Recycling treatment method of fluorine-containing waste acid

Abstract

The invention provides a fluorine-containing waste acid resourceful treatment method, which is applied to the technical field of waste acid resourceful recovery, and specifically comprises the following steps: S1, adding a sodium source into fluorine-containing waste acid, fully reacting, and adjusting the pH value of the solution to 6-7; s2, carrying out heat preservation and aging on the adjusted solution in a continuous stirring state, and carrying out solid-liquid separation on the obtained turbid liquid to obtain a first solid matter and a primary mother solution; s3, collecting and drying the first solid matter to obtain a sodium fluoride product, adding a calcium source into the primary mother liquor, and performing solid-liquid separation after full reaction to obtain a second solid matter and secondary mother liquor; s4, collecting and drying the second solid matter to obtain a calcium fluoride product, and evaporating and concentrating the secondary mother liquor to obtain sodium nitrate crystals and distillate water; and S5, mixing the residual mother liquor after evaporation and concentration with the fluorine-containing waste acid raw material, and reusing. By adopting the method, the total recycling of most anions in the waste acid solution can be realized.

Description

Technical Field

[0001] The present application relates to the technical field of waste acid resource recovery, and specifically to a resource treatment method for fluorine-containing waste acid. Background Art

[0002] In the integrated circuit industry, since a large amount of hydrofluoric acid and nitric acid are needed to clean silicon wafers or other components, the mixed waste acid produced has the characteristics of high fluorine content, high acidity, and a small amount of organic matter. It is understood that in at least some cases, the fluorine content in the mixed waste acid can reach 40-400g / L, of which the mass fraction of nitric acid is 10-40%. For the recovery and treatment of this type of fluorine-containing waste acid, the conventional method is chemical precipitation, that is, adding soluble calcium salts to the waste acid solution, preparing calcium fluoride sludge while removing fluorine, and the calcium fluoride sludge can be used as a substitute for fluorite in chemical production after purification. There are some defects in the use of chemical precipitation. For example, when adding soluble calcium salts, excessive addition is required to ensure the defluorination effect, which will lead to an increase in unreacted calcium salts and other impurities in the calcium fluoride sludge, and the purity of the calcium fluoride sludge will decrease, making it difficult to purify or recycle the calcium fluoride sludge. The secondary wastewater and sludge generated will also pollute the environment and fail to meet the requirements of clean production.

[0003] In response to this, a Chinese patent with publication number CN117776218A and publication date 2024-01-03 proposed a method for preparing sodium fluoride using fluorine-containing waste acid. The method is to add sodium salt to the waste acid to prepare sodium fluoride products while removing fluorine. Sodium fluoride products have a wide range of industrial uses, such as for the preparation of water treatment agents or wood preservatives. Although this method can prepare sodium fluoride products with higher purity to a certain extent, the method only discloses a single treatment of fluorine-containing waste acid. In fact, after filtering and separating the sodium fluoride suspension, the remaining mother liquor still contains a large amount of unrecovered anions such as fluoride ions and nitrate ions.

[0004] Therefore, from the perspective of the overall process of recovery and treatment of fluorine-containing waste acid, on the one hand, the total utilization rate of fluorine element in fluorine-containing waste acid by the above method is still low, and its remaining mother liquor is far from meeting the discharge standard of fluorine-containing waste liquid. On the other hand, the resource recovery rate of available major anions such as nitrate ions and residual fluoride ions is still relatively low, which not only causes a waste of potential resources, but also causes secondary pollution to the environment because these anions in the discharged waste liquid will be discharged into the environment in the form of soluble salts. Summary of the invention

[0005] In view of this, the embodiments of this specification provide a method for resource treatment of fluorine-containing waste acid, through which most of the anions in the waste acid solution can be fully recycled, and the content of the sodium fluoride product prepared in the resource treatment process is above 98%, which meets the first-level product indicators of "YST 517-2009 Sodium Fluoride", and the prepared calcium fluoride product can meet the "YB / T 5217-2019" fluorite ore standard.

[0006] The embodiments of this specification provide the following technical solutions: a method for resource recovery of fluorine-containing waste acid, comprising the following steps: S1, adding a sodium source to the fluorine-containing waste acid, fully reacting and adjusting the pH value of the solution to 6-7; S2, keeping the adjusted solution warm and aging under continuous stirring, and performing solid-liquid separation on the obtained suspension to obtain a first solid and a primary mother liquor; S3, collecting and drying the first solid to obtain a sodium fluoride product, adding a calcium source to the primary mother liquor, and performing solid-liquid separation after sufficient reaction to obtain a second solid and a secondary mother liquor; S4, collecting and drying the second solid to obtain a calcium fluoride product, and evaporating and concentrating the secondary mother liquor to obtain sodium nitrate crystals and distillate water; S5, mixing the remaining mother liquor after evaporation and concentration with the fluorine-containing waste acid raw material and reusing them.

[0007] In order to optimize the above scheme, the following technical measures are also taken: In the embodiments of the present specification, in S3, the fluorine content in the secondary mother liquor does not exceed 10 mg / L, that is, through the resource recovery treatment method provided in this embodiment, the total utilization rate of the fluorine element in the fluorine-containing waste acid raw material can reach about 99.9%.

[0008] In the examples of this specification, the calcium source is a calcium nitrate solution or a calcium chloride solution with a concentration of 15-30%, and the amount added is 1.1-1.2 times the theoretical amount. Since the addition of calcium nitrate solution does not introduce other new ions except calcium ions compared to the fluorine-containing waste acid solution containing fluorine ions and nitrate ions, it is more preferred to use calcium nitrate solution, and it is more preferred that the amount of calcium source added is 1.1 times the theoretical amount.

[0009] In the examples of this specification, in S4, the secondary mother liquor is first evaporated to a solid content of 10-15%, and then the evaporated solution is filtered to obtain sodium nitrate crystals.

[0010] In the embodiments of the present specification, the fluoride ion content in the fluorine-containing waste acid should not be too low, as too low a content will slow down the reaction rate and make it difficult to form a precipitate, thereby seriously affecting the yield of the fluorine element. At the same time, the fluoride ion content should not be too high, as too high a content will increase the amount of sludge and there is a risk of secondary pollution. Therefore, the fluoride ion content is preferably 40-400 g / L, more preferably 80-400 g / L, the acidity is 7-12 mmol / g, and the mass fraction of nitric acid is 10-40%.

[0011] In the embodiments of the present specification, S1 specifically includes: S1-1, adding sodium bicarbonate solid to the fluorine-containing waste acid and fully reacting; S1-2, adding sodium hydroxide solution to the fully reacted solution to adjust the pH value of the solution to 6-7. Here, the sodium bicarbonate solid is 99% sodium bicarbonate solid, and the sodium hydroxide solution is 32% sodium hydroxide solution. The reason for adopting this sequential combination of adding alkali is that, on the one hand, sodium bicarbonate as an alkaline compound can also provide the alkalinity required for treating the waste acid, thereby reducing the amount of sodium hydroxide solution added, and then reducing the amount of water added, thereby reducing the degree of dilution of the fluorine element in the solution. On the other hand, adding part of sodium bicarbonate as a sodium source can also control the speed of the solution temperature rise, avoiding the temperature rise too fast due to the violent reaction, thereby causing acid gas atomization or water vapor boiling and other operational risks. However, if the amount of sodium bicarbonate solid added is too large, it will also cause the purity of the sodium fluoride product to decrease.

[0012] In the examples of this specification, after measurement, the alkalinity ratio of the sodium bicarbonate solid to the sodium hydroxide solution is preferably to .

[0013] In the embodiments of the present specification, in the S1-1, the endpoint of the full reaction is that no bubbles are generated in the solution and the pH value does not change. In step S1-1, the endpoint of the full reaction is specifically that no bubbles are generated in the solution and the pH value does not change within 5-10 minutes. In step S1-2, on the one hand, the pH value of the solution should not be too large. A large pH value means that more alkaline substances are dissolved in the water. These alkaline substances will not only mix with the sodium fluoride in the solution, reducing the purity of the sodium fluoride product, but also make the separated product sticky due to hydration, thereby making it difficult to reduce the water content of the product. At the same time, the pH value should not be too small. A small pH value means that the waste acid solution does not react thoroughly. Suitably, the solution pH value is adjusted to 6-7, and a better pH value is 7.

[0014] In the embodiments of the present specification, in S2, the stirring rate is controlled at 100-200 rpm, the temperature of the heat preservation aging is 20-60°C, and the aging time is 0.5-1.5h.

[0015] Insulation aging can promote the precipitation and separation of fluoride ions in the solution. More preferably, the aging time is 1-1.5h. Continuous stirring can accelerate the formation of the suspension. Here, a magnetic stirrer can be used to stir the solution, and the stirring rate is preferably controlled at 100-200rpm. Compared with the water bath heating scheme, this embodiment realizes the self-maintenance of the aging temperature through the reaction process of the nanosource and the fluorine-containing waste acid solution, which can achieve the desired temperature control effect and further simplify the operating conditions, thereby improving the efficiency of waste acid resource treatment.

[0016] The solid-liquid separation method can be suction filtration separation or centrifugal separation. Taking centrifugal separation as an example, in the embodiment of this specification, S2 includes the following steps: S2-1, adding a flocculant such as 1‰ polyacrylamide (PAM) solution to the suspension obtained by aging and slowly stirring until alum flowers appear; S2-2, centrifuging the suspension after standing for 0.5h, and obtaining a sodium fluoride product with a water content of 1-2% after drying. Here, when adding the polyacrylamide solution, the magnetic stirrer is controlled to be in a slow stirring state at a speed of 100-200rpm, and the suspension will produce a large number of large precipitates. In this way, after centrifugation, the water content of the sodium fluoride product can be reduced to less than 2% by drying.

[0017] In the embodiments of this specification, in S4, the drying temperature is 100-110° C., and the drying time is 1-3 hours. Preferably, the drying temperature is 105° C., and the drying time is 2 hours.

[0018] Compared with the prior art, the at least one technical solution adopted in the embodiments of this specification can achieve the following beneficial effects: First, by this method, a sodium source and a calcium source are sequentially added to a fluorine-containing waste acid solution, which can fully react with the fluorine ions in the fluorine-containing waste acid solution to prepare sodium fluoride products and calcium fluoride products that meet corresponding standards, so that the fluoride ion yield in the solution reaches 99.9%, and at the same time, nitrate ions in the secondary mother liquor are precipitated in the form of sodium nitrate crystals, so that the nitrate ions in the solution can be fully recovered and utilized, that is, most of the anions in the waste acid solution can be fully recovered and utilized.

[0019] Furthermore, in the embodiments of the present specification, a sodium source is first added to the fluorine-containing waste acid raw material to prepare sodium fluoride, so as to ensure sufficient reaction between the sodium source and the fluoride ions, thereby forming a sodium fluoride precipitate with a higher purity, and then a sodium fluoride product with a higher content can be obtained. After measurement, the content of the sodium fluoride product prepared by this method can reach more than 98%, and then a calcium source is added to the remaining primary mother liquor to prepare calcium fluoride. At this time, since the concentration of fluoride ions in the primary mother liquor is greatly reduced compared with the raw material, the amount of calcium source to be added is also reduced. Using less calcium source can reduce the content of unreacted calcium salt in the second solid, that is, reduce the content of impurities in the second solid, and improve the purity of the second solid, so that a calcium fluoride product with a higher content can be obtained after drying. After measurement, the content of the calcium fluoride product prepared by this method meets the relevant fluorite ore standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 It is a process flow chart for resource treatment of fluorine-containing waste acid in this application; Figure 2 It is a summary list of some process parameters of Example 1 and Example 2 in this application; Figure 3 It is a summary table of some process parameters of the embodiments and comparative examples in this application. DETAILED DESCRIPTION

[0022] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0023] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0024] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0025] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. The illustrations only show the components related to the present application rather than being drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed at will, and the component layout may also be more complicated.

[0026] The embodiments of this specification propose a method for resource treatment of fluorine-containing waste acid, which aims to solve the problem of low recovery rate of main anions in fluorine-containing waste acid in the prior art. The method can achieve complete recovery and utilization of most anions in fluorine-containing waste acid raw materials, including fluoride ions and nitrate ions, and can also prepare high-purity sodium fluoride products with a content of more than 98% and calcium fluoride products with a content of more than 70%, thereby improving the recovery rate of fluorine element.

[0027] like Figure 1 As shown, the resource recovery treatment method is particularly suitable for the treatment of the following fluorine-containing waste acid, wherein the fluorine ion concentration in the fluorine-containing waste acid is 40-400g / L, the acidity is 7-12mmol / g, and the mass fraction of nitric acid is 10-40%. The treatment method specifically includes the following steps: Add 99% sodium bicarbonate solid to the fluorine-containing waste acid and allow it to react fully; here, the reaction endpoint is when no bubbles are generated in the solution and the pH value does not change within 5-10 minutes. It should be noted that when adding sodium bicarbonate, the dosing speed needs to be controlled to prevent the generation of a large number of bubbles that may cause the tank to overflow. In addition, when adding sodium bicarbonate, the solution will cool down significantly.

[0028] 32% sodium hydroxide solution is added to the fully reacted solution and the pH value of the solution is adjusted to 6-7; the following description is based on the adjusted solution, i.e., the pH value of the reaction end point is 7 as an example. It should be noted that the solution temperature rises significantly when the reaction end point is reached. In addition, the alkalinity ratio of the sodium bicarbonate solid to the sodium hydroxide solution is controlled at to The necessity of this value will be further verified through subsequent experiments.

[0029] The adjusted solution is kept warm and aged under continuous stirring to obtain a sodium fluoride suspension; the temperature of the warm aging is 20-60° C., the aging time is 0.5-1.5 h, and the solution can be stirred by a magnetic stirrer at a stirring rate of 100-200 rpm.

[0030] The obtained sodium fluoride suspension is subjected to solid-liquid separation to obtain a first solid and a primary mother liquor. The solid-liquid separation can be performed by suction filtration or by centrifugal separation. Taking the centrifugal separation as an example, the method includes the following steps: adding a flocculant such as a 1‰ polyacrylamide solution to the sodium fluoride suspension and slowly stirring until alum flowers appear. The stirring rate can also be set to 100-200rpm; after standing for 0.5h, the sodium fluoride suspension is centrifuged.

[0031] The first solid obtained is collected and dried to obtain a sodium fluoride product, a calcium source is added to the primary mother liquor, and a calcium fluoride suspension is obtained after sufficient reaction, and the calcium fluoride suspension is subjected to solid-liquid separation to obtain a second solid and a secondary mother liquor; the drying temperature here is 100-110°C, and the drying time is 1-3h. As a result of drying, the water content of the first solid is reduced to 1-2%, preferably less than 1%. The calcium source is selected from a calcium nitrate solution or a calcium chloride solution or other soluble calcium salt, with a concentration of 15-30%, and the amount added is 1.1-1.2 times the theoretical amount. The following description is based on the case where the amount added is 1.1 times the theoretical amount.

[0032] The second solid is collected and dried to obtain a calcium fluoride product, and the secondary mother liquor is evaporated and concentrated to obtain sodium nitrate crystals and distillate water; the fluorine content in the secondary mother liquor is required to be no more than 10 mg / L. The secondary mother liquor is evaporated and concentrated to obtain sodium nitrate crystals and distillate water, specifically, the secondary mother liquor is first evaporated to a solid content of 10-15%, and then the evaporated solution is filtered to obtain sodium nitrate crystals, and the sodium nitrate crystals meet the industrial sodium nitrate standard GB / T 4553-2016, which will be further verified later.

[0033] The remaining mother liquor after evaporation and concentration is mixed again with the fluorine-containing waste acid raw material to achieve the recycling of the mother liquor.

[0034] In order to demonstrate the core of the technical solution in this specification in detail and to further verify the technical effects produced, several groups of comparative examples and embodiments are listed below.

[0035] Embodiment 1: The fluorine content of the raw material fluorine-containing waste acid is 81250 mg / L and the acidity is 7.88 mmol / g.

[0036] Take 500g of fluorine-containing waste acid solution, add 138.4g of 99% sodium bicarbonate solid, after sufficient reaction, add 309.2g of 32% sodium hydroxide solution, adjust the solution pH to 7, then the solution temperature is 68°C, continue stirring for 1h while keeping warm for aging, then add 1‰ polyacrylamide solution, continue stirring slowly until large pieces of precipitation appear. After standing for 0.5h, the first solid was centrifuged and dried to obtain 84.3g of sodium fluoride product, of which the sodium fluoride content was 98.1%, and silicon dioxide, sulfate, carbonate, water-insoluble matter, and free acid were not detected, which met the first-level product index of "YST 517-2009 Sodium Fluoride". The yield of fluorine element in sodium fluoride was 92.1%, and 789.8g of primary mother liquor was obtained, with a fluorine content of 7230mg / L. 90.4g of 30% calcium nitrate solution was added to the primary mother liquor, and filtered and separated after sufficient reaction. The second solid was dried to obtain 16.7g of calcium fluoride product, with a calcium fluoride content of 70.6%, a silicon dioxide content of 1.2%, a sulfur content of 0.11%, and a phosphorus content of ND (not detected). It meets the "YB / T 5217-2019" fluorite block ore standard. The fluorine content in the filtered filtrate, that is, the secondary mother liquor, is 4.37mg / L. After the secondary mother liquor was evaporated and concentrated, 92.1 g of sodium nitrate crystals were obtained, with a sodium nitrate content of 98.43%, a water content of 1.2%, an iron content of ND, a calcium nitrate content of 0.01%, sodium carbonate ND, and magnesium nitrate ND, which met the sodium nitrate qualified product standard, that is, the industrial sodium nitrate standard (GB / T 4553-2016), 561.7 g of distilled water, and 197.7 g of the remaining mother liquor.

[0037] Embodiment 2: The fluorine content of the raw material fluorine-containing waste acid is 214000 mg / L, and the acidity is 11.07 mmol / g.

[0038] Take 500g of fluorine-containing waste acid solution, add 232.9g of 99% sodium bicarbonate solid, and after sufficient reaction, add 346.1g of 32% sodium hydroxide solution. Adjust the solution pH to 7, and the solution temperature is 52℃. Stir continuously for 1h while keeping warm for aging, then add 1‰ polyacrylamide solution and continue to stir slowly until large pieces of precipitation appear. After centrifugation, the first solid was dried to obtain 191.5g of sodium fluoride product with a content of 98.3%. The yield of fluorine in sodium fluoride was 95.5%. Silicon dioxide, sulfate, carbonate, water-insoluble matter, and free acid were not detected, which met the first-level product index of "YST 517-2009 Sodium Fluoride". 727.6g of primary mother liquor was obtained with a fluorine content of 5170mg / L. 59.5g of 30% calcium nitrate solution was added to the primary mother liquor. After sufficient reaction and filtration, 10.4g of calcium fluoride product was obtained by drying, with a calcium fluoride content of 74.3%, a silicon dioxide content of 0.7%, a sulfur content of 0.04%, and a phosphorus content of ND, which met the "YB / T5217-2019" fluorite block ore standard. The fluorine content in the filtered filtrate, i.e., the secondary mother liquor, was 7.46mg / L. After the secondary mother liquor was evaporated and concentrated, 42.8 g of sodium nitrate crystals were obtained, with a sodium nitrate content of 98.57%, a water content of 1.1%, an iron content of ND, a calcium nitrate content of 0.01%, sodium carbonate ND, and magnesium nitrate ND, which met the sodium nitrate qualified product standard, 663.1 g of distilled water, and 62.8 g of the remaining mother liquor.

[0039] Embodiment three: The fluorine content of the raw material fluorine-containing waste acid is 82700 mg / L, and the acidity is 7.85 mmol / g.

[0040] Take 500g of fluorine-containing waste acid solution, add 173.4g of 99% sodium bicarbonate solid, after sufficient reaction, add 256.5g of 32% sodium hydroxide solution, adjust the solution pH to 7, then the solution temperature is 58°C, continue stirring for 1h while keeping warm for aging, then add 1‰ polyacrylamide solution, continue stirring slowly until large pieces of precipitation. After centrifugation and drying, 70.1g of dry sodium fluoride product is obtained, the sodium fluoride content is 98.4%, and 733.6g of primary mother liquor is obtained, the fluorine content is 4150mg / L, and the yield of fluorine element in sodium fluoride is 90.5%.

[0041] The following is a comparative example, in which the fluorine content of the fluorine-containing waste acid is 82700 mg / L and the acidity is 7.85 mmol / g, which can be compared with the above-mentioned Example 3.

[0042] Comparative Example 1: When only sodium hydroxide solution is added: Take 500g of fluorine-containing waste acid solution, directly add 514.9g of 32% sodium hydroxide solution, fully react, and the solution temperature is 86°C. After drying, the generated sodium fluoride obtains 63.9g of sodium fluoride product with a sodium fluoride content of 98.9%. The output of the primary mother liquor is 920.9g, with a fluorine content of 6280mg / L, and the yield of fluorine element in sodium fluoride is 82.97%.

[0043] Comparative Example 2: Sodium hydroxide solution is mixed with sodium bicarbonate and added, when sodium bicarbonate accounts for 10%: Take 500g of fluorine-containing waste acid solution, add 34.6g of 99% sodium bicarbonate and 463.4g of 32% sodium hydroxide solution, and react fully, showing that the solution temperature is 78°C. After drying, the generated sodium fluoride has a sodium fluoride content of 83.96%. 862g of primary mother liquor is produced, with a fluorine content of 6715mg / L, and the yield of fluorine element in sodium fluoride is 86.02%.

[0044] Comparative Example 3: First add sodium hydroxide solution, then add sodium bicarbonate. When sodium bicarbonate accounts for 10%: Take 500g of fluorine-containing waste acid solution, add 463.4g of 32% sodium hydroxide solution, after sufficient reaction, add 34.6g of 99% sodium bicarbonate solid, and fully react, the solution temperature is 76°C. After drying, the generated sodium fluoride has a sodium fluoride content of 82.77%. 868.3g of primary mother liquor is produced, the fluorine content is 6894mg / L, and the yield of fluorine element in sodium fluoride is 85.54%.

[0045] Comparative Example 4: Add sodium bicarbonate first, then sodium hydroxide solution. When sodium bicarbonate accounts for 10%: Take 500g of fluorine-containing waste acid solution, add 34.6g of 99% sodium bicarbonate, after sufficient reaction, add 463.4g of 32% sodium hydroxide solution, and fully react, showing the solution temperature of 82°C. After drying, the generated sodium fluoride obtains 65.2g of dry sodium fluoride product with a sodium fluoride content of 98.6%. The output of the primary mother liquor is 893.3g, the fluorine content is 5870mg / L, and the yield of fluorine element in sodium fluoride is 84.40%.

[0046] like Figure 2 and 3As shown, based on the above embodiments 1 to 3, statistics show that the content of sodium fluoride products obtained by the treatment method is more than 98%, based on the above embodiments 1 to 2, statistics show that the content of calcium fluoride products obtained is more than 70%, and the fluorine content of the secondary mother liquor is less than 10 mg / L, that is, the fluoride ions in the waste acid solution are basically fully recovered, and the nitrate ions in the secondary mother liquor are precipitated in the form of sodium nitrate crystals, and the content of sodium nitrate crystals is more than 98%, so that the nitrate ions in the solution can be fully recovered, that is, most of the anions in the waste acid solution can be fully recovered.

[0047] like Figure 3 As shown, when adding sodium source, the fluorine-containing waste acid solution is treated once by following a certain alkalinity ratio and first adding sodium bicarbonate, and then adding sodium hydroxide solution after sufficient reaction, so that the system temperature can be significantly reduced during the reaction process, and at the same time, the fluorine element yield in sodium fluoride can be increased to more than 90%.

[0048] In this specification, the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the embodiments described later, the description is relatively simple, and the relevant parts can be referred to the partial description of the previous embodiments.

[0049] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for recycling fluorine-containing waste acid, characterized in that: The following steps are involved: S1, adding a sodium source to the fluorine-containing waste acid, fully reacting and adjusting the pH value of the solution to 6-7; S2, keeping the adjusted solution warm and aging it under continuous stirring, and performing solid-liquid separation on the obtained suspension to obtain a first solid and a primary mother liquor; S3, collecting and drying the first solid to obtain a sodium fluoride product, adding a calcium source to the primary mother liquor, and performing solid-liquid separation after sufficient reaction to obtain a second solid and a secondary mother liquor; S4, collecting and drying the second solid to obtain a calcium fluoride product, and evaporating and concentrating the secondary mother liquor to obtain sodium nitrate crystals and distillate water; S5. Mix the mother liquor remaining after evaporation and concentration with the fluorine-containing waste acid raw material and reuse them.

2. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: The fluorine content in the secondary mother liquor does not exceed 10 mg / L.

3. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: The calcium source is a calcium nitrate solution or a calcium chloride solution with a concentration of 15-30%, and the added amount is 1.1-1.2 times the theoretical amount.

4. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: In S4, the secondary mother liquor is first evaporated to a solid content of 10-15%, and then the evaporated solution is filtered to obtain sodium nitrate crystals.

5. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: The fluorine ion concentration in the fluorine-containing waste acid is 40-400 g / L, the acidity is 7-12 mmol / g, and the mass fraction of nitric acid is 10-40%.

6. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: The S1 specifically includes: S1-1, adding solid sodium bicarbonate to the fluorine-containing waste acid and allowing it to react fully; S1-2. Add sodium hydroxide solution to the fully reacted solution to adjust the pH value of the solution to 6-7.

7. The method for recycling fluorine-containing waste acid according to claim 6, characterized in that: The alkalinity ratio of the sodium bicarbonate solid to the sodium hydroxide solution is to .

8. The method for recycling fluorine-containing waste acid according to claim 6, characterized in that: In S1-1, the endpoint of the sufficient reaction is that no bubbles are generated in the solution and the pH value does not change.

9. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: In S2, the stirring rate is controlled at 100-200 rpm.

10. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: In S2, the temperature of the heat preservation aging is 20-60°C, and the aging time is 0.5-1.5h.

11. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: The S2 comprises the following steps: S2-1, adding a flocculant to the suspension obtained by aging and slowly stirring until alum flowers appear; S2-2, after standing for 0.5 h, the suspension was centrifuged.

12. The method for recycling fluorine-containing waste acid according to claim 1, characterized in that: In S4, the drying temperature is 100-110°C, and the drying time is 1-3h.

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