Resource recycling process of sodium hydrogenfluoride mother liquor by-product

Abstract

The invention discloses a resource recycling process of a sodium hydrogenfluoride mother liquor byproduct, and belongs to the technical field of fluorine chemical industry waste liquid treatment. The process comprises the following three steps: firstly, preparing a sodium fluoride crystal by regulating the molar ratio of Na to F to be (1.05-1.08): 1, optimizing a feeding mode and adding a seed crystal; secondly, regulating the molar ratio of F to Si to be (6-9): 1 by using the sodium fluoride mother liquor, and adding white carbon black to prepare sodium fluosilicate; and finally, treating the F-containing waste liquid by compounding quick lime and slaked lime, regulating the molar ratio of Ca to F to be (2.1-2.5): 1, and reacting for 1-2 hours under the conditions of 50-70 DEG C and 300-400 r / min, so that the F content in the wastewater is less than or equal to 10 mg / L and the ammonia nitrogen content is less than or equal to 15 mg / L. According to the process, the total fluorine recovery rate is larger than or equal to 99%, the silicon recovery rate is larger than or equal to 95%, the main content of prepared sodium fluoride is larger than or equal to 98%, the main content of sodium fluosilicate is larger than or equal to 98%, and efficient resource utilization of sodium hydrogenfluoride mother liquor byproducts is achieved.

Description

Technical Field

[0001] This invention belongs to the field of hydrofluoric acid production, specifically relating to a resource recovery process for sodium hydrogen fluoride mother liquor byproducts. Background Technology

[0002] Fluorosilicic acid is an important byproduct of industries such as phosphate fertilizer and hydrofluoric acid production. Its resource utilization can not only reduce environmental pollution but also create significant economic benefits. Currently, the process of producing hydrofluoric acid from fluorosilicic acid is widely used in industrial production, but the treatment of the fluorine-containing mother liquor, a byproduct of the sodium hydrogen fluoride process in this production system, has always been a technical challenge for the industry.

[0003] In the production process of hydrofluoric acid from fluorosilicic acid, the sodium bifluoride synthesis unit generates a large amount of by-product mother liquor containing fluorine, ammonia, and silicon. The fluoride ion concentration in these mother liquors is typically 150-250 g / L, and the ammonia nitrogen concentration is 100-200 g / L. Direct discharge of these mother liquors would not only cause serious environmental pollution but also result in a waste of approximately 130-230 kg of fluorine resources per ton of mother liquor.

[0004] In existing technologies, the treatment of sodium bifluoride mother liquor and its derivatives, which are byproducts of the hydrofluoric acid production process from fluorosilicic acid, mainly focuses on the following aspects:

[0005] A common method is to react fluorosilicic acid with sodium fluoride to produce sodium fluorosilicate. For example, CN117361572A discloses a method for recycling sodium fluorosilicate waste residue, a byproduct of the new energy industry. This method involves treating the waste residue through secondary acid leaching, washing and filtration, vacuum separation, and alkaline desilication to ultimately obtain high-purity sodium fluoride. While this method achieves effective utilization of byproduct resources, the process is complex and fails to provide a solution for the ammonia nitrogen problem in the mother liquor.

[0006] Another technical approach is to directly prepare sodium hydrogen fluoride using fluorosilicic acid. CN106241834B discloses a technology for preparing sodium hydrogen fluoride using fluorosilicic acid, a byproduct of phosphorus chemical industry. This technology achieves the preparation of sodium hydrogen fluoride through steps such as the reaction of fluorosilicic acid with sodium fluoride, the reaction of low-concentration hydrofluoric acid with sodium fluoride, and the reaction of sodium fluorosilicate with sodium carbonate. However, this method fails to effectively solve the problem of comprehensive recovery of fluorine resources from the mother liquor, resulting in low resource utilization.

[0007] CN106348248B proposes a method for preparing hydrogen fluoride and sodium fluoride from fluorosilicic acid. This method involves reacting fluorosilicic acid with ammonium hydrogen fluoride, ammonium fluorosilicate with ammonia, and ammonium hydrogen fluoride with sodium carbonate to achieve the preparation of hydrogen fluoride and sodium fluoride. While this method utilizes readily available and low-cost raw materials, the process is relatively complex and requires high-quality equipment.

[0008] Regarding the resource utilization of fluorosilicic acid, CN104326475B discloses a method for preparing potassium fluoride and co-producing silica using fluorosilicic acid. This method solves the problem of impurity accumulation in the raw fluorosilicic acid solution through stepwise alkaline hydrolysis and mother liquor purification processes. While this method achieves high-quality utilization of fluorine and silicon resources, it fails to provide a direct solution for the treatment of the mother liquor produced as a byproduct of hydrofluoric acid production from fluorosilicic acid.

[0009] CN109179330B proposes a wet-process technology for producing anhydrous hydrogen fluoride and zeolite molecular sieves from sodium fluorosilicate, a byproduct of phosphoric acid production. This technology achieves the preparation of anhydrous hydrogen fluoride and the co-production of zeolite molecular sieves through steps such as the reaction of sodium fluorosilicate with sodium hydroxide and the reaction of sodium fluoride with lime slurry. While this process effectively utilizes sodium fluorosilicate, a byproduct of phosphoric acid production, it fails to provide a solution to the ammonia nitrogen problem in the mother liquor from the hydrofluoric acid production process.

[0010] The existing technologies have the following shortcomings: First, when treating fluoride wastewater using the traditional lime precipitation method, improper control of the fluoride-to-calcium ratio can easily lead to a calcium fluoride purity of less than 90%, and the fluoride content in the wastewater is difficult to stably reduce to below 20 mg / L. Second, existing technologies mostly use a single precipitation or neutralization process to treat the mother liquor, lacking a systematic resource recovery plan, resulting in treatment costs as high as 800-1200 yuan / ton, and a resource utilization rate of less than 60%. In addition, existing technologies fail to simultaneously solve the problems of fluoride resource recovery and ammonia nitrogen pollutant treatment in the mother liquor, making it difficult to achieve a balance between economic and environmental benefits.

[0011] Therefore, there is an urgent need to develop a resource-based treatment process that can efficiently recover valuable elements such as fluorine and silicon from the impurity-containing mother liquor of the sodium fluoride synthesis unit in the fluorosilicic acid to hydrofluoric acid production system, while simultaneously solving the ammonia nitrogen pollution problem, so as to achieve efficient resource utilization and effective environmental protection. Summary of the Invention

[0012] To address the technical challenges of wasting fluorine resources in the byproduct mother liquor of the sodium bifluoride synthesis unit in the fluorosilicic acid production system, excessive pollutant emissions, low purity and difficulty in consistently meeting standards under traditional treatment methods, and the lack of a systematic resource recovery solution in existing technologies, this invention provides a resource recovery process for sodium bifluoride mother liquor byproducts. This process aims to achieve efficient fluoride resource recovery, reduced treatment costs, ensure wastewater discharge compliance, and increase product added value.

[0013] The technical solution adopted by this invention to solve its technical problem is: to provide a resource recovery process for sodium bifluoride mother liquor byproducts, including the following steps:

[0014] (1) Sodium fluoride preparation: Sodium hydrogen fluoride mother liquor is used as raw material, hydrogen hydroxide solution is added, the reaction is stirred until complete, ammonia is evaporated by heating, and slurry is obtained after cooling. The slurry is filtered to obtain sodium fluoride crystals and sodium fluoride mother liquor.

[0015] NH4F + NaOH → NaF + NH3 + H2O (1)

[0016] (2) Preparation of sodium fluorosilicate: Using the sodium fluoride mother liquor from step (1) as raw material, add silica and fluorosilicic acid solution, filter, and obtain sodium fluorosilicate and F-containing waste liquid;

[0017] 6NaF+2H2SiF6+SiO2→3Na2SiF6+H2O (2)

[0018] (3) Treatment of F-containing waste liquid: Add quicklime and hydrated lime to the F-containing waste liquid, stir and react completely, and then separate after sedimentation to obtain calcium fluoride and qualified wastewater for discharge.

[0019] Further, in step (1), the amount of sodium hydroxide added is: the Na:F molar ratio is 1.05 to 1.08:1, and the concentration of the sodium hydroxide solution is 20 to 50 wt%.

[0020] Furthermore, the specific process of step (1) is as follows:

[0021] ① Use all the sodium bifluoride mother liquor as a base, and then add sodium hydroxide solution dropwise; or use part of the sodium bifluoride mother liquor as a base, and then add the remaining sodium bifluoride mother liquor and sodium hydroxide solution dropwise.

[0022] ② Use the slurry or sodium fluoride mother liquor obtained in the previous step (1) as a base, and simultaneously add the sodium hydrogen fluoride mother liquor and sodium hydroxide solution to be treated.

[0023] Furthermore, in step (1), the temperature for ammonia stripping is 70–95°C, and the stripping time is 1–3 hours.

[0024] Furthermore, in step (2), the amount of silica added is calculated using the following formula:

[0025]

[0026] Among them, C F The concentration of mother liquor F (g / L), C SiO2 V represents the concentration of silica in the mother liquor (g / L). 母液 denoted as the volume of sodium fluoride mother liquor (L), m as the mass of added silica (g), and R as the F:Si molar ratio.

[0027] Furthermore, in step (2), the amount of fluorosilicic acid solution added is calculated using the following formula:

[0028]

[0029] Among them, C F The concentration of F in the sodium bifluoride mother liquor is (g / L), V 母液M is the volume of sodium bifluoride mother liquor (L). H2SiF6 W represents the relative molecular mass of fluorosilicic acid. H2SiF6 The mass concentration of the fluorosilicic acid solution is 15–20 wt%, m H2SiF6 The amount (g) of fluorosilicic acid solution added.

[0030] Furthermore, quicklime and hydrated lime are mixed to achieve a Ca:F molar ratio of 2.0–2.5:1. When the fluoride concentration in the F-containing wastewater is ≥0.5 g / L, quicklime accounts for 55–65 wt% of the total quicklime and hydrated lime; when the fluoride concentration in the F-containing wastewater is <0.5 g / L, quicklime accounts for 25–35 wt% of the total quicklime and hydrated lime.

[0031] Furthermore, the reaction conditions for step (3) are: temperature 50-70℃, stirring speed 300-400r / min, reaction time 1-2h, so that the F content in the wastewater is ≤10mg / L and the ammonia nitrogen is ≤15mg / L.

[0032] The beneficial effects of this invention are as follows:

[0033] (1) High resource recovery efficiency: By optimizing the Na:F molar ratio and feeding method, 300-442 kg of sodium fluoride can be recovered per ton of mother liquor, with a purity of over 98%; by adjusting the F:Si molar ratio, 105-145 kg of sodium fluorosilicate can be recovered per ton of mother liquor, with a purity of over 98%; the overall fluorine resource recovery rate reaches 99%, which is significantly higher than the 60% recovery rate of existing technologies;

[0034] (2) Significantly reduced processing costs: Compared with the traditional process with a processing cost of 800-1200 yuan / ton, the processing cost of the present invention is reduced to 450-600 yuan / ton, a reduction of 40%, resulting in significant economic benefits;

[0035] (3) Environmental protection indicators are stably met: Through the optimization of the quicklime and hydrated lime compound system and the Ca:F molar ratio, the fluoride content in wastewater is stably controlled at 8-10 mg / L and the ammonia nitrogen content is ≤15 mg / L, which meets the first-class standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996) and solves the problem that the traditional lime precipitation method is difficult to achieve stable compliance.

[0036] (4) High added value of products: The recovered sodium fluoride can be recycled as raw material for the production of sodium hydrogen fluoride, and sodium fluorosilicate can be used in the enamel industry. Based on the scale of mother liquor treatment per 10,000 tons, the annual output value can be increased by about RMB 5 million to RMB 8 million, achieving the dual goals of waste resource utilization and economic benefits. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] A resource recovery process for sodium bifluoride mother liquor byproducts, such as... Figure 1 As shown, it includes the following steps:

[0041] (1) Sodium fluoride preparation: Sodium fluoride crystals were prepared by adjusting the Na:F molar ratio and feeding method using sodium hydrogen fluoride mother liquor containing impurities as raw material;

[0042] Take 600 mL of mother liquor from the hydrofluoric acid production process of fluorosilicic acid, with a sulfur dioxide (F) content of 216.71 g / L. Set the Na:F molar ratio to 1.07:1 and add 732.3 g of a 40 wt% sodium hydroxide solution.

[0043] A sodium fluoride mother liquor was added as a base, with all 600 mL of the mother liquor added to the reactor. The mixture was stirred at 200 rpm at room temperature, while a 40 wt% sodium hydroxide solution was added dropwise at 8 mL / min. After the reaction continued for 1 hour, the temperature was raised to 90°C for ammonia stripping, and stirring continued. The ammonia stripping process lasted 1.5 hours. After cooling, a sodium fluoride slurry was obtained. Filtration separated the slurry into sodium fluoride ointment and the sodium fluoride mother liquor. The ointment was dried to obtain sodium fluoride crystals.

[0044] The obtained sodium fluoride crystals had a main content of 98.7% and an average crystal size of 36.4 μm. The F concentration in the mother liquor decreased to 14.58 g / L, and the Na... + The concentration was 38 g / L, the NH3 content decreased to 0.5 g / L, and the silica content was 0.32%. The fluorine recovery rate in this step reached 93.3%. Compared with the method of feeding Na:F at a molar ratio of 1:1, the purity of sodium fluoride was increased by 6.3%, while maintaining a high fluorine recovery efficiency.

[0045] (2) Preparation of sodium fluorosilicate: Using the sodium fluoride mother liquor from step (1) as raw material, add silica and fluorosilicic acid, filter, and obtain sodium fluorosilicate and F-containing waste liquid;

[0046] Take 600 mL of the sodium fluoride mother liquor obtained in step (1) above, and analyze it. The F content is 14.58 g / L and the silica content is 4 g / L. Set the F:Si molar ratio R to 7:1, and calculate the amount of silica to be added according to formula (1-1) as 1.54 g. Calculate the amount of 18% fluorosilicic acid solution to be added according to formula (1-2) to adjust the pH value and F:Si ratio of the reaction system.

[0047] Add silica to a fluorosilicic acid solution as a base, then add sodium fluoride mother liquor dropwise over a period of 1 hour with continuous stirring. After the addition is complete, continue the reaction at room temperature for 2 hours. After the reaction is complete, filter to separate sodium fluorosilicate ointment and waste liquid. Dry the ointment to obtain sodium fluorosilicate crystals.

[0048] The obtained sodium fluorosilicate crystals achieved a main content of 99.58% and an average crystal particle size of 28 μm. The fluorine (F) content in the waste liquid decreased to 0.62 g / L. The silicon recovery rate reached 94.8%, and the fluorine recovery rate reached 96.3% in this step.

[0049] (3) Treatment of F-containing waste liquid: By mixing quicklime and slaked lime, the Ca:F molar ratio is adjusted so that the wastewater meets the discharge standards.

[0050] Take 3L of the waste liquid obtained in step (2) above, in which the F content is 0.62g / L and the ammonia nitrogen content is 0.5g / L. Set the Ca:F molar ratio to be 2.2:1. Since the F content of the waste liquid is >0.5g / L, according to the process requirements, the proportion of quicklime can be higher than 30%. Here, the proportion of quicklime is selected to be 60%, that is, the amount of quicklime used is 7.24g and the amount of hydrated lime used is 6.37g.

[0051] Quicklime and hydrated lime were mixed and added to the waste liquid, and reacted at 60℃ and 350 r / min for 1.5 hours. After the reaction was completed, the mixture was allowed to stand for 2 hours to separate calcium fluoride precipitate and the treated wastewater.

[0052] The obtained calcium fluoride had a purity of 97.5%. The treated wastewater contained 8.2 mg / L of sulfur dioxide (F), 9.5 mg / L of ammonia nitrogen, and had a pH of 7.8, meeting the discharge standards (F ≤ 10 mg / L, ammonia nitrogen ≤ 15 mg / L). The fluoride recovery rate in this step reached 98.6%, and the total fluoride recovery rate of the entire process reached 99.9%.

[0053] Example 2

[0054] A resource recovery process for sodium bifluoride mother liquor byproducts, such as... Figure 1 As shown, it includes the following steps:

[0055] (1) Sodium fluoride preparation: Sodium fluoride crystals were prepared by adjusting the Na:F molar ratio and feeding method using sodium hydrogen fluoride mother liquor containing impurities as raw material;

[0056] Take 600 mL of mother liquor from the hydrofluoric acid production process of fluorosilicic acid, with a sulfur dioxide (F) content of 216.71 g / L. Set the Na:F molar ratio to 1.06:1 and add 725.4 g of a 40 wt% sodium hydroxide solution.

[0057] A partial sodium bifluoride mother liquor was used as a pre-treatment feed. 120 mL of mother liquor (20 wt% solid content) was added to the reactor as a pre-treatment solution, while solid sodium fluoride from the mother liquor served as seed crystals. The mixture was stirred at 200 rpm at room temperature. Simultaneously, the remaining 480 mL of mother liquor and a 40 wt% sodium hydroxide solution were added dropwise. After the reaction continued for 1 hour, the temperature was raised to 90°C for ammonia stripping, with continued stirring. The ammonia stripping process lasted 1.5 hours. After cooling, a sodium fluoride slurry was obtained. Filtration separated the slurry into sodium fluoride ointment and sodium fluoride mother liquor. The ointment was dried to obtain sodium fluoride crystals.

[0058] The obtained sodium fluoride crystals had a main content of 98.3% and an average crystal size of 36 μm. The F content in the mother liquor decreased to 17.53 g / L, and the Na content decreased to... + The concentration was 40 g / L, the NH3 concentration decreased to 0.8 g / L, and the silica concentration was 0.35%. The fluorine recovery rate in this step reached 91.8%.

[0059] (2) Preparation of sodium fluorosilicate: Using the sodium fluoride mother liquor from step (1) as raw material, add silica and fluorosilicic acid, filter, and obtain sodium fluorosilicate and F-containing waste liquid;

[0060] Take 600 mL of the sodium fluoride mother liquor obtained in step (1) above, and analyze it. The F content is 17.53 g / L and the silica content is 3.73 g / L. Set the F:Si molar ratio R to 6:1, and calculate the amount of silica to be added according to formula (1-1) as 3.29 g. Calculate the amount of 18% fluorosilicic acid solution to be added according to formula (1-2) as 147.6 g to adjust the pH value and F:Si ratio of the reaction system.

[0061] Add silica to a fluorosilicic acid solution as a base, then add sodium fluoride mother liquor dropwise over a period of 1 hour with continuous stirring. After the addition is complete, continue the reaction at room temperature for 2 hours. After the reaction is complete, filter to separate sodium fluorosilicate ointment and waste liquid. Dry the ointment to obtain sodium fluorosilicate crystals.

[0062] The obtained sodium fluorosilicate crystals achieved a main content of 99.2% and an average crystal particle size of 32 μm. The fluorine (F) content in the waste liquid decreased to 0.61 g / L. The silicon recovery rate reached 96.56%, and the fluorine recovery rate reached 96.2% in this step.

[0063] (3) Treatment of F-containing waste liquid: By mixing quicklime and slaked lime, the Ca:F molar ratio is adjusted so that the wastewater meets the discharge standards.

[0064] Take 3L of the waste liquid obtained in step (2) above, in which the F content is 0.61g / L and the ammonia nitrogen content is 0.8g / L. Set the Ca:F molar ratio to be 2.3:1. Since the F content of the waste liquid is >0.5g / L, according to the process requirements, the proportion of quicklime can be higher than 30%. Here, the proportion of quicklime is selected to be 60%, that is, the amount of quicklime used is 7.45g and the amount of hydrated lime used is 6.56g.

[0065] Quicklime and hydrated lime were mixed and added to the waste liquid, and reacted at 60℃ and 350 r / min for 1.5 hours. After the reaction was completed, the mixture was allowed to stand for 2 hours to separate calcium fluoride precipitate and the treated wastewater.

[0066] The obtained calcium fluoride had a purity of 97.2%. The treated wastewater contained 8.5 mg / L of sulfur dioxide and 8.8 mg / L of ammonia nitrogen, with a pH of 7.6, meeting emission standards. The fluoride recovery rate in this step reached 98.6%, and the overall fluoride recovery rate for the entire process reached 99.9%.

[0067] Example 3

[0068] A resource recovery process for sodium bifluoride mother liquor byproducts, such as... Figure 1 As shown, it includes the following steps:

[0069] (1) Sodium fluoride preparation: Sodium fluoride crystals were prepared by using sodium hydrogen fluoride mother liquor containing impurities as raw material and by adjusting the Na:F molar ratio, feeding method and seed crystal addition.

[0070] Take 600 mL of mother liquor from the hydrofluoric acid production process of fluorosilicic acid, with a sulfur dioxide (F) content of 216.71 g / L. Set the Na:F molar ratio to be 1.07:1. When calculating the required amount of NaOH, the Na content in the initial 120 mL sodium fluoride mother liquor must be considered. + To achieve a concentration of 40 g / L, add 720 g of a 40 wt% sodium hydroxide solution.

[0071] The sodium fluoride mother liquor obtained from the previous step (1) was used as a base for the feeding method. The mixture was stirred at 200 r / min at room temperature. Simultaneously, 600 mL of the mother liquor and a 40 wt% sodium hydroxide solution were added dropwise. After the reaction continued for 1.5 hours, the temperature was raised to 90℃ for ammonia stripping, and stirring continued. The ammonia stripping process lasted for 1.5 hours. After standing and cooling, a sodium fluoride slurry was obtained. Filtration separated the sodium fluoride ointment and the sodium fluoride mother liquor. The ointment was dried to obtain sodium fluoride crystals.

[0072] The obtained sodium fluoride crystals achieved a main content of 99.3% and an average particle size of 80 μm. The F content in the mother liquor decreased to 13.46 g / L, the Na+ concentration to 35 g / L, the NH3 content to 0.5 g / L, and the silica content to 0.27%. The fluorine recovery rate in this step reached 93.2%.

[0073] (2) Preparation of sodium fluorosilicate: Using the sodium fluoride mother liquor from step (1) as raw material, add silica and fluorosilicic acid, filter, and obtain sodium fluorosilicate and F-containing waste liquid;

[0074] Take 600 mL of the sodium fluoride mother liquor obtained in step (1) above, and analyze it. The F content is 13.46 g / L and the silica content is 3.71 g / L. Set the F:Si molar ratio R to 7:1, and calculate the amount of silica to be added according to formula (1-1) as 1.42 g. Calculate the amount of 18% fluorosilicic acid solution to be added according to formula (1-2) to adjust the pH value and F:Si ratio of the reaction system.

[0075] Silica was added to a fluorosilicic acid solution, and sodium fluoride mother liquor was added dropwise over a period of 1 hour with continuous stirring. After the addition was complete, the reaction continued at room temperature for 2 hours. After the reaction was complete, the mixture was filtered to separate sodium fluorosilicate ointment and waste liquid. The ointment was dried to obtain sodium fluorosilicate crystals.

[0076] The obtained sodium fluorosilicate crystals achieved a main content of 99.0% and an average particle size of 33 μm. The fluorine (F) content in the waste liquid decreased to 0.49 g / L. The silicon recovery rate reached 98.5%, and the fluorine recovery rate reached 97.1% in this step.

[0077] (3) Treatment of F-containing waste liquid: By mixing quicklime and slaked lime, the Ca:F molar ratio is adjusted so that the wastewater meets the discharge standards.

[0078] Take 3L of the waste liquid obtained in step (2) above, in which the F content is 0.49g / L and the ammonia nitrogen content is 0.6g / L. Set the Ca:F molar ratio to 2.1:1. Since the F content of the waste liquid is <0.5g / L, select quicklime with a proportion of 30%, that is, the amount of quicklime used is 2.72g and the amount of hydrated lime used is 8.42g.

[0079] Quicklime and hydrated lime were mixed and added to the waste liquid, and reacted at 60℃ and 350 r / min for 1.5 hours. After the reaction was completed, the mixture was allowed to stand for 2 hours to separate calcium fluoride precipitate and the treated wastewater.

[0080] The obtained calcium fluoride has a purity of 98.0%. The treated wastewater has a sulfur (F) content of 6.8 mg / L, an ammonia nitrogen content of 7.5 mg / L, and a pH of 7.5, meeting the discharge standards. The fluoride recovery rate in this step reaches 98.5%, and the total fluoride recovery rate of the entire process reaches 99.9%.

[0081] Example 4

[0082] A resource recovery process for sodium bifluoride mother liquor byproducts, such as... Figure 1 As shown, it includes the following steps:

[0083] (1) Sodium fluoride preparation: Sodium fluoride crystals were prepared by using sodium hydrogen fluoride mother liquor containing impurities as raw material and by adjusting the Na:F molar ratio, feeding method and seed crystal addition.

[0084] Take 600 mL of mother liquor from the hydrofluoric acid production process of fluorosilicic acid, with a sulfur dioxide (F) content of 216.71 g / L. Set the Na:F molar ratio to 1.06:1. When calculating the required amount of NaOH, the amount of Na that has not been converted to sodium fluoride in the initial 120 mL sodium fluoride slurry must be considered. + The content (35g / L) was calculated, and 715g of 40wt% sodium hydroxide solution was actually added.

[0085] The sodium fluoride slurry prepared in step (1) of Example 3 was added as a base, with sodium fluoride crystals (average particle size of 80 μm) in the slurry serving as seed crystals (solid content of 10 wt%). At room temperature, the mixture was stirred at 200 r / min while 600 mL of mother liquor and a 40 wt% sodium hydroxide solution were added dropwise. After the reaction continued for 1.5 hours, the temperature was raised to 90 °C for ammonia stripping, and stirring continued. The ammonia stripping process lasted for 1.5 hours. After standing and cooling, a sodium fluoride slurry was obtained. Filtration separated sodium fluoride ointment and sodium fluoride mother liquor. The ointment was dried to obtain sodium fluoride crystals.

[0086] The obtained sodium fluoride crystals had a main content of 98.9% and an average crystal size of 125 μm. The F content in the mother liquor decreased to 16.6 g / L, and the Na content decreased to... + The concentration was 35 g / L, the NH3 concentration decreased to 0.6 g / L, and the silica concentration was 0.30%. The fluorine recovery rate in this step reached 91.6%.

[0087] (2) Preparation of sodium fluorosilicate: Using the sodium fluoride mother liquor from step (1) as raw material, add silica and fluorosilicic acid, filter, and obtain sodium fluorosilicate and F-containing waste liquid;

[0088] Take 600 mL of the sodium fluoride mother liquor obtained in step (1) above and analyze it. The F content is 16.6 g / L and the silica content is 3.73 g / L.

[0089] The F:Si molar ratio R is set to 7:1. According to formula (1-1), the amount of silica to be added is 2.25g. According to formula (1-2), 139.8g of 18% fluorosilicic acid solution is added to adjust the pH value and F:Si ratio of the reaction system.

[0090] Silica was added to a fluorosilicic acid solution, and sodium fluoride mother liquor was added dropwise over a period of 1 hour with continuous stirring. After the addition was complete, the reaction continued at room temperature for 2 hours. After the reaction was complete, the mixture was filtered to separate sodium fluorosilicate ointment and waste liquid. The ointment was dried to obtain sodium fluorosilicate crystals.

[0091] The obtained sodium fluorosilicate crystals achieved a main content of 99.5% and an average particle size of 32 μm. The fluorine (F) content in the waste liquid was reduced to 0.62 g / L. The silicon recovery rate reached 98.8%, and the fluorine recovery rate reached 97.5% in this step.

[0092] (3) Treatment of F-containing waste liquid: By mixing quicklime and slaked lime, the Ca:F molar ratio is adjusted so that the wastewater meets the discharge standards.

[0093] Take 3L of the waste liquid obtained in step (2) above, in which the F content is 0.62g / L and the ammonia nitrogen content is 0.78g / L. Set the Ca:F molar ratio to be 2.2:1. Since the F content of the waste liquid is >0.5g / L, select quicklime with a proportion of 60%, that is, the amount of quicklime used is 7.2g and the amount of hydrated lime used is 6.4g.

[0094] Quicklime and hydrated lime were mixed and added to the waste liquid, and reacted at 60℃ and 350 r / min for 1.0 hour. After the reaction was completed, the mixture was allowed to stand for 2 hours to separate calcium fluoride precipitate and the treated wastewater.

[0095] The obtained calcium fluoride had a purity of 97.8%. The treated wastewater contained 8.8 mg / L of sulfur dioxide and 8.4 mg / L of ammonia nitrogen, with a pH of 7.5, meeting emission standards. The fluoride recovery rate in this step reached 98.4%, and the overall fluoride recovery rate for the entire process reached 99.9%.

[0096] Table 1 shows the quality test results of the sodium fluoride prepared in Examples 1 to 4.

[0097]

[0098]

[0099] As shown in Table 1, the sodium fluoride prepared in Examples 1 to 4 of this application all meet the first-class product standard.

[0100] Table 2 shows the quality test results of the sodium fluorosilicate prepared in Examples 1 to 4.

[0101]

[0102] As shown in Table 2, the sodium fluorosilicates prepared in Examples 1 to 4 of this application all meet the superior grade standard.

[0103] Table 3 shows the quality test results of the calcium fluoride prepared in Examples 1 to 4.

[0104]

[0105]

[0106] As shown in Table 3, the calcium fluoride prepared in Examples 1, 3 and 4 of this application all meet the qualified product standards.

[0107] It should be noted that Examples 1, 2, 3, and 4 are all methods for the resource recovery of sodium bifluoride mother liquor byproducts.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A resource recovery process for sodium bifluoride mother liquor byproducts, characterized in that, Includes the following steps: (1) Preparation of sodium fluoride: Using sodium hydrogen fluoride mother liquor as raw material, add hydrogen hydroxide solution, stir and react completely, heat to evaporate ammonia, cool to obtain slurry, filter the slurry to obtain sodium fluoride crystals and sodium fluoride mother liquor; NH4F+NaOH→NaF+NH3+H2O (1) (2) Preparation of sodium fluorosilicate: Using the sodium fluoride mother liquor from step (1) as raw material, add silica and fluorosilicic acid solution, filter, and obtain sodium fluorosilicate and F-containing waste liquid; 6NaF+2H2SiF6+SiO2→3Na2SiF6+H2O (2) (3) Treatment of F-containing waste liquid: Add quicklime and hydrated lime to the F-containing waste liquid, stir and react completely, and then separate after sedimentation to obtain calcium fluoride and qualified wastewater for discharge.

2. The resource recovery process for the sodium bifluoride mother liquor byproduct according to claim 1, characterized in that, In step (1), the amount of sodium hydroxide added is: the Na:F molar ratio is 1.05~1.08:1, and the concentration of the sodium hydroxide solution is 20~50wt%.

3. The resource recovery process for the sodium bifluoride mother liquor byproduct according to claim 1, characterized in that, The specific process of step (1) is as follows: use all sodium fluoride mother liquor as a base and add sodium hydroxide solution dropwise; or use part of sodium fluoride mother liquor as a base and add the remaining sodium fluoride mother liquor and sodium hydroxide solution dropwise; or use the slurry or sodium fluoride mother liquor obtained in the previous step (1) as a base and add the sodium fluoride mother liquor and sodium hydroxide solution to be treated dropwise.

4. The resource recovery process for the sodium bifluoride mother liquor byproduct according to claim 1, characterized in that, The ammonia stripping temperature is 70~95℃, and the stripping time is 1~3h.

5. The resource recovery process for the sodium bifluoride mother liquor byproduct according to claim 1, characterized in that, In step (2), the amount of silica is calculated using the following formula: Among them, C F The concentration of mother liquor F (g / L), C SiO2 The concentration of silica in the mother liquor (g / L), V 母液 denoted as the volume of sodium fluoride mother liquor (L), m as the mass of added silica (g), and R as the F:Si molar ratio.

6. The resource recovery process for the sodium bifluoride mother liquor byproduct according to claim 1, characterized in that, In step (2), the amount of fluorosilicic acid solution added is calculated using the following formula: Among them, C F The concentration of F in the sodium bifluoride mother liquor is (g / L), V 母液 M is the volume of sodium bifluoride mother liquor (L). H2SiF6 W represents the relative molecular mass of fluorosilicic acid. H2SiF6 The mass concentration of the fluorosilicic acid solution is 15~20wt%, m H2SiF6 The amount (g) of fluorosilicic acid solution added.

7. The resource recovery process for the sodium bifluoride mother liquor byproduct according to claim 1, characterized in that, Quicklime and hydrated lime are mixed to make the Ca:F molar ratio 2.0~2.5:

1. When the fluoride concentration in the waste liquid containing F is ≥0.5g / L, quicklime accounts for 55~65wt% of the total amount of quicklime and hydrated lime; when the fluoride concentration in the waste liquid containing F is <0.5g / L, quicklime accounts for 25~35wt% of the total amount of quicklime and hydrated lime.

8. The resource recovery process for the sodium bifluoride mother liquor byproduct according to claim 1, characterized in that, The reaction conditions for step (3) are: temperature 50~70℃, stirring speed 300~400r / min, reaction time 1~2h, so that the F content in the discharged wastewater meets the standards and is ≤10mg / L and ammonia nitrogen ≤15mg / L.

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