A process for preparing high molecular ratio cryolite and ammonium sulfate using fluorine-containing etching waste liquid

Abstract

The application discloses a process for preparing high-molecular-ratio cryolite and ammonium sulfate by using fluorine-containing etching waste liquid, and comprises the following steps: adding sodium metaaluminate slurry and sodium sulfate solution into the fluorine-containing etching waste liquid, then adjusting pH to be acidic by using a sulfuric acid solution, carrying out heating reaction, then carrying out centrifugal separation treatment, and drying the obtained cryolite precipitate; adding sodium metaaluminate slurry into the fluorine-containing supernatant, and obtaining defluorination filtrate by treatment; adding a sulfuric acid solution into the defluorination filtrate, carrying out neutralization reaction, then carrying out vacuum evaporation on the reaction mixture containing ammonium sulfate, carrying out centrifugal separation treatment after cooling, drying the obtained ammonium sulfate precipitate, and obtaining ammonium sulfate product. The fluorine ion in the fluorine-containing etching waste liquid can be effectively utilized, the generated cryolite product can reach the national standard of high-molecular ratio, the fluorine ion content of the generated filtrate is less, so that the filtrate can enter the synthesis of ammonium sulfate, and no waste liquid is generated in the process.

Description

Technical Field

[0001] This invention relates to the field of waste liquid resource utilization technology, and in particular to a process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid. Background Technology

[0002] Cryolite, also known as sodium fluoroaluminate, has the molecular formula Na3AlF6. Based on the ratio of sodium fluoride to aluminum fluoride molecules, it can be divided into high-molecular-weight cryolite and low-molecular-weight cryolite. High-molecular-weight cryolite (nNaF.AlF3, n: 2.8–3.0) has advantages such as lower volatilization loss, better thermal stability, and less environmental pollution, making it superior to low-molecular-weight cryolite in terms of both environmental protection and economic benefits.

[0003] Currently, the main processes for producing cryolite include the hydrofluoric acid method, the fluorosilicic acid method, the carbonation method, and the aluminum industry recycling method. These methods mostly use an alkaline environment to prepare cryolite. In an alkaline environment, AlO2⁻ in sodium aluminate (NaAlO2) can be hydrolyzed to generate Al(OH)3, which further combines with F⁻ to form stable hexafluoroaluminate (AlF6³⁻). This process avoids the problem of Al³⁺ easily hydrolyzing to form colloidal Al(OH)3 under acidic conditions, thereby improving the utilization rate of aluminum. Therefore, alkaline conditions have advantages in improving reaction selectivity and product purity. However, under alkaline conditions, ammonium fluoride is prone to decomposition and release of ammonia gas, reducing the utilization rate of ammonium.

[0004] Fluorine-containing etching wastewater is a common type of wastewater in the electronics industry, containing large amounts of ammonium fluoride, hydrofluoric acid, and aluminum ions. Traditional treatment methods mainly involve chemical precipitation to remove fluoride ions, but this method suffers from high processing costs and resource waste, and there are even fewer processes that use fluorine-containing etching wastewater in strongly acidic solutions to produce cryolite. Summary of the Invention

[0005] The main objective of this invention is to provide a process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid.

[0006] To achieve the above objectives, the present invention provides a process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid, comprising the following steps: S1. Preparation of Cryolite S11. Reaction: Sodium aluminate slurry and sodium sulfate solution are added to the fluorine-containing etching waste liquid. Then, the pH is adjusted to acidic with sulfuric acid solution, and the reaction is carried out by heating to obtain a reaction mixture containing cryolite. S12. Centrifugation: Cool the reaction mixture containing cryolite to room temperature, and then centrifuge to separate it, obtaining a fluorine-containing supernatant and cryolite precipitate. S13. Drying: The cryolite precipitate is dried to obtain the cryolite product; S14. Defluorination: Add sodium aluminate slurry to the fluoride-containing supernatant, then adjust the pH to neutral with sulfuric acid solution, carry out precipitation reaction, and then filter to obtain defluorinated filtrate. S2, Preparation of ammonium sulfate S21. Reaction: Add sulfuric acid solution to the defluorinated filtrate to carry out a neutralization reaction, and obtain a reaction mixture containing ammonium sulfate. S22. Concentration: The reaction mixture containing ammonium sulfate is evaporated under reduced pressure to obtain ammonium sulfate concentrate; S23. Centrifugation: After cooling the ammonium sulfate concentrate, centrifugation is performed to obtain supernatant and ammonium sulfate precipitate. The supernatant is then reused in the S22 concentration step. S24. Drying: The ammonium sulfate precipitate is dried to obtain the ammonium sulfate product.

[0007] Furthermore, in the fluorine-containing etching solution waste liquid, the content of ammonium fluoride is 10-20 wt%, the content of hydrofluoric acid is 2-15 wt%, and the content of aluminum ions is 0.1-1 wt%.

[0008] Further, in step S11, the ratio of the fluorine-containing etching waste liquid, sodium aluminate slurry, and sodium sulfate solution is such that the molar ratio of Na:Al:F reaches 2.3-3:1-1.2:6 (the amount of aluminum to be added is calculated based on the fluoride and aluminum ion content in the fluorine-containing etching waste liquid, and then the amount of sodium to be added is calculated). Further, in step S11, the concentration of the sulfuric acid solution is 20-30 wt%, and the pH value is adjusted to 3-4; Furthermore, in step S11, the heating reaction conditions are a temperature of 75–85°C and a time of 1–2 hours.

[0009] Furthermore, in step S14, the amount of sodium aluminate slurry added is such that the Al:F molar ratio reaches 1.2:6, and the precipitation reaction time is 0.5h.

[0010] Furthermore, in step S21, the concentration of the sulfuric acid solution is 20-30 wt%, the pH value is adjusted to 5-6, and the neutralization reaction time is 1-1.5 h.

[0011] Furthermore, in step S22, the conditions for reduced pressure evaporation are a temperature of 80–100°C and a pressure of -0.06–-0.08 MPa.

[0012] The design principle of this invention is as follows: To improve ammonium utilization, this invention prepares high-molecular-weight cryolite and ammonium sulfate under acidic conditions using fluorine-containing etching wastewater as raw materials. To address the hydrolysis of Al in acidic water, this invention adjusts the pH to less than 4 using sulfuric acid solution. Under these acidic conditions, aluminum hydroxide colloids are difficult to form, significantly reducing the generation of aluminum hydroxide impurities and reducing H+ in the acidic medium. + Can promote Al 3+ With F - The complexation reaction rapidly generates hexafluoroaluminate (AlF6) ions. 3- ).

[0013] In step S11, the reaction equation for the heating reaction is as follows: 4NH4F+2HF+Na2SO4+NaAlO2+H2SO4→Na3AlF6↓+2(NH4)2SO4+2H2O The reaction produces cryolite precipitate. To reduce the water content in the cryolite crystals and make them easier to preserve, the cryolite precipitate obtained from subsequent centrifugation is dried to obtain the finished product. At this point, the supernatant obtained from centrifugation in step S12 still contains 2000–3000 ppm of fluorine. Further, in step S14, excess fluorine is utilized using sodium aluminate; the reaction that occurs is as follows: 3AlO2 - +3F - +6H + →2Al(OH)3+AlF3 The reaction produces aluminum hydroxide precipitate, which encapsulates fluoride ions to achieve a defluorination effect. After subsequent filtration, the fluoride content of the defluorinated filtrate is reduced to 50-100 ppm.

[0014] In step S21, the reaction equation for the neutralization reaction is as follows: 2NH4 + +SO4 2- →(NH4)2SO4 The remaining ammonia in the defluorinated filtrate reacts with sulfuric acid to further generate ammonium sulfate. After evaporation and concentration, and centrifugation, ammonium sulfate precipitate is obtained. Similarly, in order to reduce the moisture in the ammonium sulfate crystals and make them easier to preserve, they are dried to obtain the finished product.

[0015] The beneficial effects of this invention are reflected in: This invention enables the effective utilization of fluoride ions in fluorine-containing etching waste liquid, and the generated cryolite product can meet the national standard for high molecular weight ratio. The filtrate produced has a low fluoride ion content, which can then be used in the synthesis of ammonium sulfate, with no waste liquid generated in the process.

[0016] This invention makes the evaporation system less affected by the impurities in the concentrated mother liquor, resulting in a more stable production line. The steam used after the triple-effect evaporator is used for preheating, which can reduce steam loss. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid. Detailed Implementation

[0018] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0019] Unless otherwise specified, the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial sources or by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0020] Example 1 High-molecular-weight cryolite and ammonium sulfate were prepared using fluorinated etching wastewater. For the preparation process, please refer to [link / reference]. Figure 1 .

[0021] (1) Preparation of cryolite To 100 kg of fluorine-containing etching waste liquid containing 10.1 wt% ammonium fluoride, 2.5 wt% hydrofluoric acid, and 0.5 wt% aluminum ions, 30 wt% sodium aluminate slurry and 20 wt% sodium sulfate solution were added to achieve a Na:Al:F molar ratio of 2.3:1:6. The pH was then adjusted to 3 with 20 wt% sulfuric acid solution. The reaction was carried out at 75°C for 2 hours to obtain a reaction mixture containing cryolite. After cooling to room temperature, the mixture was piped into a sealed centrifuge for centrifugal separation (centrifuge speed 3000 rpm). m), a fluorine-containing supernatant and cryolite precipitate were obtained; the cryolite precipitate was dried with hot air at 80℃ for 0.5h to obtain cryolite product, which was sent to the product silo and packaged using an automatic packaging machine; the fluorine-containing supernatant was found to contain 2500ppm of fluoride ions, and a sodium aluminate slurry with a concentration of 5.01wt% was added to it to make the Al:F molar ratio 1.2:6, and the pH was adjusted to neutral with a sulfuric acid solution with a concentration of 20wt% and reacted for 0.5h. After that, the precipitate was filtered off with a filter bag to obtain a defluorinated filtrate for later use, and its fluoride ion content was measured to be 79ppm; (2) Preparation of ammonium sulfate The defluorinated filtrate and 20wt% sulfuric acid solution were separately fed into a concentration preheater. The amount of sulfuric acid added was enough to adjust the pH of the solution to 5.5. After a neutralization reaction of 1 hour (the solution could be preheated to 50°C using steam from the triple-effect evaporator after neutralization), the solution was fed into the triple-effect evaporator for continuous reduced-pressure evaporation. The evaporation temperature was controlled at 80°C and the pressure at -0.08 MPa to obtain ammonium sulfate concentrate. After cooling to 30°C, the concentrate was piped into a closed continuous centrifuge for centrifugal separation (centrifuge speed 2500 rpm) to obtain supernatant and ammonium sulfate precipitate. The supernatant was recycled to the triple-effect evaporator. The ammonium sulfate precipitate was dried with hot air at 75°C for 0.5 hours to obtain ammonium sulfate product, which was then sent to the product silo and packaged using an automatic packaging machine.

[0022] Example 2 High-molecular-weight cryolite and ammonium sulfate were prepared using fluorinated etching wastewater. For the preparation process, please refer to [link / reference]. Figure 1 .

[0023] (1) Preparation of cryolite To 100 kg of fluorine-containing etching waste liquid containing 20.0 wt% ammonium fluoride, 15 wt% hydrofluoric acid, and 0.1 wt% aluminum ions, a sodium aluminate slurry of 29.8 wt% and a sodium sulfate solution of 20 wt% were added to achieve a Na:Al:F molar ratio of 3:1.2:6. The pH was then adjusted to 3.5 with a 25 wt% sulfuric acid solution. The reaction was carried out at 85°C for 1 hour to obtain a reaction mixture containing cryolite. After cooling to room temperature, the mixture was piped into a sealed centrifuge for centrifugal separation (centrifuge speed 3000 rpm). The supernatant containing fluoride and cryolite precipitate were obtained by drying the cryolite precipitate with hot air at 80°C for 0.5 h to obtain the cryolite product, which was then sent to the product silo and packaged using an automatic packaging machine. The supernatant containing fluoride contained 2435 ppm of fluoride ions. A sodium aluminate slurry with a concentration of 4.98 wt% was added to the supernatant to make the Al:F molar ratio 1.2:6. The pH was then adjusted to neutral with a sulfuric acid solution with a concentration of 25 wt%, and the reaction was carried out for 0.5 h. The precipitate was then filtered off with a filter bag to obtain a defluorinated filtrate with a fluoride ion content of 57 ppm. (2) Preparation of ammonium sulfate The defluorinated filtrate and 25wt% sulfuric acid solution were separately fed into a concentrator and preheater. The amount of sulfuric acid added was enough to adjust the pH of the solution to 6. After a neutralization reaction of 1.2 hours (the solution was preheated to 50°C using steam from the triple-effect evaporator after neutralization), it was fed into the triple-effect evaporator for continuous reduced-pressure evaporation. The evaporation temperature was controlled at 95°C and the pressure at -0.06 MPa to obtain ammonium sulfate concentrate. After cooling to 30°C, it was fed into a closed continuous centrifuge through a pipeline for centrifugal separation (centrifuge speed was 2500 rpm) to obtain supernatant and ammonium sulfate precipitate. The supernatant was recycled to the triple-effect evaporator. The ammonium sulfate precipitate was dried with hot air at 75°C for 0.5 hours to obtain ammonium sulfate product, which was then sent to the product silo and packaged using an automatic packaging machine.

[0024] Example 3 High-molecular-weight cryolite and ammonium sulfate were prepared using fluorinated etching wastewater. For the preparation process, please refer to [link / reference]. Figure 1 .

[0025] (1) Preparation of cryolite To 100 kg of fluorine-containing etching waste liquid containing 18.74 wt% ammonium fluoride, 10.14 wt% hydrofluoric acid, and 1.0 wt% aluminum ions, 29.89 wt% sodium aluminate slurry and 20 wt% sodium sulfate solution were added to achieve a Na:Al:F molar ratio of 2.8:1.1:6. The pH was then adjusted to 4 with 30 wt% sulfuric acid solution. The reaction was carried out at 82℃ for 1.5 h to obtain a reaction mixture containing cryolite. After cooling to room temperature, the mixture was piped into a sealed centrifuge for centrifugal separation. The machine was operated at 3000 rpm to obtain a fluorine-containing supernatant and cryolite precipitate. The cryolite precipitate was dried with hot air at 80°C for 0.5 h to obtain the cryolite product, which was then sent to the product silo and packaged using an automatic packaging machine. The fluorine-containing supernatant was found to contain 2873 ppm of fluoride ions. A sodium aluminate slurry with a concentration of 4.99 wt% was added to it to make the Al:F molar ratio 1.2:6. The pH was then adjusted to neutral with a sulfuric acid solution with a concentration of 30 wt%. The reaction was allowed to proceed for 0.5 h, and the precipitate was then filtered out using a filter bag. The fluoride ion content was found to be 98 ppm. (2) Preparation of ammonium sulfate The defluorinated filtrate and 30wt% sulfuric acid solution were separately fed into a concentration preheater. The amount of sulfuric acid added was enough to adjust the pH of the solution to 5.8. After a neutralization reaction of 1.5 hours (the solution was preheated to 50°C using steam from the triple-effect evaporator after neutralization), it was fed into the triple-effect evaporator for continuous reduced-pressure evaporation. The evaporation temperature was controlled at 100°C and the pressure at -0.07 MPa to obtain ammonium sulfate concentrate. After cooling to 30°C, it was fed into a closed continuous centrifuge through a pipeline for centrifugal separation (centrifuge speed was 2500 rpm) to obtain supernatant and ammonium sulfate precipitate. The supernatant was recycled to the triple-effect evaporator. The ammonium sulfate precipitate was dried with hot air at 75°C for 0.5 hours to obtain ammonium sulfate product, which was then sent to the product silo and packaged using an automatic packaging machine.

[0026] Experimental Example 1 The effect of different pH environments on the synthesis of cryolite Based on Example 1, the pH value adjusted to 3 with sulfuric acid solution during the reaction to generate cryolite was replaced with pH values ​​adjusted to 2.5 and 4.2, respectively. Then, the fluoride content of the fluoride-containing supernatant and the defluorinated filtrate was measured, and the results are shown in Table 1 below: Table 1 It can be seen that when cryolite is formed, a pH that is too high or too low will reduce the utilization rate of fluorine, and excessive fluorine residue will affect the quality of ammonium sulfate and corrode production equipment.

[0027] Experiment Example 2 The Influence of Different Temperature Environments on Synthetic Cryolite Based on Example 1, the reaction temperature of 75°C when cryolite is formed was changed to 60°C and 90°C, respectively. Then, the fluoride content of the fluoride-containing supernatant and the defluorinated filtrate was measured, and the results are shown in Table 2 below: Table 2 It can be seen that when cryolite is formed, excessively high or low temperatures will reduce the utilization rate of fluorine, and excessive fluorine residue will affect the quality of ammonium sulfate and corrode production equipment.

[0028] Experimental Example 3 The effect of different raw material addition ratios on the quality of cryolite products Based on Example 1, sodium aluminate slurry and sodium sulfate solution were added according to the Na:Al:F molar ratio in Table 3, and the molecular ratio of the obtained cryolite product was detected. The results are shown in Table 3 below: Table 3 Molecular ratio = Cryolite with a molecular ratio of 2.8 to 3.0 is considered to have a high molecular ratio, and the national standard requires that the fluorine content be no less than 52%.

[0029] Experiment Example 4 Effect of acidic conditions on the synthesis of cryolite Based on Example 1, the step of adjusting the pH to 3 with a 20wt% sulfuric acid solution during the reaction to generate cryolite was omitted. Then, the fluoride content of the fluoride-containing supernatant and the defluorinated filtrate was measured, and the results are shown in Table 4 below: Table 4 The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid, characterized in that, Includes the following steps: S1. Preparation of Cryolite S11. Reaction: Sodium aluminate slurry and sodium sulfate solution are added to the fluorine-containing etching waste liquid. Then, the pH is adjusted to acidic with sulfuric acid solution, and the reaction is carried out by heating to obtain a reaction mixture containing cryolite. S12. Centrifugation: Cool the reaction mixture containing cryolite to room temperature, and then centrifuge to separate it, obtaining a fluorine-containing supernatant and cryolite precipitate. S13. Drying: The cryolite precipitate is dried to obtain the cryolite product; S14. Defluorination: Add sodium aluminate slurry to the fluoride-containing supernatant, then adjust the pH to neutral with sulfuric acid solution, carry out precipitation reaction, and then filter to obtain defluorinated filtrate. S2, Preparation of ammonium sulfate S21. Reaction: Add sulfuric acid solution to the defluorinated filtrate to carry out a neutralization reaction, and obtain a reaction mixture containing ammonium sulfate. S22. Concentration: The reaction mixture containing ammonium sulfate is evaporated under reduced pressure to obtain ammonium sulfate concentrate; S23. Centrifugation: After cooling the ammonium sulfate concentrate, centrifugation is performed to obtain supernatant and ammonium sulfate precipitate. The supernatant is then reused in the S22 concentration step. S24. Drying: The ammonium sulfate precipitate is dried to obtain the ammonium sulfate product.

2. The process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid as described in claim 1, characterized in that, The fluorine-containing etching solution waste liquid contains 10-20 wt% ammonium fluoride, 2-15 wt% hydrofluoric acid, and 0.1-1 wt% aluminum ions.

3. The process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid as described in claim 1, characterized in that, In step S11, the ratio of fluorine-containing etching waste liquid, sodium aluminate slurry and sodium sulfate solution is such that the molar ratio of Na:Al:F reaches 2.3-3:1-1.2:

6.

4. The process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid as described in claim 1, characterized in that, In step S11, the concentration of the sulfuric acid solution is 20-30 wt%, and the pH value is adjusted to 3-4.

5. The process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid as described in claim 1, characterized in that, In step S11, the heating reaction conditions are a temperature of 75–85°C and a time of 1–2 hours.

6. The process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid as described in claim 1, characterized in that, In step S14, the amount of sodium aluminate slurry added is such that the Al:F molar ratio reaches 1.2:6, and the precipitation reaction time is 0.5h.

7. The process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid as described in claim 1, characterized in that, In step S21, the concentration of the sulfuric acid solution is 20-30 wt%, the pH value is adjusted to 5-6, and the neutralization reaction time is 1-1.5 h.

8. The process for preparing high-molecular-weight cryolite and ammonium sulfate using fluorine-containing etching waste liquid as described in claim 1, characterized in that, In step S22, the conditions for reduced pressure evaporation are a temperature of 80 to 100°C and a pressure of -0.06 to -0.08 MPa.

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