Method and system for preparing silica sol by utilizing photovoltaic wastewater

Abstract

The invention provides a method and a system for preparing silica sol by utilizing photovoltaic wastewater, and belongs to the technical field of photovoltaic wastewater treatment. The method comprises the following steps: taking photovoltaic wastewater as a raw material, and obtaining active silicic acid mother liquor by adopting an ion exchange technology; using tetraethoxysilane to generate a specific seed crystal in an alkaline buffer solution; and cross-linking the active silicic acid mother liquor with the seed crystal, and inducing the colloidal particle growth of the silica sol to obtain the silica sol. According to the method, the photovoltaic wastewater is taken as a raw material, and the silica sol is prepared by combining an ion exchange technology and a seed crystal induction mixed growth technology, so that the full utilization of photovoltaic wastewater resources is realized, the TDS index of the wastewater in the photovoltaic industry is controlled, the environmental protection property and the economical efficiency of battery piece production in the photovoltaic industry are improved, and a silica sol product with relatively high economic value is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of photovoltaic wastewater treatment, and in particular to a method and system for preparing silica sol by utilizing photovoltaic wastewater. Background Art

[0002] In the production of photovoltaic industry, various concentrated acid and concentrated alkali wastewater will be generated. The concentrated alkali wastewater mainly comes from the process of cell texturing and alkali polishing: under specific conditions, Si and alkali solution (NaOH) undergo a series of chemical reactions to form a pyramid velvet surface on the surface of silicon wafers by utilizing the anisotropic corrosion characteristics of Si in low-concentration alkali solution. This process can remove organic dirt and metal impurities on the surface of silicon wafers; remove the mechanical damage layer generated by the wire cutting process of silicon wafers; increase the absorption of sunlight by silicon wafers and reduce reflectivity. Therefore, concentrated alkali wastewater is rich in elements such as Si and Na. At present, commonly used treatment methods often cannot effectively remove multiple pollutants in wastewater at the same time, and the presence of silicon will affect the reuse of wastewater, resulting in waste of resources and environmental pollution.

[0003] The prior art discloses a method for preparing a high-purity nano-silica sol with controllable particle size. Referring to Chinese patent CN117049553A, the patent obtains a polysilicic acid solution by passing a sodium silicate aqueous solution through an ion exchange column loaded with a DC voltage, and then uses part of the polysilicic acid solution to prepare nano-silica sol colloidal particle seeds, and then controls the injection speed of the newly formed polysilicic acid solution to grow nano-silica sol colloidal particle hydrates with a desired particle size on the nano-silica sol colloidal particle seeds, and then obtains a nano-silica sol product with a sodium ion content of less than 500 ppm or a total metal ion content of less than 10 ppm and a sol colloidal particle particle size that meets the requirements after concentration, aging and addition of an auxiliary agent.

[0004] Although this method achieves the preparation of nano-silica sol with controllable particle size by controlling the injection speed of the newly formed polysilicic acid solution, the raw material used must be pure sodium silicate aqueous solution, and it is impossible to achieve the reuse of photovoltaic wastewater while preparing nano-silica sol with controllable particle size. Summary of the invention

[0005] The present invention provides a method for preparing silica sol by utilizing photovoltaic wastewater. The method comprises the following steps: separating silicon and sodium from photovoltaic wastewater and removing impurities to obtain active silica mother liquor, and then cross-linking the active silica mother liquor with silica sol seed liquid through seed induction to obtain silica sol of target product, thereby realizing the reuse of photovoltaic wastewater.

[0006] The present invention also provides a system for executing the above-mentioned method of preparing silica sol with controllable particle size using photovoltaic wastewater. The system promotes the all-round recycling of wastewater Si and Na resources, improves the environmental protection and economy of photovoltaic industry battery cell production, and obtains silica sol products with higher economic value.

[0007] The first aspect of the present invention provides a method for preparing silica sol using photovoltaic wastewater, comprising:

[0008] 1) Separation of silicon and sodium elements from wastewater: After removing peroxides from photovoltaic wastewater, silicon and sodium elements are separated to obtain silicon-rich wastewater and sodium hydroxide solution;

[0009] 2) Preparation of active silicate mother liquor: The silicon-rich wastewater is sequentially freed from impure anions, impure cations and C4-C 10 The fatty chain of the active silicate is obtained to obtain an active silicate solution with a pH of 2.0-3.5; a catalyst is added to obtain an active silicate mother solution;

[0010] 3) Preparation of silica sol seed solution: adjust the pH of the alkaline catalyst to 8-9 with an alkaline buffer solution, heat to 50-70°C, add ethyl orthosilicate ethanol solution dropwise, and react for 4-8 hours to form a silica sol seed solution;

[0011] 4) Preparation of silica sol: the sodium hydroxide solution is prepared by removing impurities and diluting it to a mass concentration of 1-3%; the silica sol seed solution is heated to 80-90° C., and then the active silicic acid mother solution is added to obtain a mixed system; the pH of the mixed system is adjusted to 10-11 with the sodium hydroxide solution having a mass concentration of 1-3%, and a cross-linking reaction is carried out for 5-10 hours to obtain silica sol.

[0012] In a possible implementation, in step 4), the silica sol concentrated to a SiO2 mass concentration of 10-25%, the active silicate mother liquor and the sodium hydroxide solution with a mass concentration of 1-3% are subjected to at least one or more cross-linking reactions to obtain silica sols with different particle sizes.

[0013] In a possible embodiment, in step 2), the catalyst includes at least one of polyacrylamide, ethanolamine, and carboxymethyl cellulose;

[0014] Preferably, the mass ratio of polyacrylamide, ethanolamine and carboxymethyl cellulose in the active silicate mother solution is 1:0.3-0.8:0.2-0.8;

[0015] Preferably, in the active silicate mother solution, the mass ratio of the total mass of the polyacrylamide, ethanolamine and carboxymethyl cellulose to SiO2 is 1-8:100.

[0016] In a possible implementation, in step 3), the alkaline catalyst includes at least one of L-glutamic acid, L-arginine, L-aminobutyric acid and L-lysine.

[0017] In a possible implementation, in step 3), the ethanol solution of tetraethyl orthosilicate comprises tetraethyl orthosilicate, ethanol and water; wherein the mass ratio of tetraethyl orthosilicate, ethanol and water is 1:0.2-1:1.5-5.

[0018] In a possible implementation, in step 3), the mass ratio of the alkaline catalyst to tetraethyl orthosilicate is 1.5-6:100.

[0019] In a possible implementation, in step 4), the mass ratio of the active silicic acid mother solution to the silica sol seed solution is 3-12:1.

[0020] In a possible implementation, in step 4), after the cross-linking reaction is completed, the uniformity of the colloid particles is adjusted, including the following steps:

[0021] After the cross-linking reaction is completed, the reaction solution is cooled, the pH is adjusted to 11-12, and heated to 70-80°C for 1-3 hours;

[0022] And / or, when stirring is performed under heating, the stirring speed is 1 / 3 to 1 / 5 of the stirring speed during the cross-linking reaction.

[0023] A second aspect of the present invention provides a system for executing the above method, comprising:

[0024] Peroxide removal device, silicon sodium separation device, impurity anion removal device, impurity cation removal device, C4-C 10 Fat chain device, active silicate mother liquor device, seed crystal generation device, silica sol growth device, sodium hydroxide impurity removal device and sodium hydroxide solution preparation device;

[0025] The peroxide removal device is used to remove peroxides in photovoltaic wastewater, the silicon-sodium separation device is used to separate silicon and sodium elements in photovoltaic wastewater to obtain silicon-rich wastewater and sodium hydroxide solution, the impurity anion removal device is used to remove impurity anions in silicon-rich wastewater, the impurity cation removal device is used to remove metal cations in silicon-rich wastewater, and the C4-C 10 The fat chain device is used to remove the fat chain substances with carbon atoms of 4-10 in silicon-rich wastewater, the active silicate mother liquor device is used to prepare and store active silicate mother liquor, the seed generation device is used to prepare silica sol seed solution, the silica sol growth device is used to prepare silica sol, the sodium hydroxide impurity removal device is used to remove metal cations other than sodium ions and anions other than hydroxide ions, and the sodium hydroxide solution preparation device is used to adjust the mass concentration of the sodium hydroxide solution to 1-3%;

[0026] The silicon-sodium separation device comprises a first outlet and a second outlet, the first outlet is used for circulating the separated sodium-containing feed liquid, and the second outlet is used for circulating the silicon-containing feed liquid;

[0027] The silica sol growth device comprises a first inlet, a second inlet and a third inlet, the first inlet is used for circulating sodium hydroxide solution, the second inlet is used for circulating active silicate mother solution, and the third inlet is used for circulating silica sol seed solution;

[0028] The outlet of the peroxide removal device is connected to the inlet of the silicon-sodium separation device; the first outlet of the silicon-sodium separation device is connected to the inlet of the sodium hydroxide solution preparation device through the sodium hydroxide impurity removal device, and the outlet of the sodium hydroxide solution preparation device is connected to the first inlet of the silica sol growth device;

[0029] The second outlet of the silicon-sodium separation device is passed through the impurity anion removal device, the impurity cation removal device, the C4-C 10 The fat chain device is connected to the inlet of the active silica mother solution device, the outlet of the active silica mother solution device is connected to the second inlet of the silica sol growth device; the outlet of the seed generation device is connected to the third inlet of the silica sol growth device;

[0030] The residence time of the silicon-rich wastewater in the anion impurity removal device is 0.5-1h; the residence time in the cation impurity removal device is 2-3h; 10 The residence time in the fat chain device is 0.5-1h.

[0031] The system as described above, wherein the system further comprises a concentration device and at least one silica sol growth device;

[0032] The concentrating device is used to concentrate the silica sol from the silica sol growing device;

[0033] Each of the silica sol growth devices comprises a first inlet, a second inlet and a third inlet, wherein the first inlet is used for circulating sodium hydroxide solution, the second inlet is used for circulating active silica mother liquor, and the third inlet is used for circulating concentrated silica sol;

[0034] The first inlet of each of the silica sol growth devices is connected to the outlet of the sodium hydroxide solution preparation device, the second inlet of each of the silica sol growth devices is connected to the outlet of the active silicate mother liquor device, and the third inlet of each of the silica sol growth devices is connected to the outlet of the concentrating device; the outlet of each of the silica sol growth devices is connected to the inlet of the concentrating device; the concentrating device also includes an outlet for outputting silica sol that meets the target particle size.

[0035] The present invention uses photovoltaic wastewater as raw material, adopts a combination of ion exchange technology and seed induced mixed growth technology to prepare silica sol, realizes full utilization of photovoltaic wastewater resources, controls the TDS index of photovoltaic industry wastewater, improves the environmental protection and economy of photovoltaic industry battery production, and obtains silica sol products with higher economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of a method provided in one embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a system provided in one embodiment of the present invention;

[0038] Figure 3 A schematic diagram of a method provided in one embodiment of the present invention;

[0039] Figure 4 A schematic diagram of a system provided in one embodiment of the present invention.

[0040] Description of reference numerals:

[0041] 1. Peroxide removal device; 2. Silicon sodium separation device; 3. Impurity anion removal device; 4. Impurity cation removal device; 5. C4-C removal device 10 Fat chain device; 6. Sodium hydroxide impurity removal device; 7. Sodium hydroxide solution preparation device; 8. Silica sol fourth growth device; 9. Tertiary product storage device; 10. Silica sol third growth device; 11. Secondary product storage device; 12. Silica sol secondary growth device; 13. Silica sol product storage device; 14. Silica sol growth device; 15. Crystal seed generation device; 16. Active silica mother liquor device; 17. Concentration device; 18. Product concentration device; 19. Fourth product storage device.

[0042] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0043] The technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0044] At present, the photovoltaic industry produces a large amount of wastewater, and direct discharge will cause resource waste and environmental pollution. When preparing silica sol, the existing technology mostly uses a high-purity sodium silicate aqueous solution, etc. Although silica sol can also be produced, the cost is relatively high. After research, the inventor found that, first, photovoltaic wastewater mainly contains sodium hydroxide, sodium silicate and organic additives, rich in elements such as Si and Na; second, because the photovoltaic production and processing processes use high-purity electronic-grade silicon wafers and electronic-grade chemicals, the silicon-rich wastewater obtained is of high purity, especially low metal content (1-2ppm); third, in the photovoltaic industry, the organic additives (stabilizers, nucleating agents, etc.) used in the texturing and alkali polishing of battery cells can be used as organic additives for the growth of silica sol to promote the uniform dispersion of silica sol particles; the water produced after the sodium-silicon separation of wastewater (sodium hydroxide solution) can be used for pH adjustment during the growth of silica sol, realizing the comprehensive utilization of waste.

[0045] Based on this, the present invention provides a method for preparing silica sol using photovoltaic wastewater, comprising:

[0046] 1) Separation of silicon and sodium elements from wastewater: After removing peroxides from photovoltaic wastewater, silicon and sodium elements are separated to obtain silicon-rich wastewater and sodium hydroxide solution;

[0047] 2) Preparation of active silicate mother liquor: The above silicon-rich wastewater is sequentially treated with the removal of impure anions, impure cations and C4-C 10 The fatty chain of the active silicate is obtained to obtain an active silicate solution with a pH of 2.0-3.5; a catalyst is added to obtain an active silicate mother solution;

[0048] 3) Preparation of silica sol seed solution: adjust the pH of the alkaline catalyst to 8-9 with an alkaline buffer solution and heat to 50-70°C, add ethyl orthosilicate ethanol solution dropwise, and react for 4-8 hours to form a silica sol seed solution;

[0049] 4) Preparation of silica sol: remove impurities from the above sodium hydroxide solution and dilute it to a mass concentration of 1-3%; heat the above silica sol seed solution to 80-90°C, add the above active silicate mother solution to obtain a mixed system; adjust the pH of the mixed system to 10-11 with a sodium hydroxide solution with a mass concentration of 1-3%, perform a cross-linking reaction, and the reaction time is 5-10 hours to obtain silica sol. The flow chart is Figure 1 .

[0050] Specifically, in step 1), after removing the peroxide in the photovoltaic wastewater, silicon and sodium elements are separated to obtain silicon-rich wastewater and sodium hydroxide solution, respectively.

[0051] The present invention does not specifically limit the source of photovoltaic wastewater, which can be conventional photovoltaic wastewater. In one embodiment, photovoltaic wastewater comes from the photovoltaic industry, especially the alkali-containing and silicon-containing wastewater generated in the production process of solar cells, wherein the mass concentration of NaOH is 0.5-4%, the mass concentration of SiO2 is 0.3-1.6%, the mass concentration of peroxide is 0.5-3%, the COD content is 200-3000ppm, and contains ethylenediaminetetraacetic acid, polyacrylamide, ethanolamine, carboxymethyl cellulose, ethylene glycol ether, methacrylic acid, etc.

[0052] The present invention does not specifically limit the flow rate of photovoltaic wastewater when removing peroxides; in one embodiment, the flow rate is 2-4 m / h, for example, the flow rate is 2 m / h, 3 m / h, 4 m / h; preferably, the flow rate is 3 m / h.

[0053] The present invention does not specifically limit the method for removing peroxides; in one embodiment, peroxides can be removed by using a catalyst such as manganese sand, iron oxide, aluminum oxide, etc. Preferably, manganese sand is used.

[0054] The present invention does not specifically limit the method for separating silicon and sodium elements, for example, membrane separation, chromatography separation, etc. are used; in a specific embodiment, membrane separation is used; further, silicon and sodium element separation membrane is used for separation. Silicon-rich wastewater and sodium hydroxide solution are obtained by separation, and the silicon-rich wastewater is used for the subsequent preparation of silica sol; the sodium hydroxide solution is used to adjust the pH when preparing silica sol, so as to realize the comprehensive utilization of waste.

[0055] Furthermore, the mass concentration of SiO2 in the separated silicon-rich wastewater is 3-6%, the mass concentration of NaOH is 0.5-2%, and the COD content is less than 3000ppm; the mass concentration of the separated sodium hydroxide solution is 2-4%.

[0056] In step 2), the silicon-rich wastewater separated in step 1) is firstly treated to remove impure anions, then to remove impure cations, and finally to remove C4-C 10 The fatty chain is removed to obtain an active silicate solution with a pH of 2.0-3.5, for example, a pH of 2.0, 2.5, 3.0, or 3.5; finally, a catalyst is added to the active silicate solution to obtain an active silicate mother solution.

[0057] Furthermore, the C4-C 10 The fatty chains are mainly substances that have no promoting effect on the silica sol reaction, such as ethylenediaminetetraacetic acid, ethylene glycol ether, methacrylic acid and other organic substances.

[0058] The present invention is effective in removing impure anions, impure cations (such as sodium ions) and C4-C 10In one embodiment, an anion exchange resin is used to remove impure anions in the silicon-rich wastewater, a cation exchange resin is used to remove impure cations in the silicon-rich wastewater, and a macroporous adsorption resin is used to remove C4-C 10 The silicon-rich wastewater itself contains some catalysts, namely polyacrylamide, ethanolamine and carboxymethyl cellulose.

[0059] The present invention does not specifically limit the types of anion exchange resins, cation exchange resins and macroporous adsorption resins, as long as they can remove impure anions, impure cations and C4-C 10 For example, the anion exchange resin can be selected from any one of primary amino resin, secondary amino resin, tertiary amino resin, and alcohol amine resin, and preferably, the anion exchange resin is a primary amino resin; the cation exchange resin can be selected from any one of sulfonic acid resin, phenolic resin, and carboxyl resin, and preferably, the cation exchange resin is a sulfonic acid resin; the macroporous adsorption resin can be selected from any one of styrene-vinyl copolymer adsorption resin and methyl acrylate-vinyl copolymer adsorption resin, and preferably, the macroporous adsorption resin is styrene-vinyl copolymer adsorption resin.

[0060] The pore size of the macroporous adsorption resin is preferably 400-1000 μm.

[0061] The present invention does not specifically limit the sources of the anion exchange resin, the cation exchange resin and the macroporous adsorption resin, and conventional commercial products may be used.

[0062] Furthermore, the macroporous adsorption resin was purchased from Huzhou Keshi Technology Co., Ltd., model KSA410 ion exchange resin.

[0063] Furthermore, the present invention also pre-treats anion exchange resin, cation exchange resin, and macroporous adsorption resin to achieve the effect of removing impurities from anion exchange resin, cation exchange resin, and macroporous adsorption resin. The present invention does not limit the method of pre-treating anion exchange resin, cation exchange resin, and macroporous adsorption resin, as long as the impurity removal effect is achieved.

[0064] In one embodiment, the pretreatment method of the anion exchange resin comprises: soaking the anion exchange resin in a NaCl solution and a NaOH solution in sequence, and then washing the anion exchange resin with distilled water until it becomes neutral.

[0065] Furthermore, the anion exchange resin is immersed in the NaCl solution for 1-2 hours, such as 1 hour, 1.5 hours or 2 hours; the anion exchange resin is immersed in the NaOH solution for 2-3 hours, such as 2 hours, 2.5 hours or 3 hours.

[0066] Furthermore, the mass concentration of the NaCl solution is 10-12%, such as 10%, 11% or 12%; the mass concentration of the NaOH solution is 5-6%, such as 5%, 5.5% or 6%.

[0067] Furthermore, the volumes of the NaCl solution and the NaOH solution used are 3-5 times the volume of the anion exchange resin, for example, 3 times, 4 times or 5 times the volume of the anion exchange resin.

[0068] In one embodiment, the pretreatment method of the macroporous adsorption resin comprises: soaking the macroporous adsorption resin in an HCl solution and a Na2CO3 solution in sequence, and then washing with distilled water until neutral.

[0069] Furthermore, the immersion time of the macroporous adsorption resin in the HCl solution is 2-3h, for example, the immersion time is 2h, 2.5h or 3h; the immersion time of the macroporous adsorption resin in the Na2CO3 solution is 1-2h, for example, the immersion time is 1h, 1.5h or 2h.

[0070] Furthermore, the mass concentration of the HCl solution is 4-5%, for example, 4%, 4.5% or 5%; the mass concentration of the Na2CO3 solution is 8-10%, for example, 8%, 9% or 10%.

[0071] Furthermore, the volumes of the HCl solution and the Na2CO3 solution used are 3-5 times the volume of the macroporous adsorption resin, for example, 3 times, 4 times or 5 times the volume of the macroporous adsorption resin.

[0072] In one embodiment, the pretreatment method of the cation exchange resin includes: soaking the cation exchange resin in a NaOH solution and an HCl solution in sequence, and then washing with distilled water until the cation exchange resin is neutral.

[0073] Furthermore, the cation exchange resin is immersed in the NaOH solution for 0.5-1.5 h, for example, the immersion time is 0.5 h, 1 h or 1.5 h; the cation exchange resin is immersed in the HCl solution for 2-3 h, for example, the immersion time is 2 h, 2.5 h or 3 h.

[0074] Furthermore, the mass concentration of the NaOH solution and the HCl solution are both 4-5%, for example, the mass concentration is 4%, 4.5% or 5%.

[0075] Furthermore, the volumes of the NaOH solution and the HCl solution used are 3-5 times the volume of the cation exchange resin, for example, 3 times, 4 times or 5 times the volume of the cation exchange resin.

[0076] Anion exchange resins, cation exchange resins and macroporous adsorption resins can be recycled to achieve the effect of reducing costs and recycling resources.

[0077] In step 3), the pH of the alkaline catalyst is adjusted to 8-9 with an alkaline buffer solution, and then heated to a temperature of 50-70°C, for example, a pH of 8, 8.5 or 9; heated to a temperature of 50°C, 55°C, 60°C, 65°C or 70°C; then an ethanol solution of ethyl orthosilicate is added dropwise to the above system, and after the addition is completed, the temperature is maintained at 50-70°C for a reaction of 4-8 hours, for example, a reaction time of 4h, 5h, 6h, 7h or 8h; to form a silica sol seed solution.

[0078] The present invention does not specifically limit the preparation method of the alkaline buffer solution, as long as the pH of the alkaline catalyst can be adjusted to 8-9; in one embodiment, the alkaline buffer solution is prepared by mixing NH4Cl, ammonia water, and deionized water, and a conventional alkaline buffer solution preparation method is adopted. The raw materials are cheap and easy to obtain, and the preparation method is simple.

[0079] The present invention does not limit the heating rate during heating, as long as the mixed system of the alkaline buffer solution and the alkaline catalyst can be heated to 50-70°C; in one embodiment, the heating rate can be 4-6°C / min, for example, the heating rate is 4°C / min, 5°C / min, 6°C / min; preferably, the heating rate is 5°C / min.

[0080] Furthermore, the present invention does not limit the dripping speed of the ethanol solution of tetraethyl orthosilicate, as long as the tetraethyl orthosilicate is fully reacted with the alkaline catalyst and the alkaline buffer, and the seed particle size in the obtained silica sol seed solution is uniform. In one embodiment, the dripping speed of the ethanol solution of tetraethyl orthosilicate is 2-10mL / min, for example, the dripping speed is 2mL / min, 6mL / min, 8mL / min or 10mL / min; preferably, the dripping speed is 6mL / min.

[0081] In step 4), the sodium hydroxide solution separated in step 1) is decontaminated and diluted to obtain a sodium hydroxide solution with a mass concentration of 1-3%, for example, 1%, 2%, or 3%; the silica sol seed solution obtained in step 3) is heated to 80-90° C., for example, 80° C., 85° C., or 90° C., and the active silica mother solution obtained in step 2) is added, and the pH of the system is adjusted to 10-11, for example, 10 or 11, with a sodium hydroxide solution with a mass concentration of 1-3%; the system is subjected to a cross-linking reaction at 80-90° C. for 5-10 hours, for example, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours; and silica sol is obtained.

[0082] The present invention does not limit the impurity removal method of the sodium hydroxide solution, and only needs to remove metal cations other than sodium ions and anions other than hydroxide in the solution.

[0083] Furthermore, metal ion exchange resin is used to remove metal cations other than sodium ions. In one embodiment, the metal cation exchange resin is one or more of sulfonic acid resin and carboxyl resin; anion exchange resin is used to remove anions other than hydroxide. In one embodiment, the anion exchange resin is one or more of aminoacrylic resin and aminostyrene resin.

[0084] The present invention does not limit the heating rate of the silica sol seed solution, and it only needs to reach a predetermined temperature.

[0085] Furthermore, the active silicate mother solution is added in batches, with each batch adding 5-10% of the total mass of the active silicate mother solution, for example, 5%, 6%, 7%, 8%, 9% or 10% of the total mass. Adding the active silicate mother solution in batches allows for a more complete reaction and more uniform silica sol particles.

[0086] The present invention uses photovoltaic wastewater as raw material, removes impurities first, and then prepares silica sol by combining ion exchange technology and seed induced mixed growth technology. At the same time, the sodium hydroxide solution prepared in step 1) is used as a raw material to adjust the pH, and some organic matter contained in the photovoltaic wastewater is used as a catalyst, which only needs to be supplemented to the required amount according to actual conditions, thereby saving costs and realizing resource recycling. The cost of preparing silica sol is reduced, and the full utilization of Si and Na resources in photovoltaic wastewater is realized, reducing pollution.

[0087] In a specific embodiment, in step 4), the silica sol concentrated to a mass concentration of 10-25% SiO2, the active silicate mother liquor and the sodium hydroxide solution with a mass concentration of 1-3% are subjected to at least one or more cross-linking reactions to obtain silica sols of different particle sizes. The silica sol is concentrated to a mass concentration of 10-25% SiO2, for example, a mass concentration of 10%, 15%, 20% or 25% SiO2; preferably, the mass concentration of SiO2 is 15%. The silica sol is concentrated to increase the concentration so that the silica sol can react better during the next cross-linking.

[0088] Furthermore, the present invention does not specifically limit the concentration treatment method, and only needs to concentrate the mass concentration of SiO2 in the silica sol to 10-25%. In one embodiment, the concentration treatment method adopts any one of membrane concentration, evaporation concentration, and freeze concentration; preferably, membrane concentration is adopted.

[0089] The present invention does not limit the number of cross-linking reactions, which is determined specifically according to the desired particle size of the silica sol, as long as the desired particle size is reached. For example, the cross-linking reaction can be performed once, twice, three times, four times or more.

[0090] In one embodiment, the silica sol particle size in the silica sol seed solution is 5-15nm; the particle size of the silica sol primary growth product is 15-25nm; the particle size of the silica sol secondary growth product is 40-50nm; the particle size of the silica sol tertiary growth product is 60-70nm; the particle size of the silica sol quadruple growth product is 80-90nm; the particle size of the silica sol product after the silica sol fifth growth can reach more than 100nm.

[0091] Further, taking two cross-linking reactions as an example:

[0092] The silica sol obtained in step 4) is concentrated to a mass concentration of SiO2 of 10-25%, and heated to 80-90°C, for example, 80°C, 85°C or 90°C; active silica mother liquor is added in batches under stirring, 10% of the total mass of the active silica mother liquor is added each time, the pH is adjusted to 10-11 with 1-3% sodium hydroxide solution, the reaction is carried out for 5-10 hours, and the uniformity of the colloidal particles is adjusted to obtain the desired silica sol.

[0093] Further, taking a total of four cross-linking reactions as an example, the flow chart is shown in Figure 3 , Figure 3 A schematic diagram of a method provided in one embodiment of the present invention.

[0094] The method of performing a total of four cross-linking reactions includes:

[0095] 1) Separation of silicon and sodium elements in wastewater: After removing peroxides from photovoltaic wastewater, silicon and sodium elements are separated to obtain silicon-rich wastewater and sodium hydroxide solution.

[0096] 2) Preparation of active silicate mother liquor: The above silicon-rich wastewater is sequentially treated with the removal of impure anions, impure cations and C4-C 10 The fatty chain is removed to obtain an active silicate solution with a pH of 2.0-3.5; a catalyst is added to obtain an active silicate mother solution.

[0097] 3) Preparation of silica sol seed solution: Mix an alkaline buffer solution with a pH of 8-9 and an alkaline catalyst, heat to 50-70°C, add an ethanol solution of ethyl orthosilicate dropwise, and react for 4-8 hours to form a silica sol seed solution.

[0098] 4) Preparation of silica sol: prepare the above sodium hydroxide solution to a mass concentration of 1-3%; heat the above silica sol seed solution to 80-90°C, add the above active silicic acid mother solution to obtain a mixed system; adjust the pH of the mixed system to 10-11 with a sodium hydroxide solution with a mass concentration of 1-3%, carry out a cross-linking reaction, the reaction time is 5-10h, and obtain a silica sol primary growth product.

[0099] 5) Preparation of silica sol secondary growth product: The silica sol primary growth product obtained in step 4) is concentrated to a mass concentration of SiO2 of 10-25%, and heated to 80-90°C. Active silica mother liquor is added in batches under stirring, and the pH is adjusted to 10-11 with 1-3% sodium hydroxide solution. The reaction is carried out for 5-10 hours to obtain a silica sol secondary growth product.

[0100] 6) Preparation of silica sol tertiary growth product: The silica sol secondary growth product obtained in step 5) is concentrated to a mass concentration of SiO2 of 10-25%, and heated to 80-90°C. Active silica mother liquor is added in batches under stirring, and the pH is adjusted to 10-11 with 1-3% sodium hydroxide solution. The reaction is carried out for 5-10 hours to obtain a silica sol tertiary growth product.

[0101] 7) Preparation of silica sol quadruple growth product: Using the silica sol tertiary growth product obtained in step 6) as a raw material, the silica sol tertiary growth product is concentrated to a SiO2 mass concentration of 10-25%, and heated to 80-90°C, and active silicate mother liquor is added in batches under stirring, and the pH is adjusted to 10-11 with 1-3% sodium hydroxide solution. The reaction is carried out for 5-10 hours to obtain a silica sol quadruple growth product.

[0102] In a specific embodiment, in step 2), the catalyst includes at least one of polyacrylamide, ethanolamine, and carboxymethyl cellulose; for example, the catalyst can be any one of polyacrylamide, ethanolamine, and carboxymethyl cellulose; or any one of polyacrylamide and ethanolamine, polyacrylamide and carboxymethyl cellulose, and ethanolamine and carboxymethyl cellulose; or a mixture of polyacrylamide, ethanolamine, and carboxymethyl cellulose.

[0103] Since photovoltaic wastewater contains polyacrylamide, ethanolamine and carboxymethyl cellulose, the prepared active silicate solution contains polyacrylamide, ethanolamine and carboxymethyl cellulose, but the content is insufficient, so it is necessary to add catalyst according to the content of polyacrylamide, ethanolamine and carboxymethyl cellulose in the active silicate solution. In the photovoltaic industry, organic additives (stabilizers, nucleating agents, etc.) used in cell texturing and alkali polishing can be used as catalysts for silica sol growth again to promote uniform dispersion of silica sol particles.

[0104] In a specific embodiment, the mass ratio of polyacrylamide, ethanolamine and carboxymethyl cellulose in the active silicate mother solution is 1:0.3-0.8:0.2-0.8; for example, the mass ratio is 1:0.3:0.2, 1:0.6:0.2 or 1:0.8:0.8. The present invention does not limit the amount of catalyst added or the specific number of catalysts added, because the content of polyacrylamide, ethanolamine and carboxymethyl cellulose in photovoltaic wastewater from different batches or manufacturers will be different, and can be added according to actual conditions. It is only necessary to achieve a mass ratio of polyacrylamide, ethanolamine and carboxymethyl cellulose in the prepared active silicate mother solution of 1:0.3-0.8:0.2-0.8.

[0105] In a specific embodiment, in the active silica mother solution, the mass ratio of the total mass of polyacrylamide, ethanolamine and carboxymethyl cellulose to SiO2 is 1-8:100; for example, the mass ratio is 1:100, 3:100, 6:100 or 8:100. After the addition is completed, the mass ratio of the total mass of polyacrylamide, ethanolamine and carboxymethyl cellulose to SiO2 in the active silica mother solution is 1-8:100, and the mass ratio of polyacrylamide, ethanolamine and carboxymethyl cellulose is 1:0.3-0.8:0.2-0.8. It is avoided that the mass ratio is too high to affect the purity of the subsequent product, and the growth effect is poor if the mass ratio is too low.

[0106] In a specific embodiment, the alkaline catalyst includes at least one of L-glutamic acid, L-arginine, L-aminobutyric acid and L-lysine. For example, it can be any one of L-glutamic acid, L-arginine, L-aminobutyric acid, L-lysine; or any two of L-glutamic acid, L-arginine, L-aminobutyric acid, L-lysine; or a mixture of L-glutamic acid, L-arginine, L-aminobutyric acid and L-lysine.

[0107] When the alkaline catalyst is a mixture of the aforementioned specific compounds, the present invention does not specifically limit the ratio between the specific compounds.

[0108] The present invention does not limit the source of the alkaline catalyst, and conventional commercially available products may be used.

[0109] The present invention utilizes alkaline amino acid as alkaline catalyst, uses alkaline buffer solution to maintain appropriate pH value, provides mild reaction environment, makes product monodisperse, and obtains silica sol seed crystal with good chemical uniformity, fine particles, high purity and high reaction activity, and is suitable for being used as seed crystal for silica sol growth in the next step.

[0110] In a specific embodiment, in step 3), the ethanol solution of tetraethyl orthosilicate comprises tetraethyl orthosilicate, ethanol and water; wherein the mass ratio of tetraethyl orthosilicate, ethanol and water is 1:0.2-1:1.5-5. For example, the mass ratio is 1:0.2:1.5, 1:0.5:3.5 or 1:1:5. Within this range, the production of silica sol seeds is more easily promoted.

[0111] In a possible implementation, the mass ratio of the alkaline catalyst to tetraethyl orthosilicate in step 3) is 1.5-6:100, for example, 1.5:100, 3:100 or 6:100. Within this mass ratio range, the formation of silica sol seed solution can be better promoted.

[0112] Furthermore, silica sol seeds are prepared with tetraethyl orthosilicate, and the content thereof is regulated so that the reaction process can be prepared quantitatively and the reaction can be controlled.

[0113] In a possible implementation, in step 4), the mass ratio of active silicic acid mother solution to silica sol seed solution is 3-12:1, for example, the mass ratio is 3:1, 6:1, 9:1 or 12:1. Within this mass ratio range, the formation of silica sol can be better promoted.

[0114] In a specific embodiment, in step 4), after the cross-linking reaction is completed, the uniformity of the colloid particles is adjusted, including the following steps: after the reaction solution after the cross-linking reaction is completed is cooled, the pH is adjusted to 11-12, for example, the pH is 11 or 12; then heated to a temperature of 70-80°C, for example, the temperature is 70°C, 75°C or 80°C; maintained for 1-3h, for example, the reaction time is 1h, 2h or 3h.

[0115] The present invention does not impose any limitation on the stirring speed, as long as a silica sol with uniform particle size is obtained.

[0116] In a specific embodiment, when heating and stirring, the stirring speed is 1 / 3-1 / 5 of the stirring speed during the cross-linking reaction, for example, it can be 1 / 3, 1 / 4, 1 / 5 of the stirring speed during the cross-linking reaction; preferably, it is 1 / 5 of the stirring speed during the cross-linking reaction. The silica sol particles obtained at this stirring speed are more uniform.

[0117] Furthermore, the present invention does not limit the raw materials used for adjusting the pH, as long as the pH of the cooled silica sol reaction solution can be adjusted to 11-12. In a specific embodiment, ammonia water is used to adjust the pH, which is more stable and avoids excessive alkalinity that damages the solution, and is easy to remove.

[0118] The growth process of silica sol particles has great requirements on the surface properties of the seed particles. The process of adjusting the uniformity of the particles can also improve the sphericity of the silica sol, making its surface smooth and the structure dense, thereby improving the uniformity of the product and facilitating multiple particle growth.

[0119] A second aspect of the present invention provides a system for executing the above method, comprising:

[0120] Peroxide removal device, silicon sodium separation device, impurity anion removal device, impurity cation removal device, C4-C 10 Fat chain device, active silicate mother liquor device, seed crystal generation device, silica sol growth device, sodium hydroxide impurity removal device and sodium hydroxide solution preparation device;

[0121] The peroxide removal device is used to remove peroxides from photovoltaic wastewater. The silicon-sodium separation device is used to separate silicon and sodium elements from photovoltaic wastewater to obtain silicon-rich wastewater and sodium hydroxide solution. The impurity anion removal device is used to remove impurity anions from silicon-rich wastewater. The impurity cation removal device is used to remove metal cations from silicon-rich wastewater. 10 The fat chain device is used to remove the fat chain substances with carbon atoms of 4-10 in silicon-rich wastewater, the active silicate mother liquor device is used to prepare and store the active silicate mother liquor, the seed generation device is used to prepare silica sol seed solution, the silica sol growth device is used to prepare silica sol, the sodium hydroxide impurity removal device is used to remove metal cations other than sodium ions and anions other than hydroxide ions, and the sodium hydroxide solution preparation device is used to adjust the mass concentration of the sodium hydroxide solution to 1-3%;

[0122] The silicon-sodium separation device comprises a first outlet and a second outlet, the first outlet is used for circulating the separated sodium-containing feed liquid, and the second outlet is used for circulating the silicon-containing feed liquid;

[0123] The silica sol growth device comprises a first inlet, a second inlet and a third inlet, the first inlet is used for circulating sodium hydroxide solution, the second inlet is used for circulating active silicate mother solution, and the third inlet is used for circulating silica sol seed solution;

[0124] The outlet of the peroxide removal device is connected to the inlet of the silicon-sodium separation device; the first outlet of the silicon-sodium separation device is connected to the inlet of the sodium hydroxide solution preparation device through the sodium hydroxide impurity removal device, and the outlet of the sodium hydroxide solution preparation device is connected to the first inlet of the silica sol growth device;

[0125] The second outlet of the silicon-sodium separation device is passed through an impurity anion removal device, an impurity cation removal device, a C4-C 10 The fat chain device is connected to the inlet of the active silica mother solution device, the outlet of the active silica mother solution device is connected to the second inlet of the silica sol growth device; the outlet of the seed generation device is connected to the third inlet of the silica sol growth device;

[0126] The residence time of silicon-rich wastewater in the anion impurity removal device is 0.5-1h; the residence time in the cation impurity removal device is 2-3h; 10 The residence time in the fat chain device is 0.5-1h.

[0127] Figure 2 FIG. 1 is a schematic diagram of the structure of the system of the present invention in one embodiment. Figure 2 As shown, the system includes a peroxide removal device 1, a silicon-sodium separation device 2, an impurity anion removal device 3, an impurity cation removal device 4, a C4-C 10 The fat chain device 5, the active silicate mother liquor device 16, the seed generating device 15, the silica sol growing device 14, the sodium hydroxide impurity removing device 6 and the sodium hydroxide solution preparing device 7.

[0128] The silica sol growth device 14 includes a first inlet, a second inlet and a third inlet. The first inlet is connected to the outlet of the sodium hydroxide solution preparation device 7 for circulating the sodium hydroxide solution; the second inlet is connected to the outlet of the active silicate mother liquor device 16 for circulating the active silicate mother liquor; the third inlet is connected to the outlet of the seed generating device 15 for circulating the silica sol seed solution.

[0129] The silicon-sodium separation device 2 includes a first outlet and a second outlet; the first outlet of the silicon-sodium separation device 2 is used to circulate the sodium-containing feed liquid obtained by separation, that is, to discharge the sodium hydroxide solution, and the first outlet of the silicon-sodium separation device 2 is connected to the first inlet of the silica sol growth device 14 through the sodium hydroxide impurity removal device 6 and the sodium hydroxide solution preparation device 7; the second outlet of the silicon-sodium separation device 2 is used to circulate the silicon-containing feed liquid, that is, to discharge silicon-rich wastewater, and the second outlet of the silicon-sodium separation device 2 is connected to the first inlet of the silica sol growth device 14 through the impurity anion removal device 3, the impurity cation removal device 4, and the C4-C removal device 7. 10 The fat chain device 5 is connected to the inlet of the active silicate mother solution device 16.

[0130] Among them, the peroxide removal device 1 is used to remove peroxides in photovoltaic wastewater. The photovoltaic wastewater enters from the inlet of the peroxide removal device 1, stays therein, and the peroxides are removed; the outlet of the peroxide removal device 1 is connected to the inlet of the silicon-sodium separation device 2, and the photovoltaic wastewater with peroxides removed is passed into the silicon-sodium separation device 2.

[0131] The silicon-sodium separation device 2 is used to separate silicon and sodium elements in photovoltaic wastewater. The second outlet of the silicon-sodium separation device 2 is connected to the inlet of the impurity anion removal device 3, and the first outlet of the silicon-sodium separation device 2 is connected to the inlet of the sodium hydroxide impurity removal device 6. After the photovoltaic wastewater from which peroxide is removed passes through the silicon-sodium separation device 2, it is divided into a sodium hydroxide route and a silicon-rich wastewater route. The material in the sodium hydroxide route is discharged from the first outlet of the silicon-sodium separation device 2 and enters the sodium hydroxide impurity removal device 6; the material in the silicon-rich wastewater route is discharged from the second outlet of the silicon-sodium separation device 2 and enters the impurity anion removal device 3.

[0132] Furthermore, the present invention does not specifically limit the selection of elements used in the silicon-sodium separation device 2, which can be selected conventionally in the art, as long as they can separate silicon and sodium elements. In one embodiment, the element used is a silicon-sodium element separation membrane element.

[0133] Furthermore, the present invention does not limit the type of silicon-sodium element separation membrane element. In one embodiment, the silicon-sodium element separation membrane element is selected from at least one of a polysulfone membrane element, a polyamide membrane element, a sulfonated polyethersulfone membrane element or a sulfonated polysulfone membrane element. Preferably, a polysulfone membrane element is used.

[0134] Furthermore, the present invention does not limit the source of the silicon-sodium element separation membrane element, and conventional commercially available elements may be used.

[0135] The impurity anion removal device 3 is used to remove impurity anions in photovoltaic wastewater, and the outlet of the impurity anion removal device 3 is connected to the inlet of the impurity cation removal device 4. After the silicon-rich wastewater separated from the silicon-sodium separation device 2 enters the impurity anion removal device 3, it stays until the impurity anions are removed, and then the silicon-rich wastewater with impurity anions removed is discharged from the outlet of the impurity anion removal device 3 and enters the impurity cation removal device 4.

[0136] Furthermore, the present invention does not limit the residence time of the silicon-rich wastewater in the impurity anion removal device 3, as long as the effect of removing the impurity anions is achieved. In one embodiment, the residence time is 0.5-1h, for example, the residence time is 0.5h, 0.8h, 1h; preferably, the residence time is 0.8h. Within this residence time range, the impurity anions can be better removed.

[0137] The impurity cation removal device 4 is used to remove metal cations in photovoltaic wastewater. The outlet of the impurity cation removal device 4 and the C4-C 10 After the silicon-rich wastewater from which the impurity anions have been removed enters the impurity cation removal device 4, it stays there until the metal cations are removed. Then, the silicon-rich wastewater from which the metal cations have been removed is discharged from the outlet of the impurity cation removal device 4 and enters the C4-C 10The fat chain device 5.

[0138] Furthermore, the present invention does not limit the residence time of the silicon-rich wastewater in the impurity cation removal device 4, as long as the effect of removing metal cations is achieved. In one embodiment, the residence time is 2-3 hours, for example, the residence time is 2 hours, 2.5 hours or 3 hours; preferably, the residence time is 2.5 hours. Within this residence time range, impurity cations can be better removed.

[0139] Except C4-C 10 The fatty chain device 5 is used to remove organic substances such as ethylenediaminetetraacetic acid, ethylene glycol ether, methacrylic acid, etc. in photovoltaic wastewater that have no promoting effect on the reaction with silica sol, and retain the polyacrylamide, ethanolamine and carboxymethyl cellulose contained in the silicon-rich wastewater itself; except for C4-C 10 The outlet of the fat chain device 5 is connected to the inlet of the active silicate mother liquor device 16. The silicon-rich wastewater after the removal of metal cations enters the C4-C 10 After the fatty chain device 5, it is stopped until the C4-C 10 The fatty chain of C4-C 10 The precipitate is discharged from the outlet of the fat chain device 5 and enters the active silicate mother liquor device 16.

[0140] The present invention is used to treat silicon-rich wastewater in the process of removing C4-C 10 The residence time of the fatty chain device 5 is not limited, as long as the removal of C4-C 10 In one embodiment, the residence time is 0.5-1h, for example, the residence time is 0.5h, 0.6h, 0.8h or 1h; preferably, the residence time is 0.8h. Within this residence time range, C4-C 10 of fat chains.

[0141] The active silicate mother liquor device 16 provides a place for preparing active silicate mother liquor and stores the obtained active silicate mother liquor; the outlet of the active silicate mother liquor device 16 is connected to the second inlet of the silica sol growth device 14 .

[0142] Furthermore, in order to facilitate the addition of catalyst, the active silicate mother liquor device 16 is provided with a feed port. After the catalyst is added, the active silicate mother liquor is obtained.

[0143] The seed generating device 15 provides a place for preparing silica sol seed solution, and the outlet of the seed generating device 15 is connected to the third inlet of the silica sol growth device 14. After the alkaline buffer and the alkaline catalyst enter the seed generating device 15, they react with the ethanol solution of ethyl orthosilicate to obtain the silica sol seed solution.

[0144] Furthermore, in order to facilitate the addition of alkaline buffer and alkaline catalyst, the seed generating device 15 is provided with a feed pipe.

[0145] The sodium hydroxide impurity removal device 6 is used to remove metal cations other than sodium ions and anions other than hydroxide ions in the sodium hydroxide solution discharged from the silicon-sodium separation device 2. The outlet of the sodium hydroxide impurity removal device 6 is connected to the inlet of the sodium hydroxide solution preparation device 7. The sodium hydroxide impurity removal device 6 is used to adjust the pH of the sodium hydroxide solution without other impurities.

[0146] The sodium hydroxide solution preparation device 7 is used to dilute the mass concentration of the sodium hydroxide solution after impurities removal to 1-3%. The outlet of the sodium hydroxide solution preparation device 7 is connected to the first inlet of the silica sol growth device 14 to adjust the pH of the cross-linking reaction.

[0147] The silica sol growth device 14 provides a place for the cross-linking reaction between the silica sol seed solution and the active silicate mother solution. The active silicate mother solution, the silica sol seed solution, and the sodium hydroxide solution with a mass concentration of 1-3% react in the silica sol growth device 14 to produce silica sol.

[0148] Furthermore, the outlet of the silica sol growth device 14 is connected to a silica sol product storage device 13 , and the silica sol product storage device 13 is used to store the obtained silica sol with a desired particle size.

[0149] The process of preparing silica sol is as follows: photovoltaic wastewater is sequentially passed through a peroxide removal device 1 and a silicon-sodium separation device 2 to obtain silicon-rich wastewater and a sodium hydroxide solution; the silicon-rich wastewater is first passed through an impurity anion removal device 3 and then passed through an impurity cation removal device 4 and a C4-C removal device. 10 After the fatty chain device 5, the active silicate mother liquor device 16 is introduced, and a catalyst is added to the active silicate mother liquor device 16 to obtain an active silicate mother liquor; the active silicate mother liquor is introduced into the silica sol growth device 14. Then, the silica sol seed solution prepared in the seed generating device 15 is introduced into the silica sol growth device 14, and the material in the sodium hydroxide solution preparation device 7 is introduced into the silica sol growth device 14. After the cross-linking reaction, the uniformity of the colloidal particles is adjusted to obtain a silica sol with a target particle size.

[0150] Furthermore, the present invention does not limit the communication method between the devices. For example, pipeline communication can be used.

[0151] In one embodiment, the system further comprises a concentration device and at least one silica sol growth device;

[0152] The concentrating device is used for concentrating the silica sol from the silica sol growing device;

[0153] Each silica sol growth device comprises a first inlet, a second inlet and a third inlet, the first inlet is used for circulating sodium hydroxide solution, the second inlet is used for circulating active silicate mother liquor, and the third inlet is used for circulating concentrated silica sol;

[0154] The first inlet of each silica sol growth device is connected to the outlet of the sodium hydroxide solution preparation device, the second inlet of each silica sol growth device is connected to the outlet of the active silicate mother liquor device, and the third inlet of each silica sol growth device is connected to the outlet of the concentrating device; the outlet of the silica sol growth device is connected to the inlet of the concentrating device; the concentrating device also includes an outlet for outputting silica sol that meets the target particle size.

[0155] The present invention does not limit the number of silica sol growth devices, as long as the particle size obtained reaches the target particle size.

[0156] In one embodiment, taking a total of four cross-linking reactions as an example, the device diagram is shown in Figure 4 .

[0157] Figure 4 This is a schematic diagram of a system provided in an embodiment of the present invention. As shown in the figure, the silica sol growth device also includes a concentration device 17, a silica sol secondary growth device 12, a silica sol tertiary growth device 10 and a silica sol quaternary growth device 8.

[0158] The concentrating device 17 is used to concentrate the silica sol prepared last time to a SiO2 mass concentration of 10-25% in the silica sol; the silica sol secondary growth device 12 is used to mix the silica sol primary growth product, active silica acid mother liquor and sodium hydroxide solution with a mass concentration of 1-3%, and prepare the silica sol secondary growth product by cross-linking reaction; the silica sol tertiary growth device 10 is used to mix the silica sol secondary growth product, active silica acid mother liquor and sodium hydroxide solution with a mass concentration of 1-3%, and prepare the silica sol tertiary growth product by cross-linking reaction; the silica sol quaternary growth device 8 is used to mix the silica sol tertiary growth product, active silica acid mother liquor and sodium hydroxide solution with a mass concentration of 1-3%, and prepare the silica sol quaternary growth product by cross-linking reaction.

[0159] The concentration device 17 includes a first inlet, a second inlet and a third inlet, and a first outlet, a second outlet and a third outlet; the first inlet, the second inlet and the third inlet are respectively used to receive materials discharged from the silica sol growth device 14, the silica sol secondary growth device 12, and the silica sol tertiary growth device 10; the first outlet, the second outlet and the third outlet are respectively used to provide materials to the silica sol secondary growth device 12, the silica sol tertiary growth device 10, and the silica sol quaternary growth device 8.

[0160] Furthermore, the present invention does not limit the components of the concentrator, as long as the concentrating effect can be achieved. In one embodiment, a membrane concentrator or an evaporation concentrator is used; preferably, a membrane concentrator is used, and the membrane concentrator is any one of a ceramic membrane, a silicon carbide inorganic membrane or a PVDF organic membrane.

[0161] Furthermore, the present invention does not limit the operation mode of the membrane concentrator, as long as the concentration effect can be achieved. In one embodiment, a cross-flow parallel operation mode is adopted.

[0162] Furthermore, the present invention does not limit the concentration temperature of the membrane concentrator. In one embodiment, the concentration temperature is 60-80°C, such as 60°C, 65°C, 70°C, 75°C or 80°C; preferably, the temperature is 70°C.

[0163] Furthermore, the present invention does not limit the concentration multiple of the membrane concentrator. In one embodiment, the concentration multiple is set to 1-5 times, for example, the concentration multiple is 1 times, 2 times, 3 times, 4 times or 5 times.

[0164] The silica sol secondary growth device 12 includes a first inlet, a second inlet and a third inlet, a first outlet and a second outlet; the silica sol tertiary growth device 10 includes a first inlet, a second inlet and a third inlet, a first outlet and a second outlet; the silica sol quaternary growth device 8 includes a first inlet, a second inlet and a third inlet, a first outlet and a second outlet.

[0165] The first inlet of each silica sol growth device is used for circulating a sodium hydroxide solution with a mass concentration of 1-3%, the second inlet is used for circulating an active silica mother liquor, and the third inlet is used for circulating concentrated silica sol.

[0166] The first inlet of each silica sol growth device is connected to the outlet of the sodium hydroxide solution preparation device 7, the second inlet of each silica sol growth device is connected to the outlet of the active silicate mother liquor device 16, and the third inlet of each silica sol growth device is connected to the outlet of the concentrating device 17; the outlet of each silica sol growth device is connected to the inlet of the concentrating device 17; the concentrating device also includes an outlet for outputting silica sol meeting the target particle size.

[0167] Furthermore, the active silicate mother liquor device 16 is connected and provided with a first pipeline, a second pipeline, a third pipeline and a fourth pipeline; the first pipeline is connected to the second inlet of the silica sol growth device 14, and is used to provide active silicate mother liquor to the silica sol growth device 14; the second pipeline is connected to the second inlet of the silica sol secondary growth device 12, and is used to provide active silicate mother liquor to the silica sol secondary growth device 12; the third pipeline is connected to the second inlet of the silica sol tertiary growth device 10, and is used to provide active silicate mother liquor to the silica sol tertiary growth device 10; the fourth pipeline is connected to the second inlet of the silica sol quaternary growth device 8, and is used to provide active silicate mother liquor to the silica sol quaternary growth device 8.

[0168] The sodium hydroxide solution preparation device 7 is connected to a first pipeline, a second pipeline, a third pipeline and a fourth pipeline; the first pipeline is connected to the first inlet of the silica sol growth device 14, and is used to provide the silica sol growth device 14 with a sodium hydroxide solution with a mass concentration of 1-3%; the second pipeline is connected to the first inlet of the silica sol secondary growth device 12, and is used to provide the silica sol secondary growth device 12 with a sodium hydroxide solution with a mass concentration of 1-3%; the third pipeline is connected to the first inlet of the silica sol tertiary growth device 10, and is used to provide the silica sol tertiary growth device 10 with a sodium hydroxide solution with a mass concentration of 1-3%; the fourth pipeline is connected to the first inlet of the silica sol quaternary growth device 8, and is used to provide the silica sol quaternary growth device 8 with a sodium hydroxide solution with a mass concentration of 1-3%.

[0169] The outlet of the silica sol growth device 14 is connected to the first inlet of the concentrator 17, the second outlet of the silica sol secondary growth device 12 is connected to the second inlet of the concentrator 17, the first outlet of the silica sol secondary growth device 12 is used to output the silica sol secondary product, the second outlet of the silica sol tertiary growth device 10 is connected to the third inlet of the concentrator 17, and the first outlet of the silica sol tertiary growth device 10 is used to output the silica sol tertiary product.

[0170] The first outlet of the concentrator 17 is connected to the third inlet of the silica sol secondary growth device 12 , the second outlet of the concentrator 17 is connected to the third inlet of the silica sol tertiary growth device 10 , and the third outlet of the concentrator 17 is connected to the third inlet of the silica sol quaternary growth device 8 .

[0171] The process is as follows: the silica sol in the silica sol growth device 14 is concentrated by the concentrating device 17, and then introduced into the silica sol secondary growth device 12, and the materials in the active silica acid mother solution device 16 and the materials in the sodium hydroxide solution preparation device 7 are introduced into the silica sol secondary growth device 12, and after the cross-linking reaction, the uniformity of the colloidal particles is adjusted to obtain a silica sol secondary growth product; the obtained silica sol secondary growth product is introduced into the concentrating device 17, and after concentration, it is introduced into the silica sol tertiary growth device 10, and the silica sol tertiary growth device 10 is introduced into the silica sol tertiary growth device 10. The material in the active silica mother solution device 16 and the material in the sodium hydroxide solution preparation device 7 are introduced, and after the cross-linking reaction, the uniformity of the colloid particles is adjusted to obtain a silica sol three-time growth product; the obtained silica sol three-time growth product is introduced into the concentration device 17, and after concentration, it is introduced into the silica sol four-time growth device 8, and the material in the active silica mother solution device 16 and the material in the sodium hydroxide solution preparation device 7 are introduced into the silica sol four-time growth device 8, and after the cross-linking reaction, the uniformity of the colloid particles is adjusted to obtain a silica sol four-time growth product. In the above process, the reaction can be stopped when the product obtained at any time reaches the desired target particle size.

[0172] Furthermore, in order to better collect the product, in one embodiment, a product concentrating device 18 is further included. The concentrating device 17 is used to concentrate the silica sol prepared last time to a SiO2 mass concentration of 10-25% in the silica sol; the product concentrating device 18 is used to concentrate the product reaching the target particle size to obtain silica sol.

[0173] Furthermore, in order to better collect products, in one embodiment, the silica sol secondary growth device 12, the silica sol tertiary growth device 10 and the silica sol quaternary growth device 8 are all connected to the secondary product storage device 11, the tertiary product storage device 9 and the quaternary product storage device 19 through the product concentration device 18, respectively, and are used to collect the silica sol secondary product, the silica sol tertiary product and the silica sol quaternary product, respectively.

[0174] The silica sol product with the target particle size can be discharged from each silica sol growth device and concentrated to a specific concentration for use by the product concentration device 18. The silica sol product that needs to be grown again can be concentrated by the concentration device 17 with a fixed concentration multiple and then passed to the next silica sol growth device.

[0175] The solution provided by the present invention is further described below in conjunction with specific embodiments.

[0176] Example 1

[0177] In the production of photovoltaic cells, the mass concentration of NaOH in photovoltaic wastewater is 2%, the mass concentration of Si is 0.8%, the mass concentration of peroxide is 0.7%, the COD content is 1000ppm, and it contains organic matter such as ethylenediaminetetraacetic acid, polyacrylamide, ethanolamine, carboxymethyl cellulose, ethylene glycol ether, and methacrylic acid.

[0178] The method for preparing silica sol with controllable particle size in this embodiment comprises the following specific steps:

[0179] Step 1) Separation of silicon and sodium elements in wastewater: The photovoltaic wastewater is subjected to peroxide removal treatment and silicon and sodium element separation treatment at a flow rate of 3m / h to obtain silicon-rich wastewater and sodium hydroxide liquid. A secondary membrane is used to separate silicon and sodium elements, and a polysulfone membrane element is used as the silicon and sodium element separation membrane.

[0180] The SiO2 mass concentration, NaOH concentration and COD content of the silicon-rich wastewater obtained were 5%, 0.8% and 1200 ppm, respectively; the concentration of the separated sodium hydroxide liquid was 2%.

[0181] Step 2) Preparation of active silicate mother liquor: 500L of silicon-rich wastewater first passes through an anion exchange device for impurity removal, then passes through a cation exchange device for impurity removal and a C4-C 10 The residence time of silicon-rich wastewater in the impurity removal anion exchange device is 0.8h; the residence time in the impurity removal cation exchange device is 2.5h; 10 The residence time of the fatty chain device is 0.6h; the active silicate liquid with a pH of 3.0 is obtained. The content of organic matter polyacrylamide, ethanolamine and carboxymethyl cellulose in the active silicate liquid is analyzed. The total mass of the three is 0.11% of the mass of silicon-rich wastewater (accounting for 2.2% of the SiO2 content of the active silicate mother liquor). The mass ratio of polyacrylamide, ethanolamine and carboxymethyl cellulose is 1:0.6:0.2. The mass of the added catalyst reaches 4% of the SiO2 content of the active silicate mother liquor, that is, the total amount of catalyst to be added is 450g, polyacrylamide 171g, ethanolamine 198g, and carboxymethyl cellulose 81g. After addition, the mass ratio of the three is 1:0.8:0.3, and the active silicate mother liquor is obtained.

[0182] The impurity removal anion exchange device uses 1000L primary amino resin; the impurity removal cation exchange device uses 2500L sulfonic acid resin to remove C4-C 10 The device for removing the fatty chain of the anion exchange device uses 800L of styrene-vinyl copolymer adsorption resin. Before using the impurity removal anion exchange device, soak it in 10% NaCl solution for 1 hour and 5% NaOH solution for 2 hours; 10The device for removing fat chains should be soaked in 4% HCl solution for 3 hours and 8% Na2CO3 solution for 2 hours before use; the impurity removal cation exchange device should be soaked in 4% NaOH solution for 1 hour and 5% HCl solution for 3 hours before use.

[0183] Step 3) Preparation of silica sol seed solution: 20 kg of deionized water was mixed with NH4Cl and ammonia water to form an alkaline buffer solution with a pH of 8.5. After adding L-arginine, the mixture was heated to 70°C under mixing and stirring. 8 kg of ethyl orthosilicate and 3.5 kg of ethanol were mixed into a 70% ethanol solution, which was added dropwise to the alkaline buffer solution. After the addition was completed, the solution was reacted for 5 hours to form a silica sol seed solution.

[0184] Step 4) Silica sol primary growth: Heat the silica sol seed solution in step 3 to 90°C, add 220kg of active silicate mother solution in batches under stirring, adjust the pH to 10.5 with 1% sodium hydroxide solution, and carry out cross-linking reaction for 8 hours under stirring; after cooling, adjust the pH to 11 with ammonia water, heat to 70°C, stir and react for 8 hours to adjust the uniformity of the colloidal particles, and obtain the silica sol primary growth product after the reaction, and put it into the primary growth product storage tank. Among them, the stirring speed when adjusting the uniformity of the colloidal particles is 1 / 3 of the stirring speed during the cross-linking reaction.

[0185] Step 5) Secondary growth of silica sol: If the silica sol primary growth product does not meet the target particle size, the silica sol primary growth product enters the growth concentrator to concentrate the SiO2 mass concentration in the silica sol to 15%, heat to 90°C, add 230kg of active silicic acid mother liquor in batches with stirring, adjust the pH to 11 with 1% sodium hydroxide solution, keep reacting for 10h, adjust the pH to 11 with ammonia water after cooling, heat to 60°C, react for 6h, and obtain the silica sol secondary growth product.

[0186] Step 6) Silica sol tertiary growth: If the silica sol secondary growth product does not meet the target particle size, the silica sol secondary growth product is concentrated to a SiO2 mass concentration of 15%, and step 5) is repeated to obtain the silica sol tertiary growth product.

[0187] Step 7) Silica sol quadruple growth: If the silica sol tertiary growth product does not meet the target particle size, the silica sol tertiary growth product is concentrated to a SiO2 mass concentration of 15%, and step 5) is repeated to obtain the silica sol quadruple growth product.

[0188] The silica sol particle size in the silica sol seed solution is 5-15nm; the particle size of the silica sol primary growth product is 15-25nm; the particle size of the silica sol secondary growth product is 40-50nm; the particle size of the silica sol tertiary growth product is 60-70nm; and the particle size of the silica sol quaternary growth product is 80-90nm.

[0189] Finally, it should be noted that those skilled in the art will readily conceive of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include common knowledge or customary technical means in the art not disclosed by the present invention, are not limited to the precise structure described above and shown in the drawings, and may be modified and changed in various ways without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing silica sol using photovoltaic wastewater, characterized in that: include: 1) Separation of silicon and sodium elements from wastewater: After removing peroxides from photovoltaic wastewater, silicon and sodium elements are separated to obtain silicon-rich wastewater and sodium hydroxide solution; 2) Preparation of active silicate mother liquor: The silicon-rich wastewater is sequentially freed from impure anions, impure cations and C4-C 10 The fatty chain of the active silicate is obtained to obtain an active silicate solution with a pH of 2.0-3.5; a catalyst is added to obtain an active silicate mother solution; 3) Preparation of silica sol seed solution: adjust the pH of the alkaline catalyst to 8-9 with an alkaline buffer solution, heat to 50-70°C, add ethyl orthosilicate ethanol solution dropwise, and react for 4-8 hours to form a silica sol seed solution; 4) Preparation of silica sol: the sodium hydroxide solution is prepared by removing impurities and diluting it to a mass concentration of 1-3%; the silica sol seed solution is heated to 80-90° C., and then the active silicic acid mother solution is added to obtain a mixed system; the pH of the mixed system is adjusted to 10-11 with the sodium hydroxide solution having a mass concentration of 1-3%, and a cross-linking reaction is carried out for 5-10 hours to obtain silica sol.

2. The method according to claim 1, characterized in that In step 4), the silica sol concentrated to a SiO2 mass concentration of 10-25%, the active silicate mother solution and the sodium hydroxide solution with a mass concentration of 1-3% are subjected to at least one or more cross-linking reactions to obtain silica sols with different particle sizes.

3. The method according to claim 1 or 2, characterized in that: In step 2), the catalyst includes at least one of polyacrylamide, ethanolamine, and carboxymethyl cellulose; The mass ratio of polyacrylamide, ethanolamine and carboxymethyl cellulose in the active silicate mother solution is 1:0.3-0.8:0.2-0.8; In the active silicate mother solution, the mass ratio of the total mass of the polyacrylamide, ethanolamine and carboxymethyl cellulose to SiO2 is 1-8:

100.

4. The method according to claim 1, characterized in that: In step 3), the alkaline catalyst includes at least one of L-glutamic acid, L-arginine, L-aminobutyric acid and L-lysine.

5. The method according to claim 4, characterized in that In step 3), the ethanol solution of tetraethyl orthosilicate comprises tetraethyl orthosilicate, ethanol and water; wherein the mass ratio of tetraethyl orthosilicate, ethanol and water is 1:0.2-1:1.5-5.

6. The method according to claim 5, characterized in that In step 3), the mass ratio of the alkaline catalyst to tetraethyl orthosilicate is 1.5-6:

100.

7. The method according to claim 1, characterized in that In step 4), the mass ratio of the active silicic acid mother solution to the silica sol seed solution is 3-12:

1.

8. The method according to claim 1, characterized in that In step 4), after the cross-linking reaction is completed, the uniformity of the particles is adjusted, including the following steps: After the cross-linking reaction is completed, the reaction solution is cooled, the pH is adjusted to 11-12, and heated to 70-80°C for 1-3 hours; And / or, when stirring is performed under heating, the stirring speed is 1 / 3 to 1 / 5 of the stirring speed during the cross-linking reaction.

9. A system for executing the method according to any one of claims 1 to 8, characterized in that: include: Peroxide removal device, silicon sodium separation device, impurity anion removal device, impurity cation removal device, C4-C 10 Fat chain device, active silicate mother liquor device, seed crystal generation device, silica sol growth device, sodium hydroxide impurity removal device and sodium hydroxide solution preparation device; The peroxide removal device is used to remove peroxides in photovoltaic wastewater, the silicon-sodium separation device is used to separate silicon and sodium elements in photovoltaic wastewater to obtain silicon-rich wastewater and sodium hydroxide solution, the impurity anion removal device is used to remove impurity anions in silicon-rich wastewater, the impurity cation removal device is used to remove metal cations in silicon-rich wastewater, and the C4-C 10 The fat chain device is used to remove the fat chain substances with carbon atoms of 4-10 in silicon-rich wastewater, the active silicate mother liquor device is used to prepare and store active silicate mother liquor, the seed generation device is used to prepare silica sol seed solution, the silica sol growth device is used to prepare silica sol, the sodium hydroxide impurity removal device is used to remove metal cations other than sodium ions and anions other than hydroxide ions, and the sodium hydroxide solution preparation device is used to adjust the mass concentration of the sodium hydroxide solution to 1-3%; The silicon-sodium separation device comprises a first outlet and a second outlet, the first outlet is used for circulating the separated sodium-containing feed liquid, and the second outlet is used for circulating the silicon-containing feed liquid; The silica sol growth device comprises a first inlet, a second inlet and a third inlet, the first inlet is used for circulating sodium hydroxide solution, the second inlet is used for circulating active silicate mother solution, and the third inlet is used for circulating silica sol seed solution; The outlet of the peroxide removal device is connected to the inlet of the silicon-sodium separation device; the first outlet of the silicon-sodium separation device is connected to the inlet of the sodium hydroxide solution preparation device through the sodium hydroxide impurity removal device, and the outlet of the sodium hydroxide solution preparation device is connected to the first inlet of the silica sol growth device; The second outlet of the silicon-sodium separation device is passed through the impurity anion removal device, the impurity cation removal device, the C4-C 10 The fat chain device is connected to the inlet of the active silica mother solution device, the outlet of the active silica mother solution device is connected to the second inlet of the silica sol growth device; the outlet of the seed generation device is connected to the third inlet of the silica sol growth device; The residence time of the silicon-rich wastewater in the anion impurity removal device is 0.5-1h; the residence time in the cation impurity removal device is 2-3h; 10 The residence time in the fat chain device is 0.5-1h.

10. The system according to claim 9, characterized in that The system also includes a concentration device and at least one silica sol growth device; The concentrating device is used to concentrate the silica sol from the silica sol growing device; Each of the silica sol growth devices comprises a first inlet, a second inlet and a third inlet, wherein the first inlet is used for circulating sodium hydroxide solution, the second inlet is used for circulating active silica mother liquor, and the third inlet is used for circulating concentrated silica sol; The first inlet of each of the silica sol growth devices is connected to the outlet of the sodium hydroxide solution preparation device, the second inlet of each of the silica sol growth devices is connected to the outlet of the active silicate mother liquor device, and the third inlet of each of the silica sol growth devices is connected to the outlet of the concentrating device; the outlet of each of the silica sol growth devices is connected to the inlet of the concentrating device; the concentrating device also includes an outlet for outputting silica sol that meets the target particle size.

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