阅读说明：本技术 一种低成本制备高纯硅酸的方法 (Method for preparing high-purity silicic acid at low cost ) 是由 高逸飞 李洪深 吕毅 张剑 于 2021-07-05 设计创作，主要内容包括：本发明涉及一种低成本制备高纯硅酸的方法。本发明以水玻璃或硅酸钠为原料,向其中溶解一定量的强酸强碱盐,再先后进行阳离子交换和阴离子交换,得到低杂质金属含量的硅酸。本发明利用强酸的酸根离子在阳离子交换时原位生成的强酸来降低溶液的pH值,使氧化铝、氧化铁等金属氧化物转化为相应的金属阳离子并被离子交换树脂捕获,达到除去金属杂质的目的,其特点是将离子交换次数从三次减少到了两次,所得硅酸的杂质金属离子含量低。(The invention relates to a method for preparing high-purity silicic acid at low cost. The invention takes water glass or sodium silicate as raw material, dissolves a certain amount of strong acid strong alkali salt into the water glass or sodium silicate, and then carries out cation exchange and anion exchange in sequence to obtain silicic acid with low impurity metal content. The present invention utilizes strong acid generated in situ during cation exchange of acid radical ion of strong acid to reduce pH value of solution, so that metal oxides of alumina, ferric oxide, etc. are converted into corresponding metal cations and are captured by ion exchange resin to attain the goal of removing metal impurity.)

1. The method for preparing high-purity silicic acid at low cost is characterized by comprising the following steps:

adding strong acid strong base salt into water glass, and carrying out cation exchange to obtain acid silicic acid containing strong acid;

and carrying out anion exchange on the acidic silicic acid to obtain a silicic acid finished product.

2. The method according to claim 1, wherein the acidic silicic acid has a pH of 0.5 to 2.0.

3. The method according to claim 1 or 2, wherein the pH of the silicic acid product is 5.0-5.5.

4. The process according to claim 1, wherein the strong acid strong base salt is one of the following: sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium nitrate, sodium perchlorate, potassium tetrafluoroborate, sodium hexafluorophosphate, sodium methanesulfonate, sodium trifluoromethanesulfonate, sodium benzenesulfonate, sodium p-toluenesulfonate.

5. The method of claim 1, wherein the adding of the strong acid and strong base salt to the water glass comprises: dissolving industrial water glass or sodium silicate in water with the weight of 4-20 times, adding 0.25-4.5 kg of strong acid strong alkali salt, and fully stirring.

6. The method according to claim 1, wherein the cation exchange resin used for the cation exchange is one of the following: 732 resin, Amberlite IR-120, Dowex-50, Diaion SK-1.

7. The method of claim 1, wherein the anion exchange resin used for anion exchange is one of the following: 717 resin, 702 resin, Amberlite IRA-400, Lewatit M500.

8. A highly pure silicic acid produced by the process according to any one of claims 1 to 7.

Technical Field

The invention belongs to the technical field of chemical industry, and relates to a method for preparing high-purity silicic acid at low cost.

Background

Chemical Mechanical Polishing (CMP) is currently the best silicon wafer global planarization technique recognized in IC processes, and silica sol is the only abrasive available in silicon wafer CMP slurries. With the continuous reduction of the characteristic size of semiconductors, the CMP process has higher and higher requirements on the metal content of the abrasive, because impurity metal ions in the abrasive are easy to adsorb on the surface of a silicon wafer to cause the reduction of the product performance and the yield.

The existing process for preparing the silica sol abrasive mainly comprises an orthosilicate hydrolysis method, an ion exchange method and a silicon powder method. The ion exchange method has the advantages of cheap raw materials, simple equipment and process, easy operation and controllable technical parameters of products, thereby being widely adopted. The method uses water glass (water solution of sodium silicate) as raw material, and obtains silicic acid through ion exchange process, and the silicic acid is nucleated and grows under alkaline condition to obtain silica sol. During ion exchange, iron, aluminum and other impurities in the water glass must be removed to prepare high-purity silicic acid, and then the silica sol meeting the requirements of monocrystalline silicon CMP can be finally prepared.

Patents relating to the preparation of highly pure silicic acid by ion exchange have been published. CN104591192A takes water glass as raw material, and then undergoes cation, cation and anion exchange. Wherein before the second cation exchange, organic acid or inorganic acid is added to adjust the pH value so as to convert hydroxides of elements such as aluminum, iron and the like into cations, so that the content of metal ions in the silicic acid is low. However, the content of the metal silicate prepared by the method is still relatively high, and the requirement of silicon wafer fine polishing is difficult to meet. CN112299424A has improved the above patent, adopts acidic buffer solution to replace inorganic acid, has guaranteed the stability of pH in the ion exchange process, has improved ion exchange efficiency, and the silicic acid metal ion content that makes is less than CN 104591192A. Both of the above two methods adopt three times of ion exchange process, and the process is complex in general, and there is room for improvement in terms of cost and production period.

Disclosure of Invention

Aiming at the problems, the invention provides a method for preparing high-purity silicic acid at low cost, which reduces the ion exchange times from three times to two times, and the obtained silicic acid has low impurity metal ion content.

The invention relates to a method for preparing high-purity silicic acid at low cost, which comprises the following steps:

adding strong acid strong base salt into water glass, and carrying out cation exchange to obtain acid silicic acid containing strong acid;

and carrying out anion exchange on the acidic silicic acid to obtain a silicic acid finished product.

Further, the pH of the acidic silicic acid is 0.5 to 2.0.

Further, the pH value of the silicic acid finished product is 5.0-5.5.

Further, the strong acid strong base salt is one of the following: sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium nitrate, sodium perchlorate, potassium tetrafluoroborate, sodium hexafluorophosphate, sodium methanesulfonate, sodium trifluoromethanesulfonate, sodium benzenesulfonate, sodium p-toluenesulfonate.

Further, the addition of strong acid and strong base salt to the water glass comprises: dissolving industrial water glass or sodium silicate in water with the weight of 4-20 times, adding 0.25-4.5 kg of strong acid strong alkali salt, and fully stirring.

Further, the cation exchange column used for the cation exchange is filled with 732 resin, Amberlite IR-120, Dowex-50, Diaion SK-1 and the like.

Further, the anion exchange resin filled in the anion exchange column used for anion exchange is 717 resin, 702 resin, Amberlite IRA-400, Lewatit M500 and the like.

The present invention also provides a high purity silicic acid prepared according to the above method.

The invention takes water glass or sodium silicate with various modulus as raw materials, dissolves a certain amount of strong acid strong alkali salt into the water glass or sodium silicate, and then carries out cation exchange and anion exchange in sequence to obtain the silicic acid with low impurity metal content. The innovation point of the invention is that the strong acid generated in situ during cation exchange by acid radical ions of the strong acid is utilized to reduce the pH value of the solution, so that metal oxides such as aluminum oxide, ferric oxide and the like are converted into corresponding metal cations and are captured by ion exchange resin, and the aim of removing metal impurities is achieved.

The method for preparing high-purity silicic acid at low cost has the characteristics and beneficial effects that the ion exchange times are reduced from three times to two times, the content of metal ions in the obtained silicic acid impurities is low, and the cost is lower than that of the existing method. SiO in silicic acid prepared by the invention₂The content is 1-6% (mass fraction, the same below), the pH is 5.0-5.5, when SiO₂When the content is 2%, the content of sodium ions is less than or equal to 200ppb, the content of aluminum ions is less than or equal to 100ppb, and the content of other metal ions is less than or equal to 50ppb, and the method can be used for producing silica sol suitable for Chemical Mechanical Polishing (CMP) of monocrystalline silicon.

Drawings

FIG. 1 is a flow chart of the steps of the method of the present invention.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, the present invention shall be described in further detail with reference to the following detailed description and accompanying drawings.

The invention is an improvement of CN104591192A and CN112299424A, which reduces the ion exchange times from three to two. As shown in FIG. 1, a certain amount of strong acid and strong base salt is added to water glass, and then cation exchange is carried out. In the ion exchange process, acid radical anions are converted into acid to obtain acidic silicic acid containing strong acid, and the pH value is 0.5-2.0. Then carrying out anion exchange on the acidic silicic acid to convert the strong acid into water, thus obtaining a silicic acid finished product. The silicic acid prepared by the invention can achieve the following technical indexes: SiO 2₂Content of 1-6%, pH 5.0-5.5, when SiO₂When the content is 2%, the content of sodium ions is less than or equal to 200ppb, the content of aluminum ions is less than or equal to 100ppb, and the content of other metal ions is less than or equal to 50 ppb. To achieve this object, the present invention adopts the following embodiments.

(1) Taking industrial water glass or sodium Silicate (SiO)₂：Na₂1.0-4.0) is dissolved in water with the weight of 4-20 times, 0.25-4.5 kg of strong acid strong alkali salt is added, and the mixture is fully stirred. The strong alkali salt of strong acid can be selected from inorganic salts such as sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, sodium nitrate, sodium perchlorate, potassium tetrafluoroborate, sodium hexafluorophosphate, etc., and organic acid salts such as sodium methanesulfonate, sodium trifluoromethanesulfonate, sodium benzenesulfonate, sodium p-toluenesulfonate, etc.

(2) And (3) passing the solution obtained in the step (1) through a cation exchange column (filled with 732 resin), and collecting liquid with pH <2 to obtain primary ion-exchange silicic acid.

(3) And (3) passing the primary exchange silicic acid through an anion exchange column (filled with 717 resin), and collecting all effluent liquid to obtain secondary ion exchange silicic acid with the pH value of 5.0-5.5.

The principle of the preparation method of the invention is as follows: the water glass contains a large amount of metallic impurities such as iron and aluminum, and these metallic ions are mainly present as electrically neutral hydroxides and oxides at a pH of silicic acid (4 to 6), and therefore cannot react with the ion exchange resin and cannot be efficiently removed. According to the invention, strong acid and strong base salt are added into water glass, so that strong acid can be generated in situ in the cation exchange process, and the pH value of silicic acid is reduced to 0.5-2.0. At lower pH, both metal hydroxides and oxides are converted to metal cations and subsequently separated by capture with a cation exchange resin, resulting in silicic acid with very low metal content but low acid content. And carrying out primary anion exchange on the silicic acid, and converting the acid into water to obtain a silicic acid finished product with the pH value of 5.0-5.5.

Example 1: 15kg of water glass (containing SiO)₂ 25％，SiO₂：Na₂O3.3, the same as below) was dissolved in 300kg of water, and 0.25kg of sodium chloride was added thereto and dissolved with stirring. The solution was passed through a cation exchange column (packed with 732 resin) to collect the pH<2 to give an acidic silicic acid containing hydrochloric acid at a pH of 2.0. Passing the acidic silicic acid through an anion exchange column (packed 717 resin) and collecting the pH<5.5 to obtain the silicic acid finished product, and the characterization results are shown in table 1.

Example 2: 70kg of water glass (containing SiO)₂ 25％，SiO₂：Na₂O ═ 4.0) was dissolved in 300kg of water, and 4.5kg of sodium nitrate was added and dissolved with stirring. The solution was passed through a cation exchange column (packed with 732 resin) to collect the pH<2 to obtain an acidic silicic acid containing nitric acid, the pH of which is 0.5. Passing the acidic silicic acid through an anion exchange column (packed 717 resin) and collecting the pH<5.5 to obtain the silicic acid finished product, and the characterization results are shown in table 1.

Example 3: 60kg of anhydrous sodium silicate solid (containing SiO)₂ 49.2％，SiO₂：Na₂O ═ 1.0) was dissolved in 400kg of water, and 4.5kg of sodium perchlorate was added and dissolved with stirring. The solution was passed through a cation exchange column (packed with 732 resin) to collect the pH<2, acid silicic acid containing perchloric acid was obtained at a pH of 1.0. Passing the acidic silicic acid through an anion exchange column (packed 717 resin) and collecting the pH<5.5 to obtain the silicic acid finished product, and the characterization results are shown in table 1.

Example 4: 25kg of sodium silicate nonahydrate solid(containing SiO)₂ 21.1％，SiO₂：Na₂O ═ 1.0) was dissolved in 150kg of water, and 1.5kg of sodium p-toluenesulfonate was added thereto and dissolved with stirring. The solution was passed through a cation exchange column (packed with 732 resin) to collect the pH<2 to give an acidic silicic acid containing p-toluenesulfonic acid, pH 1.2. Passing the acidic silicic acid through an anion exchange column (packed 717 resin) and collecting the pH<5.5 to obtain the silicic acid finished product, and the characterization results are shown in table 1.

TABLE 1 characterization of silicic acid for the examples

In the above embodiment, 732 resin packed by cation exchange column can be replaced by other cation exchange resin, such as 717 resin packed by anion exchange column (Amberlite IR-120, Dowex-50, Diaion SK-1, etc.), or replaced by other anion exchange resin, such as 702 resin, Amberlite IRA-400, Lewatit M500, etc. in principle, the salt mentioned in step (1) of the embodiment can be replaced by any strong base salt, including but not limited to halide, sulfate, nitrate of elements in IA group and IIA group, and salt formed by organic strong acid radical.

The particular embodiments of the present invention disclosed above are illustrative only and are not intended to be limiting, since various alternatives, modifications, and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The invention should not be limited to the disclosure of the embodiments in the present specification, but the scope of the invention is defined by the appended claims.