example 1 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 200-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 160℃ for 2 hours. The generated gas was introduced into a gas-phase collection and conversion system, where hydrogen fluoride was absorbed by a saturated sodium carbonate solution and the tail gas was absorbed by a 15wt% sodium hydroxide solution, yielding 81.07g of sodium fluoride product with a purity of 98.63% and a yield of 83.66%. The remaining solid residue after pyrolysis was washed and dried to obtain 166.01g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 204.65g of sodium carbonate solid.

[0021] Example 2 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 200-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 180℃ for 2 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 83.22g of sodium fluoride product with a purity of 98.77%, a yield of 85.88%. The remaining solid residue after pyrolysis was washed and dried to obtain 170.40g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 210.08g of sodium carbonate solid.

[0022] Example 3 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 100-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 200℃ for 2 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 85.07g of sodium fluoride product with a purity of 99.02%, a yield of 87.79%. The remaining solid residue after pyrolysis was washed and dried to obtain 174.19g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 214.75g of sodium carbonate solid.

[0023] Example 4 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 100-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 2 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 86.13g of sodium fluoride product with a purity of 99.05%, a yield of 88.89%. The remaining solid residue after pyrolysis was washed and dried to obtain 176.36g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 217.43g of sodium carbonate solid.

[0024] Example 5 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 100-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 240℃ for 2 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 86.15g of sodium fluoride product with a purity of 99.05%, a yield of 88.91%. The remaining solid residue after pyrolysis was washed and dried to obtain 176.40g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 217.48g of sodium carbonate solid.

[0025] Example 6 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 100-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:2. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 2 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 83.24g of sodium fluoride product with a purity of 99.01%, a yield of 85.90%. The remaining solid residue after pyrolysis was washed and dried to obtain 170.44g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 210.13g of sodium carbonate solid.

[0026] Example 7 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 100-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:4. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 2 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 86.18g of sodium fluoride product with a purity of 99.31%, a yield of 88.93%. The remaining solid residue after pyrolysis was washed and dried to obtain 176.46g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 217.55g of sodium carbonate solid.

[0027] Example 8 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 200-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 2 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 86.24g of sodium fluoride product with a purity of 99.31%, a yield of 89.00%. The remaining solid residue after pyrolysis was washed and dried to obtain 176.59g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 217.71g of sodium carbonate solid.

[0028] Example 9 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 300-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 2 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 86.51g of sodium fluoride product with a purity of 99.54%, a yield of 89.28%. The remaining solid residue after pyrolysis was washed and dried to obtain 177.14g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 218.39g of sodium carbonate solid.

[0029] Example 10 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 300-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 2.5h. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 87.29g of sodium fluoride product with a purity of 99.51%, a yield of 90.08%. The remaining solid residue after pyrolysis was washed and dried to obtain 178.74g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 220.36g of sodium carbonate solid.

[0030] Example 11 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 300-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 3 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 88.56g of sodium fluoride product with a purity of 99.53%, a yield of 91.39%. The remaining solid residue after pyrolysis was washed and dried to obtain 181.34g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 223.56g of sodium carbonate solid.

[0031] Example 12 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 130℃ to a moisture content of 8%, then pulverized and sieved through a 300-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 3 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 88.61g of sodium fluoride product with a purity of 99.61%, a yield of 91.44%. The remaining solid residue after pyrolysis was washed and dried to obtain 181.44g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 223.69g of sodium carbonate solid.

[0032] Example 13 100g of fluoride-containing sludge A (calcium fluoride content 60%, calcium carbonate content 37%) was dried at 150℃ to a moisture content of 6%, then pulverized and sieved through a 300-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 3 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 88.53g of sodium fluoride product with a purity of 99.59%, a yield of 91.36%. The remaining solid residue after pyrolysis was washed and dried to obtain 181.28g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 223.49g of sodium carbonate solid.

[0033] Example 14 100g of fluoride-containing sludge B (calcium fluoride content 65%, calcium carbonate content 32%) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 300-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 3 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 89.56g of sodium fluoride product with a purity of 99.71%, a yield of 92.43%. The remaining solid residue after pyrolysis was washed and dried to obtain 177.24g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 226.09g of sodium carbonate solid.

[0034] Example 15 100g of fluoride-containing sludge C (70% calcium fluoride, 28% calcium carbonate) was dried at 110℃ to a moisture content of 10%, then pulverized and sieved through a 300-mesh sieve. The pretreated raw material was mixed with concentrated sulfuric acid at a solid-liquid ratio of 1:3. The mixed slurry was placed in a corrosion-resistant reaction vessel and heat-treated at 220℃ for 3 hours. The generated gas was discharged from the exhaust port into a gas phase capture and conversion system. Hydrogen fluoride was absorbed by a saturated sodium carbonate solution to obtain 90.48g of sodium fluoride product with a purity of 99.69%, a yield of 93.37%. The remaining solid residue after pyrolysis was washed and dried to obtain 179.13g of gypsum material. The tail gas absorption liquid was crystallized at 5℃ to obtain 228.41g of sodium carbonate solid.

[0035] The present invention and its embodiments have been described above. This description is not restrictive. In short, if a person skilled in the art is inspired by this description and designs a similar structure and embodiment without departing from the spirit of the present invention, such design should fall within the protection scope of the present invention.

Claims

1. A method for preparing sodium fluoride using calcium fluoride sludge, comprising the following steps: S1. The pretreated calcium fluoride sludge is mixed with concentrated sulfuric acid in a corrosion-resistant reactor to carry out a thermochemical conversion reaction, generating a mixed gas of hydrogen fluoride and carbon dioxide and solid residue. S2. Capture and absorb the hydrogen fluoride gas produced in step S1 to obtain sodium fluoride product. This absorption process also produces tail gas containing carbon dioxide. S3. Collect and process the carbon dioxide-containing tail gas generated during the reaction to obtain a sodium carbonate solution, and further precipitate sodium carbonate solid by cooling. S4. Post-process the solid residue after the reaction in step S1 to obtain solid byproducts.

2. The method for preparing sodium fluoride from calcium fluoride sludge according to claim 1, characterized in that: In step S1, the pretreated calcium fluoride sludge needs to be mixed with concentrated sulfuric acid at a mass ratio of 1:(2-5) and stirred for 2-3 hours under sealed conditions at 160-240℃. The pretreated calcium fluoride sludge needs to be dried until the moisture content is less than 10% and crushed to a particle size of 50-160μm.

3. The method for preparing sodium fluoride from calcium fluoride sludge according to claim 1, characterized in that: In step S2, sodium carbonate solution is used to absorb hydrogen fluoride gas. Sodium carbonate is then cooled to 5-10°C to crystallize sodium fluoride from the absorbent solution. The sodium carbonate solution is a saturated solution.

4. The method for preparing sodium fluoride from calcium fluoride sludge according to claim 1, characterized in that: In step S3, sodium hydroxide solution is used to absorb the carbon dioxide-containing tail gas, and the mass fraction of the sodium hydroxide solution is 10%-30%.

5. The method for preparing sodium fluoride from calcium fluoride sludge according to claim 1, characterized in that: The post-processing in step S4 includes washing and drying the solid residue, wherein washing is done by washing with water until neutral, and drying is done by drying at 105°C.

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