A method for resourceful treatment of quartz sand pickling waste liquid

Abstract

The application provides a quartz sand acid washing waste liquid resource treatment method, and belongs to the field of industrial waste water treatment, and comprises the following steps: adding magnetic composite seeds to the quartz sand acid washing waste liquid, and performing magnetic separation after stirring treatment; adding soluble potassium salt to the treated waste liquid to recover potassium fluosilicate; treating the filtrate through diffusion dialysis to obtain recovered acid and dialysis residual liquid; the diffusion dialysis treatment adopts an asymmetric membrane, the asymmetric membrane has a physical gradient of one side being a dense structure and the other side being a loose structure, and the dense structure side is in contact with the waste liquid; and adding calcium oxide or calcium hydroxide to the dialysis residual liquid for deep treatment and calcium recovery. The application provides a quartz sand acid washing waste liquid resource treatment method which is low in treatment cost, high in resource recovery rate and friendly to the environment, and realizes the differentiated resource recovery of the quartz sand acid washing waste liquid.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment, specifically relating to a method for the resource-based treatment of quartz sand pickling waste liquid. Background Technology

[0002] Quartz sand is an important raw material for industries such as glass, photovoltaics, and electronics. Its high purity requirements make pickling a key purification process. The pickling process generates a large amount of waste acid containing high concentrations of acid, fluorides, metal ions, and suspended solids. If such waste acid is not properly treated, it will cause serious environmental pollution.

[0003] Currently, the main methods for treating quartz sand pickling waste liquid include neutralization precipitation and coagulation precipitation. However, traditional treatment methods have the following drawbacks: First, resource waste: valuable acid components are completely neutralized and cannot be recovered; second, low product value: the generated mixed sludge has a complex composition, is classified as hazardous waste, has high disposal costs, and poses a significant environmental risk; third, low treatment efficiency: a large amount of acid interferes with the precipitation process, resulting in large reagent dosages and high sludge yields.

[0004] Diffusion dialysis technology is widely used in the field of waste acid resource recovery due to its simple operation, low energy consumption, and lack of secondary pollution. Chinese patent application CN119430587A discloses a method for recovering mixed acid waste liquid containing hydrofluoric acid. This method removes fluorosilicic acid through a pretreatment step and then uses diffusion dialysis combined with membrane analysis to recover high-purity mixed acid. However, it has the following problems: First, no pretreatment is performed before fluorosilicic acid precipitation to remove suspended solids and other impurities from the waste acid, resulting in low purity of the prepared fluorosilicate. Second, the diffusion dialysis membrane used is prone to rapid flux decay due to surface fouling, requiring frequent cleaning or even replacement, and it is difficult to achieve high flux and high metal rejection rates. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a resource-based treatment method for quartz sand pickling waste liquid that is low in processing cost, high in resource recovery rate, and environmentally friendly, thereby achieving the differentiated resource recovery of quartz sand pickling waste liquid.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for resource recovery treatment of quartz sand pickling waste liquid includes the following steps:

[0008] S1. Impurity removal: After adding magnetic composite seed crystals to the pretreated quartz sand pickling waste liquid and stirring, magnetic separation is performed to obtain impurity-removed waste liquid and magnetic composite seed crystals that adsorb impurities.

[0009] S2. Recover potassium fluorosilicate: Add soluble potassium salt to the waste liquid obtained in step S1, stir and react, then filter to obtain solid potassium fluorosilicate and filtrate.

[0010] S3. Acid recovery by diffusion dialysis: The filtrate obtained in step S2 is subjected to diffusion dialysis to obtain recovered acid and residual dialysis liquid; the diffusion dialysis treatment uses an asymmetric membrane, which has a physical gradient with one side being a dense structure and the other side being a loose structure.

[0011] S4. Deep treatment and calcium recovery: Add calcium oxide or calcium hydroxide to the dialysis residue obtained in step S3, adjust the pH of the system to alkaline, filter after reaction, and obtain precipitate and calcium chloride solution.

[0012] In this scheme, firstly, magnetic composite seed crystals are added to the waste acid solution. These crystals can efficiently induce and adsorb micro- and nano-sized suspended matter that is difficult to remove through natural sedimentation. The matter is then rapidly separated by magnetic separation, which effectively improves the purity of the subsequent potassium fluorosilicate precipitate product. Furthermore, it reduces the pollution and clogging of the subsequent diffusion dialysis membrane by micro- and nano-sized suspended matter, laying the foundation for efficient acid recovery. At the same time, the magnetic composite seed crystals can also adsorb metal ions in the wastewater, reducing the concentration of metal ions and further reducing the impact of metal ions on the purity of acid recovery.

[0013] Secondly, by adding soluble potassium salts, the fluorosilicic acid in the wastewater is converted into potassium fluorosilicate precipitate, which improves the resource utilization value of the wastewater.

[0014] By recovering mixed acid resources through diffusion dialysis, the mixed acid can be directly reused in the quartz sand pickling process, reducing the cost of purchasing new acid. Using an asymmetric membrane as the diffusion dialysis membrane, its dense side is in contact with the waste acid, ensuring the retention rate of metal ions by the diffusion dialysis membrane. At the same time, its loose structure design reduces mass transfer resistance, ensures high throughput, and improves acid recovery rate.

[0015] The waste liquid after acid recovery can be precipitated by adding a small amount of calcium oxide or calcium hydroxide, and calcium chloride solution can be obtained for the preparation of de-icing agents.

[0016] Preferably, the magnetic composite seed crystal in step S1 is a Fe3O4@SiO2@SiO2 particle with a double-shell structure, wherein the core is superparamagnetic Fe3O4, the inner shell is a dense SiO2 protective layer, and the outer shell is a porous SiO2 functional layer.

[0017] In this solution, a specially made magnetic composite seed crystal (Fe3O4@SiO2@SiO2) is used. Its outer porous SiO2 layer can efficiently induce and adsorb suspended solids in the waste liquid, and can also be quickly separated by magnetic separation, thereby improving the treatment efficiency of waste acid liquid.

[0018] Preferably, in step S1, the stirring speed is 300-500 rpm; the amount of magnetic composite seed crystals added is 1.0‰-2.0‰ of the pretreated waste liquid.

[0019] More preferably, in step S1, the mixing time is 10-15 min.

[0020] In this scheme, by applying high-intensity stirring and strictly controlling the short mixing window, the rapid mass transfer and adsorption process of magnetic composite seed crystals on suspended matter is enhanced, while minimizing the contact time between the seed crystals and waste acid. Thus, while achieving efficient impurity removal, the chemical erosion loss of the seed crystals is significantly reduced.

[0021] Preferably, the method for preparing the magnetic composite seed crystal is as follows:

[0022] (1) Disperse nano Fe3O4 powder in ethanol solution, adjust pH to 8-9, add tetraethyl orthosilicate, mix and react at 25-30℃ for 2-4h, separate solid and liquid, wash, dry, and obtain primary Fe3O4@SiO2;

[0023] (2) Disperse primary Fe3O4@SiO2 in deionized water, adjust pH to 8-9, heat to 40-60℃, add sodium silicate solution dropwise, adjust pH to 8-9, mix and react for 1-3 hours, separate solid and liquid, wash, dry, and obtain Fe3O4@SiO2@SiO2 magnetic composite seed crystals.

[0024] Preferably, the mass-to-volume ratio of the nano-Fe3O4 powder, tetraethyl orthosilicate, and sodium silicate solution is 1.5-2.5 g: 1 mL: 40 mL; wherein the concentration of the sodium silicate solution is 7 wt%-9 wt%, and the modulus of the sodium silicate is 2.

[0025] Preferably, the dropping rate of the tetraethyl orthosilicate in step (1) is 8-12 mL / min.

[0026] Preferably, the dropping rate of the sodium silicate solution in step (2) is 18-22 mL / min.

[0027] By strictly controlling the reaction conditions, a double-shell magnetic composite seed crystal was prepared, consisting of a core of nano-Fe3O4, an inner shell of dense SiO2 protective layer, and an outer shell of porous SiO2 functional layer.

[0028] Preferably, in step S3, the method for preparing the asymmetric film includes the following steps:

[0029] a. Preparation of casting solution: Under an inert or nitrogen atmosphere, polyvinylidene fluoride containing carbon-carbon double bonds is dissolved in a solvent, N-isopropylacrylamide and an initiator are added, and the mixture is stirred at 55-65℃ for 3-4 hours. Then, acrylic acid and an initiator are added, and the mixture is stirred at 55-65℃ for 7-10 hours to obtain a polymer solution. Polyethyleneimine and modified nano-SiO2 are then added and stirred to obtain the casting solution.

[0030] b. Film formation and phase separation: The casting liquid is cast onto a heating plate at 40-50℃ to form a liquid film. After being placed in the air, it is immersed in an ice-water bath to solidify, forming a primary solid base film with a dense layer and a porous support layer.

[0031] c. Gradient crosslinking: The dense side of the nascent solid substrate film is exposed to glutaraldehyde vapor for crosslinking reaction; then it is successively immersed in polyethyleneimine solution and N,N-dimethylethylenediamine solution for further reaction;

[0032] d. Quaternization: The cross-linked membrane is obtained by quaternization treatment.

[0033] In this scheme, polyvinylidene fluoride is used as the base membrane component, and N-isopropylacrylamide (NIPAM) and acrylic acid (AA) are added to form polyacrylic acid (PAA) and poly-N-isopropylacrylamide (PNIPAM) segments. On the one hand, this improves the hydrophilicity of the membrane surface, which is beneficial to increasing the membrane flux; on the other hand, the PNIPAM segments undergo hydrophobic shrinkage at the acid washing waste liquid treatment temperature, forming a dynamic membrane surface, thereby reducing the adsorption of pollutants.

[0034] In the asymmetric membrane preparation process: the casting solution is cast onto a heated glass plate and then immersed in an ice-water bath for solidification. Due to the significant temperature difference and the contraction of the PNIPAM molecular chains at the bottom of the casting solution, the phase separation rate at the bottom (near the glass plate) is much faster than at the top (away from the glass plate), resulting in a dense, porous surface structure at the bottom and a loose, macroporous structure at the top, thus creating a physical structural gradient from dense to loose in the liquid membrane. The base membrane is then exposed to glutaraldehyde vapor with the bottom facing upwards. Glutaraldehyde preferentially reacts with the active groups of PAA and PNIPAM on and near the membrane surface, forming a highly cross-linked layer on the dense surface. The crosslinking density also exhibits a gradient change from the surface to the interior; that is, the crosslinking density is high at the bottom of the base membrane, resulting in a dense membrane structure; while the crosslinking density is low on the other side away from the bottom of the base membrane or inside the membrane, resulting in a loose membrane structure; thus, the membrane achieves a high rejection rate while maintaining a high flux; further, the base membrane is immersed in a polyethyleneimine solution, and since the large molecules of PEI are mainly adsorbed on the surface and undergo crosslinking reactions, the crosslinking density of the surface layer is further strengthened, improving the mechanical strength of the membrane; then, it is immersed in an N,N-dimethylethylenediamine solution, where the small molecules of N,N-dimethylethylenediamine can diffuse into the entire membrane structure and react to facilitate subsequent quaternization and improve the ion exchange capacity of the membrane.

[0035] Preferably, the polyvinylidene fluoride containing carbon-carbon double bonds is obtained by treating polyvinylidene fluoride with an alkali.

[0036] Preferably, the preparation method of the polyvinylidene fluoride containing carbon-carbon double bonds is as follows: polyvinylidene fluoride powder is added to potassium hydroxide ethanol solution and ultrasonically treated, then tetrabutylammonium bromide is added, the mixture is stirred and reacted, filtered and washed until the pH of the filtrate is 7 to obtain powder, and then dried to obtain polyvinylidene fluoride containing carbon-carbon double bonds.

[0037] Preferably, the concentration of the potassium hydroxide ethanol solution is 1~2 mol / L, and the mass ratio of potassium hydroxide ethanol solution, polyvinylidene fluoride, and tetrabutylammonium bromide is 3~5:1:0.01~0.02; the stirring reaction temperature is 55~65℃, and the time is 1-2 h.

[0038] Preferably, in step a, the mass ratio of polyvinylidene fluoride (PVDF), N-isopropylacrylamide (NIPAM), and acrylic acid (AA) containing carbon-carbon double bonds is (6-8):(2-4):1, the solvent is N,N-dimethylacetamide, the initiator is azobisisobutyronitrile, and the amount of initiator added is 0.8wt%-1.2wt% of the total monomers.

[0039] Preferably, the amount of polyethyleneimine added is 3%-5% of the total mass of PVDF, NIPAM, and AA; and the amount of modified nano-SiO2 added is 9%-11% of the total mass of PVDF, NIPAM, and AA.

[0040] Preferably, the thickness of the liquid film in step b is 250 μm; the time spent in air is 30-60 s; and the curing time in an ice-water bath is 20-30 min.

[0041] Preferably, the crosslinking reaction time in glutaraldehyde vapor in step c is 12-24 h; the concentration of the polyethyleneimine solution is 0.5 wt%-2.0 wt%; the immersion time in the polyethyleneimine solution is 4-8 h; the concentration of N,N-dimethylethylenediamine is 4 wt%-6 wt%; and the immersion time in the N,N-dimethylethylenediamine solution is 12-24 h.

[0042] Preferably, the molecular weight of the polyethyleneimine is 1000-2000.

[0043] Preferably, the quaternization treatment in step d specifically involves: washing the membrane with deionized water and then immersing it in a quaternization reagent solution, reacting at 30-40℃ for 6-10 hours, and then removing the membrane and soaking it in NaCl solution.

[0044] Preferably, the quaternizing reagent solution is obtained by dissolving dimethyl carbonate in an ethanol solution.

[0045] Preferably, the mass concentration of dimethyl carbonate in the quaternizing reagent solution is 4%-8%.

[0046] Preferably, the concentration of the ethanol solution is 70 vol.

[0047] Preferably, the modified nano-SiO2 is expanded graphite-supported nano-SiO2.

[0048] In this scheme, expanded graphite loaded with nano-SiO2 avoids the aggregation of nano-SiO2; at the same time, the synergistic effect of expanded graphite and nano-SiO2 avoids membrane fouling and ensures membrane flux; expanded graphite and nano-SiO2 construct a hydrophilic-hydrophobic gradient structure on the membrane surface, so as to achieve both high flux and avoidance of membrane fouling.

[0049] Preferably, the method for preparing the modified nano-SiO2 is as follows: dispersing expanded graphite in an ethanol solution, adjusting the pH to 2-4, ultrasonically treating, adding a silicon source and an epoxidizing agent, and stirring the reaction to obtain the final product.

[0050] Preferably, the mass ratio of the expanded graphite, silicon source, and epoxidizing agent is 0.8-1.2:5:0.5.

[0051] Preferably, the stirring reaction temperature is 40-50℃ and the time is 4-6h.

[0052] In this scheme, the above method facilitates the uniform loading of nano-SiO2 into the sheet and pore structure of expanded graphite, avoiding the aggregation of nano-SiO2. The modification with epoxidizing agent improves the uniform dispersion of modified nano-SiO2 in the membrane substrate, and the epoxy groups can also chemically bond with carboxyl groups, amino groups, etc. in the membrane substrate, acting as crosslinking agents to improve the stability of the membrane substrate.

[0053] Preferably, the silicon source is tetraethyl orthosilicate; the epoxidizing agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0054] Preferably, in step S3, the temperature of the diffusion dialysis treatment is 35-40°C.

[0055] Diffusion dialysis at this temperature not only improves mass transfer efficiency but also enhances membrane antifouling capabilities: the PNIPAM segments on the membrane surface undergo hydrophobic shrinkage, reducing adsorption sites for pollutants and preventing membrane structure damage.

[0056] Preferably, the soluble potassium salt in step S2 is potassium chloride.

[0057] Preferably, the alkalinity in step S4 is pH=8-10.

[0058] The beneficial effects of this invention are:

[0059] 1. High-efficiency impurity removal: This invention first adds magnetic composite seed crystals (Fe3O4@SiO2@SiO2) to the pretreated pickling waste liquid for impurity removal. These crystals can efficiently induce and adsorb suspended solids in the waste liquid, and then quickly separate them through magnetic separation. On the one hand, this effectively improves the purity of potassium fluorosilicate products; on the other hand, it reduces the pollution and clogging of the subsequent diffusion dialysis membrane by suspended solids, slows down the decrease in flux caused by membrane fouling, and lays the foundation for high-efficiency acid recovery.

[0060] 2. Anti-fouling and high-flux diffusion dialysis: The present invention preferably uses an asymmetric membrane prepared by a specific method as a diffusion dialysis membrane. Its dense surface ensures a high metal ion rejection rate, and its loose surface ensures a high flux. The PNIPAM segments introduced into the membrane material undergo hydrophobic shrinkage at an operating temperature of 35-40℃, reducing the adsorption sites of pollutants.

[0061] 3. Full-process resource utilization: This invention realizes the tiered recovery of multiple valuable components in waste liquid. The recovered acid can be directly reused in production, reducing the consumption of new acid. Fluorosilicic acid is recovered in the form of high-value-added potassium fluorosilicate. The final calcium chloride solution can be used to make de-icing agents, realizing the transformation of waste liquid into treasure with near-zero emissions.

[0062] 4. Significantly reduced treatment costs: Most of the acid is recovered in step S3, which greatly reduces the amount of calcium oxide or calcium hydroxide required for neutralization in step S4, and also significantly reduces the amount of sludge produced, thus reducing treatment costs. Detailed Implementation

[0063] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0064] The quartz sand pickling waste liquid used in the example is the waste liquid after natural sedimentation pretreatment. Its chemical composition analysis is mainly as follows: fluorosilicic acid 11.5wt%, hydrochloric acid 8.3wt%, iron 382ppm, aluminum 271ppm, sodium 74ppm, potassium 64ppm, magnesium 10ppm, and suspended solids 500mg / L.

[0065] Preparation Examples 1-3: Preparation of Magnetic Composite Seed Crystals (Fe3O4@SiO2@SiO2)

[0066] Preparation Example 1

[0067] 2.0 kg of Fe3O4 nanoparticles were weighed and dispersed in 200 L of 75 vol% ethanol solution, and ultrasonically dispersed for 30 min. 25 wt% ammonia was added dropwise to adjust the pH to 8.5, and 1.0 L of tetraethyl orthosilicate was added dropwise (dropping rate 10 mL / min). After the addition was completed, the mixture was stirred and reacted at 28 °C for 3 h. The solid and liquid were separated, washed, and vacuum dried to obtain primary Fe3O4@SiO2.

[0068] Primary Fe3O4@SiO2 was dispersed in 200 L of deionized water and ultrasonically dispersed for 20 min. 25 wt% ammonia was added dropwise to adjust the pH to 8.5, and the temperature was raised to 50 °C. 40 L of 8 wt% sodium silicate solution was added dropwise (dropping rate 20 mL / min), while simultaneously adding 0.1 mol / L HCl solution to maintain pH 8.5. After the addition was complete, the reaction was stirred for another 2 hours. Solid-liquid separation was performed, and the filtrate was washed with deionized water until the pH reached 7. The filtrate was then vacuum dried to obtain Fe3O4@SiO2@SiO2 magnetic composite seed crystals; the sodium silicate modulus was 2.

[0069] Preparation Example 2

[0070] 1.5 kg of Fe3O4 nanoparticles were weighed and dispersed in 200 L of 75 vol% ethanol solution, and ultrasonically dispersed for 30 min. 25 wt% ammonia was added dropwise to adjust the pH to 8.0, and 1.0 L of tetraethyl orthosilicate was added dropwise (dropping rate 8 mL / min). After the addition was completed, the mixture was stirred and reacted at 25 °C for 4 h. The solid and liquid were separated, washed, and vacuum dried to obtain primary Fe3O4@SiO2.

[0071] Primary Fe3O4@SiO2 was dispersed in 200L of deionized water and ultrasonically dispersed for 20min. 25wt% ammonia was added dropwise to adjust the pH to 8.0, and the temperature was raised to 40℃. 40L of 7wt% sodium silicate solution was added dropwise (dropping rate 22mL / min), while 0.1mol / L HCl solution was added dropwise to maintain pH=8.0. After the addition was complete, the reaction was stirred for 3 hours. Solid-liquid separation was performed, and the filtrate was washed with deionized water until the pH=7. The filtrate was then vacuum dried to obtain Fe3O4@SiO2@SiO2 magnetic composite seed crystals; the sodium silicate modulus was 2.

[0072] Preparation Example 3

[0073] 2.5 kg of Fe3O4 nanoparticles were weighed and dispersed in 200 L of 75 vol% ethanol solution, and ultrasonically dispersed for 30 min. 25 wt% ammonia was added dropwise to adjust the pH to 9.0, and 1.0 L of tetraethyl orthosilicate was added dropwise (dropping rate 12 mL / min). After the addition was completed, the mixture was stirred at 30 °C for 2 h. The solid and liquid were separated, washed, and vacuum dried to obtain primary Fe3O4@SiO2.

[0074] Primary Fe3O4@SiO2 was dispersed in 200L of deionized water and ultrasonically dispersed for 20min. 25wt% ammonia was added dropwise to adjust the pH to 9, and the temperature was raised to 60℃. 40L of 9wt% sodium silicate solution was added dropwise (dropping rate 18mL / min), while 0.1mol / L HCl solution was added dropwise to maintain pH=9. After the addition was complete, the reaction was stirred for 1 hour. Solid-liquid separation was performed, and the filtrate was washed with deionized water until the pH=7. The filtrate was then vacuum dried to obtain Fe3O4@SiO2@SiO2 magnetic composite seed crystals, in which the sodium silicate modulus was 2.

[0075] Preparation Examples 4-7: Preparation of Modified Nano-SiO2

[0076] Preparation Example 4

[0077] 100g of expanded graphite was dispersed in 3.6L of 75vol% ethanol solution, and 10wt% acetic acid was added to adjust the pH to 3. The mixture was ultrasonically dispersed for 30min. 500g of tetraethyl orthosilicate was added, stirred until homogeneous, and the temperature was raised to 45℃. The mixture was stirred for 2h. Then, 100g of an ethanol dispersion of γ-(2,3-epoxypropoxy)propyltrimethoxysilane (the mass ratio of γ-(2,3-epoxypropoxy)propyltrimethoxysilane to ethanol was added dropwise at a rate of 2g / min. After the addition was complete, the mixture was stirred for another 2h. The mixture was then filtered and vacuum dried to obtain modified nano-SiO2.

[0078] Preparation Example 5

[0079] 80g of expanded graphite was dispersed in 3.6L of 75vol% ethanol solution, and 10wt% acetic acid was added to adjust the pH to 2.5. The mixture was ultrasonically dispersed for 30min. 500g of tetraethyl orthosilicate was added and stirred until homogeneous. The mixture was heated to 40℃ and stirred for 3h. Then, 100g of an ethanol dispersion of γ-(2,3-epoxypropoxy)propyltrimethoxysilane (the mass ratio of γ-(2,3-epoxypropoxy)propyltrimethoxysilane to ethanol was added dropwise at a rate of 2g / min. After the addition was complete, the mixture was stirred for 2h. The mixture was then filtered and vacuum dried to obtain modified nano-SiO2.

[0080] Preparation Example 6

[0081] 120g of expanded graphite was dispersed in 3.6L of 75vol% ethanol solution, and 10wt% acetic acid was added to adjust the pH to 3.5. The mixture was ultrasonically dispersed for 30min. 500g of tetraethyl orthosilicate was added, stirred until homogeneous, and the temperature was raised to 50℃. The mixture was stirred for 1.5h. Then, 100g of an ethanol dispersion of γ-(2,3-epoxypropoxy)propyltrimethoxysilane (the mass ratio of γ-(2,3-epoxypropoxy)propyltrimethoxysilane to ethanol was added dropwise at a rate of 2g / min. After the addition was complete, the mixture was stirred for another 1.5h. The mixture was then filtered and vacuum dried to obtain modified nano-SiO2.

[0082] Preparation Example 7

[0083] This preparation example is basically the same as preparation example 4, except that expanded graphite was not added.

[0084] Preparation Examples 8-10: Preparation of PVDF Containing Carbon-Carbon Double Bonds (U-PVDF)

[0085] Preparation Example 8

[0086] Add 1 kg of polyvinylidene fluoride powder to 4 kg of 1.5 mol / L potassium hydroxide ethanol solution, sonicate for 10 min, then add 15 g of tetrabutylammonium bromide; heat to 60 °C, stir at 400 rpm for 1.5 h; filter and wash until the pH of the filtrate is 7 to obtain powder, dry to obtain polyvinylidene fluoride containing carbon-carbon double bonds (denoted as U-PVDF-1), wherein the molecular weight of polyvinylidene fluoride is 300,000.

[0087] Preparation Example 9

[0088] Add 1 kg of polyvinylidene fluoride powder to 3 kg of 2 mol / L potassium hydroxide ethanol solution, sonicate for 10 min, then add 10 g of tetrabutylammonium bromide; heat to 55 °C, stir at 400 rpm for 2 h; filter and wash until the pH of the filtrate is 7 to obtain powder, dry to obtain polyvinylidene fluoride containing carbon-carbon double bonds (denoted as U-PVDF-2); wherein, the molecular weight of polyvinylidene fluoride is 300,000.

[0089] Preparation Example 10

[0090] Add 1 kg of polyvinylidene fluoride powder to 5 kg of 1 mol / L potassium hydroxide ethanol solution, sonicate for 10 min, then add 20 g of tetrabutylammonium bromide; heat to 65 °C, stir at 400 rpm for 1 h; filter and wash until the pH of the filtrate is 7 to obtain powder, dry to obtain polyvinylidene fluoride containing carbon-carbon double bonds (denoted as U-PVDF-3); wherein, the molecular weight of polyvinylidene fluoride is 300,000.

[0091] Preparation Examples 11-15: Preparation of Asymmetric Films

[0092] Preparation Example 11

[0093] a. Preparation of casting solution: Under a nitrogen atmosphere, 70 kg of DMAc was added to 7 kg of U-PVDF-1, heated to 60 °C and stirred to dissolve. 3 kg of NIPAM was added and stirred to dissolve. Then, 300 g of a 10 wt% azobisisobutyronitrile (AIBN) DMAc solution was added dropwise at a rate of 2 g / min. After the addition was complete, the mixture was stirred for 3.5 h. Then, 1 kg of AA was added and stirred to dissolve. Then, 100 g of a 10 wt% azobisisobutyronitrile (AIBN) DMAc solution was added dropwise at a rate of 2 g / min. After the addition was complete, the mixture was stirred for 9.5 h. Subsequently, 2.2 kg of a 20% PEI / DMAc solution was added under stirring, followed by 1.1 kg of the modified nano-SiO2 obtained in Preparation Example 4. The mixture was stirred until homogeneous, and after vacuum degassing and cooling, the casting solution was obtained.

[0094] b. Film formation and phase separation: Place the glass plate on a 45°C heating plate and preheat for 15 minutes. Flow the degassed casting liquid onto the hot glass plate and control the liquid film thickness to be 250 μm. After standing in air at 25°C for 45 seconds, immerse the glass plate together in an ice-water bath at 0-4°C and solidify for 25 minutes to form a primary solid base film.

[0095] c. Gradient crosslinking: The dense side of the nascent solid substrate film is placed in a sealed container filled with glutaraldehyde vapor and crosslinked for 18 hours. After removal, it is immersed in a 1.0 wt% aqueous solution of polyethyleneimine (molecular weight 1500) for 6 hours; then, it is immersed in a 5 wt% aqueous solution of N,N-dimethylethylenediamine for 18 hours.

[0096] d. Quaternization: Take out the cross-linked membrane, wash it with deionized water, and immerse it in a 6wt% dimethyl carbonate ethanol-water solution (ethanol concentration is 70 vol%) and react at 35℃ for 8 hours; take out the membrane and stabilize it by soaking it in 1 mol / L NaCl solution to obtain the final product.

[0097] Preparation Example 12

[0098] a. Preparation of casting solution: Under a nitrogen atmosphere, 70 kg of N,N-dimethylacetamide (DMAc) was added to 6 kg of U-PVDF-2, and the mixture was heated to 60 °C and stirred to dissolve. 2 kg of NIPAM was added and stirred to dissolve. Then, 160 g of a 10 wt% azobisisobutyronitrile (AIBN) DMAc solution was added dropwise at a rate of 2 g / min. After the addition was complete, the mixture was stirred and reacted for 3 h. Then, 1 kg of AA was added and stirred to dissolve. Then, 80 g of a 10 wt% azobisisobutyronitrile (AIBN) ethanol solution was added dropwise at a rate of 2 g / min. After the addition was complete, the mixture was stirred and reacted for 7 h. Then, 1.35 kg of a 20% PEI / DMAc solution was added under stirring, followed by 0.81 kg of the modified nano-SiO2 obtained in Preparation Example 5. The mixture was stirred until homogeneous, and after vacuum degassing and cooling, the casting solution was obtained.

[0099] b. Film formation and phase separation: Place the glass plate on a 40℃ heating plate and preheat for 20 minutes; cast the degassed film liquid onto the hot glass plate and control the film thickness to be 250μm; after standing in the air at 25℃ for 30 seconds, immerse the glass plate together in an ice-water bath at 0-4℃ and solidify for 20 minutes to form the initial solid base film.

[0100] c. Gradient crosslinking: The dense side of the nascent solid substrate film is placed in a sealed container filled with glutaraldehyde vapor and crosslinked for 12 hours. After removal, it is immersed in a 0.5 wt% aqueous solution of polyethyleneimine (molecular weight 2000) for 4 hours. Then, it is immersed in a 4 wt% aqueous solution of N,N-dimethylethylenediamine for 12 hours.

[0101] d. Quaternization: Take out the cross-linked membrane, wash it with deionized water, and immerse it in a 4wt% dimethyl carbonate ethanol-water solution (ethanol concentration is 70 vol%) and react at 30℃ for 6 h; take out the membrane and stabilize it by soaking it in 1 mol / L NaCl solution to obtain the final product.

[0102] Preparation Example 13

[0103] a. Preparation of casting solution: Under a nitrogen atmosphere, 70 kg of N,N-dimethylacetamide (DMAc) was added to 8 kg of U-PVDF-3, and the mixture was heated to 55 °C and stirred to dissolve. 4 kg of NIPAM was added and stirred to dissolve. Then, 480 g of a 10 wt% azobisisobutyronitrile DMAc solution was added dropwise at a rate of 2 g / min. After the addition was complete, the mixture was stirred and reacted for 4 h. Then, 1 kg of AA was added and stirred to dissolve. Then, 120 g of a 10 wt% azobisisobutyronitrile DMAc solution was added dropwise at a rate of 2 g / min. The mixture was stirred and reacted for 10 h. Subsequently, 3.25 kg of a 20% PEI / DMAc solution was added under stirring, followed by 1.43 kg of the modified nano-SiO2 obtained in Preparation Example 6. The mixture was stirred until homogeneous, and after vacuum degassing and cooling, the casting solution was obtained.

[0104] b. Film formation and phase separation: Place the glass plate on a 50℃ heating plate and preheat for 10 min; cast the degassed film liquid onto the hot glass plate and control the film thickness to be 250 μm; after standing in air at 25℃ for 60 s, immerse the glass plate together in an ice-water bath at 0-4℃ and solidify for 30 min to form a primary solid base film.

[0105] c. Gradient crosslinking: Place the dense side of the nascent solid substrate film upwards in a sealed container filled with glutaraldehyde vapor and crosslink for 24 hours; after removal, immerse it in a 2wt% aqueous solution of polyethyleneimine (molecular weight 1000) for 6 hours; then immerse it in a 6wt% aqueous solution of N,N-dimethylethylenediamine for 24 hours.

[0106] d. Quaternization: Take out the cross-linked membrane, wash it with deionized water, and immerse it in an 8wt% dimethyl carbonate ethanol-water solution (ethanol concentration is 70 vol%) and react at 40℃ for 10 h; take out the membrane and stabilize it by soaking it in 1 mol / L NaCl solution to obtain the final product.

[0107] Preparation Example 14

[0108] Preparation Example 14 is basically the same as Preparation Example 11, except that: a) Preparation of casting solution: Under a nitrogen atmosphere, 70 kg of DMAc was added to 7 kg of U-PVDF-1, heated to 60 °C and stirred to dissolve, 1 kg of AA was added, and after stirring to dissolve, 100 g of 10 wt% azobisisobutyronitrile (AIBN) DMAc solution was added dropwise, and the dropping rate was controlled at 2 g / min; after the dropping was completed, the reaction was stirred for 9.5 h; then 2.2 kg of 20% PEI / DMAc solution was added under stirring, and then 1.1 kg of modified nano-SiO2 obtained in Preparation Example 4 was added, stirred evenly, and after vacuum degassing and cooling, the casting solution was obtained;

[0109] All other steps are the same as in Preparation Example 11.

[0110] Preparation Example 15

[0111] Preparation Example 15 is basically the same as Preparation Example 11, except that: a) Preparation of casting solution: Under a nitrogen atmosphere, 70 kg of DMAc was added to 7 kg of U-PVDF-1, heated to 60 °C and stirred to dissolve, 1 kg of AA was added, and after stirring to dissolve, 100 g of 10 wt% azobisisobutyronitrile (AIBN) DMAc solution was added dropwise, and the dropping rate was controlled at 2 g / min; after the dropping was completed, the reaction was stirred for 9.5 h; then 2.2 kg of 20% PEI / DMAc solution was added under stirring, and then 1.1 kg of modified nano-SiO2 obtained in Preparation Example 7 was added, stirred evenly, and after vacuum degassing and cooling, the casting solution was obtained;

[0112] All other steps are the same as in Preparation Example 11.

[0113] The diffusion dialysis performance of the asymmetric membranes prepared in the preparation examples was evaluated:

[0114] Asymmetric membranes with the same area from Preparation Examples 11-15 were used as sample membranes and fixed between two separate chambers, wherein the effective area (A) of the sample membrane was 10 cm². 2 The side closer to the dense membrane structure is the simulated waste acid side, and the side closer to the loose membrane structure is the dialysis liquid side. Waste acid is injected into the waste acid side, and deionized water is injected into the dialysis liquid side. The effective volume of each chamber is 200 mL, and the stirring speed of both chambers is the same. Diffusion dialysis is carried out under a 38℃ water bath. After 2 hours of diffusion dialysis, the solution from the dialysis liquid side is taken for analysis. The acid recovery flux is calculated. Acid recovery flux (J) H + )=(C H + 渗析液 ×V 渗析液 ) / (A×t), where C H + 渗析液 For the dialysis side H + Concentration, V 渗析液 Where A is the volume of the dialysis solution, A is the effective area of ​​the sample membrane, and t is the diffusion dialysis time.

[0115] After 2 hours of diffusion dialysis, the sample membrane was removed and dried to constant weight. The amount of contaminant adsorbed on the sample membrane surface (mg / cm³) was then calculated. 2 = (W1-W0) / A (where W0 is the dry weight of the sample membrane before treatment, W1 is the dry weight of the sample membrane after 2 hours of diffusion dialysis treatment, and A is the effective area of ​​the sample membrane); the calculation results are recorded in Table 1.

[0116] Table 1. Antifouling performance and acid flux test results of asymmetric membranes.

[0117]

[0118] As shown in Table 1, the initial (2h) acid flux of the asymmetric membranes prepared in Examples 11-15 of this invention all reached 80.0 mol / m. 2 The initial acid flux was above h, among which the asymmetric membrane prepared in Preparation Example 11 had the highest initial acid flux.

[0119] Compared to Preparation Example 11, Preparation Example 14 did not add NIPAM when preparing the asymmetric membrane. The initial flux of the membrane obtained was lower than that of Preparation Example 11, and the amount of surface pollutants adsorbed was higher than that of Preparation Example 11. This indicates that the hydrophobic shrinkage of the PNIPAM segments formed by adding NIPAM when preparing the asymmetric membrane can reduce the amount of pollutants adsorbed.

[0120] Compared to Preparation Example 11, in Preparation Example 15, no expanded graphite was added when preparing the asymmetric membrane using modified nano-SiO2. The initial flux of the prepared membrane was reduced, and the amount of surface pollutants adsorbed was increased, indicating that the modified nano-SiO2 and expanded graphite worked synergistically to improve the membrane's antifouling ability.

[0121] Example 1

[0122] A method for the resource-based treatment of quartz sand pickling waste liquid specifically includes the following steps:

[0123] S1. Impurity removal: Add 15g of the magnetic composite seed obtained in Example 1 to 10kg of pretreated quartz sand pickling waste liquid, stir and mix at 400rpm for 13min, and then use a magnetic separator to separate the solid and liquid to obtain the impurity removal waste liquid and the magnetic composite seed. The magnetic composite seed can be reused after washing and desorbing impurities.

[0124] S2. Recovery of potassium fluorosilicate: Add 1.8 kg of potassium chloride to the waste liquid after impurity removal, stir and react for 60 min, filter to obtain filtrate and solid, wash and dry the solid to obtain high-purity potassium fluorosilicate (K2SiF6) product.

[0125] S3. Acid recovery by diffusion dialysis: The filtrate from step S2 was heated to 38°C, and the acid was recovered by diffusion dialysis using the asymmetric membrane prepared in Preparation Example 11; the acid recovery rate reached 90%, and the metal ion rejection rate reached 95%.

[0126] S4. Advanced treatment and calcium recovery: Add calcium oxide powder to the dialysis residue of S3, adjust the pH to 9.0, stir and react, then filter to obtain mixed sludge and calcium chloride solution.

[0127] Example 2

[0128] A method for the resource-based treatment of quartz sand pickling waste liquid specifically includes the following steps:

[0129] S1. Impurity Removal: Add 10g of the magnetic composite seed obtained in Preparation Example 2 to 10kg of pretreated quartz sand pickling waste liquid, and stir and mix at 500rpm for 10min; then use a magnetic separator to separate the solid and liquid to obtain the impurity-removed waste liquid and the magnetic composite seed loaded with impurities; the magnetic composite seed loaded with impurities can be reused after washing and desorbing the impurities.

[0130] S2. Recovery of potassium fluorosilicate: Add 1.8 kg of potassium chloride to the waste liquid removed in step S1, stir and react for 60 min, filter to obtain filtrate and solid; wash and dry the solid to obtain high-purity potassium fluorosilicate (K2SiF6) product.

[0131] S3. Acid recovery by diffusion dialysis: The filtrate from step S2 was heated to 35°C, and the acid was recovered by diffusion dialysis using the asymmetric membrane prepared in Preparation Example 11; the acid recovery rate reached 85%, and the metal ion rejection rate reached 92%.

[0132] S4. Advanced treatment and calcium recovery: Add calcium oxide powder to the dialysis residue from step S3, adjust the pH to 8.0, stir and react, then filter to obtain a mixed sludge and calcium chloride solution.

[0133] Example 3

[0134] A method for the resource-based treatment of quartz sand pickling waste liquid specifically includes the following steps:

[0135] S1. Impurity removal: Add 20g of the magnetic composite seed obtained in Preparation Example 3 to 10kg of pretreated quartz sand pickling waste liquid, and stir and mix at 300rpm for 15min; then use a magnetic separator to separate the solid and liquid to obtain the impurity-removed waste liquid and the magnetic composite seed loaded with impurities; the magnetic composite seed loaded with impurities can be reused after washing and desorbing the impurities.

[0136] S2. Recovery of potassium fluorosilicate: Add 1.8 kg of potassium chloride to the waste liquid removed in step S1, stir and react for 60 min, filter to obtain filtrate and solid; wash and dry the solid to obtain high-purity potassium fluorosilicate (K2SiF6) product.

[0137] S3. Acid recovery by diffusion dialysis: The filtrate from step S2 was heated to 40°C, and the acid was recovered by diffusion dialysis using the asymmetric membrane prepared in Preparation Example 11; the acid recovery rate reached 88%, and the metal ion rejection rate reached 93%.

[0138] S4. Advanced treatment and calcium recovery: Add calcium oxide powder to the residual liquid from S3 dialysis, adjust the pH to 10, stir and react, then filter to obtain mixed sludge and calcium chloride solution.

[0139] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for resourceful treatment of quartz sand pickling waste liquid, characterized in that, The method comprises the following steps: S1, impurity removal: adding magnetic composite seeds to the pretreated quartz sand acid washing waste liquid, stirring and mixing, and then performing magnetic separation to obtain impurity removal waste liquid and magnetic composite seeds adsorbing impurities; S2, recovery of potassium fluosilicate: adding a soluble potassium salt to the impurity removal waste liquid obtained in step S1, stirring and reacting, and then filtering to obtain potassium fluosilicate solid and filtrate; S3, diffusion dialysis recovery of acid: subjecting the filtrate obtained in step S2 to diffusion dialysis treatment to obtain recovered acid and dialysis residual liquid; the diffusion dialysis treatment uses an asymmetric membrane, the asymmetric membrane has a physical gradient of one side being a dense structure and the other side being a loose structure; the temperature of the diffusion dialysis treatment is 35-40°C; S4, deep treatment and calcium recovery: adding calcium oxide or calcium hydroxide to the dialysis residual liquid obtained in step S3, adjusting the pH of the system to alkaline, and then filtering after reaction to obtain a precipitate and a calcium chloride solution; In step S1, the magnetic composite seeds are Fe3O4@SiO2@SiO2 particles with a double-shell structure, the inner core is superparamagnetic Fe3O4, the inner shell is a dense SiO2 protective layer, and the outer shell is a porous SiO2 functional layer; The preparation method of the asymmetric membrane comprises the following steps: a, casting solution preparation: under an inert atmosphere, polyvinylidene fluoride containing a carbon-carbon double bond is dissolved in a solvent, N-isopropyl acrylamide and an initiator are added, stirring and reaction is carried out at 55-65°C for 3-4h, then acrylic acid and an initiator are added, stirring and reaction is carried out at 55-65°C for 7-10h, a polymer solution is obtained; polyethyleneimine and modified nano-SiO2 are added and stirred to obtain a casting solution; b, film formation and phase separation: the casting solution is cast on a heating plate at 40-50°C to form a liquid film, after being placed in air, it is immersed in an ice water bath for solidification to form a nascent solid-state base membrane with a dense layer and a porous support layer; c, gradient crosslinking: the dense side of the nascent solid-state base membrane is exposed to glutaraldehyde vapor for crosslinking reaction; then it is sequentially immersed in polyethyleneimine solution and N,N-dimethyl ethylenediamine solution for further reaction; d, quaternization: after the crosslinked membrane is subjected to quaternization treatment, the asymmetric membrane is obtained; The modified nano-SiO2 is nano-SiO2 supported on expanded graphite.

2. The quartz sand pickle liquor resource treatment method according to claim 1, characterized by, In step S1, the stirring speed is 300-500rpm; the mixing time is 10-15min; and the addition amount of the magnetic composite seeds is 1.0‰-2.0‰ of the pretreated waste liquid.

3. The quartz sand pickle liquor resource treatment method according to claim 1, characterized by, The preparation method of the magnetic composite seeds is as follows: (1) dispersing nano-Fe3O4 powder in ethanol solution, adjusting the pH to 8-9, adding tetraethyl orthosilicate, mixing and reacting at 25-30°C for 2-4h, solid-liquid separation, washing, and drying to obtain primary Fe3O4@SiO2; (2) dispersing the primary Fe3O4@SiO2 in deionized water, adjusting the pH to 8-9, heating to 40-60°C, adding sodium silicate solution dropwise, adjusting the pH to 8-9, mixing and reacting for 1-3h, solid-liquid separation, washing, and drying to obtain Fe3O4@SiO2@SiO2 magnetic composite seeds.

4. The quartz sand pickle liquor resource treatment method according to claim 3, characterized by, The mass-volume ratio of the nano-Fe3O4 powder, tetraethyl orthosilicate and sodium silicate solution is 1.5-2.5 g:1 mL:40 mL; wherein the concentration of the sodium silicate solution is 7wt%-9wt%, and the modulus of the sodium silicate is 2.

5. The quartz sand pickle liquor resource recovery method according to claim 3, characterized by, The dropping speed of the tetraethyl orthosilicate in step (1) is 8-12 mL / min; and the dropping speed of the sodium silicate solution in step (2) is 18-22 mL / min.

6. The quartz sand pickle liquor resource recovery method according to claim 1, characterized by, In step a, the mass ratio of the carbon-carbon double bond-containing polyvinylidene fluoride, N-isopropyl acrylamide and acrylic acid is (6-8):(2-4):1, the solvent is N,N-dimethylacetamide; the initiator is azobisisobutyronitrile; the adding amount of the initiator is 0.8wt%-1.2wt% of the total amount of monomers; the adding amount of the polyethyleneimine is 3%-5% of the total mass of the carbon-carbon double bond-containing polyvinylidene fluoride, N-isopropyl acrylamide and acrylic acid; and the adding amount of the modified nano-SiO2 is 9%-11% of the total mass of the carbon-carbon double bond-containing polyvinylidene fluoride, N-isopropyl acrylamide and acrylic acid.

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