A method and system for preparing sodium silicate from waste silica sludge

Abstract

This invention provides a method and system for preparing sodium silicate from waste silica sludge. The method includes the following steps: 1) sequentially subjecting the waste silica sludge to acid washing, water washing, and pulverization to obtain silicon powder and silicon carbide with a particle size of 200-300 mesh; 2) sequentially subjecting the silicon powder and silicon carbide to magnetic separation and oxidation to obtain silicon dioxide; 3) reacting the silicon dioxide with sodium hydroxide to obtain sodium silicate. The method and system of this invention enable efficient utilization of waste silica sludge, and the obtained sodium silicate has high purity.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering technology, specifically to a method and system for preparing sodium silicate from waste silica sludge. Background Technology

[0002] Monocrystalline silicon is a relatively reactive non-metallic element widely used in strategic emerging industries such as photovoltaic power generation and semiconductors. Currently, monocrystalline silicon wafers are the mainstream application form of monocrystalline silicon, which are obtained by cutting monocrystalline silicon ingots. Due to the friction of the cutting wire, a large amount of silicon powder is usually generated during the production of monocrystalline silicon. At the same time, the use of cutting fluid and cutting wires also leads to the doping of silicon powder (approximately 50-73% of the total waste silicon sludge), silicon carbide (approximately 20 wt% of the total waste silicon sludge), metals, organic matter, and other impurities into the silicon powder, forming waste silicon sludge, causing environmental pollution and resource waste. How to utilize the waste silicon sludge from monocrystalline silicon wafer cutting in a high-value manner has become a major challenge facing the industry.

[0003] However, in the existing technology, when using waste silica sludge to prepare high value-added products, silicon carbide is usually ignored. It is not only not removed from the waste silica sludge, but also not converted into high value-added products. This results in a low utilization rate of waste silica sludge, and the incomplete removal of metal impurities will also result in a large number of impurities in the high value-added products.

[0004] Therefore, how to improve the utilization rate of waste silica sludge and convert it into high-purity products is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for preparing sodium silicate from waste silica sludge, which simultaneously converts silicon powder and silicon carbide in the waste silica sludge into sodium silicate, thereby improving the utilization rate of waste silica sludge and obtaining high-purity sodium silicate.

[0006] This invention provides a method for preparing sodium silicate from waste silica sludge, comprising the following steps:

[0007] 1) The waste silicon mud is subjected to acid washing, water washing and crushing treatment in sequence to obtain silicon powder and silicon carbide with a particle size of 200-300 mesh.

[0008] 2) The silicon powder and silicon carbide are subjected to magnetic separation and oxidation treatments in sequence to obtain silicon dioxide;

[0009] 3) React the silicon dioxide with sodium hydroxide to obtain sodium silicate.

[0010] According to one embodiment of the present invention, the acid used in the acid washing treatment includes at least one of salicylic acid, benzoic acid, and levulinic acid, as well as an inorganic acid.

[0011] According to one embodiment of the present invention, the volume ratio of the waste silica sludge to the acid used in the acid washing treatment is 1:(1.5-6).

[0012] According to one embodiment of the present invention, the volume ratio of the waste silica sludge to the water used for water washing treatment is 1:(5-50).

[0013] According to one embodiment of the present invention, the magnetic separation process takes 10 to 20 minutes and the magnetic field strength is 1.2 to 1.6 T.

[0014] According to one embodiment of the present invention, the silica reacts with an aqueous solution of sodium hydroxide in the presence of a VPM catalyst, the VPM catalyst being prepared by a method comprising the following steps:

[0015] Vanadium oxide, phosphoric acid, aromatic alcohol, fatty alcohol, and surfactant are mixed and reacted at 140–150 °C and 0.4–0.6 MPa for 1–3 h with stirring to obtain the precursor.

[0016] The precursor is calcined to obtain the VPM catalyst;

[0017] The calcination process is carried out in an oxygen atmosphere at a temperature of 500-600℃ for 6-12 hours; the molar ratio of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol is 1:(1.2-2.5):(2-4):(10-50); and the mass ratio of the total mass of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol to the mass of surfactant is 100:(1-5).

[0018] The vanadium oxide includes at least one of vanadium pentoxide and vanadium trioxide; the aromatic alcohol includes at least one of phenol, benzyl alcohol, and phenylethanol; the fatty alcohol includes at least one of isopropanol, isobutanol, and isopentyl glycol; and the surfactant includes at least one of Tween-80, PEG-1500, fatty alcohol polyoxyethylene ether, and propylene glycol monooleate.

[0019] According to one embodiment of the present invention, the mass ratio of silicon dioxide to catalyst is 1:(0.01 to 0.1).

[0020] According to one embodiment of the present invention, the product generated by the reaction of silicon dioxide and the aqueous solution of sodium hydroxide is filtered to obtain a solid substance, which is then recycled to react with the aqueous solution of sodium hydroxide.

[0021] According to one embodiment of the present invention, the silica and an aqueous solution of sodium hydroxide are reacted at 0-0.2 MPa and 100-120°C for 1-3 hours to obtain sodium silicate;

[0022] The concentration of the sodium hydroxide aqueous solution is 10-32%.

[0023] According to one embodiment of the present invention, the oxidation treatment includes: reacting the silicon powder and silicon carbide with oxygen to obtain silicon dioxide; the reaction temperature is 900-1400°C and the time is 1-3 hours.

[0024] The method of the present invention can simultaneously convert silicon powder and silicon carbide in waste silica sludge into sodium silicate, and the prepared sodium silicate has a low impurity content, thus realizing the efficient recycling of waste silica sludge. Attached Figure Description

[0025] Figure 1 This is the process flow for preparing sodium silicate in Example 1 of the present invention. Detailed Implementation

[0026] 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.

[0027] This invention provides a method for preparing sodium silicate from waste silica sludge, comprising the following steps:

[0028] 1) The waste silica mud is subjected to acid washing, water washing and crushing treatment in sequence to obtain silicon powder and silicon carbide with a particle size of 200-300 mesh.

[0029] 2) Silicon powder and silicon carbide are subjected to magnetic separation and oxidation treatments in sequence to obtain silicon dioxide;

[0030] 3) React silicon dioxide with sodium hydroxide to obtain sodium silicate.

[0031] The present invention does not limit the type of acid used in the above-mentioned acid washing treatment, and may select sulfuric acid, hydrochloric acid, nitric acid, formic acid, acetic acid, phosphoric acid, benzoic acid, oxalic acid, levulinic acid, salicylic acid, etc.

[0032] This invention does not limit the specific method of oxidation treatment. It can be a reaction between silicon powder and silicon carbide and any oxygen-containing substance, as long as the silicon powder and silicon carbide can be converted into silicon dioxide.

[0033] This invention does not limit the reaction method between silicon dioxide and sodium hydroxide; it can be a reaction between sodium hydroxide solution and silicon dioxide, or a reaction between solid sodium hydroxide and silicon dioxide, as long as sodium silicate is obtained. The amounts of silicon dioxide and sodium hydroxide can also be adjusted according to the desired modulus of sodium silicate.

[0034] By acid washing the waste silica sludge, impurities such as metals and organic matter can be dissolved. The dissolved impurities are then separated from the silicon powder and silicon carbide in the waste silica sludge by water washing. Magnetic separation of the silicon powder containing silicon carbide can remove the metal impurities that are inevitably introduced during the pulverization process. Then, the silicon powder containing silicon carbide is oxidized to obtain silicon dioxide with low impurity content.

[0035] The method of the present invention can remove impurities such as metals and organic matter from waste silica sludge, convert silicon powder and silicon carbide in waste silica sludge into silicon dioxide, and then convert silicon dioxide into sodium silicate, which significantly improves the utilization rate of waste silica sludge and reduces impurities in sodium silicate.

[0036] It should be noted that the particle size of silicon powder has a significant impact on its conversion rate. When the particle size is too large, the silicon powder cannot be fully oxidized; while when the particle size is too small, the silicon powder is prone to agglomeration, which also leads to insufficient conversion of silicon carbide and elemental silicon into silicon dioxide. By controlling the particle size of silicon powder to 200-300 mesh, the silicon powder can be fully converted into silicon dioxide, with a conversion rate as high as 99%, thus enabling efficient utilization of waste silica sludge.

[0037] It is understood that the waste silica sludge after water washing exists in a slurry form. Directly sending it to crusher is energy-intensive, causes significant damage to equipment, and easily clogs pipes and valves. Therefore, this invention includes a drying process after water washing, followed by crushing to obtain silicon powder and silicon carbide with a particle size of 200-300 mesh. The drying temperature is 100-120°C, and the time is 30-60 minutes. For energy saving and improved production efficiency, the drying temperature is preferably 100°C, and the time is preferably 50 minutes.

[0038] In specific implementation, in order to accelerate the dissolution rate of impurities on the surface of waste silica mud by acid and ensure that the impurities on the surface of waste silica mud are fully dissolved, the present invention also stirs the waste silica mud in the acid solution for 20-120 minutes and at a stirring rate of 100-900 rpm.

[0039] Similarly, considering the impurity removal rate and effect, the present invention also stirs the mixture of waste silica mud and water for 20-120 min and 100-900 rpm.

[0040] Meanwhile, to ensure that silicon dioxide and sodium hydroxide react fully, the mixture of silicon dioxide and sodium hydroxide can be stirred at a speed of 100-300 rpm, and the stirring time can be adjusted according to the actual situation.

[0041] In this invention, the acids used in the acid washing treatment include at least one of salicylic acid, benzoic acid, and levulinic acid, as well as an inorganic acid. Compared with the traditional method of using sulfuric acid, hydrochloric acid, or other inorganic acids alone, using the above-mentioned organic and inorganic acids simultaneously to wash waste silica sludge results in better impurity removal and is more conducive to improving the purity of sodium silicate.

[0042] In practice, controlling the volume ratio of waste silica sludge to acid used in acid washing treatment to 1:(1.5-6) ​​can ensure that impurities are fully removed while reducing the amount of acid used and lowering costs.

[0043] Furthermore, the volume ratio of waste silica sludge to water used in the washing treatment is 1:(5-50). This process ensures that impurities dissolved by acid are separated from silicon powder and silicon carbide in the waste silica sludge.

[0044] In this invention, when the magnetic separation time is 10 to 20 minutes and the magnetic field strength is 1.2 to 1.6 T, the metal impurities introduced during the crushing process can be removed, which is beneficial to improving the purity of sodium silicate.

[0045] The above-mentioned silica reacts with an aqueous solution of sodium hydroxide in the presence of a VPM catalyst, which is prepared by a method including the following process:

[0046] Vanadium oxide, phosphoric acid, aromatic alcohol, fatty alcohol, and surfactant are mixed and reacted at 140–150 °C and 0.4–0.6 MPa for 1–3 h with stirring to obtain the precursor.

[0047] The precursor was calcined to obtain the VPM catalyst;

[0048] The calcination process is carried out in an oxygen atmosphere at a temperature of 500-600℃ for 6-12 hours. The molar ratio of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol is 1:(1.2-2.5):(2-4):(10-50). The mass ratio of the total mass of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol to the mass of surfactant is 100:(1-5).

[0049] The M mentioned above refers to the carrier.

[0050] The VPM catalyst prepared by the above method can be used to improve the reaction rate of the reaction between silica and sodium hydroxide aqueous solution, as well as the conversion rate of silica, which is beneficial to improving the utilization rate of waste silica sludge.

[0051] In specific implementations, the VPM catalyst can also be loaded onto a support to improve its service life. The precursor and support are impregnated in equal volumes and then calcined to prepare the VPM catalyst. This invention does not limit the type of support; considering both cost and service life, the support is preferably at least one of zirconium oxide, alumina, and titanium oxide. Specifically, the precursor is impregnated and loaded onto a support in equal volumes, then dried to obtain a second precursor; the second precursor is then calcined to obtain the VPM catalyst. This invention does not limit the drying temperature and time, as long as the second precursor is ensured to be dried.

[0052] This invention improves the utilization rate of waste silica sludge by controlling the mass ratio of silica to catalyst to be 1:(0.01~0.1).

[0053] Furthermore, the product generated by the reaction of silicon dioxide with an aqueous solution of sodium hydroxide is filtered to separate the unreacted solid material, which is then recycled to react with the aqueous solution of sodium hydroxide.

[0054] It is understood that the products of the reaction between silicon dioxide and sodium hydroxide aqueous solution include sodium silicate, unreacted silicon dioxide, and a catalyst, forming a solid-liquid mixture. Therefore, by filtering the products of the reaction between silicon dioxide and sodium hydroxide, sodium silicate can be obtained, and the filtered solid substances are unreacted silicon dioxide and catalyst. Recycling these solid substances to react with sodium hydroxide can further improve the conversion rate of silicon dioxide, thereby increasing the utilization rate of waste silica sludge.

[0055] In practice, the product generated by the reaction of silicon dioxide and sodium hydroxide is at a high temperature, which can easily damage the filtration equipment. Therefore, the present invention first cools the product before filtering it. The temperature of the cooled product is 5 to 50°C, preferably 15 to 30°C.

[0056] Furthermore, considering transportation costs, the present invention also adds an aqueous solution of sodium hydroxide to the obtained solid material to form a slurry. The stirring rate of this process is 300-600 rpm, and the stirring time is controlled at 10-30 min, preferably 15-25 min. The slurry is then recycled to participate in the reaction with the aqueous solution of sodium hydroxide.

[0057] Considering equipment wear and tear costs and reaction energy consumption costs, the above-mentioned aqueous solution of silicon dioxide and sodium hydroxide is reacted at 0-0.2 MPa and 100-120°C for 0.4-2 hours to obtain sodium silicate; preferably, the reaction temperature is 100-105°C and the reaction time is 1.5 hours.

[0058] When the concentration of the sodium hydroxide aqueous solution is controlled at 10-32%, the conversion rate of silicon dioxide can be balanced and the reaction cost can be reduced. More preferably, it is 25-30%.

[0059] The above oxidation treatment includes: reacting silicon powder and silicon carbide with oxygen to obtain silicon dioxide; the reaction temperature is 900-1400℃ and the time is 1-3h.

[0060] The following chemical reaction occurs during this process:

[0061] Si + O₂ → SiO₂

[0062] SiC + O2 → SiO2 + CO2↑

[0063] Under the above conditions, both silicon powder and silicon carbide can be fully converted into silicon dioxide, which is beneficial to increasing the yield of sodium silicate, thereby eliminating the need for silicon carbide separation and improving the utilization rate of waste silica sludge. Preferably, the reaction temperature is 1250–1300℃ and the reaction time is 1.5–2 hours.

[0064] It is understandable that the silicon dioxide obtained after the above oxidation treatment is at a high temperature and needs to be cooled before reacting with the sodium hydroxide aqueous solution. However, the heat of the silicon dioxide itself is insufficient to maintain the temperature within the aforementioned range (100-120°C) throughout the entire reaction process with sodium hydroxide; therefore, additional heat supply is required.

[0065] The present application will be described in more detail below through specific embodiments.

[0066] The process flow of Embodiment 1 of the present invention is shown below. Figure 1 The remaining embodiments are in Figure 1 Adjustments can be made based on existing foundations.

[0067] Example 1

[0068] 1) The waste silica mud was subjected to acid washing, water washing, drying and crushing treatment in sequence to obtain silicon powder and silicon carbide with a particle size of 250 mesh.

[0069] The acid used in the acid washing treatment is a mixture of hydrochloric acid and benzoic acid; the volume ratio of waste silica sludge to acid is 1:3; and the volume ratio of waste silica sludge to water is 1:20.

[0070] The stirring time for acid washing was 30 min and the stirring rate was 300 rpm; the stirring time for water washing was 30 min and the stirring rate was 200 rpm; the drying temperature was 100℃ and the time was 50 min.

[0071] 2) Silicon powder and silicon carbide are subjected to magnetic separation and oxidation treatments in sequence to obtain silicon dioxide;

[0072] The magnetic separation process took 10 minutes and the magnetic field strength was 1.5 T.

[0073] Oxidation treatment refers to the reaction of silicon powder and silicon carbide with oxygen at a reaction temperature of 1400℃ for 1.5 hours. The oxidation treatment is carried out in a rotary tube oxidation reactor at a rotation speed of 20 rpm.

[0074] 3) React silica with an aqueous solution of sodium hydroxide under the catalysis of VPM catalyst at a reaction pressure of 0.2 MPa, a reaction temperature of 115 °C, and a reaction time of 1.5 h.

[0075] The mass ratio of silicon dioxide to catalyst is 1:0.05; the molar ratio of silicon dioxide to sodium hydroxide is 1:0.43; and the concentration of the sodium hydroxide aqueous solution is 30%.

[0076] The VPM catalyst was prepared by the following method: vanadium oxide, phosphoric acid, aromatic alcohol, fatty alcohol, and surfactant were mixed and reacted at 140℃ and 0.4MPa for 2.5h to obtain a precursor; the precursor was impregnated with an equal volume of support and dried to obtain a second precursor; the second precursor was calcined to obtain the VPM catalyst.

[0077] The calcination process was carried out in an oxygen atmosphere at a temperature of 550℃ for 8 hours. The molar ratio of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol was 1:2.2:2.5:20. The total mass ratio of phosphoric acid, aromatic alcohol, fatty alcohol, and surfactant to surfactant was 100:1. The vanadium oxide was vanadium pentoxide; the aromatic alcohol was benzyl alcohol and phenylethanol; the fatty alcohol was isopropanol; the surfactant was propylene glycol monooleate; and the carrier was alumina.

[0078] 4) After cooling the reaction product of silica and sodium hydroxide aqueous solution to 25°C, filter it to obtain a liquid substance of sodium silicate and a solid substance of catalyst and silica. Mix the solid substance with sodium hydroxide aqueous solution and stir, then recycle it to participate in the reaction of step 3). The stirring rate is 400 rpm and the stirring time is 0.25 h.

[0079] Example 2

[0080] The difference between this embodiment and Embodiment 1 is that the acid used in the acid washing treatment is a mixture of hydrochloric acid and salicylic acid.

[0081] Example 3

[0082] The difference between this embodiment and Embodiment 1 is that the acid used in the acid washing treatment is a mixture of hydrochloric acid and acetylacetonate.

[0083] Example 4

[0084] The difference between this embodiment and Embodiment 1 is that the acid used in the acid washing treatment is hydrochloric acid.

[0085] Example 5

[0086] The difference between this embodiment and Embodiment 1 is that the acid used in the acid washing treatment is sulfuric acid.

[0087] Example 6

[0088] The difference between this embodiment and Embodiment 1 is that the volume ratio of waste silica sludge to water used in the water washing treatment is 1:1.

[0089] Example 7

[0090] The difference between this embodiment and Embodiment 1 is that the volume ratio of waste silica sludge to the acid used in the acid washing treatment is 1:1.5.

[0091] Example 8

[0092] The difference between this embodiment and Embodiment 1 is that the intensity of the magnetic separation process is 0.8T.

[0093] Example 9

[0094] The difference between this embodiment and Embodiment 1 is that no VPM catalyst was added.

[0095] Example 10

[0096] The difference between this embodiment and Embodiment 1 is that the silicon dioxide reacts with the aqueous solution of sodium hydroxide at 110°C.

[0097] Example 11

[0098] The difference between this embodiment and Embodiment 1 is that the concentration of the sodium hydroxide aqueous solution is 5%.

[0099] Example 12

[0100] The difference between this embodiment and Embodiment 1 is that the concentration of the sodium hydroxide aqueous solution is 20%.

[0101] Example 13

[0102] The difference between this embodiment and Embodiment 1 is that the temperature at which silicon powder and silicon carbide react with oxygen is 1200°C.

[0103] Example 14

[0104] The difference between this embodiment and Embodiment 1 is that the oxidation reaction device is a fixed-bed oxidation reactor.

[0105] Example 15

[0106] The difference between this embodiment and Example 1 is that the VPM catalyst is obtained by impregnating the precursor and the support with equal volumes, and the support is zirconium oxide.

[0107] Example 16

[0108] The difference between this embodiment and Example 1 is that the VPM catalyst is obtained by impregnating the precursor and the support with equal volumes, and the support is titanium oxide.

[0109] Example 17

[0110] The difference between this embodiment and Embodiment 1 is that the mass ratio of silicon dioxide to catalyst is 1:0.005.

[0111] Example 18

[0112] 1) The waste silica mud was subjected to acid washing, water washing, drying and crushing treatment in sequence to obtain silicon powder and silicon carbide with a particle size of 300 mesh.

[0113] The acid used in the acid washing treatment is a mixture of sulfuric acid and levulinic acid; the volume ratio of waste silica sludge to acid is 1:5; and the volume ratio of waste silica sludge to water is 1:40.

[0114] The stirring time for acid washing was 20 min and the stirring rate was 500 rpm; the stirring time for water washing was 20 min and the stirring rate was 400 rpm; the drying temperature was 110℃ and the time was 30 min.

[0115] 2) Silicon powder and silicon carbide are subjected to magnetic separation and oxidation treatments in sequence to obtain silicon dioxide;

[0116] The magnetic separation process takes 20 minutes and the magnetic field strength is 1.3T; the oxidation reaction device is a rotary tube oxidation reactor with a rotation speed of 30 rpm.

[0117] Oxidation treatment refers to the reaction of silicon powder and silicon carbide with oxygen at a temperature of 1350℃ for 2 hours.

[0118] 3) React silica and sodium hydroxide aqueous solution under the catalysis of VPM catalyst at a reaction pressure of 0.15 MPa, a reaction temperature of 110℃, and a reaction time of 2 h; the mass ratio of silica to catalyst is 1:0.01; the molar ratio of silica to sodium hydroxide is 1:0.45; and the concentration of sodium hydroxide aqueous solution is 28%.

[0119] The VPM catalyst was prepared by the following method: vanadium oxide, phosphoric acid, aromatic alcohol, fatty alcohol, and surfactant were mixed and reacted at 150℃ and 0.5MPa for 1.5h to obtain a precursor; an oxide support was impregnated with an equal volume of the precursor and then dried to obtain a second precursor; the second precursor was calcined to obtain the VPM catalyst; the support was alumina.

[0120] The calcination process was carried out in an oxygen atmosphere at a temperature of 600℃ for 6 hours. The molar ratio of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol was 1:1.5:3:30. The mass ratio of the total mass of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol to the mass of the surfactant was 100:3. The vanadium oxide was vanadium trioxide; the aromatic alcohol was phenylethanol; the fatty alcohol was isobutanol (isopropanol, isobutanol, or isopentyl glycol were optional); and the surfactant was Tween-80.

[0121] 4) After cooling the reaction product of silica and sodium hydroxide aqueous solution to 25°C, filter it to obtain a liquid substance of sodium silicate and a solid substance of catalyst and silica. Mix the solid substance with sodium hydroxide aqueous solution and stir, then recycle it to participate in the reaction of step 3). The stirring rate is 600 rpm and the stirring time is 0.15 h.

[0122] Example 19

[0123] The difference between this comparative example and Example 1 is that the precursor is not impregnated with the support, and the VPM catalyst is obtained directly through calcination.

[0124] Comparative Example 1

[0125] The difference between this comparative example and Example 1 is that the silicon powder has a mesh size of 400.

[0126] Comparative Example 2

[0127] The difference between this comparative example and Example 1 is that the silicon powder has a mesh size of 100.

[0128] Experimental Example 1

[0129] This invention uses ICP-OES to detect the impurity content in silica and sodium silicate, with the units for both being ppm. The utilization rate of waste silica sludge in silica sludge is evaluated by calculating the yields of sodium silicate and silica. The results are shown in Table 1.

[0130] Wherein, the silica yield = silica mass / silica mass theoretically achievable from silicon powder and silicon carbide × 100%;

[0131] Sodium silicate yield = mass of sodium silicate / theoretical mass of sodium silicate that can be produced from silicon dioxide × 100%.

[0132] Table 1

[0133]

[0134]

[0135] Experimental Example 2

[0136] The lifespan of VPM catalysts is characterized by the number of catalyst cycles. Specifically, after each reaction, the product liquid is filtered out, and reactants are added to the catalyst containing the used catalyst for further reaction. The silica conversion rate of each reaction is recorded. When the silica conversion rate drops to 70-65% of the first conversion rate, the catalyst is considered to have undergone significant deactivation. The cumulative number of cycles is recorded, and the average conversion rate of multiple cycles is calculated. The results are shown in Table 2.

[0137] The average conversion rate of silica is calculated as follows: (conversion rate 1 + conversion rate 2 + ... + conversion rate n) / n × 100%.

[0138] Table 2

[0139]

[0140] 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 preparing sodium silicate from waste silica sludge, characterized in that, Includes the following steps: 1) The waste silicon mud is subjected to acid washing, water washing and crushing treatment in sequence to obtain silicon powder and silicon carbide with a particle size of 200-300 mesh. 2) The silicon powder and silicon carbide are subjected to magnetic separation and oxidation treatments in sequence to obtain silicon dioxide; 3) React the silicon dioxide with sodium hydroxide to obtain sodium silicate.

2. The method according to claim 1, characterized in that, The acids used in the acid washing process include at least one of salicylic acid, benzoic acid, and levulinic acid, as well as inorganic acids.

3. The method according to claim 1, characterized in that, The volume ratio of the waste silica sludge to the acid used in the acid washing treatment is 1:(1.5-6).

4. The method according to claim 1, characterized in that, The volume ratio of the waste silica sludge to the water used for washing treatment is 1:(5-50).

5. The method according to claim 1, characterized in that, The magnetic separation process takes 10 to 20 minutes and the magnetic field strength is 1.2 to 1.6 T.

6. The method according to claim 1, characterized in that, The silica reacts with an aqueous solution of sodium hydroxide in the presence of a VPM catalyst, which is prepared by a method comprising the following steps: Vanadium oxide, phosphoric acid, aromatic alcohol, fatty alcohol, and surfactant are mixed and reacted at 140–150 °C and 0.4–0.6 MPa for 1–3 h with stirring to obtain the precursor. The precursor is calcined to obtain the VPM catalyst; The calcination process is carried out in an oxygen atmosphere at a temperature of 500-600℃ for 6-12 hours; the molar ratio of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol is 1:(1.2-2.5):(2-4):(10-50); and the mass ratio of the total mass of vanadium oxide, phosphoric acid, aromatic alcohol, and fatty alcohol to the mass of surfactant is 100:(1-5). The vanadium oxide includes at least one of vanadium pentoxide and vanadium trioxide; the aromatic alcohol includes at least one of phenol, benzyl alcohol, and phenylethanol; the fatty alcohol includes at least one of isopropanol, isobutanol, and isopentyl glycol; and the surfactant includes at least one of Tween-80, PEG-1500, fatty alcohol polyoxyethylene ether, and propylene glycol monooleate.

7. The method according to claim 6, characterized in that, The mass ratio of silicon dioxide to catalyst is 1:(0.01~0.1).

8. The method according to claim 6, characterized in that, The product generated by the reaction of silicon dioxide and the aqueous solution of sodium hydroxide is filtered to obtain a solid substance, which is then recycled to react with the aqueous solution of sodium hydroxide.

9. The method according to claim 1, characterized in that, The silica and an aqueous solution of sodium hydroxide are reacted at 0-0.2 MPa and 100-120°C for 1-3 hours to obtain sodium silicate. The concentration of the sodium hydroxide aqueous solution is 10-32%.

10. The method according to any one of claims 1-9, characterized in that, The oxidation treatment includes: reacting the silicon powder and silicon carbide with oxygen to obtain silicon dioxide; the reaction temperature is 900-1400℃ and the time is 1-3h.

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