A method and system for preparing silica sol using photovoltaic wastewater

Abstract

The present invention provides a method and a system for preparing silica sol by using photovoltaic wastewater, belonging to the technical field of photovoltaic wastewater treatment. The method includes: using photovoltaic wastewater as a raw material, obtaining an active silicic acid mother liquor by adopting an ion exchange technology; generating specific seeds with tetraethyl orthosilicate in an alkaline buffer solution; crosslinking the active silicic acid mother liquor with the seeds to induce the growth of silica sol particles and obtaining silica sol. By using photovoltaic wastewater as a raw material and combining the ion exchange technology with the seed-induced mixed growth technology, the present invention prepares silica sol, realizes the full utilization of photovoltaic wastewater resources, controls the TDS index of wastewater in the photovoltaic industry, improves the environmental protection and economy of cell production in the photovoltaic industry, and obtains a silica sol product with high economic value.

Description

Technical Field

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

[0002] In the production of the photovoltaic industry, various strong acid and strong base wastewaters are generated. The strong base wastewater mainly comes from the processes of cell texturing and alkaline polishing: under specific conditions, by using the anisotropic etching characteristics of Si in low-concentration alkaline solution, a series of chemical reactions occur between Si and the alkaline solution (NaOH), and a pyramid-shaped textured surface is formed on the silicon wafer surface. This process can remove the organic dirt and metal impurities on the silicon wafer surface; remove the mechanical damage layer generated during the wire cutting process of the silicon wafer; increase the absorption of sunlight by the silicon wafer and reduce the reflectivity. Therefore, the strong base wastewater is rich in elements such as Si and Na. At present, the commonly used treatment methods often cannot effectively remove multiple pollutants in the wastewater at the same time, and the presence of silicon elements will affect the reuse of the wastewater, resulting in waste of resources and environmental pollution.

[0003] The prior art discloses a method for preparing high-purity controllable particle size nano-silica sol. Referring to Chinese Patent CN117049553A, this patent obtains a polysilicic acid solution by passing an aqueous sodium silicate solution through an ion exchange column loaded with a DC voltage, then prepares nano-silica sol particle seeds with part of the polysilicic acid solution, and then controls the injection speed of the freshly formed polysilicic acid solution to grow on the nano-silica sol particle seeds to obtain nano-silica sol particle hydrates with the required particle size, and then obtains a nano-silica sol product with a sodium ion content <500 ppm or a total metal ion content <10 ppm and the particle size of its sol particles meeting the requirements after concentration and aging and adding additives.

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

[0005] The present invention provides a method for preparing silica sol by using photovoltaic wastewater. This method separates silicon and sodium from the photovoltaic wastewater, removes impurities to obtain an active silicic acid mother liquor, and then through seed induction, cross-links the active silicic acid mother liquor with a silica sol seed solution to prepare the target product of silica sol, realizing the reuse of photovoltaic wastewater.

[0006] The present invention also provides a system for implementing the above method for preparing controllable particle size silica sol by using photovoltaic wastewater. This system promotes the all-round recycling of wastewater Si and Na resources, improves the environmental protection and economy of battery production in the photovoltaic industry, and obtains a silica sol product with high 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 the photovoltaic wastewater, silicon and sodium elements are separated to obtain silicon-rich wastewater and sodium hydroxide solution;

[0009] 2) Preparation of active silicic acid mother liquor: The silicon-rich wastewater is successively removed of impurity anions, impurity cations and C 4 -C 10 fatty chains to obtain an active silicic acid feed liquid with a pH of 2.0 - 3.5; A catalyst is added to prepare an active silicic acid mother liquor;

[0010] 3) Preparation of silica sol seed solution: After adjusting the pH of the alkaline catalyst to 8 - 9 with an alkaline buffer solution, heating to 50 - 70 °C, dropping an ethanol solution of tetraethyl orthosilicate, and reacting for 4 - 8 h to form a silica sol seed solution;

[0011] 4) Preparation of silica sol: The sodium hydroxide solution is purified and diluted to a mass concentration of 1 - 3%; After heating the silica sol seed solution to 80 - 90 °C, adding the active silicic acid mother liquor to obtain a mixed system; Adjusting the pH of the mixed system to 10 - 11 with the sodium hydroxide solution with a mass concentration of 1 - 3% for crosslinking reaction, and the reaction time is 5 - 10 h to obtain silica sol.

[0012] In a possible implementation manner, in step 4), the silica sol with a mass concentration of 10 - 25% concentrated to SiO 2 , the active silicic acid mother liquor and the sodium hydroxide solution with a mass concentration of 1 - 3% are subjected to at least one or more crosslinking reactions to obtain silica sols with different particle sizes.

[0013] In a possible implementation manner, 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 silicic acid mother liquor is 1:0.3 - 0.8:0.2 - 0.8;

[0015] Preferably, the mass ratio of the total mass of polyacrylamide, ethanolamine, and carboxymethyl cellulose in the active silicic acid mother liquor to SiO 2 is 1 - 8:100.

[0016] In a possible implementation manner, 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 contains 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 basic catalyst to tetraethyl orthosilicate is 1.5 - 6:100.

[0019] In a possible implementation, in step 4), the mass ratio of the active silica mother liquor 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 adjustment of the colloidal particle uniformity is carried out, including the following steps:

[0021] Cool the reaction solution after the cross-linking reaction is completed and adjust the pH to 11 - 12, heat it to 70 - 80 °C, and keep it for 1 - 3 h;

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

[0023] The second aspect of the present invention provides a system for implementing the above method, including:

[0024] Peroxide removal device, silicon-sodium separation device, impurity anion removal device, impurity cation removal device, device for removing C 4 -C 10 fatty chain device with 4 - 10 carbon atoms, active silica mother liquor device, seed 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, the device for removing C 4 -C 10 fatty chain device with 4 - 10 carbon atoms is used to remove fatty chain substances with 4 - 10 carbon atoms in silicon-rich wastewater, the active silica mother liquor device is used to prepare and store active silica 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 sodium-silicon separation device includes a first outlet and a second outlet. The first outlet is used for the flow of the separated sodium-containing feed liquid, and the second outlet is used for the flow of the silicon-containing feed liquid;

[0027] The silica sol growth device includes a first inlet, a second inlet, and a third inlet. The first inlet is used for the flow of the sodium hydroxide solution, the second inlet is used for the flow of the active silica mother liquor, and the third inlet is used for the flow of the silica sol seed liquid;

[0028] The outlet of the peroxide removal device is communicated with the inlet of the sodium-silicon separation device; the first outlet of the sodium-silicon separation device is communicated with 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 communicated with the first inlet of the silica sol growth device;

[0029] The second outlet of the sodium-silicon separation device passes through the impurity anion removal device, the impurity cation removal device, and the device for removing the C 4 -C 10 fatty chain device to be communicated with the inlet of the active silica mother liquor device, the outlet of the active silica mother liquor device is communicated with the second inlet of the silica sol growth device; the outlet of the seed generation device is communicated with the third inlet of the silica sol growth device;

[0030] The residence time of the silicon-rich wastewater in the impurity anion removal device is 0.5 - 1 h; the residence time in the impurity cation removal device is 2 - 3 h; the residence time in the device for removing the C 4 -C 10 fatty chain device is 0.5 - 1 h.

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

[0032] The concentration device is used for concentrating the silica sol from the silica sol growth device;

[0033] Each silica sol growth device includes a first inlet, a second inlet, and a third inlet. The first inlet is used for the flow of the sodium hydroxide solution, the second inlet is used for the flow of the active silica mother liquor, and the third inlet is used for the flow of the concentrated silica sol;

[0034] The first inlet of each silica sol growth device is communicated with the outlet of the sodium hydroxide solution preparation device, the second inlet of each silica sol growth device is communicated with the outlet of the active silica mother liquor device, and the third inlet of each silica sol growth device is communicated with the outlet of the concentration device; the outlet of each silica sol growth device is communicated with the inlet of the concentration device; the concentration device further includes an outlet for outputting the silica sol meeting the target particle size.

[0035] The present invention uses photovoltaic wastewater as a raw material, combines ion exchange technology and seed-induced mixed growth technology to prepare silica sol, realizes the full utilization of photovoltaic wastewater resources, controls the TDS index of wastewater in the photovoltaic industry, improves the environmental protection and economy of cell production in the photovoltaic industry, and obtains a silica sol product with high economic value. Description of the Drawings

[0036] Figure 1 It is a schematic diagram of the method provided in an embodiment of the present invention;

[0037] Figure 2 It is a schematic diagram of the system provided in an embodiment of the present invention;

[0038] Figure 3 It is a schematic diagram of the method provided in an embodiment of the present invention;

[0039] Figure 4 It is a schematic diagram of the system provided in an embodiment of the present invention.

[0040] Description of the Reference Numerals:

[0041] 1, peroxide removal device; 2, sodium silicate separation device; 3, impurity anion removal device; 4, impurity cation removal device; 5, device for removing C 4 -C 10 fatty chain device; 6, sodium hydroxide impurity removal device; 7, sodium hydroxide solution preparation device; 8, four-time silica sol growth device; 9, three-time product storage device; 10, three-time silica sol growth device; 11, two-time product storage device; 12, two-time silica sol growth device; 13, silica sol product storage device; 14, silica sol growth device; 15, seed generation device; 16, active silicic acid mother liquor device; 17, concentration device; 18, product concentration device; 19, four-time product storage device.

[0042] Through the above-mentioned drawings, specific embodiments of the present application have been shown, and there will be more detailed descriptions hereinafter. These drawings and text descriptions are not intended to limit the scope of the concept 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 Embodiments

[0043] The technical solutions of the present application and how the technical solutions of the present application solve the above technical problems will be described in detail below with specific embodiments. These several 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 with reference to the drawings.

[0044] At present, the photovoltaic industry generates a large amount of wastewater, and direct discharge will cause waste of resources and environmental pollution. When preparing silica sol in the prior art, sodium silicate aqueous solutions with relatively high purity are mostly used. Although silica sol can also be prepared, the cost is relatively high. Through research, the inventor found that, firstly, photovoltaic wastewater mainly contains sodium hydroxide, sodium silicate and organic additives, and is rich in elements such as Si and Na; secondly, due to the use of high-purity electronic-grade silicon wafers and electronic-grade chemicals in the photovoltaic production and processing processes, the obtained silicon-rich wastewater has high purity, especially low metal content (1-2 ppm); thirdly, in the photovoltaic industry, when making the battery wafers velvet and alkali polishing, the organic additives (stabilizers, nucleating agents, etc.) used can be used as organic additives during the growth of silica sol to promote the uniform dispersion of silica sol particles; the produced water (sodium hydroxide solution) after sodium-silicon separation of the wastewater 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 by using photovoltaic wastewater, including:

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

[0047] 2) Preparation of active silicic acid mother liquor: The above-mentioned silicon-rich wastewater is successively removed of impurity anions, impurity cations and C 4 -C 10 fatty chains to obtain an active silicic acid feed liquid with a pH of 2.0-3.5; add a catalyst to prepare an active silicic acid mother liquor;

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

[0049] 4) Preparation of silica sol: The above-mentioned sodium hydroxide solution is purified and diluted to a mass concentration of 1-3%; after heating the above-mentioned silica sol seed liquid to 80-90 °C, add the above-mentioned active silicic acid mother liquor 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% and carry out a cross-linking reaction for 5-10 h to obtain silica sol. The flow chart is Figure 1 .

[0050] Specifically, in step 1), after removing peroxides in the photovoltaic wastewater, separate silicon and sodium elements 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, the photovoltaic wastewater is derived from the alkali-containing and silicon-containing wastewater generated during the production of photovoltaic cells in the photovoltaic industry, where the mass concentration of NaOH is 0.5 - 4%, SiO 2 The mass concentration of is 0.3 - 1.6%, the mass concentration of peroxide is 0.5 - 3%, the COD content is 200 - 3000 ppm, and it contains ethylenediaminetetraacetic acid, polyacrylamide, ethanolamine, carboxymethylcellulose, ethylene glycol ether, methacrylic acid, etc.

[0052] When the present invention removes peroxide, the flow rate of the photovoltaic wastewater is not specifically limited; in one embodiment, the flow rate is 2 - 4 m / h, such as 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 peroxide; in one embodiment, peroxide can be removed by using catalysts such as manganese sand, iron oxide, alumina, 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 adopted; further, a silicon and sodium element separation membrane is used for separation. The silicon-rich wastewater and sodium hydroxide solution are separated. The silicon-rich wastewater is used for the subsequent preparation of silica sol; the sodium hydroxide solution is used to adjust the pH during the preparation of silica sol to achieve comprehensive utilization of waste.

[0055] Further, in the separated silicon-rich wastewater, the mass concentration of SiO 2 is 3 - 6%, the mass concentration of NaOH is 0.5 - 2%, and the COD content < 3000 ppm; 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 first treated to remove impurity anions, then impurity cations, and then the C 4 -C 10 fatty chain to obtain an active silicic acid feed liquid with a pH of 2.0 - 3.5, such as 2.0, 2.5, 3.0, 3.5; finally, a catalyst is added to the active silicic acid feed liquid to prepare an active silicic acid mother liquor.

[0057] Further, the C 4 -C 10 fatty chain in the present invention is mainly a substance that has no promoting effect on the reaction of silica sol, such as organic substances like ethylenediaminetetraacetic acid, ethylene glycol ether, methacrylic acid, etc.

[0058] The present invention does not specifically limit the removal of impurity anions, impurity cations (such as sodium ions) and C4 -C 10 There is no limitation on the method for the aliphatic chain of 4 -C 10 ; in one embodiment, an anion exchange resin is used to remove impurity anions in the silicon-rich wastewater, a cation exchange resin is used to remove impurity cations in the silicon-rich wastewater, and a macroporous adsorption resin is used to remove -C 4 -C 10 of the aliphatic chain that has no promoting effect on the silica sol reaction, and a part of the catalysts contained in the silicon-rich wastewater itself is retained, namely polyacrylamide, ethanolamine, and carboxymethyl cellulose.

[0059] The present invention does not specifically limit the types of the anion exchange resin, the cation exchange resin, and the macroporous adsorption resin, as long as they can remove impurity anions, impurity cations, and -C 4 -C 10 of the aliphatic chain. For example, the anion exchange resin can be selected from any one of primary amino resins, secondary amino resins, tertiary amino resins, and alkanolamine resins. Preferably, the anion exchange resin is a primary amino resin; the cation exchange resin can be selected from any one of sulfonic acid group resins, phenolic group resins, and carboxyl group resins. Preferably, the cation exchange resin is a sulfonic acid group resin; the macroporous adsorption resin can be selected from any one of styrene divinyl copolymer adsorption resins and methyl acrylate divinyl copolymer adsorption resins. Preferably, the macroporous adsorption resin is a styrene divinyl copolymer adsorption resin.

[0060] Among them, the pore diameter 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 commercially available products can be used.

[0062] Further, the macroporous adsorption resin is purchased from Huzhou Kesi Technology Co., Ltd., and the model is KSA410 ion exchange resin.

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

[0064] In one embodiment, the pre-treatment method of the anion exchange resin includes: soaking the anion exchange resin in NaCl solution and NaOH solution in sequence, and then rinsing it with distilled water until it is neutral.

[0065] ​​​​​​​​Further, the soaking time of the anion exchange resin in the NaCl solution is 1-2 h, for example, the soaking time is 1 h, 1.5 h or 2 h; the soaking time of the anion exchange resin in the NaOH solution is 2-3 h, for example, the soaking time is 2 h, 2.5 h or 3 h.

[0066] Further, the mass concentration of the NaCl solution is 10-12%, for example, the mass concentration is 10%, 11% or 12%; the mass concentration of the NaOH solution is 5-6%, for example, the mass concentration is 5%, 5.5% or 6%.

[0067] Further, the usage volumes of the NaCl solution and the NaOH solution are respectively 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 includes: sequentially soaking the macroporous adsorption resin in the HCl solution and the Na 2 CO 3 solution, and rinsing with distilled water until neutral.

[0069] Further, the soaking time of the macroporous adsorption resin in the HCl solution is 2-3 h, for example, the soaking time is 2 h, 2.5 h or 3 h; the soaking time of the macroporous adsorption resin in the Na 2 CO 3 solution is 1-2 h, for example, the soaking time is 1 h, 1.5 h or 2 h.

[0070] Further, the mass concentration of the HCl solution is 4-5%, for example, the mass concentration is 4%, 4.5% or 5%; the mass concentration of the Na 2 CO 3 solution is 8-10%, for example, the mass concentration is 8%, 9% or 10%.

[0071] Further, the usage volumes of the HCl solution and the Na 2 CO 3 solution are respectively 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: sequentially soaking the cation exchange resin in the NaOH solution and the HCl solution, and rinsing with distilled water until neutral.

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

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

[0075] Furthermore, the volumes of the NaOH solution and the HCl solution used are respectively 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] The anion exchange resin, the cation exchange resin and the macroporous adsorption resin can be recycled, achieving the effects of cost reduction and resource recycling.

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

[0078] The present invention does not specifically limit the preparation method of the alkaline buffer solution, as long as it can adjust the pH of the alkaline catalyst to 8 - 9; in one embodiment, NH 4 Cl, ammonia water and deionized water are mixed and formulated into an alkaline buffer solution. Using the conventional preparation method of an alkaline buffer solution, the raw materials are cheap and easily available, and the preparation method is simple.

[0079] The present invention does not limit the heating rate during heating, as long as it can heat the mixed system of the alkaline buffer solution and the alkaline catalyst 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 dropping rate of the ethanol solution of tetraethyl orthosilicate, as long as it can make tetraethyl orthosilicate react fully with the alkaline catalyst and the alkaline buffer solution, and the seed particle size in the prepared silica sol seed solution is uniform. In one embodiment, the dropping rate of the ethanol solution of tetraethyl orthosilicate is 2 - 10 mL / min, for example, the dropping rate is 2 mL / min, 6 mL / min, 8 mL / min or 10 mL / min; preferably, the dropping rate is 6 mL / min.

[0081] In step 4), the sodium hydroxide solution separated in step 1) is purified and diluted to prepare a sodium hydroxide solution with a mass concentration of 1-3%, such as 1%, 2%, or 3%; after heating the silica sol seed solution prepared in step 3) to 80-90 °C, such as heating to 80 °C, 85 °C, or 90 °C, the active silicic acid mother liquor prepared in step 2) is added, and then the pH of the above system is adjusted to 10-11 with a sodium hydroxide solution with a mass concentration of 1-3%, such as pH 10 or 11; the above system is subjected to a crosslinking reaction at 80-90 °C for 5-10 h, such as the reaction time being 5 h, 6 h, 7 h, 8 h, 9 h, or 10 h; to obtain silica sol.

[0082] The present invention does not limit the method for purifying the sodium hydroxide solution, and only metal cations other than sodium ions and anions other than hydroxide ions in the solution need to be removed.

[0083] Further, a 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 group resin and carboxyl group resin; an anion exchange resin is used to remove anions other than hydroxide ions. In one embodiment, the anion exchange resin is one or more of amino acrylic resin and amino styrene resin.

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

[0085] Further, the active silicic acid mother liquor is added in batches, and 5-10% of the total mass of the active silicic acid mother liquor is added in each batch, such as 5%, 6%, 7%, 8%, 9%, or 10% of the total mass added in each batch. Adding the active silicic acid mother liquor in batches makes the reaction more complete and the obtained silica sol particles more uniform.

[0086] The present invention uses photovoltaic wastewater as a raw material, first conducts purification, and then combines ion exchange technology and seed-induced mixed growth technology to prepare silica sol. At the same time, the pH is adjusted with the sodium hydroxide solution prepared in step 1), and part of the organic matter contained in the photovoltaic wastewater itself is used as a catalyst, and only needs to be supplemented to the required amount according to the actual situation, saving costs and realizing resource recycling. The cost of preparing silica sol is reduced, the Si and Na resources in photovoltaic wastewater are fully utilized, and pollution is reduced.

[0087] In a specific embodiment, in step 4), the silica sol with a mass concentration of 10-25% concentrated to SiO 2 the active silicic acid mother liquor and the sodium hydroxide solution with a mass concentration of 1-3% are subjected to at least one or more crosslinking reactions to obtain silica sols with different particle sizes. The silica sol is concentrated to SiO 2The mass concentration is 10 - 25%, for example, SiO 2 The mass concentration is 10%, 15%, 20% or 25%; preferably, the mass concentration of SiO 2 is 15%. The silica sol is concentrated to increase the concentration so that it can react better during the next cross - linking of the silica sol.

[0088] Furthermore, the present invention does not specifically limit the method of concentration treatment. It is only necessary to concentrate the mass concentration of SiO 2 in the silica sol to 10 - 25%. In one embodiment, the concentration treatment method is any one of membrane concentration, evaporation concentration, and freeze concentration; preferably, membrane concentration is used.

[0089] The present invention does not limit the number of cross - linking reactions. Specifically, the number of cross - linking reactions is determined according to the required particle size of the silica sol, as long as the required particle size is achieved. For example, one, two, three, four or more than four cross - linking reactions can be carried out.

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

[0091] Furthermore, taking the case of a total of two cross - linking reactions as an example:

[0092] The silica sol obtained in step 4) is concentrated to make the mass concentration of SiO 2 concentrated to 10 - 25%, and heated to 80 - 90 °C, for example, heated to 80 °C, 85 °C or 90 °C; under stirring, the active silicic acid mother liquor is added in batches, 10% of the total mass of the active silicic acid mother liquor is added each time, and the pH is adjusted to 10 - 11 with a 1 - 3% sodium hydroxide solution, and the reaction is carried out for 5 - 10 h to adjust the uniformity of the colloidal particles to obtain the required silica sol.

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

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

[0095] 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.

[0096] 2) Preparation of active silicic acid mother liquor: The above-mentioned silicon-rich wastewater is successively removed of impurity anions, impurity cations, and the aliphatic chain of -C 4 -C 10 to obtain an active silicic acid feed liquid with a pH of 2.0 - 3.5; a catalyst is added to prepare the active silicic acid mother liquor.

[0097] 3) Preparation of silica sol seed liquid: An alkaline buffer solution with a pH of 8 - 9 is mixed with an alkaline catalyst and heated to 50 - 70 °C. After dropping an ethanol solution of tetraethyl orthosilicate, the reaction is carried out for 4 - 8 h to form a silica sol seed liquid.

[0098] 4) Preparation of silica sol: The above-mentioned sodium hydroxide solution is prepared into a mass concentration of 1 - 3%; after heating the above-mentioned silica sol seed liquid to 80 - 90 °C, the above-mentioned active silicic acid mother liquor is added to obtain a mixed system; the pH of the mixed system is adjusted to 10 - 11 with a sodium hydroxide solution with a mass concentration of 1 - 3% for cross-linking reaction, and the reaction time is 5 - 10 h to obtain a primary growth product of silica sol.

[0099] 5) Preparation of secondary growth product of silica sol: The primary growth product of silica sol obtained in step 4) is concentrated to make the mass concentration of SiO 2 concentrated to 10 - 25%, and heated to 80 - 90 °C. The active silicic acid mother liquor is added in batches under stirring, and the pH is adjusted to 10 - 11 with a 1 - 3% sodium hydroxide solution, and the reaction is carried out for 5 - 10 h to obtain a secondary growth product of silica sol.

[0100] 6) Preparation of tertiary growth product of silica sol: The secondary growth product of silica sol obtained in step 5) is concentrated to make the mass concentration of SiO 2 concentrated to 10 - 25%, and heated to 80 - 90 °C. The active silicic acid mother liquor is added in batches under stirring, and the pH is adjusted to 10 - 11 with a 1 - 3% sodium hydroxide solution, and the reaction is carried out for 5 - 10 h to obtain a tertiary growth product of silica sol.

[0101] 7) Preparation of quaternary growth product of silica sol: Using the tertiary growth product of silica sol obtained in step 6) as raw material, the tertiary growth product of silica sol is concentrated to make the mass concentration of SiO 2 concentrated to 10 - 25%, and heated to 80 - 90 °C. The active silicic acid mother liquor is added in batches under stirring, and the pH is adjusted to 10 - 11 with a 1 - 3% sodium hydroxide solution, and the reaction is carried out for 5 - 10 h to obtain a quaternary growth product of silica sol.

[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 polyacrylamide, ethanolamine, and carboxymethyl cellulose are contained in the photovoltaic wastewater itself, the prepared active silica stock solution contains polyacrylamide, ethanolamine, and carboxymethyl cellulose, but the content is insufficient. Therefore, the catalyst needs to be supplemented according to the content of polyacrylamide, ethanolamine, and carboxymethyl cellulose in the active silica stock solution. In the photovoltaic industry, organic additives (stabilizers, nucleating agents, etc.) used in wafer texturing and alkaline etching can be used again as catalysts for the growth of silica sol, promoting the uniform dispersion of silica sol particles.

[0104] In a specific embodiment, the mass ratio of polyacrylamide, ethanolamine, and carboxymethyl cellulose in the active silica mother liquor 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 supplementation or the specific number of supplements, because the contents of polyacrylamide, ethanolamine, and carboxymethyl cellulose in photovoltaic wastewater from different batches or manufacturers may vary, and can be supplemented according to the actual situation. It is only necessary to make the mass ratio of polyacrylamide, ethanolamine, and carboxymethyl cellulose in the prepared active silica mother liquor be 1:0.3 - 0.8:0.2 - 0.8.

[0105] In a specific embodiment, in the active silica mother liquor, the total mass of polyacrylamide, ethanolamine, and carboxymethyl cellulose and SiO 2 has a mass ratio of 1 - 8:100; for example, the mass ratio is 1:100, 3:100, 6:100, or 8:100. After supplementation, make the total mass of polyacrylamide, ethanolamine, and carboxymethyl cellulose and SiO 2 in the active silica mother liquor have a mass ratio of 1 - 8:100, and the mass ratio of polyacrylamide, ethanolamine, and carboxymethyl cellulose is 1:0.3 - 0.8:0.2 - 0.8. This avoids the influence of too high a mass ratio on the purity of subsequent products and too low a mass ratio resulting in poor growth effect.

[0106] In a specific embodiment, the basic 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, and L-lysine; or any two of L-glutamic acid, L-arginine, L-aminobutyric acid, and L-lysine; or a mixture of L-glutamic acid, L-arginine, L-aminobutyric acid, and L-lysine.

[0107] When the basic 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 basic catalyst, and conventional commercially available products can be used.

[0109] The present invention uses basic amino acids as basic catalysts, uses a basic buffer solution to maintain an appropriate pH value, provides a mild reaction environment, enables the product to have monodispersity, and the prepared silica sol seeds have good chemical uniformity, fine particles, high purity, high reaction activity, and are suitable for use as seeds for the next-step growth of silica sol.

[0110] In a specific embodiment, in step 3), the ethanol solution of tetraethyl orthosilicate contains 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, it is easier to promote the production of silica sol seeds.

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

[0112] Furthermore, when using tetraethyl orthosilicate to prepare silica sol seeds, by controlling its content, the reaction process can be metered and prepared, and the reaction can be controlled.

[0113] In a possible embodiment, in step 4), the mass ratio of the active silica mother liquor to the 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, it can better promote the formation of silica sol.

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

[0115] The present invention does not limit the stirring speed here, as long as colloidal silica with uniform particle size can be obtained.

[0116] In a specific embodiment, when stirring is carried out during heating, 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 colloidal silica 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 colloidal silica reaction solution can be adjusted to 11-12. In a specific embodiment, ammonia water is used to adjust the pH. Using ammonia water to adjust the pH is more stable, avoiding excessive alkalinity from damaging the solution and being easy to remove at the same time.

[0118] The growth process of colloidal silica particles has relatively high requirements for the surface properties of the seed colloidal particles. The process of adjusting the uniformity of the colloidal particles can also improve the sphericity of the colloidal silica, make its surface smooth, the structure dense, improve the uniformity of the product, and is beneficial to the growth of colloidal particles multiple times.

[0119] The second aspect of the present invention provides a system for implementing the above method, including:

[0120] Peroxide removal device, silicon-sodium separation device, impurity anion removal device, impurity cation removal device, device for removing C 4 -C 10 fatty chain device, active silica mother liquor device, seed generation device, colloidal silica growth device, sodium hydroxide impurity removal device and sodium hydroxide solution preparation device;

[0121] 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 the silicon-rich wastewater. The impurity cation removal device is used to remove metal cations in the silicon-rich wastewater. For removing C 4 -C 10The fatty chain device is used to remove fatty chain substances with 4-10 carbon atoms in the silicon-rich wastewater. The active silicic acid mother liquor device is used to prepare and store the active silicic acid mother liquor. The seed crystal generation device is used to prepare the silica sol seed crystal solution. The silica sol growth device is used to prepare the silica sol. The sodium hydroxide impurity removal device is used to remove metal cations other than sodium ions and anions other than hydroxide ions. The sodium hydroxide solution preparation device is used to adjust the mass concentration of the sodium hydroxide solution to 1-3%.

[0122] The sodium-silicon separation device includes a first outlet and a second outlet. The first outlet is used for the flow of the separated sodium-containing feed liquid, and the second outlet is used for the flow of the silicon-containing feed liquid.

[0123] The silica sol growth device includes a first inlet, a second inlet, and a third inlet. The first inlet is used for the flow of the sodium hydroxide solution, the second inlet is used for the flow of the active silicic acid mother liquor, and the third inlet is used for the flow of the silica sol seed crystal solution.

[0124] The outlet of the peroxide removal device is connected to the inlet of the sodium-silicon separation device. The first outlet of the sodium-silicon separation device is connected to the inlet of the sodium hydroxide impurity removal device and then to the inlet of the sodium hydroxide solution preparation device through the sodium hydroxide impurity removal device. 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 sodium-silicon separation device passes through the impurity anion removal device, the impurity cation removal device, and the C 4 -C 10 fatty chain device and is connected to the inlet of the active silicic acid mother liquor device. The outlet of the active silicic acid mother liquor device is connected to the second inlet of the silica sol growth device. The outlet of the seed crystal generation device is connected to the third inlet of the silica sol growth device.

[0126] The residence time of the silicon-rich wastewater in the impurity anion removal device is 0.5-1 h; the residence time in the impurity cation removal device is 2-3 h; and the residence time in the C 4 -C 10 fatty chain device is 0.5-1 h.

[0127] Figure 2 is a schematic structural diagram of the system of the present invention in an embodiment. As Figure 2 shown, the system includes a peroxide removal device 1, a sodium-silicon separation device 2, an impurity anion removal device 3, an impurity cation removal device 4, a C 4 -C 10 fatty chain device 5, an active silicic acid mother liquor device 16, a seed crystal generation device 15, a silica sol growth device 14, a sodium hydroxide impurity removal device 6, and a sodium hydroxide solution preparation 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 silicic acid mother liquor device 16 for circulating the active silicic acid mother liquor; the third inlet is connected to the outlet of the seed crystal generation device 15 for circulating the silica sol seed crystal 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 for circulating the separated sodium-containing feed liquid, that is, discharging the sodium hydroxide solution. 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 purification device 6 and the sodium hydroxide solution preparation device 7; the second outlet of the silicon-sodium separation device 2 is used for circulating the silicon-containing feed liquid, that is, discharging the silicon-rich wastewater. The second outlet of the silicon-sodium separation device 2 is connected to the inlet of the active silicic acid mother liquor device 16 through the impurity anion removal device 3, the impurity cation removal device 4, and the device 5 for removing the aliphatic chain of -C 4 -C 10 of the fat chain.

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

[0131] The silicon-sodium separation device 2 is used to separate silicon and sodium elements in the 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 purification device 6. The photovoltaic wastewater with peroxides removed is divided into a sodium hydroxide route and a silicon-rich wastewater route after passing through the silicon-sodium separation device 2. The materials in the sodium hydroxide route are discharged from the first outlet of the silicon-sodium separation device 2 and enter the sodium hydroxide purification device 6; the materials in the silicon-rich wastewater route are discharged from the second outlet of the silicon-sodium separation device 2 and enter the impurity anion removal device 3.

[0132] Further, the present invention does not make specific limitations on the selection of elements used in the silicon-sodium separation device 2, which can be a conventional selection in the art, as long as it can separate silicon and sodium elements. In one embodiment, the element used is a silicon-sodium element separation membrane element.

[0133] Further, the present invention does not limit the type of the 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 can be used.

[0135] The impurity anion removal device 3 is used to remove impurity anions in the photovoltaic wastewater. 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 the 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 impurity anions is achieved. In one embodiment, the residence time is 0.5 - 1 h, for example, the residence time is 0.5 h, 0.8 h, 1 h; preferably, the residence time is 0.8 h. 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 the photovoltaic wastewater. The outlet of the impurity cation removal device 4 is connected to the inlet of the -C 4 -C 10 fatty chain device 5. After the above-mentioned silicon-rich wastewater with the impurity anions removed enters the impurity cation removal device 4, it stays until the metal cations are removed, and then the silicon-rich wastewater with the metal cations removed is discharged from the outlet of the impurity cation removal device 4 and enters the -C 4 -C 10 fatty 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 h, for example, the residence time is 2 h, 2.5 h, or 3 h; preferably, the residence time is 2.5 h. Within this residence time range, the impurity cations can be better removed.

[0139] The -C 4 -C 10 fatty chain device 5 is used to remove organic substances such as ethylenediaminetetraacetic acid, ethylene glycol ether, and methacrylic acid in the photovoltaic wastewater that have no promoting effect on the reaction with silica sol, and retain polyacrylamide, ethanolamine, and carboxymethyl cellulose contained in the silicon-rich wastewater itself; the outlet of the -C 4 -C 10 fatty chain device 5 is connected to the inlet of the active silica mother liquor device 16. After the above-mentioned silicon-rich wastewater with the metal cations removed enters the -C 4 -C 10 fatty chain device 5, it stays until the -C 4-C 10 of the fatty chain, and then an active silicic acid feed liquid is obtained. The active silicic acid feed liquid is discharged from the outlet of the device 5 for removing -C 4 -C 10 of the fatty chain and enters the active silicic acid mother liquor device 16.

[0140] In the present invention, there is no limitation on the residence time of the silicon-rich wastewater in the device 5 for removing -C 4 -C 10 of the fatty chain, as long as the effect of removing -C 4 -C 10 of the fatty chain is achieved. In one embodiment, the residence time is 0.5 - 1 h, for example, the residence time is 0.5 h, 0.6 h, 0.8 h or 1 h; preferably, the residence time is 0.8 h. Within this residence time range, -C 4 -C 10 of the fatty chain that has no promoting effect on the reaction of silica sol can be better removed.

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

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

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

[0144] Furthermore, in order to facilitate the addition of the alkaline buffer solution and the alkaline catalyst, the seed crystal generating device 15 is provided with a feeding 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 sodium-silicon separation device 2. The outlet of the sodium hydroxide impurity removal device 6 is communicated with the inlet of the sodium hydroxide solution preparation device 7. The sodium hydroxide impurity removal device 6 makes the sodium hydroxide solution used for adjusting the pH free of other impurities.

[0146] The sodium hydroxide solution preparation device 7 is used to dilute the mass concentration of the impurity-removed sodium hydroxide solution to 1 - 3%. The outlet of the sodium hydroxide solution preparation device 7 is communicated with the first inlet of the silica sol growth device 14 for adjusting the pH of the crosslinking 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 silicic acid mother liquor. The active silicic acid mother liquor, 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 obtain silica sol.

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

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

[0150] Furthermore, the present invention does not limit the connection method between each device. For example, pipeline connection can be adopted.

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

[0152] The concentration device is used to concentrate the silica sol from the silica sol growth device.

[0153] Each silica sol growth device includes a first inlet, a second inlet, and a third inlet. The first inlet is used for flowing the sodium hydroxide solution, the second inlet is used for flowing the active silicic acid mother liquor, and the third inlet is used for flowing the 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 silicic acid mother liquor device, and the third inlet of each silica sol growth device is connected to the outlet of the concentration device; the outlet of the silica sol growth device is connected to the inlet of the concentration device; the concentration device further includes an outlet for outputting the silica sol meeting 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 four cross-linking reactions in total as an example, the device diagram is shown in Figure 4 .

[0157] Figure 4 It is a schematic diagram of the system provided in an embodiment of the present invention. As shown in the figure, the silica sol growth device further 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 concentration device 17 is used to concentrate the silica sol obtained in the previous step to a SiO 2 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, the active silicic acid mother liquor, and a sodium hydroxide solution with a mass concentration of 1 - 3% for cross-linking reaction to prepare a silica sol secondary growth product; the silica sol tertiary growth device 10 is used to mix the silica sol secondary growth product, the active silicic acid mother liquor, and a sodium hydroxide solution with a mass concentration of 1 - 3% for cross-linking reaction to prepare a silica sol tertiary growth product; the silica sol quaternary growth device 8 is used to mix the silica sol tertiary growth product, the active silicic acid mother liquor, and a sodium hydroxide solution with a mass concentration of 1 - 3% for cross-linking reaction to prepare a silica sol quaternary growth product.

[0159] The concentration device 17 includes a first inlet, a second inlet, and a third inlet, 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 the 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 supply 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 concentration 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 used.

[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, for example, the temperature is 60 °C, 65 °C, 70 °C, 75 °C, or 80 °C; preferably, the temperature is 70 °C.

[0163] Further, 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 time, 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 flowing a sodium hydroxide solution with a mass concentration of 1 - 3%, the second inlet is used for flowing the mother liquor of active silicic acid, and the third inlet is used for flowing the concentrated silica sol.

[0166] The first inlet of each silica sol growth device is communicated with the outlet of the sodium hydroxide solution preparation device 7, the second inlet of each silica sol growth device is communicated with the outlet of the mother liquor device 16 of active silicic acid, and the third inlet of each silica sol growth device is communicated with the outlet of the concentration device 17; the outlet of each silica sol growth device is communicated with the inlet of the concentration device 17; the concentration device further includes an outlet for outputting the silica sol meeting the target particle size.

[0167] Further, the mother liquor device 16 of active silicic acid is connected with a first pipeline, a second pipeline, a third pipeline and a fourth pipeline; the first pipeline is communicated with the second inlet of the silica sol growth device 14 for providing the mother liquor of active silicic acid to the silica sol growth device 14; the second pipeline is communicated with the second inlet of the silica sol secondary growth device 12 for providing the mother liquor of active silicic acid to the silica sol secondary growth device 12; the third pipeline is communicated with the second inlet of the silica sol tertiary growth device 10 for providing the mother liquor of active silicic acid to the silica sol tertiary growth device 10; the fourth pipeline is communicated with the second inlet of the silica sol quaternary growth device 8 for providing the mother liquor of active silicic acid to the silica sol quaternary growth device 8.

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

[0169] The outlet of the silica sol growth device 14 is communicated with the first inlet of the concentration device 17, the second outlet of the silica sol secondary growth device 12 is communicated with the second inlet of the concentration device 17, the first outlet of the silica sol secondary growth device 12 is used for discharging the silica sol secondary product, the second outlet of the silica sol tertiary growth device 10 is communicated with the third inlet of the concentration device 17, and the first outlet of the silica sol tertiary growth device 10 is used for discharging the silica sol tertiary product.

[0170] The first outlet of the concentration device 17 is communicated with the third inlet of the silica sol secondary growth device 12, the second outlet of the concentration device 17 is communicated with the third inlet of the silica sol tertiary growth device 10, and the third outlet of the concentration device 17 is communicated with 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 concentration device 17 and then introduced into the silica sol secondary growth device 12, and the materials in the active silica mother liquor device 16 and the materials in the sodium hydroxide solution preparation device 7 are introduced into the silica sol secondary growth device 12. After the crosslinking reaction, the uniformity of the colloidal particles is adjusted to obtain the silica sol secondary growth product; the obtained silica sol secondary growth product is introduced into the concentration device 17, and after concentration, it is introduced into the silica sol tertiary growth device 10, and the materials in the active silica mother liquor device 16 and the materials in the sodium hydroxide solution preparation device 7 are introduced into the silica sol tertiary growth device 10. After the crosslinking reaction, the uniformity of the colloidal particles is adjusted to obtain the silica sol tertiary growth product; the obtained silica sol tertiary growth product is introduced into the concentration device 17, and after concentration, it is introduced into the silica sol quaternary growth device 8, and the materials in the active silica mother liquor device 16 and the materials in the sodium hydroxide solution preparation device 7 are introduced into the silica sol quaternary growth device 8. After the crosslinking reaction, the uniformity of the colloidal particles is adjusted to obtain the silica sol quaternary growth product. In the above process, the reaction can be stopped when the product obtained at any time reaches the required target particle size.

[0172] Further, in order to better collect the product, in one embodiment, a product concentration device 18 is further included. The concentration device 17 is used to concentrate the silica sol obtained in the previous step to a mass concentration of SiO 2 in the silica sol of 10 - 25%; the product concentration device 18 is used to concentrate the product that reaches the target particle size to obtain silica sol.

[0173] Further, in order to better collect the product, 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 communicated with the secondary product storage device 11, the tertiary product storage device 9, and the quaternary product storage device 19 respectively through the product concentration device 18, and are respectively used to collect the silica sol secondary product, the silica sol tertiary product, and the silica sol quaternary product.

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

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

[0176] Example 1

[0177] In the production of battery chips in the photovoltaic industry, 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 1000 ppm, and it contains organic substances 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 example specifically comprises the following steps:

[0179] Step 1) Separation of silicon and sodium elements from wastewater: The photovoltaic wastewater is sequentially subjected to peroxide removal treatment and silicon-sodium element separation treatment at a flow rate of 3 m / h to obtain silicon-rich wastewater and sodium hydroxide liquid. The silicon-sodium element separation is carried out by a two-stage membrane separation, and the silicon-sodium element separation membrane selects a polysulfone membrane element.

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

[0181] Step 2) Preparation of active silicic acid mother liquor: 500 L of silicon-rich wastewater first passes through an impurity-removing anion ion exchange device and then through an impurity-removing cation ion exchange device and a device for removing C 4 -C 10 fatty chain device. The residence time of the silicon-rich wastewater in the impurity-removing anion ion exchange device is 0.8 h; the residence time in the impurity-removing cation ion exchange device is 2.5 h; the residence time in the device for removing C 4 -C 10 fatty chain device is 0.6 h; an active silicic acid feed liquid with a pH of 3.0 is obtained. Analyze the contents of organic substances polyacrylamide, ethanolamine, and carboxymethyl cellulose in the active silicic acid feed liquid. The total mass of the three is 0.11% of the mass of the silicon-rich wastewater (accounting for 2.2% of the SiO 2 content of the active silicic acid mother liquor), and the mass ratio of polyacrylamide, ethanolamine, and carboxymethyl cellulose is 1:0.6:0.2. The mass of the added catalyst reaches the SiO 24% of the content, that is, a total of 450 g of catalyst needs to be added, 171 g of polyacrylamide, 198 g of ethanolamine, and 81 g of carboxymethyl cellulose. After addition, the mass ratio of the three is 1:0.8:0.3 to obtain the active silica mother liquor.

[0182] The anion exchange device for removing impurities uses 1000 L of primary amino resin; the cation exchange device for removing impurities uses 2500 L of sulfonic acid group resin. For the device removing the C 4 -C 10 fatty acid chain uses 800 L of styrene divinyl copolymer adsorption resin. Before use, the anion exchange device for removing impurities is soaked in 10% NaCl solution for 1 h and 5% NaOH solution for 2 h in sequence; for the device removing the C 4 -C 10 fatty acid chain, before use, it is soaked in 4% HCl solution for 3 h and 8% Na 2 CO 3 solution for 2 h; before use, the cation exchange device for removing impurities is soaked in 4% NaOH solution for 1 h and 5% HCl solution for 3 h in sequence.

[0183] Step 3) Preparation of silica sol seed solution: 20 kg of deionized water is mixed with NH 4 Cl and ammonia water to prepare an alkaline buffer solution with a pH of 8.5. After adding L-arginine, it is heated to 70 °C under stirring. 8 kg of tetraethyl orthosilicate and 3.5 kg of ethanol are configured into a 70% ethanol solution, which is added dropwise to the alkaline buffer solution. After the addition is completed, the reaction is carried out for 5 h to form a silica sol seed solution.

[0184] Step 4) Primary growth of silica sol: The silica sol seed solution in Step 3 is heated to 90 °C, and 220 kg of active silica mother liquor is added in batches under stirring. The pH is adjusted to 10.5 with 1% sodium hydroxide solution, and under stirring conditions, a cross-linking reaction is carried out for 8 h; after cooling, the pH is adjusted to 11 with ammonia water, then the heating temperature is 70 °C, and the stirring reaction is carried out for 8 h to adjust the uniformity of the colloidal particles. After the reaction, the primary growth product of silica sol is obtained and enters the primary growth product storage tank. Among them, the stirring speed during the adjustment of the colloidal particle uniformity is 1 / 3 of the stirring speed during the cross-linking reaction process.

[0185] Step 5) Secondary growth of silica sol: If the primary growth product of silica sol does not meet the target particle size, the primary growth product of silica sol is fed into the growth concentrator to concentrate the mass concentration of SiO 2 in the silica sol to 15%, heated to 90 °C, and 230 kg of active silica mother liquor is added in batches under stirring. The pH is adjusted to 11 with 1% sodium hydroxide solution, and the reaction is maintained for 10 h. After cooling, the pH is adjusted to 11 with ammonia water, then the heating temperature is 60 °C, and the reaction is carried out for 6 h to obtain the secondary growth product of silica sol.

[0186] Step 6) Third growth of silica sol: If the product of the second growth of silica sol does not meet the target particle size, concentrate the product of the second growth of silica sol to a SiO 2 mass concentration of 15%, repeat Step 5) to obtain the product of the third growth of silica sol.

[0187] Step 7) Fourth growth of silica sol: If the product of the third growth of silica sol does not meet the target particle size, concentrate the product of the third growth of silica sol to a SiO 2 mass concentration of 15%, repeat Step 5) to obtain the product of the fourth growth of silica sol.

[0188] The particle size of the silica sol in the silica sol seed solution is 5 - 15 nm; the particle size of the product of the first growth of the prepared silica sol is 15 - 25 nm; the particle size of the product of the second growth of silica sol is 40 - 50 nm; the particle size of the product of the third growth of silica sol is 60 - 70 nm; the particle size of the product of the fourth growth of silica sol is 80 - 90 nm.

[0189] Finally, it should be noted that: After considering the specification and practicing the invention disclosed herein, those skilled in the art will readily think of other embodiments of the present invention. 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 general knowledge or conventional technical means in the technical field not disclosed in the present invention. It is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited 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 silicon-rich wastewater is retained, and the catalyst in the silicon-rich wastewater is obtained to obtain an active silicate solution with a pH of 2.0-3.5; the catalyst is added to obtain an active silicate mother solution; the catalyst includes polyacrylamide, ethanolamine and carboxymethyl cellulose; after adding the catalyst, 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; 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 to a mass concentration of 1-3%; the silica sol seed solution is heated to 80-90° C., and then the active silicate 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; 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; 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.

2. 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.

3. The method according to claim 2, 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.

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

100.

5. 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.

6. The method according to claim 1, characterized in that When the cross-linking reaction is performed once, the obtained product is a silica sol once-grown product, and the particle size of the silica sol once-grown product is 15-25nm; when the cross-linking reaction is performed twice, the obtained product is a silica sol twice-grown product, and the particle size of the silica sol twice-grown product is 40-50nm; when the cross-linking reaction is performed three times, the obtained product is a silica sol three-times grown product, and the particle size of the silica sol three-times grown product is 60-70nm; when the cross-linking reaction is performed four times, the obtained product is a silica sol four-times grown product, and the particle size of the silica sol four-times grown product is 80-90nm; when the cross-linking reaction is performed five times, the obtained product is a silica sol five-times grown product, and the particle size of the silica sol five-times grown product is above 100nm.

7. A system for executing the method according to any one of claims 1 to 6, 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.

8. The system according to claim 7, 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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