Method for preparing high-purity cristobalite
By drying, calcining, and treating amorphous silicon dioxide with coupling agents, the method addresses inefficiencies in producing high-purity silica sand, achieving high-purity cristobalite with reduced impurities and hydroxyl groups, enhancing product quality and energy efficiency.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- ANHUI ESTONE MATERIAL TECH CO LTD
- Filing Date
- 2024-03-25
- Publication Date
- 2026-07-29
AI Technical Summary
Conventional methods for producing high-purity silica sand are lengthy, inefficient, introduce foreign impurities, generate hazardous waste, and fail to effectively remove gas-liquid inclusions and isomorphic impurities, leading to quality issues in quartz products.
A method involving the drying, calcining, and dispersing of amorphous silicon dioxide, followed by treatment with a silane or titanate coupling agent, to produce high-purity cristobalite with reduced impurities and hydroxyl groups, using controlled temperature and time conditions.
The method results in high-purity cristobalite with minimal impurities and reduced hydroxyl groups, improving product quality and reducing energy consumption and waste generation.
Smart Images
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Abstract
Description
[Technical Field]
[0001] The present invention relates to the field of silica sand technology, and more particularly to a method for preparing high-purity cristobalite. [Background technology]
[0002] Quartz (SiO2) is a silicon oxide with a shelf-like structure and has many homogeneous forms. At atmospheric pressure, it exists in seven crystalline forms: α-quartz, β-quartz, α-schizoquartz, β1-schizoquartz, β-schizoquartz, α-cristobalite, and β-cristobalite. The transition temperatures between these forms at atmospheric pressure are shown in Figure 4. Note that the β-form represents the crystalline form that exists stably at high temperatures, and the α-form represents the crystalline form that exists stably at low temperatures. It is very widely distributed in nature, and unless otherwise specified, the term "quartz" usually refers to α-quartz.
[0003] High-purity silica sand typically refers to quartz with a silicon dioxide content exceeding 99.9%. Based on SiO2 purity, high-purity quartz products can be divided into four levels: high-end ω(SiO2)≧99.998%(4N8), middle-high-end ω(SiO2)≧99.995%(4N5), mid-end ω(SiO2)≧99.99%(4N), and low-end ω(SiO2)≧99.9%(3N) (see "Concept of High-Purity Quartz and Classification of Raw Material Levels," Mineral Protection and Utilization, October 2022, No. 5). However, unprocessed natural quartz has difficulty meeting the quality requirements for high-purity quartz. In other words, high-purity silica sand is a silica sand product with extremely high SiO2 purity obtained from natural quartz ore through a relatively complex refining process. Furthermore, due to limitations in the subsequent product preparation process, high-purity silica sand has strict requirements regarding the particle size of the product (usually 40-200 mesh) and the mineral phase. Therefore, amorphous silicon dioxide such as silicon powder and white carbon black, which are commonly mentioned, are not high-purity silica sand, even if their purity is very high.
[0004] The impurity elements in natural silica sand mainly include Al, K, Na, Li, Ca, Cu, B, Fe, Mn, Co, Ti, and P. Of these impurity elements, monovalent and divalent ions exist as compensating charges in the form of interstitial atoms at charge imbalance defects within the quartz crystal lattice, while trivalent, tetravalent, and pentavalent ions (isomorphic impurities) mainly exist within the crystal lattice. To remove impurities from silica sand, engineers have proposed various processes. For example, the article "Research Progress on Impurity Characteristics and Deep Chemical Purification Techniques in High-Purity Quartz" by Zhang Haiqi et al. (Protection and Utilization of Minerals, August 2022, No. 4) describes existing silica sand purification techniques, and currently, the main methods for purifying natural silica sand are physical and chemical methods. Physical purification methods mainly include processes such as color sorting, scrubbing, specific gravity sorting, magnetic sorting, and flotation. However, gas-liquid inclusions and isomorphic impurities within the crystal lattice are the main sources of impurities and are significant factors limiting the production of high-purity quartz products. Physical purification methods cannot remove these impurities, and chemical deep purification is necessary. Chemical deep purification mainly includes acid (alkali, salt) treatment and heat treatment. Acid (alkali, salt) treatment mainly removes impurities that are present on the surface of silica sand particles or inlaid within the particles in the form of gas-liquid inclusions. Heat treatment mainly reduces gas-liquid impurities by rupturing gas-liquid inclusions with high temperatures (complete removal is not possible).
[0005] Compared to physical purification methods, chemical purification is more complex and relatively more expensive, but when producing high-purity quartz, chemical treatment is the most effective and essential method. [Overview of the project] [Problems that the invention aims to solve]
[0006] However, conventional technology has the following problems.
[0007] 1) Before processing silica into high-purity silica sand, steps such as pickling, flotation, magnetic separation, specific gravity separation, high-temperature water quenching, and chlorinated roasting must be performed. As a result, the process is long, the efficiency of impurity removal by pickling is poor, the process is complex, and foreign impurities such as metallic elements like iron, sodium, and aluminum are easily introduced during the impurity removal process.
[0008] 2) Hydrofluoric acid, hydrochloric acid, and nitric acid used in pickling are highly concentrated and used in large quantities, resulting in the generation of a large amount of waste containing fluorine and chlorine during pickling, which increases disposal costs.
[0009] In the paper "Thermodynamic Desorption of Gas-Liquid Impurities in Natural Quartz" by Jiang Xuexin et al. (Journal of the Silicate Society, October 2004), further research was conducted on the effects of impurities in quartz on quartz products. The results showed that silica sand contains gas-liquid inclusions and a relatively large amount of hydroxyl groups (usually 80 ppm or more) on its surface, which makes it easy for bubbles to form during the manufacturing of quartz products, affecting the quality of the product. [Means for solving the problem]
[0010] To solve the problems in the background technology described above, the present invention provides a method for preparing high-purity cristobalite, which is obtained by drying, calcining, and dispersing amorphous silicon dioxide.
[0011] Preferably, the amorphous silicon dioxide includes, but is not limited to, that obtained by oxidation of metallic silicon.
[0012] The oxidation of the metallic silicon includes one of the following: combustion of the metallic silicon, high-temperature reaction of metallic silicon with high-purity water, or conversion of metallic silicon into a silicon-containing organic substance such as silane, followed by calcination to convert it into amorphous nano-silicon oxide.
[0013] Preferably, the particle size of the amorphous silicon dioxide is 5 nanometers to 1 micron.
[0014] Preferably, the drying conditions are 100°C to 150°C for 1 to 2 hours.
[0015] Preferably, the firing conditions are 1100°C to 1700°C for 2 to 10 hours.
[0016] Preferably, the particle size of the high-purity cristobalite is 120 to 450 microns.
[0017] Preferably, the total content of the elements Al, B, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Ti, and Zn in the high-purity cristobalite is less than 20 ppm.
[0018] Preferably, the method for preparing high-purity cristobalite further comprises the step of treating it with a coupling agent after drying.
[0019] Preferably, the coupling agent is one selected from a silane coupling agent and a titanate coupling agent.
[0020] Preferably, in order to reduce the inclusion of impurities, the silane coupling agent is a silane coupling agent that contains only the elements carbon, silicon, hydrogen, and oxygen.
[0021] Preferably, the carbon chain length of the silane coupling agent, which contains only the elements carbon, silicon, hydrogen, and oxygen, is 5 or less. [Effects of the Invention]
[0022] Compared to the prior art, the beneficial effects of the present invention are as follows:
[0023] 1. Amorphous silicon dioxide has a relatively large specific surface area, is rich in hydroxyl groups on the surface, and is likely to contain holes in cristobalite during the process of converting to cristobalite. In order to eliminate such holes, the present invention employs surface treatment using a coupling agent and then baking. The data shows that the hydroxyl groups are significantly reduced.
[0024] 2. In the case of the same mass of coupling agent, the inventor of the present application selects a silane coupling agent with a shorter chain length, resulting in fewer holes in cristobalite and a certain reduction in the baking temperature and time. The reason is that the silane coupling agent decomposes at high temperature to form silicon dioxide, and the particle size of the silicon dioxide formed by decomposition is relatively small, which may preferentially form crystal nuclei and promote the conversion of the overall crystal form.
[0025] 3. The high-purity cristobalite obtained by the invention has relatively fewer hydroxyl groups in addition to elements such as Al, B, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Ti, Zn, etc. compared with existing high-purity quartz.
[0026] 4. The present invention employs silane coupling agent treatment, which can reduce the pores in cristobalite, the baking temperature and time, and save energy consumption.
Brief Description of the Drawings
[0027] [Figure 1] It is an XRD diagram of the high-purity cristobalite of Example 7. [Figure 2] It is an infrared spectrum of amorphous silicon dioxide A. [Figure 3] It is an infrared spectrum of the high-purity cristobalite of Example 7. [Figure 4] It is a normal pressure transition temperature diagram between various crystal forms of silicon dioxide.
Modes for Carrying Out the Invention
[0028] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available or can be prepared by existing methods.
[0029] The amorphous silicon dioxide of the present invention has a particle size of 5 nanometers to 1 micron and a specific surface area of 90 to 200 m². 2 It is per gram. The source can be purchased from the market, for example, Aladdin, or it can be made at home using the following method.
[0030] By burning polycrystalline silicon of solar power generation grade in oxygen and controlling the conditions using conventional methods, high-purity amorphous silicon dioxide of different particle sizes can be obtained.
[0031] In this invention, amorphous silicon dioxide (with a particle size of 5 nanometers and a specific surface area of 200 m²) 2 / g) is written as amorphous silicon dioxide A.
[0032] Amorphous silicon dioxide (with a particle size of 10 nanometers and a specific surface area of 150 m²) 2 / g) is written as amorphous silicon dioxide B.
[0033] Amorphous silicon dioxide (particle size 1 micron, specific surface area 90 m²) 2 / g) is written as amorphous silicon dioxide C.
[0034] <Example 1> High-purity cristobalite with a particle size of 120 microns is obtained by drying amorphous silicon dioxide A at 100°C for 2 hours, firing it at a high temperature of 1170°C for 10 hours, allowing it to cool naturally, and then dispersing it with an airflow.
[0035] <Example 2> High-purity cristobalite with a particle size of 200 microns is obtained by drying amorphous silicon dioxide A at 150°C for 1 hour, firing it at a high temperature of 1700°C for 2 hours, allowing it to cool naturally, and then dispersing it with an airflow.
[0036] <Example 3> High-purity cristobalite with a particle size of 380 microns is obtained by drying amorphous silicon dioxide B at 100°C for 2 hours, firing it at a high temperature of 1170°C for 10 hours, allowing it to cool naturally, and then dispersing it with an airflow.
[0037] <Example 4> (This reflects the results of manufacturing high-purity cristobalite from micron-sized raw materials.) High-purity cristobalite with a particle size of 630 microns is obtained by drying amorphous silicon dioxide C at 100°C for 2 hours, calcining at a high temperature of 1170°C for 10 hours, allowing it to cool naturally, and then dispersing it with an airflow.
[0038] <Example 5> 3 kg of amorphous silicon dioxide A was dried at 100°C for 2 hours, and 30 g of the coupling agent (CH3O)3Si(CH2) was added. 10 A modified solution is obtained by mixing CH3 with 100g of ethanol. This modified solution is then uniformly mixed with the dried amorphous silicon dioxide, dried at 100°C for 2 hours, calcined at a high temperature of 1170°C for 10 hours, allowed to cool naturally, and dispersed by airflow to obtain high-purity cristobalite with a particle size of 180 microns.
[0039] <Example 6> 3 kg of amorphous silicon dioxide A is dried at 100°C for 2 hours, and a modified solution is obtained by mixing 30 g of the coupling agent (CH3O)3Si(CH2)7CH3 with 100 g of ethanol. The modified solution is then uniformly mixed with the dried amorphous silicon dioxide, dried at 100°C for 2 hours, calcined at a high temperature of 1170°C for 10 hours, allowed to cool naturally, and dispersed by airflow to obtain high-purity cristobalite with a particle size of 157 microns.
[0040] <Example 7> 3 kg of amorphous silicon dioxide A is dried at 100°C for 2 hours, and a modified solution is obtained by mixing 30 g of the coupling agent (CH3O)3Si(CH2)5CH3 with 100 g of ethanol. The modified solution is then uniformly mixed with the dried amorphous silicon dioxide, dried at 100°C for 2 hours, calcined at a high temperature of 1170°C for 6 hours, allowed to cool naturally, and dispersed by airflow to obtain high-purity cristobalite with a particle size of 135 microns.
[0041] (Comparative Example 1) 3 kg of amorphous silicon dioxide A is dried at 100°C for 2 hours, and a modified solution is obtained by mixing 30 g of the coupling agent (CH3O)3Si(CH2)7CH3 with 100 g of ethanol. The modified solution is then uniformly mixed with the dried amorphous silicon dioxide, dried at 100°C for 2 hours, calcined at a high temperature of 1170°C for 8 hours, allowed to cool naturally, and dispersed by airflow to obtain high-purity cristobalite with a particle size of 163 microns.
[0042] (Comparative Example 2) High-purity cristobalite with a particle size of 230 microns is obtained by drying Unimin's ITOA-6 high-purity quartz at 100°C for 2 hours, firing it at a high temperature of 1170°C for 10 hours, allowing it to cool naturally, and then dispersing it with an airflow.
[0043] <Results and Detection> The obtained samples were tested for impurity ions using ICP-OSE (detection limit of 1 ppb), and the results are shown in Table 1.
[0044] [Table 1]
[0045] The particle size, porosity, and crystallinity of the obtained samples were measured. Pore size was measured by nitrogen adsorption / desorption, particle size by particle size analyzer, and crystallinity by XRD. The results are shown in Table 2.
[0046] [Table 2]
[0047] Table 3 shows the hydroxyl group content (unit: ppm) in the samples before and after treatment with the coupling agent in Examples 5-7. The hydroxyl group content is calculated based on the infrared spectrum. The results are shown in Table 3.
[0048]
Table 3
[0049] Data analysis: As can be seen from Table 1, the impurity content of the product has increased to some extent compared with the raw material. The possible reason is that there is inevitable contamination in the preparation process.
[0050] The samples treated with the coupling agent in Table 2 show a significant decrease in the pore rate when fired at high temperature. In Example 6, compared with Example 7, the use of long-chain silane coupling results in a relatively high pore rate. On the other hand, by using a short-chain silane coupling agent, a relatively high crystallinity can be achieved within a relatively short time, thus realizing more energy savings.
[0051] After the samples in Table 3 are treated with the coupling agent, the hydroxyl group content decreases significantly, and the hydroxyl group content further decreases in the cristobalite obtained by firing.
[0052] Figure 2 is the infrared spectrum of high-purity silicon dioxide of the raw material. There are vibration peaks at 3410 cm -1 and 1642 cm -1 , so it can be seen that there are hydroxyl groups on its surface.
[0053] Figure 3 is the infrared spectrum of cristobalite. There are no vibration peaks at 3410 cm -1 and 1642 cm -1 , so it can be seen that hydroxyl groups cannot be detected on its surface.
[0054] The embodiments described above are merely relatively preferred specific embodiments of the present invention and do not limit the scope of protection of the present invention. Those skilled in the art will know that, within the scope of the art disclosed herein, any equivalent substitutions or modifications completed based on the proposed art and the inventive concept thereof should be covered within the claims of the present invention.
Claims
1. A method for preparing high-purity cristobalite, comprising drying, calcining, and dispersing amorphous silicon dioxide, wherein high-purity cristobalite is obtained. The drying conditions are to treat at 100°C to 150°C for 1 to 2 hours. The aforementioned firing conditions involve processing at 1100°C to 1700°C for 2 to 10 hours. A method for preparing high-purity cristobalite, further comprising the step of treating with a coupling agent after drying.
2. The method for preparing high-purity cristobalite according to claim 1, characterized in that the amorphous silicon dioxide includes one obtained by oxidation of metallic silicon.
3. The method for preparing high-purity cristobalite according to claim 2, characterized in that the oxidation of the metallic silicon includes one of the following: combustion of metallic silicon, high-temperature reaction of metallic silicon with high-purity water, or conversion of metallic silicon into a silicon-containing organic substance such as silane, followed by calcination to convert it into amorphous nanosilicon oxide.
4. The method for preparing high-purity cristobalite according to Claim 1, characterized in that the particle size of amorphous silicon dioxide measured by a particle size analyzer is 5 nanometers to 1 micron.
5. The method for preparing high-purity cristobalite according to Claim 1, characterized in that the particle size of the high-purity cristobalite measured by a particle size analyzer is 120 to 450 microns.
6. The method for preparing high-purity cristobalite according to claim 1, characterized in that the total content of the elements Al, B, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Ti, and Zn in the high-purity cristobalite is less than 20 ppm.
7. The method for preparing high-purity cristobalite according to claim 1, characterized in that the coupling agent is one selected from a silane coupling agent and a titanate coupling agent.
8. The method for preparing high-purity cristobalite according to claim 7, characterized in that the silane coupling agent is a silane coupling agent containing only the elements carbon, silicon, hydrogen, and oxygen.
9. The method for preparing high-purity cristobalite according to claim 8, characterized in that the length of the carbon chain of the silane coupling agent, which contains only the elements carbon, silicon, hydrogen, and oxygen, is 5 or less.