Method for preparing high-purity silicon dioxide from fluorine-containing silicon slag

Abstract

The invention belongs to the field of chemical materials, and particularly relates to a method for preparing high-purity silicon dioxide from fluorine-containing silicon slag. The method comprises the following steps: carrying out first washing and first filtering on the fluorine-containing silicon slag to obtain a first washing object; pickling the first washing object by adopting a pickling agent to obtain a pickled object; carrying out second washing and second filtering on the acid pickling substance to obtain a second washing substance; and burning the second washings to obtain the high-purity silicon dioxide. According to the method, the fluorine-containing silicon slag is used for preparing the high-purity silicon dioxide, the waste fluorine-containing silicon slag is comprehensively utilized, dependence on natural silicon ore is reduced, and the method has the advantages that environmental pollution is reduced, and the purity of the obtained silicon dioxide is high. The method provided by the invention almost only adopts steps based on physical reaction, is simple and convenient to operate, does not need special equipment, is low in cost, is green and environment-friendly, and has important value in industrial production of high-purity silicon dioxide.

Description

Technical Field

[0001] The present invention belongs to the field of chemical materials, and particularly relates to a method for preparing high-purity silicon dioxide from fluorosilicate slag. Background Art

[0002] During the production process of the phosphate fertilizer industry, a large amount of fluosilicic acid is by-produced. When producing anhydrous hydrogen fluoride with fluosilicic acid as the raw material, a large amount of fluorosilicate slag is by-produced. This silicon dioxide has poor activity and contains fluorine, and cannot be directly used as a filler. Stacking it will cause environmental pollution due to the fluorine content. Therefore, how to make good use of the silicon and fluorine resources in the fluorosilicate slag has attracted increasing attention in environmental protection and comprehensive utilization of solid waste resources.

[0003] Since the silicon in the fluorosilicate slag mainly exists in the form of silicon dioxide (SiO2), and high-purity silicon dioxide has excellent properties such as chemical corrosion resistance, poor thermal conductivity, good insulation, low expansion, and stable chemical properties, it has a wide range of applications in many fields. Such as a reinforcing agent in the rubber and plastic fields, an abrasive and thickening agent in the toothpaste field, an anti-caking agent in the food field, and a glidant in the pharmaceutical field; in addition, high-purity silicon dioxide has become an indispensable important basic material in the world's current electronics industry, optoelectronics industry, and energy conversion technology. Such as the quartz glass crucible urgently needed in the semiconductor industry, the quartz glass bulb indispensable for manufacturing new light sources, the quartz optical fiber as the carrier of optical signals in optical communication, the radiation-resistant quartz glass used in the aerospace industry, the low-expansion and high-temperature-resistant quartz glass used at high temperatures, etc. Therefore, preparing high-purity silicon dioxide from fluorosilicate slag can not only make full use of natural resources but also meet the demand for high-purity silicon dioxide in many industries.

[0004] Chinese Patent Application CN105271254A discloses a method for preparing white carbon black (a general term for anhydrous and hydrated silicon dioxide or silicate) from waste silicon slag. First, the waste silicon slag containing silicon dioxide is chemically reacted with ammonium fluoride to generate ammonium fluorosilicate and ammonia. Then, the obtained ammonium fluorosilicate is chemically reacted with ammonia water to generate silicon dioxide and ammonium fluoride. Finally, the obtained silicon dioxide is aged, washed, and dried to obtain white carbon black. This application requires a large amount of ammonium fluoride and ammonia water, with a high economic cost, and the purity of the finally prepared silicon dioxide is relatively low, only 91%.

[0005] Chinese Patent Application CN113461021A discloses a method for purifying and extracting silica white by adding sulfur in a wet process using fluorosilicate slag. The method uses the solid waste fluorosilicate slag produced from the production of aluminum fluoride with fluorosilicic acid and aluminum hydroxide as the raw material. After drying and dehydration pretreatment, sulfuric acid is used in the wet process to remove residual aluminum and fluorides in the fluorosilicate slag, and silica white is prepared. This application uses a wet purification method with sulfur addition, which requires a large amount of 98% concentrated sulfuric acid (the weight ratio of concentrated sulfuric acid to dry fluorosilicate slag is 50:18 - 22). Concentrated sulfuric acid has strong corrosiveness and strong oxidizing properties. Using a large amount of concentrated sulfuric acid not only results in high costs, but also has certain operation risks and environmental pollution risks. Moreover, the purity of the finally obtained silicon dioxide is only 97.38%, which does not meet the requirements of high-purity silicon dioxide.

[0006] Currently, most methods for preparing high-purity silicon dioxide from fluorosilicate slag in this field involve complex chemical reactions and require a large amount of chemical reagents, resulting in high costs. There are also certain risks of environmental pollution, and most of the prepared silicon dioxide products do not meet the requirements of high purity. Summary of the Invention

[0007] In order to overcome the defects of the prior art, the present invention proposes a new method for preparing high-purity silicon dioxide from fluorosilicate slag. This method does not rely on chemical reactions, and most steps only involve physical reactions. It is easy to operate, and the purity of the prepared silicon dioxide is higher than 99%.

[0008] The technical solution provided by the present invention is as follows:

[0009] In one aspect, the present invention provides a method for preparing high-purity silicon dioxide from fluorosilicate slag, and the method includes the following steps:

[0010] (1) Perform the first washing and the first filtration on the fluorosilicate slag to obtain the first washed product;

[0011] (2) Pickle the filter residue with an acid pickling agent to obtain the pickled product;

[0012] (3) Perform the second washing and the second filtration on the pickled product to obtain the second washed product;

[0013] (4) After burning the second washed product, high-purity silicon dioxide is obtained.

[0014] In some embodiments, the first washing in step (1) uses an aqueous solution, including, but not limited to: aqueous solution, inorganic salt solution, organic salt solution.

[0015] In some preferred embodiments, the pH of the aqueous solution is preferably neutral.

[0016] During the experiment, the applicant found that directly burning without washing would cause two problems. One is that a large amount of acidic gas will overflow, causing equipment damage and environmental pollution. The other is that during the preparation of high-purity silica, high temperature will integrate impurities into the crystal lattice of the substance, resulting in an increase in impurity content and a decrease in purity. Therefore, the applicant combines aqueous solution washing and acid washing to wash away surface impurities as much as possible before burning.

[0017] Those skilled in the art should note that the first washing in step (1) is a rough wash, so there is no limit on the number of washings. Technicians can choose the number of washings according to their needs, and any number of washings is acceptable.

[0018] In some embodiments, the first filtration in step (1) uses vacuum filtration, pressure filtration, and / or centrifugal filtration.

[0019] In some embodiments, the acid cleaning agent in step (2) includes, but is not limited to: hydrochloric acid, sulfuric acid, nitric acid, and / or hydrofluoric acid.

[0020] In some preferred embodiments, the acid cleaning agent in step (2) is hydrochloric acid and / or hydrofluoric acid.

[0021] In some preferred embodiments, the hydrogen ion concentration of the acid cleaning agent in step (2) is 3.0 - 5.0 mol / L.

[0022] In some preferred embodiments, the hydrogen ion concentration of the acid cleaning agent in step (2) is 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0 mol / L.

[0023] In some embodiments, the time for acid washing in step (2) is 20 - 40 min, preferably 30 min.

[0024] In some embodiments, the second washing in step (3) uses an aqueous solution.

[0025] In some embodiments, the aqueous solution includes, but is not limited to: aqueous solution, inorganic salt solution, organic salt solution.

[0026] In some preferred embodiments, the pH of the aqueous solution is preferably neutral.

[0027] In some embodiments, the number of times of the second washing in step (3) is 1 - 10 times.

[0028] In some preferred embodiments, the second washing in step (3) is 8 - 10 times.

[0029] In some embodiments, the second filtration in step (3) uses vacuum filtration, pressure filtration, and / or centrifugal filtration.

[0030] In some embodiments, the temperature of the calcination in step (4) is 800 - 1200 °C.

[0031] In some preferred embodiments, the temperature of the calcination in step (4) is 1000 - 1100 °C.

[0032] In some preferred embodiments, the temperature of the calcination in step (4) can be 1000 °C, 1010 °C, 1020 °C, 1030 °C, 1040 °C, 1050 °C, 1060 °C, 1070 °C, 1080 °C, 1090 °C, 1100 °C.

[0033] The applicant found in experimental studies that high-temperature calcination to decompose residual fluorosilicic acid and fluorosilicates can effectively improve the purity of silica. In addition, the applicant also found that the timing of high-temperature calcination has a significant impact on the purity of silica, and only by performing high-temperature calcination after pickling can high-purity silica be obtained.

[0034] In some embodiments, the time of the calcination in step (4) is 0.5 - 1.5 h.

[0035] In some preferred embodiments, the time of the calcination in step (4) is 1.0 h.

[0036] In some embodiments, crushing is performed after calcination.

[0037] In some embodiments, step (4) further includes the following conditions:

[0038] Drying is performed before high-temperature calcination.

[0039] In some preferred embodiments, the temperature of the drying is 100 - 300 °C.

[0040] On the other hand, the present invention provides high-purity silica obtained by any of the foregoing methods.

[0041] In some embodiments, the purity of the high-purity silica is ≥ 99.5%.

[0042] In some preferred embodiments, the purity of the high-purity silica is 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%, 99.98%, 99.99%, 99.999%, 99.9999%.

[0043] The present invention utilizes fluorosilicate slag to prepare high-purity silica, comprehensively utilizes the waste fluorosilicate slag, reduces the dependence on natural silica ore, and has the advantages of reducing environmental pollution and high purity of the obtained silica.

[0044] The present invention also overcomes the defects that the preparation of silica products from traditional fluorosilicate slag seriously depends on chemical reactions and has a large demand for chemical reagents. The method provided by the present invention almost only adopts steps based on physical reactions, is easy to operate, does not require special equipment, has low costs, and is green and environmentally friendly. The silica prepared by the method of the present invention has a purity as high as 99.93% and a loss on ignition as low as 0.010%.

[0045] Through exploration and in-depth research, the present invention provides an optimized method for preparing high-purity silica. By adopting this preparation method, not only are costs saved (no need to add NaCl), but also pollution and equipment loss are reduced (direct calcination will cause pollution and loss). The present invention also unexpectedly discovers that the timing of high-temperature calcination and the number of water washing times have an important impact on the purity of the final silica product, providing a new technical solution and improvement idea for subsequent industrial production and technical improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flow chart for preparing high-purity silica using fluorosilicate slag. DETAILED DESCRIPTION OF THE INVENTION

[0047] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly used in the field to which the present invention belongs. For the purpose of explaining this specification, the following definitions will be applied, and where appropriate, terms used in the singular form will also include the plural form, and vice versa.

[0048] Unless the context clearly indicates otherwise, the expressions "a" and "an" used herein include plural referents.

[0049] The numerical ranges used herein should be understood to have enumerated all the numbers within that range. For example, the range of 1 to 20 should be understood to include any number, number combination, or sub-range from the following group: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20.

[0050] As used herein, the term "comprises" or "comprising" means "including but not limited to". This term is intended to be open-ended, specifying the presence of any stated feature, element, integer, step, or component, but not precluding the presence or addition of one or more other features, elements, integers, steps, components, or groups thereof. Thus, the term "comprising" includes the more restrictive terms "consisting of" and "consisting essentially of". In one embodiment, the term "comprising" as used throughout the application, particularly in the claims, may be replaced by the term "consisting of".

[0051] As used herein, the terms "optionally", "either", "any", or "any one" mean that the subsequent described event or circumstance may but need not occur, and this description includes the instances where the event or circumstance occurs or does not occur. As used in the present invention, "a" and "an" are used in the present invention to refer to one or more than one grammatical object.

[0052] As used herein, the term "and / or" should be understood to mean any one of the alternatives or any combination of any two or more of the alternatives.

[0053] As used herein, the term "fluorosilicate slag" refers to the waste containing silicon dioxide and fluorine generated in industrial production. The content of silicon dioxide depends on the specific process in production practice and varies according to different processes. Considering the technical level in this field, generally, the content of silicon dioxide is about 30% - 40%, and the total fluorine content is 3% - 8%.

[0054] As used herein, the term "pH" refers to the negative logarithm of the hydrogen ion concentration.

[0055] As used herein, the term "high-purity silicon dioxide" refers to silicon dioxide with a purity ≥ 99.5%.

[0056] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to embodiments. For those not specifying specific conditions in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For all reagents or instruments without indicating the manufacturer, they are all conventional products that can be purchased commercially. To better illustrate the present invention, numerous specific details are given in the following specific embodiments. The specific embodiments described herein are only used to explain the present invention and do not constitute any limitation to the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessarily confusing the concepts of the present invention. Such structures and technologies have also been described in many publications.

[0057] The fluorosilicate slag used in the present invention contains about 30-40% of silicon dioxide, about 50%-70% of water, and about 3%-8% of hydrogen fluoride and fluosilicic acid.

[0058] After the composition and content of the used fluorosilicate slag were determined in the present invention, the results are shown in Table 1.

[0059] Table 1

[0060] Project Test Results Adopted Method Moisture (%) 55.40 GB / T 35924-2018 Silicon Dioxide (%) 34.21 GB / T4209-2008 Fluoride Content (%) 6.7360 GB / T21057-2007

[0061] The fluorine in the fluorosilicate slag includes free fluorine and lattice fluorine. The free fluorine is mainly fluosilicic acid adhering to the surface of silicon dioxide and can be removed by rinsing. The lattice fluorine is mainly due to the fact that fluorine in the solution occupies the position of oxygen element during the crystallization of silicon dioxide, which is caused by crystal defects. Since the lattice fluorine forms a chemical bond with silicon atoms, it cannot be removed by physical washing, and traditional methods all remove it by chemical methods.

[0062] Example 1 Preparation of high-purity silicon dioxide from fluorosilicate slag

[0063] The preparation method of high-purity silicon dioxide is as follows:

[0064] Take 200 g of fluorosilicate slag and add 300 g of water for the first water wash;

[0065] After the first water wash, filter and add 300 g of 3M HCl for pickling for 30 min;

[0066] After pickling, perform the second water wash, add 300 g of aqueous solution for the second water wash, and wash once;

[0067] After the second water wash, filter, dry at 200 °C, calcine at 1000 °C for 1 h, and crush to obtain high-purity silicon dioxide.

[0068] Detect the obtained high-purity silicon dioxide (GB / T4209-2008), and the detection results are shown in Table 2.

[0069] Table 2

[0070] Component Content (%) IL (Loss on Ignition) 0.028 <![CDATA[Al2O3]]> 0.05 <![CDATA[SiO2]]> 99.72 <![CDATA[Fe2O3]]> 0.034 CaO 0.037 MgO 0.015 <![CDATA[K2O]]> 0.059 <![CDATA[Na2O]]> 0.039 <![CDATA[TiO2]]> 0.0006

[0071] The results show that the content of silicon dioxide in the finally obtained high-purity silicon dioxide is 99.72%.

[0072] Example 2 Preparation of high-purity silicon dioxide from fluorosilicate slag

[0073] The preparation method of high-purity silicon dioxide is as follows:

[0074] Take 200 g of fluorosilicate slag and add 300 g of water for the first water wash;

[0075] Filter after the first water wash and add 300 g of 4M HCl for pickling for 30 min;

[0076] After pickling, perform the second water wash. Add 300 g of aqueous solution for the second water wash and wash 8 times;

[0077] Filter after the second water wash, dry at 200 °C, calcine at 1100 °C for 1 h, and crush to obtain high-purity silica. Detect the obtained high-purity silica (GB / T4209-2008), and the detection results are shown in Table 3.

[0078] Table 3

[0079] Component Content (%) IL (Loss on Ignition) 0.01 <![CDATA[Al2O3]]> 0.007 <![CDATA[SiO2]]> 99.93 <![CDATA[Fe2O3]]> 0.0075 CaO 0.014 MgO 0.0054 <![CDATA[K2O]]> 0.003 <![CDATA[Na2O]]> 0.012 <![CDATA[TiO2]]> <0.0001

[0080] The results show that the content of silica in the finally obtained high-purity silica is 99.93%.

[0081] Example 3 Preparation of High-Purity Silica from Fluorosilicate Residue

[0082] The preparation method of high-purity silica is as follows:

[0083] Take 200 g of fluorosilicate residue and add 300 g of water for the first water wash;

[0084] Filter after the first water wash and add 300 g of 4M HCl and 0.15M HF for pickling for 30 min;

[0085] After pickling, perform the second water wash. Add 300 g of aqueous solution for the second water wash and wash 10 times;

[0086] Filter after the second water wash, dry at 200 °C, calcine at 1100 °C for 1 h to obtain high-purity silica. Detect the obtained high-purity silica (GB / T4209-2008), and the detection results are shown in Table 4.

[0087] Table 4

[0088] Component Content (%) IL (Loss on Ignition) 0.0085 <![CDATA[Al2O3]]> 0.007 <![CDATA[SiO2]]> 99.92 <![CDATA[Fe2O3]]> 0.0043 CaO 0.019 MgO 0.0087 <![CDATA[K2O]]> 0.0062 <![CDATA[Na2O]]> 0.016 <![CDATA[TiO2]]> 0.0001

[0089] The results show that the content of silica in the finally obtained high-purity silica is 99.92%.

[0090] Comparative Example 1

[0091] The preparation method of high-purity silica is as follows:

[0092] Take 200 g of fluorosilicate residue and add 300 g of water for the first water wash;

[0093] After drying at 200 °C, obtain the crude silica product.

[0094] The obtained crude silica was detected (GB / T4209-2008), and the detection results are shown in Table 5.

[0095] Table 5

[0096]

[0097]

[0098] The results showed that the content of silica finally obtained was only 86.50%. The results of Comparative Example 1 indicated that the content of silica obtained by conventional direct washing and then drying was low, and the purity could not meet the industrial requirements.

[0099] Comparative Example 2

[0100] The preparation method of high-purity silica is as follows:

[0101] Take 200 g of fluorine-containing silicon slag, add 300 g of water for the first water wash;

[0102] After the first water wash, filter, dry at 200 °C, and calcine at 1100 °C for 1 h to obtain crude silica.

[0103] The obtained crude silica was detected (GB / T4209-2008), and the detection results are shown in Table 6.

[0104] Table 6

[0105] Component Content (%) IL (Loss on Ignition) 0.085 <![CDATA[Al2O3]]> 0.03 <![CDATA[SiO2]]> 99.3 <![CDATA[Fe2O3]]> 0.025 CaO 0.3 MgO 0.09 <![CDATA[K2O]]> 0.067 <![CDATA[Na2O]]> 0.095 <![CDATA[TiO2]]> 0.0019

[0106] The results showed that the content of silica finally obtained was 99.3%. The results of Comparative Example 2 indicated that only using high-temperature calcination could not increase the content of silica to more than 99.5%.

[0107] Comparative Example 3

[0108] The difference between Comparative Example 3 and Comparative Example 2 is only that: during high-temperature calcination, water quenching is carried out, and the specific step of water quenching is to directly pour the product into water.

[0109] The results showed that the content of silica finally obtained was 99.36%, indicating that the introduction of water quenching had little improvement on silica.

[0110] Comparative Example 4

[0111] The preparation method of high-purity silica is as follows:

[0112] Take 200 g of fluorine-containing silicon slag, add 300 g of water for the first water wash;

[0113] After the first water wash, filter, dry at 200 °C, and calcine at 1100 °C for 1 h;

[0114] After high-temperature calcination, pickling is carried out with 300 g of 4M HCl for 30 min;

[0115] After pickling, the second water washing is carried out. Add 300 g of aqueous solution for the second water washing. The pH of the aqueous solution is 3.4, and the water washing is carried out 8 times;

[0116] After the second water washing, filter and dry at 200 °C to obtain high-purity silicon dioxide.

[0117] The results show that the content of silicon dioxide finally obtained is 99.04%. It shows that the timing of high-temperature calcination is very important. Carrying out high-temperature calcination after the first water washing and before pickling has relatively limited improvement in the content of silicon dioxide.

[0118] Comparative Example 5

[0119] The preparation method of high-purity silicon dioxide in this comparative example is compared with that of Example 2. The only difference is that the number of times of the second water washing is changed, and the number of water washing times is changed to 1 time.

[0120] The results show that the content of silicon dioxide finally obtained is 99.65%.

[0121] Comparative Example 6

[0122] The preparation method of high-purity silicon dioxide in this comparative example is compared with that of Example 2. The only difference is that high-temperature calcination is changed to adding 2% NaCl and calcining at 820 °C for 2 h.

[0123] The obtained high-purity silicon dioxide is detected (GB / T4209-2008), and the detection results are shown in Table 7.

[0124] Table 7

[0125] Component Content (%) IL (Loss on Ignition) 0.06 <![CDATA[Al2O3]]> 0.04 <![CDATA[SiO2]]> 99.52 <![CDATA[Fe2O3]]> 0.053 CaO 0.04 MgO 0.02 <![CDATA[K2O]]> 0.01 <![CDATA[Na2O]]> 0.09 <![CDATA[TiO2]]> <0.01

[0126] The results show that the content of silicon dioxide finally obtained is 99.52%. Judging from the content of each component, calcination with NaCl improves the content of silicon dioxide to a certain extent, but at the same time significantly increases the content of impurity Fe2O3 (only 0.0075% in Example 2). Therefore, the present invention uses separate high-temperature calcination instead of adding NaCl for calcination, with a simpler process and higher purity of silicon dioxide.

[0127] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than a limitation on the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art does not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing high-purity silica from fluorosilicate slag, characterized in that, The method comprises the following steps: (1) Perform a first washing and a first filtration on the fluorosilicate slag to obtain a first washed product; (2) Pickle the first washed product with a pickling agent to obtain a pickled product; (3) Perform a second washing and a second filtration on the pickled product to obtain a second washed product; (4) After calcining the second washed product, high-purity silicon dioxide is obtained.

2. The method according to claim 1, characterized in that, In step (1), the first washing is performed using an aqueous solution; And / or, in step (1), the first filtration is performed using vacuum filtration, pressure filtration, and / or centrifugal filtration.

3. The method according to claim 1, wherein In step (2), the pickling agent includes hydrochloric acid, sulfuric acid, nitric acid, and / or hydrofluoric acid.

4. The method according to claim 1, wherein In step (2), the pickling agent is hydrochloric acid and / or hydrofluoric acid; And / or, in step (2), the pickling time is 20 - 40 min.

5. The method according to claim 1, wherein In step (2), the hydrogen ion concentration of the pickling agent is 3.0 - 5.0 mol / L.

6. The method according to claim 1, wherein In step (3), the second washing is performed using an aqueous solution.

7. The method according to any one of claims 1-6, characterized in that, In step (3), the number of times of the second washing is 1 - 10 times.

8. The method according to claim 7, wherein In step (3), the second washing is 8 - 10 times; And / or, in step (3), the second filtration is performed using vacuum filtration, pressure filtration, and / or centrifugal filtration; And / or, in step (4), the calcining temperature is 800 - 1200 °C.

9. The method according to claim 8, characterized in that, In step (4), the calcining temperature is 1000 - 1100 °C; And / or, in step (4), the calcining time is 0.5 - 1.5 h; And / or, step (4) further includes the following condition: drying is performed before calcining.

10. High-purity silicon dioxide obtained by any of the methods according to claims 1 - 9.

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