Preparation method and application of sodium silicate-layered double hydroxide compound
By preparing a sodium silicate-layered double hydroxide complex, the problem of poor purification effect of small and medium-sized microplastics in existing water treatment processes was solved, efficient adsorption and purification were achieved, and the industrial pure water standards were met.
Patent Information
- Application Number
- CN202510919299.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-03
- Publication Date
- 2025-09-19
AI Technical Summary
Existing water treatment processes are ineffective in purifying small and medium-sized microplastics, leading to potential water safety and health risks.
A sodium silicate-layered double hydroxide complex is prepared by saponification reaction, adding complex salt and ammonia water to form a layered double hydroxide, which is then intercalated with sodium silicate to form a stable sodium silicate-layered double hydroxide for adsorbing microplastics.
It significantly improves the adsorption effect on small and medium-sized microplastics, synergistically improves the purification of small-sized MPs substances in sewage, and the water quality after treatment reaches the industrial pure water standard.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of water treatment material preparation, in particular to a preparation method and application of a sodium silicate-layered double metal hydroxide composite. Background Art
[0002] Microplastics (MPs), particles smaller than 5 mm in size, are considered emerging environmental pollutants. They primarily originate from the weathering and abrasion of plastic products and the release of plastic particles from personal care products. MPs are widespread, reaching every corner of the world and even the remote polar environments. Over time, these microplastics, through the combined effects of weathering, hydraulic shear, and biological processes, transform into countless tiny plastic particles, further exacerbating the global ecological crisis. Aquatic environments are the primary reservoirs of MPs. Primary and secondary microplastics can enter drinking water through surface runoff and sewage treatment plant effluent, where they can be ingested by humans and cause a variety of toxic effects. The importance and severity of MPs pollution prevention and control in aquatic bodies are self-evident.
[0003] Currently, existing water treatment processes at water and sewage treatment plants primarily target suspended solids and colloids, including coagulation, filtration, and membrane separation. However, these technologies are generally ineffective against MPs, particularly microplastics with a particle size of less than 50 μm. This results in some MPs remaining in the water after treatment, posing potential water quality and health risks.
[0004] Existing water treatment processes usually add chemicals PAC (polyaluminum chloride) and PAM (polyacrylamide) to the water inlet. However, these chemicals only have an adsorption purification effect on larger particles of MPs substances, and the purification effect on small and medium-sized MPs substances is not ideal.
[0005] Therefore, the study of adsorption materials for efficient adsorption of small and medium-sized MPs in water bodies has become an urgent problem to be solved in the field of water treatment. Summary of the Invention
[0006] The present invention provides a preparation method and application of a sodium silicate-layered double metal hydroxide composite. The sodium silicate-layered double metal hydroxide composite is prepared to efficiently adsorb small and medium particle size MPs in water.
[0007] In view of this, the solution of the present invention is: The first aspect of the present invention is to provide a method for preparing a sodium silicate-layered double hydroxide composite, comprising the steps of: S1. saponifying the fatty acid with an alkali to prepare an aqueous solution; S2. A complex salt and aqueous ammonia were added to the aqueous solution obtained in S1 to obtain a suspension, and the endpoint pH was controlled to be 8-10; the complex salt includes a divalent inorganic salt and a trivalent inorganic salt; S3. Add sodium silicate solution to the suspension obtained in S2, and react at 70-80° C. for 2-4 hours to obtain a sodium silicate-layered double hydroxide complex.
[0008] Furthermore, in step S1, the fatty acid is a fatty acid with a carbon chain length of 12-22, such as palmitic acid, stearic acid or oleic acid, preferably stearic acid; And / or, the base is at least one of sodium hydroxide and potassium hydroxide; and / or, the molar ratio of the fatty acid to the base is 1:1; And / or, the reaction temperature is 70-80° C., and the reaction is kept warm for 2-4 hours.
[0009] Furthermore, the divalent inorganic salt is a salt formed by divalent metal ions, and the metal ions are selected from Mg 2+ 、Zn 2 + or Ni 2+ At least one of; And / or, the trivalent inorganic salt is a salt formed by a trivalent metal ion, and the trivalent metal ion is selected from Al 3+ or Fe 3+ At least one of .
[0010] Furthermore, the amount of the trivalent inorganic salt is 1 to 5 times the mass of the fatty acid; And / or, the amount of the divalent inorganic salt is 1 to 5 times the mass of the fatty acid.
[0011] Furthermore, the molar ratio of the trivalent inorganic salt to the divalent inorganic salt in the composite salt is 1:(1-3).
[0012] Preferably, the trivalent inorganic salt is an iron salt, selected from at least one of ferric chloride and ferric sulfate; And / or, the divalent inorganic salt is a magnesium salt, selected from at least one of magnesium chloride and magnesium sulfate.
[0013] Furthermore, the concentration of the ammonia water is 10-28 wt %, preferably industrial ammonia water (25-28%) is diluted to a concentration of 15%, and the amount used is 15-20 times the mass of the stearic acid.
[0014] Furthermore, the amount of sodium silicate is 5-25% of the mass of the fatty acid; And / or, the sodium silicate has a modulus of 1-3, where the modulus refers to the molar ratio of silicon dioxide (SiO2) to sodium oxide (Na2O) in its molecule.
[0015] The second aspect of the present invention is to provide a sodium silicate-layered double hydroxide composite obtained by the preparation method described in the first aspect.
[0016] The third aspect of the present invention is to provide use of the sodium silicate-layered double hydroxide composite described in the second aspect in water treatment.
[0017] Furthermore, the sodium silicate-layered double hydroxide complex is used to adsorb microplastics.
[0018] Furthermore, when the sodium silicate-layered double hydroxide complex is used to adsorb microplastics, the dosage is 1-20‰ of the water volume.
[0019] A fourth aspect of the present invention is to provide a water treatment method comprising the steps of introducing polyaluminum chloride, acrylamide, and a sodium silicate-layered double metal hydroxide complex into a water body. The addition of the sodium silicate-layered double metal hydroxide complex synergistically improves the adsorption and purification of small-sized MPs in wastewater, resulting in excellent water purification. Through a multi-stage coagulation and filtration device, the small-sized MPs can be filtered out, and the resulting treated water meets industrial pure water standards. This method is intended to address the problem of excessively high small-sized MPs content in wastewater in the prior art.
[0020] Compared with the prior art, the present invention has the following beneficial effects: The sodium silicate-layered double hydroxide complex provided by the present invention is prepared by simultaneously adding a composite salt and an ammonia solution to a saponification reactant to form a layered double hydroxide (LDHs). The layered double hydroxides (LDHs) are connected by metal cations and hydroxide ions to form octahedral structural units, which are interconnected to form two-dimensional plate layers and carry a positive charge. Subsequently, sodium silicate is added to carry out an intercalation reaction to obtain a stable sodium silicate-layered double hydroxide complex. The sodium silicate and the layered double hydroxide complex synergistically enhance the adsorption of microparticles as a whole, thereby being suitable for the prevention and control of MPs pollution in water bodies. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 Schematic diagram of the particle size distribution of MPs after the sodium silicate-layered double hydroxide composite obtained by the preparation method described in Example 1 of the present invention is used in combination with PAC and PAM for water treatment.
[0022] Figure 2 Schematic diagram of the particle size distribution of MPs after the layered double hydroxide is used in combination with PAC and PAM for water treatment in Comparative Example 1 of the present invention.
[0023] Figure 3Schematic diagram of the particle size distribution of MPs after the water sample used as a control in the present invention is treated with PAC and PAM. DETAILED DESCRIPTION
[0024] The technical solutions of the present invention will be clearly and completely described below in conjunction with preferred embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.
[0025] Example 1
[0026] 1) Prepare Solution A
[0027] Put 1000 kg of water and 40.1 kg of sodium hydroxide into a reactor, heat it to 75 ° C, and gradually add 284.5 kg of stearic acid over 1 hour. 2) Prepare solution B Put 4000kg of water, 723.55kg of anhydrous magnesium chloride and 1232.7kg of anhydrous ferric chloride into the batching kettle and stir until they are completely dissolved.
[0028] 3) Prepare Solution C
[0029] Put 1800kg of water and 2700kg of ammonia water (25%) into the batching kettle and stir evenly.
[0030] 4) Prepare solution D: Add 30 kg sodium silicate (modulus 2.3) and 270 kg water into the batching kettle and stir until the sodium silicate is completely dissolved.
[0031] 5) Water purification agent synthesis
[0032] The temperature of solution A was controlled at 75°C, and solution B and solution C were simultaneously pumped into solution A at a constant speed using a constant flow pump. The pumping was completed in 3 hours, and the pH was confirmed to be 9. The solution was kept warm at 75°C for 3 hours, and the pH was again confirmed to be 9 to obtain a white suspension of layered double metal hydroxide. Solution D was slowly pumped into the above layered double metal hydroxide suspension, and the solution was kept warm at 75°C for 3 hours to obtain a sodium silicate-layered double metal hydroxide complex DMS.
[0033] Example 2
[0034] 1) Prepare Solution A
[0035] Put 1000kg water and 40.1kg sodium hydroxide into the reactor, heat to 80℃, gradually add 256.4kg palmitic acid, add the mixture over 1 hour, and set aside; 2) Prepare solution B Put 4000kg of water, 769.2kg of anhydrous magnesium sulfate and 1025.6kg of anhydrous ferric sulfate into the batching kettle and stir until they are completely dissolved.
[0036] 3) Prepare Solution C
[0037] Put 1800kg of water and 2700kg of ammonia water (25%) into the batching kettle and stir evenly.
[0038] 4) Prepare solution D: Add 30.8 kg of sodium silicate (modulus 1.8) and 270 kg of water into the batching kettle and stir until the sodium silicate is completely dissolved.
[0039] 5) Water purification agent synthesis
[0040] The temperature of solution A was controlled at 80°C, and solution B and solution C were simultaneously pumped into solution A at a uniform speed using a constant flow pump. The pumping was completed in 2.5 hours, and the pH was confirmed to be 9. The solution was kept at 80°C for 2.5 hours, and the pH was confirmed to be 9 again to obtain a white layered double hydroxide suspension. Solution D was slowly pumped into the above white layered double hydroxide suspension, and the solution was kept at 80°C for 2.5 hours to obtain a sodium silicate-layered double hydroxide complex DMS.
[0041] Example 3
[0042] 1) Prepare Solution A
[0043] Put 1000kg water and 40.1kg sodium hydroxide into the reactor, heat it to 80℃, add 284.5kg stearic acid gradually, add it over 1 hour, and set aside; 2) Prepare solution B Put 4000kg of water, 915kg of anhydrous magnesium sulfate and 1232.7kg of anhydrous ferric chloride into the batching kettle and stir until they are completely dissolved.
[0044] 3) Prepare Solution C
[0045] Put 1800kg of water and 2700kg of ammonia water (25%) into the batching kettle and stir evenly.
[0046] 4) Prepare solution D: Add 30 kg sodium silicate (modulus 2.0) and 270 kg water into the batching kettle and stir until the sodium silicate is completely dissolved.
[0047] 5) Water purification agent synthesis
[0048] The temperature of solution A was controlled at 80°C, and solution B and solution C were simultaneously pumped into solution A at a uniform speed using a constant flow pump. The pumping was completed in 2.5 hours, and the pH was confirmed to be 9. The solution was kept at 80°C for 2.5 hours, and the pH was confirmed to be 9 again to obtain a white layered double hydroxide suspension. Solution D was slowly pumped into the above white layered double hydroxide suspension, and the solution was kept at 80°C for 2.5 hours to obtain a sodium silicate-layered double hydroxide complex DMS.
[0049] Comparative Example 1
[0050] The difference from Example 1 is that only a layered double hydroxide composite is prepared without adding sodium silicate.
[0051] Comparative Example 2
[0052] The difference from Example 1 is that the sodium silicate solution is directly mixed with the white layered double hydroxide suspension at room temperature.
[0053] Comparative Example 3
[0054] The difference from Example 1 is that the modulus of the sodium silicate used is 3.4, and other conditions and preparation processes are the same.
[0055] Test example: small particle size MPs removal performance experiment
[0056] Test conditions: At 25°C, the amount of PAC added was 1‰ of the total sewage volume, the amount of PAM added was 0.5‰ of the total sewage volume, and the amount of DMS added was 10‰ of the total sewage volume. The mixture was aerated and stirred for 3 hours, and allowed to stand for 3 hours. The total solid content (TSS) of the treated sewage and the particle size less than 50 μm (particle size distribution) were measured.
[0057] 1. Determination method of total solids (TSS) in wastewater
[0058] The water sample is passed through a pre-weighed glass fiber filter, which captures solids larger than 0.1 μm and smaller than 50 μm. The filter is then dried in an oven to remove any remaining water and weighed again. The weight difference across the sample volume provides the TSS concentration in mg / L.
[0059] The specific operations are: Use a 0.1 μm aqueous filter membrane and dry it at 75°C to a constant weight, recorded as m1. Take 1 L of on-site sewage (pre-treated by filtering through a 50-micron aqueous filter membrane, and Micro-FTIR detection confirmed that the main pollutants are microplastics) and filter it through a 0.1 μm aqueous filter membrane. Dry the filter membrane together with the filter residue at 75°C to a constant weight, recorded as m2. Calculate the TSS value (total suspended solids) according to the following formula: TSS = (m2-m1) × 1000; Where: TSS - total solids in water, mg / L; m1——filter membrane weight, g; m2——weight of filter membrane plus filter residue, g.
[0060] The total solid content (TSS) was determined by performing three parallel measurements.
[0061] The test results are shown in Table 1.
[0062] Table 1:
[0063] Note: The control example is to add only PAC and PAM.
[0064] 2. Particle size less than 50 μm (particle size distribution)
[0065] Test method: At 25°C, debug the laser particle size analyzer and set the instrument parameters to material refractive index 1.605; material absorption rate 0.01; medium refractive index 1.00. Test 300mL of water sample and scan three times to obtain the particle size distribution diagram.
[0066] The test results are shown in Table 2.
[0067] Table 2:
[0068] It is not difficult to see from the above test examples that the DMS prepared in Examples 1-3 is used in conjunction with PAC and PAM to treat microplastics. Compared with the control group, it can significantly reduce the total solid content of sewage and reduce the particle size after treatment. Since the main pollutants in the pretreated sewage are microplastics, it can be judged that DMS can effectively adsorb and treat microplastics and reduce the particle size of residual microplastics. When Comparative Example 1 is LDHs, when Comparative Example 2 directly blends LDHs with sodium silicate solution at room temperature, the microplastic adsorption and treatment capabilities are significantly reduced; when Comparative Example 3 uses sodium silicate with a higher modulus to prepare DMS, the microplastic treatment capacity also shows a decrease. The possible reason is that when the modulus of sodium silicate increases, the solubility decreases and the viscosity increases, making it difficult to undergo intercalation reaction to form DMS, thereby reducing the adsorption and treatment capacity of sodium silicate synergistically enhanced layered bimetallic salts.
[0069] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.
Claims
1. A method for preparing a sodium silicate-layered double hydroxide composite, characterized in that the steps include: S1. saponifying the fatty acid with an alkali to prepare an aqueous solution; S2. A complex salt and aqueous ammonia were added to the aqueous solution obtained in S1 to obtain a suspension, and the endpoint pH was controlled to be 8-10; the complex salt includes a divalent inorganic salt and a trivalent inorganic salt; S3. Add sodium silicate solution to the suspension obtained in S2, and react at 70-80° C. for 2-4 hours to obtain a sodium silicate-layered double hydroxide complex.
2. The preparation method according to claim 1, characterized in that In step S1, the fatty acid is a fatty acid with a carbon chain length of 12-22; And / or, the base is at least one of sodium hydroxide and potassium hydroxide; and / or, the molar ratio of the fatty acid to the base is 1:1; And / or, the reaction temperature is 70-80°C.
3. The preparation method according to claim 1, characterized in that The divalent inorganic salt is a salt formed by divalent metal ions, and the metal ions are selected from Mg 2+ 、Zn 2+ or Ni 2+ At least one of; And / or, the trivalent inorganic salt is a salt formed by a trivalent metal ion, and the trivalent metal ion is selected from Al 3+ or Fe 3+ At least one of .
4. The preparation method according to claim 1, characterized in that The amount of the trivalent inorganic salt is 1 to 5 times the mass of the fatty acid; And / or, the amount of the divalent inorganic salt is 1 to 5 times the mass of the fatty acid.
5. The preparation method according to claim 1, characterized in that The molar ratio of the trivalent inorganic salt to the divalent inorganic salt in the composite salt is 1:(1-3).
6. The preparation method according to claim 1, characterized in that The concentration of the ammonia water is 10-28%.
7. The preparation method according to claim 1, characterized in that The amount of sodium silicate is 5-25% of the mass of the fatty acid; And / or, the sodium silicate modulus is 1-3.
8. The sodium silicate-layered double hydroxide complex obtained by the preparation method according to any one of claims 1 to 7.
9. Use of the sodium silicate-layered double hydroxide composite according to claim 8 in water treatment.
10. A water treatment method, characterized in that: The method comprises the steps of adding polyaluminium chloride, acrylamide and a sodium silicate-layered double metal hydroxide complex into a water body; the sodium silicate-layered double metal hydroxide complex is a sodium silicate-layered double metal hydroxide complex obtained by the preparation method according to any one of claims 1 to 7.