Process for the defluorination of a mixture of fluorochlorohydrocarbons

Abstract

The application provides a defluorination method of fluorochloromix acid, and steps of the method comprise: mixing lime with water to obtain lime milk; adding the lime milk into defluorination liquid obtained by one-stage defluorination of the fluorochloromix acid to perform deep defluorination, and filtering to obtain defluorination liquid and defluorination residue; adding the defluorination residue after slurry into the fluorochloromix acid to perform one-stage defluorination, and filtering to obtain calcium fluoride precursor and defluorination liquid; and drying the calcium fluoride precursor in a rotary kiln to obtain fluorite product. The defluorination method of fluorochloromix acid is economic, efficient, green and environment-friendly, can reduce the fluorine content in the fluorochloromix acid to below 30 mg / L, and can reach the recycling standard of returning to a zinc hydrometallurgy system as industrial secondary water for continuous utilization after a subsequent dechlorination process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgical wastewater zero discharge, and particularly relates to a defluorination method of fluorine-chlorine mixed acid. BACKGROUND

[0002] The consumption of water resources in the wet zinc smelting process is 9 tons of water per ton of zinc, and the amount of wastewater discharged up to standard is 10 tons of water per ton of zinc. However, the discharged water still contains trace amounts of heavy metals, which is harmful to the environment and wastes resources. Fluorine-chlorine mixed acid is a mixed solution containing 65-125 g / L of F + , 25-55 g / L of Cl - , and 12-28 g / L of F - , which is obtained by removing impurities from waste acid wastewater treated by acid-making process from the roasting flue gas of sulfide ore. The content of heavy metals in the fluorine-chlorine mixed acid is trace amount. At present, the zinc smelting industry uses lime defluorination technology to treat the fluorine-chlorine mixed acid, that is, one-stage defluorination, defluorination time of 30 min, and end point pH of 8-9. After defluorination, the fluorine content in the liquid is 50-70 mg / L, the fluorine content in the product calcium fluoride is 55-70%, and the product is difficult to sell, which occupies a large amount of working capital. The sales price of the first-grade fluorite powder on the market is more than 4000 yuan / ton.

[0003] Fluoride ions have strong corrosion function in acidic solutions. In the zinc electrolysis process, when the F - content exceeds 30 mg / L, the fluoride ions will corrode the passivated aluminum oxide film on the surface of the protective cathode aluminum plate, causing the exposed metal aluminum inside the passivated aluminum oxide film on the cathode plate, shortening the service life of the cathode plate, and forming an alloy of zinc and metal aluminum, which makes it difficult to strip the zinc, resulting in increased production cost and decreased quality of the stripped zinc. Therefore, for small polar plates with a short electrolysis period, the F content in the new liquid is required to be less than 50 mg / L, and for large polar plates with an electrolysis time of more than 32 h, the F content is required to be less than 30 mg / L. Therefore, the fluorine-chlorine mixed acid with high F content cannot be directly used in the zinc smelting system.

[0004] A method for removing fluorine and chlorine from zinc smelting waste acid is disclosed in Chinese Patent Application CN 112028208 A, which comprises: removing arsenic and mercury from the zinc smelting waste acid to obtain attenuated waste acid; adding a copper-containing agent to the attenuated waste acid to remove chlorine, and filtering to obtain chlorine-removed liquid and chlorine-containing residue; adding a calcium-containing agent to the chlorine-removed liquid to remove fluorine, and filtering to obtain fluorine and chlorine-removed backwater and fluorine-containing residue. The method reduces the amount of waste acid residue to some extent, but the arsenic and mercury removal residue is a hazardous waste, and the calcium-containing agent is complex and difficult to prepare, containing additives such as zinc oxide, zinc carbonate, metallic zinc, zirconium oxide, and aluminum oxide, resulting in high heavy metal content in the backwater and a large amount of residue, and the backwater is not a product. At the same time, the fluorine removal rate of the method is less than 87%, the F content in the backwater exceeds 130 mg / L, the backwater is difficult to return to the zinc smelting system for use as make-up water, and the application range of F is only within 1000-4000 mg / L, in addition, the valuable substances zinc, lead, copper and sulfuric acid in the waste acid are not reasonably recovered.

[0005] A method for deeply removing fluorine from zinc sulfate solution and its application are disclosed in Chinese Patent Application CN 116875814 A. The method does not change the main process route, but adds aluminum sulfate particles after the original pre-neutralization of the liquid, and produces defluorination residue by pressure filtration. The method also produces colloidal iron to remove fluorine from the solution, and the total fluorine removal rate reaches more than 90%. However, this method should be used in the main zinc hydrometallurgy system, and it removes fluorine from zinc sulfate solution, producing a large amount of aluminum hydroxide and iron hydroxide colloid, which is difficult to filter, and a large amount of valuable metal zinc is carried away, reducing the direct recovery rate of zinc. Moreover, this method is aimed at removing fluorine from zinc sulfate system, which is completely different from the fluorine and chlorine mixed acid system.

[0006] Therefore, there is an urgent need for a green and environmentally friendly, economical and efficient fluorine and chlorine mixed acid wastewater treatment method, which can reduce the fluorine content in the fluorine and chlorine mixed acid wastewater to less than 30 mg / L after treatment, and then achieve the industrial backwater recycling standard of returning to the zinc hydrometallurgy system for further utilization after the subsequent dechlorination process. SUMMARY

[0007] The technical problem to be solved by the present application is to provide an economical and efficient fluorine and chlorine mixed acid defluorination method, which can reduce the fluorine content in the fluorine and chlorine mixed acid to less than 30 mg / L, and then achieve the recycling standard of returning to the zinc hydrometallurgy system for further utilization as industrial backwater after the subsequent dechlorination process.

[0008] To solve the above technical problems, the present application provides a fluorine and chlorine mixed acid defluorination method, comprising the following steps:

[0009] Mixing lime with water to obtain lime milk;

[0010] The defluorination liquid obtained by one-stage defluorination of the fluoro-chloro mixed acid is added with lime milk for deep defluorination, and the defluorination residue and the defluorination liquid after defluorination are obtained by filtration;

[0011] The defluorination residue after slurry is added into the fluoro-chloro mixed acid for one-stage defluorination, and the calcium fluoride precursor and the defluorination liquid are obtained by filtration;

[0012] The calcium fluoride precursor is dried in a rotary kiln to obtain the fluorite product.

[0013] Further, the mixing mass ratio of the lime and water is 1:1.2-1:2.5, the mixing temperature is 20-95℃, and the mixing time is 8-24h.

[0014] Further, the lime milk is slowly added when the defluorination liquid is added with lime milk for deep defluorination, the pH is controlled to be 9-11 at the end point of the addition of the lime milk, the deep defluorination temperature is 20-70℃, and the deep defluorination time is 30-90min.

[0015] Further, the defluorination residue is slurried with the fluoro-chloro mixed acid as the slurry liquid, and the liquid-solid mass ratio during the slurry of the defluorination residue is 1.5:1-3:1, and the slurry time is 20-45min.

[0016] Further, the defluorination temperature of the fluoro-chloro mixed acid during the one-stage defluorination is 75-95℃, the defluorination time is 120-240min, and the mass-volume concentration of H + in the solution at the end point of the one-stage defluorination is controlled to be 10-50g / L.

[0017] Further, the calcium fluoride precursor is purified before being dried in the rotary kiln, the purified water is deionized water, the liquid-solid ratio of the calcium fluoride precursor and the purified water is 1:1-1:3.5, and the purification time is 15-60min.

[0018] Further, the rotary kiln has 6-10 circumferential paddles, the paddle material is 316L, the paddle thickness is 3-5mm, the folded edge is 12-18mm, the height is 45-600mm, the installation inclination angle of the rotary kiln is 1-6°, and the rotation speed is 2-8r / min.

[0019] Further, the heating speed of the rotary kiln during the drying of the calcium fluoride precursor is 2.0-2.5℃ / min, the drying temperature is 350-550℃, and the calcium fluoride outlet temperature is controlled to be 45-80℃.

[0020] Further, the fluoro-chloro mixed acid is obtained in the process of treating the waste acid produced in zinc smelting or sulfur concentrate smelting, and the fluoro-chloro mixed acid contains H + , F - , and Cl -Mixed solutions with mass-volume concentrations of 65–125 g / L, 25–55 g / L, and 12–28 g / L, respectively.

[0021] This invention provides a defluorination method for mixed fluorochlorine acid. It applies the principles of ferrous metallurgical technologies, such as using a rotary kiln to enrich and remove zinc impurities from the flue dust of calcium fluoride precursors and using lime precipitation to treat fluoride-containing wastewater, along with the industry standard "YB / T 5217-2019 Fluorite," to the treatment of non-ferrous metallurgical wastewater. This method can deeply defluorinate mixed fluorochlorine acid obtained during the treatment of waste acid from zinc smelting or sulfur concentrate smelting, removing the fluoride (F) from the mixed fluorochlorine acid. - The content is reduced to below 30 mg / L, ensuring zero wastewater discharge. Furthermore, the calcium fluoride product obtained during the defluorination process of fluorochlorinated mixed acids has a CaF2 content exceeding 97%, meeting the requirements for Grade I fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard. This gives the product stronger market competitiveness and higher economic value. Simultaneously, the lime consumption in the defluorination process of fluorochlorinated mixed acids is reduced by 20-25% compared to the original process, reducing auxiliary material consumption and lowering treatment costs. Therefore, the defluorination method for fluorochlorinated mixed acids provided by this invention not only efficiently defluorinates the fluorochlorinated mixed acids, allowing them to be recycled back to the zinc hydrometallurgical system as industrial secondary wastewater after subsequent dechlorination processes, but also has lower process costs, more competitive products, and better economic benefits.

[0022] Furthermore, the defluorination method for fluorochlorinated mixed acid provided by this invention is simple in process and reasonable in process flow. It can be applied only by modifying existing equipment. At the same time, no other raw materials that have an impact on the environment are introduced in the process. The waste residue and waste liquid generated in the process are recycled, achieving zero discharge of wastewater. The process is green and environmentally friendly, meets the requirements of resource recycling and sustainable development, has been industrialized, and has a very broad application prospect. Attached Figure Description

[0023] Figure 1 This is a flowchart of a defluorination method for a fluorochlorinated mixed acid provided in an embodiment of the present invention. Detailed Implementation

[0024] See Figure 1 The present invention provides a method for defluorinating a fluorochlorinated mixed acid, comprising the following steps:

[0025] Step 1) Pretreatment: Lime and water are mixed and reacted to obtain a fully slurried lime slurry. The following reactions occur during this process:

[0026] CaO + H₂O = Ca(OH)₂

[0027] The mass ratio of lime to water in the reaction is 1:1.2-1:2.5, and the reaction time is 8-24 hours. Controlling the reaction temperature and time not only activates the resulting lime slurry, improving the defluorination rate of the fluorochlorinated mixed acid, but also helps remove large, incompletely sintered calcium carbonate precipitates from the lime, thus improving the quality of the final product, calcium fluoride. Furthermore, to increase the reaction rate and ensure complete reaction of calcium oxide in the lime into calcium hydroxide, the reaction temperature is appropriately increased, controlled between 20-95℃.

[0028] Step 2) Deep Defluorination: Lime slurry is added to the defluorinated solution obtained after a first-stage defluorination process of the fluorochlorine-mixed acid to carry out deep defluorination. After deep defluorination is completed, the solution is filtered to obtain the defluorinated liquid and defluorinated residue. The following reactions occur during the deep defluorination process:

[0029] Ca(OH)₂ + 2HF = CaF₂↓ + 2H₂O

[0030] Ca(OH)2 + 2HCl = CaCl2 + 2H2O.

[0031] The F in the defluorinated solution obtained after deep defluorination of fluorochlorine mixed acid - The concentration was reduced to below 30 mg / L, ensuring zero wastewater discharge. The resulting defluorinated liquid was then fed into a subsequent dechlorination process. After meeting dechlorination standards, the defluorinated liquid could be returned to the zinc hydrometallurgical system as industrial wastewater for continued recycling, achieving zero wastewater discharge and ensuring the green and environmentally friendly nature of the process. This made the defluorination process of the fluorinated and chlorinated mixed acid of this invention meet the requirements of resource recycling and sustainable development.

[0032] The defluorination residue obtained from deep defluorination is recycled back to a first-stage defluorination process after being pulped and reused for defluorination. By recycling the waste residue generated in the process, waste emissions are reduced and the impact on the environment is minimized. The process is green and environmentally friendly, and meets the requirements of resource recycling and sustainable development.

[0033] In order to ensure that the amount of lime slurry added is within a controllable range and reduce production costs, when adding lime slurry to the defluorination solution obtained from the first stage of defluorination, the lime slurry should be added slowly, and the pH of the solution should be controlled at 9-11 at the end of the lime slurry addition.

[0034] By controlling the pH at the endpoint when lime slurry is added, the sulfur (F) content in the defluorination solution obtained from the first stage of defluorination can be kept below 30 mg / L. This ensures that the F content in the defluorinated water discharged into the zinc smelting system is less than 30 mg / L, thus preventing the formation of F during the zinc smelting electrolysis process. - Burning of the plate occurred.

[0035] Meanwhile, in order to ensure that lime slurry fully removes fluoride from the defluorination solution, the temperature during deep defluorination is controlled at 20-70℃ and the deep defluorination time is controlled at 30-90min.

[0036] Step 3) First-stage defluorination: Add the defluorination residue after pulping to the fluorinated and chlorinated mixed acid to carry out first-stage defluorination.

[0037] The fluorochlorine mixed acid is obtained during the treatment of waste acid from zinc smelting or sulfur concentrate smelting. The fluorochlorine mixed acid contains H... + F - Cl - Mixed solutions with mass-volume concentrations of 65–125 g / L, 25–55 g / L, and 12–28 g / L, respectively.

[0038] Since the main component of the defluorination slag obtained from deep defluorination is calcium fluoride, it also contains residual lime, calcium carbonate residue from incompletely calcined lime, calcium silicate impurities carried in the calcium carbonate used to burn lime, and calcium hydroxide that has not fully reacted in the deep defluorination process. In order to activate the calcium carbonate and calcium oxide in the defluorination slag obtained from deep defluorination and to prevent the defluorination slag from agglomerating during the first-stage defluorination process and affecting the reaction efficiency, and also to facilitate the transportation of the defluorination slag obtained from deep defluorination through pipelines to reduce production costs, the defluorination slag is first pulped before the first-stage defluorination of the fluorine-chlorine mixed acid.

[0039] When pulping the defluorination residue, a fluorochlorine mixed acid is used as the pulping liquid. This avoids introducing other environmentally harmful raw materials into the process, making it more green and environmentally friendly.

[0040] Furthermore, in order to make the defluorination residue more fully and effectively pulped, the liquid-solid mass ratio of the fluorinated chlorine mixed acid to the defluorination residue during pulping is controlled at 1.5:1-3:1, and the pulping time is controlled at 20-45 min.

[0041] By pulping the defluorination slag, the calcium carbonate and calcium oxide in the slag can be activated, ensuring the complete reaction of residual calcium carbonate and calcium oxide, reducing the impurity content, guaranteeing the calcium fluoride content in the final fluorite product, and improving its grade. It also prevents the agglomeration of calcium fluoride with impurities, avoiding the incomplete reaction caused by the encapsulation of impurities such as calcium carbonate and calcium oxide.

[0042] During a defluorination process involving the addition of defluorinated residue after pulping to a fluorochlorine mixed acid, the following reaction occurs:

[0043] CaCO3+2HF=CaF2↓+CO2↑+H2O

[0044] CaSiO3 + 2HF = CaF2↓ + H2SiO3

[0045] Ca(OH)₂ + 2HF = CaF₂↓ + 2H₂O

[0046] Ca(OH)₂ + 2HCl = CaCl₂ + 2H₂O

[0047] CaCO3+2HCl=CaCl2↓+CO2↑+H2O

[0048] In order to ensure that the unreacted calcium carbonate, calcium silicate and lime milk in the defluorination residue can be completely reacted, thus ensuring the quality of the final product calcium fluoride and improving economic efficiency, and also to ensure that the fluorine in the fluorine-chlorine mixed acid can be fully and effectively removed, the defluorination temperature of the fluorine-chlorine mixed acid during the first stage of defluorination is 75-95℃ and the defluorination time is 120-240min.

[0049] Furthermore, to ensure the complete reaction of substances such as calcium oxide, calcium hydroxide, and calcium carbonate in the defluorination residue, thereby improving the grade and quality of the calcium fluoride product, it is necessary to minimize the residual acid in the solution at the endpoint of the first-stage defluorination process. To achieve this, the H+ in the solution at the endpoint of the first-stage defluorination process should be reduced. + The mass-volume concentration is controlled at 10-50 g / L.

[0050] After a single-stage defluorination process, the mixed fluorinated and chlorinated acid is filtered to obtain a calcium fluoride precursor and a defluorination solution. The defluorination solution obtained from the first-stage defluorination is used in step 2) for further defluorination with lime. The resulting calcium fluoride precursor is used in step 4) to prepare the fluorite product.

[0051] Step 4) The calcium fluoride precursor is dried in a rotary kiln to obtain the fluorite product.

[0052] Because residual F is present in the calcium fluoride precursor obtained after filtration following a defluorination process. - Cl - H + Soluble harmful positive and negative ions can remain in fluorite products during subsequent preparation, affecting product quality. Furthermore, residual F... - Cl - H + The acid formed by the plasma can also corrode the rotary kiln used for drying the calcium fluoride precursor, increasing production costs and reducing product quality. Therefore, the calcium fluoride precursor must be purified before drying.

[0053] The purified water used for purifying the calcium fluoride precursor was deionized water, in order to fully remove F from the calcium fluoride precursor. - Cl - H +Using positive and negative ions, the liquid-solid ratio of calcium fluoride precursor to purified water is controlled at 1:1-1:3.5, and the purification time is controlled at 15-60 min.

[0054] Purifying the calcium fluoride precursor removes soluble impurity ions, thereby improving the grade of the final fluorite product and ensuring its quality. Furthermore, replacing the residual solution in the calcium fluoride precursor with deionized water during the purification process further guarantees the quality of the final fluorite product.

[0055] Since the calcium fluoride precursor obtained after filtration after defluorination contains only 50-70% calcium fluoride, and about 30-50% of it is water due to incomplete filtration, and deionized water used in the purification process will also remain, the calcium fluoride precursor needs to be dried to obtain the fluorite product.

[0056] In one specific embodiment of the present invention, the drying of calcium fluoride precursor to prepare fluorite products is carried out in a rotary kiln.

[0057] In order to effectively crush the materials, prevent the fluorite products from clumping during the drying process, and make the calcium fluoride precursor dry more evenly, the rotary kiln's lifting plates are made of 316L steel with a thickness of 3-5mm, an edge thickness of 12-18mm, a height of 45-600mm, and 6-10 circumferential lifting plates.

[0058] Furthermore, to ensure the feed rate of calcium fluoride precursor into the rotary kiln, improve the designed production capacity, and ensure that the product is completely dried, the installation angle of the rotary kiln is 1-6 degrees, and the rotation speed is 2-8 rpm.

[0059] Meanwhile, in order to effectively control the moisture content of fluorite products and ensure product quality, and also to prevent the rotary kiln from being damaged or oxidized, thus reducing the entry of impurities such as iron oxide that could affect the product, and further ensuring product quality, the heating rate during the drying of the calcium fluoride precursor is controlled at 2.0-2.5℃.

[0060] The drying rate is 1000 m / min, the drying temperature is controlled at 350-550℃, and the temperature of calcium fluoride when it exits the kiln is controlled at 45-80℃.

[0061] This invention provides a defluorination method for fluorochlorinated mixed acid. During the process, without adding other reagents but only adding the conventional defluorinating agent lime, the defluorination effect in the fluorochlorinated mixed acid can be increased. This reduces the fluoride content in the defluorinated solution produced in the original defluorination process from 50-70 mg / L to below 30 mg / L in the defluorinated solution produced by this invention. Under the process technology of this invention, the secondary return water can be fully recycled to the main zinc system, reducing the amount of fresh water used, lowering production costs, and ensuring the normal operation of zinc electrolysis in the main system.

[0062] Furthermore, the calcium fluoride content in the fluorite product prepared by this invention is increased from 55-70% to 97%, significantly improving product quality. This results in first-grade fluorite concentrate that meets the "YB / T 5217-2019 Fluorite" industry standard, leading to a price increase of 2500 yuan / ton and improved economic efficiency. Moreover, the calcium carbonate in the raw material lime is fully utilized, and there is no residual lime slurry in the product. Lime usage is reduced by 20-25%, lowering production costs and further enhancing economic benefits.

[0063] Meanwhile, the process of this invention is simple and reasonable, and can be put into use with only the modification of existing equipment. The process achieves zero discharge of waste residue and wastewater, realizing green production, energy saving and environmental protection, which meets the requirements of resource recycling and sustainable development, and has a very broad application prospect.

[0064] The following examples illustrate a method for defluorinating a fluorochlorinated mixed acid provided by the present invention.

[0065] Example 1

[0066] For a kind of H + F - Cl - Fluorochloroacid mixtures with mass-volume concentrations of 98 g / L, 51 g / L, and 18 g / L, respectively, were prepared according to... Figure 1 The process involves the following steps:

[0067] First step of pretreatment: Lime and water are mixed at a mass ratio of 1:2.5 for 8 hours at a temperature of 95℃ to obtain a fully slurried lime slurry;

[0068] The second step is deep defluorination: lime slurry is slowly added to the defluorination liquid after the first stage of defluorination for deep defluorination. The defluorination temperature is 20℃, the defluorination time is 90min, and the final pH is 9. The defluorinated liquid obtained by filtration is sent to the subsequent dechlorination process, and the defluorination residue is returned to the previous process for a first stage of defluorination.

[0069] The third step is primary defluorination: The well-slurried defluorination residue is added to the fully stirred fluorochlorine mixed acid for primary defluorination. The defluorination temperature is T = 95℃, the time is t = 120 min, and the endpoint is H. +The mass-volume concentration was controlled at 10 g / L, and the calcium fluoride precursor and defluorination solution were obtained by filtration.

[0070] Step 4: Preparation of calcium fluoride: The purified calcium fluoride precursor, after being purified at a liquid-to-solid mass ratio of 1:3.5 and a purification time of 15 min, is added to a rotary kiln with an installation angle of 1 degree, a rotation speed of 8 rpm, a 316L material for the lifting plates, a plate thickness of 3 mm, a folded edge of 12 mm, a height of 45 mm, and 10 circumferential lifting plates for drying. The drying conditions are: heating rate of 2.5℃ / min, drying temperature of 350℃, and the kiln outlet temperature of calcium fluoride = 45℃. After vacuum packaging, first-grade fluorite concentrate is obtained.

[0071] F in the deep defluorination solution obtained by defluorination treatment of fluorochlorine mixed acid - With a content of 21 mg / L, the calcium fluoride product prepared has a CaF2 content of 97.46%, and the contents of impurities SiO2, CaCO3, S, P, As and organic matter are 0.41%, 0.28%, 0.007%, 0.004% and 0.002%, respectively. The moisture content is 2.16%, which meets the requirements of Grade I fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard. At the same time, because the calcium carbonate content in the product is reduced to 0.28%, the consumption of auxiliary materials is reduced, and its F is removed and reused, with a recovery rate of 99.96%.

[0072] Example 2

[0073] For a kind of H + F - Cl - Fluorochloroacid mixtures with mass-volume concentrations of 73 g / L, 42 g / L, and 14 g / L, respectively, were prepared according to... Figure 1 The process involves the following steps:

[0074] First step of pretreatment: Lime and water are mixed at a mass ratio of 1:1.2 at 20℃ for 24 hours to obtain a fully slurried lime slurry;

[0075] The second step is deep defluorination: lime slurry is slowly added to the defluorination liquid after the first stage of defluorination for deep defluorination. The defluorination temperature is 70℃, the defluorination time is 30min, and the final pH is 11. The defluorinated liquid obtained by filtration is sent to the subsequent dechlorination process, and the defluorination residue is returned to the previous process for a first stage of defluorination.

[0076] The third step is primary defluorination: The well-slurried defluorination residue is added to the completely stirred fluorochlorine-fluorinated mixed acid for primary defluorination. The defluorination temperature is T = 75℃, the time is t = 240 min, and the endpoint is H. + The mass-volume concentration was controlled at 50 g / L, and the calcium fluoride precursor and defluorination solution were obtained by filtration.

[0077] Step 4: Preparation of calcium fluoride: The purified calcium fluoride precursor, after being purified at a liquid-to-solid mass ratio of 1:1 and a purification time of 60 min, is added to a rotary kiln with an installation angle of 6 degrees, a rotation speed of 2.5 rpm, a 316L material for the lifting plates, a plate thickness of 5 mm, an edge fold of 18 mm, a height of 60 mm, and 6 circumferential lifting plates. The drying conditions are: heating rate of 2.5℃ / min, drying temperature of 550℃, and the kiln outlet temperature of calcium fluoride = 80℃. After vacuum packaging, first-grade fluorite concentrate is obtained.

[0078] F in the deep defluorination solution obtained by defluorination treatment of fluorochlorine mixed acid - With a content of 12 mg / L, the calcium fluoride product prepared has a CaF2 content of 97.32%, and the contents of impurities SiO2, CaCO3, S, P, As and organic matter are 0.38%, 0.24%, 0.006%, 0.003% and 0.001%, respectively. The moisture content is 2.31%, which meets the requirements of Grade I fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard. At the same time, because the calcium carbonate content in the product is reduced to 0.24%, the consumption of auxiliary materials is reduced, and its F is removed and reused, with a recovery rate of 99.97%.

[0079] Example 3

[0080] For a kind of H + F - Cl - Fluorochloroacid mixtures with mass-volume concentrations of 117 g / L, 35 g / L, and 18 g / L, respectively, were prepared according to... Figure 1 The process involves the following steps:

[0081] First step of pretreatment: Lime and water are mixed at a mass ratio of 1:2.0 at 65℃ for 16 hours to obtain a fully slurried lime slurry;

[0082] The second step is deep defluorination: lime slurry is slowly added to the defluorination liquid after the first stage of defluorination for deep defluorination. The defluorination temperature is 50℃, the defluorination time is 60min, and the final pH is 10. The defluorinated liquid obtained by filtration is sent to the subsequent dechlorination process, and the defluorination residue is returned to the previous process for a first stage of defluorination.

[0083] The third step is primary defluorination: The well-slurried defluorination residue is added to the fully stirred fluorochlorine mixed acid for primary defluorination. The defluorination temperature is T = 85℃, the time is t = 180 min, and the endpoint is H. + The mass-volume concentration was controlled at 30 g / L, and the calcium fluoride precursor and defluorination solution were obtained by filtration.

[0084] Step 4: Preparation of calcium fluoride: The purified calcium fluoride precursor, after being purified at a liquid-to-solid mass ratio of 1:2.5 and a purification time of 35 min, is added to a rotary kiln with an installation angle of 4 degrees, a rotation speed of 6 rpm, 316L material for the lifting plates, a plate thickness of 4 mm, a folded edge of 15 mm, a height of 55 mm, and 8 circumferential lifting plates for drying. The drying conditions are: heating rate of 2.2℃ / min, drying temperature of 450℃, and the kiln outlet temperature of calcium fluoride = 65℃. After vacuum packaging, first-grade fluorite concentrate is obtained.

[0085] F in the deep defluorination solution obtained by defluorination treatment of fluorochlorine mixed acid - With a content of 7 mg / L, the calcium fluoride product prepared has a CaF2 content of 97.29%, and the contents of impurities SiO2, CaCO3, S, P, As and organic matter are 0.30%, 0.25%, 0.004%, 0.005% and 0.003%, respectively. The moisture content is 1.11%, which meets the requirements of Grade I fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard. At the same time, because the calcium carbonate content in the product is reduced to 0.25%, the consumption of auxiliary materials is reduced, and its F is removed and reused, with a recovery rate of 99.98%.

[0086] Comparative example:

[0087] For a kind of H + F - Cl - Fluorochloroacid mixtures with mass-volume concentrations of 95 g / L, 41 g / L, and 24 g / L, respectively, were treated using conventional processes, including the following steps:

[0088] First step of pretreatment: Mix lime and water at a mass ratio of 1:2.0 for 15 hours under natural room temperature conditions to obtain a fully slurried lime slurry;

[0089] The second step is deep defluorination: lime milk is slowly added to a fluorinated and chlorinated mixed acid for defluorination at a temperature of 65°C for 30 minutes. The final pH is 8. The defluorinated liquid obtained by filtration is then sent to the subsequent dechlorination process. The defluorinated residue is the calcium fluoride precursor.

[0090] The third step is the preparation of calcium fluoride: the calcium fluoride precursor is added to a rotary kiln for drying. The drying conditions are: heating rate 2.0℃ / min, drying temperature 480℃, and the temperature of calcium fluoride exiting the kiln is 55℃. The calcium fluoride product is obtained by vacuum packaging.

[0091] The defluorinated solution obtained by defluorination treatment of fluorochlorine mixed acid contains F -The prepared calcium fluoride product, with a content of 70 mg / L, contained 67.18% CaF2 and 9.13% CaCO3, along with some calcium hydroxide and a moisture content of 1.04%, failing to meet the requirements for fluorite concentrate in the industry standard "YB / T 5217-2019 Fluorite". Furthermore, due to the 9.13% calcium carbonate content in the calcium fluoride and the incomplete reaction of some lime slurry, the consumption of lime as an auxiliary material increased significantly, leading to higher levels of F in the defluorination solution. - The content did not reach the level required for F in the electrolyte during zinc electrolysis. - The requirement of a content of less than 30 mg / L means that the secondary return water prepared by this process can only be used as makeup water in a small amount of zinc return system, and it is difficult to achieve the requirement of zero wastewater discharge.

[0092] The F in the defluorinated liquid obtained through Examples 1-3 and comparative examples of the present invention was... - Comparison of content and quality of the prepared fluorite products shows that the defluorination method for fluorochlorinated mixed acid provided by this invention performs two-stage defluorination, namely primary defluorination and deep defluorination, ensuring that the mass-volume content of F in the defluorination solution is less than 30 mg / L. The calcium fluoride product meets the requirements of Grade I fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard. The lime consumption is reduced by 20-25% compared with the lime consumption used in conventional fluorochlorinated mixed acid defluorination, providing a guarantee for achieving zero wastewater discharge.

[0093] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for defluorinating a fluorochlorinated mixed acid, characterized in that, Includes the following steps: Lime milk is obtained by reacting lime with water. Lime slurry was added to the defluorination solution obtained from the first stage of defluorination of fluorine-chlorine mixed acid for deep defluorination, and the solution was filtered to obtain the defluorinated liquid and defluorinated residue. A first-stage defluorination process was carried out by adding defluorinated residue after pulping to a fluorinated and chlorinated mixed acid, followed by filtration to obtain calcium fluoride precursor and defluorination liquid. The calcium fluoride precursor was dried in a rotary kiln to obtain the fluorite product. The mass ratio of lime to water is 1:1.2-1:2.5, the mixing temperature is 20-95℃, and the mixing time is 8-24h. During the deep defluorination process, lime slurry is added slowly to the defluorination solution. The pH is controlled at 9-11 at the endpoint of lime slurry addition, the deep defluorination temperature is 20-70℃, and the deep defluorination time is 30-90min. The defluorination slag slurrying process uses a fluorochlorine mixed acid as the slurrying liquid to slurry the defluorination slag. The liquid-solid mass ratio during the defluorination slag slurrying process is 1.5:1-3:1, and the slurrying time is 20-45 min. The defluorination temperature of the fluorochlorine mixed acid during the first-stage defluorination is 75-95℃, the defluorination time is 120-240min, and the mass-volume concentration of H+ in the solution at the end of the first-stage defluorination is controlled at 10-50g / L.

2. The defluorination method for fluorochlorinated mixed acid according to claim 1, characterized in that: Before drying in a rotary kiln, the calcium fluoride precursor is purified using deionized water. The liquid-to-solid ratio of the calcium fluoride precursor to the purified water is 1:1 to 1:3.5, and the purification time is 15-60 min.

3. The defluorination method for fluorochlorinated mixed acid according to claim 1, characterized in that: The rotary kiln has 6-10 circumferential lifting plates, made of 316L steel with a thickness of 3-5mm, an edge thickness of 12-18mm, and a height of 45-600mm. The rotary kiln is installed at an angle of 1-6° and rotates at a speed of 2-8 rpm.

4. The defluorination method for fluorochlorinated mixed acid according to claim 1, characterized in that: The rotary kiln heats up at a rate of 2.0-2.5℃ / min to dry the calcium fluoride precursor, and the drying temperature is 350-550℃. The temperature at which the calcium fluoride exits the kiln is controlled at 45-80℃.

5. The defluorination method for fluorochlorinated mixed acid according to claim 1, characterized in that: The fluorochlorine mixed acid is a fluorochlorine mixed acid obtained during the treatment of waste acid in zinc smelting or sulfur concentrate smelting, and the mass-volume concentrations of H+, F-, and Cl- in the fluorochlorine mixed acid are 65-125 g / L, 25-55 g / L, and 12-28 g / L, respectively.

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