Method for preparing high-purity cristobalite

Abstract

The present invention relates to the technical field of quartz sand, and particularly relates to a method for preparing high-purity cristobalite, which method comprises: drying, calcining and scattering amorphous silica to obtain high-purity cristobalite. Compared with the prior art, the present invention has the following beneficial effects: 1, the amorphous silica has a relatively large specific surface area, with the surface thereof rich in hydroxyl, the cristobalite is apt to contain pores during the process of converting the amorphous silica into the cristobalite, and in order to eliminate the pores, the present invention uses a coupling agent for surface treatment and then conducts calcination, which results in, as shown in data, significant reduction in hydroxyl; and 2, under the condition of the same mass of the coupling agent, the inventor selects a silane coupling agent having a shorter chain, which results in fewer pores in the cristobalite and reduction in the calcining temperature and time to a certain extent, and possible reasons therefor are that the silane coupling agent is decomposed at a high temperature to form silicon oxide and the silicon oxide formed by decomposition has a smaller particle size and preferentially forms a crystal nucleus, thereby promoting the overall crystal form conversion.

Description

A method for preparing high-purity cristobalite Technical Field

[0001] The invention relates to the technical field of quartz sand, in particular to a method for preparing high-purity cristobalite. Background Art

[0002] Quartz (SiO2) is a framework-like silicon oxide with multiple isomorphous variations. Under normal pressure, there are seven crystal forms: α-quartz, β-quartz, α-tridymite, β1-tridymite, β-tridymite, α-cristobalite, and β-cristobalite. The normal-pressure transition temperatures between these crystal forms are shown in Figure 4. The β-form represents a crystal form that is stable at high temperatures, while the α-form represents a crystal form that is stable at low temperatures. Quartz is widely distributed in nature, and unless otherwise specified, quartz generally refers to α-quartz.

[0003] High-purity quartz sand generally refers to quartz with a silicon dioxide content greater than 99.9%. High-purity quartz products can be divided into four grades based on SiO2 purity: high-end ω(SiO2) ≥99.998% (4N8), mid-to-high-end ω(SiO2) ≥99.995% (4N5), mid-range ω(SiO2) ≥99.99% (4N), and low-end ω(SiO2) ≥99.9% (3N) (see "The Concept of High-Purity Quartz and Its Raw Material Grade Classification," Mineral Conservation and Utilization, October 2022, Issue 5). However, unprocessed natural quartz cannot meet the quality requirements of high-purity quartz. In other words, high-purity quartz sand is a quartz sand product with extremely high SiO2 purity obtained from natural quartz ore through a relatively complex purification process. At the same time, due to the limitations of the subsequent product preparation process, high-purity quartz sand also has strict requirements on product particle size (usually 40-200 mesh) and mineral composition. Therefore, commonly mentioned amorphous silicon dioxide such as silica powder and white carbon black, even if they are very pure, are not high-purity quartz sand.

[0004] Impurity elements in natural quartz sand primarily include Al, K, Na, Li, Ca, Cu, B, Fe, Mn, Co, Ti, and P. Among these impurity elements, monovalent and divalent ions exist as interstitial atoms at charge imbalance defects in the quartz lattice. Trivalent, tetravalent, and pentavalent ions (isomorphic impurities) compensate for the charge imbalance and are primarily present within the lattice. To remove impurities from quartz sand, various processes have been proposed. Zhang Haiqi et al.'s article, "Research Progress on Impurity Characteristics and Deep Chemical Purification Technology in High-Purity Quartz," (Mineral Conservation and Utilization, August 2022, Issue 4), describes existing quartz sand purification technologies. Currently, the main methods for purifying natural quartz sand include physical and chemical methods. Physical purification methods primarily include color sorting, scrubbing, gravity separation, magnetic separation, and flotation. However, gas-liquid inclusions and isomorphic impurities within the lattice are the primary sources of impurities, and these impurities are key factors restricting the production of high-purity quartz products. Physical purification cannot remove these impurities, requiring chemical deep purification. Chemical deep purification primarily involves acid (alkali, salt) treatment and heat treatment. Acid (alkali, salt) treatment primarily removes impurities that exist on the surface of quartz sand particles in the form of gas-liquid inclusions or embedded within the particles. Heat treatment primarily utilizes high temperatures to cause inclusions to burst, reducing gas-liquid impurities (which cannot be completely removed).

[0005] Compared with physical purification methods, chemical purification operations are complex and costly, but chemical treatment is the most effective and indispensable method for preparing high-purity quartz.

[0006] However, the prior art has the following problems:

[0007] 1) Before being processed into high-purity quartz sand, quartz stone needs to undergo pickling, flotation, magnetic separation, gravity separation, high-temperature water quenching, chlorination roasting and other steps. The process is long, the pickling impurity removal efficiency is low, and it is complicated. In the impurity removal process, exogenous impurities such as iron, sodium, aluminum and other metal elements are easily introduced.

[0008] 2) The hydrofluoric acid, hydrochloric acid and nitric acid used in pickling are of high concentration and large amount, which will produce a large amount of fluorine-containing and chlorine-containing wastewater during pickling, increasing the treatment cost.

[0009] In the article "Thermodynamic Desorption of Gas-Liquid Impurities in Natural Quartz" (Journal of the Chinese Ceramic Society, October 2004), Jiang Xuexin et al. conducted a further in-depth study on the impact of impurities in quartz on quartz products. They found that quartz sand, because it contains gas-liquid inclusions and a large number of hydroxyl groups on its surface (generally above 80 ppm), is prone to generate bubbles when manufacturing quartz products, affecting the quality of the products.

[0010] Summary of the Invention

[0011] In order to solve the problems mentioned in the above background technology, the present invention provides a method for preparing high-purity cristobalite, wherein amorphous silicon dioxide is dried, calcined, and broken up to obtain high-purity cristobalite.

[0012] Preferably, the amorphous silicon dioxide includes but is not limited to being obtained by oxidation of metallic silicon;

[0013] The metal silicon oxidation includes any one of the following steps: burning metal silicon, reacting metal silicon with high-purity water at high temperature, or converting metal silicon into silicon-containing organic matter, such as silane, and then calcining the metal silicon into amorphous nano-silicon oxide.

[0014] Preferably, the particle size of the amorphous silica is 5 nanometers to 1 micron.

[0015] Preferably, the drying condition is: 100°C-150°C for 1-2 hours.

[0016] Preferably, the calcination conditions are: 1100° C.-1700° C. for 2-10 hours.

[0017] Preferably, the high-purity cristobalite has a particle size of 120-450 microns.

[0018] Preferably, the total content of Al, B, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Ti, and Zn elements in the high-purity cristobalite is less than 20 ppm.

[0019] Preferably, after drying, the method further comprises a step of treating with a coupling agent.

[0020] Preferably, the coupling agent is selected from any one of a silane coupling agent and a titanate coupling agent.

[0021] Preferably, in order to reduce the introduction of impurities, the silane coupling agent is a silane coupling agent containing only carbon, silicon, hydrogen and oxygen elements.

[0022] Preferably, the carbon chain length of the silane coupling agent containing only carbon, silicon, hydrogen and oxygen elements does not exceed 5.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Amorphous silica has a large specific surface area and is rich in hydroxyl groups. This easily leads to holes in the cristobalite during its conversion to cristobalite. To eliminate these holes, the present invention uses a coupling agent for surface treatment and then calcination. The data show that the hydroxyl groups are greatly reduced.

[0025] 2. Under the same mass of coupling agent, the inventors selected a silane coupling agent with a shorter chain length, which resulted in fewer pores in the cristobalite and a certain degree of reduction in calcination temperature and time. This may be due to the high-temperature decomposition of the silane coupling agent to form silicon oxide. Since the decomposed silicon oxide has a smaller particle size, it preferentially forms crystal nuclei, promoting the overall crystal transformation.

[0026] 3. Compared with existing high-purity quartz, the high-purity cristobalite obtained by the invention has fewer hydroxyl groups, except for elements such as Al, B, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Ti, and Zn.

[0027] 4. The present invention adopts silane coupling agent treatment to reduce the pores in cristobalite and the calcination temperature and time, thereby saving energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is an XRD pattern of high-purity cristobalite of Example 7;

[0029] FIG2 is an infrared spectrum of amorphous silicon dioxide A;

[0030] FIG3 is an infrared spectrum of high-purity cristobalite of Example 7;

[0031] FIG4 is a diagram showing the normal pressure transition temperatures between various crystalline forms of silicon oxide. DETAILED DESCRIPTION

[0032] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0033] The amorphous silicon dioxide of the present invention has a particle size of 5 nanometers to 1 micron and a specific surface area of ​​90-200m 2 / g. Sources can be purchased from the market, such as Aladdin, or made by yourself using the following method.

[0034] Photovoltaic-grade polysilicon is burned in oxygen, and the conditions are controlled by conventional means to obtain high-purity amorphous silicon dioxide of different particle sizes.

[0035] In the present invention, amorphous silicon dioxide (particle size 5 nanometers, specific surface area 200m 2 / g) is marked as amorphous silica A;

[0036] Amorphous silica (particle size 10 nm, specific surface area 150 m 2 / g) is marked as amorphous silicon dioxide B;

[0037] Amorphous silicon dioxide (particle size 1 micron, specific surface area 90m 2 / g) is marked as amorphous silica C.

[0038] Example 1

[0039] Amorphous silica A was dried at 100°C for 2 hours, calcined at 1170°C for 10 hours, cooled naturally, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 120 μm.

[0040] Example 2

[0041] Amorphous silica A was dried at 150°C for 1 hour, calcined at 1700°C for 2 hours, cooled naturally, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 200 μm.

[0042] Example 3

[0043] Amorphous silica B was dried at 100°C for 2 hours, calcined at 1170°C for 10 hours, cooled naturally, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 380 μm.

[0044] Example 4 (Results of preparing high-purity cristobalite from micron-sized raw materials)

[0045] Amorphous silica C was dried at 100°C for 2 hours, calcined at 1170°C for 10 hours, cooled naturally, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 630 μm.

[0046] Example 5

[0047] Amorphous silica A3Kg, dried at 100℃ for 2 hours, 30g coupling agent (CH3O)3Si(CH2) 10 CH3 was mixed with 100 g of ethanol to obtain a modified liquid, which was then mixed evenly with the dried amorphous silica, dried (100°C, 2 h), calcined at 1170°C for 10 h, cooled naturally, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 180 μm.

[0048] Example 6

[0049] Amorphous silica A3 kg was dried at 100 ° C for 2 hours, 30 g of coupling agent (CH3O)3Si(CH2)7CH3 was mixed with 100 g of ethanol to obtain a modified liquid, the modified liquid was mixed evenly with the dried amorphous silica, and dried (100 ° C, 2 hours), calcined at 1170 ° C for 10 hours, naturally cooled, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 157 microns.

[0050] Example 7

[0051] Amorphous silica A3 kg was dried at 100 ° C for 2 hours, 30 g of coupling agent (CH3O)3Si(CH2)5CH3 was mixed with 100 g of ethanol to obtain a modified liquid, the modified liquid was mixed evenly with the dried amorphous silica, and dried (100 ° C, 2 hours), calcined at 1170 ° C for 6 hours, naturally cooled, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 135 μm.

[0052] Comparative Example 1

[0053] Amorphous silica A3 kg was dried at 100 ° C for 2 hours, 30 g of coupling agent (CH3O)3Si(CH2)7CH3 was mixed with 100 g of ethanol to obtain a modified liquid, the modified liquid was mixed evenly with the dried amorphous silica, and dried (100 ° C, 2 hours), calcined at 1170 ° C for 8 hours, naturally cooled, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 163 μm.

[0054] Comparative Example 2

[0055] ITOA-6 high-purity quartz produced by Unimin Corporation of the United States was dried at 100°C for 2 hours, calcined at 1170°C for 10 hours, cooled naturally, and dispersed with air flow to obtain high-purity cristobalite with a particle size of 230 microns.

[0056] Results and Testing

[0057] The prepared samples were tested for impurity ions using ICP-OSE (detection limit of 1 ppb), and the results are shown in Table 1:

[0058] Table 1 Test results of impurity ions of raw materials and example samples (unit: ppm)

[0059] The particle size, porosity, and crystallinity of the prepared samples were measured. Porosity was measured by nitrogen adsorption-desorption, particle size was measured by a particle size analyzer, and crystallinity was measured by XRD. The results are shown in Table 2.

[0060] Table 2

[0061] Table 3 shows the hydroxyl content (in ppm) in the materials of Examples 5-7 before and after treatment with the coupling agent. The hydroxyl content was calculated based on infrared spectroscopy, and the results are shown in Table 3.

[0062] Table 3

[0063] Data analysis: From Table 1, it can be seen that the impurity content of the product has increased compared with the raw material, which may be due to the inevitable contamination during the preparation process.

[0064] The porosity of the materials treated with coupling agents in Table 2 was significantly reduced after high-temperature calcination. Compared with Example 7, Example 6 used a long-chain silane coupling agent, which resulted in a relatively higher porosity. The use of a short-chain silane coupling agent can achieve a higher crystallinity in a shorter time, which is more energy-efficient.

[0065] After the materials in Table 3 were treated with coupling agents, the hydroxyl content was significantly reduced, and the hydroxyl content in the cristobalite obtained after calcination was further reduced.

[0066] Figure 2 is the infrared spectrum of raw material high-purity silica, at 3410 cm -1 Chuhe 1642cm -1 The presence of a vibration peak at indicates that there are hydroxyl groups on its surface.

[0067] Figure 3 is the infrared spectrum of cristobalite. -1 Chuhe 1642cm -1 The absence of vibration peaks indicates that no hydroxyl groups can be detected on its surface.

[0068] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing high-purity cristobalite, characterized in that: The amorphous silicon dioxide is dried, calcined and broken up to obtain high-purity cristobalite.

2. The method for preparing high-purity cristobalite according to claim 1, characterized in that: The amorphous silicon dioxide includes, but is not limited to, that obtained by oxidation of metallic silicon.

3. The method for preparing high-purity cristobalite according to claim 2, characterized in that: The metal silicon is oxidized to burn the metal silicon, or react with high-purity water at high temperature, or convert the metal silicon into silicon-containing organic matter, such as silane, and then calcined to convert into amorphous nano silicon oxide.

4. The method for preparing high-purity cristobalite according to claim 1, characterized in that: The particle size of the amorphous silicon dioxide is 5 nanometers to 1 micrometer.

5. The method for preparing high-purity cristobalite according to claim 1, characterized in that: The drying conditions are: 100°C-150°C for 1-2h.

6. The method for preparing high-purity cristobalite according to claim 1, characterized in that: The calcination conditions are: 1100° C.-1700° C. for 2-10 hours.

7. The method for preparing high-purity cristobalite according to claim 1, characterized in that: The particle size of the high-purity cristobalite is 120-450 microns.

8. The method for preparing high-purity cristobalite according to claim 1, characterized in that: The total content of Al, B, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Ti and Zn elements in the high-purity cristobalite is less than 20 ppm.

9. The method for preparing high-purity cristobalite according to claim 1, characterized in that: After drying, the step of treating with a coupling agent is also included.

10. The method for preparing high-purity cristobalite according to claim 8, characterized in that: The coupling agent is selected from any one of a silane coupling agent and a titanate coupling agent.

11. The method for preparing high-purity cristobalite according to claim 10, characterized in that: The silane coupling agent is a silane coupling agent containing only carbon, silicon, hydrogen and oxygen elements.

12. The method for preparing high-purity cristobalite according to claim 11, characterized in that: The carbon chain length of the silane coupling agent containing only carbon, silicon, hydrogen and oxygen elements does not exceed 5.

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