Preparation method of low-metal-impurity high-purity acidic silica sol

Abstract

The invention belongs to the field of silica sol materials, and relates to a preparation method of low-metal-impurity high-purity acidic silica sol. According to the method, alkali is added into silica sol, aluminum hydroxide or oxide with the highest impurity content is dissolved to form aluminum anions, then anion resin exchange is carried out, the aluminum anions are removed, and therefore the aluminum metal impurities are effectively removed; then continuously adding acid into the silica sol to introduce anions without introducing metal impurity ions, and then carrying out cation exchange to dissolve hydroxides or oxides of metal impurities such as aluminum, iron, magnesium, calcium and the like to form corresponding metal cations which are captured by cation resin; according to the method, reagents which are simpler and easier to obtain are used, the removal effect on metal impurities such as aluminum, iron, magnesium and calcium is good, especially through two-time aluminum removal, the content of aluminum impurity elements which are most difficult to remove and have the highest content is effectively reduced, the operation method is simple and efficient, the cost is low, and the method is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of silica sol materials, specifically relating to a method for preparing a high-purity acidic silica sol with low metal impurities. Background Technology

[0002] Silica sol is a colloidal solution formed by dispersing amorphous nano-silica particles in water or organic solvents, with the molecular formula mSiO2·nH2O. As an important inorganic nanomaterial, it possesses a series of excellent properties such as high specific surface area, good dispersibility, good adhesion, good fire resistance and heat insulation, and good insulation. Therefore, it is widely used in casting, chemical mechanical polishing, coatings, and special ceramic composite materials. In particular, the demand for high-purity acidic silica sol is constantly increasing in microwave-transparent ceramic matrix composites, and the purity requirements are also becoming increasingly stringent.

[0003] There are three main methods for preparing silica sol: ion exchange, orthosilicate hydrolysis, and silica powder hydrolysis. Orthosilicate hydrolysis produces silica sol with uniform particle size and the lowest metal impurity content, but this method has extremely high raw material costs and requires the use of flammable alcohol solvents. Silica powder hydrolysis uses silicon powder waste from wafer fabs as raw material, hydrolyzing it in an alkaline solution to generate silicic acid, which then polymerizes into silica sol. Silica powder hydrolysis is a strongly exothermic reaction that generates a large amount of hydrogen gas, making the reaction difficult to control in practice. The temperature of the reactants can easily run out of control, causing the reaction rate to accelerate rapidly, and the generation of hydrogen gas creates a large amount of foam, resulting in relatively high production costs. Ion exchange, with its inexpensive raw materials, simple equipment and processes, ease of operation, and controllable product technical parameters, is widely used in the preparation of silica sol.

[0004] The preparation of silica sol by ion exchange typically uses water glass as a raw material. After ion exchange treatment, most metal ion impurities such as sodium and potassium are removed, resulting in a silicic acid solution. This solution is then subjected to polymerization at specific temperature and pH values ​​to obtain silica sol. After cation exchange with resin, metallic impurities such as aluminum, iron, zinc, magnesium, calcium, and nickel still remain in the silicic acid. These metal ions mainly exist as electrically neutral hydroxides and oxides at the pH of silicic acid (4-6), and therefore cannot react with the ion exchange resin, making them ineffective for removal. This results in a high content of aluminum, iron, zinc, magnesium, calcium, and nickel in the final silica sol product, with aluminum impurities >100 ppm and iron impurities >10 ppm.

[0005] Patent CN 104591192 A discloses a method for improving the purity of orthosilicic acid solution, using water glass as raw material and subjecting it to sequential cation, cation, and anion exchange. Before the second cation exchange, acid is added to adjust the pH, converting hydroxides of elements such as aluminum into cations, thereby reducing the content of metallic impurities such as aluminum. Patent CN 101475180 A discloses a method for purifying silica sol, controlling the silica sol temperature between 0 and 60°C, sequentially passing it through a strong acid cation exchange bed and a strong base anion exchange bed, then adding a chelating agent, and finally passing it through a mixed strong acid and strong base ion exchange bed to obtain purified silica sol. Patent CN 102583406 A further improves upon CN 101475180 A by mixing silica sol with a mixed strong acid and strong base resin, stirring at a certain temperature, adding a composite chelating agent and flocculant, and controlling the pH between 1 and 5 to achieve silica sol purification.

[0006] With the continuous development of the silica sol industry, the requirements for silica sol are becoming increasingly stringent, and silica sol purification technology will continue to evolve. This invention provides a method for preparing a high-purity acidic silica sol with low metal impurities, which can effectively remove metal impurities such as aluminum, iron, magnesium, and calcium, and has minimal impact on the viscosity, stability, and other properties of the acidic silica sol. Summary of the Invention

[0007] To address the above-mentioned problems, this invention provides a method for preparing high-purity acidic silica sol with low metal impurities.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for preparing a high-purity acidic silica sol with low metal impurities includes the following steps:

[0010] The strong acid cation exchange resin and the strong base anion exchange resin were activated and regenerated using strong acid solution and strong base solution, respectively.

[0011] Prepare a water glass solution and reflux it with stirring to form silicon dioxide seed crystals;

[0012] The activated and regenerated cation exchange resin was used to perform ion exchange on the water glass solution that had been refluxed and stirred and the water glass solution that had not been refluxed and stirred, to remove the main cations and obtain the orthosilicic acid-seed crystal solution containing seed crystals and the orthosilicic acid solution without seed crystals.

[0013] After diluting the orthosilicic acid-seed crystal solution to a certain concentration, it is put into a reaction vessel with stirring and heating function as the reaction base liquid, and alkali is added as a pH adjuster. The mixture is heated to boiling and stirred. While boiling, orthosilicic acid solution without seed crystal is continuously passed into the reaction liquid to carry out the polymerization growth reaction, forming silica sol particles, and obtaining alkaline silica sol with a certain particle size.

[0014] An alkali is added to alkaline silica sol as a pH adjuster, and the mixture is stirred at a certain temperature to dissolve aluminum hydroxide and oxides, forming free aluminum anions. Ion exchange is then performed using an activated and regenerated anion exchange resin to achieve the initial removal of aluminum metal impurities.

[0015] Acid is added to the silica sol after aluminum metal impurities have been initially removed, and then ion exchange is performed using activated and regenerated cation exchange resin to dissolve the hydroxides or oxides of the metal impurities, forming corresponding metal cations, which are then captured by the cation exchange resin. The solid content of the silica sol is then increased by ultrafiltration or evaporation concentration to obtain a high-purity acidic silica sol with low metal impurities.

[0016] Preferably, the mass concentration of SiO2 in the water glass solution is 0.5-6%.

[0017] Preferably, the reflux stirring temperature is 60–100°C and the time is 4–12 hours.

[0018] Preferably, the ion exchange is carried out by static or dynamic exchange, and the pH value of the orthosilicic acid solution is 3 to 6.

[0019] Preferably, the mass concentration of SiO2 in the reaction substrate is 0.2-1.0%, and the pH value of the reaction solution is controlled at 9-12.

[0020] Preferably, the particle size of the obtained alkaline silica sol is 10–100 nm.

[0021] Preferably, the addition of alkali to the alkaline silica sol as a pH adjuster is to adjust the pH to 13-14; the stirring at a certain temperature to dissolve aluminum hydroxide and oxide is carried out at a temperature of room temperature to 60°C for a stirring time of 2-4 hours.

[0022] Preferably, acid is added to the silica sol after the aluminum metal impurities have been initially removed, and the amount of acid added is based on the pH of the sol, adjusting the pH of the sol to 6-8.

[0023] Preferably, the pH value of the prepared high-purity acidic silica sol with low metal impurities is 2 to 2.5.

[0024] The present invention also provides a high-purity acidic silica sol with low metal impurities prepared according to the above method.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention provides a method for preparing high-purity acidic silica sol with low metal impurities, eliminating the need for multiple ion exchanges and further acidification to prepare orthosilicic acid solution, thereby reducing production costs. This method uses simpler and more readily available reagents, and through two ion exchanges, it achieves good removal of metallic impurities such as aluminum, iron, magnesium, and calcium. In particular, the two aluminum removal processes effectively reduce the content of aluminum, the most difficult-to-remove and most abundant impurity element. The method is simple, efficient, and uses simple and inexpensive raw materials, making it suitable for large-scale industrial production and of practical significance. Detailed Implementation

[0027] The present invention will be further described in detail below through specific embodiments.

[0028] This invention provides a method for preparing a high-purity acidic silica sol with low metal impurities. The method includes: (1) adding an alkali to the prepared silica sol to adjust the pH to 13-14, and stirring at room temperature to 60°C to dissolve the aluminum hydroxide or oxide, which has the highest impurity content, to form aluminum anions (AlO2). - (1) Then anion exchange is performed to remove aluminum anions, thereby effectively removing aluminum metal impurities; (2) Acid is added to the silica sol to introduce anions without introducing metal impurity ions, and then cation exchange is performed. During the cation exchange process, the pH value of the silica sol is ≤2.5, and the hydroxides or oxides of metal impurities such as aluminum, iron, magnesium, and calcium dissolve to form corresponding metal cations, which are captured by the cation resin. The acidic silica sol prepared according to this method can effectively reduce the content of aluminum impurity elements, which are the most difficult to remove and have the highest content, due to the two aluminum removals. The final technical indicators are: when the SiO2 content is 25%, the sodium content is ≤5ppm, the potassium content is ≤5ppm, the aluminum content is ≤5ppm, the iron content is ≤2ppm, the magnesium content is ≤2ppm, the calcium content is ≤2ppm, the pH is 1~2, the viscosity is ≤3mpa·s, and the storage stability is greater than 1 year. The steps included in this method are as follows:

[0029] 1) Activation and regeneration of ion exchange resins: The strong acid type cation exchange resin (brand name 732) and the strong base type anion exchange resin (brand name 717) are activated and regenerated respectively with strong acid solution and strong base solution.

[0030] 2) Preparation of water glass solution and preparation of seed crystals: Water glass is diluted to a certain concentration with deionized water to obtain a water glass solution. The solution is then refluxed and stirred at a certain temperature to pre-form a certain amount of silicon dioxide seed crystals.

[0031] 3) Preparation of orthosilicic acid solution by cation exchange: The activated and regenerated 732 cation exchange resin is used to perform ion exchange on the water glass solution that has been refluxed and stirred in step 2) and the water glass solution that has not been refluxed and stirred in step 2) through static exchange or dynamic exchange to remove the main cations such as sodium and potassium, so as to prepare orthosilicic acid-seed crystal solution containing certain seed crystals and orthosilicic acid solution without seed crystals.

[0032] 4) Preparation of alkaline silica sol: The orthosilicic acid-seed crystal solution obtained in step 3) is diluted to a certain concentration and put into a reaction vessel with stirring and heating function as the reaction base liquid. Alkali is added as a pH adjuster, heated to boiling and stirred. Under boiling conditions, orthosilicic acid solution without seed crystal is continuously passed into the reaction liquid to carry out polymerization and growth reaction to form silica sol particles. The size of silica particles can be controlled by controlling the amount of orthosilicic acid fed, and alkaline silica sol with a certain particle size is obtained.

[0033] 5) Preliminary purification treatment: At this time, the alkaline silica sol contains a lot of aluminum impurities. Add alkali as a pH adjuster to the silica sol, and then stir at a certain temperature to dissolve aluminum hydroxide and oxide, forming free aluminum anions. Use activated and regenerated 717 type anion exchange resin to carry out ion exchange through static exchange or dynamic exchange. The aluminum anions are captured by the anion exchange resin, realizing the preliminary removal of aluminum metal impurities.

[0034] 6) Preparation of high-purity acidic silica sol: Add acid to the silica sol obtained in step (5) to introduce certain anions, and then use 732 cation exchange resin after activation and regeneration to carry out ion exchange through static exchange or dynamic exchange, so that the hydroxides or oxides of metal impurities such as aluminum, iron, magnesium, and calcium are dissolved to form corresponding metal cations, which are captured by the cation resin. Then, the solid content of silica sol is increased by ultrafiltration or evaporation concentration to obtain high-purity acidic silica sol with low metal impurities.

[0035] In step 1), the activation and regeneration of the ion exchange resin is a common method.

[0036] Preferably, in step 2), the concentration of water glass is based on the content of silicon dioxide (SiO2), and the mass concentration is 0.5-6%.

[0037] Preferably, in step 2), the reflux stirring temperature is 60–100°C and the time is 4–12 h.

[0038] In step 3), dynamic or static exchange of ion exchange resin is a common method, and the pH value of the prepared orthosilicic acid solution is 3 to 6.

[0039] Preferably, in step 4), the mass concentration (SiO2%) of the reaction substrate is 0.2-1.0%.

[0040] Preferably, in step 4), the alkali is a commonly used alkali in the prior art, such as sodium hydroxide, potassium hydroxide, ammonia, tetramethylammonium hydroxide, etc.

[0041] Preferably, in step 4), the pH value of the reaction solution is controlled between 9 and 12.

[0042] Preferably, in step 4), the orthosilicic acid can be introduced by dripping at a constant rate or by adding it in batches.

[0043] In step 4), the particle size of the obtained silica sol is 10-100 nm.

[0044] Preferably, in step 5), the alkali is a commonly used alkali in the prior art, such as sodium hydroxide, potassium hydroxide, ammonia, tetramethylammonium hydroxide, etc.

[0045] Preferably, in step 5), an alkali is added to adjust the pH to 13-14.

[0046] Preferably, in step 5), the temperature is room temperature to 60°C, and the stirring time is 2 to 4 hours.

[0047] Preferably, in step 6), the acid is a commonly used acid in the prior art, such as hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, formic acid, acetic acid, phosphoric acid, etc.

[0048] Preferably, in step 6), the amount of acid added is based on the pH of the sol, and the pH of the sol is adjusted to 6-8.

[0049] In step 6), dynamic or static exchange of ion exchange resin is a common method, and the pH value of the prepared silica sol is 2 to 2.5.

[0050] In step 6), ultrafiltration or evaporation concentration is a common method, the purpose of which is to increase the solid content of silica sol to the required solid content.

[0051] To enable those skilled in the art to gain a more comprehensive understanding of this invention, specific embodiments are provided below.

[0052] In the embodiments, commercially available liquid water glass with a modulus of 3.3 (SiO2 content: 28.7%; Na2O content: 9.12%) was used to activate and regenerate the strong acid cation exchange resin (brand name 732) and the strong base anion exchange resin (brand name 717) using hydrochloric acid and sodium hydroxide solutions with a concentration of 1 mol / L, respectively.

[0053] Example 1:

[0054] Take 300g of water glass, add 1500g of water, mix well to obtain a dilute water glass solution; prepare two portions of water glass solution, take one portion and reflux and stir at 80℃ for 8h to prepare seed crystals; use 732 cation exchange resin to prepare an orthosilicic acid-seed crystal solution containing certain seed crystals and an orthosilicic acid solution without seed crystals, the pH value of the obtained orthosilicic acid solution is about 4.

[0055] Take 100g of orthosilicic acid-seed crystal solution containing a certain amount of seed crystals, add 200g of deionized water to prepare the reaction base solution, add 5g of 1mol / L sodium hydroxide solution to make the pH of the reaction solution 11, heat to boiling and stir, and add orthosilicic acid solution dropwise to the reaction solution at a rate of 2mL / min under boiling conditions to carry out the polymerization growth reaction. After adding a total of 600g of orthosilicic acid solution, stop the reaction to obtain alkaline silica sol.

[0056] Add 5g of 1mol / L sodium hydroxide solution to alkaline silica sol, adjust the pH to 13, and then stir at 50℃ for 3h. Subsequently, use 717 type anion exchange resin to carry out ion exchange through static exchange to remove aluminum metal impurities and achieve preliminary impurity removal.

[0057] 10 g of 1 mol / L hydrochloric acid was added to the silica sol, setting the pH to 7.5. Ion exchange was performed using 732 cation exchange resin via static exchange, followed by ultrafiltration and concentration to a solid content (SiO2 content) of 25%, yielding a high-purity acidic silica sol. The characterization results are shown in Table 1.

[0058] Example 2:

[0059] Take 300g of water glass, add 1800g of water, mix well to obtain a dilute water glass solution; prepare two portions of water glass solution, take one portion and reflux and stir at 90℃ for 6h to prepare seed crystals; use 732 cation exchange resin to prepare an orthosilicic acid-seed crystal solution containing certain seed crystals and an orthosilicic acid solution without seed crystals, the pH value of the obtained orthosilicic acid solution is about 4.4;

[0060] Take 50g of orthosilicic acid-seed crystal solution containing a certain amount of seed crystals, add 250g of deionized water to prepare the reaction base solution, add 6g of 1mol / L potassium hydroxide solution to make the pH of the reaction solution 11.2, heat to boiling and stir, and add orthosilicic acid solution to the reaction solution in batches at a rate of 20g / time with an interval of 0.5h to carry out the polymerization growth reaction. After adding a total of 800g of orthosilicic acid solution, stop the reaction to obtain alkaline silica sol.

[0061] Add 8g of 1mol / L potassium hydroxide solution to alkaline silica sol, adjust the pH to 13.5, and then stir at 40℃ for 4h. Subsequently, use 717 type anion exchange resin to carry out ion exchange through static exchange to remove aluminum metal impurities and achieve preliminary impurity removal.

[0062] 15 g of 1 mol / L hydrochloric acid was added to the silica sol, setting the pH to 7.0. Ion exchange was performed using 732 cation exchange resin via dynamic exchange, followed by ultrafiltration to concentrate the sol to a solid content (SiO2 content) of 25%, yielding a high-purity acidic silica sol. The characterization results are shown in Table 1.

[0063] Example 3:

[0064] Take 300g of water glass, add 2100g of water, and mix well to obtain a dilute water glass solution; prepare two portions of water glass solution, take one portion and reflux and stir at 100℃ for 4h to prepare seed crystals; use 732 cation exchange resin to prepare an orthosilicic acid-seed crystal solution containing certain seed crystals and an orthosilicic acid solution without seed crystals. The pH value of the obtained orthosilicic acid solution is about 4.6.

[0065] Take 60g of orthosilicic acid-seed crystal solution containing a certain amount of seed crystals, add 240g of deionized water to prepare the reaction base solution, add 8g of 10% tetramethylammonium hydroxide solution to make the pH of the reaction solution 12, heat to boiling and stir, and add orthosilicic acid solution to the reaction solution in batches at a rate of 25g / time with an interval of 0.5h to carry out the polymerization growth reaction. After adding a total of 1500g of orthosilicic acid solution, stop the reaction to obtain alkaline silica sol.

[0066] Add 7.5g of 10% tetramethylammonium hydroxide solution to alkaline silica sol, adjust the pH to 13, and then stir at 60℃ for 4h. Subsequently, use 717 type anion exchange resin to carry out ion exchange through static exchange to remove aluminum metal impurities and achieve preliminary impurity removal.

[0067] 17 g of 1 mol / L nitric acid was added to the silica sol, setting the pH to 7.0. Ion exchange was performed using 732 cation exchange resin via dynamic exchange, followed by ultrafiltration and concentration to a solid content (SiO2 content) of 25%, yielding a high-purity acidic silica sol. The characterization results are shown in Table 1.

[0068] Comparative Example 1:

[0069] Take 300g of water glass, add 1500g of water, mix well to obtain a dilute water glass solution; prepare two portions of water glass solution, take one portion and reflux and stir at 80℃ for 8h to prepare seed crystals; use 732 cation exchange resin to prepare an orthosilicic acid-seed crystal solution containing certain seed crystals and an orthosilicic acid solution without seed crystals, the pH value of the obtained orthosilicic acid solution is about 4.

[0070] Take 100g of orthosilicic acid-seed crystal solution containing a certain amount of seed crystals, add 200g of deionized water to prepare the reaction base solution, add 5g of 1mol / L sodium hydroxide solution to make the pH of the reaction solution 11, heat to boiling and stir, and add orthosilicic acid solution dropwise to the reaction solution at a rate of 2mL / min under boiling conditions to carry out the polymerization growth reaction. After adding a total of 600g of orthosilicic acid solution, stop the reaction to obtain alkaline silica sol.

[0071] Ion exchange was performed directly using 732 cation exchange resin via static exchange, followed by ultrafiltration concentration to a solid content (SiO2 content) of 25%, yielding high-purity acidic silica sol. Characterization results are shown in Table 1.

[0072] Table 1 Characterization results of the target silica sol in each embodiment

[0073]

[0074] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a low metal impurity high purity acidic silica sol, characterized by, The method comprises the following steps: The strong acid type cation exchange resin and the strong base type anion exchange resin are respectively activated and regenerated by using strong acid solution and strong base solution; A water glass solution is prepared and refluxed and stirred to form silica seed crystals; The cation exchange resin after activation and regeneration is used to exchange ions in the refluxed and stirred water glass solution and the water glass solution without refluxing and stirring to remove main cations, so as to obtain a silicic acid-seed crystal solution containing seed crystals and a silicic acid solution without seed crystals; The silicic acid-seed crystal solution is diluted to a certain concentration, and then is put into a reactor with stirring and heating function as a reaction bottom solution, and an alkali is added as a pH regulator, and the reaction liquid is heated to boiling and stirred, and the silicic acid solution without seed crystals is continuously introduced into the reaction liquid under boiling state to perform a polymerization growth reaction, so as to form silica sol particles and obtain an alkali silica sol with a certain particle size; An alkali is added into the alkali silica sol as a pH regulator, and the hydroxide and oxide of aluminum are dissolved by stirring at a certain temperature to form free aluminum anions, and the anion exchange resin after activation and regeneration is used to exchange ions to remove aluminum metal impurities; An acid is added into the silica sol after preliminary removal of aluminum metal impurities, and then the cation exchange resin after activation and regeneration is used to exchange ions, so that the hydroxide or oxide of metal impurities is dissolved to form corresponding metal cations and is captured by the cation exchange resin, and then the solid content of the silica sol is increased by ultrafiltration or evaporation concentration to obtain a low-metal-impurity high-purity acidic silica sol.

2. The method of claim 1, wherein, The mass concentration of SiO2 in the water glass solution is 0.5-6%.

3. The method of claim 1, wherein, The refluxing and stirring temperature is 60-100°C, and the refluxing and stirring time is 4-12h.

4. The method of claim 1, wherein, The ion exchange is performed by static exchange or dynamic exchange, and the pH value of the silicic acid solution is 3-6.

5. The method of claim 1, wherein, The mass concentration of SiO2 in the reaction bottom solution is 0.2-1.0%, and the pH value of the reaction liquid is controlled to be 9-12.

6. The method of claim 1, wherein, The particle size of the obtained alkali silica sol is 10-100nm.

7. The method of claim 1, wherein, The pH value of the alkali silica sol is adjusted to 13-14 by adding an alkali as a pH regulator, and the hydroxide and oxide of aluminum are dissolved by stirring at a temperature of room temperature-60°C for 2-4h.

8. The method of claim 1, wherein, The pH value of the silica sol after preliminary removal of aluminum metal impurities is adjusted to 6-8 by adding an acid.

9. The method of claim 1, wherein, The pH value of the obtained low-metal-impurity high-purity acidic silica sol is 2-2.

5.

10. A low-metal-impurity high-purity acidic silica sol prepared by the method according to any one of claims 1-9.

Images