Defluorination method of fluorine-chlorine mixed acid

Abstract

The invention provides a fluorine-chlorine mixed acid defluorination method. The fluorine-chlorine mixed acid defluorination method comprises the following steps: mixing lime and water for reaction to obtain lime milk; lime milk is added into defluorination liquid obtained through fluorine-chlorine mixed acid first-stage defluorination for deep defluorination, and defluorination liquid and defluorination residues are obtained through filtering; adding pulpified defluorination residues into fluorine-chlorine mixed acid to carry out first-stage defluorination, and filtering to obtain a calcium fluoride precursor and defluorination liquid; and drying the calcium fluoride precursor in a rotary kiln to obtain a fluorite product. The defluorination method of the fluorine-chlorine mixed acid is economical, efficient, green and environmentally friendly, the fluorine content in the fluorine-chlorine mixed acid can be reduced to 30 mg / L or below, and the fluorine-chlorine mixed acid can reach the recovery standard that the fluorine-chlorine mixed acid can be returned to a zinc hydrometallurgy system to serve as industrial secondary return water to be continuously utilized after being subjected to a subsequent dechlorination procedure.

Description

Technical Field

[0001] The invention relates to the technical field of zero discharge of metallurgical wastewater, and in particular to a defluorination method of fluorine-chlorine mixed acid. Background Art

[0002] The water consumption of hydrometallurgy is 9 tons of water per ton of zinc, and the amount of wastewater discharged that meets the standards is 10 tons of water / ton of zinc. However, there are still trace amounts of heavy metals in the wastewater, which harms the environment and wastes resources. Fluorine-chlorine mixed acid is the H obtained by removing impurities from the waste acid wastewater after the roasting flue gas of sulfide ore is treated by the acid production process. + 、F - , Cl - The contents of the mixed solution are 65-125g / L, 25-55g / L, and 12-28g / L respectively. The heavy metal content in the fluorine-chlorine mixed acid is trace. At present, the zinc smelting industry uses lime defluorination technology for fluorine-chlorine mixed acid - one-stage defluorination, defluorination time 30min, end point pH = 8-9, the fluorine content in the liquid after defluorination is 50-70mg / L, and the mass percentage of calcium fluoride in the product calcium fluoride is 55-70%, which is difficult to sell and occupies a large amount of working capital; and the current market price of first-grade fluorite concentrate exceeds 4,000 yuan / ton.

[0003] Fluoride ions have strong corrosive properties in acidic solutions. - When the content exceeds 30mg / L, fluoride ions will corrode the aluminum oxide film that has been passivated on the surface of the protective cathode aluminum plate, causing the metal aluminum coated in the passivated aluminum oxide film to be exposed, shortening the use time of the cathode plate, and forming an alloy with the precipitated zinc and the metal aluminum, making it difficult to peel off the precipitated zinc, resulting in increased production costs and reduced quality of precipitated zinc. Therefore, for small plates with a short electrolysis cycle, the F content in the new solution is required to be less than 50mg / L, while for large plates, the F content is required to be less than 30mg / L because the electrolysis time is greater than 32h. Therefore, fluorine-chlorine mixed acid with a high F content cannot be directly reused in the zinc smelting system.

[0004] Chinese patent application CN 112028208 A discloses a method for removing fluorine and chlorine from zinc smelting waste acid, which comprises: removing arsenic and mercury from zinc smelting waste acid to obtain attenuated waste acid; adding a copper-containing agent to the attenuated waste acid for dechlorination, filtering to obtain a dechlorinated liquid and a chlorine-containing slag; adding a calcium-containing agent to the dechlorinated liquid for defluorination, filtering to obtain a defluorinated and chlorinated return water and a fluorine-containing slag. This method reduces the amount of waste acid slag to a certain extent, but the arsenic and mercury-removing slag is a hazardous waste slag, and the calcium-containing agent is complex and cumbersome to prepare, and contains additives such as zinc oxide, zinc carbonate, metallic zinc, zirconium oxide, and aluminum oxide, resulting in a high content of heavy metals in the secondary return water, a large amount of slag, and it is not a product. At the same time, the fluorine removal rate of this method is less than 87%, and the F content in the secondary return water produced exceeds 130 mg / L. The secondary return water is difficult to return to the zinc smelting system for use as supplementary water, and the application range of F is only within 1000-4000 mg / L. In addition, valuable substances such as zinc, lead, copper and sulfuric acid in the waste acid are not reasonably recovered.

[0005] Chinese patent application CN 116875814 A discloses a method for deep removal of fluorine from zinc sulfate solution and its application. The method of the present invention does not change the main process route, but only adds aluminum sulfate particles after the original pre-neutralized liquid, and presses the output of defluorinated slag to open the circuit. At the same time, with the help of 10% of iron ions in the process, the colloid is used to secondary remove fluorine from the solution. The aluminum sulfate pre-removal reaches 60%, and the colloidal iron deeply removes fluorine, and the total fluorine removal rate reaches more than 90%. However, this method should be used in the main system of zinc hydrometallurgy, defluorination in zinc sulfate solution, and a large amount of aluminum hydroxide and iron hydroxide colloids are produced, which are difficult to filter, and a large amount of valuable metal zinc is mixed and taken away, and the direct yield of zinc decreases. And this type of method is completely different from the fluorine-chlorine mixed acid system for defluorination of zinc sulfate system.

[0006] Therefore, there is an urgent need for a green, environmentally friendly, economical and efficient method for treating fluorochloroacid wastewater, so that the fluorine content in the fluorochloroacid wastewater after treatment is lower than 30 mg / L, and then after the subsequent dechlorination process, it reaches the industrial secondary water recovery standard that can be returned to the zinc hydrometallurgical system for continued use. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide an economical, efficient and environmentally friendly defluorination method for fluorinated chloroacid, which reduces the fluorine content in the fluorinated chloroacid to below 30 mg / L, and then after a subsequent dechlorination process, reaches a recovery standard that allows it to be returned to the zinc hydrometallurgical system for continued use as industrial secondary return water.

[0008] In order to solve the above technical problems, the present invention provides a defluorination method for fluorinated mixed acid, comprising the following steps:

[0009] Mixing lime and water to produce lime milk;

[0010] Adding lime milk to the defluorinated liquid obtained by the primary defluorination of fluorinated and chlorinated mixed acid to perform deep defluorination, and filtering to obtain the defluorinated liquid and defluorinated residue;

[0011] Adding the slurried defluorination residue to the fluorine-chlorine mixed acid to carry out a first-stage defluorination, and filtering to obtain a calcium fluoride precursor and a defluorination liquid;

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

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

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

[0015] Furthermore, the defluorination slag slurrying is carried out by using fluorine-chlorine mixed acid as slurrying liquid, the liquid-solid mass ratio of the defluorination slag slurrying is 1.5:1-3:1, and the slurrying time is 20-45min.

[0016] Furthermore, the defluorination temperature of the fluorine-chlorine mixed acid during the first stage of defluorination is 75-95°C, the defluorination time is 120-240min, and the H in the solution at the end of the first stage of defluorination is + The mass-volume concentration is controlled at 10-50g / L.

[0017] Furthermore, 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 to the purified water is 1:1-1:3.5, and the purification time is 15-60 minutes.

[0018] Furthermore, the rotary kiln has 6-10 circumferential scrapers, the scraper material is 316L, the plate thickness is 3-5mm, the folding edge is 12-18mm, the height is 45-600mm, the installation angle of the rotary kiln is 1-6°, and the rotation speed is 2-8 rpm.

[0019] Furthermore, the heating rate of the rotary kiln when drying the calcium fluoride precursor is 2.0-2.5°C / min, the drying temperature is 350-550°C, and the temperature of the calcium fluoride out of the kiln is controlled at 45-80°C.

[0020] Furthermore, the fluorine-chlorine mixed acid is a fluorine-chlorine mixed acid obtained in the waste acid treatment process of zinc smelting or sulfur concentrate smelting, and H + 、F - , Cl -The mass-volume concentrations of the mixed solutions are 65-125 g / L, 25-55 g / L, and 12-28 g / L respectively.

[0021] The present invention provides a defluorination method for fluorine-chlorine mixed acid, which applies the ferrous metallurgical technical principles such as using a rotary kiln to treat a calcium fluoride precursor to enrich and remove the impurity zinc in its smoke, using lime precipitation to treat fluorine-containing wastewater, and the "YB / T 5217-2019 Fluorite" industry standard to the treatment of non-ferrous metallurgical wastewater, and can deeply defluorinate the fluorine-chlorine mixed acid obtained in the waste acid treatment process of zinc smelting or sulfur concentrate smelting, and can remove the F in the fluorine-chlorine mixed acid. - The content is reduced to below 30 mg / L, which provides a guarantee for achieving zero discharge of wastewater. In addition, the CaF2 content of the calcium fluoride product obtained in the defluorination process of fluorochloroacid exceeds 97%, which can meet the requirements of the first-grade fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard. The product has stronger market competitiveness and higher economic value. At the same time, the consumption of lime in the defluorination process of fluorochloroacid also saves 20-25% of the lime consumption in the original treatment process, reduces the consumption of auxiliary materials, and has lower processing costs. Therefore, the defluorination method of fluorochloroacid provided by the present invention can not only efficiently defluorinate fluorochloroacid, but also enable the defluorinated fluorochloroacid to reach the recovery standard for returning to the zinc hydrometallurgical system as industrial secondary return water for continued use after the subsequent dechlorination process, and the defluorination process cost is lower, the product is more competitive in the market, and the economic benefits are better.

[0022] In addition, the defluorination method of fluorinated and chloroacid mixed acid provided by the present invention has a simple process method and a reasonable process flow, and 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, and the waste residues and waste liquids generated in the process are recycled, achieving zero discharge of wastewater. The process is green and environmentally friendly, and meets the requirements of resource recycling and sustainable development. It has been industrialized and has a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flow chart of a defluorination method for fluorinated and chlorous mixed acid provided in an embodiment of the present invention. DETAILED DESCRIPTION

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

[0025] Step 1) Pretreatment: Mix lime and water to obtain fully slurried lime milk. The following reactions occur during this process:

[0026] CaO+H2O=Ca(OH)2

[0027] The mass ratio of lime to water in the mixed reaction is 1:1.2-1:2.5, and the mixed reaction time is 8-24h. By controlling the reaction temperature and reaction time of lime and water, it can not only activate the generated lime milk, which is beneficial to the subsequent improvement of the defluorination rate of fluorinated mixed acid by lime milk, but also help to remove the large pieces of calcium carbonate precipitate that are not completely sintered in the lime, which can improve the quality of the final product calcium fluoride. In addition, in order to increase the reaction rate of lime and water and make the calcium oxide in the lime completely react to become calcium hydroxide, the temperature of the reaction of lime and water is appropriately increased, and the temperature of the mixed reaction of lime and water is controlled to be 20-95°C.

[0028] Step 2) Deep defluorination: Add the prepared lime milk to the defluorinated liquid obtained by a stage of defluorination of fluorinated and chlorous mixed acid for deep defluorination. After the deep defluorination is completed, filter 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] F in the defluorinated liquid obtained after deep defluorination of fluorinated and chlorofluorocarbon mixed acid - The content is reduced to below 30 mg / L, which provides a guarantee for achieving zero discharge of wastewater. The obtained defluorinated liquid enters the subsequent dechlorination process, and after the defluorinated liquid meets the dechlorination standard, it can be returned to the zinc hydrometallurgical system as industrial secondary return water for continuous recycling, achieving zero discharge of wastewater, ensuring the green environmental protection of the process, and making the defluorination process of fluorine-chlorine mixed acid of the present invention meet the requirements of resource recycling and sustainable development.

[0032] The defluorination slag obtained by deep defluorination is returned to the first defluorination process for recycling after pulping and is continued to be used for defluorination. By recycling the waste slag generated in the process, waste emissions are reduced and the impact on the environment is reduced. 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 milk added is within a controllable range to reduce production costs, when adding lime milk to the defluorination liquid obtained by the first stage defluorination, the lime milk should be added slowly to the defluorination liquid, and the pH of the solution should be controlled to 9-11 at the end of the lime milk addition.

[0034] By controlling the pH at the end point of adding lime milk to 9-11, the F content in the defluorinated liquid obtained by the first stage of defluorination can be controlled below 30 mg / L, thereby ensuring that the F content in the defluorinated water discharged and entering the zinc smelting system is less than 30 mg / L, ensuring that no F will appear in the zinc smelting electrolysis process. - Burning occurs.

[0035] At the same time, in order to ensure that the lime milk fully removes the fluorine in the defluorination liquid, the temperature during deep defluorination is controlled to 20-70°C and the deep defluorination time is controlled to 30-90 minutes.

[0036] Step 3) primary defluorination: adding the slurried defluorination residue to the fluorine-chlorine mixed acid to carry out primary defluorination.

[0037] The fluorine-chlorine mixed acid is obtained in the waste acid treatment process of zinc smelting or sulfur concentrate smelting. + 、F - , Cl - The mass-volume concentrations of the mixed solutions are 65-125 g / L, 25-55 g / L, and 12-28 g / L respectively.

[0038] Since the main component of the defluorination slag obtained by deep defluorination is calcium fluoride, there are also residual lime, residual calcium carbonate that has not been completely calcined in the lime, impurity calcium silicate entrained in the calcium carbonate used to burn lime, and calcium hydroxide that has not reacted completely in the deep defluorination process, in order to activate the calcium carbonate and calcium oxide in the defluorination slag obtained by deep defluorination, and to prevent the defluorination slag from agglomerating into agglomerates in the first-stage defluorination process to affect the reaction efficiency, and at the same time to facilitate the transportation of the defluorination slag obtained by deep defluorination using pipelines to reduce production costs, the defluorination slag is first slurried before the defluorination slag is subjected to the first-stage defluorination of fluorinated chloroacid.

[0039] When slurrying the defluorination slag, fluorine-chlorine mixed acid is used as the slurrying liquid. This can avoid the introduction of other raw materials that have an impact on the environment during the process, which is more green and environmentally friendly.

[0040] In addition, in order to make the defluorination slag more fully and effectively slurried, the liquid-solid mass ratio of the fluorine-chlorine mixed acid to the defluorination slag during slurrying is controlled to be 1.5:1-3:1, and the slurrying time is controlled to be 20-45 minutes.

[0041] By slurrying the defluorination slag, the calcium carbonate and calcium oxide in the defluorination slag can be activated, so that the residual calcium carbonate and calcium oxide in the defluorination slag react completely, reducing the content of impurities, ensuring the content of calcium fluoride in the final fluorite product, and improving its grade. At the same time, it also avoids the agglomeration of calcium fluoride and its impurities, and avoids impurities such as calcium carbonate and calcium oxide being wrapped and reacting incompletely.

[0042] The following reactions occur during the process of adding slurried defluorinated slag to the fluorine-chlorine mixed acid for a first-stage defluorination process:

[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] Among them, in order to ensure that the unreacted calcium carbonate, calcium silicate and lime milk in the defluorination slag can react completely, ensure the quality of the final product calcium fluoride, improve economic benefits, and also to ensure that the fluorine in the fluorinated chloroacid can be fully and effectively removed, the defluorination temperature of the fluorinated chloroacid in the first stage of defluorination is 75-95°C, and the defluorination time is 120-240min.

[0049] In addition, in order to ensure that the calcium oxide, calcium hydroxide and calcium carbonate in the defluorination slag react completely and improve the grade and quality of calcium fluoride products, the residual acid in the solution at the end of the first stage of defluorination should be reduced as much as possible. + The mass-volume concentration is controlled at 10-50g / L.

[0050] After the fluorine-chlorine mixed acid is defluorinated in one stage, the calcium fluoride precursor and the defluorination liquid are obtained by filtration. The defluorination liquid obtained by the first stage defluorination is used for deep defluorination by adding lime in step 2). The obtained calcium fluoride precursor is used for preparing fluorite products in step 4).

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

[0052] After the first stage of defluorination, the calcium fluoride precursor obtained by filtration contains residual F - , Cl - , H + In the subsequent preparation process of fluorite products, these soluble harmful positive and negative ions will remain in the fluorite products and affect the product quality. - , Cl - , H + The acid formed by the plasma will also corrode the rotary kiln used to dry the calcium fluoride precursor, increasing production costs and reducing product quality. Therefore, the calcium fluoride precursor is purified before drying.

[0053] The purified water used to purify the calcium fluoride precursor is deionized water. - , Cl - , H +The positive and negative ions are equal, the liquid-solid ratio of the calcium fluoride precursor and purified water is controlled to be 1:1-1:3.5, and the purification time is controlled to be 15-60min.

[0054] By purifying the calcium fluoride precursor, the soluble impurity ions carried in the calcium fluoride precursor can be washed away, thereby improving the grade of the final fluorite product and ensuring the quality of the product. In addition, during the purification of the calcium fluoride precursor, the deionized water used to replace the solution remaining in the calcium fluoride precursor can also further ensure the quality of the final fluorite product.

[0055] After the first stage of defluorination, the calcium fluoride precursor obtained by filtration contains only 50-70% calcium fluoride, of which about 30-50% is residual water due to incomplete filtration. In addition, during the purification of the calcium fluoride precursor, deionized water used in the purification process will also remain. Therefore, the calcium fluoride precursor needs to be dried to obtain the fluorite product.

[0056] As a specific embodiment of the present invention, the calcium fluoride precursor is dried to prepare the fluorite product in a rotary kiln.

[0057] Among them, in order to effectively crush the materials, prevent the fluorite product from agglomerating during the drying process, and make the calcium fluoride precursor dry more evenly, the rotary kiln's copying plate is made of 316L, with a plate thickness of 3-5mm, a folding edge of 12-18mm, a height of 45-600mm, and 6-10 circular copying plates.

[0058] In addition, in order to ensure the feeding speed of the 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] At the same time, in order to effectively control the moisture content of fluorite products and ensure product quality, and also to ensure that the rotary kiln is not burned and oxidized, so as to reduce the entry of impurities such as iron oxide into the product and further ensure the quality of the product, the heating rate of the calcium fluoride precursor during drying is controlled at 2.0-2.5℃

[0060] / min, the drying temperature is controlled at 350-550℃, and the temperature of calcium fluoride out of the kiln is controlled at 45-80℃.

[0061] The present invention provides a defluorination method for fluorinated chlorinated mixed acid. In the process, only conventional defluorinating agent lime is added without adding other reagents, so that the defluorination effect in the fluorinated chlorinated mixed acid can be increased, and the fluorine content in the defluorinated liquid produced in the original defluorination process is reduced from 50-70 mg / L to the fluorine content in the defluorinated liquid of the present invention below 30 mg / L. Under the process and technical conditions of the present invention, the secondary return water can be fully returned to the zinc main system, thereby reducing the amount of new water used, reducing the production cost, and ensuring the normal zinc electrolysis of the main system.

[0062] In addition, the mass percentage of calcium fluoride in the fluorite product prepared by the present invention is increased from 55-70% to 97%, and the product quality is greatly improved, and the first-grade fluorite concentrate that meets the "YB / T 5217-2019 Fluorite" industry standard is obtained, and its sales price has increased by 2,500 yuan / ton, which improves the economic benefits. In addition, the calcium carbonate in the raw material lime is also fully utilized, and there is no residual lime milk in the product, and the amount of lime is reduced by 20-25%, which reduces the production cost and further improves the economic benefits.

[0063] At the same time, the process of the present invention is simple and reasonable, and can be put into use only by modifying existing equipment. The process achieves zero discharge of waste residue and wastewater, achieves green production, energy conservation and environmental protection, meets the requirements of resource recycling and sustainable development, and has a very broad application prospect.

[0064] The defluorination method of a fluorine-chlorine mixed acid provided by the present invention is specifically described below through examples.

[0065] Example 1

[0066] For a H + 、F - , Cl - The mass-volume concentrations of fluorinated and chlorofluorocarbon mixed acids are 98 g / L, 51 g / L, and 18 g / L, respectively. Figure 1 The process comprises the following steps:

[0067] The first step is pretreatment: lime and water are mixed at a mass percentage of 1:2.5 for 8 hours at a temperature of 95°C to obtain a completely slurried lime milk;

[0068] The second step is deep defluorination: slowly add lime milk into the defluorination liquid after the first defluorination for deep defluorination, the defluorination temperature is 20℃, the defluorination time is 90min, the end point pH is 9, the defluorination liquid obtained by filtration is sent to the subsequent process for dechlorination, and the defluorination residue is returned to the previous process for first defluorination;

[0069] Step 3: One-stage defluorination: Add the slurried defluorination slag to the fully stirred fluorine-chlorine mixed acid for one-stage defluorination. Defluorination T = 95 ° C, t = 120 min, end point H +The mass-volume concentration was controlled at 10 g / L, and the calcium fluoride precursor and the defluorination liquid were obtained by filtration;

[0070] The fourth step is the preparation of calcium fluoride: the purified calcium fluoride precursor with a liquid-solid mass percentage of 1:3.5 and a purification time of 15 minutes is added to a rotary kiln with an installation inclination angle of 1 degree, a rotation speed of 8 revolutions / min, a copy board material of 316L, a board thickness of 3mm, a folding edge of 12mm, a height of 45mm, and 10 circular copy boards for drying. The drying conditions are a heating rate of 2.5°C / min, a drying temperature of 350°C, and a kiln outlet temperature of calcium fluoride = 45°C. After vacuum packaging, a first-class fluorite concentrate is obtained.

[0071] F in the deep defluorinated liquid obtained by defluorination treatment of fluorine-chlorine mixed acid - The content is 21 mg / L, the CaF2 content in the prepared calcium fluoride product is 97.46%, 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, and the moisture content is 2.16%, which meets the requirements of first-grade fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard; at the same time, because the calcium carbonate content in the product calcium fluoride is reduced to 0.28%, the consumption of auxiliary materials is reduced, the F is removed and reused, and the recovery rate reaches 99.96%.

[0072] Example 2

[0073] For a H + 、F - , Cl - The mass-volume concentrations of fluorinated and chlorofluorocarbon mixed acids are 73g / L, 42g / L, and 14g / L, respectively. Figure 1 The process comprises the following steps:

[0074] The first step is pretreatment: lime and water are mixed at a mass percentage of 1:1.2 for 24 hours at a temperature of 20°C to obtain a completely slurried lime milk;

[0075] The second step is deep defluorination: slowly add lime milk into the defluorination liquid after the first defluorination for deep defluorination, the defluorination temperature is 70℃, the defluorination time is 30min, the end point pH is 11, the defluorination liquid obtained by filtration is sent to the subsequent process for dechlorination, and the defluorination residue is returned to the previous process for first defluorination;

[0076] Step 3: One-stage defluorination: Add the slurried defluorination slag to the fully stirred fluorine-chlorine mixed acid for one-stage defluorination. Defluorination T = 75 ° C, t = 240 min, end point H + The mass-volume concentration is controlled at 50 g / L, and the calcium fluoride precursor and the defluorination liquid are obtained by filtration;

[0077] The fourth step is the preparation of calcium fluoride: the purified calcium fluoride precursor with a liquid-solid mass percentage of 1:1 and a purification time of 60 minutes is added to a rotary kiln with an installation inclination angle of 6 degrees, a rotation speed of 2.5 revolutions / min, a copy board material of 316L, a board thickness of 5mm, a folding edge of 18mm, a height of 60mm, and 6 circular copy boards for drying. The drying conditions are a heating rate of 2.5°C / min, a drying temperature of 550°C, and a kiln outlet temperature of calcium fluoride = 80°C. After vacuum packaging, a first-class fluorite concentrate is obtained.

[0078] F in the deep defluorinated liquid obtained by defluorination treatment of fluorine-chlorine mixed acid - The content is 12 mg / L, the CaF2 content in the prepared calcium fluoride product is 97.32%, 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, and the moisture content is 2.31%, which meets the requirements of first-grade fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard; at the same time, because the calcium carbonate content in the product calcium fluoride is reduced to 0.24%, the consumption of auxiliary materials is reduced, the F is removed and reused, and the recovery rate reaches 99.97%.

[0079] Example 3

[0080] For a H + 、F - , Cl - The mass-volume concentrations of fluorinated and chlorofluorocarbon mixed acids are 117 g / L, 35 g / L, and 18 g / L, respectively. Figure 1 The process comprises the following steps:

[0081] The first step is pretreatment: lime and water are mixed at a mass percentage of 1:2.0 for 16 hours at a temperature of 65°C to obtain a completely slurried lime milk;

[0082] The second step is deep defluorination: slowly add lime milk into the defluorination liquid after the first defluorination for deep defluorination, the defluorination temperature is 50℃, the defluorination time is 60min, the end point pH is 10, the defluorination liquid obtained by filtration is sent to the subsequent process for dechlorination, and the defluorination residue is returned to the previous process for first defluorination;

[0083] The third step is to add the slurried defluorination slag to the fully stirred fluorine-chlorine mixed acid for one-stage defluorination. The defluorination temperature is 85°C, t is 180 min, and the end point is H + The mass-volume concentration was controlled at 30 g / L, and the calcium fluoride precursor and the defluorination liquid were obtained by filtration;

[0084] Step 4 Preparation of calcium fluoride: Add the purified calcium fluoride precursor with a liquid-to-solid mass percentage of 1:2.5 and a purification time of 35 minutes into a rotary kiln with an installation inclination angle of 4 degrees, a rotation speed of 6 revolutions / min, a copy board material of 316L, a board thickness of 4mm, a folding edge of 15mm, a height of 55mm, and 8 circular copy boards for drying. The drying conditions are a heating rate of 2.2°C / min, a drying temperature of 450°C, and a kiln outlet temperature of calcium fluoride = 65°C. After vacuum packaging, a first-class fluorite concentrate is obtained.

[0085] F in the deep defluorinated liquid obtained by defluorination treatment of fluorine-chlorine mixed acid - The content is 7mg / L, the CaF2 content in the prepared calcium fluoride product is 97.29%, 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, and the moisture content is 1.11%, which meets the requirements of first-grade fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard; at the same time, because the calcium carbonate content in the product calcium fluoride is reduced to 0.25%, the consumption of auxiliary materials is reduced, the F is removed and reused, and the recovery rate reaches 99.98%.

[0086] Comparative Example:

[0087] For a H + 、F - , Cl - Fluorine-chlorine mixed acid with mass-volume concentrations of 95 g / L, 41 g / L and 24 g / L, respectively, is treated according to a conventional process, including the following steps:

[0088] The first step is pretreatment: lime and water are mixed at a mass percentage of 1:2.0 for 15 hours at natural room temperature to obtain a completely slurried lime milk;

[0089] The second step is deep defluorination: slowly add lime milk into fluorine-chlorine mixed acid for defluorination, the defluorination temperature is 65℃, the defluorination time is 30min, the end point pH is 8, the defluorinated liquid obtained by filtration is sent to the subsequent process for dechlorination, and the defluorination residue is the calcium fluoride precursor;

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

[0091] The F in the defluorinated liquid obtained by defluorination of fluorinated and chlorinated mixed acid -The content is 70mg / L, the CaF2 content in the prepared calcium fluoride product is 67.18%, the impurity CaCO3 content is 9.13%, and the product contains some calcium hydroxide and the moisture content is 1.04%, which does not meet the requirements of fluorite concentrate in the industry standard "YB / T 5217-2019 Fluorite"; at the same time, because the calcium carbonate content in the product calcium fluoride is 9.13%, and some lime milk has not reacted completely, the consumption of auxiliary material lime has increased significantly, and the F in the defluorination liquid - The content does not reach the electrolyte content of F in zinc electrolysis - The content is less than 30 mg / L. The secondary return water prepared by this process is allowed to return a small amount to the zinc system for replenishment, which is difficult to achieve the requirement of zero wastewater discharge.

[0092] The F in the defluorinated liquid obtained by Examples 1-3 of the present invention and the comparative example - From the comparison of content and quality of the prepared fluorite products, it can be seen that the defluorination method of fluorine-chloro mixed acid provided by the present invention carries out two-stage defluorination of fluorine-chloro mixed acid, namely, one-stage defluorination and deep defluorination, to ensure that the F mass-volume content in the defluorination liquid is less than 30 mg / L, and the product calcium fluoride meets the requirements of first-grade fluorite concentrate in the "YB / T 5217-2019 Fluorite" industry standard, and the consumption of lime is reduced by 20-25% compared with the consumption of lime used in defluorination of conventional fluorine-chloro mixed acid, thereby providing a guarantee for achieving zero discharge of wastewater.

[0093] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for defluorinating a fluorinated and chlorinated mixed acid, characterized in that: The following steps are involved: Mixing lime and water to produce lime milk; Adding lime milk to the defluorinated liquid obtained by the primary defluorination of fluorinated and chlorinated mixed acid to perform deep defluorination, and filtering to obtain the defluorinated liquid and defluorinated residue; Adding the slurried defluorination residue to the fluorine-chlorine mixed acid to carry out a first-stage defluorination, and filtering to obtain a calcium fluoride precursor and a defluorination liquid; The calcium fluoride precursor is dried in a rotary kiln to obtain the fluorite product.

2. The defluorination method of fluorinated chlorinated mixed acid according to claim 1, characterized in that: The mass ratio of lime to water is 1:1.2-1:2.5, the mixing temperature is 20-95° C., and the mixing time is 8-24 hours.

3. The defluorination method of fluorinated chlorinated mixed acid according to claim 1, characterized in that: When the defluorination liquid is added with lime milk for deep defluorination, the lime milk is slowly added, the pH is controlled to be 9-11 when the lime milk is added to the end point, the deep defluorination temperature is 20-70° C., and the deep defluorination time is 30-90 minutes.

4. The defluorination method of fluorinated and chlorous mixed acid according to claim 1, characterized in that: The defluorination slag slurrying is carried out by using fluorine-chlorine mixed acid as slurrying liquid, the liquid-solid mass ratio of the defluorination slag slurrying is 1.5:1-3:1, and the slurrying time is 20-45 minutes.

5. The defluorination method of fluorinated and chlorous mixed acid according to claim 1, characterized in that: The defluorination temperature of the fluorine-chlorine mixed acid during the first stage of defluorination is 75-95°C, the defluorination time is 120-240 minutes, and the H + The mass-volume concentration is controlled at 10-50g / L.

6. The defluorination method of fluorinated and chlorous mixed acid according to claim 1, characterized in that: 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 to the purified water is 1:1-1:3.5, and the purification time is 15-60 minutes.

7. The defluorination method of fluorinated and chlorous mixed acid according to claim 1, characterized in that: The rotary kiln has 6-10 circumferential scrapers, the scrapers are made of 316L, have a thickness of 3-5mm, a folding edge of 12-18mm, and a height of 45-600mm. The rotary kiln has an installation inclination of 1-6° and a rotation speed of 2-8 rpm.

8. The defluorination method of fluorinated and chlorous mixed acid according to claim 1, characterized in that: The rotary kiln has a heating rate of 2.0-2.5°C / min when drying the calcium fluoride precursor, a drying temperature of 350-550°C, and a temperature of the calcium fluoride out of the kiln controlled at 45-80°C.

9. The defluorination method of fluorinated and chlorous mixed acid according to claim 1, characterized in that: The fluorine-chlorine mixed acid is obtained in the waste acid treatment process of zinc smelting or sulfur concentrate smelting. + 、F - , Cl - The mass-volume concentrations of the mixed solutions are 65-125 g / L, 25-55 g / L, and 12-28 g / L respectively.

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