Cristobalite and preparation method thereof

Abstract

The present invention provides cristobalite and a method for preparing the same. The method comprises the steps of: pre-treating waste quartz glass to obtain 80-200 mesh coarse quartz glass sand; alkali-leaching the coarse quartz glass sand to obtain refined quartz glass sand; subjecting the refined quartz glass sand to a high-temperature crystallization treatment to completely convert the amorphous fused quartz into a crystalline phase to obtain coarse cristobalite sand; and acid-leaching the coarse cristobalite sand to obtain refined cristobalite. The method has the advantages of high crystallization conversion, low environmental pollution, and high-quality finished products. Furthermore, by utilizing waste quartz glass as raw material, it alleviates the environmental pollution and space pressure of waste quartz glass, thereby conserving resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of quartz preparation, and in particular relates to cristobalite and a preparation method thereof. Background Art

[0002] Quartz glass is produced from quartz sand with a SiO2 content exceeding 95%, or even as high as 99.9%. Quartz glass is a material consumed in large quantities in production and daily life. However, in my country, the utilization rate of discarded quartz glass after decommissioning is only around 13%, resulting in a significant waste of valuable resources and harm to the environment.

[0003] Cristobalite boasts excellent properties such as high whiteness, high scattering power, excellent matting effect, corrosion resistance, scratch resistance, scrub resistance, and high-temperature resistance. In recent years, it has been widely used in precision casting, electronic materials, biochemical engineering, aerospace, and other fields. Currently, cristobalite is primarily produced by high-temperature calcination of quartz raw materials. However, my country still relies heavily on imports for high-quality quartz raw materials. With the continuous expansion and development of my country's high-tech industries, the demand for cristobalite is also increasing. Summary of the Invention

[0004] The present invention aims to address at least one of the aforementioned deficiencies in the prior art. For example, one objective of the present invention is to provide a short-process, high-efficiency, and low-cost method for preparing cristobalite, and another objective is to address the difficulty in disposing of waste quartz glass.

[0005] To achieve the above objectives, one aspect of the present invention provides a method for preparing cristobalite. The method may include the following steps: pre-treating waste quartz glass to obtain coarse quartz glass sand with a mesh size of 80 to 200; alkali-leaching the coarse quartz glass sand to obtain refined quartz glass sand; high-temperature crystallization of the refined quartz glass sand to completely convert the amorphous fused quartz into a crystalline phase to obtain coarse cristobalite sand; and acid-leaching the coarse cristobalite sand to obtain refined cristobalite.

[0006] In an exemplary embodiment of the present invention, the step of pre-treating the waste quartz glass may include: crushing the waste quartz glass to 0.2-0.5 cm to obtain waste quartz glass slag; and washing and drying the waste quartz glass slag; the dried waste quartz glass slag may be ground to 80-200 mesh and scrubbed to obtain coarse quartz glass sand.

[0007] In an exemplary embodiment of the present invention, the grinding can be performed using a mechanical mill such as a ball mill or a rod mill. The grinding time can be 10 to 15 minutes, and the rotation speed can be 300 to 600 r / min.

[0008] In an exemplary embodiment of the present invention, the grinding medium used in the grinding step may be a material with a Mohs hardness greater than 7, and the grinding medium may be one or more of zirconia balls and agate balls.

[0009] In an exemplary embodiment of the present invention, the scrubbing step may include: soaking the ground waste quartz glass in a scrubbing liquid, placing it in a cleaning vessel, and scrubbing it for 10 to 20 minutes; the scrubbing liquid may include oxalic acid, ascorbic acid, citric acid, and water. The scrubbing liquid includes acidic solutions of oxalic acid, ascorbic acid, citric acid, etc., with a mass ratio of acid to industrial water of (0 to 10):(10 to 100). The solid-liquid mass ratio of the quartz glass slag to the scrubbing liquid is (1 to 5):(5 to 25).

[0010] In an exemplary embodiment of the present invention, the concentration of the alkali solution used in the alkali leaching treatment may be 0.1 to 3 mol / L, the alkali leaching treatment temperature may be 60 to 90° C., the alkali leaching treatment time may be 8 to 15 hours, and the alkali solution may include one or two of potassium hydroxide, sodium hydroxide, etc.

[0011] In an exemplary embodiment of the present invention, the temperature of the high-temperature crystallization treatment may be 1400° C. to 1600° C., and the holding time may be 1 to 10 hours.

[0012] In an exemplary embodiment of the present invention, the acid leaching treatment is to place the calcined coarse cristobalite sand in an acid-resistant reaction device with heating and stirring functions, add mixed acid, and the solid-liquid ratio of the mixed acid to the coarse cristobalite sand is (1-5):(5-25), and the acid leaching treatment is carried out at 60°C to 90°C, the stirring rate is 100-200 r / min, and the acid leaching treatment time is 8-20 hours.

[0013] The acid leaching treatment may further include filtering the coarse cristobalite sand after the acid leaching treatment, washing it to a pH of 6.5 to 7, and drying the washed coarse fused quartz sand.

[0014] In an exemplary embodiment of the present invention, the preparation method may further include washing the refined cristobalite until the pH value of the filtrate is neutral, and drying to obtain cristobalite with a SiO2 content greater than 99%.

[0015] Another aspect of the present invention provides a cristobalite, which can be prepared by the above-mentioned cristobalite preparation method, wherein the SiO2 content in the cristobalite is greater than 99% and the particle size of the cristobalite is 80-200 mesh.

[0016] Compared with the prior art, the beneficial effects of the present invention may include at least one of the following:

[0017] (1) The present invention utilizes waste quartz glass as raw material, which differs from the conventional method of preparing cristobalite from quartz ore raw material. The present invention transforms amorphous quartz glass from the glass phase to the cristobalite phase through crystallization treatment; whereas the method of using quartz ore raw material transforms crystalline α-quartz into the cristobalite phase in the solid state.

[0018] (2) The present invention adopts a combined crushing-high temperature process to remove impurities in waste quartz glass, and at the same time, it can break the internal bubbles, which is conducive to the preparation of high-purity cristobalite.

[0019] (3) The present invention adopts a high-temperature calcination method to solve the problems of crystal phase transformation, removal of hydroxyl groups and bubbles, and at the same time simplifies the process flow, making the production process more energy-efficient and efficient, and improving the quality of the product.

[0020] (4) The present invention uses waste quartz glass to prepare high-purity cristobalite through a method of crystal phase transformation and deep purification. The process is short, the operation is simple, and the crystal phase transformation is above 90%.

[0021] (5) The present invention can realize the resource utilization of waste quartz glass, protect the environment, improve the economic benefits of enterprise production, and save production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A process flow chart showing a method for preparing cristobalite according to an exemplary embodiment of the present invention is shown;

[0023] Figure 2 A diagram showing the pre-processing steps of a method for preparing cristobalite according to an exemplary embodiment of the present invention;

[0024] Figure 3 The XRD patterns of the waste quartz glass before and after the 1470° C. crystal phase transformation according to Example 1 of the present invention are shown;

[0025] Figure 4 The XRD patterns of the waste quartz glass before and after the 1470° C. crystal phase transformation according to Example 2 of the present invention are shown;

[0026] Figure 5 The XRD patterns of the waste quartz glass before and after the crystal phase transformation at 1500° C. of Example 3 of the present invention are shown;

[0027] Figure 6 The XRD patterns of the waste quartz glass before and after the crystal phase transformation at 1500° C. of Example 4 of the present invention are shown.

[0028] Description of reference numerals:

[0029] A01-quartz glass before conversion, A02-cristobalite, A03-quartz glass after conversion; B01-quartz glass before conversion, B02-cristobalite, B03-quartz glass after conversion; C01-quartz glass before conversion, C02-cristobalite, C03-quartz glass after conversion; D01-quartz glass before conversion, D02-cristobalite, D03-quartz glass after conversion. DETAILED DESCRIPTION

[0030] Hereinafter, a cristobalite and a preparation method thereof according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0031] It should be noted that “first”, “second”, “third” and “fourth” are only for the convenience of distinction and description, and do not indicate or imply importance or sequence.

[0032] Quartz glass is produced using quartz sand with a SiO2 content exceeding 95%. With the increasing demand for quartz glass in both domestic and industrial settings, its consumption and waste are also increasing. Furthermore, waste quartz glass is difficult to recycle and is often dumped or landfilled, placing significant pressure on the environment and space, and represents a waste of secondary resources. However, the SiO2 content of waste quartz glass remains at 95%, resulting in less contamination and a high potential for utilization. Furthermore, current cristobalite materials are primarily produced from high-purity quartz ore.

[0033] In order to recycle and reuse waste quartz glass, according to one aspect of the present invention, a method for preparing cristobalite is provided, which is a green processing technology for preparing high-purity cristobalite from waste quartz glass.

[0034] Figure 1 A process flow chart of a method for preparing cristobalite according to an exemplary embodiment of the present invention is shown. Figure 2 A diagram showing pre-processing steps of a method for preparing cristobalite according to an exemplary embodiment of the present invention is shown.

[0035] like Figure 1 and Figure 2 As shown in , in an exemplary embodiment, the preparation method of cristobalite may include the following steps:

[0036] S1, pre-treating the waste quartz glass to obtain 80-200 mesh coarse quartz glass sand;

[0037] In this embodiment, the waste quartz glass is quartz glass that is discarded due to crystallization, cracking and stress failure, and its SiO2 purity is above 95%. Specifically, the steps of pre-treating the waste quartz glass may include:

[0038] S101, crushing the waste quartz glass into pieces of 0.2-0.5 cm to obtain waste quartz glass slag.

[0039] Specifically, a zirconia-lined jaw crusher can be used to crush the glass into 0.2-0.5 cm glass slag. Alternatively, the crusher can be a hammer crusher, a double-roll crusher, or the like.

[0040] S102: cleaning and drying the waste quartz glass slag.

[0041] Specifically, the waste quartz glass slag is rinsed with clean water to remove surface dust or suspended impurities, and then dried and ground.

[0042] S103, grinding the dried waste quartz glass slag to 80-200 mesh.

[0043] Grinding can be performed using a mechanical mill such as a ball mill or a rod mill. The grinding time can be 10 to 15 minutes, and the rotation speed can be 300 to 600 r / min.

[0044] For example, the grinding time may be 12.5 min, 13.6 min, 14 min, or 14.8 min, and the rotation speed may be 300 r / min, 400 r / min, 500 r / min, or 600 r / min.

[0045] Optionally, the ball mill can be a powder making machine, etc., and the grinding medium used for grinding can be a material with a Mohs hardness greater than 7, for example, the grinding medium can be one or more of zirconia balls and agate balls.

[0046] S104: scrubbing the waste quartz glass to obtain crude quartz glass free of suspended impurities and organic impurities.

[0047] The scrubbing step may include: soaking the ground waste quartz glass in a scrubbing liquid, placing the waste quartz glass in an ultrasonic cleaner, and scrubbing the waste quartz glass. The scrubbing time may be 10 to 20 minutes. For example, the scrubbing time may be 10 minutes, 15 minutes, or 20 minutes.

[0048] The scrubbing liquid may include acidic solutions of oxalic acid, ascorbic acid, citric acid, etc. at different concentrations, and the mass ratio of acid to industrial water in the scrubbing liquid may be (0-10):(10-100). For example, the ratio of the scrubbing liquid may be 1:1, (1-5):(5-25), or 1:10.

[0049] The solid-liquid mass ratio of the quartz glass slag and the scrubbing liquid is (1-5):(5-25).

[0050] In the embodiment, the scrubbing liquid used is 5-10 parts oxalic acid and 100-200 parts water. However, the present invention is not limited thereto. The oxalic acid in the scrubbing liquid can be replaced by a weak organic acid such as ascorbic acid or citric acid. Ultrasonic scrubbing can also be performed by mechanical scrubbing.

[0051] S2. Alkali leaching is performed on the crude quartz glass sand to obtain refined quartz glass sand.

[0052] Specifically, quartz glass particles can be alkali-leached using potassium hydroxide or sodium hydroxide as the alkali solution. The potassium hydroxide or sodium hydroxide should be of premium purity, with a potassium hydroxide concentration of 0.1 to 3 mol / L. The alkali-leaching temperature can be 60 to 90°C, and the alkali-leaching time can be 8 to 15 hours. This alkali-leaching treatment can etch certain cavities on the surface of the quartz particles and effectively remove some alkali metal impurities.

[0053] For example, the concentration of potassium hydroxide can be 0.1 mol / L, 1 mol / L, 2 mol / L, or 3 mol / L, the alkali leaching temperature can be 60°C, 70°C, 80°C, or 90°C, and the alkali leaching time can be 8h, 10h, 12h, or 15h.

[0054] S3. Performing a high-temperature crystallization treatment on the refined quartz glass sand to completely convert the amorphous fused quartz into a crystalline phase to obtain coarse cristobalite sand.

[0055] Specifically, the high-temperature crystallization temperature can be between 1400°C and 1600°C, with a holding time of 1 to 10 hours. High-temperature calcination activates impurity sites, causing them to concentrate and migrate near the corroded cavities. It also removes some suspended impurities. Furthermore, it creates similarities between the medium-range ordered structure of amorphous SiO2 and the dynamically disordered structure of cristobalite. High temperatures not only provide increasing energy within the crystal, but also facilitate the nucleation of cristobalite. Furthermore, this enhances the activity of quartz and produces a certain amount of liquid phase, which in turn strengthens the viscous flow in the system, facilitating the phase transition of SiO2 and ultimately its transformation to cristobalite.

[0056] For example, the furnace temperature may be 1450° C., 1500° C., 1550° C., or 1600° C.; the holding time may be 1 h, 3 h, 5 h, 7 h, or 10 h, until the amorphous molten quartz is substantially completely converted into the crystalline cristobalite phase.

[0057] S4. Acid leaching is performed on the coarse cristobalite sand to obtain refined cristobalite.

[0058] An organic weak mixed acid is used for acid leaching to treat impurities that migrate to the surface due to calcination. The acid leaching temperature is 60-90° C. and the acid leaching time is 8-20 hours.

[0059] For example, the acid leaching treatment temperature may be 60° C., 70° C., or 80° C., and the acid leaching treatment time may be 8 h, 10 h, 15 h, or 20 h.

[0060] Specifically, the acid leaching step may include placing the coarse cristobalite sand in an acid-resistant reaction device with heating and stirring functions and adding mixed acid, wherein the mixed acid has a solid-liquid ratio of 1:5 and is treated at 60°C to 90°C. The stirring rate may be 100 to 200 r / min, and the acid leaching time may be 8 to 20 hours.

[0061] For example, the stirring rate can be 115r / min, 123r / min, 138r / min, 146r / min, 157r / min, 168r / min, the temperature of the constant temperature equipment for acid leaching treatment can be 60℃, 70℃, 80℃, and the immersion treatment time of acid leaching can be 8h, 10h, 15h, 20h.

[0062] Optionally, the acid used for the acid leaching treatment is ultrapure or Moss pure acid. The mixed acid used is oxalic acid and acetic acid in a mass ratio, which comprises, by mass, 0-10 parts of oxalic acid, 0-30 parts of glacial acetic acid, and 100-200 parts of water.

[0063] Optionally, the preparation method may further include washing the refined cristobalite until the pH value of the filtrate is neutral, and drying to obtain high-purity cristobalite with a SiO2 content greater than 99%.

[0064] The exemplary embodiment of the present invention provides a short-process, high-efficiency, and low-cost method for preparing high-purity cristobalite from waste quartz glass. The method has the advantages of high crystal phase conversion, low environmental pollution, and high product quality. It alleviates the environmental pollution and space pressure caused by waste quartz glass and has far-reaching significance for research on the preparation of high-purity cristobalite.

[0065] Another aspect of the present invention provides cristobalite. In an exemplary embodiment, the cristobalite is prepared by the preparation method of cristobalite as described above. The SiO2 content of the quartz is greater than 99%; and the particle size of the quartz is 80-200 mesh.

[0066] In order to better understand the above exemplary embodiments of the present invention, a cristobalite and a preparation method thereof are described below with reference to specific examples.

[0067] Example 1

[0068] The waste quartz glass selected in this example is mainly quartz glass. The content of main impurity elements is shown in Table 1. The unit of element content in the table is: ×10 -6 ; SiO2 content is mass percentage (%).

[0069] Table 1 Impurity element content of waste quartz glass in Example 1

[0070] Element Al Ca Cr Cu Fe K Mg <![CDATA[SiO2(%)]]> Quartz glass 124.7 62.4 2.2 1 25.8 8.5 18.3 94.77

[0071] The specific steps include:

[0072] (1) Place the waste quartz glass in a zirconia-lined jaw crusher, crush the waste quartz glass block into glass slag of 0.2 to 0.5 cm, rinse the glass slag with ultrapure water, and dry it.

[0073] (2) Put the waste quartz glass slag into the ball mill for grinding. Agate balls can be selected as the grinding medium. The ball milling time is 10 minutes. Use a nylon screen to select waste quartz glass sand with a particle size of 80 to 200 mesh.

[0074] (3) The waste quartz glass sand was placed in a beaker filled with citric acid solution, including 20 g of oxalic acid and 200 g of water, and placed in an ultrasonic cleaning instrument with an ultrasonic frequency of 10 kHz and an ultrasonic time of 10 min to obtain crude quartz glass sand.

[0075] (4) 100 g of crude quartz glass sand was screened and placed in a polytetrafluoroethylene stirring tank. 500 ml of 0.1 mol / L potassium hydroxide solution was added. The alkali leaching temperature was 60 ° C. and the alkali leaching time was 10 h. After the alkali leaching treatment, it was washed with ultrapure water and filtered until the filtrate was neutral to obtain refined quartz glass sand.

[0076] (5) The refined quartz glass sand is placed in a molten gold crucible and placed in a high-temperature furnace for crystallization treatment. The temperature is raised to 1470°C and kept at this temperature for 1 hour. After natural cooling, the crucible is taken out to obtain coarse cristobalite sand. Figure 3 The XRD patterns of the waste quartz glass before and after the 1470°C crystal phase transformation in this example are shown. The horizontal axis represents the 2θ angle, which scans the entire diffraction area at an angle of 2θ; the vertical axis represents the diffraction peak intensity. A01 represents the quartz glass before transformation, A02 represents cristobalite, and A03 represents the quartz glass after transformation.

[0077] Depend on Figure 3 It can be seen that before the high-temperature conversion, the waste quartz glass is mainly amorphous fused quartz. After being kept at 1470℃ for 1h, the quartz glass is basically transformed into cristobalite crystal phase, but the background of the diffraction peak in the low-angle region is slightly higher, indicating that the sample still contains a very small amount of amorphous SiO2.

[0078] (6) Prepare mixed acid and acid-leach the crude cristobalite sand. Take 100g of powder and place it in an acid-resistant reaction device with heating and stirring functions. Add 500ml of the prepared mixed acid and heat it in a water bath at 60℃. The acid leaching time is 500min to obtain refined cristobalite sand. The mixed acid formula is: 250ml each of 0.6mol / L oxalic acid solution and 0.8mol / L acetic acid solution mixed evenly with 500ml of deionized water.

[0079] (7) The sample after acid leaching was filtered and washed with ultrapure water until the filtrate was neutral. The sample was placed in a drying oven for drying to obtain high-purity cristobalite with a SiO2 content of 99.59%.

[0080] Table 2 shows the impurity element content of quartz in this example. The unit of impurity element content in the table is: ×10 -6 ; SiO2 content is mass percentage (%).

[0081] Table 2 Impurity element content of cristobalite in Example 1

[0082] Element Al Ca Cr Cu Fe K Mg <![CDATA[SiO2(%)]]> Cristobalite 40.2 37.3 0.9 0.3 10 6.5 8.7 99.59

[0083] Example 2

[0084] The waste quartz glass used in this example is mainly quartz glass. The content of its main impurity elements is shown in Table 3. The unit of the impurity element content in the table is: ×10 -6 ; SiO2 content is mass percentage (%).

[0085] Table 3 Impurity element content of waste quartz glass in Example 2

[0086] Element Al Ca Cr Cu Fe K Mg <![CDATA[SiO2(%)]]> Quartz glass 188.2 47.3 1.4 3 18 8.5 9.9 94.73

[0087] The specific steps include:

[0088] (1) The waste quartz glass is placed in a zirconia-lined jaw crusher, the waste quartz glass blocks are crushed into glass slag of 0.2 to 0.5 cm, washed with ultrapure water, and dried.

[0089] (2) The waste quartz glass slag is put into a ball mill for grinding, agate balls are selected as the grinding medium, the ball milling time is 10 minutes, and a nylon screen is used to select waste quartz glass sand with a particle size of 80 to 200 mesh.

[0090] (3) The waste quartz glass sand was placed in a beaker containing citric acid solution, including 30 g of oxalic acid and 200 g of water, and placed in an ultrasonic cleaning instrument with an ultrasonic frequency of 20 kHz and an ultrasonic time of 10 min to obtain crude quartz glass sand.

[0091] (4) 100 g of crude quartz glass sand was screened and placed in a polytetrafluoroethylene stirring tank. 500 ml of 0.5 mol / L KOH solution was added. The alkali leaching temperature was 70 ° C and the alkali leaching time was 10 h. After the alkali leaching treatment, it was washed with ultrapure water and filtered until the filtrate was neutral to obtain refined quartz glass sand.

[0092] (5) The refined quartz glass sand is placed in a melting cup and placed in a high-temperature furnace for crystallization treatment. The temperature is raised to 1470°C and kept warm for 1 hour. After natural cooling, the sand is taken out to obtain coarse cristobalite sand.

[0093] Figure 4 The XRD patterns of the scrap quartz glass in this example before and after 1470°C crystal phase transformation are shown. The abscissa represents the 2θ angle, which scans the entire diffraction area. The ordinate represents the diffraction peak intensity. B01 represents the quartz glass before transformation, B02 represents cristobalite, and B03 represents the quartz glass after transformation. The figure shows that the quartz glass in the scrap has essentially transformed in its crystal phase, but some amorphous phase remains behind.

[0094] (6) Prepare mixed acid and acid-leach the crude cristobalite sand. 100 g of powder was placed in an acid-resistant reaction apparatus with heating and stirring functions, 500 ml of mixed acid was added, and the mixture was reacted at 70°C for 600 min to obtain refined cristobalite sand. The mixed acid was prepared by mixing 200 ml of 1 mol / L oxalic acid and 200 ml of 1 mol / L acetic acid with 100 ml of deionized water.

[0095] (7) The sample after acid leaching was filtered and washed with ultrapure water until the filtrate was neutral. The sample was placed in a drying oven for drying to obtain high-purity cristobalite with a SiO2 content of 99.79%. The impurity element content is shown in Table 4, where the unit of impurity element content is: ×10 -6 ; SiO2 content is mass percentage (%).

[0096] Table 4 Impurity element content of example 2 cristobalite

[0097] Element Al Ca Cr Cu Fe K Mg <![CDATA[SiO2(%)]]> Cristobalite 40.2 37.3 0.9 0.3 10 6.5 8.7 99.79

[0098] Example 3

[0099] This example specifically includes the following steps:

[0100] (1) The waste quartz glass is placed in a zirconia-lined jaw crusher, the waste quartz glass blocks are crushed into glass slag of 0.2 to 0.5 cm, washed with ultrapure water, and dried.

[0101] (2) The waste quartz glass slag is put into a ball mill for grinding, and zirconia balls are selected as the grinding medium. The ball milling time is 10 minutes. A nylon screen is used to select waste quartz glass sand with a particle size of 80 to 200 mesh.

[0102] (3) The waste quartz glass sand was placed in a beaker containing citric acid solution, including 30 g of oxalic acid and 200 g of water, and placed in an ultrasonic cleaning instrument. The temperature was set at 80°C, the ultrasonic frequency was set at 30 kHz, and the ultrasonic time was set at 10 min to obtain crude quartz glass sand.

[0103] (4) 100 g of crude quartz glass sand was screened and placed in a polytetrafluoroethylene stirring tank. 500 ml of 1 mol / L potassium hydroxide solution was added. The alkali leaching temperature was 80 ° C. and the alkali leaching time was 12 h. After the alkali leaching treatment, it was washed with ultrapure water and filtered until the filtrate was neutral to obtain refined quartz glass sand.

[0104] (5) The refined quartz glass sand is placed in a melting cup and placed in a high-temperature furnace for crystallization treatment. The temperature is raised to 1500°C and kept at this temperature for 1 hour. After natural cooling, the sand is taken out to obtain coarse cristobalite sand. Figure 5 The XRD patterns of the waste quartz glass before and after crystalline phase transformation at 1500°C in this example are shown. The horizontal axis represents the 2θ angle, which scans the entire diffraction area at an angle of 2θ; the vertical axis represents the diffraction peak intensity. C01 represents the quartz glass before transformation, C02 represents cristobalite, and C03 represents the quartz glass after transformation.

[0105] from Figure 5 It can be seen from the figure that the waste quartz glass before conversion is mainly fused quartz in the amorphous phase. After being kept at 1500℃ for 1h, the quartz glass is basically transformed into the cristobalite phase, and the conversion rate reaches 98%.

[0106] Through analysis, it can be found that the impurity content of waste quartz glass will decrease with the extension of reaction time. Therefore, appropriately extending the reaction time is beneficial to removing the impurity content in waste quartz glass.

[0107] (6) Prepare mixed acid and acid-leach the crude cristobalite sand. Place 100g of powder in an acid-resistant reaction apparatus equipped with heating and stirring functions, add 500ml of mixed acid, heat at 70°C, and acid-leach for 600 minutes to obtain refined cristobalite sand. The mixed acid formula in this example is 200ml each of 1mol / L oxalic acid and 1mol / L acetic acid, mixed evenly with 100ml of deionized water.

[0108] (7) The sample after acid leaching was filtered and washed with ultrapure water until the filtrate was neutral. The sample was placed in a drying oven for drying to obtain high-purity cristobalite with a SiO2 content of 99.91%. The impurity element content is shown in Table 5. The unit of element content in the table is: ×10 -6 ; SiO2 content is mass percentage (%).

[0109] Table 5 Impurity element content of cristobalite

[0110] Element Al Ca Cr Cu Fe K Mg <![CDATA[SiO2(%)]]> Cristobalite 35.2 32.3 0.45 0.13 7.12 5.77 8.11 99.91

[0111] Example 4

[0112] The main impurity element contents of the waste quartz glass used in this example are shown in Table 6. The unit of element content in the table is: ×10 -6 ; SiO2 content is mass percentage (%).

[0113] Table 6 Impurity element content of waste quartz glass in Example 4

[0114] Element Al Ca Cr Cu Fe K Mg <![CDATA[SiO2(%)]]> Quartz glass 190.2 57.3 1.4 3 18 8.5 9.9 94.73

[0115] The specific steps include:

[0116] (1) The waste quartz glass is placed in a zirconia-lined jaw crusher, the waste quartz glass blocks are crushed into glass slag of 0.2 to 0.5 cm, washed with ultrapure water, and dried.

[0117] (2) The waste quartz glass slag is put into a ball mill for grinding, and zirconia balls are selected as the grinding medium. The ball milling time is 10 minutes. A nylon screen is used to select waste quartz glass sand with a particle size of 80 to 200 mesh.

[0118] (3) The waste quartz glass sand was placed in a beaker containing citric acid solution, including 30 g of oxalic acid and 200 g of water, and placed in an ultrasonic cleaning instrument. The temperature was set at 90°C, the ultrasonic frequency was set at 40 kHz, and the ultrasonic time was set at 20 min to obtain crude quartz glass sand.

[0119] (4) 100 g of crude quartz glass sand was screened and placed in a polytetrafluoroethylene stirring tank. 500 ml of 3 mol / L KOH solution was added. The alkali leaching temperature was 90 ° C and the alkali leaching time was 15 h. After the alkali leaching treatment, it was washed with ultrapure water and filtered until the filtrate was neutral to obtain refined quartz glass sand.

[0120] (5) The refined quartz glass sand is placed in a melting cup and placed in a high-temperature furnace for crystallization treatment. The temperature is raised to 1500°C and kept at this temperature for 1 hour. After natural cooling, the sand is taken out to obtain coarse cristobalite sand. Figure 6The XRD patterns of the waste quartz glass before and after 1500°C crystal phase transformation in this example are shown. The horizontal axis represents the 2θ angle, which scans the entire diffraction area at an angle of 2θ; the vertical axis represents the diffraction peak intensity. D01 represents the quartz glass before transformation, D02 represents cristobalite, and D03 represents the quartz glass after transformation.

[0121] from Figure 6 It can be seen from the figure that the waste quartz glass before transformation is mainly fused quartz in amorphous phase. After being kept at 1500℃ for 1h, the crystal phase of the fused quartz in the waste quartz glass is basically transformed, but there is a part of amorphous phase at the bottom.

[0122] (6) Prepare the mixed acid and acid-leach the crude cristobalite sand. Place 100g of the powder in an acid-resistant reaction apparatus equipped with heating and stirring functions, add 500ml of the mixed acid, heat at 70°C, and acid-leach for 600min to obtain refined cristobalite sand. The mixed acid formula in this example is 200ml each of 2mol / L oxalic acid and 2mol / L acetic acid, mixed evenly with 100ml of deionized water.

[0123] (7) The sample after acid leaching was filtered and washed with ultrapure water until the filtrate was neutral. The sample was placed in a drying oven for drying to obtain high-purity cristobalite with a SiO2 content of 99.97%. The impurity element content is shown in Table 7. The unit of element content in the table is: ×10 -6 ; SiO2 content is mass percentage (%).

[0124] Table 7 Impurity element content of example 4 cristobalite

[0125] Element Al Ca Cr Cu Fe K Mg <![CDATA[SiO2(%)]]> Cristobalite 35.2 32.3 0.45 0.13 7.12 5.77 8.11 99.97

[0126] The present invention adopts a method of preparing high-purity cristobalite from waste quartz glass through crystal phase transformation and deep purification. This method not only makes waste quartz glass a resource, saves space resources, and protects the environment, but also is easy to operate. The crystal phase transformation is above 90%, and the SiO2 content is above 99.9%.

[0127] Compared with the traditional cristobalite manufacturing process, the method of the present invention for recycling waste quartz glass to produce high-purity cristobalite material can realize the recycling and reuse of waste quartz glass, significantly alleviate the over-exploitation of quartz ore, realize the recycling of quartz sand, and is beneficial to the protection of land resources. It greatly reduces the manufacturing cost of high-purity cristobalite material and also solves the pollution and emission problems of solid waste in quartz glass production and use enterprises.

[0128] Although the present invention has been described above with reference to the exemplary embodiments, it will be apparent to those skilled in the art that various modifications and variations may be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined in the claims.

Claims

1. A method for preparing cristobalite, characterized in that: The preparation method comprises the following steps: Pre-treating waste quartz glass to obtain 80-200 mesh coarse quartz glass sand; Alkali leaching is performed on the crude quartz glass sand to obtain refined quartz glass sand with corroded surface; Performing a high-temperature crystallization treatment on the refined quartz glass sand to completely convert the amorphous phase of the fused quartz glass into a crystalline phase to obtain coarse cristobalite sand; and The crude cristobalite sand is subjected to acid leaching to obtain refined cristobalite; The pretreatment includes a scrubbing step, wherein the ground waste quartz glass slag and scrubbing liquid are placed in a sand and gravel scrubbing machine with a zirconia lining for scrubbing, wherein the solid-liquid mass ratio of the quartz glass slag to the scrubbing liquid is (1-5): (5-25); and the scrubbing time is 10-20 minutes; The scrubbing liquid comprises an acidic solution of oxalic acid, ascorbic acid and citric acid, and the mass ratio of the acid to industrial water in the scrubbing liquid is (0-10):(10-100); The acid leaching treatment comprises placing the calcined coarse cristobalite sand in an acid-resistant reaction device with heating and stirring functions, adding mixed acid, wherein the solid-liquid ratio of the mixed acid to the coarse cristobalite sand is (1-5): (5-25), performing the acid leaching treatment at 60° C. to 90° C., stirring at a rate of 100-200 r / min, and performing the acid leaching treatment for 8-20 hours; The high temperature crystallization is to place the refined quartz glass sand in a quartz crucible and keep it in a high temperature device at a temperature of 1400° C. to 1600° C. for 1 to 10 hours; The preparation method has a cristobalite crystal phase conversion rate of over 90%.

2. The method for preparing cristobalite according to claim 1, characterized in that: The step of pre-treating the waste quartz glass comprises: Crushing the waste quartz glass into pieces of 0.2 to 0.5 cm to obtain waste quartz glass slag; and washing and drying the waste quartz glass slag; The dried waste quartz glass slag is ground into 80-200 mesh and scrubbed to obtain coarse quartz glass sand.

3. The method for preparing cristobalite according to claim 2, wherein: The grinding machine lining and grinding medium used in the grinding process of the dried waste quartz glass slag are one or more of zirconium oxide and agate.

4. The method for preparing cristobalite according to claim 1, characterized in that: The concentration of the alkali solution used in the alkali leaching treatment is 0.1~3 mol / L, the alkali leaching treatment temperature is 60~90°C, the alkali leaching treatment time is 8~15h, the alkali solution includes potassium hydroxide and / or sodium hydroxide aqueous solution, and the solid-liquid ratio of the alkali solution to the crude quartz glass sand is (1~5):(5~25).

5. The method for preparing cristobalite according to claim 1, characterized in that: The alkali leaching treatment further includes filtering the quartz glass sand after the alkali leaching treatment, washing it to a pH value of 7 to 7.5, and drying it.

6. The method for preparing cristobalite according to claim 1, characterized in that: The acid leaching treatment further includes filtering the refined cristobalite sand after the acid leaching treatment, washing it until the pH value is neutral, and drying the washed cristobalite sand.

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