A method for reusing silica mud

Abstract

This invention provides a method for reusing silica sludge, comprising: 1) pretreating the silica sludge to obtain silica powder; the pretreatment including alcohol washing; 2) reacting the silica powder with alcohol to obtain silicate esters. This method can convert silica sludge from silicon wafer cutting into high-value silicate esters, broadening the application range of silica sludge and avoiding the waste of silica sludge resources.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical engineering, and specifically relates to a method for the reuse of silica mud. Background Technology

[0002] Silicon wafers for solar cells are made by cutting silicon blocks or rods using a multi-wire dicing machine. During the diamond wire dicing process of monocrystalline or polycrystalline silicon, silicon powder and other impurities are deposited into the cutting slurry, forming silicon sludge. Silicon sludge has high purity but is quite fine, and improper handling can cause environmental pollution and resource waste. Currently, there are several methods for recycling silicon sludge, such as: using silicon sludge with a liquid content (1-4%) to prepare silicon carbide, recovering nano-silicon from silicon sludge to prepare silicon / carbon composite materials, and using silicon sludge to prepare silicon particles and silicon filaments.

[0003] Based on this, how to further broaden the application scope of silica mud is a question that those skilled in the art continue to explore. Summary of the Invention

[0004] This invention provides a method for reusing silica mud, which can convert the silica mud generated during the cutting of silicon wafers into silicate esters, thereby making efficient use of silica mud and broadening its application range.

[0005] This invention provides a method for reusing silica mud, comprising:

[0006] 1) Pre-treat silica mud to obtain silica powder; the pre-treatment includes alcohol washing treatment;

[0007] 2) React the silicon powder with an alcohol to obtain a silicate ester;

[0008] The pretreatment includes acid soaking and alcohol washing.

[0009] According to one embodiment of the present invention, the method further includes: hydrolyzing the silicate ester with water to form a silica sol; adding an alkaline substance to the silica sol to obtain a gel; washing the gel until the pH is neutral; and then calcining the gel to obtain quartz sand.

[0010] According to one embodiment of the present invention, the pretreatment includes: sequentially filtering the silica mud, soaking it in acid, washing it with water, washing it with alcohol, and crushing and sieving it.

[0011] The acid used in the acid soaking treatment includes at least one of concentrated sulfuric acid and nitric acid; the mass ratio of the silica mud to the alcohol in the alcohol washing treatment is 1:(1-10).

[0012] According to one embodiment of the present invention, the reaction in step 2) is carried out in the presence of a catalyst, wherein the catalyst includes at least one of a copper-containing catalyst and an alkali metal catalyst;

[0013] The mass ratio of the silicon powder to the catalyst is 1:(0.1~1.5); and / or,

[0014] The reaction is carried out at a pressure of 0.1–1.0 MPa and a temperature of 70–120 °C.

[0015] According to one embodiment of the present invention, the reaction solution after the reaction of silicon powder and alcohol is subjected to solid-liquid separation treatment, alcohol removal water treatment, and distillation treatment in sequence to obtain the silicate ester;

[0016] The temperature for the de-alcoholization water treatment is 100–150°C, and the pressure is 0.1–0.5 MPa.

[0017] The distillation process is carried out at a temperature of 80–120°C and a pressure of 0.1–0.5 MPa.

[0018] According to one embodiment of the present invention, the hydrolysis reaction is carried out under an acidic catalyst, the acidic catalyst including 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;

[0019] 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 ester to the water is 1:(4–15).

[0020] According to one embodiment of the present invention, the temperature of the hydrolysis reaction is 40–90°C.

[0021] According to one embodiment of the present invention, the alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, ammonia, 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.

[0022] When adding the alkaline substance, the temperature of the silica sol is controlled to be 10-30°C higher than the temperature of the hydrolysis reaction.

[0023] According to one embodiment of the present invention, the alkaline substance is added to the silica sol to adjust the pH of the system to 7.5-12, followed by aging treatment for 1-12 hours to obtain the gel.

[0024] According to one embodiment of the present invention, the roasting process sequentially includes a first roasting process and a second roasting process;

[0025] The first calcination treatment is carried out in an oxygen-containing atmosphere at a temperature of 600–1000°C for 5–40 hours.

[0026] The second calcination process is carried out under vacuum conditions, with the temperature increased by 300–600°C compared to the first calcination process, and the time is 3–30 hours.

[0027] This invention pretreats the silica sludge generated from silicon wafer cutting through acid immersion and alcohol washing, thereby converting the silica sludge into silicate esters. This broadens the application of silica sludge, avoids the waste of silica sludge resources, and has both economic and environmental significance. Attached Figure Description

[0028] Figure 1 This is a schematic flowchart of the silica mud reuse method according to Embodiments 1 to 21 of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a method for reusing silica mud, comprising:

[0031] 1) Pre-treat the silica mud to obtain silica powder;

[0032] 2) React silicon powder with alcohol to obtain silicate ester;

[0033] The pretreatment includes acid soaking and alcohol washing.

[0034] The present invention does not limit the alcohol used in the alcohol washing treatment in step 1). For example, it may be methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, etc.

[0035] The present invention is not limited to the acid used in the acid soaking treatment in step 1). For example, it can be concentrated sulfuric acid, hydrochloric acid, nitric acid, etc.

[0036] The present invention 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). However, from the perspective of recycling cost, it is preferred to be the same.

[0037] Acid soaking can dissolve and remove metallic impurities from silica sludge. Alcohol washing can remove organic matter and residual chemical reagents from the surface of the silica sludge, reduce surface tension, and improve the dispersibility of the silica sludge. In practice, acid soaking should be performed first, followed by alcohol washing, to ensure that organic matter and residual chemical reagents on the surface of the silica sludge are fully removed, which is beneficial for the preparation of silicate esters.

[0038] By pretreating silica mud with acid immersion and alcohol washing, the obtained silica powder can be converted into silicate esters with a conversion rate of not less than 70% and a yield of not less than 60%, effectively avoiding resource waste and realizing the sustainable value of silica mud.

[0039] It is understood that after acid soaking and alcohol washing, the silica powder in the silica sludge remains in the alcohol washing solution. The silica sludge needs to be separated from the alcohol washing solution and dried to obtain the silica powder. Therefore, in practice, the silica sludge can be separated from the alcohol washing solution by centrifugation. This invention does not limit the specific method of drying; for example, it can be vacuum drying, hot air drying, etc.

[0040] It should be explained that during the reaction, the alcohol should be controlled to be in excess relative to the silicon powder to ensure that the silicon powder is fully converted into silicate ester. Hydrogen gas is generated during the conversion of silicon powder into silicate ester; therefore, this invention can determine whether the reaction is complete by monitoring whether more hydrogen gas is being generated.

[0041] In this invention, the reaction solution after the reaction of silicon powder and alcohol includes alcohol, water, and solid impurities. The alcohol originates from excess reactants; due to the presence of hydroxyl groups on the surface of silicon powder, it reacts with alcohol to produce water; simultaneously, the pretreated silicon powder may still contain other impurities that cannot react with alcohol to prepare silicate esters, thus existing as solid impurities in the reaction solution after the silicon powder and alcohol reaction; therefore, post-treatment of the reaction solution is necessary to separate the silicate esters from the product.

[0042] In one embodiment, silica sol obtained by the hydrolysis of silicate esters can be used as a raw material for preparing quartz sand. Specifically, silicate esters are hydrolyzed with water to form silica sol; an alkaline substance is added to the silica sol to obtain a gel, which is then washed until the pH is neutral and calcined to obtain quartz sand.

[0043] Converting silicate esters into silica sol first can yield gels with better uniformity and avoid gel agglomeration during the gelation process, which would cause some silicon sources to be encapsulated and unable to be converted into quartz sand.

[0044] 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.

[0045] The above methods can further broaden the application scope of silica mud.

[0046] It should be noted that after washing the gel to a neutral pH, the gel contains residual moisture, which needs to be dried to remove the moisture from the wet gel, thereby avoiding damage to the calcination equipment caused by directly calcining the wet gel; specifically, the drying temperature is 100-300℃ and the time is 1-12h.

[0047] In step 1) above, the pretreatment includes: sequentially filtering the silica mud, acid soaking, water washing, alcohol washing, and crushing and sieving.

[0048] The acid used in the acid soaking treatment includes at least one of concentrated sulfuric acid and nitric acid; the mass ratio of alcohol in the silica mud and alcohol washing treatment is 1:(1-10).

[0049] The above filtration process can be carried out using conventional filtration methods, such as vacuum filtration, pressure filtration, centrifugal filtration, membrane filtration, sedimentation filtration, etc.

[0050] The above-mentioned acid soaking treatment refers to immersing the solid obtained after filtration in an acid solution. This invention does not limit the specific amount of acid and silica mud used in the acid soaking treatment process, as long as it ensures that the silica mud can be completely soaked in the acid solution.

[0051] Water washing is achieved by rinsing the acid-soaked silica mud with deionized water.

[0052] Alcohol washing treatment refers to the process of mixing water-washed silica sludge with alcohol and allowing it to stand. Preferably, the standing time is 2 to 12 hours.

[0053] This invention does not limit the specific conditions of the crushing and sieving process, as long as it can produce silicon powder of uniform size.

[0054] By sequentially filtering, acid soaking, water washing, and alcohol washing, large impurities, foreign matter, metallic impurities, organic matter, and residual chemical reagents in the silica mud can be removed, which is beneficial for obtaining high-purity silica powder and thus for preparing silicate esters. Through crushing and sieving, silica powder with uniform particle size can be obtained, which facilitates the conversion of silica powder into silicate esters and quartz sand.

[0055] In the specific pretreatment process, when the above-mentioned acid solution is used for acid immersion treatment, the silicon powder conversion rate is higher, and the yield of silicate ester and quartz sand is also better.

[0056] Furthermore, when the mass ratio of silica mud to alcohol in the alcohol washing process is controlled to be 1:(1~10), the surface tension of the silica mud can be effectively reduced, the dispersibility of the silica mud can be improved, which is beneficial to converting the silica mud into silicate esters and avoiding the waste of alcohol solvent.

[0057] It is understood that the size of the filter screen affects the filtration effect during filtration. Therefore, this invention preferably uses a 50-500 mesh (297-30μm) filter screen to filter the silica sludge. During the alcohol washing process, simply allowing the mixture to stand is too slow; therefore, the mixture of silica sludge and alcohol can be stirred first, followed by standing, to accelerate the alcohol washing process.

[0058] The reaction in step 2) above is carried out in the presence of a catalyst, which includes at least one of a copper-containing catalyst and an alkali metal catalyst.

[0059] The mass ratio of the silicon powder to the catalyst is 1:(0.1 to 1.5).

[0060] This invention does not limit the specific type of copper-containing catalyst, which may include copper, copper oxide, etc.

[0061] This invention does not limit the specific type of alkali metal catalyst, but includes alkali metal salts, alkali metal alkoxides, etc., and alkali metals include sodium, potassium, lithium, rubidium, cesium, etc.

[0062] Studies have shown that alkali metal alkoxides with epoxy and hydroxyl groups can significantly improve the yield of silicate esters and quartz sand when catalyzing the reaction of silicon powder with alcohols. Therefore, the present invention preferably uses alkali metal alkoxides with epoxy and hydroxyl groups to catalyze the reaction of silicon powder with alcohols. Exemplarily, the alkali metal alkoxides with epoxy and hydroxyl groups can be 1,4-dioxane-hexanol, 1,3-dioxane-pentanol, 1,3-trioxane-pentanol, 2-oxacyclopentane-1-ol, 3-oxacyclohexanol, 2-oxacyclooctane-1-ol, 2-oxacyclononane-1-ol, 3-oxacycloheptane-1-ol, 4-oxacyclohexanol, 1,4-dioxane-heptane, and 2-oxacycloheptane-1-ol.

[0063] In this invention, the pressure for the reaction between silicon powder and alcohol is 0.1–1.0 MPa, and the temperature is 70–120 °C.

[0064] Under these conditions, the reaction is easy to operate and requires less sophisticated equipment, which helps reduce the cost of silicate preparation. To improve the utilization rate of the alcohol, the reaction can also be carried out under reflux.

[0065] Of course, the reaction can also be carried out under 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 the alcohol will boil and produce vapor, resulting in waste of raw materials.

[0066] After the reaction in step 2) is completed, the reaction solution after the reaction of silicon powder and alcohol is subjected to solid-liquid separation treatment, alcohol removal water treatment and distillation treatment in sequence to obtain silicate ester;

[0067] The temperature for treating the de-alcoholized water is 100–150℃, and the pressure is 0.1–0.5 MPa.

[0068] The distillation process is carried out at a temperature of 80–120℃ and a pressure of 0.1–0.5 MPa.

[0069] The above solid-liquid separation process can remove solid impurities from the reaction solution; the alcohol removal process can remove alcohol and water from the reaction solution; and the distillation process can remove byproducts from the reaction solution.

[0070] The above process enables the post-treatment of the reaction solution after the reaction of silicon powder and alcohol to obtain high-purity silicate esters, which is beneficial for the preparation of quartz sand.

[0071] In practical implementation, this invention does not limit the specific form of solid-liquid separation treatment; for example, it can be centrifugal separation or filtration separation. Given that the reaction liquid contains fine-particle silicate solids, traditional filtration methods are difficult to effectively separate them, while centrifugal separation can fully utilize the centrifugal force generated by high-speed rotation to quickly and effectively separate the liquid and solid phases. At the same time, centrifugal separation equipment has lower investment and operating costs and is simpler to operate, making it more suitable for the application scenario of this invention as a small-scale experimental study. Therefore, centrifugal separation technology is preferred to improve solid-liquid separation efficiency and obtain high-purity silicate products.

[0072] The above-mentioned treatment of the de-alcoholized water and the distillation process are carried out in a de-alcoholized water tower and a distillation tower, respectively. This invention does not limit the specific types of the de-alcoholized water tower and the distillation tower; they can be tray type or packed type. In the de-alcoholized water tower, alcohol and water are separated from the top, and the bottom material containing silicates enters the distillation tower; in the distillation tower, silicates are separated from the top, and impurities are separated from the bottom.

[0073] After the above-described alcohol removal water treatment and distillation, the removed alcohol and the alcohol washing liquid produced by the alcohol washing treatment can both be used to extract alcohol from water, allowing the alcohol to be recycled to participate in the alcohol washing treatment in step 1) and the reaction in step 2). The resulting water can also be recycled to participate in the water washing treatment in step 1). This invention can also treat solid impurities obtained from solid-liquid separation. By performing chemical analysis and physical testing on the solid impurities, a reasonable treatment method can be obtained to avoid environmental pollution from solid impurities. For example, the treatment method may include washing, extraction, calcination, and recrystallization. Based on this, this invention can significantly reduce raw material costs and reduce waste liquid and solid impurity emissions, possessing both environmental and economic value.

[0074] In this invention, the hydrolysis reaction is carried out under an acidic catalyst, which 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.

[0075] 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 silicate ester to water is 1:(4–15).

[0076] The acidic catalyst is preferably at least one of hydrochloric acid, oxalic acid, nitric acid, and acetic acid. In this invention, the selection of the acidic catalyst takes into account factors such as catalytic activity, operational safety, and environmental friendliness. Hydrochloric acid and nitric acid, being strong inorganic acids, are highly effective at catalyzing hydrolysis reactions; oxalic acid and acetic acid, being organic acids, are naturally sourced and have minimal environmental impact; furthermore, hydrochloric acid and nitric acid are highly water-soluble; and oxalic acid and acetic acid have fewer inorganic salts, making them safer and more convenient to use and operate. Considering catalytic performance, environmental impact, and usability, this invention preferably selects one or more of hydrochloric acid, oxalic acid, nitric acid, and acetic acid as the acidic catalyst to achieve optimal results in catalytic activity and practical applications.

[0077] Because silicates undergo both hydrolysis to produce silica sol and polycondensation to produce gel, these two processes compete with each other. If the polycondensation rate is too fast, the resulting gel can encapsulate the silica sol, inhibiting the full utilization of silicon. However, under the action of an acidic catalyst of the aforementioned concentration, controlling the amounts of acidic catalyst, water, and silicate ensures that the hydrolysis rate is greater than the polycondensation rate, allowing the silicate to be fully converted into silica sol, and thus into quartz sand. Therefore, this invention controls the concentration of the acidic catalyst to 0.1–2 mol / L, the mass ratio of acidic catalyst to water to be (0.1–0.5):1, and the molar ratio of 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 acidic catalyst to water to be (0.2–0.4):1, and the molar ratio of silicate to water to be 1:(8–12), the conversion of silicate to silicate can be further promoted.

[0078] In the specific implementation process, the hydrolysis reaction temperature is 40–90℃, preferably 45–70℃. Temperature control of the hydrolysis reaction is crucial for optimizing yield and quality. Too low a temperature results in a slow reaction, while too high a temperature can trigger complex side reactions. This invention optimizes the temperature range of 45–70℃, balancing reaction rate, yield, and quality. This temperature range provides a moderate reaction rate, is easy to operate and control, prevents reaction stagnation, avoids side reactions, and enables the production of higher yields and higher quality quartz sand.

[0079] The alkaline substances added to the silica sol in this invention include at least one of sodium hydroxide, potassium hydroxide, ammonia, 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.

[0080] When adding the alkaline substance, the temperature of the silica sol is controlled to be 10-30°C higher than the temperature of the hydrolysis reaction.

[0081] In specific implementation, sodium hydroxide, potassium hydroxide, ammonia, and ethylenediamine are preferred as alkaline substances added to silica sol, mainly 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 handle, while organic amines such as ammonia and ethylenediamine are naturally sourced and have little environmental impact. Therefore, this invention preferentially uses the above-mentioned alkaline substances to participate in the reaction, ensuring both good reaction results and operational convenience and environmental friendliness.

[0082] When the alkaline substance is added, controlling the temperature of the silica sol to be 10–30°C higher than the hydrolysis reaction temperature can reduce the likelihood of gel agglomeration, improve the uniformity and stability of the gel, and avoid the problem of silicon not being converted into quartz sand due to gel agglomeration, thus preventing resource waste. Therefore, controlling the temperature of the silica sol to be 10–30°C higher than the hydrolysis reaction temperature is beneficial for obtaining high-quality quartz sand. Further, this temperature is preferably 15–25°C higher than the hydrothermal reaction temperature.

[0083] According to the inventor's research, an alkaline substance is added to the silica sol to make the pH of the system 7.5-12, followed by aging treatment for 1-12 hours to obtain a gel.

[0084] The inventors discovered that excessively high or low pH values ​​can lead to uncontrolled gel formation rate and gelation degree, affecting the uniformity of the gel structure and hindering the production of hard, dense, high-quality quartz sand. Controlling the pH value between 7.5 and 12 effectively controls the reaction rate and extent, ensuring good gel properties and structural uniformity, and providing high reproducibility of the experiment. Preferably, the pH value is between 8.5 and 10.5.

[0085] Meanwhile, the addition of alkaline substances allows the silica sol to age for 1–12 hours under alkaline conditions, which promotes the strengthening of the gel skeleton and further facilitates the production of high-quality quartz sand.

[0086] In practice, the pH value of the silica sol during the aging process can be monitored to understand the reaction status during gel formation in real time, and the pH value can be fine-tuned according to actual needs to optimize the uniformity of the gel.

[0087] Further research revealed that the roasting process sequentially includes a first roasting process and a second roasting process.

[0088] The first calcination treatment is carried out in an oxygen-containing atmosphere at a temperature of 600–1000℃ for 5–40 hours.

[0089] The second calcination process is carried out under vacuum conditions, with the temperature increased by 300–600°C compared to the first calcination process, and the time is 3–20 hours.

[0090] The oxygen-containing atmosphere mentioned above can be air, pure oxygen, or any gas mixed with oxygen in an inert gas.

[0091] After the first calcination treatment, the organic matter in the gel can be oxidized and decomposed, thereby improving the purity of the quartz sand. At the same time, oxygen can also fully convert the silicon element in the gel into silicon oxide, helping to stabilize the gel structure and strengthen the silicon-oxygen-silicon bonds, which is beneficial for obtaining quartz sand. The preferred temperature for the first calcination treatment is 650-900℃, and the preferred time is 8-32h. Within this temperature and time range, organic matter can be fully removed without affecting the silicon oxide structure, ensuring complete oxidation and decomposition of organic matter. Furthermore, this process is highly repeatable and efficient, thus obtaining high-quality quartz sand at low cost.

[0092] The second calcination process is carried out under vacuum conditions, and the temperature is controlled to be higher than that of the first calcination process. This allows the hydroxyl groups in the gel to be removed quickly and effectively, thereby obtaining quartz sand. Preferably, the temperature of the second calcination process is 350–500°C higher than that of the first calcination process, and the time is 5–16 hours.

[0093] The present invention will now be described in more detail through specific embodiments.

[0094] The process flow of the silica mud recycling method in Examples 1-21 of this invention is as follows: Figure 1 As shown.

[0095] Example 1

[0096] A method for reusing silica mud includes the following steps:

[0097] 1) Filter the silica mud using a 200-mesh filter.

[0098] The filtered silica mud was completely immersed in concentrated sulfuric acid for acid soaking treatment.

[0099] The silica mud after acid soaking is washed with water.

[0100] The silica mud after water washing was mixed with ethanol and stirred, and then left to stand for 2 hours to complete the alcohol washing treatment; the mass ratio of silica mud to ethanol was 1:5.

[0101] The silica mud, after being washed with alcohol, is then centrifuged, dried, pulverized, and sieved to obtain silica powder; the particle size of the obtained silica powder is less than 200 mesh.

[0102] 2) React silicon powder with excess ethanol under the catalysis of sodium ethoxide. When no more hydrogen is produced, the reaction is complete. Centrifuge the reaction solution and send the separated liquid to a de-alcoholization water tower for de-alcoholization water treatment. Then send the bottom liquid of the de-alcoholization water tower to a distillation tower for distillation treatment to obtain silicate ester.

[0103] The mass ratio of silica powder to sodium ethoxide is 1:0.2, the reaction temperature is 80℃, and the pressure is 0.2MPa; the temperature of the de-alcoholization water tower is 120℃, and the pressure is 0.2MPa; the temperature of the distillation tower is 100℃, and the pressure is 0.1MPa.

[0104] 3) Mix silicate ester with water, then add 1 mol / L hydrochloric acid, and carry out a hydrolysis reaction at 60℃ to form silica sol; wherein the molar ratio of silicate ester to water is 1:11.6, and the mass ratio of hydrochloric acid to water is 0.25:1;

[0105] 4) Raise the temperature of the silica sol to 80°C, add 28% ammonia solution dropwise until the pH reaches 10, and then age it for 1 hour to form a gel.

[0106] Wash the gel until neutral and dry it at 120°C for 8 hours;

[0107] The dried product was placed in an air atmosphere and heated from 50°C to 800°C and held for 6 hours at a heating rate of 2°C / min. Then, a vacuum was drawn to an absolute pressure of 5 Pa, and the temperature was increased from 800°C to 1400°C and held for 24 hours. Finally, it was cooled to obtain quartz sand.

[0108] 5) The alcohol washing liquid obtained from the centrifugal separation process in step 1) and the alcohol-water mixture obtained from the de-alcoholization water treatment in step 2) are transported to the alcohol extraction tower. The alcohol obtained is recycled to participate in the alcohol washing treatment in step 1) and the reaction in step 2), and the water obtained is recycled to participate in the water washing treatment in step 1).

[0109] Example 2

[0110] The difference between this embodiment and Example 1 is that the catalyst used is potassium 1,4-dioxanehexanoate, whose structural formula is:

[0111]

[0112] Example 3

[0113] The difference between this embodiment and Example 1 is that the catalyst used is sodium 3-oxacyclohexane-1-ol, whose structural formula is:

[0114]

[0115] Example 4

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

[0117] Example 5

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

[0119] Example 6

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

[0121] Example 7

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

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

[0124] In step 3), the mass ratio of silicate ester to water is 1:1.5, the acid 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℃.

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

[0126] Example 8

[0127] The difference between this embodiment and Embodiment 1 is that the silica mud was not crushed and sieved.

[0128] Example 9

[0129] The difference between this embodiment and Embodiment 1 is that the mass ratio of silica 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 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 ester is increased so that the mass ratio of silicate ester 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℃.

[0142] Example 16

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

[0144] Example 17

[0145] The difference between this embodiment and Embodiment 1 is that when adding alkaline substances, the pH is controlled at 12.

[0146] Example 18

[0147] The difference between this embodiment and Embodiment 1 is that when adding alkaline substances, the pH is controlled at 7.5.

[0148] Example 19

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

[0150] Example 20

[0151] The difference between this embodiment and Embodiment 1 is that the temperature of the de-alcoholized water treatment is 90°C and the pressure is 0.3 MPa.

[0152] The distillation process was carried out at a temperature of 75°C and a pressure of 0.15 MPa.

[0153] Example 21

[0154] The difference between this embodiment and Embodiment 1 is that in step 1), the mass ratio of silica mud to alcohol used in the 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℃.

[0156] The temperature for the de-alcoholization water treatment was 125℃ and the pressure was 0.25MPa, while the temperature for the distillation treatment was 105℃ and the pressure was 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, the molar ratio of silicate ester to water is 1:6, and the hydrolysis reaction temperature is 90℃.

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

[0159] The dried product was placed in an air atmosphere and heated from 50°C to 600°C and held for 40 hours at a heating rate of 2°C / min. Then, a vacuum was drawn to an absolute pressure of 5 Pa, and the temperature was increased from 800°C to 1100°C and held for 3 hours. Finally, it was 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 silica mud was 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 silica mud was not subjected to acid soaking or alcohol washing treatment.

[0164] Comparative Example 3

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

[0166] Experimental Example 1

[0167] This invention evaluates the utilization rate of silica powder in silica sludge by calculating the yields of silicate esters and quartz sand, as well as the conversion rate of silica powder. The results are shown in Table 1. The yields of silicate esters and quartz sand, and the conversion rate of silica powder, were calculated using the following method:

[0168] Silicate yield = mass of silicate / theoretical mass of silicate that can be prepared from silicon powder × 100%;

[0169] Quartz sand yield = (mass of quartz sand / theoretically achievable mass of quartz sand from silica powder) × 100%;

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

[0171] Table 1

[0172] Examples / Comparative Examples Silicate yield (%) Quartz sand yield (%) Silica powder conversion rate (%) Example 1 68.7 64.1 82.3 Example 2 72.4 68.5 81.6 Example 3 88.4 83.5 92.5 Example 4 64.2 61.1 70.5 Example 5 75.9 71.3 85.1 Example 6 71.3 68.4 79.9 Example 7 69.1 66.2 85.7 Example 8 63.2 59.7 79.1 Example 9 66.3 62.5 81.7 Example 10 69.6 65.9 80.2 Example 11 64.5 60.8 81.2 Example 12 68.9 63.9 81.5 Example 13 68.9 63.9 82.1 Example 14 69.0 63.8 83.4 Example 15 69.2 63.6 82.8 Example 16 68.8 63.3 83.2 Example 17 68.9 63.9 82.6 Example 18 69.1 63.7 81.7 Example 19 69.2 63.6 82.3 Example 20 69.1 63.7 82.1 Example 21 67.3 64.3 81.1 Comparative Example 1 37.4 34.3 50.7 Comparative Example 2 28.6 26.4 42.8 Comparative Example 3 28.7 26.9 43.7

[0173] As shown in Table 1, compared with Comparative Examples 1-3, the yields of silicate esters and quartz sand prepared in Examples 1-21 of the present invention were significantly improved. This indicates that acid soaking and alcohol washing treatment can effectively remove impurity components in silica mud and improve the dispersibility of silica mud.

[0174] Compared to Examples 1 and 10, Examples 2 and 3 of the present invention have higher yields of silicate esters and quartz sand, indicating that catalysts with cyclic ether structures and hydroxyl structures can fully convert silicon powder into silicate esters and quartz sand.

[0175] The silicon powder conversion rates in Examples 1 and 5 of this invention are significantly higher than those in Example 4, indicating that acid soaking treatment of silica mud with concentrated sulfuric acid and nitric acid is more effective than acid soaking treatment with hydrochloric acid.

[0176] Compared to Examples 8-9 and 11-20, the quartz sand prepared in Example 1 of this invention has a higher yield. This indicates that the effective conversion rate of silica powder can be improved by controlling the crushing and sieving process in step 1), controlling the mass ratio of silica mud to alcohol in the alcohol washing process, controlling the reaction temperature and pressure in step 2), controlling the concentration and amount of acidic catalyst in step 3), the ratio of silicate ester to water, the temperature of the hydrolysis reaction, the pH during gel preparation, the silica sol temperature during gel preparation, and the process parameters of de-alcoholization water treatment and distillation treatment of silicate ester.

[0177] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention have been clearly and completely described above in conjunction with specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

Claims

1. A method for reusing silica mud, characterized in that, include: 1) Pre-treat the silica mud to obtain silica powder; The pretreatment includes: sequentially filtering the silica mud, acid soaking, water washing, alcohol washing, and crushing and sieving; the acid used in the acid soaking treatment includes at least one of concentrated sulfuric acid and nitric acid; the mass ratio of the silica mud to the alcohol in the alcohol washing treatment is 1:(1~10). 2) React the silicon powder with alcohol, and then subject the reaction solution after the reaction of silicon powder and alcohol to solid-liquid separation, de-alcoholization, and distillation to obtain silicate ester; The reaction is carried out in the presence of a catalyst, which includes at least one of a copper-containing catalyst and an alkali metal catalyst; the mass ratio of silicon powder to the catalyst is 1:(0.1~1.5). The reaction is carried out at a pressure of 0.1~1.0 MPa and a temperature of 70~120℃; the de-alcoholization water treatment is carried out at a temperature of 100~150℃ and a pressure of 0.1~0.5 MPa. The distillation process is carried out at a temperature of 80~120℃ and a pressure of 0.1~0.5MPa.

2. The method according to claim 1, characterized in that, Also includes: The silicate ester is hydrolyzed with water to form a silica sol; After adding an alkaline substance to the silica sol to obtain a gel, the gel is washed until the pH is neutral and then calcined to obtain quartz sand.

3. The method according to claim 2, characterized in that, The hydrolysis reaction is carried out under an acidic catalyst, which 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 acidic catalyst is 0.1~2 mol / L; the mass ratio of the acidic catalyst to the water is (0.1~0.5):1; the molar ratio of the silicate ester to the water is 1:(4~15).

4. The method according to claim 2 or 3, characterized in that, The hydrolysis reaction occurs at a temperature of 40~90℃.

5. The method according to claim 4, characterized in that, The alkaline substance includes at least one of sodium hydroxide, potassium hydroxide, ammonia, 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 adding the alkaline substance, the temperature of the silica sol is controlled to be 10-30°C higher than the temperature of the hydrolysis reaction.

6. The method according to claim 5, characterized in that, The alkaline substance is added to the silica sol to adjust the pH of the system to 7.5-12, followed by aging treatment for 1-12 hours to obtain the gel.

7. The method according to claim 5 or 6, characterized in that, The roasting process includes a first roasting process and a second roasting process in sequence. The first calcination treatment is carried out in an oxygen-containing atmosphere at a temperature of 600~1000℃ for 5~40h; The second calcination process is carried out under vacuum conditions, with the temperature increased by 300~600℃ compared to the first calcination process, and the time is 3~30h.

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