Method for recovering fluorine from high-fluorine waste acid solution and application

Abstract

The invention provides a method for recovering fluorine from a high-fluorine waste acid solution and application, and the method comprises the following steps: adding first anhydrous sodium sulfate particles into a first waste acid solution, stirring to react, standing to obtain a first upper suspension and first sodium sulfate bottom slag, discharging the first sodium sulfate bottom slag, filtering the upper suspension, and drying to obtain a second upper suspension; according to the method, the liquid subjected to fluorine precipitation is recycled to serve as the flue gas leacheate, and the total amount of follow-up deep fluorine precipitation treatment of the leacheate can be reduced. The sodium fluoride solid and the liquid subjected to fluorine precipitation are obtained, and finally the liquid subjected to fluorine precipitation is returned to smelting to serve as the flue gas leacheate. The sodium sulfate in the liquid after fluorine precipitation is saturated, the liquid is recycled to serve as flue gas leacheate, the sodium sulfate in the liquid can also be recycled, only a small amount of sodium sulfate needs to be supplemented for subsequent fluorine precipitation, the operation process is simplified, and the efficient resourceful treatment requirement of non-ferrous metal smelting waste acid is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fluorine-containing waste acid treatment, and particularly relates to a method for recovering fluorine from a high-fluorine waste acid solution. BACKGROUND

[0002] In the pyrometallurgical process of non-ferrous metals such as copper, lead, zinc and molybdenum, the flue dust gas is usually treated by circulating absorption with leaching water. With the continuous leaching process, the fluorine in the leaching solution is continuously enriched. When the concentration reaches the tolerance limit of the equipment, it needs to be discharged for disposal. This discharged leaching solution is usually referred to as waste acid. The fluorine in the waste acid mainly exists in the form of hydrofluoric acid (HF) with a concentration of 10-60 g / L, which has significant resource recovery value. However, the waste acid has strong acidity (H + with a concentration of 0.5-3 mol / L) and complex impurity components (such as heavy metals, arsenic, etc.), and direct recovery of fluorine has technical difficulties. At present, the methods for recovering fluorine from solution in industry mainly include extraction method, concentration stripping method, electrodialysis method, calcium salt precipitation method and sodium salt precipitation method, etc., among which the sodium salt precipitation method is concerned due to its simple operation and high added value of product.

[0003] The sodium salt precipitation method is usually suitable for ammonium fluoride system, and fluorine is precipitated in the form of sodium fluoride by adding sodium sulfate to the solution under weak alkaline conditions. For example, CN118084015A proposes a method for preparing sodium fluoride from ammonium fluoride and sodium sulfate, and CN115403056A utilizes by-product fluorosilicic acid, dilute ammonia water and sodium sulfate to realize resource recovery of fluorine. However, this method has significant limitations: first, the pH of the solution needs to be strictly controlled to be weakly alkaline during the fluorine precipitation process, but the waste acid itself is extremely acidic, and a large amount of alkali (such as ammonia water or sodium hydroxide) needs to be consumed for neutralization and alkalization, resulting in high cost; second, the reaction temperature needs to be maintained at 50-80℃ to ensure the precipitation efficiency, which has high energy consumption; third, the sodium fluoride precipitate needs to be filtered while hot, which has strict requirements on the high-temperature resistance and corrosion resistance of the equipment, further increasing the process complexity and operating cost.

[0004] In summary, although the existing sodium salt precipitation method can effectively recover fluorine, its dependence on alkaline environment and high temperature conditions limits its application in the treatment of acidic waste acid. In view of the characteristics of high acidity and low pH of waste acid, it is a key problem to be solved to develop a technology that can recover fluorine efficiently at low temperature under acidic conditions. This technology needs to break through the pH and temperature limitations of the traditional sodium salt precipitation method, reduce the neutralization cost and energy consumption, and simplify the operation process to meet the efficient resource recovery requirements of non-ferrous metal smelting waste acid. SUMMARY

[0005] The present application aims to at least solve one of the above technical problems in the prior art. To this end, the present application provides a method for recovering fluorine from a high-fluorine contaminated acid solution, which simplifies the operation process and adapts to the efficient resource treatment demand of non-ferrous metal smelting contaminated acid.

[0006] The present application also provides a method for recovering fluorine from a high-fluorine contaminated acid solution in copper, lead, zinc, and molybdenum pyrometallurgy.

[0007] The first aspect of the present application provides a method for recovering fluorine from a high-fluorine contaminated acid solution, comprising the following steps:

[0008] S1: adding first anhydrous sodium sulfate particles to the first contaminated acid solution, stirring and reacting, and then standing to obtain a first upper suspension and a first sodium sulfate bottom residue, and discharging the first sodium sulfate bottom residue;

[0009] S2: filtering the first upper suspension to obtain sodium fluoride solids and a post-fluoride precipitation liquid;

[0010] S3: returning the post-fluoride precipitation liquid to smelting as a flue gas leaching liquid, when the difference between the fluorine concentration in the flue gas leaching liquid and the fluorine concentration in the first contaminated acid solution is less than 20%, adding the first sodium sulfate bottom residue, dissolving the first sodium sulfate bottom residue, adding second anhydrous sodium sulfate particles, stirring and reacting, and then standing to obtain a second upper suspension and a second sodium sulfate bottom residue, filtering the second upper suspension to obtain sodium fluoride solids and a post-fluoride precipitation liquid, returning the post-fluoride precipitation liquid to smelting as a flue gas leaching liquid, and forming a cycle.

[0011] The method for recovering fluorine from a high-fluorine contaminated acid solution has at least the following beneficial effects:

[0012] By adding anhydrous sodium sulfate solids to the contaminated acid, the single fluorine recovery rate is ≥50%. The post-fluoride precipitation liquid is recycled as a flue gas leaching liquid, which can reduce the total amount of subsequent deep fluorine precipitation treatment of the leaching liquid. The sodium sulfate in the post-fluoride precipitation liquid is already saturated, and recycling it as a flue gas leaching liquid can also recycle the sodium sulfate inside, and only a small amount of sodium sulfate needs to be added for subsequent fluorine precipitation.

[0013] Sodium sulfate dissolution is an endothermic reaction, and the temperature of the flue gas leaching liquid is between 50-80℃, which is exactly the heat energy used to dissolve sodium sulfate. The solubility of sodium fluoride is less affected by temperature, while the solubility of sodium sulfate is maximum between 35℃-45℃, and subsequent reactions can be well insulated without additional heating. The present application provides an energy-saving method.

[0014] The fluorine-sedimented liquid is returned to continue to be the flue gas washing liquid, and when the difference between the fluorine concentration in the flue gas washing liquid and the fluorine concentration of the first waste acid solution is less than 20%, sodium sulfate bottom slag is added, and after all the sodium sulfate bottom slag is dissolved, large-particle sodium sulfate solid is added again, because the particle size of the sodium sulfate bottom slag is reduced after the last dissolution. If it is only partially dissolved when the fluorine is settled later, the particle size may be as fine as sodium fluoride, and the settling speed may be as high as that of sodium fluoride, so that a large amount of sodium sulfate is contained in the obtained sodium fluoride crystal, affecting the purity of sodium fluoride. The method of the present application avoids the above problems.

[0015] The "high-fluorine waste acid solution" of the present application refers to a waste acid solution with a fluorine concentration of 10-60 g / L, i.e., the first waste acid solution in step S1.

[0016] When the difference between the fluorine concentration in the flue gas washing liquid and the fluorine concentration of the first waste acid solution is less than 20%, the "fluorine concentration" here refers to the fluorine content in the flue gas washing liquid and the first waste acid solution, and the unit can be "g / L".

[0017] According to some embodiments of the present application, the temperature of the stirring reaction is 35-45°C.

[0018] According to some embodiments of the present application, the temperature of the stirring reaction is any one of 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, such as 40°C, or a range value formed by any two, such as 40-42°C.

[0019] According to some embodiments of the present application, the time of the stirring reaction is 4-24 h.

[0020] According to some embodiments of the present application, the time of the stirring reaction is any one of 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, such as 16 h, or a range value formed by any two, such as 12-18 h.

[0021] According to some embodiments of the present application, the time of the standing is 2-5 min.

[0022] According to some embodiments of the present application, the time of the standing is any one of 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, such as 3 min, or a range value formed by any two, such as 3-4 min.

[0023] According to some embodiments of the present application, the addition amount of the first anhydrous sodium sulfate particles is 350-500 g / L.

[0024] According to some embodiments of the present invention, the amount of the first anhydrous sodium sulfate particles added is any value among 350 g / L, 400 g / L, 420 g / L, 440 g / L, 460 g / L, 480 g / L, and 500 g / L, such as 400 g / L, or any range formed by both, such as 400 g / L to 440 g / L.

[0025] According to some embodiments of the present invention, the amount of the first anhydrous sodium sulfate particles added is 400 g / L to 500 g / L.

[0026] Controlling the addition of the first anhydrous sodium sulfate granules to 350 g / L to 500 g / L can avoid affecting the fluorine recovery rate due to insufficient sodium sulfate addition, and can also avoid sodium fluoride adsorbing onto sodium sulfate crystals and precipitating out due to excessive sodium sulfate bottom residue, making it impossible to separate sodium fluoride and sodium sulfate by standing, thus affecting the separation effect of sodium fluoride and sodium sulfate.

[0027] According to some embodiments of the present invention, in the first anhydrous sodium sulfate particles, more than 90% of the particles have a particle size greater than 425 micrometers.

[0028] The sodium fluoride precipitate formed by the reaction has a particle size of less than 100 micrometers in over 90%. Adding an excess of large-particle anhydrous sodium sulfate solid results in a sodium sulfate bottom residue with a particle size of more than 200 micrometers in over 90% of its particles. Sodium fluoride has a specific gravity of 2.79, while anhydrous sodium sulfate has a specific gravity of 2.70. According to Stokes' equation, the settling velocity of sodium sulfate is approximately 3.5-3.8 times that of sodium fluoride. Therefore, the sodium sulfate bottom residue can be preferentially discharged for sodium sulfate recovery.

[0029] According to some embodiments of the present invention, in the sodium fluoride solid, more than 90% of the particles have a particle size of less than 100 micrometers.

[0030] According to some embodiments of the present invention, the fluorine recovery rate of the method in a single run is ≥50%.

[0031] According to some embodiments of the present invention, the fluoride content in the high-fluoride acid solution is 10-60 g / L.

[0032] The second aspect of the present invention provides the application of the method of the first aspect of the present invention in the pyrometallurgical smelting of copper, lead, zinc and molybdenum. Detailed Implementation

[0033] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0034] In a first aspect, some embodiments of the present invention provide a method for recovering fluoride from a high-fluoride acidic waste solution, comprising the following steps:

[0035] S1: Add the first anhydrous sodium sulfate particles to the first waste acid solution, stir and react, then let stand to obtain the first upper suspension and the first sodium sulfate bottom residue, and discharge the first sodium sulfate bottom residue.

[0036] S2: Filter the first upper suspension to obtain sodium fluoride solid and fluoride-precipitated liquid;

[0037] S3: The fluoride-precipitated liquid is returned to the smelting process as a flue gas scrubbing liquid. When the difference between the fluoride concentration in the flue gas scrubbing liquid and the fluoride concentration in the first waste acid solution is less than 20%, the first sodium sulfate bottom residue is added. After the first sodium sulfate bottom residue dissolves, the second anhydrous sodium sulfate particles are added. After stirring and reacting, the mixture is allowed to stand to obtain the second upper suspension and the second sodium sulfate bottom residue. The second upper suspension is filtered to obtain sodium fluoride solid and the fluoride-precipitated liquid. The fluoride-precipitated liquid is returned to the smelting process as a flue gas scrubbing liquid to form a cycle.

[0038] It is understandable that by adding anhydrous sodium sulfate solid to the waste acid, the fluoride recovery rate in a single step can be ≥50%. Recycling the fluoride-precipitated liquid as flue gas scrubbing liquid can reduce the total amount of scrubbing liquid required for subsequent deep fluoride precipitation treatment. Since the sodium sulfate in the fluoride-precipitated liquid is already saturated, recycling it as flue gas scrubbing liquid also allows for the reuse of the sodium sulfate; subsequent fluoride precipitation only requires the addition of a small amount of sodium sulfate.

[0039] Sodium sulfate dissolution is an endothermic reaction. The temperature of the flue gas scrubbing liquid is between 50-80℃, which is the perfect heat energy to dissolve sodium sulfate. Sodium fluoride solubility is less affected by temperature, while sodium sulfate solubility is highest between 35℃ and 45℃. Subsequent reactions only require proper temperature control and no additional heating is needed. This invention provides an energy-saving method.

[0040] After fluoride precipitation, the liquid is returned to be used as flue gas scrubbing liquid. When the difference between the fluoride concentration in the flue gas scrubbing liquid and the fluoride concentration in the first waste acid solution is less than 20%, sodium sulfate bottom residue is added. After complete dissolution, large-particle sodium sulfate solid is added. This is because the particle size of the sodium sulfate bottom residue has decreased after the previous dissolution. If it only partially dissolves during subsequent fluoride precipitation, the particles may be as fine as sodium fluoride, and the settling velocity may be the same. The separated sodium fluoride crystals will contain a large amount of sodium sulfate, affecting the purity of sodium fluoride. The method of this invention avoids the above problems.

[0041] It should be noted that in existing technologies, the waste acid produced during the pyrometallurgical smelting of non-ferrous metals such as copper, lead, zinc, and molybdenum is highly acidic and has a high fluoride concentration. Traditional sodium salt precipitation methods require weakly alkaline conditions, consuming large amounts of alkali to neutralize the acidity. Furthermore, these methods demand high temperatures and complex equipment, resulting in high costs and complex operations. For example, existing technologies require adjusting the solution pH to weakly alkaline and maintaining a reaction temperature of 50–80°C, while the waste acid itself has a high H₂ content. +When the concentration reaches 0.5–3 mol / L, direct application of traditional methods requires additional neutralization and filtration, increasing the burden on the equipment.

[0042] To address the aforementioned issues, and considering the direct utilization of the acidic conditions of the wastewater, the possibility of fluoride precipitation in an acidic system was explored. Analysis of the chemical reaction characteristics of sodium sulfate and fluoride revealed that sodium sulfate can still combine with fluoride ions to form sodium fluoride precipitate under acidic conditions, but the reaction efficiency and precipitate separation issues need to be addressed. Further research showed that controlling the particle size of sodium sulfate and the reaction conditions can promote precipitate formation without adjusting the pH. This led to the development of a technical approach: directly adding sodium sulfate particles of a specific size to the wastewater and recovering sodium fluoride through solid-liquid separation.

[0043] Therefore, the present invention proposes a method comprising the following steps: adding first anhydrous sodium sulfate particles to a first waste acid solution, stirring and reacting, and then allowing it to stand to obtain a first upper suspension and a first sodium sulfate bottom residue, and discharging the first sodium sulfate bottom residue; filtering the upper suspension to obtain sodium fluoride solid and fluoride-precipitated liquid; returning the fluoride-precipitated liquid to the smelting process as flue gas scrubbing liquid; when the difference between the fluoride concentration in the flue gas scrubbing liquid and the fluoride concentration in the first waste acid solution is less than 20%, adding the first sodium sulfate bottom residue, dissolving it, adding second anhydrous sodium sulfate particles, stirring and reacting, and then allowing it to stand to obtain a second upper suspension and a second sodium sulfate bottom residue, filtering to obtain sodium fluoride solid and fluoride-precipitated liquid, and returning the fluoride-precipitated liquid for recycling.

[0044] The amount of anhydrous sodium sulfate granules added can be from 350 g / L to 500 g / L. This range ensures that fluoride ions react fully while avoiding excessive reagent waste.

[0045] In this case, more than 90% of the particles in the first and second anhydrous sodium sulfate particles have a particle size greater than 425 micrometers. The larger particle size of sodium sulfate can ensure the slow release of sodium ions, forming fine particles of sodium fluoride, which facilitates the separation of sodium sulfate bottom residue particles and sodium fluoride.

[0046] The temperature of the stirring reaction can be between 35°C and 45°C. This low temperature condition reduces energy consumption while maintaining reaction kinetics.

[0047] The stirring reaction can be carried out for 4 to 24 hours to ensure that the reaction is fully completed.

[0048] The settling time can be 2 to 5 minutes, which utilizes the density difference to quickly separate the precipitate and suspension.

[0049] Among them, more than 90% of the particles in sodium fluoride solid are smaller than 100 micrometers in diameter, and the fine particles are easy to filter in subsequent processes.

[0050] Specifically, anhydrous sodium sulfate granules are directly added to the first batch of acidic waste solution under acidic conditions. During stirring, fluoride ions react with sodium sulfate to form sodium fluoride precipitate. After settling, the sodium sulfate bottom residue settles due to its higher density. The upper suspension is filtered to separate the sodium fluoride solid, and the remaining fluoride-laden liquid is returned to the flue gas scrubbing system for recycling. When the fluoride concentration in the scrubbing liquid increases again, the initial sodium sulfate bottom residue is dissolved, and new granules are added to continue the reaction, forming a closed-loop cycle.

[0051] Compared to existing technologies, conventional sodium salt precipitation methods require adjusting the solution to a weakly alkaline state and maintaining a high temperature. This method, however, reacts directly in acidic waste acid, eliminating the neutralization step and high-temperature conditions, thus reducing reagent and energy consumption. For example, traditional methods require the addition of ammonia to adjust the pH to 8-9, while this method reacts directly in the original H₂O. + Fluorine precipitation can be achieved at concentrations of 0.5–3 mol / L. Furthermore, the settling time is reduced to a few minutes, simplifying the separation process.

[0052] Through the above technical solution, the present invention can efficiently recover fluorine under acidic conditions, avoid the consumption of neutralizing agent, reduce the reaction temperature requirement, and at the same time reduce the amount of reagent replenishment by recycling sodium sulfate bottom residue, thereby achieving low-cost recovery of fluorine resources in waste acid.

[0053] In conjunction with the first aspect, in some embodiments of the present invention, the temperature of the stirring reaction is 35°C to 45°C.

[0054] In conjunction with the first aspect, in some embodiments of the present invention, the temperature of the stirring reaction is any value among 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, and 45°C, such as 40°C, or a range of any two, such as 40°C to 42°C.

[0055] The temperature range was set to ensure that sodium sulfate fully dissolves and reacts with fluoride ions while avoiding high temperatures that could increase the solubility of sodium fluoride.

[0056] The solubility of sulfates in water can be found in Table 1.

[0057] Table 1

[0058]

[0059] Specifically, after adding anhydrous sodium sulfate granules to the acidic waste acid solution, the reaction system temperature is maintained between 35°C and 45°C using an external temperature control device. Under these temperature conditions, the sodium sulfate granules undergo a displacement reaction with fluoride ions to form sodium fluoride precipitate, while simultaneously preventing excessively high temperatures from causing the sodium fluoride to dissolve or the acid in the system to volatilize. During the reaction, temperature control is achieved through real-time monitoring and adjustment of the heating power, for example, by using a jacketed reactor in conjunction with a circulating water bath to maintain a constant temperature environment.

[0060] Compared to existing technologies, traditional sodium salt precipitation processes require maintaining reaction temperatures above 50°C to accelerate the reaction. This invention, by optimizing the temperature window, reduces energy consumption while maintaining sodium fluoride precipitation efficiency. Existing technologies, with their high-temperature operations, not only increase steam or electricity consumption but also exacerbate equipment corrosion risks. This invention, utilizing a temperature range of 35°C to 45°C, effectively avoids these problems.

[0061] Through the above technical solution, this invention achieves efficient precipitation of fluorine at near-room temperature, significantly reducing process energy consumption and equipment temperature resistance requirements. This temperature range maintains sufficient reaction kinetics while avoiding redissolution of the precipitate due to temperature fluctuations, making it particularly suitable for treating highly acidic and corrosive waste acid systems.

[0062] In conjunction with the first aspect, in some embodiments of the present invention, the stirring reaction time is 4h to 24h.

[0063] In conjunction with the first aspect, in some embodiments of the present invention, the stirring reaction time is any value among 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, and 24h, such as 16h, or a range of any two, such as 12h to 18h.

[0064] The selection of the stirring reaction time range is based on the solid-liquid reaction kinetics of fluoride ions and sodium sulfate in the waste acid system, ensuring complete reaction while avoiding excessive extension that would increase energy consumption.

[0065] Specifically, in acidic, high-fluoride wastewater solutions, the process of sodium sulfate particles reacting with fluoride ions to form sodium fluoride precipitate is controlled by the diffusion rate. When the reaction time is less than 4 hours, the sodium fluoride coating formed on the particle surface hinders the further dissolution of unreacted nuclei, leading to a decrease in fluoride recovery. When the reaction time exceeds 24 hours, the reaction tends to reach equilibrium, and the precipitated particles may undergo secondary dissolution. By controlling the reaction time within the range of 4–24 hours, the sodium sulfate particles can be fully dissolved and sodium ions released, while ensuring that fluoride ions are fully converted into sodium fluoride precipitate, and energy waste is avoided.

[0066] Compared to existing technologies, traditional sodium salt precipitation methods typically require the reaction to be maintained at above 50°C for 2–3 hours, while this technology extends the reaction time to 4–24 hours under ambient temperature conditions. This wider time range eliminates the need for additional heating equipment and allows for flexible adjustment of the reaction time according to actual production needs. Compared to existing processes that require precise control of short-duration high-temperature reactions, this technology is more adaptable to the fluctuations in operating conditions during industrial production.

[0067] Through the above technical solution, this invention achieves efficient formation of sodium fluoride precipitate by optimizing the stirring reaction time window while maintaining acidic reaction conditions. The reasonable setting of the reaction time avoids both incomplete reaction due to insufficient time and energy waste caused by excessive time, effectively improving fluoride recovery efficiency without the need to adjust the solution pH.

[0068] In conjunction with the first aspect, in some embodiments of the present invention, the settling time is 2 min to 5 min.

[0069] In conjunction with the first aspect, in some embodiments of the present invention, the settling time is any value among 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, and 5 min, such as 3 min, or a range of any two, such as 3 min to 4 min.

[0070] Settling time refers to the period of time required for the liquid to remain still after the reaction to achieve solid-liquid stratification. This can be achieved by controlling the operating parameters of the settling tank or adjusting the sequence of process steps. In acidic wastewater systems, the density difference between the precipitate and the liquid phase is significant. A settling time of 2–5 minutes promotes rapid sedimentation of sodium sulfate solids while preventing sodium fluoride solids from settling together due to excessively long residence times or increased equipment downtime.

[0071] Specifically, in steps S1 and S3, the settling time is controlled within the range of 2 to 5 minutes. During this time period, the sodium sulfate solid generated by the reaction quickly settles to the bottom due to gravity, forming sodium sulfate bottom sludge, while the upper suspension is filtered to separate sodium fluoride solid. The shorter settling time is suitable for the highly acidic environment of the waste acid, reduces the risk of sodium fluoride settling in the liquid phase, and avoids the reduced treatment efficiency and equipment utilization caused by long settling times in traditional processes.

[0072] Compared to existing technologies, traditional sodium salt precipitation methods typically require longer settling times to ensure solid-liquid separation, especially under high-temperature conditions where changes in solution viscosity may further extend the settling period. This invention, by optimizing the settling time, achieves rapid stratification under acidic conditions, avoiding additional energy consumption and simplifying the operation process. It is particularly suitable for waste acid systems with high acidity and high impurity content.

[0073] Through the above technical solution, the present invention can efficiently complete solid-liquid separation in acidic wastewater environment, significantly shorten the process cycle, reduce equipment operating load, and reduce the dissolution loss of sodium fluoride due to prolonged contact with acidic liquid phase, thereby improving the stability and economy of fluorine recovery.

[0074] In conjunction with the first aspect, in some embodiments of the present invention, the amount of the first anhydrous sodium sulfate particles added is 350 g / L to 500 g / L.

[0075] The first amount of anhydrous sodium sulfate granules added refers to the mass range of anhydrous sodium sulfate added per liter of waste acid solution. It can be achieved by adding it in several batches or all at once. This amount range can ensure that the reaction between sulfate ions and fluoride ions is fully carried out, while avoiding excessive addition that would lead to material waste or incomplete dissolution.

[0076] Specifically, anhydrous sodium sulfate granules are directly added to the acidic waste acid solution. By controlling the dosage within the range of 350 g / L to 500 g / L, the sodium ions released after the sodium sulfate dissolves combine with fluoride ions in the waste acid to form sodium fluoride precipitate. This dosage range can maintain a sufficient sodium ion concentration in the reaction system to drive the precipitation reaction forward, while also reducing the load on the subsequent solid-liquid separation process.

[0077] Compared to existing technologies, traditional sodium salt precipitation methods typically use a low amount of sodium sulfate added in the ammonium fluoride system (e.g., below 200 g / L) and require operation under weakly alkaline conditions to ensure precipitation efficiency. In contrast, this invention achieves highly efficient fluoride precipitation without the need for pre-neutralization of the contaminated acid by increasing the amount of sodium sulfate added and matching the acidic environment, thus avoiding the consumption of neutralizing agents and the pH adjustment step.

[0078] Through the above technical solution, the present invention can directly precipitate sodium fluoride in highly acidic waste acid, effectively reducing the amount of neutralizing agent used and operating costs. At the same time, by optimizing the range of sodium sulfate addition, the reaction system is kept in the best solid-liquid equilibrium state, thereby improving the fluoride recovery efficiency.

[0079] In conjunction with the first aspect, in some embodiments of the present invention, the amount of the first anhydrous sodium sulfate particles added is any value among 350 g / L, 400 g / L, 420 g / L, 440 g / L, 460 g / L, 480 g / L, and 500 g / L, such as 400 g / L, or any range formed by both, such as 400 g / L to 440 g / L.

[0080] In conjunction with the first aspect, in some embodiments of the present invention, the amount of the first anhydrous sodium sulfate particles added is 350 g / L to 500 g / L.

[0081] Controlling the initial sodium sulfate addition to 350 g / L to 500 g / L can prevent insufficient sodium sulfate addition from affecting the fluorine recovery rate. It can also prevent excessive sodium sulfate residue from causing sodium fluoride to adsorb onto sodium sulfate crystals and precipitate out, making it impossible to separate sodium fluoride and sodium sulfate by standing, thus affecting the separation effect of sodium fluoride and sodium sulfate.

[0082] In conjunction with the first aspect, in some embodiments of the present invention, more than 90% of the first anhydrous sodium sulfate particles have a particle size greater than 425 micrometers.

[0083] The sodium fluoride precipitate formed by the reaction has a particle size of less than 100 micrometers in over 90%. Adding an excess of large-particle anhydrous sodium sulfate solid results in a sodium sulfate bottom residue with a particle size of more than 200 micrometers in over 90% of its particles. Sodium fluoride has a specific gravity of 2.79, while anhydrous sodium sulfate has a specific gravity of 2.70. According to Stokes' equation, the settling velocity of sodium sulfate is approximately 3.5-3.8 times that of sodium fluoride. Therefore, the sodium sulfate bottom residue can be preferentially discharged for sodium sulfate recovery.

[0084] Furthermore, in acidic wastewater systems, the dissolution kinetics of large-diameter sodium sulfate particles are limited by their surface contact area. Sodium ions are gradually released and combine with fluoride ions to form sodium fluoride precipitate. Because the particle size is greater than 425 micrometers, its specific surface area is significantly lower than that of finely powdered sodium sulfate. This reduced dissolution rate keeps the sodium ion concentration in the reaction system below the critical saturation level for sodium fluoride crystallization, thus avoiding disordered crystal growth caused by instantaneous supersaturation. This process promotes the orderly precipitation of sodium fluoride crystals, forming a precipitate with a uniform particle size distribution, which is beneficial for subsequent solid-liquid separation operations.

[0085] Compared to existing technologies, traditional sodium salt precipitation methods typically use finely powdered sodium sulfate or dissolved sodium salts. Under acidic conditions, rapid dissolution can lead to localized supersaturation of sodium ions, causing sodium fluoride precipitate to encapsulate unreacted sodium sulfate, forming dense agglomerates that hinder the continued reaction. In contrast, the application of large-diameter particles controls the dissolution rate through physical size, achieving a continuous supply of sodium ions without the need for pH adjustment, thus overcoming the dependence of traditional methods on an alkaline environment.

[0086] Through the above technical solution, this invention achieves efficient precipitation of sodium fluoride in acidic wastewater systems, avoiding the large consumption of neutralizing agents and reducing the risk of reaction interruption due to rapid dissolution. The slow dissolution characteristic of large-particle sodium sulfate maintains a stable ion concentration in the reaction system, ensuring the orderly growth of sodium fluoride crystals, improving the filtration performance of the precipitated product, and reducing equipment scaling.

[0087] In conjunction with the first aspect, in some embodiments of the present invention, more than 90% of the particles in the sodium fluoride solid have a particle size of less than 100 micrometers.

[0088] Sodium fluoride solid refers to the precipitate product generated by the reaction of sodium sulfate with fluoride ions in waste acid. This can be achieved by controlling the reaction conditions and solid-liquid separation process. Its particle size distribution directly affects the purity of the product and the efficiency of subsequent treatment.

[0089] Among them, the particle size of less than 100 micrometers refers to the size range of the precipitated particles, which can be achieved by adjusting the reaction temperature, stirring speed or adding crystal form control agents. Smaller particle size helps to reduce impurity encapsulation and improve the solid-liquid separation speed.

[0090] Specifically, in acidic wastewater systems, sodium sulfate reacts with fluoride ions to form sodium fluoride precipitate. By controlling the reaction conditions, the particle size of the precipitate can be kept within a small range. For example, when the reaction is carried out under low-temperature stirring conditions, the nucleation rate is higher than the crystal growth rate, promoting the formation of a large number of microcrystals, thus forming fine-particle precipitates. In addition, shortening the settling time can prevent excessive particle aggregation and maintain the particle size distribution. In the sodium fluoride solid obtained in this way, more than 90% of the particles are smaller than 100 micrometers in diameter, which can be directly separated efficiently by conventional filtration equipment.

[0091] Compared to existing technologies, traditional sodium salt precipitation methods require weakly alkaline and high-temperature conditions to generate sodium fluoride precipitate. The particles tend to coarse or agglomerated due to the long crystal growth time, leading to impurity entrainment and filtration difficulties. In contrast, this invention directly generates fine-particle precipitate under acidic conditions, eliminating the need for pH adjustment or heating. This reduces neutralizing agent and energy consumption, and avoids the special equipment requirements of high-temperature filtration.

[0092] Through the above technical solution, the present invention can directly obtain sodium fluoride precipitate with uniform particle size in acidic wastewater, reduce impurity adsorption and improve solid-liquid separation efficiency, while simplifying the process flow and reducing equipment investment and operating costs.

[0093] In conjunction with the first aspect, in some embodiments of the present invention, the fluorine recovery rate of the method is ≥50% per run.

[0094] Fluorine single-cycle recovery rate refers to the proportion of fluorine removed from the waste acid during a single cycle. Specifically, it can be achieved by controlling the amount of anhydrous sodium sulfate particles added, the stirring reaction time, and the settling conditions. For example, add 350-500 grams of sodium sulfate particles with a particle size greater than 425 micrometers per liter of waste acid and stir at 35-45℃ for 4-24 hours to allow sodium fluoride precipitate to fully form and be quickly separated, thereby ensuring that at least 50% of the fluorine is recovered in a single treatment.

[0095] Specifically, when the waste acid solution comes into contact with anhydrous sodium sulfate particles under acidic conditions, fluoride ions combine with sodium ions to form sodium fluoride precipitate. Through a stepwise precipitation and bottom residue recycling strategy, sodium sulfate particles react directly with waste acid to generate sodium fluoride during the first treatment. In subsequent recycling stages, sodium sources are replenished by dissolving bottom residue and adding new particles to continuously maintain the sodium ion concentration in the reaction system, thereby ensuring that the fluoride precipitation efficiency of each cycle remains stable at over 50%.

[0096] Compared to existing technologies, traditional sodium salt precipitation methods require a weakly alkaline environment and rely on high temperatures. This invention, by optimizing the particle size distribution of sodium sulfate and reaction parameters, allows the sodium fluoride precipitation process to proceed directly in acidic wastewater without additional neutralization. Simultaneously, the reaction temperature is reduced to 35-45℃, significantly decreasing energy consumption. Furthermore, the recycling of bottom sludge reduces sodium sulfate consumption, further lowering operating costs.

[0097] Through the above technical solution, the present invention achieves efficient fluorine recovery under acidic conditions. More than half of the fluorine in the waste acid can be removed in a single treatment, avoiding the need for multiple cycles or deep treatment in traditional processes. At the same time, it simplifies the operation process and is suitable for the industrial treatment of high-fluorine waste acid in copper, lead, zinc and molybdenum smelting processes.

[0098] In conjunction with the first aspect, in some embodiments of the present invention, the fluoride content in the high-fluoride acid solution is 10–60 g / L.

[0099] High-fluoride acid wastewater refers to fluoride-containing acidic wastewater generated during the pyrometallurgical processes of copper, lead, zinc, and molybdenum. The fluoride exists in the form of hydrofluoric acid, which can be achieved by enriching and discharging the wastewater solution after circulating the flue gas scrubbing liquid. A fluoride content of 10–60 g / L refers to the range of fluoride ion concentration in the solution, which can be determined using ion chromatography or fluoride ion selective electrode method. This concentration range satisfies the economic value of resource recovery while avoiding a decrease in precipitation reaction efficiency due to excessively high concentrations.

[0100] Specifically, when the fluoride content in the waste acid solution is between 10 and 60 g / L, anhydrous sodium sulfate granules are added in stages to directly induce a precipitation reaction under acidic conditions. In the initial stage, the first batch of anhydrous sodium sulfate granules is added to the waste acid solution. Stirring causes the sodium sulfate to react with hydrofluoric acid to form sodium fluoride precipitate. After settling, the bottom sludge and the upper suspension are separated. In subsequent stages, the fluoride-precipitated liquid is returned to the flue gas scrubbing system for recycling. When the fluoride concentration is enriched again to a level less than 20% lower than the initial fluoride concentration in the waste acid, the bottom sludge is dissolved and a second batch of anhydrous sodium sulfate granules is added to achieve the cyclic precipitation and recovery of sodium fluoride.

[0101] In some specific embodiments, the fluoride content of the waste acid solution is, for example, 15 g / L, 30 g / L, or 45 g / L, and the corresponding amount of anhydrous sodium sulfate added can be adjusted according to the actual concentration. For example, when the fluoride content is 20 g / L, the amount of the first anhydrous sodium sulfate granules added can be 400 g / L, the stirring reaction time is controlled at 8 hours, and the standing time is selected as 3 minutes.

[0102] Compared to existing technologies, conventional sodium salt precipitation methods primarily target ammonium fluoride systems, requiring pH adjustment to a weakly alkaline state and maintenance of high temperatures. This invention, however, directly treats acidic wastewater without additional neutralization, and the reaction temperature can be controlled between 35 and 45°C. For example, traditional methods operate at pH 8–9 and temperatures of 50–80°C, while this method operates even at the naturally acidic (H+) pH of the wastewater. + The precipitation reaction can be completed under conditions of concentration (0.5–3 mol / L) and temperature (35–45°C).

[0103] Through the above technical solution, this invention can directly treat acidic waste acid with a fluoride content of 10-60 g / L, avoiding the consumption of neutralizing agents and high-temperature operation, thus reducing operating costs. Simultaneously, by recycling the fluoride-precipitated liquid as a rinsing solution, the amount of waste acid discharged is reduced, achieving continuous recovery of fluoride resources.

[0104] In conjunction with the first aspect, in some embodiments of the present invention, the amount of the second anhydrous sodium sulfate particles added is = a × 142 / 38 × fluorine concentration × solution volume - weight of sodium sulfate bottom residue in step S1, where a is 0.5-2.0.

[0105] The second aspect of the present invention provides the application of the method of the first aspect of the present invention in the pyrometallurgical smelting of copper, lead, zinc and molybdenum.

[0106] Pyrometallurgical smelting of copper, lead, zinc, and molybdenum refers to the process of extracting metals from ores or concentrates through high-temperature smelting, which can be achieved using equipment such as reverberatory furnaces, flash furnaces, or blast furnaces. During this process, the flue gas is absorbed by the leaching liquid to form fluoride-containing waste acid, and the concentration of fluoride in the waste acid can reach 10–60 g / L.

[0107] The application refers to integrating the waste acid treatment process with the smelting process. Specifically, this can be achieved by returning the fluoride-precipitated liquid to the smelting system as a flue gas scrubbing liquid. By recycling the scrubbing liquid, fluoride in the waste acid can be continuously recovered without interrupting smelting production.

[0108] Specifically, in the flue gas treatment stage of pyrometallurgical processes, the scrubbing liquid forms high-fluoride waste acid after multiple cycles. By adding anhydrous sodium sulfate particles to the waste acid, sodium fluoride precipitate is directly generated under acidic conditions. The fluoride-precipitated liquid after precipitation is returned to the scrubbing system to continue absorbing flue gas. When the fluoride concentration increases again, the precipitation process is repeated by adding sodium sulfate particles. This method eliminates the need to adjust the solution pH and controls the reaction temperature within the range of 35 to 45 degrees Celsius, matching the waste heat conditions of the smelting system, thereby reducing additional energy consumption.

[0109] Compared to existing technologies, traditional sodium salt precipitation methods require a weakly alkaline environment, while the waste acid itself is strongly acidic, leading to the consumption of a large amount of alkali during the neutralization process. This invention optimizes the addition method of sodium sulfate and reaction conditions to achieve direct fluoride precipitation in an acidic environment, avoiding neutralization costs. Furthermore, existing technologies require high-temperature precipitation followed by hot filtration, while this invention employs low-temperature reaction and conventional filtration equipment, simplifying the operation process and reducing the corrosion resistance requirements on the equipment.

[0110] Through the above technical solution, this invention solves the problems of frequent pH adjustment and reliance on high-temperature conditions required for fluoride recovery in the treatment of waste acid from pyrometallurgical processes, and achieves continuous recovery of fluoride resources within the acidic leaching solution system. The recycling of the fluoride-precipitated liquid reduces the amount of waste acid discharged, while the sodium fluoride precipitate can be directly utilized as a byproduct, lowering the overall operating cost of the smelting system.

[0111] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0112] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0113] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0114] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0115] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0116] Example

[0117] Fluorine was recovered from the high-fluoride acidic solution obtained from zinc pyrometallurgical processes. Ion chromatography analysis showed that the fluorine content in the high-fluoride acidic solution was 16.9 g / L.

[0118] The specific steps are as follows:

[0119] S1: Add the first anhydrous sodium sulfate particles to the first waste acid solution, stir and react, then let stand to obtain the first upper suspension and the first sodium sulfate bottom residue, and discharge the first sodium sulfate bottom residue.

[0120] S2: Filter the first upper suspension to obtain the first sodium fluoride solid and the first fluoride-precipitated liquid;

[0121] S3: The first fluoride-precipitated liquid is returned to the smelting process as a flue gas scrubbing liquid. When the difference between the fluoride concentration in the flue gas scrubbing liquid and the fluoride concentration in the first waste acid solution is less than 20%, the first sodium sulfate bottom residue is added. After the first sodium sulfate bottom residue dissolves, the second anhydrous sodium sulfate particles are added. After stirring and reacting, the mixture is allowed to stand to obtain the second upper suspension and the second sodium sulfate bottom residue. The second upper suspension is filtered to obtain sodium fluoride solid and the second fluoride-precipitated liquid. The second fluoride-precipitated liquid is returned to the smelting process as a flue gas scrubbing liquid, forming a cycle.

[0122] In step S1, the stirring reaction temperature is approximately 40℃, the stirring reaction time is 16 hours, and the settling time is 3 minutes. The amount of the first anhydrous sodium sulfate granules added is 400 g / L. More than 90% of the first anhydrous sodium sulfate granules have a particle size greater than 425 micrometers.

[0123] In step S2, more than 90% of the particles in the sodium fluoride solid have a particle size of less than 100 micrometers.

[0124] The test results are shown in Tables 2 and 3. Among them, the fluorine content and SO4 content... 2- The content was determined by ion chromatography.

[0125] Table 2

[0126]

[0127] The first acidic waste solution contains 16.9 g / L of fluoride, has a volume of 1000 L, and a total fluoride content of 16900 g.

[0128] After the first fluoride precipitation, the fluoride content in the liquid decreased to 4.3 g / L, the volume was 1100 L, and the residual fluoride amount was 4730 g.

[0129] Based on the fluoride content of the first waste acid solution and the first fluoride-precipitated liquid obtained from the test, the total fluoride precipitation rate was calculated to be (16900-4730) / 16900×100% = 72.0%. The fluoride recovery rate of 72.0% in a single treatment demonstrates the high efficiency of the method of this invention.

[0130] Table 3

[0131] Name Weight kg F content SO4 2- content <!-- 10 -->]]> First sodium fluoride solid 19.9 44.30％ 0.33％ First sodium sulfate bottom 42.3 7.96％ 54.80％

[0132] The theoretical F content in sodium fluoride is 19 / 42 × 100% = 45.24%. In Table 3, the first sodium fluoride solid weighs 19.9 kg and has an F content of 44.30% (close to the theoretical value of 45.24%), indicating high purity. SO4 2- The content is only 0.33%, indicating that there is very little sodium sulfate residue and the separation effect is good.

[0133] After the first fluoride precipitation, the liquid is returned to continue as flue gas scrubbing liquid. When the fluoride content reaches 17.2 g / L, 42.3 kg of the first sodium sulfate bottom residue is added, and 101.7 kg of the second anhydrous sodium sulfate granules are added.

[0134] Table 4

[0135]

[0136]

[0137] Wherein, the total precipitation rate of F = (total initial fluoride - total residual fluoride in the fluoride-precipitated solution) / total initial fluoride × 100%

[0138] The initial total fluorine content = 17.2 × 1120 = 19264 g.

[0139] Total residual fluoride = 4.7 × 1150 = 5405g.

[0140] The amount of fluorine precipitated = 19264 - 5405 = 13859g.

[0141] Total sedimentation rate F = 13859 / 19264 × 100% = 71.9%.

[0142] In Table 4, the fluorine concentration recovered to 17.2 g / L (close to the initial value), with a volume of 1120 L. In the liquid after the second fluorine precipitation, the fluorine concentration was 4.7 g / L, with a volume of 1150 L, and the total fluorine precipitation rate was 71.9%. This indicates that the circulating process has good stability, the fluorine recovery rate remains at a high level, and the repeatability of the method is verified.

[0143] Table 5

[0144] Name Weight kg F content SO4 2- content]]> Second sodium fluoride solid 22.6 44.60％ 0.33％ Second sodium sulfate bottom 39.6 9.56％ 53.20％

[0145] In Table 5, the solid F content of sodium fluoride II is 44.60%, and SO4 content is... 2- The content is 0.33%, consistent with the first round, indicating that the product purity is stable.

[0146] This invention provides a method for recovering fluoride from high-fluoride acidic solutions, achieving a single-pass fluoride recovery rate exceeding 70%, far surpassing industry norms (typically 50%-60%). Fluoride can be directly precipitated under acidic conditions, eliminating the need for a neutralization step and reducing costs.

[0147] The fluoride precipitation solution is recycled, and the sodium sulfate saturated rinsing solution reduces the amount of reagent replenishment (only 101.7 kg is added in the second round vs. 400 g / L × 1000 L = 400 kg in the first round).

[0148] Regarding product purity, the sodium fluoride solid F content is close to the theoretical value, and SO4 content is low. 2- The residue is extremely low (0.33%), and it can be directly utilized as a resource.

[0149] Furthermore, the method for recovering fluoride from high-fluoride waste acid solutions in this invention utilizes the residual heat of the rinsing solution (50-80℃) to dissolve sodium sulfate, eliminating the need for additional heating and thus saving energy. The direct reaction under acidic conditions eliminates the need for pH adjustment, making operation convenient. Sodium fluoride is recovered as a byproduct, and sodium sulfate is recycled, meeting the requirements of green smelting. These results fully verify the high efficiency and economy of this invention in the resource recovery of high-fluoride waste acid.

[0150] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for recovering fluoride from a high-fluoride contaminated acid solution, characterized in that, Includes the following steps: S1: Add the first anhydrous sodium sulfate particles to the first waste acid solution, stir and react, then let stand to obtain the first upper suspension and the first sodium sulfate bottom residue, and discharge the first sodium sulfate bottom residue. S2: Filter the first upper suspension to obtain sodium fluoride solid and fluoride-precipitated liquid; S3: The fluoride-precipitated liquid is returned to the smelting process as a flue gas scrubbing liquid. When the difference between the fluoride concentration in the flue gas scrubbing liquid and the fluoride concentration in the first waste acid solution is less than 20%, the first sodium sulfate bottom residue is added. After the first sodium sulfate bottom residue dissolves, the second anhydrous sodium sulfate particles are added. After stirring and reacting, the mixture is allowed to stand to obtain the second upper suspension and the second sodium sulfate bottom residue. The second upper suspension is filtered to obtain sodium fluoride solid and the fluoride-precipitated liquid. The fluoride-precipitated liquid is returned to the smelting process as a flue gas scrubbing liquid to form a cycle.

2. The method according to claim 1, characterized in that, The temperature of the stirring reaction is 35℃~45℃.

3. The method according to claim 1, characterized in that, The stirring reaction time is 4h to 24h.

4. The method according to claim 1, characterized in that, The settling time is 2 to 5 minutes.

5. The method according to claim 1, characterized in that, The amount of the first anhydrous sodium sulfate granules added is 350 g / L to 500 g / L.

6. The method according to claim 1, characterized in that, In both the first and second anhydrous sodium sulfate particles, more than 90% of the particles have a diameter greater than 425 micrometers.

7. The method according to claim 1, characterized in that, In the sodium fluoride solid, more than 90% of the particles have a particle size of less than 100 micrometers.

8. The method according to any one of claims 1 to 7, characterized in that, The method achieves a single-pass fluorine recovery rate of ≥50%.

9. The method according to any one of claims 1 to 7, characterized in that, The fluoride content in the high-fluoride acid solution is 10–60 g / L.

10. The application of the method according to any one of claims 1 to 7 in the pyrometallurgical smelting of copper, lead, zinc, and molybdenum.

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