Method for preparing potassium fluosilicate from mixed waste acid

Abstract

The invention belongs to the field of waste liquid recycling, and discloses a method for preparing potassium fluosilicate by using mixed waste acid, which comprises the following steps: S1, silica fume acidification pretreatment: soaking silica fume in an acid solution for acidification, carrying out precipitation separation on the silica fume, drying, and grinding to obtain acidified silica fume; s2, mixing the raw materials: uniformly mixing the acidified silica fume and the silicon dioxide powder; s3, preparation of fluosilicic acid: adding a mixture of acidified silica fume and silicon dioxide powder into the mixed waste acid, and uniformly stirring by a mechanical stirrer; and S4, preparation of potassium fluosilicate: adding a potassium chloride saturated solution into the fluosilicic acid solution to generate potassium fluosilicate precipitate. The method has the advantages and effects of being high in fluorine ion utilization efficiency, low in production cost and high in finished product purity.

Description

Technical Field

[0001] This invention belongs to the field of waste liquid recycling technology, and specifically relates to a method for preparing potassium fluorosilicate using mixed waste acid. Background Technology

[0002] Fluorinated waste acid is a major waste liquid generated in the photovoltaic industry. This fluorinated waste acid is primarily produced during the texturing and etching processes of polycrystalline silicon solar cells, and the pickling and etching processes of monocrystalline silicon solar cells. While the composition of the fluorinated waste acid may vary depending on the type of photovoltaic cell and the manufacturing process, the basic components are generally the same, typically containing large amounts of fluorosilicic acid, hydrofluoric acid, nitric acid, sulfuric acid, hydrochloric acid, and trace amounts of metal salts.

[0003] Currently, photovoltaic fluorine-containing waste acid is mainly used to prepare potassium fluorosilicate. The mainstream process typically uses silica in powder form, such as precipitated silica or ultrafine silica powder. Silica powder has a large specific surface area, which improves contact and reaction with liquid waste acid. However, the reaction between ordinary silica powder and photovoltaic fluorine-containing waste acid is slow, resulting in insufficient fluoride ion reaction and wasted fluoride ions. Furthermore, silica powder is expensive; ordinary industrial-grade powder typically costs between 5500 and 6000 yuan per ton, while ultrafine silica powder usually exceeds 10000 yuan per ton. The high cost of industrial-grade silica powder significantly increases the production cost of potassium fluorosilicate, hindering its widespread application. Therefore, this invention uses acid-modified ordinary silica fume to replace silica powder, improving the reaction rate and degree, increasing the amount of fluoride ions reacted, and reducing the amount of silica powder used, thereby reducing the production cost of potassium fluorosilicate and promoting its widespread application. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing potassium fluorosilicate using mixed waste acid, which solves the above-mentioned technical problems, has high fluoride ion utilization efficiency, low production cost, and high product purity.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for preparing potassium fluorosilicate using mixed waste acid, comprising the following steps:

[0006] S1. Pretreatment of silica fume acidification: The silica fume is immersed in an acidic solution for acidification, then the silica fume is separated by precipitation, and then dried and ground to obtain acidified silica fume.

[0007] S2. Raw material mixing: Mix the acidified silica ash and silica powder evenly;

[0008] S3, Fluorosilicic acid preparation: Add a mixture of acidified silica ash and silica powder to the mixed waste acid, and stir evenly with a mechanical stirrer;

[0009] S4. Preparation of potassium fluorosilicate: Add a saturated potassium chloride solution to a fluorosilicic acid solution to generate potassium fluorosilicate precipitate.

[0010] A further setting of the present invention is as follows: In step S1, the silica fume is 90% industrial ordinary silica fume, the acidic solution is a 15-20% hydrochloric acid solution, the ratio of silica fume to hydrochloric acid solution is 1-2:4, the reaction temperature is 75-80℃, the pressure is 0.12-0.15MPa, and the mixture is stirred by a mechanical stirrer for 30 minutes at a speed of 200 r·min. -1 After standing for 20 minutes, solid-liquid separation was performed.

[0011] A further provision of the present invention is that, in step S1, the silica fume separated after acidification is dried in a dryer at a temperature of 120°C for 120 minutes. The dried silica fume is then ground in a grinder for 10 minutes.

[0012] A further provision of the present invention is that in step S2, the mixing ratio of acidified silica ash to silica powder is 3:1, the mixing is carried out using a pneumatic mixer, the feeding air ratio is 12~15, and the inlet air pressure is 0.6-0.8MPa.

[0013] A further setting of the present invention is as follows: in step S3, the mixture from S2 is added to the mixed waste acid for reaction, the amount of silica added is 3 times the mass of fluoride ions in the waste acid, the reaction temperature is 80-90℃, and the stirring time is 45min.

[0014] A further setting of the present invention is as follows: a saturated potassium chloride solution is added to a fluorosilicic acid solution to generate potassium fluorosilicate precipitate; the molar ratio of fluorosilicic acid to potassium chloride is 1:1.2~1.5; the reaction temperature is 50~60℃; and the stirring speed is 60 r·min. -1 Stirring time is 30-40 minutes. Solid-liquid separation, filtration and drying are performed to obtain potassium fluorosilicate with a content of more than 98.5%.

[0015] The beneficial effects of this invention are:

[0016] 1. This application uses ordinary silica fume instead of silica powder. Silica fume can provide acidic sites for reaction with hydrofluoric acid. On the one hand, the acidic sites can adsorb and polarize HF molecules in hydrofluoric acid, making them easier to dissociate into H+ and F-. On the other hand, they can also attract fluoride ions through positive charge, weakening the strength of silicon-oxygen bonds and reducing the activation energy of the reaction. Finally, under the electrostatic guidance of the acidic sites, fluoride ions attack silicon atoms, gradually replacing oxygen and generating Si–F bonds, accelerating the reaction between silica fume and hydrofluoric acid. This application uses hydrochloric acid to acidify ordinary silica fume, which can effectively remove Al2O3, Fe2O3, and CaO impurities from silica fume, separate solid and liquid, and improve the purity of silica fume, thereby improving the purity of subsequent potassium fluorosilicate. The acidification treatment can also further improve the activity of the acidic reaction sites of silanol groups (≡Si-OH) on the surface of silica fume, increase the degree of reaction between silica fume and hydrogen fluoride in mixed waste acid, thereby improving the utilization efficiency of fluoride ions in mixed waste acid.

[0017] 2. Ordinary silica fume is smelted at temperatures above 1000℃, with an average particle size of 0.2–0.5 micrometers and a very large specific surface area. Its main component is amorphous silica. Amorphous silica has the characteristics of disordered structure, high specific surface area and porosity, thermodynamic metastable state, and many surface active sites. Therefore, the chemical reaction rate of ordinary silica fume is significantly higher than that of traditional crystalline silica. The reaction rate of amorphous silica is 5–10 times faster than that of crystalline silica. The amorphous silica in silica fume can react more rapidly with hydrofluoric acid, and can quickly react with fluorides in mixed waste acid to generate fluorosilicic acid.

[0018] 3. Ordinary silica fume is inexpensive and is an industrial byproduct generated during the industrial production of ferrosilicon alloys or metallic silicon. After acid treatment, ordinary silica fume has high purity and can replace most industrial-grade silica powder. The price of treated silica fume is usually 40%-50% of the price of silica powder, which can effectively reduce the production cost of potassium fluorosilicate.

[0019] 4. This invention uses inexpensive potassium chloride as the potassium source. Potassium chloride is cheaper than potassium sulfate, potassium nitrate, and potassium carbonate. At the same time, potassium chloride reacts with fluorosilicic acid to produce potassium fluorosilicate precipitate, which in turn produces hydrochloric acid. The hydrochloric acid is used as a raw material for acidifying ordinary silica fume, which can be recycled and further reduce production costs.

[0020] 5. This invention uses inexpensive ordinary silica fume to prepare potassium fluorosilicate with a content of over 98.5% by precisely controlling the acidification concentration of ordinary silica fume, reaction temperature, reaction pressure, stirring speed, and reaction time during the preparation process of potassium fluorosilicate. Detailed Implementation

[0021] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] A method for preparing potassium fluorosilicate using mixed waste acid includes the following steps:

[0024] S1. Pretreatment of silica fume acidification: Silica fume is immersed in an acidic solution for acidification, then the silica fume is precipitated and separated, dried, and ground to obtain acidified silica fume. The silica fume is 90% industrial ordinary silica fume, the acidic solution is a 15% hydrochloric acid solution with a silica fume to hydrochloric acid solution ratio of 1:4, the reaction temperature is 75℃, the pressure is 0.12MPa, and the mixture is stirred for 30 minutes at a mechanical stirrer speed of 200 r·min. -1 After standing for 20 minutes, solid-liquid separation is performed. The separated silica fume after acidification is put into a dryer for drying at 120℃ for 120 minutes. The dried silica fume is then ground in a grinder for 10 minutes.

[0025] S2. Raw material mixing: The acidified silica ash and silica powder are mixed evenly, wherein the mixing ratio of acidified silica ash to silica powder is 3:1. The mixing is carried out by a pneumatic mixer with a feeding air ratio of 12~15 and an inlet air pressure of 0.6-0.8MPa.

[0026] S3, Fluorosilicic acid preparation: Add an acidified silica ash and silica powder mixture to the mixed waste acid, stir evenly with a mechanical stirrer, add the mixture of S2 to the mixed waste acid for reaction, the amount of silica added is 3 times the mass of fluoride ions in the waste acid, the reaction temperature is 80-90℃, and the stirring time is 45min.

[0027] S4. Preparation of potassium fluorosilicate: A saturated potassium chloride solution is added to a fluorosilicic acid solution to form potassium fluorosilicate precipitate. The molar ratio of fluorosilicic acid to potassium chloride is 1:1.2~1.5. The reaction temperature is 50~60℃, and the stirring speed is 60 r·min. -1 Stirring time is 30-40 minutes, solid-liquid separation, filtration and drying are performed to obtain potassium fluorosilicate.

[0028] Example 2

[0029] S1. Pretreatment of silica fume acidification: Silica fume is immersed in an acidic solution for acidification, then the silica fume is precipitated and separated, dried, and ground to obtain acidified silica fume. The silica fume is 90% industrial ordinary silica fume, the acidic solution is a 17% hydrochloric acid solution with a silica fume to hydrochloric acid ratio of 1.5:4, the reaction temperature is 77℃, the pressure is 0.14MPa, and the mixture is stirred for 30 minutes at a mechanical stirrer speed of 200 r·min. -1 After standing for 20 minutes, solid-liquid separation is performed. The separated silica fume after acidification is put into a dryer for drying at 120℃ for 120 minutes. The dried silica fume is then ground in a grinder for 10 minutes.

[0030] S2. Raw material mixing: The acidified silica ash and silica powder are mixed evenly, wherein the mixing ratio of acidified silica ash to silica powder is 3:1. The mixing is carried out by a pneumatic mixer with a feeding air ratio of 12~15 and an inlet air pressure of 0.6-0.8MPa.

[0031] S3, Fluorosilicic acid preparation: Add an acidified silica ash and silica powder mixture to the mixed waste acid, stir evenly with a mechanical stirrer, add the mixture of S2 to the mixed waste acid for reaction, the amount of silica added is 3 times the mass of fluoride ions in the waste acid, the reaction temperature is 80-90℃, and the stirring time is 45min.

[0032] S4. Preparation of potassium fluorosilicate: A saturated potassium chloride solution is added to a fluorosilicic acid solution to form potassium fluorosilicate precipitate. The molar ratio of fluorosilicic acid to potassium chloride is 1:1.2~1.5. The reaction temperature is 50~60℃, and the stirring speed is 60 r·min. -1 Stirring time is 30-40 minutes, solid-liquid separation, filtration and drying are performed to obtain potassium fluorosilicate.

[0033] Example 3

[0034] S1. Pretreatment of silica fume acidification: The silica fume is immersed in an acidic solution for acidification, then the silica fume is precipitated and separated, dried, and ground to obtain acidified silica fume. The silica fume is 90% industrial ordinary silica fume, the acidic solution is a 20% hydrochloric acid solution with a silica fume to hydrochloric acid solution ratio of 2:4, the reaction temperature is 80℃, the pressure is 0.15MPa, and the mixture is stirred for 30 minutes with a mechanical stirrer at a speed of 200 r·min. -1 After standing for 20 minutes, solid-liquid separation is performed. The separated silica fume after acidification is put into a dryer for drying at 120℃ for 120 minutes. The dried silica fume is then ground in a grinder for 10 minutes.

[0035] S2. Raw material mixing: The acidified silica ash and silica powder are mixed evenly, wherein the mixing ratio of acidified silica ash to silica powder is 3:1. The mixing is carried out by a pneumatic mixer with a feeding air ratio of 12~15 and an inlet air pressure of 0.6-0.8MPa.

[0036] S3, Fluorosilicic acid preparation: Add an acidified silica ash and silica powder mixture to the mixed waste acid, stir evenly with a mechanical stirrer, add the mixture of S2 to the mixed waste acid for reaction, the amount of silica added is 3 times the mass of fluoride ions in the waste acid, the reaction temperature is 80-90℃, and the stirring time is 45min.

[0037] S4. Preparation of potassium fluorosilicate: A saturated potassium chloride solution is added to a fluorosilicic acid solution to form potassium fluorosilicate precipitate. The molar ratio of fluorosilicic acid to potassium chloride is 1:1.2~1.5. The reaction temperature is 50~60℃, and the stirring speed is 60 r·min. -1 Stirring time is 30-40 minutes, solid-liquid separation, filtration and drying are performed to obtain potassium fluorosilicate.

[0038] Example 4

[0039] The preparation method is the same as in Example 1, except that the ordinary silica fume in S1 is not subjected to acidification pretreatment.

[0040] Example 5

[0041] The preparation method is the same as in Example 1, except that ordinary silica fume in S1 is replaced with silica powder.

[0042] The purity of potassium fluorosilicate prepared using Examples 1 to 5 and the corresponding raw material prices are shown in Table 1.

[0043] Table 1

[0044] Potassium fluorosilicate purity (%) Silicon raw material price (RMB / ton) Example 1 98.7 Silica fume + acidification price: 3000-3500 Example 2 99.3 Silica fume + acidification price: 3000-3500 Example 3 98.8 Silica fume + acidification price: 3000-3500 Example 4 77.5 Silica fume price 2700-3200 Example 5 98.5 Silica powder 5000-6000

[0045] As shown in the table above, the purity of potassium fluorosilicate prepared by this process can reach 99.3%, which is 21.8% higher than that of potassium fluorosilicate without pre-acidification treatment with ordinary silica fume. The purity is almost the same as that of potassium fluorosilicate prepared from silica powder. However, the price of silica fume + acidification raw materials used in the preparation process of this application is 1500-3000 yuan less than that of silica powder alone, which is more cost-effective. Therefore, this invention reduces the production cost of potassium fluorosilicate by using acidified and modified ordinary silica fume to replace silica powder, thereby reducing the amount of silica powder used and promoting the application of potassium fluorosilicate.

Claims

1. A method for preparing potassium fluorosilicate using mixed waste acid, characterized in that: Includes the following steps: S1. Pretreatment of silica fume acidification: The silica fume is immersed in an acidic solution for acidification, then the silica fume is separated by precipitation, and then dried and ground to obtain acidified silica fume. S2. Raw material mixing: Mix the acidified silica ash and silica powder evenly; S3, Fluorosilicic acid preparation: Add a mixture of acidified silica ash and silica powder to the mixed waste acid, and stir evenly with a mechanical stirrer; S4. Preparation of potassium fluorosilicate: Add a saturated potassium chloride solution to a fluorosilicic acid solution to generate potassium fluorosilicate precipitate.

2. The method for preparing potassium fluorosilicate using mixed waste acid according to claim 1, characterized in that: In step S1, the silica fume is 90% industrial ordinary silica fume, and the acidic solution is a 15-20% hydrochloric acid solution.

3. The method for preparing potassium fluorosilicate using mixed waste acid according to claim 1, characterized in that, The ratio of silica fume to hydrochloric acid solution is 1~2:

4.

4. The method for preparing potassium fluorosilicate using mixed waste acid according to claim 1, characterized in that, The reaction temperature for hydrochloric acid acidification of silica fume is 75~80℃, the pressure is 0.12-0.15MPa, and the mixture is stirred for 30 minutes with a mechanical stirrer at a speed of 200 r·min. -1 After standing for 20 minutes, solid-liquid separation was performed.

5. The method for preparing potassium fluorosilicate using mixed waste acid according to claim 1, characterized in that: In step S1, the silica fume separated after acidification is dried in a dryer at a temperature of 120°C for 120 minutes, and then ground in a grinder for 10 minutes.

6. The method for preparing potassium fluorosilicate using mixed waste acid according to claim 1, characterized in that: In step S2, the mixing ratio of acidified silica ash to silica powder is 3:1, and a pneumatic mixer is used for mixing. The feeding air ratio is 12~15, and the inlet air pressure is 0.6-0.8MPa.

7. The method for preparing potassium fluorosilicate using mixed waste acid according to claim 1, characterized in that: In step S3, the mixture from S2 is added to the mixed waste acid for reaction. The amount of silica added is three times the mass of fluoride ions in the waste acid. The reaction temperature is 80-90℃ and the stirring time is 45 min.

8. The method for preparing potassium fluorosilicate using mixed waste acid according to claim 1, characterized in that: Adding a saturated potassium chloride solution to a fluorosilicic acid solution produces a potassium fluorosilicate precipitate, with a molar ratio of fluorosilicic acid to potassium chloride of 1:1.2~1.

5.

9. The method for preparing potassium fluorosilicate using mixed waste acid according to claim 1, characterized in that: The reaction temperature of fluorosilicic acid solution with saturated potassium chloride solution is 50–60 °C, and the stirring speed is 60 r·min. -1 Stirring time is 30-40 minutes. Solid-liquid separation, filtration and drying are performed to obtain potassium fluorosilicate with a content of more than 98.5%.