Method for removing fluorine from fluorine-chlorine mixed acid and application

Abstract

The invention provides a method for removing fluorine from fluorine-chlorine mixed acid and application. The invention relates to a method for removing fluorine from fluorine-chlorine mixed acid. The method comprises the following steps: neutralization reaction: adding a neutralizer into the fluorine-chlorine mixed acid to adjust the pH value to 1.5-3.5; cryolite is prepared, specifically, sodium metaaluminate is added at the temperature of 80-95 DEG C, a cryolite preparation solution is obtained, and the mass molar concentration ratio of Al to F is 1.03-1.08; and activating and removing impurities: adding fluorine-chlorine mixed acid into the cryolite preparation solution to activate cryolite, adjusting the pH value to 4.5-7.2, and filtering to obtain a defluorinated solution. And slurrying and drying the cryolite precursor to obtain a cryolite product. According to the method, the F in the fluorine-chlorine mixed acid with high F content can be deeply removed, the fluorine removal rate reaches 99% or above, the use standard requirement that the content of the F in the recycled secondary return water is smaller than 30 mg / L in zinc hydrometallurgy is met, and the production cost of removing fluorine and chlorine in the subsequent zinc hydrometallurgy process is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgical environmental protection, and specifically relates to a method for defluorination from a mixed hydrofluoric and hydrochloric acid and its application. Background Art

[0002] Zinc is a commonly used metal, with China's production capacity exceeding 6.5 million tons, and 85% of the smelting processes using hydrometallurgy. At present, after technological improvement, the water consumption for hydrometallurgical zinc smelting is 9 tons of water per ton of zinc, and the discharged wastewater meeting the standards is 10 t of water / t of zinc. The "Action Plan for Water Pollution Prevention and Control" clearly states to intensify sewage treatment and promote the recycling of sewage resources; it requires new enterprises to adopt zero-emission technologies. The mixed hydrofluoric and hydrochloric acid is a mixed solution obtained from the acid wastewater after the roasting flue gas of sulfide ore is treated by the acid-making process through the improved separation and recovery technology of valuable substances, with the contents of H + , F - , Cl - being 65 - 125 g / L, 25 - 55 g / L, and 12 - 28 g / L respectively, and the contents of other valuable substances in the mixed hydrofluoric and hydrochloric acid being trace. Currently, the zinc smelting industry commonly uses the direct single-stage lime defluorination technology for the mixed hydrofluoric and hydrochloric acid. After defluorination, the fluorine content in the liquid is 50 - 70 mg / L, and the mass percentage content of calcium fluoride in the product calcium fluoride is 55 - 70%, making it difficult to sell and only being able to be disposed of at a low price.

[0003] Fluoride ions have a strong corrosive function in acidic solutions. During 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 metal aluminum inside the passivated aluminum oxide film of the cathode plate to be exposed. This shortens the service life of the cathode plate, and the precipitated zinc and metal aluminum form an alloy, making it difficult to strip the precipitated zinc. As a result, the production cost increases and the quality of the precipitated zinc decreases. Therefore, for small electrode plates with a shorter electrolysis cycle, the F content in the fresh liquid is required to be less than 50 mg / L, while for large electrode plates with an electrolysis time greater than 32 h, the F content is required to be less than 30 mg / L. Therefore, the mixed hydrofluoric and hydrochloric acid with a high F content cannot be directly recycled to the zinc smelting system.

[0004] The Chinese patent document "A Method for Removing Fluorine and Chlorine from Zinc Smelting Acid Wastewater" (CN112028208A) discloses: removing arsenic and mercury from zinc smelting acid waste water to obtain detoxified acid waste water; adding a copper-containing reagent to the detoxified acid waste water for chlorine removal, and after filtration, obtaining the liquid after chlorine removal and a chlorine-containing residue; adding a calcium-containing reagent to the liquid after chlorine removal for fluorine removal, and after filtration, obtaining the water returned after fluorine and chlorine removal and a fluorine-containing residue. In this method, the calcium-containing reagent is complex, the preparation is cumbersome, and it contains oxide additives such as zinc, zirconium, and aluminum, resulting in a high heavy metal content in the secondary return water and the residue not being a product. At the same time, the fluorine removal rate is less than 87%, and the F content in the secondary return water exceeds 130 mg / L, so the secondary return water cannot be returned to the zinc smelting system for use as makeup water.

[0005] The inventive method of "A Method for Deep Removal of Fluorine in Zinc Sulfate Solution and Its Application" (CN116875814A) in Chinese patent literature does not change the main process route. It only adds aluminum sulfate particles after the original pre-neutralized solution, filters to produce defluorinated slag for open circuit, and at the same time, with the help of 10% iron ions in the process, produces colloid to remove fluorine in the solution for the second time. The pre-removal of aluminum sulfate reaches 60%, and the colloid iron deeply removes fluorine, with the total fluorine removal rate exceeding 90%. However, when this method is applied to defluorination in the main system of zinc hydrometallurgy, a large amount of aluminum hydroxide and iron hydroxide colloids that are difficult to filter are produced, and a large amount of valuable metal zinc is entrained, resulting in a decrease in the direct recovery rate of zinc.

[0006] Therefore, there are still many problems in the existing technologies for treating fluorine-containing wastewater. Currently, there is an urgent need for a green, environmentally friendly, economical and efficient method for treating fluorine-chlorine mixed acid wastewater, so that the fluorine content in the treated fluorine-chlorine mixed acid wastewater is less than 30 mg / L, and after the subsequent dechlorination process, it meets the industrial secondary return water recovery standard that can be returned to the zinc hydrometallurgy system for continued utilization. Summary of the Invention

[0007] In view of this, the present invention proposes a method and application for removing fluorine from fluorine-chlorine mixed acid. After treatment, the F content is less than 30 mg / L, meeting the reuse standard, being green, environmentally friendly, economical and efficient.

[0008] The present invention provides a method for removing fluorine from fluorine-chlorine mixed acid, comprising the following steps:

[0009] Neutralization reaction: Adding a neutralizing agent to the fluorine-chlorine mixed acid to adjust the pH to 1.5 - 3.5;

[0010] Cryolite preparation: Adding sodium metaaluminate at 80 - 95 °C to obtain a cryolite preparation solution, and the mass molar concentration ratio of Al to F is 1.03 - 1.08;

[0011] Activation and impurity removal: Adding fluorine-chlorine mixed acid to the cryolite preparation solution to activate cryolite, and adjusting the pH to 4.5 - 7.2, then filtering to obtain a defluorinated solution.

[0012] Preferably, the cryolite precursor is slurried and dried to obtain a cryolite product.

[0013] Preferably, the neutralizing agent includes one or more of sodium carbonate, sodium bicarbonate and sodium hydroxide.

[0014] Preferably, the concentration of the neutralizing agent is 15 - 28 g / L.

[0015] Preferably, the reaction temperature in the neutralization reaction step is 55 - 75 °C.

[0016] Preferably, during the cryolite preparation step, sodium metaaluminate is added while stirring to obtain a cryolite preparation solution with a pH ≥ 9.0.

[0017] Preferably, the reaction time in the cryolite preparation step is 60 - 90 min, and the stirring speed is 450 - 680 r / min.

[0018] Preferably, the reaction time in the activation and impurity removal step is 30 - 120 min.

[0019] Preferably, in the fluorochloric mixed acid, the content of H + is 65 - 125 g / L, the content of F - is 25 - 55 g / L, and the content of Cl - is 12 - 28 g / L.

[0020] The present invention also provides the application of any of the above methods for defluorinating fluorochloric mixed acid in wastewater treatment and reuse.

[0021] Compared with the prior art, the method for defluorinating fluorochloric mixed acid by preparing cryolite process provided by the present invention can deeply remove F in fluorochloric mixed acid with an F content exceeding 25 g / L, and the defluorination rate of F reaches 99% or more, meeting the usage standard requirement of less than 30 mg / L of F content in the secondary recycled water for zinc hydrometallurgy recovery and reuse, reducing the internal production costs of enterprises such as defluorination and dechlorination in the subsequent zinc hydrometallurgy process. And the present invention uses F in fluorochloric mixed acid to prepare cryolite products with relatively high value, having good economic benefits, which can greatly improve the industry competitiveness of zinc hydrometallurgy enterprises, thus realizing the harmless comprehensive recovery and utilization of fluorochloric mixed acid, reducing the impact on the environment. It can not only achieve resource recycling and save resources, but also be low-carbon, safe, green and environmentally friendly, reducing production costs, and improving economic and social benefits.

[0022] Meanwhile, the method for defluorinating fluorochloric mixed acid by preparing cryolite process provided by the present invention not only has a reasonable process flow and is easy to operate, but also the products in the process are basically recycled and reused, and basically realizes zero discharge of waste and wastewater, belonging to green production, meeting the requirements of the national dual-carbon policy, resource recycling and sustainable development, and being easy to industrialize. The application prospect of the present invention is very broad. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the flow chart of the method for defluorinating fluorochloric mixed acid in Example 1.

[0024] Figure 2 It is the XRD pattern of the cryolite product in Example 1.

[0025] Figure 3 It is the XRD pattern of the cryolite product in Example 2.

[0026] Figure 4 It is the XRD pattern of the cryolite product in Example 3.

[0027] Figure 5 XRD pattern of the cryolite product of Comparative Example 1

[0028] Figure 6 XRD pattern of the cryolite product of Comparative Example 2

[0029] Figure 7 XRD pattern of the cryolite product of Comparative Example 3 Detailed implementation manners

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein.

[0031] The content of H + in the hydrofluoric and hydrochloric acid mixture is 65 - 125 g / L, the content of F - is 25 - 55 g / L, and the content of Cl - is 12 - 28 g / L. A method for defluorinating the hydrofluoric and hydrochloric acid mixture includes the following steps:

[0032] Neutralization reaction: Add a neutralizing agent to the hydrofluoric and hydrochloric acid mixture to adjust the pH to 1.5 - 3.5. If the pH exceeds 3.5, other substances such as aluminum fluoride and chabazite will be produced when adding sodium metaaluminate, resulting in impure products; if the pH is less than 1.5, the end point pH will be too low when adding the activator hydrofluoric and hydrochloric acid, and the F content in the defluorinated solution will be too high, exceeding 30 mg / L, and it cannot be used as the second return water for the zinc smelting system. The reaction principle and equations are as follows:

[0033] Na2CO3 + 2HF = 2NaF + CO2↑ + H2O,

[0034] Na2CO3 + 2HCl = 2NaCl + CO2↑ + H2O,

[0035] NaHCO3 + HF = NaF + CO2↑ + H2O,

[0036] NaHCO3 + HCl = NaCl + CO2↑ + H2O,

[0037] NaOH + HF = NaF + H2O,

[0038] NaOH + HCl = NaCl + H2O.

[0039] The neutralizing agent includes one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide. The concentration of the neutralizing agent is 15 - 28 g / L. The reaction temperature in the neutralization reaction step is 55 - 75°C.

[0040] Preparation of cryolite: While stirring, slowly add sodium aluminate at 80 - 95°C. Using other reagents may introduce impurities. The reaction principle and equation are as follows: 4H + + 6NaF + NaAlO2 → Na3AlF6↓ + H2O + 4Na + , with a stirring speed of 450 - 680 r / min and a reaction time of 60 - 90 min, to obtain a cryolite preparation solution with pH ≥ 9.0. The mass molar concentration ratio of Al to F is 1.03 - 1.08. If it exceeds this range, the quality of the prepared cryolite will be affected and the filtration performance of the solution will deteriorate.

[0041] Activation and impurity removal: Add a fluorochloric mixed acid to the cryolite preparation solution to activate cryolite, with a reaction time of 30 - 120 min. Adjust the pH to 4.5 - 7.2 and filter to obtain a defluorinated solution.

[0042] Among them, for example, the reaction equations for impurity removal of bayerite (β - Al2O3·3H2O), Al2(OH) 2.76 F 3.24 ·H2O and chlorkaluminite (Al3F 14 Na5) are as follows:

[0043] β - Al2O3·3H2O + 6NaF + 6HF = 2Na3AlF6↓ + 6H2O,

[0044] Al2(OH) 2.76 F 3.24 ·H2O + NaF → Na3AlF6↓ + H2O,

[0045] Al3F 14 Na5 + 4NaF → 3Na3AlF6↓.

[0046] In the present invention, sometimes certain auxiliary materials are added or reduced according to the types and contents of impurities in the fluorochloric mixed acid, but as long as the basic process flow remains unchanged, it also belongs to the protection scope of the present invention.

[0047] Example 1

[0048] The content of H + in the selected fluorochloric mixed acid is 72.62 g / L, the content of F - is 27.19 g / L, the content of Cl - is 14.37 g / L, and it contains trace amounts of heavy metals such as Zn, Cd, Pb, Cu, and As. The method for defluorination from the fluorochloric mixed acid, as Figure 1 shown, includes the following steps:

[0049] Neutralization reaction: Sodium carbonate as the neutralizing agent with a concentration of 28 g / L was added to the fluorochloric mixed acid at a temperature of 55 °C, and the pH was adjusted to 3.5.

[0050] Preparation of cryolite: Sodium metaaluminate was slowly added with stirring at 95 °C, and the stirring speed was 450 r / min to obtain a cryolite preparation solution. The end-point pH after the addition of sodium metaaluminate was 9.01, and the reaction time was 60 min. The mass molar concentration ratio of Al to F was 1.03.

[0051] Activation and impurity removal: Fluorochloric mixed acid was added to the cryolite preparation solution to activate cryolite, the pH was adjusted to 4.5, the reaction time was 30 min, and then filtration was carried out to obtain a defluorinated solution with an F content of 9.12 mg / L and a cryolite precursor. The cryolite precursor was slurried and dried to obtain a cryolite product meeting the "Cryolite - GB / T 4291 - 2017" standard, as shown in Table 1.

[0052] Table 1 Chemical composition and physical property indexes

[0053]

[0054] The fluorine removal rate in the fluorochloric mixed acid reached 99.97%, the F in the defluorinated solution was 9.12 mg / L, and the F recovery rate exceeded 99.78%. After subsequent dechlorination treatment, secondary return water was obtained and recycled as water resources in the zinc smelting hydrometallurgical system. The produced cryolite was detected by XRD as Figure 2 shown, and the impurity content was detected as shown in Table 2. It can be seen from Table 2 that the impurity content in this example is less than the requirement for impurity content in the "Cryolite - GB / T 4291 - 2017" standard.

[0055] Table 2 Impurity composition table of cryolite in Example 1

[0056]

[0057] Example 2

[0058] The content of H + in the selected fluorochloric mixed acid was 118.33 g / L, the content of F - was 45.71 g / L, the content of Cl - was 27.19 g / L, and it contained trace amounts of heavy metals such as Zn, Cd, Pb, Cu, and As. The method for defluorination from the fluorochloric mixed acid includes the following steps:

[0059] Neutralization reaction: Sodium bicarbonate as the neutralizing agent with a concentration of 15 g / L was added to the fluorochloric mixed acid at a temperature of 75 °C, and the pH was adjusted to 1.5.

[0060] Preparation of cryolite: While stirring at 80 °C, sodium metaaluminate was slowly added, and the stirring speed was 680 r / min to obtain a cryolite preparation solution. The end point pH after adding sodium metaaluminate was 11.62, and the reaction time was 90 min. The mass molar concentration ratio of Al to F was 1.08.

[0061] Activation and impurity removal: Fluorochlorohydric acid was added to the cryolite preparation solution to activate cryolite, the pH was adjusted to 7.2, the reaction time was 120 min, and then filtration was carried out to obtain a defluorinated solution with an F content of 12.62 mg / L and a cryolite precursor. The cryolite precursor was slurried and dried to obtain a cryolite product meeting the "Cryolite - GB / T 4291 - 2017" standard.

[0062] The fluorine removal rate in the fluorochlorohydric acid reached 99.97%, the F in the defluorinated solution was 12.62 mg / L, and the recovery rate of F exceeded 99.72%. After subsequent dechlorination treatment, second - recycled water was obtained and returned to the zinc smelting hydrometallurgical system for water resource recovery. The produced cryolite was detected by XRD as Figure 3 shown, and the impurity content detection is shown in Table 3. It can be seen from Table 3 that the impurity content in this example is less than the requirement for impurity content in the "Cryolite - GB / T 4291 - 2017" standard.

[0063] Table 3 Impurity composition table of cryolite in Example 2

[0064]

[0065] Example 3

[0066] The content of H + in the selected fluorochlorohydric acid was 123.15 g / L, the content of F - was 51.10 g / L, the content of Cl - was 14.49 g / L, and it contained trace amounts of heavy metals such as Zn, Cd, Pb, Cu, and As. The method for defluorination from fluorochlorohydric acid includes the following steps:

[0067] Neutralization reaction: Sodium hydroxide with a concentration of 20 g / L as a neutralizing agent was added to the fluorochlorohydric acid at 65 °C, and the pH was adjusted to 2.5.

[0068] Preparation of cryolite: While stirring at 90 °C, sodium metaaluminate was slowly added, and the stirring speed was 580 r / min to obtain a cryolite preparation solution. The end point pH after adding sodium metaaluminate was 10.72, and the reaction time was 75 min. The mass molar concentration ratio of Al to F was 1.05.

[0069] Activation and impurity removal: Add fluorochloric mixed acid to the cryolite preparation solution to activate cryolite, adjust the pH to 6.2, with a reaction time of 75 min, then filter to obtain a defluorinated solution with an F content of 6.18 mg / L and a cryolite precursor. The cryolite precursor is slurried and dried to obtain a cryolite product that meets the "Cryolite - GB / T 4291 - 2017" standard.

[0070] The fluorine removal rate in the fluorochloric mixed acid reaches 99.99%, the F in the defluorinated solution is 6.18 mg / L, and the recovery rate of F exceeds 99.80%. After subsequent dechlorination treatment, second - recycled water is obtained and returned to the zinc smelting wet - process system for water resource recovery. The produced cryolite is detected by XRD as Figure 4 shown, and the impurity content detection is shown in Table 4. It can be seen from Table 4 that the impurity content in this example is less than the requirement for impurity content in the "Cryolite - GB / T 4291 - 2017" standard.

[0071] Table 4 Composition of impurities in cryolite of Example 3

[0072]

[0073] Comparative Example 1

[0074] The content of H + in the selected fluorochloric mixed acid is 98.26 g / L, the content of F - is 39.16 g / L, the content of Cl - is 19.14 g / L, and it contains trace amounts of heavy metals such as Zn, Cd, Pb, Cu, and As. The following process is carried out:

[0075] I. Cryolite preparation: At a temperature of 88 °C and a stirring speed of 600 r / min, slowly add sodium meta - aluminate according to the mass - molar concentration ratio of Al:F = 1.05. The end - point pH after adding sodium meta - aluminate is 1.18, and the time for preparing cryolite is 70 min.

[0076] II. Neutralization reaction: Add sodium carbonate with a concentration of 18 g / L as a neutralizing agent to the reaction solution, adjust the pH to 6.5, and the reaction time is 78 min.

[0077] III. Filtration and slurrying: Filter the above - mentioned reaction solution to obtain a defluorinated solution with an F content of 121.35 mg / L and a cryolite precursor. The cryolite product is obtained after the cryolite precursor is slurried and dried.

[0078] The fluorine removal rate in the hydrofluoric and hydrochloric mixed acid reaches 99.69%, the F content in the defluorinated liquid is 121.35 mg / L, and the F recovery rate exceeds 99.53%. After subsequent dechlorination treatment, the secondary recycled water is obtained. When it is returned to the zinc smelting hydrometallurgical system as water resources, it causes difficulties in zinc electrolysis due to the high F content, and it is difficult to strip the precipitated zinc. The produced cryolite is detected by XRD as Figure 5 shown, and it can be concluded from Figure 5 that the cryolite product contains impurity chabazite, which clearly does not meet the requirements of the "Cryolite - GB / T 4291 - 2017" standard.

[0079] Comparative Example 2

[0080] The selected hydrofluoric and hydrochloric mixed acid contains 88.05 g / L of H + , 35.18 g / L of F - , 17.73 g / L of Cl - , and trace amounts of heavy metals such as Zn, Cd, Pb, Cu, and As. The treatment is carried out according to the following process:

[0081] I. Neutralization reaction: Sodium hydroxide with a concentration of 19 g / L is added to the hydrofluoric and hydrochloric mixed acid at a temperature of 58 °C to adjust the pH to 5.5.

[0082] II. Preparation of cryolite: Sodium aluminate is slowly added with stirring at 89 °C, and the stirring speed is 560 r / min to obtain a cryolite preparation solution. The end - point pH after adding sodium aluminate is > 11, and the reaction time is 64 min. The mass molar concentration ratio of Al to F is 1.05.

[0083] III. Filtration and pulping: The above reaction solution is filtered to obtain a defluorinated liquid with an F content of 25.84 mg / L and a cryolite precursor. The cryolite product is obtained after the cryolite precursor is pulped and dried.

[0084] The fluorine removal rate in the hydrofluoric and hydrochloric mixed acid reaches 99.93%, the F in the defluorinated liquid reaches 25.84 mg / L, and the F recovery rate exceeds 99.51%. After subsequent dechlorination treatment, the secondary recycled water is obtained. When it is returned to the zinc smelting hydrometallurgical system as water resources, it is recycled. The produced cryolite is detected by XRD as Figure 6 shown, and it can be concluded from Figure 6 that the cryolite product contains impurities Al2(OH) 2.76 F 3.24 ·H2O and bayerite, which clearly do not meet the requirements of the "Cryolite - GB / T 4291 - 2017" standard.

[0085] Comparative Example 3

[0086] The selected hydrofluoric and hydrochloric mixed acid contains 65.01 g / L of H + ...- The content of [substance] is 25.05 g / L, and the content of Cl - is 12.91 g / L, and it contains trace amounts of heavy metals such as Zn, Cd, Pb, Cu, and As. The treatment is carried out according to the following process steps:

[0087] I. Neutralization reaction: Sodium carbonate as a neutralizing agent with a concentration of 24 g / L is added to the fluorochlorohydric acid mixture at a temperature of 65 °C to make the pH of the solution 6.5.

[0088] II. Cryolite preparation: Sodium aluminate is slowly added at a mass molar concentration ratio of Al:F = 1.05 under the conditions of a temperature of 94 °C and a stirring speed of 650 r / min. The end point pH after the addition of sodium aluminate is > 12, and the time for preparing cryolite is 85 min.

[0089] III. Activation and impurity removal: The fluorochlorohydric acid mixture is used to activate cryolite in the cryolite preparation solution, and the pH is adjusted to 6.0. The activation and impurity removal time is 80 min. A defluorinated solution with an F content of 5.63 mg / L and a cryolite precursor are obtained by filtration. The cryolite precursor is slurried and dried to obtain a cryolite product.

[0090] The fluorine removal rate in the fluorochlorohydric acid mixture reaches 99.98%, the F in the defluorinated solution is 5.63 mg / L, and the recovery rate of F exceeds 99.80%. After subsequent dechlorination process treatment, second recycled water is obtained and returned to the zinc smelting hydrometallurgical system for water resource recovery. The produced cryolite is detected by XRD as Figure 7 shown. From Figure 7 it can be concluded that the cryolite product contains an impurity, bayerite, which obviously does not meet the requirements of the "Cryolite - GB / T 4291 - 2017" standard.

[0091] It should be understood that the embodiments of the present invention are only preferred implementation schemes and are not used to limit the protection scope of the present invention. For those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and retouches can still be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A method for defluorination from fluorochlorohydric acid, characterized in that, It includes the following steps: Neutralization reaction: adding a neutralizing agent to the fluorochlorohydric acid to adjust the pH to 1.5 - 3.5; Cryolite preparation: adding sodium metaaluminate at 80 - 95 °C to obtain a cryolite preparation solution, and the mass molar concentration ratio of Al to F is 1.03 - 1.08; Activation and impurity removal: adding the fluorochlorohydric acid to the cryolite preparation solution to activate cryolite, and adjusting the pH to 4.5 - 7.2, followed by filtration to obtain a defluorinated solution and a cryolite precursor.

2. The method for defluorination from fluorochloric mixed acid according to claim 1, wherein, The cryolite precursor is slurried and dried to obtain a cryolite product.

3. The method for defluorination from fluorochlorohydric acid according to claim 1, wherein The neutralizing agent includes one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

4. The method for defluorination from fluorochloric mixed acid according to claim 1, characterized in that, The concentration of the neutralizing agent is 15 - 28 g / L.

5. The method for defluorination from fluorochloric mixed acid according to claim 1, characterized in that, The reaction temperature in the neutralization reaction step is 55 - 75 °C.

6. The method for defluorination from fluorochloric mixed acid according to claim 1, characterized in that, During the cryolite preparation step, sodium metaaluminate is added while stirring to obtain a cryolite preparation solution with a pH ≥ 9.

0.

7. The method for defluorination from fluorochloric mixed acid according to claim 1, characterized in that, In the cryolite preparation step, the reaction time is 60 - 90 min, and the stirring speed is 450 - 680 r / min.

8. The method for defluorination from fluorochlorohydric acid according to claim 1, characterized in that, The reaction time in the activation and impurity removal step is 30 - 120 min.

9. The method for defluorination from fluorochlorohydric acid according to claim 1, characterized in that, The content of H + in the fluorochlorohydric acid is 65 - 125 g / L, the content of F - is 25 - 55 g / L, and the content of Cl - is 12 - 28 g / L.

10. Application of the method for defluorination from fluorochlorohydric acid according to any one of claims 1 - 9 in wastewater treatment and reuse.

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