Reutilization method for silicon sludge

Abstract

A reutilization method for silicon sludge, comprising: 1) performing pre-processing on the silicon sludge, to obtain silicon powder, the pre-processing comprising acid soaking processing and alcohol washing processing; 2) causing the silicon powder to react with alcohol, to obtain a silicate ester. The present method can convert silicon sludge from cutting crystalline silicon wafers into high-value silicate ester, broaden the application range of silicon sludge, and avoid waste of silicon sludge resources.

Description

A method for recycling silicon mud

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 13, 2023, with application number CN202311178842.1 and application name “A Method for Recycling of Silicon Mud”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to the field of inorganic chemical industry, and specifically relates to a method for recycling silicon mud. Background Art

[0003] Solar cell silicon wafers are cut from silicon blocks or ingots using a multi-wire saw. During the diamond wire sawing process of single-crystalline or polycrystalline silicon, silicon powder and other impurities are deposited into the cutting slurry, forming silicon sludge. While silicon sludge is relatively pure, it is also very fine and, if not handled properly, can cause environmental pollution and waste resources. Several methods are currently available to recycle silicon sludge, including using 1-4% liquid silicon sludge to produce silicon carbide, recovering nanosilicon from silicon sludge to create silicon / carbon composites, and using silicon sludge to produce silicon granules and filaments.

[0004] On this basis, how to further broaden the application scope of silicon mud is a problem that technicians in this field continue to explore.

[0005] Summary of the Invention

[0006] The present application provides a method for recycling silicon mud, which can convert the silicon mud generated during the cutting process of silicon wafers into silicate esters, thereby efficiently utilizing the silicon mud and broadening the application range of the silicon mud.

[0007] The present application provides a method for recycling silicon sludge, comprising:

[0008] 1) pre-treating silicon mud to obtain silicon powder; the pre-treatment includes alcohol washing;

[0009] 2) reacting the silicon powder with alcohol to obtain silicate;

[0010] The pretreatment includes acid soaking treatment and alcohol washing treatment.

[0011] According to one embodiment of the present application, the method further includes: allowing the silicate to undergo a hydrolysis reaction with water to form a silica sol; adding an alkaline substance to the silica sol to obtain a gel, and then washing the gel to a neutral pH value and performing a calcination treatment to obtain quartz sand.

[0012] According to one embodiment of the present application, the pretreatment includes: filtering the silicon mud, acid soaking, water washing, alcohol washing, and crushing and screening in sequence;

[0013] The acid used in the acid soaking treatment includes at least one of concentrated sulfuric acid and nitric acid; the mass ratio of the silicon mud to the alcohol used in the alcohol washing treatment is 1:(1-10).

[0014] According to one embodiment of the present application, the reaction in step 2) is carried out under the action of a catalyst, and the catalyst includes at least one of a copper-containing catalyst and an alkali metal catalyst;

[0015] The mass ratio of the silicon powder to the catalyst is 1:(0.1-1.5); and / or,

[0016] The reaction pressure is 0.1-1.0 MPa, and the temperature is 70-120°C.

[0017] According to one embodiment of the present application, the reaction liquid after the reaction of the silicon powder and alcohol is sequentially subjected to solid-liquid separation treatment, dealcoholization water treatment, and distillation treatment to obtain the silicate;

[0018] The temperature of the dealcoholization water treatment is 100-150°C and the pressure is 0.1-0.5MPa;

[0019] The temperature of the distillation treatment is 80-120° C., and the pressure is 0.1-0.5 MPa.

[0020] According to one embodiment of the present application, the hydrolysis reaction is carried out under an acidic catalyst, and the acidic catalyst includes at least one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, formic acid, propionic acid, acetic acid, benzoic acid, and oxalic acid;

[0021] The concentration of the acidic catalyst is 0.1-2 mol / L; the mass ratio of the acidic catalyst to the water is (0.1-0.5):1; and the molar ratio of the silicate to the water is 1:(4-15).

[0022] According to one embodiment of the present application, the temperature of the hydrolysis reaction is 40-90°C.

[0023] According to one embodiment of the present application, the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, ammonia water, methylamine, ethylamine, propylamine, tert-butylamine, p-toluidine, aniline, dimethylamine, ethylenediamine, ethanolamine, propylenediamine, vinylamine, sodium carbonate, calcium hydroxide, potassium carbonate, sodium bicarbonate, ammonium hydroxide, sodium dihydrogen phosphate, and potassium dihydrogen phosphate;

[0024] When the alkaline substance is added, the temperature of the silica sol is controlled to be 10-30° C. higher than the temperature of the hydrolysis reaction.

[0025] According to one embodiment of the present application, the alkaline substance is added to the silica sol to adjust the pH of the system to 7.5 to 12, followed by aging treatment for 1 to 12 hours to obtain the gel.

[0026] According to one embodiment of the present application, the roasting process includes a first roasting process and a second roasting process in sequence;

[0027] The first calcination treatment is carried out in an oxygen-containing atmosphere at a temperature of 600 to 1000° C. for 5 to 40 hours;

[0028] The second calcination process is performed under vacuum conditions, with the temperature increased by 300 to 600° C. compared to the first calcination process, and the time is 3 to 30 hours.

[0029] The present application pre-treats the silicon mud generated by cutting silicon wafers through acid soaking and alcohol washing, thereby converting the silicon mud into silicate, broadening the application of silicon mud, avoiding the waste of silicon mud resources, and having both economic and environmental significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic flow chart of the silicon mud recycling method of Examples 1 to 21 of the present application. DETAILED DESCRIPTION

[0031] To enable those skilled in the art to better understand the solutions of the present application, the present application is further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present application. The examples cited are only used to explain the present application and do not limit the scope of the present application. Based on the embodiments of the present application, all other implementation methods obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of this application.

[0032] The present application provides a method for recycling silicon sludge, comprising:

[0033] 1) Pre-treating silicon mud to obtain silicon powder;

[0034] 2) reacting silicon powder with alcohol to obtain silicate;

[0035] The pretreatment includes acid soaking treatment and alcohol washing treatment.

[0036] The present application does not limit the alcohol used in the alcohol washing treatment in step 1), and illustratively, it can be methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, etc.

[0037] The present application also does not limit the acid used for the acid soaking treatment in step 1). For example, it can be concentrated sulfuric acid, hydrochloric acid, nitric acid, etc.

[0038] The present application does not limit the specific type of alcohol in step 2), which may be the same as or different from the alcohol in step 1). For the sake of recovery cost, the alcohol is preferably the same.

[0039] Acid soaking can dissolve and remove metallic impurities from the silicon sludge. Alcohol washing can remove organic matter and residual chemicals from the silicon sludge surface, reducing surface tension and improving the dispersibility of the silicon sludge. In practice, acid soaking should be performed before alcohol washing to ensure that organic matter and residual chemicals on the silicon sludge surface are fully removed, thereby facilitating the preparation of silicate esters.

[0040] By pre-treating the silicon mud including acid soaking and alcohol washing, the obtained silicon powder can be converted into silicate, and the conversion rate of silicon powder is not less than 70%, and the yield of silicate is not less than 60%, which effectively avoids resource waste and brings into play the sustainable value of silicon mud.

[0041] It is understood that after the acid soaking and alcohol washing treatments, the silicon powder in the silicon sludge is present in the alcohol washing solution. The silicon sludge needs to be separated from the alcohol washing solution and dried to obtain the silicon powder. Therefore, in a specific implementation, the silicon sludge can be separated from the alcohol washing solution by centrifugation. This application does not limit the specific drying method; for example, vacuum drying, hot air drying, etc. may be used.

[0042] It should be noted that during the reaction, the alcohol should be in excess relative to the silicon powder to ensure that the silicon powder is fully converted into silicate esters. Hydrogen is produced during the conversion of silicon powder into silicate esters, so the present application can determine whether the reaction is complete by monitoring whether hydrogen is still produced.

[0043] In this application, the reaction liquid after the reaction of silicon powder and alcohol contains alcohol, water, and solid impurities. The alcohol originates from excess reactants; due to the presence of hydroxyl groups on the surface of the silicon powder, these react with the alcohol to produce water. Furthermore, other impurities may remain in the pre-treated silicon powder. These impurities are unable to react with the alcohol to produce silicate esters and thus remain as solid impurities in the reaction liquid after the reaction of silicon powder and alcohol. Therefore, post-treatment of the reaction liquid is necessary to separate the silicate esters from the product.

[0044] In one embodiment, silica sol obtained by hydrolyzing silica esters can be used as a raw material for preparing quartz sand. Specifically, the silica esters are hydrolyzed with water to form silica sol. An alkaline substance is added to the silica sol to form a gel, which is then washed to a neutral pH and calcined to produce quartz sand.

[0045] By converting the silicate into silica sol first, a gel with better uniformity can be obtained, and the gel agglomeration during the gelation process can be avoided, which causes part of the silicon source to be wrapped and unable to be converted into quartz sand.

[0046] The prepared gel contains cations of alkaline substances. Washing the gel until the pH is neutral can replace the ions in the alkaline substances with hydrogen, thereby obtaining quartz sand.

[0047] Through the above method, the application scope of silicon mud can be further broadened.

[0048] It should be noted that after the gel is washed to a neutral pH, there is residual moisture inside the gel, and it needs to be dried to remove the moisture from the wet gel, thereby avoiding damage to the calcination equipment by directly calcining the wet gel; specifically, the drying temperature is 100-300°C and the time is 1-12 hours.

[0049] In the aforementioned step 1), the pretreatment includes: filtering the silicon mud, acid soaking, water washing, alcohol washing, and crushing and screening in sequence;

[0050] The acid used in the acid soaking treatment includes at least one of concentrated sulfuric acid and nitric acid; the mass ratio of the silicon mud to the alcohol used in the alcohol washing treatment is 1:(1-10).

[0051] The above-mentioned filtration treatment can adopt conventional filtration methods, such as vacuum filtration, pressure filtration, centrifugal filtration, membrane filtration, sedimentation filtration, etc.

[0052] The above-mentioned acid soaking treatment refers to soaking the solid obtained after the filtration treatment in acid solution. This application does not limit the specific amount of acid and silicon mud during the acid soaking treatment, as long as the silicon mud can be completely soaked in the acid solution.

[0053] The water washing treatment is achieved by rinsing the silicon mud after the acid soaking treatment with deionized water.

[0054] Alcohol washing refers to the process of mixing the silicon sludge after water washing with alcohol and allowing it to stand for a while. Preferably, the standing time is 2 to 12 hours.

[0055] The present application does not limit the specific conditions of the crushing and screening process, as long as silicon powder of uniform size can be obtained.

[0056] By sequentially filtering, acid soaking, water washing, and alcohol washing, large impurities and foreign matter, metallic impurities, organic matter, and residual chemical reagents can be removed from the silicon sludge, thereby facilitating the production of high-purity silicon powder and, in turn, the preparation of silicates. Crushing and screening can yield silicon powder of uniform particle size, facilitating its conversion into silicates and quartz sand.

[0057] In the specific pretreatment process, when the acid solution is used for acid soaking treatment, the obtained silicon powder conversion rate is higher and the yield of silicate and quartz sand is also better.

[0058] Furthermore, when the alcohol washing process is controlled, the mass ratio of silicon mud to alcohol in the alcohol washing treatment is 1: (1 to 10), which can effectively reduce the surface tension of silicon mud, improve the dispersibility of silicon mud, facilitate the conversion of silicon mud into silicate, and avoid waste of alcohol solvent.

[0059] It is understood that the filter size affects the filtration effect during the filtration process. Therefore, this application preferably uses a 50-500 mesh (297-30 μm) filter to filter the silicon mud. During the alcohol washing process, simply standing the mixture is slow. Therefore, the silicon mud and alcohol mixture can be stirred first and then allowed to stand to speed up the alcohol washing process.

[0060] The reaction in step 2) is carried out under the action of a catalyst, wherein the catalyst comprises at least one of a copper-containing catalyst and an alkali metal catalyst;

[0061] The mass ratio of the silicon powder to the catalyst is 1:(0.1-1.5).

[0062] The present application does not limit the specific type of copper-containing catalyst, which may include copper, copper oxide, etc.

[0063] The present application also does not limit the specific type of alkali metal catalyst, which includes alkali metal salts, alkali metal alcoholates, etc., and alkali metals include sodium, potassium, lithium, rubidium, cesium, etc.

[0064] It has been found that when alkali metal alkoxides having epoxy groups and hydroxy groups catalyze the reaction of silicon powder and alcohol, the yield of silicate and quartz sand can be significantly improved. Therefore, the present application preferably uses alkali metal alkoxides having epoxy groups and hydroxy groups to catalyze the reaction of silicon powder and alcohol. For example, the alkali metal alkoxides having epoxy groups and hydroxy groups can be 1,4-dioxanol salts, 1,3-dioxolanolates, 1,3-trioxolanolates, 2-oxolane-1-olate, 3-oxanane-1-olate, 2-oxocane-1-olate, 2-oxonane-1-olate, 3-oxepane-1-olate, 4-oxanane-1-olate, 1,4-dioxepane-1-olate, 2-oxepane-1-olate.

[0065] In the present application, the pressure of the reaction between silicon powder and alcohol is 0.1-1.0 MPa and the temperature is 70-120°C.

[0066] Under these conditions, the reaction is easy to operate, has low requirements on reaction equipment, and is conducive to reducing the preparation cost of silicate. In order to improve the utilization rate of alcohol, the reaction can also be carried out under reflux.

[0067] Of course, you can also choose to carry out the reaction at a higher pressure to increase the reaction rate. Correspondingly, the increase in pressure will also increase the reaction temperature. It is necessary to ensure that the pressure is greater than the saturated vapor pressure of the alcohol at the reaction temperature, otherwise it will cause the alcohol to boil and produce steam, resulting in waste of raw materials.

[0068] Step 2) After the reaction is completed, the reaction liquid after the reaction of silicon powder and alcohol is subjected to solid-liquid separation treatment, dealcoholization water treatment, and distillation treatment in sequence to obtain silicate;

[0069] The temperature of dealcoholization water treatment is 100-150°C and the pressure is 0.1-0.5MPa;

[0070] The temperature of the distillation treatment is 80-120°C and the pressure is 0.1-0.5 MPa.

[0071] The solid-liquid separation treatment can remove solid impurities in the reaction liquid; the dealcoholization water treatment can remove alcohol and water in the reaction liquid; and the distillation treatment can remove by-products in the reaction liquid.

[0072] The above process can realize post-treatment of the reaction liquid after the reaction of silicon powder and alcohol to obtain high-purity silicate, which is beneficial to the preparation of quartz sand.

[0073] During specific implementation, this application does not limit the specific form of solid-liquid separation treatment. For example, it can be a centrifugal separation treatment or a filtration separation treatment. In view of the fact that the reaction liquid contains fine particles of silicate solids, traditional filtration methods are difficult to effectively separate, and centrifugal separation can make full use of the centrifugal force generated by high-speed rotation to quickly and effectively separate the liquid / solid phases. At the same time, the investment and operating costs of centrifugal separation equipment are low, and the operation is simple, which is more suitable for this application as an application scenario for small-scale experimental research. Therefore, it is preferred to adopt centrifugal separation treatment technology to improve the solid-liquid separation efficiency and obtain a high-purity silicate product.

[0074] The above-mentioned dealcoholization water treatment and rectification treatment are carried out in a dealcoholization water tower and a rectification tower, respectively. The specific types of the dealcoholization water tower and the rectification tower are not limited in this application and can be tray-type or packed-type. In the dealcoholization water tower, alcohol and water are separated at the top of the tower, and the bottom materials containing silicate enter the rectification tower; in the rectification tower, silicate is separated from the top of the tower, and impurities are separated from the bottom of the tower.

[0075] After the above-mentioned dealcoholization water treatment and distillation treatment, the removed alcohol and the alcohol washing liquid produced by the alcohol washing treatment can be extracted from the water, so that the alcohol can be recycled to participate in the alcohol washing treatment of step 1) and the reaction of step 2), and the obtained water can also be recycled to participate in the water washing treatment of step 1). The present application can also treat the solid impurities obtained by the solid-liquid separation treatment, and obtain a reasonable treatment method by performing chemical analysis and physical testing on the solid impurities to avoid solid impurities from polluting the environment. Exemplarily, the treatment method may include washing, extraction, roasting and recrystallization. Based on this, the present application can significantly reduce the cost of raw materials, reduce the discharge of waste liquid and solid impurities, and has both environmental and economic value.

[0076] In the present application, the hydrolysis reaction is carried out under an acidic catalyst, and the acidic catalyst includes at least one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, formic acid, propionic acid, acetic acid, benzoic acid, and oxalic acid;

[0077] The concentration of the acid catalyst is 0.1-2 mol / L; the mass ratio of the acid catalyst to water is (0.1-0.5):1; and the molar ratio of the silicate to water is 1:(4-15).

[0078] The acidic catalyst is preferably at least one of hydrochloric acid, oxalic acid, nitric acid, and acetic acid. In the present application, the selection of the acidic catalyst takes into account many factors such as catalytic activity, operational safety, and environmental friendliness. Among them, inorganic acids such as hydrochloric acid and nitric acid are highly acidic and can effectively catalyze hydrolysis reactions; organic acids such as oxalic acid and acetic acid are of natural origin and have little impact on the environment; in addition, hydrochloric acid and nitric acid are highly water-soluble; oxalic acid and acetic acid have few inorganic salts, and are safer and more convenient to use and operate. Taking into account factors such as catalytic performance, environmental impact, and performance in use, the present application preferably uses one or more of hydrochloric acid, oxalic acid, nitric acid, and acetic acid as acidic catalysts to achieve the best catalyst effect.

[0079] Because silicate undergoes a hydrolysis reaction to produce silica sol and a polycondensation reaction to produce gel, the two are in a competitive relationship. When the polycondensation reaction rate is too fast, the formed gel will encapsulate the silica sol, inhibiting the full utilization of the silicon element. Under the action of the above-mentioned concentration of acidic catalyst, controlling the amount of acidic catalyst, water, and silicate can ensure that the hydrolysis reaction rate is greater than the polycondensation reaction rate, thereby allowing the silicate to be fully converted into silica sol and, in turn, into quartz sand. Therefore, the present application controls the concentration of the acidic catalyst to be 0.1-2 mol / L, the mass ratio of the acidic catalyst to water to be (0.1-0.5):1, and the molar ratio of the silicate to water to be 1:(4-15). Furthermore, when the concentration of the acidic catalyst is controlled to be 0.6-1.2 mol / L, the mass ratio of the acidic catalyst to water to be (0.2-0.4):1, and the molar ratio of the silicate to water to be 1:(8-12), the conversion of the silicate to silica sol can be further promoted.

[0080] During the specific implementation process, the temperature of the hydrolysis reaction is 40-90°C, preferably 45-70°C. Temperature control of the hydrolysis reaction is critical to yield and quality optimization. Too low a temperature will cause a slow reaction, while too high a temperature will induce complex side reactions. The present application takes into account multiple factors such as reaction rate, yield and quality by optimizing the temperature range of 45-70°C; the reaction rate in this temperature range is moderate and easy to operate and control, which prevents reaction delays and side reactions, and can obtain higher yields and high-quality quartz sand.

[0081] The alkaline substance added to the silica sol in the present application includes at least one of sodium hydroxide, potassium hydroxide, ammonia water, methylamine, ethylamine, propylamine, tert-butylamine, p-toluidine, aniline, dimethylamine, ethylenediamine, ethanolamine, propylenediamine, vinylamine, sodium carbonate, calcium hydroxide, potassium carbonate, sodium bicarbonate, ammonium hydroxide, sodium dihydrogen phosphate, and potassium dihydrogen phosphate;

[0082] When the alkaline substance is added, the temperature of the silica sol is controlled to be 10-30° C. higher than the temperature of the hydrolysis reaction.

[0083] In specific implementations, at least one of sodium hydroxide, potassium hydroxide, ammonia, and ethylenediamine is preferably added to the silica sol as an alkaline substance. This is primarily based on the following considerations: First, these substances all have strong alkalinity, which can quickly neutralize the reaction solution and facilitate the precipitation of silicates; second, inorganic strong bases such as sodium hydroxide and potassium hydroxide are easy to operate, while organic amines such as ammonia and ethylenediamine are naturally derived and have little impact on the environment. Therefore, this application prefers the use of the above alkaline substances in the reaction, which not only ensures a good reaction effect, but also takes into account operational convenience and environmental protection.

[0084] When adding the alkaline substance, controlling the silica sol temperature to be 10-30°C higher than the hydrolysis reaction temperature can reduce the possibility of gel agglomeration, improve the uniformity and stability of the gel, and avoid gel agglomeration that prevents the conversion of silicon into quartz sand, which in turn leads to resource waste. Therefore, controlling the silica sol temperature to be 10-30°C higher than the hydrolysis reaction temperature is beneficial for obtaining high-quality quartz sand. Furthermore, this temperature is preferably 15-25°C higher than the hydrothermal reaction temperature.

[0085] According to the applicant's research, an alkaline substance is added to the silica sol to adjust the pH of the system to 7.5 to 12, followed by aging treatment for 1 to 12 hours to obtain a gel.

[0086] The applicants have found that excessively high or low pH values ​​can lead to uncontrolled gel formation and gelation, affecting the uniformity of the gel structure and hindering the production of hard, dense, high-quality quartz sand. However, controlling the pH between 7.5 and 12 effectively controls the reaction rate and extent, ensuring good gel properties and structural uniformity, and making the experiment highly reproducible. Preferably, the pH is between 8.5 and 10.5.

[0087] At the same time, after adding alkaline substances, aging the silica sol under alkaline substances for 1 to 12 hours can promote the strengthening of the gel skeleton, which is further conducive to obtaining high-quality quartz sand.

[0088] In specific implementation, the pH value of the silica sol during the aging treatment can be monitored to understand the reaction status of the gel formation process in real time, and the pH value can be fine-tuned according to actual needs to optimize the uniformity of the gel.

[0089] After further research, it was found that the roasting treatment includes the first roasting treatment and the second roasting treatment in sequence;

[0090] The first calcination treatment is carried out in an oxygen-containing atmosphere at a temperature of 600-1000°C for 5-40 hours;

[0091] The second calcination process is performed under vacuum conditions, with the temperature increased by 300-600° C. compared to the first calcination process, and the time is 3-20 hours.

[0092] The oxygen-containing atmosphere may be air, pure oxygen, or any gas containing oxygen mixed with an inert gas.

[0093] After the first calcination, the organic matter in the gel is oxidized and decomposed, thereby increasing the purity of the quartz sand. Simultaneously, the oxygen also fully converts the silicon element in the gel into silicon oxide, helping to stabilize the gel structure and strengthen the silicon-oxygen-silicon bond, thus facilitating the production of quartz sand. The first calcination temperature is preferably 650-900°C, and the duration is preferably 8-32 hours. Within this temperature and time range, the organic matter can be fully driven off without affecting the silicon oxide structure, ensuring complete oxidation and decomposition of the organic matter. This process is highly repeatable and efficient, resulting in high-quality quartz sand at a low cost.

[0094] The second calcination is performed under vacuum conditions at a temperature higher than the first calcination temperature, enabling the rapid and effective removal of hydroxyl groups from the gel, thereby producing quartz sand. Preferably, the second calcination temperature is 350-500°C higher than the first calcination temperature, and the calcination time is 5-16 hours.

[0095] Hereinafter, the present application will be described in more detail through specific embodiments.

[0096] The process flow of the silicon mud recycling method of Examples 1-21 of the present application is shown in Figure 1.

[0097] Example 1

[0098] A method for recycling silicon mud comprises the following steps:

[0099] 1) Filter the silicon mud with a filter size of 200 mesh;

[0100] The filtered silicon mud is completely immersed in concentrated sulfuric acid for acid soaking treatment;

[0101] Washing the acid-soaked silicon mud with water;

[0102] The silicon mud after water washing was mixed with ethanol and stirred, and then allowed to stand for 2 hours to complete the alcohol washing treatment; the mass ratio of silicon mud to ethanol was 1:5;

[0103] The silicon mud after alcohol washing is subjected to centrifugal separation, drying, crushing and screening to obtain silicon powder; the particle size of the obtained silicon powder is less than 200 mesh;

[0104] 2) reacting silicon powder with excess ethanol under the catalysis of sodium ethoxide. When no more hydrogen is produced, indicating that the reaction is complete, the reaction liquid is centrifuged, and the separated liquid is transported to a dealcoholization water tower for dealcoholization water treatment, and then the bottom liquid of the dealcoholization water tower is transported to a distillation tower for distillation treatment to obtain silicate;

[0105] The mass ratio of silicon powder to sodium ethoxide is 1:0.2, the reaction temperature is 80°C, and the pressure is 0.2 MPa; the temperature of the dealcoholization water tower is 120°C, and the pressure is 0.2 MPa; the temperature of the distillation tower is 100°C, and the pressure is 0.1 MPa;

[0106] 3) mixing the silicate with water, adding 1 mol / L hydrochloric acid, and performing a hydrolysis reaction at 60° C. to form a silica sol; wherein the molar ratio of the silicate to water is 1:11.6, and the mass ratio of the hydrochloric acid to water is 0.25:1;

[0107] 4) Raising the temperature of the silica sol to 80° C., adding 28% ammonia water dropwise until the pH reaches 10, and then aging for 1 hour to form a gel;

[0108] The gel was washed to neutrality and dried at 120 °C for 8 h;

[0109] The dried product was placed in an air atmosphere, heated from 50°C to 800°C and maintained for 6 hours at a heating rate of 2°C / min, then evacuated to an absolute pressure of 5 Pa, heated from 800°C to 1400°C and maintained for 24 hours, and finally cooled to obtain quartz sand;

[0110] 5) The alcohol washing liquid obtained by the centrifugal separation treatment in step 1) and the alcohol-water mixed liquid obtained by the dealcoholization water treatment in step 2) are transported to an alcohol extraction tower, the resulting alcohol is recycled to participate in the alcohol washing treatment in step 1) and the reaction in step 2), and the resulting water is recycled to participate in the water washing treatment in step 1).

[0111] Example 2

[0112] The difference between this embodiment and embodiment 1 is that the catalyst used is potassium 1,4-dioxanol, whose structural formula is:

[0113] Example 3

[0114] The difference between this embodiment and embodiment 1 is that the catalyst used is sodium 3-oxacyclohexane-1-olate, and its structural formula is:

[0115] Example 4

[0116] The difference between this embodiment and embodiment 1 is that the acid used in the acid soaking treatment is hydrochloric acid.

[0117] Example 5

[0118] The difference between this embodiment and embodiment 1 is that the acid used in the acid soaking treatment is nitric acid.

[0119] Example 6

[0120] The difference between this embodiment and embodiment 1 is that the alcohol in step 1) and step 2) is methanol.

[0121] Example 7

[0122] The difference between this embodiment and embodiment 1 is that the alcohol used in step 1) and step 2) is methanol, and in step 1), the mass ratio of silicon mud to methanol is 1:8;

[0123] The catalyst in step 2) is potassium methoxide, the reaction temperature is 78°C, and the mass ratio of silicon powder to potassium methoxide is 1:0.1;

[0124] In step 3), the mass ratio of silicate to water is 1:1.5, the acidic catalyst is 1 mol / L oxalic acid, the mass ratio of oxalic acid to water is 0.1:1, and the hydrolysis reaction temperature is 65°C;

[0125] In step 4), the temperature of the silica sol is raised to 85° C., the pH is adjusted to 9.5, and the silica sol is dried at 110° C. for 12 h.

[0126] Example 8

[0127] The difference between this embodiment and embodiment 1 is that the silicon mud is not subjected to crushing and screening treatment.

[0128] Example 9

[0129] The difference between this embodiment and embodiment 1 is that the mass ratio of silicon mud to alcohol is 1:0.8.

[0130] Example 10

[0131] The difference between this embodiment and embodiment 1 is that the catalyst in step 2) is copper.

[0132] Example 11

[0133] The difference between this embodiment and embodiment 1 is that the reaction pressure in step 2) is 2 MPa and the temperature is 60°C.

[0134] Example 12

[0135] The difference between this embodiment and embodiment 1 is that in step 3), the concentration of hydrochloric acid is 2.5 mol / L.

[0136] Example 13

[0137] The difference between this embodiment and embodiment 1 is that in step 3), the amount of the acidic catalyst is increased so that the mass ratio of hydrochloric acid to water is 1:1.

[0138] Example 14

[0139] The difference between this embodiment and embodiment 1 is that in step 3), the amount of silicate is increased so that the mass ratio of silicate to water is 1:0.3.

[0140] Example 15

[0141] The difference between this embodiment and embodiment 1 is that the hydrolysis reaction temperature is 90°C.

[0142] Example 16

[0143] The difference between this embodiment and embodiment 1 is that the hydrolysis reaction temperature is 120°C.

[0144] Example 17

[0145] The difference between this embodiment and embodiment 1 is that when the alkaline substance is added, the pH is controlled to be 12.

[0146] Example 18

[0147] The difference between this embodiment and embodiment 1 is that when the alkaline substance is added, the pH is controlled to be 7.5.

[0148] Example 19

[0149] The difference between this embodiment and embodiment 1 is that the temperature of the silica sol is not increased when the alkaline substance is added.

[0150] Example 20

[0151] The difference between this embodiment and embodiment 1 is that the temperature of the dealcoholization water treatment is 90°C and the pressure is 0.3 MPa;

[0152] The temperature of the distillation treatment is 75°C and the pressure is 0.15 MPa.

[0153] Example 21

[0154] The difference between this embodiment and embodiment 1 is that: in step 1), the mass ratio of silicon mud to alcohol used in alcohol washing treatment is 1:1;

[0155] In step 2), the mass ratio of silicon powder to catalyst is 1:1.5; the reaction pressure is 1 MPa and the temperature is 120°C;

[0156] The temperature of dealcoholization water treatment is 125℃ and the pressure is 0.25MPa, and the temperature of distillation treatment is 105℃ and the pressure is 0.2MPa;

[0157] In step 3), the acidic catalyst is acetic acid, the concentration of the acidic catalyst is 2 mol / L, the mass ratio of the acidic catalyst to water is 0.4:1, and the molar ratio of the silicate to water is 1:6; the temperature of the hydrolysis reaction is 90°C;

[0158] In step 4), the temperature of the silica sol is raised to 100° C., and a 28% mass concentration of ethylenediamine solution is added dropwise, followed by aging for 5 hours to form a gel;

[0159] The dried product was placed in an air atmosphere, heated from 50°C to 600°C and maintained for 40 hours at a heating rate of 2°C / min, then evacuated to an absolute pressure of 5 Pa, heated from 800°C to 1100°C and maintained for 3 hours, and finally cooled to obtain quartz sand.

[0160] Comparative Example 1

[0161] The difference between this comparative example and Example 1 is that in step 1), the silicon sludge is not subjected to alcohol washing treatment.

[0162] Comparative Example 2

[0163] The difference between this comparative example and Example 1 is that in step 1), the silicon mud is not subjected to acid soaking treatment or alcohol washing treatment.

[0164] Comparative Example 3

[0165] The difference between this embodiment and embodiment 1 is that in step 1), the silicon mud is not subjected to acid soaking treatment.

[0166] Test Example 1

[0167] This application evaluates the utilization rate of silicon powder in silicon mud by calculating the yield of silicate and quartz sand, as well as the conversion rate of silicon powder. The results are shown in Table 1. The yield of silicate and quartz sand, as well as the conversion rate of silicon powder, are calculated by the following method:

[0168] Silicate yield = silicate mass / silicate mass theoretically produced from silicon powder × 100%;

[0169] Quartz sand yield = quartz sand mass / quartz sand mass that can be prepared theoretically from silicon powder × 100%;

[0170] Silicon powder conversion rate = (1-mass of silicon contained in solid impurities / mass of silicon powder) × 100%.

[0171] Table 1

[0172] According to Table 1, compared with Comparative Examples 1-3, the yield of silicate and quartz sand prepared in Examples 1-21 of the present application is significantly improved, which shows that the impurity components in the silicon mud can be effectively removed through acid soaking treatment and alcohol washing treatment, thereby improving the dispersibility of the silicon mud.

[0173] Compared with Example 1 and Example 10, the yields of silicate and quartz sand in Examples 2 and 3 of the present application are higher, which indicates that the catalyst having a cyclic ether structure and a hydroxyl structure can fully convert silicon powder into silicate and quartz sand.

[0174] The silicon powder conversion rates of Examples 1 and 5 of the present application are significantly higher than those of Example 4, which indicates that the effect of acid soaking of silicon mud using concentrated sulfuric acid and nitric acid is better than that of acid soaking using hydrochloric acid.

[0175] Compared with Examples 8 to 9 and 11 to 20, the yield of quartz sand prepared in Example 1 of the present application is higher, which indicates that the effective conversion rate of silicon powder can be improved by controlling the crushing and screening treatment in step 1), controlling the mass ratio of silicon mud to alcohol in the alcohol washing treatment, controlling the reaction temperature and pressure in step 2), controlling the concentration of the acidic catalyst in step 3), the amount of the acidic catalyst, the ratio of silicate to water, the temperature of the hydrolysis reaction, the pH when preparing the gel, the temperature of the silica sol when preparing the gel, the dealcoholization water treatment of the silicate, and the process parameters of the distillation treatment.

[0176] To make the objectives, technical solutions, and advantages of this application more clear, the above technical solutions of this application are clearly and completely described in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

Claims

1. A method for recycling silicon mud, wherein: include: 1) Pre-treating silicon mud to obtain silicon powder; 2) reacting the silicon powder with alcohol to obtain silicate; The pretreatment includes an acid soaking treatment and an alcohol washing treatment.

2. The method according to claim 1, wherein: The alcohol used in the alcohol washing treatment in step 1) is the same as the alcohol used in step 2).

3. The method according to claim 1 or 2, wherein: Also includes: Allowing the silicate to undergo a hydrolysis reaction with water to form a silica sol; After adding alkaline substances to the silica sol to obtain gel, the gel is washed until the pH is neutral and then calcined to obtain quartz sand.

4. The method according to any one of claims 1 to 3, wherein: The pretreatment includes: filtering, acid soaking, water washing, alcohol washing, crushing and screening the silicon mud in sequence; The acid used in the acid soaking treatment includes at least one of concentrated sulfuric acid and nitric acid; the mass ratio of the silicon mud to the alcohol used in the alcohol washing treatment is 1:(1-10).

5. The method according to claim 4, wherein: The alcohol washing treatment refers to a process of mixing the silicon mud after the water washing treatment with alcohol and subjecting the mixture to a standing treatment, wherein the standing treatment time is 2 to 12 hours.

6. The method according to claim 4 or 5, wherein: Use a 50-500 mesh filter to filter the silica mud.

7. The method according to any one of claims 1 to 6, wherein: The reaction in step 2) is carried out under the action of a catalyst, wherein the catalyst comprises at least one of a copper-containing catalyst and an alkali metal catalyst; The mass ratio of the silicon powder to the catalyst is 1:(0.1-1.5).

8. The method according to claim 7, wherein: The alkali metal catalyst includes an alkali metal alkoxide having an epoxy group and a hydroxyl group.

9. The method according to any one of claims 1 to 8, wherein: In step 2), the reaction pressure is 0.1-1.0 MPa and the temperature is 70-120°C.

10. The method according to any one of claims 1 to 9, wherein: The reaction liquid after the silicon powder and alcohol react is subjected to solid-liquid separation treatment, dealcoholization water treatment, and distillation treatment in sequence to obtain the silicate; The temperature of the dealcoholization water treatment is 100-150°C and the pressure is 0.1-0.5MPa; The temperature of the distillation treatment is 80-120° C. and the pressure is 0.1-0.5 MPa.

11. The method according to claim 10, wherein: After the dealcoholization water treatment and distillation treatment, the removed alcohol and the alcohol in the alcohol washing liquid produced by the alcohol washing treatment can be extracted from water, so that the alcohol is recycled to participate in the alcohol washing treatment of step 1) and the reaction of step 2), and the water is recycled to participate in the water washing treatment of step 1).

12. The method according to claim 3, wherein: The hydrolysis reaction is carried out under an acidic catalyst, and the acidic catalyst includes at least one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, formic acid, propionic acid, acetic acid, benzoic acid, and oxalic acid; The concentration of the acid catalyst is 0.1-2 mol / L; the mass ratio of the acid catalyst to the water is (0.1-0.5):1; the molar ratio of the silicate to the water is 1:(4-15).

13. The method according to claim 12, wherein: The acidic catalyst includes at least one of hydrochloric acid, oxalic acid, nitric acid and acetic acid.

14. The method according to claim 12 or 13, wherein: The concentration of the acid catalyst is 0.6-1.2 mol / L; the mass ratio of the acid catalyst to the water is (0.2-0.4):1; the molar ratio of the silicate to the water is 1:(8-12).

15. The method according to any one of claims 3 or 12-14, wherein: The temperature of the hydrolysis reaction is 40-90°C.

16. The method according to claim 15, wherein: The temperature of the hydrolysis reaction is 45-70°C.

17. The method according to any one of claims 3 or 12-16, wherein: The alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, ammonia water, methylamine, ethylamine, propylamine, tert-butylamine, p-toluidine, aniline, dimethylamine, ethylenediamine, ethanolamine, propylenediamine, vinylamine, sodium carbonate, calcium hydroxide, potassium carbonate, sodium bicarbonate, ammonium hydroxide, sodium dihydrogen phosphate, and potassium dihydrogen phosphate; When the alkaline substance is added, the temperature of the silica sol is controlled to be 10-30° C. higher than the temperature of the hydrolysis reaction.

18. The method according to claim 17, wherein: When the alkaline substance is added, the temperature of the silica sol is controlled to be 15-25° C. higher than the temperature of the hydrolysis reaction.

19. The method according to claim 17 or 18, wherein: The alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, ammonia water and ethylenediamine.

20. The method according to any one of claims 3 or 12-19, wherein: The alkaline substance is added to the silica sol to make the pH of the system be 7.5 to 12, followed by aging treatment for 1 to 12 hours to obtain the gel.

21. The method according to claim 20, wherein: The alkaline substance is added to the silica sol to make the pH of the system be 8.5-10.

5.

22. The method according to any one of claims 3 or 12-21, wherein: The calcination process includes a first calcination process and a second calcination process in sequence; The first calcination treatment is carried out in an oxygen-containing atmosphere at a temperature of 600 to 1000° C. for a time of 5 to 40 hours; The second calcination process is performed under vacuum conditions, the temperature is increased by 300 to 600° C. compared to the first calcination process, and the time is 3 to 30 hours.

23. The method according to claim 22, wherein: The temperature of the first calcination treatment is 650-900°C and the time is 8-32h; The temperature of the second calcination treatment is increased by 350-500° C. and the time is 5-16 hours compared to the first calcination treatment.

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