Preparation method of diatomite-based porous ceramic material and application of diatomite-based porous ceramic material in wastewater pollutant treatment

Abstract

The invention relates to the technical field of ceramic materials, in particular to a preparation method of a diatomite-based porous ceramic material and application of the diatomite-based porous ceramic material in wastewater pollutant treatment. The preparation method of the diatomite-based porous ceramic material comprises the following steps: mixing a basic raw material, a sintering aid, a pore forming agent and a binder, performing compression molding to obtain a green body, and sintering the green body, the basic raw materials comprise 80-85% of diatomite, 5-10% of kaolin, 0-5% of feldspar and 5-10% of sodium silicate; the mass of the sintering aid is 5% higher than that of the basic raw material; the mass of the pore-forming agent is 25-45% of that of the basic raw material, and the pore-forming agent is selected from one or more than two of crystalline flake graphite, polymethyl methacrylate and spherical graphite. By controlling the composition and dosage of the basic raw materials, the sintering aid and the pore-forming agent, a micro-nano hierarchical pore structure is formed, mechanical properties and permeability are improved at the same time, and good filtration and interception performance on pollutants in wastewater is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic materials, and particularly relates to a preparation method of diatomite-based porous ceramic material and application thereof in wastewater pollutant treatment. BACKGROUND

[0002] Porous ceramics have the advantages of both ceramic materials and porous structures, and have many remarkable advantages, including high porosity and specific surface area, good high-temperature resistance, corrosion resistance and heat insulation performance, uniform pore structure and long service life, and thus have wide applications in wastewater pollutant treatment, seawater desalination, catalyst carriers and solid waste utilization. The sintering temperature of commonly used porous ceramics such as silicon carbide, alumina and mullite is high, and the raw materials are expensive, so the production cost is high; some of these porous ceramics have low mechanical properties, some have low permeation flux, and their adsorption performance is not good, and the treatment effect of wastewater containing multiple pollution sources such as particle suspensions, oil-water mixtures and organic dyes is poor. Therefore, it is very important to develop porous ceramic materials with cheap and easily available raw materials, low sintering temperature, good mechanical properties, high permeation flux and comprehensive performance for efficient treatment of pollutants and reduction of treatment cost.

[0003] Commonly used preparation methods of porous ceramics include sacrificial template method, pore-forming agent addition method, freeze-drying method, direct foaming method, gel casting method, and 3D printing method developed recently. Among them, the pore-forming agent addition method is widely used in the preparation of porous ceramics due to its simple process and easy control of pore size. However, the introduction of pore structure into ceramic materials will inevitably damage the mechanical properties of the materials, thus limiting their application, and even failing to meet the requirements of the use scenarios for the mechanical properties of porous ceramics. However, the main method to improve the mechanical properties of ceramic materials is to improve the density of the materials. Under normal circumstances, researchers improve the density of the materials by increasing the sintering temperature, but this will increase the preparation cost of porous ceramics and may damage the pore structure of porous ceramics. Therefore, in order to solve this problem, the addition of appropriate sintering aids helps to reduce the sintering temperature of porous ceramics, achieve low-temperature sintering, and at the same time obtain high mechanical properties. However, sintering aids often form glass phases, which will reduce the porosity of porous ceramics to some extent, thus reducing the permeation flux of porous ceramics.

[0004] Diatomaceous earth is a biogenic sedimentary rock, a porous material formed from the siliceous remains of aquatic diatoms. Its main chemical component is amorphous SiO2, and the particles are generally in the shape of regular discs, ranging in diameter from a few micrometers to tens of micrometers. Diatomaceous earth possesses a natural nanoscale porous structure, with numerous circular, interconnected pores arranged regularly on its discs, mostly with a pore size between 150 and 200 nm. Therefore, diatomaceous earth has the characteristics of high porosity and specific surface area, excellent adsorption performance, and low cost, making it an ideal raw material for preparing porous ceramics. In recent years, it has become an indispensable raw material in the preparation of wastewater pollutant treatment materials. Diatomaceous earth-based porous ceramics, made primarily from diatomaceous earth, are expected to be applied in the treatment of various pollutants in wastewater, including suspended particulate matter, oil-water mixtures, organic dyes, pathogenic microorganisms, and heavy metal ions. However, the sintering temperature of existing diatomite-based porous ceramics is relatively high, which often results in high density and low porosity. In addition, the inherent closed pores of diatomite lead to low permeation flux in the prepared diatomite-based porous ceramics.

[0005] Chinese patent application CN108997002A, published on December 14, 2018, discloses a method for preparing diatomaceous earth-based porous ceramic materials. The method involves mixing 50-80 parts of calcined diatomaceous earth, 2-6 parts of clay, 1-10 parts of pore-forming agent, sintering aid (one or more of kaolin, quartz, and feldspar), and dispersant (sodium silicate), then extruding the mixture and firing it at 900-1000℃. The resulting diatomaceous earth-based porous ceramic material not only has a high porosity (50-60%), but also a low thermal conductivity (0.11-0.12 W / (m·K) at 200℃).

[0006] However, while lowering the sintering temperature can reduce the density and increase the porosity of diatomaceous earth-based porous ceramics, and retain the inherent pore structure of diatomaceous earth to some extent, it also reduces the mechanical properties of these ceramics. Both of these factors affect the overall performance of diatomaceous earth porous ceramics, thus limiting their application in wastewater treatment. Therefore, finding a way to lower the sintering temperature while simultaneously achieving high mechanical properties and permeability has become crucial for preparing high-performance diatomaceous earth-based porous ceramics. Summary of the Invention

[0007] The first objective of this invention is to provide a method for preparing diatomaceous earth-based porous ceramic materials, thereby solving the problem that existing diatomaceous earth-based porous ceramic materials cannot simultaneously achieve both mechanical properties and permeability.

[0008] The second objective of this invention is to provide a method for preparing diatomaceous earth-based porous ceramic materials and to apply these materials in wastewater pollutant treatment, thereby solving the problem that existing diatomaceous earth-based porous ceramic materials cannot simultaneously achieve both mechanical properties and permeability.

[0009] To solve the above-mentioned technical problems, the technical solution of the preparation method of the diatomite-based porous ceramic material of the present invention is as follows: A method for preparing a diatomaceous earth-based porous ceramic material includes the following steps: mixing basic raw materials, sintering aids, pore-forming agents, and binders, pressing the mixture into a green body, and then sintering the green body; the basic raw materials, by mass percentage, include 80-85% diatomaceous earth, 5-10% kaolin, 0-5% feldspar, and 5-10% sodium silicate; the sintering aids are present at a mass greater than 5% of the basic raw materials; the pore-forming agent is present at a mass of 25-45% of the basic raw materials, and the pore-forming agent is selected from one or more of flake graphite, polymethyl methacrylate, and spherical graphite.

[0010] This invention improves upon existing technology by providing a method for preparing diatomaceous earth-based porous ceramic materials. By controlling the ratio of basic raw materials and sintering aids, low-temperature sintering of diatomaceous earth-based porous ceramics is achieved, resulting in superior performance. Specifically, the sintering aids lower the sintering temperature, thereby maximizing the preservation of the inherent nanoporous structure of diatomaceous earth. The glass melt formed by the melting of the sintering aids facilitates the sintering and bonding between diatomaceous earth particles, thus improving the mechanical properties of the diatomaceous earth-based porous ceramics. By selecting specific types of pore-forming agents and controlling their dosage, the pore-forming agents burn and decompose into gases during sintering, leaving micron-level pore structures in situ, improving the permeability of the porous ceramics. Furthermore, they can combine with the nano-level pore structure of diatomaceous earth itself to form a micro-nano hierarchical pore structure, thus providing excellent permeability while also ensuring filtration and retention of various pollutants. The combined effect of the sintering aids and pore-forming agents provides sufficient mechanical and permeability properties for the diatomaceous earth-based porous ceramics.

[0011] The diatomaceous earth-based porous ceramic material prepared by this invention has a micro-nano hierarchical pore structure, low bulk density, and high apparent porosity, water absorption, flexural strength and permeability. It has better filtration and retention performance for suspended particulate matter, oil-water mixtures, organic dyes, pathogenic microorganisms and heavy metal ions in water bodies, and has good application prospects in the field of wastewater treatment.

[0012] To further improve mechanical properties and permeation flux, preferably, the pore-forming agent comprises flake graphite and spherical graphite in a mass ratio of (1~1.5):(3~3.5).

[0013] To further synergistically improve mechanical properties and permeation flux, preferably, the sintering aid is selected from one or more of boric acid, zinc oxide, and lithium carbonate; the mass of the sintering aid is 8-20% of the base raw material; the binder is a 5-6% (by mass) polyvinyl alcohol aqueous solution; the mass of the binder is 10-20% of the base raw material. More preferably, the mass of the sintering aid is 15-18% of the base raw material.

[0014] To further improve mechanical properties and permeation flux, preferably, the sintering aid comprises zinc oxide, boric acid and lithium carbonate in a mass ratio of (5~6):(3~4):(1~2).

[0015] To further improve sintering performance, preferably, the sintering includes a heating stage and a holding stage; the holding temperature during the holding stage is 800~1000℃, and the holding time is 2~4h. More preferably, the holding temperature during the holding stage is 825~900℃.

[0016] To further improve sintering performance, preferably, the heating stage includes sequentially performing a first heating and a second heating; the first heating is performed at a heating rate of 3~4℃ / min to raise the temperature to 300~400℃; the second heating is performed at a heating rate of 5~6℃ / min to raise the temperature from 300~400℃ to 800~1000℃.

[0017] To further improve the molding ability, preferably, the pressure during pressing is 60~80MPa and the time is 2~5min; the green body is dried before sintering at a temperature of 60~80℃ for 5~10h.

[0018] Preferably, the basic raw materials include 80-85% diatomite, 5-10% kaolinite, 2-5% feldspar and 5-10% sodium silicate.

[0019] The technical solution for the application of the diatomaceous earth-based porous ceramic material prepared by the method of the present invention in wastewater pollutant treatment is as follows: The application of the diatomaceous earth-based porous ceramic material prepared by the aforementioned method in wastewater pollutant treatment.

[0020] The application of the diatomaceous earth-based porous ceramic material provided by this invention in wastewater pollutant treatment demonstrates that, when applied to wastewater treatment, the micron-sized pores formed by the pore-forming agent facilitate liquid passage and increase permeability. Furthermore, the well-preserved nanopores on the surface of the diatomaceous earth discs help intercept suspended particulate matter in the water. The large number of pores between diatomaceous earth particles results in high apparent porosity, water absorption rate, and permeability. Therefore, this diatomaceous earth-based porous ceramic material can efficiently separate suspended particulate matter, oil-water mixtures, organic dyes, pathogenic microorganisms, and heavy metal ions from wastewater.

[0021] Preferably, the wastewater pollutants include suspended particulate matter, oil-water mixtures, organic dyes, pathogenic microorganisms and / or heavy metal ions in the wastewater. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the micro-nano porous structure of the diatomite-based porous ceramic material in Embodiment 1 of the present invention; Figure 2 The XRD pattern of the diatomaceous earth-based porous ceramic material of Example 1 of the present invention is shown below. Figure 3 This is a SEM image of the diatomaceous earth-based porous ceramic material of Example 4 of the present invention; Figure 4 The image shows the SEM morphology of the diatomite-based porous ceramic material in Comparative Example 1. Detailed Implementation

[0023] The technical concept of the preparation method of diatomaceous earth-based porous ceramic material provided by the present invention is as follows: Existing diatomaceous earth-based porous ceramic materials are obtained by sintering calcined diatomaceous earth, clay, pore-forming agent, sintering aid (kaolin, quartz, feldspar, etc.), and dispersant (sodium silicate). The resulting diatomaceous earth-based porous ceramic materials have high porosity and heat resistance, but poor mechanical properties.

[0024] This invention, by controlling the composition and dosage of basic raw materials, sintering aids, and pore-forming agents, maximizes the preservation of the inherent nanoporous structure of diatomaceous earth. The glass melt formed by the melting of the sintering aids facilitates the sintering and bonding between diatomaceous earth particles, thereby improving the mechanical properties of diatomaceous earth-based porous ceramics. The pore-forming agent forms a micron-level pore structure in situ and connects with the inherent nanoporous structure of diatomaceous earth, forming a micro-nano hierarchical pore structure. This simultaneously improves both mechanical and permeability properties, and provides good filtration and retention performance for pollutants in wastewater.

[0025] The method for preparing diatomaceous earth-based porous ceramic materials provided by this invention includes the following steps: mixing basic raw materials, sintering aids at a concentration higher than 5% of the basic raw materials, pore-forming agents at 25-45% of the basic raw materials, and binders at 10-20% of the basic raw materials, pressing the mixture into a green body, drying it, and then sintering the green body. The basic raw materials, by mass percentage, include 80-85% diatomaceous earth, 5-10% kaolin, 0-5% feldspar, and 5-10% sodium silicate. The pore-forming agent is selected from one or more of flake graphite, polymethyl methacrylate, and spherical graphite; the sintering aid is selected from one or more of boric acid, zinc oxide, and lithium carbonate; the binder is a 5-6% (by mass) aqueous solution of polyvinyl alcohol. The diameter of the flake graphite is less than 300 μm, the particle size of the spherical graphite is 10-20 μm, and the particle size of the polymethyl methacrylate is 4-6 μm.

[0026] This invention selects diatomaceous earth as the main raw material, which serves as the framework for porous ceramics and provides a large number of natural nanopores; kaolin can improve the plasticity and binding properties of the green body, and decomposes into alumina and silica during sintering to participate in solid-phase reactions; feldspar, as a fluxing agent, reacts with other sintering aids during sintering to generate a liquid phase, which helps to lower the sintering temperature; sodium silicate helps to improve the strength of the green body, lower the sintering temperature, and promote the sintering process; boric acid, zinc oxide, and lithium carbonate, as sintering aids, react with other components... The reaction occurs at a lower temperature, forming a eutectic, which promotes the bonding of solid particles and improves the mechanical properties of porous ceramics, thus reducing the sintering temperature of porous ceramics. After the pore-forming agent decomposes or burns and is converted into gas and escapes, it can provide a large number of micron-sized pores for the ceramic matrix, providing a wider channel for water to pass through. At the same time, these micron-sized pores, together with the inherent nanopores of diatomaceous earth, constitute a micro-nano hierarchical pore structure, which can achieve both high permeability and improved filtration and retention performance for water pollutants.

[0027] Preferably, the pore-forming agent comprises flake graphite and spherical graphite in a mass ratio of (1~1.5):(3~3.5). Preferably, the mixing is ball milling.

[0028] Preferably, the sintering aid comprises zinc oxide, boric acid and lithium carbonate in a mass ratio of (5~6):(3~4):(1~2).

[0029] Preferably, the pressure during compression molding is 60~80MPa and the time is 2~5min.

[0030] Preferably, the drying temperature is 60~80℃ and the drying time is 5~10h.

[0031] Preferably, sintering includes a heating stage and a holding stage. The heating stage includes sequentially performing a first heating and a second heating. The first heating is performed at a heating rate of 3~4℃ / min to raise the temperature to 300~400℃. The second heating is performed at a heating rate of 5~6℃ / min to raise the temperature from 300~400℃ to 800~1000℃. The holding temperature during the holding stage is 800~1000℃, and the holding time is 2~4h.

[0032] The bulk density of the diatomaceous earth-based porous ceramic material prepared by this invention is 0.8~1.05 g·cm³. -3 It has an apparent porosity of 57-65%, a water absorption rate of 54-73%, a flexural strength of 6-14 MPa, and a permeability of 480-1300 L·m. -2 ·h -1 ·bar -1 .

[0033] The embodiments of the present invention will be further described below with reference to specific examples. Unless otherwise specified, the chemical reagents involved in the following examples are all commercially available conventional products.

[0034] I. Specific Embodiments of the Preparation Method of Diatomite-Based Porous Ceramic Material of the Present Invention Example 1 The preparation method of the diatomaceous earth-based porous ceramic material in this embodiment is as follows: 1) Preparation of billet: First, weigh the basic raw materials, sintering aid, pore-forming agent and binder according to the formula, and mix them evenly by ball milling. After drying, the billet is obtained. The basic raw materials are composed of the following raw materials in the following mass percentages: 80 wt.% diatomaceous earth, 10 wt.% kaolin, 5 wt.% feldspar, and 5 wt.% sodium silicate. The sintering aid is zinc oxide, boric acid and lithium carbonate in a mass ratio of 5:3:1, and the mass of the sintering aid is 15 wt.% of the basic raw materials. The pore-forming agent is flake graphite with a diameter of less than 300 μm, and the mass is 40 wt.% of the basic raw materials. The binder is 5 wt.% polyvinyl alcohol aqueous solution, and its amount is 1 / 6 of the mass of the basic raw materials.

[0035] 2) Molding: The blank obtained in step 1) is pressed at 60 MPa for 2 min in a powder press to obtain a ceramic green blank; 3) Sintering: The ceramic green body obtained in step 2) was dried in a vacuum drying oven at 60°C for 6 hours, and then placed in a high-temperature resistance furnace with the temperature increased to 300°C at a rate of 3°C / min, and then increased to 875°C at a rate of 5°C / min. It was then sintered at this temperature for 2 hours, and finally cooled to room temperature with the furnace to obtain a diatomaceous earth-based porous ceramic material. This diatomaceous earth-based porous ceramic material has a micro / nano porous structure, as shown in the schematic diagram below. Figure 1 As shown.

[0036] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 0.9783 g·cm³. -3 The apparent porosity is 60.98%, the water absorption rate is 62.38%, the flexural strength is 9.28 MPa, and the permeability flux is 878.72 L·m. -2 ·h -1 ·bar -1 .

[0037] The XRD pattern of the diatomite-based porous ceramic material obtained in this embodiment is as follows: Figure 2 As shown, from Figure 2 It can be seen that the phase composition of diatomite-based porous ceramics is mainly composed of quartz and cristobalite, with a small amount of zinc silicate.

[0038] Example 2 The preparation method of the diatomite-based porous ceramic material in this embodiment is basically the same as that in Example 1, except that: in step 1), the mass fraction of diatomite in the basic raw materials is 85%, the mass fraction of kaolinite is 5%, the mass fraction of feldspar is 0%, and the mass fraction of sodium silicate is 10%.

[0039] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 1.0268 g·cm³. -3 The apparent porosity is 58.93%, the water absorption rate is 56.78%, the flexural strength is 7.78 MPa, and the permeability flux is 610.24 L·m. -2 ·h -1 ·bar -1 .

[0040] Example 3 The preparation method of the diatomite-based porous ceramic material in this embodiment is basically the same as that in Example 1, except that the mass of the sintering aid in step 1) is 20 wt.% of the base raw material.

[0041] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 1.0477 g·cm³. -3 The apparent porosity is 58.63%, the water absorption rate is 55.96%, the flexural strength is 12.41 MPa, and the permeability flux is 590.80 L·m. -2 ·h -1 ·bar -1 .

[0042] Example 4 The preparation method of the diatomaceous earth-based porous ceramic material in this embodiment is basically the same as that in Example 1, except that: in step 3), during sintering, the material is placed in a high-temperature resistance furnace and heated to 300°C at 3°C / min, then heated to 825°C at 5°C / min, and then sintered at this temperature for 2 hours.

[0043] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 0.9531 g·cm³. -3 The apparent porosity is 61.12%, the water absorption rate is 64.13%, the flexural strength is 7.25 MPa, and the permeability flux is 1210.19 L·m. -2 ·h -1 ·bar -1 .

[0044] The SEM morphology image of the diatomite-based porous ceramic material obtained in this embodiment is as follows: Figure 3 As shown, from Figure 3 It can be seen that there are many micron-sized pores formed by the pore-forming agent.

[0045] Example 5 The preparation method of the diatomite-based porous ceramic material in this embodiment is basically the same as that in Example 1, except that: in step 3), during sintering, the material is placed in a high-temperature resistance furnace and heated to 300°C at 3°C / min, then heated to 900°C at 5°C / min, and then sintered at this temperature for 2 hours.

[0046] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 0.9965 g·cm³. -3 The apparent porosity is 60.12%, the water absorption rate is 60.33%, the flexural strength is 9.83 MPa, and the permeability flux is 644.74 L·m. -2 ·h -1 ·bar -1 .

[0047] Example 6 The preparation method of the diatomaceous earth-based porous ceramic material in this embodiment is basically the same as that in Example 1, except that: in step 3), during sintering, the material is placed in a high-temperature resistance furnace and heated to 300°C at 3°C / min, then heated to 925°C at 5°C / min, and then sintered at this temperature for 2 hours.

[0048] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 1.0483 g·cm³. -3 The apparent porosity is 57.53%, the water absorption rate is 54.88%, the flexural strength is 11.55 MPa, and the permeability flux is 483.56 L·m. -2 ·h -1 ·bar -1 .

[0049] Example 7 The preparation method of the diatomaceous earth-based porous ceramic material in this embodiment is basically the same as that in Example 1, except that the pore-forming agent in step 1) is polymethyl methacrylate with a particle size of 4~6μm.

[0050] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 0.8887 g·cm³. -3 The apparent porosity is 64.86%, the water absorption rate is 72.97%, the flexural strength is 6.52 MPa, and the permeability flux is 690.24 L·m. -2 ·h -1 ·bar -1 .

[0051] Example 8 The preparation method of the diatomite-based porous ceramic material in this embodiment is basically the same as that in Example 1, except that the pore-forming agent in step 1) is spherical graphite with a particle size of 10~20μm.

[0052] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 1.0243 g·cm³. -3 The apparent porosity is 58.97%, the water absorption rate is 57.58%, the flexural strength is 12.40 MPa, and the permeability flux is 698.04 L·m. -2 ·h -1 ·bar -1 .

[0053] Example 9 The preparation method of the diatomite-based porous ceramic material in this embodiment is basically the same as that in Example 1, except that the pore-forming agent in step 1) is flake graphite and spherical graphite in a mass ratio of 1:3.

[0054] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this embodiment is 1.0245 g·cm³. -3 The apparent porosity is 59.71%, the water absorption rate is 58.28%, the flexural strength is 13.80 MPa, and the permeability flux is 878.82 L·m. -2 ·h -1 ·bar -1 .

[0055] This embodiment uses a combination of two pore-forming agents. Compared with the same amount of single-component pore-forming agents (Example 1 and Example 8), it has higher flexural strength and permeation flux, indicating that the two-component pore-forming agent can synergistically improve the flexural strength and permeation performance of porous ceramic materials.

[0056] II. Specific Examples of the Application of the Diatomite-Based Porous Ceramic Material of the Present Invention in Wastewater Pollutant Treatment Example 10 The application of diatomaceous earth-based porous ceramic materials in wastewater pollutant treatment in this embodiment involves using diatomaceous earth-based porous ceramic materials prepared by any one of the preparation methods described in Examples 1-9 to filter and retain alumina suspensions; using diatomaceous earth-based porous ceramic materials prepared by any one of the preparation methods described in Examples 1-9 to filter and retain oil-water mixtures; and using diatomaceous earth-based porous ceramic materials prepared by any one of the preparation methods described in Examples 1-9 to filter and adsorb RhB solutions.

[0057] III. Comparative Example Comparative Example 1 The preparation method of the diatomite-based porous ceramic material in this comparative example is basically the same as that in Example 1, except that the mass of the sintering aid in step 1) is 5 wt.% of the base material.

[0058] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this comparative example is 0.9545 g·cm³. -3 The apparent porosity is 57.76%, the water absorption rate is 60.47%, the flexural strength is 2.63 MPa, and the permeability is 521.25 L·m. -2 ·h -1 ·bar -1 .

[0059] The SEM morphology image of the diatomite-based porous ceramic material obtained in this comparative example is shown below. Figure 4 As shown, from Figure 4 It can be seen that the diatomaceous earth disc has nanoscale pores.

[0060] This comparative example, by adjusting the amount of sintering aid added, found that reducing the amount of sintering aid is detrimental to improving the mechanical properties and permeability of porous ceramics. This is because as the amount of sintering aid decreases, the glass phase content in the ceramic matrix decreases, which is not conducive to sintering. This results in insufficient bonding between solid particles, leading to a decrease in the flexural strength of the porous ceramic. Simultaneously, the unsintered micro-solid particles inside the ceramic are also prone to clogging the pores during filtration, further reducing permeability.

[0061] Comparative Example 2 The preparation method of the diatomite-based porous ceramic material in this comparative example is basically the same as that in Example 1, except that the mass of the pore-forming agent flake graphite in step 1) is 0 wt.% of the base raw material.

[0062] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this comparative example is 1.2673 g·cm³. -3 The apparent porosity is 48.89%, the water absorption rate is 38.60%, the flexural strength is 25.44 MPa, and the permeability flux is 89.96 L·m. -2 ·h -1 ·bar -1 .

[0063] In this comparative example, without the addition of a pore-forming agent, the resulting porous ceramic material exhibited high flexural strength but extremely low permeability. This is because the pore structure within the ceramic matrix was primarily composed of the nanopores of diatomaceous earth itself. While this pore structure helps filter and trap various contaminants, it is insufficient to provide adequate channels for pure water transport. The purpose of adding a pore-forming agent is to construct a sufficient microporous structure within the ceramic matrix, forming an interconnected pore network, which manifests as an increase in permeability.

[0064] Comparative Example 3 The preparation method of the diatomite-based porous ceramic material in this comparative example is basically the same as that in Example 1, except that the mass of the pore-forming agent flake graphite in step 1) is 20 wt.% of the base raw material.

[0065] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this comparative example is 1.1485 g·cm³. -3 The apparent porosity is 53.31%, the water absorption rate is 46.42%, the flexural strength is 13.76 MPa, and the permeability flux is 373.07 L·m. -2 ·h -1 ·bar -1 .

[0066] Although the porous ceramic material obtained by adding a low content of pore-forming agent in this comparative example has high flexural strength, its permeation flux is still not high. This indicates that although a small amount of pore-forming agent will leave a microporous structure in the ceramic matrix during sintering, the number of micropores is small, so the pore connectivity is limited, and the resulting permeation performance is also very limited.

[0067] Comparative Example 4 The preparation method of the diatomite-based porous ceramic material in this comparative example is basically the same as that in Example 1, except that the mass of the pore-forming agent flake graphite in step 1) is 50 wt.% of the base raw material.

[0068] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this comparative example is 0.9114 g·cm³. -3 The apparent porosity is 63.35%, the water absorption rate is 69.53%, the flexural strength is 5.51 MPa, and the permeability flux is 1236.19 L·m. -2 ·h-1 ·bar -1 .

[0069] Although the porous ceramic material prepared by the high content of pore-forming agent in this comparative example has extremely high permeation flux, its flexural strength is poor.

[0070] Comparative Example 5 The preparation method of the diatomite-based porous ceramic material in this comparative example is basically the same as that in Example 1, except that the pore-forming agent in step 1) is calcium carbonate with a particle size of 10~30μm.

[0071] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this comparative example is 1.1427 g·cm³. -3 The apparent porosity is 57.36%, the water absorption rate is 50.21%, the flexural strength is 7.05 MPa, and the permeability flux is 204.08 L·m. -2 ·h -1 ·bar -1 .

[0072] Although the porous ceramic material prepared by using calcium carbonate as a pore-forming agent in this comparative example has good flexural strength, its permeation flux is poor. This is because the decomposition product of calcium carbonate, calcium oxide, may react with oxides such as silicon oxide to form a glassy phase, which blocks the pore structure inside the porous ceramic, resulting in poor pore connectivity and thus impairing its permeation performance.

[0073] Comparative Example 6 The preparation method of the diatomaceous earth-based porous ceramic material in this comparative example is basically the same as that in Example 1, except that the pore-forming agent in step 1) is corn starch with a particle size of 5~15μm.

[0074] The bulk density of the diatomaceous earth-based porous ceramic material obtained in this comparative example is 0.9374 g·cm³. -3 The apparent porosity is 62.29%, the water absorption rate is 67.27%, the flexural strength is 4.03 MPa, and the permeability flux is 334.07 L·m. -2 ·h -1 ·bar -1 .

[0075] The porous ceramic material prepared using corn starch as a pore-forming agent in this comparative example exhibits poor flexural strength and permeability. This is because corn starch has a wide particle size distribution, and during the batching and mixing process, corn starch particles break down, resulting in smaller particles and an increased particle number. Furthermore, starch swells to some extent upon contact with water. Therefore, compared to other pore-forming agents of the same dosage, the diatomaceous earth porous ceramic prepared using corn starch as a pore-forming agent has a relatively high porosity and reduced flexural strength. In addition, the micropores formed after the decomposition and combustion of corn starch are mostly closed pores. Even if the micropores are interconnected, the resulting channels are relatively tortuous, thus leading to poor permeability of the resulting porous ceramic.

[0076] IV. Experimental Examples Experimental Example 1 This experimental example examines the filtration and retention performance of the diatomaceous earth-based porous ceramic material from Example 1 as a wastewater pollutant treatment material for alumina suspended particles. An alumina powder suspension was prepared, and the porous ceramic material was used to perform filtration and retention experiments. Then, a nanoparticle size analyzer was used to test the particle size distribution of the alumina powder suspension before and after filtration to evaluate the filtration and retention effect of the prepared porous ceramic sample on suspended particles in wastewater.

[0077] 0.5 g of alumina powder was added to 100 mL of deionized water to prepare an alumina powder suspension. Then, the alumina powder suspension was filtered and retained using diatomaceous earth-based porous ceramics.

[0078] Experimental results showed that the filtrate of the alumina powder suspension was very clear after filtration through the diatomaceous earth-based porous ceramic material. However, laser particle size analysis confirmed the presence of residual alumina particles in the filtrate. Before filtration, the particle size distribution ranged from 4.92 to 972.00 nm, while after filtration, it ranged from 0.87 to 121.50 nm. This indicates that alumina particles larger than 121.50 nm were retained by the diatomaceous earth-based porous ceramic material, suggesting that the nanoporous structure on the surface of the diatomaceous earth disc played a crucial role in both filtration and retention. Furthermore, the D50 of the alumina particles in the filtrate was 8.57 nm, a significant decrease from 69.80 nm before filtration, indicating that the prepared diatomaceous earth-based porous ceramic material also had a certain retention effect on alumina particles smaller than 121.50 nm.

[0079] Experiment Example 2 This experimental example examines the filtration and retention performance of the diatomaceous earth-based porous ceramic material of Example 1 as a wastewater pollutant treatment material for oil-water mixtures.

[0080] A surfactant-stabilized oil-in-water emulsion was prepared by mechanically stirring 100 mL of deionized water, 0.1 g of lubricating oil, and 0.01 g of surfactant hexadecyltrimethylammonium chloride at 500 rpm for 2 h. Oil-water emulsion separation experiments were conducted using a laboratory-made dead-end filtration device via natural filtration, and the emulsion separation efficiency was calculated.

[0081] After filtration and retention by porous ceramic materials, the turbidity of the oil-in-water emulsion decreased from 551.0 NTU to 41.9 NTU, with a turbidity reduction rate of 92.4%, indicating that diatomaceous earth-based porous ceramic materials can effectively separate oil-water mixtures.

[0082] Example 3 This experimental example examines the filtration and adsorption performance of the diatomaceous earth-based porous ceramic material described in Example 1 as a wastewater pollutant treatment material for organic dyes. Diatomaceous earth-based porous ceramic discs were used as filter media and installed on a self-made laboratory filtration device to filter 500 mL of RhB solution. By changing the initial concentration of the RhB solution, the effect of RhB solution concentration on the filtration-adsorption performance of the porous ceramic was investigated.

[0083] It can be seen that the removal rate of RhB molecules from the diatomaceous earth-based porous ceramic filter gradually decreases with increasing initial concentration of RhB solution. Within a 10-minute filtration time, the removal rates for RhB solutions with initial concentrations of 5 mg / L, 10 mg / L, 15 mg / L, and 20 mg / L were 97.4%, 91.4%, 66.2%, and 48.4%, respectively. This is because diatomaceous earth itself not only has numerous micropores but also a surface covered with many hydroxyl groups. It can adsorb small particles and organic pollutants in wastewater through surface forces such as intermolecular forces and electrostatic adsorption. As the initial concentration of RhB solution increases, the adsorption sites in the diatomaceous earth-based porous ceramic filter reach adsorption saturation more quickly. This causes the pore size of the diatomaceous earth-based porous ceramic material to gradually decrease or even become filled with RhB molecules, thus gradually reducing its filtration and adsorption performance.

[0084] In addition, the removal rate of RhB solutions with initial concentrations of 15 mg / L and 20 mg / L by diatomaceous earth-based porous ceramics did not change significantly after 10 minutes of filtration. This time point was earlier than that for RhB solutions with initial concentrations of 5 mg / L and 10 mg / L, indicating that as the initial concentration of RhB solution increases, the time for diatomaceous earth-based porous ceramics to reach adsorption equilibrium for RhB molecules is earlier during the filtration process.

[0085] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a diatomaceous earth-based porous ceramic material, characterized in that, The process includes the following steps: mixing basic raw materials, sintering aids, pore-forming agents, and binders, pressing them into a green body, and then sintering the green body; the basic raw materials, by mass percentage, include 80-85% diatomaceous earth, 5-10% kaolin, 0-5% feldspar, and 5-10% sodium silicate; the sintering aids are at least 5% more than the basic raw materials by mass; the pore-forming agent is 25-45% of the basic raw materials by mass, and the pore-forming agent is selected from one or more of flake graphite, polymethyl methacrylate, and spherical graphite.

2. The method for preparing diatomaceous earth-based porous ceramic materials as described in claim 1, characterized in that, The pore-forming agent comprises flake graphite and spherical graphite in a mass ratio of (1~1.5):(3~3.5).

3. The method for preparing diatomaceous earth-based porous ceramic materials as described in claim 1, characterized in that, The sintering aid is selected from one or more of boric acid, zinc oxide and lithium carbonate; the mass of the sintering aid is 8-20% of the base raw material; the binder is a polyvinyl alcohol aqueous solution with a mass fraction of 5-6%; the mass of the binder is 10-20% of the base raw material.

4. The method for preparing diatomaceous earth-based porous ceramic materials as described in claim 1 or 3, characterized in that, The sintering aids include zinc oxide, boric acid and lithium carbonate in a mass ratio of (5~6):(3~4):(1~2).

5. The method for preparing diatomaceous earth-based porous ceramic materials as described in claim 1, characterized in that, The sintering process includes a heating stage and a holding stage; the holding temperature during the holding stage is 800~1000℃, and the holding time is 2~4h.

6. The method for preparing diatomaceous earth-based porous ceramic material as described in claim 5, characterized in that, The heating stage includes a first heating and a second heating in sequence; the first heating is to raise the temperature to 300-400℃ at a heating rate of 3-4℃ / min; the second heating is to raise the temperature from 300-400℃ to 800-1000℃ at a heating rate of 5-6℃ / min.

7. The method for preparing diatomaceous earth-based porous ceramic material as described in claim 1, characterized in that, The pressure during pressing is 60~80MPa and the time is 2~5min; the green body is dried before sintering at a temperature of 60~80℃ for 5~10h.

8. The method for preparing diatomaceous earth-based porous ceramic material as described in claim 1, characterized in that, The basic raw materials include 80-85% diatomite, 5-10% kaolinite, 2-5% feldspar and 5-10% sodium silicate.

9. The application of a diatomite-based porous ceramic material prepared by the method described in any one of claims 1-8 in wastewater pollutant treatment.

10. The application as described in claim 9, characterized in that, Wastewater pollutants include suspended particulate matter, oil-water mixtures, organic dyes, pathogenic microorganisms, and heavy metal ions.

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